Effects of enhanced heating by surface oxides on arc cathodes

Heat conduction into and production within a metallic electrode can be affected drastically by the presence of thin surface oxides. Analytic expressions are derived for the temperature distribution in time and depth for a stratified oxide/metal cathode subjected to a pulsed DC arc with finite risetime. Results for cathode materials representing a wide spectrum of metallic and oxide properties indicate that oxides 50¿¿250 ¿¿ thick can reduce premelt conditions at the electrode surface to nanosecond time scales for even modest current densities during the formative stage of arcs several millimetres long in atmospheric pressure air.