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

• Main Author: 錢元俊
• Other Authors: 陳信文
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/47618064835598764992

碩士 === 國立清華大學 === 化學工程學系 === 101 === 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.