Synthesis and Tribological Properties of the Phosphonium Ionic Liquid Lubricating Grease

As new lubricating materials, high performance ionic liquid lubricating grease is one of the hot and important topics in the field of tribology. In this regard, three kinds lubricating greases with high dropping points were prepared using tributyl(alkyl) phosphonium ionic liquids as the base oil and the PTFE powder as a thickening agent. The tribological properties of the lubricating greases were investigated on steel/steel pairs. The results show that the tributyl(alkyl)phosphonium ionic liquid lubricating greases showed better friction reducing and anti-wear properties than 1-methyl-3-octyl imidazolium dioctylphosphate ionic liquid lubricating grease at room temperature and high temperature (100 ℃). The worn surfaces were analyzed by X-ray photoelectron spectroscope and the friction coefficients of the lubricating greases were investigated under electronic field. The possible friction mechanisms were proposed, i.e. the chemical reaction film containing FeF₂ was generated by the tribo-chemical reaction between PTFE and the steel surface, the ionic liquid cation and anion were physically adsorbed on the worn steel surface.