Preparation of Porous Oxide Beads Using Polymeric Beads to Control Bead Size and Shape

A method was developed for preparing silica gels by silicon alkoxide hydrolysis usingwater-swellable polymers to control the shape. A variety of polymer beads with different water absorbencies and different bead sizes were used. Silica beads in a wide range of sizes were prepared from polymer beads. The final bead size was dependent on the size and water absorbency of the beads, on the extent of reaction, and on the final density. It was shown that porosity could be formed in two regions. The silica beads contained pores of 3–4 nm that were attributed to the intrinsic gel structure. In addition, when large amounts of polymer were removed, additional porosity on the scale of 20–50 nm was formed. It was also shown that surface areas varied dramatically with calcining. For beads containing only small pores, surface areas varied from 400 m2/g to less than 0.2 m2/g as the calcining temperature was increased from 600°C to 1000°C. Beads containing porosity formed by removal of the polymer remained porous even after calcining at 1000°C.