THE COMPARATIVE ROLES OF OXYGEN AND INHIBITORS IN THE PASSIVATION OF IRON. I. NON-OXIDIZING INHIBITORS

Conflicting views are held as to the respective roles of oxidizing agent and inhibitor in the passivation of iron in aerated solutions of certain inhibitors. In the first paper of this series, experiments with inhibitors having no oxidizing properties are presented. It was found that passivation at a noble potential may be achieved under conditions in which oxygen is necessarily the oxidizing agent, though without the inhibitor it leads to corrosion. It was found also that the passive potential is destroyed by low concentrations of sulfate ions, and thus exhibits the same behavior as that previously observed with oxidizing inhibitors. By means of cathodic polarization measurements, the magnitude of the cathodic current density in the reduction of oxygen on passive iron at potentials above or somewhat below the Flade potential was determined. It was found, further, that addition of sulfate ions in low concentration sensitizes the system to activation under cathodic polarization. The results are interpreted as further evidence that the inhibitor's essential function is related to its adsorption, in competition with other ions or molecules.