The Influence of Ionic Conductivity on the Electric Strength of KCl and NaCl

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Abstract
At high temperatures, the electric strengths of the alkali halides appear to decrease rapidly with rise in temperature. This behaviour is qualitatively similar to that predicted by Frohlich's high temperature theory of breakdown. It can also be explained in terms of space charge and thermal effects due to the transport of ions and therefore speculation exists about the operative mechanism. The ionic conductivity of alkali halide crystals depends upon the amount of bivalent impurity they contain. This fact has been used to determine the influence of ionic conductivity upon the electric breakdown of KCl and NaCl. No evidence is provided to support Frohlich's high temperature theory, the observed negative temperature coefficient of KCl being attributed to ionic phenomena. Changes of up to sixtyfold in the ionic conductivity of NaCl did not influence the impulse electric strength of this material except at temperatures below about - 50 c, when the effect of increased conductivity was to increase the electric strength.

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