Oxidation behavior of hot-pressed Si3N4 with Re2O3 (Re = Y, Yb, Er, La)

Four different beta-Si3N4 ceramics with silicon oxynitrides [Y-10(SiO4)(6)N-2, Yb4Si2N2O7, Er2Si3N4O3, and La-10(SiO4)(6)N-2, respectively] as secondary phases have been fabricated by hot-pressing the Si3N4-Re4Si2N2O7 (Re= Y, Yb, Er, and La) compositions at 1820 degrees C for 2h under a pressure of 25 MPa. The oxidation behavior of the hot-pressed ceramics was characterized and compared with that of the ceramics fabricated from Si3N4-Re2Si2O7 compositions. All Si3N4 ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400 degrees C and the oxidation products of the ceramics were SiO2 and Re2Si2O7. The Si3N4-Re4Si2 N2O7 compositions showed inferior oxidation resistance to those from Si3N4-Re2Si2O7 compositions, owing to the incompatibility of the secondary phases of those ceramics with SiO2, the oxidation product of Si3N4. Si3N4 ceramics from a Si3N4-Er4Si2N2O7 composition showed the best oxidation resistance of 0.198 mg cm(-2) after oxidation at 1400 degrees C for 192h in air among the compositions investigated herein. (C) 1999 Elsevier Science Ltd. All rights reserved.