Thermal cyclic charge and discharge stability of nanocrystalline Mg2Ni alloy

The hydrogen storage properties and the thermal cyclic charge and discharge capability of the nanocrystalline Mg,Ni alloy powder prepared by high ener gy ball milling are examined to evaluate the potential use of these materia ls in vehicular applications. Repetitive hydriding and dehydriding of nanoc rystalline Mg2Ni alloy is performed at different cycling temperatures and p ressures of absorption and desorption. It was found that the cycling did no t affect the kinetic rates of absorption/desorption. X-ray crystal structur e analysis and pressure concentration isotherms of the alloy, after initial activation and after 2100 cycles, reveal significant changes in the dynami c phase structure and the thermodynamic properties. In addition to these ex periments, we have also performed scanning electron microscopy, Brunauer Em mett-Teller (BET) specific surface area and specific heat characterizations . These have indicated that the changes in volume during the 2100 hydriding /dehydriding cycles do not produce severe decrepitation. However, inherent deterioration in the charge capacity of the alloy, apparently related to th e formation of the MgNi2 phase, was observed. (C) 1999 Elsevier Science S.A . All rights reserved.