Фазовая диаграмма системы Sc-V

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Sc-V (Scandium-Vanadium) J.F. Smith and K.J. Lee The phase diagram of [70Sav] and [71Sav] was used as the basis for the calculated assessed Sc-V phase diagram. The original phase diagram proposed by these authors was a simple eutectic with two straight-line segments that represent the liquidus. Because the slope of the (V) liquidus is not consistent with the van't Hoff constraint, a subregular solution model was tentatively established by the evaluators considering the data on the eutectic point reported by [71Sav]. The calculated phase diagram predicts the presence of a miscibility gap in the liquid phase with the monotectic reaction at 1459 C. The validity of this diagram must be examined. The calculated diagram shows agreement within experimental uncertainties for the temperatures and compositions at the eutectic and eutectoid reactions. A study of the superconducting behavior of Sc-V alloys [64Vol] is disregarded because it found a continuous variation with composition of the superconducting transition temperature, Tc, from 0 to 60% Sc, but did not specify whether values were in atomic percent or weight percent. Such a compositional trend is incompatible with a wide two-phase field if the alloys are in equilibrium because the transforming phase should, in a two-phase field, have constant composition and thereby constant Tc. Thus, reported continuous variation of Tc with composition implies a solid solution, but size and electronegativity differences between Sc and V, as well as analogy with the immiscibility between V and all other members of the rare earth group, argue in favor of the results of [70Sav] and [71Sav], and against any extensive solid solubility. 64Vol: N.V. Volkenshtein and E.V. Galoshina, Zh. Eksp. Teor. Fiz., 47, 812-813 (1964) in Russian; TR: Sov. Phys. JETP, 47, 543-544 (1965). 70Sav: E.M. Savitskii, V.F. Terekhova, R.S. Torchinova, I.A. Markova, O.P. Naumkin, V.E. Kolesnichenko, and V.F. Stroganova, Les Elementes des Terres Rares, Centre National de la Recherche Scientifique, Paris, 47-60 (1970). 71Sav: E.M. Savitskii, O.P. Naumkin, and Yu.V. Efimov, Izv. Akad. Nauk SSSR, Met., (2), 178-179 (1971) in Russian; TR: Russ. Metall., (2), 119 (1971). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 1 figure, 2 tables, and 9 references. Special Points of the Sc-V System