INFLUENCE OF THE MICROSTRUCTURE ON THE DESORPTION-KINETICS OF SINGLEPHASE AND MULTIPHASE LANIFE ALLOYS

The influence of the microstructure on the desorption kinetics of deut erium was studied on single-phase La(Ni0.7Fe0.3)(5) and multi-phase La (Ni0.7Fe0.3)(5)-Ni0.7Fe0.3 alloys. At low hydrogen concentrations [D]/ [AB(5)]less than or equal to 0.5, the desorption kinetics of activated microcrystalline alloys are dominated by the influence of dislocation s, which act as trapping sites for hydrogen atoms. At higher concentra tions, where both the a and hydride phase are present, the phase trans formation of the latter or diffusion in the beta phase is the rate-con trolling process with an activation enthalpy of 0.39+/-0.03 eV for deu terated samples. The deuterium concentration range of the a: phase ext ends up to [D]/[AB(5)]=1.2 for the nanocrystalline material and this r ange broadening allows the study of the deuterium diffusion in the alp ha phase without the influence of traps. The measured activation entha lpy for deuterium diffusion in the a phase is Q=0.50+/-0.03 eV. (C) 19 98 Elsevier Science S.A.