A Three Part History Series

A Three Part History Series Grease Thickeners: A History of Their Development as Disclosed in the NLGI Spokesman Base Oils and Additives: A History of Their Development as Disclosed in the NLGI Spokesman Test Methods: A History of Their Development as Disclosed in the NLGI Spokesman

William Tuszynski, The Unami Group LLC J. Andrew Waynick, Consulting Research Chemist

EXECUTIVE SUMMARY The following three papers have been published as follows: William Tuszynski, J. Andrew Waynick, “Grease Thickeners: A History of Their Development as Disclosed in the NLGI Spokesman”, NLGI Spokesman, Jan/Feb 2024.

William Tuszynski, J. Andrew Waynick, “Base Oils and AddiPves: A History of Their Development as Disclosed in the NLGI Spokesman”, NLGI Spokesman, May/Jun 2024.

William Tuszynski, J. Andrew Waynick, “Test Methods: A History of Their Development as Disclosed in the NLGI Spokesman”, NLGI Spokesman, Jan/Feb 2025.

These three papers resulted from the Industry Speaker PresentaPon that Tuszynski and Waynick gave at the 90th NLGI annual meePng in June 2023. That presentaPon provided a decade-bydecade summary of key lubricaPng grease developments as documented in the Spokesman from 1941 through 2019. Based on the response to that presentaPon, the presenters were asked to write a series of three papers that covered the same material in more detail.

The first paper was 25 pages long (in PDF format) and included 173 enumerated references of Spokesman papers. The second paper was 34 pages long and included 261 references. The third was 56 pages long and included 394 references.

While not intended to be an exhausPve review of the Spokesman content, each paper highlights the seminal papers in their subject area and provides an entry point for those seeking to understand the background behind the development of modern-day grease technology. The reader will also be introduced to the technical leaders of the grease industry daPng back to the 1940s.

Taken as a whole, these three papers provide a unique reference guide through the 1,800+ papers published in the Spokesman from its earliest available issue in 1941 through 2019.

Grease Thickeners: A History of Their Development as Disclosed in the NLGI Spokesman William Tuszynski, The Unami Group LLC J. Andrew Waynick, Consulting Research Chemist

ABSTRACT The NLGI Spokesman has been published since at least 1937, although the first archived article dates to 1941. As such, the technical papers included therein provide a progressive picture of the development of lubricating grease chemistry and technology in its various aspects. This paper is the first in series of three, and provides a summary of Spokesman papers as related to the development and evaluation of thickeners.

After an introductory discussion, major thickener types are discussed. Soap thickeners are discussed first, followed by non-soap thickeners. The soap thickeners discussed are: simple lithium; lithium complex; titanium complex; calcium, sodium, barium; calcium complex, sodium complex, barium complex; aluminum; and aluminum complex. Non-soap thickeners discussed are: calcium sulfonate; polyurea; clay; silica; polytetrafluoroethylene; and polyolefins/polypropylene.

Each major section has its own corresponding reference section at the end of the paper. This allows the reader to more easily research the thickener areas of interest while not becoming entangled in areas of lesser interest. While not exhaustive, the information in this paper does serve as a valuable starting point for those who wish to obtain a more complete understanding of this subject matter.

The scope of the discussion covers the period from the first archived article in 1941 through 2019.

Articles from 2020 forward are outside the scope of this review.

INTRODUCTION NLGI has digitized all available technical articles from the NLGI Spokesman. While it is known that the Spokesman was published at least as early as 1937, the earliest archived issue dates to 1941, and some issues are missing, particularly in the early years. Nevertheless, there are over 1,800 technical articles archived and available for review. The number of available articles by decade through 2019 is given in Figure 1.

Figure 1: NLGI Spokesman articles by decade.

The history of grease development as presented in the Spokesman was presented at the NLGI 90th Annual Meeting [1]. While the presentation gave a decade-by-decade review of all grease-related topics, this paper and the subsequent two will look at a single area of technology across the time period covered (1941-2019). This paper is focused on the development and evaluation of the major - 10 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

thickener types, while the second paper will cover base oils and additives. The third paper will review the development of grease testing methods.

This literature review will be in large measure limited to Spokesman articles. While some relevant patents will be cited, the primary focus is on the Spokesman. A thorough review of the key patent literature on the major thickener types has been given elsewhere [2]. Additional citations of patents not provided in the reference sections at the end of this paper can be found there. Note that articles published in a given year were typically presented at the previous year’s Annual Meeting.

DISCUSSION Major Trends There are multiple trends that span the decades. The first is the growth and development of higher performing greases. This growth has been the result of new developments in thickener, base oil, and additive technology. Thickener developments are covered in the first paper in this series, while the second will discuss base oils and additives.

Although not discussed, better grease manufacturing has also led to improved and more consistent greases. Better process control, continuous production, and new technology have moved grease production from being an art to a science [3].

Environmental responsibility became increasingly important starting in the 1970s, spurred by the establishment of the US Environmental Protection Agency in 1970. While industry acceptance was, at times, grudging [4], sustainability and life cycle analysis have moved to the forefront [5-6].

The importance of automotive applications, particularly wheel bearing greases, is shown by the large number of papers from 1943 through 1998 discussing the latest technology and lubrication requirements for the upcoming model year [7]. The advent of jet aviation in the 1940s and 1950s required a step change in grease technology [8]. Papers discussing grease applications in constant velocity joints, steel mills, mining, oil and gas production, and railroad use appeared in the 1990s. [9] An ongoing theme throughout is the attempt to use bench tests to predict field life and performance.

This will be discussed in detail in the third paper in the series.

Over the first decades of the Spokesman, the great majority of papers came from grease manufacturers. End users such as General Electric and the US Military also submitted papers but additive suppliers’ contributions are rare until the 1970s.

Thickener Types The NLGI has reported on grease production volumes since 1957. The reported data through the 1970s were only for the US and Canada with global volumes being reported starting in the 1980s.

While the full report was published in the Spokesman through the 1970s, only summary information was published starting in the 1980s. Representative data as presented in the Spokesman through the 1990s along with the results as published in the formal Production Surveys for 2007 and 2014 are given in Figure 2 [10].

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The data are best understood when viewed as percentages of the total production. What is noticeable is the rapid ascent to dominance by simple lithium greases by the 1958 Production Survey, just 16 years after the first of Clarence E. Earle’s five patents [11]. This growth is remarkable as it occurred when both the Earle patents and the Fraser patent for lithium 12-hydroxystearate greases [12] were still in force. Earle was part of the WWII effort at the time he developed lithium stearate greases.

There is some indication that the US government allowed the technology to be used freely during and after the war.

This contrasts with the much slower market acceptance for greases based on aluminum complex, first patented in 1952, polyurea, first patented in 1955, lithium complex, first patented in 1959, and calcium sulfonate complex thickeners, first patented in 1985.

SOAP THICKENERS Simple Lithium Greases First introduced during the war years in the 1940s, simple lithium greases rapidly became the preferred grease for many applications, representing nearly one-third of US and Canadian grease production by 1958. Lithium greases offered superior high temperature properties than calcium greases and much better water resistance than sodium soap greases.

The first reference to lithium greases in the archived Spokesman issues is in a 1942 paper comparing the low temperature properties of various greases [1]. Papers on the use of lithium greases indicated for low temperature applications in military aircraft appeared in 1943 and 1948 [2-3]. A key study examining the effect of fatty acid chain length on grease properties appeared in 1946 [4]. While the use of lithium greases was growing, in 1947 the NLGI Technical Committee reported that lithium greases were only used in specialty applications due to their higher cost [5].

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A step-change in the utility of lithium grease came about with the substitution of 12-hydroxystearic acid for stearic acid. First patented in 1946, Fraser and Spooner published a 1948 paper on the utility of lithium 12-hydroxystearate soaps to make multi-purpose automotive greases [6].

Following the introduction of lithium 12-hydroxystearate greases, there were few innovations in basic simple lithium thickening technology. Rather the focus turned to developing applications and modifying formulations to suit. A parallel development was the introduction of new analytical methods to study grease structure and evaluate performance. Lithium bentonite complexes were evaluated in 1965 [7] and the use of mixed soap thickeners was reviewed in 1972 [8]. More recent work showed the use of borate esters to dramatically increase the dropping point of lithium 12-hydroxystearate greases [9].

Lithium Complex Greases First patented in 1959 [10], high dropping point lithium complex greases did not achieve a meaningful share of grease production until the 1980s. The first mention in the Spokesman was not until 1976 [11], roughly coincident with the expiration of the first patent, with other researchers quickly following suit [12], although the earlier commercialization of a lithium complex grease in 1962 was reported by Ehrlich and Musilli [13].

These same authors recognized that the C9 and C10 straight chain diacids (azelaic and sebacic acids) made the most effective complexing acids [13]. Much of the process development work appeared in the patent literature [14] although a process for making ester-containing lithium greases was published [15]. A more recent review of lithium complex grease technology appeared in 1995 [16].

As with simple lithium greases in the previous decades, many, Spokesman papers were concerned with the use of lithium complex greases in various end-use applications [17].

More recently, the growth of electric vehicles (EVs) has put sustained pressure on lithium availability and price. Two 2018 papers discussed the impact of EV battery demand on the lithium market and proposed possible alternative thickeners [18].

Titanium Complex Greases The Indian subcontinent lacks local deposits of lithium, making lithium grease manufacture problematic. However, titanium ore is available in significant amounts. This led to the development of titanium complex greases as an alternative to lithium complex greases. These results were published in a series of eight papers by Kumar, et. al. between 1994 and 2006 [19] Calcium, Sodium, and Barium The first lubricating greases were almost certainly thickened by simple soaps of calcium and sodium [1]. The initial development of simple barium soap greases was not far behind, most likely owing to barium’s position on the periodic table compared to calcium. However, these greases had limitations that prevented them from maintaining an important role as lubricating grease chemistry advanced [2].

Within the first few years of the first publication of the Spokesman, a paper described a military application where calcium soap was being used at 3 wt% in an otherwise sodium soap-thickened grease [3]. The stated purpose of the calcium soap was to impart a smoother texture. A few years later another paper described a similar grease for U.S. Army wheel bearing lubrication [4]. These - 13 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

two papers represented the Spokesman’s first disclosure of a mixed soap grease. Two years after the introduction of lithium soap greases, calcium and sodium soap greases comprised most of U.S. grease production [5-6]. As already mentioned above, that would significantly change in a few more years as lithium soap greases began to dominate.

Several papers evaluated the structure and properties calcium, sodium, and barium soap greases using various fatty (thickener) acids in various base oils and model hydrocarbons [7-12].

Anhydrous calcium soap greases using 12-hydroxystearic acid were apparently first introduced in 1952 as an improvement over temperature-limited hydrous calcium soap greases [1-2]. However, such improvement was not sufficient to eliminate significant performance limitations, as a 1966 paper by the British Ministry of Defense documented [13].

Only one paper specifically focusing on simple barium soap greases could be found in the Spokesman [14].

Calcium, Sodium, and Barium Complex Calcium complex greases were first documented in 1940, just two years before the first documentation of lithium soap greases. The first grease specifically identified as barium complex was introduced in 1947. Both thickener types used acetic acid as the preferred complexing acid [1-2].

The thickener structures of calcium and barium complex greases were investigated in several papers [15-20]. X-ray diffraction data and some interesting solubility studies were reported.

Calcium complex greases never became a significant contributor to global grease production and use.

The primary reason for this was the very serious age hardening problem that these greases had [12]. Perhaps the most interesting thing about the information reported in the Spokesman concerning calcium complex greases was the absence of any paper that specifically, explicitly, and in a focused way discussed this age hardening problem.

Aluminum Soap The history of the early development simple aluminum soap greases has been provided elsewhere [1]. However, these greases never became an important player in the world lubricating grease market, especially with the introduction of lithium soap greases [2].

Simple aluminum soap greases were made from pre-formed aluminum soaps, with the monoand di-stearate soaps being the most commonly used. These aluminum soaps were commercially available as powdered solids. A so-called aluminum tristearate was also available. However, there was disagreement concerning the structure of this material [1]. Although a good grease structure could be obtained with as little as about 3 wt% thickener, such greases had rather low dropping points, and the texture could be inconsistent from batch to batch.

Not surprisingly, almost no Spokesman papers deal with simple aluminum greases except when being compared to other thickener types. One 1949 Spokesman paper claimed that the distearate salt gave the best overall grease structure [3]. Just two years later, another Spokesman paper provided an evaluation of the structure of the powdered aluminum mono and distearate salts and the greases made from them [4]. In a few early papers, simple aluminum greases were compared to greases thickened with the simple soaps of calcium, sodium lithium and barium [5-7].

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Aluminum Complex In 1952, Hotten and co-workers first described how to make pre-formed aluminum complex soaps [8].

In 1956, the same authors first disclosed the use of these complex aluminum soaps to make aluminum complex greases [9]. The preferred complex aluminum soap contained one stearate anion and one benzoate anion. The third valence of aluminum was satisfied by hydroxide.

Two methods to make aluminum complex grease by forming the thickener in the base oil were developed in subsequent years. One method used highly basic aluminum alkoxide (preferably isopropoxide). The other method used a cyclic oxyaluminum compound given the brand name Kolate®. In 1961, a new Kolate was developed where the isopropyl groups of the original Kolate were replaced by stearate groups. A series of papers have been published in the Spokesman discussing various processes to make aluminum complex greases using these reactive aluminum materials [1014].

The first aluminum complex grease approved for use in food plants was published in 1966 [15]. This was followed by to other papers providing additional developments in food machinery aluminum complex greases [16-17].

A paper published in 1995 provided the first disclosure of the manufacture of biodegradable aluminum complex greases made in vegetable oils and synthetic ester base oils [18].

Several other papers were published that evaluated aluminum complex greases by various standard bench tests and compared them to greases using other thickeners such as polyurea, simple lithium, lithium complex, calcium sulfonate complex, and bentonite [19-23].

NON-SOAP THICKENERS Calcium Sulfonate The development of the first (simple) calcium sulfonate greases and the subsequent development of calcium sulfonate complex greases has been disclosed primarily in the U.S. patent literature. That information has been recently summarized elsewhere [1-2], and will not be repeated here. Likewise, the development of the highly overbased calcium sulfonates used to make the greases has been described in detail in a well-known review paper [3].

No Spokesman paper has been published that describes as its central topic the original simple calcium sulfonate greases. The first disclosure of calcium sulfonate complex greases occurred in a paper from 1988 [4]. The information in this paper ? Only one paper cited derived from the corresponding U.S. Patent that issued two years earlier. Ten years later, another paper by the same authors gave more information on the general structure of calcium sulfonate complex greases and the FTIR behavior during the manufacturing process [5]. Test data were provided comparing a calcium sulfonate complex grease with other greases as pertaining to various commercial applications including CV joints, paper mills, electricity generation, marine applications, and steel mills.

In 2003, the first H-1 approved calcium sulfonate complex greases were discussed [6]. The approval was obtained via a legal letter of opinion submitted to the NSF for H-1 approval. Test data for two H-1 approved calcium sulfonate complex greases were provided. The base oil in one was a white mineral oil; the other used PAO. Nine years later, another paper provided more information on such H-1 approved calcium sulfonate complex greases [7].

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A paper from 2016 provided a discussion of a chemistry/technology improvement first disclosed in two 1994 U.S. Patents [8]. This technology provided a way to significantly improve the thickener yield of calcium sulfonate complex greases (reducing the amount of overbased calcium sulfonate in the grease). Test results were provided that showed good performance, including improved low temperature properties due the lower overbased calcium sulfonate content of the grease.

The effect of various synthetic base oils on a calcium sulfonate complex grease formulation was determined using a set of eight greases [9]. One grease was made using only a mineral oil base oil. Five used blends of that mineral oil with one of five different synthetic base oils. The remaining two used only synthetic base oil. Test data on all eight greases were provided. In another paper, limited test data were provided on how the degree and kind of alkalization on the benzene ring of overbased calcium sulfonates can affect the properties of the resulting calcium sulfonate-based greases [10].

In a 2009 paper, a brief review of previously documented processes to make calcium sulfonate-based greases was provided. Then, a new process was disclosed wherein the highly overbased calcium sulfonate contained a form of the primary non-aqueous converting agent [11]. By adding only water and heating, the conversion process occurred, providing the desired grease structure. Three years later, the same company provided a review paper discussing the chemistries and technologies of calcium sulfonate-based greases (simple and complex) that had been disclosed up until that point in time [12].

Two papers discussed how calcium sulfonate complex greases worked in various steel mill applications [13-14]. Comparisons were made with a diurea and an aluminum complex grease. Several atypical test methods were used. These included a high temperature roll stability test and a thin film panel test with immersion in a strong alkali solution.

One paper from 2017 compared the EP/AW properties of overbased calcium sulfonate and overbased calcium oleate greases [15]. Another paper from nearly the same time described the first documented attempts to make calcium sulfonate complex greases using a contactor and the challenges that resulted [16].

In 2016, new calcium sulfonate grease chemistry/technology was described based on a U.S. Patent that issued about the same time [17]. This paper showed for the first time that the final properties of a calcium sulfonate complex grease can depend on the strong base number (direct base number) of the overbased calcium sulfonate. Two years later, another paper by the same author provided additional information on this new chemistry/technology and several others related to it. This was done by testing four assertions found in the prior literature relating to calcium sulfonate-based greases [18].

Not all of those assertions were found to be correct when using the new chemistries/technologies.

Based on those results, several new calcium sulfonate-based greases were developed and evaluated in several commercial applications.

Polyurea As with lithium greases, the driving force for the development of polyurea greases was a military requirement. With the introduction of jet aircraft, greases that can be used at both the low temperatures encountered at altitude and the high temperatures associated with jet engines were required. Silicone oils thickened with aryl diureas proved to be a viable solution [1]. These were first introduced in a 1954 Spokesman article which appeared more than a year before the issuance of the first patents [2].

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Following the publication of this work, the only other activity in the 1950s was a 1959 paper on a preformed polyurea powder [3]. This subject was next revisited in 2005 [4] and again in 2019 [5].

After 1959, it was not until 1965 that another paper on polyureas appeared [6]. The market potential for polyurea greases began to develop with the introduction of alkyl polyurea thickeners in the 1970s in a series of four papers [7], including greases for food machinery based on technology patented in the 1960s [8]. Although aryl polyureas continued to be the preferred thickener for silicone greases, polyureas of all kinds do not appear in the Grease Production Survey as a stand-alone item until 1979 at 2.3% [9]. Prior to that, polyureas were counted as part of the “Non-Soap” classification.

The 1980s saw several papers on the development and application of polyurea greases [10]. This trend continued in the 1990s [11]. The widespread adoption of front wheel drive vehicles in the 1990s provided a significant increase in interest in polyurea greases for constant velocity (CV) joints [12].

The 2000s saw the largest number of polyurea grease papers of any decade. Application development continued throughout the decade, particularly by Japanese grease makers, reflective of the greater market penetration of polyurea greases in Japan [13]. Along with CV joints [14], applications included continuous casters in steel mills [15], low-noise bearing greases [16], H1 sugar mill greases [17], and greases for both low [18] and high [19] temperature use.

In addition to the papers on application development, a number of fundamental studies on the behavior of polyurea greases were published. Among the papers, the anti-wear performance of a series of polyurea greases was modeled by ferrography [20], and bearing performance was studied in two papers [21]. Other studies covered the effect of processing on the structure and properties of polyurea greases [22], their wear properties and film thickness [23], and degradation mechanisms [24].

The development of new uses for polyurea greases continued in the 2010s. Wind turbine greases [25] and greases for electric vehicles [26] were new uses for polyurea greases. Work was done on greases for plastic gears [27] and the effect of vehicle electrification came under consideration [28]. Lithiumpolyurea hybrid greases were also investigated [29] and a novel paper looked at the effect of the number of urea groups in the chain on grease properties [30].

Clay Clay is a complex ionic material comprising various metal cations, silicate anions, and hydroxide anions. An important class of clays are the montmorillonite clays. Two members of this class are bentonite and hectorite. Bentonite contains aluminum and sodium as its metallic constituents.

Hectorite contains aluminum, magnesium, and lithium. As one would expect from their ionic, inorganic nature, such clays do not have any affinity for organic compounds (such as base oils) in their unmodified form. For this reason, such clays do not thicken the base oils typically used in greases.

Instead of being oleophilic, they are oleophobic. In fact, bentonite has been known to adsorb water to the point where the structure of the clay swells. Nonetheless, bentonite and hectorite clay have been used to provide lubricating grease thickeners [1].

The first Spokesman papers to discuss clay greases described the primary method that oleophobic bentonite clay can be modified to become oleophilic, thereby making it a suitable grease thickener [23]. In this method, an organo-quaternary ammonium salt was reacted with bentonite clay. The organo- 17 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

cation replaced the most labile inorganic cation (typically sodium) on the surface of the microscopic clay platelets. The resulting surface treated (activated) bentonite clay was referred to as organobentonite.

Another paper showed for the first time that regardless of how a specific organo-bentonite grease was initially milled, upon being subjected to subsequent specific shearing forces the consistency changed to a new value that corresponded to the magnitude of the imparted shearing force. If the grease was yet again subjected to a different magnitude of shear, the consistency again changed. This effect was reversable if the grease was re-milled [4].

Additional papers evaluated the use of a different surface activators [5] and a different kind of clay [6]. In the same time period, another paper disclosed a process whereby bentonite was surface activated in the presence of lithium soap in base oil [7]. Clay-based thickeners were compared with silica and urea-based thickeners in more severe lubricating grease applications [8]. By the mid-1960’s clay greases were being formulated to provide specific levels of shear stability and corrosion (rust) protection [9].

The unique ability of clay grease consistency to reversibly flex according to the level of shear it experienced eventually resulted in a series of papers that progressively explained the micro-structure of these greases [10-14].

Several papers have been published that evaluated PAO, diesters, silicone oils [15], and vegetable oils [16-17] as base oils for organo-clay greases. In the case of vegetable oils, the apparent driver was improved biodegradability.

Silica Two types of silica that have found early utility as grease thickeners are silica gel and fumed silica (also called pyrogenic silica). Information on the structure and early synthesis work covering these two materials is provided elsewhere [1].

The first disclosure in the Spokesman of a grease thickened by a silica-based material occurred in 1954 [2]. This paper addressed one of the major disadvantages of early silica-thickened greases: their extreme sensitivity to water. Even small amounts of water, especially when combined with heat, could collapse the thickener, thereby destroying the grease structure. In this 1954 Spokesman paper, a new type of silica-based grease thickener, estersils, was described. Various alcohols were reacted with a portion of the hydroxyl groups on the surface of amorphous silica particles. The result was silica with a portion of the surface being coated with alkyl silicate ester groups. Thus modified, these estersils could thicken base oil to form greases that had greatly improved resistance to water. One month after this paper was published, the transcript of a forum discussion on this technology was published [3].

Two papers further explored how various surface treatments and additives can affect the properties of silica greases [4-5]. One paper evaluated such surface treatments of precipitated silica and fumed (pyrogenic) silica with the emphasis on the latter [4].

Silica and clays have related compositions since they are all based on silicate chemistry. Like polyurea, they are also non-soap thickeners. Not surprisingly, several papers compared various clay, silica, and polyurea greases [6-8].

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In 1960, the first paper was published discussing the measurement of permeability coefficients as it relates to lubricating greases [9]. This resulted in a series of papers on the measurement of the permeability coefficient of silica greases and its implications on structure [10-13].

A paper from 1984 provided information on a different method to surface treat fumed silica [14].

Organosilicon compounds were reacted with the fumed silica to provide the surface treatment.

Greases made with the resulting modified silicas were compared with ones made with the unmodified silica.

Polytetrafluoroethylene (PTFE) The first mention of PTFE in the NLGI Spokesman dates to a 1968 article discussing its use as an EP agent [1] with the first reference to PTFE as a thickener coming in 1970 [2].

There were a number of other papers in the 1970s, either linked to military applications [3] or as part of the development of silicone and fluorosilicone base fluids [4].

Although several papers discussed PTFE as an additive, only one paper in the 1980s mentioned PTFE as a thickener as part of an evaluation of grease volatility [5]. Despite the lack of public disclosures, PTFE-thickened grease development and commercialization continued throughout the decade. [6].

Several papers in the 1990s marked a renewed publication interest for PTFE-thickened greases [7], including the development of an H1 grease formulation [8]. This trend continued in the 2000s with several papers on fundamental performance characteristics [9] and one on space-based applications [10].

A handful of papers were published in the 2010s, including PTFE-thickened ester-based H1 greases [11], a study on compatibility with plastic gears [12], and the use of PTFE to thicken a novel fluorinated co-polymer [13].

Polyolefins/Polypropylene Although commercial interest in polyolefin thickeners is a relatively recent development dating to the late 2000s, their use appears in the patent literature as early as the 1950s into the 1970s [1]. These patents disclose the use of polyolefins, both polyethylene and polypropylene, as thickeners, often as mixtures. Their use in conjunction with soap thickeners is also covered.

Despite the patent activity, the only mentions of polyolefin thickeners in the NLGI Spokesman before 2008 is in two parenthetical references, one in 1972 [2] and the other in 1989 [3].

The issuance of two late-1990s patents [4] presaged a renewed interest in polypropylene as a thickener in the 2000s and 2010s, improved friction being cited as a major advantage [5]. Oxidation stability and water-resistance are other identified benefits [6] with electric motor greases cited as an application [7].

CONCLUSIONS The NLGI Spokesman has been an accurate barometer of the development and evaluation of lubricating grease chemistries and associated technologies. This can be seen by comparing the initial disclosure of grease thickeners (usually in the patent literature) with their first appearance - 19 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

in the Spokesman. In some cases, there has been a significant delay between the two disclosures.

However, most of the important developments in lubricating grease thickeners have been eventually discussed in the Spokesman, even if such discussions are not entirely comprehensive. Lithium soap thickened greases were first disclosed in the patent literature in 1942. Within a few years, they were being discussed in Spokesman papers. Similar situations hold true for calcium complex, barium complex, bentonite clay, hectorite clay, aluminum complex, lithium complex, polyurea, calcium sulfonate complex, and polyethylene thickened greases. Therefore, those wishing to quickly obtain an understanding of the fundamentals of lubricating grease thickener chemistry/technology will be well-served by using the NLGI Spokesman as their primary information gateway. For those intending to conduct a research project or write research papers on lubricating grease thickeners, citation of relevant Spokesman papers should be considered a requirement. The same holds true for the NLGI Lubricating Grease Guide (7th Edition), as referenced in the introductory section of this paper.

ACKNOWLEDGEMENTS Each author acknowledges the other for putting up with him.

REFERENCES

The references for each section are presented as stand-alone groups. While this results in several references cited more than once, doing so makes it easier for the reader to find relevant papers for further study.

References: Introduction, Discussion [1] W. Tuszynski, A. Waynick “A Walk Though History – Grease Development in the NLGI Spokesman”, Presented at the 90th Annual NLGI Meeting, 6 Jun 2023.

[2] A. Waynick NLGI Grease Guide, 7th Edition, Chapter 1, 2022.

[3] J.T. Ronan, W.A Graham, C.F. Carter “New Equipment Shortens Grease Processing Cycle”, NLGI Spokesman, Jan 1968; W.B. Green, A.C. Witte Jr. “Texaco’s Continuous Grease Manufacturing Process”, NLGI Spokesman, Jan 1969; Samil Beret, Thomas J. Boersig, William Loh, Peter K. Wong “Continuous Lithium Complex Grease Formation Using Methyl Esters of 12-Hydroxystearic Acid and Azelaic Acid’, NLGI Spokesman”, Feb 1999; Lou A. Honary, Wesley James, “Manufacturing Biobased Greases Using Microwaves”, NLGI Spokesman, Sep/Oct 2012.

[4] C. B. Scott “Can The Petroleum Industry Survive Present and Future Environmental Regulations”, NLGI Spokesman, Aug 1977.

[5] Dr. Lou A. T. Honary, “Market Opportunities for [Soy] Biobased Lubricants”, NLGI Spokesman, Mar 2007.

[6] Graham Gow “ISAIAH 11: Getting Back In Balance”, NLGI Spokesman, May/Jun 2012.

[7] Walter E. Blaine “Reviewing the 1942 Cars-What They Need for 1943”, NLGI Spokesman, May 1943; Roger L. Fennema “Technology and Lubricants of the 1998 Domestic Automobiles”, NLGI Spokesman, Jan 1998.

[8] C. C. Currie “Performance of Silicone Greases”, NLGI Spokesman, Jun 1950.

[9] Dr. Gareth Fish “Constant Velocity Joint Greases”, NLGI Spokesman, Dec 1999; Richard E. Rush “Greases for Steel Mill Lubrication”, NLGI Spokesman, Sep 1993; Cesare P.M. Dalle-Carbonare, Arthur Langdon “Rockdrill Grease Lubrication in South African Gold Mines”, NLGI Spokesman, Oct 1990; R. Hissa, J.C. Monteiro “Shore and Off-Shore Drilling Greases in Brazil”, NLGI Spokesman, Apr 1998; Mark A. Mulvihill, Arnold C. Witte, Sudhir Kumar “A New Approach to Wheel Rail Lubrication”, NLGI Spokesman, Mar 1995.

[10] Dr. J.V. Starr “An Interpretation of N.L.G.I.’s 1958 Production Survey”, NLGI Spokesman, Nov 1959; M. L. Carter “NLGI 1969 Production Survey An Analysis of the Report”, NLGI Spokesman, Jul 1970; - 20 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

J.L Murray “1979 NLGI Grease Survey”, NLGI Spokesman, Sep 1981; J.L Murray “Lithium Complex Grease In The NLGI Production Survey – Addendum to the 1979 Production Survey”, NLGI Spokesman, Dec 1981; Charles P. Monti “1985 Grease Production Survey”, NLGI Spokesman, May 1987; George R. Trabert “Review of 1991 NLGI Worldwide Production Survey”, NLGI Spokesman, Feb 1993; 2007 NLGI Lubricating Grease Production Survey; 2014 NLGI Lubricating Grease Production Survey.

[11] C. E. Earle, US 2,274,673, Mar 3, 1942.

[12] Harold M. Fraser, US 2,397,956, Apr 9, 1946.

References: Lithium, Lithium Complex, Titanium Complex [1] T. A. Maxwell NLGI Spokesman, Nov 1942.

[2] E. R. Irwin, Capt. S. C. Britton NLGI Spokesman, Dec 1943.

[3] Col. G. H. Vogel “The Armed Services Present and Future Lubricant Requirements”, NLGI Spokesman, Jul 1948.

[4] W. F. Luckenbach Jr., H. C. Meyer Jr. “The Effect Of Fatty Acid Molecular Weight On Lithium Greases”, NLGI Spokesman, Jul 1946.

[5] C. W. Georgi, J. B. Stucker “Fats and Fatty Acids for Lubricating Grease Manufacture”, NLGI Spokesman, Jul, 1947.

[6] H. M. Fraser, F. W. Spooner “Multi-Purpose Automotive Grease”, NLGI Spokesman, Dec 1948.

[7] B.R. Citui, M. Cesari, M. Borza “Lithium Soaps - Organophilic Bentonite Complexes as Lubricating Grease Thickening Agents”, NLGI Spokesman, May 1965.

[8] A. T. Polishuk “Physical and Chemical Properties of Mixed Base Greases”, NLGI Spokesman, Apr 1972.

[9] J. J. Lorimor “An Investigation Into the Use of Boron Esters to Improve the High-Temperature Capability of Lithium 12-Hydroxystearate Soap Thickened Grease”, NLGI Spokesman, Sep-Oct 2010.

[10] W. C. Pattendon, et. al., US 2,898,296, Aug 4, 1959.

[11] I. D. Campbell, G. L. Harting “A New Generation of Lithium Greases: The Lithium Complex Greases”, NLGI Spokesman, Sep 1976.

[12] R.L. Coleman, A.C. Witte “High Dropping Point Grease Thickeners”, NLGI Spokesman, May 1978.

[13] M. Ehrlich, T. G. Musilli “The Development of Lithium Complex Grease”, NLGI Spokesman, Jun 1980.

[14] S. Gilani, et. al., US 3,681,242, Aug 1, 1972; S. Gilani, D. Murray, US 3,791,973, Feb 2, 1974.

[15] J.P. Roberts, A.C. Witte “High Dropping Point Grease Thickeners In Synthetic Fluids”, NLGI Spokesman¸ Aug 1982.

[16] Luo Ruibin, Wang Ping, Liu Fushing “A Study of Composition and Technology of Lithium Complex Grease”, NLGI Spokesman, Aug 1995.

[17] R.L Schafer, W.E. Patey “Greases & Gear Oil Lubrication Applications In The Pulp And Paper Industry”, NLGI Spokesman, Jun 1980; Richard E. Rush “Greases for Steel Mill Lubrication”, NLGI Spokesman, Sep 1993; Gordon D. Latos “Lubricant Selection Process for a Downhole Tool”, NLGI Spokesman, Mar 1994; Rolf P. Heckler, Dr. Wilfried H. Dresel “New Greases for CV-Joints”, NLGI Spokesman, Jul 1996; Dr. K. K. Mistry, D. R. Lucas, Dr. P. Shiller “Grease Selection for Main Shaft Bearings in Wind Turbines-Connecting Field Trial Results to Application Testing”, NLGI Spokesman, Mar/Apr 2019.

[18] Dr. G. Fish, Dr. C. Hsu, Dr. R. Dura “Lubricating Grease Thickeners: How to Navigate your Way through the Lithium Crisis”, NLGI Spokesman, Mar/Apr 2018; Dr. Raj Shah, Shana Braff, “Lithium Ion Battery Demands and a Discussion of The Lithium Supply Crisis: How Worried Should We Be?”, NLGI Spokesman, Nov/Dec 2018.

- 21 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

[19] Anoop Kumar, et. al. “A New Generation High Performance Titanium Complex Grease”, NLGI Spokesman, Apr 2004; “Details Related to the Composition of Titanium Complex Grease”, NLGI Spokesman, Sep 1995; “Titanium Complex Grease – A Product of High Potential”, NLGI Spokesman, Dec 1995; “Titanium Complex Grease – Some New Findings”, NLGI Spokesman, May 1996; “Ecofriendly Titanium Complex Grease”, NLGI Spokesman, Nov 1997; “Enhancing Further Performance Properties of Titanium Complex Grease”, NLGI Spokesman, Sep 1998; “Titanium Complex Grease for Girth Gear Applications”, NLGI Spokesman, Sep 1999; “Titanium-Lithium Complex Grease – A High Performance Grease for Industrial Applications”, NLGI Spokesman, May 2006.

References: Calcium, Sodium, and Barium Greases [1] A. Waynick NLGI Lubricating Grease Guide, 7th Edition, Chapter 1.

[2] R. Britton, A. Waynick “Lithium Greases”, Lubrication Explained Podcast, Episode 45.

[3] O.L. Maag “Antifriction Bearing Lubricants”, NLGI Spokesman, Dec 1941.

[4] Lt. Col. N.W. Faust “U.S. Army Specifications For Wheel Bearing Lubricants”, NLGI Spokesman, May 1946.

[5] Lt. Col. C.E. Cummings “Lubricating Grease In Ordnance”, NLGI Spokesman, Feb 1944.

[6] S. Bevin, C.W. Georgi “Grease Production And Fat-Fatty Acid Consumption By The Lubricating Grease Industry”, NLGI Spokesman, Mar 1944.

[7] T.G. Roehner, R.C. Robinson “The Effect Of Soap Structures On Apparent Viscosities Of Lubricating Greases”, NLGI Spokesman, Mar 1947.

