Characterization of the Passive State on Zinc

Abstract

Despite intensive investigations, the nature of the passive state is one of the most complex and unresolved subjects in the electrochemistry of zinc in alkaline solutions. In this paper, we explore the electrochemistry of the passive state on zinc in 0.1 M sodium borate/i M sodium hydroxide solution of pH 10.5. During the course of passivation, several charac-teristic features in the anodic region are observed, including a wide passive range extending over>2 V and a secondary passivation phenomenon that occurs at high anodic potentials. The steady-state current in the passive state is found to be independent of the applied voltage, which is consistent with the barrier layer being an interstitial zinc conductor or an oxygen vacancy conductor (or both) with interstitial zinc being the most likely defect. This model is also consistent with the well-known n-type character of the passive film on zinc. Infroduction Many authors have studied the electrochemical behavior of zinc in alkaline media over wide ranges in both zincate and alkali concentration, and also by using numerous ex-perimental techniques,'24 and an extensive summary of this work has been recently published by Zhang.24 For ex-