Silica structure evolution

Davidson (2002) Mesoporous silica Structure evolution, role of templates crystallization variables + + n.a. Synthesis of mesoporous silica with defined properties... 

Sherer, G.W., Calas, S., and Sempere, R., Densification kinetics and structural evolution during sintering of silica aerogel, J. Non-Crystl. Solids, 240, 118, 1998. 

Structural Evolution of Silica and Feldspar Glasses by Shock Compression... 

Well ordered mesoporous silicate films were prepared in supercritical carbon dioxide.[218] In the synthesis in aqueous or alcoholic solution, film morphology of preorganized surfactants on substrate cannot be fully prescribed before silica-framework formation, because structure evolution is coincident with precursor condensation. The rapid and efficient preparation of mesostructured metal oxides by the in situ condensation of metal oxides within preformed nonionic surfactants can be done in supercritical CCU- The synthesis procedure is as follows. A copolymer template is prepared by spin-coating from a solution containing a suitable acid catalyst. Upon drying and annealing to induce microphase separation and enhance order, the acid partitions into the hydrophilic domain of the template. The template is then exposed to a solution of metal alkoxide in humidified supercritical C02. The precursor diffuses into the template and condenses selectively within the acidic hydrophilic domain of the copolymer to form the incipient metal oxide network. The templates did not go into the C02 phase because their solubility is very low. The alcohol by-product of alkoxide condensation is extracted rapidly from the film into the C02 phase, which promotes rapid and extensive network condensation. Because the template and the metal oxide network form in discrete steps, it is possible to pattern the template via lithography or to orient the copolymer domains before the formation of the metal oxide network. 

Fig. 15 (a) Top SEM images for the structural evolution of bimodal colloidal clusters of silica microspheres and nanospheres for n = 2. Bottom Surface Evolver simulated structural evolution for = 2 as a function of the amount of silica ntinospheres. (b) SEM images of silica-silica composite clusters for n = 2 8. Scale bar. 2 tm. The size ratio of large and small silica particles was... 

Figure 11.12 Schematics of the proposed structural evolution during silica synthesis from reverse liquid crystals (a) Initial state. Micelles with a PDMS corona (thin lines) and solubilizing an aqueous phase (W) in their cores are arranged hexagonally, surrounded by TEOS molecules (thick lines). Arrows indicate the possible interfacial diffusion of W (b) After hydrolysis and partial...

R. Desphande, D. M. Smith, and C. J. Drinker, Pore Structure Evolution of Silica Gel during Aging/Drying Effect of Surface Tension, Better Ceramics through Chemistry V, 271 (M. J. Hampden-Smith, W. G. Klemperer, and C. J. Drinker, Eds.), Materials Research Society, Pittsburgh, pp. 553-58, 1992. 

Deshpande R, Hua, DW, Smith DM, Brinker CJ (1992) Pore structure evolution in silica gel during aging/ drying. III. Effects of surface tension. J Non-Cryst Solids 144 32-34... 

The subject of sol-gel science is cova-ed in great depth in Ref. 1. We outlined the basic steps in sol-gel processing in ChaptCT 1 when we surveyed the common methods used for the production of ca-amics. This chapter provides a more detailed examination of the science and practice of the process for the fabrication of ceramics and glasses. We shall pay particular attention to the sol-gel processing of silica glass not only because of its practical interest but also because of the heightened understanding of the process mechanisms and structural evolution developed from numerous studies. 

Figure 5.27 Schematic representation of the structural evolution during drying for (a) acid-catalyzed gels, (b) base-catalyzed gels, (c) coUoidal gel aged under conditions of high silica solubility, and (d) colloidal gel composed of weakly bonded particles. (From Ref. 40.)...

J. Lee, J. Won, J. Kim, K. Kim, S. Lee, Evaporation-induced, self-assembled, silica colloidal particle-assisted nanoporous structure evolution of poly (ethylene terephthalate) nonwoven composite separators for high-safety/high-rate lithium ion batteries, J Power Sour 216 (2012) 42-47. 

Yoshino H., Kamiya K., Nasu H. IR study on the structure evolution of the sol-gel derived Si02 gels in the early stage of conversion to glasses. J. Non-Crystalline Solids 1990 126 68-76 Zhang S.C., Cannon W.G. Preparation of silicon nitride from silica. J. Am. Ceram. Soc. 1984 67 691-695... 

From what has been said, it is obvious that the systems are very complex and many different routes from the molecular precmsor to the final silica gel are possible. The chemical parameters discussed in the following determine which route is taken. Because of this complexity, a detailed understanding (and awareness) of the parameters influencing the reaction rates and thus the structure evolution is necessary in order to tailor the texture and properties of sol-gel materials. The most important parameters influencing hydrolysis and condensation (and their relative rate) are... 

Order-disorder transitions and evolution of silica structure in self-assembled mesostructured silica films studied through FTIR spectroscopy. /. 

Figure 2.20. Transformation of silica supported dinitrosyl complexes of nickel(II) leading to formation of nitrogen dioxide and its final stabilization on the support. The picture shows the molecular structure and the spin density contours calculated with BP/DNP method of the involved species, and evolution of the X-band EPR spectra of the NiN02 Si02 complex due to spillover of the ligand (adopted from [71]).

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