Фазовая диаграмма системы Al-H

К оглавлению: Другие диаграммы (Others phase diargams)

Al-H (Aluminum-Hydrogen) A. San-Martin and F.D. Manchester In metal-hydrogen (metal hydride) systems, the equilibrium pressure of the hydrogen surrounding the metal is always a significant thermodynamic variable, in contrast to most situations involving metallic alloys. Two sections of the P-T-X surface (T-X and P-X diagrams) are therefore necessary. The assessed Al- H phase diagram is a T-X diagram for a pressure of 100 MPa (1 kbar); it is based on [81Sha], with review of the data of [61Eic] and [75Gab]. The solubility of H in solid Al is very small at atmospheric pressure and increases (but always remains small) with the melting of Al. The assessed diagram contains a eutectic-type reaction near the melting point of Al, 660. 452 C [Melt]. The only noticeable solubility increase occurs at high hydrogen pressures. The assessed diagram shows the effects of hydrogen pressures of 100 MPa (1 kbar), and H absorption of around 5 at.% H in the GPa range [84Bar] has been reported. [81Sha] reported that no deviations from Sieverts' law were observed up to 100 MPa. Studies [83Bar, 84Bar, 85Bar] on the existence and properties of a high- pressure phase of the Al-H system having hexagonal structure and nominal AlH3 stoichiometry used as a starting product (apart from hydrogen) the crystalline AlH3 phase [69Tur] synthesized by chemical methods [76Bro]. [83Bar] exposed a fresh surface of the AlH3 phase to the air and observed that the surface was almost immediately covered by an oxide layer that prevented further decomposition. Below 140 C, [83Bar] found limited decomposition of AlH3. The pressure for the plateau of the decomposition isotherm was estimated [83Bar, 84Bar] to be 0.71 GPa (7.1 kbar); however, [84Bar] indicated that the true value of the equilibrium pressure should be higher than 0.71 GPa, because the decomposition and formation of new phases in metal-hydrogen systems are usually subject to hysteresis effects. According to [84Bar], the formation of the hydride under high hydrogen pressures requires the use of Al powder obtained by thermal decomposition of the initial AlH3 product. Samples with an atomic ratio of 2.7 resulted after heating for 3.5 h at 300 C followed by another 16 h at 200 C under a hydrogen pressure of 2.8 GPa. [ 84Bar] also found that an Al foil under the same pressure and temperature conditions as the Al powders (but never before subjected to the action of hydrogen) dissolved the gas only up to a composition of ~4.8 at.% H. [85Bar] investigated the influence of pressures of up to 35 GPa (350 kbar) on the AlH3 phase and reported that no transformation of the initial hexagonal structure was observed. 49Str: M.E. Straumanis, J. Appl. Phys., 20, 726-734 (1949). 61Eic: W. Eichenauer, K. Hattenbach, and A. Pebler, Z. Metallkd., 52, 682-684 ( 1961). 69Tur: J.W. Turley and H.W. Rinn, Inorg. Chem., 8, 18-22 (1969). 75Gab: R.M. Gabidulin, B.A. Kolachev, and L.N. Zhuravlev, V.U.Z. Tsvetn. Metall., (3), 112-117 (1975) in Russian; TR: Sov. Non-Ferrous Met. Res., (3), 115-117 (1975). 76Bro: F.M. Brower, N.E. Matzek, P.F. Reigler, H.W. Rinn, C.B. Roberts, D.L. Schmidt, J.A. Snover, and K. Terada, J. Am. Chem. Soc., 98/99, 2450-2453 (1976) . 80Her: P.J. Herley, O. Christofferson, and J.A. Todds, J. Solid State Chem., 35, 391-401 (1980). 81Sha: B.I. Shapovalov, N.P. Serdyuk, and O.P. Semik, Dop. Akad. Nauk Ukr. RSR, A, Fiz.-Mat. Tekh., (6), 99-101 (1981) in Ukrainian. 83Bar: B. Baranowski and M. Tkacz, Z. Phys. Chem. Neue Folge, 135, 27-38 (1983) . 84Bar: B. Baranowski, M. Tkacz, and S. Filipek, Mater. Res. Soc. Symp. Proc., 1984, 22, High Pressure Sci. Technol., Pt. 3, 53-56 (1984). 85Bar: B. Baranowski, H.D. Hochheimer, K. Strossner, and W. Honle, J. Less- Common Met., 113, 341-347 (1985). Submitted to the APD Program. Complete evaluation contains 3 figures, 1 table, and 44 references. 1