Abstract
Effect of Si and temperature on an initial stage of oxidation of Fe-Si (01.5 mass%) alloys in air was investigated for up to 150s at temperatures between 1323 and 1473K. Iron and the Fe-0.1Si alloy formed a triplex oxide layer structure of FeO (Fe3O4 included)/Fe3O4/Fe2O3, obeying a parabolic rate law and the temperature dependence of the parabolic rate constants yield activation energies of 101 and 156 kJ/mol for Fe and an Fe-0.1%Si alloy, respectively. The alloys containing 1.0 and 1.5 Si showed very slow oxidation below 1373K due to a formation of duplex Fe2O3 and SiO2 layers. These alloys oxidized faster, obeying a linear rate law owing to liquid Fe2SiO4 formation in the triplexlayer structure of FeO (Fe3O4 included)/Fe3O4/Fe2O3 at 1473K. At temperatures of 1373 and 1423K the alloys containing 0.4, 0.5, and 1.0 Si oxidized slowly during initial periods and then the oxidation rate increased rapidly due to liquid Fe2SiO4 formation. Measurements of sample temperatures showed that this is due to over-heating of the sample by the rapid oxidation. The composite FeO and Fe3O4 layer between the FeO and Fe3O4 layers was suppressed in the Fe and Fe-low Si alloys, when oxidized at temperatures below 1173K, while it appeared even in rapidly quenched samples oxidized above 1273K..
