Date of Award

Fall 1994

Document Type

Thesis

Degree Name

Master of Science in Engineering Science- (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Roland A. Levy

Second Advisor

James M. Grow

Third Advisor

David S. Kristol

Abstract

This study is focused on development of highly selective ceramic membrane structures consisting of silicon dioxide films synthesized by low pressure chemical vapor deposition (LPCVD) on mesoporous Vycor substrates. The ability of easily altering the composition of such films by varying the LPCVD processing parameters affords the opportunity of microengineering the pore structure by reducing the diameters of pre-existing pores in the support. The process parameters investigated include, deposition temperature, total pressure, and flow rate of oxygen. Both the kinetics and select properties of the deposits were examined. The growth rate as a function of temperature was seen to follow an Arrhenius behavior in the range 350-475 °C with an apparent activation energy of 9 kcal/mol. The growth rate was seen to increase with higher oxygen flow rate and to vary as a function of the square root of pressure. Within the framework of the process window investigated a temperature of 450 °C, total pressure of 500 mTorr, oxygen and DES flow rate of 15 sccm and 30 scorn, respectively, yielded the best quality oxide with density 2.11 g/cm3, RI 1.45, and compressive stress 210 MPa. Permeation studies on Silicon Oxide/ Vycor composite membrane synthesized by the same side reaction geometry indicated poor permselectivity performance followed by cracking of the membrane structure. Opposing reactant geometry technique resulted in membrane structures of significantly higher selectivity than that predicted by Knudsen mechanism.

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