ABSTRACT
In this article, the experimental measurements of the absorption/desorption P-C-T isotherms of hydrogen in the LaNi4.4Fe0.3Al0.3 alloy at different temperatures and constant hydrogen pressure have been studied using a numerical model. The mathematics equations of this model contain parameters, such as the two terms, nα and nß, representing the numbers of hydrogen atoms per site; Nmα and Nmß are the receptor sites' densities, and the energetic parameters are Pα and Pß. All these parameters are derived by numerically adjusting the experimental data. The profiles of these parameters during the absorption/desorption process are studied as a function of temperature. Thereafter, we examined the evolution of the internal energy versus temperature, which typically ranges between 138 and 181 kJmol-1 for the absorption process and between 140 and 179 kJmol-1 for the desorption process. The evolution of thermodynamic functions with pressure, for example, entropy, Gibbs free energy (G), and internal energy, are determined from the experimental data of the hydrogen absorption and desorption isotherms of the LaNi4.4Al0.3Fe0.3 alloy.
ABSTRACT
In the present study, the absorption and desorption kinetics of hydrogen and the isotherm (P-C-T)) of the LaNi4Mn0·5Co0.5 alloy were measured at values of 283 K, 303 K, and 313 K. The morphological states of this sample were examined using characterization techniques, including X-ray diffraction and scanning electron microscopy. The thermodynamic functions for the absorption-desorption of hydrogen by hydrides, such as enthalpy (H) and entropy (S), were calculated from the experimental data or by using a model that exists in the literature and is premised on the adjustment of isotherm curves at various temperatures. This model is based on an integrated form of the Van't Hoff equation and a simultaneous examination of the isotherms. According to the experimental results, the amount of hydrogen absorbed or desorbed by the sample is significantly affected by the partial substitution of the nickel atom by the elements Mn and Co. However, this substitution increased the absorption or de-sorption plateau pressure.
