Mechanical and dielectric properties of gelcasted Si3N4 porous ceramic using CaHPO4 as an additive

The phase composition, relative density, mechanical properties and dielectric properties of silicon nitride porous ceramics with different content of CaHPO4 as an additive prepared by gelcasting method were investigated. The addition of CaHPO4 can improve the sintering ability and the phase transformation from α-Si3N4 to β-Si3N4, so the relative density and β-Si3N4 content both increase with the increase of CaHPO4 content. As a result, when the CaHPO4 addition content is 15 wt.%, the flexural strength, elastic modulus, fracture toughness of Si3N4 ceramic reach to 365.1 MPa, 107.9 GPa and 3.82 MPa m1/2, respectively. The dielectric constant of Si3N4 ceramics increases with the increase of CaHPO4 addition content due to the increase of relative density and the relative content of β-Si3N4.