Triboemission from alumina, single crystal sapphire, and aluminum

The purpose of this paper is to present experimental research work seeking a better understanding of triboemission and its role in tribochemistry. A new instrument is described for measuring the intensity and retarded-energy spectra of electrons and ions triboemitted from various sliding contacts. This instrument was designed to accommodate a variety of contact geometries and it features a wide range of applied loads and sliding speeds under high vacuum or controlled atmosphere conditions. The particle-measurement technique employs a channel electron multiplier in the pulse-counting mode. Experimental results are reported on triboemission intensity from sliding contact of diamond on three related materials: alumina, single crystal sapphire (Al2O3), and aluminum. Significant negatively-charged particle triboemission was observed from diamond-on-alumina and diamond-on-sapphire contacts. The retarded-energy spectrum of the negative-particle triboemission also was measured. Emission of positively-charged particles was found to be of relatively low intensity. Lower levels of negatively-charged triboemission, as compared to those from alumina and sapphire, were found from diamond-on-aluminum. These results are discussed with a focus on the possible role of charged particle emission in tribochemical processes and, in particular, on tribopolymerization as an effective mechanism of ceramic lubrication.