Densification and Texture Control in Carbon Fiber/Carbon Composites by Pressure Carbonization

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By using pressure carbonization technique, the processes for densification and texture control of the matrix in carbon fiber/carbon composites (C/C composites) were investigated. The present work consisted of three parts; (1) the study on crack propagation in the matrix of a commercial C/C composite, (2) the study on the pressure effect on the interaction between pitch and phenol resin, and also on the texture of resultant carbons, and (3) the preliminary production of C/C composites by using two different precursors and by pressure carbonization.The crack propagation in a C/C composite was observed under polarized liaht microscope. The texture of the matrix of C/C composite was shown to govern its mechanical properties. A fine mosaic texture of the matrix was suggested to be essential for slowing down the propagation of deteriorative crack and for getting high toughness of the C/C composite.The size of optica units in the matrix of C/C composites was found to be controlled by mixing either polyethylene terephthalate(PET) or phenol resin into pitch. With increasing the amount of additives (PET or phenol resin), the texture of the matrix changed continuously from coarse mosaic to isotropic through medium and fine mosaic textures. The interaction between these two precursors was accelerated under pressure and the matrix with homogeneous optical texture was obtained.In the present work, we could not have the composites with sufficiently high density and large size for studying on their fracture behavior because of the limited size of the autoclave used and the difficulty of repeated precursor impregnation. However, we could confirm the possibility for carbon fiber/carbon composite to get high density and also to control the texture of the matrix by mixing two different precursors and by carbonization under pressure.