Oxidation kinetics of cobalt and cobalt—iron alloys at high temperatures

The oxidation kinetics for cobalt and two cobalt—iron alloys alloys, CoFe and CoFe₃, were determined between 1073 and 1280 K in 1 atm. of oxygen. The oxidation of cobalt and CoFe follows a parabolic law, while the oxidation of CoFe₃ is better described by a direct logarithmic law. The oxidation rates for the cobalt—iron alloys alloys are lower than those expected from combining oxidation kinetics of pure iron and pure cobalt, thus suggesting a significant cobalt enrichment occurs at the oxide surface. This cobalt enrichment is observed using energy dispersive analyses. The logarithmic kinetics of CoFe₃ during oxidation is discussed, and a model is proposed to explain this behavior.