The preparation of porous Si₃N₄ ceramic material for radome application

The low-density silicon nitride ceramics with global macro-pores were prepared by adding pore-forming agent through reactive sintering technique. The effects of pore and processing of reaction on the properties of porous silicon nitride ceramics were investigated. The experimental results show that the porosity of samples with 40wt% pore-forming agent increase visibly compared to the samples with no pore-forming agent, which leads to the decrease in the dielectric constant and loss in the sample. Adding of the global macro-pores can promote the formation of needle-like phase and decrease the partial overheating of green compacts to avoid silicon fusion. The α-Si₃N₄ phase increases and the needle-like phase decrease with the decrease of heating-rate. It is found that the free silicon in the ceramics is oxidized and leads to the decrease in the dielectric constant and loss when the sintered compacts are heat-treated in air.