Charge-relaxation process dominates contact charging of a particle in atmospheric condition: II. The general model

In this paper, the `charge-relaxation model' proposed in our preceding paper as a scheme determining the impact charge is discussed in detail, especially for the case of an arbitrary initial charge. It is shown that the model explains well not only the `equilibrium charge' but also the `charging line' in terms of a proportional dependence of the impact charge on the initial charge. The comparison between the measured impact charge and the theoretical value shows that the measured value increases with increasing impact velocity and impact angle and has a value at saturation about 110% of that estimated by our non-empirical theory. In the case of impact charging between a conducting particle and metal plate, the charge relaxed completely. This could be explained in terms of the two-dimensional relaxation of charge on the particle surface. Discussion and experiments on the particle-size dependence of the maximum charge showed that the maximum charge was proportional to the particle size raised to the power 1.5.