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Precipitated silica is an amorphous form of silica (silicon dioxide, SiO 2); it is a white, powdery material. Precipitated silica is produced by precipitation from a solution containing silicate salts. The three main classes of amorphous silica are pyrogenic silica, precipitated silica and silica gel.
The solubility of silica strongly depends on the temperature and pH value of the environment [3] where pH9 is the controlling value. [1] Under a condition of pH lower than 9, silica precipitates out of the fluid; when the pH value is above 9, silica becomes highly soluble. [3]
These products are often called precipitated silica or silica sols. Hydrogen ions from the surface of colloidal silica tend to dissociate in aqueous solution, yielding a high negative charge. Substitution of some of the Si atoms by Al is known increase the negative colloidal charge, especially when it is evaluated at pH below the neutral point ...
When pH slowly drops due to the progress of the silica dissolution reaction, the solubility of calcium hydroxide increases, and the alkali gel reacts with Ca 2+ ions. Its viscosity increases due to gelation process and its mobility (fluidity) strongly decreases when C-S-H phases start to precipitate after reaction with calcium hydroxide ...
The tables below provides information on the variation of solubility of different substances (mostly inorganic compounds) in water with temperature, at one atmosphere pressure. Units of solubility are given in grams of substance per 100 millilitres of water (g/(100 mL)), unless shown otherwise. The substances are listed in alphabetical order.
Reversed phase columns are quite difficult to damage compared to normal silica columns, thanks to the shielding effect of the bonded hydrophobic ligands; however, most reversed phase columns consist of alkyl derivatized silica particles, and are prone to hydrolysis of the silica at extreme pH conditions in the mobile phase.
Equilibria involving hydrolysis of silicate minerals are difficult to study. The chief challenge is the very low solubility of SiO 4 4-and its various protonated forms. Such equilibria are relevant to the processes occurring on geological time scales.
The initial silica nanoparticles are in an amorphous crystalline phase and the solvent is composed of trimethylsilyl chloride (TMCS) and ethyl alcohol. To synthesize hydrophobic nanostructured silica using this method, the colloid precursor containing the solvent and silica particles is sprayed by an aerosol generator.