Microstructure evolution of nanostructured and submicrometric porous refractory ceramics induced by a continuous high-energy proton beam

The production of radioactive ion beams by the isotope mass separation online (ISOL) method requires a fast diffusion and effusion of nuclear products from thick refractory target materials under high-energy particle beam irradiation. A new generation of ISOL nanostructured and submicrometric porous materials have been developed, exhibiting enhanced release of exotic isotopes, compared to previously used conventional micrometric materials. A programme was developed at PSI within the framework sof the Design Study of EURISOL, the next generation European ISOL-type facility to study aging under irradiation on porous ceramic pellets and dense thin metal foils at high temperatures. Ceramic oxides and carbide samples underwent proton damage with fluence up to 3.0 × 1020 and 1.3 × 1021 cm−2 respectively. The post-irradiation examination on Al2O3, Y2O3 and SiC – C nanotube composite matrices show a proton-induced densification region in which a moderate grain growth occurred. The microstructural evolution effects were associated to the combination of radiation-enhanced diffusion and thermal diffusion. The irradiated Al2O3 shows higher sintering rates than in similar non-irradiation isothermal conditions, in particular at the lowest irradiation temperature, subjected to a proton fluence inferior to 1.1 × 1015 cm−2. The apparent activation energy for its sintering controlling mechanism was found to be between 44 and 88 kJ mol−1. However, despite the enhanced sintering, shrinkage and increased grain growth, the selected nanostructured and submicrometric TARPIPE materials did not display an average grain diameter above 2 μm, which confirms that these materials are suited as production targets for present and next generation ISOL facilities.