Pore structure and permeation properties of kaolin-silica-alumina ceramics

The pore structure and permeation properties of kaolin-silica (quartz)-alumina (corundum) ceramics have been investigated using kaolin, SiO2 and Al2O3 powders as staring materials. The Al2O3 powders used are of different particle sizes, 0.8 and 4.0 mum. Mullite phase appears at approximately 1373 K and mullite phase content in the sintered samples increases with the increase in sintering temperature from 1373 to 1573 K for 1 h. Open porosity decreases from 48.4 and 46.8% to 32.3% for the 0.8- and 4.0-mum Al2O3 powders, respectively. The maximum average pore sizes have been noted to be 0.51- and 0.63-mum for the 0.8- and 4.0-mum Al2O3 powders as-sintered at 1473 K, respectively. The maximum penetrating porosity is 24.1% for the 0.8-mum Al2O3 powder as-sintered at 1473 K; it decreases with the increase in temperature for the 4.0-mum Al2O3 powder. The tortuosity of the 0.8-mum Al2O3 powder does not change significantly, but that of the 4.0-mum Al2O3 powder decreases from 0.85 to 0.29 with the increase in sintering temperature. Seemingly, the mullite-based filtration material has been shown to be more efficient and durable than conventional polymeric and diatomite materials.