Investigation of Mg 2 Si formation from Si and Mg by using spark plasma sintering synthesis
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Investigation of Mg2Si formation from Si and Mg by using spark plasma sintering synthesis Kota Sunohara1, Koya Arai1, Tomoyuki Nakamura1,2, Kenjiro Fujimoto3, Yuki Yamaguchi3, Tsutomu Iida1 and Keishi Nishio1 1
Department of Materials Science and Technology, Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan 2 SWCC Showa Cable Systems Co., LTD. 4-1-1 Minami-Hashimoto Chuo-Ku Sagamihara, Kanagawa, Japan 3 Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan Abstract In this study, we fabricated Mg2Si from metal Mg and Si with different particle sizes (425 300, 300 - 180, and 75 μm or less) using spark plasma sintering (SPS) equipment. Additionally, the Mg2Si formation was investigated. A sieved Si powder was mixed with metal Mg powder in an inert gas (Ar) atmosphere. The mixture was placed in a graphite die while still in an Ar atmosphere and subjected to SPS at 923 K and 1113 K. The obtained sintering bodies were Mg2Si particles with a size of about 5 μm. Then, the sintered bodies were evaluated by X-ray diffraction (XRD). As a result, it was confirmed that generation of Mg2Si increased with decreasing Si particle size. Introduction As thermoelectric material, magnesium silicide (Mg2Si) is a less toxic and comparatively abundant raw material resource compared to other TE materials. Generally, Mg2Si has been used as n-type thermoelectric material that operates in a temperature range from 500 to 800 K [1-5]. Compared to other thermoelectric materials, Mg2Si has many benefits such as being non-poisonous, light, and abundant. Commonly, Mg2Si is synthesized by all-molten synthesis or solid-state reaction [1-5]. However, these synthesis methods have several problems. For example, in the all-molten synthesis method, the melting point of Mg2Si is very close to the boiling point of Mg, synthesizing Mg2Si causes incorporation of impurities, and composition deviation occurs. In the solid-state reaction method and mechanical alloying method, high purity Mg2Si is difficult to obtain. Kajikawa et al. [6] reported that high purity Mg2Si could be obtained easily without MgO by using the spark plasma sintering (SPS) method in a lower temperature range heat treatment of shorter duration compared to the all-molten synthesis method, solid-state reaction method, and mechanical alloying method. However, the formation of Mg2Si has not been
discussed in detail. In this paper, we investigated and discussed the formation of Mg2Si from metal Mg and Si. Experiment Magnesium silicide samples were synthesized from metal Mg and Si powder classified into four particle sizes (300 - 425 μm, 180 - 300 μm, 75 μm or less, and about 5 μm) using SPS equipment. A mixture powder of Si and Mg was placed in a graphite die under Ar atmosphere, and two-step heat treatment was performed. The first step was for fabrication of the Mg2Si, and the second step was densification of the Mg2Si bulk. During SPS, the powder mix was placed into a graphite die in Ar atmospher
