Hydrogen absorption properties of a mechanically milled Mg-50wt%LaNi5 composite

Mechanical milling was used to make composite Mg-50 wt.% LaNi5 powders. The structural changes during the milling process and the hydrogen storage properties of the mechanically milled composite were characterized. Mechanical milling lends to a nano-composite, which is not stable upon high temperature (573 K) hydriding and dehydriding cycling. The nano-composite transforms to a new Mg+LaHx+Mg2Ni composite, which is stable upon further cycling. The new composite has excellent hydrogen absorption kinetics at low temperatures. The storage capacity reaches 2.5 wt.% in 500 s under 1.5 MPa hydrogen at 302 K. The optimum capacity is 4.1 wt.% at intermediate temperatures (523-573 K). The high absorption rate is explained by the high quantity of phase boundaries and the porous surface structure. (C) 1998 Elsevier Science S.A.