Abstract
Higher manganese silicides (HMS) are attractive alternative materials for high-temperature thermoelectric applications. One of the main factors that determine the sustainability of thermoelectric materials is their sufficient oxidation resistance in the desired temperatures and the ability to form oxides that impede the oxidation propagation. In the current work, the oxidation process and high-temperature oxidation resistance of HMS powder, which is innovatively synthesized by the economic and ecological method of pack cementation, are presented in a detailed study for the first time. The oxides developed during the oxidation in air are examined up to 1473 K, along with the thermal stability of HMS powder at cyclic procedures between 298 and 823 K. Additionally, the oxidation kinetics are investigated by focusing on temperatures in the range of interest for thermoelectric applications (723–793 K). The thermal analysis tests were conducted by using thermogravimetry. X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were employed for the material characterization. HMS powder demonstrated remarkable oxidation resistance up to at least 823 K with a limited mass increase of ~0.7% maximum, and a tendency to approach a stable state during the cyclic procedure. The oxidation reaction at 723–793 K was found to be more properly described by the Mampel chemical reaction model. The oxidation and thermal decomposition products detected at different temperature region include MnSi, Si, SiOx (x<2), SiO2, Mn2O3, Mn3O4 and MnSiO3. HMS powder synthesized by pack cementation exhibited sufficiently good resistance to oxidation and is promising for the high-temperature thermoelectric applications up to at least 823 K.
Published Version
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