Oxidation of Iron at Room Temperature

Abstract

Oxidation of (001), (011), (112)monocrystalline, and of large-grained and small-grained polycrystalline, pure Iron has been studied in laboratory air at room temperature at 44–46% relative humidity for 120 days by gravimetric methods, electron diffraction and electron microscopy. After the initial oxide growth, no significant oxidation occurred for about 20–30 days, when oxidation re-commenced slowly and became rapid, until after 90 days the rate became irregular and was associated with decreasing epitaxy. The rate of oxidation in decreasing order was(001), large grained, small grained, (011) and (112). Up to 70 days the outer layer was cubic Fe₃O₄ but after 90 days it was α-Fe₂O₃, probably with some γ-Fe₂O₃ and otherminor impurtties such as hydroxides. The influence of impurities on the oxide is emphasised by a weight loss of 5–7 % which occurred upon heating the specimens to 300° in vacuo after 120 days. γ-Fe₂O₃ and other minor impurities such as hydroxides. The influence of impurities on the oxide is emphasised by a weight loss of 5–7% which occurred upon heating the specimens to 300° in vacuo after 120 days.