Фазовая диаграмма системы Bi-Cs

К оглавлению: Другие диаграммы (Others phase diargams)

Bi-Cs (Bismuth-Cesium) J. Sangster and A.D. Pelton The assessed phase diagram for the Bi-Cs system is based on [58Zhu] and [ 61Gnu1]. Because neither [58Zhu] nor [61Gnu1] gave tables of data, the points shown in the assessed diagram were taken from small diagrams. In the assessed diagram, the data of [61Gnu1] generally are given preference over those of [58Zhu] because the former study is somewhat more complete and because, in the very similar Bi-Rb system, which was studied by the same authors, the data of [61Gnu1] agree closely with a recent third study, whereas those of [58Zhu] do not agree as well. However, at higher temperatures at high Cs contents, Cs losses by evaporation in the open crucibles of [61Gnu1] could have caused errors. Hence, near the congruent melting point of BiCs3 in the assessed diagram, the results of [58Zhu] are given more weight. In view of the large atomic size difference and low melting points of Bi and Cs, the solid solubilities of Cs in (Bi) and of Bi in (Cs) are expected to be extremely small. At Cs contents above 75 at.%, the liquidus in the assessed diagram is shown tentatively as having an S-shape because such behavior is observed in the similar Bi-Na, Bi-K, and Bi-Rb systems. The compound BiCs was reported as being formed temporarily during the vacuum deposition of thin films of Cs on Bi [43Som]. However, there is no evidence of its existence from thermal analysis [58Zhu, 61Gnu1] nor from X-ray analysis of an alloy containing 57 at.% Cs. On the other hand, there is indirect evidence for the existence of the compound BiRb in the Bi-Rb system [90Pel], even though [61Gnu1] did not find X-ray evidence for its existence either. Hence, the possibility that BiCs may exist should not be entirely ruled out. [61Gnu1] reported an invariant reaction at 501 C, with which they associated the peritectic melting of Bi2Cs3. [58Zhu] reported an invariant at 490 C, which he tentatively proposed as the peritectic associated with BiCs2. An X- ray powder pattern of this compound was obtained by [61Gnu1]. Although it could not be indexed, it resembled the powder pattern of the compound Bi2Rb3, which melts congruently near the 2:3 composition [61Gnu1]. Hence, the stoichiometry Bi2Cs3 seems more likely than BiCs2. In the assessed diagram, this compound is shown as melting incongruently. However, within the experimental error limits, congruent melting near 500 C is equally likely. 43Som: A. Sommer, Proc. Phys. Soc. (London), 55(2), 145-154 (1943). 58Zhu: N.N. Zhuravlev, Zh. Eksper. Teor. Fiz., 34(7), 827-829 (1958) in Russian; TR: Sov. Phys. JETP, 34(7), 571-573 (1958). 60Zhu: N.N. Zhuravlev and V.A. Smirnov, Kristallografiya, 4(4), 534-537 (1959) in Russian; TR: Sov. Phys.-Crystallogr., 4(4), 503-505 (1960). 61Gnu1: G. Gnutzmann and W. Klemm, Z. Anorg. Allg. Chem., 309, 181-188 (1961) in German. 61Gnu2: G. Gnutzmann, F.W. Dorn, and W. Klemm, Z. Anorg. Allg. Chem., 309, 210- 225 (1961) in German. 61Oer: G. Oertel, Ann. Phys. (Leipzig), Ser. 7, 8, 137 (1961) in German. Submitted to the APD Program. Complete evaluation contains 1 figure, 2 tables, and 13 references. Special Points of the Bi-Cs System