The Effect of Embedding Conditions on the Thermal Conductivity of β-Si_3N_4(<Special Issue>Guest Editors Dedicated to Prof. Gunter Petzow: Modern Trends in Advanced Ceramics)

概要

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Dense β-Si_3N_4 ceramics were prepared from the α-Si_3N_4 raw powder by sintering at 1900℃ for 12h at a nitrogen pressure of 1 MPa, using a mixture of Y_2O_3 and MgSiN_2 as the sintering additives. The effect of embedding conditions on the thermal conductivity of β-Si_3N_4 ceramics was investigated by changing the number of samples and the embedded fraction in BN packing powder with BN crucible. It was found that the embedment had no effect on the densification, but had an effect on the weight loss, crystalline secondary phase and microstructure. The thermal conductivity was found to increase linearly with the weight loss, but independent of the grain size. The complete embedment and the increased number of sintered samples tended to suppress the weight loss and thus lowered the thermal conductivity. The optimum condition led to a significant improvement in the thermal conductivity from 96 to 117 Wm^<-1> K^<-1>. It is proposed that the enhanced thermal conductivity is attributed to the removal of lattice oxygen by the reaction Si_3N_4(s) +3 SiO_2(1) ⇔6 SiO(g) +2N_2(g). In addition, the decreased amount of secondary phases also contributes to the thermal conductivity. This work suggests that the increased weight loss may also be an important strategy for enhancing the thermal conductivity of β-Si_3N_4 ceramics by controlling the sintering atmosphere.
2006-11-01