Reinforcing effect of Lewis acid–base interaction on the high-temperature colloidal stability and tribological performance of lubricating grease

Abstract

Abstract The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis acid borate ester, which could interact with Lewis base RCO 2 − of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis acid–base complex. Important details about the Lewis acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–acid interaction between the boron atom of borate ester or boric acid and the oxygen atom of RCO 2 − . Lewis acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.