Atmospheric corrosion of iron in an SO 2-containing atmosphere with saturated humidity leads to the formation of Fe(OH) 3 which transforms to crystalline FeOOH with amorphous FeOOH as a transition product. In an aqueous 0.2 M Na 2SO 4 electrolyte FeOOH is reduced at least to Fe 3O 4, and α-FeOOH at the most negative potential. By air exposure Fe 3O 4 is not re-oxidized in any appreciable amount. Therefore, it is proposed to replace Fe 3O 4 by Fe(OH) 2 as the reduced state in the Evans model of atmospheric corrosion.
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