"利用席貝克效應(Seebeck Effect)與皮爾特效應(Peltier Effect)直接實現電能 與熱能之間相互轉換的熱電技藝，長久以來就被視為一潛在的能源轉換技術，然 而由於轉換效率偏低，因此其應用僅限於軍事及太空上而無法普遍化，但隨著具 優異熱電性能的奈米熱電材料被成功開發後，熱電技術在未來的應用潛能開始受 到廣泛的重視。在不同型態的奈米熱電材料中，具複合材料型態的奈米熱電塊材 除具高熱電優值外，更可以低成本快速大量製造，故是目前最具潛力、可實用化 的熱電材料。然為更進一步提升熱電性能，在熱電材料中添加第二相奈米粒子使 其扮演聲子散射中心以降低熱傳導率的構思乃應運而生，在各種型態的添加物 中，非晶質合金是一符合PGEC (phonon-glass/electron-crystal)構想的材料，因此 將其添加入熱電材料中，預期可同時降低熱傳導率及提升電傳導率並藉此提高熱 電優值。但文獻調查發現利用此種途徑來增加熱電性能的研究至今仍無人進行， 因此實有必要對此構思展開調查以瞭解其可行性。 綜上所述，本研究之目的旨在探討利用應用高能量球磨及真空熱壓製程製備 出具非晶/奈米複合材料結構之熱電複合材料塊材的可行性。研究工作之進行是 先利用高能量球磨機製備出Ti50Cu28Ni15Sn7與Ni50Ta50兩種非晶質合金粉末，接著 將此兩種非晶質相粉末分別添加入鉍、碲、銻、硒之純元素混合粉末後，再以高 能量球磨機合成具非晶/ 奈米複合材料結構之Ti50Cu28Ni15Sn7/Bi2Te3 、 Ti50Cu28Ni15Sn7/(Bi,Sb)2Te3 、Ti50Cu28Ni15Sn7/Bi2(Te,Se)3 、Ni50Ta50/Bi2Te3 、 Ni50Ta50/(Bi,Sb)2Te3、Ni50Ta50/Bi2(Te,Se)3熱電複合材料粉末，最後再利用真空熱 壓成型技術將此熱電複合材料粉末製備成具非晶/奈米複合材料結構之熱電複合 材料塊材，所製備之熱電複合材料粉末與塊材，除將依序以X光繞射儀、DSC 熱 差分析儀、SEM 掃瞄式電子顯微鏡、TEM穿透式電子顯微鏡及HRTEM高分辨穿 透式電子顯微鏡進行分析及研究其微觀組織結構外，另亦針對熱電複合材料塊材 進行席貝克係數、電傳導率、熱傳導率、ZT值的檢測及微硬度與壓縮試驗，藉 此瞭解熱電複合材料塊材的熱電與機械性質，由於研究範圍頗廣，一年內無法完 成所有的實驗工作，故本計畫將以二年的時間進行，第一年先進行球磨製程合成 具非晶/奈米複合材料結構之熱電複合材料粉末工作，並以X-ray等儀器對球磨粉 末進行檢測，以瞭解所製造之具非晶/微米複合材料結構之熱電複合材料粉末的 結構及相關特性。第二年之工作重點除進行熱電複合材料塊材之真空熱壓成型製 備工作外，也針對塊材進行熱電性能與壓縮試驗檢測以瞭解熱電複合材料塊材的 熱電與機械性質；詳細評估二年工作所得之數據資料後，將可獲知非晶/奈米碲 化鉍基熱電複合材料塊材的材料特性與熱電性能的關聯性外，同時也可開發出應 用高能量球磨及真空熱壓製程製備具高熱電性能之奈米熱電複合材料塊材的最 佳化條件。" "Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in specific military and aerospace markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of bulk nanostructured thermoelectric materials, the nanocomposite type bulk materials have shown the most promise for commercial use because, unlike many other type nanostructured materials, its ZT values can be increased by reducing the thermal conductivity while allowing for large scale, quick, and inexpensive fabrication. To further decrease the thermal conductivity, additional phases have been dispersed into the nanocomposite thermoelectric materials. It is postulated that the addition of second-phase nanoparticles will work as phonon scattering centers and further decrease thermal conductivity. Among the various types of additional phases, metallic amorphous materials fulfill the criterion of PGEC. It is suggested that the addition of amorphous particles into the thermoelectric materials can contribute to the decrease in thermal conductivity and raise the electric conductivity, both effects finally can yield the increase of ZT values. However, a detailed literature survey indicates the enhancements in thermoelectric properties by this approach have never been reported. Therefore, it is necessary to initiate a proposal to study the validity of this concept which has never been discussed. Consequently, the purpose of present work is to investigate the feasibility of preparing new amorphous/nanocrystal nanocomposites by a combination of ball milling and vacuum hot-pressing techniques. A high-energy ball mill will be employed to produce Ti50Cu28Ni15Sn7 and Ni50Ta50 amorphous powders. The amorphous/nanocrystal nanocomposite powders including Ti50Cu28Ni15Sn7/Bi2Te3, Ti50Cu28Ni15Sn7/(Bi,Sb)2Te3, Ti50Cu28Ni15Sn7/Bi2(Te,Se)3, Ni50Ta50/Bi2Te3, Ni50Ta50/(Bi,Sb)2Te3, Ni50Ta50/Bi2(Te,Se)3 will be prepared by ball milling of amorphous powders and mixtures of Bi, Sb, Te and Se elemental powders using same ball mill. The successfully prepared amorphous/nanocrystal nanocomposite powders will than be consolidated into bulk forms by using a uniaxial vacuum hot press machine. The structure of as-prepared powders and bulk nanocomposites materials will be examined by XRD, SEM, and TEM. In addition, the measurement of thermal conductivity, Seebeck coefficient and electrical conductivity as well as compression tests on the bulk nanocomposites materials also will be conducted in order to understand the thermoelectric and mechanical property of the resultant amorphous/nanocrystal bulk nanocomposite materials. The whole program will be carried out in two years after careful consideration of huge experimental works. The main goal in the first year is the preparation of amorphous/nanocrystal nanocomposite powders by high energy ball mill process. The experimental work in the second year will be focused on the consolidation of resultant nanocomposite powders into bulk forms by using a uniaxial vacuum hot press machine. In addition, the thermoelectric and mechanical properties of amorphous/nanocrystal bulk nanocomposite also will be investigated by measuring the thermal conductivity, Seebeck coefficient and electrical conductivity as well as compression tests. After comprehensive evaluation of all the experimental results obtained in this work, the influence of the microstructure on the thermoelectric property can be elucidated. The optimum conditions for the production of high thermoelectric performance amorphous/nanocrystal bulk nanocomposite through ball milling and vacuum hot pressing routes also can be established."
Bulk nanocomposite thermoelectric materials
Figure of merit
Amorphous alloy powder
High energy ball milling
Vacuum hot pressing