Injection and stabilization of mesophase pitch in the fabrication of carbon-carbon composites: Part II. Stabilization process

In the fabrication of carbon-carbon composites by mesophase injection through a fiber preform, it is essential to stabilize the flow-induced microstructure in the flow channels and to prevent relaxation and exudation of the mesophase. Oxidation stabilization studies were conducted on preforms injected with the naphthalene-based AR mesophase pitch. Oxidation mass gain (OMG) curves at 170, 222, and 270degreesC were generated for 60degrees-wedges cut from full size composite disks. The rates of OMG at 170degreesC of first- and second-cycle injection wedges and full-size disks were comparable to those using as-spun filaments 30 mum in diameter, and particles sieved to 200 to 340 mum. The results suggest that oxygen is accessible deep into a mesophase matrix and the transport is facilitated by connected array of shrinkage cracks. Oxidation at 170degreesC has strong advantage over higher oxidation temperatures by having a higher carbon yield and lower OMG threshold and thus oxidation time required for stabilization. The 60degrees-wedges could be stabilized at 170degreesC after a 25h oxidation with a 7.2% OMG and attaining a carbon yield above 85%. (C) 2004 Elsevier Ltd. All rights reserved.