The efficiency and mechanism of densification of 2-D C/C composites by coal-tar pitch impregnation Original Research Article

A low QI, impregnation coal-tar pitch was used to study the efficiency and mechanism of densification of a carbonised 2-D C/C preform by a low-pressure impregnation/carbonisation processing route. Changes occurring in the porous structure of the preform as densification proceeded were followed by weight and density measurements as well as by analysis of optical microscope images of polished sections. For the latter purpose, voids visible in polished sections were classified into co-planar and bundle voids, and large and small inter-fibre voids. The filling of each void category was studied at each densification step and marked differences in the efficiency of filling of the various types of void were observed. The overall densification efficiency is a function of liquid pitch impregnation efficiency, pitch expulsion and carbon yield of the pitch.