ABSTRACT
Si3N4–SiO2 ceramic composites were prepared by gel-casting method and pressure-less sintering using Si3N4 and SiO2 as starting powders, and Al2O3 and Y2O3 as sintering additives. The effects of SiO2 on the microstructure and dielectric properties of Si3N4–SiO2 ceramic were investigated. After sintering for 2 h at 1500°C, Si3N4–SiO2 ceramic composites, having a bending strength of 60.59~178.47 MPa and a dielectric constant of 3.2~6.8 at 1~30 MHz frequency were obtained. β-Si3N4 grains and Si2N2O phase make the sintered body. The formation of β-Si3N4 grains was demonstrated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of SiO2 content on the dielectric and mechanical properties has also been discussed in this work. The mechanical properties of Si3N4-based ceramics are found to decrease with the increase of SiO2 content, while the dielectric properties are improved. The low dielectric properties of porous Si3N4–SiO2 ceramic composites made them one of the most candidate materials for wave transparent applications.
