| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 101 === Thermoelectric material which converts electrical energy into thermal energy directly, and vice versa, has been regarded as a potential energy conversion material. Recent studies have found nanostructured thermoelectric materials can create better thermoelectric properties and lead to better thermoelectric conversion efficiency. In this study, Bi-Sb-Te compounds nano-powders were prepared by wet bead milling process and pressed into a sample. The effects of processing conditions on thermoelectric properties of cold-pressed Bi-Sb-Te are investigated.
In this study, Bi-Sb-Te powders of micro-meter size were first prepared by a planetary ball milling, and then refined into nano-size particles by wet beads milling method. Finally, these powders were pressed into a bulk at room temperature. We found some problems occurring during the wet-milling process. Bi-Sb-Te alloy powders prepared by wet bead milling are subjected to serious damage of crystal structure and oxidation. The oxidation affects the metallurgical properties of the Bi-Sb-Te material and crystal structure, results in specimen's compactness. Here, we added an additional hydrogen reduction process to recover the ground B-Sb-Te powders by removing the oxidized part and restoring the thermoelectric properties of the pressed Bi-Sb-Te compound. The results show that the Bi-Sb-Te powders have a (00l) preferred orientation and the Bi2Te3 crystal reveals laminar structure. The pressed Bi-Sb-Te with (00l) preferred orientation has enhanced electricity conductivity and thermal conductivity as well as thermoelectric figure-of-merit.
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