TY - JOUR
T1 - Attempts to improve Mg2Ni hydrogen storage by aluminium addition
AU - Sato, Toyoto
AU - Blomqvist, Helen
AU - Noréus, Dag
N1 - Funding Information:
The authors thank K. Jansson for helpful technical assistance. H. Blomqvist thanks MISTRA (Foundation for Strategic Environmental Research) for financial support.
PY - 2003/8/11
Y1 - 2003/8/11
N2 - In an attempt to destabilize Mg2NiH4, the starting alloy, Mg2Ni, was doped with aluminium by ball milling before hydrogenation. The structure of Mg2NiH4 is based on an electron-rich d10 [NiH4]-complex stabilized by a Mg ion framework and from theoretical calculations it had been suggested that a further destabilization of the hydride could be obtained by substituting some Mg for Al. After hydrogenation, the structure, color and phase transition temperature of Mg2NiH4 was found to be affected by Al addition. The conventional monoclinic low-temperature (LT) structure of Mg2NiH4 was not observed by X-ray diffraction for Mg2-xAlxNiH4, which instead could be indexed with a cubic unit cell, a=6.519 Å, that is very close to the dynamically disordered, cubic, high-temperature (HT) phase of Mg2NiH4 (a=6.490 Å). In contrast, the Al-doped Mg2NiH4 is stable at room temperature. Furthermore, the typical orange color of Mg2NiH4 was not observed and differential scanning calorimetric measurements (DSC) of the Al-containing hydride showed a 10 °C decrease in phase transition temperature. This is interpreted as a transition from a statically disordered pseudo-HT structure to the dynamically disordered HT phase. However, the monoclinic structure of the LT phase of Mg2NiH4 could again be observed at room temperature after 10 hydriding/dehydriding cycles, indicating that the Al-doping of Mg2NiH4 is counteracted by cycling and only has a temporary influence on the properties.
AB - In an attempt to destabilize Mg2NiH4, the starting alloy, Mg2Ni, was doped with aluminium by ball milling before hydrogenation. The structure of Mg2NiH4 is based on an electron-rich d10 [NiH4]-complex stabilized by a Mg ion framework and from theoretical calculations it had been suggested that a further destabilization of the hydride could be obtained by substituting some Mg for Al. After hydrogenation, the structure, color and phase transition temperature of Mg2NiH4 was found to be affected by Al addition. The conventional monoclinic low-temperature (LT) structure of Mg2NiH4 was not observed by X-ray diffraction for Mg2-xAlxNiH4, which instead could be indexed with a cubic unit cell, a=6.519 Å, that is very close to the dynamically disordered, cubic, high-temperature (HT) phase of Mg2NiH4 (a=6.490 Å). In contrast, the Al-doped Mg2NiH4 is stable at room temperature. Furthermore, the typical orange color of Mg2NiH4 was not observed and differential scanning calorimetric measurements (DSC) of the Al-containing hydride showed a 10 °C decrease in phase transition temperature. This is interpreted as a transition from a statically disordered pseudo-HT structure to the dynamically disordered HT phase. However, the monoclinic structure of the LT phase of Mg2NiH4 could again be observed at room temperature after 10 hydriding/dehydriding cycles, indicating that the Al-doping of Mg2NiH4 is counteracted by cycling and only has a temporary influence on the properties.
KW - Calorimetry
KW - Hydrogen storage materials
KW - Mechanical alloying
KW - X-ray diffraction
UR - http://www.scopus.com/inward/record.url?scp=0042063734&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0042063734&partnerID=8YFLogxK
U2 - 10.1016/S0925-8388(02)01247-1
DO - 10.1016/S0925-8388(02)01247-1
M3 - Conference article
AN - SCOPUS:0042063734
VL - 356-357
SP - 494
EP - 496
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
SN - 0925-8388
T2 - Proceedings of the Eight International Symposium on Metal Hyd (MH 2002)
Y2 - 2 September 2002 through 6 September 2002
ER -