Kinetic evaluation of the uranyl peroxide synthetic route on morphology

Abstract

An important challenge in utilizing particle morphology in nuclear forensic or fuel fabrication applications is understanding why differences in morphologies are observed following varying processing conditions. This is often due to competition and interplay between thermodynamic and kinetic influences. To that end, some of the kinetic influences in the uranyl peroxide precipitation reaction were evaluated and compared to thermodynamic influences studied previously. Metastudtite (UO2O2·2H2O) was synthesized from solutions of uranyl nitrate or chloride, and the reaction time was varied from 100 s to 230 min enabling an evaluation of kinetic and thermodynamic influences. The metastudtite was then calcined to U3O8, and all materials were analyzed by powder X-ray diffraction (p-XRD) and scanning electron microscopy (SEM). Analysis by p-XRD confirmed the sample purity of metastudtite and U3O8. SEM images were analyzed using the Morphological Analysis for Materials (MAMA) software to measure the size and shape of the nanoparticles for a statistical comparison between materials. Metastudtite produced at shorter reaction times exhibited a kinetically controlled shape by forming smaller and rounder particles than metastudtite produced at longer reaction times. Metastudtite produced at the longer reaction times exhibited differences between the uranyl nitrate and uranyl chloride routes with the nitrate exhibiting a more angular and faceted morphology than the chloride. Overall, the control of the supersaturation ratio (S) played a significant role in determining the morphology of the metastudtite. Morphological differences between the U3O8 confirmed the role of nanoparticle agglomeration in forming larger sintered particles. The results help demonstrate the importance of understanding particle formation mechanisms in the long-term development of morphology in nuclear forensics or in developing advanced fuels with specific characteristics.