The electric strength of mica and its variation with temperature

The electric strength of mica in air, and the intrinsic electric strength and d.c. conductivity of mica, have been measured over extensive ranges of temperature. The effects of thickness and pre-conditioning on electric strength have also been investigated. The experimental conditions necessary for the determination of intrinsic electric strength are considered and two methods suitable for mica are described. The intrinsic electric-strength values thereby obtained are shown to compare satisfactorily with the predictions of Fröhlich´s theory of electric breakdown in polar crystals. The relevance of the results to industrial applications of mica is discussed.