Fabrication of porous ceramic composites with improved compressive strength from coal fly ash

Abstract

A freeze–gel casting method has been proposed to fabricate porous mullite–alumina composite with controlled ‘designer’ pore structure and improved compressive strength. In this work, a tertiary butyl alcohol–coal fly ash slurry system with appropriate addition of Al₂O₃ was used. Unidirectional aligned macropore channels were developed by controlling the solidification direction of the tertiary butyl alcohol solvent. Simultaneously, microsized pores formed in the walls of the pore channels; consequently, the inner section of the walls of the pore channels exhibited a more porous structure than the outer walls. The compressive strength of the sintered porous composite increased as the porosity decreased, i.e. the low porosity gave a high compressive strength. After sintering at 1500°C with 40 wt-% solid loading, the mullite–alumina composite with a porosity of 61·2% exhibited a compressive strength of ∼64·3 MPa.