Фазовая диаграмма системы I-Rb

К оглавлению: Другие диаграммы (Others phase diargams)


Bi-Rb (Bismuth-Rubidium) A.D. Pelton and A. Petric The assessed Bi-Rb phase diagram is based primarily on the experimental data of [61Gnu] and [88Pet] and was obtained by thermodynamic modeling. For the BiRb3 liquidus above 450 C, [88Pet] reported only two points. For this reason, the liquidus is shown by a dashed line in this region, and the reported [61Gnu] melting point of BiRb3 of 642 C is assigned error limits of с20 C. The liquidus points of [88Pet] at Rb content above 96 at.% were obtained by measuring the activity of Rb in the two-phase (liquid + BiRb3) region and then applying Raoult's law to calculate the liquid compositions. [61Gnu] concluded that a 1:1 compound does not exist. However, this is not clear from their diffraction patterns. It may be noted that 1:1 compounds are present in both the Bi-Na and Bi-Li systems. The existence of this compound clearly requires confirmation. The stoichiometry Bi4Rb5 is that assigned by [61Gnu]. Because their X-ray patterns could not be interpreted, however, the stoichiometry of this compound is uncertain. The stoichiometry of Bi2Rb3 has not been confirmed by X-ray studies. However, the liquidus data indicate a congruent melting point of 465 с 5 C near the 2:3 composition. BiRb3 undergoes an allotropic transformation at 230 с 4 C. A eutectic at 268 C was measured by [61Gnu]. From the limiting liquidus slope equation, the eutectic composition can be calculated thermodynamically as 1.6 at.% Rb. This is in good agreement with the liquidus data of [88Pet]. A eutectic at 370 с 5 C was observed by [88Pet] from the change in slope of emf with temperature. A eutectic at 455 с 5 C was reported by [61Gnu]. In view of the relative atomic sizes and low melting points of Bi and Rb, the solid solubilities of Rb in (Bi) and of Bi in (Rb) are expected to be extremely small. The solubility of Bi in liquid Rb at the melting point of Rb is extremely small. Hence, the temperature of the eutectic involving (Rb) and BiRb3 is indistinguishable from the temperature of melting of pure Rb. 58Zhu: N.N. Zhuravlev, T.A. Mingazin, and G.S. Zhdanov, Sov. Phys. JETP, 34(7), 566-573 (1958). 60Zhu: N.N. Zhuravlev, G.S. Zhdanov, and R.N. Kuz›min, Sov. Phys. Crystallogr., 5, 532-539 (1960). 61Gnu: G. Gnutzmann and W. Klemm, Z. Anorg. Chem., 309, 181-188 (1961). 77Chu: K.A. Chuntonov, S.P. Yatsenko, A.N. Kuznetsov, S.I. Alyamovskii, and K. K. Abrashev, Sov. Phys. Crystallogr., 22(3), 367 (1977). 88Pet: A. Petric, A.D. Pelton, and M.-L. Saboungi, J. Electrochem. Soc., 135, 2754-2760 (1988). Submitted to the APD Program. Complete evaluation contains 2 figures, 3 tables, and 8 references. Special Points of the Bi-Rb System