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Studies of H2 uptake by aluminum carbide (Al4C3) using volumetric absorption and elemental combustion analyses and FT-IR

Karol Fijalkowski 1,  Wojciech Grochala 1,2

1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
2. Interdyscyplinarne Centrum Modelowania Matematycznego i Komputerowego (ICM), Żwirki i Wigury 93, Warszawa 02-089, Poland

Abstract
Aluminum carbide (Al4C3) is a low atomic mass (144 u) and low density (2.36 g/cm3) compound and its hydrogen absorption ability has not yet been studied. Al4C3 consists of elements which form hydrides of large gravimetric hydrogen capacity: AlH3 (10.1 wt. %) and CH4 (25 wt. %). It was therefore presumed that heterolytic addition of the dihydrogen molecule (H2) to Al4C3 (with the concomitant formation of the Al-H and C-H bonds) might be possible. Thermodynamic analysis of various possible reactions showed that full degradation of Al4C3 to CH4 and AlH3 (or metallic Al) is not thermodynamically privileged.

Here we present our experimental studies on the ability of Al4C3 for the absorption of H2 in a broad range of [p, T] conditions, with or without of the hydrogenation catalysts (Ti, TiH2). Hydrogenations have been carried out at various conditions, from mild (T = 30oC, p = 50 bar) to very aggressive (T = 450oC, p = 100 bar). Doping with catalysts (~10 mol. %) was achieved by high-energy disc-milling (5 min, tungsten carbide mill) under an inert gas atmosphere. Hydrogen uptake has been scrutinized by volumetric absorption and elemental combustion analyses, supplemented by infrared spectroscopy (FT-IR).

None of the samples studied have shown any significant uptake of hydrogen. Elemental analysis suggests that the samples are virtually H-free (method's sensitivity is 0,2 wt. %). IR spectra do not exhibit bands attributable to the Al-H, C-H and Ti-H stretching modes. Ti and TiH2 do not serve as H2-transfer catalysts to Al4C3. Aluminum carbide does not absorb any significant quantities of hydrogen (even under harsh [p, T] conditions) and therefore it could serve as a lightweight protective shield or seal against compressed H2.
 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium D, by Karol Fijalkowski
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 12:43
Revised:   2009-06-07 00:44