Tungsten , or wolfram , is a chemical element with the symbol W (referring to the other name, tungsten) and atomic number 74. Name tungsten is derived from the Swedish name for tungstate mineral scheelite , from stung heavy stone. Tungsten is a rare metal that is found naturally on Earth almost exclusively in chemical compounds. It was identified as a new element in 1781 and was first isolated as a metal in 1783. The important ores include wolframite and scheelite.
The exceptional free element for its durability, especially the fact that it has the highest melting point of all found elements, melts at 3422 Â ° C (6192 Â ° F, 3695 Â ° K). It also has the highest boiling point, at 5930 Â ° C (10706 Â ° F, 6203 Â ° K). Its density is 19.3 times that of water, proportional to uranium and gold, and much higher (about 1.7 times) than lead. Polycrystalline tungsten is a material that is intrinsically fragile and hard (under standard conditions, when not combined), making it difficult to work. However, single pure crystal tungsten is more brittle and can be cut with a hard steel hacksaw.
Many Tungsten alloys have many applications, including incandescent light filaments, X-ray tubes (both as filaments and targets), electrodes in TIG welding, superalloys, and radiation shields. Tungsten hardness and high density provide military applications in penetrating projectiles. Tungsten compounds are also often used as industrial catalysts.
Tungsten is the only metal of the third transition series known to occur in biomolecules, where it is used in several species of bacteria and archaea. This is the hardest element known to be important to any living organism. Tungsten interferes with the metabolism of molybdenum and copper and is somewhat toxic to animal life.
Video Tungsten
Characteristics
Physical properties
In its raw form, tungsten is a hard gray metal that is often fragile and difficult to work. If made very purely, tungsten retains its hardness (which exceeds that of a lot of steel), and becomes softer that it can be done easily. It works by forging, drawing, or extruding. Tungsten objects are also usually formed by sintering.
Of all metals in pure form, tungsten has the highest melting point (3422 ° C, 6192 ° F), the lowest vapor pressure (at temperatures above 1650 ° C, 3000 ° F), and highest tensile strength. Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure rather than melting, thus having no melting point. Tungsten has the lowest thermal expansion coefficient of any pure metal. The low thermal expansion and high melting point and tungsten tensile strength come from the strong covalent bonds formed between the tungsten atoms by the 5d electrons. Tungsten alloys in small quantities with steel greatly increase its toughness.
Tungsten exists in two major crystalline forms:? and? The first has a cubic structure that is centered on the body and is a more stable form. Structure of? the phase is called A15 cubic; it is metastable, but can coexist with? phase in ambient conditions due to non-equilibrium synthesis or stabilization by impurities. On the contrary to? phase crystallize in isometric grains, which? the form shows the columnar habit. That? phase has one-third of the electrical resistance and the superconducting transition temperature much lower T C relative to? phase: ca. 0.015 K vs. 1-4 K; mixing two phases allows obtaining an intermediate T C value. The value of T C can also be increased by tungsten alloys with other metals (eg 7.9 K for W-Tc). Such tungsten alloys are sometimes used in low-temperature superconducting circuits.
Isotope
Tungsten naturally consists of five isotopes that are very long half-life so can be considered stable. Theoretically, the fifth can decompose into 72 element isotopes (hafnium) by alpha emissions, but only 180 W has been observed to do with half-life (1.8 Â ± 0.2) ÃÆ' - 10 18 year; on average, this yields about two decays of alpha 180 W per gram of natural tungsten per year. Other naturally occurring isotopes have not been observed to decay, inhibiting their half-life at least 4Ã, ÃÆ'â € "10 21 year.
Other artificial tungsten radioisotopes have been characterized, the most stable being 181 W with half-life of 121.2 days, 185 W with a half-life of 75.1 days, 188 W with half-life of 69.4 days, 178 W with a half-life of 21.6 days, and 187 W with a half-life of 23.72 hours. All remaining radioactive isotopes have a half-life of less than 3 hours, and most have half-lives under 8 minutes. Tungsten also has 4Ã, meta states, the most stable is 179m W ( t 1/2 6.4 min). Chemical Properties
Elemental tungsten rejects attacks by oxygen, acids, and alkalis.
