Фазовая диаграмма системы Be-Cl

К оглавлению: Другие диаграммы (Others phase diargams)

Be-Cl (Beryllium-Chlorine) H. Okamoto and L.E. Tanner Only one intermediate compound, BeCl2, exists in the Be-Cl system. Four allotropic forms of BeCl2 (a, b, b›, and a›) have been reported, for which the nomenclature of [60Kuv] has been adopted. The assessed pressure-temperature phase diagram of BeCl2 is slightly modified from the proposed diagram of [ 65Mcd], who assumed that the a and a› phases are identical but separated by intrusions of b and b› phases. According to [65Mcd], the a, b›, and b phases are stable and the a› phase is metastable. The present evaluators assume that the a› phase also is stable, because only this phase forms when vapor is condensed at low temperatures. A crystalline Be-Cl compound was observed to precipitate from gas [1828Woh] . The molecular formula of the compound was established as BeCl2 in the gaseous state [1884Nil] and in the solid state [1899Leb]. Until the clarification of [65Mcd], the presence of allotropic forms caused disagreement in the property evaluations of BeCl2. [60Kuv] found that a rapidly cooled melt transformed to the SiS2-type a›, which changed to the cubic form b› at 250 C when heated. The b› form then changed, at 340 C, to the stable b form. However, the melt solidified to a at 425 C, which then transformed to b at 405 C when cooled slowly. [65Mcd] also reported that an additional transition from b to b› occasionally was found on cooling at about 340 C. According to [65Mcd], the presence of this transition is consistent with the thermal effect in this temperature range observed by [60Fur]. Therefore, b› was considered to be a stable phase. The assessed diagram differs from the diagram of [65Mcd] at low temperatures, where the a› phase was assumed to be stable. The room-temperature phases of the Be-Br and Be-I systems are isomorphous to a›. 1828Woh: F. Wohler, Ann. Phys. Chem., 13, 577-582 (1828) in German. 1884Nil: L.F. Nilson and O. Pettersson, Ber. Dtsch. Chem. Gesellschaft., 17, 987-995 (1884) in German. 1899Leb: M.F. Lebeau, Ann. Chim. Phys., 16, 457-503 (1899) in French. 52Run: R.E. Rundle and P.H. Lewis, J. Chem. Phys., 20(1), 132-134 (1952). 60Fur: E. Furby and K.L. Wilkinson, J. Inorg. Nucl. Chem., 14(1/2), 123-126 ( 1960). 60Kuv: O.N. Kuvyrkin, O.N. Breusov, A.V. Novoselova, and K.N. Semenenko, Zh. Fiz. Khim., 34(2), 343-349 (1960) in Russian; TR: Russ. J. Phys. Chem., 34(2), 160-163 (1960). 65Mcd: R.A. McDonald and F.L. Oetting, J. Phys. Chem., 69(11), 3839-3845 (1965) . Published in Phase Diagrams of Binary Beryllium Alloys, 1987. Complete evaluation contains 3 figures, 3 tables, and 34 references. 1