Фазовая диаграмма системы Mg-Th

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Mg-Th (Magnesium-Thorium) A.A. Nayeb-Hashemi and J.B. Clark The assessed Mg-Th phase diagram was constructed after evaluation of the literature [Elliott; Metals; Hansen; Hultgren,B; Smith; 56Pet; 58Yam], although further experiments are needed before a definitive equilibrium diagram can be given. The phases of the assessed Mg-Th phase diagram are (1) the liquid, L; (2) the terminal (Mg) solid solution, with the cph structure and a maximum solid solubility of 0.52 at.% (4.75 wt.%) Th; (3) the Mg23Th6 line compound, with fcc structure, that decomposes peritectically (L + Mg2Th = Mg23Th6) at 722 C; (4) the Mg2Th line compound, which undergoes a polymorphic transformation at a temperature between 700 and 800 C, is a Laves phase, and decomposes peritectically (L + (aTh) = Mg2Th) at a temperature above 772 C ( possibly close to 812 C); and (5) the terminal (Th) solid solution, with no reported solid solubility of Mg. Th undergoes an allotropic phase change-below ~1360 C, the structure is fcc (aTh). The formation of a metastable Mg2Th precipitate has been reported to occur during the aging process of a commercial Mg-Th-Zr alloy known as HK31A. Transitional Mg2Th forms before the formation of the equilibrium compound Mg23Th6. The only transitional compound that has found general acceptance, however, is Mg3Th. 56Pet: D.T. Peterson, P.F. Diljak, and C.L. Vold, Acta Crystallogr., 9, 1036- 1037 (1956). 58Yam: A.S. Yamamoto and W. Rostoker, Trans. ASM, 50, 1090-1105 (1958). Published in Phase Diagrams of Binary Magnesium Alloys, 1988, and Bull. Alloy Phase Diagrams, 5(1), Feb 1984. Complete evaluation contains 2 figures, 5 tables, and 33 references. 1