Initial stages of nickel passivation and dissolution in acidic sulfate solutions

Regularities of the electrochemical dissolution of freshly formed surface (FFS) of iron and nickel are similar as a whole, but exhibit a number of distinctions. At an oxidation stage Me0-Me+, a water molecule chemisorbs to form a surface complex with charge transfer; however, a mean fraction of transferred charge in the complex of nickel (0.8) is significantly higher than that of iron (0.5). In weakly acid sulfate solutions (pH 1.7–3.2), the iron FFS dissolution is predominantly inhibited by hydrogen atoms formed by the discharge of hydroxonium ions and adsorbed at the dissolution centers. On nickel at pH > 2.7, the inhibition is caused by the formation of adsorbed oxygen corresponding to more positive potentials in a range of active nickel dissolution.