Difference between revisions of "Tungsten" - New World Encyclopedia

From New World Encyclopedia
 
(22 intermediate revisions by 7 users not shown)
Line 1: Line 1:
{{otheruses}}
+
{{Copyedited}}{{Paid}}{{Submitted}}{{Images OK}}{{Approved}}
 +
[[Category:Public]]
 
{{Elementbox_header | number=74 | symbol=W | name=tungsten | left=[[tantalum]] | right=[[rhenium]] | above=[[molybdenum|Mo]] | below=[[seaborgium|Sg]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_header | number=74 | symbol=W | name=tungsten | left=[[tantalum]] | right=[[rhenium]] | above=[[molybdenum|Mo]] | below=[[seaborgium|Sg]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_series | [[transition metal]]s }}
 
{{Elementbox_series | [[transition metal]]s }}
Line 60: Line 61:
 
{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
  
'''Tungsten''' (formerly '''wolfram''') is a [[chemical element]] that has the symbol '''W''' ([[Latin (language)|L.]] '''''wolframium''''') and [[atomic number]] 74. A very hard, heavy, steel-gray to white [[transition metal]], tungsten is found in several [[ore]]s including [[wolframite]] and [[scheelite]] and is remarkable for its robust physical properties, especially the fact that it has a higher [[melting point]] than any other non-[[alloy]] in existence. The pure form is used mainly in electrical applications but its many compounds and alloys are widely used in many applications (most notably in [[light bulb]] filaments, and as both the filament and target in most [[X-ray tube]]s and in space-age [[superalloys]]).
+
'''Tungsten''' (formerly '''wolfram''') is a [[chemical element]] with the symbol '''W''' and [[atomic number]] 74. This heavy metal, steel-gray to white in color, is remarkable for its robust physical properties, making it very useful for many applications. Its [[melting point]] is higher than that of any other non-[[alloy]], and it is therefore used in filaments in [[light bulb]]s and heating elements in electrical furnaces. Its extreme hardness makes it suitable for use in "high speed steel," which can cut materials at higher speeds than carbon steel, and in "superalloys" that perform well even at elevated temperatures. Tungsten carbide, a compound of tungsten and [[carbon]], is one of the hardest known substances and is the most common material to make milling and turning tools. [[Calcium]] and [[magnesium]] tungstates are widely used in fluorescent lighting, and tungsten oxides are used in [[paint]]s and [[ceramic]] glazes.
 
+
{{toc}}
 
== History ==
 
== History ==
 
[[Image:TungstenMetalUSGOV.jpg|thumb|left|Tungsten powder]]
 
[[Image:TungstenMetalUSGOV.jpg|thumb|left|Tungsten powder]]
  
Tungsten ([[Swedish language|Swedish]], [[Danish language|Danish]] and [[Norwegian language|Norwegian]] ''tung sten'' meaning "heavy stone", even though the current name for the element in all three languages is ''Wolfram'' (sometimes spelled in Swedish as ''volfram''), from the denomination ''volf rahm'' by [[Johan_Gottschalk_Wallerius|Wallerius]] in 1747, translated from the description by [[Georg_Agricola|Agricola]] in 1546 as ''Lupi spuma'') was first hypothesized to exist by [[Peter Woulfe]] in 1779 who examined [[wolframite]] and concluded that it must contain a new substance. In 1781 [[Carl Wilhelm Scheele]] ascertained that a new [[acid]] could be made from tungstenite. Scheele and [[Torbern Bergman]] suggested that it could be possible to obtain a new metal by reducing tungstic acid. In 1783, [[José Elhuyar|José]] and [[Fausto Elhuyar]] found an acid in wolframite that was identical to tungstic acid. In [[Spain]] later that year the brothers succeeded in isolating tungsten through reduction of this acid with [[charcoal]]. They are credited with the discovery of the element.  
+
Tungsten was first hypothesized to exist by [[Peter Woulfe]] in 1779, when he examined the mineral [[wolframite]] and concluded it must contain a new substance. In 1781, [[Carl Wilhelm Scheele]] ascertained that a new [[acid]] could be made from tungstenite. Scheele and [[Torbern Bergman]] suggested the possibility of obtaining a new metal by reducing this acid, named ''tungstic acid''. In 1783, two brothers, José and Fausto Elhuyar, found an acid in wolframite that was identical to tungstic acid. In [[Spain]] later that year, the brothers succeeded in isolating tungsten from the acid, through a chemical process called ''reduction'', using [[charcoal]]. They are credited with discovering the element.
  
In World War II, tungsten played an enormous role in background political dealings. [[Portugal]], as the main European source of the element, was put under pressure from both sides, because of its sources of wolframite ore. The resistance to high temperatures, as well as the extreme strength of its alloys, made the metal into a very important raw material for the weaponry industry.
+
In [[World War II]], tungsten played an enormous role in background political dealings. The metal's resistance to high temperatures, as well as the extreme strength of its alloys, made tungsten a very important raw material for the weapons industry. Thus both sides in the war sought the element, putting pressure on [[Portugal]], the main European source of wolframite ore.
  
