CHARACTERIZATION OF THE PASSIVE STATE ON ZINC

Despite intensive investigations, the nature of;he passive state is on e of the most complex and unresolved subjects in the electrochemistry of zinc in alkaline solutions. In this paper, we explore the electroch emistry of the passive state on zinc in 0.1 M sodium borate/1 M sodium hydroxide solution of pH 10.5. During the course of passivation, seve ral characteristic features in the anodic region are observed, includi ng a wide passive range extending over >2 V and a secondary passivatio n phenomenon that occurs at high anodic potentials. The steady-state c urrent in the passive state is found to be independent of the applied voltage, which is consistent with the barrier layer being an interstit ial zinc conductor or an oxygen vacancy conductor (or both) with inter stitial zinc being the most likely defect. This model is also consiste nt with the well-known n-type character of the passive film on zinc.