Two phosphonium cation-based ionic liquids used as lubricant additive. Part II: Tribofilm analysis and friction torque loss in cylindrical roller thrust bearings at constant temperature

Two phosphonium cation-based ionic liquids (ILs): [P66614][(iC8)2PO2] (IL1) and [P66614][BEHP] (IL2) were used as an additive to a mineral oil at 0.5 and 1.0 wt%. All IL-containing mixtures and the base oil were tested using a cylindrical roller thrust bearings test configuration. Friction and torque tests were performed and different analytical techniques were used for wear evaluation. The results showed that: IL-containing mixtures decreased friction in comparison with the neat base oil; IL2 performed better than IL1 as antifriction and antiwear additive; and chemical reaction of the ILs with the surface was found related to the tribological behaviour.