INHIBITORY AND OSCILLATORY PHENOMENA CAUSED BY IODIDES DURING THE ELECTRODISSOLUTION OF COBALT IN SULFURIC-ACID-SOLUTIONS - COMPARISON WITH THE EFFECT OF OTHER HALIDES

The electrodissolution of a cobalt rotating disc electrode in sulphuric acid solutions containing iodide ions was studied using both anodic and cathodic polarization measurements. As a result of the presence of iodide ions, significant changes were observed in the characteristic I-E polarization curves of the Co/1.58 M H2SO4 system. Thus, the adsorption of iodide ions results in strong inhibition of cobalt electrodissolution and in the appearance of current oscillations under potentiostatic conditions. The current oscillations are observed within a finite potential regime in the current plateau region. Both the inhibitory effect and the initiation of oscillatory phenomena depend on the concentration of iodide ions in the solution. The rotation rate of the cobalt disc mainly affects the oscillatory response, which was shown to be strongly associated with pitting corrosion phenomena. The effect of iodide ions on the polarization behaviour of cobalt in sulphuric acid solutions was compared with that of other halides (F-, Cl-, Br-).