Multiple CVD densification of PAN-based carbon-fibre reinforced carbon laminates

Abstract

Image analysis, to quantify the void structure, together with polarised-light microscopy were used to study the densification of PAN-based woven carbon-fibre reinforced carbon laminates by multiple CVD treatment. The densification occurred by filling of co-planar and bundle cracks, with inter-fibre cracks and pores being relatively unaffected. According to its densification behaviour, the void structure in the composites can be described as an array of globe-domains interconnected by thin capillaries. The co-planar cracks acted as the thin capillaries and the bundle cracks as the globes. The co-planar cracks were densified to a greater extent than the bundle cracks in the early stages of the densification process. Initially, the overall reaction was controlled by a chemical reaction in the void volume, but soon diffusion control became dominant. A barrier to the mass transport of reactant was formed at a distance from the external surface equal to one half the thickness of a layer of cloth and tended to move towards the external surface as densification proceeded.