July / August 2015 NLGI Spokesman

NLGI

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 3, JULY/AUGUST 2015

In this issue . . .

7 2015 NLGI Recognition Awards 12 T he Effect of Thickener on EP Additive Response 22 PTFE

for Lubricating Greases 40 F ullerene-like Inorganic Nanoparticles (IFWS2) as Extreme Pressure and Antiwear Additive in Grease Applications

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PRESIDENT:

VICE-PRESIDENT:

Bruce M. Urban FMC-Lithium Division 2801 Yorkmont Rd., Ste. 300 Charlotte, NC 28208

David Como Dow Corning Corp.

P.O. Box 0994 Midland, MI 48686

SECRETARY:

TREASURER:

Kim Smallwood Citgo Petroleum Corp.

1293 Eldridge Pkwy.

Houston, TX 77077

Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

PAST-PRES./ADVISORY:

EXECUTIVE DIRECTOR:

Chuck Coe Grease Technology Solutions LLC 7010 Bruin Ct. Manassas, VA 20111

Kimberly Hartley NLGI Inter­national Headquarters 249 SW Noel, Suite 249 Lee’s Summit, MO 64063

DIRECTORS Barbara Bellanti Battenfeld Grease & Oil Corp. of NY P.O. Box 728 • 1174 Erie Ave. N. Tonawanda, NY 14120-0728 Richard Burkhalter Covenant Engineering Services 140 Corporate Place Branson, MO 65616 Faith Corbo King Industries, Inc. Science Road Norwalk, CT 06852 Gary Dudley Exxon Mobil Corporation 3225 Gallows Road Room 7C1906 Fairfax, VA 22037 Gian L. Fagan Chevron Lubricants 100 Chevron Way Room 71-7338 Richmond, CA 94802-0627 Jim Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720 Tyler Jark Lubricating Specialties Co. 8015 Paramount Blvd.

Pico Rivera, CA 90660 Dr. Anoop Kumar Royal Manufacturing Co., LP 516 S, 25th West Ave. Tulsa, Oklahoma 74127 Wayne Mackwood Chemtura 199 Benson Rd. Middlebury, CT 06749

Dennis Parks Texas Refinery Corp.

One Refinery Place Ft. Worth, TX 76101 Tom Schroeder Axel Americas, LLC P.O. Box 12337 Kansas City, MO 64116 Raj Shah Koehler Instrument Co. 85 Corporate Dr. Holtsville, NY 11716-1796 Dr. Huafeng “Bill” Shen Bel-Ray Co. P.O. Box 526 Farmingdale, NJ 07727 Terry Smith Lubrication Engineers, Inc. P.O. Box 16447 Wichita, KS 67216 Thomas W. Steib The Elco Corporation 1000 Belt Line Street Cleveland, OH 44109 Lisa Tocci Lubes ’n’ Greases 6105 Arlington Blvd., Suite G Falls Church, VA 22044 William (Bill) Ward The Lubrizol ­Corpo­ration 29400 ­Lakeland Blvd.

Mail Drop 051E Wickliffe, OH 44092 Ruiming “Ray” Zhang R.T. Vanderbilt Company, Inc. 30 Winfield St. Norwalk, CT 06855

NLGI

OFFICERS

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 3, JULY/AUGUST 2015

4

President’s Podium

7 2015 NLGI Recognition Awards 12 The Effect of Thickener on EP Additive Response Gaston A. Aguilar; Joseph P. Kaperick, Michael Lennon and Grant Pollard. Afton Chemical Corporation, Virginia

22 PMary TFE for Lubricating Greases Moon, Ph.D. Shamrock Technologies, Inc., New Jersey

40 F ullerene-like Inorganic Nanoparticles (IF-WS2) as Extreme Pressure and Antiwear Additive in Grease Applications

George Diloyan 1, Alexander Margolin2, Larissa Drangai2.

1. Nanotech Industrial Solutions Inc., Avenel 07001, NJ, USA. 2. NanoMaterials LTD. Yavne 8122101, Israel

51 Advertiser’s Index

Dwaine (Greg) Morris Shell Lubricants 526 S. Johnson Drive Odessa, MO 64076

TECHNICAL COMMITTEE CO-CHAIRS:

CHAIR, SESSION PLANNING:

J oe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

David Turner 22110 Stone Cross Court Katy, TX 77450

SERVICE INDUSTRY ASSISTANCE COMMITTEE

ON THE COVER

David Turner receives NLGI’s highest honor, the Award for Achievement. See his biographical information beginning on page 7.

CHAIR: J im Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720

EDITORIAL REVIEW COMMITTEE CHAIR: Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

Published bi-monthly by NLGI. (ISSN 0027-6782) KIMBERLY HARTLEY, Editor NLGI International Headquarters 249 SW Noel, Suite 249, Lee’s Summit, MO 64063 USA Phone (816) 524-2500, FAX: (816) 524-2504 Web site: http://www.nlgi.org — E-mail: nlgi@nlgi.org One-year subscriptions: U.S.A. $65.00; Canada $80.00; International $109.00; Airmail $147.00. Claims for missing issues must be made within six months for foreign subscribers and three months for domestic. Periodicals postage paid at Kansas City, MO. The NLGI Spokesman is indexed by INIST for the PASCAL database, plus by Engineering Index and Chemical Abstracts Service. Microfilm copies are available through University Microfilms, Ann Arbor, MI. The NLGI assumes no responsibility for the statements and opinions advanced by contributors to its publications. Views expressed in the editorials are those of the editors and do not n­ ecessarily represent the official position of NLGI. Copyright 2015, NLGI. Postmaster: Send address corrections to the above address.

PRESIDENT’S PODIUM

President’s Podium Welcomes Joe Kaperick

Afton Chemical Corp.

NLGI Treasurer

Recap of the 2015 82nd Annual Meeting NLGI 2015 – Digging into Grease Lubrication

The 82nd NLGI Annual Meeting was held at the Coeur D’Alene Resort in the beautiful lakeside town of Coeur D’Alene, Idaho on June 6 – 9, 2015. This year’s focus on mining lubrication not only paid tribute to one of the largest industries in the area but also to the critical role of lubrication in the protection and maintenance of the equipment used in these endeavors. The technical portion of the program was kicked off by our Industry Speaker, Luke Stavros, Chief Sales Officer and Vice President of Product Support for Ground Force Worldwide. This local company builds mine support equipment for both open pit and underground mines, with one of their monster lubrication trucks parked in front of the hotel for a “show-and-tell” session for the duration of the meeting. True to this year’s theme, this was the beginning of a lot of hard work on the part of the attendees as they dug into working groups, networking opportunities, and technical sessions. Even those taking advantage of Sunday morning’s short break on the gorgeous resort golf course had to do some excavating in sand and tall grass!

Diamonds in the Rough

Awards presented for best technical papers from the 2014 meeting continued to highlight the gems that have been produced by researchers within NLGI’s technical population. The winners of the two NLGI Author awards were Paul Bertin (Elevance Renewable Sciences - “Novel Long-Chain Dibasic Complexing Agents for Lithium Thickened Grease”) for Development and Gaston Aguilar (Afton Chemical Corporation - “The Effect of Thickener on EP Additive Response”) for

Applications while Bill Tuszynski (Ivanhoe Industries, Inc.) picked up the Clarence E. Earle Award for Contribution to Technical Literature in recognition of his tireless efforts for coordinating the 6thEdition of the NLGI Lubricating Grease Guide.

Yours, Mines and Ours

With a record attendance of 389 plus 81 guests at this year’s meeting, five of the seven continents sent representatives. With attendees from such areas as Singapore, Australia, Japan, China, and the United Kingdom, more than 80 grease enthusiasts traveled to Idaho from over twenty different countries to increase the depth of their knowledge. Presentations were also made by Dr. E. Sayanna, Vice President of NLGI’s India Chapter, and Terry Dicken, Chairman of ELGI (the European counterpart of NLGI), with updates from their respective organizations. And new this year was a rousing Closing Festival with yet more networking and business opportunities.

Meeting of the Mines

Members of the Working Groups that are sponsored by both NLGI and ELGI continued tunneling through a variety of issues to make good progress in several different areas. Meetings of each of the Joint Working Groups (Food Grade, Grease Particle Evaluation, and Bio-Based) were held with continued progress in each.

These groups draw their membership from both ELGI and NLGI with sessions being held in Europe and North America. Additionally, the ELGI has two Working Groups (Railway and Test Methods) which are currently specific to the European region but attract attendees

-4VOLUME 79, NUMBER 3

from both organizations. This year a new NLGI Working Group was started to begin discussion on updating NLGI’s Automotive Service Grease specification based on enthusiastic response to a poll of the membership. Those with an interest in participating in this discussion should contact the chair, Dr. Gareth Fish (Gareth.Fish@Lubrizol. com). These working groups are chaired by volunteers from within the industry and are aimed at addressing current topics of real interest and concern to the global grease community.

Hidden Treasure

For those interested in learning more about grease issues in various regions, meeting new potential customers outside of the United States or looking for new reserves of grease knowledge, the opportunities continue to flourish.

NLGI-India Chapter will hold their next annual meeting in February 2016, while ELGI will host their 28th Annual General Meeting on April 16 – 19, 2016 in Venice, Italy.

Finally, NLGI’s next Annual Meeting will be held June

11 – 14, 2016 in the Shenandoah mountains at The Homestead Resort in Hot Springs, Virginia. All of these meetings welcome technical contributions and attendees from all over the globe.

So whether you’re interested in digging into new veins of technical knowledge in your own backyard, or you want to prospect in distant lands, the opportunities to shore up technical gaps and build strong networks continue to grow as the world of grease is brought within reach by organizations such as NLGI. As is the case in gold and silver mines, there are nuggets of great value to those in the grease industry that can be unearthed with a little hard work, the right equipment and a good grease formulation.

Joe Kaperick Afton Chemical Corporation NLGI Treasurer

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2015 NLGI Recognition Awards Nine Receive Recognition

John A. Bellanti, Sr. Memorial Meritorious Service Award “Acknowledges meritorious service on the NLGI Board for three or more years, on Technical Committee projects, or to the industry.”

