Effects of porosity and pore size on the dielectric properties of reaction bonded porous silicon nitride ceramics

The dielectric properties of reaction bonded porous silicon nitride ceramics with global macro-pores which were prepared by adding pore-forming agent benzoic acid into silicon powders were investigated under varied porosity and pore size. The porosity and pore size of the powder compact can be controlled by changing the size and amount of pore-forming agent added. The experimental results show that the porosity of samples increases with the amount of pore-forming agent added, and the phase of α-Si₃N₄ in the sintered compact also increases, but the dielectric constant and the dielectric loss of the samples decrease. When the mass fraction of pore-forming agent added is 30%, with the increase of the size of the pore-forming agent, the pore size in the sample increases but the porosity has no change, the dielectric constant and the dielectric loss of the ceramics decrease too. Among all the obtained samples, the minimum dielectric constant is about 2.4297.