Kinetics of growing oxide layers studied by means of X-ray diffraction.

The growth of oxide scales on Ni at high temperatures was observed by means of X-ray diffraction using a diffractometer combined with a high temperature device for temperatures between 20 and 1700 degree Celsius. A procedure for a kinetic evaluation is described, which detects the increase of the oxide peaks during the experiment. The resulting curves were calibrated to the growth of the scale with time xsubm (t) or with temperature xsubm (T) respectively. Mathematical curves describing the absorption conditions in the growing layer and the expected time law of its growth were fitted to the measured data yielding the rate constants. In the non-isothermal case the temperature dependence of the oxidation rate constant, described by the Arrhenius relation, is obtained in only one experiment.