Thermodynamic evaluation of the uranyl peroxide synthetic route on morphology

Understanding the mechanisms controlling the morphology of uranium ore concentrates (UOCs) is impactful for both the nuclear forensics and nuclear fuels communities. In forensics, this understanding enables predicting the morphology of materials to help determine provenance and processing history. In fuels, this understanding aids in optimizing the morphology for higher fuel efficiency. To elucidate the influence of thermodynamics on the morphology of UOCs, uranyl peroxide, specifically metastudtite (UO ₂O ₂·2H ₂ O), was precipitated from solutions of varying complexing strength to the uranyl ion. Specifically, metastudtite was precipitated from solutions of equal ionic strength of uranyl nitrate and uranyl chloride, where the nitrate ion has greater complexing strength with the uranyl ion. Following precipitation, the metastudtite was calcined to U ₃O ₈ , and the phase purity of each sample was confirmed by powder X-ray diffraction (p-XRD). The surface features were characterized using scanning electron microscopy (SEM), and the morphology was quantified using the Morphological Analysis for Materials (MAMA) software. Nanoparticles of metastudtite precipitated from uranyl nitrate, which has the higher complexing strength, were larger, more angular, and more elongated than nanoparticles produced by precipitation from uranyl chloride. Overall, a more rigid morphology was produced when replacing the nitrate with the peroxide while more rounded particles were produced when replacing a chloride with the peroxide. Even after sintering at high temperatures, differences in morphology between the two routes were still present in the U ₃O ₈.