Characterization of porous silicon nitride ceramics by pressureless sintering using fly ash cenosphere as a pore-forming agent

摘要

A new method for fabricating porous silicon nitride ceramics has been developed by using fly ash cenosphere (FAC) with mean diameter of 87 mu m as.a pore-forming agent. Sintering was carried out at 1780 deg C for 2h under a nitrogen atmosphere. FAC can also act as a sintering aid besides a pore-forming agent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that YSiO_2N forms instead of Y_2Si_3O_3N_4 when FAC is incorporated. Microstructural analysis revealed that large spherical cavities are scattered in a relative dense matrix. Porous Si_3N_4 ceramics with density of 2.17-2.30 g/cm~3, Young's modulus of 141-150 GPa and strength of 180-320 MPa were obtained by changing the FAC content.