Injection and stabilization of mesophase pitch in the fabrication of carbon-carbon composites. Part III: Mesophase stabilization at low temperatures and elevated oxidation pressures

Micrography and infrared spectroscopy were applied to explore microstructural stabilization of mesophase pitch at oxidation temperatures as low as 130degreesC. AR mesophase pitch synthesized from naphthalene was drawn to rods and thick filaments with fine fibrous microstructures that coarsen upon carbonization without adequate stabilization. At 270degreesC, the stabilization front advances rapidly to a depth of about 7 mum, after which no further growth is perceptible. At low temperatures, there is a time lag before a stabilized layer can be observed near the surface, but thereafter the stabilization front advances relatively rapidly. For longer oxidation times, the low-temperature stabilization depths can exceed those attained at higher temperatures. FTIR spectra confirmed chemical reactivity and the formation of oxygen-bearing functional groups even at the low oxidation temperatures. Oxidation under a moderate pressure of 0.7 MPa can be effective in raising the oxygen uptake and increasing the stabilization depths significantly. All evidences point to the advantageous use of lower oxidative temperatures: more effective penetration of stabilization depth, lessen destructive effects of over-oxidation, and potentially shorter processing times. (C) 2004 Elsevier Ltd. All rights reserved.