Freeze casting of aqueous coal fly ash/alumina slurries for preparation of porous ceramics

A porous mullite-matrix composite with a bimodal pore structure has been prepared by a freeze casting route using water/coal fly slurry system. The top and bottom parts of the sintered freeze cast body consisted of solid particles and micropores, which were irregularly distributed. However, the middle section was made up of small lamellar pores and porous ceramic walls, aligned along the solidification direction. The porosity of mullite composites was in the range 67–55% after sintering at 1300–1500 °C. The addition of 3Y-ZrO2 reduced the porosity, especially material in sintered at 1500 °C due to relatively high densification. The compressive strength of the porous composite with 10 wt% 3Y-ZrO2 addition, sintered at 1500 °C exhibited a maximum value of ∼41 MPa.