Synthesis of higher manganese silicides by pack cementation

Higher Manganese Silicides (HMS), commonly referred to as MnSi1.7, have currently attracted great attention due to their potential use in high temperature thermoelectric applications. These compounds demonstrate attractive thermoelectric properties –with a maximum value of figure of merit ZT at least 0.7 for the undoped material –good thermal and chemical stability at high temperatures, low cost of the raw materials and environmental friendliness. A wide variety of techniques has been applied for the fabrication of MnSi1.7, however, many of these are facing problems. The current study focuses on the synthesis of MnSi1.7 powder via an innovative way, using the pack cementation process which is economical, simple and ecological. The effect of main experimental parameters –e.g. synthesis temperature, composition of the initial pack powder mixture –on the formation and properties of the silicide powder were studied. The structure and phase identification of the samples were performed by X-Ray diffraction analysis (XRD), while the morphology and the chemical composition were determined by Scanning Electron Microscopy (SEM) equipped with an EDS analyzer. Additionally, in order to test the oxidation resistance selected powders were exposed to high-temperature air environment using a thermogravimetric setup (TGA). The optimized MnSi1.7 powder was successfully formed free of oxides and secondary phases, and exhibited remarkable oxidation resistance.