Parabolic laws during high temperature oxidation: relations with the grain size and thickness of the oxide

A judicious and general procedure to calculate the parabolic constant which accounts for pure diffusion control, mixed diffusion-reaction control and a transient regime is examined. When diffusion is operative, deviations from the ideal parabolic growth laws occur during oxidation of metallic materials. One possibility considered consists in the evolution of the oxide grain size during oxidation which leads to a change in parabolic rate constant at least at the beginning of the oxidation. Moreover, in the case compact scales, the experimental oxide thickness can be smaller than the thickness calculated from thermogravimetric data in relation with a more or less pronounced anisotropic growth of the oxide.