Frequency Analysis and Modeling of Charged-Particle Triboemission from Ceramics

The triboemission of charged particles during sliding contact is one measurable but often neglected output during wear of ceramics. Previous research work by the authors suggested that some boundary-lubricant reactions may be initiated and controlled by triboemitted electrons, but the origin and mechanisms of the triboemission phenomena remain largely unknown. The authors used a new tribometer, whose features and capabilities were previously reported, to measure electron triboemission outputs from the sliding contacts of diamond-on-ceramics and other material systems under vacuum. Characterizations were previously presented in the time-domain for those outputs. This paper introduces a new characterization of electron triboemission from ceramics by considering the frequency of occurrence of the emission events. A literature review is included on statistical models for the triboemission phenomena. A transformation to frequency-domain reveals patterns of decaying frequencies of occurrence for increasing number of events in the triboemission outputs from diamond-on-alumina and diamond-on-sapphire contacts. The patterns are complex and several classic frequency distributions are tested for describing it. A new distribution, which was developed by the authors as a "truncated compound Poisson", shows the best fit to the triboemission data. Finally, the possibility is discussed of using frequency-domain analysis to obtain new understanding of possible mechanisms for charged-particle triboemission.