AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS1+MC-ThA

Paper SS1+MC-ThA5
Water Reactions at Plutonium Oxide: Surface Chemistry

Thursday, October 5, 2000, 3:20 pm, Room 208

Session: Oxidation and Molecule-Oxide Interactions
Presenter: J.D. Farr, Los Alamos National Laboratory
Authors: J.D. Farr, Los Alamos National Laboratory
R.K. Schulze, Los Alamos National Laboratory
M.P. Neu, Los Alamos National Laboratory
L.A. Morales, Los Alamos National Laboratory
Correspondent: Click to Email
We have examined the surface chemistry of water at both monolithic and high surface area plutonium oxide using Auger and X-ray photelectron spectroscopy (AES and XPS). This work investigates the chemical reactions at the Pu oxide surfaces, primarily to help address issues that are critical for plutonium stabilization and 50-year storage. Interactions between PuO@sub 2@ particles and the adsorbed water vapor play a dominant role in potential catalytic gas generation reactions. Understanding the chemistry at this interface, particularly with respect to reactions with water and water vapor is crucial for predicting the storage behavior of Pu oxide powders. XPS indicates that water adsorbs initially at active sites to form surface hydroxyls groups. Upon saturation of these sites and at substantially higher exposures, particularly with high surface area oxides, the water adsorbs in molecular form as part of the surface layer. Heating the oxide to 200°C in vacuum results in removal of the adsorbed water and partial removal (conversion) of the hydroxyl. Above 400°C the oxide surface continues to undergo a transformation and the removal of hydroxyl is largely complete at 600°C. The tenacious nature of these surface groups suggests that most of the active sites at the surface are irreversibly saturated at room temperature and up to a temperature in excess of 200°C, with some of them irreversibly saturated up to 600°C, or greater. The surface reaction will be discussed in the context of reaction energetics for the active sites at the PuO@sub 2@ surface.