Abstract
The oxidation of Cr and Fe‐Cr alloys which form 
scales involves at least two processes: (i) the solid‐state, diffusive transport of ionic species, with parabolic kinetics, and (ii) the oxidation of 
to a volatile species, probably 
, with linear kinetics. The effects of this second reaction cannot be neglected, either in interpretation of short‐term oxidation results, or in predicting long‐term oxidation behavior. In this paper equations are derived which describe the oxidation behavior of a system in which both diffusive and gas/oxide interface processes occur simultaneously. According to the model, the oxide scale grows to a limiting thickness which is determined by the parabolic rate constant and the surface‐reaction rate constant; as the limiting thickness is approached, a transition from parabolic to linear kinetics takes place. The model is applied to the oxidation of Cr and Fe‐Cr alloys, and good agreement with experimental data is found.