Cross-sectional texture of carbon fibres analysed by scanning microbeam X-ray diffraction

Scanning microbeam X-ray diffraction analysis of single carbon fibres allows the cross-sectional orientation distribution (texture) of the carbon layers to be determined, even when the fibre axis is oriented perpendicular to the X-ray beam (fibre geometry). The fibre is scanned across a microbeam with a diameter significantly smaller than the fibre diameter, and fibre diffraction patterns are recorded for every scanning step. The cross-sectional texture information is obtained from the integrated intensities of two different equatorial reflections as a function of the position on the fibre. As an example, results from two different types of carbon fibres are presented: a polyacrylonitrile-based fibre, with random cross-sectional texture, and a fibre based on mesophase pitch, which exhibits a radially folded cross-sectional texture. Detailed modelling of the diffraction data allows a quantitative description of the radial folded texture.