Effect of oxygen partial pressure on oxidation of iron at 573K.

概要

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The oxidation of iron was investigated by Rutherford backscattering spectroscopy at 573 K under the oxygen partial pressure from 10-1 to 105 Pa for 324 h. In the first stage of oxidation, thickness of the oxide film reached the maximum around 1 Pa. In the second stage the oxidation obeyed the parabolic rate law. From 10-1 to 10-0.5 Pa the parabolic rate constant increased with increasing oxygen partial pressure due to the growth of magnetite, whereas from 1 to 100.5 Pa hematite covered magnetite but the parabolic rate constants were kept still high values possibly due to the presence of grain boundaries. Between 10 and 104.3 Pa the protective hematite coverage over magnetite kept the parabolic rate constants low regardless of oxygen partial pressure. At 105 Pa a sharp increase of the parabolic rate constant was observed due to the simultaneous growth of hematite and magnetite. The oxygen concentration in water for the inhibition of the corrosion may correspond to the oxygen partial pressure for the formation of protective film in gas phase around 573 K.
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