 
== Occurrence ==  
 
== Occurrence ==  
  
Tungsten is found in the [[mineral]]s wolframite ([[iron]]-[[manganese]] tungstate, FeW[[oxygen|O]]<sub>4</sub>/MnWO<sub>4</sub>), [[scheelite]] ([[calcium]] tungstate, CaWO<sub>4</sub>),  [[ferberite]] and [[hübnerite]]. There are important deposits of these minerals in [[Bolivia]], [[California]], [[China]], [[Colorado]], [[Portugal]], [[Russia]], and [[South Korea]] (with China producing about 75&nbsp;% of the world's supply). The metal is commercially produced by reducing tungsten oxide with hydrogen or [[carbon]].
+
Tungsten is found in the [[mineral]]s wolframite ([[iron]]-[[manganese]] tungstate, FeW[[oxygen|O]]<sub>4</sub>/MnWO<sub>4</sub>), [[scheelite]] ([[calcium]] tungstate, CaWO<sub>4</sub>),  [[ferberite]], and [[hübnerite]]. Important deposits of these minerals have been found in [[California]] and [[Colorado]] in the [[United States]], and in the nations of [[Bolivia]], [[China]], [[Portugal]], [[Russia]], and [[South Korea]]. China produces about 75&nbsp;percent of the world's supply. The metal is commercially produced by reducing tungsten oxide with hydrogen or [[carbon]].
  
World tungsten reserves have been estimated at 7 million t W. Unfortunately, most of these reserves are not economically workable so far. At our current annual consumption rate, these reserves will only last for about 140 years. China has been the largest supplier thus far. According to further estimates, it has been suggested that 30% of the reserves are Wolframite and 70% are Scheelite ores. Another factor that controls the tungsten supply is scrap recycling of tungsten and it has been proven to be a very valuable raw material in comparison to ore.
+
World tungsten reserves have been estimated at 7 million t W. It has been suggested that 30 percent of the reserves are wolframite and 70 percent are scheelite ores. Unfortunately, most of these reserves are not economically workable, so far. At our current annual consumption rate, these reserves will last for only about 140 years. Another factor that controls the tungsten supply is scrap recycling of tungsten, which has been proven to be a very valuable source.
  
 
== Notable characteristics ==
 
== Notable characteristics ==
  
Pure tungsten is steel-gray to tin-white and is a hard metal. Tungsten can be cut with a [[hacksaw]] when it is very pure (it is brittle and hard to work when impure) and is otherwise worked by [[forging]], [[drawing (manufacturing)|drawing]], or [[extrusion|extruding]]. This element has the highest [[melting point]] (3422&nbsp;°[[Celsius|C]]) (6192&nbsp;°[[Fahrenheit|F]]), lowest [[vapor pressure]] and the highest [[tensile strength]] at temperatures above 1650&nbsp;°C (3000&nbsp;°F) of all metals. Its corrosion resistance is excellent and it can only be attacked slightly by most [[mineral acid]]s. Tungsten metal forms a protective [[oxide]] when exposed to air but can be oxidized at high temperature. When alloyed in small quantities with [[steel]], it greatly increases its hardness.
+
Tungsten is a chemical element classified as a ''transition metal''. Its symbol, W, is taken from the [[Latin (language)|Latin]] word, ''wolframium''. In the [[periodic table]], it lies in period 6, between tantalum (Ta) and rhenium (Re).
 +
 
 +
The pure metal is hard, with a steel-gray to tin-white color. When impure, it is brittle and hard to work with, but in the pure form it can be cut with a [[hacksaw]]. In addition, it can be worked by [[forging]], [[drawing (manufacturing)|drawing]], or [[extrusion|extruding]].
 +
 
 +
Of all metals, this element has the highest [[melting point]] (3422° [[Celsius|C]] or 6192° [[Fahrenheit|F]]) and lowest [[vapor pressure]]. It also has the highest [[tensile strength]] (the maximum stress it can withstand before deformation or breakage) at temperatures above 1650° C (3000° F). It is extremely resistant to corrosion and can be attacked only slightly by most [[mineral acid]]s. When exposed to air, a protective [[oxide]] is formed on the surface of the metal, but tungsten can be oxidized more fully at high temperature. When alloyed in small quantities with [[steel]], tungsten greatly increases the hardness of steel.
  
