Effectiveness of phosphonium cation-based ionic liquids as lubricant additive

Two phosphonium cation-based ionic liquids (ILs) were studied as additive to a mineral oil. Solubility tests and TGA of neat samples were performed. Three concentrations of the ILs were used in the tribological tests. Base oil-ZDDP mixtures were used as comparison samples. Tribological tests were made using a reciprocating ball-on-disc configuration. Load ramp and Stribeck curve tests were also performed. The worn surface was studied by different techniques. The results showed similar and better friction reduction properties for ILs- or ZDDP-containing mixtures than the neat base oil. The [P66614][(iC8)2PO2]-containing mixtures outperformed the antiwear behavior of the other samples. XPS results showed different mechanisms of lubrication when using ILs or ZDDP.