Factors influencing oxidation resistance of B4C/C composites with self-healing properties

The factors that influence oxidation resistance of B4C/C composites with self-healing properties during oxidation are discussed in this paper. Isothermal oxidation behavior of B4C/C composites with different B4C content is examined from 600 to 900 degrees C. Analysis of oxidation kinetics of B4C/C composites at the temperature range of 600-900 degrees C showed that nominal activation energies are 125, 133, 241 and 299 kJ mol(-1) for the composites with B4C content of 5, 10, 15 and 20%, respectively, closely related with the self-healing properties of the corresponding composites during oxidation. The sensitivity of B2O3 to moisture accounts for the larger weight losses of the composites in moist air than in dry air. The higher air flow rate may have reduced the thickness of the boundary layer over the surface of the composites and influenced the uniformity of the B2O3 layer which spreads on the surface of the composites, leading to larger weight losses. The fact that B4C/C composites possess self-healing properties is verified by the experimental results that the physical and mechanical properties of the composites do not deteriorate progressively with continued oxidative exposure. (C) 1998 Elsevier Science Ltd. All rights reserved.