Iridium and Outer Ring Road (Tianjin): Difference between pages

From Wikipedia, the free encyclopedia
(Difference between pages)
Content deleted Content added
VisualWikitext
 
Jaraalbe (talk | contribs)
105,816 edits
m location category
 
Line 1: Line 1:
The '''Outer Ring Road''' in [[Tianjin]], [[China]] is a city express road, 71.322 kilometres in length, which encircles [[Tianjin municipality]].
{{Otheruses4|the chemical element|the satellite phone service|Iridium (satellite)}}
{{infobox iridium}}
<!-- 1. intro, properties, compounds, isotopes -->
'''Iridium''' ({{pronEng|ɪˈrɪdiəm}}) is a [[chemical element]] that has the symbol '''Ir''' and [[atomic number]] 77. A very hard, brittle, silvery-white [[transition metal]] of the [[platinum group|platinum family]], iridium is the second densest element and is the most [[corrosion]]-resistant metal, even at temperatures as high as 2000&nbsp;°C. Although only certain molten salts and [[halogen]]s are corrosive to solid iridium, finely divided iridium dust is much more reactive and can even be flammable. The most important iridium compounds in terms of use are the salts and acids it forms with [[chlorine]], though iridium also forms a number of [[organometallic compound]]s used in [[catalysis]] and in research. <sup>191</sup>Ir and <sup>193</sup>Ir are the only two naturally-occurring [[isotope]]s of iridium as well as the only [[stable isotope]]s; the latter is the more abundant of the two.


Although its distance markers indicate its status as an expressway-grade road, it is not, strictly speaking, an expressway, as it has at-grade crossings, a low speed limit (60 km/h or 80 km/h), and even traffic lights.
<!-- 2. History, occurrence, production, applications -->
Iridium was discovered in 1803 by [[Smithson Tennant]] among insoluble impurities in natural [[platinum]] from [[South America]]. It is one of the rarest elements in the [[Crust_(geology)#Earth.27s_crust|Earth's crust]], with annual production and consumption of only three [[tonne]]s. However, iridium does find a number of specialized industrial and scientific applications. Iridium is employed when high corrosion resistance and high temperatures are needed, as in [[spark plug]]s, [[crucible]]s for recrystallization of semiconductors at high temperatures, electrodes for the production of chlorine in the [[chloralkali process]], and [[radioisotope thermoelectric generator]]s used in unmanned [[spacecraft]]s. Iridium compounds also find applications as catalysts for the production of [[acetic acid]].


The [[Jinghu Expressway|Jinghu]], [[Jinbin Expressway|Jinbin]], [[Jingjintang Expressway|Jingjintang]], [[Baojin Expressway|Baojin]] and [[Jinji Expressway]]s are all linked by this ring road. Major [[China National Highway]]s and roads to [[Zibo]], [[Tangshan]], [[Wuxi]] and other nearby localities, as well as to other regions in the municipality, are also linked.
<!-- 3. dinosaurs, a bit more geology -->
Iridium has been linked with the extinction of the dinosaurs and many other species 65&nbsp;million years ago. The unusually high abundance of iridium in the clays of the [[K-T boundary|K–T geologic boundary]] was a crucial clue that led to the theory that the extinction was caused by the impact of a massive extraterrestrial object with Earth—the so-called [[Alvarez hypothesis]]. Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. It is thought that due to the high density and [[Goldschmidt classification|siderophilic character]] of iridium, most of the iridium on Earth is found in the [[inner core]] of the planet.


{{Roads and Expressways of Tianjin}}
==Characteristics==
[[Category:Orbital roads]]
A [[platinum group]] metal, iridium is white, resembling [[platinum]], but with a slight yellowish cast. One of the lesser-known members of the platinum group, iridium possesses quite remarkable chemical and physical properties. Due to its [[hardness]], brittleness, and very high melting point (the [[List of elements by melting point|tenth highest]] of all elements), solid iridium is difficult to machine, form, or work, and thus [[powder metallurgy]] is commonly employed instead.<ref name="greenwood" /> It is also the only metal to maintain good mechanical properties in air at temperatures above 1600&nbsp;°C.<ref name="hunt" /> Iridium also has a very high boiling point ([[List of elements by boiling point|11th among all elements]]) and becomes a [[superconductor]] under 0.14&nbsp;[[Kelvin|K]].<ref>{{cite book | last = Kittel | first = C. | coauthors = | title=Introduction to Solid state Physics, 7th Edition| publisher=Wiley-India | year=2004 | isbn=8126510455| oclc = }}</ref>
[[Category:Transportation in Tianjin]]

[[Image:Iridium 1.jpg|left|thumb|100px|Iridium metal has a yellowish cast.]]
Iridium is the most corrosion-resistant metal known:<ref name="Emsley" /> it is not attacked by any [[acid]], by [[aqua regia]], by any molten metals, or by silicates at high temperatures. It can, however, be attacked by some molten [[salt]]s, such as [[sodium cyanide]] and [[potassium cyanide]],<ref name="Emsley" /> as well as [[oxygen]] and the [[halogen]]s (particularly [[fluorine]])<ref name="perry">{{cite book |title = Handbook of Inorganic Compounds |author=Perry, D. L. |pages = 203&ndash;204 | date = 1995 | isbn = 0-8492-8671-3 | publisher = CRC Press |ISBN status = May be invalid - please double check |unused_data = |ISBN status = May be invalid - please double check}}</ref> at higher temperatures.<ref name="lagowski">{{cite book |title = Chemistry Foundations and Applications | volume = 2 |editor = Lagowski, J. J. | pages=250&ndash;251 | date = 2004 | isbn = 0-02-865732-3 | publisher = Thomson Gale |ISBN status = May be invalid - please double check |unused_data = |ISBN status = May be invalid - please double check}}</ref>

Iridium's [[modulus of elasticity]] is the second highest among the metals, only being surpassed by [[osmium]].<ref name="hunt" /> This, together with a high [[modulus of rigidity]] and a very low figure for [[Poisson's ratio]] (the relationship of longitudinal to lateral strain), indicate the high degree of [[stiffness]] and resistance to deformation that have rendered its fabrication into useful components a matter of great difficulty over the long period since its discovery. Despite these limitations and iridium's high cost, a number of applications have developed in more recent years where mechanical strength is an essential factor in some of the extremely severe conditions encountered in modern technology.<ref name="hunt" />

