Systematic structural characterization of the high-temperature behavior of nearly stoichiometric silicon oxycarbide glasses

Three silicon oxycarbide glasses (SiCO) with increasing C content were obtained through pyrolysis in inert atmosphere at 1000 degreesC of sol-gel derived siloxane networks containing Si-CH3 and Si-H bonds. The glasses were further annealed at 1200, 1400, and 1500 degreesC to follow their evolution at high temperature. Quantitative information concerning the structure of glasses before and after annealing at high temperature was collected with a wide range of techniques (some of them used for the first time in this field) with the aim of probing the following: (i) the short-range order and chemical composition (Si-29 and H-1 MAS NMR, RDF derived from X-ray and neutron scattering, inelastic neutron scattering, FT-IR, and elemental analysis), and (ii) the long-range order (X-ray and neutron diffraction) and microstructural features (HR-TEM combined with electron diffraction, Raman, porosity, and surface area measurements). This extensive collection of data, carried out on the same set of specimens, provided detailed and sound structural information on nearly-stoichiometric SiCO glasses and their high-temperature behavior.