AVS 46th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS-WeA

Paper AS-WeA7
Reactivity of Formic Acid (HCOOD and DCOOH) at Uranium and UO2 Surfaces

Wednesday, October 27, 1999, 4:00 pm, Room 6A

Session: Oxides and Insulators
Presenter: M.T. Paffett, Los Alamos National Laboratory
Authors: M.T. Paffett, Los Alamos National Laboratory
W.L. Manner, Los Alamos National Laboratory
Correspondent: Click to Email
Interactions of DCOOH and HCOOD with uranium and UO2.0 surfaces have been examined using surface specific techniques of thermal desorption mass spectroscopy (TDMS), x-ray photoelectron spectroscopy (XPS), and static secondary ion mass spectroscopy (SSIMS). Formic acid dissociates on both surfaces below 100 K to yield surface formate in relatively high yield. On the clean uranium surface a wide range of products are observed after annealing to 200 K which include formate, hydroxyl, and C-Hx (C-Dx,), Oads, and Hads(Dads) groups. Adsorbed formate decomposes by 300 K increasing the concentration of the remaining surface products (especially C-Hx (C-Dx) type moieties). The only gaseous species created in high yields from the clean surface upon annealing are H2, HD, and D2. A small amount of water and methane desorb at higher temperatures. Between 100 and 300 K the predominant species on the UO2.0 surface is surface formate and hydroxyl groups. The presence of surface oxygen stabilizes the formate groups to further dissociation in comparison to the clean uranium surface. Hydroxyl groups react between 300 and 350 K to release water from the surface. Adsorbed formate groups decompose between 400 and 500 K to release CO, COH2 (COD2) groups. Carbon was not detected on the surface by XPS after annealing to 500 K indicating that all carbon containing species either desorb in the form of CO-containing products or dissolve into the surface.