ELECTROCHEMICAL-BEHAVIOR OF SURFACE ZIRCONIUM-OXIDES IN THE PRESENCE OF SOME ELECTROACTIVE SPECIES

The open circuit potential, capacitance and resistance techniques were used to investigate the behaviour of two types of surface zirconium o xides in pure 0.5 N H2SO4 and in the presence of additives of K2CrO4, KI, FeSO4 and HCOOH. The air-formed preimmersion oxide film grows in a ll solutions following a logarithmic rate law. Depending on the nature of the additive the oxide grows directly by oxidation of the surface by the oxidizing additive (K2CrO4) or indirectly by mediating the oxid ation by atmospheric oxygen in the presence of reducing additives. Ano dically formed zirconium oxide films dissolve in all solutions. The re sults of impedance measurements indicate that adsorption of HCOOH acti vates the oxide surface owing, possibly: to its hydrophilic nature whi le iodide adsorption diminishes the reactivity of active sites (probab ly oxygen vacancies) where the dissolution process is initiated.