Tribological Characteristics of Alkylimidazolium Diethyl Phosphates Ionic Liquids as Lubricants for Steel-Steel Contact

Tribological properties of three novel phosphates-based ionic liquids (ILs), i.e., 1,3-diethyl imidazolium diethylphosphate, 1-ethyl-3-butyl imidazolium diethylphosphate, and 1-ethyl-3-octyl imidazolium diethylphosphate, were evaluated as lubricants for the steel-steel sliding pair by using an Optimol-SRV oscillating friction and wear tester. The chemical compositions of the boundary films generated on steel contact surfaces were analyzed with the use of a scanning electron microscope (SEM) with a Kevex energy dispersive X-ray analyzer attachment (EDS), and an X-ray photoelectron spectrometer (XPS). The results showed that these phosphate functional group-containing ionic liquids exhibit excellent tribological performance especially at a moderate temperature. The imidazole phosphate ionic liquid has no corrosion to steel. The mechanism for the friction-reduction and anti-wear effect of ionic liquids has also been proposed and discussed from the tribochemistry point of view.