The measured [[density]] of iridium is only slightly lower (by about 0.1%) than that of [[osmium]], the [[List of elements by density|densest element]] known.<ref>{{cite journal |title=Osmium, the Densest Metal Known |author=Arblaster, J. W. |journal=Platinum Metals Review |volume=39 |issue=4 |year=1995 |pages=164 |url=http://www.platinummetalsreview.com/dynamic/article/view/pmr-v39-i4-164-164}}</ref> There has been some ambiguity regarding which element is the densest due to the small size of the difference in density and the difficulty in measuring it accurately,<ref name="crc">{{cite book | author=Lide, D. R. | title=CRC Handbook of Chemistry and Physics (70th Edn.) | publisher=Boca Raton (FL):CRC Press | year=1990}}</ref> but the best available calculations from [[X-ray crystallography|X-ray crystallographic]] data give densities of 22.56&nbsp;g/cm<sup>3</sup> for iridium and 22.59&nbsp;g/cm<sup>3</sup> for osmium.<ref>{{cite journal |url=http://www.platinummetalsreview.com/pdf/pmr-v33-i1-014-016.pdf |title=Densities of osmium and iridium: recalculations based upon a review of the latest crystallographic data |author=Arblaster, J. W. |journal=Platinum Metals Review |volume=33 |issue=1 |year=1989 |pages=14&ndash;16}}</ref>

===Isotopes===
{{main|Isotopes of iridium}}
Iridium has two naturally occurring, stable [[isotope]]s, <sup>191</sup>Ir and <sup>193</sup>Ir, with [[natural abundance]]s of 37.3% and 62.7%, respectively.<ref name="nubase" /> At least 34 [[radioisotope]]s have also been synthesized, ranging in [[mass number]] from 164 to 199. Twenty-seven of these are lighter than the [[stable isotope]]s, whereas only six are heavier than the stable isotopes. [[iridium-192|<sup>192</sup>Ir]], which falls between the two stable isotopes, is the most stable radioisotope, with a [[half-life]] of 73.827&nbsp;days, and finds application in [[brachytherapy]].<ref name="mager" /> Three other isotopes have half-lives of at least a day—<sup>188</sup>Ir, <sup>189</sup>Ir, <sup>190</sup>Ir—while the rest usually have a half-life of at least 1&nbsp;ms.<ref name="nubase" /> One of the least stable isotopes is <sup>165</sup>Ir with a half-life of 1&nbsp;[[microsecond|µs]]. Isotopes with masses below 191 decay by some combination of [[Beta_decay#.CE.B2.E2.88.92_decay|β<sup>+</sup> decay]], [[alpha decay|α decay]], and [[proton emission]], with the exceptions of <sup>189</sup>Ir, which decays by [[electron capture]], and <sup>190</sup>Ir, which decays by [[positron emission]]. Synthetic isotopes heavier than 191 decay by [[Beta_decay#.CE.B2.2B_decay|β<sup>−</sup> decay]], although <sup>192</sup>Ir also has a minor [[electron capture]] decay path.<ref name="nubase">{{cite journal| last = Audi| first = G. | title = The NUBASE Evaluation of Nuclear and Decay Properties| journal = Nuclear Physics A| volume = 729| pages = 3&ndash;128| publisher = Atomic Mass Data Center| date = 2003| doi=10.1016/j.nuclphysa.2003.11.001}}</ref> All known isotopes of iridium were discovered between 1934 and 2001; the most recent is <sup>171</sup>Ir.<ref>{{cite journal |title=The discoverers of the iridium isotopes: the thirty-six known iridium isotopes found between 1934 and 2001 |author=Arblaster, J. W. |journal=Platinum Metals Review |volume=47 |issue=4 |year=2003 |pages=167–174 |url=http://www.platinummetalsreview.com/dynamic/article/view/47-4-167-174}}</ref>

At least 32 [[nuclear isomer|metastable isomers]] have been characterized, ranging in mass number from 164 to 197. The most stable of these is <sup>192m2</sup>Ir, which decays by [[isomeric transition]] with a half-life of 241&nbsp;years,<ref name="nubase"/> making it more stable than any of iridium's synthetic isotopes in their ground states. The least stable isomer is <sup>190m3</sup>Ir with a half-life of only 2&nbsp;µs.<ref name="nubase"/> The isotope <sup>191</sup>Ir was the first one of any element to be shown to present a [[Mössbauer effect]]. This renders it useful for [[Mössbauer spectroscopy]] for research in physics, chemistry, biochemistry, metallurgy, and mineralogy.<ref name="ir-191" />

===Compounds===
<div style="float: right; margin: 5px;">
{|class="wikitable"
! colspan=2 | Oxidation states<br />of iridium<small><ref group=note>Common oxidation states are in bold.</ref></small>
|-
| −3 ||{{chem|[Ir(CO)|3|]<sup>3−</sup>}}
|-
| −1 ||{{chem|[Ir(CO)|3|(P[[phenyl|Ph]]|3|)]<sup>−</sup>}}
|-
| '''0''' ||{{chem|Ir|4|(CO)|12}}
|-
| +1 ||{{chem| [Ir(CO)Cl(PPh|3|)|2|]}}
|-
| +2 ||{{chem|IrCl|2}}
|-
| '''+3''' ||{{chem|IrCl|3}}
|-
| '''+4''' ||{{chem|IrO|2}}
|-
| +5 ||{{chem|Ir|4|F|20}}
|-
| +6 ||{{chem|IrF|6}}
|}</div>
{{seealso|Category:Iridium compounds}}
Iridium forms compounds in the [[oxidation state]]s of −3 and all in the range from −1 to +6; the most common oxidation states are +3 and +4.<ref name="greenwood" /> Well-characterized examples of the highest oxidation state are rare, but include {{chem|IrF|6}} and two mixed oxides {{chem|Sr|2|MgIrO|6}} and {{chem|Sr|2|CaIrO|6}}.<ref name="greenwood">{{cite book | last=Greenwood |first = N. N. |coauthors = Earnshaw, A. | title=Chemistry of the Elements |edition = 2nd Edition |publisher=Oxford:Butterworth-Heinemann | year=1997 | isbn=0-7506-3365-4 |pages=1113–1143,1294 | oclc=213025882 37499934 41901113}}</ref><ref>{{cite journal| last = Jung | first = D. | title = High Oxygen Pressure and the Preparation of New Iridium (VI) Oxides with Perovskite Structure: Sr<sub>2</sub>MIrO<sub>6</sub> (M = Ca, Mg) | journal = Journal of Solid State Chemistry | volume = 115 | issue = 2 | year = 1995 |pages = 447–455| publisher = | date = | doi= 10.1006/jssc.1995.1158}}</ref>

