Graphite Intercalation Compounds as Solid Lubricants

The results presented in this paper demonstrate that the process of intercalation; i.e., the formation of chemical compounds via insertion of atomic or molecular species in the van der Waals gap between planes of lamellar solids can substantially improve the intrinsic lubricating properties of solids. Using graphite as a model host compound, various transition metals and metal chlorides intercalated into graphite were formulated into solid film lubricants and their lubricating properties determined in a laboratory wear test device. Comparisons of endurance life and load-carrying capacity are made relative to molybdenum disulfide and unintercalated graphite. Graphite/19.8 wt. percent CoCl2 was found to exhibit over a fivefold increase in endurance life while graphite/19.3 wt. percent NiCl2 provided a greater than twofold increase in load-carrying capacity relative to graphite and was equivalent to MoS2. The degree of improvement in endurance life was found to be dependent on the concentration of intercalant in graphite and the resulting increase in interlayer carbon spacing due to intercalation. A total of 23 different intercalate compounds were investigated at various concentration levels.