[8] C.W. Georgi, J.B. Stucker “Fats And Fatty Acids For Lubricating Grease Manufacture”, NLGI Spokesman, May 1947.

[9] R.D. Vold, H.F. Coffer, R.F. Baker “Rheological Studies And Electron Microscopy Of Calcium Stearate – Cetane Gels”, NLGI Spokesman, Jan 1952.

[10] M. J. Vold “N.L.G.I. Fellowship Report: X-Ray Diffraction Studies Of Oriented Soap Structures In Grease-Like System”, NLGI Spokesman, Nov 1952.

[11] G. W. Miller “Lubricating Grease”, NLGI Spokesman, Jun 1954.

[12] M. J. Vold, V. A. Elersich, R. F. Baker, R. D. Vold “N.L.G.I. Fellowship Report: Grease Structures…

Indicated By X-Ray Orientation Analysis And Electron Microscopy”, NLGI Spokesman, Aug 1954.

[13] R.H. Newman, R.P. Langston “The Performance Of Calcium Hydroxystearate Greases In Wet Conditions”, NLGI Spokesman, Aug 1966.

[14] C.J. Boner, G.W. Miller “Barium Lubricating Grease”, NLGI Spokesman, Jun 1948.

[15] E. Amott, L.W. McLennan “Complexes In Lubricating Oil Greases”, NLGI Spokesman, Mar 1951.

[16] J.J. Kolfenbach, A.J. Morway, “New Thickener System Extends Range Of Multipurpose Greases”, NLGI Spokesman, Aug 1960.

[17] J. Panzer “Nature Of Acetate Complexes In Greases”, NLGI Spokesman, Nov 1961.

[18] R. Barretto, J. Gonzalez “Characteristics Of Lubricating Greases From Calcium Complex Synthesized In Different Reaction Media”, NLGI Spokesman, Sep 1966.

[19] J.L. Dreher, C.F. Carter “Manufacture And Properties Of Calcium Hydroxystearate Complex Greases”, NLGI Spokesman, Nov 1968.

[20] M.M. Guerassimov, I.T. Zahariev, K.G. Stanulov “Effect Of Acetic Acid The Structural-Mechanical And Some Exploitation Properties Of Calcium-Complex Lubricants”, NLGI Spokesman, May 1973.

References: Aluminum and Aluminum Complex [1] A. Waynick NLGI Lubricating Grease Guide, 7th Edition, Chapter 1.

[2] R. Britton, A. Waynick “Lithium Greases”, Lubrication Explained Podcast, Episode 45.

[3] K. Parker, E.F. Wagner “Recent Developments In Aluminum Stearates”, NLGI Spokesman, Sep 1949.

- 22 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

[4] W.K. Dean “The Structure Of Aluminum Greases”, NLGI Spokesman, Sep 1951.

[5] Lt. Col. N.W. Faust “U.S. Army Specifications For Wheel Bearing Lubricants”, NLGI Spokesman, May 1946.

[6] T.G. Roehner, R.C. Robinson “The Effect Of Soap Structures On Apparent Viscosities Of Lubricating Greases”, NLGI Spokesman, Mar 1947.

[7] C.W. Georgi, J.B. Stucker “Fats And Fatty Acids For Lubricating Grease Manufacture”, NLGI Spokesman, May 1947.

[8] B. W. Hotten, et. al. “Complex Aluminum Soap”, U.S Patent No. 2,599,553, Jun 10, 1952.

[9] B. W. Hotten, et. al. “Aluminum Basic Aluminum Complex Greases”, U.S. Patent No. 2,768,138, Oct 23, 1956.

[10] J.L. Dreher, T.H. Koundakjian, C.F. Carter “Manufacture And Properties Of Aluminum Complex Greases”, NLGI Spokesman, Jul 1965.

[11] T.H. Koundakjian, J.L. Dreher “Production of Complex Basic Aluminum Soap Greases”, U.S. Patent No. 3,345,291, Oct 3, 1967.

[12] H.W. Kruschwitz “The Development Of Formulations For Aluminum Complex Thickener Systems”.

NLGI Spokesman, May 1976.

[13] N. Samman “Chemistry Of Aluminum Complex Grease Revisited”, NLGI Spokesman, Nov 1992.

[14] S. Kay, D. Morgan “Evaluation Of Various Raw Material Options For Producing Aluminum Complex Greases”, NLGI Spokesman, Jul 2006.

[15] J.L. Dreher, W.L. Smithson, C.F. Carter “A Special Grease For The Food Industry”, NLGI Spokesman, Jul 1966.

[16] C. Kyriakopoulos “Fully Formulated H1 Aluminum Complex Food Machinery Greases”, NLGI Spokesman, Jul 1994.

[17] D. Loderer, S. Retzer “Performance Of USDA H1 Authorized Fully Synthetic Lubricating Greases”, NLGI Spokesman, Sep 1997.

[18] Constantine Kyriakopoulos “Aluminum Complex Greases Formuated With Biodegradable Base Oils”, NLGI Spokesman, May 1995.

[19] J. Bhatia, A. K. Bhatta, S. K. Mukherjee “Development And Performance Evaluation Of A High Performance Extreme Pressure Aluminum Complex Grease”, NLGI Spokesman, Jul 1990.

[20] P. A. Bessette “The Influence Of Thickener Type On The Apparent Viscosity Of Lubricating Grease”, NLGI Spokesman, Jan 1999.

[21] L. A. T. Honary “Performance Characteristics Of Soybean-Based Greases Thickened With Clay”, NLGI Spokesman, Nov 2001.

[22] J. Scholobohm Sr., H. Faci, B. Cisler “Steel Mill Greases- Evaluation And Analysis”, NLGI Spokesman, Nov 2005.

[23] E. McDaniel, J. Sander, T. Smith “Study Of Synthetic Fluid Based Aluminum Complex Grease”, NLGI Spokesman, Oct 2007.

References: Calcium Sulfonate [1] A. Waynick NLGI Lubricating Grease Guide, 7th Edition, Chapter 1.

[2] R. Britton, A. Waynick “Lithium Greases”, Lubrication Explained Podcast, Episode 45.

[3] J.A. Waynick “Days Of Future Passed A Critical Review Of The Development Of Highly Overbased Calcium Alkylbenzene Sulfonates”, NLGI Spokesman, Sep/Oct 2017.

[4] R.J. Muir “High Performance Calcium Sulfonate Complex Lubricating Grease”, NLGI Spokesman, Jul 1988.

[5] W. Mackwood, R.J. Muir “Calcium Sulfonate Grease…One Decade Later”, NLGI Spokesman, Aug 1999.

[6] W. Mackwood, R.J. Muir, W. Dunn “Calcium Sulfonate Complex Grease The Next Generation Food - 23 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

Machinery Grease”, NLGI Spokesman, May 2003.

[7] W. Mackwood “The Next Generation Food Machinery Grease 10 Years On”, NLGI Spokesman, Jul/Aug 2012.

[8] S. Wilson, W. Mackwood “The Effect Of Composition Of A Calcium Sulfonate Complex Grease On The Key Parameters For Electric Motor Bearing Grease”, NLGI Spokesman, Mar/Apr 2016.

[9] Y. Kimura, K. Takemura, J. Araki, H. Kojima “Study Of Synthetic Oil Based Calcium Sulfonate Complex Greases”, NLGI Spokesman, Dec 2006.

[10] L. Wei “The Path Leading To A Novel OBCS Grease With Superior High Temperature Performance For Extended Use”, NLGI Spokesman, Sep/Oct 2013.

[11] R. Denis, M. Sivik “Calcium Sulfonate Grease-Making Processes”, NLGI Spokesman, Sep/Oct 2009.

[12] G. Fish, W.C. Ward Jr. “Calcium Sulfonate Greases Revisited”, NLGI Spokesman, Nov/Dec 2012.

[13] M. Iwasaki, Y. Kimura, H. Youda, K. Takemura “The Case Studies Of Industrial Applications Of Calcium Sulfonate Complex Grease In Japan”, NLGI Spokesman, Aug 2009.

[14] L. Jiwei, C. Shutian, Z. Wei, W. Baojie “The Typical Application Of Calcium Sulfonate Complex Greases In Steel Mills”, NLGI Spokesman, Mar/Apr 2018.

[15] R. Zhang “A Discussion On Intrinsic Antiwear And Extreme-Pressure Performance Of Overbased Calcium Sulfonate Complex Grease And Overbased Calcium Oleate Complex Grease”, NLGI Spokesman, Mar/Apr 2017.

[16] J. Lorimor “The Stratco Contactor Reactor And Its Use In The Production Of Calcium Sulfonate Based Greases”, NLGI Spokesman, Mar/Apr 2018.

[17] J.A. Waynick “Calcium Sulfonate Complex Greases Using Calcium Hydroxyapatite As A HydroxideContaining Basic Reactant”, NLGI Spokesman, May/Jun 2016.

[18] J.A. Waynick “Application Of New Calcium Sulfonate-Based Grease Technologies From Laboratory To Field”, NLGI Spokesman, Mar/Apr 2018.

References: Polyurea [1] E. A. Swakon, C. G. Brannon, L. C. Brunstrum “Substituted Ureas As Grease Thickeners”, NLGI Spokesman, Apr 1954.

[2] E. A. Swakon, C. G. Brannon US 2,710,839; US 2,710,840; US 2,710,841, Jun 14, 1955.

[3] J.E. Kline, W.L. Hayne, Jr, T.P. Traise “A Preformed Organic Thickener for Lubricating Grease”, NLGI Spokesman, Mar 1959.

[4] Thomas Rossrucker “Polyurea Powder Technology For Greases – Latest Results”, NLGI Spokesman, May 2005.

[5] Xu Hui, Tian Zhiyuan “Study on the Application of DPU-B Prefabricated Biuret (Preformed Diurea) Thickener”, NLGI Spokesman, Mar/Apr 2019.

[5] T. P. Traise “Chemistry of Polyurea Grease Thickeners”, NLGI Spokesman, Sep 1965.

[6] J. L. Dreher, C. F. Carter “New Polyurea Greases”, NLGI Spokesman, Feb 1970; J. L. Dreher, C. F. Crocker “Polyurea-Acetate Greases”, NLGI Spokesman, Mar 1976; C. M. Solzman, R. E. Warren “Field Testing and Marketing a New Food Machinery Grease”, NLGI Spokesman, Mar, 1978; R. E. Crocker “A Polyurea Grease for the Food Processing Industry”, NLGI Spokesman, Feb 1979.

[7] J. L. Dreher, J. E Goodrich US 3,242,372, Mar 29, 1966; J. L. Dreher, J. E. Goodrich US 3,243,372, Mar 29, 1966; J. L. Dreher, B. W. Hotten US 3,346,497, Oct 10, 1967; J. F. Hedenburg, C. S. Tempalski US 3,374,170, Mar 19, 1968; J. L. Dreher, D. W. Criddle US 3,401,027, Sep 10, 1968.

[8] G.J. Quall, G.V. Kubczak “A New Alkylmethylsilicone Lubricating Grease for Extended Life and High Loads”, NLGI Spokesman, Jun 1974.

[9] ; J.L Murray 1979 NLGI Grease Survey, NLGI Spokesman, Sep 1981.

[10] R.L Schafer, W.E. Patey “Greases & Gear Oil Lubrication Applications In The Pulp And Paper - 24 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

Industry”, NLGI Spokesman, Jun 1980; J.P. Roberts, A.C. Boersig “High Dropping Point Grease Thickeners In Synthetic Fluids”, NLGI Spokesman, Aug 1982.

[11] Richard E. Rush “Greases for Steel Mill Lubrication”, NLGI Spokesman, Sep 1993; Gordon D. Latos “Lubricant Selection Process for a Downhole Tool, NLGI Spokesman”, Mar 1994; Jon C. Root “A Comparative Study of Polyurea and Lithium Complex Grease Thickeners”, NLGI Spokesman, Dec 1994; Jon Root “The World’s First Fibrous Polyurea Grease”, NLGI Spokesman, Feb 1995; Paul F. Vartanian “Polyurea Complex Greases - Ten Years Later”, NLGI Spokesman, Jun 1995; Jon C. Root, Paul J. Scruton “Second Generation Multi-Purpose Polyureas and Marketing 101”, NLGI Spokesman, Aug 1995; Mark W. Baum “The First Polyurea Thickened Grease Developed Specifically for Railroad Journal Bearings”, NLGI Spokesman, May 1999; Dr. Dirk Loderer, Herbert Kardinal “Lifetime Lubrication of Bearings at High Temperatures”, NLGI Spokesman, Oct, 1999.

[12] K. Hatekayama “Lubricating Grease for a Plunging Type CV Joint”, NLGI Spokesman, Sep 1992, R. Heckler, W. Dresel “New Grease for CV Joints, NLGI Spokesman”, Jul. 1996; Dr. Gareth Fish “Constant Velocity Joint Greases”, NLGI Spokesman, Dec 1999.

[13] 2007 NLGI Lubricating Grease Production Survey.

[14] Mitsuhiro Kakizaki, Hisayuki Osawa, Shinya Kondo, Toshiaki Endo “Flow Observation of Lubricating Greases in Constant Velocity Joints”, NLGI Spokesman, Mar 2003; Aldra Taniguchi, Shinya Kondo, Daming Dong “Development of Constant Velocity Join Grease with Improved Rolling Contact Fatigue”, NLGI Spokesman, Feb 2005.

[15] Satoshi Nakajima, Kenta Izaki, Kunio Takemura, Yasuhiro Kimura, P.M. Cann “Development of New Urea Grease for Steel Continuous Casting Machine Under Boundary Lubrication”, NLGI Spokesman, Nov 2004; Minoru Namiki, Takeshi Kagoshima “Development of Grease for Continuous Casting Machines - Achievement in Bearing Life Extension (Development to Solve Water-Related Problems)”, NLGI Spokesman, Sep 2007.

[16] L Kenichirou Matsubara, Daming Dong, Toshiaki Endo “Low Noise Greases for Bearings”, NLGI Spokesman, Sep 2008.

[17] Chuck Coe, Roger Miller, Carsten Heck, Gerhard Arnold “Development and Field Testing of a Heavy Duty Synthetic Polyurea Grease”, NLGI Spokesman, Nov/Dec 2008.

[18] Thomas J. Boersig “An Unconventional Approach to Low Temperature Grease”, NLGI Spokesman, Mar 2001.

[19] T. Tim Nadasdi “Next Generation Long-Life Polyurea Greases”, NLGI Spokesman, Nov 2001; Nicolas Samman “High Temperature Greases”, NLGI Spokesman, Feb 2007.

[20] Jusei Maeda, Takao Yoshimatsu, Seiji Okamura “A Study of the Behavior of Diurea Greases by Ferrography Analysis”, NLGI Spokesman, Nov 2000.

[21] Carl F. Kernizan, Herman F. George, William W. Wetsel “Polyurea Greases - Part 1 Tapered Bearing Performance Correlation Study”, NLGI Spokesman, Oct 2001; Herman F. George, Carl F. Kernizan, Melinda E. Bartlett “Polyurea Greases - Part 2- Rheological Test Development and Correlation Study”, NLGI Spokesman, Oct 2001.

[22] Yang Wei, Yao Lidan, Zheng Shanwei “A Study on Structure and Mechanism of Diurea Grease”, NLGI Spokesman, Jul 2003.

[23] Masashi Mitsuoka, Yoshiaki Nakajima, Yasuhiro Miyamoto, Hirkoi Iwamatsu, Seji Okamura “A Study on Wear Properties and Film Thickness of Urea Greases”, NLGI Spokesman, Mar 2003.

[24] Yuki Onuki “A Fundamental Study on Degradation Process of Urea Greases Based on Synthetic Fluids”, NLGI Spokesman, Jun 2006.

[25] Terasu Yoshinari, Minoru Namiki “Main Rotor Bearing Grease for Wind Turbine Based on the New Design Concept”, NLGI Spokesman, Jan/Feb 2013.

[26] Masamichi Yamamoto, Junichi Imai “Development of Grease Focusing on Improved Energy - 25 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

Efficiency”, NLGI Spokesman, Sep/Oct 2014.

[27] Dr. Gareth Fish “The Influence of Vehicle Electrification on Future Lubricating Greases”, NLGI Spokesman, Mar/Apr 2019.

[28] Daisuke Tsutsui “Lubricating Grease for Plastic Gear”, NLGI Spokesman, Jul/Aug 2010.

[29] You Shu, Ting Chen, Shi Qi Ng, Hak Hong, Seiji Okamura “A Study On A Hybrid Grease Of A Lithium Grease And A Diurea Grease Applied for Wide Temperature Range”, NLGI Spokesman, Nov/ Dec 2017.

[30] Vijay Deshmukh, Chetan Pagare “The Study of Relationships of Urea Groups in Polyurea Greases and Their Properties”, NLGI Spokesman, Nov/Dec 2019.

References: Clay [1] A. Waynick. NLGI Lubricating Grease Guide, 7th Edition, Chapter 1.

[2] C. M. Finlayson, P.R. McCarthy. “Bentone Greases”, NLGI Spokesman, May 1950.

[3] R.E. Fariss, “Some Aspects Of Bentone Greases”, NLGI Spokesman, Jan 1957.

[4] H.F. Sutter, “Shear Stability Of A Bentone Grease”, NLGI Spokesman, Jan 1958.

[5] R.E. Fariss, “A Modified Clay Thickener For Lubricating Fluids”, NLGI Spokesman, Feb 1960.

[6] D.E. Loeffler, G.P. Caruso, J.D. Smith.“Development And Characteristics Of Microgel Greases”, NLGI Spokesman, Oct 1963.

[7] B.R. Citui, M. Cesari, M. Borza, “Lithium Soaps – Organophilic Bentonite Complexes As Lubricating Grease Thickening Agents”, NLGI Spokesman, Jun 1965.

[8] L.C. Brunstrum. “Non-Soap Lubricating Greases”, NLGI Spokesman, Oct 1960.

[9] R.F. House. “A Modified Clay Thickener For Corrosion Resistant Greases”, NLGI Spokesman, Apr 1966.

[10] T.W. Powell Jr. “Activators For Organophilic Clays In Lubricating Grease”, NLGI Spokesman, Nov 1982.

[11] C.A. Cody, W.W. Reichert. “Studies Of Fundamental Organoclay Rheological Relationships”, NLGI Spokesman, Jan 1986.

[12] M. D. Kieke. “The Properties Of Organoclay Grease Attributed To Milling”, NLGI Spokesman, Mar 1986.

[13] E.D. Magauran, A. Chiavoni, W.W. Reichert, C.A. Cody. “Studies Of The Behavior Of Dispersed Organoclays In Grease Systems”, NLGI Spokesman, Jun 1986.

[14] E.D. Magauran, M.D. Kieke, W.W. Reichert, A. Chiavoni “Effective Utilization Of Organoclay Dispersants”, NLGI Spokesman, Mar 1987.

[15] M.D. Kieke.“Synthetic Base Greases Thickened With Organophilic Clay”, NLGI Spokesman, Mar 1977.

[16] L.A.T. Honary.“Performance Characteristics Of Soybean-Based Greases Thickened With Clay”, NLGI Spokesman, Nov 2001.

[17] M.D. Kieke, R.J, Klein. “Earth Friendly Vegetable Oil Based Greases Thickened With Organophilic Clay”, NLGI Spokesman, Dec 2003.

References: Silica [1] A. Waynick NLGI Lubricating Grease Guide, 7th Edition, Chapter 1.

[2] G.C. Meyer, R.O. Braendle “Estersils A New Class Of Thickening Agents”, NLGI Spokesman, Dec 1954.

[3] A. Bondi, W.H. Peterson “Discussion Of Estersils A New Class Of Siliceous Thickening Agents”, NLGI Spokesman, Jan 1955.

[4] P.B. Marsden, G.L. Cabot “Pyrogenic Silica-Thickened Greases”, NLGI Spokesman, Aug 1958.

[5] J.J. Chessick “Non-Soap Grease Iii A Systemization Of The States Of Solics Dispersed In Organic Media”, NLGI Spokesman, Nov 1959.

- 26 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

[6] G.C. Meyer “Inorganic Thickeners Their Use In Grease Manufacture”, NLGI Spokesman, Sep 1956.

[7] L.C. Brunstrum “Non-Soap Lubricating Greases”, NLGI Spokesman, Oct 1960.

[8] J.J. Chessick “Non-Soap Greases IV: Present Status Of The Science With Special Consideration To High Temperature Applications”, NLGI Spokesman, May 1961.

[9] A.W. Sisko, L.C. Brunstrum “Permeability Of Lubricating Greases”, NLGI Spokesman, Jun 1961.

[10] J.L. Zakin, H.H. Lin “Permeability Of Silica Greases”, NLGI Spokesman, Oct 1966.

[11] J.L McAtee Jr., J.P. Freeman “Fundamental Aspects Of The Permeability And Gel Strength Of Inorganic Thickened Greases”, NLGI Spokesman, Sep 1968.

[12] J.C. Webster, W.J. Ewbank “The Effect Of Thickener Shape On The Permeability Of Lubricating Grease”, NLGI Spokesman, Oct 1968.

[13] C.S. Fan, J.L. Zakin “Permeability Of Silica Greases II – Effect Of Thickener Variations”, NLGI Spokesman, Jan 1970.

[14] D.G. Miller, W.F. Moll “Improving Grease Performance With Surface-Modified Fumed Silica”, NLGI Spokesman, Feb 1984.

References: PTFE [1] R.L. Johnson “A Review of the Early Use of Molybdenum Disulfide as a Lubricant”, NLGI Spokesman, Nov 1968.

[2] J.T. Skehan “The Development of Fluorinated Greases for Aerospace Military and Industrial Applications”, NLGI Spokesman, Oct 1970.

[3] J.B. Christian “Polyfluoroalkyl-Alkyl Polysiloxane Grease for Instrument Lubrication”, NLGI Spokesman, Feb 1976; L.G. Schneider “Evaluating Wash-off Resistance of Greases for Sliding Contact Bearings in Underwater Service”, NLGI Spokesman, Apr 1976; J.B. Christian “Torque Characteristics Of Lubricating Greases In Miniature Bearings”, NLGI Spokesman, Aug 1979.

[4] L.H. Aultn G.J. Quaal “Development of Fluorosilicone Greases For the Chemical Process Industry”, NLGI Spokesman, Apr 1972; G.J. Quaal “Properties and Performance of Dimethylsilicone Lubricating Grease”, NLGI Spokesman, Mar 1973; A.J. DiSapio, D.F. King Jr., “Silicone Greases Applications and New Technology”, NLGI Spokesman, Nov 1975.

[5] P.A. Bessette “Volatility Of Lubricating Greases In Thin Film, NLGI Spokesman”, Aug 1984.

[6] Paul A. Bessette, personal communication.

[7] Fritz Wunsch “Synthetic Fluid Based Lubricating Greases”, NLGI Spokesman, Feb 1991; Gregory A. Bell “The Effect of PTFE Thickener Particle Characteristics on Grease Formulation and Performance”, NLGI Spokesman, Jul 1996; Paul A. Bessette “The Influence of Thickener Type on the Apparent Viscosity of Lubricating Grease”, NLGI Spokesman, Jan 1999.

[8] Dr. Dirk Loderer Dr. Susanne Retzer “Performance of USDA H1 Authorized Fully Synthetic Lubricating Greases”, NLGI Spokesman, Sep 1997.

[9] Ernie Ballester, Manshi Sui, Christophe Fillion “Effect of PTFE Particle Size on Wear and Coefficient of Friction”, NLGI Spokesman, Sep 2001; Kenneth N. Baker “Characterization of the Corrosion Resistance and Tribology Properties of PFPAE Greases”, NLGI Spokesman, Aug 2004; Kenneth N. Baker “Tribological Comparison of Pennzane-based Grease to PFPAE-based Grease by ASTM D3704”, NLGI Spokesman, Jun 2007.

[10] Mario Maretti, William R. Jones Jr., Kenneth W. Street, Stephen V. Pepper, Mark J. Jansen “Preliminary Evaluation of Greases for Space Mechanisms using a Vacuum Spiral Orbit Tribometer”, NLGI Spokesman, May 2002.

[11] Tyler Housel, Sarah Plimpton Murphy “Food Grade High Temperature Grease”, NLGI Spokesman, May/Jun 2010.

[12] Daisuke Tsutsui “Lubricating Grease for Plastic Gear”, NLGI Spokesman, Jul/Aug 2010.

- 27 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

[13] G. Boccaletti, S. Rovinetti ,M. Avataneo, E. Di Nicolo “PFPE-TFE Copolymer- The New Frontier of Fluorinated Lubricants”, NLGI Spokesman, Nov/Dec 2013.

References: Polyolefins [1] GB 710,109, Jun 9, 1954; Arnold J. Morway, Charles W. Seelbach, Samuel P. Lippincott US 2,917,458, Dec 15, 1959; Arthur T. Polishuk, Herbert L. Johnson US 3,290,244, Dec 12, 1966; Bill Mitacek US 3,392,119, Jul 9, 1968; Stanley Charles Dodson, Robert Henry Newman, US 3,850,828, Nov 26, 1974.

[2] A.T. Polishuk “Physical and Chemical Properties of Mixed Base Greases”, NLGI Spokesman, Apr 1972.

[3] Jason E. Barnes “John H. Wright, Silicone Greases and Compounds- Their Components Properties and Applications”, NLGI Spokesman, Jun 1989.

[4] Dick Meijer, Bo Olov Jacobson, Herman Lankamp EP 0700,986A2, Mar 13, 1996; Dick Meijer, Herman Lankamp US 5,874,391, Feb 23, 1999.

[5] Graham Gow “Ecclesiastes 3:1...Time For A New Epoch”, NLGI Spokesman, Oct 2008; Graham Gow “ISAIAH 11: Getting Back In Balance”, NLGI Spokesman, May/Jun 2012.

[6] Johan Leckner, Rene Westbroek “Polypropylene: A New Thickener Technology For Energy Efficient Lubrication”, NLGI Spokesman, Mar/Apr2017; S. Chatra, D. Muller, C. Matta, R. Thijssen, M. N. bin Yusof, M. C. P. van Eijk “Novel Polymer Grease Microstructure and its Proposed Lubrication Mechanism”, NLGI Spokesman, Mar/Apr 2018.

[7] John Lorimor, Mihir Patel, Brian Stunkel, Rob Heverly “Development of Next Generation Electrical Motor Greases Offering Improved Frictional Characteristics”, NLGI Spokesman, Jan/Feb 2016.

NLGI RESEARCH GRANT REPORTS Pyrylium- and Pyridinum-Based Ionic Liquids as Friction Modifiers for Grease 2022 - University of California – Merced Research Grant

Electrically Conductive Nanoparticle Additives for Greases Used in Electric Vehicles and Other Applications

Available to Members Only

2021 - Auburn University

Strategies for Optimizing Greases to Mitigate Fretting Wear in Rolling Bearings 2020 – The University of Akron

Summary & Full Reports Available

Grease Lubrication of New Materials for Bearing in EV Motors 2019 - University of California – Merced

Strategies for Optimizing Greases to Mitigate Fretting Wear 2018 - The University of Akron

Determination of Grease Life in Bearings via Entropy 2017 - Louisiana State University

Login to the members’ only area to read the report today: https://www.nlgi.org/my-account/

- 28 NLGI Spokesman | VOLUME 87, NUMBER 6 | January/February 2024

Base Oils and Additives: A History of Their Development as Disclosed in the NLGI Spokesman William Tuszynski, The Unami Group LLC J. Andrew Waynick, Consulting Research Chemist ABSTRACT The NLGI Spokesman has been published since at least 1937, although the first archived article dates to 1941. As such, the technical papers included therein provide a progressive picture of the development of lubricating grease chemistry and technology in its various aspects. This paper is the second in series of three, and provides a summary of Spokesman papers as related to the development and evaluation of base oils and additives.

After an introductory discussion, major base oil and additive types are discussed. Base oils are discussed first, followed by additives.

Each major section has its own corresponding reference section at the end of the paper. This allows the reader to more easily research the areas of interest while not becoming entangled in areas of lesser interest. While not exhaustive, the information in this paper does serve as a valuable starting point for those who wish to obtain a more complete understanding of this subject matter.

The scope of the discussion covers the period from the first archived article in 1941 through 2019.

Articles from 2020 forward are outside the scope of this review.

INTRODUCTION NLGI has digitized all available technical articles from the NLGI Spokesman. While it is known that the Spokesman was published at least as early as 1937, the earliest archived issue dates to 1941, and some issues are missing, particularly in the early years. Nevertheless, there are over 1,800 technical articles archived and available for review. The number of available articles by decade through 2019 is given in Figure 1.

1: Issues dating before 1941 not preserved. Earliest known from 1937 2: Includes numerous patent and literature abstracts by Arthur Polishuk 3: The Spokesman switched to bimonthly editions beginning with the June/July 2009 issue Figure 1: NLGI Spokesman articles by decade.

The history of grease development as presented in the Spokesman was presented at the NLGI 90th Annual Meeting [1]. While the presentation gave a decade-by-decade review of all grease-related topics, this paper, the previous one, and the subsequent one will look at a single area of technology across the time period covered (1941-2019). The previous paper focused on thickeners. This paper is focused on the development and evaluation of the major base oil and additive types. The final paper will review the development of grease testing methods.

- 44 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

This literature review will be in large measure limited to Spokesman articles. While some relevant patents will be cited, the primary focus is on the Spokesman. A thorough review of the key patent literature on the major thickener types has been given elsewhere [2]. Additional citations of patents not provided in the reference sections at the end of this paper can be found there. Note that articles published in a given year were typically presented at the previous year’s Annual Meeting.

DISCUSSION Major Trends - Overview The presentation upon which this series of papers is based [1] summarized the industry-wide trends that appeared consistently in the NLGI Spokesman over the decades. Of particular interest was the ongoing development of better performing greases. Users required better performance at both low and high temperatures, better thermal and oxidative stability, higher load carrying capability, and extended service life, including fill-for-life bearing applications. While thickener chemistry has some influence on these properties, base oil and additive selection are the major factors impacting performance. Environmental considerations and sustainability began to be of significance starting with the establishment of the US EPA in the 1970s, forcing changes in additive technology and spurring the growth of Environmentally Acceptable Lubricants (EALs) together with the use of biobased base fluids.

Major Trends – Base Oils While animal and vegetable fats and oils were the initial grease basestocks, the development of the petroleum industry drove the switch to mineral oils in the early part of the 20th century. The advent of military and commercial jet aviation led to the introduction of ester and silicone greases in the 1940s. Polyalkyeneglycols (PAGS) were also first mentioned in the 1940s with fluorinated basestocks first appearing in the Spokesman in the 1950s. Polyalphaolefins (PAOs) are first described in the Spokesman in the 1970s. Although the first Spokesman article on biobased greases appeared in 1961, they do not gain traction until the 1990s.

While NLGI has been tracking grease production since the 1950s, collecting base oil use by class only began in 2007 [2]. Figure 2 shows the usage by region for 2017[3].

Figure 2: Base Oil Usage By Region for 2017

The use of alternative basestocks is greatest in Japan, North America, and Europe. Biobased greases make up a small share and feature most prominently in Europe.

This section will highlight published studies on the various base oil types, beginning with mineral oils, followed by each of the classes of synthetic fluids. Fish has provided an excellent overview of the characteristics of each base oil class in the NLGI Grease Guide, Vol. 7 [5].

- 45 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

Major Trends – Additives Relatively few additive papers were published until the 1970s as shown in Figure 3.

Figure 3: Additive Papers By Category By Decade

The growth in additive papers was a combination of multiple trends. First, old-line additives such as lead compounds and sulfurized sperm whale oil either came under scrutiny or were banned outright beginning in the 1970s. In addition, the performance requirements for greases continued to become more stringent to the point where switching to a synthetic basestock was insufficient to achieve the necessary improvement. Finally, grease manufacturers provided the bulk of the papers in the early days of NLGI. Additive suppliers became much more active in presenting papers at the Annual Meeting with follow-on Spokesman articles starting in the 1970s.

As a result, there are significantly more papers on additive development than papers concerning basestocks, which is reflected in the sections of this review.

BASE OILS Mineral Oils As noted above, mineral oils were and continue to be the dominant basestock used in lubricating greases. While technically in Group V, naphthenic oils will be covered in this section.

The first papers to examine the how base oil’s properties influence the final properties of a grease appeared in 1942 and 1944 [1-3]. The importance of base oil and thickener for high temperature grease performance was discussed in 1949 [4] and again in 1961 [5]. Two 1962 papers looked at the effect of base oil composition on grease performance. The first looked at how variation in the viscosity and type of base oil, ranging from paraffinic to naphthenic, affected oil separation in a mixed lithium calcium grease [6]. The second looked at the effect of a similar range of basestocks on the properties - 46 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

of a lithium grease [7]. Yield, roll stability, oxidation stability, apparent viscosity, and low-temperature torque data were reported for paraffinic and naphthenic oils over a wide range of viscosities. A third 1962 article examined the influence of base oil viscosity on the peak bearing temperature and bearing life in electric motor greases [8].

Papers related to mineral oil properties largely disappeared from the Spokesman until the introduction of hydrotreated (Group II) basestocks. A 1980 paper investigated the properties and structures of lithium soaps made in hydrotreated, solvent refined, and naphthenic basestocks, including blends [9]. The subject was revisited in 1993 when oil separation, yield, low temperature torque, wheel bearing leakage, and elastomer compatibility were correlated to percent aromatic carbon [10]. The impact of the growth of Group II, II+, and Group III basestocks at the expense of Group I stocks on the grease market was examined in a 2002 paper [11]. Group II+ basestocks were used in the development of a series of high-temperature greases [12]. The effect of base oil solvency on grease properties was studied in a 2018 paper [13].

While papers discussing naphthenic oils date back to the 1940s [1], the systematic evaluation of naphthenic basestocks began in earnest in the 2000s through the 2010s. Their use in CV joints [14] and as bright-stock replacements [15, 16] were studied in 2007, 2009, and 2017, respectively. Highviscosity naphthenic oils were compared to polyisobutylene basestocks [17] and the effect of viscosity for a series of heavy naphthenic base oil on the performance of lithium soap, lithium complex, and bentonite clay greases was reported in 2019 [18].

Synthetic Hydrocarbons Synthetic hydrocarbon basestocks, ex PAOs, will be reviewed here. Polyphenylethers (PPEs) and alkyldiphenylethers (ADEs) represent the largest class of synthetic hydrocarbon basestocks presented in the Spokesman. They were first mentioned in 1960 as basestocks for extreme environments [1] and again in 1961 as being suitable for use in nuclear power plants [2]. These applications were covered in a 1974 review article [3]. ADEs were investigated as basestocks for bearing greases for extreme environments in 1996 [4] while six-ring PPEs were studied in a 2000 paper [5]. Polyurea degradation in ADE-based greases was the subject of a 2006 paper [6], while a second paper looked at ADEs as basestocks for calcium sulfonate complex greases [7] In a 1977 study, dalkylbenzenes were used to make low temperature hydraulic fluids, gear oils, and greases for use in Arctic service [8]. Multiply alkylated cyclopentanes, also known as Pennzanes, were compared to silicone and fluorinated basestocks in aerospace greases in 2003 [9] and 2007 [10]. The use of alkylated naphthalenes as co-basestocks was discussed in 2015 [11].

