Structural Studies of PAN-Based Carbon Fibers

In the years since Reynolds reviewed the structure and physical properties of carbon fibers, profound changes have taken place, in particular the successful development of carbon fibers from mesophase pitch and the decline of carbon fibers from rayon precursors. This chapter summarizes the essential structures of PAN-based carbon fibers as discovered by the application of x-ray diffraction and electron microscopy and shows how the physical properties are related to the inherent structure. The bright-field mode is the normal mode of operation, but the dark-field mode is used increasingly in all carbon work since it allows positive identification of the regions in a specimen that contribute to a particular reflection in the diffraction pattern. Polished cross sections of carbon fibers from various sources, when examined in an optical microscope with polarized light, exhibit "Maltese cross" patterns with interference colors in alternate quadrants.