[[Iridium(IV) oxide|Iridium dioxide]], {{chem|IrO|2}}, a brown powder, is the only well-characterized oxide of iridium.<ref name="greenwood" /> A [[sesquioxide]], {{chem|Ir|2|O|3}}, has also been described as a blue-black powder which is oxidized to {{chem|IrO|2}} by {{chem|HNO|3}}.<ref name="perry"/> The corresponding disulfides, diselenides, sesquisulfides and sesquiselenides are known and {{chem|IrS|3}} has also been reported.<ref name="greenwood" /> Iridium also forms iridates with oxidation states +4 and +5, such as K<sub>2</sub>IrO<sub>3</sub> and KIrO<sub>3</sub>, which can be prepared from the reaction of [[potassium oxide]] or [[potassium superoxide]] with iridium at high temperatures.<ref>{{cite journal |title=The chemistry of ruthenium, osmium, rhodium, iridium, palladium and platinum in the higher oxidation states |journal=Coordination Chemistry Reviews |volume=46 |year=1982 |pages=1–127 |author=Gulliver, D. J; Levason, W. |doi=10.1016/0010-8545(82)85001-7}}</ref>

While no [[binary compound|binary]] [[hydride]]s of iridum, {{chem|Ir|x|H|y}} are known, complexes are known that contain {{chem|IrH|5}}<sup>4−</sup> and {{chem|IrH|6}}<sup>3−</sup>, where iridium has the +1 and +3 oxidation states, respectively.<ref>{{cite book | last = Holleman | first = A. F. | coauthors = Wiberg, E.; Wiberg, N. | title=Inorganic Chemistry, 1st Edition | publisher=Academic Press | year=2001 | isbn=0123526515| oclc = }}</ref> The ternary hydride {{chem|Mg|6|Ir|2|H|11}} is believed to contain both the {{chem|IrH|5}}<sup>4−</sup> and the 18-electron {{chem|IrH|4}}<sup>5−</sup> anion.<ref>{{cite journal| last = Černý | first = R. |coauthors = Joubert, J.-M.; Kohlmann, H.; Yvon, K. | title = {{chem|Mg|6|Ir|2|H|11}}, a new metal hydride containing saddle-like {{chem|IrH|4}}<sup>5−</sup> and square-pyramidal {{chem|IrH|5}}<sup>4−</sup> hydrido complexes| journal = Journal of Alloys and Compounds| volume = 340| issue = 1-2 | year = 2002 |pages = 180-188 | publisher = | date = | doi=10.1016/S0925-8388(02)00050-6 }}</ref>

No monohalides or dihalides are known, whereas trihalides, IrX<sub>3</sub>, are known for all of the halogens.<ref name = "greenwood"/> For oxidation states +4 and above, only the tetrafluoride, pentafluoride and hexafluoride are known.<ref name = "greenwood"/> [[Iridium hexafluoride]], IrF<sub>6</sub>, is a volatile and highly reactive yellow solid, composed of octahedral molecules. It decomposes in water and is reduced to [[iridium tetrafluoride|IrF<sub>4</sub>]], a crystalline solid, by<!-- the [[halogen]]s.<ref name="perry"/> .this is what Perry says but as it is implausible and Greenwood has the reduction performed by iridium black I have changed this to Greenwoods version--><!-- why is it implausible? Cl2 would give ClF3, perfectly reasonable--><!-- some pre 1950 work did indeed claim this - however as IF4 identification was suspect prior to around 1974/75 and other synthetic methods are cleaner e.g. reduction of IrF6 with H2 -Paine and Asprey 1975- i.e no possibility of halogen exchange-synthetically its dubious--> iridium black.<ref name = "greenwood"/> [[Iridium pentafluoride]] has similar properties but it is actually a [[tetramer]], {{chem|Ir|4|F|20}}, formed by four corner-sharing octahedra.<ref name = "greenwood"/>

[[Image:Vaska's-complex-2D.png| thumb | left| Vaska's complex]]
Hexachloroiridic(IV) acid, {{chem|H|2|IrCl|6}}, and its ammonium salt are the most important iridium compounds from an industrial perspective.<ref name="ullmann-pt" /> They are involved in the purification of iridium and used as precursors for most other iridium compounds, as well as in the preparation of [[anode]] coatings. The [IrCl<sub>6</sub>]<sup>2−</sup> ion has an intense dark brown color, and can be readily reduced to the lighter-colored [IrCl<sub>6</sub>]<sup>3−</sup> and vice versa.<ref name="ullmann-pt" /> [[Iridium(III) chloride|Iridium trichloride]], IrCl<sub>3</sub>, which can be obtained in anhydrous form from direct oxidation of iridium powder by [[chlorine]] at 650&nbsp;°C,<ref name="ullmann-pt" /> or in hydrated form by dissolving Ir<sub>2</sub>O<sub>3</sub> in [[hydrochloric acid]], is often used as a starting material for the synthesis of other Ir(III) compounds.<ref name="greenwood" /> Another compound used as a starting material is ammonium hexachloroiridate(III), ({{chem|NH|4|)|3|IrCl|6}}. Iridium(III) complexes are [[diamagnetic]] ([[low-spin]]) and generally have an [[octahedral molecular geometry]].<ref name="greenwood" />

