In situ formed ionic liquids in lard oil as high-performance lubricants for steel/steel contacts at elevated temperature

This paper presents a “green” way of in situ forming ionic liquids (ILs) as high-temperature lubricants by dissolving high content of lithium bis(trifluoromethylsulfonyl)imide in lard oil (LO). Nuclear magnetic resonance spectroscopy result indicated that lithium bis(trifluoromethylsulfonyl)imide could have a reaction with triacylglycerols, which are the major component of LO and formed the IL (Li[triacylglycerol])bis(trifluoromethylsulfonyl)imide. Differential scanning calorimetry result shown that ILs could effectively enhance the thermal-oxidation stability of LO. Tribological behaviours of lubricant application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester at 250°C. It was found that the in situ formed ILs possessed excellent friction-reducing and antiwear properties in LO compared with perfluoropolyether (as a reference lubricant) under the same conditions. The wear mechanisms are tentatively discussed according to the morphology observation of worn surfaces of steel discs by scanning electron microscope and the surface composition analysis by X-ray photoelectron spectroscopy.