Factors governing microstructure development of Cr2O3-doped UO2 during sintering

Sintering and grain growth of compacted uranium dioxide powder pellets doped with Cr2O3 were investigated at constant heating rates ranging from 75 to 500 K h−1. The influence of parameters such as the oxygen potential of the sintering atmosphere and pellet green density on the final microstructure was studied. Dilatometric analysis and monitoring of microstructural development revealed a phenomenon of abnormal grain growth promoting densification. The existence of a eutectic between Cr and Cr2O3 is also discussed. Grain growth does not appear to be widely affected by small differences in residual porosity, which is a function of green density, so that it is possible to propose a solubility limit for Cr2O3 in stoichiometric UO2 at 1700°C. Examination of microstructural changes during annealing, with or without pore formers, showed the existence of limiting grain sizes for doped samples above the solubility limit. Lastly, experimental sintering conditions need to be checked in order to obtain reproducible results.