[[Organoiridium compound]]s contain iridium–[[carbon]] bonds where the metal is usually in lower oxidation states. For example, oxidation state zero is found in [[tetrairidium dodecacarbonyl]], {{chem|Ir|4|(CO)|12}}, which is the most common and stable binary [[metal carbonyl|carbonyl]] of iridium.<ref name="greenwood" /> In this compound, each of the iridium atoms is bonded to the other three, forming a tetrahedral cluster. Some organometallic Ir(I) compounds are notable enough to be named after their discoverers. One is [[Vaska's complex]], {{chem|IrCl(CO)[P(C|6|H|5|)|3|]|2}}, which has the unusual property of binding to the [[dioxygen molecule]], O<sub>2</sub>.<ref>{{cite journal| first =L. | last= Vaska | coauthors = DiLuzio, J.W. | title = Carbonyl and Hydrido-Carbonyl Complexes of Iridium by Reaction with Alcohols. Hydrido Complexes by Reaction with Acid |journal=[[Journal of the American Chemical Society]] |date = 1961 |volume = 83 |pages = 2784&ndash;2785 | doi = 10.1021/ja01473a054| authorlink=Lauri Vaska}}</ref> Another one is [[Crabtree's catalyst]] ([[:Image:Crabtree.png|image]]), a [[homogeneous catalyst]] for [[hydrogenation]] reactions.<ref>{{cite journal |first = R. H. | last = Crabtree | authorlink =Robert H. Crabtree | title = Iridium compounds in catalysis | journal = Accounts of Chemical Research | year = 1979 | volume = 12 | pages = 331&ndash;337 | doi = 10.1021/ar50141a005}}</ref> These compounds are both [[square planar]], d<sup>8</sup> complexes, with a total of 16 [[valence electron]]s, which accounts for their reactivity.<ref>{{cite book | title=The Organometallic Chemistry of the Transition Metals| url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471662569.html| author=Crabtree, R. H.| date=2005| publisher=Wiley| isbn=978-0-471-66256-3 | oclc=224478241 61520528 85820471 |authorlink=Robert H. Crabtree}}</ref>
<br clear="all" />
===Occurrence===

[[Image:Willamette Meteorite AMNH.jpg|thumb|The [[Willamette meteorite]], the largest meteorite found in the U.S., has 4.7&nbsp;ppm iridium.<ref>{{cite journal |title=The chemical classification of iron meteorites—VII. A reinvestigation of irons with Ge concentrations between 25 and 80 ppm |author=Scott, E. R. D.; Wasson, J. T.; Buchwald, V. F. |journal=Geochimica et Cosmochimica Acta |year=1973 |volume=37 |pages=1957&ndash;1983 |doi=10.1016/0016-7037(73)90151-8}}</ref>]]
Iridium is one of the [[abundance of the chemical elements|rarest elements]] in the Earth's [[crust (geology)|crust]]; with an average abundance of 0.001&nbsp;[[parts per million|ppm]] in crustal rock, it is 4 times less abundant than [[gold]], 10 times less abundant than [[platinum]], and 80 times less abundant than [[silver]] and [[mercury (element)|mercury]].<ref name="greenwood" /> [[Tellurium]] is about as abundant as iridium, and only three naturally-occurring elements are less abundant: [[rhenium]], [[ruthenium]], and [[rhodium]], the last two being 10 times less abundant than iridium.<ref name="greenwood" /> In contrast to its low abundance in crustal rock, iridium is relatively common in [[meteorite]]s, with concentrations of 0.5&nbsp;ppm or more.<ref name="argonne" /> It is thought that the overall concentration of iridium on Earth is much higher than what is observed in crustal rocks, but because of the density and [[Goldschmidt classification|siderophilic nature]] of iridium, it descended below the crust and into the [[inner core|Earth's core]] at a time when the planet was young and still molten.<ref name="ullmann-pt">{{cite book |author=Renner, H.; Schlamp, G.; Kleinwächter, I.; Drost, E.; Lüschow, H. M.; Tews, P.; Panster, P.; Diehl, M.; Lang, J.; Kreuzer, T.; Knödler, A.; Starz, K. A.; Dermann, K.; Rothaut, J.; Drieselman, R. |chapter=Platinum group metals and compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley |year=2002 |doi=10.1002/14356007.a21_075}}</ref>

Iridium is found in nature as an uncombined element or in natural [[alloy]]s; especially the iridium–[[osmium]] alloys, [[osmiridium]] (osmium rich), and [[iridiosmium]] (iridium rich).<ref name="Emsley">{{cite book | title = Nature's Building Blocks: An A-Z Guide to the Elements | last = Emsley | first=J. | publisher = Oxford University Press | year = 2003 | location = Oxford, England, UK | isbn = 0198503407 | chapter = Iridium | pages=201–204}}</ref> In the [[nickel]] and [[copper]] deposits the platinum group metals occur as [[sulfide]]s (i.e. (Pt,Pd)S)), [[telluride (chemistry)|tellurides]] (i.e. PtBiTe), [[antimonide]]s (PdSb), and [[arsenide]]s (i.e. PtAs<sub>2</sub>), in all of these compounds platinum is exchanged by a small amount of iridium and osmium. All the platinum group metals end up as alloys with raw nickel or [[native copper|raw copper]].<ref>{{cite journal | doi = 10.1016/j.mineng.2004.04.001 | journal = Minerals Engineering | volume = 17 | year = 2004 | pages = 961&ndash;979 | title =Characterizing and recovering the platinum group minerals—a review | first = Z. | last = Xiao | coauthors= Laplante, A. R.}}</ref>{{Clarifyme|How does the previous sentence relate to iridium?|date=September 2008}}

The largest known primary reserves are in the [[Bushveld igneous complex]] in [[South Africa]],<ref name="kirk-pt" /> the large copper–nickel deposits near [[Norilsk#Norilsk-Talnakh nickel deposits|Norilsk]] in [[Russia]], and the [[Sudbury Basin]], [[Canada]] with its large ore deposits are the two other large deposits. Smaller reserves can be found in the United States.<ref name="kirk-pt" /> Iridium is also found in secondary deposits, combined with platinum and other platinum group metals in [[alluvium|alluvial]] deposits. The alluvial deposits used by [[pre-Columbian]] people in the [[Chocó Department]], [[Colombia]] are still a source for platinum group metals. <!-- The second large alluvial deposit was found in the [[Ural mountain]]s, Russia, which is still mined.{{Fact|date=September 2008}} --> Total world reserve amounts have not been estimated.<ref name="Emsley"/>

