UNIQUE SPHERICAL NANOPARTICLES of TUNGSTEN DISULFIDE (IF-WS2) as High Performance Additives for Greases Elena McDaniel, George Diloyan, PhD Nanotech Industrial Solutions Inc. Abstract
Solid particles have been widely used in greases to improve EP performance in demanding applications and in various industries. The most common solid particles for the past several decades have been platelet shaped micron sized particles of 2H-MoS2 (2 dimensional hexagonal Molybdenum DiSulfide). In this paper the properties of novel spherical shaped nanoparticles of IF-WS2 (Inorganic Fullerene Tungsten disulfide) solid additives in greases will be shown as a potential replacement of micron platelet 2H-MoS2 additives. Spherical like nanoparticles of tungsten disulfide (IF-WS2) are considered to be excellent anti-wear, antifriction and EP additives. Due to their unique spherical shape, these particles are protecting metal surfaces from load shock, micro pitting and wear from constant metal to metal contact under high temperatures and loads.
Introduction
Antifriction, anti-wear and EP (Extreme Pressure) properties in greases play a very important role in order to produce high quality products that protect equipment in industrial applications such as mining, automotive, steel production etc. There are many additives in the market that are reducing wear and friction (i.e. MoDTP, MoDTC, ZnDTP, 2H-MoS2)
and increasing EP properties (i.e.heavy metals, sulfur, phosphorous). Anti-wear characteristics of ZnDTP (Zinc dialkyldithiophosphate) are attributed to the formation of phosphate films that can react with abrasive iron oxides [1]. On the other hand MoDTC (molybdenum dialkyl-dithiocarbamate) has been used primarily as a friction modifier due to the formation of MoS2 at high Hertzian pressure points. MoDTP (molybdenum dialkyl-dithiophosphate) possesses combined anti-wear and friction reduction properties [2]. Both MoDTP and MoDTC require the presence of temperature and friction in order to start the generation of MoS2 layers. 2H-MoS2 particles (Figure 1a [3]) are platelet shape micron size particles that in the presence of shear stress exfoliate layers of MoS2 thus reducing friction. IF-WS2 nanoparticles (Figure 1b) are novel spherical particles that were invented in 1992 by Professor Reshef Tenne in the Weizmann Institute of Science. These particles currently are produced on a commercial scale and are available in various forms of dispersions (water, paste, oil). In this paper the commercially available paste dispersion of IF-WS2 nanoparticles has been tested in LiX grease. Wear, friction, and EP characteristic along with other physical properties have been evaluated.
-8VOLUME 81, NUMBER 5
