Preparation of microporous membranes by TEOS/O3 CVD in the opposing reactants geometry

The pore size of porous Vycor glass with a pore diameter of 4 nm was controlled by TEOS/O-3 CVD in the opposing reactant geometry. TEOS vapor and O-3 were fed with O-2 carrier through the bore and the outside of the tubes respectively. The influence of the TEOS and O-3 concentrations in the feed, as well as the temperature and period of the CVD reaction were analyzed in terms of gas transport properties of the resulting membranes. The control of reaction parameters enabled us to synthesize molecular sieve membranes with He/N-2 perm-selectivity values as high as 950 at 40 degrees C. Gas molecules such as O-2 and N-2 exhibited activated diffusion through the membranes, though their permeability values were insignificantly low compared with the permeability of He molecules. The permeability of He molecules was found to be limited by the resistance of the support Vycor glass pores. (C) 2000 Elsevier Science B.V. All rights reserved.