Direct thermal-to-electric energy conversion material consisting of environmentally-benign Mg 2 Si synthesized using was
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1218-Z05-17
Direct thermal-to-electric energy conversion material consisting of environmentally-benign Mg2Si synthesized using waste Si sludge and recycled Mg alloy Yasuhiko Honda1, Tsutomu Iida1, Tatsuya Sakamoto1, ShiroSakuragi2, Yutaka Taguchi2, Yohiko Mito3, Takashi Nemoto4, Tadao Nakajima4, Hirohisa Taguchi1, Keishi Nishio1 and Yoshifumi Takanashi1 1
Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan 2 Union Material Inc., 1640 Oshido-jyoudai, Tone-machi, Ibaraki 300-1602, Japan 3 Showa KDE Co.,Ltd., 5-17-14 Nishiikebukuro Toshima-ku, Tokyo 171-0021, Japan 4 Nippon Thermostat Co., Ltd., 6-59-2 Nakazato, Kiyose-shi, Tokyo 204-0003, Japan ABSTRACT Mg2Si was fabricated using Si sludge and recycled Mg alloys of the Mg-Al-Zn-Mn system. Its thermoelectric properties, such as the Seebeck coefficient, electrical conductivity and thermal conductivity, were measured, and then a dimensionless figure-of-merit, ZT, was estimated over the temperature range from 300 to 860 K. The actual output power measurements were made using specimens that were equipped with monobloc-sintered Ni electrodes under a temperature gradient ∆T ranging from 100 to 500 K. The ZT values for the samples fabricated from reused-Si and recycled Mg-alloys were about 0.6 at 860 K, presenting no notable difference compared with specimens fabricated from pure Si and Mg sources. The observed maximum output power for a sample size of 2x2x10 mm3 was 35 mW at ∆T = 500 K, where the sample was initiated from a reused Si source with 2 at% of Al doping. INTRODUCTION Mg2Si has been identified as a promising advanced thermoelectric material operating in the temperature range from 500 to 800 K. [1-8] Mg2Si exhibits many promising attributes, such as the abundance of its constituent elements in the earth’s crust and the non-toxicity of its processing by-products, resulting in ‘freedom from care’ regarding prospective extended restrictions on hazardous substances. As a target for practical use, ZT values that exceed unity are required, which would yield about 10% conversion efficiencies. So far, we have succeeded in identifying Mg2Si, for which ZT = 1.08. [9] In order to realize thermoelectric devices that are based on Mg2Si, together with improvements in its thermoelectric properties, cost reductions in its source materials and manufacturing processes are also necessary. Mg2Si has now been synthesized by using waste Si sludge. Si, which is a component of Mg2Si, is used as a substrate material for electronic devices, and its industrial scale of usage is huge. However, about 70% of a Si ingot is discarded in the process of creating a product. The Si sludge that is a by-product of the slicing and polishing processes is partially reused, but most is discharged as an industrial waste. The use of Si sludge as a source material for Mg2Si could be an effective means of lowering its production cost, with the additional benefit of reducing industrial waste. We have also attempted to synthesize Mg2Si usin
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