Фазовая диаграмма системы B-Be

К оглавлению: Другие диаграммы (Others phase diargams)

B-Be (Boron-Beryllium) H. Okamoto and L.E. Tanner The assessed phase diagram for the B-Be system is tentative, and is based on the experimental data of [60Mar1], [60Mar3], [61Hoe], [71Kri], [73Ste], and [ 74Hol]. There are many uncertainties in the diagram, and even the true equilibrium phases have not been definitely established. The liquidus boundaries are also uncertain for a wide composition range. The region between pure B and B6Be is the most ambiguous, due to coexistence of several compounds or allotropic forms. The structures of B-rich compounds are dependent on the initial form of B, which, according to [Pearson3], has as many as nine allotropic forms. Therefore, some of the observed states of the compounds must be metastable. The equilibrium phases tentatively included in the assessed diagram are (1) the liquid, L; (2) the rhombohedral terminal solid solution, (bB); (3) tetragonal B12Be; (4) aAlB12-type B6Be; (5) hexagonal B2Be with the composition displaced to B3Be; (6) tetragonal B3Be2, stable in a limited temperature range; (7) CaF2-type BBe2, also stable in a limited temperature range; (8) tetragonal BBe4; and (9) the bcc and cph terminal solid solutions, ( bBe) and (aBe). The L/[L + BBe2] liquidus as proposed by [73Ste] is not plausible thermodynamically, so a possible alternative is shown in the assessed diagram. The other portion of the liquidus, developed from the melting and peritectic temperatures of B-rich compounds, is similar to that shown in [73Ste]. The eutectic composition in the assessed diagram is at 88.5 at.% Be, and was estimated from the liquidus data of [73Ste]. Sintering experiments of [69Vek] revealed that rhombohedral (bB) transforms to the tetragonal B-type or the aAlB12-type, depending on temperature and composition. Tetragonal B was formed by substituting a Be atom with B in B12Be [63Bec]. Therefore, a metastable tetragonal phase extends over the composition range from pure B to B6Be. The melting point of B6Be was bracketed between 2120 and 2220 C by [61Hoe]; [ 71Kri] and [74Hol] gave ~2070 and 2100 C, respectively. [61Hoe] suggested that B6Be has an extended range to pure B because the structure of B6Be resembles one of the allotropic forms of B; [69Vek] confirmed this. [69Vek] also showed that both rhombohedral bB-type and tetragonal B6Be can be formed at lower temperatures. [73Ste] tentatively showed B3Be2 as stable down to low temperatures. However, in order to avoid conflict with the low-temperature decomposition of BBe2, it was assumed for the assessed diagram that B3Be2 is only stable in a limited temperature range. Further study on the temperature stability of this phase is needed. According to [61Hoe], BBe2 melted incongruently when heated to 1400 C. Thermal arrest data of [73Ste] indicated a peritectic reaction at ~1500 C. The melting point of BBe2 was reported as ~1520 and 1380 C by [71Kri] and [ 74Hol], respectively. This phase decomposes sluggishly at low temperatures into B2Be (not B3Be2) and BBe4 [62Bec]. The eutectoid temperature is somewhere between 900 and 1050 C. The peritectic formation temperature of BBe4 is 1140 C [73Ste]. BBe4 has no significant homogeneity range [62Bec]. According to [60Mar1], BBe5 has a possible homogeneity range to BBe4, and is stable up to ~1500 C (?), at which temperature it decomposes into metallic Be and borides of higher B content. This feature is inconsistent with the assessed diagram. The melting point of bBe and the bBe = aBe allotropic transformation temperature are 1289 с 5 and 1270 с 6 C, respectively [Melt, Massalski]. 55Mar1: L.Ya. Markovskii, Yu.D. Kondrashev, and I.A. Goryacheva, Dokl. Akad. Nauk SSSR, 101, 97-98 (1955) in Russian. 55Mar2: L.Ya. Markovskii, Yu.D. Kondrashev, and G.V. Kaputovskaya, Zh. Obshch. Khim., 25, 1045-1052 (1955) in Russian; TR: J. Gen. Chem. USSR, 25, 1007-1012 ( 1955). 58Mcc: L.V. McCarty, J.S. Kasper, F.H. Horn, B.F. Decker, and A.E. Newkirk, J. Am. Chem. Soc., 80, 2592 (1958). 60Hoa: J.L. Hoard and A.E. Newkirk, J. Am. Chem. Soc., 82(1), 70-76 (1960). 60Mar1: G.S. Markevich, Yu.D. Kondrashev, and L.Ya. Markovskii, Zh. Neorg. Khim., 5(8), 1783-1787 (1960) in Russian; TR: Russ. J. Inorg. Chem., 5(8), 865- 867 (1960). 60Mar2: G.S. Markevich and L.Ya. Markovskii, Tr. Gos. Inst. Prikl. Khim., (45), 139-144 (1960) in Russian. 60Mar3: L.Ya. Markovskii and G.S. Markevich, Zh. Prikl. Khim., 33(7), 1667- 1669 (1960) in Russian; TR: J. Appl. Chem., USSR, 33(7), 1647-1648 (1960). 61Hoe: C.L. Hoenig, C.F. Cline, and D.E. Sands, J. Am. Ceram. Soc., 44, 385- 389 (1961). 61San: D.E. Sands, C.F. Cline, A. Zalkin, and C.L Hoenig, Acta Crystallogr., 14(3), 309-310 (1961). 62Bec: H.J. Becher and A. Schafer, Z. Anorg. Chem., 318(5/6), 304-312 (1962) in German. 63Bec: H.J. Becher, Z. Anorg. Chem., 321(5/6), 217-223 (1963) in German. 66Kon: Yu.D. Kondrashev, G.S. Markevich, and L.Ya. Markovskii, Zh. Neorg. Khim. , 11, 1461-1462 (1966) in Russian; TR: Russ. J. Inorg. Chem., 11, 780-781 ( 1966). 69Vek: N.V. Vekshina, L.Ya. Markovskii, Yu.D. Kondrashev, and I.M. Stroganova, Zh. Prikl. Khim. (Leningrad), 42(6), 1229-1234 (1969) in Russian; TR: J. Appl. Chem., USSR, 42(6), 1168-1171 (1969). 71Kri: O.H. Krikorian, Report UCRL-51043, Lawrence Livermore Laboratory, Livermore, CA (1971). 73Ste: J. Stecher and F. Aldinger, Z. Metallkd., 64(10), 684-689 (1973) in German. 74Hol: J.B. Holt, J. Am. Ceram. Soc., 57(3), 126-129 (1974). 75Mat: R. Mattes, K.F. Tebbe, H. Neidhard, and H. Rethfeld, Z. Anorg. Chem., 413(1), 1-9 (1975) in German. 77Cal: B. Callmer, Acta Crystallogr. B, 33, 1951-1954 (1977). Published in Phase Diagrams of Binary Beryllium Alloys, 1988. Complete evaluation contains 2 figures, 4 tables, and 40 references. 1