Reactivity of formic acid (HCOOD and DCOOH) at uranium and UO2.0 surfaces

Interactions of DCOOH and HCOOD with uranium and UO2.0 surfaces have been e xamined using surface-specific techniques of thermal desorption mass spectr oscopy (TDMS), X-ray photoelectron spectroscopy (XPS), and static secondary ion mass spectroscopy (SSIMS). On the clean Uranium surface, formate is th e predominant product following formic acid adsorption at 100 K. A wide ran ge of products is observed after annealing to 200 K, including formate, hyd roxyl, O-ads, and H-ads (D-ads) groups. Adsorbed formate decomposes by 300 K increasing the concentration of the remaining surface products, Surface-a dsorbed carbon following TDMS measurements remains as the carbide, as indic ated from XPS and SSIMS measurements. The only gaseous species created in h igh yields from the clean surface upon annealing are H-2, HD, and D-2. On t he oxide surface (UO2.0) adsorbed formate groups are more stable toward dis sociation in comparison with the clean uranium surface. Between 100 and 300 K the predominant species on the UO2.0 surface are surface formate and hyd roxyl groups. Hydroxyl groups react between 300 and 350 K to release water from the surface. Adsorbed formate groups decompose between 400 and 500 K t o release CO and H2CO (D2CO) groups from the oxide surface. Carbon was not detected on the oxide surface by XPS or SSIMS after annealing to 500 K, ind icating that all carbon-containing species either desorb in the form of GO- containing products or migrate into the surface. (C) 1999 Elsevier Science B.V. All rights reserved.