Improvement of the Tribological Properties of a Lithium-Based Grease by Addition of Graphene.

Graphene with layer number less than seven, prepared by a mechanical exfoliation method, was used as a friction-reducing additive to a lithium-based grease. The graphene was characterized via AFM, TEM, and Raman spectroscopy. The as-prepared graphene had few defects according to the characterization analysis and appeared to be composed primarily of sheets averaging 1-4 atomic layers. When the graphene was added to a lithium-based grease, the lubrication and antiwear properties of the grease were improved, as quantified by friction coefficient and wear scar measurements. The weld point of the lithium-based grease increased proportionally with graphene loading. At the maximum graphene loading tested (2 wt%), the weld point was 1.6 times that of the pure lithium-based grease. Hence the mechanical properties of the graphene sheets played an important role in improving the tribological properties of the grease.