Effects of solid content on the phase assemblages, mechanical and dielectric properties of porous α-SiAlON ceramics fabricated by freeze casting

Porous Y-α-SiAlON ceramics were prepared by freezing camphene-based suspensions at 0 °C and subsequently sintering at 1900 °C for 1 h. The effects of solid loading content in the suspensions on porosities and formation of α-SiAlON as well as mechanical and dielectric properties of the porous ceramics were investigated. An XRD analysis performed on sintered samples indicated that the α-SiAlON did not fully form in the sample with initial solid loading content of 10 vol%, due to the high porosity of 90 vol% and interconnected pore of the green body. With the increase of initial solid loading content from 10 vol% to 30 vol%, the porosity decreased from 62.3% to 23.1% and the average pore size decreased from 19 μm to 8 μm. As a result, the flexural strength increased significantly from 72.4 MPa to 190.2 MPa, fracture toughness increased from 1.20 MPa m^1/2 to 3.48 MPa m ^1/2, as well as the dielectric constant increased from 3.3 to 6.3. The dielectric loss (tan δ) of obtained material varied between 1.4×10^-2 and 2.8×10^-2, which did not depend on the porosity of samples.