Strengthening of carbon fibers by imposition of a high magnetic field in a carbonization process

Carbon fibers produced from PAN (polyacrylonitrile) as a precursor are generally subjected to the three heat treatment processes of stabilization and carbonization followed by graphitization. Stabilized fibers and high-temperature heat-treated fibers were carbonized in a high magnetic field imposed parallel to the fiber axis under a temperature of 1773 K and a tension of 8N per 12000 pieces of fibers. The carbon fibers produced from the stabilized fibers in a magnetic field of 5 T showed higher tensile strength than those done in no magnetic field, and the high-temperature heat-treated fibers processed in the magnetic field resulted in reverse. It is found that the fibers processed in the magnetic field have a larger crystallite size than those treated in no magnetic field. The mechanism of increase in the crystallite size due to the imposition of a high magnetic field has been discussed on the basis of an intermolecular cross-linking reaction model, in which the radical pair theory is modified by taking account of magnetic field.