===K–T boundary presence===
[[Image:K-T boundary.jpg|thumb|left|200px|K–T boundary in Colorado, US. The iridium-rich ash (the boundary) is indicated by the red arrow.]]
{{Main|Cretaceous–Tertiary extinction event|K–T boundary}}
The [[K–T boundary]] of 65 million years ago, marking the temporal border between the [[Cretaceous]] and [[Tertiary]] periods of [[Geologic time scale|geological time]], was identified by a thin [[stratum]] of [[iridium anomaly|iridium-rich clay]].<ref name="Alvarez" /> A team led by [[Luis Walter Alvarez|Luis Alvarez]] proposed in 1980 an extraterrestrial origin for this iridium, attributing it to an [[asteroid]] or [[comet]] impact.<ref name="Alvarez">{{cite journal|title=Extraterrestrial cause for the Cretaceous–Tertiary extinction |author=[[Luis Walter Alvarez|Alvarez, L. W.]]; Alvarez, W.; Asaro, F.; Michel, H. V. |year=1980 |journal=Science |volume=208 |issue=4448 |pages=1095&ndash;1108 |doi=10.1126/science.208.4448.1095 |pmid=17783054}}</ref> Their theory, known as the [[Alvarez hypothesis]], is now widely accepted to explain the demise of the [[dinosaur]]s. A large buried impact crater structure with an estimated age of about 65 million years was later identified near what is now [[Yucatán Peninsula]] (the [[Chicxulub crater]]).<ref>{{cite journal|last =Hildebrand | first = A. R. | coauthors = Penfield, Glen T.; Kring, David A.; Pilkington, Mark; Zanoguera, Antonio Camargo; Jacobsen, Stein B.; Boynton, William V. |title=Chicxulub Crater; a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico |year = 1991 | month = September | volume = 19| issue = 9 | journal = [[Geology (journal)|Geology]]| pages = 867&ndash;871 | url=http://geology.geoscienceworld.org/cgi/content/abstract/19/9/867 | doi = 10.1130/0091-7613(1991)019<0867:CCAPCT>2.3.CO;2}}</ref><ref>{{cite book|author=Frankel, C.|title=The End of the Dinosaurs: Chicxulub Crater and Mass Extinctions|year=1999|publisher=Cambridge University Press|language=English|isbn=0521474477|oclc=40298401 59413198}}</ref> Dewey M. McLean and others argue that the iridium may have been of [[volcano|volcanic]] origin instead, as the [[Earth]]'s core is rich in iridium, and active volcanoes such as [[Piton de la Fournaise]], in the island of [[Réunion]], are still releasing iridium.<ref>{{cite book |title=The Cretaceous-Tertiary Event and Other Catastrophes in Earth History |author=Ryder, G.; Fastovsky, D. E.; Gartner, S. |publisher=Geological Society of America |year=1996 |isbn=0813723078 |pages=47}}</ref><ref>{{cite journal |author=Toutain, J.-P.; Meyer, G. |year=1989 |title=Iridium-Bearing Sublimates at a Hot-Spot Volcano (Piton De La Fournaise, Indian Ocean) |journal=Geophysical Research Letters |volume=16 |issue=12 |pages=1391–1394}}</ref>

==History==
[[Image:Winged goddess Cdm Paris 392.jpg|thumb|150px|The Greek goddess Iris]]

The discovery of iridium is intertwined with that of [[platinum]] and the other metals of the [[platinum group]]. [[Native metal|Native]] platinum used by ancient Ethiopians<ref name="Egypt">{{cite journal | title = The So-Called 'Platinum' Inclusions in Egyptian Goldwork | first = J. M. | last = Ogden | journal = The Journal of Egyptian Archaeology | volume = 62 | year = 1976 | pages = 138&ndash;144 | url = http://www.jstor.org/stable/3856354 | doi = 10.2307/3856354}}</ref> and by South American
<ref name ="preCol">{{cite journal | journal = Platinum Metals Rev.| year = 1980| volume = 24 | issue = 21 | pages = 70&ndash;79 | title =The Powder Metallurgy of Platinum| first = J. C. | last =Chaston}}</ref> cultures always contained a small amount of the other platinum group metals, including iridium. Platinum reached Europe as ''platina'' ("small silver"), found in the 17th century by the Spanish conquerors in a region today known as [[Department of Chocó]], in [[Colombia]].<ref>{{cite journal |title=The Platinum of New Granada: Mining and Metallurgy in the Spanish Colonial Empire |author=McDonald, M. |journal=Platinum Metals Review |volume=3 |issue=4 |year=959 |pages=140–145 |url=http://www.platinummetalsreview.com/dynamic/article/view/pmr-v3-i4-140-145}}</ref> The discovery that this metal was not an alloy of known elements, but instead a distinct new element, did not occur until 1748.<ref>{{cite book|author=Juan, J.; de Ulloa, A.|year=1748|title=Relación histórica del viage a la América Meridional|volume=1|pages=606 |language=Spanish}}</ref>

Chemists who studied platinum dissolved it in [[aqua regia]] (a mixture of [[hydrochloric acid|hydrochloric]] and [[nitric acid]]s) to create soluble salts. They always observed a small amount of a dark, insoluble residue.<ref name="hunt" /> [[Joseph Louis Proust]] thought that the residue was [[graphite]].<ref name="hunt" /> The French chemists [[Victor Collet-Descotils]], [[Antoine François, comte de Fourcroy]], and [[Louis Nicolas Vauquelin]] also observed the black residue in 1803, but did not obtain enough for further experiments.<ref name="hunt" />

