Impact charging experiments with single particles of hundred micrometre size

This paper reports the results of an ongoing program, which investigates the electrostatic charge generated when a particle impacts and rebounds from a metal plate. Previous studies were conducted with particles, which were several millimetres in size. From those experiments, a theory of ‘charge relaxation’ was developed which predicts the equilibrium charge, which a particle will acquire after multiple impacts. In this paper, we report the development of a new apparatus, which is more sensitive by several decades. With this equipment, the experiments could be repeated with particles as small as 100 μm. The results show that the charge relaxation theory is still relevant in this range. However, it is necessary to modify this theory, both for the larger and the smaller particles, to account for the distribution of the charge on the surface of the particle.