The most common form of tungsten formal oxidation is 6, but shows all oxidation from -2 to 6. Tungsten is usually joined with oxygen to form yellow tungsten oxides, WO 3 , soluble in aqueous alkaline solution to form tungstate ions , WO 2 - inherited; line-height: inherited; vertical-align: baseline "> 4 .
Tungsten carbide (W 2 C and WC) is produced by heating tungsten powder with carbon. W 2 C is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl 6 ).
In aqueous solutions, tungstate provides heteropolyacids and polyoxometalate anions in neutral and acidic conditions. Since tungstate is progressively treated with acids, it first produces the soluble and metastatic anesthetic "paratungstate A", W
7 6 -
24 , from time to time convert to "paratungstate B" anion less soluble, H
2 W
12 10 - > 42 Further acidification results in a very soluble metatungstate anion H
2 W
12 O 6 -
40 , once the equilibrium is reached, the metatungstat ion exists as a symmetrical group of two oxygen-octahedral octahedra known as the Keggin anion.Many other polyoxometalate anions exist as metastable species. Different atoms such as phosphorus in place of two hydrogen centers in metatungstate produce various heteropoly acids, such as phosphotungstic acid H 3 PW 12 40 .
Tungsten trioxide can form intercalation compounds with alkali metals. This is known as
bronze ; an example is tungsten bronze sodium.
Maps Tungsten
History
In 1781, Carl Wilhelm Scheele discovered that the new acid, tungstic acid, can be made from scheelite (at that time named tungsten). Scheele and Torbern Bergman suggested that it is possible to obtain new metals by reducing this acid. In 1783, JosÃÆ'Â © and Fausto Elhuyar discovered an acid made of wolframite that was identical to tungstic acid. Later that year, at the Royal Basque Society in Bergara, Spain, the brothers managed to isolate tungsten by reducing this acid with charcoal, and they were credited with the discovery of that element.
The strategic value of tungsten emerged in the early 20th century. The British authorities acted in 1912 to free the Carrock mine from the German Cumbrian Mining Company and, during World War I, restricted German access elsewhere. In World War II, tungsten played a more significant role in the background of political affairs. Portugal, as Europe's main source of elements, is under pressure from both sides, due to the deposit of wolframite ore in Panasqueira. The desired properties of Tungsten such as its resistance to high temperatures, hardness and density, and strengthening of alloys make it an essential raw material for the weapon industry, both as arms and equipment compilers and used in the production itself, for example, in tungsten carbide cutting tools for steel machines.
Etymology
The name "tungsten" (from Sweden tung sten , "heavy stone") is used in English, French and many other languages ​​as element names but not in Nordic countries. Tungsten is an old Swedish name for scheelite minerals. "Wolfram" (or "volfram") is used in most European languages ​​(mainly Germanic and Slavic) and derived from the wolframite mineral, which is the origin of the chemical symbol W . The name "wolframite" comes from the German "wolf jackf" ("wolf soot" or "wolf cream"), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, comes from "lupi spuma ", Georg Agricola's name was used for the element in 1546, translated into English as "the foam of wolves" and is a reference to the large amount of lead that is consumed by minerals during extraction.
Genesis
Tungsten is found mainly in the mineral wolframite (iron-manganese tungstate (Fe, Mn) WO 4 , which is a solid solution of two ferberite minerals FeWO 4 , and hÃÆ'¼bnerite MnWO 4 ) and scheelite (calcium tungstate (CaWO 4 ).The range of other tungsten minerals in abundance from moderate to very rare, and almost no economic value.
Production
Approximately 61,300 tons of tungsten concentrate was produced in 2009, and by 2010, the world's tungsten production was around 68,000 tons. The main producers are as follows (data in tons):
There is additional production in the US, but the amount is proprietary company information. US reserves are 140,000 tons. The use of tungsten industry in the US is 20,000 tons: 15,000 tons are imported and the remaining 5,000 tons are from domestic recycling.
Tungsten is considered a mineral conflict due to unethical mining practices observed in the Democratic Republic of Congo.
There is a large deposit of tungsten ore at the edge of Dartmoor in England, which was exploited during World War I and World War II as the Hemerdon Mine. With the recent increase in tungsten prices, by 2014, the mine has been reactivated.
