HYDROGEN ABSORPTION PROPERTIES OF A MECHANICALLY MILLED MG-50WT-PERCENT-LANI5 COMPOSITE

Mechanical milling was used to make composite Mg-50 wt.% LaNi5 powders . The structural changes during the milling process and the hydrogen s torage properties of the mechanically milled composite were characteri zed. 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 s table upon further cycling. The new composite has excellent hydrogen a bsorption 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 absorp tion rate is explained by the high quantity of phase boundaries and th e porous surface structure. (C) 1998 Elsevier Science S.A.