Silica growth reaction

Fig. 2.1.2 Reaction rate of the Stober silica particle growth reaction at a constant TEOS concentration of 0.2 mol/L each data triplei indicates the reaction temperature of 293, 313. and 333 K, respectively. (From Ref. 37.)...

In principle, silica growth kinetics may be controlled by (1) slow release of monomer via alkoxide hydrolysis in the particle-free reverse micelles, (2) slow surface reaction of monomer addition to the growing particle, and (3) slow transport processes as determined by the dynamics of intermicellar mass transfer. There is strong experimental evidence to support the view that the rate of silica growth in the microemulsion environment is controlled by the rate of hydrolysis of TEOS (23,24,29). Silica growth kinetics can be analyzed in terms of the overall hydrolysis and condensation reactions ... 

In the absence of water treatment the first reaction cycle in the growth from metal chlorides at elevated growth temperatures leads to metal oxide agglomerates. Depending on the growth temperature anatase or rutile crystalline structures of Ti02 are produced [45,46,50]. On 560 °C silica the reaction temperature 350 °C leads exclusively to anatase, 450 C to both anatase and rutile, and 550 °C exclusively to rutile. The anatase/rutile transformation temperature is somewhat lower than that for bulk Ti02 oxide, and perhaps because of the small particle size. 

Herbert Giesche Synthesis of monodispersed silica powders. //. Controlled growth reaction and continuous production process, J. Eur. Ceram. Soc., 14 (1994) 205-214... 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

---