Properties of Porous Si ₃ N ₄ /BN Composites Fabricated by RBSN Technique

Reaction bonding of silicon nitride (RBSN) technique combined with slip‐casting shaping process was used to fabricate porous Si ₃ N ₄ /BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of α‐Si ₃ N ₄ , β‐Si ₃ N ₄ , and h‐BN. The composites exhibit homogeneous microstructure consisting of faceted particles, α‐Si ₃ N ₄ nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60–300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies.