Фазовая диаграмма системы Pb-U

К оглавлению: Другие диаграммы (Others phase diargams)


Pb-U (Lead-Uranium) R.I. Sheldon, E.M. Foltyn, and D.E. Peterson The assessed phase diagram for the Pb-U system is based primarily on the work of [52Tei], [53Fro], and [56Tei]. It includes three eutectic reactions, a disputed syntectic reaction and liquid miscibility gap, two intermetallic compounds (PbU and Pb3U), and low intersolubility of the solids. Pb-U alloys are pyrophoric, except in dilute solutions, making experimental work difficult. The high vapor pressure of Pb made thermal analysis difficult above 1200 C. The first comprehensive investigation of the Pb-U system was published by [ 52Tei]. Attempts to fabricate samples above 1280 C resulted in separation of the liquids, the first indication of a liquid miscibility gap in this system. Because the composition of the eutectic between Pb and Pb3U contained less than 0.1 at.% U, and no crystallographic changes in Pb were observed with the addition of U, [52Tei] proposed little solubility of U in (Pb). Addition of Pb to U had little effect on the allotropic transformation temperatures of U, and the eutectic between U and PbU lies very close to pure U (~99.5 at.% U), indicating low solubility of Pb in (U). A substantial disagreement concerning the phase behavior above 1280 C exists between [52Tei] and [53Fro]. Instead of the liquid miscibility gap reported by [52Tei], [53Fro] proposed a flattened liquidus extending from congruently melting PbU (Tfus, 1280 C) to the eutectic reaction between PbU and U at 1125 C and ~99 at.% U. [53Fro] observed thermal arrests at 1190 C (85 at.% U), 1275 C (59 at.% U), and 1280 C (50 at.% U). The 5 C difference between 50 and 59 at.% alloys is probably insignificant, but the single arrest at 1190 C is supporting evidence for the interpretation of [53Fro]. However, [53Fro] stated that undercooling during thermal analysis made determination of liquidus curves difficult. They proposed gravitational separation as the reason for the phase segregation observed by [52Tei]. The assessed diagram reflects the interpretation of [52Tei]. [83Sar] proposed the existence of several compounds in addition to PbU and Pb3U, based on observation of the Pb-Pu system, but no experimental evidence for these compounds has been found. 52Tei: R.J. Teitel, Trans. Am. Inst. Min. Metall. Eng., 194, 397-400 (1952). 53Fro: B.R.T. Frost and J.T. Maskrey, J. Inst. Met., 82, 171-180 (1953-1954). 58Tei: R.J. Teitel, J. Inst. Met., 85, 409-412 (1956-1957). 61Bro: A. Brown, Acta Crystallogr., 14, 856-860 (1961). 83Sar: C. Sari, F. Vernazza, and W. Muller, J. Less-Common Met., 92, 301-306 ( 1983). Published in Bull. Alloy Phase Diagrams, 8(6), Dec 1987. Complete evaluation contains 2 figures, 5 tables, and 16 references. Special Points of the Pb-U System