Application of a high magnetic field in the carbonization process to increase the strength of carbon fibers

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 were carbonized in a high magnetic field of 5 T imposed parallel to the fiber axis at a temperature of 1445 K and graphitized without a magnetic field at 2273 K. The tensile strength of these treated fibers is increased by 14% in comparison with those of no magnetic treatment. The reason why the imposition of the magnetic field could improve the strength of the fibers has been studied through microscopic observation of the fiber surface as well as a statistical analysis by use of Weibull distributions.