Porous Si3N4 ceramics prepared via slip casting of Si and reaction bonded silicon nitride

Slip casting process combined with reaction bonded silicon nitride (RBSN) was used to prepare porous Si3N4 ceramic with near-net and complex shape. A butyl stearate (BS) coated process was introduced to restrain the hydrolysis of Si, and ammonium polyacrylate (NH4PAA) was used to enhance the dispersion of coated Si. The measured oxygen content showed that the hydrolysis of Si was strongly prohibited by BS coating, and relatively low viscosity was obtained with the addition of 0.25–1.5 wt% NH4PAA to the 60 wt% solid load slurry. 40–60 wt% solid load slurries were used for slip casting in the experiment. After vacuum degassing, slip casting, debindering and nitridation, a density of 1.57–1.92 g/cm3 (porosity 50.9–40%) and a flexural strength of 47–108 MPa were obtained. The samples without vacuum degassing showed a large number of nanowires grown in the large pores.