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^-, WO₄^2-, MoO₄^2-, 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 (I_PAI) 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 I_PAI 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 (E_pit) of nickel in solutions containing the two anions ClO₄^- and SO₄^2- shifts to the positive direction by addition of WO₄^2-, MoO₄^2-, NO₂^- anions and shifts to the negative direction by addition NO₃^- anion. E_pit increased by 0.67, 0.37 and 0.15 V in the presence of WO₄^2-, MoO₄^2- and NO₂^-, respectively. WO₄^2- > MoO₄^2- > NO₂^- was the order in which the inhibitors were most effective.