THE RATE RELATION OF THE ELECTRODE-REACTIONS OF ZINC CORROSION IN OXY-ACID SOLUTIONS AND THE ROLE OF ANODICALLY ACTIVE INTERMEDIATES

A mechanism of zinc dissolution was studied at a potential of -0.73 V in sulfate solutions containing chromates and hydrogen peroxide at pH 1.60, 1.95, and 3.00. The rate of cathodic process was shown to be a s um of the rates of three interrelated reactions, namely, the discharge of hydronium ions existing in the background solution and the dischar ge of the hydrogen ions and anions formed as a result of the dissociat ive adsorption of the oxy-acid molecules on the electrode, The maximum possible rate of discharge of all components of the system depends on the bulk concentration of hydrogen ions and is stoichiometrically rel ated to the corresponding limiting diffusion current density (when the hydronium ion acts as a proton donor in the reaction of oxy-anion red uction). Anodic reaction of zinc ionization is accelerated by the inte rmediate products of the oxidizer reduction. These are the surface hyd roxide ions. Therefore, depending on the relation between the stoichio metric coefficients of the oxy-anion reduction, either cathodic or ano dic current can be generated in the external circuit of the electrode at a constant potential.