Colloidal silica applications

Griessbach (17) showed that five companies produced silica sols in 1933. Most products were very dilute, and only one could be considered concentrated. The most concentrated sol available at that time was a product called Kieselsol I.G. (made by I.G. Farbenindustries), which contained 10% silica and was stabilized with ammonium hydroxide. The characteristics of most of the sols were undetermined. Moreover, the difficulty of making a reproducible product that would perform in a predictable manner for specific uses was technically impossible at that time. This difficulty, most likely, was the major reason that colloidal silica applications did not increase rapidly. Iler (18) pointed out that colloidal silica was not accepted for wide commercial use until methods were discovered for producing sols with high concentrations that would not gel or settle with time. The first steps to achieving that goal occurred in 1941 (discussed in the preceding section on preparation procedures). 

Colloidal particles, foams used to collect and separate, 12 22 Colloidal powders, 23 55-56 Colloidal silica, 22 380, 382, 384 applications of, 22 394 modification of, 22 393-394 preparation of, 22 392-393 properties of, 22 391-392 purification of, 22 393 Colloidal silica gels, 23 60 Colloidal solids, 7 293-294 Colloidal stability, 7 286-291 10 116 22 55 Colloidal stabilizers, in polychloroprene latex compounding, 19 857 Colloid mills, 8 702 10 127 Colloids, 7 271-303 23 54. See also Polymer colloids analysis, 7 296 applications, 7 292-296 conducting, 7 524... 

V. M. Gun ko and A. A. Chuiko, Chemical Reactions at Fumed Silica Surfaces, in Colloidal Silica Fundamentals and Applications, edited by H.E. Bergna (Taylor Francis LLC, Salisbury, 2005), pp. 465-497. 

Colloidal Silica Fundamentals and Applications, edited by Horacio E. Bergna and William O. Roberts... 

Ceramic Ablators, Several types of subliming or melting ceramic ablators have been used or considered tor use in dielectric applications particulady with quartz or boron nitride [10043-11-5] fiber reinforcements to form a nonconductive char. Fused silica is available in both nonporous (optically transparent) and porous (slip cast) forms. Ford Aerospace manufactures a 3D silica- fiber-reinfo reed composite densified with colloidal silica (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see Composite materials, ceramic matrix). 

Similarly, Sano et al. [1994] added colloidal silica to a stirred solution of tetrapropylammonium bromide and sodium hydroxide to synthesize a hydrogel on a stainless steel or alumina support with a mean pore diameter of 0.5 to 2 pm. The composite membrane is then dried and heat treated at 500 C for 20 hours to remove the organic amine occluded in the zeolite framework. The silicalite membranes thus obtained are claimed to be free of cracks and pores between grains, thus making the membranes suitable for more demanding applications such as separation of ethanol/water mixtures where the compound molecules are both small. The step of calcination is critical for synthesizing membranes with a high permselectivity. 

Gore, A.Y. Banker, G.S. Surface chemistry of colloidal silica and a possible application to stabilize aspirin in solid 68. matrixes. J. Pharm. Sci. 1979, 68, 197-202. 

The -potential of colloidal silica surface treated by acrylate copolymers is affected by pH. The -potential of untreated colloidal silica at a pH of 4 is -7 mV and it decreases to -32 mV at a pH of 7. Modification of the surface of colloidal silica changes its surface properties and behavior. In another study on filler modification, hydroxyapatite was modified for medical applications with several differ-... 

There are numerous industrial products of colloidal silicas in various forms. The methods of industrial synthesis and main applications are briefly surveyed as follows. Ultra-fine particles of nanometer order such as aerosil (commercial name) are produced by the hydrolysis of tetrachlorosilane in air. A similar material can be obtained from oxidation of tetralkoxysilane in a gas phase. The former is used as a thixotropic additive of composite materials, heat insulator and etc. 

This carbon membrane consisted of 10-20 nm pores and 200 nm pores. The pore size of 200 nm corresponds to the size of polystyrene used in this preparation process and the pore size of 10-20 nm reflects the size of colloidal silica. This carbon had high surface area, which was 1,004 m g . Such high surface area is suitable for capacitor application. 

One of the most exciting developments of the past decade in the study of colloidal silica is the application of the fractal approach to the study of sols and gels. Fractals are disordered systems for which disorder can be described in terms of nonintegral dimension. The concept of fractal geometry, developed by Mandelbrot (II) in the early 1980s, provides a means of quantitatively describing the average structure of certain random objects. The fractal dimension of an object of mass M and radius r is defined by the relation... 

Since the publication of these books, colloidal silica research has been driven forward not only by new applications in the conventional glass and ceramic industries and in metallurgy but also by the development of new and more sophisticated needs, for example, in the areas of electronic materials, catalysis, chromatographic substrates, and paper and pulp processes. 

B. A. Keiser s contribution to this book (the introduction to the section Preparation and Stability of Sols ) constitutes an excellent introduction to silica nucleation, polymerization, and growth in both aqueous and alcoholic systems for the preparation of silica sols. Yoshida s chapter (Chapter 2) focuses on industrial development in the preparation of monodisperse sols from sodium silicate and predicts further progress in the development of silica sols that have shapes other than spherical, such as elongated, fibrous, and platelet. Colloidal silica particles with these shapes show novel properties and open the possibility of new industrial applications. 

In the modern world, colloidal silica powders and sols have different fields of application, with a few overlapping areas. As modern technology develops, new opportunities for silica proliferate, and new uses are constantly replacing the classic applications soon to become overshadowed by even newer uses. 

At the risk of the list soon becoming obsolete, the current major applications of colloidal silica powders and sols can be summarized as follows (93) ... 

Ludox Colloidal Silica. Ludox colloidal silicas (DuPont) were among the first silica materials studied by FFF. In the first paper describing the applicability of FFF to colloidal silica (4), Ludox and related silicas were fractionated by flow FFF the fractionation was verified by transmission electron microscopy (TEM). The theory behind the fractionation and the acquisition of size distribution data was developed, and evidence of aggregation was examined. An example of the fractionation of four colloidal silicas from that study is shown in Figure 2. The primary drawback of this earlier work was the lengthy runs, in some cases requiring over 10 h. Most of the experimental runs on Ludox described in this section were completed in less than 10 min. 

Applications of Colloidal Silica Past, Present, and Future... 

Early uses of colloidal silica for catalysis, ceramics, paper and textile applications, strength enhancement in rubber, tobacco treatment, and medicine are discussed. A historical view of the development of applications is highlighted, and future uses are discussed. 

Colloidal silica technology proceeded slowly. The early products were not suitable for most applications because (1) only low silica concentrations were available, (2) the materials were not stable with time, or (3) the products did not have reproducible properties. By 1915, only one patent for preparation of a commercial colloidal silica had been issued (9). Using electrodialysis (Figure 1) to make a product, Schwerin marketed a 2.4% silica sol as a stable material. Schwerin suggested the use of this product for medicinal purposes but did not specify how or where it should be used. 

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