Effect of structure of ZnO and SiO2 core-shell composite nanoparticles as lubricant additive on tribological properties of greases

Nano-additives can enhance the tribological properties of greases. In particular, core-shell composite nanoparticles, which combine multiple nanoparticles, have been the subject of recent research due to their superior properties. In this study, based on the friction pairs material, GCr15, by choosing ZnO with low hardness and SiO2 with high hardness, core-shell composite nanoparticles with soft shell hard core SiO2@ZnO and hard shell soft core ZnO@SiO2 were prepared by chemical deposition and calcination methods. The impact of different structural forms of these composite nanoparticles as grease additives were investigated for the first time by adding them into lithium grease. The results show that ZnO@SiO2 have good tribological properties under light load, reducing the COF by 18 % and decreasing the WSD by 22 %. SiO2@ZnO exhibit the best anti-friction effect under heavy load conditions, reducing the COF by 15 % and decreasing the WSD by 28 %. The GCr15-ZnO-SiO2 surface composite film structure is the key to improve the performance of grease in the two composite nanoparticles. It not only has good wear resistance, but also can increase the bearing capacity of the oil film. The two core-shell structure nano-additives provide a new idea for the design of lubricants under special conditions.