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

Two types of silica-zirconia amorphous membranes were synthesized on the ou ter surface of porous alumina supports using the sol-gel method. The molar ratios of ZrO2 in SiO2 were 15 and 25 mol.%, respectively. Transmission ele ctron microscopy (TEM) specimens of the membranes were prepared in a focuse d ion beam system. The microstructural characterizations were achieved by T EM and the chemical compositions of the amorphous material were analysed by energy-dispersive x-ray spectroscopy (EDX). Structural investigation of bo th membranes using TEM revealed two structures: continuous pores similar to 100 nm in diameter in the amorphous material filling the crevices of the p orous alumina supports; and layered structures of amorphous him on the poro us alumina support formed by the coating process. Because the former struct ure has such large continuous pores, gases should be separated in the layer ed amorphous film. Therefore, the amorphous film on the porous alumina supp ort should play the most important role in the gas separation mechanism. Fu rthermore, Zr/Si ratios of those amorphous films were revealed by TEM and E DX. 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.