The void structure of 2-D C/C preforms and composites: Effect of the nature of the matrix precursor coal-tar pitch Original Research Article

Four coal-tar pitches were used in conjunction with a woven carbon fibre cloth to produce carbon/carbon preforms and, after densification by impregnation/carbonisation using the same pitch, densified composites. Analysis of microscope images from polished sections was used to allow study of the effect of the nature of the matrix-precursor pitch on the void structure in the two materials. Voids were classified into co-planar, bundle and inter-fibre cracks, and inter-fibre pores. The total voidage of the carbonised preforms varied with the QI content of the precursor pitch, the effect being associated largely with the voidage in the co-planar voids. For each class of void, densification generally resulted in marked decreases in voidage and the number of voids per unit area, while the mean dimensions of the voids were affected to a lesser extent. Results are discussed in terms of the three-dimensional void structure of 2-D composites.