Tribological properties of conductive lubricating greases

Three kinds of new conductive lubricating greases were prepared using lithium ionic liquids as the base oil and the polytetrafluoroethylene (PTFE) as the thickener. These lithium ionic liquids ([Li(PEG)X]) were obtained by blending lithium salts (LiBF₄, LiPF₆ and LiNTf₂) with poly(ethylene glycol) (PEG) because lithium salts have an extremely high solubility in PEG. The conductivities and contact resistances of the prepared lubricating greases were investigated using the DDSJ-308A conductivity meter and the reciprocating ball-on-disk UMT-2MT sliding tester. In addition, their tribological properties were investigated in detail. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to explore the friction mechanisms. The results suggest that the prepared lubricating greases have high conductivities and excellent tribological properties. The high conductivities are attributed to ion diffusion or migration of the lithium ionic liquids with an external electric field, and the excellent tribological properties depend on the formation of boundary protective films.