Extrusion of highly porous silicon nitride ceramics with bimodal pore structure and improved gas permeability

Highly porous Si 3 N 4 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‐Si 3 N 4 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 m 2 , 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.