Effect of CeO2 on low temperature pressureless sintering of porous Si3N4 ceramics

Abstract

Porous silicon nitride (Si3N4) ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si3N4 powders as raw materials, and MgO-CeO2 as sintering additives. The effects of CeO2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Archimedes' displacement method and three-point bending strength, respectively. The results suggested that MgO-CeO2 was a much more effective sintering additive for Si3N4 than MgO alone. When CeO2 concentration was 4 wt.%−5 wt.% and sintering temperatures were in a range of 1500 to 1550 °C, the obtained porous silicon nitride ceramics had the porosity of 45.78%−42.81% and flexural strength of 49.44−84.09 MPa. Moreover, when sintering temperature was 1550 °C and CeO2 concentration was 5%, large elongated β-Si3N4 grains were well developed.