Properties of Si<sub>3</sub>N<sub>4</sub> Based Nanocomposites Prepared by Pressureless Sintering Method

Abstract

Si3N4 based nanocomposites were prepared with nano-sized amorphous SiO2 and Si3N4 powders by pressureless sintering method. The microstructures, phase composition, mechanical and dielectric properties of the nanocomposites were investigated. The scanning electrical microscope (SEM) photographs reveal that the grains are big and elongated. The X-ray diffraction (XRD) analysis shows that the main crystalline phase in the composites is Si2N2O formed during the sintering process. More β-Si3N4 phases were retained in the nanocomposites with the increase amount of the amorphous Si3N4 powders and no phase of SiO2 were observed. The densities and the strength of the nanocomposites decreased with the increase of amorphous SiO2 content. Despite low density, the flexural strengths of the composites reaches 220MPa and the ceramic has excellent dielectric properties with dielectric constant as low as 3.2-4.7 and dielectric loss in the range 2.6-3.9×10-3.