Effect of gas pressure on the triboluminescence and contact electrification under mutual sliding of insulating materials

Abstract

Uniform and/or burst triboluminescence (TL) modes were observed during sliding of a diamond pin along a soda-lime disc in an Ar atmosphere in the pressure range between 105 and 10−2 Pa. Various combinations of these modes in different pressure regions produced four behaviour patterns of TL: chaotic weak bursts, periodic strong bursts, chaotic bursts with uniform TL and only uniform TL. The surface electrostatic potential was measured simultaneously with TL in order to evaluate the rates of charge build-up and recombination. Optimal conditions for charge recombination through the gas discharge were in the pressure range 0.17–4 kPa. The configuration of the electric field was simulated using a finite element model and the experimental data. The electric field was dominated by the concentrated positive charge on a tiny surface area of the pin, while the influence of a negative charge spread over a larger area on the disc was negligible. It was concluded that, in contrast to the prevalent belief, the electric discharge producing TL around the contact zone was a positive corona rather than bipolar. Using the Townsend approach, a model of the corona TL offering a plausible explanation for the experimentally observed TL features and behaviour was proposed.