Microstructural and hydrogen interaction properties of multisubstituted AB5 intermetallics

N.M. CERÓN-HURTADO; M.R. ESQUIVEL

Ciudad de San Juan

Congreso; HYFUSEN 2009 - Tercer Congreso Nacional –Segundo Congreso Iberoamericano Hidrógeno y Fuentes Sustentables de EnergíaTercer Congreso; 2009

Instituto de Energía y Desarrollo Sustentable (IEDS)-CNEA

Two intermetallics were obtained by low energy mechanical alloying. La0,25Ce0,52Nd0,17Pr0,06(Ni4,70Sn0,3) was synthesized from raw La0,25Ce0,52Nd0,17Pr0,06, Sn and Ni and LaCeNdPr(NiSnAl)5 was mechanically alloyed from a mixture of the first intermetallic and La(Ni4,70Al0,30). The materials were milled during 100 h up to completion stage. At this integrated milling time, no further changes are produced in the chemical composition due to mechanical alloying. The typical microstructure characteristics corresponding to traces of cold welding and fracture were identified and characterized by Scanning Electron Microscopy (SEM). The evolution of the particle size distribution during milling was analyzed using an ad-hoc designed software. The chemical composition of reactants and products was analyzed by Neutron Activation Analysis (NAA) and Energy Dispersive Spectroscopy (EDS). The structural properties were analyzed by X-ray Diffraction (XRD). The thermal stability of the compounds was done using Scanning Differential Calorimetry (DSC) and the Hydrogen sorption properties under dynamic and equilibrium conditions were studied by Volumetry. The diffraction experimental patterns of as-milled samples indicated that both compounds are iso-structural to the family base compound LaNi5. The structures were assigned to the space group P6/mmm.  Lanthanides in La0,25Ce0,52Nd0,17Pr0,06(Ni4,70Sn0,3) occupy the Wyckoff positions (1a) while Sn and Ni are distributed among the  (2c, 3g) ones. The cell parameters found are a = 4,91(2) Å and c =  4,06(7) Å. The as-milled samples show a highly distorted structure and no plateau in the pressure-composition isotherms. To improve both the structural and hydrogen sorption properties, the intermetallics were annealed under Ar atmosphere at 200, 400 and 600 °C during 24 h. As annealing temperature increases, the structure is refined, the crystallite size is increased and the pressure composition isotherms show the presence of plateaus. The application of the results to a hydrogen compression scheme in the 0-50 atm is presented.