Uses of Silica Gels and Powders

The long-established uses of silica gels and powders were surveyed by Vail in 1952 (557). The largest uses of silica gels in granular or pelleted form appear to be as a catalyst base and as an adsorbent or desiccant. 

Based on the scientific, patent, and manufacturers literature, the uses of silica gels and powders can be grouped according to the following functions  

Kress (558) has summarized the major flelds of use and Teicher (55 ) has listed specific silica aerogels and xerogels and their uses. No attempt is made here to review all the literature on catalysts or adsorbents or in any one of the listed areas. Instead, some of the mechanisms of action are discussed and a few technically interesting points noted.  

Silicas Precipitated from Sodium Silicate Solution 

Manufacturer Product Surface.. Area BET (m g ) Oil Absorption (gg ) Bulk Density (gl-) Remarks 

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Iler devoted one of the seven chapters of The Chemistry of Silica (1) entirely to the manufacture, characterization, and uses of silica gels and powders . In the 160 pages of Chapter 5, Iler covered so many products, processes, and applications that it is difficult for anyone not already in the field to distinguish between what is of commercial importance and what is of theoretical interest. 

The hardness and abrasive properties of silica gels and powders are of interest in their use as reinforcing agents in composite materials. 

The following fundamental aspects of the colloid chemistry of silica are briefly reviewed in this chapter nucleation, polymerization, and preparation stability of sols surface structure characterization methods sol-gel science gels and powders and uses of silica sols and powders. Silica in biology is not within the scope of this book. Scientists working in this area should soon put together a protocol covering progress done since the publication of Iler s book. 

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/... 

Adsorption of Zn(e/i) on silica gels and powders was already mentioned ih Chapter 4 and can be used to determine surface areas of silica powders free from... 

The iridoids, plumericin, isoplumericin, plumieride and fulvoplumierin, were present in the extracts of Plumeria rubra bark. After maceration of the powdered bark (3.5 kg) with dichloro-methane/methanol (1 1) and pure methanol, the combined extracts were partitioned between water and ethyl acetate. To isolate the four iridoids, the organic layer was chromatographed twice in a column using silica gel and gradient of increasing polarity with hexane and ethyl acetate, ethyl acetate and methanol, and then pure methanol. The amounts of the compounds isolated were not reported [75]. 

A TLC system comprises three elements. As its name implies, one of the elements is thin layer coated mostly on a glass or plastic plate, which acts as a stationary phase. Such a plate is termed chromatoplate . The most popular materials (adsorbent) used to form the thin layer are silica gel and alumina powder. The other elements are a sample, and a solvent or solvent mixture (developer) which acts as a mobile phase to develop (elute) the sample. A stock solution of sample is prepared in advance of the TLC experiment and applied to the thin layer to form a spot. After removal of solvent contained in the spot, the sample is eluted with an appropriate... 

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