Rayleigh and Raman images of the bulk/surface nanostructure of SiC based fibres

SiC based fibres are complex systems of nanophases. Raman and Rayleigh microspectrometries, which are non-destructive and remote analysis methods, were used to map concentration and size distribution of the carbon grains in whole fibres sections. Imaging of stoichiometric (C/Si atomic ratio similar to 1) Tyranno SA3(R) (UBE Industry) and Sylramic(R) (Dow-Corning Corporation) fibres polished section showed that core and surface carbon species have different concentrations, natures and short range order, which result from the elaboration process. Grain size distribution was also calculated after a 1600 degreesC under reducing atmosphere ageing treatment, revealing a crystal growth of the carbon moieties. Monitoring of the fibre's surface nanostructure and geometry evolution was performed by Raman, Energy Dispersive Spectrometry and Scanning Electron Microscope. Corrosion tests under an alkali and oxidant environment (modelled by molten NaNO3) were performed on fibres sections. A reactivity difference was observed between the core and the surface, which was assigned to the nature of the carbon moieties and to their location (at triple points and grain boundaries), which constitutes a direct diffusion pathway. (C) 2003 Elsevier Ltd. All rights reserved.