Use of silica gels and precipitated silicas

Preparation and Uses of Silica Gels and Precipitated Silicas... 

Other Uses. Numerous other uses of silica gels and precipitated silicas are found in the literature. Two relatively new applications that are expected to be significant in the future are battery separators, in which the silica pore structure provides a path for the migration of conductive ions, and low-temperature insulation, in which the low thermal conductivity of dry silica powders makes them useful in consumer products such as refrigerators (Chapter 24). 

Abrasive-polishing agent, use of silica gels and precipitated silicas, 625 Abrasive powder, preparation, 426, 427f Acetic acid, catalysis of silica sol-gel precursor hydrolysis, 406, 407t, 408/ Acid-neutralization manufacturing method for silica sol, procedure, 53, 54/... 

Adhesives, use of soluble silica, 595 Adsorbent, use of silica gels and precipitated silicas, 624 Adsorption... 

Numerous other uses of sihca gels and precipitated silicas are found in the literature, but in this article the focus has been on applications of significant commercial importance. While is it difficult to predict what applications could become significant in the future, one recent development in particular appears promising. 

There are at least five types of synthetic silicas that can be considered for use in polymers. These are generally known as fumed, arc, fused, gel and precipitated. A detailed review of their production and uses has been given by Watson [96]. The types most often encountered in thermoplastics are the gel and precipitated silicas which are frequently used as antiblocking agents in polymer films and as gloss reducing agents in polymer sheets. 

A less significant but nevertheless interesting application is the use of SAS to adsorb certain substances in beer to prevent the beer from becoming cloudy as a result of lengthy periods of storage or excessive cooling. Both silica gels and precipitated silicas are used for this application. Approximately 50-100 g/hL are required. This field of application is... 

Since 1955, many others have extended these principles of particle packing, and now secondary and tertiary assemblages can be identified within the microstructures of certain silica gels and precipitates (2, 3). Iler had proposed (I) that the minimum size of the dense silica globule was about 1 nm. Later Barby (2), making use of transmission electron microscopy, came to the conclusion that in many amorphous silicas the primary particle size was indeed 1-1.5 nm. 

Abrasive-Polishing Agent. Both silica gels and precipitates are found as abrasives (as well as thickeners) in toothpaste. Silicas are especially useful in the production of clear gel-type toothpastes, because it is possible to match the index of refraction of the liquid components of the formulation to that of the silica to provide the desired level of abrasivity while retaining the transparency of the toothpaste. This cannot be done with conventional abrasive agents, such as calcium carbonate. 

The aim of this chapter is more limited the emphasis is to provide an overview of the uses of synthetic silica gels and precipitated silicas that are of significant commercial importance. Excluded from this discussion are naturally occurring silicas, including products such as diatomaceous earth and so-called amorphous silica minerals (which are actually microcrystalline). Also excluded are fumed and arc silicas, forms of synthetic silica made at high temperature (in contrast to silica gels and precipitated silicas, which are generally made in aqueous solution and... 

In this chapter, only gels and precipitates are covered. Payne discusses the preparation and uses of colloidal silicas in Chapter 54, and Ferch discusses the preparation and uses of pyrogenic silicas in Chapter 14. 

A more recent application for silicas is in the specialty papers used for inkjet printing. Silica gels and precipitated silicas offer superior absorption of water-based inks, which allows for high resolution printing. Silica may be also found in high-quality direct thermal papers because of its superior insulation and absorption properties. 

Sol-gel and precipitation methods are simple and commonly used wet-chemical synthesis methods of ceramic nanoparticles such as calcium phosphates, iron oxides, silica, titanium oxides, and zinc oxides. Basically, the sol-gel method uses inorganic precursors (i.e., meal salts or organometalhc molecules) that react in aqueous environment and subsequently form integrated network (gel). For example, metal oxide nanoparticles are often synthesized via the hydrolysis and condensation reactions of metal alkoxides ... 

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