Influence of the microstructure on the desorption kinetics of single- and multiphase LaNiFe alloys

The influence of the microstructure on the desorption kinetics of deuterium 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 dislocations, which act as trapping sites for hydrogen atoms. At higher concentrations, where both the a and hydride phase are present, the phase transformation of the latter or diffusion in the beta phase is the rate-controlling process with an activation enthalpy of 0.39+/-0.03 eV for deuterated samples. The deuterium concentration range of the a: phase extends up to [D]/[AB(5)]=1.2 for the nanocrystalline material and this range broadening allows the study of the deuterium diffusion in the alpha phase without the influence of traps. The measured activation enthalpy for deuterium diffusion in the a phase is Q=0.50+/-0.03 eV. (C) 1998 Elsevier Science S.A.