In 1803, British scientist [[Smithson Tennant]] analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternatively with alkali and acids<ref name="Emsley"/> and obtained a volatile new oxide, which he believed to be of this new metal—which he named ''ptene'', from the Greek word πτηνος (ptènos) for winged.<ref>{{cite book |title=A System of Chemistry of Inorganic Bodies |author=Thomson, T. |publisher=Baldwin & Cradock, London; and William Blackwood, Edinburgh |year=1831 |pages=693}}</ref><ref name=griffith>{{cite journal |doi=10.1595/147106704X4844 |title=Bicentenary of Four Platinum Group Metals. Part II: Osmium and iridium – events surrounding their discoveries |author=Griffith, W. P. |journal=Platinum Metals Review |volume=48 |issue=4 |year=2004 |pages=182–189}}</ref> However, Tennant, who had the advantage of a much greater amount of residue, continued his research and identified the two previously undiscovered elements in the black residue, iridium and [[osmium]].<ref name="hunt" /><ref name="Emsley"/> He obtained dark red crystals (probably of {{chem|Na|2|[IrCl|6}}]·''n''{{chem|H|2|O}}) by a sequence of reactions with [[sodium hydroxide]] and [[hydrochloric acid]].<ref name=griffith/> He named iridium after [[Iris (mythology)|Iris]] (Ιρις), the Greek winged goddess of the rainbow and the messenger of the Olympian gods, because many of the [[salts]] he obtained were strongly colored.<ref group="note">''Iridium'' literally means "of rainbows".</ref><ref name="weeks">{{cite book| title = Discovery of the Elements | pages = 414&ndash;418 | author = Weeks, M. E. | year= 1968 | edition = 7 | publisher = Journal of Chemical Education| isbn = 0848685792| oclc = 23991202}}</ref> Discovery of the new elements was documented in a letter to the [[Royal Society]] on June 21, 1804.<ref name="hunt">{{cite journal | title= A History of Iridium | first =L. B. | last =Hunt | journal = Platinum Metals Review| volume =31 | issue = 1 | year = 1987 | url = http://www.platinummetalsreview.com/dynamic/article/view/pmr-v31-i1-032-041 <!-- | accessdate = 2008-09-15 --> | pages= 32&ndash;41}}</ref><ref>{{cite journal | title= On Two Metals, Found in the Black Powder Remaining after the Solution of Platina | first = S. | last = Tennant | journal = Philosophical Transactions of the Royal Society of London | volume = 94 | year =1804| pages= 411&ndash;418 | url = http://www.jstor.org/pss/107152 | doi= 10.1098/rstl.1804.0018}}</ref>

[[John George Children]] was the first to manage to melt a sample of iridium in 1813 with the aid of "the greatest galvanic battery that has ever been constructed" (at that time).<ref name="hunt" /> The first to obtain iridium in a high purity was [[Robert Hare (chemist)|Robert Hare]] in 1842. He found that it had a density of around 21.8&nbsp;g/cm<sup>3</sup> and noted that the metal is nearly unmalleable and very hard. The first melting in appreciable quantity was done by [[Henri Sainte-Claire Deville]] and Jules Henri Debray in 1860. They required burning more than 300&nbsp;L of pure {{chem|O|2}} and {{chem|H|2}} for each kilogram of iridium.<ref name="hunt"/>

These extreme difficulties in melting the metal limited the possibilities for handling iridium. [[John Isaac Hawkins]] was looking to obtain a fine and hard point for fountain pen nibs and in 1834 managed to create an iridium pointed gold pen. In 1880 John Holland and William Lofland Dudley were able to melt iridium by adding [[phosphorus]] and patented the process in the United States; British company [[Johnson Matthey]] later stated that they were using a similar process since 1837 and had already presented fused iridium at a number of [[Expo (exhibition)|World Fairs]].<ref name="hunt"/> The first use of an alloy of iridium with ruthenium in [[thermocouple]]s was made by Otto Feussner in 1933. These allowed for the measurement of high temperatures in air, up to 2000&nbsp;°C.<ref name="hunt"/>

In 1957, [[Rudolf Mössbauer]], in what has been called one of the "landmark experiments in twentieth century physics",<ref>{{cite book |pages=179–190 |title=Landmark Experiments in Twentieth Century Physics |author=Trigg, G. L. |publisher=Courier Dover Publications |isbn=048628526X}}</ref> discovered the resonant and [[recoil]]-free emission and absorption of [[gamma ray]]s by atoms in a solid metal sample containing only <sup>191</sup>Ir.<ref>{{cite journal | first=R. L. | last = Mössbauer | authorlink = Rudolf Mössbauer | title = Gammastrahlung in Ir<sup>191</sup> | journal = Zeitschrift für Physik A Hadrons and Nuclei | volume = 151 | pages = 124&ndash;143 | year = 1958 | language = German | doi = 10.1007/BF01344210}}</ref> This phenomenon, known as the [[Mössbauer effect]], has since been observed for other nuclei, such as [[iron-57|<sup>57</sup>Fe]], and, developed as [[Mössbauer spectroscopy]], has made important contributions to research in physics, chemistry, biochemistry, metallurgy, and mineralogy.<ref name=ir-191>{{cite book |title=Handbook of Ceramics and Composites |author=Chereminisoff, N. P. |publisher=CRC Press |year=1990 |isbn=082478006X |pages=424}}</ref> Mössbauer received the [[Nobel Prize in Physics]] in 1961, just three years after he published his discovery.<ref>{{cite book |title=Nobel Lectures, Physics 1942-1962 |publisher=Elsevier |year=1964 |chapter=The Nobel Prize in Physics 1961: presentation speech| first =I. | last =Waller | url =http://nobelprize.org/nobel_prizes/physics/laureates/1961/press.html}}</ref>

==Production==
<div style="float: right; margin: 5px;">
{|class="wikitable"
!Year !! Price<br />([[United States dollar|$]]/[[troy ounce|oz]])<ref name="usgs2008-summary">{{cite journal |author=George, M. W. |title = Platinum-group metals | journal = U.S. Geological Survey Mineral Commodity Summaries| publisher=USGS Mineral Resources Program | format=pdf| year=2008 |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/mcs-2008-plati.pdf}}</ref><ref>{{cite journal |author=George, M. W. |title = Platinum-group metals | journal = U.S. Geological Survey Mineral Commodity Summaries| publisher=USGS Mineral Resources Program | format=pdf| year=2006 |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/platimcs06.pdf}}</ref>
|-
|2001 || 415.25
|-
|2002 || 294.62
|-
|2003 || 93.02
|-
|2004 || 185.33
|-
|2005 || 169.51
|-
|2006 || 349.45
|-
|2007 || 440.00
|}
</div>
Iridium is obtained commercially as a by-product from [[nickel]] and [[copper]] mining and processing. During [[Copper_extraction_techniques#Electrorefining|electrorefining of copper]] and nickel, noble metals such as silver, gold and the platinum group metals as well as [[selenium]] and [[tellurium]] settle to the bottom of the cell as ''anode mud'', which forms the starting point for the extraction of the platinum group metals.<ref name=usgs2008-summary/><ref name="MinYb2006">{{cite book | url = http://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf |publisher = United States Geological Survey USGS <!-- | accessdate = 2008-09-16 --> | title = 2006 Minerals Yearbook: Platinum-Group Metals| first = M. W. | last = George}}</ref>

