A technique of trace element doping to modify the solidification
mechanisms of the faceted/non-faceted eutectic Mg–Mg
2 Ni alloy system has been developed
[2]. It was demonstrated that the mi-cro- and nano-structure of cast hypoeutectic Mg–Mg2
Ni alloys
can be varied by trace additions of Na, Ca or Eu to the liquid prior
to solidification. As a result, a reversible hydrogen absorption capa-
bility in excess of 90% of the theoretical value of 6.8 wt% under the
absorption parameters of 350
C and 1 MPa for 24 min and subse-
quent desorption at 0.2 MPa for 24 min after activation has been
achieved
[3]
. The hydrogen absorption kinetics have been dramat-
ically improved under realistic industrial conditions, and the alloys
also show no sign of reduced capacity even after 200 hydride/
dehydride cycles
[4]
. The solidification processing route results in
a non-pyrophoric material that may be produced in large quanti-
ties at comparatively low cost
[4]
. The exact mechanisms of im-
proved kinetics are still not understood, however, it is expected
that the combination of the morphological change and trace ele-
ment distribution along with possible changes in the density of
crystallographic defects and the chemical nature of the modifying
additions are all likely to contribute to the unique hydrogen stor-
age properties of modified magnesium based hydrogen storage al-
loys[5]
. It has been found that Mg–Ni alloys in machined ‘chips’
react with the external atmosphere (air/oxygen) at a slower rate
than samples of higher specific surface area such as – powders
which are produced by high energy ball milling under inert atmo