Hydrides phase equilibria

Assuming the composition of the hydride to be expressed by PdjH2 (which corresponds to PdH0. 7) and bearing in mind the interstitial positioning of the hydrogen in the palladium lattice, the authors postulate the existence of the following equilibrium at the surface of the j8-hydride phase... 

The thermodynamic aspects of hydride formation from gaseous hydrogen are described by means of pressure-composition isotherms in equilibrium (AG = 0). While the solid solution and hydride phase coexist, the isotherms show a flat plateau, the length of which determines the amount of H2 stored. In the pure P-phase, the H2 pressure rises steeply vfith increase in concentration. The two-phase region ends in a critical point T, above which the transition from the a- to the P-phase is continuous. The equilibrium pressure peq as a function of temperature is related to the changes AH° and AS° of enthalpy and entropy ... 

Starting from point 1, a small amount of hydrogen goes into solution in the metal phase as the H2 pressure increases. At point 2, the hydriding reaction begins (Eq, l) and H2 is absorbed at nearly constant pressure. This pressure Pp is termed the "plateau pressure" and corresponds to a two-phase mixture of metal. Me, and metal hydride, MeHx. At point 3, the metal has been completely converted to the hydride phase. Further increases in H2 pressure (point h) result in only a small addition of hydrogen in solution in the hydride phase. In principle this curve is reversible. Extraction of H2 from the gas phase results in the dissociation of the hydride phase in an attempt to maintain the equilibrium plateau pressure. 

Abstract. A phase equilibriums in intermetallic compounds hydrides in the area of disordered a-, (3-phase in the framework of the model of non-ideal lattice gas are description. LaNi5 hydride was chosen as the subject for the model verification. Position of the critical point of the P—w.-transition in the LaNi5-hydrogen system was definite. 

Keywords Hydrogen, metal hydrides, intermetallic compounds, phase equilibriums, model of non-ideal lattice gas. 

The results given in Figs. 1 and 2 shows that application of thermodynamic perturbation theory for simulating phase equilibriums in IMC hydrides gives, mainly, correct description of the main peculiarities of the PCT diagrams of the LaNi5-H2 system in the area of disordered phases over the wide pressure range. 

The subject for further investigations in frameworks of proposed method for calculation of phase equilibriums is description of equilibrium isotopic effect in intermetallic hydrides the method is used for isotope isolation and hydrogen... 

One of new methods of magnesium, transition and rare-earth metals hydrides and their compounds obtaining is mechanical-chemical method. Numerous quantity of works are devoted to the improving kinetic, sorption properties of hydrides which were treated mechanically or were obtained by this method in hydrogen medium under pressure [1-7]. Great consideration is given to the influence of dispersity on phase equilibrium. At the same time the investigation of mechanical... 

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