Niobium-based sputtered thin films for Corrosion Protection of proton-irradiated liquid water targets for [18F] production

Chemically inert Coatings on Havar entrance foils of the targets for [18F] production via proton irradiation of enriched water at pressurized conditions are needed to decrease the amount of ionic contaminants released from Havar. In order to find the most effective protective coatings, the Nb-based coating microstructure and barrier properties have been correlated with deposition parameters as: substrate temperature, applied bias, deposition rate and sputtering gas pressure. Aluminated quartz used as a substrate allowed us to verify the protection efficiency of the desirable coatings as diffusion barriers. Two modeling corrosion tests based on the extreme susceptibility of aluminum to liquid gallium and acid corrosion were applied. Pure Niobium coatings have been found less effective barriers than Niobium-titanium coatings. But Niobium oxide films, according to the corrosion tests performed, showed superior barrier properties. Therefore Multi-layered Niobium-Niobium oxide films have been suggested, since they combine the high thermal conductivity of Niobium with the good barrier properties of Niobium oxide.