HIGH-TEMPERATURE CORROSION KINETICS BY A FAST X-RAY-DIFFRACTION METHOD APPLIED TO NICKEL

Temperature and time resolved X-ray diffraction was used as an in situ method, which allows the determination of kinetic data combined with the identification of the corrosion products. The performance of the method was demonstrated on the high temperature oxidation of nickel in isothermal and non-isothermal experiments. The kinetic parameters were obtained by means of the difference method. The resulting curves show the global changes as a function of time or temperature. These curves were calibrated to the microscopically measured end thickness of the oxide layer yielding the growth of the layer with time x(t) or with temperature x(T), respectively. Calculated curves were fitted to the measured data yielding the kinetic parameters. In the non-isothermal case the temperature dependence of the oxidation rate constant, described by the Arrhenius relation, is obtained in one single experiment.