Фазовая диаграмма системы B-Sm

К оглавлению: Другие диаграммы (Others phase diargams)

B-Sm (Boron-Samarium) P.K. Liao and K.E. Spear Very little experimental data are available on the phase equilibria for the Sm- B system. The assessed phase diagram is based primarily on [72Sol] and [76Spe]. The liquidus curves of the system were estimated by assuming similar behavior of the Sm-B system with the Ce-B, Pr-B, Nd-B, and Pm-B systems. The equilibrium phases are (1) the liquid, L; (2) the terminal solid solutions, bcc (gSm), dcph (bSm), and rhombohedral (aSm); (3) the terminal solid solution rhombohedral (bB); and (4) four intermediate compounds, Sm2B5, SmB4, SmB6, and SmB66. The assessed diagram includes estimated melting temperatures for Sm2B5 and SmB4, the transition temperature for metallic Sm, and the presence of a 1-atm vapor phase. The SmB4 phase is shown with a narrow homogeneity range. The Sm- Sm2B5 eutectic temperature of 1010 с 20 C was measured by [72Sol]. The dashed boundary curve separating the metal-rich liquid from the two-phase liquid-vapor region was positioned by assuming thermodynamic ideality for Sm metal in the liquid. However, this dashed boundary curve probably increases its slope considerably as the composition increases in B content. Because SmB6 vaporizes congruently, the Sm partial pressure over this phase must be smaller than that of B over SmB6, which in turn must be smaller than the vapor pressure of pure B. At the melting temperature of SmB6, the vapor pressure of elemental B is only about 1 torr [Hultgren, E]. Both (B) and (Sm) solid solutions have negligible composition ranges. The homogeneity ranges of Sm borides are small, except for SmB6. [76Spe, 77Spe] discuss the rather wide homogeneity ranges for a number of REB6 phases. All available experimental data indicate that the hexaboride is stoichiometric at its metal-rich phase boundary, and becomes B-rich by the formation of up to approximately 30% metal vacancies [76Spe, 77Spe]. 59Eic: H.A. Eick and P.W. Gilles, J. Am. Chem. Soc., 81, 5030-5032 (1959). 65Gie: R.F. Giese, Jr., J. Economy, and V.I. Matkovich, Z. Kristallogr., 122, 144-147 (1965). 70Car: J.-O. Carlsson and T. Lundstrom, J. Less-Common Met., 22, 317-320 (1970) . 71Nii: K. Niihara, Bull. Chem. Soc. Jpn., 44(4), 963-967 (1971). 71Yaj: S. Yajima and K. Niihara, Preprint of paper presented at 9th Rare Earth Research Conference, Blacksburg, VA, Oct 10-14 (1971). 72Fis: Z. Fisk, A.S. Cooper, P.H. Schmidt, and R.N. Castellano, Mater. Res. Bull., 7(4), 285-288 (1972). 72Sch: K. Schwetz, P. Ettmayer, R. Kieffer, and A. Lipp, J. Less-Common Met., 26, 99-104 (1972) in German. 72Sol: G.I. Solovyev and K.E. Spear, J. Am. Ceram. Soc., 55(9), 475-479 (1972). 72Spe: K.E. Spear and G.I. Solovyev, Solid State Chemistry, Proc. 5th Mater. Res. Symp., R.S. Roth and S.J. Schneider, Ed., NBS Spec. Publ. 364, July (1972) . 74Sch: P.H. Schmidt, A.S. Cooper, and S.J. LaPlaca, Acta Crystallogr., (1974). 76Spe: K.E. Spear, Phase Diagrams: Materials Science and Technology, Vol. 4, Academic Press, New York, 91-159 (1976). 77Cal: B. Callmer, Acta Crystallogr. B, 33, 1951-1954 (1977). 77Spe: K.E. Spear, Boron and Refractory Borides, V.I. Matkovich, Ed., Springer- Verlag, New York, 439-456 (1977). 83Pad: Yu.B. Paderno and T. Lundstrom, Acta Chem. Scand., A37, 609-616 (1983). Submitted to the APD Program. Complete evaluation contains 1 figure, 3 tables, and 22 references. Special Points of the Sm-B System