Фазовая диаграмма системы Bi-K

К оглавлению: Другие диаграммы (Others phase diargams)


Bi-K (Bismuth-Potassium) A. Petric and A.D. Pelton The assessed phase diagram for the Bi-K system is based primarily on the experimental data of [61Gnu] and [88Pet], with review of other significant data [08Smi]. The existence of four stoichiometric compounds is well established. Bi2K, Bi2K3, and BiK3 melt congruently at 565 с 10, 445 с 5, and 715 с 25 C, respectively. Bi4K5 (or possibly Bi7K9) decomposes peritectically at 381 C. The liquidus is well established, except in the composition range from 72 to 95 at.% K. At high temperatures and high K concentrations, the liquidus points of [88Pet] are considerably higher than those of the thermal analysis studies [08Smi, 61Gnu]. The disagreement may be due to K losses by volatilization or oxidation, which could have occurred at high temperatures and high K concentrations from the open crucibles used by [08Smi] and [61Gnu]. Consequently, the liquidus points of [08Smi] at 80 and 82 at.% K, which are the only points reported in the range from 75 to 96 at.% K, could also be very imprecise. As such, the liquidus in this composition range is drawn as a dashed line in the assessed diagram. The liquidus points of [88Pet] at K contents above 96 at.% were obtained by measuring the activity of K in the two-phase (liquid + BiK3) region and then applying Raoult's Law to calculate the liquidus compositions. The entropy of mixing and excess Gibbs energy of the liquid are very negative with excess stability peaks at 50 and 75 at.% K indicating strong local structural ordering. In view of the relative atomic sizes and the low melting points of K and Bi, the solid solubilities of K in (Bi) and of Bi in (K) are expected to be extremely small. The solubility of Bi in liquid K at the melting point of K is extremely small. Hence, the temperature of the eutectic involving (K) and BiK3 is indistinguishable from the temperature of melting of pure K. 08Smi: D.P. Smith, Z. Anorg. Allg. Chem., 56, 125-129 (1908) in German. 32Zin: E. Zintl and A. Harder, Z. Phys. Chem., B16, 206-212 (1932) in German. 37Bra: G. Brauer and E. Zintl, Z. Phys. Chem., B37, 323-352 (1937) in German. 60Zhu: N.N. Zhuravlv, G.S. Zhadanov, and R.N. Kuz›min, Sov. Phys. Crystallogr., 5, 532-539 (1960). 61Gnu: G. Gnutzmann and W. Klemm, Z. Anorg. Allg. Chem., 309, 181-188 (1961) in German. 63San: D.E. Sands, D.H. Wood, and W.J. Ramsey, Acta Crystallogr., 16, 316 ( 1963). 88Pet: A. Petric, A.D. Pelton, and M.-L. Saboungi, J. Phys. F, Met. Phys., 18, 1473-1489 (1988). Submitted to the APD Program. Complete evaluation contains 4 figures, 2 tables, and 12 references. Special Points of the Bi-K System