Dielectric and Mechanical Properties of Porous Si<sub>3</sub>N<sub>4</sub>-BN Ceramic Composites

Abstract

Recently, ceramic composites with low dielectric constant, low loss tangent, high flexural strength and high thermal shock resistance have received a considerable attention as candidate materials for certain high speed radome. In this paper, Si3N4-BN ceramic composites were fabricated by dry-press processing and cold isostatic pressing, with α-Si3N4 and BN as starting powder, Al2O3 and Yb2O3 as sintering additives, PMMA as pore-forming agenSubscript textt. After sintering for 2 h at 1750°C, porous Si3N4-BN ceramic composites with a three-point bending strength of 50~120MPa and a dielectric constant of 3.2~4.4 at 7~18 GHz frequency were obtained. The sintered body was mainly β-Si3N4 grains; BN was dispersed in the grains. The formation of β-Si3N4 grains was demonstrated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. Furthermore, the influence of the BN content on the dielectric and mechanical properties was also studied. The porous Si3N4-BN ceramic composites showed a lower dielectric constant and shrinkage. For above excellent properties, Si3N4-BN ceramic composites have been became one of the most hopeful candidate materials for high speed radome.