Mechanical and dielectric properties of silicon nitride ceramics with high and hierarchical porosity

Silicone resin (SR) processed Si3N4 porous ceramics with high and hierarchical porosity were prepared by adding naphthalene as a pore-forming agent via pressureless sintering technique. The porosity of the obtained Si3N4 porous ceramics is 40 ∼ 71% with pores sizes ranging 0.1 ∼ 1.0 μm, 5 ∼ 30 μm and 50 ∼ 200 μm, which is determined by the pyrolysis of SR, partial sintering of Si3N4, and the volatilization of naphthalene, respectively. The bending strength is 6.8 ∼ 80 MPa and the dielectric constant is 2.29 ∼ 4.84. The results suggest that the hierarchical structure is responsible for a low dielectric constant with excellent mechanical property of the Si3N4 porous ceramics, making this material a good candidate for electromagnetic radome application.