Novel, Nanoporous Silica and Titania Layers Fabricated by Magnetron Sputtering

Composite asymmetric membranes are fabricated through the deposition of submicrometer, thick (100 nm) silica (SiO2) and titania (TiO2) films onto flat nanoporous silica and zirconia substrates by magnetron sputtering. The deposition conditions for both coating types were systematically altered to determine their influence on the deposited coating morphology and thickness. Ideal He/N-2 gas selectivity was measured for all of the membranes. The TiO2 coatings, when deposited onto a ZrO2 support layer with a pore size of 3 nm, formed a long columnar grain structure with average column diameter of 38 nm. A similar columnar structure was observed for TiO2 coatings deposited onto a SiO2 support layer with a pore size of 1 nm. Under the same conditions, SiO2 coatings, deposited onto the same SiO2 supports, formed a closely packed spherical grain structure whereas, when deposited onto ZrO2 supports, the SiO2 coatings formed an open grain structure. The average SiO2 grain diameter was 36 urn in both cases. This preliminary investigation was aimed at studying the effect of sputtering parameters on the density and morphology of the, deposited coatings. For the depositions carried out, the coating material was found to be very dense. However, the presence of grain boundaries resulted in poor ideal He/N-2 separation efficiencies.