Preparation and properties of porous silicon nitride ceramics with polymethyl methacrylate as pore-forming agent

Porous Si3N4 ceramics were prepared by adding polymethyl methacrylate (PMMA) as pore-forming agent, combined with cold isostatic pressing and pressureless sintering at nitrogen atmosphere. The composition of phases, microstructure, density and porosity, flexural strength, dielectric properties of samples with different content of PMMA were studied in this paper. With an increase of PMMA content, the density and flexural strength of samples were decreased, while the porosity and dielectric properties were improved. Two types of pores in the sample were found in the experiment, the micropores formed by beta-Si3N4 bridging, while the macropores formed by the pore-forming agent, and the macropores were the main factor for reducing the flexural strength and improving the dielectric properties by increasing porosity. When the PMMA content was 15 wt%, the comprehensive performance of sample was optimal, the porosity of 33.49%, the flexural strength of 103.62 MPa, the dielectric constant of 5.82 and dielectric loss tangent of 6.0 x 10(-3).