Synergistic promotion of dielectric and thermomechanical properties of porous Si3N4 ceramics by a dual-solvent template method

Porous Si3N4 ceramics are promising high-temperature wave transparent materials for use as radomes or antenna windows in hypersonic aircraft. However, a trade-off between the dielectric and thermomechanical properties is still challenging. Therefore, tailoring the microstructure and properties of porous Si3N4 is highly important. In this work, porous Si3N4 ceramics with uniform and fine structures were obtained via dual-solvent templating combined with the freeze-casting method. The as-prepared porous Si3N4 ceramic, with 56% porosity, possesses high mechanical properties, with flexural strength and compressive strength values of 95 +/- 14.8 and 132 +/- 4.5 MPa, respectively. The uniform spherical pore structure improved the mechanical properties, and the rod-shaped Si3N4 grains facilitated crack deflection. The decreased pore size effectively blocks phonon transport, leading to a low thermal conductivity of only 4.2 W/(K<middle dot>m). Moreover, the porous Si3N4 ceramic maintains a small dielectric constant of 3.3, and the dielectric loss is stable between 1.0x10-3-4.0x10-3, which guarantees its potential application in high-temperature wave-transparent components. These results significantly advanced the development of high-performance wave-transparent materials used in hypersonic aircraft.