Effect of in-situ formed Y2O3 by metal hydride reduction reaction on thermal conductivity of β-Si3N4 ceramics

The effect of YH 2 on densification, microstructure, and thermal conductivity of Si 3 N 4 ceramics were investigated by adjusting the amount of YH 2 in the range of 0–4 wt% using a two-step sintering method. Native SiO 2 was eliminated, and Y 2 O 3 was in situ formed by a metal hydride reduction reaction, resulting in various Y 2 O 3 /SiO 2 ratios. Full densification of YH 2 -doped samples could be achieved after sintering at 1900 °C for 4 h. The Y 2 O 3 /SiO 2 ratio had a significant influence on the composition of crystalline secondary phases. Besides, the increased Y 2 O 3 /SiO 2 ratio is conducive not only to the grain growth but also to the reduction of activity of SiO 2 in the liquid phase, resulting in enlarged purified grains, reduced volume fraction of intergranular phases and increased Si 3 N 4 -Si 3 N 4 contiguity. Ultimately, the thermal conductivity increased by 29 % from 95.3 to 123.0 W m −1  K −1 after sintering at 1900 ℃ for 12 h by the substitution of Y 2 O 3 with YH 2 .