Oxidation of a polycrystalline silver foil by reaction with ozone

The surface oxidation of a polycrystalline silver foil by reaction with ozo ne (5 mol% O-3 in O-2) at 300 K and ambient pressure was investigated. The morphology, microstructure and chemical composition of the oxide scale whic h developed on the foil surface during exposure to ozone was characterised by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Rama n spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface of s ilver foil was rapidly oxidised upon contact with ozone, initially producin g a thick Ag2O protective film. After LO min reaction, the oxide film thick ness was around 8-10 um. SEM analysis revealed that Ag2O film thickening oc curred via a discontinuous film growth mechanism. Growth stresses, resultin g from the large lattice volume mismatch between the oxide and the metal, c aused the oxide film to crack and flake extensively during development. Spa llation of the oxide film exposed fresh silver metal to ozone, which lead t o further Ag2O deposition. The continued recurrence of this process resulte d in the formation a thick, discontinuous Ag2O film on the silver foil. Aft er foil exposure to ozone for 300 min, the oxide film thickness was 17-20 m um. Furthermore, Ag2O at the surface of the oxide film was slowly oxidised to Ago with prolonged exposure to ozone. The combined results of our experi mental studies were used to develop a better understanding of the oxidation of silver surfaces by O-3. (C) 2001 Elsevier Science B.V. All rights reser ved.