Transmission electron microscopy studies of microstructures of silica-zirconia membranes for gas separation

Two types of silica-zirconia amorphous membranes were synthesized on the outer surface of porous alumina supports using the sol-gel method. The molar ratios of ZrO2 in SiO2 were 15 and 25 mol.%, respectively. Transmission electron microscopy (TEM) specimens of the membranes were prepared in a focused ion beam system. The microstructural characterizations were achieved by TEM and the chemical compositions of the amorphous material were analysed by energy-dispersive x-ray spectroscopy (EDX). Structural investigation of both membranes using TEM revealed two structures: continuous pores similar to 100 nm in diameter in the amorphous material filling the crevices of the porous alumina supports; and layered structures of amorphous him on the porous alumina support formed by the coating process. Because the former structure has such large continuous pores, gases should be separated in the layered amorphous film. Therefore, the amorphous film on the porous alumina support should play the most important role in the gas separation mechanism. Furthermore, Zr/Si ratios of those amorphous films were revealed by TEM and EDX. They were constant for the 15% ZrO2-SiO2 membrane but not constant for the 25% ZrO2-SiO2 membrane. Copyright (C) 2001 John Wiley & Sons, Ltd.