 
=== Isotopes ===
 
=== Isotopes ===
  
Naturally occurring tungsten consists of five [[isotope]]s whose [[half-life|half-lives]] are so long that they can be considered [[stable isotope|stable]]. All can decay into isotopes of element 72 ([[hafnium]]) by [[alpha emission]]. Alpha decay has only been observed, in 2003, in the lightest and rarest of them, <sup>180</sup>W. On average, two alpha decays of <sup>180</sup>W occur in one gram of natural tungsten per year.
+
Naturally occurring tungsten consists of five [[radioactivity|radioactive]] [[isotope]]s, but they have such long [[half-life|half-lives]] that they can be considered [[stable isotope|stable]]. All five can decay into isotopes of hafnium-72 by the emission of [[alpha decay|alpha]] particles (corresponding to nuclei of helium-4). Alpha decay has been observed (in 2003) in only <sup>180</sup>W, the lightest and rarest of these isotopes. On average, two alpha decays of <sup>180</sup>W occur in one gram of natural tungsten per year.
 +
 
 +
In addition, 27 artificial [[radioisotope]]s of tungsten have been characterized. The most stable of these are <sup>181</sup>W, with a [[half-life]] of 121.2&nbsp;days; <sup>185</sup>W, with a half-life of 75.1&nbsp;days; <sup>188</sup>W, with a half-life of 69.4&nbsp;days; and <sup>178</sup>W, with a half-life of 21.6&nbsp;days. All the other artificial isotopes have half-lives of less than 24&nbsp;hours, and most of these have half-lives under eight&nbsp;minutes. Tungsten also has four "metastable" states, of which the most stable is <sup>179m</sup>W (half-life of 6.4 minutes). (A metastable state of an atom is an unstable state in which a proton or neutron in the nucleus is in an energetically higher, or excited, state.)
  
27 artificial [[radioisotope]]s of tungsten have been characterized, the most stable of which are <sup>181</sup>W with a [[half-life]] of 121.2&nbsp;days, <sup>185</sup>W with a half-life of 75.1&nbsp;days, <sup>188</sup>W with a half-life of 69.4&nbsp;days and <sup>178</sup>W with a half-life of 21.6&nbsp;days.  All of the remaining [[radioactive]] isotopes have half-lives of less than 24&nbsp;hours, and most of these have half-lives that are less than 8&nbsp;minutes. Tungsten also has 4&nbsp;[[meta state]]s, the most stable being <sup>179m</sup>W (t<sub>½</sub> 6.4 minutes).
+
== Compounds ==
  
== Applications ==
+
In chemical terms, tungsten forms compounds in which its "oxidation state" ranges between +2 and +6, but the most common is +6. (Oxidation state is a measure of the degree of oxidation of an atom in a compound; it is the ''hypothetical'' electrical charge an atom would have if its bonds to all other atoms in the compound were entirely ionic.) Tungsten typically combines with oxygen to form the yellow tungstic oxide (WO<sub>3</sub>). This oxide dissolves in aqueous alkaline solutions to form tungstate ions (WO<sub>4</sub><sup>2&minus;</sup>). Some useful compounds of tungsten are described below.
Tungsten is a metal with a wide range of uses, the largest of which is as [[tungsten carbide]] (W<sub>2</sub>[[carbon|C]], WC) in cemented [[carbide]]s. Cemented carbides (also called hardmetals) are wear-resistant materials used by the metalworking, [[mining]], [[petroleum]] and construction industries. Tungsten is widely used in [[light bulb]] and [[vacuum tube]] filaments, as well as [[electrode]]s, because it can be drawn into very thin metal wires that have a high melting point.  Other uses;
+
 
*A high melting point also makes tungsten suitable for space-oriented and high temperature uses which include electrical, heating, and welding applications, notably in the [[Gas tungsten arc welding|GTAW]] process (also called [[TIG]] welding).
+
=== Tungsten carbide ===
*Hardness and density properties make this metal ideal for making [[heavy metals|heavy metal]] [[alloy]]s that are used in armaments, [[heat sink]]s, and high-density applications, such as weights, counterweights and ballast keels for yachts.
 
*The high [[density]] makes it an ideal ingredient for [[darts]], normally 80% and sometimes up to 97&nbsp;%.
 
*[[High speed steel]] contains tungsten and some tungsten steels contain as much as 18&nbsp;% tungsten. 
 
*[[Superalloy|Superalloys]] containing tungsten are used in [[turbine]] blades and wear-resistant parts and coatings.  Examples are [[Hastelloy]] and [[Stellite]].
 
*Composites are used as a substitute for [[lead]] in [[bullet]]s and shot. 
 
*Tungsten chemical compounds are used in [[catalyst]]s, inorganic pigments, and tungsten disulfide high-temperature [[lubricant]]s which is stable to 500&nbsp;°C (930&nbsp;°F).
 
*Since this element's thermal expansion is similar to [[borosilicate glass]], it is used for making glass-to-metal seals.
 
*It is used in [[kinetic energy penetrator]]s, usually alloyed with nickel and iron or cobalt to form tungsten heavy alloys, as an alternative to [[depleted uranium]].  
 
*Tungsten is used as an interconnect material in integrated circuits.  Contact holes are etched in silicon dioxide dielectric material, filled with tungsten and polished to form connections to transistors.  Typical contact holes can be as small as 65nm.
 
*Tungsten carbide is one of the hardest substances in existence and is used in, among other things, machine tools such as milling cutters. Tungsten carbide is the most common material to make milling and turning tools from and often the best choice for such applications.
 
