Stable uranium sols as precursors for the elaboration of nanostructured nc-UO2 materials A Physicochemical and engineering aspects

This study presents a colloidal sol-gel and templating method to elaborate sols as precursors for nanostructured and nanocrystallized nc-UO2 materials. Several parameters were controlled in order to obtain such sols and materials, such as nanoparticles size, sol stability, target pore size and pores organization. In this study, the nanoparticles formation was managed controlling the thermodynamics of the surfactant solution and the U(IV) species polycondensation kinetics The kinetics of the nanoparticles formation has been limited by the availability of the uranium species either by their complexation either by their diffusion limitation. To reach this goal, two types of surfactant at a concentration allowing to obtain micelles were used: a carboxylate surfactant with a non-ionic ployethoxylated part able to complex multicharged ions (AKYPO® RO 90 VG), and alkyl polyglucosides (Glucopon® 215) in sufficient concentration allowing the decrease of the uranium species diffusion. The surfactant solutions, the sols elaborated by indirect precipitation from U(IV) solution, the sols after freeze-drying and the final materials were characterized by Small and Wide Angle X-ray Scattering, Infrared Spectroscopy and microscopy at various scale. The results show that the complexation by AKYPO and the good degradation of these molecules allowed to obtain stable sols and a promising partially nanostructured nc-UO2 materials. With Glucopon, its high concentration in the sol, led to a carbon enriched material with few nc-UO2 zones.