Se-Hun Chang, Makoto Nanko, Koji Matsumaru, Kozo Ishizaki and Masatoshi Takeda
Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188
β-FeSi2, which is one of the thermoelectric materials, has been more attractive in high-temperature range because of its low cost of raw materials. Oxidation resistance of sintered β-FeSi2 was investigated at temperatures ranging from 1073 to 1223 K in air. Fully densified and porous β-FeSi2 samples were fabricated by using the pulsed electric current sintering method. They were annealed at 1173 K for 5d to obtain β-FeSi2 phase. Microstructure of oxidized sample was observed by scanning electron microscopy with energy dispersion X-ray spectroscopy. Phase identification of samples oxidized was carried out by X-ray diffraction. Oxide layer, which is most likely an amorphous SiO2, was formed on β-FeSi2 samples after oxidation. Growth of the oxide layer obeyed a parabolic law. Growth rate of the oxide layer on sintered β-FeSi2 was comparable to that of Si. Granular ε-FeSi was developed below the oxide layer as a result of oxidation of β-FeSi2. Grain boundary oxidation was not observed. Formation of cracks in the SiO2 layer and β-FeSi2 was not observed even in on the porous samples. Oxidation resistance of sintered β-FeSi2 was excellent for high-temperature thermoelectric applications.
β-FeSi2, ε-FeSi, SiO2, oxidation layer, oxidation resistance, parabolic rate constant
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