Coating of gibbsite platelets with silica

In this work, gibbsite particles are synthesized from aluminum alkoxides in an acidic environment at 85 degreesC. After centrifugation, coating with silica is investigated following two different methods. Practical aspects and the feasibility to produce significant amounts of material are studied. The first method, analogous to a procedure used for boehmite, is a three-step procedure that starts from the addition of water glass and ends with Stober growth of silica. In the second method, poly(vinylpyrrolidone) is used to stabilize gibbsite in the Stober-like mixture for silica growth. Both methods lead to silica-coated particles. The first method is elaborate, but can be used to make very thin (<4 nm) silica layers. The second method is quick and produces smooth layers. The particles are characterized by scanning and transmission electron microscopy and energy-dispersive X-ray analysis and show a smooth silica layer of 10-25 nm thick. These particles can be used for confocal microscopy and in mixtures with different shaped particles to study phase behavior. By acid leaching the gibbsite can be removed and hollow silica platelets remain.