Inert matrices preparation by SOL-GEL (IONMAT project. Subtask 1.4)

Abstract

Zirconium–neodymium oxide microspheres were synthesized by the internal gelation (IG) sol–gel route. Aqueous nitrate solutions of Zr and Nd were gelled through the thermal decomposition of HMTA/urea in hot silicone oil, producing homogeneous spheres without powder handling. Process parameters—including metal concentration, HMTA/urea ratio, gelation temperature and washing protocol—were optimized to obtain stable microspheres containing 0–30 wt% Nd. Compositions with 50 wt% Nd did not gel under the explored conditions. The products were characterized by ICP-MS, TGA, SEM-EDX and XRD. Calcination at 600 °C ensured complete removal of organics and development of crystalline ZrO2 with Nd uniformly distributed across the sphere radius. The washing step proved critical: TCE followed by dilute NH4OH preserved surface integrity, whereas ethanol, acetone or concentrated ammonia induced degradation and Nd leaching. The resulting microspheres exhibit suitable size, homogeneity and dust-free handling characteristics, making them promising precursors for the fabrication of mixed (Zr,U)O2 fuels for PCI simulation.