Silicon dioxide (chemical formula: SiO2, silica) is a colorless crystalline, glassy or amorphous substance. This mineral in the form of quartz sand is widely used in construction, in the production of chemical products and radio engineering, in aircraft construction and many other industries.
Distribution of silica in nature
Silicon dioxide is contained in the earth's crust in the form of mixtures with some other minerals (they are called granites) and in the form of silicates, it is part of rocks. The most common mineral in nature is quartz, cristobalite, chalcedony, tridimite, opals, and lecherite (quartz glass) are much less common. Small quartz crystals form the so-called "vein" quartz. With the gradual destruction of rocks, quartz sands are formed, which, when compacted, lead to the appearance of quartzites and sandstones.
Rhinestone is the purest quartz, colorless. Its crystals can weigh tens of tons and reach a length of several meters. Also, quartz can be colored with various impurities in purple (amethyst), yellow (citrine), black (morion), smoky (rauchtopaz). Cryptocrystalline forms of quartz are also found in nature: they are red-pink carnelian, green-apple chrysoprase, bluish sapphire, finely colored jasper, onyx and agate sand, hornfels and flint.
The “noble" opal is unique, which consists of homogeneous colloidal particles with a diameter of about 0.2 microns. These particles are densely packed in ordered agglomerates, their water contains less than one percent (in most opals - about seven percent). Natural deposits of silicon dioxide can also form diatomite, tripoli. From this mineral, shells of diatoms, skeletons of some sponges are built. It is part of the stems of plants - such as reed, horsetail, bamboo.
How to get silicon dioxide?
Synthetic SiO2 can be obtained:
- by exposure to hydrochloric (HCl) or sulfuric (H2SO4) acids on sodium silicate, less often on other soluble silicates (this method is the main one in developed countries);
- using silicon colloidal dioxide (by freezing or coagulating it under the influence of F-, Na + ions);
- by hydrolysis of silicon fluoride SiF4, silicon tetrachloride SiCl4, tetraethoxysilane (C2H5O) 4Si, solid desublimate (NH4) 2SiF6 in gas form, as well as in aqueous ammonia and aqueous solutions (sometimes with the addition of organic bases or ethanol).
Amorphous silicon dioxide is obtained:
- from diatomite and tripoli;
- calcination of rice husk;
- grinding fused silica sand.
Anhydrous silica powders receive:
- using chemical vapor deposition;
- by hydrolysis and oxidation of vapors of esters of fumed silica and silicon fluoride;
- by burning vapors of silicon tetrachloride SiCl4 in a mixture of O2 and H2.
How to use silicon dioxide?
- natural silica is used in the manufacture of products from porcelain, concrete, abrasives, silicate brick, ceramics, faience, dinas, silicate glasses;
- synthetic silica ("white soot") is used as a filler in the production of rubbers;
- quartz single crystals are used in radio engineering (filters, piezoelectric frequency stabilizers, resonators), in acoustoelectronics and acousto-optics, in jewelry, in optical instrument making;
- rock crystal and synthetic silicon dioxide are used as raw materials for the production of quartz glass, quartz single crystals, quartz fibers and ceramics. In turn, ceramics and quartz glass are used in the aviation industry, optics, electronics and other industries. Quartz fabric is used as a material that retains heat, and quartz fibers are used to create fiber-optic systems for transmitting information and communication lines.