Dynamic particle-surface tribocharging: The role of shape and contact mode

摘要

Triboelectric charging of particles is exploited in a variety of industrial processes, such as electrophotographic toner charging and triboelectric separation. Dynamic particlesurface contact is a key charging mechanism in many types of particle tribocharger (e.g. cyclones, slides and baffled drop columns), and has therefore been studied in some detail. Models of dynamic charging have tended to assume that the particle is spherical, but this is rarely the case in practice. Experiments have shown that particle shape can strongly influence the charging behaviour via both the mean contact area and the time-varying character of the contact. We review some of the experimental work, then present a 2D model of the dynamic contact of an elliptical particle, of varying roundness ratio, with a flat surface. It incorporates a simple sub-model of the cumulative surface charge transfer. This model captures a rich variety of contact modes not exhibited by spherical particles, including sliding, rolling, tumbling and bouncing. All of these contact modes produce very different charge transfer and accumulation behaviours, and these are studied and compared.