Tatsuo Maekawa1 and Nobuo Nakajima1
1Engineering and Research Laboratory, Mitsubishi Atomic Power Industries Incorporated, Saitama
Anodic behaviors of pure iron and its oxides in acid and alkaline solutions were investigated to clarify the significance of passivation potential and other oxidizing potential of iron. The anodic polarization curve of pure iron indicated four current peaks at the potentials of about -0.1, 0.3, 0.6 and 1.4 V in 1 N H2SO4, and -0.9, -0.8, -0.4 and 0∼0.4 V(vs S.C.E.) in 1 N KOH, respectively. The anodic polarization curves of FeO1.05, FeO1.1 and Fe3O4 indicated three, two and one peaks, respectively. And the potentials of the peaks of the oxides agreed with those of pure iron. From these anodic behaviors of oxides, it was suggested that the four potentials at the current peaks in the potential-current curve show four redox potentials of Fe/FeO1.05, FeO1.05/FeO1.1, FeO1.1/Fe3O4, and Fe3O4/Fe2O3. These potentials were also confirmed from the measurements of potential decay curves of iron and its oxides. It was concluded that the passivation potential of iron in 1 N H2SO4 solution corresponded with the redox potential of FeO1.05/FeO1.1, where as the passivation potential in 1 N KOH solution corresponded with the redox potential of Fe/FeO1.05 or FeO1.05/FeO1.1.
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