Difference between revisions of "Tungsten" - New World Encyclopedia
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{{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 }} | ||
{{Elementbox_groupperiodblock | group=6 | period=6 | block=d }} | {{Elementbox_groupperiodblock | group=6 | period=6 | block=d }} | ||
{{Elementbox_appearance_img | W,74| grayish white, lustrous }} | {{Elementbox_appearance_img | W,74| grayish white, lustrous }} | ||
| − | {{Elementbox_atomicmass_gpm | [[1 E-25 kg|183.84(1)]] }} | + | {{Elementbox_atomicmass_gpm | [[1 E-25 kg|183.84]][[List of elements by atomic mass|(1)]] }} |
{{Elementbox_econfig | [[[xenon|Xe]]] 4f<sup>14</sup> 5d<sup>4</sup> 6s<sup>2</sup> }} | {{Elementbox_econfig | [[[xenon|Xe]]] 4f<sup>14</sup> 5d<sup>4</sup> 6s<sup>2</sup> }} | ||
{{Elementbox_epershell | 2, 8, 18, 32, 12, 2 }} | {{Elementbox_epershell | 2, 8, 18, 32, 12, 2 }} | ||
| Line 12: | Line 11: | ||
{{Elementbox_density_gpcm3nrt | 19.25 }} | {{Elementbox_density_gpcm3nrt | 19.25 }} | ||
{{Elementbox_densityliq_gpcm3mp | 17.6 }} | {{Elementbox_densityliq_gpcm3mp | 17.6 }} | ||
| − | {{Elementbox_meltingpoint | k= | + | {{Elementbox_meltingpoint | k=3683 | c=3410 | f=6192 }} |
{{Elementbox_boilingpoint | k=5828 | c=5555 | f=10031 }} | {{Elementbox_boilingpoint | k=5828 | c=5555 | f=10031 }} | ||
{{Elementbox_heatfusion_kjpmol | 52.31 }} | {{Elementbox_heatfusion_kjpmol | 52.31 }} | ||
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{{Elementbox_isotopes_begin | isotopesof=tungsten | color1=#ffc0c0 | color2=black }} | {{Elementbox_isotopes_begin | isotopesof=tungsten | color1=#ffc0c0 | color2=black }} | ||
{{Elementbox_isotopes_decay | mn=180 | sym=W | {{Elementbox_isotopes_decay | mn=180 | sym=W | ||
| − | | na=0.12% | hl=[[1 E19 s and more|1.8 | + | | na=0.12% | hl=[[1 E19 s and more|1.8×10<sup>18</sup> y]] |
| dm=[[alpha decay|α]] | de=2.516 | pn=176 | ps=[[hafnium|Hf]] }} | | dm=[[alpha decay|α]] | de=2.516 | pn=176 | ps=[[hafnium|Hf]] }} | ||
{{Elementbox_isotopes_decay | mn=181 | sym=W | {{Elementbox_isotopes_decay | mn=181 | sym=W | ||
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| dm=[[electron capture|ε]] | de=0.188 | pn=181 | ps=[[tantalum|Ta]] }} | | dm=[[electron capture|ε]] | de=0.188 | pn=181 | ps=[[tantalum|Ta]] }} | ||
|- | |- | ||
| − | | <sup>182</sup>W || 26.50% || | + | | <sup>182</sup>W || 26.50% || colspan="4" | W is [[stable_isotope|stable]] with 108 [[neutrons]] |
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|- | |- | ||
| − | | <sup>183</sup>W || 14.3% || | + | | <sup>183</sup>W || 14.3% || colspan="4" | W is [[stable_isotope|stable]] with 109 [[neutrons]] |
| − | |||
|- | |- | ||
| − | | <sup>184</sup>W || 30.64% || | + | | <sup>184</sup>W || 30.64% || colspan="4" | W is [[stable_isotope|stable]] with 110 [[neutrons]] |
| − | |||
{{Elementbox_isotopes_decay | mn=185 | sym=W | {{Elementbox_isotopes_decay | mn=185 | sym=W | ||
| na=[[synthetic radioisotope|syn]] | hl=75.1 [[Day|d]] | | na=[[synthetic radioisotope|syn]] | hl=75.1 [[Day|d]] | ||
| dm=[[beta emission|β]]<sup>-</sup> | de=0.433 | pn=185 | ps=[[rhenium|Re]] }} | | dm=[[beta emission|β]]<sup>-</sup> | de=0.433 | pn=185 | ps=[[rhenium|Re]] }} | ||
|- | |- | ||
| − | | <sup>186</sup>W || 28.43% || | + | | <sup>186</sup>W || 28.43% || colspan="4" | W is [[stable_isotope|stable]] with 112 [[neutrons]] |
| − | |||
{{Elementbox_isotopes_end}} | {{Elementbox_isotopes_end}} | ||
{{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 | + | '''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]]). |
== 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, or extruding. This element has the highest [[melting point]] (3422 °[[Celsius|C]]) (6192 °[[Fahrenheit|F]]) , lowest [[vapor pressure]] and the highest [[tensile strength]] at temperatures above 1650 °C (3000 °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. | + | 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 °[[Celsius|C]]) (6192 °[[Fahrenheit|F]]), lowest [[vapor pressure]] and the highest [[tensile strength]] at temperatures above 1650 °C (3000 °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. |
== Applications == | == Applications == | ||
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*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). | *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). | ||
