Improved thermal conductivity of β-Si3N4 ceramics through the modification of the liquid phase by using GdH2 as a sintering additive

The effect of the GdH2 on the shrinkage behavior, microstructure, thermal conductivity, and flexural strength was investigated. The pre-sintering enables the elimination of native SiO2 and the simultaneous formation of Gd2O3. The N/O ratio in the liquid phase was increased because of the increasing Gd2O3/SiO2 ratio, resulting in the restricted shrinkage during gas pressure sintering. The high N/O ratio in the liquid phase benefits not only the nucleation and growth of beta-Si3N4 but also the removal of lattice oxygen, leading to the increase of thermal conductivity. Although the replacement of Gd2O3 by GdH2 leads to enhanced flexural strength at low temperature, it tends to reduce the flexural strength at high temperature. This variation related largely to the exaggerated bimodal microstructure. This work signifies that GdH2 is an effective sintering additive for obtaining Si3N4 ceramics with both high flexural strength and high thermal conductivity.