Фазовая диаграмма системы Cd-Hg

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Cd-Hg (Cadmium-Mercury) C. Guminski and L.A. Zabdyr The assessed Cd-Hg phase diagram is based primarily on [Hultgren,B], with review of the data of [64Dob], [66Pre], and [Hansen]. The equilibrium phases are (1) the gas, g; (2) the liquid, L; (3) the (Cd) phase, with a maximum solid solubility of 25 at.% Hg at 188 C; (4) the disordered w phase extending from 29 at.% Hg at 188 C to about 90 at.% Hg at -100 C; (5) the ordered w› ( Cd2Hg) and w› (CdHg2) phases, with maximum homogeneity ranges of 33 to 42 and 58 to 71 at.% Hg, respectively; and (6) the (aHg) phase, with a minimum Hg content of 96.5 at.% at -34 C. The existence of a "CdHg3" phase, postulated by [84Buk], is not reflected in the assessed diagram, because the evidence for its existence is inconclusive. The solubility of Cd in (Hg) is not available. [66Pre] constructed the liquid-gas part of the diagram on the basis of vapor pressure measurements of Cd amalgams. The liquid curve (beginning of boiling) is in close agreement with experimental data mentioned in [Hansen] and [64Dob]. The gas curve (end of boiling) is in close agreement with [64Dob], but temperatures reported in [Hansen] are 20 C higher. Values calculated from the thermodynamic data agree very well with those of [64Dob] and [66Pre]. The two ordered phases w› and w› correspond to the approximate formulas Cd2Hg and CdHg2, respectively. Their existence and homogeneity ranges were established by numerous investigators. [83Shi] and [84Buk] reported a solid phase with CdHg3 stoichiometry, which was isolated by pressure-forced filtration. The composition corresponds exactly to the solidus value of w phase at room temperature, but the XRD pictures of the CdHg3 and w phases proved to be different. The compound formed very slowly by direct melting of the appropriate amounts of the metals. [82Bel] showed that a metastable oversaturation of the liquid amalgam took place at a concentration 12% higher than that corresponding to equilibrium conditions at about 25 C. [20Coh] questioned even the serviceability of Weston's cell as a standard element, because the equilbria in the vicinity of the solidus were found to be metastable below 12 C. The phenomenon of CdHg3 is probably an example of metastability, but further investigations are needed because CdHg3 associates in the liquid phase were also reported by [ 72Koz]. [86Vij] investigated the bct = cph phase transformation in a Cd65Hg35 alloy, which occurred under a pressure of 2 GPa at room temperature; this reversible process was traced by electrical resistance and XRD. Near the transition point, the lattice parameters determined were a = 0.3897 and c = 0.290 nm for the bct form and a = 0.2927 and c = 0.5463 nm for the cph form. Analogous investigations were carried out by [86Pry] with a Cd55Hg45 alloy. The pressure dependencies of the lattice parameters, determined by the least-squares method, were a = 0.3911 - 0.034 P and c = 0.2883 - 0.002 P, where a and c are in nm and P is in GPa. In contrast to the findings of [86Vij], a smooth bct = cph structure transformation was observed, and traces of the cph phase were detected by [86Pry] even at 3 to 4 GPa. Both groups of investigators worked with different alloy compositions and did not describe times of equilibration at variable pressure; [86Vij] did not specify purity of the metals. Preference is given to the results of [86Pry] because the lattice parameters found by [ 86Vij] at normal pressure differed more from other data than did those of [ 86Pry]. [86Vij] examined the solid solution with 15 at.% Hg under pressures up to 8 GPa; no transformation was observed, as is the situation for pure Cd. The influence of pressure on the w/[w + (Cd)] boundary was studied by [80But] using resistance measurements; the composition changed linearly from 35 at.% Hg at ambient pressure to 50 at.% Hg at 7.6 GPa. [79Ser] reported that the zone energy of electrons affected the formation of the w phase and its ordering. Determination of the solubility of Cd in (Hg) and more information about the thermodynamic properties of the w› and w› phases would be useful for calculation of the phase boundaries in the assessed diagram. 20Coh: E. Cohen and A.L.T. Moesveld, Z. Phys. Chem., 95, 293-304 (1920) in German. 64Dob: B. Dobovisek and A. Paulin, Rud.-Metal. Zb., (3), 271-279 (1964) in Slovenian. 66Cla: T. Claeson, H.L. Luo, T.R. Anantharaman, and M.F. Meriam, Acta Metall., 14, 285-290 (1966). 66Pre: B. Predel and D. Rothacker, J. Less-Common Met., 10, 392-401 (1966) in German. 71Pre: B. Predel and W. Schwermann, J. Inst. Met., 99, 209-212 (1971). 72Koz: L.F. Kozin and M.B. Dergacheva, Tr. Inst. Org. Katal. Elektrokhim. Akad. Nauk Kazakh. SSR, 3, 31-44 (1972) in Russian. 72Str: J. Stringer, J. Hill, and A.S. Huglin, Phys. Status Solidi (a), 13, 67- 71 (1972). 72Sve: I.V. Svechkarev and D.D. Solnyshkin, Tr. Fiz. Tekh. Inst. Nizk. Temp. Akad. Nauk Ukr. SSR, (18), 119-125 (1972) in Russian. 79Kub: R. Kubiak and M. Wolcyrz, J. Less-Common Met., 68, 23-28 (1979). 79Ser: Yu.P. Sereda and I.V. Svechkarev, Fiz. Niskikh Temp., 5, 491-499 (1979) in Russian. 80But: A.K. Butylenko, I.V. Svechkarev, and Yu.P. Sereda, Metallofizika, 2(5), 22-24 (1980) in Russian. 82Bel: S. Beladi, J. Bensaid, L. Bougarfa, J.P. Dumas, and A. Jouanneau, J. Phys., 43, 945-951 (1982) in French. 83Shi: A.V. Shirinskikh, M.I. Grigoreva, and S.P. Bukhman, Izv. Akad. Nauk Kazakh. SSR, Khim.,(5), 20-23 (1983) in Russian. 84Buk: S.P. Bukhman, A.A. Lange, and A.A. Kairabaeva, Izv. Akad. Nauk Kazakh. SSR, Khim., (1), 31-34 (1984) in Russian. 86Pry: V.V. Prytkin, L.M. Lityagina, and E.V. Biblik, Metallofizika, 8(1), 76- 80 (1986) in Russian. 86Vij: V. Vijayakumar, S.M. Sharma, S.K. Sikka, and R. Chidambaram, J. Phys. F, 16, 831-835 (1986). Submitted to the APD Program. Complete evaluation contains 1 figure, 7 tables, and 57 references. Special Points of the Cd-Hg System