Kinetic evaluation of growing oxide scales studied by time and temperature resolved X-ray diffraction.

Time and temperature resolved X-ray diffraction was applied as an in situ method to the investigation of high-temperature corrosion. Series of diffraction patterns are recorded during the reaction yielding the peak widths, intensities and the lattice plane distances as a function of time or temperature. The corrosion products are identified in situ at each state of the corrosion process. An evaluation procedure was developed, which enables the determination of the kinetic parameters for each single corrosion product. The variation of the peak intensities is detected by means of a difference method. The resulting curves show the global changes as a function of time or temperature and describe the growth of the oxide scale. Taking into account the increasing absorption of the X-ray beam in this scale calculated curves were fitted to the measured data yielding the kinetic parameters. The temperature dependence of the oxidation rate constant, described by the Arrhenius relation, is obtaine d in one single experiment on linear heating.