Pyrogenic silicas

Property Colloidaln silica Silica gels Precipitated silica Pyrogenic silica... 

Silicon tetrachloride can be used to produce a smoke like powder known commercially as silica fume (fumed silica, pyrogenic silica) by reaction in an oxygen-hydrogen flame ... 

Names fumed silica, pyrogenic silica, thermal silica... 

Silica powders in the form of precipitated silica, pyrogenic or fumed silicas (aerosils), and silica gels are the largest volume specialty silicas. Silica gel is the term commonly used to refer to the xerogels obtained by drying silica hydrosols. 

CAS 112945-52-5 EINECS/ELINCS 231-545-4 Synonyms Amorphous silica dust Cl 77711 Colloidal silica Colloidal silicon dioxide Eossil flour Eumed silica Fumed silicon dioxide Pigment white 27 Silica, amorphous Silica, amorphous fumed Silica, pyrogenic Silicic anhydride Silicon dioxide Definition High surface area aggregate particles of silica, with min. 89.5% SiOj content Empirical OjSi Formula SiOj... 

Silica, precipitated. See Silica, hydrated Silica, pyrogenic. See Silica, fumed Silica, quartz. See Quartz Silica sol. See Silica, colloidal... 

Silica, pyrogenic Silicic anhydride Silicon dioxide... 

The main inorganic thickeners used are silicas (pyrogenic, precipitated, aerogels), sodium aluminium silicates, and also certain clays (laponite or hectonite). 

Very finely divided fumed silica (pyrogenic silica) is another important inorganic thickener used in the coating industry that... 

Fig. 8. Different forms of commercially important amorphous silica (a) sol, (b) gel, (c) precipitate, and (d) pyrogenic.

The typical range of properties for commercial coUoidal silicas, silica gels, precipitated silicas, and pyrogenic silicas is given in Table 1. 

An advanced solution to the problem of decreasing the free mobility of the electrolyte in sealed batteries is its gel formation. By adding some 5-8 wt.% of pyrogenic silica to the electrolyte, a gel structure is formed due to the immense surface area (-200-300 m2 g ) of such silicas, which fixes the sulfuric acid solution molecules by van der Waals bonds within a lattice. These gels have thixotropic properties i.e., by mechanical stirring they can be liquefied and used to Filled into the... 

Several silaceous materials have been used successfully to induce flow. Among those quoted in the literature are pyrogenic silica in concentrations as low as 0.25% and hydrated sodium silioaluminate in concentrations of around 0.75%. The former has the additional property of being able to scavenge moisture, which might otherwise contribute to restricted flow characteristics. 

Figures 3 and 4 give displacement isotherms of PVP adsorbed on pyrogenic silica. The polymer surface excess is plotted versus the volume fraction of displacer < >d. Results in Figure 3 are for water as the solvent and in Figure 4 for dioxane as the solvent. Various displacers were used, as indicated in the figures. One of the displacers was N-ethyl pyrrolidone (NEP), which can be considered as the monomer of PVP. From the isotherm in dioxane, it was found that In = 0.14. The aqueous system shows strong...

Flocculation of Precipitated and Pyrogenic Silica Hydrosols by Polyethylene Glycols... 

In contrast to the behaviour of pyrogenic silica precipitated silica can only be flocculated with PEG by lowering the pH value below pH = 3.5 or by addition of an electrolyte. 

The pyrogenic flame hydrolyzed silica Aerosil 200, a commercial product from Degussa, was used as a dispersion in doubly distilled water (1). The precipitated silica was prepared by hydrolysis of orthosilicic acid tetraethylester in ammoniacal solution according to the method of Stober, Fink and Bohn (11). The prepared suspension was purified by repeated centrifugation, separation from solvent and redispersion of the sediment in fresh water. Finally, the water was evaporated and the wet silica dried at 150°C for about half an hour. 

The adsorption isotherms of PEG 6000 and AO,000 in fig. 1 show the typical high affinity character for precipitated and for pyrogenic silica with the following trends ... 

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