Small-angle X-ray scattering in carbon fibers

Small-angle X-ray scattering (SAXS) has been used as an analytical tool to study microporosity in polyacrylonitrile- (PAN-) and pitch-based carbon fibers. Microporosity in carbon fibers consists primarily of needle-shaped voids whose long axes are oriented preferentially along the fiber axis. This preferred orientation is seen to be independent of the nature of the fiber precursor and is the major deciding factor in controlling the modulus of carbon fibers. As the modulus increases, the general trend for both PAN- and pitch-based fibers is to move from a system consisting of many small pores to one with few larger pores. At very small angles, the steep rise in scattered intensity is due to reflection effects for PAN-based fibers and multiple scattering effects from voids for pitch-based fibers.