Reexamination of the fundamental interactions of water with uranium

Interactions of D2O with uranium metal at 85 and 300 K have been examined u sing surface specific techniques of thermal desorption mass spectroscopy (T DMS), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spe ctroscopy (XPS) and static secondary ion mass spectroscopy (SSIMS). At low temperatures (85 K), D2O adsorbs dissociatively at low exposures (less than or equal to 0.5 L) forming a mixture of surface-bound OD, O and D species while at higher exposures both molecular and dissociative adsorption is obs erved. The OD species are relatively stable up to similar to 200 K, above t his temperature their concentration rapidly decreases (undetectable at T gr eater than or equal to 400 K). Three D-2 desorption states are observed upo n annealing a 40 layer(s) on uranium prepared at 85 K: deuterium atoms reco mbining directly from dissociating OD/D2O groups between 120 and 300 K; rec ombination of deuterium adsorbed directly on the metal surface at similar t o 395 K(less than or equal to 1.2 L); and deuterium atoms that interact wit h the metal and recombine and desorb in the presence of an oxygen layer at similar to 435 K ( greater than or equal to 1.2 L). At 300 K, adsorption is primarily dissociative with the formation of OD groups at higher exposures (greater than or equal to 3.0 L). Similar to the 85 K adsorption, three D2 desorption states are observed in the TDMS spectra when D2O is adsorbed at 300 K. The origin of these peaks is the same as for the 85 K except that th e desorption temperature for the last peak is notably higher. This differen ce in T-max for the high-temperature peak when dosing at 300 K is attribute d to thicker oxide/oxygen layer obtained when exposing the surface to D2O a t 300 K. (C) 1999 Elsevier Science B.V. All rights reserved.