Effect of EDTA on the Cathodic Reduction of Oxide Films on Iron in Sodium Hydroxide Solution

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Abstract
Simultaneous electrochemical and ellipsometric investigations of the behavior of iron in solution (pH 12) with and without the addition of EDTA showed that EDTA did not affect the passive film formation but drastically enhanced cathodic reduction of the passive film. Cathodic reduction of the passive film in EDTA‐free resulted in the formation of an unreducible porous layer on the iron surface. This layer grew progressively in thickness when periodic passivation‐reduction cycles were applied but did not influence the passive film formation. The cathodically formed layer probably consisted of some kind of iron hydroxide and elemental iron. In contrast, when EDTA was added to , the cathodic reduction and removal of the passive film was complete and occurred very rapidly. Cathodic polarization of passive iron carried out potentiostatically in the presence of EDTA was found to provide reliable data on the charge consumed for reduction of the passive film.
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