Transitions from Parabolic to Linear Kinetics in Scaling of Metals

Abstract

A general rate equation is derived for a model of a barrier scale layer being formed by a diffusion process and simultaneously being depleted at a constant rate by a secondary process. The equation, derived to satisfy rate curves for sulflde scaling of iron in hydrogen sulfide, is shown to be applicable to the oxidation of aluminum and hafnium over ranges of conditions where two or three rate equations have been used previously to explain the experimental data. The validity of this equation emphasizes the importance of secondary processes, such as scale recrystallization, in determining the over‐all rate of high‐temperature corrosion reactions.