Influence of environment on the size of the elemental wear debris of graphite

The elemental particles forming the wear debris or transfer particles of graphitic materials were systematically assessed by AFM and TEM techniques. They typically consist of two populations : relatively large particles (0.1 to a few mum) visibly formed by cleavage along the basal planes and nanoparticles (ranking from 10 to 50 nm). The proportion and size of the nanoparticles as determined by image analysis were shown to display systematic variations as a function of moisture and oxygen contents in air. By analogy with the unidirectional tensile fracture of thin brittle films (suggested by the observation of the precursor step of nanoparticles on the basal planes) a new hypothesis is proposed for the mechanism of particle detachment.