Toward a Quantitative Understanding of the Electric Field in Thermal Metal Oxidation and a Self-Consistent Wagner Theory.
The electric field in the growing oxide film is important to the kinetics and mechanism of metal oxidation. However, understanding of the essential characteristics of the electric field during oxidation remains insufficient. A special-case analytical model is presented that provides a unified understanding for the electric field from the viewpoints of kinetics and thermodynamics. More general cases are studied by computer simulations that show similar characteristics in the electric field. In particular, simulations indicate that in many situations, the electrostatic potential drop across the bulk oxide is limited to ∼kBT/e, which means that the total electrostatic potential drop across the oxide film, if on the order of 1 V by rough estimation, should have contributions mostly from the electrified interfaces. Finally, regarding the Gibbs-Duhem relation, the commonly used isobaric assumption for the diffusing species is refuted. The results contained herein also provide a self-consistent understanding of Wagner's oxidation theory.
National Energy Technology Laboratory, 1450 Queen Avenue Southwest, Albany, Oregon 97321, United States.
Tian-Le
TL
Cheng
National Energy Technology Laboratory, 1450 Queen Avenue Southwest, Albany, Oregon 97321, United States.
You-Hai
YH
Wen
Gibbs−Duhem relations; Wagner theory; electric double layer; high-temperature oxidation; ion transport; local equilibrium; phase-field modeling