Preparation And Characterization Of SiGe Alloy & The Dimensional Design Of Thermoelectric Couple Legs

Thermoelectric material could directly and reversibly convert heat energy into electrical power, as a result. It has been applied in the field of the space exploration, and industry waste heat, etc. With good mechanical properties, thermal stability and thermoelectric properties, SiGe has played an important role in the RTGs. Unfortunately, the ZT value is still low. As reported, the highest ZT value is 1.15@973K, which is so far below the theoretical ZT value. To solve the above-mentioned problem, this paper try to improve ZT value and design the RTGs with appropriate size.At first, this paper pay attation to prepare Si80Ge20B5 and Si80Ge20P2 alloyed powders by mechanical alloying (high energy ball miling), which is ball milled for 10h, 20h,30h,40h and 50h respectively. Then, the mechanically prepared powers are hot pressed by vacuum hot-pressing sinter at temperature of 1200℃ and 1050℃. After hot-pressing, the resulting bulk sample are characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and energy dispersive spectroscopy (EDS) to study their crystallinity, compositon and the average grain size. The XRD confirms that both the two kinds of prepared powder are a single phase and are well mached with those obtained for Si80Ge20 alloys. Meanwhile, the SEM show that the the grain size of the prepared alloys are ranging from lum to 500nm. And we can essily find that the grain size keep decreseing with the milling time increasing. At last, we gian the temperature dependence of the electrical conductivity, Seebeck coefficient, power factor, thermal conductivity and ZT of the nanostructure dense bulk Si80Ge20B5 and Si80Ge20P2 (volume mass density 2.95 g/cm3 measured by Archimedes technique). The highest value of ZT is 0.83@973K for p-type SiGe alloy which is milled for 50h, and the highest value of ZTis 1.3@973K for p-type SiGe alloy which is milled for 20hIn order to ensure the long term reliability of their TE modules which are working in a complex environment, we have to pay attation to the mechanical properties. Such as nanoindentation test, Vickers-indentation test, fracture toughness and thermal shock resistance. As a result, we can get the elastic modulus from the slope of nanoindentation curves, which is 197.05GPa for the Si80Ge20B5 and 182.76GPa for another. The highest value of Vickers-indentation test of Si80Ge20B5 is 930HV and another is 910HV, meanwhile, we can know that the value of Vickers-indentation test of both of them are increasing with the the milling time increasing. Besides, we get the fracture toughness, p-type SiGe KIC=2.0MPam1/2, n-type SiGe KIC=1.8MPam1/2. Last, we gain the value of thermal shock resistance, p-type RT=455.14W/m, n-type RT=449.56W/m.For purpose of enhancing the output power and conversion efficiency of the RTGs, this paper try to design and optimize the cross-section and length of TE modules by ANSYS. In this paper, p-type and n-type SiGe alloy milled for 20h work as the PN mudules. Taking the contact resistance into consideration, we get the result as the following:the RTGs with L=2.5mm and a=2mm has a highest output power and conversion efficiency. Besides, when RL is equal with the resistence of RTGs, we gain a highest output power and conversion efficiency.