Passive film breakdown during anodic oxidation of zirconium in pH 8 buffercontaining chloride and sulfate

Metal passivation and passive film breakdown in aqueous systems are complex processes. Zirconium passive films grown in basic solutions containing buf fer, chloride and buffer; and chloride, sulfate and buffer have been examin ed with particular attention to the passive and transpassive regions using cyclic voltammetry (CV). Mechanically polished zirconium electrodes have be en oxidized anodically in pH 8 buffer solutions containing 0.021 M chloride , with varying sulfate concentration. The CV curves show that zirconium for ms passive layers under these conditions, which are more stable with increa sing sulfate concentration. A model is proposed to explain the passive to t ranspassive transition taking oxygen evolution, crystallization and ohmic b ehavior into account. (C) 2001 Elsevier Science Ltd. All rights reserved.