[[Image:Ir,77.jpg||left|thumb|Iridium powder]]
After ruthenium and osmium have been removed, iridium is separated by precipitating (NH<sub>4</sub>)<sub>2</sub>IrCl<sub>6</sub> or by extracting [IrCl<sub>6</sub>]<sup>2−</sup> with organic amines. The first method is similar to the procedure Tennant and Wollastone used for their separation. The second method can be planned as continuous [[liquid–liquid extraction]] and is therefore more suitable for industrial scale production. In either case, the product is reduced using hydrogen, yielding the metal as a powder or sponge that can be treated using [[powder metallurgy]] techniques.<ref>{{cite journal | title =Processing of Iridium and Iridium Alloys | first = E. K. | last = Ohriner | journal = Platinum Metals Review | volume = 52 | issue = 3 | year = 2008 | pages = 186&ndash;197 | doi =10.1595/147106708X333827}}</ref><ref>{{cite journal | first = L. B. | last = Hunt | coauthors = Lever, F. M. | journal = Platinum Metals Review | volume = 13 | issue = 4 | year = 1969 | pages = 126&ndash;138 | title = Platinum Metals: A Survey of Productive Resources to industrial Uses | url = http://www.platinummetalsreview.com/pdf/pmr-v13-i4-126-138.pdf | accessdate =<!-- 2008-10-02 -->}}</ref>

Annual production of iridium circa 2000 was around 3&nbsp;[[tonne]]s or about 100,000&nbsp;[[troy ounce]]s.<ref group="note">Like other precious metals, iridium is customarily traded in troy ounces, which are equivalent to about 31.1&nbsp;grams.</ref><ref name="Emsley"/> The price of iridium as of 2007 was $440&nbsp;USD/oz,<ref name="usgs2008-summary" /> but the price fluctuates considerably, as shown in the table. The high [[volatility (finance)|volatility]] of the prices of the platinum group metals has been attributed to supply, demand, [[speculation]], and hoarding, amplified by the small size of the market and instability in the producing countries.<ref>{{cite journal |author=Hagelüken, C. |journal=Metall |volume=60 |issue=1–2 |year=2006 |pages=31–42 |title=Markets for the catalysts metals platinum, palladium, and rhodium |url=http://www.preciousmetals.umicore.com/publications/articles_by_umicore/general/show_Metal_PGMmarkets_200602.pdf}} </ref>

==Applications==

The global demand for iridium in 2007 was 119,000&nbsp;[[troy ounce]]s (3,700&nbsp;kg), out of which 25,000 oz&nbsp;(780&nbsp;kg) were used for electrical applications such as spark plugs; 34,000&nbsp;oz (1,100&nbsp;kg) for electrochemical applications such as electrodes for the [[chloralkali process]]; 24,000&nbsp;oz (750&nbsp;kg) for catalysis; and 36,000&nbsp;oz (1,100&nbsp;kg) for other uses.<ref name="platinum2008">{{cite book | first = D. | last = Jollie | title=Platinum 2008 |publisher=Johnson Matthey |date=May 2008 | ISSN = 0268-7305 |url=http://www.platinum.matthey.com/uploaded_files/Pt2008/08_complete_publication.pdf| format = pdf}}</ref>

===Industrial===
The high melting point, hardness and corrosion resistance of iridium and its alloys determine most of its applications. Iridium and especially iridium–platinum alloys or osmium–iridium alloys have a low wear and are used for example for multi-pored [[spinneret#Other uses of the word|spinnerets]], through which a plastic polymer melt is extruded to form fibers, such as [[rayon]].<ref>{{cite journal |title= Spinnerets for viscose rayon cord yarn | journal = Fibre Chemistry | volume =10 | issue = 4 | year = 1979 | doi = 10.1007/BF00543390 | pages = 377–378 | first = R. V. | last = Egorova | coauthors = Korotkov, B. V.; Yaroshchuk, E. G.; Mirkus, K. A.; Dorofeev N. A.; Serkov, A. T.}}</ref> Osmium–iridium is used for [[compass]] bearings and for balances.<ref>{{cite web | url = http://www.rsc.org/chemsoc/visualelements//PAGES/pdf/iridium.PDF | title = Iridium |publisher = Royal Society of Chemistry | work = Visual Elements Periodic Table | format = PDF | author = Emsley, J. | date = 2005-01-18 | accessdate = 2008-09-17}}</ref>

Corrosion and heat resistance makes iridium an important alloying agent. Certain long-life aircraft engine parts are made of an iridium alloy and an iridium–[[titanium]] alloy is used for deep-water pipes because of its corrosion resistance.<ref name="Emsley"/> Iridium is also used as a hardening agent in platinum alloys. The [[Vickers hardness]] of pure platinum is 56&nbsp;HV while platinum with 50% of iridium can reach over 500&nbsp;HV.<ref>{{cite journal | url = http://www.platinummetalsreview.com/pdf/pmr-v4-i1-018-026.pdf | journal = Platinum Metals Review | title = Iridium Platinum Alloys | first = A. S. |last = Darling | year = 1960 | volume =4| issue =l | pages = 18&ndash;26}}</ref><ref>{{cite journal |doi = 10.1595/147106705X24409 | title = The Hardening of Platinum Alloys for Potential Jewellery Application| first = T. |last = Biggs| coauthors= Taylor, S. S.; van der Lingen, E.| journal = Platinum Metals Review | year = 2005 | volume = 49 | issue = 1 | pages = 2&ndash;15}}</ref>

