La-y-ni - Mn-al Of The Hydrogen Storage Properties

On the basis of an investigation on continuous transfers of hydrogen,La-Y-Ni-M-M'(M and M' are Al or Mn,while M and M' can be the same or not)alloys were chosen to study in present work.By the means of X-Ray diffraction(XRD),scanning electron microscope(SEM)and hydriding-dehydriding test, material characteristics such as the crystal structure,hydriding-dehydriding behavior, thermodynamics,kinetics characteristics and cyclic hydrogen storage properties were systematically studied.Moreover,different composing alloys were studied as comparison.It is found that the crystal cell volume and the |△H| of the metal hydride became lager and the system became steady with more Al and Mn.The crystal cell volume increase,which are propitious for the reduction of equilibrium hydrogen pressure.But the equilibrium hydrogen pressure and the crystal cell volume increase when Y concentrating.The anisotropic elongation along the a axis and c axis as a function of Al concentration,and the effort on the hydrogen storage,because of the number of the interspace which could hold H reducing,which won't happen when Mn concentrating, were also discussed.Hysteresis coefficient decreased both with increasing Al and Mn and decreasing Y at a given temperature and with increasing temperature at a given sample.The rates of absorption of alloys tend to increase with increasing the Al or Mn content,so hydrides with low plateau pressure form faster than those with high plateau pressures.The reaction rates of absorption are directly proportional to hydride stability. Reaction rates in theβphases are faster than those in the two-phase(α+β)region.In theα+βandβphase regions,the rate-determining step was characterized as the nucleation and growth,and diffusion of hydrogen atoms to the hydride layer,respectively.After 500 cycles,the equilibrium hydrogen pressure of La_0.4Y_0.6Ni_4.8Al_0.2and La_0.4Y_0.6Ni_4.8Mn_0.1Al_0.1decreased,thus the alloys became steady;no obvious change in hydrogen storage capacity was found,and the rate of absorption of alloy decreased a little.