An Interpretation of the Significance of the Potentials of Passive Iron

The steady‐state value of the passive potential of iron in anodic inhibitors forming hydrated oxide corrosion products with ferrous ions becomes less noble with increasing p H and with increasing inhibitor concentration. Values of passive potentials in phosphate solutions become more noble with increasing p H. The effect of surface pre‐ treatment and of the addition of small amounts of chloride on the passive potentials is more pronounced at high p H values. Increasing the oxygen concentration of the solutions results in a shift in the steady‐state values of the passive potentials in the more noble direction. An explanation of these effects, based on the oxide film theory of anodic inhibition, is advanced.