AVS 57th International Symposium & Exhibition
    Actinides and Rare Earths Topical Conference Monday Sessions
       Session AC+SS-MoM

Paper AC+SS-MoM4
The Behavior of Gallium During the Initial Stages of Plutonium/Gallium Alloy Oxidation

Monday, October 18, 2010, 9:20 am, Room Isleta

Session: Surface Science of Actinides
Presenter: D.L. Pugmire, Los Alamos National Laboratory
Authors: D.L. Pugmire, Los Alamos National Laboratory
H.G. Garcia Flores, University of Nebraska-Lincoln
D.P. Moore, Los Alamos National Laboratory
A.L. Broach, Los Alamos National Laboratory
P. Roussel, Atomic Weapons Establishment
Correspondent: Click to Email

An area of significant importance to the oxidation of any alloy is the role that the constituent metals play. It has been previously shown that the oxidation rate for the δ-phase stabilized, plutonium/gallium alloy can be significantly affected by the gallium content as well as composition of the oxidizing atmosphere (O2, O2/H2O, H2O). Reasons for the observed rate changes upon alloying with gallium are not understood. A previous study of a variety of δ-plutonium alloys shows that the significant structure difference between unalloyed α-plutonium and alloyed δ-plutonium cannot be the sole cause of different oxidation rates. This implies that the alloying metal must play some role in the slower oxidation rates observed for gallium-stabilized δ-plutonium. In order to elucidate the oxidation mechanism of this commonly employed alloy, it is important to understand the role gallium plays during oxidation. The relatively low concentrations of alloying metals used, typically several atomic percent, can make the activities of gallium during oxidation of δ-plutonium difficult to follow. This complication is compounded by the fact that the initial stages of oxidation are inherently a surface phenomenon, thereby significantly limiting the relative amount of affected material. Significant questions remain as to what is a realistic description for the Pu/Ga-oxide, thin-film system during the initial stages of oxidation.

An ultra-high vacuum (UHV) system equipped with surface sensitive techniques, such as x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy ( AES ), provides a controlled environment ideally suited to study the behavior of gallium during the initial stages of Pu/Ga oxidation. In addition to information about the oxidation states of the plutonium species in the near surface region provided by XPS, both XPS and AES are very useful for studying the relative atomic concentration of elements present at the sample surface (such as oxygen and gallium). While these surface sensitive techniques suffer from relatively high limits of detection, we have been able to qualitatively, and in some cases quantitatively, study the behavior of gallium during the oxidation of the δ-plutonium alloy. The gallium content relative to plutonium is observed to decrease within the oxide film during oxidation, with the displaced gallium apparently moving to the oxide/metal interface to form a thin gallium rich region. The results of these studies and their implications on the mechanism of gallium-stabilized, δ-plutonium oxidation will be discussed.