Polyalphaolefins (PAOs) Notwithstanding a 1970 reference to a “synthetic hydrocarbon” of undisclosed composition [1], and another in 1977 [2], the first paper to explicitly reference PAOs was published in 1979 [3]. Subsequent papers looked at producing high droppingpoint greases in PAOs [4] and the field performance of PAO-based greases [5]. Seal compatibility was the subject of a 1986 paper [6]. The properties of PAOs were compared with other synthetic basestocks in a 1987 review paper [7] and with synthetic esters in 1989 [8]. The performance PAO, PAO/Mineral Oil blends and straight mineral oil-based polyurea greases in high temperature, high-speed applications was studied in a 1994 paper [9]. PAO-based calcium sulfonate complex greases were investigated in 2005 [10] and 2016 [11]. PAO-6 was used to make a high-performance lithium complex EP grease in 2007 [12].

- 47 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

Polyalphaolefins appear in nearly 200 papers between their first mention in 1970 and 2020. As PAOs became accepted as synthetic basestocks, relatively few papers had a specific focus on base oil properties per se. The advent of metallocene PAOs (mPAOs) and their use as high viscosity basestocks was the subject of 2017 and 2018 papers [13, 14]. Papers in 2017 and 2019 focused on the use of additives to enhance the performance of PAO-based greases. [15, 16] Synthetic Esters The first Spokesman paper on synthetic esters was published in 1951 [1]. The authors referenced 1944 as the first use of a lithium grease based on di-(2-ethyl) hexyl sebacate for antenna bearings in B-17 and B-24 aircraft. Further work on low-temperature aviation greases was published in 1958 [2].

A 1961 paper reported on a 1948 study of ester and mineral oil-ester blended lithium and sodium wheel bearing greases for military trucks in both high and low temperature environments [3]. The project was code-named “Operation Greaseball.”

The performance of lithium greases in a variety of isostearate esters, including polyol esters, were compared with both di-(2-ethyl)hexyl azelate and di-(2-ethyl)hexyl sebacate [4] in a 1967 paper. In two 1977 papers, ester-based clay greases were evaluated versus mineral oil and synthetic basestocks [5, 6].

A pair of 1980s papers compared the properties of a variety of synthetic esters with mineral oil, PAOs, polyglycols, and silicone basestocks [7,8]. A third paper evaluated diesters as basestocks for synthetic gear oils [9]. This trend continued in the 1990s with esters compared with multiple synthetic basestocks in conventional [10] and in H1 greases [11]. Biodegradability was recognized as a positive characteristic for esters in the 1990s as well [12].

Two 2006 papers looked at the performance and stability of urea [13] and calcium sulfonate complex [14] greases, respectively, in a number of base oils, including esters.

The use of high viscosity polyol esters to prepare a variety of H1 greases was investigated in 2010.

[15].

Silicone Greases Silicone basestocks first appeared in the Spokesman in 1946, being noted for their high temperature stability and low volatility [1]. As with synthetic esters, the initial impetus for the development of silicone-based greases came from military aviation, specifically the advent of jet-powered flight [2, 3]. Military aviation continued to drive the development of silicone greases through the 1950s [4-7], although automotive applications were cited in a 1962 paper [8]. The use of silicone greases in electric motors was disclosed in 1972 [9] while the use of polydimethylsiloxane in food-machinery lubricants was noted in a 1975 paper [10]. A second 1975 paper reviewed multiple application areas for silicone greases.

Most of the early silicones were thickened with simple lithium soaps. Copper phthanocyanine [12] was an early alternative. Aryl polyurea thickeners were developed specifically for use in silicone aviation greases [13]. Clay thickeners were evaluated in a 1976 paper [14}.

In addition to dimethylpolysiloxanes, which were the first developed, methylphenylpolysiloxanes were introduced as high-performance siloxanes in the 1950s [5, 13]. Advances in silicone fluids were - 48 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

documented in 1973 and 1974 [15, 16]. Fluorosilicones were introduced in 1972 [17] and a thorough review of the state of silicone grease technology was published in 1989 [18]. The advantages and drawbacks of silicone fluids were reviewed in 1987 and 1991 reviews of a wide variety of synthetic basestocks [19-20]. A further review appeared in 2004 [21}.

More recently, advances in silicone fluid technology were presented in 2016 and 2017 focusing on optimizing performance for high temperature stability and lubrication performance [22, 23].

Biobased Prior to the development of the petroleum industry, animal and vegetable fats and oils formed the basis for lubricating greases [1]. Although the first reference in the Spokesman to a biobased grease dates to 1961 [2], interest only revived years later in the 1980s and early 1990s [3-5], driven by the need for biodegradable lubricants. Biobased greases were covered in a 1998 review of biodegradable lubricants [6].

Papers on soy-based greases appeared in the Spokesman beginning in 2000 [7-9] with railway switch plates identified as an application area. Subsequent papers showed that the use of a variety of soap and non-soap thickeners could be used [10, 11], and microwave heating was developed as a manufacturing technique [12, 13]. A 2014 paper identified process adjustments required to make grease using vegetable oil basestocks [14]. A compatibility study of biobased and mineral oil greases was conducted in 2012 [15] while the effects of water contamination were documented in 2018 [16].

Along with manufacturing and property studies, several papers explored the market opportunities for biobased greases. Along with a general survey [17], papers focused on the established railway curve grease application [18, 19], sugar mill greases [20], steel mills,[21] and tunnel boring equipment [22].

Polyalkyleneglycols (PAGs) PAGs are first mentioned in the Spokesman in a 1948 article [1]. The bulk of the article is concerned with other uses of PAGs as a basestock, most notably hydraulic fluids, with greases referenced in a short comment at the end. Two 1950s articles discussed PAGS, one in a general article about synthetic basestocks [2], and the other in a discussion of the effect of basestock on oil bleed [3]. The next mention of note is a 1977 article on producing clay greases in various basestocks [4]. Two reviews of synthetic basestocks, one in the 1980s [5], and one in the 1990s [6], include PAGs among the basestocks covered. The introduction of oil-soluble PAGs in the 2010s was documented in series of three papers [7-9].

Fluorinated Basestocks The first reference to fluorocarbon greases is in a 1952 article discussing phthalocyanine as a thickener for high-temperature greases [1]. A 1957 article describes the performance and properties of a newly commercialized fluorocarbon grease [2]. The ability of fluorinated greases to resist missile fuels and oxidizers was highlighted in 1963 [3]. Fluorocarbon greases for aerospace, military, and industrial applications were discussed in 1970 [4]. A 1974 review paper included fluorocarbon greases [5] while their torque characteristics in miniature bearings was discussed in 1979 [6].

While there were no significant papers on fluorocarbon greases in the 1980s, they were discussed in a 1991 review of synthetic greases [7]. The fire-resistance properties of perfluoropolyether (PFPE) greases were highlighted in 1993 [8], and the effect of the grade of PTFE thickener on the final properties of the grease were discussed in 1999 [9].

- 49 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

A 2004 review paper covered PFPEs as base stocks [10] while a second 2004 paper discussed their tribological properties and corrosion resistance [11]. Oil migration was the subject of a 2008 study [12] while the performance of PFPE greases in lubricating plastic parts was highlighted in 2010 [13].

PFPE-TFE co-polymers were introduced as new high-performance fluorinated basestocks in 2013 [14].

ADDITIVES General Review by Additive Type From 1941 to 1996 there were six papers that provided reviews of the various types of additives available for use in lubricating greases [1-6]. The additive types discussed in the first review included oiliness additives, pour point depressants (PPD), detergents, antioxidants (AO), and extreme pressure (EP) additives [1]. The second paper included consistency improvers, heat stabilizers, rust inhibitors, and water resistance additives. It is noteworthy that both of these review papers discussed Pbcontaining additives as being important EP additives.

In a review paper from 1953, EP additives containing various combinations of sulfur, chlorine, and phosphorus were evaluated [3]. Di-alkyl selenides as AO’s were discussed for the first time. Solid additives including graphite, molybdenum disulfide, zinc oxide, powdered Pb, and powdered Zn were also discussed. However, these were referred to as fillers, not additives. A paper from 1962 provided similar general information [4].

A review paper from 1970 provided evaluations of various types of additives in lithium soap, calcium complex, aluminum complex, and bentonite greases [5]. A 1996 paper provided evaluations of various representatives of some of the commonly used additive types in oil blends [6]. No evaluations in grease were provided. Although the stated theme of this paper involved additives for environmentally acceptable lubricants, very little data was provided to justify environmental acceptability.

Graphite/Molybdenum Disulfide Graphite and molybdenum disulfide (MoS2) are well-known grease additives used to improve the EP and antiwear (AW) properties, and modify (reduce) friction. However, due to the large number of papers focusing specifically on one or both of these solid additives, they are discussed here in their own section. Papers discussing other EP/AW/Friction Modifiers are discussed in the next section.

The first paper to discuss graphite as a solid lubricant additive was published in 1951 [1]. Different types of graphite (flake, vein, and amorphous) were dispersed in an unspecified oil and evaluated using the Timken tester. Two other papers provided a discussion of the structure of natural and synthetic graphites [2-3]. Once again, dispersions in oil instead of grease were used for experimental evaluation [2]. In 1982, another paper provided an evaluation of dispersions of several natural and synthetic graphites in an unspecified carrier [4]. Testing was done using the SRV, and dispersions of MoS2 and a graphite fluoride were also evaluated for comparison.

By the 1990’s the use of Pb-based chemistry had mostly been eliminated in the U.S. Two papers by the same authors described a pipe threading compound based on graphite and compared it to formulations based on Pb [5-6].

- 50 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

The effect of graphite type, purity, and concentration on the properties of a clay/PAO grease was described in a paper from 2002 [7]. A paper published a few years earlier evaluated an expanded graphite (one with increased interlaminar distance) as a grease thickener [8]. The base oils used included several mineral oils and several synthetic base oils. Oil separation, structural stability, and load carrying properties were determined.

MoS2 was evaluated as a grease additive in a 1956 paper [9]. Greases thickened by lithium soap, calcium soap, aluminum soap, and Microgel (Hectorite) were used. This was the first of many papers that would evaluate various properties of greases additized with MoS2. One early paper compared MoS2 to WS2, WSe2, and a synthetic graphite in lithium soap grease using a diester base oil [10]. In another paper, MoS2 and PTFE were separately added to a commercially available lithium 12-hydrosystearate grease, lithium complex grease, and polyurea grease. They were evaluated by standard laboratory tests [11]. Using an unspecified lithium soap grease as a base grease, MoS2 was evaluated for its EP/AW. The effect on rust protection and oxidation stability was also determined [12]. The effect of MoS2 on the oxidation stability and ball bearing life was determined in a lithium 12-hydroxystearate grease containing three different antioxidants [13].

In a very large study using 58 MoS2-free commercial greases from 15 manufacturers, MoS2 was added to each. All greases with and without MoS2 were evaluated by Timken, Falex, Four Ball EP and Four Ball Wear tests [14]. A continuation of this work by the same author expanded the test data to include oxidation stability and the results of a ball joint tester [15]. A few years later, the same author reported additional work in two more papers using the same ball joint tester. In one paper, nine lithium soap greases with up to 3% MoS2 were evaluated [16]. In the other paper, four commercial lithium 12-hydroxystearate greases with and without 5% MoS2 were evaluated [17]. Another paper provided data showing that 5% MoS2 reduced abrasive wear in two lithium 12-hydroxystearate and two polyurea greases that had been intentionally additized with Si-abrasive solids [18]. Tests used in this study included the previously mentioned ball joint tester (now referred to as the GMR ball joint tester).

In another large study, greases using lithium 12-hydroxystearate, lithium complex, polyurea, and bentonite were evaluated. Each grease for each thickener system was additized with one of five commonly used oil-soluble EP/AW additives. Corresponding greases using 1.5% MoS2 and one-half the amount of the oil-soluble additives were evaluated by several standard laboratory EP/AW tests [19].

One paper from 1986 focused on the effect of MoS2 on greases thickened with higher dropping point thickeners. The thickeners chosen were lithium complex, aluminum complex, and polyurea [20].

Three papers evaluated MoS2 as a dispersed additive in fluid lubricant formulations [21-23]. Two of these papers focused on how MoS2 improved the efficiency of worm gear oils [21-22]. In the third, the effect of dispersed MoS2 in oil blends with 8 different oil soluble additives and 5 different dispersants were determined using Four Ball testing, FZG testing, and a diesel engine test rig. The performance of MoS2 was shown to be decreased in the presence of highly active EP additives or dispersants [23].

Two papers discussed how graphite and MoS2 behave together [24,25]. In the first, the effect of using both graphite and MoS2 in dry powder forms or in oil dispersions was determined using various test methods including the SRV [24]. In the second, a calcium 12-hydroxystearate grease was additized - 51 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

with 1% to 50% MoS2, and with 1% to 50% of a graphite. The greases were evaluated using the Four Ball EP test. Thermal conductivity was also determined. Graphite gave higher thermal conductivity compared to MoS2 [25].

Only one paper could be found that discussed potential future hazard reclassification of MoS2 and its increasing cost as an incentive to look for alternatives to either reduce or replace MoS2 in greases.

Using a lithium 12-hydroxysterate base grease already containing an unspecified additive package, MoS2 and three unspecified solid additives were evaluated using Four Ball Wear and Weld Load determinations [26].

Three reviews of the use of MoS2 as a lubricant additive were published in 1968, 1993, and 2006 [2729].

Extreme Pressure/Antiwear/Friction Modifiers The first paper to specifically evaluate various EP/AW additives in grease was published in 1958 [1]. Greases made using five synthetic base oils and substituted urea thickener were prepared and evaluated. Base oils included three modified silicone oils and two polyol esters. This was the first paper to use the new polyurea thickener technology patented only a few years earlier by another company. About 20 additives using various combination of Cl, S, and P were evaluated. Most additives either failed to significantly improve EP/AW or caused other issues such as increased corrosion.

This was more likely attributed to the solvency and polarity of the base oils used rather than the substituted urea thickener.

At least seven subsequent papers evaluated various additives based on Cl, S, P, and Zn [2-8]. In one paper, the effect of adding a zinc dithiophosphate, sulfurized olefin, and a fully formulated S-P additive package at 90 C and 120 C to a Li-12HSt base grease was determined using Timken, Four Ball EP, and Four Ball Wear tests. Only the sulfurized olefin showed a significant response to the addition temperature. Four Ball EP Weld Load and Four Ball Wear were improved when the sulfurized olefin was added at 120 C compared to 90 C [6]. As early as 1968, the effect of nine different thickeners on reducing the coefficient of friction was shown to be as important as many of the additives used for that purpose at that time [2].

A few EP/AW additive papers reflected toxicological and environmental concerns. In the 1960s, Pbbased chemistry had begun to be removed from most products. However, as late as 1989, lubricating grease additive studies were still comparing various S, P, Zn, and Sb-containing additives to Pb-based chemistries [5,7]. One paper from 2001 reviewed the toxicity test results and regulatory status of chlorinated paraffins as subdivided by carbon chain length and wt% Cl [8]. For decades sulfurized sperm oil had been a commonly used EP/AW/friction modifier additive for fluid lubricants and greases. However, the hunting of sperm whales had been mostly outlawed by the 1970s. Starting in 1973, six papers provided reviews of the properties of sulfurized sperm oil and evaluations of various alternatives [9-14].

Zinc dithiophosphates were a focus of five papers [15-19]. In a two-part paper, various combinations of a zinc dithiophosphate, sulfurized additives, corrosion inhibitors, and antioxidants were evaluated separately and in combinations in lithium 12-hydroxystearate and lithium complex greases [16-17].

The resulting greases were evaluated by various bearing life tests including ASTM D3527, FAG FE-9, and ASTM D3336. As a result, a multifunctional additive system was developed to provide compliance - 52 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

with ASTM D4950 (NLGI GC-LB). In another two-part paper, an unspecified new orthophosphoric acid ester was evaluated against and in combination with a zinc dithiophosphate in oil blends [18-19].

The SRV was the primary test method used.

With Pb-based additive chemistry falling out of favor, two of the alternative organo-metallic chemistries that in the 1970s began to be used more frequently were based on Sb and Mo. At least nine papers were published between 1979 and 2017 where Sb-based additives and/or Mo-based additives were evaluated in greases with various thickeners including lithium 12-hydroxystearate, lithium complex, aluminum complex, polyurea, calcium sulfonate complex, and bentonite [20-28].

These additives were also evaluated in combination with other additives.

The first of these nine papers provided a good general discussion of the structure of dithiocarbamates and their mechanism as AW additives and antioxidants [20]. Commonly used EP/AW tests were typically used in evaluating the performance of organo-Sb and organo-Mo additives. Frequently, such testing was coupled with surface analysis of the test specimens after the test was concluded [22-25].

For instance, in a two-part paper, portions of a common lithium 12-hydroxystearate base grease were individually additized with an Sb dithiocarbamate, sulfurized olefin, zinc dithiophosphate, and with various combinations of those three additives [22-23]. The greases were evaluated using the Timken test. Timken block scars were surface analyzed using X-ray photoelectron spectroscopy and scanning Auger microscopy. In another paper, the same authors replaced the Sb additive with potassium triborate [24]. Results were compared to what had been reported in the first two papers.

In another two-part paper, the effect of combinations of a zinc dithiophosphate, molybdenum dithiocarbamate, molybdenum dithiophosphate, and several other ashless additives were evaluated in three commercially available calcium sulfonate complex greases. Evaluations were performed using the Mini-Traction Machine (MTM) [27-28].

In 1992/1993, California listed MoS2 as a hazardous material if present at concentrations higher than 350 ppm. This action was challenged by MoS2 manufacturers and ultimately reversed [29].

However, concerns remained about possible future reclassification of MoS2 and the impact of any such reclassification on the lubricants industry. As a result, at least twelve papers were published from 1984 to 2017 on ways to either reduce or eliminate MoS2 from lubricating greases [30-41]. Some of the approaches included using other solid additives such as graphite, CeF3, complex sulfides of two different metals, WS2, SnS2, and Bi2S3. One two-part paper evaluated nano-scale fullerene WS2 [37-38].

Three papers evaluated PTFE as an antiwear additive in lithium 12-hydroxystearate grease [39-41].

Four papers within a two-year period discussed the ability of various additives to address fretting wear and fretting corrosion [42-45]. The first three were specific to lithium complex greases. Test methods included ASTM D4170 to measure fretting wear as well as other methods such as Four Ball Wear, HFRR, and SRV [42-44]. The fourth paper provided an excellent interpretive review of previous work on fretting wear and (to a lesser extent) fretting corrosion. Then, a summary was provided of a previously-performed large study by the author’s company on the effect of grease thickener and additive chemistry on fretting wear. Finally, the results of a recent experimental program were provided where lithium 12-hydroxystearate, lithium complex, di-urea, aluminum complex, and calcium sulfonate complex greases were additized with one of two different inorganic borates or with various combinations of zinc, sulfur, and phosphorus-containing additives. Evaluation of fretting wear was determined by ASTM D4170 and SEM surface analysis [45].

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Two papers provided information on bismuth chemistry as an alternative to Pb-based additives in greases [46-47]. Perhaps the most interesting thing about these papers was that they were published in 1993 and 2005, long after Pb-based chemistry had been virtually eliminated from lubricants in much of the world.

One review paper on the development and use of EP/AW additives in lubricating greases was published in 2011 [48]. In this work, an excellent interpretive review was provided on the history of the development of the commonly used types of EP/AW additives and the test methods used to evaluate them. This included a discussion of how certain EP additives perform in specific EP/ AW tests. Timken OK Load and Four Ball Weld Load test data were provided for various grease formulations using some P-containing, S/P-containing and inorganic borate compounds.

In an interesting paper by Ward and Fish, the use of overbased calcium sulfonates to provide passive EP in combination with oil-soluble sulfurized additives was evaluated [49]. Test results were compared to a previously identified combination of an Sb dithiocarbamate and a potassium borate [24]. Combinations of two different overbased calcium sulfonates with a sulfurized olefin or sulfurized ester or a combination of both sulfurized additives were evaluated using Timken OK Load, Four Ball EP Weld Load, Four Ball Wear, and copper corrosion tests. Timken block wear scars were surface analyzed by X-ray Photoelectron Spectroscopy (XPS). Results showed that certain combinations of overbased calcium sulfonates and sulfurized additives provided EP/AW performance equaling or exceeding that provided by the antimony/borate system.

Several other papers published since 1973 provided additional information on how various other EP/ AW additives perform in lubricating greases [50-53].

Corrosion Inhibitors The first paper to discuss corrosion inhibitors in lubricating grease as the central topic apparently was not published until 1990 [1]. In it, two unspecified rust inhibitor additives were evaluated in lithium soap, calcium soap, organo-clay, and silica-thickened greases. The authors claimed the additives worked by forming true coordination complexes with the metal surface but provided no analytical evidence to prove this.

One year later, a paper provided a brief discussion of petroleum and synthetic metal sulfonates. New “stabilized” metal dinonylnaphthylene sulfonates were introduced [2]. The stabilized zinc sulfonate was evaluated in a lithium 12-hydroxystearate and a lithium complex grease. The test results were compared to a petroleum sulfonate and a previously established dinonylnaphthylene sulfonate. In a follow-up paper, various calcium and barium sulfonates were used alone and in combination with one of three unspecified carboxylates as rust inhibitors in three base greases. The base greases were two lithium 12-hydroxystearate greases and one lithium complex grease. ASTM D1743, D5969 (5% synthetic sea water), and D6138 (EMCOR, 5% synthetic sea water) were the tests used [3].

In another paper by the same authors, a brief discussion of the mechanism of ferrous corrosion (rust) was provided. Then, a lithium 12-hydroxystearate grease was additized with 0.5% to 5.0% calcium dinonylnaphthylene sulfonate. These greases were evaluated by ASTM D1743, D5969, and D6138 and compared to each other and to the unadditized base grease [4].

In a large study from 1992, a base lithium 12-hydroxystearate grease and a series of 21 lithium 12-hydroxystearate greases containing various combinations of EP/AW additives and various - 54 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

metal sulfonates were evaluated by ASTM D1743, D2266, and D2596. Metal sulfonates included didodecylbenzene sulfonates and dinonylnaphthylene sulfonates of zinc and calcium. The previously mentioned new “stabilized” calcium and zinc dinonylnaphthylene sulfonates were also used. The effect of these sulfonates on rust protection, Four Ball Wear, and Four Ball EP test results were provided [5].

The performance of eight unspecified ashless rust inhibitors were determined in two lithium 12-hydroxystearate greases, two lithium complex greases, and one calcium sulfonate-based grease [6]. Testing was done using ASTM D6138 at 5% and 100% synthetic sea water. Four Ball EP, Four Ball Wear, and Cu corrosion (ASTM D4048) tests were also used.

A discussion of the regulatory requirements of using barium sulfonates in lubricants and their eventual disposal was provided in a paper published in 1994 [7].

In a paper from 2018, the effect of excess LiOH in simple Li soap greases on rust inhibitor effectiveness was evaluated using ASTM D1743, D5969, and D6138. Testing was also done using only base oil and adding LiOH to the test water in an amount that corresponded to the amount of excess LiOH in the lithium soap greases. Overall results appeared to indicate that the excess LiOH in and of itself was not interfering with the performance of the two rust inhibitors used in the study. However, the overall lithium soap thickener did appear to have an interfering effect. Three borated additives were also evaluated for their ability to improve rust protection of the lithium soap greases when a standard multifunctional additive package had already been added. All three borated additives improved the rust protection [8].

Oxidation Inhibitors Many published papers included antioxidants in the lubricating grease formulations disclosed as part of the experimental work. However, only five papers explicitly focused on antioxidants as the central topic. The first was a large study published in 1956 by the U.S. military involving 70 greases [1]. Most were lithium soap, but a few were Ca soap or Li-Ca mixed soap. The oxidation stability was by determined by ASTM D942 run at 99 C (210 F) and 121 C (250 F). Copper corrosion was also determined using an old method, VVL-791E. Antioxidants used in this study included various hindered phenols, aryl amines, and S or S-P-containing additives. Most greases used a mineral oil base oil. A few used mono-ester or di-ester base oil.

Another paper evaluated the sorption and extraction of phenyl alpha-naphthylamine (PAN), a commonly used aryl amine antioxidant, in a lithium 12-hydroxystearate and clay grease [2].

A higher molecular weight phenolic antioxidant was compared to two commonly used hindered phenolic antioxidants in base oil blends in a paper from 2005 [3]. The higher molecular weight resulted in longer retention of the AO in oil blends due to reduced volatility and lower extractability by water.

In a study reported in 2009, six antioxidants were evaluated in a 6 cSt PAO and in an unspecified ester base oil. Two hindered phenolic, one aminic, and three unspecified new aminic antioxidants were evaluated. The evaluation procedure involved heating additized oil blends at either 150 C or 180 C for 500 hours. Evaporation loss, final TAN increase, and viscosity increase after each test were used to determine antioxidant effectiveness [4].

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One review paper provided a discussion on the mechanisms of how the various types of primary and secondary AO’s work [5].

Polymers Interestingly, the first paper discussing the effect of polymers on lubricating grease properties as the central topic did not appear until 1987. Four styrene-isoprene polymers were compared with a polyalkylene and olefin copolymer in five greases have different thickener systems. Tests included mechanical stability, dropping point, oil separation, water spray off, wheel bearing leakage, and low temperature flow [1]. As the title of this paper indicated, the styrene-isoprene polymers were framed by the authors as new generation chemistry.

At least nine subsequently published papers evaluated such polymers in greases containing a variety of thickeners and base oils. In the first such paper, nine commercially available polymer additives were added to an unspecified lithium complex base grease. The polymers included polyisobutylene, olefin copolymer, styrene-ethylene-butylene copolymer, and four proprietary polymers. The additized greases were evaluated by worked 10,000 stroke penetrations, roll stability, water spray off, and thickener yield [2].

In another paper, six different polymers were added to a lithium complex and a calcium sulfonate complex grease [3]. The additized greases were evaluated for their low temperature mobility using the Lincoln ventmeter run at ambient temperature and at -1 C. Penetration values at both temperatures and water spray off results were also reported.

One year later, the same authors reported a similar study where four polymers were added to an organo-clay grease and a fumed silica grease [4]. The polymers were an ethylene-propylene (a type of olefin copolymer), polyisobutylene, polyisoprene, and a modified olefin copolymer of undisclosed composition. The two thickener systems were chosen because they do not form fiber structures and therefore cannot exhibit thickener-polymer entanglement. Additized greases were evaluated by worked penetration, water washout, water spray off, and U.S. Steel mobility at 0 C. The solubility compatibility and viscosity increasing properties of four different polymers with eight different ester-based oils were determined in a paper published in 2013 [5].

One problem associated with high molecular weight tackifier polymers is their thermal instability. At higher temperatures, such polymers can degrade to lower molecular weights and lose their ability to impart tackiness to the greases to which they were added. Two papers published 14 years apart investigated the effect of the base oil on polymer thermal stability. In the first paper, the thermal instability of high molecular weight polyisobutylene polymers was determined by monitoring oil/ polymer viscosity during extended storage at elevated temperatures [6]. Polymer thermal instability appeared to be due to free radical initiated oxidation of the Group I base oil. When Group III or IV base oils were used, polymer thermal stability was greatly improved. But adding even very small amounts of the Group I base oil to the Group III base oil blends dramatically decreased polymer thermal stability.

In the second paper, the thermal stability of high molecular weight polyisobutylene and olefin copolymer tackifier polymers was evaluated in a Group III base oil that had been spiked with 0.1% of various compounds representative of materials found in Group I/II base oils but not in group III - 56 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

[7]. Results showed that the relationship between mono and polycyclic aromatic compounds and polyisobutylene thermal stability is complex. The sulfur-containing dopant used appeared to have a stabilizing effect on polymer thermal stability. The nitrogen-containing dopant appeared to aggravate polymer thermal stability.

Two papers discussed how the impact of more traditional polymers on grease properties can depend on when they are added during the grease making process. In the first of these papers, a brief discussion was provided on how polymers can interact with the grease thickener to modify the overall structure, thereby affecting properties such as shear stability and water resistance. In the experimental portion of this paper, nine polymers of varying composition were added to a lithium 12-hydroxystearate base grease in a Group 1 base oil and to a similar base grease in a vegetable oil. Shear stability by worked 10,000 stroke penetration and water resistance by water spray off were determined for all polymer-additized greases. The authors claimed that heating the lithium soap grease in the presence of the polymer to temperatures sufficient to disrupt the thickener fiber structure (partially melt the thickener in the base oil) is important to allow interpenetration networks to form in the cooled down grease. However, such a procedure was not apparently used in the greases of this experimental program [8].

The second paper, published at the same time as the first, did investigate the effect of when polymers are added during the grease making process [9]. Polymer-treated lithium 12-hydroxystearate greases were made using a naphthenic base oil. Eight polymers were used. Each polymer was added at three concentrations. For each selected polymer and each concentration, the polymer was added either at the beginning of the process or after partial cool down from top processing temperature.

This full factorial design resulted in 48 polymer treated greases plus the untreated base grease. Ten test methods were used to evaluate all greases including FTIR, unworked and worked 60 stroke penetration, dropping point, Four Ball Wear, Four Ball EP, Water Spray off, alkalinity, color, and texture.

Polymer type, concentration, addition timing had no significant effect on penetration, dropping point, Four Ball Wear, or alkalinity. Oil separation and water spray off did show a dependency on those factors.

One paper evaluated the effect of three different pour point depressants on the low temperature properties of lithium 12-hydroxystearate greases. The greases were made in both a naphthenic and a paraffinic Group I base oil. Low temperature oscillatory rheometry was used to determine low temperature properties of the greases. Results showed that pour point depressants did not improve low temperature properties of the greases of this study [10].

The polymers discussed in the previously cited papers had one thing in common: they did not modify the structure of the lubricating grease by chemically reacting with the thickener or thickener components. At best, their long molecular structure entangled with the thickener fiber structure thereby modifying grease properties. In the 1990’s, a new class of polymers began to be discussed that actually modified grease structure by chemically reacting with thickener or thickener reactants.

Such polymers were called functionalized polymers. Making such polymers typically involved grafting monomer groups with pendant functional groups (usually acid groups) into the polymer backbone.

The functional groups could then chemically react during the thickener formation process to modify the final thickener structure.

One feature of functionalized polymers was the much lower concentration needed to significantly alter the final grease properties. In the first published paper that discussed the use of - 57 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

functionalized polymers, the effect of adding 0.5% of an unspecified functionalized polymer to a lithium 12-hydroxystearate grease was determined using standard laboratory grease tests as well as controlled stress rheometry [11]. Results were compared to similar greases that used two conventional non-functionalized polymers. Another paper reported similar work using 0.23% of a functionalized olefin copolymer [12].

In a two-part paper, five fully formulated lithium 12-hydroxystearate greases were evaluated using the KRL-modified Four Ball test and oscillatory rheometry. Three contained a functionalized polymer (olefin copolymer); two did not [13,14].

Two other papers provided additional evaluations of functionalized polymers compared to more traditional polymers [15,16].

Miscellaneous At least eleven published papers on lubricating grease additives did not neatly fit into the six categories discussed above [1-11]. One paper evaluated the effect of eleven lead-containing additives on the dropping point of a lithium 12-hydroxystearate grease [2]. All additives lowered the dropping point, with lead dinonylnaphthylene sulfonate having the greatest effect. The most interesting thing about this paper was that it was published in 1980, well after lead-containing compounds had been removed from most products in the U.S. A paper from 1997 discussed the use of sterically hindered carbodiimides as a means to protect diester base oils from hydrolysis [6]. As already discussed, certain organo-bismuth chemistry had been disclosed as EP/AW additives. However, another paper published in 2003 disclosed an unspecified bismuth carboxylate as an additive in a lithium 12-hydroxystearate grease to improve water resistance [7].

Finally, starting in 2010, four papers were published discussing the use of borated additives as a way to increase the dropping point of lithium 12-hydroxystearate greases [8-11]. It is likely not a coincidence that these papers began to be published shortly after the series of U.S. Patents covering this technology had expired [12].

CONCLUSIONS The NLGI Spokesman has been an accurate barometer of the development and evaluation of lubricating grease chemistries and associated technologies. The development of high-performance synthetic basestocks and performance-enhancing additives has been well documented since the 1940s. In the case of some synthetic basestocks and additives, there was a significant delay between their initial development and their first documentation in the Spokesman. Nonetheless, documentation of such developments eventually did occur. Therefore, those wishing to quickly obtain an understanding of both the history and current state of lubricating grease chemistry/technology will be well-served by using the NLGI Spokesman as their primary information gateway. For those intending to conduct a research project or write research papers on lubricating grease base oils and additives, citation of relevant Spokesman papers should be considered a requirement. The same holds true for the NLGI Lubricating Grease Guide (7th Edition), as referenced in the introductory section of this paper.

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ACKNOWLEDGEMENTS Each author acknowledges that they did not realize they would be asked to write a series of papers when they presented this information at the 2023 NLGI Annual Meeting.

REFERENCES The references for each section are presented as stand-alone groups. While this results in several references cited more than once, doing so makes it easier for the reader to find relevant papers for further study.

References: Introduction, Discussion [1] W. Tuszynski, A. Waynick, “A Walk Though History – Grease Development in the NLGI Spokesman”, Presented at the 90th Annual NLGI Meeting, 6 Jun 2023.

[2] A. Waynick, NLGI Grease Guide, 7th Edition, Chapter 1, 2022.

[3] 2007 NLGI Grease Production Survey.

[4] 2017 NLGI Grease Production Survey.

[5] G. Fish, NLGI Lubricating Grease Guide, 7th Edition, Chapter 2.

References: Mineral Oils [1] Gus Kaufman, “Consistency of Lubrication Greases and Oils at Low Temperatures”, NLGI Spokesman, Mar 1942.

[2] Thomas A. Maxwell, “Low Temperature Characteristics of Greases”, NLGI Spokesman, Nov 1942.

[3] C.W. Georgi, John F. O’Connell, “The Effect of Mineral Oil Pour Point on the Flow Characteristics of Lubricating Greases”, NLGI Spokesman, Dec. 1944.

[4] H.A. McConville, “What is Known About High-Temperature Greases”, NLGI Spokesman, Jun 1949.

[5] J. E. Goodrich, J. J. Burke, “Oxidation of Lubricating Greases”, NLGI Spokesman, Jan. 1961.

[6] J.L. Zakin, G.W. Murray Jr., “The Effects of Variation of The Viscosity and Type of The Mineral Oil Component on Oil Separation from Greases Of a Lithium-Calcium Soap”. NLGI Spokesman, Mar 1962.

[7] G.S. Bright, J.H. Greene, “Effect of Oil Characteristics on the Properties of Lithium Soap Greases”, NLGI Spokesman, Dec 1962.

[8] K.H. Warren, “The Role of Base Oil Viscosities In Performance of Electric Motor Greases”, NLGI Spokesman, Jun 1962.

[9] Dr. R. Lanthier, “Compatibility Studies Of Lithium 12-Hydroxystearate In Hydrotreated Base Stocks”, NLGI Spokesman, May 1980.

[10] Samil Beret, “Impact of Base Oil Changes on Grease Performance”, NLGI Spokesman, Aug 1993.

[11] Thomas F. Glenn, Wes L. Cosgriff, “The Outlook for Group II II+ and Group III Base Oils in the U.S. Grease Market”, NLGI Spokesman, Sep 2002.

[12] Nicolas Samman, “High Temperature Greases”, NLGI Spokesman, Feb 2007.

[13] Edward Casserly, Timothy Langlais, Staci Springer, Anoop Kumar, Bill Mallory, “The Effect of Base Oils on Thickening and Physical Properties of Lubricating Greases”, NLGI Spokesman, May/June 2018.

[14] Valentina Serra-Holm, “Development of a Novel Naphthenic Base Oil for Application in CVJ Greases “, NLGI Spokesman, Mar 2007.

[15] Valentina Serra-Holm, “Super-heavy Naphthenics- An Alternative to Bright Stocks”, NLGI Spokesman, Mar 2009.

