Kinetics of the α-Fe₂O₃ formation on Fe₃O₄ between 400 and 570°C studied by means of X-ray diffraction with grazing incidence

Summary

The formation of α-Fe₂O₃ on Fe₃O₄ during the oxidation of iron below 570°C occurs very slowly and the scales are so thin that they cannot be detected by microscopy. X-ray diffraction with grazing incidence, equipped with a high temperature device, allows an ‘in situ’ study of the α-Fe₂O₃ formation even the initial reactions. The formation of α-Fe₂O₃ was studied in isothermal experiments at 400, 450, 500 and 550°C. α-Fe₂O₃ could already be detected at the beginning of the experiments. The difference method, a numerical treatment for kinetic evaluation, yields curves showing the growth of the α-Fe₂O₃ layer. Fitting the parabolic time law to these curves yields the rate constants.