  
Miscellaneous: Oxides are used in [[ceramic]] glazes and [[calcium]]/[[magnesium]] tungstates are used widely in fluorescent lighting. Crystal tungstates are used as [[scintillator|scintillation detectors]] in [[nuclear physics]] and [[nuclear medicine]]. The metal is also used in [[X-ray]] targets and heating elements for electrical furnaces. Salts that contain tungsten are used in the chemical and [[tanning]] industries. Tungsten 'bronzes' (so-called due to the colour of the tungsten oxides) along with other compounds are used in [[paint]]s.  Tungsten Carbide has recently been used in the fashioning of jewelry due to its [[hypoallergenic]] nature and the fact that due to its extreme hardness it is not apt to lose its luster like other polished metals. Some types of [[Strings (music)|strings]] for musical instruments are wound with tungsten wire.
+
'''Tungsten carbide''' (WC or W<sub>2</sub>C) is a chemical compound containing [[tungsten]] and [[carbon]]. Its extreme [[hardness]] makes it useful in the manufacture of cutting [[tools]], abrasives, and [[Bearing (mechanical)|bearing]]s, as a cheaper alternative to [[diamond]]. It is also used as a scratch-resistant material for jewelry, including watch bands and [[wedding ring]]s.
  
 +
=== Tungsten(VI) fluoride ===
  
 +
'''Tungsten(VI) fluoride''' (WF<sub>6</sub>), also known as '''tungsten hexafluoride''', is a colorless gas. It is nonflammable, but highly corrosive and toxic. It is produced by the reaction of [[fluorine]] gas with [[tungsten]] metal. The gas is most commonly used in the production of [[semiconductor]] [[circuits]] and [[circuit boards]], through a process called "chemical vapor deposition."
  
== Biological role ==  
+
=== Oxides of tungsten ===
[[Enzyme]]s called [[oxidoreductase]]s use tungsten in a way that is similar to [[molybdenum]] by using it in a tungsten-[[pterin]] complex.
 
  
On [[August 20]], [[2002]] officials representing the U.S.-based [[Centers for Disease Control and Prevention]] announced that [[urine]] tests on [[leukemia]] patient families and control group families in the [[Fallon, Nevada]] area had shown elevated levels of the metal tungsten in the bodies of both groups. 16 recent cases of [[cancer]] in children were discovered in the Fallon area which has now been identified as a [[cancer cluster]], (it should be noted, however, that the majority of the cancer victims are not long time residents of Fallon). Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia is not available at present.
+
'''Tungsten oxide''' (or '''tungstic oxide''', WO<sub>3</sub>) is a yellow compound of [[tungsten]] and [[oxygen]], with a melting point of 1473° C. It is synthesized by heating tungsten or other tungsten oxides in excess oxygen. It is commonly used in the manufacture of alloys, ceramics, pigments, and fireproofing. Another oxide, brown WO<sub>2</sub>, is made by reducing WO<sub>3</sub> with hydrogen (H<sub>2</sub>).
  
 +
=== Phosphotungstic acid ===
  
 +
'''Phosphotungstic acid''' (PTA), also called '''tungstophosphoric acid''' or '''tungsten hydrogen oxide phosphate''' (HPW), is a chemical with the formula 12 WO<sub>3</sub> . H<sub>3</sub>PO<sub>4</sub> . x H<sub>2</sub>O. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with a melting point of 89&deg; C (24 H<sub>2</sub>O hydrate). It is odorless and well soluble in water (200 g/100 ml). It is not especially toxic but is a mild acidic irritant.
  
== Compounds ==
+
Phosphotungstic acid is used in [[histology]] as a component for [[staining]] of cell specimens. It binds to [[fibrin]], [[collagen]], and fibers of [[connective tissue]]s, and replaces the anions of dyes from these materials, selectively decolorizing them. In addition, it is opaque for [[electron]]s and is therefore useful as a negative stain for [[virus]]es, [[nerve]]s, [[polysaccharide]]s, and other biological materials for imaging by a [[transmission electron microscope]].
The most common [[oxidation state]] of tungsten is +6, but it exhibits all oxidation states from +2 to +6. Tungsten typically combines with oxygen to form the yellow [[tungsten oxide | tungstic oxide]], WO<sub>3</sub>, which dissolves in aqueous alkaline solutions to form tungstate ions, WO<sub>4</sub><sup>2&minus;</sup>.
 
  
 
=== Aqueous polyoxoanions ===
 
=== Aqueous polyoxoanions ===
Aqueous tungstate solutions are noted for the formation of [[polyoxoanion]]s under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" [[anion]], W<sub>7</sub>O<sub>24</sub><sup>6&minus;</sup>, which over hours or days converts to the less soluble "paratungstate B" anion, H<sub>2</sub>W<sub>12</sub>O<sub>42</sub><sup>10&minus;</sup>. Further acidification produces the very soluble metatungstate anion, H<sub>2</sub>W<sub>12</sub>O<sub>40</sub><sup>6&minus;</sup>, after equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-[[oxygen]] [[octahedron|octahedra]] known as the "[[Keggin]]" anion. Many other polyoxoanions exist as [[metastable]] species.  The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of the so-called heteropolyanions.
 
