Impact of some inorganic anions on the corrosion of nickel in a solution containing Na2SO4 and NaClO4

Abstract

Potentiodynamic study was carried out on nickel in Na2SO4 solution in the presence of ClO4–, WO42–, MoO42–, NO2– and NO3– ions. The anodic excursion spans of the metal nickel in a solution of Na2SO4 are marked by the appearance of clearly defined anodic peak, passive region, and transpassive shoulder. According to the data, the anodic peak current density (IPAI) rise from 1.82 to 8.12 mA cm–2 as the concentration of the Na2SO4 solution rises from 0.2 to 1.0 M. It is clear that as scan rate increases, the IPAI rises reaching to 11.8 mA cm–2. The apparent activation energy of nickel corrosion in Na2SO4 is 33.25 kJ mol–1. ClO4– anion addition speeds up nickel’s active dissolution, as well tends to break down the passive layer, and causes pitting penetration. It was found that, the pitting potential (Epit) of nickel in solutions containing the two anions ClO4– and SO42– shifts to the positive direction by addition of WO42–, MoO42–, NO2– anions and shifts to the negative direction by addition NO3- anion. Epit increased by 0.67, 0.37 and 0.15 V in the presence of WO42–, MoO42– and NO2–, respectively. WO42– > MoO42– > NO2– was the order in which the inhibitors were most effective.