Фазовая диаграмма системы B-Tm

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B-Tm (Boron-Thulium) P.K. Liao and K.E. Spear Experimental work on the phase equilibria for the Tm-B system is sparse. The assessed phase diagram is from [76Spe] and is based primarily on the similarity between the Tm-B and Er-B systems. The liquidus curves of the Tm-B system were largely estimated by [76Spe], and a 1-atm vapor phase is also included in the assessed diagram. The boiling point of Tm is much lower than the boiling points of Er and Lu, and the slope of the dashed boundary curve that separates the metal-rich liquid from the two-phase liquid-vapor region probably increases considerably as the composition increases in B content. The equilibrium phases are (1) the liquid, L; (2) the terminal solid solution, cph (Tm); (3) the terminal solid solution, rhombohedral (bB); and (4) four intermediate compounds, TmB2, TmB4, TmB12, and TmB66. Both (bB) and (Tm) solid solutions have negligible composition ranges. The hexaborides are the most studied of the RE-boride phases and have been reported for all of the RE metals. However, the Tm hexaboride appears to be unstable with respect to the other condensed phases in the Tm-B system. The melting behavior and melting temperatures of the Tm-boride phases have not been studied in most cases. TmB4 is expected to melt congruently, whereas TmB2, TmB12, and possibly TmB66 are expected to melt by peritectic reactions [76Spe] . The only reported melting temperature in the Tm-B system is that of TmB12. However, it was reported for the TmB6 phase by [68Mor]. Because Tm does not form the hexaboride phase, mixtures of TmB4 and TmB12 must have been present in their "hexaboride" samples. If the dodecarboride of Tm melts by a peritectic reaction as expected [76Spe], then a mixture of tetra- and dodecarboride would begin to melt at the peritectic melting temperature of the dodecarboride. The homogeneity ranges of all Tm borides are expected to be small, though no experimental results have been reported. 61Lap: S. LaPlaca, I. Binder, and B. Post, J. Inorg. Nucl. Chem., 18, 113-117 ( 1961). 61Pad: Yu.B. Paderno and G.V. Samsonov, Russ. J. Struct. Chem., 2(2), 202-203 ( 1961). 65Gie: R.F. Giese, Jr., J. Economy, and V.I. Matkovich, Z. Krist., 122, 144- 147 (1965). 68Mor: O.A. Mordovin and E.N. Timofeeva, Russ. J. Inorg. Chem., 13(12), 1627- 1629 (1968). 70Car: J.-O. Carlsson and T. Lundstrom, J. Less-Common Met., 22, 317-320 (1970) . 71Pad: Yu.B. Paderno, V.V. Odintsov, I.I. Timofeeva, and L.A. Klochkov, High Temp., 9(1), 175-177 (1971). 72Cas: R.N. Castellano, Mater. Res. Bull., 7(4), 261-265 (1972). 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. 73Bau: J. Bauer and J. Debuigne, C.R. Acad. Sci. Paris, Ser. C, 277, 851-853 ( 1973) in French. 76Spe: K.E. Spear, Phase Diagrams, Vol. 4, Materials Science and Technology, Academic Press, New York, 91-159 (1976). 77Cal: B. Callmer, Acta Crystallogr. B, 33, 1951-1954 (1977). Submitted to the APD Program. Complete evaluation contains 1 figure, 3 tables, and 19 references. Special Points of the Tm-B System