Фазовая диаграмма системы Ga-Na

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Ga-Na (Gallium-Sodium) A.D. Pelton and S. Larose The assessed phase diagram for the Ga-Na system was calculated thermodynamically, with review of the experimental data of [56Fes], [60Rin1], [ 61Fes], [73Gam], [80Zha], and [86Ita], except for the consolute point of the miscibility gap and the liquidus above 90 at.% Na. Although the melting points of Ga and Na are very low, the phase diagram is dominated by stable intermetallic compounds with melting points of 499 and 556 C. The stability of these compounds is most likely the result of a strong ionic bond due to the large difference in the electronegativities of Ga and Na. The existence of a region of liquid immiscibility extending from approximately 60 to 90 at.% Na at a monotectic temperature of 519 C seems reasonably certain, although some authors contend that the critical point actually lies ( metastably) below the liquidus. In the assessed diagram, a critical temperature of approximately 550 C [80Zha] is shown. However, thermodynamic analysis indicates a consolute temperature above 620 C. Therefore, the boundary of the miscibility gap is shown as a dashed curve. In the range 5 to 60 at.% Na, the assessed liquidus is probably accurate to с3 C. For Na contents greater than 90 at.% the liquidus points measured by [ 56Fes], [60Rin1], and [80Zha] are all in good agreement. The approximate solubility of Ga in liquid Na is 0.2 ppm at the melting point of Na. The solubility of Na in liquid Ga at its melting point is also expected to be very small. [34Gil] gave an approximate solubility of Na in liquid Ga of 0.001 wt.% at 30 C. An invariant reaction has been reported between 497 and 500 C [56Fes, 80Zha, 86Ita]. In the assessed diagram, this is shown as a eutectic at 498 с 1 C, associated with the congruent melting of Ga4Na at 499 с 1 C. However, the eutectic composition (20.5 at.% Na) is so close to that of Ga4Na (20 at.% Na), that, within the limits of accuracy of the various measurements, Ga4Na could very well melt incongruently, as shown by [86Ita]. [86Ita] also report one clear thermal analysis peak of 18 at.% Na at 488 C, which they tentatively take to indicate an invariant reaction, possibly associated with a transformation of Ga4Na. A compound, melting congruently at 556 C, was reported by [56Fes] to have the stoichiometry Ga8Na5 (38.5 at.% Na). [60Rin2] confirmed this stoichiometry. However, in view of the scarcity of data, an error limit of 2 or 3 at.% should be assigned. Recent detailed crystal structure determinations indicate that the correct stoichiometry may be Ga39Na22 (36.1 at.% Na) [82Lin] or Ga13Na7 ( 35 at.% Na) [82Fra1, 82Fra2]. [86Ita] interpret their thermal analysis results in terms of a compound with a range of stoichiometry between 36.3 and 37.0 at.% Na. This would tend to support the proposed [82Lin] stoichiometry of Ga39Na22, tentatively indicated in the assessed diagram. It may be that two or more compounds with very similar stoichiometries, stabilities, and crystal structures actually exist side by side in this system. 34Gil: E.S. Gilfillian, Jr., and H.E. Bent, J. Am. Chem. Soc., 56, 1661-1663 ( 1934). 56Fes: P. Feschotte and E. Rinck, Compt. Rend., 243, 1525-1528 (1956) in French. 60Rin1: E. Rinck and P. Feschotte, Compt. Rend., 250, 1489-1491 (1960) in French. 60Rin2: E. Rinck and P. Feschotte, Compt. Rend., 251, 869-871 (1960) in French. 61Fes: P. Feschotte, Ann. Chim. (Paris), 6, 1029-1070 (1961) in French. 69Bru: G. Bruzzone, Acta Crystallogr., B25, 1206-1207 (1969). 73Gam: M. Gamino and J.-P. Bros, Thermochim. Acta, 6, 129-136 (1973) in French. 80Zha: Sh.R. Zhakupov, K.A. Chuntonov, G.G. Ugodnikov, S.P. Yatsenko, and Kh.O. Shakarov, Russ. J. Phys. Chem., 54, 584-586 (1980). 82Fra1: U. Frank-Cordier, G. Cordier, and H. Sch„fer, Z. Naturforsch. B., 37, 119-126 (1982) in German. 82Fra2: U. Frank-Cordier, G. Cordier, and H. Sch„fer, Z. Naturforsch. B., 37, 127-135 (1982) in German. 82Lin: R.G. Ling and C. Belin, Acta Crystallogr., B38, 1101-1104 (1982). 86Ita: T. Itami, M. Shimoji, J. Meijer, G.J.B. Vinke, C. Van der Marel, and W. Van der Lugt, Physica, 142B, 145-151 (1986). Published in Bull. Alloy Phase Diagrams, 11(4), Aug 1990. Complete evaluation contains 4 figures, 3 tables, and 25 references. Special Points of the Ga-Na System