Mixed H2O/H2 Plasma-Induced Redox Reactions of Thin Uranium Oxide Films under UHV Conditions

X-Ray Photoelectron Spectroscopy (XPS) has been used to study the effect of mixed H2/H2O gas plasma on the surface of UO2, U2O5 and UO3 thin films at 400 °C. The experiments were performed in-situ under UHV. Deconvolution of the U4f7/2 peaks into the U(IV), U(V) and U(VI) components revealed the surface composition of the films after 10 minutes plasma exposure as function of H2 content in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analyzed using Grazing-Incidence X-Ray Diffraction (GIXRD). The XPS results show that U(V) is formed as a dominating product upon 10 minutes exposure of UO3 to a mixed H2/H2O plasma in a fairly wide H2 concentration range. When starting with U(V) (U2O5), fairly high H2 concentrations are needed to reduce U(V) to U(IV) in 10 minutes. In the plasma induced oxidation of UO2, U(V) is never observed as a major product after 10 minutes and it would seem that once U(V) is formed in the oxidation of UO2 it is rapidly oxidized further to U(VI). The Grazing Incidence X-Ray Diffraction analysis show that there is a considerable impact of the plasma and heating condition on the crystallographic structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(IV) and U(V) in both directions.

EL JAMAL Ghada;  GOUDER Thomas;  ELOIRDI Rachel;  TERESHINA Evgenia;  HORAK Lukas;  JONSSON Mats; 

2021-09-29

ROYAL SOC CHEMISTRY

JRC124504

1477-9226 (online),   

https://pubs.rsc.org/en/content/articlelanding/2021/DT/D1DT01020D,    https://publications.jrc.ec.europa.eu/repository/handle/JRC124504,   

10.1039/d1dt01020d (online),