Irradiation-enhanced Interactions at UO₂/Al₂O₃/Al Interfaces

Combustion synthesis is used to preparethin UO2 filmson aluminum alloy substrates. This simple preparation method involveselectrospraying uranyl nitrate + acetylacetone + 2-methoxyethanol solution on the substrate, followedby a short annealing at 350 or 550 degrees C. The irradiation of filmswith a Ar-40(2+) ion beam (energy of 1.7 MeV andfluences of 7.7 x 10(16) and 1.3 x 10(17) ions/cm(2)) is conducted to investigate irradiation-inducedrestructuring processes. High-resolution transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy (XPS) investigations showthat the annealing temperature significantly influences the crystallinityand stability of materials during irradiation. A small amount of Mgin the alloy substrate diffuses into the amorphous Al2O3 interfacial layer between the film and the substrate. Localthermal spikes from the incoming ions facilitate the irradiation-inducedmixing of immiscible Al2O3 and UO2 for the materials prepared at 350 degrees C. This mass diffusion producesrelatively large cavities at the interface. Selective diffusion ofa more significant amount of Mg for the materials prepared at 550 degrees C suppresses the mixing of the Al2O3 interlayerwith the film but forms Mg y U1-y O2 +/- x solid solutions during irradiation.Local thermal heating triggers the precipitation of a discontinuouscrystalline MgO layer close to the film surface. The enhanced andselective diffusion of Mg into the film makes the materials preparedat 550 degrees C more robust and mechanically stable than those preparedat 350 degrees C.