The Passivation of Iron in the Presence of Pertechnetate and Chromate Ions

Experiments were carried out to determine whether reducible inorganic inhibitors passivate iron solely by their own cathodic reduction or have some additional role in the passivation process. Passivation was effected potentiostatically in pertechnetate and chromate solutions at potentials noble to the calculated reversible potential of the inhibitor couple under the conditions prevailing. It was found that the inhibitors reduce greatly both the critical current density and charge required for anodic passivation when they are not themselves reduced. It was shown also that neither of the inhibitors is capable of supplying more than a very small fraction of the current density required for passivation in the absence of the additional effect which arises, presumably, through adsorption of the inhibiting anions. The results show the inadequacy of the hypothesis that the oxidation-reduction properties of the inhibitor alone are sufficient to account for its passivating action. © 1966, The Electrochemical Society, Inc. All rights reserved.