Journal of the Korean Crystal Growth and Crystal Technology (한국결정성장학회지)

The Korea Association of Crystal Growth (한국결정성장학회)
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Synthesis and characterization of Mg-Si thermoelectric compound subjected to mechanical alloying

기계적 합금화에 의한 Mg-Si계 열전화합물의 합성 및 평가

  • Lee, Chung-Hyo (Dept. of Advanced Materials Science and Engineering, Mokpo University)
  • 이충효 (목포대학교 신소재공학과)
  • Published : 2007.06.30
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Abstract

We have applied mechanical alloying (MA) to get $Mg_2Si$ thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of $Mg_2Si$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Mg_{66.7}Si_{33.3}$ MA samples ball-milled for $20{\sim}180\;hrs$ exhibit two broad exothermic heat releases around $220^{\circ}C$ and $570^{\circ}C$. On the other hand, MA sample ball-milled far 260 hrs exhibits only a sharp exothermic peak at $230^{\circ}C$ Single phase Mg2Si powder can be obtained by MA of $Mg_{66.7}Si_{33.3}$ mixture for 60 hours and subsequently heated up to $620^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $800{\sim}900^{\circ}C$ under 50 MPa. The shrinkage of sintering sample during SPS was significant at about $200^{\circ}C$. All compact bodies have a high relative density above 94% with metallic glare on the surface.

본 연구에서는 나노결정립의 $Mg_2Si$ 열전화합물을 제조하기 위하여 기계적 합금화(MA)를 적용하였다. 단상의 초미세 $Mg_2Si$ 열전화합물을 얻기 위하여 최적 볼밀조건 및 열처리 조건을 X선 회절분석과 시차주사 열량분석을 이용하여 조사하였다. $Mg_{66.7}Si_{33.3}$ 혼합분말을 $20{\sim}180$시간까지 볼밀 처리한 경우 모든 시료에서 $220^{\circ}C$ 및 $570^{\circ}C$ 근방에 broad한 발열 반응이 관찰되었다. 한편 $Mg_{66.7}Si_{33.3}$ 혼합분말을 260시간 동안 볼밀 처리한 경우 $230^{\circ}C$에 예리한 발열피크를 보였다. 단상의 $Mg_2Si$ 화합물은 $Mg_{66.7}Si_{33.3}$ 혼합분말을 60시간 동안 MA처리 후 $620^{\circ}C$까지 열처리함으로써 얻을 수 있었다. MA분말시료의 치밀화는 50MPa, $800{\sim}900^{\circ}C$에서 흑연다이를 사용하여 SPS 소결을 실시하였다. Mg-Si계 MA 분말시료의 SPS 소결시 수축은 $200^{\circ}C$ 근방에서 현저하게 관찰되었다. SPS법으로 고화된 성형체의 밀도측정 결과, 모든 시료에서 이론밀도의 94% 이상 금속광택을 나타내는 치밀한 소결체임을 알 수 있었다.

Keywords

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