silicon dioxide (chemical formula: SiO2, silica) - is a colorless crystalline, glassy or amorphous material.This mineral is in the form of quartz sand is widely used in construction, in the manufacture of chemicals and radio, aviation construction and many other industries.
Distribution silica in nature
Silicon dioxide in the earth's crust in the form of mixtures with some other minerals (called granites) and in the form of silicates, is part of the rock.The most common naturally occurring minerals - quartz, cristobalite are much rarer, chalcedony, tridymite, opal, lechatelierite (quartz glass).Small quartz crystals form a so-called "core" quartz.With the gradual destruction of rocks formed quartz sand, which, compacted, lead to the appearance of quartzite and sandstone.
rhinestone - this is the most pure quartz, colorless.Its crystals can weigh tens of tons and reach a length of several meters.Also, quartz can be colored with different impurities in the color purple (amethyst), yellow (citrine), black (morion), smoky (rauchtopaz).In nature, there are also cryptocrystalline form of quartz: it carnelian red-pink, green-apple chrysoprase, bluish sapphire thin-colored jasper, onyx and agate sand, hornfels and silicon.
is unique "noble" opal, which consists of a homogeneous colloidal particles with a diameter of about 0.2 microns.These particles are packed tightly into ordered agglomerates in water containing less than one percent (in most opals - about seven percent).Natural deposits of silica can also form diatomite, tripoli.This mineral built shells of diatoms, the skeletons of some sponges.It is part of the stalks of the plants - such as cane, horsetail, bamboo.
How to get silica?
Synthetic SiO2 can be obtained:
- by the action of hydrochloric (HCl) or sulfuric (H2SO4) acids for the sodium silicate, at least - for other soluble silicates (this method is mainly in developed countries);
- using colloidal silicon dioxide (through its freezing or coagulation under the influence of ions F-, Na +);
- by hydrolysis of SiF4 silicon fluoride, silicon tetrachloride SiCl4, tetraethoxysilane (C2H5O) 4Si, desublimata solid (NH4) 2SiF6 in gaseous form as well as in water-ammonia and an aqueous solution (sometimes with the addition of organic bases or ethanol).
amorphous silica is obtained:
- diatomite and tripoli;
- calcination of rice husk;
- grinding the fused silica sand.
anhydrous silica powders obtained:
- using a chemical vapor deposition;
- by hydrolysis and oxidation of vapor esters fumed silica and silicon fluoride;
- by burning silicon tetrachloride SiCl4 vapor in the mixture of O2 and H2.
As used silica?
- natural silica used in the manufacture of porcelain, concrete, abrasive, sand-lime bricks, ceramics, earthenware, Dinas, silicate glasses;
- synthetic silica ("white carbon black") is used as a filler in rubber production;
- single crystals of quartz have been used in electronics (filters, piezoelectric frequency stabilizers, resonators) in acoustoelectronics and acousto-optics, in jewelry, in optical instrument;
- rhinestone and synthetic silica is used as a raw material for the production of quartz glass, single crystals of quartz, quartz and ceramic fibers.In turn, ceramics and quartz glass is used in the aviation industry, optics, electronics and other industries.Quartz is used as a fabric material that retains heat and quartz fiber - to create a fiber-optic communication systems and communication links.