利用急冷旋鑄及真空熱壓製備β-Zn4Sb3 奈米/微 米晶塊材之熱電性質探討;The characterization of thermal electric properties for the nano/micro-grain β-Zn4Sb3 fabricated by the combination of melt spinning and vacuum hot pressing

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题名:	利用急冷旋鑄及真空熱壓製備β-Zn4Sb3 奈米/微米晶塊材之熱電性質探討;The characterization of thermal electric properties for the nano/micro-grain β-Zn4Sb3 fabricated by the combination of melt spinning and vacuum hot pressing
作者:	顏潤賢;Yen,Jun-hsien
贡献者:	機械工程學系
关键词:	熱電;Zn4Sb3;急冷旋鑄法;thermal electrical;Zn4Sb3;melt spinning
日期:	2014-07-21
上传时间:	2014-10-15 17:18:35 (UTC+8)
出版者:	國立中央大學
摘要:	β-Zn4Sb3是一種具有成本低廉及易製備等優點的熱電材料，同時也是在350~400℃溫度區間內熱電性能最佳的熱電材料，有文獻指出其zT值在400℃時可高達1.37。但由於Zn-Sb二元合金在Zn含量35~45wt%相變化較為複雜，當微量調整成分配比就會產生其他介金屬相，傳統製備方式是以熔融擴散法持溫一段時間後水淬，利用急速冷卻方式維持元素比例並避免偏析，但是此種製程製備出的塊材會因熱應力而產生大量裂縫，導致機械性質不佳，因此，後續有研究學者嘗試利用粉末冶金的方式，將原料磨成粉末再經燒結獲得具有較佳機械性質的塊材。現今主流提高熱電材料的熱電性能的方式主要有兩種，摻雜及結構奈米化，本研究即是以結構奈米化作為探討方向。本研究中利用急冷旋鑄法(線速度20與30 m/s)製備具有奈米晶的β-Zn4Sb3薄帶，將其研磨成粉末後與熔融法製備的微米晶粉體互相混合並以真空熱壓法燒結成塊材。期望藉由晶粒細化效果提高材料的Seebeck係數，由於奈米/微米複合結構會造成長波聲子散射而降低材料的晶格導熱率，進而提高其zT值。研究結果顯示奈米/微米複合結構熱壓塊材的熱傳導係數會因熱擴散係數下降而降低，其中以摻雜30 wt% 急冷旋鑄粉體的熱壓塊材在兩組摻雜粉體中都表現出最低的熱傳導係數(30 m/s30%：8.00 mW/cmK，20 m/s30%：7.37 mW/cmK)，但其數值和完全由急冷旋鑄粉體製備的熱壓塊材相近(30m/s：7.64 mW/cmK，20m/s：7.60 mW/cmK)；摻雜粉體的塊材其zT值並沒有高於完全由急冷旋鑄薄帶的製備成的熱壓塊材，急冷旋鑄薄帶熱壓塊材有最高的zT值，20 m/s熱壓塊材在350℃時為0.97，30 m/s熱壓塊材則為1.06較於熔融粉體熱壓塊材的0.85。 ;The thermoelectric(TE) material β- Zn4Sb3 has the best performance during 350~400℃. Its advantages include cheap and simply fabrication. Some research indicated that its zT value can reach 1.37 at 400℃[2]. However, Zn-Sb phase diagram shows complex phase transformation as Zn content is 35~45 wt%. In other words, it will produce other phase if composition had shift. Therefore, traditional manufacture method using melt diffusion and quenching to prevent segregation. But quenching process always results in forming many crack and crack inside the bulk β-Zn4Sb3 due to thermal chock, and then degraded mechanical properties. To resolve this problem, powder metallurgy process was selected to be the solution. In recent, doping and nanostructure is the major way to enhance TE performance. In this study, we select nanostructure as direction. We use two methods to make β-Zn4Sb3 powder. One is melt spinning process(20、30 m/s), which belong to one kind of rapid solidification process(RSP), to make β-Zn4Sb3 ribbon with has nano-grain. The other is melt diffusion, can make bulk β-Zn4Sb3 with large grain micrometer to nanometer. The RSP ribbons and melt diffused bulk material were grinded into powders of particle size <76 μm .Then mix these two kind powders and hot compress (HP) to make bulk samples. We wish this hybrid structure can increase the phonon scattering and decreasing the lattice thermal conductivity and then enhance zT value. The results proved that nano/micro grained structure can decrease thermal conductivity, those HP bulk sample composed of 30 wt% RSP powder and 70 wt% bulk powder have the lowest thermal conductivity(30m/s30%：8.00mW/cmK，20m/s30%：7.37：mW/cmK) among all of the TE samples in this study. However HP bulk sample composed of 100% RSP powder have similar thermal conductivity(30m/s：7.64 mW/cmK，20m/s：7.60 mW/cmK), and the zT value of RSP HP bulk sample are higher than the others. At 350℃, zT value of 30 m/s RSP HP bulk sample is 1.06；20 m/s RSP HP bulk sample is 0.97, compare the bulk HP ingot (0.85), its zT value shows significant improving.
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