Фазовая диаграмма системы Si-V

К оглавлению: Другие диаграммы (Others phase diargams)

Si-V (Silicon-Vanadium) J.F. Smith The V-Si system is characterized by the presence of four intermediate phases- V3Si, V5Si3, VSi2, and V6Si5. The assessed phase diagram is based on review of the experimental data [56Kie, 63Efi, 67Bru, 73Koc, 74Koc, 78Sav, 81Smi1, 81Smi2], with major revisions based on the recent work of [82Jor] and [85Sto]. Early work showed V3Si as decomposing by a peritectic reaction near 2000 C, and only the diagram of [73Koc] and [74Koc] showed congruent melting. The recent study of [82Jor], however, strongly supports congruent melting and other details of their diagram. In addition, thermodynamic measurements of [ 85Sto] show that V6Si5 is a stable phase, but its stability is restricted in temperature range. The selection of ~7 at.% Si for the composition of the terminal solid solution, (V), at the eutectic equilibrium is a compromise among the available data, but favors the work of [73Koc] and [74Koc]. Measurements of thermodynamic activities by [85Sto] in the temperature range 1300 to 1725 C indicate that V6Si5 is stable in that temperature region, but extrapolation of the activities to lower temperatures indicates instability with respect to VSi2 and V5Si3 at temperatures below 1160 с 100 C. There is a large uncertainty in the decomposition temperature, because it was determined from the intersection of semilogarithmic plots of thermodynamic activities vs reciprocal temperatures for the two-phase regions VSi2-V6Si5 and V6Si5-V5Si3. [ 85Sto] also confirmed that the homogeneity range of VSi2 is negligible, and it is likely that V6Si5 and V5Si3 also have negligible homogeneity ranges. There is appreciable interest in the low-temperature superconductivity of V3Si. For stoichiometric material, the martensitic and superconducting transitions are most often reported in the ranges 21.7 to 21.9 K and 16.7 to 16.9 K, respectively. Both transitions are correlated with soft phonon modes. Not all V3Si samples under these conditions become superconducting, but the superconducting transition temperature is sample dependent. 56Kie: R. Kieffer, F. Benesovsky, and H. Schmid, Z. Metallkd., 47, 247-253 ( 1956) in German. 63Efi: Yu.V. Efimov, Zh. Neorg. Khim., 8, 1522-1524 (1963) in Russian; TR: Russ. J. Inorg. Chem., 8, 790-792 (1963). 67Bru: H.A.C.M. Bruning, Philips Res. Rep., 22, 349-354 (1967). 73Koc: Yu.A. Kocherzhinskii, O.G. Kulik, and E. Shiskin, Dokl. Akad. Nauk SSSR, 209, 1347-1349 (1973) in Russian. 74Koc: Yu.A. Kocherzhinskii, O.G. Kulik, and E. Shiskin, Strukt. Faz., Fazovye Prevrasch. Diagr. Sostoyaniyz Met. Sist., O.S. Ivanov, Ed., Izd. Nauka, Moscow, 136-139 (1974) in Russian. 78Sav: E.M. Savitskii, Yu.V. Efimov, K. Eichler, and P. Paufler, Wissenschaft, Z. Tech. Univ. (Dresden), 27, 675-676 (1978) in German. 81Smi1: J.F. Smith, Bull. Alloy Phase Diagrams, 2(1), 42-48 (1981). 81Smi2: J.F. Smith, Bull. Alloy Phase Diagrams, 2(1), 40-41 and 2(2), 172 ( 1981). 82Jor: J.L. Jorda and J. Muller, J. Less-Common Met., 84, 39-48 (1982). 85Sto: E.K. Storms and C.E. Myers, High-Temp. Sci., 20(1), 87-96 (1985). Published in Phase Diagrams of Binary Vanadium Alloys, 1989, and Bull. Alloy Phase Diagrams, 6(3), Jun 1985. Complete evaluation contains 1 figure, 3 tables, and 48 references. 1