Highly porous corundum–mullite ceramics – Structure and properties

Abstract The aim of this study was to improve the mechanical properties of porous corundum ceramics by adding various types of SiO 2 source (SiO 2 , SiC and Si 3 N 4 ), but at the same time retaining high porosity (at least 55%). Ceramics were fabricated by slip casting. Pores were formed using aluminium's reaction with water. It was found that the bending strength of the material can be improved and relatively high porosity retained by producing corundum–mullite composites. Addition of 3.7 equivalent wt% of SiO 2 source increased the bending strength by up to 250% in comparison with unmodified corundum ceramics. The apparent porosity decreased by up to ca. 8%. If the amount of SiO 2 source was increased from 3.7 equivalent wt% to 7.3 equivalent wt%, the bending strength decreased. The best mechanical properties were achieved with samples that were modified with SiC and Si 3 N 4 nanopowders. This is due to better dispersion in Al 2 O 3 matrix.