MR. TERRY SMITH LUBRICATION ENGINEERS, INC.

Terry graduated from the College of Liberal Arts at University of Kansas with majors in chemistry and comparative biochemistry & physiology. His career in the lubricant industry began in April, 1969 as a chemist for Southwest Grease & Oil / Southwest Petrochem in Wichita, Kansas. After spending 12 years with Southwest, his career with Lubrication Engineers, Inc. began in 1981 when LE’s manufacturing plant came online in Wichita. He has worked for LE in various laboratory-related capacities for 34-plus years.

Terry is a 33-year member of the American Chemical Society, Society of Automotive Engineers, and the STLE. He holds CLGS®, CLS and OMA certifications. Terry has served on the NLGI Board of Directors since 2008 and has worked with the Technical Committee focusing on the NLGI CLGS® program.

Terry resides in Wichita with his wife of 45 years, Vicki. They have two daughters, Jennifer and Amy.

NLGI Achievement Award

“The Institute’s highest award, it honors the achievement of those who have made exceptional contributions to the growth and development of the Institute.”

MR. DAVID TURNER

David recently became a Product Specialist with CITGO Petroleum Corp. He is a graduate of Lamar University in Beaumont, Texas, holding a B.S. degree in Chemical Engineering. He has more than 33 years of experience in the lubricants industry, in formulation, manufacturing, selection, application, and technical service of greases and industrial lubricants. He is a member of STLE and ASTM, and has authored several papers for NLGI. He is the chairman of ASTM D02.G on Lubricating Grease and is co-chair of the NLGI Technical Committee. He is the recipient of the NLGI Clarence E. Earl Memorial Award, the ASTM Award of Excellence, the NLGI Meritorious Service Award, the NLGI Fellows Award, the NLGI Chevron Lubricants Award, and the NLGI Shell Lubricants Award for Instructor Excellence. He is an NLGI Certified Lubricating Grease Specialist (CLGS), an STLE Oil Monitoring Analyst (OMA I), and an STLE Certified Lubrication Specialist (CLS).

-7NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI Fellow Award

“Acknowledges valuable work within the Institute, in the technical development of greases, grease tests, grease usage, or the promotion of grease usage.”

NLGI Author Award – Development MR. CHUCK COE GREASE TECHNOLOGY SOLUTIONS LLC

Chuck holds a B.S. in Chemical Engineering from Pennsylvania State University. He also holds the NLGI CLGS and STLE CLS professional certifications. He worked for Mobil and ExxonMobil for 32 years, including 6 years as ExxonMobil’s Grease Technology Manager and many years as an industrial oil and grease formulator and technical advisor. He retired from ExxonMobil and launched Grease Technology Solutions LLC, a grease training and consulting business in 2009. He is the immediate past president of NLGI and is the Grease Education Course Chair of STLE. He has authored several technical papers and articles on grease, and received Best Marketing Paper and Best Paper awards from both NLGI (2008) and ELGI (2009), and the John A. Bellanti Memorial Meritorious Service Award (2012) from NLGI.

(Sponsored by Royal Manufacturing Co. LP) “Commends the author of a paper of special significance, as presented at the Annual Meeting of the Institute”

MR. PAUL BERTIN ELEVANCE RENEWABLE SCIENCES For his paper entitled “Novel Long-Chain Dibasic Complexing Agents for Lithium Thickened Grease” Bertin currently holds the title of Scientist–Product Development at Elevance Renewable Sciences headquartered near Chicago, IL (2012-present). He is a native of Cleveland, OH and earned his B.A. and B.S. degrees in chemistry and business at Miami University (2000). Paul received his Ph.D. in organic chemistry from Northwestern University (2005) for the development of polymer-based nanostructures from ring-opening metathesis polymerization.

Prior to Elevance, Paul worked as a Principal Scientist at Ohmx Corporation (2005-2011). He is the author or co-author of more than 40 research publications, patents, and patent applications.

His research interests broadly include sustainable chemistry, electron transfer processes in hybrid organic-inorganic systems, and advanced functional materials. At Elevance, Paul designs, synthesizes, and evaluates natural oil metathesis biorefinery products and downstream derivatives in lubricant, engineered polymer, and coatings applications that address critical customer objectives and/or urgent market trends.

-8VOLUME 79, NUMBER 3

Clarence E. Earle Memorial Award

(Sponsored by Rockwood Lithium) “For an outstanding contribution to the technical literature relating to lubricating greases during the year”

MR. BILL TUSZYNSKI IVANHOE INDUSTRIES, INC. “For his tireless work on developing the 6th Edition of the NLGI Lubricating Grease Guide.”

Bill is currently Managing Partner and co-owner of Ivanhoe Industries, a Tullytown, PA distributor of industrial and specialty chemicals. In that role, he manages the company’s lubricant additive business.

Prior to joining Ivanhoe, he held various technical, business development and management positions with Inolex Chemical Company, Elf Atochem and Pennwalt (both now Arkema).

He holds a Ph.D. in Physical Organic Chemistry from Cornell University and a B.S. in Biochemistry from Manhattan College.

NLGI Author Award Application

(Sponsored by Chevron Global Lubricants Company) “For the best paper presented at our Annual Meeting that focuses on selection, application, or use of lubricating grease.”

MR. GASTON AGUILAR AFTON CHEMICAL CORPORATION For his paper entitled “The Effect of Thickener on EP Additive Response” Gaston received a Doctorate degree in organic chemistry from Texas A&M University in 1996. After post-doctoral work at the University of Florida, he joined Conoco Inc. in 1997 as a research chemist working in the Lubricant R&D Department. He moved to R. T. Vanderbilt in August, 2000 where he worked for 13 years holding multiple positions including Product Manager for Lubricant Additives and Research Director. In 2013, he joined Afton Chemical as a Sr. R&D Scientist focusing his work on grease technology and formulation.

-9NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI Award for Education Excellence (Sponsored by Shell Lubricants) “For outstanding instruction as exemplified by subject knowledge and presentation skills in NLGI education courses”

MR. DICK BURKHALTER COVENANT ENGINEERING SERVICES LLC Burkhalter received his bachelor’s degree in Chemical Engineering at the Missouri School of Mines and Metallurgy, Rolla, Missouri, in 1967, now known as the Missouri University of Science and Technology (MS&T).

He has more than twenty years plant operations experience, and has served as project manager for a leading consulting firm in the design of lubricating oil and grease manufacturing plants for twelve years. In 1995, he founded Covenant Engineering Services to serve the lubricants and chemical industries where he serves as President. He is a member of the American Institute of Chemical Engineers and has been an active member of NLGI since 1986. He has served on the NLGI Board of Directors for ten years, authored and presented six technical papers at the annual meetings, co-chaired two panel discussions, and has been published in The Spokesman, STLE, and Machinery Lubrication. Mr. Burkhalter has also retired from the U.S. Army at the rank of Colonel with 27½ years of service, both active and reserve.

NLGI Honorary Membership Award

“Entitles lifetime honorary membership to those who, over a period of years, have served the Institute in some outstanding capacity and are not now with a member company.”

MR. ED ORAVEC SHELL CANADA LTD. – RETIRED Ed received a BaSC in Mechanical Engineering from the University of Waterloo, 1981, and an MBA from McMaster University, 1989. He is retiring after 34 years service with Shell Canada Ltd., Ed began his career in 1981 as a Research Engineer at Shell’s Oakville Research Center. He moved to Calgary in 1989 and held various business development and planning roles in Shell’s head office until 1994. He then joined Thermoshell Home Comfort, a wholly owned subsidiary of Shell Canada Ltd., as Operations Manager overseeing the provision of home heating oil and equipment services to residential and commercial customers. He progressed to V.P. of Operations and Marketing for this business until 2001. Oravec then moved to London, England, for an expatriate assignment with Shell

International as a Business Development Manager to work on Home Comfort business startups in Greece, Turkey, and Germany. Led project to select and implement IT systems to support this business.

He returned to Shell Canada in 2004 and joined the Product Quality group as a Grease Product Manager, responsible for overall grease product quality and plant manufacturing implementation of new grease products.

He then progressed to Senior Product Implementation Manager for Grease lubricants in the Americas and led major plant quality improvement programs, introduced new grease products for manufacture, and participated in development of new grease formulas and product specifications for the rail and mining sectors.

Mr. Oravec served on the NLGI Board of Directors from 2008 to 2015.

NLGI President’s Plaque “In recognition and appreciation for having served the NLGI in the office of president for the previous year”

MR. BRUCE URBAN FMC – LITHIUM DIVISION

- 10 VOLUME 79, NUMBER 3

NLGI SPOKESMAN

GOING DIGITAL! The NLGI Spokesman will be offered in print, as well as, digital for the 2015 calendar year. During this year, we will be ensuring that we have correct email addresses for all of our subscribers, to ensure a seamless transition in 2016 to all digital.

If you would like to see the magazine digitally, click below:

https://issuu.com/link here Oh, our apologies, you can’t click!

One of the many advantages of having a digital version of the NLGI Spokesman. If you would like to begin receiving the magazine in digital form only, please let us know at nlgi@nlgi.org

The Effect of Thickener on EP Additive Response Gaston A. Aguilar; Joseph P. Kaperick, Michael Lennon and Grant Pollard Afton Chemical Corporation 500 Spring Street • Richmond, Virginia 23219

Abstract

It is recognized in the industry that thickener used in lubricating greases can interfere and negatively impact additive function. Extreme pressure and antiwear additives that function at the interface of the lubricant and mating surfaces are particularly affected. This study measured the effect of thickener concentration on load-carrying ability of lithium complex grease system. Specifically, Timken EP tests were conducted on grease formulation at three consistencies treated with a constant amount of a sulfur-phosphorus (S-P) gear oil additive package. The testing showed that Timken OK loads were not affected by soap thickener concentration.

