LAUSR

Abstract In the present work, three kinds of halogen-free ionic liquids (ILs) incorporating long-chain quaternary phosphonium as cations and dioctylsulfosuccinate (DOSS) as the anion were synthesized and characterized and the tribological properties of phosphonium ionic liquids were investigated as neat lubricants for steel ball–steel disc friction pairs at room temperature (RT) and elevated temperature (100 °C). The ILs were found to be noncorrosive and highly thermally stable and showed better antiwear and friction reduction performance than commercially available synthetic lube base oil poly-α-olefin (PAO10) and conventionally used IL 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106). Scanning electron microscopy (SEM) and energy-dispersive spectroscopic (EDS) analysis of the worn-out surfaces of the steel discs was performed and the results revealed that physical adsorption and tribochemical reactions occurred and formed a protective boundary film on the worn steel surface to prevent direct steel–steel contact between rubbing surfaces.