  
''See also [[:Category:Tungsten compounds|tungsten compounds]].''
+
Aqueous tungstate solutions are noted for the formation of [[polyoxoanion]]s (anions that contain tungsten and oxygen) under neutral and acidic conditions. As tungstate is progressively treated with acid, it first produces the soluble, metastable "paratungstate A" [[anion]], W<sub>7</sub>O<sub>24</sub><sup>6&minus;</sup>. After hours or days, paratungstate A converts to the less soluble "paratungstate B" anion, H<sub>2</sub>W<sub>12</sub>O<sub>42</sub><sup>10&minus;</sup>. Further acidification produces the very soluble "metatungstate" anion, H<sub>2</sub>W<sub>12</sub>O<sub>40</sub><sup>6&minus;</sup>, after equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-[[oxygen]] [[octahedron|octahedra]] known as the "Keggin" anion. Many other polyoxoanions exist as [[metastable]] species. The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of the so-called "heteropolyanions."
  
 +
== Applications ==
  
 +
=== Uses of tungsten metal, alloys, and composites ===
 +
 +
*As tungsten has an extremely high melting point and is ductile (can be readily drawn into wires), it is widely used in filaments for [[light bulb]]s and [[vacuum tube]]s, and for heating elements in electrical furnaces.
 +
*Its high melting point also makes tungsten useful for other high-temperature applications such as welding. One notable use is in the "gas tungsten arc welding" (GTAW) process, also called "TIG" welding.
 +
*Based on its hardness, tungsten is ideal for making [[heavy metals|heavy metal]] [[alloy]]s for armaments.
 +
*Given its high density, it is used in weights, counterweights, and ballast keels for yachts, and it is also used in darts (normally 80 percent and sometimes up to 97 percent tungsten).
 +
*"High speed steel" (which can cut material at higher speeds than carbon steel) contains tungsten, and some tungsten steels contain as much as 18 percent tungsten.
 +
*[[Turbine]] blades and wear-resistant parts and coatings use "superalloys" containing tungsten. (Superalloys are high-performance alloys that function well at elevated temperatures.)
 +
*Composites containing tungsten are used as substitutes for [[lead]] in [[bullet]]s and shot.
 +
*Tungsten's thermal expansion is similar to that of [[borosilicate glass]], so it is used for making glass-to-metal seals.
 +
*When alloyed with nickel and iron or cobalt, tungsten is used in a form of ammunition called ''kinetic energy penetrators''. Like a bullet, such a penetrator uses kinetic energy to penetrate its target.
 +
*Tungsten is used as an interconnect material in integrated circuits, to form connections to transistors.
 +
*Some types of strings for musical instruments are wound with tungsten wire.
 +
 +
=== Uses of tungsten compounds ===
 +
 +
*Based on its extreme hardness, tungsten carbide (W<sub>2</sub>C, WC) (classified as a "cemented carbide") is the most common material to make milling and turning tools. It is used in the metalworking, [[mining]], [[petroleum]], and construction industries.
 +
*Tungsten carbide is also used in fashioning jewelry, as it is [[hypoallergenic]] and not apt to lose its luster like other polished metals.
 +
*Oxides of tungsten are used in [[ceramic]] glazes.
 +
*Tungsten 'bronzes' (so-called due to the color of tungsten oxides) and other compounds are used in [[paint]]s.
 +
*[[Calcium]]/[[magnesium]] tungstates are widely used in fluorescent lighting.
 +
*Crystalline tungstates are used as [[scintillator|scintillation detectors]] in [[nuclear physics]] and [[nuclear medicine]].
 +
*Salts that contain tungsten are used in the chemical and [[tanning]] industries.
 +
*Tungsten disulfide is useful in high-temperature [[lubricant]]s, as it is stable to 500° C (930° F).
 +
*Some tungsten compounds are used as [[catalyst]]s.
 +
 +
== Biological role ==
 +
 +
In the body, a class of [[enzyme]]s called ''oxidoreductases'' use tungsten in a complex with the organic compound ''pterin''. (This is similar to the use of [[molybdenum]] by these enzymes.)
 +
 +
On August 20, 2002, officials representing the U.S.-based [[Centers for Disease Control and Prevention]] (CDC) announced that [[urine]] tests on [[leukemia]] patient families and control group families in the Fallon, [[Nevada]], area had shown elevated levels of the metal tungsten in the bodies of both groups. Sixteen recent cases of [[cancer]] in children were discovered in the Fallon area, which has now been identified as a [[cancer cluster]]. It should be noted, however, that most of the cancer victims were not long-time residents of Fallon. In addition, Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia is not available at present.
  
