Coefficients of hyd
rogen diffusion in Mg
2NiH
4 we
re measu
red by a volumet
ric method at tempe
ratu
res
ranging f
rom 449 to 576
K. Expe
rimental mate
rial was p
repa
red in two ways: by melting and casting, and by ball-milling and compacting into pellets. Hyd
rogen cha
rging was pe
rfo
rmed f
rom the hyd
rogen gas phase at elevated p
ressu
re and tempe
ratu
re. Pellets we
re cha
rged in two diffe
rent modes,
resulting in st
ructu
res with eithe
r a high f
raction of twinned low-tempe
ratu
re phase LT2 o
r a low f
raction of LT2. It was obse
rved that LT2 conside
rably slowed down the hyd
rogen deso
rption
rate. Activation enthalpy of hyd
rogen diffusion in high-tempe
ratu
re phase (above t
ransition tempe
ratu
re
Ttr ![]()
rc="http://www.sciencedi
rect.com/scidi
rimg/entities/223c.gif" alt="not, ve
rt, simila
r" title="not, ve
rt, simila
r" bo
rde
r="0"> 508 K) is app
roximately half of the value obtained fo
r the low-tempe
ratu
re
region. Coefficients of hyd
rogen diffusion in low-tempe
ratu
re un-twinned phase LT1 a
re by a multiplication facto
r of about 20 highe
r than those of the twinned phase LT2.