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Statistical physics treatment is used to study the desorption of hydrogen on LaNi 4.75 Fe 0.25 , in order to obtain new physicochemical interpretations at the molecular level. Experimental desorption isotherms of hydrogen on LaNi 4.75 Fe 0.25 are fitted at three temperatures (293 K, 303 K and 313 K), using a monolayer desorption model. Six parameters of the model are fitted, namely the number of molecules per site n α and n β , the receptor site densities N αM and N βM , and the energetic parameters P α and P β . The behaviors of these parameters are discussed in relationship with desorption process. A dynamic study of the α and β phases in the desorption process was then carried out. Finally, the different thermodynamical potential functions are derived by statistical physics calculations from our adopted model. [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]