Microporous silica membranes deposited on porous supports by filtration

Water based particulate silica sols have been coated onto Anodisc(R) filters by filtration. The membranes prepared by this technique are more uniform than those formed by slip-casting. The average diameter of the silica particles used in these studies is 6 nm. Unsupported silica membranes formed from these sols have a microporous structure. The adhesion between silica and the alumina support is influenced by the sol pH. Coating thickness can be controlled by the concentration and volume of the sol filtered. Polyvinyl alcohol (PVA) was used to improve adhesion and to prevent cracking during drying. When the PVA/SiO2 ratio by weight is less than 20%, the membranes retain their microporosity after firing. The membranes prepared by this filtration method have their pore size in Knudsen diffusion range.