The lowest friction coefficient reported in the literature is ~0.003 for highly-hydrogenated diamond-like carbon (DLC) tested in inert environments. DLC films with low hydrogen contents also show a friction coefficient lower than 0.1 in hydrogen gas environments. Graphite is another carbon form that is widely known to exhibit good lubricity in ambient air; it was speculated that the layered crystalline structure is responsible for the good lubricity. But graphite does not work as a lubricant in vacuum or dry nitrogen conditions. Boric acid is also a lamellar compound with a hexagonal crystal structure similar to graphite.  A solid boric acid coating can give a friction coefficient as low as 0.06 for a variety of materials in humid air, but exacerbates friction and wear in an inert environment. Thus, the lamellar structure with weak inter-layer interactions alone cannot explain the excellent lubricity of these materials. In this talk, the chemical origin of super-lubricity of DLC, graphite, and boric acid will be discussed.

Origins of ultra-low friction behaviors of carbon and boric acid surfaces

248th National Meeting (2014)

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