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In the present work, experimental absorption isotherms of hydrogen in LaNi 5 at three temperatures have been fitted using a monolayer model treated by statistical physics by means of the grand canonical ensemble. Six parameters of the model are fitted, namely two numbers of absorbed atoms per, site n 1 and n 2 , two receptor site densities, N 1M and N 1M and two energetic parameters, P 1 and P 2 . The behaviors of these parameters are discussed in relationship with absorption process. Starting from the monolayer model, we determined the absorption energies which are typically ranged between 85 and 101 kJ/mol comparable to usual chemical bond energies. Calculated thermodynamic potentials such as internal energy (E int ) and Gibbs free energy (G) suggested that the absorption processes was exothermic and spontaneous. [ABSTRACT FROM AUTHOR]

Analytical expression for the modeling of hydrogen sorption isotherms on LaNi 4.75 Fe 0.25 alloy at three temperatures (293 K, 303 K and 313 K) is developed using statistical mechanics formalism. Our objective in this modeling is to select the adequate model that presents a high correlation with the experimental curves in order to obtain new physicochemical interpretations at a molecular level. The parameters involved in the model, such as the number of sorbed hydrogen atom per site, n, the receptor sites' density, N M , and the energetic parameters, P 1 and P 2 , were determined directly from the experimental sorption isotherms by numerical simulation. The results of fitting are interpreted. A dynamic study of the α and β phases of sorption was carried out by focusing on the formation of one of these phases in relation to the other, depending on the pressure and the evolution of the adjustment parameters. Then, the model is further applied to calculate thermodynamic functions which govern the sorption mechanisms such as entropy, free enthalpy of Gibbs and internal energy. [ABSTRACT FROM AUTHOR]