Kinetics of subsurface hydrogen adsorbed on niobium: Thermal desorption studies
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Johan Jonsson-Akerman and Ivan K. Schuller Department of Physics, University of California at San Diego, La Jolla, California 92093-0319 (Received 25 January 2002; accepted 29 July 2002)
The adsorption/absorption of hydrogen and the adsorption of carbon monoxide by niobium foils, at room temperature, was studied using thermal desorption spectroscopy. Two hydrogen desorption peaks were observed with a maximum at 404 and 471 K. The first hydrogen desorption peak is regarded as hydrogen desorbing from surface sites while the second peak, which represents desorption from surface sites stronger bound to the surface, also has a component—due to its tailing to higher temperatures—of hydrogen diffusing from subsurface sites. Carbon monoxide adsorption was used to determine the number of surface sites, since it does not penetrate below the surface. Two carbon monoxide desorption peaks are observed in these experiments: at 425 and 608 K. The first peak is regarded as the adsorption of molecular carbon monoxide, and the second, as carbon monoxide dissociated on the niobium surface. The crystallographic orientation of the foils was determined by x-ray diffraction and showed a preferential (110) orientation of the untreated foil due to the effect of cold rolling. This preferential orientation decreased after hydrogen/heat treatment, appearing strong also in the (200) and (211) orientations. This change in texture of the foils is mainly due to the effect of heat treatment and not to hydrogen adsorption/desorption cycling. The kinetics of hydrogen and CO desorption is compared with that of Pd and Pd alloys.
I. INTRODUCTION
The interaction of hydrogen with metals is still a subject of current interest due to the potentially important applications that this research might generate. Areas of active technological development such as the chemical industry, hydrogen storage, hydrogen sensors, and magnetic recording, among others, might benefit from these studies in the near future. Examples of research results in these areas that are closely related to future technological developments are the following: (i) Gryaznov1,2 pioneered work on hydrogen diffusion through thin-walled pure metal membranes for catalytic applications. The facile permeation of hydrogen through palladium and palladium alloys suggests a number of applications in some chemical processes: the design of more efficient reactors3 for several hydrogenation or dehydrogenation reactions. Nevertheless, the feasibility of an industrial application (on a large scale) relies on reducing the reactors’ cost since a reactor made of Pd would be extremely expensive.
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J. Mater. Res., Vol. 17, No. 10, Oct 2002 Downloaded: 18 Mar 2015
(ii) Klose and co-workers4,5 have recently demonstrated a continuous reversible change in magnetic coupling between Fe and Nb layers induced by hydrogen absorption by Nb. These results are potentially useful in the development of hydrogen sensors. The difference betwe
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