Crystallized silica

The so-called dry gel method [20-22] is another alternative for membrane synthesis where vapors containing templates (i.e., amines) and water are employed to crystallize silica or silica-alumina layers previously deposited onto the support (vapor-phase transport method) or where steam is used to crystallize silica and template or sUica-alumina and template dry layers previously deposited onto the support (steam-assisted crystallization). Using this approach, the reactant consumption is clearly diminished, an important issue for scale-up purposes on the other hand, synthesis time is delayed due to transport-controlled phenomena. 

J. Turkevich (Princeton University, Princeton, N. J. 08540) In connection with Figure 3, I would like to know how the silicon-aluminum ratio is determined. The synthetic zeolites and maybe natural ones are obtained from silica-rich gels which increase in silica-alumina ratio in the mother liquid as the silicon-aluminum ratio increases in the crystals. Silica may be occluded and adsorbed as a colloidal gel on the zeolite and difficult to wash off. The silica ratio as measured will be higher and the lines asymetrically lower. 

Amorphons or poorly crystallized silica contained in aggregate reacts with sodium or potassium hydroxide in aqneons solntion, and, as it is commonly known, in concrete pore solution, a significant amonnt of these hydroxides can be present. To this reactive silica belong the most freqnently opal, tridymite with defected stractnre [77] or siliceous glass. The two-stage process occurs the first stage is the typical acid-base reaction, in which the acidic silanol groups react with sodium or potassium hydroxide ... 

FIGURE 5.1 Number of listed results as of June 2012 for ISI Web of Knowledge searches containing the topic strings shown. Nanotube title search string ranks either first or second for all applications listed (clay shows the largest number of listed results for mechanical nanocomposites and crystallization silica ranks first for optical nanocomposites). 

Westfahl, H., Jr. (2005) Smectic ordering in polymer liquid crystal-silica aerogel nanocomposites. /. Therm. Anal. 

Recent research has indicated that, when evaluated on a normalized size basis, insoluble nanoparticles are more potent than larger particles of the same composition in causing lung inflammation and tumors in animals. A complicating factor in this research is that nanoparticle toxicity is also affected by the chemicals that comprise individual particles. For example, nanoparticles made of titanium oxide showed little if any lung toxicity, while particles made of crystallized silica caused severe lung toxicity. 

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