Twist disclinations in the carbonaceous mesophase

Abstract Disclinations are prominent features of the microstructures of coke and graphite because their lamelliform structures are formed via a liquid crystal, the carbonaceous mesophase. Polarized-light techniques have been applied to study disclination structures in the fibrous and lamellar microconstituents which result from uniaxial and biaxial extension, respectively, of the plastic mesophase. The strong preferred orientations of these characteristic microconstituents of needle coke aid in resolving their disclination structures. The fibrous microconstituent contains primarily wedge disclinations in parallel, with rotations of ± π and ±2 π . Disclinations with appreciable twist character have been identified at the boundaries of the folds which characterize the lamellar microconstituent. The twist disclinations are not rare, but their inherent structure makes identification difficult on a random plane of section. The folded regions constitute disclination loops of rotation π. Vestiges of the doubly curved surfaces of undeformed mesophase are found in the double curvature of some folded regions; the rotation vector along the disclination loop bounding such folds is conserved in magnitude but not in direction.