Kinetics of hydrogen absorption by scandium at high temperature

✍ Scribed by Giovanni Mazzolai

• Publisher: Elsevier Science
• Year: 2011
• Tongue: English
• Weight: 550 KB
• Volume: 36
• Category: Article
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2011.01.002

✦ Synopsis

Hydrogen absorption by Sc has been investigated over wide ranges of temperature (790e1280 K) and pressure (10e150 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 gasesolid 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 AE 0.1 eV (202 AE 10 kJ/mol$H 2 ). 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.