Фазовая диаграмма системы Al-B

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Al-B (Aluminum-Boron) O.N. Carlson The Al-B system is fraught with contradictory or controversial evidence that makes its evaluation difficult. The assessed phase diagram is based on [60Wri], [61Ser], and [67Ser], with review of the data of [36Hof]. There is negligible solid solubility of B in Al according to [36Hof] and [ 67Ser], who found no significant change in the lattice parameter of Al on the addition of B. Although some broadening of the (420) reflection was observed by [67Ser], it was concluded that this was not definitive evidence for solid solubility because of the possibility of mechanical stresses in the powder. [Hultgren,E] lists one stable form of B, identified as bB (complex rhombohedral), and indicates that aB (simple rhombohedral) may be stable at low temperatures. Two tetragonal forms are also listed in [Pearson3], although these are generally considered to be metastable allotropes. bB forms from the melt on freezing and is readily retained in that crystalline state on cooling to room temperature. aB is obtained on deposition from the vapor phase at 1000 C and transforms to bB on heating to 1300 C or above according to [60Hor]. On the basis of these observations, [60Hoa] concluded that an a <259> b transformation occurs in B at about 1100 C, although this was questioned by [65Hoa]. An a <259> b transformation in B is tentatively represented in the assessed diagram. [Elliott] identified the break at 1550 C with the b <259> a transformation in AlB12. This transformation is shown as a dashed line. The thermal arrest at 1850 C has been widely interpreted as being associated with the formation of AlB10 by the peritectic reaction L + bAlB12 = AlB10 and the one at 1660 C with its decomposition by an inverse peritectic reaction, AlB10 = L + bAlB12. [58Koh] observed AlB10 in alloys cooled slowly from 1700 C, whereas [67Ser] identified it by X-ray patterns of alloys quenched from the 1660 to 1850 C range but found aAlB12 to be the dominant phase in slow- cooled alloys. Although [64Mat] reported that AlB10 is a C-stabilized ternary compound, their evidence is somewhat tenuous in view of the precautions reportedly taken by [67Ser] to exclude C from their samples. The Al used by [61Ser] in their investigation was of 99.99% purity and the C content of the B was <0.08 wt.%. Furthermore, their high- temperature studies were carried out in a C-free environment. This lends support to their contention that the bAlB12 phase observed on quenching between 1550 and 1660 C is a true binary phase and is so considered here. Editor's note: A review by [89Ner] concludes that there are no reliable data which confirm the existence of bAlB12 and AlB10 in the binary system, believing these structures to be stabilized by impurities. 36Hof: W. Hoffman and W. Janiche, Z. Metallkd., 28, 1-5 (1936) in German. 36Nar: S. Naray-Szabo, Z. Kristallogr., 94, 367-374 (1936) in German. 58Koh: J.A. Kohn, G. Katz, and A.A. Giardini, Z. Kristallogr., 111, 53-62 ( 1958). 60Hoa: J.L. Hoard and A.E. Newkirk, J. Am. Soc. Chem., 82, 70-76 (1960). 60Hor: F.H. Horn, Boron: Synthesis, Structures, and Properties, J.A. Kohn, W.F. Nye, and G.K. Gaulle, Ed., Plenum Press, New York, 110-115 (1960). 60Koh: J.A. Kohn and D.W. Eckhart, Anal. Chem., 32, 296-298 (1960). 60Wri: E.H. Wright and L.A. Willey, Alcoa Research Lab. Tech. Paper No. 15, 1- 46 (1960). 61Ser: V.T. Serebryanskii, V.A. Epel'baum, and G.S. Zhdanov, Dokl. Akad. Nauk SSSR, 141, 1244-1246 (1961) in Russian; TR: Proc. Acad. Sci. USSR, 141, 1244- 1246 (1961). 64Mat: V.I. Matkovich, J.E. Economy, and R.F. Giese, J. Am. Chem. Soc., 86, 2337-2340 (1964). 67Ser: V.T. Serebryanskii, V.A. Epel'baum, and G.S. Zhdanov, Russ. J. Inorg. Chem., 12, 1311-1316 (1967). 89Ner: V.A. Neronov, Poroshk. Metall., (10), 58-62 (1989) in Russian. Submitted to the APD Program. Complete evaluation contains 3 figures, 3 tables, and 24 references. Special Points of the Al-B System