Pressureless Sintering of α‐Si3N4 Porous Ceramics Using a H3PO4 Pore‐Forming Agent

A new method for preparing high bending strength porous silicon nitride (Si3N4) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H3PO4) 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 Si3N4 ceramics are investigated, as a function of the content of H3PO4. The resultant high porous Si3N4 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 H3PO4 and by the continous reaction of SiP2O7 binder, which could bond on to the Si3N4 grains. Porous Si3N4 ceramics with a porosity of 42%–63%, the bending strength of 50–120 MPa are obtained.

[1]  Yuping Zeng,et al.  Oxidation bonding of porous silicon nitride ceramics with high strength and low dielectric constant , 2007 .

[2]  Q. Shen,et al.  Preparation of zirconium pyrophosphate bonded silicon nitride porous ceramics , 2006 .

[3]  André R. Studart,et al.  Processing Routes to Macroporous Ceramics: A Review , 2006 .

[4]  R. Janssen,et al.  Porous Silicon Nitride Ceramics Prepared by Reduction–Nitridation of Silica , 2005 .

[5]  Guo‐Jun Zhang,et al.  Synthesis of Porous Si3N4 Ceramics with Rod‐Shaped Pore Structure , 2005 .

[6]  S. Kanzaki,et al.  Comparison of Mechanical Properties of Silicon Nitrides with Controlled Porosities Produced by Different Fabrication Routes , 2005 .

[7]  C. Kawai,et al.  Effect of Porosity and Microstructure on the Strength of Si3N4: Designed Microstructure for High Strength, High Thermal Shock Resistance, and Facile Machining , 2005 .

[8]  F. Riley.  Silicon Nitride and Related Materials , 2004 .

[9]  S. Hampshire,et al.  Characterisation of porous silicon nitride materials produced with starch , 2004 .

[10]  Bao-lin Zhang,et al.  Combustion synthesis of network silicon nitride porous ceramics , 2003 .

[11]  S. Kanzaki,et al.  Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze‐Drying Process , 2002 .

[12]  T. Ohji,et al.  High performance porous silicon nitrides , 2002 .

[13]  Guo‐Jun Zhang,et al.  Porosity and microstructure control of porous ceramics by partial hot pressing , 2001 .

[14]  S. Bryan,et al.  The SiO2-Si3N4 Interface, Part I: Nature of the Interphase , 1995 .

[15]  A. Evans,et al.  Mechanical Properties of Partially Dense Alumina Produced from Powder Compacts , 1994 .

[16]  A. Pyzik,et al.  Microstructure and Properties of Self-Reinforced Silicon Nitride , 1993 .

[17]  James H. Adair,et al.  Evolution of the Formation of Inorganic Polymers in the CaO-SiO2-P2O5 System Using Metal Alkoxides , 1990 .

[18]  J. Heinrich,et al.  Relationships between processing, microstructure and properties of dense and reaction-bonded silicon nitride , 1987 .

[19]  R. M. Spriggs.  Expression for Effect of Porosity on Elastic Modulus of Polycrystalline Refractory Materials, Particularly Aluminum Oxide , 1961 .

[20]  Robert L. Coble,et al.  Effect of Porosity on Physical Properties of Sintered Alumina , 1956 .