PARTICULAR FEATURES OF THE DEPASSIVATION OF NICKEL-ALLOYS IN NEUTRAL SOLUTIONS

The effect of the chemical nature of dissolved anions on the local depassivation of Fe-Ni alloys (0, 3, 5, 10, 20, 40, 60, and 80% Ni) was studied. It was shown that pitting on alloy phases may be regarded as that occurring on pseudo-pure alloy components with changed free energies. A definite pitting potential, epsilon(pit), which corresponds to each alloy phase, characterizes the sensitivity of the particular phase to the anionic composition of the electrolyte. The applicability of the heterogeneous complex formation concept for a quantitative description of the dependence of epsilon(pit) on the nucleophilicity of activators has been considered. Relations between epsilon(pit) and the hydrophobic and electronic parameters of the electrolyte anions were obtained. The effect of the nature of alloying components on the corrosion properties of alloys and on the slopes in the dependences of pitting overvoltage on the hydrophobicity of activators was discussed.