Oxidation of a polycrystalline silver foil by reaction with ozone

The surface oxidation of a polycrystalline silver foil by reaction with ozone (5 mol% O3 in O2) at 300 K and ambient pressure was investigated. The morphology, microstructure and chemical composition of the oxide scale which developed on the foil surface during exposure to ozone was characterised by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface of silver foil was rapidly oxidised upon contact with ozone, initially producing a thick Ag2O protective film. After 10 min reaction, the oxide film thickness was around 8–10 μm. SEM analysis revealed that Ag2O film thickening occurred via a discontinuous film growth mechanism. Growth stresses, resulting from the large lattice volume mismatch between the oxide and the metal, caused the oxide film to crack and flake extensively during development. Spallation of the oxide film exposed fresh silver metal to ozone, which lead to further Ag2O deposition. The continued recurrence of this process resulted in the formation a thick, discontinuous Ag2O film on the silver foil. After foil exposure to ozone for 300 min, the oxide film thickness was 17–20 μm. Furthermore, Ag2O at the surface of the oxide film was slowly oxidised to AgO with prolonged exposure to ozone. The combined results of our experimental studies were used to develop a better understanding of the oxidation of silver surfaces by O3.