*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. | *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%. | + | *The high [[density]] makes it an ideal ingredient for [[darts]], normally 80% and sometimes up to 97 %. |
| − | *High | + | *[[High speed steel]] contains tungsten and some tungsten steels contain as much as 18 % tungsten. |
| − | *Superalloys containing | + | *[[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. | *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 °C (930 °F). | + | *Tungsten chemical compounds are used in [[catalyst]]s, inorganic pigments, and tungsten disulfide high-temperature [[lubricant]]s which is stable to 500 °C (930 °F). |
*Since this element's thermal expansion is similar to [[borosilicate glass]], it is used for making glass-to-metal seals. | *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]]. | + | *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. | + | 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. |
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== Biological role == | == Biological role == | ||
[[Enzyme]]s called [[oxidoreductase]]s use tungsten in a way that is similar to [[molybdenum]] by using it in a tungsten-[[pterin]] complex. | [[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 | + | 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. |
== 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 [[ | + | 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 % of the world's supply). The metal is commercially produced by reducing tungsten oxide with hydrogen or [[carbon]]. |
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| + | 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. | ||
== Compounds == | == Compounds == | ||
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=== 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−</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−</sup>. Further acidification produces the very soluble metatungstate anion, H<sub>2</sub>W<sub>12</sub>O<sub>40</sub><sup>6−</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. | 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−</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−</sup>. Further acidification produces the very soluble metatungstate anion, H<sub>2</sub>W<sub>12</sub>O<sub>40</sub><sup>6−</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. | ||
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| + | ''See also [[:Category:Tungsten compounds|tungsten compounds]].'' | ||
== 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 [[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. | ||
| − | 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 days, <sup>185</sup>W with a half-life of 75.1 days, <sup>188</sup>W with a half-life of 69.4 days and <sup>178</sup>W with a half-life of 21.6 days. All of the remaining [[radioactive]] isotopes have half-lives of less than 24 hours, and most of these have half-lives that are less than 8 minutes. Tungsten also has 4 [[meta state]]s, the most stable being <sup>179m</sup>W (t<sub>½</sub> 6.4 minutes). | + | 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 days, <sup>185</sup>W with a half-life of 75.1 days, <sup>188</sup>W with a half-life of 69.4 days and <sup>178</sup>W with a half-life of 21.6 days. All of the remaining [[radioactive]] isotopes have half-lives of less than 24 hours, and most of these have half-lives that are less than 8 minutes. Tungsten also has 4 [[meta state]]s, the most stable being <sup>179m</sup>W (t<sub>½</sub> 6.4 minutes). |
== 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 | ||
== External links == | == External links == | ||
{{Commons|Tungsten}} | {{Commons|Tungsten}} | ||
| − | * [http://www.webelements.com/webelements/elements/text/W/index.html WebElements.com | + | {{wiktionary|tungsten}} |
| − | * [http://www.sciencelab.com/data/elements/W.shtml ScienceLab.com | + | * [http://www.webelements.com/webelements/elements/text/W/index.html WebElements.com – Tungsten] |
| − | * [http://www.pniok.de/w.htm | + | *[http://www.tungsten.com/mtstung.html Properties, Photos, History, MSDS] |
| − | * [http://www.tungsten-scrap.com/scrap_links.html Tungsten-Scrap.com | + | * [http://www.sciencelab.com/data/elements/W.shtml ScienceLab.com – Tungsten] |
| − | * [http://www.vanderkrogt.net/elements/elem/w.html Elementymology & Elements Multidict by Peter van der Krogt | + | * [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]] | ||
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[[Category:Chemical elements]] | [[Category:Chemical elements]] | ||
