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.

Squeezing out hydrated protons: low-frictional-energy triboelectric insulator charging on a microscopic scale

“…20 Triboemitted charge carriers of both polarities have been detected in experiments for different insulating materials, and the quantity of emitted charge carriers has been found to increase for higher loads (∼1 N) and surface damage. 110,111 The triboemitted electrons rapidly react with the rubbing materials to form free radicals and negative ions, rendering the rubbed surface highly reactive and thereby inducing tribochemical reactions. 20 The quantity of ion and radical formation by cutting or grinding of polymers has been determined by electron spin resonance measurements (see Table II).…”

Spatially Resolved Triboemission Measurements

“…Here, an almost constant low emission level is seen, onto which several high bursts of emission are superimposed. As observed by Nakayama et al [12] and Molina et al [16] for alumina specimens, electrons are emitted in bursts, shortly after scratching starts. The coefficient of friction throughout this test was measured at 0.1.…”

“…In most triboemission studies found in the literature, emission ceases as soon as the scratching stops [12]. For instance, Molina et al observed this for semi-conductors, though they mentioned that significant post-contact emission occurred for insulators [23].…”

“…To achieve this, they used a low-voltage biased collector positioned close to the contact that registered bursts of the electrical current due to the emission of negatively and positively particles [11], while photon emission was measured using a photomultiplier [12]. Their results showed that insulator materials produced significantly higher levels of emission when scratched than metals.…”

General Approach to Mechanochemistry and Its Relation to Tribochemistry

“…radio waves; IR, visible, UV light; and X-rays [34]. Significant research in the field of triboemission was carried out by Nakayama et al [35]. Kim et al [36] investigated electron and photon evolvement (phE) from magnesia (MgO) under friction with diamond; they found that during indentation, prior to any fracture of MgO, only phE was observed.…”