Tungsten is extracted from the ore in several stages. The ore is finally converted into tungsten (VI) oxide (WO 3 ), which is heated with hydrogen or carbon to produce tungsten powder. Because of the high melting point of tungsten, it is not commercially feasible to produce tungsten ingot. In contrast, the tungsten powder is mixed with a small amount of nickel or other metal powder, and sintered. During the sintering process, the nickel diffuses into the tungsten, producing an alloy.
Tungsten can also be extracted by hydrogen reduction from WF 6 :
- WF 6 3 H 2 -> W 6 HF
atau dekomposisi pirolitik:
- WF 6 -> W 3 F 2 (? H r = )
Tungsten is not traded as a futures contract and can not be traced on exchanges like the London Metal Exchange. Prices are usually quoted for tungsten concentrate or WO 3 . If converted to equivalent metals, they are about US $ 19 per kilogram in 2009.
Apps
About half of the tungsten is consumed for the production of hard materials - namely tungsten carbide - with the primary use remaining in alloys and steels. Less than 10% is used in other chemical compounds.
Hardware
Tungsten is mainly used in the production of hard materials based on tungsten carbide, one of the hardest carbides, with a melting point of 2770 ° C. WC is an efficient electrical conductor, but W 2 C is less so. WC is used to make wear-resistant abrasives, and "carbide" cutlery such as knives, drills, circular saws, grinding and turning tools used by metalworking, carpentry, mining, oil and construction industries. The carbide tool is actually a ceramic/metal composite, in which the metal cobalt acts as a binder (matrix) to hold the WC particles in place. This type of industrial usage accounts for about 60% of current tungsten consumption.
The jewelry industry makes sintered tungsten carbide rings, tungsten carbide/metallic composites, as well as metallic tungsten. The WC/metal composite ring uses nickel as a metal matrix instead of cobalt because it requires higher luster when polished. Sometimes a manufacturer or retailer refers to a tungsten carbide as a metal, but it is a ceramic. Due to the hardness of the tungsten carbide, the ring made of this material is highly abrasion resistant, and will hold a layer longer than a ring made of tungsten metal. The tungsten carbide ring is brittle, however, and can be cracked under a sharp blow.
Alloy
Hardness and density of tungsten is applied in obtaining heavy metal alloys. A good example is high-speed steel, which can contain as much as 18% tungsten. Tungsten's high melting point makes tungsten a good material for applications such as rocket nozzles, for example in ballistic missiles launched by Polaris-27 Polaris UGM. Tungsten alloys are used in a variety of different applications, including the aerospace and automotive industry and radiation shields. Tungsten-containing superalloys, such as Hastelloy and Stellite, are used in turbine blades and components and wear resistant coatings.
The extinguished tungsten (martensitic) steel (about 5.5% to 7.0% W with 0.5% to 0.7% C) is used to make permanent permanent magnets, due to their high remanent and coercivity, as noted by John Hopkinson (1849 - 1898) as early as 1886. The magnetic properties of metals or alloys are very sensitive to microstructures. For example, while the tungsten element is not ferromagnetic (but iron), when present in steels in this proportion, it stabilizes the martensitic phase, which has an enhanced ferromagnetism, compared with the ferrite phase (iron), due to greater resistance to magnetic domain wall motion.
Tungsten heat resistance makes it useful in arc welding applications when combined with other conductive metals such as silver or copper. Silver or copper provides the required conductivity and tungsten allowing the welding rod to withstand the high temperatures of the arc welding environment.
War equipment
Tungsten, usually mixed with nickel and iron or cobalt to form heavy alloys, is used in penetrator kinetic energy as an alternative to uranium, in applications where uranium radioactivity is problematic even in discharged form, or where additional pyrophoric uranium properties are not required (eg, bullet of small arms designed to penetrate body armor). Similarly, tungsten alloys have also been used in cannon, grenade and missile shells, to make supersonic bullet shards. Germany used tungsten during World War II to produce shells for the design of anti-tank weapons using Gerlich's "extortion" principle to achieve very high muzzle velocities and increased armor penetration of relatively small caliber and light field artillery. The weapons are very effective but the lack of tungsten used in the shell core limits that effectiveness.
Tungsten has also been used in Solid Metal Explosives, which use it as a solid powder to reduce collateral damage while increasing lethality of explosives in small radius.
Chemical applications
Tungsten (IV) sulphide is a high-temperature lubricant and is a catalyst component for hydrodesulfurization. MoS 2 is more commonly used for such applications.