Timken EP tests were also performed on corresponding base oil formulation over a range of passing loads that encompassed the highest passing load and ensuing failure load of the greases. The effect of the thickener was demonstrated by comparing differences in test temperatures, wear scar widths and tribo-film coverage and composition. Another objective of this study was to elucidate mechanism by which thickener interferes with S-P additive system. For this effort, oil separation experiments were conducted and the resulting oils were analyzed to measure decreases in additive concentration.

These experiments showed that sulfur concentrations in the grease bleed oils were not significantly different than the formulated oil. On the other hand, phosphorus was not detected in the separated oil indicating that phosphorus antiwear additives were completely retain in the bulk of the grease, probably due strong interaction with soap thickener. These results correlated well and

helped explain differences in test temperatures, wear scar widths and tribo-film compositions observed between the greases and the corresponding base oil formulation.

Introduction

Greases are typically described as lubricating compositions composed of base oil and additives entrapped in a network of solid thickener particles, platelets, clumps and/or fibers. Thus, the physical and chemical interactions of thickener with additives are recognized by many in the industry as having a significant effect on additive performance1-2. However, there are few published studies that have detected these interactions and/or measured the effect of these interactions on lubrication performance. This does not imply that grease lubrication, specifically of rolling bearing, has not been studied. Numerous models have been published to explain the mechanism by which grease lubricate roller bearings in elastohydrodynamic lubrication (EHL) regime. For the most part, bleeding, which is the separation of base fluid, additives and/or thickener from the bulk grease is recognized as an important factor in these models2-3. In one such study, Cousseau and co-workers used a ball-on disc test rig and optical interferometry to measure the film thickness produced by different formulated greases, their bleeds and base oils.

They found film thickness of grease resembled that of their bleeds more than their base oils. This observation underscores the importance of understanding how thickener-additive interaction and surface competition effect load-carrying ability of greases.

- 12 VOLUME 79, NUMBER 3

NLGI In one study focused on thickener-additive interactions, Sivik and co-workers utilized phosphorus Nuclear Resonance Spectroscopy (31P NMR) to analyze the interaction of zinc dithiophosphate (ZDDP) with lithium 12-hydroxystearate grease4. Their analysis revealed that ZDDP underwent chemical changes in grease containing residue amounts of lithium hydroxide raw material. The changes involved the formation of lithium dithiophosphate along with a decrease in neutral ZDDP and an increase in basic ZDDP levels. Sivik proposed a mechanism in which neutral ZDDP reacts with lithium hydroxide to form lithium dithiophosphate, zinc oxide and water. The resulting ZnO then reacts with neutral ZDDP to produce additional basic ZDDP. More pertinent to effect of these interactions was the analysis of the basic lithium 12-hydroxystearate grease after “exhaustive” hexane washing. The result of 13P NMR study showed that a significant amount of neutral ZDDP was retained in grease, which Sivik and co-workers proposed was due to polar-polar “association” of the ZDDP with the lithium soap fibers.

In another study, Kaperick used Timken test methods to compare the load-carrying capacity of a sulfurphosphorus gear oil additive package treated into lithium complex grease and the corresponding base oil formulation5. Since the rate of lubricant delivery for the grease and oil test methods are different, Kaperick first adjusted the delivery systems to investigate the effect of lubricant delivery rates. It was found that differences in delivery rate of the lubricant did not affect Timken response. The major finding was a large decrease in Timken response for the S-P gear oil package in the grease formulation. It was concluded that decrease response was due to thickener-additive interactions that reduced the ability of additives to get to the mating surfaces or interfered with additive function.

This paper is an extension of the Kaperick’s work.

Specifically, the Timken test methods were again used to compare the response of an S-P additive package in lithium complex grease and the corresponding base oil formulation. The study was broadened to include

different grease consistency grades to determine if additive response was affected by thickener/base oil concentration. The thought was that softer grease formulations containing less thickener would behave more like the base oil formulation. The study also incorporated an extended test protocol to further demonstrate differences in the lubricating mechanism of grease versus its corresponding base oil formulation.

These measurements and techniques are briefly described below: •T emperature readings were taken to measure rate and extent of temperature increase generated by frictional forces during Timken runs.

•W ear widths on test blocks were measured on some partial grease Timken runs and all complete Timken runs.

• S canning Electron Microscope-Energy-Dispersive X-Ray Spectroscopy (SEM-EDX) was used to get a measure of tribo-film coverage and composition.

•O il separation experiments were performed on greases to compare additive content of bleed oils against base oil formulation.

The investigation showed that grease consistency did not affect the load-carrying capacity. All grease consistencies were judged to pass the Timken test at a 40 lb. load and to fail at a 50 lb. load due to metal pulling or scoring after complete 10 minute runs. As expected, the base oil formulation passed the Timken test at 30, 40, 50 and 60 lb. loads. Additional measurements showed that the base oil formulation at all test loads had rapid rates of temperature increase that plateau at approximately 2 minutes and produced relatively constant wear scar widths covered with tribo-films rich in phosphorus content. On the other hand, grease formulations had much slower rates temperature increase, generated wider wear widths that increased with test time and produced sparser tribo-films rich in sulfur content and containing none detectable to trace amounts of phosphorus. These results are consistent with oil separation experiments that revealed that phosphorus components in additive package were unable to bleed away from greases regardless of consistency while sulfur levels matched that of the oil

- 13 NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI formulation.

Experimental Timken Testing

Tests were carried out using “Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Timken Method)”, ASTM D-2782 and “Standard Test Method for Measurement of LoadCarrying Capacity of Lubricating Grease (Timken Method)”, ASTM D 2509 on oil and greases respectively.

Both Timken test methods consist of passing lubricant through an interface that consists of steel cup rotating against steel block at a static spindle speed of 800 ± 5 rpm and static load for a 10 minute test period. For each test, loads are increased until film rupture is detected by either excessive wear or scoring on the test block. For this study, temperature readings were collected at one minute intervals using Control Company Traceable® infrared thermometer gun. Temperature readings were taken on test cups at approximately 180 degree position from ring on block contact. Wear scar widths were measured using low power microscope (4X) with filar micrometer to measure with accuracy of ±0.05 mm (±0.002 in.). Contact pressures were calculated using measured scar widths on blocks and the equation provided in ASTM D 2509.

Surface Analysis

Test block surfaces were analyzed FEI Quanta 650 Scanning Electron Microscope (SEM) and Oxford Instruments X-Max 150 Energy-Dispersive X-Ray (EDX) detector. Analyses were performed on the same 4 mm by 3.5 mm area of each block containing part of the wear scar. The beam energy was kept at 5 kV to increase surface sensitivity. AZtec Version 2.2 software by Oxford Instruments was used to create images of the mapped area that consisted of three phases: 1) block background, 2) tribo-film and 3) carbon deposits. The AZtec software was also used to perform elemental quants of EDX spectra.

1) 2) 3) 4) 5) 6) 7)

Heptane rinse Wiping with heptane-soaked Kim wipes Heptane rinse Isopropyl alcohol rinse Wiping with isopropyl alcohol-soaked Kim wipes Isopropyl alcohol rinse Nitrogen blow dry

Oil Separation Experiments

Greases were subjected to a modified IP 121 standard test method. In the standard method, grease is placed in a 240 mesh woven wire cloth cone and loaded with 100 gram weight. The cone is placed on stainless steel cup and bleed is collected for 168 hours at 40 °C. For this study, the collection period was decreased to 8 hours and collection temperature was increased to 140 °C. The 140 °C temperature was selected based on maximum temperatures measured during Timken tests. The test time was decreased to eliminate any oxidation effects.

Collected bleed samples were analyzed for phosphorus and sulfur content. Phosphorus content was measured by inductively coupled plasma atomic emission spectroscopy (ICP) using a modified version of ASTM D 4951 standard test method. Sulfur content was measured using LECO Corporation SC-432 analyzer following ASTM D 1552 standard test method.

Lubricant Compositions

All lubricant compositions, oil and greases, were based on ISO 220 mineral oil blend and were formulated with 3 mass percent of a proprietary gear oil package consisting of sulfur based extreme pressure agents and phosphorus based antiwear additives. The grease formulations were made using unadditized, lithium complex base grease with penetration (60 x worked) of 185 m-1. All compositions were blended with standard laboratory equipment with mild heating (60 ± 5 °C) for time judged sufficient to thoroughly incorporate the additive package and achieve homogeneous mixtures (1-2 hours). A summary of lubricant compositions are provided in Table 1.

Blocks were clean before putting them in the SEM by the following procedure:

- 14 VOLUME 79, NUMBER 3

NLGI

Table 1: Lubricant Compositions:

Results and Discussion

As summarized by Figure 1, Timken testing of the oil formulation showed no significant loss of load-carrying capacity of over a range of loads (30, 40, 50, and 60 lb.). All wears scars showed no visible signs of scoring and wear scar widths were narrow and did not change significantly with load. Average scar width for the four loads was 1.04 mm with a range 0.14 mm. The grease

formulations were able to carry 40 lb. without scoring but wear widths were significantly larger than the oil formulation with average and range of 1.45 mm and 0.26 mm respectively. Not unexpectedly, the greases were unable carry 50 lb. load without scoring of the Timken blocks and wear widths jumped to average of 2.21 mm with a range of 0.39 mm.

Figure 1: Graph showing poorer anti-scoring and antiwear performance of the S-P package in grease.

Data points are an average two widths per scar.

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NLGI Wear rates were investigated by stopping Timken tests at 3 and 4.75 minutes for the NLGI 1 and 3 greases at 50 lb. test load. As per Figure 2, wear scar widths increased with test time and were equal or exceeded the widths of oil formulation at 3 minutes. Interestingly, the thickener concentration did not appear to significantly affect test results. In other words, no improvement in performance was apparent with the softer more oil like grease.

Figure 2: Graph showing wear increase of grease formulation with time.

Data points are an average two widths per scar.

