An experimental and theoretical approach to study the link between Triboemission and Tribocharging*

This work describes recent research into the causes of triboemission in sliding contacts and its links to tribocharging. The term triboemission refers to emission of electrons, ions and photons generated when surfaces are rubbed together. The term tribocharging, on the other hand, refers to the transfer of charge between rubbing components. Triboemission and tribocharging may be important in the formation of boundary lubricant films and in the degradation of lubricants.
We report the use of a unique vacuum measurement system, comprising microchannel plates and a phosphor-screen. The set-up enables triboemission events to be resolved spatially while simultaneously recording surface charge variations during the sliding of a diamond tip on silica specimens. Results show that the emission depends directly on the wear occurring and for first time that triboemission and tribocharging behavior are linked.
The two phenomena are then described by means of density functional theory (DFT) and classical Molecular Dynamics (MD). The electronic structure of the silica surface and its changes are described by DFT while Classical MD is used as a link between DFT calculations and experimental measurements. Sliding and fracture are considered as disruption events.