Crown-Type Ionic Liquids as Lubricants for Steel-on-Steel System

A series of novel imidazolium-based crown-type phosphate ionic liquid lubricants have been designed and synthesized. Because the anions of ionic liquids are organic phosphate, crown-type ionic liquids would not corrode steel. The crown-type ionic liquids exhibit better tribological properties than conventional lubricants, which were evaluated by a ball-on-flat type Optimol-SRV oscillating friction and wear tester. The chemical compositions of the boundary films generated on the steel worn surfaces were analyzed with the use of a scanning electron microscope and X-ray photoelectron spectrometer. The results indicate that crown-type ionic liquids would generate complex lubricating films, composing organometallic polymer, polyphosphate, FePO₄, Fe₃O₄, etc., lubricated under different loads to exhibit the friction reduction and anti-wear abilities.