ICT2014 Abstracts

Mg₂Si is an eco-friendly thermoelectric semiconductor whose constituted elements of both Mg and Si are non-toxic and exist in abundance on the earth. In this study, we attempted to control the thermal conductivity by grain refining in order to improve the thermoelectric performance. Three kinds of Si powders, i.e. the commercial coarse powder (≤75 μm), the commercial fine powder (≤5 μm) and the ground powder that was made by milling the commercial coarse powder for 30 min using planetary ball mill, were prepared. The Mg and Si powders were weighed with Mg/Si mole ratio of 67/33, and mixed with Al powder of 0.1 at.% in an argon atmosphere. Three kinds of Mg₂Si-based compounds were synthesized using three different Si powders by a liquid-solid phase reaction method at 680 ºC for 1 h in an argon gas flow. The compound synthesized using the commercial coarse Si powder was ground for 30 min using the planetary ball mill. By adding the ground Mg₂Si powder, four kinds of prepared powders were sintered by pulse discharge sintering method under same conditions, i.e. at 730 ºC for 30 min under compaction pressure of 30 MPa in a vacuum. The sintered samples made from commercial fine Si powder, ground Si powder and ground Mg₂Si powder had the grain-refined microstructure. Especially, the sintered sample made from ground Mg₂Si powder was effective for grain refining and for reduction of thermal conductivity, and had the best thermoelectric performance of ZT=1.15 at 600 ºC.