Structure of mesophase pitch-based carbon fibres

Abstract

The structure of five samples of commercially available carbon fibres with ultra-high modulus produced from mesophase pitch was studied by the complementary techniques of high resolution electronmicroscopy, X-ray diffraction and transverse magnetoresistance effect. The fibres with high strength and elongation to failure were found to be composed of turbostratic carbon structure, which was different from the three-dimensional graphite structure in ultra-high modulus carbon fibres. Transmission electron microscope examination revealed that the mesophase pitch-based fibres with high strength have a basic structure unit with folded sheets arranged nearly parallel to the fibre axis similar to those of high modulus carbon fibres produced from PAN. The present fold structure was suggested to contribute consequently to the lower graphitizability of the fibres and to the strong effects on the fibre strength. By controlling the microstructure, it is expected that the crystallographic as well as the mechanical properties could be improved significantly even from the same kind of precursor materials such as mesophase pitch.