Protective Engobes for Si3N4 Ceramics Sintered in Air-Atmosphere Furnace
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Silicon nitride ceramics were sintered at 1640°C in an air-atmosphere furnace using an alumina crucible, alumina packing powder, and protective Al2O3 engobes as well as glass ceramic engobes obtained from the system SiO2-ZnO-Al2O3 The Si3N4 composite was prepared from β-Si3N4 powder with addition of MgO and Al2O3 as sintering aids. It was found that the densest silicon nitride ceramic with only partial oxidation was the sample covered with the Al2O3 engobe. Three phases were identified by XRD analysis: β-Si3N4, α-Si3N4, and Si2N2O. The obtained results are promising and encourage continuous research in this field to ensure protection from and prevention of intensive oxidation.
KeywordsSi3N4 ceramics air atmosphere protective engobes sintering
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