Physical and Chemical properties 2
In my research paper, I want to talk about such an important element as silicon. I will focus on its physical and chemical properties and application in life.
Silicon is a chemical element of the subgroup (C, Si, Ge, Sn and Pb) of the periodic system of elements, nonmetal. The crystal structure of silicon is shown in Figure 1. Silicon was isolated in 1811 by Znan Gey-Lussac and L.Tenarom by passing the vapor of silicon fluoride over metallic potassium, but they did not describe it as an element. Swedish chemist Bertselius (1823) described the silicon obtained in the processing of their potassium salts K2SiF6 of metallic potassium at a high temperature; however, only in 1854 the element was obtained in the silicon crystal form by A. Devilem. Silicon is the second most common element in the earth's crust (after oxygen), where it constitutes more than 25% of the weight. It is also concentrated in nature mainly in the form of sand or silica, which is silica, a silicate. Silicon can be obtained by calcining the crushed sand with aluminum or magnesium; in the latter case it is separated from the resulting magnesium oxide MgO dissolving in hydrochloric acid. Technical silicon (Figure 2) is produced in large quantities in electric furnaces by reduction with coke or coal silica. Semiconductor silicon produced by reduction of SiCl4 or SiHCl3 hydrogen followed by decomposition of SiH4 formed at 400-600 ° C. High-purity silicon is produced by growing a single crystal of semiconductor silicon melt by the Czochralski method or the floating zone melting silicon rods (see. And zone melting). Elemental silicon is produced mainly for the semiconductor equipment. In other cases it is used as a dopant in the production of steels and non-ferrous metals (e.g., for ferrosilicon FeSi, which is formed by calcining a mixture of sand, coke and iron oxide in an electric furnace and used as a deoxidizer and the dopant in the production of steel and as a reducing agent in the production of ferroalloys).
The most widespread application of silicon in production (Figure 3) is its usage of alloys for strength in aluminum, copper and magnesium; also important in the production of steel and semiconductor technology. The resulting silicon is metallurgical grade silicon (MG-Si). It is 98% pure and is used extensively in the metallurgical industry. An even greater production of silicon is in the form of ferrosilicon that is manufactured using a similar process to that described above but is done in the presence of iron. Ferrosilicon is used extensively in metals manufacture. In 2013 the total production of silicon was 7.6 million tons and 80 % of that was in the form of ferrosilicon (USGS).
Crystals of silicon are used in solar cells and semiconductor devices - transistors and diodes. The silicon serves as a raw material for the production of organosilicon compounds, or siloxanes obtained as oils, greases, plastics, and synthetic rubbers. Inorganic silicon compound used in the technology of ceramics and glass, as an insulating material and the crystals.
Technical silicon is commonly used in:
- raw materials for steel production: component alloy (bronze, silumin); deoxidizer (in the smelting of iron and steel); modifying the properties of metals or alloying element (for example, the addition of a certain amount of silicon in the production of transformer steel reduces the coercive force of the finished product);
- raw materials for the production of a pure polycrystalline silicon and purified metallurgical silicon (in literature «umg-Si»);
- raw material for the production of silicone materials, silanes;
- sometimes the silicon and its technical purity iron alloy (FeSi) is used for hydrogen production in the field;
- for the production of solar panels;
- antiblock (anti-adhesive additive) in the plastics industry.
Silicon single crystal is grown by the Czochralski method. Ultra-pure silicon is mainly used for the production of single-electron devices (non-linear passive elements of electrical circuits) and single-chip chipset. Pure silicon, waste ultrapure silicon purified metallurgical silicon in the form of crystalline silicon is the main raw material for solar energy. Monocrystalline silicon (apart electronics and solar energy) is used in production of mirrors of gas lasers.
Metal compounds with silicon are widely used in industry (electronic and nuclear) materials with a wide range of useful chemical, electrical and nuclear properties (resistance to oxidation, neutrons, etc.). Silicides number of elements are important thermoelectric materials. Silicon compounds are the basis for glass and cement. Manufacture of glass and cement deals closely with the silicate industry. It also produces silicate ceramic - brick, porcelain, earthenware and their products.
