Фазовая диаграмма системы H-Pd

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H-Pd (Hydrogen-Palladium) A. San-Martin and F.D. Manchester The Pd-H phase diagram at a pressure higher than 1 atm, consists of a and a› phases, two random interstitial solid solutions of H based on the fcc structure of Pd. a is the low-concentration phase of the Pd-H system, separated from the high-concentration a by a mixed a + a› phase region. The boundary of this mixed phase region was delineated by taking an average of the limiting T-X values for the isotherm plateaus determined by [64Wic], [73Fri], [ 83Las], [85Las], and [87Wic] (X = H/Pd). Because hysteresis is observed in absorption and desorption isotherms for T < Tc ([36Gil, 60Eve]), it is possible to draw two different sets of boundaries for the mixed phase region at each temperature. At around 25 C, the maximum H solubility in a is X ~ 0. 017 (1.68 at.% H), whereas single- 0.60 (37.6 at.% H). The two-phase region closes at the critical point located at T = 293 C, X = 0.29 (~22.5 at.% H), and P = 20.15 bar [74Rib]. Sieverts' law is obeyed in liquid and in solid (Pd) at low H concentrations. According to [73Bur], deviations from this law appear at T < 250 C and X > 0. 006 (~0.6 at.% H). The solubility decreases as the temperature increases and, at the melting temperature of Pd, the transition from solid to liquid is marked by a positive step in the solubility. The H solubility increases at high H2 pressures and also as a result of the creation of dislocations in the Pd matrix. Solubility enhancement is also produced by the transformation from a to a› and vice versa. The presence of impurities on the surface of Pd dramatically affects absorption of H. The existence of two ordered phases, designated A2B2 and A4B, have been confirmed by neutron diffraction experiments. [83Bal] performed a comprehensive study of some of the superconducting parameters of the Pd-H (also the Pd-D) system and related the results to the phase diagram. In the X range from 0.84 to 0.91 (or between 45.7 and 47.6 at.% H), the results indicated the presence of two superconducting forms of PdHx ( both type II superconductors). These findings were also consistent with the results of [82Bon] for the Pd-D system. However, when relating the limits of [ 82Bon] for a mixed phase region to those given by [83Bal], it should be kept in mind that isotope shifts in phase boundary locations are also possible. 36Gil: L.J. Gillespie and L.S. Galstaun, J. Am. Chem. Soc., 58, 2565-2573 ( 1936). 60Eve: D.H. Everett and P. Nordon, Proc. Roy. Soc. (London) A, 259, 341-360 ( 1960). 64Wic: E. von Wicke and G.H. Nernst, Ber. Bunsenges. Phys. Chem., 68, 224-235 ( 1964) in German. 73Bur: R. Burch and N.B. Francis, J. Chem. Soc., Faraday I, 69, 1978-1982 ( 1973). 73Fri: H. Frieske and E. Wicke, Ber. Bunsenges., 77(1), 48-52 (1973). 74Rib: Y. de Ribaupierre and F.D. Manchester, J. Phys. C, Solid State Phys., 7, 2126-2139 (1974). 78And1: I.S. Anderson, C.J. Carlile, and D.K. Ross, J. Phys. C, Solid State Phys., 11, L381-L384 (1978). 78And2: I.S. Anderson, D.K. Ross, and C.J. Carlile, Phys. Lett. A, 68, 249-251 (1978). 79Ell: T.E. Ellis and C.B. Satterthwaite, Phys. Rev. Lett., 42, 7, 456-458 ( 1979). 80Bla: O. Blaschko, R. Klemencic, and P. Weinzierl, Acta Crystallogr. A, 36, 605-609 (1980). 82Bon: R.A. Bond and D.K. Ross, J. Phys. F, Met. Phys., 12, 597-609 (1982). 83Bal: I.S.L. Balbaa, thesis, Univ. Toronto (1983). 83Las: R. Lasser and K.-H. Klatt, Phys. Rev. B, 28, 748-758 (1983). 85Las: R. Lasser, J. Phys. Chem. Solids, 46, 33-37 (1985). 87Wic: E. Wicke and J. Blaurock, J. Less-Common Met., 130, 351-363 (1987). Submitted to the APD Program. Complete evaluation contains 10 figures, 4 tables, and 190 references. 1