Mechanical and dielectric properties of gelcasted Si ₃N ₄ porous ceramic using CaHPO ₄ as an additive

The phase composition, relative density, mechanical properties and dielectric properties of silicon nitride porous ceramics with different content of CaHPO ₄ as an additive prepared by gelcasting method were investigated. The addition of CaHPO ₄ can improve the sintering ability and the phase transformation from α-Si ₃N ₄ to β-Si ₃N ₄, so the relative density and β-Si ₃N ₄ content both increase with the increase of CaHPO ₄ content. As a result, when the CaHPO ₄ addition content is 15 wt.%, the flexural strength, elastic modulus, fracture toughness of Si ₃N ₄ ceramic reach to 365.1 MPa, 107.9 GPa and 3.82 MPa m ^1/2, respectively. The dielectric constant of Si ₃N ₄ ceramics increases with the increase of CaHPO ₄ addition content due to the increase of relative density and the relative content of β-Si ₃N ₄.