DENSIFICATION OF UNIDIRECTIONAL C C COMPOSITES BY MELTED PITCH IMPREGNATION/

Four unidirectional pitch-based C/C composites were densified by multi ple melted pitch impregnation under vacuum followed by recarbonization to 1273 K. The pitches used for the impregnation were the same pitche s used as carbon matrix precursors in the preparation of the C/C compo sites. Recarbonization steps in one of the composites were also perfor med under pressure in order to study the effect of pressure during the densification process. The efficiency of the impregnation was evaluat ed in terms of the voids accessible to the impregnant and was followed by the weight gain during the process and polarized-light microscopy of impregnated composites. Wide differences in the densification proce ss were observed dependent primarily on the physical and chemical prop erties of the pitch, especially the carbon yield and pitch fluidity. T he composites at different stages of densification were characterized by standard procedures (bulk density and porosity), and microscopical techniques (polarized-light microscopy, image analysis and scanning el ectron microscopy). On the basis of results a mechanism describing the whole process involved in the densification of unidirectional C/C com posites is proposed. (C) 1998 Elsevier Science Ltd. All rights reserve d.