Silica colloids evolution

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. 

Ying JY, Benziger JB, Navrotsky A (1993b) Stractrrral evolution of colloidal silica gels to glass. J Am Ceram Soc 76 2561-2570... 

The excellent electron-transfer mediator properties of nanoparticles find special use in the different oxidation [126] and reduction [143,144] reactions catalyzed by noble metal colloids. Recently, Ung et al. [145] showed how Ag particles coated with a thin layer of silica act as redox catalysts, and how the control of the rate of the catalyzed hydrogen evolution reaction was possible by tuning the silica shell thickness. It was concluded that the shell acts as a size-selective membrane, which can be used to alter the chemical yields for competing catalytic reactions. This kind of tailoring of the catalyst properties opens up very interesting prospects in future catalyst planning. 

For many of the applications the standard alkali stabilized colloidal silicas available were fine, but since the colloidal silica depended on the maintenance of fairly high pH in order to remain stable it was not compatible with lower pH wax emulsions. While the initial mixes might look quite stable the lower pH would eventually lead to slow coagulation of the silica resulting in poor shelf life for these products. The evolution of the aluminate modified materials which had much less dependence on pH for stability solved many of these problems and provided... 

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... 

These two distinct processes lead to the formation of secondary minerals mainly phyl-losilicates such as clays, of soluble products (e.g., carbonates or silica) lixiviated by percolating waters and of colloids usually iron and aluminum sesquioxides complexed by humic acids. While physical degradation involves mechanical (e.g., abrasion, impact) or thermal (e.g., thermal shock) processes, alteration involves only chemical reactions such as hydrolysis influenced by pH conditions and/or the oxidation of primary materials depending on the Eh (redox potential) conditions. Whatever the type of underlying rock, the end product is always a clay except when silica is totally absent from the bedrock, the composition of the clay depending on the type of climate and the time over which the evolution process takes place. These conditions are summarized in Table 14.1. 

In zinc-rich paints some early patents indicate the importance of a silica component. Colloidal silica was reacted with finely divided zinc to form a colloidal zinc silicate in which the excess zinc metal was suspended (654). A water-insoluble binder for zinc-containing coatings was produced by mixing alkali-stabilized colloidal silica with lithium hydroxide in suitable proportions (655). Evolution of gas from mixtures of colloidal silica with zinc powder is prevented by adding an indigoid compounds (656). Another formulation involves quaternary ammonium polysilicate solution milled with lead oxide as the binder for zinc (657). Some of the problems stem from the impurities in the zinc powder which promote reaction with the medium (658). Adhesion. of paints of this type of steel is improved by adding up to 2% of a styrene-acrylic resin dispersion (659). 

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.)...

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