Imidazolium hexafluorophosphate ionic liquids as high temperature lubricants for steel–steel contacts

A series of long-chain 1,3-dialkyl imidazoliumionic liquids (ILs)were synthesized and evaluated as lubricants for steel–steel contacts both at roomtemperature and 150 ◦C. Relationship between the alkyl chainlength and the tribological properties of the ILs was investigated in detail. The results indicated that theILs bearing long alkyl side chains have excellent friction-reducing and anti-wear properties, especiallyat high temperatures and high loads. The worn surfaces of steel discs were observed and analyzed byscanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The friction reductionand load carrying capacity were supposed to be due to the formation of high quality boundary filmconsisting of both tribochemical reaction film and the ordered absorption film.