The Role of Sulfides in Iron Activation in Chloride-Containing Solutions

摘要

The mechanism of iron activation in sulfide-containing solutions was studied. It was shown that sulfide didnot induce the activation of a prepassivated electrode in solutionsfree of chloride, however, a significant reduction of the pittingpotential occurs in the presence of chloride. The effect wasassociated with sulfide salt layer formation over activated sitesduring metastable pit growth, which prevented their repassivation.Due to a low-solubility product, ferrous sulfide can precipitateon iron surfaces at a much lower ferrous ion concentrationcompared to ferrous chloride. Hence, the transition frommetastable to stable pit growth could be expected at much lowerpit growth current densities and as a result at potentials wellbelow the breakdown potential as measured in chloride solutions.