High Performance Porous Wave-Transmitting Silicon Nitride Ceramics by Gel-Casting Technique

Abstract

Porous wave transmitting Si3N4 ceramics have been of great interest and technological importance in aerospace area. In this paper, the high performance wave transmitting porous Si3N4 ceramics was prepared by gel-casting method, without any pore-former. The porosity was controlled by the solid content of the slurry and the sintering temperature. The flexural strength and dielectric properties of the material were determined by three bending method and a resonant cavity method. The relationship of the dielectric constant versus the sintering temperature was discussed, and the effect of porosity on dielectric properties was investigated also. As a result, the flexural strength of the porous Si3N4 is 40-200MPa with porosity of 67-45%, dielectric constant of 2.2-3.4 in the frequency of 8GHz at room temperature. With the increase of porosity, both the dielectric constant and dielectric loss decreased. This technique is considered to be a potentially useful method to fabricate the porous ceramics with complex shape.