Tribological investigations of ionic liquids in ultra‐high vacuum environment

ABSTRACT A tribological investigation of two ionic liquids (ILs) that could be used as potential lubricants for vacuum or space applications is presented. Their tribological behaviour was evaluated using a ball‐on‐flat oscillating reciprocating motion CaTri ultra‐high vacuum (UHV) tribometer and the results were compared against those of a conventional perfluoropolyether (PFPE) vacuum lubricant. The thermal stability of the lubricants was investigated by thermogravimetric analysis before exposing them to UHV environment. The worn steel surfaces were studied by X‐ray photoelectron spectroscopy, optical and confocal microscope as well as scanning electron microscope. The tribological evaluations showed that ILs exhibited better friction reduction and anti‐wear properties than the PFPE lubricant. The excellent tribological properties were attributed to the formation of a surface protective film composed of iron fluoride and iron phosphate, respectively, on the lubricated metal surfaces by a tribochemical reaction with the ILs. Copyright © 2013 John Wiley & Sons, Ltd.