Improvement of Hydrogen-Storage Properties of MgH_2 by Addition of Ni and Ti via Reactive Mechanical Grinding and a Rate-Controlling Step in Its Dehydriding Reaction

摘要

In a shift from prior work, MgH_2, instead of Mg, was used as a starting material in this work. A sample with a composition of 86 wt% MgH_2-10 wt% Ni-4 wt% Ti was prepared by reactive mechanical grinding. Activation of the sample was completed after the first hydriding cycle. The effects of reactive mechanical grinding of Mg with Ni and Ti were discussed. The formation of Mg_2Ni increased the hydriding and dehydriding rates of the sample. The addition of Ti increased the hydriding rate and greatly increased the dehydriding rate of the sample. The titanium hydride, TiH_(1.924), was formed during reactive mechanical grinding. This titanium hydride, which is brittle, is thought to help the mixture pulverized by being pulverized during reactive mechanical grinding and further to prevent agglomeration of the magnesium by staying as a hydride among Mg particles. A rate-controlling step for the dehydriding reaction of the hydrided MgH_2-10Ni-4Ti was analyzed by using a spherical moving boundary model on an assumption that particles have a spherical shape with a uniform diameter.