Inhibitors of passive corrosion – application of a new test with thin oxide films

A new method to test the inhibitors of passive corrosion is presented. Potentiodynamic i(ε)‐ and C(ε)‐curves are recorded in the system Au/Fe 2+ , inhibitor. The investigations of formation and reduction of the FeOOH‐layer, of gold oxide and the oxygen evolution allow estimations of the inhibition efficiency and mechanism. Some organic nitrogencompounds are tested. Pentylamine is ineffective for oxide surfaces, but benzimidazole and its derivates show inhibition effects. The capacity data can be evaluated using a condensor model of a connection in series of the oxide and the inhibitor layer. The detailed discussion shows that adsorption at the film surface is most probable. Such layers inhibite the transfer of hydrated ions, but reactions of water molecules are not influenced, e.g. oxygen evolution. The applicability of this method to other systems is discussed.