THE BEHAVIOR OF ZINC ELECTRODE IN ALKALINE ELECTROLYTES .2. A KINETIC-ANALYSIS OF ANODIC-DISSOLUTION

A model for the kinetics of active zinc dissolution is developed taking into account the presence of an interfacial layer. From electrode impedance spectroscopy, it is shown that the metal dissolution takes place essentially at the base of pores in a conductive layer of oxidation products which is progressively degraded by the anodic current. This model accounts for the four loops observed on complex plane impedance plots with decreasing frequency: (i) a capacitive loop generally highly depressed in connection with the current penetration within pores; (ii) an inductive loop corresponding to the presence of a monovalent intermediate Zn(I) in the reactive interphase; (iii) a capacitive loop resulting from the precipitation and escape of Zn(II) ions by diffusion from the pore bases; and (iv) an inductive loop consequent on the slow decrease of the pore length with increasing anodic polarization. Inhibition of zinc corrosion by an organic additive is shown to be related to changes in both the kinetic parameters of reactions and the layer properties.