Breakdown Phenomena During the Growth of Anodic Oxide Films on Zirconium Metal: Influence of Experimental Parameters on Electrical and Mechanical Breakdown

Abstract

Different aspects of the breakdown phenomena observed during the growth of anodic films on zirconium metal in aqueous solutions have been investigated. Two different mechanisms of breakdown are suggested as a result of the experimental observations. A mechanical breakdown, which is dependent upon the logarithm of the anodizing current density, has been observed in carbonate and sulfate solutions at low concentrations of salt or acid and/or low anodizing current densities. The appearance of small fissures in the films is related to this type of breakdown. An electrical breakdown was observed in sulfamic acid solutions as well as in sulfate and carbonate solutions at high salt or acid concentrations and/or high current densities. In the case of electrical breakdown, the first spark voltage showed a significant dependence upon the value of current density only in carbonate and sulfate anion containing solutions. A possible explanation for this dependence is suggested in agreement with Christov's model, taking into account also the incorporation of anions into the films. The different influences of the electrolytic solutions upon both types of breakdown are presented and discussed.