Self-lubrication of nuclear graphite in argon at high temperature

Tribology studies in argon of nuclear graphite previously degassed at 600 degrees C show lower friction and wear at 600 degrees C than at room-temperature: the COF decreases from 0.55(14) to 0.33(5) and the specific wear rate de-creases from 0.4(3) to 0.06(3) mu g/Nm. Microstructural characterization of the wear spots via digital, polarized, and electron microscopy and Raman spectroscopy suggests formation of a Tribo-film formed by fracture perpendicular to the basal planes that exhibits crystallite alignment. The improved self-lubrication at high temperature results from the presence of a thicker and more continuous Tribo-film, attributed to the increase with temperature in the tensile strength and in the anisotropy of the chemical reactivity of graphite crystallites.