Fabrication and Characterization of Porous Silicon Nitride Bodies through Starch Consolidation Casting and Pressureless Sintering

Porous Si3N4 ceramics were prepared by a novel colloidal method called starch consolidation casting. In this method, starch plays both pore-forming and consolidating roles. The effect of starch content on the viscosity of Si3N4/starch slurry was investigated in this research. Rotational Rheometer was used to study the rheological behavior of Si3N4/starch slurry. Green samples with 5 to 10MPa flexural strength were shaped by casting slurries in a nonporous mold and held at 80C for 120min. Afterward the samples burned-out and sintered at 1650C for 4h in an air furnace under a nitride powder bed condition. Thermal behavior, phase evolution, and microstructure of sintered samples were characterized through Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The XRD results showed that β−Si3N4 was the main phase in the sintered samples. The β−Si3N4 phase content was as much as 90wt% in the sintered samples. Finally, a porous silicon nitride sample was successfully produced with 44 vol% open porosity and Flexural strength of 108.9MPa through the starch consolidation casting method.