Lattice imaging of disclinations in carbon fibers

Fibers spun from the liquid crystalline state are generally characterized by a high level of performance. Mesophase pitch-based C fibers, in particular, may be obtained with a Young's modulus approaching the theoretical value of graphite (1000 GPa) and excellent thermal and electrical conductivities. This reflects the graphitizability of the structure, itself a consequence of the initial ordering of the precursor. All properties except modulus are believed to be limited by the size, frequency and nature of structural defects. Detailed descriptions of the defect structure of liquid crystals in general, and the carbonaceous mesophase in particular, are readily available, but very little is known about the mechanism of its evolution during processing, due to the lack of high resolution structural information concerning the pitch-based C fibers themselves. Lattice images of fiber cross-sections have been obtained showing the presence of wedge disclinations, i.e., a defect structure similar to that of the precursor but at a much reduced scale. 7 ref.--AA