ON THE OXIDATION RESISTANCE OF C C COMPOSITES OBTAINED BY LIQUID-PHASE IMPREGNATION CARBONIZATION OF DIFFERENT CARBON CLOTHS/

Two commercial carbons (an activated carbon cloth and a rayon-derived carbon cloth) having vastly differing properties were used as substrat es for the preparation of low- and high-temperature carbon/carbon comp osites by the liquid-phase impregnation/carbonization technique with t wo different pitches and one resin system as matrix precursors. The pe rcentage of matrix in the composites was dependent on the surface area of the carbon cloth substrate. The oxidation behavior of the composit es and their individual components was studied over the entire burn-of f range (0-100%). The structure of the starting and partially reacted composites was investigated by X-ray diffraction, scanning electron mi croscopy and polarized-light optical microscopy. For the low-temperatu re composites, no synergism was found when thermoplastic matrices were used. When the thermosetting resin matrix was used, the oxidation beh avior of the composites could not be predicted from that of their cons tituents. For the high-temperatures composites, synergistic effects we re observed: composites obtained using high-surface-area activated car bon cloth showed improved oxidation resistance with respect to their i ndividual components. In contrast, a simple additive effect was observ ed for the low-surface-area rayon-based composites.