Properties of porous Si3N4 ceramic electromagnetic wave transparent materials prepared by technique combining freeze drying and oxidation sintering

Abstract

A simple and low-cost technique combining freeze drying and oxidation sintering is explored to prepare Si3N4 ceramics with high porosity and complex shape. The effects of sintering temperature and time on the phase composition, microstructure, porosity, pore size and dielectric constant of the porous Si3N4 ceramics are studied. Due to the variations of phase composition and microstructure, the porous Si3N4 ceramics sintered at different temperature possess characteristic in flexural strength. The porous Si3N4 ceramics sintered at 1,300 °C for 2–3 h have the highest flexural strength of 71–74 MPa. The changes of porosity and composition have much effect on the dielectric constant of porous Si3N4 ceramics. Because of the high porosity and SiO2 volume fraction, the porous Si3N4 ceramics sintered at 1,300 °C for 2–3 h possess low dielectric constant of 3.4–3.6 and small pore size of 0.9 μm. The porous Si3N4 ceramics are good structural/functional and promising electromagnetic wave transparent material.