Low-temperature fabrication of Si3N4 ceramics with high thermal conductivities using a single Mg2Si sintering additive

Silicon nitride ceramics were prepared by plasma-activated sintering at 1550 °C with 2−5 wt% Mg2Si as a sintering agent. The effects of the Mg2Si content on the phase, microstructure, and thermal conductivity of the ceramics were studied. Mg2Si reacts with SiO2 to form MgO and Si, benefiting to the transformation and densification of Si3N4. After heat treatment at 1700 °C for 6 h in a flowing N2, the residue Si reacted with N2 and lattice O to form Si3N4 and SiO, resulting in decreases in the grain-boundary phase and lattice O content. After the heat treatment, the sample prepared with 3 wt% Mg2Si achieved a relatively good balance between the thermal conductivity and strength, with values of 110 W/(m⋅K) and 705 ± 30 MPa, respectively.