Abstract
Linear perturbation theory is used to analyze the stability of a moving planar alloy‐oxide interface when oxidation of a binary solid solution alloy leads to growth of a superficial metal conducting oxide scale. The transport equations for metal and oxygen in the alloy and oxide phases are analyzed under limiting approximations consistent with ternary diffusion theory. If oxygen diffusion in the alloy occurs predominantly down its own gradient the stability criterion for a planar interface is
This criterion becomes in the case of oxygen diffusion in the alloy occurring predominantly from its interaction with the metal gradient
In these expressions, 
, 
, and 
represent self‐diffusion coefficients, mole fractions, and molar volumes of the alloy and oxide phases denoted by superscript I and II , respectively. Asterisks on these parameters refer to values at a planar alloy‐oxide interface. A and O refer to the selectively oxidized metal component and oxygen. 
is the initial concentration of A, and 
is the Wagner interaction coefficient between oxygen and A in the alloy.