Permeation and strength characteristics of macroporous supports for gas separation produced by co-sintering mixtures of α-alumina and kaolin

Porous aluminosilicate structures are being considered as supports for metallic and ceramic gas separation membrane supports. In the present work the flux and strength behaviour of partially sintered mixtures of α-alumina and kaolin powders were studied and applicable models explored. Powder compacts were sintered to between 1450 °C and 1525 °C to obtain open porosities from 18.7% to 3.3%. Application of a parallel flow model to stepped-pressure H2 flux measurements indicated effective pore radii from 180 nm to 328 nm and effective tortuosity factors from 9 to 23. Below 1500 °C, SEM of the fracture surface provided evidence of uneven grain coalescence with only a small reduction in pore size indicative of liquid phase sintering. Samples sintered to 1525 °C exhibited larger, more uniform grains and pore shapes and sizes indicative of coalescence. The flexural strength of the samples increased from 98 MPa to 174 MPa with increasing sintering temperature and was found to be independent of pore size, but highly dependent on porosity. This dependence, along with an indirect correlation with the tortuosity factor in structures produced at 1500 °C and below, allows the parallel flow model to be reformulated in terms of strength.