Remote Fluorination by Spillover of Atomic Fluorine

The phenomenon of atomic fluorine spillover was studied by comparing fluorination of an isolated platinum plate and of one welded to a nickel plate. Fluorination through the gas phase was performed by atomic fluorine generated by thermal decomposition of spatially separated TbF4. The reactions were carried out in a Knudsen effusion cell and monitored mass spectrometrically with subsequent microscopic investigation of the fluorinated Pt and Ni surfaces. We demonstrate that the contact with Ni strongly enhances the rate of Pt fluorination because of additional influx of adsorbed fluorine atoms across the nonstoichiometric NiF2–x layer that forms on the Ni surface. Related earlier studies with iron and cerium tri- and tetrafluorides suggest that diffusion of atomic fluorine to the zone of its final consumption (e.g., Pt) across vacancy-rich intermediary surface layers of transition-metal fluorides is a common phenomenon. Furthermore, such layers appear to suppress atomic fluorine recombination. We compare ou...