Dual behavior of CaCO3 as a porosifier and sintering aid in the manufacture of alumina membrane/catalyst supports

High permeability alumina membrane/catalyst supports have been prepared using CaCO3 as inorganic porosifier. Green compacts had been formed by uniaxial compaction. The effect of porosifier initial content (1–7 wt.%) and sintering temperature (1325–1400 °C) on the permeability and porous structure (average permeable pore diameter and tortuosity) of the final products have been investigated. For any porosifier initial content in the range of 1–7 wt.%, there exists an optimum sintering temperature of 1350 °C corresponding to the highest permeability. Maximum permeability is obtained using 5 wt.% initial porosifier content. It is demonstrated that such enhanced permeabilities are not due to a pore growth mechanism. Instead, they are a result of tortuosity decrease due to a “round pore shaping” mechanism induced by the establishment of a liquid-phase sintering process.