Effect of Temperature on Rheological Behaviors and Tribological Properties of Nano-silica Greases Prepared from Base Oils with Different Viscosities

Four kinds of nano-silica greases (NSGs) were prepared by poly-α-olefins (PAO4, PAO10, PAO40, and PAO100) with different viscosities, respectively. The effect of temperature on the properties of NSGs was investigated, and the difference and relation of rheological behaviors and tribological properties between various greases were compared. Results showed that the colloidal stability of NSGs was improved with the increase in the viscosity of base oils. The rheological behaviors test showed that the structural strength and apparent viscosity of greases decreased significantly with the elevation of temperature. Meanwhile, it was observed that the thixotropy of greases prepared from low-viscosity base oil was more susceptible to the influence of temperature, which was mainly related to the damage of colloidal structure. The tribological test showed that appropriate temperature rise was beneficial to improve the anti-wear and anti-friction properties of NSGs, and the higher the viscosity of the base oil was, the better the tribological properties of corresponding greases were. However, with the temperature continued to rise, the tribological performance of greases deteriorated gradually. In addition, the lubricating grease prepared from low-viscosity base oils exhibited better tribological performance than others because of the existence of a temperature spot. It was mainly related to the dispersion of the aggregated particles and the formation of deposition film on the surface of the friction pair.