Hydrogen diffusion in Mg2NiH4 intermetallic compound

Coefficients of hydrogen diffusion in Mg2NiH4 were measured by a volumetric method at temperatures ranging from 449 to 576 K. Experimental material was prepared in two ways: by melting and casting, and by ball-milling and compacting into pellets. Hydrogen charging was performed from the hydrogen gas phase at elevated pressure and temperature. Pellets were charged in two different modes, resulting in structures with either a high fraction of twinned low-temperature phase LT2 or a low fraction of LT2. It was observed that LT2 considerably slowed down the hydrogen desorption rate. Activation enthalpy of hydrogen diffusion in high-temperature phase (above transition temperature Ttr ∼ 508 K) is approximately half of the value obtained for the low-temperature region. Coefficients of hydrogen diffusion in low-temperature un-twinned phase LT1 are by a multiplication factor of about 20 higher than those of the twinned phase LT2.