Phase equilibria isothermal section and liquidus projection of thermoelectric Co-Sb-Ga alloys

Phase equilibria isothermal section and liquidus projection of thermoelectric Co-Sb-Ga alloys

錢元俊

指導教授 ： 陳信文

國立清華大學/工學院/化學工程學系/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00173

摘要

CoSb3是相當受到關注的熱電材料。近年來研究指出，摻雜Ga至CoSb3熱電材料內能改善此材料的熱電性質，因此Co-Sb-Ga三元系統便具有很高的研究價值。相圖是探討材料相變化的重要資料，同時也是了解不同微結構變化的有力工具，由於熱電材料的微結構對其熱電性質之影響十分巨大，故取得此系統的相圖對於開發此新穎熱電材料便顯得相當重要。本研究之目標在於建構Co-Sb-Ga液相線投影圖以及650℃等溫橫截面圖。在液相線投影圖部份，製備各種不同組成之Co-Sb-Ga三元合金，並從高溫熔融態下淬冷，以進行首要析出相之鑑定。以三個二元子系統的相圖定出首要析出相的二元邊界，並搭配各三元合金的實驗結果，以此建構出Co-Sb-Ga之三元液相線投影圖。首要析出相區除了三個終端固溶體相區外，尚有六個二元介金屬化合物相區，另外並發現以三元化合物- Co3Sb2Ga4為首要析出相的區域，過去之文獻並無此三元化合物之報導。在650℃等溫橫截面圖部份，配置經長時間熱處理之合金樣品，並進行相的鑑定與組成量測，實驗結果確立了四個三相區以及一個兩相區。本研究並利用熱力學計算(Calphad)的方法建構出液相線投影圖以及650℃等溫橫截面圖，其結果與實驗相當吻合。

關鍵字

熱電材料 ； 相圖 ； 液相線投影圖 ； 等溫橫截面圖 ； 鈷銻鎵

並列摘要

CoSb3 is an important thermoelectric material. Recent studies indicate that Ga alloying in CoSb3 could further improve its figure of merit, zT. The Co-Sb-Ga ternary system is thus of high interests for thermoelectric applications. Phase diagrams are fundamental for understanding of phase transformation and materials microstructures, which are closely related to the materials thermoelectric properties. Phase diagrams are thus crucial for development of thermoelectric materials. The Co-Sb-Ga liquidus projection and the 650℃ Co-Sb-Ga phase equilibria isothermal section are constructed in this study. As-cast Co-Sb-Ga alloys were prepared, and their primary solidification phases were determined. The Co-Sb-Ga liquidus projection was constructed based on the experimental results of primary phases, and the phase diagrams of its three constituent binary systems. The primary solidification phases are the three terminal solid solution phases, six binary compounds: CoGa, CoGa3, GaSb, CoSb3, CoSb2, CoSb and a ternary compound- Co3Sb2Ga4 which has not been reported before; Ternary Co-Sb-Ga alloys equilibrated at 650℃ as well. The equilibrium phases and their compositions were determined. Four three-phase regions and one two-phase region have been determined. The liquidus projection and the 650℃ isothermal section were also calculated using Calphad method. Both experimental determinations and the calculated results are qualitatively in good agreement.

並列關鍵字

Thermoelectric material ； Phase diagram ； Liquidus projection ； Isothermal section ； Co-Sb-Ga ； CoSb3

參考文獻

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