Synthesis of porosity controlled ceramic membranes

Porosity control in ceramic membranes has been achieved by controlling particle packing densities in sol-gel processing. TiO₂ xerogels with two mean pore radii of 0.7 and 1.7 nm and a porosity varying from 30% to 52% have been obtained. ZrO₂ xerogels with a mean pore radius of 0.7 nm and a porosity varying from 7% to 34% have also been prepared. The principle of controlling porosity is to make spongy aggregates and to control the degree of aggregation. Experiments have been conducted to show that spongy aggregates can be produced by gradually removing protons from the strongly charged particles. Viscosity techniques have been used to measure the relative volume fraction of the dispersed phase which, in turn, provides information on aggregate structures. Two aggregation models have been proposed to explain different structural aggregates formed through thermal destabilization in the highly charged system and through charge neutralization by gradually removing charge from the particles in the system.