The interaction of H2O with the surface of polycrystalline gadolinium at the temperature range of 300-570Â K

The interaction of water vapor with polycrystalline gadolinium surface, in the temperature range of 300-570 K and water vapor pressure from 2 × 10− 8 and up to 18 Torr, was studied by utilizing Direct-Recoil-Spectrometry, X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption. It has been found that a native Gd surface compound as well as one that was formed by an exposure to 18 Torr H2O, for 10 min, consists of a multilayer hydroxide phase, Gd(OH)3, transforming into oxide at the metal interface by heating, while emitting hydrogen. For initial exposures of water vapor on a clean metallic surface, it has been deduced that initially, full dissociation of the water molecules on the metal surface occurs, for ~ 1-2 L at 300 K and up to ~ 3 L at 570 K. On top of the formed oxide there is dissociation to H + OH and hydroxyls are adsorbed, forming, with further exposure, a multilayer hydroxide phase. Enhanced inward diffusion of oxygen starts as early as 370 K (similar to the case of oxygen exposure).