[16] Mehdi Fathi-Najaf, “There Are Many Roads To Rome But Only Few Of Them Are Cost Efficient: A Comprehensive Approach To Replace Group I Over A Wide Range Of Viscosities”, NLGI Spokesman”, Sep/Oct 2017.

[17] Mehdi Fathi-Najafi , Karin Persson, “A Comparative Study Of The Tribological Behaviour Of A Highly Viscous Naphthenic Oil And Polyisobutenes”, NLGI Spokesman, Jan/Feb 2011.

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[18] Mehdi Fathi-Najafi, Jinxia Li, Yijun Shi, “Evaluation Of The Impact Of High Viscosity Naphthenic Oils On Various Thickener Systems”, NLGI Spokesman, Nov/Dec 2019.

References: Synthetic Hydrocarbons [1] J.W. Armstrong J.R. Handschy D.E. Loeffler, “Greases for Extreme Environments”, NLGI Spokesman, Sep 1960.

[2] R.S. Barnett, “The Lubrication of Nuclear Power Plants”, NLGI Spokesman, Jul 1961.

[3] A.T. Polishuk, “Current Trends in Lubricating Greases” NLGI Spokesman, Jul 1974.

[4] Dr. Dirk Loderer, “Lifetime Lubrication of Rolling Bearings Under Extreme Conditions” NLGI Spokesman, Nov 1996.

[5] Paul A. Bessette, “The Development Of An Improved Contact Lubricant Based On A Six Ring Polyphenyl Ether Fluid”, NLGI Spokesman, Sep 2000.

[6] Yuji Onuki, “A Fundamental Study on Degradation Process of Urea Greases Based on Synthetic Fluids”, NLGI Spokesman, Jun 2006.

[7] Y. Kimura, K. Takemura, J. Araki, H. Kojima, “Study of Synthetic Oil based Calcium Sulfonate Complex Greases”, NLGI Spokesman, Dec 2006.

[8] W.P. Scott A.P. McCloud “Dialkylbenzene Based Lubricants for Extreme Temperature Service”, NLGI Spokesman, Nov 1977.

[9] Paul A. Bessette, “Advanced Lubricants Based on Multiply Alkylated Cyclopentane Polyphenyl Ether and Silahydrocarbon”, NLGI Spokesman, Feb 2003.

[10] Kenneth N. Baker, “Tribological Comparison of Pennzane-based Grease to PFPAE-based Grease by ASTM D3704” NLGI Spokesman, Jun 2007.

[11] Mareen E. Hunter, “Alkylated Naphthalenes”, NLGI Spokesman, May/Jun 2015.

References: Polyalphaolefins (PAOs) [1] W.P. Scott, C.J. Swartz, “Properties of Low Temperature Greases”, NLGI Spokesman, Sep 1970.

[2] M. D. Kieke, “Synthetic Base Greases Thickened With Organophilic Clay”, NLGI Spokesman, Mar 1977.

[3] W.W. Bailey, M. Campen, “Polyalphaolefins In Grease And Gear Oils”, NLGI Spokesman, Jul 1979.

[4] J.P. Roberts, A.C. Witte, “High Dropping Point Grease Thickeners In Synthetic Fluids”, NLGI Spokesman, Aug 1982.

[5] L.E. Tedrow, F.S. Sayles, “Field Performance Of Synthesized Hydrocarbon (Polyalphaolefin) Greases”, NLGI Spokesman, Feb 1984.

[6] Paul E. Gatza, “Compatibility of Wheel Bearing Seal Elastomers with MIL-G-10924 Greases”, NLGI Spokesman, Nov 1896.

[7] Jack B. Boylan, “Synthetic Basestocks For Use in Greases”, NLGI Spokesman, Aug 1987.

[8] G. Bert van der Waal, “Properties and Application of Ester Base Fluids and P.A.Os, ”, NLGI Spokesman Nov 1989.

[9] Seiji Okamura, Masao Toyota, Hiroshi Komiya, “Long Life Urea Grease for High Temperature and High-Speed Application”, NLGI Spokesman, Jun 1992.

[10] Y. Kimura, K. Takemura, J. Araki, H. Kojima, “Study of Synthetic Oil based Calcium Sulfonate Complex Greases”, NLGI Spokesman, Dec 2006.

[11] Solongo Wilson, Wayne Mackwood, “The Effect of Composition of a Calcium Sulfonate Complex Grease on the Key Parameters for Electric Motor Bearing Grease”, NLGI Spokesman, Mar 2016.

[12] Dr. Tarunendr Singh, “Synthetic Shear Stable Water-Resistant EP Grease Composition”, NLGI Spokesman, Jun 2007.

[13] Paul Bessette, Ken Hope, “Synthetic Grease Formulated Using PAO-6 and mPAO-65”, NLGI - 60 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

Spokesman, Jul 2017.

[14] Paul Bessette, Ken Hope “The Preparation of a Polyurea Grease Using mPAO 65 and Preformed Diurea”, NLGI Spokesman, May 2018 [15] Gareth Fish, Chris Hsu, “Technologies to Enhance Synthetic Lubricating Greases”, NLGI Spokesman, Jul62017.

[15] Erik Willet, Andrew DeVore, Daniel Vargo, “Viscometric and Low Temperature Behavior of Lubricants with Blended VI Improvers”, NLGI Spokesman, Nov 2019.

References: Synthetic Esters [1] E.M. Glass, B. Rubin, “Evaluation and Use of Synthetic Greases”, NLGI Spokesman, Feb 1951.

[2] E.A. Baniak, R.S. Barnett, “Low Temperature Operation of Aircraft Accessories”, NLGI Spokesman, Aug 1958.

[3] S. F. Calhoun, “The Experience of the Ordnance Corps With Greases Made from Low Viscosity Oils”, NLGI Spokesman, Dec 1961.

[4] R. H. Boehringer, R. T. Trites, “New Aspects in Synthetic Grease”, NLGI Spokesman, Sep 1967.

[5] M. D. Kieke, “Synthetic Base Greases Thickened With Organophilic Clay”, NLGI Spokesman, Mar 1977.

[6] F.T. Crookshank, G.S. Bright, “The Evaluation of Components For Nonsoap Thickened Greases”, NLGI Spokesman, Jun 1977.

[7] Jack B. Boylan, “Synthetic Basestocks For Use in Greases”, NLGI Spokesman, Aug 1987.

[8] G. Bert van der Waal, “Properties and Application of Ester Base Fluids and P.A.O’s”, NLGI Spokesman, Nov 1989.

[9] Scott D. Sparrow, “An Overview of Diester-Based Gear Oils for Industrial Machinery”, NLGI Spokesman, May 1986.

[10] Fritz Wunsch, “Synthetic Fluid Based Lubricating Greases”, NLGI Spokesman, Feb 1991.

[11] Dr. Dirk Loderer, Dr. Susanne Retzer, “Performance of USDA H1 Authorized Fully Synthetic Lubricating Greases”, NLGI Spokesman, Sep 1997.

[12] Dr. Dirk Loderer, “Lifetime Lubrication of Rolling Bearings with Rapidly Biodegradable Lubricating Greases”, NLGI Spokesman, Jun 1995.

[13] Yuji Onuki, “A Fundamental Study on Degradation Process of Urea Greases Based on Synthetic Fluids”, NLGI Spokesman, Jun 2006.

[14] Y. Kimura, K. Takemura, J. Araki, H. Kojima, “Study of Synthetic Oil based Calcium Sulfonate Complex Greases”, NLGI Spokesman, Dec 2006.

[15] Tyler Housel, Sarah Plimpton Murphy. “Food Grade High Temperature Grease” NLGI Spokesman, May 2010.

References: Silicones [1] T. A. Kauppi, “Silicone Lubricating Grease”, NLGI Spokesman, Jun 1946.

[2] C. C. Currie, “Performance of Silicone Greases”, NLGI Spokesman, Jun 1950.

[3] E.R. Booser, A.E. Baker, E.G. Jackson, “Performance of Synthetic Greases” NLGI Spokesman, Dec 1952.

[4] D.C. McGahey, R.S. Barnett, “Lubrication of Aircraft Oscillating Control Bearings at High Temperatures”, NLGI Spokesman, dec 1957.

[5] I.W. Armstrong, H.A. Woods, “Development of an Extreme High Temperature Grease”, NLGO Spokedman, Apr 1958.

[6] Dr. R.K. Smith, “Development of Extreme Pressure Greases “, NLGI Spokesman, Dec 1958.

[7] R.J. Horwath, “Current and Future Military Grease Requirements”, NLGI Spokesman, Jan 1959.

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[8] L.S. Rosen, “Lemonade for All!”, NLGI Spokesman, Jan 1962.

[9] E.R. Booser, “Trends in Grease Lubrication of Electric Motors” NLGI Spokesman, Feb 1972.

[10] G.W. Fiero, W.G. Domask, “Use of Lubricants in Food Packing and Processing Plants” NLGI Spokesman, May 1970.

[11] A.J. DiSapio, D.F. King Jr., “Silicone Greases Applications and New Technology”, NLGI Spokesman, Nov 1975.

[12] Vincent G. Fitzsimmons, Robert L. Merker, Curtis R. Singleterry, “Phthalocyanine Lubricating Greases”, NLGI Spokesman, Jul 1952.

[13] E. A. Swakon, C. G. Brannon, L. C. Brunstrum, “Substituted Ureas As Grease Thickeners”, NLGI Spokesman, Apr 1954.

[14] M. D. Kieke, “Synthetic Base Greases Thickened With Organophilic Clay”, NLGI Spokesman, Mar 1977.

[15] G.J. Quaal, “Properties and Performance of Dimethylsilicone Lubricating Grease”, NLGI Spokesman, Mar 1973.

[16] G.J. Quall, G.V. Kubczak, “A New Alkylmethylsilicone Lubricating Grease for Extended Life and High Loads”, NLGI Spokesman, Jun 1974.

[17] L.H. Ault, G.J. Quaal, “Development of Fluorosilicone Greases For the Chemical Process Industry”, NLGI Spokesman, Apr 1972.

[18] Jason E. Barnes, John H. Wright, “Silicone Greases and Compounds- Their Components Properties and Applications”, NLGI Spokesman, Jun 1989.

[19] Jack B. Boylan, “Synthetic Basestocks For Use in Greases”, NLGI Spokesman, Aug 1987.

[20] Fritz Wunsch, “Synthetic Fluid Based Lubricating Greases”, NLGI Spokesman, Feb 1991.

[21] Wilfried J. Bartz, “Lubricating Greases Properties and their Classification Especially Synthetic Greases”, NLGI Spokesman, Jul 2004.

[22] Manfred Jungk, Aleksandra Nevskaya, “High Temperature Grease Utilizing New Silicone Based Fluids”, NLGI Spokesman, Nov 2016.

[23] Chad Chichester, Christian Kranenberg, “Advances in Silicone Copolymer Based Lubricants” NLGI Spokesman, Jul 2017.

References: Biobased [1] A. T. Polishuk, ‘A Brief History of Lubricating Greases”, Llewellyn & McKane Inc. PA, 1998 [2] M. A. McNichol, “A Co-Op First - Rapeseed Oil Grease”, NLGI Spokesman, Jan 1961.

[3] R. Hissa J.C. Monteiro, “A Continuation of Studies in the Manufacture and Development of Sodium Based Greases Using Alternative Base Oils”, NLGI Spokesman, May 1985.

[4] E.M. Stempfel, L.A. Schmid, “Biodegradable Lubricating Grease”, NLGI Spokesman, Nov 1991.

[5] David Sukys Carmine Carmino, “Natural Ester Biodegradable Fluids and Lubrication Trends for the Future Part I- Systematic Removal of Components Based on Used Fluid Regulations”, NLGI Spokesman, Sep 1994.

[6] E.M. Stempfel, “Practical Experience with Highly Biodegradable Lubricants Especially Hydraulic Oils and Lubricating Grease”, NLGI Spokesman, Apr 1998.

[7] Lou A.T. Honary, ‘Field Test results of Soybean-Based Greases Developed by UNI-ABIL Research Program’, NLGI Spokesman, Oct 2000.

[8] Dr. Lou A.T. Honary, “A Status Report on Promoting the Use of Biobased Lubricants Made of Commodity and Enhanced Vegetable Oils” NLGI Spokesman, Jun 2002.

[9] E.M. Stempfel, M. Baumann, “Environmentally Acceptable Lubricants In Railway Applications European Trends - Especially Switch Plate Greases and Wheel Flange Lubricants”, NLGI Spokesman, May 2004.

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[10] Dr. Lou A.T. Honary, “Performance Characteristics of Soybean-based Greases Thickened with Clay Aluminum Complex and Lithium”, NLGI Spokesman, November 2001 [11] Murray D. Kieke, Robert J Klein, “Earth Friendly Vegetable Oil Based Greases Thickened with Organophilic Clay”, NLGI Spokesman, Dec 2003.

[12] Lou A. Honary, Wesley James, “Manufacturing Biobased Grease Using Microwaves”, NLGI Spokesman, Sep 2012.

[13] Lou Honary, “Economic Benefits of Innovative Microwave Grease Processing”, NLGI Spokesman, Jan 2018 [14] Dr. Anoop Kumar, Bill Mallory, “Challenges in Manufacturing of Bio-Based Greases”, NLGI Spokesman, Nov 2014.

[15] Lou Honary, Cassandra Boevers, “A Study of Compatibility of Fully Formulated Biobased and Conventional Greases”, NLGI Spokesman, Mar 2012.

[16] Johanna Larssonn Roland Ardai, “The Effect of Water Ingress on the Thickener Structure in Biobased Greases”, NLGI Spokesman, Jan 2018.

[17] Dr. Lou A.T. Honary, “Market Opportunities for [Soy] Biobased Lubricants”, NLGI Spokesman, Mar 2007.

[18] Wes James, Lou Honary, Patrick Johnston, “Energy Savings Study- Lubricating Railroad Tangent Track with Soy-based Grease”, NLGI Spokesman, Jun 2007.

[19] Lou Honary, “A Comparative Study of Bio-based & Conventional Rail Curve Grease”, NLGI Spokesman, Jul 2014.

[20] Hocine Faci, Bob Cisler, Charles Barrett, “Biodegradable Sugar Mill Lubricant What Makes It Suitable For A Sweet But Aggressive Environment”, NLGI Spokesman, Dec 2007.

[21] Hocine Faci, Bob Cisler, Alex Medrano, Michael Inns, “When Performance and Biodegradability Converge- A Superior Product in a Demanding Environment”, NLGI Spokesman, Apr 2006.

[22] Hocine Faci, Bob Cisler, “Biobased Lubricants for Tunnel Boring Machines”, NLGI Spokesman, Jul 2008.

References: Polyalkyleneglycols (PAGs) [1] W.H. Millett, “Industrial Uses of Some Polyether Synthetic Lubricants”, NLGI Spokesman, Sep 1948.

[2] E.R. Booser, A.E. Baker, E.G. Jackson, “Performance of Synthetic Greases”, NLGO Spokesman, Dec 1952.

[3] A.E. Baker, “Grease Bleeding - A Factor in Ball Bearing Performance” NLGI Spokesman, Sep 1958.

[4] M. D. Kieke, “Synthetic Base Greases Thickened With Organophilic Clay”, NLGI Spokesman, Mar 1977.

[5] Jack B. Boylan, “Synthetic Basestocks For Use in Greases”, NLGI Spokesman, Aug 1987.

[6] Fritz Wunsch, “Synthetic Fluid Based Lubricating Greases”, NLGI Spokesman, Feb 1991.

[7] Govind Khemchandani, “New Oil Soluble Polyalkylene Glycol for Making High Performance Grease”, NLGI Spokesman, May 2012.

[8] Govind Khemchandani, “Characteristics of OSP-based Lithium Complex Grease”, NLGI Spokesman, Sep 2014.

[9] Govind Khemchandani, Perry Byrd, Jeff St. Aubin, “OSP-New Group V Base Fluid for Manufacture of Sulfonate Greases”, NLGI Spokesman, May 2015.

References: Fluorinated Basestocks [1] Vincent G. Fitzsimmons, Robert L. Merker, Curtis R. Singleterry, “Phthalocyanine Lubricating Greases”, NLGI Spokesman, Jul 1952.

[2] R.J. Seffl, F.W. West, F.J. Honn, “KELF No. 90 Grease A Chemically and Thermally Stable Fluorocarbon Lubricant”, NLGI Spokesman, Jul 1957.

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[3] J. Messina, “Greases Nonreactive with Missile Fuels and Oxidizers “, NLGI Spokesman, Sep 1963.

[4] J. T. Skehan, “The Development of Fluorinated Greases for Aerospace Military and Industrial Applications” NLGI Spokesman, Oct 1970.

[5] A.T. Polishuk, “Current Trends in Lubricating Greases”, NLGI Spokesman, Jul 1974.

[6] J.B. Christian, “Torque Characteristics Of Lubricating Greases In Miniature Bearings”, NLGI Spokesman, Aug 1979.

[7] Fritz Wunsch, “Synthetic Fluid Based Lubricating Greases”, NLGI Spokesman, Feb 1991.

[8] Douglas G. Placek, “Fire Resistant Low Temperature Greaes Technology”, NLGI Spokesman, Oct 1993.

[9] Gregory A. Bell, “The Effect of PTFE Thickener Particle Characteristics on Grease Formulation and Performance”, NLGI Spokesman, Jul 1996.

[10] Wilfried J. Bartz, “Lubricating Greases Properties and their Classification Especially Synthetic Greases”, NLGI Spokesman, Jul 2004.

[11] Kenneth N. Baker, “Characterization of the Corrosion Resistance and Tribology Properties of PFPAE Greases”, NBLI Spokesman, Aug 2004.

[12] S. Nomura, H. Kojima, T. Yokotani, K. Takemura, “Study on the Prevention of Oil Migration from Fluorinated Grease”, NLGI Spokesman, Jul 2008.

[13] Daisuke Tsutsui, “Lubricating Grease for Plastic Gear”, NLGI Spokesman, Jul 2010.

[14] G. Boccaletti, S. Rovinetti, M. Avataneo, E. Di Nicolo, “PFPE-TFE Copolymer- The New Frontier of Fluorinated Lubricants”, NLGO Spokesman, Nov 2013.

References: Additives - General Review by Additive Type [1] C.F. Prutton “Additives For Petroleum Lubricants”, NLGI Spokesman, Dec 1941.

[2] G. Kaufman “Additives In Lubricating Greases”, NLGI Spokesman, Aug 1947.

[3] R.T. Macdonald, J.L. Dreher “Additives For Lubricating Greases”, NLGI Spokesman, Apr 1953.

[4] P. Kalil “Additives In Lubricants”, NLGI Spokesman, Sep 1962.

[5] D.A. Markey, B.W. Malone “Preliminary Study Of The Relationship Of Base Grease Composition To Additive Response”, NLGI Spokesman, Feb, 1970.

[6] A. Fesenbecker, I. Roehrs, R. Pegnoglou “Additives For Environmentally Acceptable Lubricants”, NLGI Spokesman, Sep 1996.

References: Graphite/Molybdenum Disulfide [1] E.S. Glauch “Graphite As A Lubricant”, NLGI Spokesman, Oct 1951.

[2] E.L. Youse “Characteristics And Selection Of Graphite As A Lubricant”, NLGI Spokesman, Jan 1962.

[3] W. M. Kenan “Characteristics Of Graphite Lubricants”, NLGI Spokesman, Feb 1993.

[4] F.G. Fischer, R.G. Huber, A.D. Cron “Graphite Powder And Other Solids In Lubrication”, NLGI Spokesman, Mar 1982.

[5] W. D. Stringfellow, N. L. Jacobs “Graphite And Lead Bearing Compounds Compared”, NLGI Spokesman, Dec 1991.

[6] W. D. Stringfellow, N. L. Jacobs “Novel Drill Pipe Thread Compound Gives Environmental Acceptability With Superior Performance”, NLGI Spokesman, Mar 1992.

[7] A. V. Tamashausky “The Effect Of Graphite Type, Purity, And Concentration On The Performance Of A Clay Filled Polyalphaolefin Grease, Based On Four Ball Wear (ASTM D2266) With Coefficient Of Friction, And Load Wear Index (ASTM D2596)”, NLGI Spokesman, Mar 2002.

[8] Y. L. Ischuk, O. I. Umans’ka, A. O. Fast, A. D. Stakhursky “Grease Whose Dispersed Phase Is Expanded Graphite”, NLGI Spokesman, Sep 1997.

[9] E.E. Smith “Molybdenum Disulfide As A Grease Additive”, NLGI Spokesman, Dec 1956.

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[10] M.J. Devine, E.R. Lamson, L. Stallings “Molybdenum Disulfide Diester Lubricating Greases”, NLGI Spokesman, Jan 1964.

[11] D. K. Landry, T. J. Risdon “Solid Lubricant Interaction: Lubricating Properties Of Molybdenum Disulfide And PTFE In Three Common Grease Types”, NLGI Spokesman, Apr 1993.

[12] H.F. Barry, J.P. Binkelman “ Evaluation Of Molybdenum Disulfide In Lubricating Greases”, NLGI Spokesman, May 1966.

[13] T.J. Risdon, J.P. Binkelman “Oxidation Stability And Antifriction Bearing Performance Of Lubricants Containing Molybdenum Disulfide”, NLGI Spokesman, Jul 1968.

[14] T.J. Risdon, D.J. Sargent “Comparison Of Commercially Available Greases With And Without Molybdenum Disulfide Part I – Bench Scale Performance Tests”, NLGI Spokesman, Jun 1969.

[15] T.J. Risdon, D.J. Sargent “Comparison Of Commercially Available Greases With And Without Molybdenum Disulfide Part II – Oxidation Stability And Ball Joint Tests”, NLGI Spokesman, Jan 1971.

[16] T.J. Risdon “Effect Of MoS2 Concentration On The Performance Of Greases In The GMR Ball Joint Tester”, NLGI Spokesman, Aug 1974.

[17] T.J. Risdon “Some Energy Implications For The Use Of MoS2 In Greases”, NLGI Spokesman, Aug 1977.

[18] T.J. Risdon, D.A. Gresty “Abrasive Contaminants The Effect Of Mos2 On Wear With Greases Containing An Abrasive Contaminant”, NLGI Spokesman, Sep 1978.

[19] T.J. Risdon “EP Additive Response In Greases Containing MoS2”, NLGI Spokesman, Nov 1999.

[20] T.J. Risdon “Evaluation Of Mos2 In Newer Grease Thickener Systems”, NLGI Spokesman, Sep 1986.

[21] R.K. Smith, Dr. K.M. Marshek “Lubricants Containing Dispersed Molybdenum Disulfide Improve Worm Gear Efficiency”, NLGI Spokesman, May 1984.

[22] P.J. Pacholke “Effects Of Stable Molybdenum Disulfide Lubricant Additives On Worm Gear Efficiency”, NLGI Spokesman, Jun 1989.

[23] W. J. Bartz “Interrelations Between Molybdenum Disulfide And Oil Soluble Additives”, NLGI Spokesman, Dec 1989.

[24] F.G. Fischer, A.D. Cron, R.G. Huber “Graphite And Molybdenum Disulphide-Synergisms”, NLGI Spokesman, Sep 1982.

[25] A. Mistry, R. Bradbury “Investigation Into The Effect Of Molybdenum Disulphide And Graphite On The Load Carrying Capacity Of A Grease”, NLGI Spokesman, June 2002.

[26] N. Samman “OEM Specifications- The Question Of Moly: What Is Next”, NLGI Spokesman, Jan/Feb 2010.

[27] R.L. Johnson “A Review Of The Early Use Of Molybdenum Disulfide As A Lubricant”, NLGI Spokesman, Nov 1968.

[28] R. F. Sebenik “Molybednum Disulfide In Grease”, NLGI Spokesman, Jun 1993.

[29] T. J. Risdon “Molybdenum Disulfide In Greases A Review”, NLGI Spokesman, Mar 2006.

References: Extreme Pressure/Antiwear/Friction Modifier [1] R.K. Smith “Development Of Extreme Pressure Greases”, NLGI Spokesman, Dec 1958.

[2] A.C. Horth, L.W. Sproule, W.C. Pattenden “Friction Reduction With Greases”, NLGI Spokesman, Aug 1968.

[3] J.M. Bish “Investigation Of Extreme Pressure Additives For Greases”, NLGI Spokesman, Mar 1970.

[4] W.T. Brannen, D.A. Lee “Laboratory Evaluation Of Sulfur-Phosphorus Industrial Gear Additive Systems”, NLGI Spokesman, May 1971.

[5] A.G. Papay “Gear Lubricant Additive Technology”, NLGI Spokesman, Sep 1975.

[6] P. R. Todd, M. R. Sivik, G. W. Wiggins “P. R. Todd, M. R. Sivik, G. W. Wiggins “An Investigation Into The Performance Of Grease Additives As Related To The Temperature Of Addition- Part 1”, NLGI Spokesman, Jun 2000.”, NLGI Spokesman, Jun 2000.

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[7] J.J. Feher, B.W. Malone “Evolution Of EP Additives For Greases And Industrial Gear Lubricants”, NLGI Spokesman, Mar 1989.

[8] R. J. Fensterheim “Chlorinated Paraffins- An Overview Of The Health, Environmental, And Regulatory Status”, NLGI Spokesman, Sep 2001.

[9] R.L. Peeler, L.M. Hartmann “Evaluation Of Sulfurized Sperm Oil Replacements”, NLGI Spokesman, Apr 1973.

[10] B.W. Hotten “Sulfurized Sperm Whale Oil History, Chemistry, Functions”, NLGI Spokesman, Aug 1973.

[11] A.D. Recchuite, C.L. Hermann “Case Study In The Development Of Sperm Oil Substitutes – Part 1”, NLGI Spokesman, Nov 1973.

[12] A.D. Recchuite, C.L. Hermann “Case Study In The Development Of Sperm Oil Substitutes – Part 2”, NLGI Spokesman, Dec 1973.

[13] E.J. Friihauf, Z.M. Holubec “The Development And Evaluation Of Sperm Oil Replacement Products For Automatic Transmission Fluids”, NLGI Spokesman, Jan 1974.

[14] P.F. Thompson “Sperm Oil Replacements For Ep Applications – 1972”, NLGI Spokesman, Apr 1974.

[15] M. R. Sivik, J. B. Zeitz, D. Bayus “Interactions Of A Zinc Dithiophosphate With Lithium 12-Hydroxystearate Grease”, NLGI Spokesman, Jun 2002.

[16] W. Ward Jr., G. Fish “Development Of Greases With Extended Grease And Bearing Life Using Pressure Differential Scanning Calorimetry And Wheel Bearing Life Testing”, NLGI Spokesman, Nov/ Dec 2010.

[17] W. Ward Jr., S. Capitosti “Ashless Multifunctional Additive Technology For Rolling Element Bearing Grease”, NLGI Spokesman, Jan/Feb 2014.

[18] K. Umehara, K. Yamamoto, N. Tanaka “New Orthophosphoric Ester With Excellent Anti-Wear Performance”, NLGI Spokesman, Nov/Dec 2011.

[19] K. Yamamoto, K. Umehara, N. Tanaka “New Orthophosphoric Ester With Excellent Anti-Wear And Heat Resistance Performance”, NLGI Spokesman, Sep/Oct 2023.

[20] A.T. Polishuk, H.H. Farmer “Dithiocarbamate Additives In Lubricating Greases”, NLGI Spokesman, Set 1979.

[21] G. Fish, Jisheng E. “The Effect Of Friction Modifier Additives On Cvj Grease Performance”, NLGI Spokesman, October 2002.

[22] W. C. Ward Jr., M. Najman “Properties Of Tribochemical Films From Various Additives In Grease Generated Under Load”, NLGI Spokesman, Oct 2006.

[23] W. C. Ward Jr, R. A. Denis, M. Najman, C. L. Cerda de Groote “EP Additive Response And Tribochemical Film Formation In Lithium And Lithium Complex Grease”, NLGI Spokesman, Oct 2007.

[24] W. C. Ward Jr., G. Fish, M. Nahman, C. McFadden “Extreme Pressure And Tribochemical Film Comparisons Of Antimony And Non-Antimony Additive-Containing Lithium Complex Grease”, NLGI Spokesman, Aug 2009.

[25] J. Yao, Jun Z. Ying Xi “The Antiwear Synergism Between A Borate Ester And A Dialkyl Dithiocarbamate In Lubricating Oil And Grease”, NLGI Spokesman, Dec 2006.

[26] A. Mal, M. Gu, J. Yaol, R. Zhang “Extreme Pressure, Antiwear, and Friction-Reducing Performances of Molybdenum Dithiophosphate and DMTD Derivatives in Grease”, NLGI Spokesman, Nov/Dec 2015.

[27] M. Patel, R. Zhang, R. Hiza, S. Donnelly “Effect Of MODTC And MODTP On Frictional And Antiwear Properties Of Overbased Calcium Sulfonate Complex Greases”, NLGI Spokesman, May/Jun 2016.

[28] A. Ma, M. Gu, J. Yao, M. Patel, R. Zhang “Performance Evaluation Of Antimony Zinc Diamyl Dithiocarbamate As Grease Additive”, NLGI Spokesman, Nov/Dec 2017.

[29] N. Samman “OEM Specifications- The Question Of Moly: What Is Next”, NLGI Spokesman, Jan/Feb 2010.

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[30] J.M. Dumdum, H.E. Aldorf, E.C. Barnum “Lubricant Grade Cerium Flouride – A New Solid Lubricant Additive For Greases”, NLGI Spokesman, Jul 1984.

[31] J. P. King, M. J. Devine “Advances In Wear Protection Of Metal Surfaces From Complex Sulfide Lubricating Greases”, NLGI Spokesman, Apr 1987.

[32] P. Aswath, K. Patel, S. Munot, R. L. Elsenbaumer “Development Of A High Performance Low Molybdenum Disulfide Grease”, NLGI Spokesman, Feb 2007.

[33] J. Phlen “Investigating Alternatives To Molybdenum Disulfide By Means Of Rvt- And DfbtTribometer”, NLGI Spokesman, May 2007.

[34] J. Landry “Part 1- Viable Alternatives To Molybdenum Disulfide (Moly) In Greases Novel Extreme Pressure Additives”, NLGI Spokesman, May/Jun 2010.

[35] J. P. Kaperick, J. Guevremont, K. Hux “A Study Of Friction Modifiers In Grease”, NLGI Spokesman, May/Jun 2011.

[36] G. Fish “Friction Modifiers For Lubricating Greases”, NLGI Spokesman, Mar/Apr 2014.

[37] G. Diloyan, A. Margolin, L. Drangai “Fullerene-Like Inorganic Nanoparticles (If-Ws2) As Extreme Pressure And Antiwear Additive In Grease Applications”, NLGI Spokesman, Jul/Aug 2015.

[38] E. McDaniel, G. Diloyan “Unique Spherical Nanoparticles Of Tungsten Disulfide If-Ws2 As High Performance Additives For Greases”, NLGI Spokesman, Nov/Dec 2017.

[39] E. Ballester, M. Sui, C. Fillion “Effect Of Ptfe Particle Size On Wear And Coefficient Of Friction”, NLGI Spokesman, Sep 2001.

[40] M. Moon “PTFE For Lubricating Greases”, NLGI Spokesman, Jul/Aug 2015.

[41] M. Moon “Lubricating Behavior Of A Superior PTFE Powder In Lithium Grease”, NLGI Spokesman,Sep/Oct 2016.

[42] J. P. Kaperick “Fretting Wear – Something To Worry About?”, NLGI Spokesman, Jul 2008.

[43] J. P. Kaperick, J. Guevremont, K. Hux, M. Sturtz “Fretting About Wear? An Evaluation Of Additive Response In The Fretting Wear Performance Of Greases”, NLGI Spokesman, Mar/Apr 2010.

[44] P. Shiller “The Effect Of Boron Additives In Grease On Fretting Wear”, NLGI Spokesman, Mar 2009.

[45] G. Fish “Grease And Additive Influences On Fretting Wear”, NLGI Spokesman, Mar/Apr 2010.

[46] O. Rohr “Bismuth A New Metallic But Non-Toxic Replacement For Lead As Ep-Additive In Greases”, NLGI Spokesman, May 1993.

[47] J. Kurosky, V. Zanfir “Extreme Pressure Properties Of Lithium Complex Grease Formualted With Bismuth Naphthenate And Various Sulfur Containing Additives”, NLGI Spokesman, Dec 2005.

[48] G. Fish “Grease And Additive Influences On Fretting Wear”, NLGI Spokesman, Mar/Apr 2010.

[49] W. C. Ward Jr., G. Fish, C. F. McFadden “Extreme Pressure Performance Of Greases- Passive Ep Additives”, NLGI Spokesman, Jul/Aug 2013.

[50] S.M. Niazy, W.H. Chappell, J.R. Soulen “Ep And Anti-Wear Properties Of Greases Containing A Complex Sulfide Additive”, NLGI Spokesman, Mar 1972.

[51] J. M. Baker, N. C. Mathur, R. M. Sheets, D. D. DeGonia, J. M. Gerardo “Novel 2-Sulfide-1,3,2Dioxaphosphorinane Anti-wear Additives”, NLGI Spokesman, Jan 2009.

[52] A. P. Malshe, W. Zhang, M. Murphy, G. Schwartz “Super-Additive Packages- The Next Generation Of Lubrication Performance Enhancing Activities”, NLGI Spokesman, Mar/Apr 2015.

[53] C. F. Kernizan, D. Kothen “Development Of A High Performance Li Complex Grease Without Using Additives Which Contain Heavy Metals”, NLGI Spokesman, Apr 2009.

References: Corrosion Inhibitors [1] G. R. John, B. Tury “ Novel Rust Preventatives”, NLGI Spokesman, Jun 1990.

[2] R. F. Baker, P. F. Vaast Jr. “Sulfonates As Corrosion Inhibitors In Greases”, NLGI Spokesman, Feb - 67 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

1991.

[3] M. E. Hunter, R. F. Baker “The Effects Of Rust Inhibitors On Grease Properties”, NLGI Spokesman, Mar 2000.

[4] M. E. Hunter, R. F. Baker “Corrosion: Rust And Beyond”, NLGI Spokesman, Mar 1999.

[5] R. F. Baker, P. F. Vaast Jr. “The Influences Of Sulfonates On Anti-Wear Properties Of Greases”, NLGI Spokesman, Mar 1992.

[6] M. E. Hunter, S. Q.A. Rizvi, R. F. Baker “Ashless Rust Inhibitors For Greases”, NLGI Spokesman, Jun 2001.

[7] R. F. Baker “Barium Sulfonates in Lubricant Applications With a Regulatory Overview”, NLGI Spokesman, Feb 1994.

[8] J. Kaperick “Rust For The Record: Significant Factors Affecting Corrosion Protection In Grease”, NLGI Spokesman, Jul/Aug 2018.

References: Oxidation Inhibitors [1] S. F. Calhoun “Antioxidants For Greases”, NLGI Spokesman, Mar 1956.

[2] J.L. Zakin, H.H. Lin, E.H. Tu “Exploratory Studies Of The Sorption And Extraction Of Additives In Lubricating Greases”, NLGI Spokesman, May 1967.

[3] M. Fletschinger, P. Rohrbach, M. Ribeaud, V. Bajpai “Non-Depleting Antioxidants For Long Term Performance Greases”, NLGI Spokesman, Jun 2005.

[4] K. Umehara, N. Tanaka, S. Lino “Study Of Antioxidant For Lubricant”, NLGI Spokesman, Jun/Jul 2009.