Tungsten oxide is used in ceramic glazes and calcium/magnesium tungstate is widely used in fluorescent lighting. Tungstate crystals are used as a luster detector in nuclear physics and nuclear medicine. Other salts containing tungsten are used in the chemical and tanning industries.
Tungsten oxide (WO 3 ) is incorporated into the selected catalytic reduction catalyst (SCR) found in a coal-fired power plant. This catalyst converts nitrogen oxide (NO x ) to nitrogen (N 2 ) and water (H 2 O) uses ammonia (NH 3 ). Tungsten oxide helps with the physical strength of the catalyst and extends the life of the catalyst.
Niche uses
Applications that require high density include weight, counterweight, ballast keels for yachts, tail ballasts for commercial aircraft, and as ballasts in race cars for NASCAR and Formula One; Drained uranium is also used for this purpose, because the density is also high. The seventy-five-kg tungsten block is used as a "mass shipping equilibrium device" on the incoming vehicle part of the 2012 Mars Science Space spacecraft. It is an ideal material for use as a dazzling puppet, in which the mass required for good results can be achieved in a compact bar. High-density tungsten alloys with nickel, copper or iron are used in high-quality darts (to allow for smaller diameters and tighter groupings) or for fishing bait (tungsten beads allow flies to sink quickly). Some cello C strings wrapped with tungsten. The extra density gives these strings more projection and often the cellist will buy just this string and use it with three strings from different sets. Tungsten is used as an absorber on an electron telescope on the Cosmic Ray System of two Voyager spacecraft.
Sodium tungstate is used in the Folin-Ciocalteu reagent, a mixture of different chemicals used in "Lowry Assay" for protein content analysis.
Gold substitution
Its density, similar to gold, allows tungsten to be used in jewelry as an alternative to gold or platinum. Hypoallergenic metallic tungsten, and harder than gold alloys (though not as hard as tungsten carbide), make it useful for rings that will withstand scratches, especially in designs with brushed finishes.
Since the density is very similar to gold (tungsten is only 0.36% denser), tungsten can also be used in counterfeiting of gold bars, such as by lining tungsten rods with gold, which have been observed since the 1980s, or taking existing gold bars, drilling holes, and replacing removed gold with tungsten rods. The density is not exactly the same, and other properties of gold and tungsten are different, but gold-plated tungsten will pass a shallow test.
Tungsten gold-plated is commercially available from China (the main source of tungsten), both in jewelry and as bars.
Electronics
Because it maintains its strength at high temperatures and has high melting point, elemental tungsten is used in many high temperature applications, such as light bulbs, cathode ray tubes, and vacuum tube filaments, heating elements, and rocket engine nozzles. Its high melting point also makes tungsten suitable for aerospace and high temperature usage such as electrical applications, heating, and welding, especially in the process of tungsten gas arc welding (also called tungsten inert gas (TIG) welding).
Due to the conductive nature and relatively chemical inertia, tungsten is also used in electrodes, and at the emitter ends in electron-beam instruments that use field emission weapons, such as electron microscopy. In electronics, tungsten is used as an interconnect material in integrated circuits, between dielectric materials of silicon dioxide and transistors. These are used in metal films, which replace cables used in conventional electronics with a tungsten (or molybdenum) layer on silicon.
The electronic structure of tungsten makes it one of the main sources for X-ray targets, and also to protect from high-energy radiation (as in the radiopharmaceutical industry to protect radioactive FDG samples). It is also used in gamma imaging as the material from which the code holes are created, due to its excellent shielding properties. Tungsten powder is used as a filler in plastic composites, used as a non-toxic replacement for lead in bullets, shots, and radiation shields. Because the heat expansion of this element is similar to borosilicate glass, it is used to make the seal from glass to metal. In addition to its high melting point, when tungsten is flowed with potassium, it leads to increased form stability (compared to non-doped tungsten). This ensures that the filament does not sag, and no unwanted changes occur.