 
== References ==
 
== References ==
 +
 
* [http://periodic.lanl.gov/elements/74.html Los Alamos National Laboratory - Tungsten]
 
* [http://periodic.lanl.gov/elements/74.html Los Alamos National Laboratory - Tungsten]
 
DC/AC Circuits and Electronics: Principles & Applications by Robert K. Herrick, Published by Delmar Learning 2003 for Purdue University
 
DC/AC Circuits and Electronics: Principles & Applications by Robert K. Herrick, Published by Delmar Learning 2003 for Purdue University
  
 
== External links ==
 
== External links ==
{{Commons|Tungsten}}
+
All links retrieved May 2, 2023.
{{wiktionary|tungsten}}
+
 
 
* [http://www.webelements.com/webelements/elements/text/W/index.html WebElements.com – Tungsten]
 
* [http://www.webelements.com/webelements/elements/text/W/index.html WebElements.com – Tungsten]
 
*[http://www.tungsten.com/mtstung.html Properties, Photos, History, MSDS]
 
*[http://www.tungsten.com/mtstung.html Properties, Photos, History, MSDS]
* [http://www.sciencelab.com/data/elements/W.shtml ScienceLab.com – Tungsten]
+
 
* [http://www.pniok.de/w.htm Picture in the collection from Heinrich Pniok]
 
* [http://www.tungsten-scrap.com/scrap_links.html Tungsten-Scrap.com – Articles about Tungsten and applications for Tungsten scrap]
 
* [http://www.vanderkrogt.net/elements/elem/w.html Elementymology & Elements Multidict by Peter van der Krogt – Tungsten]
 
  
 
[[Category:Physical sciences]]
 
[[Category:Physical sciences]]
 
[[Category:Chemistry]]
 
[[Category:Chemistry]]
 
[[Category:Chemical elements]]
 
[[Category:Chemical elements]]
[[Category:Transition metals]]
 
[[Category:Refractory materials]]
 
  
{{credit|55073442}}
+
 
 +
{{credit6|Tungsten|55073442|Tungsten_carbide|52885836|Tungsten_oxide|51796912|Phosphotungstic_acid|54422545|Tungsten(VI)_fluoride|52213264|Oxidation_state|54203056}}

Latest revision as of 18:45, 2 May 2023


74 tantalumtungstenrhenium
Mo

W

Sg
W-TableImage.png
periodic table
General
Name, Symbol, Number tungsten, W, 74
Chemical series transition metals
Group, Period, Block 6, 6, d
Appearance grayish white, lustrous
W,74.jpg
Atomic mass 183.84(1) g/mol
Electron configuration [Xe] 4f14 5d4 6s2
Electrons per shell 2, 8, 18, 32, 12, 2
Physical properties
Phase solid
Density (near r.t.) 19.25 g/cm³
Liquid density at m.p. 17.6 g/cm³
Melting point 3683 K
(3410 °C, 6192 °F)
Boiling point 5828 K
(5555 °C, 10031 °F)
Heat of fusion 52.31 kJ/mol
Heat of vaporization 806.7 kJ/mol
Heat capacity (25 °C) 24.27 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 3477 3773 4137 4579 5127 5823
Atomic properties
Crystal structure cubic body centered
Oxidation states 6, 5, 4, 3, 2
(mildly acidic oxide)
Electronegativity 2.36 (Pauling scale)
Ionization energies 1st: 770 kJ/mol
2nd: 1700 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 193 pm
Covalent radius 146 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 52.8 nΩ·m
Thermal conductivity (300 K) 173 W/(m·K)
Thermal expansion (25 °C) 4.5 µm/(m·K)
Speed of sound (thin rod) (r.t.) (annealed)
4620 m/s
Speed of sound (thin rod) (r.t.) 411 m/s
Shear modulus 161 GPa
Bulk modulus 310 GPa
Poisson ratio 0.28
Mohs hardness 7.5
Vickers hardness 3430 MPa
Brinell hardness 2570 MPa
CAS registry number 7440-33-7
Notable isotopes
Main article: Isotopes of tungsten
iso NA half-life DM DE (MeV) DP
180W 0.12% 1.8×1018 y α 2.516 176Hf
181W syn 121.2 d ε 0.188 181Ta
182W 26.50% W is stable with 108 neutrons
183W 14.3% W is stable with 109 neutrons
184W 30.64% W is stable with 110 neutrons
185W syn 75.1 d β- 0.433 185Re
186W 28.43% W is stable with 112 neutrons

Tungsten (formerly wolfram) is a chemical element with the symbol W and atomic number 74. This heavy metal, steel-gray to white in color, is remarkable for its robust physical properties, making it very useful for many applications. Its melting point is higher than that of any other non-alloy, and it is therefore used in filaments in light bulbs and heating elements in electrical furnaces. Its extreme hardness makes it suitable for use in "high speed steel," which can cut materials at higher speeds than carbon steel, and in "superalloys" that perform well even at elevated temperatures. Tungsten carbide, a compound of tungsten and carbon, is one of the hardest known substances and is the most common material to make milling and turning tools. Calcium and magnesium tungstates are widely used in fluorescent lighting, and tungsten oxides are used in paints and ceramic glazes.

