High Temperature Oxidation of Fe-Si Alloys in Ar-H₂O Atmospheres

Abstract

The oxidation of Fe-(1.5, 3%)Si alloys at 1000-1400 K has been investigated in Ar-(1, 10%)H₂O atmosphere using metallographic and electron probe microanalysis techniques.
The scale layers developed consisted in general of the external, the internal and the subscale. Oxides phases in each scale layer were identified as the mixtures of FeO, Fe₂O₃, and small amount of Fe₃O₄, the mixtures of FeO and Fe₂SiO₄, and the mixtures of Fe₂SiO₄ and SiO₂ respectively.
With increase in Si content in the alloys the rate of the total oxidation decreased significantly at 1 200-1 300 K. The oxidation kinetics of Fe-3%Si alloy and Fe-1.5%Si alloy were irregular and regular with each temperature, respectively. The latter was obeyed a parabolic rate law. The apparent activation energies for the growths of the internal scale and the subscale of Fe-1.5%Si alloy were estimated to be 123-132kJ/mol and 119-156 kJ/mol, respectively. The rate determining diffusion element for these scale growths was considered to be Fe in FeO in the internal scale and /or in the external scale.