[5] J.L. Reyes-Gavilan, P. Odorisio “A Review Of The Mechanisms Of Action Of Antioxidants”, NLGI Spokesman, Feb 2001.

References: Polymers [1] G.D. Hussey “Alteration Of Grease Characteristics With New Generation Polymers”, NLGI Spokesman, Aug 1987.

[2] B. K. Larson, W. Mroczek, D. DeVore “Benefits Of Polymer Additives In Grease”, NLGI Spokesman, Jan/Feb 2010.

[3] D. Vargo, B. Lipowski “The Effect Of Polymer Additives On Grease Flow Properties”, NLGI Spokesman, Nov/Dec 2016.

[4] D. DeVore, D. Vargo, B. Lipowski “Polymers To Enhance The Performance Of Inorganic Grease”, NLGI Spokesman, Jul/Aug 2017.

[5] D. A. Devore, D Vargo “Study On Viscosity Modifier For Biodegradable Ester-Based Lubricants?”, NLGI Spokesman, Jul/Aug 2013.

[6] V. Levin, F. Litt “Tackifiers For High Temperature Lubricants”, NLGI Spokesman, Jul 2004.

[7] E. Willett, D. Vargo “Investigation Of High Temperature Stability Of Tackifiers”, NLGI Spokesman, Jan/Feb 2018.

[8] S. Wang, D. A. DeVore “Polymers In Enhancing Water Spray Off Performance Of Mineral Oil And Vegetable Oil-Based Grease”, NLGI Spokesman, Jan/Feb 2012.

[9] C. F. Kernizan, K. Harris “Effects Of Polymers In The Manufacturing And Performance Of Lithium 12-Hydroxy Stearate Greases”, NLGI Spokesman, Jan/Feb 2012.

[10] R. A. Denis, M. R. Sivik, H. F. George “Pour Point Depressants And Their Impact On The Low Temperature Properties Of Greases”, NLGI Spokesman, Oct 2003.

[11] C. R. Scharf, H. F. George “The Enhancement Of Grease Structure Through The Use Of Functionalized Polymer Systems”, NLGI Spokesman, Feb 1996.

[12] C. F. Kernizan, P. R. Todd, M. E. Bartlett “Future Directions- Evaluation Of Greases Formulated With - 68 NLGI Spokesman | VOLUME 88, NUMBER 2 | May/June 2024

Functionalized Polymers”, NLGI Spokesman, Nov 2002.

[13] C. F. Kernizan, H. F. George, C. M. Oliveto “Fp Additized Greases – Part 1- Bearing And Analytical Performance”, NLGI Spokesman, Jun 2000.

[14] H. F. George, C. F. Kernizan, M. E. Bartlett “Fp Additized Greases – Part 2- Rheological Test Development And Correlation With Krl Bearing Results”, NLGI Spokesman, Jul 2000.

[15] W. C. Ward Jr., S. R. Twining, J. B. Zeitz “A Comparison Of Properties Of Greases Containing Functionalized Polymer”, NLGI Spokesman, Apr 2007.

[16] W. C. Ward Jr., F. Qureshi “The Impact Of Polymers Blended To A Target Viscosity Range Upon Base Grease Properties”, NLGI Spokesman, Apr 2008.

References: Miscellaneous [1] M. A. Lesser ‘Varied Role Of Glycerine In Modern Lubrication – A Literary Survey”, NLGI Spokesman, Mar 1953.

[2] A. Izcue G., S. A. Krafft “The Effects Of Lead Compounds Upon The Dropping Points Of Lithium Lubricating Grease”, NLGI Spokesman, Nov 1980.

[3] A. Drury “Review Of Greases Containing Solids For Centralized Systems”, NLGI Spokesman, Jun 1987.

[4] L. Z. Zhong, L. Qinglian, L. Gengzin, B. Shoajun “Influence Of Stearic Acid On Lubricating Greases Containing Zinc Dialkyl Dithiophosphate”, NLGI Spokesman, Jul 1995.

[5] I. Macpherson “Industrial Lubricant Additives For Hydrocracked Base Oils”, NLGI Spokesman, Apr 1997.

[6] I. Roehrs, A. Fessenbecker “A New Additive For The Hydrolytic And Oxidative Stabilization Of Ester Based Lubricants And Greases”, NLGI Spokesman, Jun 1997.

[7] J. Kurosky, W. Jerome “Lithium Complex Thickened Grease Shows Improved Water Resistance With Addition Of Bismuth Carboxylate”, NLGI Spokesman, Mar 2003.

[8] J. J. Lorimor “An Investigation Into The Use Of Boron Esters To Improve The High-Temperature Capability Of Lithium 12-Hydroxystearate Soap Thickened Grease”, NLGI Spokesman, Sep/Oct 2010.

[9] V. Deshmukh, B. Rajput “Evaluation Of Boron Esters In Lithium Complex Greases Prepared With Hydrogenated Castor Oil”, NLGI Spokesman, Sep/Oct 2016.

[10] J. Kaperick, G. Aguilar, K. Garelick, A. Miller, M. Lennon, M. Edwards “Complex Issue Of Dropping Point Enhancement In Grease”, NLGI Spokesman, Nov/Dec 2017.

[11] M. Vennampalli, N. K. Pokhriyal, V. R. Bansal, D. Saxena, S. S. V. Ramakumar “Exploratory Studies On Borate Esters As Dropping Point Enhancers”, NLGI Spokesman, May/Jun 2019.

[12] J. A. Waynick “A Fresh Look at Lithium Complex Greases, Part 1: How Did We Get Here”, NLGI Spokesman, Mar/Apr 2021.

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Test Methods: A History of Their Development as Disclosed in the NLGI Spokesman William Tuszynski, The Unami Group LLC J. Andrew Waynick, Freelance Research Chemist

Abstract The NLGI Spokesman has been published since 1937, although back editions only become available starting in 1941. The Spokesman papers archived on the NLGI website provides a historical record of the development of grease technology over the decades. This paper is the final one in series of three.

The previous two papers were: William Tuszynski, J. Andrew Waynick, “Grease Thickeners: A History of Their Development as Disclosed in the NLGI Spokesman”, NLGI Spokesman, Jan/Feb 2024.

William Tuszynski, J. Andrew Waynick, “Base Oils and Additives: A History of Their Development as Disclosed in the NLGI Spokesman”, NLGI Spokesman, May/Jun 2024.

This paper provides a summary of Spokesman papers as related to the development and evaluation of the major test methods used in the industry.

Each of these test methods are discussed in turn starting with the early references covering the development and codification of the test, often as ASTM methods, followed by examples illustrating the use of the tests in grease development and application. The discussions provided in this paper as related to the numerous cited Spokesman papers are not comprehensive in their coverage. Only summaries are provided so as to allow the reader to determine if a full reading would be useful.

Each major section has its own corresponding reference section at the end of the paper. This allows the reader to more easily research the areas of interest while not becoming entangled in areas of lesser interest. While not exhaustive, the information in this paper does serve as a valuable starting point for those who wish to obtain a more complete understanding of this subject matter.

Introduction The importance of having reliable and relevant test methods for characterizing the physical properties and performance of lubricating greases cannot be overstated. Formulators, manufacturers, and end users rely on these tests to determine if a product is fit for use and is consistent from batch to batch.

Suppliers use these tests to demonstrate that their offerings convey an advantage to their customers.

The important tests for the grease industry are described in the NGLI Lubricating Grease Guide, 7th Edition [1]. The development and validation of grease tests is governed by the ASTM D02.G Committee and the relevant sub-committees. The structure and scope of both D02 and D02.G was described in a 1997 paper [2].

Test development and improvement is an ongoing theme in the NLGI Spokesman and this paper.

New tests are developed to address more exacting performance requirements. There continues to be an ongoing search for tests to predict service life, particularly in high temperature applications.

Instrument manufacturers improve the utility and reliability of their instruments, leading to new test development.

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Of particular note is the importance of test selection and development in the creations of NLGI’s grease certification marks.

Three 1968 papers addressed the relevance of the available ASTM tests and their utility to customers, equipment designers, and in production quality control [3-5]. The second paper [4] included a call for a designation system similar to the classification system for motor oils. This was roughly the time work began on what would eventually be the NLGI GC/LB grease classification system, which was introduced in 1986 and described in a 1990 paper [6].

Similarly, the development of NLGI’s High Performance multiuse (HPM) specifications and associated tags was begun in 2019 [7].

This paper is organized into four major sections: 1. Bench tests measuring bulk structural properties 2. Bench tests measuring functional properties 3. Performance tests using equipment components 4. Analytical/Compositional tests It should be noted that the boundaries between these four sections are not always sharp or clear. So, for instance, viscometry and (especially) rheometry could be part of either of the first two major sections since aspects of those tests can relate to both structural and functional properties. Likewise, the ordering of different test methods within some of the four major sections is also somewhat subjective. However, the placement of the various test methods within each of the four major sections and their respective ordering have been done in a way that should provide a reasonable flow for most readers.

BENCH TESTS MEASURING BULK STRUCTURAL PROPERTIES Cone Penetration (ASTM D217/D1403) This section and the later ones on Roll Stability and Viscometry/Rheology discuss the need to understand the flow behavior of grease under shear conditions characteristic of in-service use.

Presented in chronological order of development, each test is increasingly sophisticated and gives a deeper insight on the mechanical stability and flow behavior of the subject grease. Some of the early references will appear in multiple sections because they either compare multiple methods or because they attempt correlations which are beyond the scope of the test. This is particularly true for cone penetration.

Cone penetration, ASTM D217, was first codified as an ASTM test in 1925 and became the basis for the NLGI Classification of Greases (Table 1) [1,2].

Table 1: NLGI Classification System - 13 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

The further development and applicability of ASTM D217 was covered in a series of four papers between 1942 and 1944 [3-6]. Another 1942 paper addressed the difficulty in measuring penetration of semi-fluid greases, grade 0 and softer, by varying cup diameter and cone weight [7]. The use of a light-weight cone for soft greases was further discussed in 1949 [8]. A second 1949 paper proposed using a perforated disk to measure the penetration of semi-fluid greases [9]. The effect of cone geometry on the penetration measurement of block greases (NLGI 4 and higher) was covered in a 1948 paper [10].

Measuring penetration beyond 60 strokes proved to be tedious, with the early mechanical workers taking a full day to prepare the sample [11]. This 1947 paper disclosed a micro-worker consisting on two syringes yoked together with a fine mesh in between, allowing for the relatively rapid application of 100K strokes on a small sample. The 1948 introduction of the mechanical grease worker was a major advance in simplifying penetration measurements at 10K and 100K strokes [12]. A 1955 paper compared the results of using a fine-holed grease worker with 250 1/16” holes with the standard 51hole worker with ¼” holes as a means of more rapidly determining the shear stability of a grease [13].

With the codification of the procedure, researchers began to use cone penetration to investigate grease properties and structures. A 1950 paper showed that a grease-like structure with similar penetration values could be obtained by treating an oil with short nylon fibers [14].

A series of five papers on the mechanical stability of greases were published in the Spokesman in 1956. These were reprinted from a February 1955 ASTM Symposium. The first paper compared ASTM D217 with the “Shell Roller Test” as indicators of grease shear stability [15]. The authors noted the importance of shear and shear rate but were unable to measure either in their testing. The second paper presented data on bench testing, again using ASTM D217 and the Shell Roller Test, and correlated those data with field performance in wheel bearings [16]. A third paper looked at the effect on penetration of low shear (103 sec-1) using 100K double strokes, and high shear (106 sec-1) with five passes through a high-pressure Gaulin homogenizer. The results were compared with both laboratory and field bearing tests [17]. The final two papers in the series provided brief synopses of the three papers cited above along with six others presented in the symposium [18-19].

Two 1957 papers looked at the storage stability of military-grade greases. The first examined aviation greases stored for 30 months at room and elevated temperature. Changes in penetration, apparent viscosity, and low temperature torque were measured [20]. The second paper studied whether the accelerated ageing of grease at elevated temperature and under oxygen pressure can be used to predict storage stability [21]. The studies are notable for using a “ring penetrometer” fashioned from piano wire (note not specified). The ring penetrometer results were correlated with cone penetration data.

A laboratory mixer with a magnetic clutch was used to develop a correlation between torque and reactor charge to estimate the penetration number of the finished grease [22] in a 1960 paper.

A similar correlation was developed in 1970 for continuous grease production using power consumption as a proxy for torque [23].

A very short, one-page, paper in 1962 showed a log-log correlation between the cone penetration at 77 F (25 C) and the apparent viscosity at 10 sec-1. The correlation was independent of thickener type

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and base oil over the range of NLGI 000 to NLGI 2 [24]. This work was extended in 1969 to include a broader range of penetration values and grease classes. This work showed that the linear correlation breaks down for firmer greases and that each thickener type has a characteristic curve [25].

A 1974 paper argued for the relevance of ASTM D217 in setting product specifications [26]. After 1974, no papers focused on the cone penetration method until 1988. This paper [27] discussed the time factor in rheology and addressed the inadequacy of ASTM D217 to the impact of time on the stress modulus (G’) of a grease. A follow-on 1991 paper from the same company cited the use of controlled stress rheometry to understand the flow properties of grease with cone penetration having utility only as a quality control tool [28].

At the same time, a 1990 article noted the poor reproducibility of ASTM D217 is inconsistent with the defined penetration ranges for NLGI Grease grades [29]. In 1993, Turner demonstrated how inconsistent surface roughness of the cone influences the reproducibility of the results [1]. A 1999 paper applied statistical tools as a means of improving the utility of cone penetration in quality control [30].

Alternatives to cone penetration were examined in two papers. The first, by Faci and Massimino, proposed using roll stability as an alternative measure [31] while Humphries and Kumar correlated Brookfield viscosity data with penetration for the range of NLGI 0 to 000 [32].

Most recently, Flemming, Sander, and Courtney contrasted the results from rheometry measurement with cone penetration as indications of pumpability and ability to flow under working conditions [33].

Subsequently Flemming and Sander proposed dropping cone penetration in favor of any of several alternative measurements, including controlled stress rheometry [34].

Both roll stability and rheometry are discussed in detail in subsequent sections of this paper.

Dropping Point (ASTM566/ASTM D2265) As might be imagined, dropping point is cited in a large number of Spokesman papers, appearing in over 550 papers, or just over 30% of the archived technical articles. The vast majority of these references use dropping point as part of the characterization of subject greases. Nevertheless, a number of papers concern themselves with the method, how it is run, and the utility of the results.

The first Spokesman paper to do so appeared in 1943 as part of a survey article on grease testing [1].

As originally envisioned, the dropping point was hoped to be indicative of the melting point of soapbased thickeners, but it was quickly realized that this was not the case.

This paper showed a total of ten different methods, including ASTM D556, and showed the variability when the same grease was tested by different methods. The following year the NLGI Technical Committee reported on ASTM D566 as the standard method, having been adopted by ASTM in 1942 [2]. The author noted that the dropping point did not represent the upper useful temperature for a grease nor was it indicative of soap content. This paper also cited the first proposal of the aluminum block method that became ASTM 2265 in the early 1960s. The same point, that dropping point is not an indicator of high temperature performance, was reiterated in a 1957 paper [3]. A second 1957 paper defined dropping point as distinct from a grease’s melting point [4].

A 1964 paper further reviewed the ASTM D566 method as a “quick and easy test” that “should be considered as having very limited bearing upon service performance” [5]. A second 1964 paper - 15 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

used gas chromatography to evaluate the fatty acid profiles of various vegetable sources on grease properties, including dropping point, in calcium and lithium-calcium soap greases [6].

The aluminum block heating method, ASTM D2265, was introduced in 1964 and described in a 1967 paper as a faster and safer way to run dropping point [7]. A correction factor was needed to align the results of D566 and D2265 so as not to force specification changes if the new method was substituted.

This paper also revised the repeatability and reproducibility of ASTM D566 with a new round robin test. The author expressed the hope that D2265 would supplant D566 as the method of choice.

The process of setting specifications and the relevant tests, including dropping point, were discussed in a 1973 paper [8]. The authors stated that dropping point “has no great significance as to service performance other than indicating an approximate temperature range for a specific application.

However, many consumers feel it is necessary to include a minimum figure for this test in their specifications.”

Although dropping point was routinely reported as part of the characterization of greases discussed in the Spokesman, it wasn’t until 1992 that a paper specific to dropping point appeared [9]. This paper discussed the issues surrounding the use of ASTM 2265, showing that the initial block temperature strongly influences the results and that the “correction factor” becomes increasingly unreliable for high temperature greases.

Coe [10] raised serious questions about the utility of dropping point to estimate the upper temperature limit of a grease, noting that the difference between the reported dropping point and manufacturer’s recommended upper use temperature for commercial greases varied from 59 C to 120 C for the greases examined.

While the scope of this review is nominally through the end of 2019, Fish’s 2020 paper [11] questioned whether either dropping point test should be retained or whether it should be taken out of use, and is accordingly worthy of inclusion here. This paper also reviewed the history of the methods described above.

Roll Stability (ASTM D1831) As noted in the discussion of cone penetration (ASTM D217), dropping the cone into a sample applies low and inconsistent shear to the grease and provides little information about mechanical stability in use [1,2]. In 1947, a paper reported on the use of a “Gulf Pressure Viscometer” to calculate apparent viscosity, and thereby allowed for grease flow in a pump or bearing to be estimated [3]. Further work using this instrument was documented in a 1951 paper [4]. More information on grease viscometers was provided in a later section of this paper.

The first citation of the “Shell Roller Test” came in a 1950 paper that used a variety of techniques, including electron microscopy to study grease structure and rheology [5]. That the test was well established at that point was apparent by how it was discussed in the text. The test and the importance of the results as indicators of mechanical stability was discussed in detail as part of a 1955 ASTM Symposium that was reported in the NLGI Spokesman [6]. The details of the test and the specification for the equipment were given in another 1955 paper [7].

As seen in the previous section, several attempts were made to correlate cone penetration and roll stability data with field performance [8,9]. The first paper explicitly stated that neither test was - 16 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

an adequate indicator of service in use while the second reported more positive results, at least in indicating the relative performance of test greases. A summary of five papers from the 1955 ASTM Symposium, including references [8] and [9], noted that four of the five authors claim that there was no true correlation between laboratory tests, either cone penetration or Shell roll stability, and field performance [10].

Despite these caveats, both cone penetration and roll stability continued to be and are still used to characterize greases. A 1974 paper noted that roll stability is mostly used for quality control, but the authors modified the test to run both for up to 96 hours and also at temperatures up to 180 F (82 C). While the greases tested hardened or softened differently, it was noted that while poor results indicated poor field performance, good performance in the test did not guarantee similar results in use [11].

A second 1974 paper noted that the shear rates in the roll stability test are 2-4 orders of magnitude less that those seen in a bearing. The authors stated that roll stability data are useful for predicting pumpability but are not relatable to performance in a bearing [12].

A 1977 paper described a MIL spec for wheel bearing greases based on a modified ASTM D1831, again running the test for longer duration at elevated temperature [13].

With the development of sophisticated rheometers [14-15], the roll stability test as described in ASTM D1831 was relegated primarily to use as a quality control tool and as a screening test.

Oil Separation/Bleed (ASTM D1742/ASTM D6184/IP121) Oil Separation or Bleed, sometimes called Syneresis, has been recognized as a phenomenon as far back as 1861 [1]. Separation of oil from a grease is undesirable in storage [2] and in centralized lubrication systems [3], but is recognized as an important in bearing lubrication [4].

ASTM D1742, and ASTM D6184 measure oil bleed at ambient and elevated temperature, primarily for storage stability [5]. IP121 was documented in a 1947 Spokesman paper [6]. The various methods to measure bleed, including several not formally codified, were summarized in a 1943 paper [7]. A 1945 paper documented an alternative test method based on using air pressure to drive grease bleeding [8]. Four tests for oil separation, the Crater Test, the Pressure Filtration test, the Centrifugation test, and the Herschel Press test, were documented and compared in 1950 [2]. A 1955 paper used the Herschel Press Test to derive data to generate syneresis curves for a variety of greases [9]. The laboratory results from the Crater test, two MIL Spec bleed tests, and the Centrifugation test were compared with field results, with the Centrifugation test showing the best correlation [10].

Two 1962 papers looked at the effect of oil viscosity on bleeding in lithium [11] and lithium calcium [12] greases made in either paraffinic or naphthenic basestocks, while a 1964 paper found ASTM D1742 and the Centrifugation test to be the best predictors of bleed in field storage [13]. This paper provoked a comment about the validity of the conclusions and author response [14].

A 1966 paper evaluated the factors effecting bleed in soap-thickened greases and ascribed 20-25% of the oil retention to molecular attraction and the remainder to capillary forces [15]. A 1969 study ran a factorial matrix using ASTM D1742 run for an extended time of seven days to derive equations related to the initial bleed rate and ultimate bleed volume for a set of conventional lithium soap greases [16].

A year later, it was demonstrated that, at least in ASTM D1742 and its variants, grease bleed occurs - 17 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

from the grease at the bottom of the sample with a corresponding increase of soap concentration at the bottom, and not homogeneously throughout the grease [17]. The same authors extended this work to show that the percent oil bleed was a linear function of the square root of the test duration [18].

A 1975 paper presented a test rig to evaluate oil separation and leakage of wheel bearing greases from a disc brake assembly [19]. The next paper of interest was a 1984 study of plugging in centralized lubricant systems. In this paper, the authors cited base oil viscosity as causing increased hardening and plugging due to oil separation [20]. A 1985 paper used centrifugation to estimate the degree of oil separation in flexible couplings, comparing ASTM and AGMA protocols [21]. Arbocus provided a summary of an NLGI seminar on plugging in centralized lubricant systems in 1986 ]22].

Bessette investigated the effect of oil separation on apparent viscosity in a 2006 paper [23].

BENCH TESTS MEASURING FUNCTIONAL PROPERTIES Extreme Pressure/Antiwear (ASTM D2266/D2509/D5706/D5707, etc.)

As should be expected, a search of Spokesman papers using terms such as “extreme pressure”, “antiwear”, or any of the most commonly used EP/AW tests or corresponding ASTM method designations yield an extremely large number of entries.

The earliest such Spokesman papers reveal a wide range of opinions regarding the importance of EP/ AW properties of lubricating greases. The first mention of EP/AW performance in greases occurs in the December, 1941 issue, the third issue available in the NLGI archives [1]. However, papers published over the next four years later gave divergent opinions. Two did not include EP/AW in its list of important grease properties [2-3]. A third acknowledged only mild EP/AW properties to be important, at least in military applications [4]. Yet another acknowledged EP properties to be important, but listed only several aluminum rolling mill applications as examples where such performance would be important [5]. None of these papers cited any specific EP/AW tests.

The first paper that could be found that cited specific EP/AW tests for greases was authored by Kaufman and published in 1947 [6]. Test methods mentioned were the Timken test, the Four Ball test, and the Falex (Pin and Vee Block) test. The Timken test was claimed to probably be the best test for determining the EP properties of a grease. Over the next 52 years, those tests and a few others would be cited in papers where multiple EP/AW tests were used in the evaluation of lubricating greases [710].

In a 1953 paper, EP/AW test methods mentioned included Timken, Four Ball, Falex, and Almen. The Timken test was again mentioned as the most important for EP properties, with an OK Load of at least 33 pounds being a frequent specification requirement [7]. In two other papers, the evaluation of MoS2 in grease was done using several EP/AW test methods including the Four Ball EP test for Mean Hertzian Load, Four Ball Wear, several procedures using the Falex Pin and Vee Block tester, and several “Timken Endurance” tests (the basis for what would eventually be called Timken Thin Film Retention tests) [8-9]. Finally, in 1969, yet another paper evaluated the combination of MoS2 with each of five oil-soluble EP/AW additives using the Four Ball EP, Four Ball Wear, Falex Pin and Vee Block, and Falex Oscillating Ball on Disk tests [10].

As would be expected, the two EP/AW tests that are most frequently mentioned in the Spokesman are the Four Ball test (EP and Wear) and the Timken test. The first paper to discuss as its central - 18 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

topic either of those EP/AW grease tests was authored by Nason and published in 1952 [11]. In that paper, the Four Ball test equipment, as developed by Royal Dutch Shell, was used to measure the Mean Hertzian Load (now called the Load Wear Index) as a superior alternative to an earlier Pressure Wear Index from an older cited government method. As a result of this initially published work, the Four Ball test equipment was commonly called the Shell Four Ball tester until the Four Ball EP and Wear tests became standardized in 1968 as ASTM D2509 and ASTM D2266, respectively [12-13].

With the use of the Shell Four Ball machine to evaluate the EP properties of greases, it was inevitable that a modified method would be used to evaluate the AW properties. In 1956, the test requirements of two U.S. military grease specifications were discussed using several greases as examples. By this time, the Four Ball Wear test and the determination of the Mean Hertzian load (LWI) using the Four Ball EP test were already part of such specifications. In 1964, a paper described commercial greases that were oxidized by a modified version of ASTM D942. At various test durations, samples were removed and evaluated using the Shell Four Ball Wear test as it was then called [15]. This was four years before D2266 became a standardized method.

Even after the ASTM had standardized the Four Ball EP test, additional investigations were reported regarding the calculation of the LWI and its relationship to the Weld Load [16-17]. Another paper from 1973 discussed the statistical integrity of the Four Ball EP test and how reliable quality assurance might be affected. The authors recommended that testing a grease in more than one laboratory was a good way to minimize the likelihood of using a grease with sub-specification test performance [18]. This recommendation was considered by them to be even more valid when using the Timken test.

A brief history of the Timken test for greases, standardized as ASTM D2509, was also published in 1973. This paper also provided a description of the equipment and a discussion of the statistical integrity of the test. The authors maintained that test equipment not being run at exactly the specified conditions was a significant reason for the poor reproducibility of the Timken EP test [19].

The well-known poor reproducibility of ASTM D2509 resulted in a re-examination of the test by the ASTM. Two 1978 papers discussed this re-examination and the revised method that resulted.

This revised method included a simpler method of applying the load, and a procedure to ensure the loading rate is as specified by the method [20-21]. A short paper published six years later reported the importance of maintaining certain Timken machine parameters such as sharp and aligned knife edges, a firm anchoring of the table to the floor, and the main shaft axial clearance. Failure to maintain these machine parameters at the correct levels were shown to cause erratic test results [22].

A study from 2007 provided experimental evidence that the reason why Timken OK Loads for oils and greases of comparable compositions (except for the thickener) were different was due to the effect of the thickener on the mobility of the base oil and additives to get to the ring and block tribo-zone during the test [23].

Another EP/AW test machine that gained significance in the 1980’s was the SRV tester. A key feature of the SRV tester was that it provided short amplitude oscillatory movement of one test specimen against another specimen separated by a thin film of the lubricant being evaluated. Different specimens could be used, thereby allowing various point, line, or area contacts during the test. The very short oscillatory amplitude resulted in negligible frictional heat between the two specimens during the test. This allowed the tribo-zone temperature to be both known and controllable, - 19 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

something not possible for the Timken and Four Ball tests. Two papers published in 1982 used the SRV to evaluate the frictional properties of graphite/oil dispersions [24-25]. By 1985, the SRV was listed in a survey of testers used to evaluate the EP/AW properties of greases [26].

Perhaps the most important application of lubricating greases where the SRV tester found utility was constant velocity (CV) joints. This was in part due to a major U.S. automotive OEM that had included an SRV EP (stepload) test procedure as a specification requirement for their initial-fill CV joint grease.

Since this application for this OEM constituted the largest single customer grease demand in the U.S., several grease manufacturers and additive suppliers had purchased SRV testers by the mid-1980’s.

Two papers provided examples of using the SRV to evaluate additives for greases that were being developed for initial-fill CV joint lubrication [27-28].

SRV test methods were standardized in 1995. In a paper published two years later, Dickey documented the standardization of three SRV test methods and provided the round robin test results.

The test methods were ASTM D5706 (EP stepload test), ASTM D5707 (AW test), and DIN 51 834 (coefficient of friction test) [29].

A few other EP/AW test methods were discussed between the years 1951 and 1978. They included a Navy Gear Wear Tester [30-31] and a Ring on Block tester [32]. The later was eventually standardized as ASTM D2714.

Water Resistance (ASTM D1264/D4049) The term “water resistance” is cited 521 times in a Spokesman search. Nearly all of those papers deal with the subject of water resistance only in a peripheral way or as just one of many test methods used to evaluate greases. However, the few papers that do discuss water resistance tests and their development reveal an interesting historical progression.

Roehner and Carmichael authored the first such paper in 1947 [1]. Two methods from ArmyNavy Aeronautical Board Specifications - a water adsorption test and a water resistance test - were discussed. The water resistance test was apparently a very early version of what would eventually become the water washout test (ASTM D1264). The lack of correlation between water resistance and corrosion (rust) preventive properties was also discussed. This lack of correlation between a grease’s ability to resist displacement by water and its ability to impart corrosion protection would be a source of confusion in some subsequent papers that discussed each of these properties.

Within the next seven years, two additional papers were published that discussed several water resistance tests that included a water washout procedure. In the first, Reynolds described two water resistance tests [2]. One involved exposing a film of the grease to a dilute solution of phenolphthalein to determine if a chemical reaction occurs. The other was the previously mentioned early U.S. military test version of what would eventually be the standardized water washout test (ASTM D1264) in 1953.

In the second paper, Hendricks and Smith provided a survey of test methods designed to evaluate the water resistance properties of a grease [3]. One method involved rubbing the grease on the bare palm of one’s hand under a stream of water from an open faucet. Such a method clearly showed a different mindset regarding toxicological/safety concerns. The same military test version of the now ASTM D1264 was also mentioned without citing the ASTM procedure that had been approved one year earlier.

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By 1975, at least two papers had cited ASTM D1264 as the only method for determining a greases resistance to water in current applications and future specifications [4-5]. This was despite the fact that the initial disclosure of a water spray off method and ongoing efforts to standardize such a method by the ASTM were already well known.

One year later, Gannon provided a history of ASTM D1264 from its earliest versions to the ASTM reexamination that began in 1965 [6]. Round robin results of that re-examination were provided along with the resulting revised precision statement. The water spray off test was also discussed as an ongoing effort within ASTM that had begun in 1973.

That same year, a modified version of ASTM D1264 using new test equipment was discussed [7]. This test method was developed as an attempt to better determine water washout properties of a grease when submerged under water, especially when the water temperatures approached the freezing point.

The authors claimed that ASTM D1264 was not adequate for such conditions.

Other water resistance test methods were being discussed during the time the D1264 was being developed. In one paper from 1965, a review of previous water resistance tests was provided, including the early Army-Navy water adsorption test first discussed in 1947. A static immersion method that determines whether an oil slick is formed, and an early water spray off method were also discussed. Then an improved water spray off method was evaluated [8]. That test equipment and procedure would eventually result in ASTM D4049. The static immersion method anticipated the much later European static immersion test DIN 51 807.

One year later, a paper provided a discussion of two methods [9]. One was a special bearing test rig where water is introduced into the running bearing. The time required for free water to be observed leaving the housing was determined as the primary measured parameter. The other was essentially the old Army-Navy water adsorption test.

As previously mentioned, development of a water spray off test began in at least 1965. ASTM began its work to standardize that method in 1973. This work resulted in ASTM D4049 being approved in 1981. One year later, Musilli provided the history of the water spray off test from its earliest reported versions to the final standardized procedure. The ASTM round robin test results were also provided [10].

Only three years after its standardization as an ASTM method, D4049 had become established as an important method to evaluate a lubricating grease’s ability to resist water exposure [11].

Corrosion Protection (ASTM D1743/D5969/D6138/D4048) The terms “corrosion protection” and “corrosion prevention” are is cited 313 and 116 times respectively in Spokesman searches. Likewise, the terms “rust protection” and “rust prevention” are cited 298 and 131 times. Only a small number of those cited papers deal with the development of corrosion and rust preventative tests and their initial usage.

The first such occurrence was a very short 1941 paper stating that “a bright copper or steel plate shall show no discoloration after being submerged in the grease for 24 hours.” No mention was made of the temperature at which the test should be run [1].

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Two years later, Bishkin cited several test procedures to determine the rust preventive properties of coating compounds [2]. These methods included salt water immersion, humidity cabinet, fresh water spray, and salt water spray. This showed that later procedures that used such approaches had their beginnings at least as early as this.

Another paper from the same year discussed in very general terms the importance of a grease to provide protection against corrosion (rust) in sealed bearings [3]. However, no specific mention of a ferrous corrosion test was provided. A footnote regarding copper corrosion protection stated that the grease should not corrode copper after three hours exposure at room temperature. This statement came on the heels of another paper published a few months earlier. In that paper, Georgi discussed two test methods to evaluate the copper corrosion properties of greases [4]. One method was a copper strip test, a forerunner of ASTM D4048. Another was a modification of the NormaHoffman Bomb (pressure vessel) test that by that time was the most common procedure to evaluate the oxidation stability of a grease. In this modified method, a copper catalyst was added to the grease before running the test. In addition to the usual pressure drop measurement, the post-test appearance of the copper was also noted. This appears to be the earliest mention of what would eventually be ASTM D1261, a method that has been withdrawn by the ASTM but is still run upon request by some testing laboratories.

Another early paper from 1947 showed several pictures of post-test tapered roller bearings (both outer race and caged rollers) [5]. No details of the test were provided. However, such work clearly anticipated the later development of ASTM D1743. In the same paper, a Naval Ordinance Specification corrosion prevention test was cited where a grease coated panel (presumably steel) is subjected to a salt water spray for 100 hours.

The earliest paper that could be found that discussed specific corrosion (rust) preventive tests for greases was published the following month of the same year. Several test procedures were mentioned including a salt spray test using 4% synthetic sea water and a humidity cabinet test using greasepacked ball bearings [6]. About the same time, another paper provided an evaluation of lithium 12-hydroxystearate greases using a static tapered roller bearing procedure very similar to what would eventually be ASTM D1743 [7]. The authors claimed that their procedure was based on a method currently under review by the Coordinating Research Council (CRC).

Another test method was described where water was introduced into a grease-packed bearing. The bearing was then rotated under specified conditions. The bearings were visually examined after the test as a measure of the corrosion protection provided by the grease under dynamic conditions [8].

In yet another paper, three new bearing test methods were discussed to evaluate the corrosion preventive properties of greases [9]. The first was a humidity cabinet test. The second was a dynamic bearing test that used previously established military test equipment and methodology (the water resistance test, an early version of ASTM D1264). This method was determined to provide results that correlated with actual in-service performance only for greases with excellent corrosion protection.

The third method was similar to the second, but used only free water after the required run-in period.

One year later, another paper further discussed the free water test [10].

The first paper that could be found where ASTM D1743 is specifically cited and used as the test procedure for determining the corrosion (rust) preventive properties of a grease was published in 1962 [11]. In 1968, a discussion of what future grease performance specifications would include was - 22 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

provided. ASTM D1743 was included as the sole method for the determination of corrosion (rust) preventive properties [12].

ASTM D1743 was originally defined to allow the use of synthetic sea water instead of the usually used distilled water. In July 1997, a separate method, ASTM D5969, was approved for such testing. At the same time, standardization of the EMCOR dynamic bearing corrosion (rust) test as ASTM D6138 was nearing completion [13]. Just two years later, all three major ASTM corrosion prevention bearing tests (D1743, D5969, and D6138) were being used to evaluate greases in published papers [14].

Finally, a paper from 2016 described a modification of the EMCOR dynamic bearing corrosion test where a water washout feature was added to the test [15].

