Fabrication of Si3N4-based seal coating on porous Si3N4 ceramics

In this study, Si3N4-based seal coatings using MgO, Al2O3 and SiO2 as the sintering additives were prepared on the porous Si3N4 substrates by room temperature spraying and pressureless sintering. The composition of the Si3N4-based seal coatings was well designed, in order to both match the coefficient of thermal expansion with that of the porous Si3N4 substrate and form the liquid phase at a relative low temperature. During the sintering process, the liquid phases promote the densification and homogenisation of the Si3N4-based seal coatings. A good combination between Si3N4-based seal coatings and substrate is achieved, as a result of the liquid-phase penetration into the pores in the porous Si3N4 substrate.