The influence of environment and pressure on the transition to dusting wear of graphite

Abstract

An examination has been made of the way in which the type of environment and its partial pressure influence the transition to high friction and wear-dusting-of graphite sliding against carbon. It is shown that the onset of dusting is invariably associated with the attainment of a critical temperature at the contacting asperities. This temperature increases with partial pressure of the vapour and, for a series of n-paraffins and alcohols, also increases with molecular size (chain length). From the variations in critical temperature with partial pressure, adsorption energies can be derived and these are broadly consistent with a mechanism of physical adsorption on graphite basal planes. It is suggested that the adsorbed vapour on basal planes functions as a 'reservoir' from which molecules can migrate to neutralise edge sites being continuously exposed during the normal, low-wear regime.