Green bodies of porous silicon nitride ceramics were shaped by the extrusion technique using starch simultaneously as binder during extrusion and as pore‐maker during subsequent thermal debinding. The different porosities, microstructures, and mechanical properties after the extrusion, drying, debinding, and sintering stages were investigated. The results showed that the porosity, density, microstructure, and flexural strength of samples varied greatly through the whole process stages. The resultant samples had a 160 MPa flexural strength at a porosity of 43% and a uniform fibrous interlocking microstructure consisting of well‐developed rod‐like β‐Si3N4 grains. In addition, porosity, microstructure, and strength can be further tailored by sintering conditions such as the sintering nitrogen pressure. Extrusion using cheap starch as binder and pore‐maker is a promising preparation route for manufacturing cost‐effective porous silicon nitride ceramics.

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Highly porous Si3N4 ceramics with bimodal pore structure were prepared by the extrusion processing with petroleum coke of 30 μm as pore‐maker. The microstructure, mechanical strength, and gas permeability were investigated. The microstructure with petroleum coke contained not only numerous fine pores by interlocking the high aspect ratio β‐Si3N4 grains, but also some large pores of 15‐25 μm left by the burnout of petroleum coke. The resultant samples obtained an improved gas permeability of 1.2 × 10−12 m2, which is approximately two times that of samples without petroleum coke addition. Furthermore, the mechanical strength is still superior even at a porosity of 67% in comparison with the other porous ceramics used in the current diesel particulate filter.

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