Triboemission of charged particles and photons from solid surfaces during frictional damage

Abstract

Triboemission is defined as the emission of electrons, ions, photons and neutral particles during tribological surface damage. Triboemission of negatively and positively charged particles and photons by the wearing of solid surfaces of metals, ceramics, glass, anodic aluminium oxide films (Al2O3), polymers and mica were studied using a special triboemission measuring apparatus which permits the simultaneous measurement of negatively and positively charged particles, photons and friction coefficients in a vacuum and in various atmospheres. The emission characteristics of the triboemission depended on the type of solid. Both charged particles and photons were emitted simultaneously in bursts during the scratching of the solid surfaces of semiconductors and insulators. In contrast, no photon emission was observed using conductors. With conductors and semiconductors, the particles emitted were mainly negatively charged particles, while with insulators both negatively and positively charged particles were emitted at the same level but with a slightly higher intensity of negative particles in air. The emission of the charged particles and the photons increased at higher loads and speeds as well as at greater thickness of Al2O3 films. The charge intensity from the insulators decreased with higher Vickers hardnesses. The intensity of the negatively and the positively charged particles was well correlated with that of photons. The mechanism of triboemission is discussed.