Effects of oxidation temperature, time, and ambient pressure on the oxidation of ZrB₂-SiC-graphite composites in atomic oxygen

The effects of oxidation temperature, time, and ambient pressure on the oxidation of ZrB₂-SiC-graphite composites in atomic oxygen were investigated. The phase formation oxidized in atomic oxygen was similar to that of ZrB₂-SiC-graphite composites oxidized in air up to 1600 °C. However, the ZrO phase that formed at 1600 °C in atomic oxygen was specific to the higher temperature treatment and the amount of this phase increased with increased oxidation time. The weight gain per unit surface area as a function of oxidation time exhibited a parabolic to linear kinetic behavior. Compared with specimens oxidized in air, the glass-phase layer that formed at 1600 °C in atomic oxygen was not thick enough to fill the holes on the exposed surface. The mechanical properties of ZrB₂-SiC-graphite composites oxidized in atomic oxygen decreased with increased oxidation temperature, time, and ambient pressure. These results can facilitate the expanded application of UHTCs.