Fretting Wear/Corrosion/Oxidation (ASTM D4170) The terms “fretting wear”, “fretting corrosion”, and ‘fretting oxidation’ are cited 115, 103, and 87 times respectively in Spokesman searches. The term “false brinelling is cited only 15 times. The first paper to mention any of those terms was authored by Morton and Patterson, and was published in 1948 [1]. Fretting wear, fretting corrosion, and false brinelling were discussed. Also, the first version of the Fafnir Fretting Wear tester was disclosed for the first time. Interestingly, a lithium soap grease was used to evaluate the tester, despite it being only six years since lithium soap greases were first disclosed in the open literature.

One year later, several test methods were briefly discussed as they relate to ability of a grease to provide satisfactory performance in bearings. In this regard, the Fafner oscillating bearing tester, as first mentioned in the 1948 paper, was discussed [2].

Three years later, Roehner and Armstrong claimed that several previous machines had been developed to determine the fretting wear properties of grease-lubricated bearings. The original Fafnir Friction Oxidation Machine (as it was then called) was compared to a modified version [3]. This modified version was used to determine the fretting wear protection properties of unadditized and additized calcium soap and lithium soap greases. This modification of the Fafnir fretting wear tester appeared to be a first step in establishing what would eventually be ASTM D4170.

Although the process of evaluating and refining the Fafnir tester had begun, the original tester as described in 1948 was cited twelve years later in a 1960 paper. In that paper, a calcium complex (stearate/acetate) grease was evaluated for “friction oxidation” properties using the original 1948 test method [4]. In an interesting sidebar, co-author Arnold J. Morway had recently received his 200th U.S. Patent when this paper was published.

In one early paper, fretting wear was discussed in general terms. However, no fretting wear test data or actual evaluations are reported [5]. In another paper spanning only two pages, brief definitions / descriptions were attempted for fretting, fretting corrosion, false brinelling, and friction oxidation [6]. One paper examined a failed bearing using X-ray diffraction to show that the specific iron oxide present was consistent with fretting wear [7].

By the early 1970’s, the Fafnir fretting wear test was considered an important test for the evaluation of grease performance in bearings [8-9]. However, around the same time at least one paper considered the Fafnir test to be not yet generally accepted as such [10].

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In a 1979 paper, the history of fretting wear research was provided followed by a discussion of the development of the original Fafnir “fretting oxidation” (fretting wear) tester and its reproducibility issues. A modified Fafnir tester was described and evaluated. Greases used in the evaluation included organo-clay, calcium soap, lithium soap, and sodium soap thickeners. Base oils included synthetic diester, synthetic hydrocarbon (PAO?) and a mineral oil [11].

Another historical discussion of fretting wear was provided three years later [12]. This paper also used the specific Fafnir fretting oxidation test method being evaluated by the ASTM to evaluate the effect of thickener type, thickener concentration, grease temperature, grease hardness, and base oil type on fretting oxidation test results.

One year later, in 1983, Verdura authored a seminal paper that provided a brief discussion of two types of observed fretting wear. Then an equally brief discussion was provided about the modified Fafnir fretting wear tester and procedure that was submitted for standardization by the ASTM. Round robin data were provided, and the finalized equipment and test procedure became ASTM D4170 [13].

During the evolution of the Fafnir tester into the final standardized D4170, a few other bearing test rigs designed to measure fretting wear properties of greases were disclosed. In one, a bearing test rig was designed to determine several grease performance properties using several different procedures.

An oscillatory procedure was used to determine fretting wear properties. Results were compared to those of the Fafnir fretting wear test [14].

In another example, published five years after ASTM D4170 was standardized, a new in-house test rig for the measurement of fretting wear was described [15]. Test data using this new rig were not compared to Fafnir test rig data. Interestingly, the Fafnir test was not mentioned.

Finally, in a paper from 2019, a brief discussion of the Riffel test, a new test to measure false brinelling and corrosion, was referenced [16].

Oxidation Stability (ASTM D942/D5483/etc.)

The ability of a lubricating grease to resist oxidation has been recognized as important as long as lubricating grease research has been reported in the Spokesman. As early as 1943, the NormaHoffman Bomb (Pressure Vessel) test was cited as the only method used to evaluate the oxidation stability of greases. The use of various temperatures and metal catalysts were discussed in this very early paper by Georgi [1]. This was an early reference to what eventually became ASTM D942 and other methods based on it. Another discussion of the Norma-Hoffman test was provided in 1949 [2].

By 1956, the test requirements of two U.S. military grease specifications were being discussed in which the Norma-Hoffman test was included [3]. By this time, the Norma-Hoffman test had been standardized as ASTM D942. Only five years later, it was being used as a research tool to evaluate the effect of various base oils and thickeners on grease oxidation [4] Limitations and problems associated with ASTM D942 had been recognized almost from the beginning of its earliest development. One major problem has to do with the peroxidation of hydrocarbons. Depending on the substrate being oxidized and other process factors, some of the final oxidation products can be gaseous. The primary measurable of D942 is the pressure drop, presumably a direct indication of how much oxygen was consumed. The evolution of gases during the test will cause the measured pressure drop to no longer be a reliable indicator of how much oxidation - 24 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

occurred. Additionally, measuring oxidation at only one temperature can make the results excessively one-dimensional. Finally, if real world grease oxidation occurs where potentially catalytic metal is present, any test that ignores that factor might give results that do not correctly predict performance.

The recognition of last two of those factors is reflected in the 1943 paper mentioned above.

As a result of these factors, papers have been published that provided various modifications to ASTM D942 [5-8]. One paper increased the test temperature to 121 C [5], while another included a post-test analysis of head space gases [6].

In an excellent paper from 1985, Chasan and associates provided a history of the development of ASTM D942. Then previously documented limitations and problems with the test were discussed.

The authors discussed four ways to modify D942: automation of pressure recording; running the test at varying temperatures; adding a metal catalyst; and speciated post-test measurement of headspace oxygen. The latter modification was in recognition of the previously noted tendency of other gases to be released during D942 that can invalidate the meaning of the total pressure drop noted at the test’s conclusion [7].

Twelve years later, a modified version of ASTM D942 was developed as a method that the authors claimed was a more accurate measure of true in-service oxidation stability for a specific lithium soap grease they were developing. Modifications included a higher test temperature and the presence of metal catalysts [8]. Test results of this modified method were provided and compared to several other methods including D942 and D5483. The latter was a pressure differential scanning calorimetry method that will be discussed later in this section.

Although the limitations of ASTM D942 were known early-on, D942 was frequently regarded as the only acceptable test method for evaluation of greases [9] and for inclusion in specifications [10].

Nonetheless, the limitations of D942 were the primary motivation for reported work to develop different test methods not based on D942.

The first such method was a dynamic oxidation test that involved a pressurized and heated roll stability procedure. This approach was first disclosed by Murphy in a 1964 paper that also described some modifications to D942. The dynamic oxidation procedure used the shell roll test where the outer cylinder was filled with 110 psi oxygen before the test began. The test was run for 400 hours at 99 C (210 F) and 10 RPM. The acid value by titration was determined at the end of the test [5]. Two other papers described essentially the same methodology [10-11].

Another dynamic oxidation test that was interesting - if not clearly disclosed - involved a tester wherein a thin film of grease was placed in an enclosed chamber. The thin grease film was exposed to one atmosphere of oxygen that was circulated during the test while the grease film was constantly being regenerated by a mechanism that the authors did not clearly describe. Gaseous oxidation biproducts were condensed in a trap at -76 C. Measured parameters were used to determine kinetic analysis of the oxidation process [12]. The authors used this method to measure the effectiveness of antioxidants. This paper also provided a summary discussion of the peroxidation free radical mechanism.

A somewhat similar but simpler approach was described in a 1995 paper. A thin film of grease was spread on various metal plates and aged at 120 C under normal atmospheric pressure of air. Metal - 25 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

plates were either Fe, Cu, or Zn. Post-test evaluation was by metal plate weight loss, grease color change, and final grease consistency. Several spectroscopic methods were also used including FTIR and SEM [13].

The use of pressure differential scanning calorimetry (PDSC) was an example of an already wellestablished analytical technique adapted to determine the oxidation stability of greases. Several papers were found discussing how PDSC can be used in this way [14-20].

In one of those papers PDSC was run on various greases in both the temperature ramp method and the iso-thermal method [15]. The first method is typically used to determine temperatures where critical physical or chemical changes occur. The second method is used to determine oxidation induction times. PDSC was compared to D942 and FE9 bearing life for a set of greases.

In a paper from 2004, Reyes-Gavilan provided an excellent primer on the PDSC methodology that by then had been standardized as ASTM D5483. This was followed by an evaluation of eight greases comprising differing thickeners. The effect of various antioxidants of measured induction periods was also determined [17].

Five years later, Bessette disclosed an interesting way to use PDSC to determine the thickener content of greases by doing temperature ramp testing [18]. About the same time, Ward and Fish used ASTM D5483 and ASTM D3527 (an automotive wheel bearing test) as screening tests in the development of extended bearing life greases. Based on this testing, FE8 and FE9 bearing tests were performed to further validate bearing life [19].

In a 2012 paper, Turner provided a brief but excellent summary of various grease test methods including a discussion of the standardized PDSC method ASTM D5483 [20].

Another method that was developed to measure the oxidation stability of various materials including lubricating greases was the Penn State Micro-Oxidation test. The first Spokesman paper to discuss this test as applied to greases was authored by Dholakia and associates, and published in April, 1994.

The test involved a thin film of grease (40 mg, about 180 microns thick) in a freshly polished lowcarbon steel catalyst cup. The chamber was immersed in a bath at the desired temperature. After a brief nitrogen purge, air was circulated through the chamber for the test duration. Post-test analysis involved a complex sequence of solvation, filtration, solvent extraction, and analysis by Gel Permeation Chromatography (GPC) [21]. A form of this test would eventually be standardized as ASTM D8206, the Rapid Small-Scale Oxidation Test (RSSOT).

In another paper by the same authors published one month later, six greases using two hydrotreated naphthenic base oils and three different thickener systems were evaluated for oxidation stability using the RSSOT method [22]. It should be noted that this paper incorrectly cited the standardized method as ASTM D7575.

Several other papers discussed various modifications and the use of this test in evaluating the oxidation stability properties of greases [22-26]. Perhaps the most significant of them was a 2002 paper where several modifications to the Penn State micro-oxidation test previously reported in the April 1994 paper were evaluated. Those modifications were based on suggestions from the ASTM subcommittee that was evaluating this test as a potential standardized method. Modifications included using a glass cup instead of the steel cup, replacing the heating bath with an aluminum block - 26 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

heater, replacing the glass reactor with a simpler system more appropriate for the lubricating grease industry, and measuring the final unreacted grease by weight rather than using GPC (which many grease manufactures do not have in-house access to) [23].

The use of voltametry as a method to determine the amount of antioxidant remaining in in-service greases was discussed by Shah and Ameye in a paper published in 2005 [27].

A final reported modification of ASTM D942 was reported in 2015. The modification involved monitoring post-test greases by FTIR (carbonyl stretch peak) instead of the usual pressure drop measurement. The effect of reducing sample size in each of the glass pans or using less grease in just one glass pan was also determined, presumably to determine the effect of oxygen availability [28].

Low Temperature Mobility (ASTM D1478/D4693/DIN 51 805/etc.)

The mobility of a lubricating grease can be considered a subset of the wider properties of apparent viscosity or rheometry. Indeed, there is an unavoidable overlapping of these properties and the terms that are used to describe them. The terms “low temperature mobility” and “low temperature torque” are cited 129 and 458 times respectively in Spokesman searches. As with other searched grease properties, most of those papers only deal with low temperature mobility testing of greases without any real emphasis on the methods themselves. However, the importance of low temperature mobility testing of greases was recognized very early in published Spokesman papers.

The first such paper was authored by Maxwell and appeared in the November, 1942 issue [1]. A simple ball bearing torque test was developed and used to evaluate the low temperature mobility of greases using several different thickener systems. The most significant feature of this paper may be the fact that a lithium soap grease was included even though the first documentation of lithium soap greases was not yet one year old.

In the same issue, the development of the S.O.D. Pressure Viscometer was first disclosed [2]. This test was used to evaluate grease mobility at a range of temperatures. More information on this test method is provided in the Viscometry/Rheometry section.

One year later, Irwin and Britton mentioned a pressure orifice instrument to measure grease mobility that apparently was a precursor to the U.S. Steel Mobility Test [3]. The use of a low temperature torque test in military grease specifications was cited. This pre-dated the development of the standardized ASTM 1478 low temperature torque method. The same year, a similar ball bearing low temperature torque test was cited along with penetration testing at low temperatures as methods to determine the low temperature mobility of greases. Several military low temperature torque methods were listed. The need for further development of a grease viscometer was recommended [4].

By 1944, an attempt to correlate base oil pour point (not yet an ASTM method) with grease low temperature mobility was being made. The S.O.D. Pressure Viscometer was the test method used. Base oil pour point and the use of pour point depressants was determined to not affect low temperature mobility in the greases tested. Instead, thickener content, thickener structure, and base oil viscosity were the factors that affected grease low temperature mobility [5].

Over the next five years at least three other papers dealt with various low temperature torque test methods and equipment, all of which were part of the historical progression that led to the eventual establishment of ASTM D1478 [6-8]. In the first, the N.G.F. (Naval Gun Factory) torque tester - 27 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

was used 0 F (-18 C). Results did not correlate well with another early military specification low temperature torque test done at -67 F (-55 C) [6]. In the second, a low temperature torque test was used to evaluate five greases at room temperature, -54 C (-65 F), and -73 C (-100 F) [7]. In the third, several test methods were briefly discussed as they relate to ability of a grease to provide satisfactory performance in bearings. Two low temperature properties tests were discussed: cold temperature penetration and another form of what would eventually be ASTM D1478 [8].

The first version of ASTM D1478 was approved in 1957, and as late as 1975 papers were citing it as the only method to evaluate a grease’s low temperature mobility [9,10]. However, additional work on other bearing torque tests were still being published [11-17]. In the first of these papers, a torque tester that could be run at temperatures from 121 C (250 F) to -54 C (-65 F) was used to test greases in several different ways. Torque vs. time curves at various running temperatures were obtained.

Torque was also measured as temperature was raised to 121 C, then cooled to -65 C, then increased back to 121 C. Hysteresis curves were obtained [11].

Two papers disclosed a new bearing tester, the Sunoco R-4 Bearing Grease Torque Tester [13,14]. This test equipment and method was developed to determine torque and bearing life properties of greases in small ball bearings. The initial test program covered test temperatures from -54 C (-65 F) to 232 C (450 F).

In 1989, a new method was disclosed by the U.S. Army to determine the low temperature torque properties of greases using automotive tapered roller bearings [17]. This work was done after investigating existing grease torque tests such as ASTM D1478 (a ball bearing test) and ASTM D4693 (a low temperature tapered roller bearing test approved two years earlier). The test used modified D4693 test equipment. The objective was to improve the precision of the test.

Another low temperature mobility method that did not use bearings was DIN 51 805. This method was discussed in a 1971 paper [18]. In this method, a tube was filled with the test grease, cooled to the test temperature, and allowed to equilibrate. Then pressure was gradually and incrementally applied to one end of the tube until grease movement is detected by a sudden pressure drop.

One of the applications of low temperature torque testing has been to evaluate the effect of functionalized polymers on grease properties [19-20].

Another test method used to evaluate lubricating grease mobility and pumpability is the Lincoln Ventmeter test. This method has been used to predict how greases can or cannot be pumped through lengths of bulk handling system piping at various temperatures.

Perhaps the earliest paper that has the Lincoln Ventmeter as its only topic was published in 1951 [21].

The general principle of the test involved filling a long metal tube with grease, cooling the tube and grease to the desired temperature, pressurizing the tube to a specified amount, allowing the cooled and pressurized tube to equilibrate, and then venting one end of the tube and noting the final pressure in the tube. The lower the final pressure, the more mobile or pumpable the grease should be.

From that 1951 paper until 1973, at least four modifications of the original test equipment were described [22-25]. The most important of those modifications was the replacement of a long straight metal tube with a coiled tube with both ends of the coil being on the same end of the coil [23]. This coiled feature has been retained on all subsequent variations of the test equipment.

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In a 1993 paper, the Lincoln Ventmeter was compared to a cone on plate viscometer and another method, the Trabon grease dispensing system. Thirteen greases with consistencies ranging from NLGI No. 2 to NLGI No. 00 were evaluated. Thickeners were lithium 12-hydroxystearate, polyurea, and calcium complex [26].

Five more papers provided additional information on how the Lincoln Ventmeter works, the significance of its results, how it compared to a capillary grease viscometer, and how its results are affected by other grease properties such as NLGI consistency grade and base oil viscosity {27-31].

The ASTM has been evaluating the Lincoln Ventmeter as a standardized method for many years. Thus far, no standardized method has resulted [32].

Viscometry/Rheometry (ASTM D1092/etc.)

As already mentioned, the shortcomings of the penetration test have been discussed many times.

Rheometry has emerged as a leading alternative to provide more meaningful information on grease structural/functional properties. However, before discussing the development of rheometers and rheometry as it relates to lubricating grease science, it is necessary to discuss the development of grease viscometers. Viscometers occupy the place as the forerunner of today’s modern rheometers.

The first Spokesman paper to discuss viscometers, more specifically pressure viscometers, as a method to evaluated lubricating grease properties was published in 1942. The shortcomings of the penetration test were discussed. Another test method, the Consadometer was also discussed. In this test, a piston was pushed through a grease-filled cylinder. Alternatively, or concurrently, the greasefilled cylinder could be rotated relative to the piston. The measured forces were an indication of grease rheology, and were considered more revealing than single penetration values [1].

That same year, a brief review of several types of grease pressure viscometers was given. A new pressure viscometer, the Standard Oil Development (S.O.D.) Pressure Viscometer was described and evaluated by Beerbower and associates [2]. The S.O.D. Pressure Viscometer utilized a grease-filled cylinder with a piston on one end. A pump used hydraulic oil (mineral oil) to push a piston at one end of the cylinder, forcing the grease into a capillary tube of known length and radius. By measuring the pressure in the capillary tube and the volumetric grease flow through the capillary tube, and by using Poiseuille’s equation, the apparent viscosity could be determined. The S.O.D. Pressure Viscometer would eventually be the basis for the first standardized grease viscometer test, ASTM D1092.

The further development of the S.O.D. Pressure viscometer and its initial use were disclosed in at least six Spokesman papers published from 1945 to 1955 [2-7]. In the first of those papers, additional information was provided on the proper calibration and use of the S.O.D. pressure viscometer [3].

Another paper described a modified grease rheometer. The author claimed that it solved certain problems associated with the S.O.D. Pressure Viscometer [4].

In an interesting paper by Brunstrum and Grubb from 1953, a modification of the S.O.D Pressure Viscometer was made where a cylinder of rectangular cross section was used instead of a circular cross section. This caused the test grease to be sheared against parallel planes instead of the inner walls of a cylinder. Nine different greases were evaluated using this modified viscometer and compared to results using the cylindrical S.O.D. viscometer. Results were not the same. The authors concluded that since the shear near the inner wall was not the same as the shear at the center of the - 29 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

tube, average apparent viscosities were actually being determined by both viscometers. Since the geometry of the cylinder and circular cross sections were different, so would the average apparent viscosity results of each method [6].

The S.O.D Pressure Viscometer, now standardized as ASTM D1092, was defined for use at room temperature only. A modified test apparatus was described by Dreher and associates that allowed evaluation at temperatures below and above room temperature by use of various immersion baths [7].

Only one year after the S.O.D Pressure Viscometer had been disclosed, and well before its standardization as ASTM D1092, a paper provided a table with eleven named viscometers that had already been discussed in the non-Spokesman literature. The need for further development of a grease viscometer was recommended [8].

In apparent response to that stated need, such work was disclosed in at least nine Spokesman papers published between 1943 and 1992 [9-17]. The first of those papers was published in 1943. Flow properties of a grease were determined by calculation of a “Plasticity Number”. Mention was made of a pressure orifice instrument as well as the development of a concentric cylinder viscometer to further explore the flow properties of greases [9].

A plunger viscometer was described in a 1950 paper by Amner and associates [10]. In this equipment, a cylinder capped at one end was partially filled with the test grease. A cylindrical plunger was inserted in the open end of the cylinder. There was a small but known gap clearance between the plunger and the inner wall of the cylinder. The plunger was forced down the cylinder and against the grease with a given constant load. The rate of grease being forced up through the gap clearance was measured. Using this value, the applied load, and the dimensions of the apparatus, the shear stress and apparent strain rate at the cylinder wall could be calculated. This could be done at several applied loads for one test run, allowing viscometric curves to be plotted for a given test grease.

Such testing was done for four different greases at various temperatures. Correlations between test results and predicted pumpability were provided.

In another paper, a rotating cone on plate viscometer was compared to a pressure viscometer (capillary flow type) using four greases. The two methods gave significantly different results, providing evidence that the effect of the thickener system and its resulting effect on grease rheology depends on how the shearing force is applied [11]. Although ASTM D1092 had already been standardized, it was not cited in this paper.

In a 1964 paper, a rotational viscometer developed by the authors was used to evaluate the rheological properties of an organo-bentone and a calcium soap grease at various shear stress/ strain levels and at various temperatures [12]. Five years later, an attempt to adapt a sliding plate viscometer typically used for asphalts was reported [13].

Several other viscometers and related approaches were reported. They included a novel “three ball tester” [14], a theoretical mathematical model [15], and the development of the Brookfield Trident Probe test [16]. The latter eventually became ASTM D3232, a method that is now obsolete.

In another paper by Plint and Alliston-Greiner, the shortcomings of capillary and cone on plate viscometers were discussed. The fact that the Trident Probe test (ASTM D3232) did not even claim - 30 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

to measure grease viscosity was also mentioned. In response to these issues, a new viscometer, the Cameron-Plint Viscometer, was discussed. A cylinder was filled with the test grease and sealed at both ends. An internal rotor turned at a specific rate, thereby providing shear in one direction while the axis of the rotor turned in the opposite direction. This double and opposed action was claimed to prevent grease from detaching from the inner cylinder wall, a claimed major issue with the previously cited viscometers [17].

In two papers from 1988 and 1991, a discussion was provided that showed inadequacies of the penetration test by the use of a rotational viscometer [18-19]. Test results using a rotational viscometer were used to propose “in-between” grades that corresponded to the range of dynamic viscosity values obtained for greases ranging from NLGI Grade 3 to 00. This was the first Spokesman paper that could be found that mentioned oscillatory and controlled stress rheometers as a central topic.

In a 1998 paper by Whittingstall and Shah, oscillatory rheometry was discussed as a means to determine various rheological properties as a function of shear stress, temperature, and time [20]. In another paper from the same year, three sets of greases were evaluated using three rheometry tests: flow (uni-directional) tests, step shear (creep/relaxation) tests, and oscillatory tests. The last two types of tests were emphasized in the reported results [21]. This paper continued to show the power of properly run rheometry tests.

A 1998 paper by Hamnelid provided a tour-de-force argument on why the penetration test provides very little useful performance-related information as well as why controlled stress rheometry is vastly superior in this regard [22]. Another paper by Flemming and Sander published 20 years later made the same point [23]. From this point on, the use of rheometry, especially controlled stress rheometry, became an increasingly important theme. At least 12 papers published from 1998 to 2019 used rheometry as a central or important tool [24-35].

A simple lithium soap grease with and without a functionalized polymer was evaluated by two rheometer test procedures: a stress ramp flow (rotational) test; and an oscillatory stress ramp test [24]. Use of hatched plate surfaces compared to smooth plate surfaces were shown to reduce grease slippage during testing for all both greases. But the grease with the functionalized polymer appeared to exhibit less slippage on the smooth plates compared to the unadditized grease. After those initial tests, all further rheometer tests were done using the hatched plates. Test temperatures ranged from 25 C to -10 C. The effect of oil separation on the apparent viscosity of seven greases over a 63-day period was determined by Bessette using ASTM D6184 (cone sieve test) at 100 C. Apparent viscosity was determined using a uni-direction cone on plate viscometer at 25 C [31]. The seven greases used simple lithium soap, lithium complex, polyurea, and PTFE thickeners. All but one used synthetic base oil.

In a 2009 paper, a set of 54 greases of varying compositions were evaluated by quarter-scale penetration and by yield stress as determined by strain sweep testing. The authors used the correlation between these two tests to argue that the penetration test should be discontinued.

Interestingly, full scale penetration, the penetration test typically used in commercial grease manufacturing, was not used [33].

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In an excellent paper by Nolan and associates, a temperature ramp test procedure using a controlled stress rheometer was described. The test was done in oscillatory mode using a constant and very low relative strain level of 0.1% to ensure that the entire test remained within the visco-elastic region.

The two flat cross-hatched plates with grease sample were enclosed in a chamber capable of heating or cooling the system from -150 C to 400 C. After a few preliminary runs, a temperature ramp of +5 C/min. was established. Greases were tested from an initial temperature of 100 C. Final test temperature depended on the dropping point as established by the authors. Storage modulus, G’, was measured as a function of temperature.

In a continuation of that work, the same authors used the controlled stress rheometer temperature sweep test on a lithium 12-hydroxystearate and a lithium (azelate) complex grease [29]. The test procedure was modified to include a cool-down step after reaching top temperature. This was done to establish to what extent each grease exhibited reversibility. Also, solid thickener samples including lithium 12-hydroxystearate and solids extracted from several test greases were evaluated by PDSC. In another paper from 2017, a similar temperature ramp oscillatory rheometry test was used.

The effect of several organo-boron additives to increase the dropping points of lithium soap grease was determined. Lithium soap greases were made using both hydrogenated castor oil and 12-hydroxystearic acid. A temperature ramp test using a controlled strain test was done to further characterize resulting greases. The ratio of G”/G’ was plotted against temperature [30].

Finally, a unidirectional (flow) rheometer test was used to characterize greases thickened with various carbon nanotubes and other graphitic solids [35].

PERFORMANCE TESTS USING EQUIPMENT COMPONENTS Ball Joint Performance (ASTM D3428) Automotive ball joints were one specific application where good EP/AW performance was required and for which test methods specific to that application were developed. For that reason, ball joint testers are described here in a separate section.

The first paper found that discussed grease performance in ball joints was authored by Goodwin and Hunstad, and was published in 1957 [1]. In that paper, the vibration experienced by the ball joint of a car driven over roads of varying roughness was monitored. As a result, a laboratory bench tester was developed to determine the ball joint steering torque after oscillations of varying frequency and magnitude were applied. A calcium soap grease was used in all such tests.

A modified version of that ball joint tester was described in another paper published five years later in 1962 [2]. Applied load could be varied. The oscillation frequency and amplitude of the ball joint seat could be varied over a wide range. When initial test results showed good correlation with field results, the ball joint tester was further modified to allow four ball joints to be simultaneously tested under the same load and oscillation conditions.

The ball joint tester from the 1962 paper was further modified to use more recent ball joint designs.

The tester was also used in a modified procedure to determine the sensitivity to exposure to brine solutions to grease and joint performance [3]. The resulting test was called the GMR (General Motors Research) Ball Joint Tester (or GMR Ball Joint Torque Tester). This tester became the basis for ASTM D3428.

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The GMR Ball Joint Tester was used to evaluate MoS2 as a grease additive in five papers by Risdon and associates, published from 1971 through 1986 [4-8]. In the first, the GMR Ball Joint Tester was used to evaluate the effect of MoS2 in 22 greases of various thickeners including two NLGI reference greases [4]. This was followed by a study where nine lithium soap greases with up to 3% MoS2 were evaluated using the GMR Ball Joint Torque Stability Tester [5]. By this time the test procedure had been standardized by General Motors and was incorporated into their ball joint grease specification.

This study also used two modified ball joint tests that were done using the same tester. In one procedure, the test duration was extended from the standard 65 hours to 131 hours. In the other, only a thin film of grease was applied to the ball joint before testing so as to determine thin film retention properties.

In another paper, the GMR Ball Joint Tester was used in the extended 131-hour procedure and in a much shorter one-hour procedure [6]. The latter was used to determine how grease composition affected break-in torque.

The GMR Ball Joint Torque Test was modified yet again to determine ball joint housing weight loss after the standard 65-hour test duration. This procedure was used to determine how well the effect of intentionally added abrasive powder would be mitigated by MoS2 added to the grease [7].

Finally, the GMR Ball Joint Torque Test was used to evaluate the effect of MoS2 in a lithium complex, aluminum complex, and polyurea grease [8]. It should be noted that the standardized procedure, ASTM D3428, that resulted from the GMR Ball Joint test was withdrawn just two years after this paper. The fact that no further papers on lubricating grease ball joint testing could be found after that date is likely not coincidental.

Bearing Life (ASTM D3527, D1263, D3336, D4290, FE8, FE9, etc.)

The use of lubricating greases in bearings pre-dates the earliest available Spokesman issues. It should therefore not be surprising that bearing grease performance and performance testing have been a topic in Spokesman papers from nearly the beginning. The earliest such paper was published in 1941.

Although a discussion of wheel bearing grease service requirements was provided, no actual bearing test method was mentioned [1]. Similarly, another early paper gave a brief statement regarding how to fill wheel bearing hubs with grease. However, no method to determine how well a wheel bearing grease performs was mentioned [2].

The first paper that could be found that discussed a bearing grease test was authored by Sproule, and was published in 1945. A very early wheel bearing test rig was used to evaluate two sodium soap greases and one mixed sodium/calcium soap grease. Also, a shackle machine used to evaluate chassis greases was discussed [3].

Between 1947 and 1954, three papers provided descriptions of other bearing grease tests [3-6]. In the first of those papers, two test rigs operating at 35,000 RPM that evaluated grease bearing life were described [4]. Later that same year, yet another test rig was described [5]. The whip test was first discussed as a method to determine the channeling properties of a grease during actual bearing use. This test involved micro (quarter scale) penetration testing of a grease before and after being overpacked in a bearing and run at high RPM [6].

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A 1956 paper discussed the test requirements of two U.S. military grease specifications, using several greases as examples. Bearing life at temperatures ranging from 121 C (250 F) to 232 C (450 F) were determined for several greases using a bearing test run at 10,000 RPM [7].

Over the next 20 years, several other papers described bearing grease test methods. A tapered roller bearing test rig was designed to determine several grease performance properties using several different procedures. Bearing life and oil bleed tendency at running temperatures up to 177 C (350 F) were two of the properties measured [8]. In another paper, a new high temperature bearing test was developed using a previously established “Roller Bearing Lubricant Research Machine-1”.

Temperature was varied from 135 C to 177 C. Thrust load was also varied. Several greases of varying thickener and base oil were tested [9]. In a 1985 paper, a previously documented test method to separate the cone oil bleed tendency and base oil evaporation tendency was used in combination with a rolling four ball test procedure to attempt to determine how base oil volatility effects high temperature bearing life [10].

None of these bearing test methods appeared to be the direct basis for any of the standardized bearing test methods that would be developed. The first paper that apparently did describe such a method was authored by Forster and published in 1954. In that reported work, testing was done using what was referred to as a tentative ASTM wheel bearing test, apparently an early version of what would become a standardized automotive wheel bearing test, ASTM D3527 [11]. However, most testing was done using actual passenger cars in field use.

A discussion of the development of ASTM D3527 was provided in a 1978 paper [12]. Two subsequent papers discussed attempted improvements to D3527. One paper gave a brief discussion of the standardization of an improved ASTM D3527 and ASTM D4290 [13]. The latter was intended as an improved alternative to ASTM D1263 (discussed in the next paragraph). In another paper, several attempted improvements to ASTM D3527 were discussed including improved thermal insulation and changing the criteria for failure from electrical current to torque measurements [14].

ASTM D1263 (Leakage Tendencies of Automotive Wheel Bearing Greases) was one of the earliest standardized methods related to automotive wheel bearing grease performance. In a 1968 paper, a discussion of what future grease performance specifications would include was provided. ASTM D1263 was included as the sole method for determining wheel bearing life [15]. In another paper, the laboratory test requirements considered to be important for greases used in bearings and ball joints were discussed. The standardized D1263 test equipment was used. Test conditions were varied and hours to failure and oil leakage were measured [16]. One year later, a set of six greases were evaluated using ASTM D1263 and an unspecified high temperature bearing test that was reported as being evaluated by the ASTM [17].

In 1958, a new bearing life test method, The Navy Test, was discussed [18]. Its development was due to a new military grease specification for higher temperature usage. The test equipment used established test equipment (the NLGI-ABEC spindle) and was modified to allow testing at 232 C (450 F). This test was an early version of what would eventually be ASTM D3336. This Navy bearing test may have had its beginnings in a Navy Silicone Motor Generator Test documented two years earlier [7].

Several other papers discussing the further development, standardization, and use of ASTM D3336 were published in subsequent years [19-22]. The first of those papers provided further evaluation - 34 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

of the Navy test. A discussion of the evolution of this method as related to the resulting CRC L-35 procedure (Pope-Texas test) was also provided [19]. In another paper, a modified CRC L-35 bearing test procedure was used to evaluate 21 greases of varying base oils and thickeners. Test results were processed in a very detailed formal statistical evaluation using variables such as thickener type, thickener concentration, base oil type, test stand used, and a specific cerium-containing additive [20].

A 1975 paper by Stallings provided a history of the development of the now standardized ASTM D3336 (high temperature spindle bearing grease life test), tracing the history from the early Navy Test, the universal grease tester, the Pope-Texas Spindle, and the CRC L-35 bearing test. The authors provided data showing how test results can vary between spindles [21]. In a follow-up paper published two years later, another group of authors provided an argument that the variations observed in D3336 test results from the 1975 paper were primarily due to variations in airflow within the test bearings during the test [22].

In a 1975 paper, a history was provided for the development and standardization of ASTM D3337 (Determination of Life and Torque of Lubricating Greases in Small Ball Bearings) [23]. This was the only Spokesman paper that could be found on this standardized method.

Like other standardized grease bearing tests discussed above, numerous Spokesman papers have included FE8 and FE9 bearing tests. However, only three papers could be found that discussed these test methods as their central topic [24-26]. Both test methods were discussed in the first of these papers [24]. The FE8 test was described along with a history of its development in the other two papers [25,26].

In a 1989 paper, several lithium soap greases were evaluated for ball bearing life using ASTM D1741 [27]. Five years later, the effect of test conditions using the test equipment for ASTM D1741 (functional life of ball bearing greases), and four other non-standardized testers were evaluated [28,29]. Interestingly, D1741 had been withdrawn by the ASTM three years earlier.

Elastomer Compatibility (ASTM D4289) While a number of papers going back to the 1950s concern themselves with measuring elastomer compatibility and interpreting the results [1-15], only a handful are concerned with the test itself.

The first paper referring to the development of the ASTM test appeared in 1978 [16], with the issuance of ASTM D4289 five years later [17]. ASTM D4289 was then incorporated in NLGI’s GC/LB specifications [18].

Subsequently, concerns were raised as the standard elastomers used in ASTM D4289 were no longer commercially available [19]. The resolution of these concerns was achieved through the identification of an alternate supplier for one reference elastomer and the qualification of a similar material for the other [20,21]. Following this effort, no further work was done on developing the test method, although it’s incorporation into the new HPM specs was anticipated in a 2019 paper [22].

ANALYTICAL/COMPOSITIONAL TESTS Infrared/FTIR Spectroscopy Infrared (IR) spectroscopy is a powerful tool that has been used in the grease industry for over 70 years. The first use of IR was in a 1951 paper discussing the chemistry of fats [1]. IR was first used in - 35 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

grease analysis six years later in analyzing a bentone grease [2] in 1957. The use of IR for diagnosing field problems was discussed in a 1959 paper [3].

