Synthesis of size-controlled UO2 microspheres from the hydrothermal conversion of U(iv) aspartate

Abstract

A simple wet chemistry route towards micrometric spherical UO₂ particles was designed through the conversion of uranium(IV) aspartate under mild hydrothermal conditions (T = 160 °C). A multiparametric study examining the effects of hydrothermal treatment duration, the initial uranium/aspartic acid molar ratio and magnetic stirring allowed us to point out the role of organic species in the shaping of the particles and to specify the operating conditions leading to monodisperse and size-controlled particles. In a turbulent flow regime (i.e. Re_a > 10⁴), particles with a diameter ranging from 400 nm to 2500 nm were obtained with a typical dispersion of less than ±10%. Moreover, the protocol was found to be robust and reproducible, with only limited size variation from one batch to another (typically less than ±5% on the particle diameter). The effect of an additional heat treatment step was also investigated which showed that residual traces of water and organics can be removed after firing at 600 °C without altering the initial morphology. This wet chemistry route appears to be very promising for the production of spherical UO₂ particles and can be simply implemented in any nuclear chemistry lab, which paves the way to applications of such materials in various scientific areas.