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Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO 2, commonly found in nature as quartz. [5] [6] In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant families of materials, existing as a compound of several minerals and as a
Like other chlorosilanes or silanes, silicon tetrachloride reacts readily with water: . SiCl 4 + 2 H 2 O → SiO 2 + 4 HCl. The reaction can be noticed on exposure of the liquid to air, as SiCl 4 vapour produces fumes as it reacts with moisture to give a cloud-like aerosol of silica and hydrochloric acid. [6]
[4] [5] [6] Dehydrating the latter yields a hard translucent form of silica with atomic-scale pores, called silica gel, which is widely used as water absorbent and drying agent. Silica dissolves very sparingly in water [citation needed] and is present in seawater at concentrations below 100 parts per million. In such dilute solutions, silica is ...
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.
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 .
Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum. In the last case, the material is properly called silica ...
The nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites. [7] Along with aluminate anions , soluble silicate anions also play a major role in the polymerization mechanism of geopolymers .
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants. Silica is an amorphous metalloid oxide formed by complex inorganic polymerization processes.