Characterization of nanoporosity in polymer-derived ceramic fibres by X-ray scattering techniques

摘要: Ceramic fibres with Si-C-O and Si-N-C-O compositions, prepared by pyrolysis of polymer precursors, generally have densities lower than those calculated from a volume additivity rule. However, techniques often used to detect porosity such as electron microscopy methods, surface area porosimetry measurements show that little surface-connected is present. X-ray scattering measurements, both wide-angle (WAXS) small-angle (SAXS), considerable in the range 1° < 2θ 10° (CuKα). Treatment data classical Guinier (low angle limit) Porod (high methods indicate closed, globular, nanometre-scale (1 3 nm diameter) present all ceramic examined. power correlates quantitatively fraction porosity, expected if dominant facto affecting scattering. Nano-particles excess carbon ofβ-SiC nanocrystallites, though present, are minor contributors X-rays these fibres. Fibres three-dimensional, not fractal dimension, oriented. As density increases increasing temperature, average pore size decreases. This results thermodynamically favourable reduction free energy apparently occurs viscous flow process.