Gas permeation and thermomechanical properties for macroporous alumina focused on necking size at grain boundaries

The gas permeation and thermomechanical properties of macroporous alumina used as a support substrate for microporous ceramic permselective membranes were investigated. The porosity, pore size, and apparent necking size between grains of macroporous alumina were systematically varied, and the relationships between the porous microstructure and material properties were examined. The grain necking size at alumina grain boundaries was evaluated by microstructural observations. The nitrogen gas permeance of the porous alumina increased with increasing pore size. All the measured thermal and mechanical properties decreased with increasing porosity. The properties of porous alumina samples with extensive grain necking showed higher values even in samples with the largest pore size. The high thermal conductivity of porous alumina with extensive grain necking was due to the low interfacial thermal resistance at grain boundaries. Porous alumina with extensive grain necking had high thermal shock strength due to the higher thermal conductivity. It was demonstrated that a porous structure combining high gas permeability and excellent fracture resistance could be successfully achieved.