Silica gels composed of micrometer-sized

Formation of Silica Gels Composed of Micrometer-Sized Particles by the Sol-Gel Method... 

Formation of silica gels composed of micrometer-sized particles from highly acidic solutions of tetramethoxysilane (TMOS) is describedr In this method a limited amount of H2O and a large amount of HCl are used in hydrolyzing TMOS. Detailed conditions and the mechanism of the formation of micrometer-sized particles in the solutions are discussed. Applications of the gels are also described. 

Acid or base is used as a catalyst for the hydrolysis of silicon alkoxide. Acid or base with a mole ratio to alkoxide as low as 0.01 or less is usually enough for the catalytic effect. On the other hand, water with a mole ratio to alkoxide as high as 10 or more is used for the complete hydrolysis of alkoxide. We have found, however, that monolithic opaque gels composed of micrometer-sized silica particles can be prepared from tetramethoxysi-lane (TMOS) when a limited amount of water and a large amount of... 

Figure 1. Flow diagram of the sol-gel process for making silica gel monoliths composed of micrometer-sized particles.

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