Morris Cohen

The Anodic Oxidation of Iron in a Neutral Solution II . Effect of Ferrous Ion and pH on the Behavior of Passive Iron

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 pH 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.

The Effect of Oxygen on Inhibition of Corrosion by Nitrite

A study has been made of the effects of the concentration of dissolved oxygen and temperature on the rate of breakdown of sodium nitrite in the presence of steel, and on the rate of corrosion of the steel. It was found that, at any given temperature, an increase in concentration of oxygen decreased the amount of nitrite required for inhibition. At high temperatures and low oxygen concentrations it was found that although the rate of corrosion was appreciable the rate of nitrite breakdown was low. In some cases, a considerable time interval before the start of breakdown of nitrite was noted. It was concluded that the mechanism proposed previously for inhibition by nitrite was further substantiated by the evidence presented here.