Study of stress effects in the oxidation of phosphated α-iron: in situ measurement by diffraction of synchrotron radiation

In the present work the development of strains in the iron-oxide layers growing on phosphated α-Fe at 400 °C in artificial air at 1 atm was investigated by X-ray diffraction (XRD) of synchrotron radiation, both in situ during oxide growth and also at room temperature after cooling. This stress state may play an important role during the oxidation process, from the phases as well as from the kinetics point of view. The oxidation kinetics of α-Fe and phosphated α-Fe at 400 °C and the phases evolution during oxidation are first presented. Then a detailed study of the strains in the oxides layers is undertaken. Correlations between the stresses measurements and the successive parabolic oxidation stages for phosphated α-iron are established. It leads to a better understanding of the oxidation behaviour.