Direct Lattice Resolution of Layer Planes in Polyacrylonitrile Based Carbon Fibres

Abstract

THE microstructure of polyacrylonitrile (PAN) based carbon fibres has been investigated by several techniques including high and low angle X-ray diffraction and electron microscopy. The results obtained with high-modulus (400 GNm−2) RAE carbon fibres1,2 and high-modulus Rolls-Royce carbon fibres3 are essentially similar; crystallites, the widths of which have a distribution of values with a mean about 65 A, enclose sharp-edged microvoids of mean width about 10 A. There is little three-dimensional order in the crystallites and the graphite layer planes are essentially turbostratic. The length of the crystallite seems to be limited by lattice defects to less than 100 A although individual layers may well be much longer. Studies of rayon-based carbon fibres4 have yielded similar evidence and recently Fourdeux, Herinckx, Perret and Ruland5 reported that the layer planes in these materials can be resolved directly by high-resolution electron microscopy following the phase-contrast method described by Heidenreich, Hess and Ban6 for carbon black specimens.