Alteration of CoO Wafers in an Oxygen Chemical Potential Gradient

Abstract

The Wagner Oxidation Theory, and its later developments, allow the parabolic rate constant to be predicted from fundamental transport coefficients and point defect thermodynamics, provided that the oxidation reaction is controlled by well-understood lattice diffusion mechanisms. In many practical cases, however, diffusion along fast paths such as grain boundaries is dominant and the actual oxidation rate is strongly influenced by the microstructure of the oxide scale. Moreover, the oxide microstructure is not static, but rather continuously evolves as new oxide grows and as the existing oxide re-structures. The growth mechanism depends upon the oxide microstructure, while the oxide microstructure is determined by the details of the growth mechanism. This creates what is essentially a feedback loop system in which the scale microstructure both influences and is influenced by the growth mechanism. A description of this loop system seems to be necessary to develop a richer understanding of oxidation.