Фазовая диаграмма системы B-Mg

К оглавлению: Другие диаграммы (Others phase diargams)

B-Mg (Boron-Magnesium) A.A. Nayeb-Hashemi and J.B. Clark The equilibrium phase diagram of the Mg-B system has not been reliably determined. The melting points of pure Mg and pure B are 650 C and 2092 C, respectively. The solid solubility of B in Mg and vice versa appears to be negligible. [77Spe] proposed the schematic for the Mg-B phase diagram and noted that representation of "the general type of diagram shown is the type that the Mg-B system will exhibit, but the given temperatures may be grossly in error." However, this diagram does not include some of the phases that were reported by [Elliott] and [Shunk]. [53Rus] showed that the compound in equilibrium with Mg had MgB2 stoichiometry. [53Rus] found the existence of a MgB4 compound and two others of unspecified composition. [54Jon] and [55Mar] confirmed that the compound in equilibrium with Mg is MgB2. [55Mar] also reported three more phases in this system and designated them as MgB6, MgB12, and the g phase. The designated g phase was noted to be a homogeneous phase between the MgB6 and MgB12 compounds with a B/Mg ratio of about 9 to 1. [55Mar] approximated the invariant reaction temperatures for the formation MgB2, MgB6, g, and MgB12 as њ 1050 C, 1150 C, 1200 C, and <301> 1700 C, respectively. [59Mar] showed that the reported Mg3B2 compound was nonexistent and noted that there was not any boride richer in Mg than MgB2. [62Duh] showed six intermediate phases in the system, which were designated as MgB2, MgB4, MgB6 (in agreement with those of [53Rus] and [55Mar]), d phase (a homogeneous phase between the MgB6 and MgB17 composition), and two more phases, X and X›, with undefined compositions. According to [62Duh], the d phase decomposed to X and X› above 1300 C, the latter phase existing primarily above 1300 C. [Shunk] noted that the g phase reported by [55Mar] appears to be the same phase that [62Duh] identified as d. [Shunk] also speculated that the MgB12 compound reported by [55Mar] was possibly a mixture of the two undefined phases (X and X›) reported by [62Duh]. However, because of low-purity materials used by [62Duh], further investigation is needed to establish the composition and stability range of the intermediate phases beyond the MgB6 composition. The existence of phases very rich in B in the Mg-B phase diagram was recognized by several investigators [55Mar, 62Duh]. However, the B-rich phases MgB6 and MgB9, reported by [62Duh] and [55Mar], respectively, were never confirmed. The structural formula of MgB7 is Mg2B14. To date, no compounds richer in B than MgB7 have been reported. 53Rus: V. Russell, R. Hirst, F.A. Kanda, and A.J. King, Acta Crystallogr., 6, 870 (1953). 54Jon: M.E. Jones and R.E. Marsh, J. Am. Chem. Soc., 76, 1434-1436 (1954). 55Mar: L.Ya. Markovskii, Yu.D. Kondrashev, and G.V. Kaputovskaya, Zh. Obshch. Khim., 25, 433-444 (1955) in Russian; TR: J. Gen. Chem. USSR, 25, 409-416 ( 1955). 59Mar: L.Ya. Markovskii, G.V. Kaputovskaya, and Yu.D. Kondrashev, Zh. Neorg. Khim., 4, 1710-1714 (1959) in Russian; TR: Russ. J. Inorg. Chem., 4, 771-773 ( 1959). 62Duh: P. Duhart, Ann. Chim. (Paris), 7, 339-365 (1962) in French. 71Vek: N.V. Vekshina, L.Ya. Markovskii, Yu.D. Kondrashev, and T.K. Voedvokskaya, Zh. Prikl. Khim., 44(5), 958-963 (1971) in Russian. 72Gue: A. Guette, R. Naslain, and J. Galy, C.R. Acad. Sci. Paris, Ser. 275(C), 41-44 (1972) in French. 73Nas: R. Naslain, A. Guette, and M. Barret, J. Solid State Chem., 8, 68-85 ( 1973) in French. 76Nas: R. Naslain, A. Guette, and P. Hagenmuller, J. Less-Common Met., 47, 1- 16 (1976). 77Cal: B. Callmer, Acta Crystallogr. B, 33, 1951-1954 (1977). 77Spe: K.E. Spear, National Bureau of Standards SP-496; Proceedings of workshop held at NBS, Gaithersburg, MD, Jan 10-12 (1977). 81Gue: A. Guette, M. Barret, R. Naslain, and P. Hagenmuller, J. Less-Common Met., 82, 325-334 (1981). Published in Phase Diagrams of Binary Magnesium Alloys, 1988. Complete evaluation contains 1 figure, 3 tables, and 20 references. 1