Highly porous corundum–mullite ceramics – Structure and properties

The aim of this study was to improve the mechanical properties of porous corundum ceramics by adding various types of SiO2 source (SiO2, SiC and Si3N4), 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 SiO2 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 SiO2 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 Si3N4 nanopowders. This is due to better dispersion in Al2O3 matrix.