Carbon-carbon composites prepared by a rapid densification process II: Structural and textural characterizations

In Part I of the present study it was shown that all carbon preforms are suitably densified by a rough laminar pyrocarbon in the processing range 900-1200 degrees C. The composites, studied by X-ray diffraction, optical microscopy and mainly by transmission electron microscopy, are homogeneous in porosity and textures (at micrometric and nanometric scales). The deposit is highly graphitizable ((d) over bar(002) = 0.336 nm and L-c > 150 nm). At a densification temperature above 1200 degrees C, the composites are heterogeneous: an increasing textural disorder occurs in the pyrocarbon and the ability to graphitize decreases. At any processing temperature, the roughness of the substrate is a leading parameter. Wavy surfaces (felt) of large period generate growth cones whereas nanometric scale roughness (T 300 type) locally disturb the pyrocarbon preferred orientation. However, accessible protruding aromatic layers on the fiber surface increase adhesion with the pyrocarbon. Smooth fiber surface (AS4) favors decohesions. (C) 1997 Elsevier Science Ltd.