The Anodic Oxidation of Iron in a Neutral Solution

The anodic polarization curve, the static passive potential, and the behavior of the decay of the polarized passive potential of iron were examined in neutral boric acid/borate solutions with and without Fe ++ ion addition. It was found that the passivation potential is a function of the [Fe ++ ] and p H and corresponds to the equilibrium potential of the reaction of . The polarized passive potential in the steady state is related to a pseudoequilibrium potential that corresponds to a higher defect concentration in the oxide surface and to a lower [Fe ++ ] at the oxide/solution interface. The potential gradient across the film appears to be very small. The decay of the polarized passive potential on open circuit is explained as due mainly to the change in the defect‐concentration and consequently of the film composition at the oxide/solution interface either by the outward migration of iron through the film or by the reaction with Fe ++ ion in solution when the latter had been added or supplied by a small amount of self‐corrosion.