Фазовая диаграмма системы Eu-V

К оглавлению: Другие диаграммы (Others phase diargams)

Eu-V (Europium-Vanadium) J.F. Smith and K.J. Lee Because only limited experimental data concerning the phase relationships in the Eu-V system are available, the assessed diagram was based on a subregular solution model for the liquid, bcc, and fcc phases and on an ideal gas model for the vapor phase. The assessed diagram illustrates the Eu-V system under a constant pressure of 1.013 bar (1 atm). There is no significant solubility of Eu in (V) or of V in (Eu) at any temperature. Eu is atypical compared with the other lanthanide elements, because its outer electron configurations can change with ligand environment from a 4f 76s2 divalent configuration to a 4f 65d16s2 trivalent configuration at an energy cost of 96 kJ/mol [83Nie]. In the commonly cited experimental data, pure metallic is shown to be in the divalent state, but alloying can favor the trivalent state. Thus, alloying of Eu with V begins with Eu in the divalent state. Increasing the concentration of V, however, requires consideration of the trivalent state. In calculating the phase equilibria for the assessed diagram, the two valence states were considered as competitive and were allowed to mix in whatever ratio produced the lowest Gibbs energy state. Data for the melting of V were taken from [81Smi], for the hypothetical fcc to bcc transition in V from [70Kau], for the temperatures of transition and melting of Eu from [Gschneidner], for the enthalpies of transition and melting of Eu from [83Cha], and for the enthalpy and temperature of boiling of Eu [ Gschneidner]. These data were combined with estimates of the interaction parameters derived with the Miedema model [76Mie, 79Deb]. 69Gsc: K.A. Gschneidner, Jr., J. Less-Common Met., 17, 13-24 (1969). 70Kau: L. Kaufman and H. Bernstein, Computer Calculation of Phase Diagrams, Academic Press, New York, 184 (1970). 76Mie: A.R. Miedema, J. Less-Common Met., 46, 167-173 (1976). 79Deb: F.R. DeBoer, W.J. Dijkman, W.C.M. Mattens, and A.R. Miedema, J. Less- Common Met., 64, 241-253 (1979). 81Smi: J.F. Smith, Bull. Alloy Phase Diagrams, 2, 40-41, 172 (1981). 83Cha: M.W. Chase, Bull. Alloy Phase Diagrams, 4(1), 124 (1983). 83Nie: A.K. Niessen, F.R. DeBoer, R. Boom, P.F. DeChatel, W.C.M. Mattens, and A.R. Miedema, Calphad, 7, 51-70 (1983). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 4 figures, 1 table, and 10 references. 1