The use of IR spectroscopy to identify soap thickener compositions was described in a 1960 paper [4]. Grease oxidative degradation was analyzed using IR in a 1961 paper [5] and again in 1964 [6]. IR was used in 1966 to study the effect of reaction medium on the properties of calcium complex greases [7]. The extraction of phenyl-α-naphthalene from lithium and clay greases was tracked by IR in a 1967 paper [8]. A 1969 paper relied on IR and carbon-type analysis to characterize a variety of mineral oil basestocks [9]. IR spectroscopy was used to track the dispersion of an organo-clay thickener system in a 1971 paper [10].

In addition to the aforementioned 1969 and 1971 papers, the period between 1969 and 1978 saw a plethora of papers describing the use of IR to characterize and quantify greases. A 1970 paper surveyed the application of IR to grease analysis [11]. The next three papers used IR for the quantitative analysis of thickener and additives. The first of these papers [12] used a recrystallization technique to prepare samples of simple lithium greases for analysis. The second paper covered a variety of thickener types and noted the importance of maintaining a controlled path length in the cell [13]. The third paper used differential IR on standard slurries of grease in white oil to quantify the soap content for lithium, calcium, and sodium soap greases [14]. A 1971 paper catalogued the IR spectra of common thickeners and base oils [15] while a 1972 paper did the same for additives [16]. Two other 1972 papers used IR, one as part of a grease compatibility study [17] while the other followed the degradation of ester base stocks in conjunction with Gel Permeation Chromatography (GPC) [18].

Stanton published two articles in 1974 and 1976 on the use of IR in grease analysis. The 1974 article [19] summarized the work of the ASTM D2 Committee on the use of IR for the qualitative and quantitative analysis of grease. The second paper [20] placed IR analysis among the techniques used as part of a multi-method approach to grease analysis.

IR was used in conjunction with liquid chromatography. to discriminate between a variety of MIL-Spec miniature bearing greases in a 1978 paper [21].

There was an eight-year hiatus until two 1986 papers on the rheology and dispersion of organoclay greases [22, 23]. A 1988 paper showed the use of IR to track the soap formation process during grease manufacture [24]. Interestingly, this paper was presented at the 1983 Golden Anniversary meeting but not published in the Spokesman until five years later in a Special Edition.

A 1989 paper followed the degradation of a lithium grease using IR [25]. The application of Fourier Transform IR (FTIR) to compare fresh and used samples of the same grease to provide guidance on the status of the in-service grease [26] was published in 1990.

Beginning with a 1992 paper [27], a series of papers appeared over the next decade concerning the use of IR to study fundamental surface interactions in grease lubrication [28-31].

Two 1990s papers studied the chemistry of aluminum complex greases [32,33]. In 2001, Mistry revisited grease compatibility with IR as one of the analytical tools used [34].

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FTIR was one of the techniques used to study a diurea grease in a 2003 paper [35]. FTIR, HPLC, and RULER tests were shown to be suitable methods to monitor antioxidant depletion for in-service greases in 2004 [36]. A 2005 paper used FTIR spectroscopy to monitor the thickener formation in a lithium complex grease [37]. Also in 2005, Kumar, et. al. used IR as one of several techniques to monitor the thermal degradation of both lithium and aluminum complex greases [38].

Turner, in a 2012 paper, surveyed various methods of evaluating used grease, including FTIR [39]. In 2015, Azad and Evans used a modified ASTM D942 in conjunction with FTIR to rapidly screen multiple greases simultaneously for oxidation resistance [40].

Electron Microscopy This section surveys the application of electron microscopy to grease research. While many of papers discuss the development and refinement of the technique, some select papers showing the utility of electron microscopy in grease research are included, particularly in the most recent decades.

Electron microscopy was first developed and commercialized in the 1930’s [1]. Grease researchers quickly recognized the utility of the technique in understanding grease structure with the first known paper appearing in 1947 [2]. The fibers were liberated from the grease matrix by washing with petroleum ether. Determining the best method for sample preparation was, and continues to be, an area of ongoing research.

A 1950 paper utilized electron microscopy to understand how the fibrous structure of grease related to grease structure and rheology [3]. A combination of X-ray diffraction and electron microscopy were used in conjunction with physical observations to infer that the addition of the corresponding acetate salts to calcium or barium greases gave a chemically distinct “complex” structure [4].

At the same time, NLGI funded research at the University of Southern California by Drs. Marjorie and Richard Vold and colleagues that led to a series of papers studying grease structures by various methods, including electron microscopy and X-ray diffraction [5-8]. The second paper [6] used cryogenic freezing followed by preparing thin microtome slices to make the samples for electron microscopy. Dr. Marjorie Vold was one of the first women, if not the first, to publish a Spokesman paper. She was a well-known colloid chemist and an award recipient from the American Chemical Society in that field.

A 1956 paper described an “aerogel” sample preparation method where excess base oil is removed in an autoclave without the use of solvent [9] and compared the differences in the resulting structures obtained by this method and solvent washing.

A second 1956 paper used electron microscopy to compare the structural changes imparted to grease fibers in a grease worker, roll stability tester, three-roll mill, and wheel-bearing tester [10].

Work published in 1960 examined how altering the phase behavior of fiber crystallization impacted the soap structure and final grease properties [11]. Thin sections of grease fibers embedded in a methacrylate matrix were studied to understand the three-dimensional structure of fibrous greases [12]. This work was extended to examine serial sections of the same grease to further characterize the three-dimensional fiber structure [13].

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A 1965 paper compared the results of electron microscopy versus using an electronic particle counter [14]. The authors concluded that electron microscopy only captures a small and non-representative sample of the thickener particles measured by the electronic particle counter. Calcium soap greases were prepared in a series of simple alcohols, and aliphatic and aromatic hydrocarbons. The fiber structure and physical properties of each was compared to a commercial calcium soap grease [15].

Sample preparation was revisited in a 1967 paper disclosing the use of wicking n-heptane through the grease to affect de-oiling with minimal disruption of the fibrous structure [16].

The effect of thickener shape on permeability was studied for a variety of soap and non-soap greases in a 1968 paper [17] while Marjorie Vold and co-workers examined the impact of phase behavior and colloidal structure on grease rheology in a 1969 paper [18]. Workers in 1969 showed that the fibers in lithium 12-hydroxystearate greases are naturally twisted and that the observation is not an artifact of the sample preparation methodology [19].

A 1973 paper looked at the effect of cooling rate on the structure of lithium greases made with a variety of fatty acids [20]. Work published in 1975 attempted unsuccessfully to correlate thickener structure with bearing vibration [20]. The effect of thickener structure on rheology was studied for clay greases in a paper from 1986 [21].

In a 1992 paper on aluminum complex greases, Samman described the use of super-critical CO2 to de-oil the grease sample prior to shadowing for electron microscopy imaging [22]. A hexane-based extraction procedure was partially disclosed in a 1996 paper [23]. Full disclosure was constrained by patent issues.

Electron microscopy was one of the methods used to investigate the thermal degradation of a variety of lithium and diurea greases in a 1995 paper [24]. A 1996 paper illustrated the structural changes caused by the use of 0.5% of a functionalized polymer additive in simple lithium greases [25].

Rather than examining grease structure, a second 1996 paper used electron microscopy as a tool for examining wear patterns. Work published in 1997 showed the impact of production methods on structure for a simple lithium grease manufactured using four different protocols [26].

In 2001, Hurley and Cann published a study of grease structure using scanning electron and atomic force microscopy [27]. This paper is notable as it contained a summary of sample preparation methodologies discussed in the literature up to that point in time.

Kernizan, et. al. [28] extended the study of functionalized polymers as additives previously published in 1996 [25]. In a 2004 paper, Harris and Hall looked at how a new method of lithium grease production altered the structure and properties of the finished grease [29], while a 2006 paper

by Onuki used electron microscopy to track the degradation of a urea grease over the course of its lifetime in a bearing tester [30].

In 2006, Ward and Najman used multiple techniques including electron and Auger microscopy in a study of tribological film formation [31]. A second 2006 paper by Reddy, et. al. studied thickener formation in overbased calcium sulfonate greases [32].

Lorimor used electron microscopy to understand how borate esters interacted with simple lithium greases to improve their high temperature properties [33] while Kaperick, et. al. used it to study the effect of friction modifiers on tribofilm formation and composition [34].

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Aguilar, et. al. used Scanning Electron Microscope-Energy-Dispersive X-Ray Spectroscopy to measure film thickness in a 2015 paper studying the impact of thickener type on additive response [35].

In 2017, Yuskihara and Moriuchi used a confocal laser fluorescence microscope to make direct observations of the thickener structure in the grease matrix [36].

Chatra, et. al. used both scanning electron microscopy and cryogenic scanning electron microscopy to characterize polypropylene thickener structure. The cryogenic scanning electron microscope was used to image the thickener structure in-situ [37].

ACKNOWLEDGEMENTS Both authors acknowledge a sense of relief and a renewed resolve to not get snookered into doing anything like this again.

REFERENCES The references for each section are presented as stand-alone groups. While this results in several references cited more than once, doing so makes it easier for the reader to find relevant papers for further study.

References: Introduction

[1] A. Kumar, R. Shah, K. Mistry, A. Kumar, “Chapter 3 – Testing of Lubricating Greases”, NLGI Lubricating Grease Guide, Volume 7, 2022.

[2] Rajesh J. Shah, Jamie E. Spagnoli, “Recent Advance in Test Procedures Development by ASTM Subcommittee D02.G on Lubricating Grease”, NLGI Spokesman, Jul 1997.

[3] L.B. Sargent Jr., J.T. Bunting, “Grease Specifications Now and Tomorrow”, NLGI Spokesman, Jan 1968.

[4] H.A. Mayor Jr., L.W. Okon, “Is There More to Grease Classification Than Consistency”, NLGI Spokesman, Mar 1968.

[5] J.C. Gebhart, “Quality Control in Compounding and Blending Lubricating Oils and Greases”, NLGI Spokesman, Apr 1968.

[6] Thomas M. Verdura, “Classification and Specification for Automotive Service Greases - A New Industry Standard”, NLGI Spokesman, May 1990.

[7] Dr. Raj Shah, Jacky Jiang, Joseph Kaperick, “Next Generation NLGI Grease Specifications”, NLGI Spokesman, Nov 2019.

References: Cone Penetration [1] David A. Turner, “How Smooth is Smooth”, NLGI Spokesman, Jul 1993.

[2] NLGI Lubricating Grease Guide, Volume 7, W. Tuszynski, R. Shah, Eds., 2022, page 73.

[2] C.M. Larson, C.L. Knopf, “Grease Consistency Investigations”, NLGI Spokesman, Apr 1942.

[3] C.L. Knopf, “Conical Cup for A.S.T.M. Penetration Test Part I”, NLGI Spokesman, Jul 1942.

[4] C.L. Knopf, “Conical Cup for A.S.T.M. Penetration Test Part II”, NLGI Spokesman, Aug 1942.

[5] Carl W. Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[6] Carl Georgi, “Technical Sub-Committee Report on the Tentative N.L.G.I. Classification of Semi-Fluid Greases”, NLGI Spokesman, Jul 1942.

[7] L.C. Brunstrum, “The Light-Weight Cone for Penetration of Soft Greases”, NLGI Spokesman, Mar 1949.

[8] R. A. Potter, L. W. McLennan, “Controlling the Consistency of Semi-Fluid Greases”, NLGI Spokesman, Dec 1949.

[9] L. C. Brunstrum, A. W. Weitkamp, “Penetration of Block Greases”, NLGI Spokesman, Mar 1948.

[10] George M. Hain, “A Microworker for Lubricating Greases”, NLGI Spokesman, Sep 1947.

[11] Carl W. Georgi, “The Motor-Driven Grease Worker and Its Application for Evaluating Consistency Stability of Lubricating Greases”, NLGI Spokesman, Mar 1948.

[12] Philip R. Sigler, Klaus Meinssen, “The Fine Hole Lubricating Grease Worker as a Rapid Shear Stability Test”, NLGI Spokesman, Aug 1955.

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[13] A. Bond, A.M. Cravath, R.J. Moore, W.H. Peterson, “Basic Factors Determining the Structure and Greases”, NLGI Spokesman, Mar 1950.

[14] Charles A. Zeiler, “Shear Stability of Lubricating Greases”, NLGI Spokesman, Jan 1956.

[15] S.F. Calhoun, F.E. Woodward, “Mechanical Stability of Greases Bench Tests Vs Field Service”, NLGI Spokesman, Jan 1956.

[16] R. O’Halloran, J.J. Kolfenbach, H.L. Leland, “How Shearing Affects Penetration of Greases”, NLGI Spokesman, Feb 1956.

[17] P.R. McCarthy, “Discussion Symposium Papers Presented in Section II - Correlation of Laboratory Tests with Simulated Field Services”, NLGI Spokesman, Jan 1956.

[18] B.B. Farrington, “Discussion Symposium Papers Presented in Section III-Technical Considerations of Mechanical Stability”, NLGI Spokesman, Feb 1956.

[19] H. Schwenkner, “Storage Stability of Aircraft Greases”, NLGI Spokesman, July 1957.

[20] G. W. Eckert, “A Method for the Prediction of Hardness Changes of Greases in Storage”, NLGI Spokesman, Aug 1957.

[21] J.L. Dreher, C.F. Carter, “New Technique for Continuous Measurement of Grease Consistency During Manufacture”, NLGI Spokesman, Sep 1960.

[22] W.A. Graham, “Development of Correlations for Continuous Consistency Control During Grease Manufacture”, NLGI Spokesman, Nov 1970.

[23] L.C. Brunstrum, A.W. Sisko, “Correlation of Viscosity with Penetration for Lubricating Greases”, NLGI Spokesman, Jan 1962.

[24] S.B. Strong, “Grease Flow Properties and Some Relationships Between Them”, NLGI Spokesman, Mar 1969.

[25] J.L. Dreher, R.E. Crocker, “Significance of ASTM Procedures for Cone Penetration and Roll Stability of Lubricating Greases”, NLGI Spokesman, Sep 1974.

[26] Graham Gow, “Judges 5-5: the Time Factor in Grease Rheology”, NLGI Spokesman, Dec 1988.

[27] Lennart Hamnelid, “Amazing Grease or Finding the Right Way to Consistency”, NLGI Spokesman, Nov 1991.

[28] S. Beret G.R. Trabert, “SPC and the NLGI Consistency Number - A Source of Conflict”, NLGI Spokesman, July 1990.

[29] Carl E. Ward, William G. Haag, “Overcoming the Impact of Variation on Quality Control Decisions Using Operating Characteristic Curves for ASTM D 217 (Cone Penetration)”, NLGI Spokesman, Sep 1999.

[30] Hocine Faci, D’Arcy Massimino, “How to Make the Roll Stability Work Where the Worked Stability Doesn’t Work”, NLGI Spokesman, Nov 2007.

[31] Steve Humphreys, Anoop Kumar, “Examining the Correlation between Cone Penetration and Brookfield Viscosity”, NLGI Spokesman, Sep 2010.

[32] Wade Flemming, John Sander, Spencer Courtney, “A Rheological Study- Do All #2 Greases Act the Same”, NLGI Spokesman, Mar 2012.

[33] Wade Flemming, John Sander, “Is it Time to Retire the Grease Penetration Test”, NLGI Spokesman, Nov 2018.

References: Dropping Point [1] Carl W. Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[2] J. C. Zimmer, Report on Grease Dropping Point Methods”, NLGI Spokesman, Mar 1944.

[3] J. L. Dreher, “Predicting High Temperature Performance of Lubricating Greases”, NLGI Spokesman, May 1957.

[4] W. J. Ewbank, “What’s in a Name - Definitions of Terms Relating to the Lubricating Grease Industry”, NLGI Spokesman, Sep 1957.

[5] H.M. Dickenson, “Significance of the ASTM Dropping Point of Lubricating Grease”, NLGI Spokesman, Apr 1964.

[6] C.F. Carter, F. Baumann, “Gas Chromatography of Fatty Acids Applied to Grease Formulation”, NLGI Spokesman, May 1964.

[7] P.R. McCarthy, “Report of ASTM Technical Committee G on Dropping Point Methods for Lubricating Grease”, NLGI Spokesman, Jun 1967.

[8] J.A. Gannon, G.H. Oechsner, “Establishment and Control of Grease Performance Properties to Meet Consumer Specifications”, NLGI Spokesman, May 1973.

[9] Katrina M. Labude, “Factors Affecting ASTM D 2265 Dropping Point Results”, NLGI Spokesman, Jan 1992.

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[1]0 Chuck Coe, “Shouldn’t Grease Upper Operating Temperature Claims Have a Technical Basis”, NLGI Spokesman, Feb 2009.

[11] Dr. Gareth Fish, “The Dropping Point Test - Time to Drop It”, NLGI Spokesman, Jul 2020.

References: Roll Stability [1] C.M. Larson, C.L. Knopf, “Grease Consistency Investigations”, NLGI Spokesman, Apr 1942.

[2] Carl W. Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[3] R.J.S. Pigott, “Some Test Equipment for Greases”, NLGI Spokesman, Dec 1947.

[4] N. Marusov, “Flow Properties of Lubricating Greases”, NLGI Spokesman, Aug 1951.

[5] A. Bondi, A.M. Cravath, R.J. Moore, W.H. Peterson, “Basic Factors Determining the Structure and Rheology of Lubricating Greases”, NLGI Spokesman, Mar 1950.

[6] H.A. Woods, H.M. Trowbridge, “Shell Roll Test for Evaluating Mechanical Stability”, NLGI Spokesman, Aug 1955.

[7] J.D. Smith, “The Design and Use of the Shell Roll Test”, NLGI Spokesman, Nov 1955.

[8] J.M. Stokely, S.R. Calish, “Correlation of Laboratory Tests with Field Observations of Grease Fluidity”, NLGI Spokesman, Dec 1955.

[9] S.F. Calhoun, F.E. Woodward, “Mechanical Stability of Greases Bench Tests Vs Field Service”, NLGI Spokesman, Jan 1956.

[10] P.R. McCarthy, “Discussion Symposium Papers Presented in Section II - Correlation of Laboratory Tests with Simulated Field Services” NLGI Spokesman, Jan 1956.

[11] D.V. Culp, J.E. Lieser, R.H. Brown, “Experience with Roll Stability Testing’, NLGI Spokesman, Jul 1974.

[12] J.L. Dreher, R.E. Crocker, “Significance of ASTM Procedures for Cone Penetration and Roll Stability of Lubricating Greases”, NLGI Spokesman, Sep 1974.

[13] J. P. Doner, “Military Specification MIL-G-10924C And Its Modified Shell Roll Stability Test, “NLGI Spokesman, Feb 1977.

[14] J.W. Pearson, “International Marketing and Development of Industrial Lubricating Greases”, NLGI Spokesman, Feb 1973.

[15] Graham Gow, “Judges 5-5: the Time Factor in Grease Rheology”, NLGI Spokesman, Dec 1988.

References: Oil Separation/Bleed [1] Thomas Graham, Philosophical Transactions of the Royal Society of London, 151, 205 (1861).

[2] T.D. Smith, E. Amott, L.W. McLennan, “The Syneresis of Lubricating Oil Greases”, NLGI Spokesman, July 1950.

[3] A.J. Jennings, “Centralized Lubrication”, NLGI Spokesman, Aug 1946.

[4] A.E. Baker, “Grease Bleeding - A Factor in Ball Bearing Performance”, NLGI Spokesman, Sep 1958.

[5] NLGI Lubricating Grease Guide, Volume 7, W. Tuszynski, R. Shah, Eds., 2022, page 81.

[6] Col. S.J.M. Auld, “The Institute of Petroleum Releases a New Test Method for Evaluating Oil Separation from Greases in Storage”, Oct 1947.

[7] Carl W. Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Sep 1943.

[8] T.G. Roehner, R.C. Robinson, “Separability Characteristics of Lubricating Greases”, NLGI Spokesman, May 1945.

[9] Bunnosuke Yamaguchi, Takashi Oki, Hachiro Kageyama, “Rheological Studies on the Syneresis of Lubricating Greases”, NLGI Spokesman, Feb 1955.

[10] J.L. Dreher, A.L. McClellan, “Comparison of Laboratory and Field Bleeding Test for Lubricating Greases “, NLGI Spokesman, Mar 1956.

[11] G.S. Bright, J.H. Greene, “Effect of Oil Characteristics on the Properties of Lithium Soap Greases”, NLGI Spokesman, Dec 1962.

[12] P J.L. Zakin, G.W. Murray Jr., “The Effects of Variation of The Viscosity and Type of The Mineral Oil Component on Oil Separation from Greases Of a Lithium-Calcium Soap, NLGI Spokesman, Mar 1962 [13] H.M. Friede, C.T. Sangster, “Evaluation of Production Control Methods For Predicting Storage Stability of Greases”, NLGI Spokesman, Dec 1964.

[14] R. Croft, “Comments on the Paper- Evaluation of Production Control Methods for Predicting Storage Stability of Greases”, NLGI Spokesman, Apr 1968.

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[15] S.F. Calhoun, “Fundamental Aspects of Grease Bleeding”, NLGI Spokesman, Jan 1966.

[16] W.J. Ewbank, R.L. Waring, “Development of a Method for Determining the Leakage Characteristics of Lubricating Grease”, NLGI Spokesman, Apr 1969.

[17] W.P. Scott, C.J. Swartz, “The Oil Release Response of Grease”, NLGI Spokesman, Jul 1970.

[18] W.P. Scott, C.J. Swartz, “Diffusion and Oil Separation from Lubricating Grease”, NLGI Spokesman, Aug 1972.

[19] R.J. Pecora Jr., E.W. Vest, M.J. Diodato, “Leakage Resistance of Wheel Bearing Greases in Disc Brake Applications”, NLGI Spokesman, Mar 1975.

[20] H. Kinoshita, H. Uemura, M. Sekiya, “Mechanism of Plugging in a Centralized Grease Lubrication System”, NLGI Spokesman, Apr 1984.

[21] Michael M. Calistrat, “Oil Separation From Lubricating Greases by Centrifuging”, NLGI Spokesman, Dec 1985.

[22] G. Arbocus, E.J. Gesdorf, J.R. Gordon, James Czerwinski, “Seminar- Dispensing Grease in Central Systems Problems and Solutions”, NLGI Spokesman Sep 1986.

[23] Paul A. Bessette, “The Impact Of Oil Separation On The Apparent Viscosity of Grease”, NLGI Spokesman, April 2006.

References: Extreme Pressure/Antiwear [1] C.F. Prutton, “Additives for Petroleum Lubricants”, NLGI Spokesman, Dec 1941.

[2] C. W. Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[3] L.W. Sproule, “Some Practical Methods for the Evaluation of Lubricating Greases”, NLGI Spokesman, Feb 1945.

[4] E.R. Irwin, S.C. Britton, “Lubricating Grease Requirements for Modern Military Aircraft”, NLGI Spokesman, Dec 1943.

[5] E. M. Kipp, H. L. Harper, “Aluminum Rolling Mill Lubrication”, NLGI Spokesman, Nov 1945.

[6] G. Kaufman, “Additives in Lubricating Greases”, NLGI Spokesman, Aug 1947.

[7] R.T. Macdonald, J.L. Dreher, “Additives for Lubricating Greases”, NLGI Spokesman, Apr 1953.

[8] E.E. Smith, “Molybdenum Disulfide as a Grease Additive”, NLGI Spokesman, Dec 1956.

[9] T.J. Risdon, D.J. Sargent, “Comparison of Commercially Available Greases with and without Molybdenum Disulfide Part I – Bench Scale Performance Tests”, NLGI Spokesman, Jun 1969.

[10] T. J. Risdon, “EP Additive Response in Greases Containing MoS2”, NLGI Spokesman, Nov 1999.

[11] D.K. Nason, “The Four-Ball E.P. Tester”, NLGI Spokesman, Mar 1952.

[12] F.S. Sayles, “The Four-Ball E.P. Tester, An ASTM Method of Test”, NLGI Spokesman, Aug 1968.

[13] L. Stallings, “The Four-Ball Wear Test – ASTM Method No. D-2266”, NLGI Spokesman, Feb 1968.

[14] J.P. Dilworth, J.R. Roach, “High Temperature Ultra High Speed Grease Lubrication”, NLGI Spokesman, Apr 1956.

[15] G.P. Murphy Jr., “Factors that Influence Grease Oxidation and Oxidative Wear”, NLGI Spokesman, Apr 1964.

[16] R.J. Sibilia, “Review of ASTM Procedures…Four-Ball EP Tester”, NLGI Spokesman, Nov 1973.

[17] C. Hunter, “Load Wear Index vs Weld Point Correlation in the Four-Ball Extreme Pressure Test”, NLGI Spokesman, Apr 1986.

[18] E.A. Baniak, R.S. Fein, “Review of ASTM Procedures…Precision of Four Ball Timken Tests and Their Relation to Service Performance”, NLGI Spokesman, Jan 1973.

[19] D.V. Culp, J.E. Lieser, “Review of ASTM Procedures…The Timken Lubricants Test 1932 to 1972”, NLGI Spokesman, Sep 1973.

[20] G.L. Harting, “Measurement Of The Extreme Pressure Properties of Lubricating Greases With the Timken Tester”, NLGI Spokesman, Jan 1978.

[21] R.S. Roberton, “Precision Studies With The Revised ASTM Timken Extreme Pressure Test Procedure For Lubricating Oils”, NLGI Spokesman, Nov 1978.

[22] W.P. Scott, “Timken Machine Maintenance – A Case History”, NLGI Spokesman, Apr 1984.

[23] J. P. Kaperick, “Timken OK Load – Media Bias? A Comparison of Timken Response to Similar Additive Systems in Both Grease and Oil Formations”, NLGI Spokesman, Aug 2007.

[24] F.G. Fischer, R.G. Huber, A.D. Cron, “Graphite Powder And Other Solids In Lubrication”, NLGI Spokesman, Mar 1982.

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[25] F.G. Fischer, A.D. Cron, R.G. Huber, “Graphite And Molybdenum Disulphide-Synergisms”, NLGI Spokesman, Sep 1982.

[26] W. A. Faville, L. R. Heerdt, “Friction and Wear Testing Machines- Basic Lubrication Evaluation Tools”, NLGI Spokesman, Nov 1985.

[27] K. Hatakeyama, “Lubricating Grease for a Plunging Type Constant Velocity Joint”, NLGI Spokesman, Sep 1992.

[28] C. F. Kernizan, G. Krishnaswamy, “A Design Approach to the Development of Additives for CVJ Greases”, NLGI Spokesman, May 2004.

[29] J. R. Dickey, “New ASTM and DIN Methods for Measuring Tribological Properties Using the SRV Test Instrument”, NLGI Spokesman, Mar 1997.

[30] N.J. Ninos, “Evaluation of the Anti-War Properties of Gear Greases”, NLGI Spokesman, Jun 1951.

[31] E.R. Booser, A.E. Baker, E.G. Jackson, “Performance of Synthetic Greases”, NLGI Spokesman, Dec 1952.

[32] G.M. Stanton, “Wear Testing Of Greases With The Falex I Ring And Block Friction And Wear Test Machine”, NLGI Spokesman, Aug 1978.

References: Water Resistance [1] T.G. Roehner, E.S. Carmichael, “Evaluation of Water Resistance Properties of Lubricating Greases”, NLGI Spokesman, Sep 1947.

[2] H. Reynolds, “Lubrication of Anti-Friction Bearings from a Bearing Manufacturer’s Standpoint”, NLGI Spokesman, Jan 1949.

[3] H.L. Hendricks, J.D. Smith, “Performance and Testing of Lubricating Grease Under Wet Operating Conditions”, NLGI Spokesman, Jul 1954.

[4] L.B. Sargent Jr., J.T. Bunting, “Grease Specifications, Now and Tomorrow”, NLGI Spokesman, Jan 1968.

[5] P.R. McCarthy, W.W. Bailey, “Laboratory Evaluation of Automotive Wheel Bearing and Ball Joint Greases”, NLGI Spokesman, Aug 1975.

[6] J.A. Gannon, “A New Look at Water Washout of Lubricating Greases”, NLGI Spokesman, Jan 1976.

[7] L.G. Schneider, “Evaluating Wash-off Resistance of Greases for Sliding Contact Bearings in Underwater Service”, NLGI Spokesman, Apr 1976.

[8] C.R. Knott, M.A. Lindeman, A.T. Polishuk, “Water Spray Resistance Grease Test”, NLGI Spokesman, Jan 1965.

[9] R.H. Newman, R.P. Langston, “The Performance of Calcium Hydroxystearate Greases in Wet Conditions”, NLGI Spokesman, Aug 1966.

[10] T.G. Musilli, “Water Spray-Off Characteristics Of Lubricating Grease”, NLGI Spokesman, Dec 1982.

[11] L.E. Tedrow, F.S. Sayles, “Field Performance Of Synthesized Hydrocarbon (Polyalphaolefin) Greases”, NLGI Spokesman, Feb 1984.

References: Corrosion Protection [1] O.L. Maag, “Antifriction Bearing Lubricants”, NLGI Spokesman, Dec 1941.

[2] S.L. Bishkin, “Slushing Type Rust Preventatives”, NLGI Spokesman, Apr 1943.

[3] E.R.Irwin, S.C. Britton, “Lubricating Grease Requirements for Modern Military Aircraft”, NLGI Spokesman, Dec 1943.

[4] C.W.Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[5] G. Kaufman, “Additives in Lubricating Greases”, NLGI Spokesman, Aug 1947.

[6] T.G. Roehner, E.S. Carmichael, “Evaluation of Water Resistance Properties of Lubricating Greases”, NLGI Spokesman, Sep 1947.

[7] J.A. Bell, “Corrosion Inhibited Automotive Greases”, NLGI Spokesman, 1956.

[8] W.H. Peterson, J.B. Accinelli, T. Skei, “A Test for Lubricating Grease Performance Under Water-Wet Conditions”, NLGI Spokesman, Nov 1957.

[9] E.W. Adams, “CRC Laboratory Technique for Determining Rust-Preventative Properties of Lubricating Greases”, NLGI Spokesman, July 1958.

[10] R.S. Barnett, “Ball and Roller Bearing Lubrication”, NLGI Spokesman, Mar 1959.

[11] C.L. Pope, “Grease Lubrication Of Sleeve Bearings”, NLGI Spokesman, May 1962.

[12] L.B. Sargent Jr., J.T. Bunting, “Grease Specifications, Now and Tomorrow”, NLGI Spokesman, Jan 1968.

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[13] R. J. Shah, J. E. Spagnoli, “Recent Advance in Test Procedures Development by ASTM Subcommittee D02.G on Lubricating Grease”, NLGI Spokesman, Jul 1997.

[14] M. E. Hunter, R. F. Baker, “Corrosion Rust and Beyond”, NLGI Spokesman, Mar 1999.

[15] R. Meshram, et.al., “Assessment of Bearing Grease Anti-Corrosion Performance Using EMCOR Washout Test Rig”, NLGI Spokesman, Mar/Apr 2016.

References: Fretting Wear/Corrosion [1] H. T. Morton, F. G. Patterson, “Friction Oxidation”, NLGI Spokesman, Aug 1948.

[2] H. Reynolds, “Lubrication of Anti-Friction Bearings from a Bearing Manufacturer’s Standpoint”, NLGI Spokesman, Jan 1949.

[3] T.G. Roehner, E.L. Armstrong, “Fretting Corrostion Studies with a Modified Fafnir Machine”, NLGI Spokesman, Jun 1952.

[4] J.J. Kolfenbach, A.J. Morway, “New Thickener System Extends Range of Multipurpose Greases”, NLGI Spokesman, Aug 1960.

[5] E.O. Forster, J.J. Kolfenbach, “Evaluation of Wheel Bearing Grease Performance”, NLGI Spokesman, May 1954.

[6] W.J. Ewbank, “What’s in a Name – Definitions of Terms Relating to the Lubricating Grease Industry Part III”, NLGI Spokesman, May 1960.

[7] R.J. Ronan, M.C. McLaren, “Scientific Detection in Grease Lubrication Problems”, NLGI Spokesman, Jan 1959.

[8] A. Schilling. “Mechanical Tests of Lubricating Greases Part I”, NLGI Spokesman, Feb 1967.

[9] G.J. Clark, “Lubricating Grease as Viewed By a Bearing Manufacturer”, NLGI Spokesman, Nov 1972.

[10] P.R. McCarthy, W.W. Bailey, “Laboratory Evaluation of Automotive Wheel Bearing and Ball Joint Greases”, NLGI Spokesman, Aug 1975.

[11] G.J. Clark, F. Arezzo, “Friction Oxidation Testing – A New Look At An Old Machine”, NLGI Spokesman, Apr 1979.

[12] R.T. Schlobohm, “Formulating Greases To Minimize Fretting Corrosion”, NLGI Spokesman, Jan 1982.

[13] T.M. Verdura, “Development Of A Standard Test To Evaluate Fretting Protection Quality Of Lubricating Grease”, NLGI Spokesman, Aug 1983.

[14] E.L. Armstrong, M.A. Lindeman, H.J. Wayne, “Wheel-Bearing Test Appparatus for Automotive Greases”, NLGI Spokesman, Jan 1970.

[15] F. G. Wunsch, “Relationship Between the Chemical Structure of a Lubricant and Fretting Corrosion”, NLGI Spokesman, Dec 1988.

[16] R. Shah, M. Moon, G. Dodos, “Let the Games Begin-New Trends in Industrial Grease Lubrication”, NLGI Spokesman, Jul/Aug 2019.

References: Oxidation Stability [1] C.W.Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[2] H. Reynolds, “Lubrication of Anti-Friction Bearings from a Bearing Manufacturer’s Standpoint”, NLGI Spokesman, Jan 1949.

[3] J.P. Dilworth, J.R. Roach, “High Temperature Ultra High Speed Grease Lubrication”, NLGI Spokesman, Apr 1956.

[4] J.E. Goodrich, J.J. Burke, “Oxidation of Lubricating Greases”, NLGI Spokesman, Jan 1961.

[5] G.P. Murphy Jr., “Factors that Influence Grease Oxidation and Oxidative Wear”, NLGI Spokesman, Apr 1964.

[6] J.L. Dreher, D.W. Criddle, T.H. Koundakjian, “Significance of the ASTM Oxidation Stability Test for Lubricating Greases”, NLGI Spokesman, Jul 1964.

[7] D. Chasan, U. Haering, “Four Modifications for Oxygen Bomb Testing”, NLGI Spokesman, Aug 1985.

[8] E. Brandolese, R. Santorelli, G. Pisaniello, G. Ponti, “An Accelerated Oxidation Stability Test for Predicting Grease Behavior Under Severe Dynamic Conditions”, NLGI Spokesman, Feb 1997.

[9] T.J. Risdon, J.P. Binkelman, ‘Oxidation Stability and Antifriction Bearing Performance of Lubricants Containing Molybdenum Disulfide’, NLGI Spokesman, Jul 1968.

[10] P.R. McCarthy, W.W. Bailey, “Laboratory Evaluation of Automotive Wheel Bearing and Ball Joint Greases”, NLGI Spokesman, Aug 1975.

[11] W.W. Bailey, S. Pratt, “Dynamic Oxidation Stability Of Lubricating Greases”, NLGI Spokesman, Apr 1982.

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[12] Y. L. Ischuk, V. V. Butovets, “Estimation of Grease Oxidation Stability Under Dynamic Conditions and Antioxidant Testing”, NLGI Spokesman, Jul 1991.

[13] Chihoria Araki, Hidetoshi Kanzaki, Toru Taguchi, “A Study on the Thermal Degradation of Lubricating Greases”, NLGI Spokesman, Nov 1995.

[14] In-Sik Rhee, “Development of a New Oxidation Stability Test method for Greses Using a Pressure Differential Scanning Calorimeter”, NLGI Spokesman, Jul 1991.

