A Preliminary Study on the Dynamics of Triboemission, Work Function and Surface Charging of Ceramics

Abstract

This paper discusses the tribological dynamics of electron triboemission and after-contact emission during scratching of ceramics. The origin of such triboemission is still unclear, but the author and colleagues consistently observed two features that can explain the emission and its observed time evolution: that a large fraction of electron is emitted for energies lower that the electron work function of the bulk material, and that there is evidence of surface charge that relaxes over a long period. These experimental findings and their analysis are reviewed. Literature data on the reduction of electron work function during dry sliding is correlated to the experimental observations. Surface charging is discussed as a factor in triboemission: trapping and release of charges from the activation and cancellation of surface lattice defects are connected to the relaxations of mechanical energy and of polarization during wear. These phenomena can help explaining the observed time evolution of electron triboemission from ceramics. This preliminary study indicates that understanding of the electron triboemission origin and evolution requires a mechanism that integrates the evolution of defects during sliding and its effects on the dynamics of electron work function change and of energy storage and release by charge trapping.