Pressure Graphitization of Matrix in Carbon Fiber/Glass-Like Carbon Composite

Abstract

The graphitization of the nongraphitizing carbon matrix in a C/C composite has been explained as a stress graphitization process caused by a large shrinkage of matrix around the fiber. In this paper the stress accumulation along the fiber axis together with the effect of adjacent fibers was investigated by means of thermal shrinkage measurement, thermogravimetric analysis, optical microscopy and X-ray diffraction techniques by using PAN CF/Furan C and Phenol CF/Phenol C composites.
The accumul ated stress by a single fiber along the fiber axis was estimated to be about 440 MPa from the measurement of the residual strain of the fiber. The effect of the distribution of fibers along the fiber axis was examined by the addition of stress with two adjacent fibers, because the direction of the accumulated stress along the fiber axis was the same as the direction of the stress by the adjacent fibers. Then, the stress accumulated between the adjacent fibers in a distance of 2.3, am was estimated to be about 660 MPa for the composite with 60vol% fibers. The stress distribution profile was also illustrated by this model. This value of 660 MPa agreed with the pressure graphitization of the glassy carbon.
It was assumed that the accumulated stress of 660 MPa induc ed on the carbonization process was large enough to form activated stage, which would act as a source for the graphitization of composites at high temperatures above 2000°C.