Thin SiO(sub 2) layers were deposited on the surface of porous Vycor glass by alternating vapor phase reaction with SiCl(sub 4) and H(sub 2)O. The membranes prepared by this technique had H(sub 2) permeance of 0.3--0.4 cm(sup 3) (STP)/(min(center dot)cm(sup 2)(-atm) and H(sub 2):N(sub 2) selectivity of 500--1000 at 600C. The SiCl(sub 4) dosage at each silylation cycle, the concentration of initial surface -OH groups, and the reaction temperature influence significantly the deposit layer thickness- After two weeks of heating at 550C under 3 atmospheres of water vapor, the membrane H(sub 2) permeance decreased by about 20%, and the selectivity increased to more than 2000. The membrane properties after this hydrothermal treatment are superior to those of membranes prepared earlier by one-sided (steady flow) deposition. A simple model incorporating diffusion and surface reaction was used to study the effect of various parameters on the formation of the deposit layer.
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