Chromium Oxide Scale Growth on Iron-Chromium Alloys

The oxidation of Fe‐28% Cr in oxygen at 800°–1200°C has been studied in detail by thermogravimetric methods, metallography, and electron probe microanalysis. The oxidation rate is critically related to the surface finish and alloy purity but not significantly to variations in specimen size or geometry. Uniform single‐layered scales, consisting of containing a low concentration of dissolved iron, are produced. The oxidation rate shows minor negative deviations from a parabolic law, with an activation energy of 36 ± 6 kcal mole−1 for the over‐all diffusion‐controlled process. The deviations from a parabolic law are discussed in light of general oxidation theory and the self‐diffusion coefficients of ions in the scales are derived.