Фазовая диаграмма системы Sc-Si

К оглавлению: Другие диаграммы (Others phase diargams)

Sc-Si (Scandium-Silicon) A.B. Gokhale and G.J. Abbaschian Due to the lack of any detailed investigation of the Sc-Si system, the assessed equilibrium phase diagram was constructed using indirect information and is therefore speculative. Three intermediate phases are shown: Sc5Si3, ScSi, and Sc3Si5. The liquidus resembles those of the Ge-Y [72Sch] and Ge-Sc [ 81Ere] systems and is based on the assumption that the component interactions in these systems are likely to be similar. The enthalpy of mixing in the liquid state was measured by [84Sud] in a narrow composition range. Their results indicate that the mixing process is exothermic. No data are available on the solid solubility of Si in (Sc). Because the difference in the atomic radii of Si and Ge is small (0.146 and 0.152 nm, respectively), it is likely that Si exhibits a solid solubility in (Sc) similar to that of Ge in (Sc). For this reason, a value of ~2 at.% is shown in the assessed diagram, by analogy with the data of [81Ere] for the Ge-Sc system. [82Vla] determined the equilibrium distribution coefficient of Sc in (Si). However, their data show an increase in the Sc concentration of the Si liquidus with increasing temperature. This result is clearly in error, and the data of [82Vla] were therefore excluded from this evaluation. The melting characteristics of the phases were determined by analogy with the Ge-Y system. Sc5Si3 melts congruently, whereas ScSi and Sc3Si5 melt peritectically. Homogeneity ranges for the intermediate phases were calculated from the data of [65Dvo], who synthesized silicides by arc melting. Calculated homogeneity ranges for the intermediate phases in at.% Si are Sc5Si3, 37.33 to 37.7; ScSi, 49.84 to 50.95; and Sc3Si5, 62.5 to 63.15. [58Mat] reported the superconducting transition temperature for "ScSi2" ( Sc3Si5) as ~1 K. [79Rud] reported that the intermediate phase ScSi is a Pauli paramagnet up to 342 C. [74Laz] investigated the electrical resistivity, thermo-emf, and Hall coefficient of the intermediate phases as a function of temperature. They found that for all three phases the electrical resistivity increased linearly, whereas the Hall coefficient remained approximately constant up to about 600 C. Furthermore, the absolute thermo-emf coefficient exhibited a negative sign, indicating that electronic conductivity predominates up to 600 C. 58Mat: B.T. Matthias, E. Corenzwit, and W.H. Zachariasen, Phys. Rev., 112, 89 ( 1958). 65Dvo: L.A. Dvorina and T.S. Verkhoglyadova, Izv. Akad. Nauk SSSR, Met., (6), 62-68 (1965) in Russian; TR: Russ. Metall., (6), 38-44 (1965). 72Sch: F.A. Schmidt, O.D. McMasters, and O.N. Carlson, J. Less-Common Met., 26( 1), 53-70 (1972). 74Laz: V.I. Lazorenko, B.M. Rud, Yu.B. Paderno, and L.A. Dvorina, Izv. Akad. Nauk SSSR, Neorg. Mater., 10(11), 2087-2088 (1974) in Russian; TR: Inorg. Mater., 10, 1790-1791 (1974). 79Rud: B.M. Rud, V.P. Lonnik, V.D. Levandovskii, and V.I. Lazorenko, Izv. Akad. Nauk SSSR, Neorg. Mater., 15(4), 711-712 (1979) in Russian; TR: Inorg. Mater., 15, 555-556 (1979). 81Ere: V.N. Eremenko, I.M. Obushenko, Yu.I. Buyanov, and K.A. Meleshevich, Dop. Akad. Nauk Ukr. RSR A, 4, 80-83 (1981) in Ukrainian. 82Vla: V.I. Vlasov, V.N. Lozovskii, and A.I. Koleshichenko, Izv. Akad. Nauk SSSR, Neorg. Mater., 18(3), 518 (1982) in Russian. 84Sud: V.S. Sudavtsova, G.I. Batalin, and V.P. Kurach, Ukr. Khim. Zh. (Russ. Ed.), 50(4), 339-340 (1984) in Russian. Published in Bull. Alloy Phase Diagrams, 7(4), Aug 1986. Complete evaluation contains 1 figure, 5 tables, and 54 references. 1