Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1276240 | International Journal of Hydrogen Energy | 2011 | 6 Pages |
Hydrogen absorption by Sc has been investigated over wide ranges of temperature (790–1280 K) and pressure (10–150 mbar). The absorbed quantities of H were in agreement with those expected from p-x-T isotherms, available in the literature, only for temperatures higher than 1000 K, where the absorption curves could be fitted to a Johnson-Mehl-Avrami type of relationships. The gas–solid reaction was first-order and the reaction-rate-constant k exhibited an Arrhenius type of temperature dependence with an associated activation energy of 2.1 ± 0.1 eV (202 ± 10 kJ/mol·H2). The step controlling the absorption rate turned out not to be H diffusion in the bulk. Namely, the values of the apparent H diffusion coefficient deduced from absorption data were found to be some orders of magnitude smaller than expected from extrapolations of lower temperature anelastic and spin-lattice relaxation data. The absorption rate appears to be governed by H penetration through a sub-surface Sc layer containing a high concentration of interstitial oxygen, originated from the decomposition of surface oxides occurring between 900 K and 1000 K.