Charge transport by solid particles in liquid dielectrics

Abstract

ONE of the more controversial aspects of the study of liquid dielectrics has been the role of natural particles in the mechanism of charge transport (see, for example, the recent review by Gallagher¹ and references therein). Theoretical estimates of the charge carried by individual particles are discrepant by several orders of magnitude. However well purified and filtered a liquid sample may be, as soon as it is subjected to electrical stress such particles may be seen in motion between the electrodes by observing scattered light from them through a microscope. They are of indeterminate composition and ∼ 1 µm in diameter. In the first attempt to make a direct study of charge transport by natural particles² reliance had to be placed on a correlation involving the human senses, which was valid for low voltages and was assumed to be capable of extrapolation to higher voltages, where speeds are too great for such methods to be used. Also, since the particles exhibit a dwell-time on the electrodes wrnch is very much greater than the transit time the experimental problem of capturing the charge waveform is considerable. Here we report preliminary results of an attempt to correlate the waveforms formerly attributed to solid particles with physical evidence of actual particle motion obtained by observation of the light scattered from them.