Hydrogen diffusion in Mg-H and Mg-Ni-H alloys

Coefficients of hydrogen diffusion in Mg2NiH4 (D-I), MgH2 (D-M), and in (Mg + Mg2Ni)-H eutectic (D-E) were measured in the temperature interval 449-723 K. Experimental material was prepared by two techniques: by melting and casting and by ball-milling and compacting into pellets. Hydrogen charging was carried out from the hydrogen gas phase at high temperature and pressure. The Mg2NiH4 pellets were prepared in different regimes resulting either in a structure with a high fraction or with a low fraction of twinned low-temperature phase LT2. It was found that the LT2 slows down the hydrogen desorption rate considerably - values of D-I in low-temperature untwinned phase LT1 are by a multiplication factor of about 20 higher than those in the twinned phase LT2. Obtained values of D-M are significantly lower than the literature values reported for the pure Mg. Hydrogen diffusion coefficients in interphase boundary were estimated from D-E .(c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.