Фазовая диаграмма системы Ce-Hg

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Ce-Hg (Cerium-Mercury) C. Guminski A theoretical phase diagram for the Ce-Hg system at constrained pressure is derived basically from [Moffatt]. The thermal stability and composition of solid phases in the Hg-rich part of the diagram require further examination. A similarity to the Pr-Hg system was presumed in the Ce-rich portion of the diagram. In the rest of the diagram, a similarity to the Hg-La system was presumed. The temperature ranges of stability of CeHg, CeHg2, and CeHg3, as drawn in the phase diagram with solid lines, were taken from [64Fla]; that of CeHg4 was based on [28Bil]. The Ce-Hg phase diagram consists of (1) the liquid phase, L; (2) the aCe, bCe, gCe, and dCe solid solutions, with solid solubilities of Hg that are very low at room temperature, probably increasing to a few at.% of Hg at higher temperature; (3) five intermetallic compounds-CeHg~6.5, Ce11Hg45, and CeHg3, formed by peritectic reactions; and CeHg2 and CeHg, formed by congruent reactions-with narrow ranges of homogeneity; and (4) the (Hg) phase, with very low solid solubility of Ce. [28Bil] and [66Kir] indicated the existence of phases richer in Hg than Ce11Hg45, but no concrete results were given. [63Olc] reported the existence of "CeHg5" with orthorhombic crystal structure, isomorphous with " LaHg5". In the review of [79Ian], CeHg5 was omitted, but the authors reported the formation of CeHg~6.5; no structural details or stability range were published. No formation of compounds richer in Ce than CeHg was found; however, [64Fla] reported that the amalgam with 7.5 at.% Hg was stable at 1000 C. This fact contradicts the theoretical phase diagram and the experiments of [ 34Juk], who totally decomposed Ce amalgam to elemental Ce and Hg at 1000 C. Only a very slow decomposition of CeHg could explain this fact but the experimental conditions of [64Fla] were, unfortunately, very briefly described. [77Bul] prepared Ce heterogeneous amalgam by cementation of Ce(III) solution with Na amalgam at ambient temperature. After filtration of this amalgam, the solid phase was identified as CeHg instead of the Hg-rich compound that might be expected. This compound subsequently retransformed itself over time to Hg- richer phases. It was calculated by [89Gum] that the Ce atom is surrounded permanently with a minimum of eight atoms of Hg in the liquid state; it is not known why CeHg precipitates first, to be further converted with additions of Hg. Possible formation of ternary Ce-Hg-H compounds was excluded by studies of [77Bul]. 28Bil: W. Biltz and F. Meyer, Z. Anorg. Allg. Chem., 176, 23-45 (1928) in German. 34Juk: E.E. Jukkola, L.F. Audrieth, and B.S. Hopkins, J. Am. Chem. Soc., 56, 303-304 (1934). 51Ian: A. Iandelli and R. Ferro, Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis. Mat. Nat., 10, 48-52 (1951) in Italian. 58Ian: A. Iandelli, The Physical Chemistry of Metallic Solutions and Intermetallic Compounds, Vol. 1, Paper 3F, Her Majesty›s Stationery Office, London (1959). 63Olc: G.L. Olcese, Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis. Mat. Nat., 35, 48-52 (1963) in Italian. 64Fla: D. Flad and F. Matthes, Z. Chem., 4, 466 (1964) in German. 66Kir: H.R. Kirchmayr and W. Lugscheider, Z. Metallkd., 57, 725-728 (1966) in German. 67Ber: A.F. Berndt, J. Less-Common Met., 13, 366-368 (1967). 77Bul: V.A. Bulina, A.I. Zebreva, and R.Sh. Enikeev, Izv. V.U.Z. Khim. Khim. Tekhnol., 20, 522-524 (1977) in Russian. 79Ian: A. Iandelli and A. Palenzona, Handbook on the Physics and Chemistry of Rare Earths, K.A. Gschneidner and L. Eyring, Ed., North-Holland Physics Publishing, Amsterdam, Ch. 13 (1979). 79Mer: F. Merlo and M.L. Fornasini, J. Less-Common Met., 64, 221-231 (1979). 89Gum: C. Guminski, J. Mater. Sci., in press (1989). Submitted to the APD Program. Complete evaluation contains 2 figures, 4 tables, and 36 references. Special Points of the Ce-Hg System