Mechanism and Kinetics of Hydrogen Diffusion in Some Zr(Cr1-x Fex)2 Laves phase

A series of Zr (Cr1-x Fex) 2 alloys with x= 0.4, 0.6 and 0.75 were prepared the major phase in these alloys had C14 Laves phase type structure. Experiments were carried out in a microbalance with a high sensibility (2.10-6 g) at different supply pressures (0.05 to 1MPa) and absorption temperatures ( 20 to 70C) in a close system. The microthermogravimetry method was applied to interpret the experimental data and to compare with each other approach and its possibility were discussed. The maximum hydrogen storage capacity of these compounds varies between 2.5 to 2.85 (H/formula). Absorption-desorption kinetics of the hydrides was realized on a sample mass equal to 50mg in the aim to minimize the heat gradient. After activation period the kinetics were found to be fast and vary linearly with the pressure values. The reactions rate are controlled by nucleation and growth in the formation and by three-dimensional diffusion outside the grains in the decomposition. Activation energy values in the above-mentioned alloys were found respectively equal: Ea 44.3, 50.2 and 54.5KJ/mol. H2