Abstract: Porous Si₃N₄ ceramics were prepared by in situ reaction-bonding technology, using Si₃N₄ and Al₂O₃ as starting materials. The effects of sintering temperature and holding time on their porosities, flexural strength, and dielectric properties were studied. The strength and dielectric constants of samples are improved with increasing of sintering temperature and holding time; but the result is reverse in the condition of sintering temperature >1350℃ and holding time >4h. The phase analyses results indicate that the porous Si₃N₄ ceramics are mainly composed of α-Si₃N₄, oxidated SiO₂ (cristobalite) and Al₂O₃. Porous Si₃N₄ ceramics with porosities from 25.34% to 43.92% and flexural strength from 42.54 to 127.85MPa are obtained. Their dielectric constants are in the range from 3.3 to 4.6 and dielectric loss is about 0.005.

Key words: porous Si₃N₄ ceramics, dielectric properties, in situ reaction bonding, porosity