Enhanced thermal conductivity in sintered reaction-bonded silicon nitride through ammonia-assisted chemical processing

To improve the thermal conductivity of sintered reaction-bonded silicon nitride (SRBSN), ammonia pretreatment was introduced before the nitridation stage of silicon compact. The Si powder compact containing Y 2 O 3 –Sc 2 O 3 additives underwent ammonia pretreatment at 850 °C for 4 h, followed by nitridation in N 2 –H 2 atmosphere at 1450 °C for 6 h. The reaction-bonded silicon nitride (RBSN) compacts were densified through gas-pressure sintering at 1900 °C for 12 h under a nitrogen pressure of 1 MPa. The ammonia pretreatment removed inherent SiO 2 impurities from the Si powder, leading to enhanced nitridation efficiency, elevated α-Si 3 N 4 phase fraction, and increased N/O ratio in the intergranular secondary phase of RBSN. These processing in RBSN facilitated the formation of larger β-Si 3 N 4 grains, reduced lattice oxygen content, diminished grain boundary phases, and improved grain contiguity in the final SRBSN. Consequently, the ammonia-assisted chemical processing significantly increased the thermal conductivity of SRBSN from 116 W/(m·K) to 130 W/(m·K).