IMAGE-ANALYSIS OF LATTICE IMPERFECTIONS IN CARBON-FIBERS

For the first time, lattice imperfections in a rang of Du Pont mesophase pitch-based fibres have been determined quantitatively from TEM micrographs by the techniques of image analysis. Following the analysis of dark-field and lattice-fringe images, new parameters which quantify lattice imperfections have been introduced, namely a crystallite imperfection factor (I-c) and lattice tortuosity (S). The value I-c can be estimated from the discrepancy between stacking size values L(c) from X-ray diffraction measurements and the values L(c)* measured directly from dark-field images. The L(c) values arise From single crystallites whereas the L(c)* values are associated with ordered aggregates containing localised imperfections. The tortuosity value S is a measure of the degree of lattice-fringe meandering and was obtained from processed lattice images. Additionally, a stacking imperfection factor D-c*, corresponding to imperfection between the layer planes, was also calculated on the basis of measured interlayer spacings. The above parameters for individual fibre types have relative merit and are not intended to represent absolute values owing to the complexity of image formation in the TEM.