Space Charge Effects in Chlorobiphenyls

The dependence of the static electric field distribution on dissolved water and air in the ranges 8-38 ppm and 0.5-4.6 percent by volume, respectively, for parallel plate electrodes, is examined for two chlorobiphenyls by means of the Kerr electro-optical technique. It is shown by measurement of the field distribution at 23°C for a 0.5-cm electrode separation and applied fields up to 160 kV/cm, dissociation of the water molecule results in an exponential distribution of positive space charge giving rise to an enhanced cathode field. The enhanced cathode field near breakdown own remains unchanged regardless of increasing water content corresponding to decreasing breakdown potential. Furthermore, it is shown that conduction is largely due to a unipolar process. The presence of air is shown to decrease the cathode field enhancement, this is thought to be due to recombination of the O2 molecules and H ions. The space charge limited current and breakdown phenomena are discussed in relation to the enhanced cathode field.