This project studies ceramic membranes modified by a chemical vapor deposition technique. The alumina precursor materials from Alcoa are asymmetric, with an alpha-alumina support and a 5 m gamma-alumina skin layer. Their minimum pore dimension (40 ) makes them inappropriate for fine molecular-sieving separations of small molecules. A series of fluorinated silanes are used to provide precisely controlled decreases in the sizes of the slit-shaped pores of the skin layer. The proposed mechanism by which the pore modification process occurs and its reproducibilty are tested in carefully designed experiments. Studies are focused on the measurement and modeling of the fundamental transport properties of these model materials. The detailed morphology of these materials are probed by gaseous and liquid systems. The data provide new insights and allow testing theories for analyzing transport phenomena in media with pore sizes approaching molecular dimensions. The new ceramic membranes should find new applications in separations of gaseous mixtures.