As summarized Table 2, surface analysis of block wear scars revealed that tribo-film compositions for grease formulations are indeed very different than the oil formulations. The oil formulation at all four loads produced tribo-films high on phosphorus and oxygen content, likely signifying the presence of phosphate films that are known to provide excellent antiwear protection6. Greases regardless of test load produced films with undetectable to trace amounts of phosphorus but four times more sulfur than the corresponding oil formulation, possibly signifying the presence iron sulfide and/or sulfate tribo-films generally generated by sulfur EP agents7. As per mapped tribo-film area data in Table 2, the sulfur rich films generated by the greases increased in area coverage with increasing grease consistency. This observation is opposite the idea that softer more oil like grease would perform more like oil counterpart. A more important observation is that the greases were unable to generate uniform tribo-film coverage at the higher 50 lb. load. SEM-EDX images in Table 3 visually depict this data.

The SEM-EDX data correlates well with wear scar width data. Both data sets suggest that thickener is interfering with phosphorus components and that load-carrying capacity for grease formulations is mostly attributed to sulfur EP additives, which function by producing sacrificial tribo-films that shear away to smooth mating surfaces and prevent metal-metal adhesion. However, sulfur EP compounds that are designed for lubricant applications typically function at high loads and temperatures. Examination of temperature data (Figures 3 and 4) reveals that grease formulations produced very different temperature profiles than the oil formulation.

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Table 2: SEM-EDX Data on 3 mm X 4.5 mm Area of Timken Block

Table 3: SEM-EDX Images of Timken Blocks for Grease Formulations and 10 minute Runs

- 17 NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI

NLGI

Figure 3: Graph summarizing temperature profiles for 40 lb. Timken test runs

Figure 4: Graph summarizing temperature profiles for 40 lb. Timken test runs.

The oil formulation at all loads produced rapid rates of temperature increase that plateau quickly at approximately 2 minutes. On the other hand, grease formulations produced much slower and linear rates of temperature increase that start to plateau at approximately 6 minutes. As per Figure 5, the test temperatures for the oil formulation were proportional to contact pressures. In this case, contact pressures were solely dependent on load since wear areas remained constant at all test loads. This relationship is indicative of steady and uniform tribo-films at the mating surfaces.

Conversely, contact wear areas for the grease formulations were not steady and increased with time (Figure 2).

The wider scars led to reduction in contact pressures

that explained the slower rates of temperature increase generated by the grease formulations but they are also indicative of thin and un-uniform film formation. As per Figure 5, the test temperature for grease formulations tested at the 50 lb. load were inversely proportional indicating temperature increase is partly due was to friction produced by metal to metal contact.

This assumption is supported by SEM-EDX examination of Timken blocks for partial Timken tests as shown in Table 4 and Table 5. The tribo-film images for 3 minute tests show almost no tribo-film formation but the wear scars had no visible scoring. These observations indicate that the thickener participated in carrying the test load.

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NLGI For the 4.75 minute tests, tribo-film coverage increased slightly for the NLGI 1 grease and significantly for NLGI 3 grease. Sulfur contents of the films were higher for 4.75 minute test than 10 minute test.

Nonetheless, the soap thickener appears to block the sulfur EP compounds from the surface, which with time and pressure lead to unsustainable tribo-films as is the case for 50 lb. 10 minute tests. A better understanding of how soap lubricates and interferes with sulfur EP additive could be gained by performing this study’s test protocol on oil formulation lacking phosphorus components and by running rheology and tribology tests with optical interferometry on grease bleeds following similar test methodology as Cousseau and co-workers.

Figure 5 Plots showing contact pressure and temperature relationship at end of test (10 minutes).

Table 4: SEM-EDX Data for Partial Timken Runs

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NLGI Table 5: SEM-EDX Image for Grease Formulation at 50 lb. Test Load

In regards to lack of phosphorus content in grease tribo-films, oil separation experiments were especially insightful. As per Table 6, bleed oil that separated from greases contained equal amount of sulfur content as the oil formulation but no detectable amount of phosphorus. Thus, it is concluded that a strong interactions with soap thickener inhibited phosphorus compounds from adhering and reacting metal surfaces.

To conclude, the study demonstrated that lithium soap thickeners can inhibit the function of EP and

antiwear additives. Two basic mechanisms were proposed based on experimental observations. One mechanism involves soap blocking additives from metal surfaces as was the case with sulfur EP additives of this study. The second mechanism involves chemical interactions between the soap and additives that prevent the additives from adhering and reacting with metal surfaces. This mechanism would be more in effect with polar and ionic additives such as phosphorus compounds that are commonly used in gear oil additive packages.

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NLGI Table 6: Phosphorus and Sulfur Contents for Oil Formulation and Grease Bleed Collected at 140 °C for 8 h.

References Canter, N. Grease additives: Important contributors not be overlooked. Tribology & Lubrication Technology, December 2013, 28-29.

Lugt, P.M., Grease Lubrication in Rolling Bearing. John Wiley & Sons; 2013.

Cousseau, T., Björling, M., Graca, B., Campos, A., Larsson, R. Film thickness in a ball-on-disc contact lubricated with greases, bleed oils and base oils. Tribology International 2012; 53: 53-60.

Sivik, M.R., Zeitz, J.B., Bayus, D., Interactions of Zinc Dithiophosphates with Lithium 12-Hydroxystearate Grease. Presented at the Annual Meeting of the NLGI, at West Palm Beach Buena, Florida, (2001).

Kaperick, J., Timken OK Load – Media Bias? A Comparison of Timken Response to Similar Additive Systems in Both Grease and Oil Formulation. Presented at the Annual Meeting of the NLGI, at Lake Buena Vista, Florida, (2006).

Phillips, W.D., Ashless Phosphorus-Containing Lubricating Additives in Lubricant Additives: Chemistry and Applications, Second Edition, CRC Press,Rudnick, L.R. ed.

(2009).

Bovington, C.H., Friction, wear and role of additives in their control in Chemistry and Technology of Lubricants, 3rd Edition, Springer, Mortier, R.M., Fox, M.F, Orszulik, S. T. ed. (2010).

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PTFE for Lubricating Greases Mary Moon, Ph.D. marymoonphd@gmail.com Consultant to Shamrock Technologies, Inc. Newark, NJ 07114 USA Abstract

The purpose of this study was to investigate the performance of seven experimental PTFE powders in grease and evaluate effects of particle size and dispersion on consistency, stability, friction and wear. Laboratoryscale batches of simple lithium greases were prepared and milled with a high-pressure homogenizer. All PTFE greases were comparable to controls in appearance (offwhite), NLGI grade (2), texture (smooth, buttery) and storage stability (<5% bleed after 4-5 months storage).

Four-ball friction and wear tests demonstrated the value of specific PTFE powders as additives. Submicron PTFE powders, formulated in grease without other extreme pressure (EP) or anti-wear additives, reduced wear, friction and temperature during mixed/ boundary lubrication. These PTFE powders prevented adhesive wear due to oil film failure at applied loads up to 180 kg. Test results suggested that PTFE was entrained in contacts and helped support loads. These results depended upon PTFE dispersion in specific formulations.

Introduction

The present paper takes a direct and pragmatic approach to investigate effects of experimental PTFE powders in simple lithium greases formulated without other additives. This Introduction provides background information about PTFE powders. In prior studies of PTFE in greases and liquid lubricants, results were situational and depended upon particle size, dispersion and tribology test conditions such as speed, load and roll-to-slide ratio. This study compares seven powders with primary (fully dispersed) particles that range from

sub-micron to larger sizes. This Introduction compares these particle sizes to nanoparticles, grease fibers and wear scars. [1] Grease preparation is the subject of the next section.

Each lab-scale batch of grease was blended and milled with the same procedure to model PTFE dispersion in manufacturing processes. Results for grease consistency and storage stability are presented next. Then, the heart of this paper focuses on four-ball friction and wear testing. Data collected during tests with ASTM D2266 [2] indicated that start-up and run-in affected test results. A four-ball technique was customized by gradually applying loads to lessen start-up and run-in effects. Friction and temperature data and wear scars were analyzed to characterize effects of PTFE powders on lubrication.

Polytetrafluoroethylene or PTFE is a synthetic fluoropolymer of tetrafluoroethylene (-CF2-CF2-)n with a chemical formula that resembles ethylene (-CH2CH2-)n but with fluorine instead of hydrogen atoms.

In contrast to hydrocarbons, PTFE chains are stiffer with a greater tendency to pack in semi-crystalline arrangements. PTFE films and solid surfaces tend to be white, waxy and smooth. (The most well-known application of PTFE is non-stick coatings on cookware.)

PTFE is extremely slippery with coefficient of friction, COF, between 0.04 (sliding friction, D1894 [3]) and 0.1.

Other useful properties include resistance to chemicals, solvents and temperature extremes (highs and lows). [4] Lubricants are formulated with PTFE particles that are either synthesized or produced by milling solids. PTFE

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powders are used as thickeners for grease and additives to improve resistance to water, chemicals and friction.

For example, PTFE is formulated in spray-on dry film lubricants, release agents and non-flammable lubricants intended for use under oxidizing or chemically aggressive conditions. [4] PTFE powders were investigated as possible friction-reducing additives in crankcase engine lubes and transmission fluids. Continued research in PTFE has observed that lubricating effects and mechanisms depend upon PTFE particle properties (size, shape, surface polarity, etc.), dispersion and test conditions (contact geometry, roll-to-slide ratio, speed, load, etc.) [5-7]

PTFE powders can be manufactured with specific size distributions of primary (non-aggregated) particles.

Sub-micron grades of PTFE contain primary particles with average diameter < 1 μm, comparable to some nanoparticles and grease fibers, Fig. 1. In other grades, the average primary particle size is larger, similar to dust, etc. [8] Aggregates or agglomerates can be microscopic or macroscopic, i.e., invisible or visible to the unaided human eye (resolution ~ 40 μm). For comparison, typical specifications for wear scars from tribology tests are approximately 0.5 mm or 500 μm.

