La-mg-ni System Ab <sub> 3.5 </ Sub>-type And Ab <sub> 3 </ Sub> Type Hydrogen Storage Alloy Hydrogen Storage Properties And Dynamics

In this thesis, La-Mg-Ni based AB₃.5 -type La₀.75Mg₀.25Ni₃.5hydrogen storage alloy was chosen as object of this study. By means of XRD analysis, P-C-T test method, the effects of Ni partially replaced by Fe, Cr, Cu, Co and Mn elements on the structure, hydrogenation-dehydrogenation characteristics, hysteresis and kinetics were studied systemically.Based on the aforesaid investigation, La₀.75Mg₀.25Ni₃.5 (M=Ni, Fe, Cr, Cu, Co, Mn) alloys were prepared with induction melting method and annealed at high temperature (900℃ X12h). It is found that the main phases of the alloys prepared with these methods were consisted of Ce₂Ni₇ and Gd₂Co₇ phases. Both the lattice parameters and the cell volumes of La₀.75Mg₀.25Ni₀.5 (M =Fe, Cr, Cu, Co, Mn) alloys were larger than those of La₀.75Mg₀.25Ni₃.5 alloy. La₀.75Mg₀.25Ni₃.5 alloy had the largest hydrogen storage capacity H/M=1.050 and La₀.75Mg₀.25Ni₃.5 the smallest H/M=0. 906. Hydrogen storage capacity of all alloys changed in the order of Ni₀.5>Cr₀.5>Co₀.5>Fe₀.5>Cu₀.5>Mn₀.5. The partial substitution of 5 different elements for Ni in La₀.75Mg₀.25Ni₃.5 alloy also, particularly Fe and Mn, decreased plateau pressure, hysteresis and flatted plateau.The hysteresis of La₀.75Mg₀.25Ni₃.5 alloy was related not only to composition, but also its cell unit volume. In order to investigate the effect of cell unit volume on the hysteresis, La₀.75Mg₀.25Ni₃.5 alloy obtained different lattice parameters after desorption at different temperatures. It is found that the alloy' s cell unit volume became smaller and plateau pressure gradually grown higher with the desorption temperature increase. When the temperature was 400℃, the plateau pressure increased to maximum value 0.08Mpa. Compared to the desorption curve, the maximum hysteresis was 0. 0551Mpa, the minimum hystersis was 0. 0181Mpa.A recently suggested normalized pressure dependence method, NPDM, was utilized in the kinetic study of La₀.75Mg₀.25Ni₃.5 hydrogen storage alloy. For the absorption process the NPDM includes a pressure dependence function F(P) = (P-Pe)/Pe which changes in the limits of 00=l. 1 X 107 S^-1 and Ea=56.7 KJ/molH₂, respectively.