History

Tungsten powder

Tungsten was first hypothesized to exist by Peter Woulfe in 1779, when he examined the mineral wolframite and concluded it must contain a new substance. In 1781, Carl Wilhelm Scheele ascertained that a new acid could be made from tungstenite. Scheele and Torbern Bergman suggested the possibility of obtaining a new metal by reducing this acid, named tungstic acid. In 1783, two brothers, José and Fausto Elhuyar, found an acid in wolframite that was identical to tungstic acid. In Spain later that year, the brothers succeeded in isolating tungsten from the acid, through a chemical process called reduction, using charcoal. They are credited with discovering the element.

In World War II, tungsten played an enormous role in background political dealings. The metal's resistance to high temperatures, as well as the extreme strength of its alloys, made tungsten a very important raw material for the weapons industry. Thus both sides in the war sought the element, putting pressure on Portugal, the main European source of wolframite ore.

Occurrence

Tungsten is found in the minerals wolframite (iron-manganese tungstate, FeWO4/MnWO4), scheelite (calcium tungstate, CaWO4), ferberite, and hübnerite. Important deposits of these minerals have been found in California and Colorado in the United States, and in the nations of Bolivia, China, Portugal, Russia, and South Korea. China produces about 75 percent of the world's supply. The metal is commercially produced by reducing tungsten oxide with hydrogen or carbon.

World tungsten reserves have been estimated at 7 million t W. It has been suggested that 30 percent of the reserves are wolframite and 70 percent are scheelite ores. Unfortunately, most of these reserves are not economically workable, so far. At our current annual consumption rate, these reserves will last for only about 140 years. Another factor that controls the tungsten supply is scrap recycling of tungsten, which has been proven to be a very valuable source.

Notable characteristics

Tungsten is a chemical element classified as a transition metal. Its symbol, W, is taken from the Latin word, wolframium. In the periodic table, it lies in period 6, between tantalum (Ta) and rhenium (Re).

The pure metal is hard, with a steel-gray to tin-white color. When impure, it is brittle and hard to work with, but in the pure form it can be cut with a hacksaw. In addition, it can be worked by forging, drawing, or extruding.

Of all metals, this element has the highest melting point (3422° C or 6192° F) and lowest vapor pressure. It also has the highest tensile strength (the maximum stress it can withstand before deformation or breakage) at temperatures above 1650° C (3000° F). It is extremely resistant to corrosion and can be attacked only slightly by most mineral acids. When exposed to air, a protective oxide is formed on the surface of the metal, but tungsten can be oxidized more fully at high temperature. When alloyed in small quantities with steel, tungsten greatly increases the hardness of steel.

Isotopes

Naturally occurring tungsten consists of five radioactive isotopes, but they have such long half-lives that they can be considered stable. All five can decay into isotopes of hafnium-72 by the emission of alpha particles (corresponding to nuclei of helium-4). Alpha decay has been observed (in 2003) in only 180W, the lightest and rarest of these isotopes. On average, two alpha decays of 180W occur in one gram of natural tungsten per year.

In addition, 27 artificial radioisotopes of tungsten have been characterized. The most stable of these are 181W, with a half-life of 121.2 days; 185W, with a half-life of 75.1 days; 188W, with a half-life of 69.4 days; and 178W, with a half-life of 21.6 days. All the other artificial isotopes have half-lives of less than 24 hours, and most of these have half-lives under eight minutes. Tungsten also has four "metastable" states, of which the most stable is 179mW (half-life of 6.4 minutes). (A metastable state of an atom is an unstable state in which a proton or neutron in the nucleus is in an energetically higher, or excited, state.)

Compounds

In chemical terms, tungsten forms compounds in which its "oxidation state" ranges between +2 and +6, but the most common is +6. (Oxidation state is a measure of the degree of oxidation of an atom in a compound; it is the hypothetical electrical charge an atom would have if its bonds to all other atoms in the compound were entirely ionic.) Tungsten typically combines with oxygen to form the yellow tungstic oxide (WO3). This oxide dissolves in aqueous alkaline solutions to form tungstate ions (WO42−). Some useful compounds of tungsten are described below.

Tungsten carbide

Tungsten carbide (WC or W2C) is a chemical compound containing tungsten and carbon. Its extreme hardness makes it useful in the manufacture of cutting tools, abrasives, and bearings, as a cheaper alternative to diamond. It is also used as a scratch-resistant material for jewelry, including watch bands and wedding rings.

Tungsten(VI) fluoride

Tungsten(VI) fluoride (WF6), also known as tungsten hexafluoride, is a colorless gas. It is nonflammable, but highly corrosive and toxic. It is produced by the reaction of fluorine gas with tungsten metal. The gas is most commonly used in the production of semiconductor circuits and circuit boards, through a process called "chemical vapor deposition."