Fig. 1 Size scales of nanoparticles (< 1 μm), grease thickener fibers (0.1 – 1 μm), ISO 4406 categories (> 4, 6 and 14 μm) for dust, etc. [8], PTFE particle diameters (0.1 – 100 μm), and wear scar specifications (0.5 mm or 500 μm) relative to the resolution of the unaided human eye (~ 40 μm).

In other studies, PTFE powders were added to greases, and friction, wear and load carrying capacity were measured. Aswath [9] mixed PTFE with ZDDP (zinc dialkyl dithiophosphate), MoS2 and FeF3 (shown to catalyze adhesion of PTFE and MoS2 on metal) in lithium stearate base grease. They performed block-on-ring tests and reported that smaller PTFE (0.2 mm or 200 μm) was better than larger PTFE (1 - 4 mm) in terms of wear resistance and weld load. Krawiec [10] added 6 wt.% PTFE powder (20 - 40 μm) to all-purpose vehicle grease and reported that PTFE increased seizure loads by 150% and decreased wear scars by 30% relative to control grease in four-ball tests.

Fish et al. [11, 12] compared effects of additives on load carrying capacity of base grease with a weld load of 160 kg (D2596, [13]). In three cases (3 wt.% PTFE; 3 wt.% MoS2; and 1.5/1.5 wt.% PTFE/MoS2), weld loads improved to 250 kg. The weld load reached 500 kg for grease with PTFE plus a borate additive. Their results suggested that PTFE (particle size not specified) showed potential as a substitute for MoS2 as an extreme pressure (EP) additive in grease.

Ballester et al. [14] compared four PTFE powders with average primary particle diameters of 0.8, 4.2, 20.5 and 46.8 μm. They mixed PTFE (1 wt.%) into commercial lithium base grease (no EP additives) using an overhead

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mixer and a Cowles blade. Four- ball friction and wear tests were performed according to D2266. One powder (20.5 μm) reduced COF (20% relative to control grease).

Wear scar diameters were comparable for control and test greases.

were comparable for control and PTFE greases. This indicated that lithium fibers determined consistency, and PTFE particles were dispersed among lithium fibers.

Consistency did not trend with weight percent PTFE-2 (appropriate for HX-1 registration) and PTFE-3, Fig. 4.

Grease Consistency and Stability [15]

Twenty-five samples of control and PTFE greases were stored in the laboratory with no exposure to light. After four to five months, there were no changes in appearance.

Less than 5% of the oil separated but mixed easily into 23 samples. Two samples (control grease, PTFE-2 grease) softened and released more oil during storage.

Greases prepared from PTFE, Li12OHSt and PAO (4/8/88) and control grease (0/8/92) were off-white in color with smooth, buttery texture and NLGI grade 2. In most cases, working grease slightly increased penetration depth, i.e., softened grease by dispersing solids and entrained air, Fig.3. Cone penetration data

Fig. 3 Control and PTFE greases were NLGI grade 2

Fig. 4 Worked cone penetration for greases prepared with different levels of PTFE-2 and PTFE-3

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Four-Ball Friction and Wear [15]

Greases were evaluated using a four-ball friction and wear machine and D2266 (75°C, 40 kg load, 1,200 rpm, sliding speed 20 rps x 2 π x 3.8 mm ≈ 0.5 m/s). This test is used to make preliminary assessments of anti-wear properties of greases in sliding contacts. In practice, fully-formulated lubricants are tested relative to specifications for qualification and quality control. In this study, friction data indicated that contacts were damaged during start-up and run-in, e.g., Fig. 5 for control grease.

Damage can form wear particles, and a few wear particles can initiate a cascade of more damage and wear particles [18, 19]. Insufficient oil bleed can contribute to wear.[20] Thus, start-up and run-in can affect performance during four-ball tests and compromise test results.

NLGI

Fig. 5 Friction data (kg) during D2266 for two samples of control grease.

To reduce damage during start-up and run-in, grease could be reformulated with EP additives. However, those additives could have unanticipated effects on testing PTFE. Instead, the four-ball test procedure was modified to reduce the severity of start-up and run-in. The load was increased gradually with a ramp. This approach resembles gradually polarizing a working electrode and measuring current flow to perform a potentiodynamic scan, which is an electrochemical technique.

Fig. 6 Four-ball friction and wear machine (circa 1982) used in this study.

In these four-ball tests, friction was measured with a load cell and force gauge, and temperature was measured with a thermocouple at the perimeter of the cup. Time series were collected at intervals of 2 using an AD converter and data acquisition software. The

laboratory was maintained at 21-23°C (70-74°F). Wear scars were measured and photographed with commercial light microscopes and cameras or calipers. The sample cup was loaded with a consistent mass of grease or volume of liquid. A torque wrench (54.2 N·m or 40 lb-ft) was used to lock balls in the cup.

To develop a load ramp procedure, simple lithium grease formulated with PTFE-3 was tested in four consecutive stages, Table 1. Friction fluctuations were not observed at the start of this test (Fig. 7). Start-up and run-in effects were significantly smaller with load ramps than D2266 Friction increased with load and possibly plateaued, corresponding to mixed and boundary lubrication, respectively.

Temperature increased smoothly. The steepness of these load ramps did not affect friction or temperature.

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NLGI Table 1 Load ramp stages in the initial four-ball friction and wear test

Simple statistics were calculated from data at each load, excluding two features discussed below. Average (mean) friction and temperature trended with load, Fig. 8. Friction fluctuations increased during the test, possibly due to wear or more asperity contacts at higher loads, Fig. 7.

Three more statistics were calculated: standard deviation divided by the mean, skew and kurtosis. The statistics showed that friction fluctuations were large (relative to the mean) and not random during run-in up to a 15 kg load, Fig. 9. These results are consistent with shearing individual asperities [21], churning grease [20], etc. during run-in. Also, sounds were shrill up to 15 kg and

then less shrill at higher loads. After run-in, friction fluctuations were relatively small (<10% of mean) and random up to 120 kg load. There was no statistical evidence that friction fluctuations changed after run-in, i.e., PTFE-lithium grease performed consistently (during abrasive wear, see below). [Note: Skew and kurtosis were statistically significant and not random (|skew| > 0.4 and |kurtosis| > 0.8 for 150 data) below 15 kg but not at higher loads.]

Much larger friction fluctuations were observed at loads of 27 and 90 kg. Temperature was steady, and welding did not occur during these events.

Fig. 7 Four-ball friction and temperature data for simple lithium grease formulated with PTFE-3 - 26 VOLUME 79, NUMBER 3

NLGI

Fig. 8 Load ramp and average friction and temperature for lithium grease formulated with PTFE-3

Fig. 9 Statistics calculated from friction data for lithium grease with PTFE-3 versus load (kg)

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PAO Base Oil

In this study, four-ball tests with load ramps were applied to PAO base oil used to formulate greases. In test PAO-a, the load was ramped from 3 to 180 kg at 3 kg/ min, held for 15 min and ramped down at the same rate.

Friction and temperature initially increased smoothly with load, Fig. 10. At 72 kg load, friction increased from 0.19 to 1.59 kg and then decreased to 0.52 kg. After this event, the friction shift (friction after – friction before event) was 0.52 - 0.19 kg or 0.33 kg. The friction ratio (friction after/friction before) was 0.52/0.19 or 2.7.

Ten minutes later, the temperature was 10°C above the

Fig. 10 Friction (FF, kg, ____) and temperature (T, °C/100, - - -) for test PAO-a. The arrow indicates the friction shift (0.33 kg) after the event.

Fig. 11 The arrow indicates the shift in PAO temperature (grey line) ten minutes after the event, which was 10°C above the projection from data prior to the event (straight black line).

temperature projected from data prior to the event, Fig. 12. PAO continued to lubricate these contacts after the friction event. FTIR spectra of tested and untested oil were nominally identical (not shown), i.e., PAO did not oxidize. The average wear scar diameter was 2.70 mm, and wear particles were visible in the oil.

The duration of this friction event for PAO was approximately 36 s. Friction events lasted longer in some replicate tests, e.g., PAO-j shown in Figs. 15 and 16. In some cases, tests were stopped when friction was near the load cell limit (2.27 kg or 5 pounds) or welding occurred.

NLGI PTFE-3 Grease

Grease prepared with sub-micron PTFE-3 was tested with a load ramp at 3 kg/min. In test PTFE-3-a (Fig. 12), the load was ramped up to 150 kg (50 min), maintained for 10 min and ramped down to 3 kg (110 min total).

At first, friction and temperature trended smoothly with load. When the applied load was 66 kg (21 - 22 min), friction increased from 0.19 to 1.06 kg and then decreased to 0.25 kg during 20 s. The friction shift was only 0.25 - 0.19 = 0.06 kg, the friction ratio was 0.25/0.19 = 1.3, and no temperature shift was observed. A sequence of additional friction events took place on the up ramp and at 150 kg, but not on the down ramp. The average wear scar diameter was 1.41 mm, and the scar appearance was consistent with abrasive wear (see below). Some wear

particles in oil were observed at the bottom of the cup.

Grease was in good condition, although perhaps slightly softer.

In Fig. 13, data from the down ramp are plotted in reverse order and compared with data from the up ramp. Temperature was higher on the down ramp due to heat stored by the grease and apparatus. As the load was reduced on the down ramp, friction decreased and approached data on the up ramp. This behavior (plus wear scars, below) suggested that these friction events were related to solids entrained in contacts [5-7] and not adhesive wear [21] or starvation of contacts [20].

Fig. 12 Friction (FF, kg, ____) and temperature (T, °C/100, - - -) for test PTFE-3-a. The load was increased from 3 to 150 kg at 3 kg/min, maintained for 10 min and decreased to 3 kg.

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NLGI

Fig.13 Friction (FF, kg) and temperature (T, °C/100) for test PTFE-3-a during up (black) and down (grey) ramps. Data from the down ramp were plotted in reverse order for comparison.

Figure 14 shows that friction data for PAO and PTFE-3 grease initially were very similar. This similarity indicated that PAO bled from PTFE-3 grease. As the load was increased, friction became higher for grease than oil. This difference may be the result of resistance from entrained solids or an artifact. Friction events occurred at 66 and 72 kg loads for grease and PAO, respectively.