[[Category:Transition metals]] | [[Category:Transition metals]] | ||
| + | [[Category:Refractory materials]] | ||
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Revision as of 17:59, 25 May 2006
- For other uses, see Tungsten (disambiguation).
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| Name, Symbol, Number | tungsten, W, 74 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | transition metals | ||||||||||||||||||||||||||||||||||||||||||||||||
| Group, Period, Block | 6, 6, d | ||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | grayish white, lustrous 
| ||||||||||||||||||||||||||||||||||||||||||||||||
| 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) | ||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||
| 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 | |||||||||||||||||||||||||||||||||||||||||||||||||
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Tungsten (formerly wolfram) is a chemical element that has the symbol W (L. wolframium) and atomic number 74. A very hard, heavy, steel-gray to white transition metal, tungsten is found in several ores 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 tubes and in space-age superalloys).
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, or extruding. This element has the highest melting point (3422 °C) (6192 °F), lowest vapor pressure and the highest tensile strength at temperatures above 1650 °C (3000 °F) of all metals. Its corrosion resistance is excellent and it can only be attacked slightly by most mineral acids. 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.
Applications
Tungsten is a metal with a wide range of uses, the largest of which is as tungsten carbide (W2C, WC) in cemented carbides. 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 electrodes, 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 GTAW process (also called TIG welding).
- Hardness and density properties make this metal ideal for making heavy metal alloys that are used in armaments, heat sinks, 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 %.
- High speed steel contains tungsten and some tungsten steels contain as much as 18 % tungsten.
- 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 bullets and shot.
- Tungsten chemical compounds are used in catalysts, inorganic pigments, and tungsten disulfide high-temperature lubricants which is stable to 500 °C (930 °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 penetrators, 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 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 paints. 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 for musical instruments are wound with tungsten wire.
Biological role
Enzymes called oxidoreductases 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.
Occurrence
Tungsten is found in the minerals wolframite (iron-manganese tungstate, FeWO4/MnWO4), scheelite (calcium tungstate, CaWO4), 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 % 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.
Compounds
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 tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO42−.
Aqueous polyoxoanions
Aqueous tungstate solutions are noted for the formation of polyoxoanions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" anion, W7O246−, which over hours or days 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.
See also tungsten compounds.
Isotopes
Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered 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, 180W. On average, two alpha decays of 180W occur in one gram of natural tungsten per year.
27 artificial radioisotopes of tungsten have been characterized, the most stable of which 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 of the remaining radioactive isotopes have half-lives of less than 24 hours, and most of these have half-lives that are less than 8 minutes. Tungsten also has 4 meta states, the most stable being 179mW (t½ 6.4 minutes).
ReferencesISBN 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
- WebElements.com – Tungsten
- Properties, Photos, History, MSDS
- ScienceLab.com – Tungsten
- Picture in the collection from Heinrich Pniok
- Tungsten-Scrap.com – Articles about Tungsten and applications for Tungsten scrap
- Elementymology & Elements Multidict by Peter van der Krogt – Tungsten
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