Films of amorphous SiO2 were deposited within the walls of porous Vycor tubes by SiH4 oxidation in an opposing-reactants geometry: SiH4 was passed inside the tube while O2 was passed outside the tube. The two reactants diffused opposite to each other and reacted within a narrow front inside the tube wall to form a thin SiO2 film. Once the pores were plugged the reactants could not reach each other and the reaction stopped. At 450°C and 0.1 and 0.33 atm of SiH4 and O2, the reaction was complete within 15 min. The thickness of the SiO2 film was estimated to be about 0.1 μ. Measurements of H2 and N2 permeation rates showed that the SiO2 film was highly selective to H2 permeation. The H2: N2 flux at 450°C varied between 2000 and 3000. Thermal annealing at 600°C reduced somewhat that selectivity. Thermal annealing in the presence of H2O vapor decreased further the flux of H2 and increased the flux of H2. Permeation of H2 is believed to occur through an activated diffusion mechanism. Applications of such H2-permeable films to membrance reactors for equilibrium-limited reactions are discussed.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering