MESOPHASE PITCHES AS MATRIX PRECURSOR OF CARBON-FIBER-REINFORCED CARBON .2. STABILIZATION OF MESOPHASE PITCH MATRIX BY OXYGEN TREATMENT

The stabilization of unidirectional (UD) composites fabricated with no n-surface-oxidized and surface-oxidized HT carbon fibers, mesogenic pi tches and mesophase pitches with oxygen was studied by variation of ox ygen pressure (up to 2 MPa), temperature (160-200 degrees C), and stab ilization time (up to 36 hours). The oxygen uptake is diffusion contro lled and can be described by Fick's second law. By stabilization, swel ling of the composites during carbonization is diminished, and the cok e yield is increased. At a pitch-specific oxygen uptake, a minimum swe lling and simultaneously a maximum coke yield were found. This specifi c oxygen uptake was assigned as optimum stabilization. This conclusion is confirmed by a decreased rate of oxygen uptake by further treatmen t. The oxygen uptake can be strongly accelerated by increased oxygen p ressure, but like the maximum temperature for optimum stabilization, t here is a maximum oxygen pressure. Both parameters are pitch-specific. In contrast to the optimum stabilization, it was surprisingly found t hat the bulk density of the carbonized composites can be increased by over-stabilization. Copyright (C) 1996 Elsevier Science Ltd