Isothermal temperature oxidation behavior and mechanism of REB2C2 ceramics (RE = Y, Gd, Dy, Ho, Er) at 800–1000 °C in air

Abstract

In this study, the isothermal oxidation behavior of several high-purity REB₂C₂ (RE = Y, Gd, Dy, Ho, Er) ceramics in air at 800–1000 °C for 20 h was investigated for the first time. The results indicated that the oxidation of most REB₂C₂ (RE = Y, Dy, Ho, Er) follows a parabolic law and demonstrates good oxidation resistance. The superior oxidation resistance of these REB₂C₂ (RE = Y, Dy, Ho, Er) ceramics can be attributed to the formation of a continuous, dense oxide layer composed of REBO₃ (RE = Y, Dy, Ho, Er) and amorphous B₂O₃ on the substrate surface during the oxidation process. This dense oxide layer effectively reduces oxygen transport and decreases the oxidation rate through a diffusion-controlled mechanism, thereby isolating the substrate from oxygen exposure and protecting the underlying material. However, as the oxidation temperature increased, the oxide layer was primarily composed of REBO₃ particles, and there were more pores resulting from the volatilization of amorphous B₂O₃. At an oxidation temperature of 1000 °C, the particle size of REBO₃ increased, which facilitated the reduction of pores and helped maintain the density of the oxide layer. Notably, ErBO₃ exhibited a significant increase in particle size, leading to the densest oxide layer and demonstrating the best oxidation resistance. In contrast, GdB₂C₂ showed a linear increase in mass gain and exhibited relatively poor oxidation resistance.