THE INFLUENCE OF DIFFERENT CATIONS ON THE ELECTROCHEMICAL AND ELLIPSOMETRIC BEHAVIOR OF IRON IN ALKALINE MEDIA

The influence of Li+, Na+, K+, Cs+, NH4+, Ca2+ and Ba2+ ions on the electrochemical and ellipsometric behaviour of Fe in alkaline solutions has been studied at 25-degrees-C. On the basis of a duplex layer structure for the anodic layer, the results show only a small influence of the nature of the cations in those process concerning the inner barrier layer specifically. Otherwise, there is a remarkable influence of the solution constituents on the growth and reactions at the outer porous portion of the anodic layer. In this case, the influence of cations can be described in terms of a specific adsorption at the outer plane of the inner barrier layer, a cation size effect and a coprecipitation effect. The relative contribution of each effect depends on both the charge and the size of cations in solution.