Shigehiko Yamada

Graphitization of carbon fibre/ glassy carbon composites

Abstract Carbon fibre/glassy carbon composites were prepared by aligning unidirectionally in furfuryl alcohol condensate the PAN-based carbon fibres treated at different temperatures and with different degrees of stretching. The graphitization of the composites was found to start at the boundary between the fibres and glassy carbon matrix, and to proceed into the matrix. This is considered to be due to the stress accumulation at the boundary caused by a large shrinkage of the matrix. The carbon fibres remain nongraphitized even after a heat-treatment at 2800°C. The composites heat-treated at high temperature (2800°C) are found to show a high overall degree of graphitization, unexpected on basis of the known graphitization behavior of carbon fibres and of glassy carbon, and a high degree of uniaxial preferred orientation of crystallites.

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.

Microstructural control of pitch matrix carbon-carbon composite by iodine treatment

Matrix microstructure of a pitch-based carbon-carbon composite was controlled by an iodine treatment. Coal-tar pitch having the softening point of 101 °C was used as a matrix precursor. The iodine treatment was carried out on a pitch-impregnated specimen at 90 °C for 3–20 h. The specimen was carbonized at 800 °C and graphitized at 2000–3000 °C. The carbon yield increased from 73% to 93% by the iodine treatment. Microstructures of carbonized specimens changed from a flow type texture to a mosaic type one by the iodine treatment. The microstructural development to graphitic structure was suppressed by the iodine treatment.

Mechanical Properties of SiC Whisker / Si3N4 Composite Prepared by an in-situ Method

During the last decade, we have investigated the in-situ whiskerization of SiC in the Si3N4 matrix, for the purpose, not only of improving the homogeneity of composite formed, but also of avoiding direct handling of the whiskers. The fracture toughness as well as strength of the composite obtained by means of this in-situ process was found to be about the same as those by the regular physical mixing as a whole, but no progress of these mechanical properties has been achieved so far.