Preparation of Low Dielectric Constant Porous Silicon Nitride Ceramics for Radome Application

The porous silicon nitride ceramics with low dielectric constant and high flexural strength were obtained by adding pore-forming agent through partial sintering technique. The effects of pore-forming agent amount on the properties of porous silicon nitride ceramics were investigated. Microstructure was analyzed by means of scanning electron microscopy. The results show that the porous structure is formed by the overlap of pillar β-Si 3 N 4 with high length diameter ratio. The porosity of samples rises with the increase of pore-forming agent content, which leads to the decrease of the dielectric constant and loss, but the decrease of flexural strength. When the pore-forming agent of PMMA with mass fraction of 20% was added, the volume density, porosity, dielectric constant and loss of porous silicon nitride ceramics were 1.17g/cm 3 , 66.5%, 2.33 and 0.8×10 -3 respectively, with higher flexural strength of 75MPa which is satisfactory as low dielectric material for core layer of broadband radome.