Action of inhibitors as oxide stabilizers

From the viewpoint of oxide stabilizer, the action of inhibitor was studied by measuring the corrosion potential and corrosion rate of carbon steel in tap waters containing various kinds of inhibitors. According to corrosion potentials (V vs. SSE) inhibitors were classified into three categories; types A: -0.1∼0.1 V, type B: -0.3∼-0.2 V, and type C: -0.7∼-0.5 V. Type A acted as a passivator, keeping the most noble potential which meant γ-Fe2O3 stable. The corrosion potential of type B corresponded to that of the electrode covered with FeO3O4 film. Type C showed less noble potential at first, but the potential was shifted to the noble direction to be brought close to that of type B gradually. This behavior was considered because of enhancing the inhibitive function of the inner oxide film with time. It is concluded that the actions of inhibitors is to stabilize the oxide film on metal.