Precipitated, hydrated, amorphous silica

Silica, from natural sources, is used as a feedstock to produce very fine particle precipitated, hydrated, amorphous silica, and fumed silica, both commonly used in different ways as reinforcing fillers in rubber technology. Also, silicone rubber, vital to aerospace and medical applications, is ultimately based on silica as a raw material. Because of the abundance of silica in nature, there will never be a shortage of this raw material. 

PVC latex BFGoodrich, Elastomers and Latex Division Precipitated hydrated amorphous silica PPG Industries Inc. 

Owing to this activation threshold, the first precipitation product from aqueous solutions of silicic acids will be an amorphous silica of some degree of hydration, while at room temperature the growth of vitreous and crystalline forms of silica from the precipitate (and thus the approach toward the absolute equilibrium) will proceed extremely slowly. With this understanding the data in Figure 1 are said to represent, an equilibrium—i.e., the reversible equilibrium between silicic acids in aqueous solution and metastable hydrated silica or polymeric silicic acid as precipitate. 

A hydrate nucleating agent (precipitated amorphous silica) and a quiescent surface inhibitor (sodium dodecyl sulfate) were used in an attempt to initiate hydrates in the bulk phase. While the induction time (for detectable hydrate formation) was not predictable, in every case hydrate was initiated at a surface—usually at the vapor-water interface, but infrequently along the sides of the sapphire tube in the gas phase, and at the metal end-plate below the liquid phase. 

Recent studies have shown the formation of altered surface layers thicker than one or two unit cell layers on feldspar surfaces, in apparent support of the leached layer theory. Thick (> 100 nm), silica-rich surface layers were detected by XPS on feldspar samples weathered in solutions having pH < 3 (Casey et at, 1988b) or >9 (Heilman et al., 1990). At these extreme pH values, the rate of release of Al and charge-balancing cations to solution is much faster than the rate of hydrolysis of silica. Under these conditions, oversaturation with respect to amorphous silica could occur, and a highly hydrated, residual leached or precipitated layer of silica could form. However, this layer is probably too porous and discontinuous to be a diffusion-limiting mechanism, but would still account for incongruence under these conditions (Hellmann et al., 1990). Whether the altered layer formed by a leached layer process or by simple precipitation from oversaturated solutions was not determined. 

Like calcium, strontium has moderate mobility in soils and sediments, and sorbs moderately to metal oxides and clays (Hayes and Traina 1998). The Sr2- ion is strongly hydrated and is firmly coordinated with six or more water molecules in aqueous solution. When Sr2- ions sorb on negatively charged mineral surface sites, the hydration sphere is retained (O Day et al. 2000). Strontium sorbs as hydrated ions on the surface of clay minerals (kaolinite), weathered minerals (amorphous silica), and iron oxides (Sahai et al. 2000). Sorbed carbonate on iron oxides enhances the sorption of Sr2- and permits the nucleation of Sr2- as strontium carbonate (Sahai et al. 2000). On calcite (calcium carbonate), Sr2 sorption occurs by electrostatic attraction as hydrated ions. However, at higher concentrations, precipitation of strontianite (strontium carbonate) occurs and strontium is likely to be less mobile (Parkman et al. 1998). 

Silica, gel and amorphous-precipitated. See Silicic acid Silica gel dessiccant. See Silica, amorphous Silica glass. See Quartz Silica hydrate. See Silica, hydrated... 

Precipitated amorphous hydrated silica and fumed anhydrous silica, inorganic reinforcing agent. 

Silicon Dioxide occurs as an amorphous substance that shows a noncrystalline pattern when examined by X-ray diffraction. It is produced synthetically, either by a vapor-phase hydrolysis process, yielding fumed silica, or by a wet process, yielding precipitated silica, silica gel, colloidal silica, or hydrous silica. Fumed silica is produced in an essentially anhydrous state, whereas the wet-process products are obtained as hydrates or contain surface-adsorbed water. 

Precipitated silica. See Silicic acid Silica, hydrated Silica, amorphous... 

Precipitated silica. See Silicic acid Silica, hydrated Silica, amorphous Precipitated sulfur. See Sulfur Precipitated zinc sulfide. See Zinc sulfide Precirol WL 2155 ATO. See Glyceryl di/tristearate... 

Synthetics - Synthetic fillers, other than Ti02, are the silicas and aluminas. The silicas are either amorphous or crystalline, and are formed by precipitating various forms of silicon dioxide fi om acidified soluble silicates. The synthetics can be hydrated silica, simple alkaline earth metal silicates, or almninum silicates. 

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