Morphological aspects of Ni corrosion in the presence of nitrite

The evolution of morphology during the corrosion of Ni in nitrite-containing acid phosphate solution was investigated by atomic force microscopy and interpreted in light of electrochemical responses. The localized dissolution and passivation processes on Ni surface are close related with a competition between adsorbed OH− and N-species with a potential dependent surface coverage. Thus, depending on their coverage fractions, different morphologies arise. The dynamics of the dissolving interface at the corrosion potential was analyzed as a function of the root mean square roughness, obtained from ex-situ AFM images, by means of the scaling dynamic theory. At low nitrite concentrations, the competition of adsorbed species leads to the appearance of rough surface with protrusions and cavities as a consequence of the localized dissolution and cathodic reaction regions. With increasing nitrite concentration, N-species adsorb preferentially displacing passivating species and the measured roughness reflects some micro-structural features related with the crystalline structure.