Evidence of an oxidation induced phase transformation for a delta phase plutonium-gallium alloy

The oxidation of an similar to 1.5 at% Ga plutonium metal alloy in dry air as a function of time was studied using a combination of FIB-SEM, AES, and XRD. Analysis of SEM images of FIB cross-sections of the oxide allowed for direct measurement of the oxide thickness as well as determination of heterogeneity in the extent of the oxide. AES analysis performed on cross-sections of the oxide allowed for quantitative analysis of the atomic composition and semi-quantitative analysis of the chemical composition. Initial preparation of the sample was found to induce a martensitic transformation to alpha-Pu with an average thickness of 233 nm. Electropolishing was found to be sufficient to fully remove the alpha layer with creation of only a minimum oxide layer. Growth of the oxide in dry air was found to initially follow parabolic kinetics, with a parabolic rate constant orders of magnitude higher than expected for delta-Pu but in-line with values extrapolated to room temperature for alpha-Pu. Following complete oxidation of the initial alpha layer, further regions of plutonium metal depleted in gallium were observed to form at the oxide / metal interface. However, gallium, as Ga2O3, was found to be enriched at the surface and present in the oxide in an amount comparable to the relative Ga:Pu ratio of the bulk metal alloy. The results presented here serve to bridge a diverse array of previous experimental and theoretical data and provide the first comprehensive view of the fate of the delta-stabilizer during formation of an oxide. Data availability: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Automated summary

The oxidation behavior of a plutonium metal alloy containing approximately 1.5% Ga in dry air was studied using a combination of FIB-SEM, AES, and XRD. The study revealed the growth of oxide layer and changes in chemical composition during oxidation process. Initial sample preparation and electropolishing were found to influence the experimental results.