Pitting corrosion of zinc in Na2SO4 solutions and the effect of some inorganic inhibitors

Abstract The pitting corrosion behaviour of Zn in neutral (pH 6.8) Na2SO4 solutions was studied by using potentiodynamic and cyclic voltammetry techniques and complemented by X-ray analysis under the effect of electrolyte concentration, scan rate, temperature and pH. The voltammograms involve active/passive transition prior to the initiation of pitting corrosion. The active region displays one anodic peak. The passivity is due to the formation of ZnO film on the anode surface. The critical pitting potential decreases with increasing sulphate ion concentration and temperature but decreases with scan rate. Increasing the acidity or alkalinity of the medium enhances the pitting corrosion. The effects of adding increasing concentrations of Cr 2 O 2− 7 , CrO 2− 4 , WO 2− 4 , MoO 2− 4 and NO − 2 anions on sulphate pitting corrosion of Zn were investigated. These anions inhibit the active dissolution and pitting corrosion and the extent of inhibition depends upon the type and concentration of the inhibitors. The adsorption characteristics of these anions on the electrode surface plays a significant role in inhibition.