Influence of the Content of B4C on Microstructure and Oxidation Resistance of Carbon/carbon Composites Modified by a Sol-gel/solvothermal Process

In order to improve the oxidation resistance property of carbon/carbon composites, the C/C matrix was modified with a borate sol precursor and B4C micro-powders by a sol-gel\solvothermal process. The phase compositions, surface and cross-section microstructures of the C/C matrix modified by different B4C contents were particularly investigated. Results show that the surface of the modified composites is covered by a coating composed of B2O3 and B4C, meanwhile, the internal micro-holes of the C/C composites are occupied by B2O3 and B4C. After oxidation in air at 973 K, the B2O3 glassy phase due to the oxidation of B4C seals the cracks and holes and effectively prevents C/C composites from oxidation. The weight loss of the modified C/C composites is only 2.21 % after oxidation in air at 973 K for 20 h.