The Kinetics of Anodic Oxidation of Iron in Neutral Solution

When passive iron is oxidized galvanostatically a potential arrest is observed in the initial region. Polarization curves obtained using the arrest potentials at different current densities lead to an equation of the form The value of β' decreases with increasing film thickness and is smaller than that observed in the steady state region. Cathodic reduction experiments showed that the ratio of iron in the outer layer of the film to charge passed is considerably smaller in the initial region than in the following steady growth region. It was concluded that in the initial region the charge passed was used in the formation of iron‐ion vacancy‐electron pairs and the transfer of oxygen from the solution to the outer layer of the oxide. The extent of this reaction depends on the film thickness in that the latter determines the distribution of the potential drops between the metal and the solution.