[15] M.J. Pohlen, “DSC – A Valuable Tool for the Grease Laboratory”, NLGI Spokesman, Jul 1998.

[16] In-Sik Rhee, “Development of a New Oxidation Stability Test Method for Lubricating Oils Using a Pressure Differential Scanning Calorimeter (PDSC)”, NLGI Spokesman, Jun 2001.

[17] J. Reyes-Gavilan, “Evaluation of the Thermo-Oxidative Characteristics of Greases by Pressurized Differential Scanning Calorimetry”, NLGI Spokesman, Feb 2004.

[18] P. A. Bessette, “Thickener Content in Organic Grease by Differential Scanning Calorimetry”, NLGI Spokesman, May 2009.

[19] W. Ward Jr., G. Fish, “Development of Greases with Extended Grease and bearing Life Using Pressure Differential Scanning Calorimetry and Wheel Bearing Life Testing”, NLGI Spokesman, Nov/Dec 2010.

[20] D. Turner, “Used Lubricating Grease Tests and Their Significance”, NLGI Spokesman, Nov/Dec, 2012.

[21] V.P. Dholakia, E.E. Klaus, J.L. Duda, “Development of a Microoxidation Test for Grease”, NLGI Spokesman, April 1994.

[22] V.P. Dholakia, E.E. Klaus, J.L. Duda, “Comparison of Grease Oxidation Tests with Seven Commercial Greases”, NLGI Spokesman, May 1994.

[23] J.W. Harris, “Relative Rates of Grease Oxidation in a Penn State Microoxidation Appratus on Glass and Steel Sample Parts”, NLGI Spokesman, Feb 2002.

[24] G. Dodos, “Study on a New Oxidation Stability Method for Lubricating Greases by Employing the Rapid Small Scale Oxidation Test”, NLGI Spokesman, Nov/Dec 2017.

[25] R. Shah, M. Moon, G. Dodos, “Let the Games Begin-New Trends in Industrial Grease Lubrication”, NLGI Spokesman, Jul/Aug 2019.

[26] M. Fathi-Najafi, J. Li, Y. Shi, “Evaluation of the Impact of High Viscosity Naphthenic Oils on Various Thickener Systems”, NLGI Spokesman, Nov/Dec 2019.

[27] R. Shah, J. Ameye, “Monitoring Antioxidants in Greases by Voltammetric Techniques – An Economic Approach to Life Cycle Assessment”, NLGI Spokesman, Mar 2005.

[28] S. Azad, J. C. Evans, “An Advanced Technique for Grease Oxidation Measurement”, NLGI Spokesman, Jan/Feb 2015.

References: Low Temperature Mobility [1] T.A. Maxwell, “Low Temperature Characteristics of Greases”, NLGI Spokesman, Nov 1942.

[2] A. Beerbower, L.W. Sprouse, J.B. Patberg, J.C. Zimmer, “Flow Characteristics of Lubricating Greases”, NLGI Spokesman, Nov 1942.

[3] E.R.Irwin, S.C. Britton, “Lubricating Grease Requirements for Modern Military Aircraft”, NLGI Spokesman, Dec 1943.

[4] C.W.Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[5] C.W. Georgi, J.F. O’Connell, “The Effect of Mineral Oil Pour Point on the Flow Characteristics of Lubricating Greases”, NLGI Spokesman, Dec 1944.

[6] J.R. Reynolds, “N.G.F. Performance Grease Tests (Grease Torque Machine)”, NLGI Spokesman, Apr 1945.

[7] E.A. Baniak, R.S. Barnett. “Low Temperature Operation of Aircraft Accessories”, NLGI Spokesman, Aug 1956.

[8] H. Reynolds, “Lubrication of Anti-Friction Bearings from a Bearing Manufacturer’s Standpoint”, NLGI Spokesman, Jan 1949.

[9] L. Stallings, M.J. Devine, “Wide Temperature Range Multipurpose Lubricating Grease”, NLGI Spokesman, Jun 1971.

[10] P.R. McCarthy, W.W. Bailey, “Laboratory Evaluation of Automotive Wheel Bearing and Ball Joint Greases”, NLGI Spokesman, Aug 1975.

[11] M.A. Lindeman, “Torque Tests on Grease Lubricated Size 204 Ball Bearings”, NLGI Spokesman, Jul 1967.

[12] E.L. Armstrong, M.A. Lindeman, H.J. Wayne, “Wheel-Bearing Test Appparatus for Automotive Greases”, NLGI Spokesman, Jan 1970.

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[13] M.A. Lindeman, N.D. Rebuck, “Torque and Life Data from an R-4 Ball-Bearing Grease Tester”, NLGI Spokesman, Aug 1971. [14] [14] J.B. Christian, “Torque Characteristics Of Lubricating Greases In Miniature Bearings”, NLGI Spokesman, Aug 1979.

[15] G.J. Clark, “Lubricating Grease as Viewed By a Bearing Manufacturer”, NLGI Spokesman, Nov 1972.

[16] S.J. Scannell, “Low Temperature Environmental Testing of Ball Bearing Greases”, NLGI Spokesman, Jul 1975.

[17] In-Sik Rhee, “Development of a New Test Method for Assessing Military Grease Performance at Low Temperatures”, NLGI Spokesman, Oct 1989.

[18] P.L. Langborne, “Grease Lubrication- A Review of Recent British Papers”, NLGI Spokesman, Jan 1971.

[19] H. F. George, P. R. Todd, I. Zinger, “Low Temperature Rheology of Greases- Functionalized Polymer Systems”, NLGI Spokesman, Dec 1998.

[20] W. C. Ward Jr., S. R. Twining, J. B. Zeitz, “A Comparison of Properties of Greases Containing Functionalized Polymer”, NLGI Spokesman, Apr 2007.

[21] L.C. Rotter, J. Wegmann, “The Lincoln Ventmeter and Its Possibilities”, NLGI Spokesman, May 1951.

[22] L.C. Rotter, J. Wegmann, “The Lincoln Ventmeter and Its Possibilities”, NLGI Spokesman, Nov 1965.

[23] F.A. Buehler, H. Raich, “Low Temperature Flow Limits for Greases”, NLGI Spokesman, May 1967.

[24] W.P. Scott, C.J. Swartz, “Properties of Low Temperature Greases”, NLGI Spokesman, Sep 1970.

[25] A. Verhoeff, “Flow of Grease in Pipes- The Lower Temperature Limits For Centralized Systems”, NLGI Spokesman, Jul 1973.

[26] S. Beret, G.R. Trabert, “Grease Pumpability – Status Report”, NLGI Spokesman, Jan 1993.

[27] P. Conley R. Shah, “An Updated on the Lincoln Ventmeter”, NLGI Spokesman, Apr 2004.

[28] P. Conley, C. He, R. Shah, “Lincoln Ventmeter Provides Invaluable Information in Addition to Aiding Lubrication System Design”, NLGI Spokesman, Dec 2007.

[29] C. He, P. Conley, “Lincoln Ventmeter Reading Could Be Used to Estimate Apparent Viscosity”, NLGI Spokesman, Nov/Dec 2009.

[30] C. Page, E. Chan, “The Lincoln Ventmeter – Going with the Flow”, NLGI Spokesman, May/Jun 2014.

[31] P. Conley, R. Shah, C. He, J. Kelly, “Use of Lincoln Ventmeter on Gauging the Impact of Various Contributing Factors on Grease Pumpability”, NLGI Spokesman, Jan/Feb 2015.

[32] G. Fish, Private Communication, Dec 5, 2024.

References: Viscometry/Rheometry [1] C.M. Larson, C.L. Knopf, “Grease Consistency Investigations”, NLGI Spokesman, Apr 1942.

[2] A. Beerbower, L.W. Sprouse, J.B. Patberg, J.C. Zimmer, “Flow Characteristics of Lubricating Greases”, NLGI Spokesman, Nov 1942.

[3] J.C. Zimmer, J.B. Patberg, “Notes on the Operation and Applications of the S.O.D. Pressure Viscometer”, NLGI Spokesman, Jul 1945.

[4[ R.J.S. Pigott, “Some Test Equipment for Greases”, NLGI Spokesman, Dec 1947.

[5] L.C. Brunstrum, R. Steinbruch, “A Simplified Pressure Viscometer for Semi-Fluid Greases”, NLGI Spokesman, Nov 1949.

[6] L.C. Brunstrum, H.M. Grubb, “Flow of Lubricating Grease Between Parallel Planes”, NLGI Spokesman, May 1953.

[7] J.L. Dreher, C.F. Carter, E.B. Reid, “Some New Approaches to the Measurement and Prediction of the Apparent Viscosity of Lubricating Greases”, NLGI Spokesman, Jan 1955.

[8] C.W.Georgi, “Survey of Lubricating Grease Test Methods”, NLGI Spokesman, Aug 1943.

[9] E.R.Irwin, S.C. Britton, “Lubricating Grease Requirements for Modern Military Aircraft”, NLGI Spokesman, Dec 1943.

[10] J.W. Amner, J.F.T. Blott, S. Dawtrey, “Relationship Between Pumpability and Viscosity of Lubricating Greases”, NLGI Spokesman, Oct 1950.

[11] W.H. Bauer, A.P. Finkelstein, D.O. Shuster, S.E. Wiberly, “Comparison of Temperature Effects on the Flow Properties of Greases in Capillary and in Cone and Plate Viscometers”, NLGI Spokesman, Apr 1959.

[12] M.H. Miles, D.W. Miles, A.F. Gabrysh, H. Eyring, “Stress-Relaxation and Recovery Time for Grease and Polymer Systems. Determination of the Relaxation-Time Paramter”, NLGI Spokesman, Sep 1964.

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[13] J. Marvillet, J. du Parquet, “Study of Greases in Bearings Using a Microviscometric Method”, NLGI Spokesman, Nov 1969.

[14] A.F. Buri, “A New Method of Grease Testing”, NLGI Spokesman, Apr 1955.

[15] D. W. Criddle, “A New Equation for Calcuating Flow of Lubricating Greases”, NLGI Spokesman, Nov 1958.

[16] G.L. Harting, ‘The Trident Probe – A New Method of Measuring Grease Consistency at High Temperatures”, NLGI Spokesman, Apr 1974.

[17] M.A. Plint, A.F. Alliston-Greiner, “A New Grease Viscometer- A Study of the Influence of Shear on the Properties of Greases”, NLGI Spokesman, May 1992.

[18] G. Gow, “Judges 5-5 the time factor in grease rheology”, NLGI Spokesman, Dec 1988.

[19] L. Hamnelid, “Amazing Grease or Finding the Right Way to Consistency”, NLGI Spokdesman, Nov 1991.

[20] P. Whittingstall, “Controlled Stress Rheometry as a tool to Measure Grease Structure and Yield at Various Temperatures”, NLGI Spokesman, Dec 1997.

[21] P. Whittingstall, R. Shah, “Yield Stress Studies on Greases”, NLGI Spokesman, Jun 1998.

[22] L. Hamnelid, “Consistency Consists in Sigma Y or The Cone Penetration’s Conclusive Condemnation”, NLGI Spokesman, Jul 1998.

[23] W. Flemming, J. Sander, “Is it Time to Retire the Grease Penetration Test”, NLGI Spokesman, Nov/Dec, 2018.

[24] H. F. George, P. R. Todd, I. Zinger, “Low Temperature Rheology of Greases- Functionalized Polymer Systems”, NLGI Spokesman, Dec 1998.

[25] P. Whittingstall, B. Costello, “A New Compressional Rheometer for the Measurement of Viscoelasticity”, NLGI Spokesman, Jul 2000.

[26] H. F. George, C. F. Kernizan, M. E. Bartlett, “Polyurea Greases – Part 2- Rheological Test Development and Correlation Study”, NLGI Spokesman, Oct 2001.

[27] S. J. Nolan, “The Use of a Controlled Stress Rheometer to Evaluate the Rheological Properties of Grease”, NLGI Spokesman, Jun 2003.

[28] S. J. Nolan, M. R. Sivik, “The Use of Controlled Stress Rheology to Sutdy the High Temperature Structural Properties of Lubricating Greases”, NLGI Spokesman, Jul 2005.

[29] M. R. Sivik, S. J. Nolan, “Studies on the High-Temperature Rheology of Lithium Complex Greases”, NLGI Spokesman, Nov/Dec 2008.

[30] J. Kaperick, et.al., “Complex Issue of Dropping Point Enhancement in Grease”, NLGI Spokesman, Nov/Dec 2017.

[31] P. A. Bessette, “The Impact of Oil Separation on the Apparent Viscosity of Grease”, NLGI Spokesman, Apr 2006.

[32] N. Zaki, T. Litters, “Investigations on low temperature behavior of lubricating greases by strain sweep rheometry – Effect of thickener and base oil on visco-elastic properties at -40C”, NLGI Spokesman, Jan 2009.

[33] B. Johnson, “The Use of a Stress Rheometer in Lieu of Cone Penetration, NLGI Spokesman, May 2009.

[34] W. Flemming, J. Sander, S. Courtney, “A Rheological Study- Doe All #2 Greases Act the Same?”, NLGI Spokesman, Mar/Apr 2012.

[35] J. A. Waynick, H.Hong, “On the Use of Single Wall Carbon Nanotubes and Other Graphitic Solids as Lubricating Grease Thickeners”, NLGI Spokesman, Sep/Oct 2019.

References: Ball Joint Performance [1] M.C. Goodwin, N.A. Hunstad, “Effect of Vibration Frequency and Amplitude on Ball-Joint Grease Steering Performance”, NLGI Spokesman, Apr 1957.

[2] A.C. Horth, W.C. Pattenden, G.F. Keller, J. Panzer, “Use of a Laboratory Ball Joint Test to Predict Chassis Grease Performance”, NLGI Spokesman, Jun 1962.

[3] A.W. Gilbert, T.M. Verdura, F.G. Rounds, “Service Station Grease Performance As Evaluated in a Laboratory Ball Joint Grease Test”, NLGI Spokesman, Feb 1966.

[4] T.J. Risdon, D.J. Sargent, “Comparison of Commercially Available Greases with and without Molybdenum Disulfide Part II – Oxidation Stability and Ball Joint Tests”, NLGI Spokesman, Jan 1971.

[5] T.J. Risdon, “Effect of MoS2 Concentration on the Performance of Greases in the GMR Ball Joint Tester”, NLGI Spokesman, Aug 1974.

[6] T.J. Risdon, “Some Energy Implications For The Use of MoS In Greases”, NLGI Spokesman, Aug 1977.

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[7] T.J. Risdon, D.A. Gresty, “Abrasive Contaminants The Effect of MoS2 on Wear With Greases Containing An Abrasive Contaminant”, NLGI Spokesman, Sep 1978.

[8] T.J. Risdon, “Evaluation of MoS2 in Newer Grease Thickener Systems”, NLGI Spokesman, Sep 1986.

References: Bearing Life [1] O.L. Maag, “Antifriction Bearing Lubricants”, NLGI Spokesman,, NLGI Spokesman, Dec 1941.

[2] Walter G. Ainsley, “Report on the Activities of the Coordinating Research Council War Advisory CommitteeGrease Advisory Group”, NLGI Spokesman, Jan 1945.

[3] L.W. Sproule, “Some Practical Methods for the Evaluation of Lubricating Greases”, NLGI Spokesman, Feb 1945.

[4] J.R. Roach, T.B. Jordan, “Evaluation of Grease Lubricated Bearings at High Rotative Speeds”, NLGI Spokesman, May 1947.

[5] R.J.S. Pigott, “Some Test Equipment for Greases”, NLGI Spokesman, Dec 1947.

[6] E.G. Jackson, E.R. Booser, “Greases for Electric Motors”, NLGI Spokesman, Mar 1954.

[7] J.P. Dilworth, J.R. Roach, “High Temperature Ultra High Speed Grease Lubrication”, NLGI Spokesman, Apr 1956.

[8] E.L. Armstrong, M.A. Lindeman, H.J. Wayne, “Wheel-Bearing Test Appparatus for Automotive Greases”, NLGI Spokesman, Jan 1970.

[9] R. McClintock, “A Laboratory Study Of Wheel Bearing Grease High-Temperature Life”, NLGI Spokesman, Mar 1980.

[10] A.R. Lansdown, R. Gupta, “The Influence of Evaporation on Grease Life”, NLGI Spokesman, Jul 1985.

[11] E.O. Forster, J.J. Kolfenbach, “Evaluation of Wheel Bearing Grease Performance”, NLGI Spokesman, May 1954.

[12] D.J. Sargent, “A Historical View Of ASTM Method D-3527”, NLGI Spokesman, Aug 1978.

[13] J.A. Keller, “ASTM D-3527 and D-4290 High Temperature Wheel Bearing Grease Performance Life and Leakage Test Methods”, NLGI Spokesman, Feb 1986.

[14] B. Carfolite, A. Chadwick, “High Temperature Wheel Bearing Testing – an Electrifying Improvement”, NLGI Spokesman, Jul/Aug 2019.

[15] L.B. Sargent Jr., J.T. Bunting, “Grease Specifications, Now and Tomorrow”, NLGI Spokesman, Jan 1968.

[16] P.R. McCarthy, W.W. Bailey, “Laboratory Evaluation of Automotive Wheel Bearing and Ball Joint Greases”, NLGI Spokesman, Aug 1975.

[17] G.L. Harting, T.C. Wilson, “Wheel Bearing Greases – Their Performance in the Laboratory and the Field”, NLGI Spokesman, Jul 1976.

[18] I.W. Armstrong, H.A. Woods, “Development of an Extreme High Temperature Grease”, NLGI Spokesman, Apr 1958.

[19] J.R. Belt, N. Glassman, “Grease Evaluation by Bearing Performance Tests”, NLGI Spokesman, Apr 1960.

[20] K.R. Bunting, A. Dobry, J. Gorman, “Statistical Studies of High Temperature Grease Life Tests”, NLGI Spokesman, Jul 1971.

[21] L. Stallings, “Performance Characteristics of Lubricating Greases at Elevated Temperatures ASTM Method D-3336”, NLGI Spokesman, Jun 1975.

[22] A.R. Wilson, “The Effect Of Airflow On Grease Life In Rolling Bearings At Elevated Temperatures”, NLGI Spokesman, Jul 1977.

[23] M.A. Lindeman, “History of an ASTM Method- Evaluation of Greases in Small Bearings – D 3337-74”, NLGI Spokesman, Jul 1975.

[24] H. D. Grasshoff, H. Maak, “Improved European Techniques for Grease Testing”, NLGI Spokesman, Apr 1985.

[25] E. Kleinlein, “Using the FE8 System as a Testing Method for Ball and Roller Bearing Greases”, NLGI Spokesman, Sep 1995.

[26] C. Lin, W. Kersey, W. Dresel, “Validating New Lubricating Grease Development Using the FAG FE 8 Test Rig”, NLGI Spokesman, May 2006.

[27] S. Hosoya, M. Hayano, “Deterioration of Lithium Soap Greases and Functional Life in Ball Bearings”, NLGI Spokesman, Sep 1989.

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[28] Y. Kawamura, et. al.. “Standardization of Tests for Grease Life and the Effect of Test Conditions Part One”, NLGI Spokesman, May 1994.

[29] Y.Kawamura, et. al., “The Effect of Grease Composition on Grease Life Part Two”, NLGI Spokesman, Jun 1994.

References: Elastomer Compatibility (ASTM D4289) [1] D.C. McGahey, R.S. Barnett, “Lubrication of Aircraft Oscillating Control Bearings at High Temperatures”, NLGI Spokesman, Dec 1957.

[2] J, Messina, “Greases Nonreactive with Missile Fuels and Oxidizers”, NLGI Spokesman, Sep 1963.

[3] J.T. Skehan, “The Development of Fluorinated Greases for Aerospace Military and Industrial Applications”, NLGI Spokesman, Oct 1970.

[4] Paul E. Gatza, “Compatibility of Wheel Bearing Seal Elastomers with MIL-G-10924 Greases”, NLGI Spokesman, Nov 1986.

[5] Jack B. Boylan, “Synthetic Basestocks For Use in Greases”, NLGI Spokesman, Aug 1987.

[6] G. Bert van der Waal, “Properties and Application of Ester Base Fluids and P.A.Os”, NLGI Spokesman, Nov 1989.

[7] Samil Beret, “Impact of Base Oil Changes on Grease Performance”, NLGI Spokesman, Aug 1993.

[8] Robert C. Richardson, Philip R. Scinto, “The Effects of Gear Lubricant Components on Oil Seal Compatibility”, NLGI Spokesman, Sep 1994.

[9] Samil Beret, Peter K. Wong, Thomas J. Boersig, “Elastomer Compatibility - Base Oil and Additive Effects”, NLGI Spokesman, Aug 1996.

[10] Ian Macpherson, “Industrial Lubricant Additives for Hydrocracked Base Oils”, NLGI Spokesman, Apr 1997.

[11] Mahmoud A. Fowzy, “New Global Aerospace Grease SAE AMS-M Aerospace Grease Core Specification”, NLGI Spokesman, Dec 2000.

[12] Gunnar Stang, Linda Salomonsson, “Rubber Interactions with Grease and Base Oil”, NLGI Spokesman, Apr 2005.

[13] Valentina Serra-Holm, “Development of a Novel Naphthenic Base Oil for Application in CVJ Greases”, NLGI Spokesman, Mar 2007.

[14] Maureen E. Hunter, “Alkylated Naphthalenes”, NLGI Spokesman”, May 2015.

[15] Chad Chichester, Christian Kranenberg, “Advances in Silicone Copolymer Based Lubricants “, NLGI Spokesman, Jul 2017.

[1] Evaluating Compatibility Of Greases With Elastomeric Seals T.M. Verdura Apr 1978 [17] ASTM D-4289-83 Standard Method of Testing Compatibility of Lubricating Grease with Elastomers Jon C. Root Aug 1985 [18] Thomas M. Verdura, “Classification and Specification for Automotive Service Greases - A New Industry Standard”, NLGI Spokesman, May 1990.

[19] Recent Activities in ASTM Subcommittee D02.G on Lubricating Grease A. Richard Scott Dec 1993.

[20] New Elastomers Revitalize NLGI Certification Thomas M. Verdura Stephanie R. Flanagan Jun 1996.

[21] Recent Advance in Test Procedures Development by ASTM Subcommittee D02.G on Lubricating Grease Rajesh J. Shah Jamie E. Spagnoli Jul 1997.

[22] Dr. Raj Shah, Jacky Jiang, Joseph Kaperick, “Next-Generation NLGI Grease Specifications”, NLGI Spokesman, Nov 2019.

References: Infrared/FTIR Spectroscopy [1] B. F. Daubert, “The Chemistry of Fats”, NLGI Spokesman, Nov 1951.

[2] E.C. Milberger, A.F. Miller, V.R. Damerell, “Infrared Studies of Bentone Grease Water Systems”, NLGI Spokesman, Aug 1957.

[3] R.J. Ronan, M.C. McLaren, “Scientific Detection in Grease Lubrication Problems”, NLGI Spokesman, Jan 1959.

[4] S.E. Wiberley, W.H. Bauer, D.B. Cox, “Infrared Studies of Greases”, NLGI Spokesman, Nov 1960.

[5] J.E. Goodrich, J.J. Burke, “Oxidation of Lubricating Greases”, NLGI Spokesman, Jan 1961.

[6] Factors that Influence Grease Oxidation and Oxidative Wear G.P. Murphy Jr. NLGI Spokesman, Apr 1964.

[7] R. Barretto, J. Gonzalez, “Characteristics of Lubricating Greases from Calcium Complex Synthesized in Different Reaction Media”, NLGI Spokesman, Sep 1966.

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[8] J.L. Zakin, H.H. Lin, E.H. Tu, “Exploratory studies of the Sorption and Extraction of Additives in Lubricating Greases”, NLGI Spokesman, May 1967.

[9] M.E. LePera, “Petroleum Oil Characterization using Carbon Type Analysis and Infrared Spectroscopy”, NLGI Spokesman, Feb 1969.

[10] F.W. Schaefer, A.C. Wright, W.T. Granquist, “Extent of Dispersion of an Organo-Clay Complex in Oil An Infrared Method”, NLGI Spokeman, Mar 1971.

[11] J.J. Elliott, G.L. Harting, “Considerations in the Use of Infrared Spectroscopy in the Analysis of Greases”, NLGI Spokesman, Jun 1970.

[12] R.O. Buttlar, R.E. Cantley, “Quantitative Infrared Spectroscopy Studies of Lithium-Soap Lubricating Greases”, NLGI Spokesman, Apr 1969.

[13] G.M. Stanton, “Infrared Analysis of Lubricating Greases”, NLGI Spokesman, Aug 1970.

[14] R.A. Putinier, “The Quantitative Analysis of Components in Lubricating Greases by Differential Infrared Spectrophotometry”, NLGI Spokesman, Sep 1970.

[15} T.M. Verdura, “Infrared Spectra of Lubricating Grease Base Oils And Thickeners - Part II”, NLGI Spokesman, Nov 1971.

[16] J.H. Marino, J.C. Root, K.L. Thomas, “Infrared Spectrophotometric Analysis of Additives Used in Lubricating Grease”, NLGI Spokesman, Jul 1972.

[17] G.C. Pedroza, C. Pettus, “Grease Compatibility Study”, NLGI Spokesman, Sep 1972.

[18] P.H. Pallady, G.C. Pedroza, “The Monitoring of Synthetic Ester Oil Degradation By the Use of Gel Permeation Chromatography (GPC)”, NLGI Spokesman, Nov 1972.

[19] G.M. Stanton, “Examination of Greases by Infrared Spectroscopy”, NLGI Spokesman, Aug 1974.

[20] G.M. Stanton, “Grease Analysis A Modern Multitechnique Approach”, NLGI Spokesman, Nov 1976.

[21] G.W. Fultz, “The Identification Of Miniature Bearing Greases By Liquid Chromatography And Infrared Spectroscopy”, NLGI Spokesman, May 1978.

[22] C.A. Cody, W.W. Reichert, “Studies of Fundamental Organoclay Rheological Relationships”, NLGI Spokesman, Jan 1986.

[23] E.D. Magauran, A. Chiavoni, W.W. Reichert, C.A. Cody, “Studies of the Behavior of Dispersed Organoclays in Grease Systems”, NLGI Spokesman, Jun 1986.

[24] A. Izcue G., “Infrared Spectroscopy in the Development and Manufacture of Lubricating Greases”, NLGI Spokesman, Aug 1988.

[25] S. Hosoya, M. Hayano, “Deterioration of Lithium Soap Greases and Functional Life in Ball Bearings”, NLGI Spokesman, Sep 1989.

[26] Janie R. Addis, “Applications of Fourier Transform Infrared Spectroscopy for Customer Support”, NLGI Spokesman, Apr 1990.

[27] P.M. Cann, H.A. Spikes, “Film Thickness Measurements of Lubricating Greases Under Normally Starved Conditions”, NLGI Spokesman, May 1992.

[28] B.P. Williamson, D.R. Kendall, P.M. Cann, “The Influence of Grease Composition on Film Thickness in EHD Contacts’, NLGI Spokesman, Nov 1998.

[29] S. Hurley, P.M. Cann, “Infrared Spectroscopic Characterization of Grease Lubricant Films on Metal Surfaces”, NLGI Spokesman, Oct 2000.

[30] P.M. Cann, S. Hurley, “Friction Properties of Grease in Elasatohydrodynamic Lubrication”, NLGI Spokesman, April 2002.

[31] S. Hurley, P.M. Cann, “Infrared Spectroscopic Analysis of a Grease-Lubricated Rolling Contact”, NLGI Spokesman, Sep 2003.

[32] Nicolas Samman, “Chemistry of Aluminum Complex Grease Revisited“, NLGI Spokesman, Nov 1992.

[33] Ronald Krol, “Quantitative Analysis of Aluminum Complex Greases by FTIR Spectroscopy”, NLGI Spokesman, March 1995.

[34] Anuj Mistry, “Grease Compatibility Revisited”, NLGI Spokesman, Jan 2001.

[35] Yang Wei, Yao Lidan, Zheng Shanwei, “A Study on Structure and Mechanism of Diurea Grease”, NLGI Spokesman, Jul 2003.

[36] Bryan Johnson, Jo Ameye, “Condition Monitoring of Anti-oxidant Chemistry of In-Service Bulk Greases”, NLGI Spokesma Nov 2004.

[37] Liu Qinglian, Zhang Suhua, Cheng Shutian, Wu Lihong, “Application of Fourier Transform Infrared - 50 NLGI Spokesman | VOLUME 88, NUMBER 6 | January/February 2025

Spectroscopy in Processing Lithium Complex Grease”, NLGI Spokesman, Jun 2005.

[38] P. Senthivel, Mary Joseph, S.C. Nagar, Anoop Kumar, K.P. Naithani, A.K. Mehta, N.R. Raje, “An Investigation Into the Thermal Behavior of Lubricating Greases by Diverse Techniques”, NLGI Spokesman, Oct 2005.

[39] David Turner, “Used Lubricating Grease Tests and Their Significance”, NLGI Spokesman, Nov 2012.

[40] Samina Azad, Jonathan C. Evans, “An Advanced Technique for Grease Oxidation Measurement”, NLGI Spokesman Jan 2015.

References: Electron Microscopy [1] https://en.wikipedia.org/wiki/Electron_microscope#History [2] B.B. Farrington, D.H. Birdsall, “An Electron Microscope Study of Lubricating Greases”, NLGI Spokesman, Apr 1947 [3] A. Bondi, A.M. Cravath, R.J. Moore, W.H. Peterson, “Basic Factors Determining the Structure and Rheology of Lubricating Greases”, NLGI Spokesman, Mar 1950 [4] Earl Amott L.W. McLennan, “Complexes in Lubricating Oil Greases”, NLGI Spokesman, Mar 1951 [5] Marjorie J. Vold, Robert D. Vold, “The Phase Study Approach to Grease Problems”, NLGI Spokesman, Aug 1949.

[6] R.D. Vold, H.F. Coffer, R.F. Baker, “Rheological Studies and Electron Microscopy of Calcium Stearate - Cetane Gels”, NLGI Spokesman, Jan 1952.

[7] Marjorie J. Vold , “N.L.G.I. Fellowship Report-X-Ray Diffraction Studies of Oriented Soap Structures in GreaseLike System”, NLGI Spokesman, Nov 1952., [8] Marjorie J. Vold, Valeria A. Elersich, Richard F. Baker, Robert D. Vold, “N.L.G.I. Fellowship Report Grease Structures Indicated by X-Ray Orientation Analysis and Electron Microscopy”, NLGI Spokesman, Aug 1954.

[9] A.L. McClellan, J. Cortes Jr, “Use of Aerogels for Examining Structure of Lubricating Grease Thickeners”, NLGI Spokesman, Sep 1956.

[10] R.H. Leet, L.C. Brunstrum, R.S. Barnes, “Similarities of Grease Fiber Dimensions in Laboratory Workers and Service”, NLGI Spokesman, Feb 1956.

[11] R.M. Suggitt, “Structural Changes and Phase Transitions in Lithium Greases”, NLGI Spokesman, Dec 1960.

[12] J.W. Wilson Jr., “Electron Microscope Examination Of Thin Sections of Lubricating Grease Thickeners”, NLGI Spokesman, Sep 1961 [13] J.W. Wilson, “Three-Dimensional Structure of Grease Thickener Particles”, NLGI Spokesman, Mar 1964.

[14] D.W. Criddle, “Use of an Electronic Counter to Study the Size Distribution of Dispersed Grease Thickener Particles”, NLGI Spokesman, Sep 1965.

[15] R. Barretto, J. Gonzalez, “Characteristics of Lubricating Greases from Calcium Complex Synthesized in Different Reaction Media”, NLGI Spokesman, Sep 1966.

[16] F.W. Anderson, R.C. Nelson, F.F. Farley, “Preparation of Grease Specimens for Electron Microscopy”, NLGI Spokesman, Oct 1967.

[17] J.C. Webster, W.J. Ewbank, “The Effect of Thickener Shape on the Permeability of Lubricating Grease”, NLGI Spokesman, Oct 1968.

[18] M.J. Vold, Y. Uzu, R.F. Bils, “New Insight into the Relationship Between Phase Behavior Colloidal Structure and Some of the Rheological Properties of Lithium Stearate Greases”, NLGI Spokesman, Jan 1969.

[19] R. Vitali, M. Borza, “Twist of the Fibres of 12 Hydroxystearate Lithium Grease”, NLGI Spokesman, Jul 1969.

[20] M.M. Gerassimov, I.T. Zahariev, K.G. Stanulov, “Effect of Cooling on the Structure Made of Different Fat Bases,” NLGI Spokesman, Sep 1973.

[21] Nicolas Sammen, “Chemistry of Aluminum Complex Grease Revisited”, NLGI Spokesman, Nov 1992.

[23] Nancy W. Rizzo, Larry Irwin, Michael D. Foster, Michael R. Funk, “Extracting Imaging and Quantifying Soap Fibers in Grease”, NLGI Spokesman, Apr 1996 [24] Chihoria Araki, Hidetoshi Kanzaki, Toru Taguchi, “A Study on the Thermal Degradation of Lubricating Greases”, NLGI Spokesman, Nov 1995.

[25] Curtis R. Scharf, Herman F. George, “The Enhancement of Grease Structure Through the Use of Functionalized Polymer Systems”, NLGI Spokesman, Feb 1996.

[26] C.V. Chandrasekharan, S. Chattopadhyay, V.N. Sharma, P.M. Ozarkar, B. Ghosh, “Thermal and Mechanical Behavior of Lithium Greases from Four Processing Systems”, NLGI Spokesman, Apr 1997.

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[27] S. Hurley, P.M Cann, “Examination of Grease Structure by SEM and AFM Techniques”, NLGI Spokesman, Aug 2001.

[28] Carl F. Kernizan, Patricia R. Todd, Melinda E. Bartlett, “Future Directions- Evaluation of Greases Formulated with Functionalized Polymers”, NLGI Spokesman, Nov 2002.

[29] J.W. Harris R.S. Hall, “A Novel Method for Manufacturing Lithium Soap Grease in Steam Heated Kettles”, NLGI Spokesman, Mar 2004., [30] Yuji Onuki, “A Fundamental Study on Degradation Process of Urea Greases Based on Synthetic Fluids”, NLGI Spokesman, Jun 2006.

[31] William C. Ward Jr., Morey Najman, “Properties of Tribochemical Films from Various Additives in Grease Generated Under Load”, NLGI Spokesman, Oct 2006.

[32] James E. Reddy, Antonio L. De Vera, Mary E. Hopkins, Joshua I. Ford, “Overbased Calcium Carboxylates as Grease Precursors” NLGI Spokesman, Nov 2006.

[33] John J. Lorimor, “An Investigation into the Use of Boron Esters to Improve the High-Temperature Capability of Lithium 12-Hydroxystearate Soap Thickened Grease”, NLGI Spokesman, Sep 2010.

[34] Joseph P. Kaperick, J. Guevremont, K. Hux, “A Study of Friction Modifiers in Grease”, NLGI Spokesman, May 2011.

[35] Gaston A. Aguilar, Joseph P. Kaperick, Michael Lennon, Grant Pollard, “The Effect of Thickener on EP Additive Response”, NLGI Spokesman, Jul 2015.

[36] Michitaka Yoshihara, Tsutomu Moriuchi, “Observation of Thickener Structure in Grease”, NLGI Spokesman, Mar 2017 [37] S Chatra, D Muller, C Matta, R Thijssen, M N bin Yusof, M C P van Eijk, “Novel Polymer Grease Microstructure and its Proposed Lubrication Mechanism”, NLGI Spokesman, Mar 2018.

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