Effect of Base Oil on Rheological Behaviors and Tribological Properties of Nano-silica Greases

Four samples were prepared by the same synthetic process with paraffinic oil, naphthenic oil, poly-α-olefin oil (PAO), and polyol ester oil (POE), respectively, and using nano-silica as the thickener. For the samples prepared into nano-silica greases (NSGs) successfully, their physiochemical properties, rheological behaviors, low-temperature fluidities, and tribological properties were investigated. Based on the materials and preparation methods selected in this experiment, it has been found that the polyol ester oil could not be prepared into NSGs and the paraffinic oil-based grease had the best colloid stability among the three greases successfully prepared. SEM analysis revealed that NSGs synthesized by different base oils had a similar chain skeleton structure. Moreover, the properties of base oils and their sensitivities to nanoparticles (nano-thickeners) determined the structural strength and thixotropy of the as-prepared NSGs. The low-temperature fluidity test also showed that PAO-based grease has the best pumpability. In addition, the tribological properties of greases were different from the corresponding base oils, which might be caused by the change of the structure after the preparation of greases and the participation of nano-silica in the friction process. This study provided guidance in selecting base oils for the development of high-performance NSGs. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.