MA법에 의한 Mn-Si계 초미세 열전재료의 제조 및 평가
Fabrication and characterization of Mn-Si thermoelectric materials by mechanical alloying
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초록
반도성 MnSi1.73 화합물은 고온 특성이 우수하고 뛰어난 내산화성을 가진 열전재료로서 알려져 있다. 본 연구에서는 순 Mn 및 Si 분말재료를 출발 원료로 기계적 합금화법(MA)을 적용하여 MnSi1.73 화합물 합성을 실시하였다. MA 처리는 P-5 유성형 볼밀장치를 이용하여 Ar 중에서 행하였다. MA 분말재료의 X선 회절, 열분석 및 전자현미경 분석을 통하여 고상반응을 관찰하였다. MA 공정 중 Si의 손실을 고려하여 화학양론 조성에서 Si 양을 증가시켜 MnSi1.73 화합물 합성을 시도하였다. 그 결과 MnSi1.73 화합물 단상은 MnSi1.88 조성의 혼합 분말을 200시간 볼밀 처리함으로써 얻을 수 있었다. 또한 200시간 볼밀 처리에 의하여 제조된 MnSi1.73 화합물의 평균결정립 크기는 40 nm 임을 X 선 회절피크의 Hall plot으로부터 알 수 있었다.
Abstract
The semiconducting MnSi1.73 compound has been recognized as a thermoelectric material with excellent oxidation resistance and stable characteristics at elevated temperature. In the present work, we applied mechanical alloying (MA)technique to produce MnSi1.73 compound using a mixture of elemental manganese and silicon powders. The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The MA powders were characterized by the X-ray diffraction with Cu-Kα radiation, thermal analysis and scanning electron microscopy. Due to the observed larger loss of Si relative to Mn during mechanical alloying of MnSi1.73, the starting composition of a mixture Mn-Si was modified to MnSi1.83 and then MnSi1.88. The single MnSi1.73 phase has been obtained by mechanical alloying of MnSi1.88mixture powders for 200 hours. It is also found that the grain size of MnSi1.73 compound powders analyzed by Hall plot method is reduced to 40 nm after 200 hours of milling.
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