Effect of β-Si3N4 Initial Powder Size on Texture Development of Porous Si3N4 Ceramics Prepared by Gel-Casting in a Magnetic Field

Abstract

ABSTRACTTextured porous Si3N4 ceramics with fine and coarse β-Si3N4 powders as the raw materials were prepared by gel casting in a strong magnetic field of 6T and subsequent pressureless sintering. These results showed that highly textured porous Si3N4 ceramics could be obtained by adjusting the ratio between fine and coarse β-Si3N4 powders in 6T. The Lotgering orientation factor in green bodies showed the value of 0.72∼0.74 with the increase of coarse powder content. The sintering process promoted texture development of the samples by Ostwald ripening owing to the big difference in the β-Si3N4 initial powder size. After sintering at 1800oC for 2 h, the degree of texture (Lotgering orientation factor) in the sample, prepared with fine and coarse powders at the ratio of 1:1, reached the maximum value (0.91), and it had relatively high density (66.91%) and low apparent porosity (34.51%). The crystallographic texture in porous Si3N4 ceramics led to the anisotropic bending strength. The method combined with gel casting in a strong magnetic field was beneficial for preparing highly textured porous ceramics with big and complex shape.