A new reactor system was constructed which can be used for CVD Of SiO[sub 2] layers on porous Vycor tubes. The system is suitable for the usual one-sided deposition and for alternating (or layer-by-layer) deposition whereby the silylating agent and water are passed one at a time in alternating periods. The main advantage of alternating deposition is that it allows membrane deposition using silica precursors for which the homogeneous hydrolysis is fast. As we have demonstrated in earlier work, fast homogeneous reaction interferes with membrane formation. The disadvantage of alternating deposition is the longer time required for membrane formation. Figure …
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California Inst. of Tech., Pasadena, CA (United States)
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A new reactor system was constructed which can be used for CVD Of SiO[sub 2] layers on porous Vycor tubes. The system is suitable for the usual one-sided deposition and for alternating (or layer-by-layer) deposition whereby the silylating agent and water are passed one at a time in alternating periods. The main advantage of alternating deposition is that it allows membrane deposition using silica precursors for which the homogeneous hydrolysis is fast. As we have demonstrated in earlier work, fast homogeneous reaction interferes with membrane formation. The disadvantage of alternating deposition is the longer time required for membrane formation. Figure 1 is a schematic of the new reactor constructed for homogeneous deposition. In each silylation period the space inside and outside of the support tube is evacuated and a small and accurately controlled amount of reactant (e.g. SiCl[sub 4]) is allowed to flow from a storage glass flask 4 into the reactor annulus by opening valve 5 for a few seconds. The silylation reaction is allowed to proceed for the desired time interval (about one minute) after which the reactor is evacuated and flow of water vapor commences by opening valve 7. After the completion of one cycle of silylation and hydrolysis, the nitrogen permeance of the support tube is measured by the techniques used in our earlier work (bubble flow meter or pressure transducer). After the nitrogen permeance has decreased by a specified factor (about thirty) from its initial value, the reactions are terminated and the membrane is annealed at 700[degrees]C for about ten hours after which the nitrogen and hydrogen permeances are measured at several temperatures.
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