A single friction event in the case of PAO was more influential than a sequence of events for PTFE-3 grease,

Fig. 14. Maximum values of friction (excluding event peaks) and temperature for PAO-a were 0.84 kg and 149°C, respectively, versus 0.75 kg and 63°C for PTFE3-a. The Li12OHSt and/or PTFE solids were responsible for overall lower friction and temperature (excluding event peaks) during four-ball tests and prevented shifts in friction and temperature. Control grease was tested to identify contributions from Li12OHSt thickener in absence of PTFE.

Fig. 14 Friction (FF, kg, ____) and temperature (T, °C/100, - - -) data for PAO-a (black) and PTFE-3-a grease (grey).

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NLGI Control Grease

Control grease, 8/92 Li12OHSt/PAO, was tested with increasing load ramps (where significant features were observed for PTFE-3 and PAO). Figure 15 shows data for test Control-b, where the first friction event occurred at a 75 kg load. Friction increased from 0.18 to 1.54 kg, stayed high for over 2 min, and then decreased to 0.47 kg. This friction shift was 0.47 - 0.18 = 0.29 kg, and the friction ratio was 0.47/0.18 = 2.6. Approximately 5 min after the start of this event, the temperature was almost 10°C higher than projected from data before the event, Fig. 16. This temperature shift was similar to the temperature

shift observed for PAO, Fig. 11. The average wear scar diameter was 3.31 mm.

Figure 16 compares four-ball data for Control-b grease, PTFE-3-c grease and PAO-j. The dominant features – friction event peaks and duration, and friction and temperature shifts – were similar for control grease and PAO. In contrast, these features were much smaller for PTFE-3 grease. Thus, PTFE-3 powder (and not Li12OHSt) was primarily responsible for less friction, temperature and wear observed for PTFE-3 grease.

Fig. 15 Friction (FF, kg, ____) and temperature (T, °C/100, - - - ) data for (left to right): PAO-j (black), Control-b grease (dark grey), and PTFE3-c grease (light grey).

Fig. 16 Friction (FF, kg, ____) and temperature (T, °C/100, - - -) data for (left to right): PAO-j (black), Control-b grease (dark grey), and PTFE-3-c grease (light grey). Arrows indicate temperature shifts.

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PTFE-2 Grease

PTFE-2 grease was formulated with sub-micron PTFE-2, suitable for HX-1 registration and food grade applications. Figure 17 shows data from test PTFE-2-a where friction increased from 0.30 to 1.98 kg, remained above 1.50 for 5 min, and decreased to 0.57 kg. The friction shift was 0.57 – 0.30 = 0.27 kg, and the friction ratio was 0.57/0.30 = 1.9. The temperature shift was similar to those for PAO and control grease, Fig. 18. The average wear scar diameter was 2.90 mm, comparable to control grease.

In test PTFE-2-a, the friction event occurred at a 90 kg load, which was higher than Control-a (51 kg) and Control-b (75 kg). This suggested that PTFE-2 powder somewhat improved the load-carrying capacity relative to control grease. However, friction and temperature shifts were larger for PTFE-2 grease than PTFE-3 grease. Only one four-ball test was performed with PTFE-2 grease in this study.

Overall, these results for PTFE-2 and PTFE-3 greases are consistent with other results from the literature where specific PTFE powders significantly enhanced loadcarrying capacity of certain greases. [3-5]

Fig. 17 Friction (FF, kg, ___) and temperature (T, °C/100, - - -) data for (left to right): Control-b grease (dark grey), PTFE-3-c grease (light grey) and PTFE2-a (black) greases.

Fig. 18 Friction (FF, kg, ____) and temperature (T, °C/100, - - -) data for (left to right): Control-b grease (dark grey), PTFE-3-c grease (light grey) and PTFE2-a (black) greases.

Arrows indicate temperature shifts.

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NLGI Wear Scars

A simple experiment was performed to identify wear mechanisms during these tests. Four-ball tests with 3 kg/min load ramps were stopped at 45, 75, 78 and 81 kg loads. Wear scars were measured and photographed under a light microscope at 5x magnification, and photographs were enlarged to examine the appearance of the scars. Figure 19 shows a representative scar from PAO-f (final load 45 kg, average scar diameter 0.41 mm).

These scars were round with smooth edges. For PAO-g (75 kg, 0.55 mm), scars were similar but larger than PAOf. Both tests PAO-f and –g were stopped before friction events occurred, and the appearance of these scars was consistent with abrasive wear. [21] Figure 20 shows a representative wear scar from PAO-h (78 kg, 2.3 mm), which was stopped immediately after the first friction event occurred. PAO-h scars were larger and more irregular and "rugged" than PAO-f and PAO-g scars.

Scars for PAO-h and -i (81 kg, 2.7 mm) were similar in appearance. Black solids were observed on one side of each scar. It appeared that these deposits were metal that softened and was displaced by the rotating ball during the test. These observations were consistent with temperature shifts following friction events for PAO and adhesive wear. [21]

The oval shape and uneven edges of PTFE-3-a scars suggested that pressure and stress concentrations may have redistributed (and/or contacts may have shifted) during this test. PTFE particles, aggregates or agglomerates can produce effects that are more localized than films. For example, Palios et al. [4] studied two types of PTFE particles (diameters ~1 and 5 μm) in EHD (elastohydrodynamic) lubrication test rigs. They observed individual PTFE particles in contacts and elastic impressions made by particles on contact surfaces, and they concluded that PTFE particles helped support applied loads.

In the present study of PAO, a single friction event corresponded to adhesive wear and failure of the oil film to support the applied load. Before an event occurred, abrasive wear gradually increased diameters of round scars, Fig. 21. A friction event corresponded to adhesive wear, which was relatively brief (~30 s) but substantially increased scar diameters. For PTFE-3 grease, wear scars and no temperature shifts showed that PTFE-3 powder prevented adhesive wear and helped support loads. A reasonable explanation for friction events is that PTFE-3 was entrained in contacts on up ramps (as loads increased and gaps narrowed) but not down ramps, consistent with observations.

In test PTFE-3-a, the load was ramped up to 150 kg and back down to 3 kg; this test was longer (2 h) than PAO-f through –i. For scars from PTFE-3-a, there was no visual evidence of softened metal or adhesive wear, Fig. 20. The average wear scar diameter was 1.41 mm. In the direction parallel to sliding, scar size (0.93 mm) was similar to abrasive wear in PAO-f and -g, Fig.21.

Fig. 19 Enlarged photograph of a magnified scar from four-ball test PAO-f. This test was stopped before the first friction event.

Average wear scar diameter was 0.41 mm.

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NLGI Fig. 20 Enlarged photograph of a magnified wear scar from four-ball test PAO-h. This test was stopped immediately after the first friction event. Average wear scar diameter was 2.4 mm.

Fig. 21 Enlarged photograph of a magnified wear scar from PTFE3-a (grease). Load was ramped up to 150 kg, maintained and ramped back down (about 2 h). A sequence of friction events occurred, which caused small friction shifts but no observable temperature shifts.

Average wear scar diameter was 1.41 mm.

Fig. 22 Average wear scar diameter (mm) versus final load for PAO before (PAO-f and –g , grey circles) and after (PAO –h and –i, black triangles) the first friction event (adhesive wear). For PTFE-3-A grease, squares are average scar diameter (middle) and components perpendicular (top) and parallel to sliding (bottom) after a longer, more severe four-ball test (2 h, maximum load 150 kg).

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NLGI PTFE-2 Liquid Dispersion

Food grade PTFE-2 powder was dispersed (20 wt.%) in white mineral oil with a polymeric dispersant.

Samples from a stability test at room temperature (after approximately 6 m) and base oil were evaluated with the four-ball procedure used for greases and PAO. For test Mineral oil-A, Fig. 23, a friction event was observed at a 99 kg load. Friction increased from 0.37 to 2.13 kg and then decreased to 0.42 kg. The friction shift was 0.42 – 0.37 = 0.05 kg, and the friction ratio was 0.42/0.37 = 1.1. A temperature shift was observed, Fig. 24.

This event plus friction and temperature shifts resembled data for PAO that were caused by adhesive wear.

In test 20% PTFE-2 dispersion-A, no events were observed on the up ramp, Fig. 23. The largest fluctuation occurred on the down ramp, and it did not shift friction or temperature, Fig. 25. The average scar diameter was

1.04 mm, and scars resembled abrasive wear. There was no evidence of adhesive wear. Photographs in Fig. 26 show that wear particles blackened mineral oil but not PTFE-2 dispersion. According to FTIR data (not shown), mineral oil did not oxidize during this test.

In this liquid dispersion, PTFE-2 prevented adhesive wear and helped support applied loads.PTFE-2 did not provide these benefits in grease, Figs. 17 and 18. A reasonable explanation is that the dispersion and mobility of PTFE-2 were better in the liquid than in the grease.

Better PTFE-2 dispersion and fewer solids entrained in contacts could also explain observations of friction fluctuations instead of events, Fig. 23. Different results for PTFE-2 in these liquid and grease formulations demonstrate that dispersion is critical to performance of PTFE additives in lubricants and greases.

Fig. 23 Friction (kg, ___) and temperature (°C//100, - - -) data for mineral oil (black) and 20% PTFE-2 in mineral oil with dispersant (grey).

- 35 NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI Fig. 24 Friction (kg, ___) and temperature (°C/100, - - -) data for mineral oil (black) and 20% PTFE-2 in mineral oil with dispersant (grey).

Arrow indicates temperature shift after friction event for oil.

Fig. 25 Friction (kg, ___) and temperature (°C/100, - - -) data for mineral oil (black) and 20% PTFE-2 in mineral oil with dispersant (grey).

Arrow indicates temperature shift after friction event for oil.

Fig. 26 Wear particles blackened mineral oil (right) but not PTFE-2 liquid dispersion (left).

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NLGI Discussion

Friction events for PTFE and control greases, a liquid dispersion and two base oils differed clearly from artifacts of start-up and run-in (from 3 to 15 kg load). Figure 27 shows the applied load at the start of each event. Loads were smaller (26 – 90 kg) for PTFE-3 grease than for PAO (72 – 104 kg). In the case of PTFE-3 grease, events were caused by entrained PTFE that helped support loads. For PAO, events corresponded to film failure and adhesive wear.

Values of the friction shift (friction after – friction before an event) in Fig. 28 show benefits of PTFE. For PAO, friction shifts were between 0.3 and 0.5 kg because adhesive wear damaged contact surfaces. For PTFE-3 grease, friction shifts were much smaller because PTFE protected contacts from damage. Values of the friction ratio (friction after/friction before) convey the same information, Fig. 29. Results for control grease and PTFE2 grease were similar to PAO and not PTFE-3 grease.

Additional replicate tests are needed to better compare mineral oil with this PTFE-2 liquid dispersion.

Fig. 27 Applied load (kg) that coincided with the first friction event in each test

Fig. 28 Friction shift (friction after minus friction before the event) in each test.

- 37 NLGI SPOKESMAN, JULY/AUGUST 2015

NLGI

Fig. 29 Friction ratio (friction after / friction before the event) in each test.

Conclusions

PTFE is useful as an anti-wear additive in grease provided it is dispersed adequately. Performance depends on PTFE grade, grease formulation, milling and tribology test procedures. In four-ball friction and wear tests, benefits of PTFE were most easily observed when run-in effects were avoided by gradually applying the load.

Seven experimental PTFE powders were formulated and milled in simple lithium greases based on PAO oil.

All seven powders (4% by weight) slightly softened grease relative to control grease but did not alter NLGI grade (2) or detract from storage stability.

Sub-micron PTFE powder significantly improved lithium grease lubrication by preventing adhesive wear and limiting friction, temperature and abrasive wear at loads up to 180 kg. Results indicated that PTFE was entrained in contacts and helped support applied loads.

Food grade PTFE powder improved friction, temperature and wear in a liquid dispersion in mineral oil. In simple lithium grease based on PAO, this particular grade of PTFE was less effective, possibly due to dispersion. Specific PTFE powders provide significant lubrication benefits that depend upon dispersion as well as lubricant formulation.

Four-ball friction and wear tests provided useful information about grease lubrication. The most meaningful results were obtained using load ramps to avoid run-in effects. Monitoring friction and temperature data was used to distinguish between abrasive and adhesive wear, and between film failure versus entrainment of solids in sliding contacts.

Acknowledgements

The author gratefully acknowledges Shamrock Technologies, Inc. for supporting this experimental project and providing the opportunity to present this paper at NLGI’s 81st Annual Meeting, June 14-17, 2014, Palm Beach Gardens, FL.

References

[1] NLGI, Lubricating Grease Guide, Fourth and Fifth Editions, National Lubricating Grease Institute, Lee’s Summit, MO, USA, 1996 and 2009.

[2] ASTM D2266 Standard Test Method for Wear Preventive Characteristics of Lubricating Grease (Four-Ball Method), ASTM International, West Conshohocken, PA, USA. [3] ASTM D1894, Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and

- 38 VOLUME 79, NUMBER 3

NLGI Sheeting, ASTM International, West Conshohocken, PA, USA. [4] R udnick, L.R., Ed., Lubricant Additives: Chemistry and Applications, Second edition, CRC Press, Taylor and Francis Group, Boca Raton, FL, USA, pp. 181-2.

[5] P alios, S., Cann, P. M. and Spikes, H. A., Behaviour of PTFE Suspensions in Rolling/Sliding Contacts, The Third Body Concept, D. Dowson et al., Editors, Elsevier Science B.V., 1996.

[6] W an, G.T.Y. and Spikes, H.A., The Behaviour of Suspended Solid Particles in Rolling Sliding Elastohydrodynamic Contacts, STLE Transactions, 31, pp. 12-24, 1987.

[7] J ia, Z. and Yang, Y., Composites Part B:Engineering, Vol 43, Issue 4, June 2012, pp. 2072-2078.

Annual General Meeting, Paris, France, 2011 and published in Eurogrease 1, 36-48, 2012.

[13] ASTM D2596 Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Grease (Four-Ball Method), ASTM International, West Conshohocken, PA, USA. [14] Ballester, E., Sui, Manshi and Fillion, C., Effect of PTFE Particle Size on Wear and Coefficient of Friction, Paper #0025, Presented at the NLGI 68th Annual Meeting, Asheville, NC, USA, 2000.

[15] Moon, M., PTFE for Lubricating Grease, Extended Abstract, Presented at the Society of Tribologists and Lubrication Engineers National Meeting, Orlando, FL, USA, May, 2014.

[16] NSF International, Ann Arbor, MI, USA, www.nsf. org.

[8] I nternational Organization for Standardization, ISO 4406:1999(E) Hydraulic fluid power – Fluids – Method for coding the level of contamination by solid particles.

[17] ASTM D217 Standard Test Methods for Cone Penetration of Lubricating Grease, ASTM International, West Conshohocken, PA, USA.

[9] A swath, P., Patel, K., Munot, S. and Elsenbaumer, R.L., Development of a High Performance Low Molybdenum Disulfide Grease, Paper #0530, Presented at the NLGI 72nd Annual Meeting, San Antonio, TX, USA, 2005.

[18] Sayles, R. S. and Macpherson, P. B., Influence of Wear Debris on Rolling Contact Fatigue, in Rolling Contact Fatigue Testing of Bearing Steels, STP771, J. J. C. Hoo, Editor, ASTM International, West Conshohocken, PA, USA, 1982.

[10] K rawiec, ST., The influence of polymers fillers in a grease lubricant, Archives of Civil and Mechanical Engineering, Vol. VII, No. 4, pp. 121-128, 2007.

[19] Moon, M., Taking Lubricant Cleanliness to the Next Level, Gear Solutions Magazine, June, 2009. (available at www.gearsolutionsonline.com)

[11] F ish, G. and Ward Jr., W.C., Extreme Pressure Performance of Greases: Testing and Additive Solutions, Paper #1002, Presented at the NLGI 77nd Annual Meeting, Bonita Springs, FL, USA, 2010.

[20] Lugt, P.M., Grease Lubrication in Rolling Bearings, John Wiley & Sons Ltd, West Sussex, UK, 2013.

[21] Bayer, R. G., Mechanical Wear Fundamentals and Testing, Second edition, Marcel Dekker, Inc., New York, NY, USA, 2004.

[12] H errero, F., Fish, G. and Ward Jr., W.C., Extreme Pressure Performance of Greases: Testing and Additive Solutions, Presented at the 23rd ELGI - 39 NLGI SPOKESMAN, JULY/AUGUST 2015

Fullerene-like Inorganic Nanoparticles (IF-WS2)

as Extreme Pressure and Antiwear Additive in Grease Applications George Diloyan 1*, Alexander Margolin2, Larissa Drangai2.

1. Nanotech Industrial Solutions Inc., Avenel 07001, NJ, USA. 2. NanoMaterials LTD. Yavne 8122101, Israel *Corresponding authors: George Diloyan – george@nisusacorp.com Alexander Margolin – alexm@apnano.com

Introduction

Naotechnology in lubricating greases have been in a focus of many research groups, laboratories and industries for a past 10 years. Unique properties of solids, brought to nano size, show significant increase of performance in lubricants and greases.

The following paper is focused on closed-caged nanoparticles of tungsten disulfide, also known as inorganic fullerene like nanoparticles (IF-WS2), and various products based on this material. It also described an importance of proper deagglomeration techniques and dispersion of IF-WS2 nanoparticles, in order to avoid sedimentation. It was also shown that stable and homogeneous solution of IF-WS2 nanoparticles in greases and oils significantly increased extreme properties and decrease wear up to 2.5 times.

Today, is a good time to reflect and provide an assessment as to the level of performance of nanosized solid based lubricants. In this paper the recent data mostly from third party research institutes and commercial customers will be presented, showing the actual benefits from using nanosized solid based lubricants.

Background

irradiation of thin films of amorphous tungsten oxide in transmission electron microscope (TEM)1 by the researches in the group of Professor Reshef Tenne in Weizmann Institute of Science (WIS) [Fig. 1].

The unusual nanosized particles attracted much attention being closely related structurally to recently reported carbon fullerenes1,2. The nanoparticles were described as inorganic closed-caged onion-like nanostructures of metal dichalcogenides.

Later, the selenides and tellurides of tungsten were reported, followed by molybdenum, vanadium, titanium, etc. compounds3,4,5. It was found that virtually any layered (2-D) material can fold into closed-caged nanostructures: either quasi-spherical onion-like or nanotubes6. The unique structure of those particles was believed to result in changed properties of nanoparticles as compared to layered predecessors, while nanometric size of particles suggests enhanced properties as compared to relative 2-D materials. Later on the methods for reproducible synthesis of gram quantities of those particles were developed7,8. The developing of synthetic pathways was a critical step, because availability of pure phase material made it possible to study its properties systematically.

Back in 1992 the first closed-caged nanostructures of tungsten disulfide were first observed under the e-beam - 40 VOLUME 79, NUMBER 3

Fig. 1. TEM image of closed-caged nanoparticle of IF-WS2 (left) and group of aligned WS2-nanotubes (right)

Since the traditional application of layered structures is lubrication, the new material was studied as solid lubricant and component for lubricating formulations.

Numerous scientific papers reported the super-lubricity as result of using and testing novel material7,9,10.

Later other possible applications resulting from unique properties of discussed nanoparticles were tested and reported by various scientific groups world-wide.

The reported behavior of the novel nanoparticles suggested possibility for promising and innovative commercial applications of the material in the field of tribological applications.

The availability of possible commercial applications and technology for production of material triggered establishing of commercial company, named NanoMaterials in 2002 with its mission to commercialize the technology developed by WIS.

