Preparation of Silicon Nitride with High Thermal Conductivity and High Flexural Strength Using YbH₂-MgO as Sintering Additive

Abstract

Silicon nitride with high thermal conductivity was obtained by two-step sintering method using YbH2-MgO as sintering additive. The effect of YbH2-MgO on shrinkage behavior, phase composition, microstructure, thermal conductivity, and flexural strength was investigated. The nitrogen-riched and oxygen-lacked oxynitride liquid phase was generated owing to the elimination of SiO2 by YbH2. Both the removal of lattice oxygen and the growth of β-Si3N4 were stimulated by the liquid phase. Therefore, compared to Yb2O3-MgO doped sample, silicon nitride with enlarged grains, purified lattice and reduced intergranular phase was obtained. Ultimately, the thermal conductivity increased by 13.7% from 115.32 to 131.15 W• m -1 •K -1 after sintering at 1900 ℃ for 24 h by substituting Yb2O3 with YbH2. Although the replacement of Yb2O3 by YbH2 leads to enhanced flexural strength at low temperature, it tends to reduce the flexural strength at high temperature. The optimal flexural strength of (1008 ±35)MPa was achieved after sintering at 1800 ℃ for 4 h. This variation related mainly to the exaggerated bimodal microstructure. This work signifies that YbH2-MgO is effective for obtaining Si3N4 ceramics with both high flexural strength and high thermal conductivity.

Enhanced thermal conductivity and flexural strength of sintered reaction‐bonded silicon nitride with addition of (Y0.96Eu0.04)2O3

“…[12][13][14][15] Second, the lattice oxygen can be reduced by using high-purity Si powder with low oxygen content. There are many studies on the use of non-oxide sintering additives to improve the thermal conductivity of Si 3 N 4 , such as rare-earth hydride, [16][17][18][19][20] rare-earth silicide, 21,22 rare-earth boride, 23,24 fluoride, [25][26][27][28] and nitrides. 29,30 Dense Si 3 N 4 ceramics were fabricated by using Si 3 N 4 powders as the raw material in those works.…”