Fabrication of gradient porous β-SiAlON ceramics via a camphene-based freeze casting process

Gradient porous β-SiAlON ceramics were prepared by unidirectional freezing of camphene-based suspensions on a cold substrate at 0 °C and subsequent sintering at 1800 °C for 2 h. Effects of solid loading content in the suspensions on porosities, pore structures and strengths of the porous ceramics were investigated. The results showed that a gradient microstructure consisting of aligned channels, dendritic and equiaxed pores from the bottom to the top of the sample was created by the freezing process. Both the microstructure observation and the pore size distribution indicated that with the increase of the solid content from 10 vol% to 30 vol%, the porosity decreased from 71.3% to 36.1% and the pore size decreased from 20 μm to 5 μm. As a result, the compressive strength increased significantly from 49 MPa to 313 MPa. The sample fabricated from the slurry with 10 vol% solid loading content showed a large strain for failure up to ∼9%.