Irradiation-enhanced Interactions at UO₂/Al₂O₃/Al Interfaces

<p dir="ltr">Combustion synthesis is used to prepare thin UO₂ films on aluminum alloy substrates. This simple preparation method involves electrospraying <i>uranyl nitrate</i> + <i>acetylacetone</i> + <i>2-methoxyethanol</i> solution on the substrate, followed by a short annealing at 350 or 550 °C. The irradiation of films with a ⁴⁰Ar²⁺ ion beam (energy of 1.7 MeV and fluences of 7.7 × 10¹⁶ and 1.3 × 10¹⁷ ions/cm²) is conducted to investigate irradiation-induced restructuring processes. High-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) investigations show that the annealing temperature significantly influences the crystallinity and stability of materials during irradiation. A small amount of Mg in the alloy substrate diffuses into the amorphous Al₂O₃ interfacial layer between the film and the substrate. Local thermal spikes from the incoming ions facilitate the irradiation-induced mixing of immiscible Al₂O₃ and UO₂ for the materials prepared at 350 °C. This mass diffusion produces relatively large cavities at the interface. Selective diffusion of a more significant amount of Mg for the materials prepared at 550 °C suppresses the mixing of the Al₂O₃ interlayer with the film but forms Mg_<em>y</em>U_1–_<em>y</em>O_2±x solid solutions during irradiation. Local thermal heating triggers the precipitation of a discontinuous crystalline MgO layer close to the film surface. The enhanced and selective diffusion of Mg into the film makes the materials prepared at 550 °C more robust and mechanically stable than those prepared at 350 °C.</p>