High Temperature Oxidation of Carbon/SiC/B4C Composite in Different Atmospheres

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Abstract
High temperature oxidation tests of carbon/SiC/B4C composite made from mixed powders of coke (51.2 wt%), SiC (38.8 wt%) and B4C (10 wt%) were carried out in different atmospheres of dry air, dry oxygen and wet air at temperature range from 600 to 1400°C. The oxidation had three different behaviours depending on the oxidation temperature ranges of below 700°C, 800-1000°C and above about 1100°C. Below about 700°C oxidation was relatively suppressed due to probably B2O3 liquid phaseformed from B4C. At about 800-1000°C protective B2O3 layer vaporized easily, and dense and homogeneous protective oxide layer was difficult to form on the surface, and then active oxidation proceeded in dry oxygen atmosphere. Particularly in wet air condition oxidation became much more active at this temperature range and oxidation proceeded deeply into inner part of the sample, because denseprotective layer could not be formed. While above about 1100°C dense and uniform protective layer formed o thesurface and protected further oxidation. The protective oxide layer formed at about 1200°C was suggested to be SiO2 rich phase and was known remarkably stable for oxidation even in wet air at about 900°C.

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