IF-WS2 nanoparticles and their applications

The powder obtained in chemical process consists from so called “primary” nanoparticles of tungsten disulfide (30-150 nm) stacked together forming agglomerates (around 50-150 µm). In most cases intermediate aggregates of several (5-10) primary nanoparticles can be distinguished [Fig. 2].

Fig. 2. Individual particles and formation of particles observed in real product.

- 41 NLGI SPOKESMAN, JULY/AUGUST 2015

The agglomeration of particles is explained mainly by high surface area enhanced by small size of primary nanoparticles. Various de-agglomeration techniques were tested: ultrasonification, high shear mixing, treatment with surfactants, etc. Some of the techniques were adopted either for laboratory or industrial use. It should be noted that individual closed caged nanoparticles of WS2 have a tendency to re-agglomerate forming aggregates and agglomerates, due to their small size and high surface area.

The availability of de-agglomerated powders of nanosized closed-caged IF-WS2 gave boost to research and development of solid lubricant based products: anti friction coatings, dry lubrication of e.g. bearings, etc. In addition the de-agglomerated powders enabled development of 1st generation of ready to use dispersions of nanoparticles of IF WS2. The lengthy study resulted in series of formulations with nanoparticles homogeneously dispersed in oils (e.g. as lubricant additives) or other

medias (e.g. as reinforcement for composite materials).

The closed caged nanoparticles of IF-WS2 have been tested for tribological applications since their first development in 1992. However the interest for closed caged nanoparticles has boosted and more detailed research have been conducted since their industrial scale production become available. It was found that earlier data with respect to the particle’s modus operandi should be reconsidered. For instance the early studies suggested that the rolling of nanoparticles between the contact surfaces is predominated mechanism of lubrication by onion-like nanostructures. The recent studies suggest that the lubricity of nanoparticles may be explained by variety of mechanisms, depending on external conditions, mainly contact pressure. It was proved, that the predominant mechanism is formation of tribofilm. The tribofilm consists from thin layer of tungsten disulfide on the contact surface, obtained via exfoliation of external layers of disulfide from nanoparticles present in contact point [Fig. 3].

Fig. 3. Tribofilm formation.

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Various researches proved tribofilm formation by study of oils and greases enhanced by closedcaged nanoparticles of IF-WS2.

Mechanism of IF – WS2 nanoparticles friction and wear reduction

There several mechanism that describe operation of IF-WS2.

• Spherical nanoparticle with a hollow core and act as a damper at applications with high loads and impact • Nano sized particles smooth a surface, covering roughness irregularities and asperities • The spherical geometry allows nanoparticles to play a role of a nano ball bearings, creating a roller friction • Multi-layer onion-like structures of IF WS2 nanoparticles start exfoliating under high pressures and create thin protective film on the friction surface.

Fig. 4. Friction, wear reduction and EP increase mechanisms of IF- WS2

The study conducted by O. Tevet et.al. shows mechanisms of IF –WS2 nanoparticle’s operation11 [Figures 5-7]. For the experiment a golden nanoparticle was deposited on a surface of IF – WS2 nanoparticle, to play a role of marker. The study showed that rotating

mechanism predominant under loads up to 0.7 GPa [Fig.5], sliding under uniaxial compression between 0.6 and 1.1 GPa [Fig. 6] and exfoliation at compressions above 1.1 GPa [Fig.7]. All the tests were conducted under low shear rate: low speed (quasi-static) 10-7 m/sec.

- 43 NLGI SPOKESMAN, JULY/AUGUST 2015

Fig. 5. SEM image of IF – WS2 nanoparticle rotation mechanism

Fig. 6. SEM image of IF – WS2 nanoparticle sliding mechanism

Fig. 7. SEM images of IF-WS2 nanoparticles damage and exfoliation

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Dispersion IF WS2 nanoparticles

It was soon realized that remarkable tribology results shown earlier were not always repeated while testing the materials by various sources. It was found that available 1st generation of dispersions lacked stability with clear tendency for sedimentation of the particles over time.

It was not only a question of the poor appearance of the dispersions, but the observed settling of the particles reduced performance of material.

A new challenging task faced the researchers: developing a way of converting the powder into liquidtype material with enhanced stability and performance.

The additional requirements to be mentioned are cost efficiency and technological compatibility as compared with available alternatives.

The efforts of researchers and engineers resulted in 2d generation of dispersions of IF-WS2 nanoparticles combining the best knowledge of nature of nanoparticles with advanced manufacturing techniques, resulting in new level of stability [Fig. 8] and performance of lubricating materials.

In addition the available data and experience in developing lubricating formulations made it possible to build dispersions of nanopowders in liquids targeting specific operation conditions. For instance the additives for engine oils, gear oils, heavy industrial equipment have been developed. The difference in formulation and way of manufacturing of this ready to use additives is a result of careful study of operation conditions and environment specific to particular application.

Fig. 8. first generation predecessor (a) vs revised second generation oil additive (b).

IF-WS2 nanoparticles as an EP additive for greases

The research in the field of grease enhancement by nanosized IF WS2 resulted in developing grease additives that are currently commercially available. The newly developed grease additive enhances extreme pressure properties of Lithium greases and outperforms greases that typically use MoS2, as their EP properties enhancer, as evidenced by ASTM D2596 test [Fig. 9].

- 45 NLGI SPOKESMAN, JULY/AUGUST 2015

Fig. 9. ASTM D2596 testing of lithium grease and derivatives.

The suggested grease additive is developed having in mind compatibility with other types of greases: lithium complex, calcium, aluminum complex and polyurea. The 4-Ball tests according to ASTM D2266 and ASTM D2596 proved that discussed grease additive improves both extreme pressure and anti-wear properties of wide range of available greases. [Fig. 10]

- 46 VOLUME 79, NUMBER 3

Fig. 10. Comparative testing of various types of greases enhanced with IF-WS2 based additive for greases: a) scar diameter (ASTM D2266) and b) welding point (ASTM D2596) In another study the anti-wear properties of lithium base grease were compared to the same grease formulated with conventional micron sized 2H-WS2 and the grease enhanced with additive based on nanosized IF-WS2.

The testing was done according to ASTM standard.

The reduction of wear scar diameter from 820 µm

(pure grease) to 682 µm (with 2H-WS2) and to 500 µm (formulation with IF-WS2) was observed [Fig. 11]. The advanced protecting properties of grease with nanoadditive were attributed to the formation of tribofilm visible on SEM image.

Fig. 11. Anti-wear properties of Li base grease and grease enhanced with different morphologies of WS2 nanoparticles. The building of tribofilm is clearly visible in case of grease enhanced with nanoadditive.

- 47 NLGI SPOKESMAN, JULY/AUGUST 2015

A recent study done by a European grease manufacturer compared the tribological behavior of grease enhanced with traditional molybdenum disulfide and two types of grease additives enhanced with nanosized IF-WS2. The series of testing were performed using 4-Ball machine (ASTM D2296 and ASTM D2596) [Fig. 12]. It was shown, that grease additives containing nanoparticles of IF-WS2 improve extreme pressure and anti-wear properties of greases. It was also shown, that the additives based on tungsten disulfide nanoparticles (IF WS2) outperform molybdenum disulfide-based formulations.

Fig. 12. Comparative testing of greases with 4-Ball machine. a) according to ASTM D2296; b) according to ASTM D2596 The intense study of greases enhanced by additives containing solid lubricants by the European grease manufacturer resulted in the following conclusions: • The nanoparticles do not affect the dropping point of the greases.

• Some nano-based additives are hydrophilic, affecting water wash-out properties, but this can be effectively controlled with specific additives.

• Extreme pressure properties are obtained with only 1% treat rate.

• Wear reduction is evident in both 4-Ball machine and SRV machine.

• Promising results in friction coefficient.

Conclusions

Today, after 10 years of intense R&D work the high quality lubricating materials based on inorganic fullerenelike nanoparticles of tungsten disulfide (IF-WS2) are commercially available. The variety of developed materials target specific needs of industry in a cost effective manner.

Novel inorganic fullerene-like nanoparticles of tungsten disulfide (IF-WS2) outperform platelet type particles (2H WS2 and MoS2) in any application, due to controlled geometry, size and unique morphology. For example, IF-WS2 enhanced grease exhibited wear scar diameter reduction up to 2.5 times with significant improvement of EP properties.

The next and immediate challenge for the researchers is to take advantage of the recently obtained data and use available nanoparticles to come up with new products saving the environment, reducing downtime costs and increasing life of equipment.

References:

1. R. Tenne, L. Margulis, M. Genut and G. Hodes, Nature, 1992, 360, 444 2. L. Margulis, G. Salitra, R. Tenne and M. Talianker, Nature, 1993, 365, 113 3. M. Hershfinkel, L. Gheber, V. Voltera, J. Hutahinson,

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L. Margulis and R. Tenne, J. Am. Chem. Soc., 1994, 116, 1914 4. T. Tsirlina, V. Lyakhovitskaya, S. Fiechter and R. Tenne, J. Mater. Res.,2001, 15, 2636 5. A. Margolin, R. Popovitz-Biro, A. Albu-Yaron, L. Rapoport, R. Tenne, Chem. Phys. Lett.

2005, 411, 162-166 6. R. Tenne, L. Margulis and G. Hodes, Adv. Mat., 1993, 5, 386 7. L. Rapoport, Yu. Bilik, Y. Feldman, M. Homyonfer, S. Cohen and R. Tenne, Nature, 1997, 387, 761 8. A. Margolin, Thesis for the degree Doctor of Philosophy, WIS, 2005 9. M. Chhowalla and G. Amaratunga, Nature 2000, 407, 164 10. L. Rapoport, M. Lvovsky, I. Lapsker, Yu. Volovik, Y. Feldman, A. Margolin, R. Rosentsveig, and R. Tenne, Nano Letters, 2001, 1, 137 11. O.Tevet, P. Von-Huth, R. Popovitz-Biro, R. Rosentsveig, H. D. Wagner, R. Tenne, PNAS, 2011, 50, 108

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