The anodic behaviour of nickel in 0.5 M H2SO4 solutions in the presence of anions: SO2-4, Cl-, Br-, I-, NO-3

The anodic behaviour of Ni in 0.5 M H 2 SO 4 de-aerated solutions, in the presence of various concentrations of SO 2 - 4 , Cl-, Br, I - , NO - 3 anions have been studied by means of the potentiostatic polarisation curves. These anions influence in different modes the corrosion and passivation electrochemical parameters of nickel, depending of their nature and concentration. In certain concentrations, SO 2 - 4 , Br and I- ions had an inhibitor effect on the Ni corrosion in active state, determining the increase of the Tafel slope and significant decrease of the critical current density. Cl - and NO - 3 ions had an accelerating role of Ni corrosion in active state, determining the increase of the critical current densities the larger the concentration. All studied anions had unfavourable effect on the passive state at high concentrations, determining the increase of the passive current density versus fond solution. The presence of 0.05 M Cl - or 0.1 M Br in fond solution determined the development of the pitting corrosion. Ni did not present a passive state in solutions containing 0.1 M Cl- or I M Br. These different effects of the anions are explained by means of their adsorption properties, of the possibility to form stable complex compounds with a metal and of their its role in corrosion processes.