Influence of Si ₃ N ₄ powder characteristics on the electrical and mechanical properties of pressureless sintered ceramics

Silicon nitride (Si3N4) ceramics, combining excellent resistivity and high-temperature stability, are widely used in SF6-insulated high-voltage DC electrical equipment. This study attempted to fabricate Si3N4 insulating ceramics with superior dielectric and good mechanical properties using the stepwise pressureless sintering method, Y2O3-Al2O3 as a sintering additive, and four types of raw Si3N4 powders. The latter’s characteristics were found to strongly influence both the mechanical and electrical properties of the ceramics. Specifically, powders with higher α-phase content, lower oxygen content, and a uniform particle size distribution contribute to obtaining dense ceramics with excellent mechanical properties. Furthermore, powders with a higher α-phase content and uniform particle size distribution enhance the volume resistivity of the Si3N4 ceramics, while smaller average particle sizes and lower oxygen content further improve the temperature stability of the ceramic resistivity.