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Silica gel is irritating to the respiratory tract and may cause irritation of the digestive tract. Dust from the beads may cause irritation to the skin and eyes, so precautions should be taken. [33] Crystalline silica dust can cause silicosis, but synthetic amorphous silica gel is indurated, so it does not cause
Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate. The gelatinous precipitate or silica gel, is first washed and then dehydrated to produce colorless microporous silica. [15] The idealized equation involving a trisilicate and sulfuric acid is:
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.
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.
Crystalline silica exists in seven different forms , depending upon the temperature of formation. The main three polymorphs are quartz, cristobalite, and tridymite. Quartz is the second most common mineral in the world (next to feldspar). [19] Microcrystalline silica consists of minute quartz crystals bonded together with amorphous silica.
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 .
Opal is a hydrated amorphous form of silica (SiO 2 ·nH 2 O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals.
Colloidal silicas are most often prepared in a multi-step process where an alkali-silicate solution is partially neutralized, leading to the formation of silica nuclei. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. Whether or not these subunits are joined depends on the conditions of polymerization.