Pressureless Sintering of α‐Si ₃ N ₄ Porous Ceramics Using a H ₃ PO ₄ Pore‐Forming Agent

A new method for preparing high bending strength porous silicon nitride (Si 3 N 4 ) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H 3 PO 4 ) as the pore‐forming agent. The fabrication process is described in detail and the sintering mechanism of porous ceramics is analyzed by the X‐ray diffraction method and thermal analysis. The microstructure and mechanical properties of the porous Si 3 N 4 ceramics are investigated, as a function of the content of H 3 PO 4 . The resultant high porous Si 3 N 4 ceramics sintered at 1000°–1200°C show a fine porous structure and a relative high bending strength. The porous structure is caused mainly by the volatilization of the H 3 PO 4 and by the continous reaction of SiP 2 O 7 binder, which could bond on to the Si 3 N 4 grains. Porous Si 3 N 4 ceramics with a porosity of 42%–63%, the bending strength of 50–120 MPa are obtained.