Фазовая диаграмма системы Hg-Tl

К оглавлению: Другие диаграммы (Others phase diargams)

Hg-Tl (Mercury-Thallium) C. Guminski The speculative phase diagram for the Hg-Tl system is based on [Hultgren,B] who took into account data from [Hansen], [Elliott], and [Shunk], with modifications from [72Ric], [73Ric], [78Ama], and [80Cla]. Composition of the eutectic on the Hg-rich side of the diagram, 8.6 at.% Tl, was selected as a compromise between 8.55 [Hultgren] and 8.7 at.% Tl [80Cla]. The corresponding temperature was adopted from [73Ric] and [80Cla], who equivocally reported -60 C. The congruent melting of Hg5Tl2 (28.6 at.% Tl) was taken as 14.5 C after [73Cla]. Parameters of the eutectic in the central part of the diagram were established as 40.5 at.% Tl and 0.3 C [80Cla]. The liquidus line suggested in [Hultgren] was very well confirmed by [80Cla] in the entire composition range. The solidus line delimiting the g phase was modified according to [78Ama] and [ 80Cla]. The homogeneity range of this phase extends from slightly >20 to about 35 at.% Tl. On the Tl-rich side of the diagram, the upper temperatures of the bTl field were taken from [80Cla]. It was further assumed that the solid solubility limit of 80 at.% Tl is not changed from -60 to -190 C. The bordering lines of the lower limit of bTl and the upper limit of aTl should be characterized by some convexity, by analogy to the upper limit of the bTl solid solution, and should approach the values reported by [78Ama] at -190 C. Existence of the solid compound Hg5Tl2 was questioned early by [Hansen] because "its crystal structure does not indicate this composition." On the other hand, maximum melting of g phase is observed exactly at composition Hg5Tl2. Additionally, data of [64Koz], [72Ric], [73Cla], [73Val], [74Pre], and [80Cla] indicate formation of this compound, although its formation is accompanied by a slightly endothermic effect. Liquid Hg-Tl alloys also exhibit distinct short-range ordering at this compound composition. The HgTl compound (b phase) detected at -190 C [78Ama] seems to be the most stable of the metastable phases formed in this system. Several other metastable phases were detected after rapid quenching to -130 C of Hg-Tl alloys. By splat cooling, the solid solution of Tl in (Hg) was retained up to 85 at.% Tl. Further on, appearance of the following phases was found: X (10 to 14 at.% Tl), crystallography unresolved; a››(<10 to 14 at.% Tl), triclinic(?); a›(~14 to 18 at.% Tl), tetragonal, A6 type; b (~50 to 55 at.% Tl), cubic, A2 or B2 type. 64Koz: L.F. Kozin, Physico-Chemical Fundamentals of the Amalgam Metallurgy, Nauka, Alma-Ata, 163 (1964) in Russian. 72Ric: P.W. Richter and C.W.F.T. Pistorius, J. Less-Common Met., 29, 217-219 ( 1972). 73Cla: Y. Claire, R. Castanet, and M. Laffitte, J. Less-Common Met., 31, 83- 100 (1973) in French. 73Ric: P.W. Richter and C.W.F.T. Pistorius, Acta Metall., 21, 391-394 (1973). 73Val: A.V. Valko, N.D. Omarova, L.M. Filippova, and A.I. Zebreva, Sbor. Rabot Khim., Alma-Ata, (3), 352-358 (1973) in Russian. 74Pre: B. Predel and G. Oehme, Z. Metallkd., 65, 509-515 (1974) in German. 78Ama: R.S. Amand and B.C. Giessen, J. Less-Common Met., 58, 161-172 (1978). 80Cla: Y. Claire and J. Rey, J. Less-Common Met., 70, 33-38 (1980) in French. Submitted to the APD Program. Complete evaluation contains 2 figures and 17 references. 1