Pressureless sintering of silicon nitride ceramics with porous gradient structure for gas filter application

In the present study, Si3N4 ceramics with high porosity and porous gradient structure are prepared by pressureless sintering technique. Si3N4 ceramics with porosity of 34–47% are prepared by using ZrP2O7 as a binder material and heat treated at 1000°C in a nitrogen atmosphere. Si3N4 ceramics with porosity of 50–70% are prepared by using ZrP2O7 as a binder material, starch or naphthalene as a pore–forming agent and then heat treated at 1000°C in a nitrogen atmosphere. Si3N4 ceramics with porous gradient structure are then formed by laminating the Si3N4 porous ceramics with ordered porosity, followed by sintering at 1000°C. The phase compositions are analysed by X–ray diffraction (XRD), and the microstructure of the sintered samples is observed by scanning electronic microscope (SEM). The results show that the obtained Si3N4 ceramics exhibit a good porous–graded structure from high porosity to low porosity. The major phase of Si3N4 ceramics is still α phase.