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The first crystalline silicic acid was prepared from the phyllosilicate natrosilite (Na 2 Si 2 O 5) in 1924. More than 15 crystalline acids are known and comprise at least six modifications of H 2 Si 2 O 5. Some acids can adsorb and intercalate organic molecules, and therefore are interesting alternatives to silica. [10]
In acidic solutions, the silicate ions react with hydrogen ions to form silicic acids, which tend to decompose into hydrated silicon dioxide gel. [citation needed] Heated to drive off the water, the result is a hard translucent substance called silica gel, widely used as a desiccant. It can withstand temperatures up to 1100 °C. [citation needed]
Crystalline silica is an occupational hazard for those working with stone countertops because the process of cutting and installing the countertops creates large amounts of airborne silica. [75] Crystalline silica used in hydraulic fracturing presents a health hazard to workers.
Hydrated silica is a form of silicon dioxide, which has a variable amount of water in the formula. When dissolved in water, it is usually known as silicic acid . It is found in nature as opal [ 2 ] (which has been mined as a gemstone for centuries), and in the cell walls of diatoms .
W-silica is an unstable low-density form involving SiO tetrahedra sharing opposite edges instead of corners, forming parallel chains similarly to silicon disulfide (SiS 2) and silicon diselenide (SiSe 2): it quickly returns to forming amorphous silica with heat or traces of water. [14] Condensed polysilicic acid. Silica is rather inert chemically.
Here, the silicic acid H 4 SiO 4, or Si(OH) 4, which is equivalent to SiO 2 · 2 H 2 O represents hydrous or amorphous silica for the sake of simplicity in aqueous chemistry. Indeed, the term silicic acid has traditionally been used as a synonym for silica, SiO 2. Strictly speaking, silica is the anhydride of orthosilicic acid, Si(OH) 4.
In order to prevent the formation of amorphous silica gels precipitating from supersaturated solutions without reacting with the aluminium or magnesium cations to form crystalline silicates, the silicic acid must be present in concentrations below the maximum solubility of amorphous silica. The principle behind this prerequisite can be found in ...
Sodium metasilicate is the chemical substance with formula Na 2 SiO 3, which is the main component of commercial sodium silicate solutions. It is an ionic compound consisting of sodium cations Na +