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

A new method for fabricating porous silicon nitride ceramics has been developed by using fly ash cenosphere (FAC) with mean diameter of 87 μm as a pore-forming agent. Sintering was carried out at 1780 °C for 2 h 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 YSiO2N forms instead of Y2Si3O3N4 when FAC is incorporated. Microstructural analysis revealed that large spherical cavities are scattered in a relative dense matrix. Porous Si3N4 ceramics with density of 2.17–2.30 g/cm3, Young’s modulus of 141–150 GPa and strength of 180–320 MPa were obtained by changing the FAC content.