Impact of sintering parameters on the microstructure of homogeneous U1-xCexO2+δ ceramics

The effects of atmosphere and cerium content on the densification and the final microstructure of homogeneous U_1-xCe_xO_2+δ solid solutions (x = 0.10; 0.25; 0.50) were investigated. Dilatometric studies first revealed that while the cerium content only slightly modifies sintering under an Ar/H₂ atmosphere, a change of the gas to argon dramatically modifies densification kinetics. As a result, samples prepared under Ar/H₂ exhibit a dense microstructure with micrometric grains. Conversely, samples sintered under argon appeared to be less densified but with larger grains. These changes were correlated with the variation of the final O/M stoichiometry (M = U+Ce) and illustrated by the construction of sintering maps. Finally, grain growth was found to be driven by grain boundary motion when the O/M ratio remained close to 2.00, while usual power laws did not apply for most hyper-stoichiometric samples. The first values of activation energy for the sintering of U_1-xCe_xO_2+δ solid solutions under an Ar/H₂ atmosphere were also determined.