Fe-低Si合金の高温初期酸化に対する温度とSi濃度の影響

抄録

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..