Oxidation behavior of liquid-phase sintered silicon carbide with aluminum nitride and rare-earth oxides (Re₂O₃, where Re = Y, Er, Yb)

Silicon carbide (SiC) ceramics have been fabricated by hotpressing and subsequent annealing under pressure with aluminum nitride (AlN) and rare-earth oxides (Y₂O₃, Er₂O₃, and Yb₂O₃) as sintering additives. The oxidation behavior of the SiC ceramics in air was characterized and compared with that of the SiC ceramics with yttrium-aluminum-garnet (YAG) and Al₂O₃-Y₂O₃-CaO (AYC). All SiC ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400°C. The SiC ceramics sintered with AlN and rare-earth oxides showed superior oxidation resistance to those with YAG and Al₂O₃-Y₂O₃-CaO. SiC ceramics with AlN and Yb₂O₃ showed the best oxidation resistance of 0.4748 mg/cm² after oxidation at 1400°C for 192 h. The minimization of aluminum in the sintering additives was postulated as the prime factor contributing to the superior oxidation resistance of the resulting ceramics. A small cationic radius of rare-earth oxides, dissolution of nitrogen to the intergranular glassy film, and formation of disilicate crystalline phase as an oxidation product could also contribute to the superior oxidation resistance.