Control of silica-zirconia nanoparticles for uniform porous SiO2-ZrO2 membranes.

Silica-zirconia composite sols were prepared by means of a sol-gel method, using tetraethylorthosilicate (TEOS) and zirconium tetra-n-butoxide (ZrTB) precursors. TEOS, ZrTB, HCl, H2O and EtOH were mixed at 70 degrees C for 24 hours to give molar ratios of 1:1:8-80:0.2-1.0:100-300. The mean particle size of the silica-zirconia sol was controlled by the concentration of the alkoxides and catalyst, as well as the water molar ratio in the starting solution. The particle size of the SiO2-ZrO2 sol, which was analyzed by dynamic light scattering (DLS) and field emission scanning electron microscopy (FE-SEM), was in the range of 20 to 350 nm. The SiO2-ZrO2 sol solutions of different sol sizes were coated onto porous stainless steel supports (O.D. 10 mm, length: 20 mm, 316L SUS, Mott corp. USA) by a dipping-rolling-freezing-fast drying (DRFF) and soaking-rolling-freezing-fast drying (SRFF) method. After coating with SiO2-ZrO2 sol, the single gas permeation characteristics (He, H2 and N2) of the resulting SiO2-ZrO2 membranes were evaluated at room temperature. This produced a decrease in the mean flow diameter and H2/N2 permselectivity in the range of 2.0-3.5. Finally, following the results of gas permeation testing, the pore size of the membranes was controlled by changing their particle size.