Effect of carbon-containing compounds on the hydriding behavior of nanocrystalline Mg sub 2 Ni

• Published in: Journal of alloys and compounds Vol. 307; no. 1-2; pp. 226 - 233
• Main Authors: Guay, D, Dodelet, J P, Bouaricha, S, Huot, J, Boily, S, Schuiz, R
• Format: Journal Article
• Language: English
• Published: 14.07.2000
• ISSN: 0925-8388

Nanocrystalline Mg sub 2 Ni was prepared by high-energy ball milling during 40 h and then further milled during 30 min with 3, 5 and 10 wt.% of carbonaceous compounds. Three carbonaceous compounds were used, namely fullerene (C sub 60 ), graphite and a highly conducting carbon support (Vulcan XC72). The structural and hydriding characteristics of the resulting materials were compared with those of the primitive material. The specific surface area of nanocrystalline Mg sub 2 Ni increases from 1.06 m exp 2 g exp -1 to 3.45 m exp 2 g exp -1 or 6.00 m exp 2 g exp -1 when it is milled with 5 or 10 wt.% C sub 60 . The dissolution of C sub 60 in toluene yields a further increase of the specific surface area. The specific surface area of Mg sub 2 Ni milled with 5 wt.% graphite is 3.61 m exp 2 g exp -1 , but almost no change in the specific surface area of Mg sub 2 Ni is observed when it is milled with Vulcan. No change in the crystallographic structure of Mg sub 2 Ni could be evidenced by X-ray diffraction as a result of the milling step with either carbonaceous compound. When normalized for the total amount of hydride-forming material, Mg sub 2 Ni/C sub 60 , Mg sub 2 Ni/graphite and Mg sub 2 Ni/Vulcan have the same hydrogen absorption capacity as that of nanocrystalline Mg sub 2 Ni. On the contrary, an irreversible loss of hydrogen absorption capacity is observed following the leaching of C sub 60 from the material. This most probably results from a slight oxidation of magnesium during the leaching process. At 275 deg C, there is no noticeable change in the kinetics of absorption between the various compounds, but the time needed to complete desorption of Mg sub 2 Ni under vacuum is drastically reduced by a factor of 2-3 for Mg sub 2 Ni/C sub 60 , Mg sub 2 Ni/graphite and Mg sub 2 Ni /Vulcan.