Oxidation Behaviors of C-ZrB2-SiC Composite at 2100 °C in Air and O2

The oxidation behaviors of graphite and ZrB2-SiC modified graphite composite were investigated at 2100 °C in 1 × 105 Pa air and 0.2 × 105 Pa O2. The oxidation tests were conducted in an induction heating furnace. The oxidation of these two materials followed the linear rate law. The determined radius loss rates of graphite and C-ZrB2-SiC at 2100 °C were 2.18 × 10−2 and 1.05 × 10−2 %/s in 1 × 105 Pa air, and 3.23 × 10−2 and 2.21 × 10−2 %/s in 0.2 × 105 Pa O2, respectively. The incorporation of ZrB2 and SiC decreased remarkably the oxidation rate of graphite because the oxide scale formed on the sample surface during oxidation helps in reducing the exposed surface area of the underneath substrate. In two different atmospheres with the same oxygen partial pressure, both graphite and C-ZrB2-SiC experienced more severe oxidation at 2100 °C in 0.2 × 105 Pa O2 than in 1 × 105 Pa air. The oxidation rate-controlling step for graphite and C-ZrB2-SiC was proposed to be the inward diffusion of oxygen through the boundary layer and through the pores in the oxide scale, respectively. A model based on diffusion theory was established to discuss the effect of the total gas pressure on their oxidation behaviors.