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 1×10⁵Pa air and 0.2×10⁵Pa 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 1×10⁵Pa air, and 3.23×10^-2 and 2.21×10^-2 %/s in 0.2×10⁵Pa 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 0.2×10⁵Pa O₂ than in 1×10⁵Pa 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.