Nanowires
Through a top-down nanofabrication process, tungsten nanowires have been manufactured and researched since 2002. Due to the extremely high surface to volume ratio, the formation of the surface oxide layer and the single crystal properties of the material, the mechanical properties differ fundamentally from those of the bulk tungsten. Such tungsten nanowires have potential applications in nanoelectronics and are important as pH and gas sensor probes. In common with silicon nanowires, tungsten nanowires are often generated from bulk tungsten precursors followed by thermal oxidation steps to control morphology in terms of length and aspect ratios. Using the Deal-Grove model it is possible to predict the oxidation kinetics of the nanowires made through the thermal oxidation process.
The role of biology
Tungsten, at atomic number 74, is the toughest element known to function biologically, with the next most severe iodine ( Z = 53). It is used by some bacteria and archaea, but not in eukaryotes. For example, an enzyme called oxidoreductase uses tungsten equal to molybdenum by using it in a tungsten-pterin complex with molybdopterin (molybdopterin, irrespective of its name, contains no molybdenum, but may be complex with molybdenum or tungsten used by living organisms). Enzymes that use tungsten usually reduce carboxylic acids to aldehydes. The tungsten oxidoreductase can also catalyze oxidation. Enzymes that require the first tungsten to be found also require selenium, and in this case the tungsten-selenium pair can function analogously with the sulfur-molybdenum pair of some enzymes that require the cofactor molybdenum. One of the enzymes in the family of oxidoreductase that occasionally use tungsten (dehydrogenase H bacteria format) is known to use a selenium version of molybdenum from molybdopterin. Acetylene hydratase is an unusual metalloenzyme because it catalyzes the hydration reaction. Two mechanisms of the reaction have been proposed, where there is a direct interaction between the tungsten atoms and the C bonds? C. Although tungsten containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been defined definitively.
On the ground, tungsten metal oxidized into tungstate anions. It can be selectively or non-selectively imported by some prokaryotic organisms and may substitute molybdate in certain enzymes. The effect on the action of this enzyme is in some cases of inhibition and the other positive. Soil chemistry determines how tungsten polymerization; alkaline earth causes tungstate monomer; acid soils cause polymeric tungstates.
Sodium tungstate and tin have been studied for their effect on earthworms. Lead is found to be lethal at low levels and the tungstate sodium is much less toxic, but tungstate actually inhibits their reproductive ability.
Tungsten has been studied as a biological antagonist of biological copper, in a role similar to that of molybdenum action. It has been found that tetrathiotungstates can be used as biological copper chelation chemicals, similar to tetrathiomolybdates.
In archaea
Tungsten sangat penting untuk beberapa archaea. Enzim yang memanfaatkan tungsten berikut ini dikenal:
- Aldehyde ferredoxin oxidoreductase (AOR) dalam Thermococcus strain ES-1
- Formaldehyde ferredoxin oxidoreductase (FOR) di Thermococcus litoralis
- Glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR) di Pyrococcus furiosus
The wtp system selectively selects tungsten at archaea:
- WtpA is a tungten binder protein of the ABC transporter family
- WptB is a permissions
- WtpC is ATPase
Health factors
Because tungsten is rare and its compounds are generally inert, the effects of tungsten on the environment are limited. It was first believed to be relatively inert and metal was only slightly toxic, beginning in 2000, the risk given by tungsten alloys, dust and particulates to induce cancer and some other adverse effects on animals and humans has been highlighted from in vitro and in vivo experiments. Median lethal dose of LD 50 is highly dependent on animal and method of administration and varies between 59 mg/kg (intravenous, rabbit) and 5000 mg/kg (tungsten, intraperitoneal, rat powder).
People may be exposed to tungsten at work by inhaling, swallowing, skin contact, and eye contact. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m 3 for 8 hours of work per day and short-term limits of 10 mg/m 3 .
Patent claims
Tungsten is unique among the elements that have been the subject of the patent process. In 1928, a US court rejected General Electric's attempt to patent it, overturning the US. Patent 1,082,933 given in 1913 to William D. Coolidge.
See also
- Sub-terrain rifle
- Tungsten oxide
- A list of etymologic names of chemical elements
- List of chemical elements that call the controversy
References
External links
- Properties, Photos, History, MSDS
- CDC - NIOSH A Pocket Guide for Chemical Hazards
- Tungsten in Periodic Video Table (University of Nottingham)
- Picture in collection from Heinrich Pniok
- Elements & amp; Multidict Elements by Peter van der Krogt - Tungsten
- The International Tungsten Industry Association
Source of the article : Wikipedia
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