Silicas production

Although hydration under hydrothermal conditions may be rapid, metastable iatermediate phases tend to form, and final equiUbria may not be reached for months at 100—200°C, or weeks at even higher temperatures. Hence, the temperatures of formation given ia Table 6 iadicate the conditions under saturated steam pressure that may be expected to yield appreciable quantities of the compound, although it may not be the most stable phase at the given temperature. The compounds are Hsted ia order of decreasiag basicity, or lime/siHca ratio. Reaction mixtures having ratios C S = 1 yield xonotHte at 150—400°C. Intermediate phases of C—S—H (I), C—S—H (II), and crystalline tobermorite ate formed ia succession. Tobermorite (1.13 nm) appears to persist indefinitely under hydrothermal conditions at 110—140°C it is a principal part of the biader ia many autoclaved cement—silica and lime—silica products. 

Parent Company Davison Silica Products Division of W. R. Grace Co. (US)... 

The filter cake is stirred with 3.1 liters of acetone. The volume of acetone used is about 1.5 times the weight of the cake resulting in about a 65% acetone concentration. The benzoic acid dissolves in the acetone and the urokinase flocculates out. Sodium benzoate, about 1% of the weight of the cake, or 21 grams, is added to speed up the formation of the precipitate. The suspension of crude urokinase in acetone Is filtered on a Buchner funnel using filter paper precoated with a diatomaceous silica product (Celite 505). The precipitate is washed with acetone until the filtrate is water clear. The precipitate is then washed with ether and air dried. The yield of powder so obtained is 2.3 grams. 

Barthel, H., Rosch, L., and Weis, J., Fumed Silica-Production, Properties, and Applications, in Organo-silicon Chemistry II From Molecules to Materials, VCH Weinheim, Germany, 1996 Vol. II, 761. 

Morse, D.E. (1999) Silicon biotechnology harnessing biological silica production to construct new materials. Trends in Biotechnology, 17, 230-232. 

Dabestani, R., M. Nelson, and M. E. Sigman, Photochemistry of Tetracene Adsorbed on Dry Silica—Products and Mechanism, Photochem. Photobiol., 64, 80-86 (1996). 

These reactions are responsive to both acid and base catalysis, and can be manipulated to give a variety of silica products, e.g., discrete particles, monolithic gels, films, and fibers. This technique of materials synthesis via alkoxide hydrolysis has become known as sol-gel processing (17). It should be noted, however, that under certain conditions, gelation may be confined only to the interior of discrete particles (base-catalyzed systems), while the sol may consist of polymeric networks rather than individual particles (acid-catalyzed systems). 

The work of Mallouk et al. (39) offers an interesting extension of the microemulsion sol-gel technique. In this case, microemulsion-derived silica nanoparticles were used as templates for preparing ordered mesoporous polymers with tailored pore sizes. Utilizing the Triton N-101/cyclohexane/hexanol/water/ammonia microemulsion, monodisperse silica nanoparticles were first synthesized. The silica product... 

Approximately 40% of synthetic amorphous silica production is in Europe, followed by North America at 30%, and Japan at 12%. Although deposits of naturally occurring amorphous silicas are found in all areas of the wodd, the most significant commercial exploitation is of diatomaceous earth in industrialized countries (see Diatomite). This is because of the high cost of transportation relative to the cost of the material. Woddwide manufacturers of amorphous silica products are listed in Table 2. 

Producer3 Silica product Manufacturing location Capacity, t x 103... 

Fig. 15. Schematic of pyrogenic silica production (54). See Figure 13 for definitions.

Fig. 3. Main characteristic of silica product powders (S denotes specific surface area, p represents apparent density).

Brzezinski, M.A., Jones, J.L., Bidle, K.D., and Azam, F. (2003) The balance between silica production and silica dissolution in the sea insights from Monterey Bay, California, applied to the global data set. Limnol. Oceanogr. 48, 1846-1854. 

Food Beverage Sealants Refining Catalysts Silica Products Construction Products... 

In both cases crystallization times were between 16-20 hours and the paths of crystallization were parallel to those of the higher silica products described in the last section. 

Vrieling, E.G. et al., Diatom silicon biomineralization as an inspirational source of new approaches to silica production, J. Biotechnol., 70, 39, 1999. 

TABLE 21.4 Colloidal Silica Products of Eminess Technologies, Inc. [5]... 

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