Tribological properties of chemical composite and physical mixture of ZnO and SiO2 nanoparticles as grease additives

Nano additives have been widely proven to significantly improve the tribological properties of traditional greases, and the synergistic effect of multiple nanomaterials to improve the performance of greases is a promising research direction. In this paper, based on the hardness of the bearing material GCr15 steel, harder SiO2 nanoparticles and softer ZnO nanoparticles were selected to synthesize hard-shelled soft-core composite nano-particles (ZnO@SiO2) by chemical deposition, and it was used as grease additive for the first time. The composite ZnO@SiO2 nanoparticles have better dispersion and tribological properties than the physically mixed nano-particles (ZnO/SiO2). When 1 wt% ZnO@SiO2 was added to the grease, the coefficient of friction and wear scar diameter were reduced by 11.5% and 25%, respectively. The special hard-shell-soft-core structure of the com-posite not only has good dispersion, but also forms a special solid friction film on the surface of the friction pairs. The SiO2 shell can absorb a large number of long-chain lubricant molecules and increase the viscosity of the lubricant in the friction zone, thus forming a solid-liquid phase composite lubricating film, which plays a sig-nificant role in friction reduction and anti-wear.