Oxidative attack of carbon/carbon substrates through coating pinholes

A critical issue with oxidation protected carbon/carbon composites used for spacecraft thermal protection is the formation of coating pinholes. In laboratory experiments, artificial pinholes were drilled through SiC-coatings on a carbon/carbon material and the material was oxidized at 600, 1000, and 1400 degrees C at reduced pressures ol air. The attack of the carbon/carbon was quantified by both weight loss and a novel cross-sectioning technique, A two-zone diffusion control model was adapted to analyze this problem. Agreement of the model with experiment was reasonable at 1000 and 1400 degrees C; however results at lower temperatures show clear deviations from the theory suggesting that surface reaction control plays a role. (C) 1999 Elsevier Science Ltd. All rights reserved.