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|Title: ||Bi-Sb-Te熱電與Au-X-Al2O3熱傳導性質研究;Thermoelectric properties of Bi-Sb-Te and thermal conductance of Au-X-Al2O3(X=Ag,In)|
|Keywords: ||熱傳導;熱電;thermal conductance;thermoelectric properties|
|Issue Date: ||2012-09-11 18:40:52 (UTC+8)|
|Abstract: ||熱傳導性質在塊材中佔了很重要的角色，量測塊材的熱傳導性質可以更加瞭解物體的物理性質。然而，準確的量測會面臨諸多的挑戰。如何改善以及增進量測的準確度，在這個論文研究中將以兩大部分呈現。 第一個部分，我們建立一套穩態量測方法即直接量測法來量測塊材的熱傳性質。首先我們參考Tirtt 所建立的系統裝置，自備材料並設計量測底座及熱電偶線，以及規劃程式LabVIEW進行自動量測系統。經過理論計算在量測過程中，經由熱傳導、熱輻射產生的熱流失可忽略不計，進而開始量測單一材料的熱傳性質。實驗結果純元素金和多晶體三氧化二鋁在室溫下，熱傳導為320 .7 W/mK 、96.2 W/mK與參考資料誤差不超過1%和6%。進而，我們將金與三氧化二鋁分別以銀膠及銦線做連接，形成由兩種材料、不同介面組成的裝置。利用所建立的穩態量測法，量測由金端流至三氧化二鋁端的熱流，反之，量測由三氧化二鋁端流至金端的熱流。實驗結果介面由銀膠所組成的裝置，由於銀膠的性質所致，當裝置交換熱流量測時，狀態不穩定導致介面熱阻改變，所量測出來的熱傳也因而改變，因此次實驗結果難以判斷左右端熱流是否不對稱。第二個裝置由銦線當作介面，此裝置狀態較為穩定，不因改變熱流方向量測而改變介面熱阻，實驗結果顯示左右兩端的熱傳並無差異，亦表示此由金與三氧化二鋁組成的裝置在我們的量測系統下沒有產生熱流不對稱。 第二個部分，近年來熱電材料在熱電製冷元件及溫差發電上極具潛力。如何了解材料的優異，最主要的量測就是求出熱電優值(ZT值)來判斷，而根據熱電優值的定義，我們知道它係由三個係數組成的:Seebeck係數(α)、電阻率係數(ρ)以及熱傳導係數(κ)。此實驗由第一部分所架設的穩態法熱傳量測系統量測熱傳導性質，以及實驗室已架設完成Seebeck系統量測電性性質，可以方便且迅速的得到這三樣係數以求得ZT值。材料為CuxBi0.5Sb1.5Te3 (x=0.01) 塊材係由物理方法配置燒結而成。實驗結果CuxBi0.5Sb1.5Te3 (x=0.01) 塊材的熱傳導係數在300 K到400 K 約為1.25 W/mK，電阻率為6.5 μΩ-m 在300 K，Seebeck係數為120~170 μV/K在300 K到400 K。求得ZT值為0.5~0.75在300 K到400 K。Thermal property plays an important role in the characteristic of bulk materials, the measurement is necessary to understand the underlying physics that leads to certain phenomena. However, the accurate measurement and characterization of thermal property of bulk materials can pose many challenges. In order to improve and modify the measurement of thermal property, two investigations of different region have been reported in this thesis.A thermal rectifier is the heat transfer analog to the familiar electrical diode. And thermal rectification is very interest because of its potential to open up new ground for the control of heat transport. In the first study, the thermal rectification in a two–terminal bulk material has been measured. We have prepared pure metal, Au, and polycrystalline insulator, Al2O3, as the two-terminal bulk material which glued with Ag paste and ductile indium wire. Hereby, we made an experimental system (steady state method) which is essentially a measurement of the heat flow through the sample to detect the thermal rectification. The observed thermal conductance of Au-X-Al2O3 (X=Ag, In) in the forward and reverse direction is no rectifying effect with the temperature difference of 10 K between heat baths. We have calculated thermal rectification using thermal conductivity data and found that the calculation is in discordancy with experimental data. In the second study, thermoelectric materials have great potential for use in solid-state power generation and cooling devices. These devices have numerous advantages over conventional methods, but they are not widely used today is because of the poor efficiency. Much of the effort in the thermoelectric field has been directed at improving the efficiency of thermoelectric devices. In order to improve the efficiency of these devices, solid understanding on the properties of the materials from which they are made is required. This usually involves extensive measurement of the thermal and electrical properties of the material. In many cases, the measurement of characteristics of bulk materials is necessary to understand the underlying physics the leads to certain phenomena. Measurement of the properties of bulk material often involves working with specific samples because of synthesis of bulks materials. The measurement of the thermal conductivity of the specific size samples has been a little bit formidable challenge for many years due to the low thermal conductance and the low mechanical strength of the sample. One of the methods developed to address this problem is the steady state method.The steady state method was modified and the results and description of the modified technique are presented in this thesis. Improvements were made to the sample stage and measurement system. The system was evaluated with standards to confirm the validity of the measurements. Investigation of thermoelectric material, the thermal conductivity of CuxBi0.5Sb1.5Te3 (x=0.01) at room temperature is 1.25 W/m-K by steady state method. In addition, the Seebeck coefficient measurement was already established, and the sample stage and measurement are similar to the steady state method. However, our research included an investigation of all properties of thermoelectric materials of CuxBi0.5Sb1.5Te3, and the figure of merit (ZT) has been reported.|
|Appears in Collections:||[物理研究所] 博碩士論文|
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