Abstract
Solid-gas reactions of Si3N4 ceramics were investigated with emphasis on the mass loss during sintering under various sagger conditions. A Si3N4 powder compact without sintering aids was heat-treated at 2023K for 0 to 8h under 0.1 and 1MPa N2 adopting three sagger conditions: a Si3N4 powder bed, without a powder bed in BN sagger, and without a powder bed in C sagger, and Si3N4 with addition of 5 mass% Y2O3 and 3 mass% Al2O3 was sintered at 2023K for 0 to 16 h under 0.1 to 100MPa N2 adopting four sagger conditions: a 50 mass% Si3N4/50 mass% BN powder bed, without a powder bed in BN sagger, a C powder bed, and without a powder bed in C sagger. In C sagger, the principal mass loss reaction was that of Si3N4 (s) with CO(g): 2Si3N4(s)+3CO(g)→6SiO(g)+4N2(g). In BN sagger, the principal mass loss reaction was that of Si3N4(s) with SiO2(l): Si3N4(s)+3SiO2(l)→6SiO(g)+N2(g). When SiO(g) generated from the sample and the powder bed (based on the above reaction between Si3N4(s) and SiO2(l)) was exhausted, the mass loss reaction of Si3N4(s) with CO(g) occurred even in BN sagger, which diffused in through a gap of the sagger.
