Protective Engobes for Si_3N_4 Ceramics Sintered in Air-Atmosphere Furnace

摘要

Silicon nitride ceramics were sintered at 1640 °C in an air-atmosphere furnace using an alumina crucible, alumina packing powder, and protective Al_2O_3 engobes as well as glass ceramic engobes obtained from the system SiO_2ZnO-Al_20_3. The Si_3N_4 composite was prepared from β-Si_3N_4 powder with addition of MgO and Al_2O_3 as sintering aids. It was found that the densest silicon nitride ceramic with only partial oxidation was the sample covered with the Al_2O_3 engobe. Three phases were identified by XRD analysis: β-Si_3N_4, α-Si_3N_4, and Si_2N_2O. The obtained results are promising and encourage continuous research in this field to ensure protection from and prevention of intensive oxidation.