Impact of silicate contaminants on tribological and thermal transport performance of greases

This work investigates the effects on thermal transport and tribological performance of incorporating silicate particles – emulating pollutants – within various greases: lithium thickened (MB), soap complex thickened (SB) and silica thickened (UB). Silicate particles (200–300 µm) were homogeneously dispersed, by a mechanical method, within the selected greases in concentrations of 1.5 g/10 ml. For tribological evaluation a four-ball tribotester was employed according to ASTM D2266 standard test method for wear preventive characteristics of lubricating greases. For the silica thickened grease (UB) the WSD increased by ~15%; for the lithium soap and the complex soap thickened greases, the changes were almost negligible due to the behavior of their soap thickener and base oil. For the thermal transport evaluation, a guarded hot-plate method-based apparatus was used to characterize the thermal conductivity of greases with and without silicate particles, showing an enhancement range of 25–70% in thermal conductivity with the addition of 1.5 g/10 ml of silicate particles. Thermal conductivity measurements offer an accuracy of ~5%. It was shown that MB and SB greases have a positive impact on the thermal conductivity as silicates are added; UB reflected a negative effect on the thermal conductivity as silicates were mixed within the grease. These results show that silicate contaminants may be able to thermal properties of greases while not affecting significantly their tribological performance.