The effect of Si concentration and temperature on initial stage of high temperature oxidation of Fe-low Si alloys

Effect of Si and temperature an an initial stage of oxidation of Fe-Si (0 s imilar to 1.5 mass%) alloys in air was investigated for up to 150 s at temp eratures between 1323 and 1473K. Iron and the Fe-0.1Si alloy formed a tripl e oxide layer structure of FeO (Fe3O4 included)/Fe3O4/Fe2O3, obeying a para bolic rate law and the temperature dependence of the parabolic rate constan ts 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. T hese alloys oxidized faster, obeying a linear rate law owing to liquid Fe2S iO4 formation in the triplex-layer structure of FeO (Fe3O4 includcd)/Fe3O4/ Fe2O3 at 1473K. At temperatures of 1373 anti 1423K the alloys containing 0. 4, 0.5, and 1.0 Si oxidized slowly during initial periods and then the oxid ation rate increased rapidly due to liquid Fe2SiO4 formation, Measurements of sample temperatures showed that this is due to over-heating of the sampl e 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 oxidi zed at temperatures below 1173K, while it appeared even in rapidly quenched samples oxidized above 1273K.