Oxides of tungsten

Tungsten oxide (or tungstic oxide, WO3) is a yellow compound of tungsten and oxygen, with a melting point of 1473° C. It is synthesized by heating tungsten or other tungsten oxides in excess oxygen. It is commonly used in the manufacture of alloys, ceramics, pigments, and fireproofing. Another oxide, brown WO2, is made by reducing WO3 with hydrogen (H2).

Phosphotungstic acid

Phosphotungstic acid (PTA), also called tungstophosphoric acid or tungsten hydrogen oxide phosphate (HPW), is a chemical with the formula 12 WO3 . H3PO4 . x H2O. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with a melting point of 89° C (24 H2O hydrate). It is odorless and well soluble in water (200 g/100 ml). It is not especially toxic but is a mild acidic irritant.

Phosphotungstic acid is used in histology as a component for staining of cell specimens. It binds to fibrin, collagen, and fibers of connective tissues, and replaces the anions of dyes from these materials, selectively decolorizing them. In addition, it is opaque for electrons and is therefore useful as a negative stain for viruses, nerves, polysaccharides, and other biological materials for imaging by a transmission electron microscope.

Aqueous polyoxoanions

Aqueous tungstate solutions are noted for the formation of polyoxoanions (anions that contain tungsten and oxygen) under neutral and acidic conditions. As tungstate is progressively treated with acid, it first produces the soluble, metastable "paratungstate A" anion, W7O246−. After hours or days, paratungstate A converts to the less soluble "paratungstate B" anion, H2W12O4210−. Further acidification produces the very soluble "metatungstate" anion, H2W12O406−, after equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the "Keggin" anion. Many other polyoxoanions exist as metastable species. The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of the so-called "heteropolyanions."

Applications

Uses of tungsten metal, alloys, and composites

  • As tungsten has an extremely high melting point and is ductile (can be readily drawn into wires), it is widely used in filaments for light bulbs and vacuum tubes, and for heating elements in electrical furnaces.
  • Its high melting point also makes tungsten useful for other high-temperature applications such as welding. One notable use is in the "gas tungsten arc welding" (GTAW) process, also called "TIG" welding.
  • Based on its hardness, tungsten is ideal for making heavy metal alloys for armaments.
  • Given its high density, it is used in weights, counterweights, and ballast keels for yachts, and it is also used in darts (normally 80 percent and sometimes up to 97 percent tungsten).
  • "High speed steel" (which can cut material at higher speeds than carbon steel) contains tungsten, and some tungsten steels contain as much as 18 percent tungsten.
  • Turbine blades and wear-resistant parts and coatings use "superalloys" containing tungsten. (Superalloys are high-performance alloys that function well at elevated temperatures.)
  • Composites containing tungsten are used as substitutes for lead in bullets and shot.
  • Tungsten's thermal expansion is similar to that of borosilicate glass, so it is used for making glass-to-metal seals.
  • When alloyed with nickel and iron or cobalt, tungsten is used in a form of ammunition called kinetic energy penetrators. Like a bullet, such a penetrator uses kinetic energy to penetrate its target.
  • Tungsten is used as an interconnect material in integrated circuits, to form connections to transistors.
  • Some types of strings for musical instruments are wound with tungsten wire.

Uses of tungsten compounds

  • Based on its extreme hardness, tungsten carbide (W2C, WC) (classified as a "cemented carbide") is the most common material to make milling and turning tools. It is used in the metalworking, mining, petroleum, and construction industries.
  • Tungsten carbide is also used in fashioning jewelry, as it is hypoallergenic and not apt to lose its luster like other polished metals.
  • Oxides of tungsten are used in ceramic glazes.
  • Tungsten 'bronzes' (so-called due to the color of tungsten oxides) and other compounds are used in paints.
  • Calcium/magnesium tungstates are widely used in fluorescent lighting.
  • Crystalline tungstates are used as scintillation detectors in nuclear physics and nuclear medicine.
  • Salts that contain tungsten are used in the chemical and tanning industries.
  • Tungsten disulfide is useful in high-temperature lubricants, as it is stable to 500° C (930° F).
  • Some tungsten compounds are used as catalysts.

Biological role

In the body, a class of enzymes called oxidoreductases use tungsten in a complex with the organic compound pterin. (This is similar to the use of molybdenum by these enzymes.)

On August 20, 2002, officials representing the U.S.-based Centers for Disease Control and Prevention (CDC) announced that urine tests on leukemia patient families and control group families in the Fallon, Nevada, area had shown elevated levels of the metal tungsten in the bodies of both groups. Sixteen recent cases of cancer in children were discovered in the Fallon area, which has now been identified as a cancer cluster. It should be noted, however, that most of the cancer victims were not long-time residents of Fallon. In addition, Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia is not available at present.

References
ISBN links support NWE through referral fees

DC/AC Circuits and Electronics: Principles & Applications by Robert K. Herrick, Published by Delmar Learning 2003 for Purdue University

External links

All links retrieved May 2, 2023.


Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.