| Autor: |
Y. Ohtani, Hirohisa Uchida, H.H. Uchida, N. Ninomiya, H. Minamitani, N. Hosoda, E. Fromm, T. Kawahata |
| Rok vydání: |
1991 |
| Předmět: |
|
| Zdroj: |
Journal of the Less Common Metals. :832-840 |
| ISSN: |
0022-5088 |
| Popis: |
The kinetics of H2 absorption by lanthanum with and without surface oxide layers has been investigated at 77 and 298 K using a volumetric method. Lanthanum film samples carefully prepared under ultrahigh vacuum conditions exhibit an initial reaction probability of unity at 77 and 298 K in the formation of a hydrogen solution in lanthanum. The dihydride formation proceeds at an almost constant rate at 298 K until the sample becomes completely hydrided whereas the reactivity decreases as the hydride layer grows at 77 K. The pressure dependence of the reaction rate indicates that the rate-controlling step in the H2 absorption by lanthanum changes according to the surface conditions of lanthanum: for lanthanum with a clean surface, H2 transport in the gas phase is rate controlling at H2 pressures lower than 10−9 mbar and with increasing H2 pressure or hydrogen surface concentration H2 dissociation as a rate-controlling step is replaced by hydride formation at the hydride-lanthanum interface. For lanthanum with oxide layers, two rate-controlling steps, the H2 dissociation on and the hydrogen permeation through the oxide layers, seem to be important. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
