ANODIC BEHAVIOR OF INDIUM IN SODIUM-CHLORIDE SOLUTIONS

Passive film growth, electrodissolution and pitting corrosion of indium electrodes in NaCl solutions in the pH range 2-12.6 were studied using potentiostatic and potentiodynamic techniques complemented with SEM. In the pH range between 10.5 and 12.6 the oxide formation should involve a mixed control, a surface reaction plus a diffusion process. On decreasing pH the process becomes more complex due to the formation of In(I). The effect of chloride ions upon the active and passive behaviour of indium has been determined. Chloride ions in neutral and alkaline solutions produce pitting at potential values more positive than those of the active-passive transition. Localized corrosion appears to be under a competitive surface mechanism involving the formation of the passive film and the nucleation and growth of an indium chloride salt layer.