Фазовая диаграмма системы Sn-U

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Sn-U (Tin-Uranium) R.I. Sheldon, E.M. Foltyn, and D.E. Peterson The assessed diagram is based almost exclusively on the work of [45Tre]. The phase Sn4U5 reported by [45Tre] is shown as Sn2U3 in the assessed diagram, and is based on the Gibbs-Duhem integration of the Sn vapor pressure [61Alc], which indicated the composition of this phase is probably closer to 60 at.% U. [45Tre] found the addition of Sn to (U) caused the liquidus to rise rather abruptly with no thermal or metallographic evidence for a eutectic. Also, no evidence of solid solution of Sn in (U) was found, and the transformation temperatures of alloys in the composition range 66.7 to 83.2 at.% U were reported as unchanged from pure U. [45Tre] reported the composition of the phase in equilibrium with U as Sn4U5. The composition of this phase is probably no more Sn-rich than Sn2U3. Thermal data indicated this compound melts congruently at 1500 C [45Tre]. For alloys between 25 and 54 at.% U, metallography revealed the presence of a phase that was definitely not Sn3U. Based on metallographic and thermal analysis data, the composition of this compound was proposed by [45Tre] to be Sn5U3, with a peritectic decomposition at 1380 C. Metallography and X-ray diffraction have also definitely established the existence of Sn3U. [45Tre] reported this compound decomposes peritectically at 1350 C. [83Sar] reported the existence of several Sn-U phases, many of which are not included in the assessed diagram. The reported phases include Sn3U, Sn7U3, Sn5U4, SnU, and Sn3U5. Also, the existence of Sn4U5 was proposed based on the ternary Sn4M5 (M = UxPu1-x, 0 њ xњ 0.75). Although several experimental techniques were used in this work, including metallography, X-ray diffraction, and microhardness measurements, the principal method of phase identification and composition determination was apparently electron microprobe analysis. Thermal analysis was limited to alloys with compositions Sn3M (M = UxPu1-x). Details of heat treatments, if any were performed to ensure alloys were true equilibrium, were not given by [83Sar]. Based on the vapor pressure measurements of [61Alc], it seems rather unlikely that all of the phases reported by [83Sar] represent true equilibrium phases. The measurements of [61Alc] clearly indicated the system to be univariant over the composition ranges 27 to 36, 40 to 55, and 64 to 83 at.% U. These results are not inconsistent with the assessed phase diagram, but they are inconsistent with the existence of several of the compounds reported by [83Sar] . Specifically, the variance of the system as indicated by vapor pressure measurements and the existence of Sn7U3, Sn2U, Sn5U, Sn5U4, and SnU are contradictory, at least over the temperatures studied by [61Alc]. 45Tre: D.A. Treick, J.H. Carter, A.I. Snow, R.R. Baldwin, and A.S. Wilson, U.S. Atomic Energy Comm. M-3107 (1945). 49Run: R.E. Rundle and A.S. Wilson, Acta Crystallogr., 2, 148-150 (1949). 61Alc: C.B. Alcock and P. Grieveson, J. Inst. Met., 90, 304-310 (1961-1962). 83Sar: C. Sari, F. Vernazza, and W. Muller, J. Less-Common Met., 92, 301-306 ( 1983). Published in Bull. Alloy Phase Diagrams, 8(4), Aug 1987. Complete evaluation contains 2 figures, 5 tables, and 14 references. Special Points of the Sn-U System