Basal plane orientation of polyacrylonitrile fibers in a commercial polyacrylonitrile-pitch carbon-carbon composite

The basal plane orientation of polyacrylonitrile (PAN) fibers in a commercial three-dimensional high-temperature-treated PAN-pitch carbon-carbon composite has been studied by conventional transmission and high resolution electron microscopy techniques. Thin foils of the composite are prepared by an atom-thinning technique. A basal plane orientation, which differs from other reported type I PAN fibers, is reported. In transverse sections, a turbostatic structure is observed across the whole fiber thickness. In longitudinal sections, the degree of perfection for basal plane alignment to the fiber axis decreases from fiber surface to the core in a gradual fashion. The lack of a well-aligned thin skin or thick sheath structure agrees with Oberlin's model but can be distinguished from the models of Bennett and Johnson and others.