PREPARATION OF SILICA PARTICLES UTILIZING THE SOL-GEL AND THE EMULSION-GEL PROCESSES

The preparation of silica particles by means of the sol-gel or emulsion-gel techniques has been studied. In the case of precipitation from homogeneous solutions, we have studied the whole solution phase in the system tetraethyl orthosilicate-ethanol-aqueous ammonia and have mapped the region for monodisperse particles. These particles have a size of 70-640 nm. Their size and monodispersity are controlled by the composition of the system. Utilizing the emulsion-gel technique it is possible to increase the particle size to some tens of micrometers, but the polydispersity increases. In the emulsion-gel process the best results were obtained for small water contents (below 15 wt.%) and low amounts of surfactant (less than 0.5 wt.%) and for considerably longer reaction times than for the conventional sol-gel process.