Journal of Inorganic Materials (无机材料学报) 2014/29:7 PP.701-705
Porous silicon nitride ceramic was fabricated by using α-Si3N4 as raw material and Y2O3 as a sintering additive, with nitrogen pressure of 0.12 MPa, 0.32 MPa and 0.52 MPa. Effects of the nitrogen pressure on grain morphology and mechanical properties of the resultant porous Si3N4 ceramics were characterized by SEM, XRD and flexural strength. With the increasing of nitrogen pressure, sintering shrinkage decreased, with a corresponding increased porosity. Due to the increase of nitrogen pressure, the viscosity of liquid phase increased due to increased N solubility, leading to the low densification in the sintering. Fibrous β-Si3N4 grains were developed in the porous microstructure and the grain morphology and aspect ratio were greatly affected by the nitrogen pressures. The high viscosity of the liquid phase in nitrogen at high pressure led to restraining of the β-Si3N4 nucleation, and preferential growth of β-Si3N4. Due to the formation of elongated β-Si3N4, flexural strength of the porous Si3N4 ceramic was improved by the increase of nitrogen pressure, while decreased with the increase of porosity. The porous Si3N4 ceramics with porosity of 58% and flexural strength of 140 MPa were obtained at the nitrogen pressure of 0.52 MPa.
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