Physical and Chemical properties.
Silicon is a dark gray, brilliant crystalline substance, fragile and very solid, crystallized in the diamond lattice. This is a typical semiconductor (conducts electricity better than an insulator such as rubber, and worse conductor - copper). At high temperature, highly reactive silicon and interacts with most of the elements forming silicides such as magnesium silicide (Mg2Si) and other compounds such as SiO2 (silica), SiF4 (silicon tetrafluoride) and SiC (silicon carbide, silicon carbide). Silica dissolves in hot alkali solution with hydrogen evolution: Si + NaOH ® Na4SiO4 + 2H2. 4 (silicon tetrachloride) is prepared from SiO2 and CCl4 at a high temperature; is a colorless liquid, boiling at 58 ° C, readily hydrolyzed to form hydrochloric (muriatic) acid HCl and orthosilicic acid H4SiO4 (This property is used to create smoke inscriptions: liberated HCl in the presence of ammonia forms a white cloud of ammonium chloride NH4Cl). Silicon tetrafluoride SiF4 is formed by the action of hydrofluoric (HF) acid on the glass:
Na2SiO3 + 6HF 2NaF + SiF4 + 3H2O
SiF4 is hydrolyzed to form orthosilicic and Fluosilicic (H2SiF6) acid. H2SiF6 is close to the strength of sulfuric acid. Most of metal fluorosilicates soluble in water (sodium, barium, potassium, rubidium, cesium relatively insoluble), so that HF is used for the transfer of minerals in solution for analyzes. H2SiF6 acid itself and its salts are toxic.
Silica (silicon dioxide) is a natural silica and found mainly in the form of quartz, although there are other minerals, such as cristobalite, tridymite, keatite, Cowes. Crystalline silica is widely distributed in nature as a clear colorless or colored single crystals (rock crystal, amethyst, smoky quartz, tridymite, quartz, rose quartz, agate, jasper, carnelian, flint, opal and chalcedony) and in the form of clastic rocks (sea sand , gravel, pebbles, sandstone and conglomerate). A coloring of amethyst is explained by the impurities of Mn and Fe, and smoky quartz - organic inclusions. Amorphous silica is met in diatoms sediments at the bottom of the seas and oceans (tripoli, diatomaceous earth); These deposits were formed from SiO2, and was a part of the diatoms and some ciliates. Diatomaceous earth and tripoli found in California, Oregon, and in different parts of Europe. Annual production is up to 2 million tons. SiO2 is used in the production of abrasives, insulation, filtration media, filler polymers, paints and compositions.
The average price for the material is illustrated in Figure 4. It is also said in the polysilicon industry, the current market price is $60 per kilogram. It said the average price of polysilicon was around $55 per kilogram in the second quarter. This was an increase of 3.8 percent from the previous quarter while the silicon wafer had an average price of $3.5 per piece, an increase of 16.7 percent. (Techeye).
Andrea Petrou. "Solar Cell Spot Prices." TechEye. N.p., 16 Aug. 2010.
Lisa A. Corathers. Mineral Commodity Summaries. U.S. Geological Survey., 2013. Web. <http://minerals.usgs.gov/minerals/pubs/commodity/silicon/mcs-2013-simet.pdf>.
Pveducation.org/. "Refining Silicon." PVEducation. N.p., n.d. <http://pveducation.org/pvcdrom/manufacturing/refining-silicon#footnote2_hy188mb>.
Georgia State University. "Silicon Crystal Structure." Graph. Department of Physics and Astronomy, N.d. Web.
ZHANG LONG. Silicon Metal. N.p., n.d. Web. <http://siliconmetal.net/>.
Figure 1. (GSU, Department of Physics and Astronomy)
Figure 2. (Siliconmetal.net)
Figure 3 (Pveducation.org)
Figure 4 (TechEye)