Devices that must withstand extremely high temperatures are often made from iridium. For example, high-temperature [[crucible]]s made of iridium are used in the [[Czochralski process]] to produce oxide single-crystals (such as [[sapphire]]s) for use in computer memory devices and in solid state lasers.<ref>{{cite journal |title= On the Use of Iridium Crucibles in Chemical Operations | first = W. | last = Crookes |authorlink=William Crookes| journal = Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character| volume = 80 | issue = 541 | year = 1908 | pages = 535&ndash;536 | url = http://www.jstor.org/pss/93031 |doi= 10.1098/rspa.1908.0046}}</ref><ref name="Handley">{{cite journal |title= Increasing Applications for Iridium | first = J. R. | last = Handley | journal = Platinum Metals Review | volume = 30 | issue = 1 | year = 1986 | pages = 12&ndash;13 | url = http://www.platinummetalsreview.com/dynamic/article/view/pmr-v30-i1-012-013}}</ref> The crystals, such as [[gadolinium gallium garnet]] and [[yttrium gallium garnet]], are grown by melting pre-sintered charges of mixed oxides under oxidizing conditions at temperatures up to 2100 <sup>o</sup>C.<ref name="hunt" /> Its resistance to [[arc erosion]] makes iridium alloys ideal for electrical contacts for [[spark plug]]s).<ref name="Handley"/><ref>{{cite book | url = http://books.google.de/books?hl=de&lr=&id=I03qepnj2IwC | title = Euromat 99 | author = Stallforth, H.; Revell, P. A. | publisher= Wiley-VCH | year = 2000}}</ref>

Iridium compounds are used as [[catalysis|catalysts]] in the [[Cativa process]] for [[carbonylation]] of [[methanol]] to produce [[acetic acid]].<ref name="ullmann-acetic">{{cite book |first=H. |last= Cheung |coauthors = Tanke, R. S.; Torrence, G. P.|chapter=Acetic acid |title=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley |year=2000 |doi=10.1002/14356007.a01_045}}</ref> Iridium itself is used as a catalyst in a type of automobile engine introduced in 1996 called the [[direct-ignition engine]].<ref name="Emsley"/>

Iridium is commonly used in [[Complex (chemistry)|complex]]es like Ir(mppy)<sub>3</sub> and other complexes in [[organic light emitting diode]] technology to increase the efficiency from 25% to almost 100% due to [[triplet harvesting]].<ref>{{cite journal |title = Electrophosphorescence from substituted poly(thiophene) doped with iridium or platinum complex | doi = 10.1016/j.tsf.2004.05.095| year = 2004 | journal = Thin Solid Films | volume = 468 | issue = 1–2| pages = 226&ndash;233 | first = X. | last = Wang| coauthors = Andersson, M. R.; Thompson, M. E.; Inganäsa, O. }}</ref> One of the major uses for these family of complexes have been the [[flat panel display]]s that are found in televisions or monitors.<ref>{{cite web|url=http://sa.rochester.edu/jur/issues/fall2002/tonzetich.pdf|title=Organic Light Emitting Diodes|publisher=Rochester University}}</ref><ref>{{cite journal| title=New Trends in the Use of Transition Metal-Ligand Complexes for Applications in Electroluminescent Devices | author = Holder, E. |coauthors = Langefeld, B. M. W.; Schubert, U. S. | publisher =<!-- WILEY-VCH Verlag GmbH & Co. --> | journal = Advanced Materials | volume = 17 | issue = 9 | pages = 1109&ndash;1121 | date = 2005-04-25 | accessdate =<!-- 2008-09-28 --> |doi=10.1002/adma.200400284}}</ref>

===Scientific and medical===
[[Image:Platinum-Iridium meter bar.jpg| right | thumb | International prototype meter bar]]
An alloy of 90% platinum and 10% iridium was used in 1889 to construct the prototype [[Metre#Prototype_metre_bar|meter bar]] and [[kilogram]] mass, kept by the [[Bureau International des Poids et Mesures|International Bureau of Weights and Measures]] near [[Paris]].<ref name="Emsley"/> The meter bar was replaced as the definition of the fundamental unit of length in 1960 by a line in the [[atomic spectrum]] of [[Krypton#Metric_role|krypton]],<ref group="note">The definition of the meter was changed again in 1983. The meter is currently defined as the distance traveled by light in a vacuum during a time interval of {{frac|299,792,458}} of a second.</ref> but the kilogram prototype is still the international standard of mass.<ref name="meter">{{cite web | url=http://www.mel.nist.gov/div821/museum/timeline.htm | publisher = NIST |first =W. B. | last = Penzes |title=Time Line for the Definition of the Meter |year=2001 |accessdate=2008-09-16}}</ref>

Iridium has been used in the [[radioisotope thermoelectric generator]]s of unmanned spacecraft such as the ''[[Voyager program|Voyager]]'', ''[[Viking program|Viking]]'', ''[[Pioneer program|Pioneer]]'', ''[[Cassini-Huygens|Cassini]]'', ''[[Galileo (spacecraft)|Galileo]]'', and ''[[New Horizons]]''. Iridium was chosen to encapsulate the [[plutonium-238]] fuel in the generator because it can withstand the operating temperatures of up to 2000&nbsp;°C and for its great strength.<ref name="hunt"/>

Another use in astronomy concerns X-ray telescopes. The mirrors of the [[Chandra X-ray Observatory]] are coated with a layer of iridium 60&nbsp;[[nanometer|nm]] thick. Iridium proved to be the best choice for reflecting X-rays after nickel, gold, and platinum were tested. The iridium layer, which had to be smooth to within a few atoms, was applied by depositing iridium vapor under [[high vacuum]] on a base layer of chromium.<ref>{{cite web |title=Face-to-Face with Jerry Johnston, CXC Program Manager & Bob Hahn, Chief Engineer at Optical Coating Laboratories, Inc., Santa Rosa, CA |publisher=Harvard-Smithsonian Center for Astrophysics; Chandra X-ray Center |url=http://chandra.harvard.edu/press/bios/johnston.html |accessdate=2008-09-24 |year=1995}}</ref>

Iridium is used in [[particle physics]] for the production of [[antiproton]]s, a form of [[antimatter]]. Antiprotons are made by shooting a high-intensity proton beam at a ''conversion target'', which needs to be made from a very high density material. Although [[tungsten]] may also be used, iridium has the advantage of better stability under the [[shock wave]]s induced by the temperature rise due to the incident beam.<ref>{{cite journal |title = Production of low-energy antiprotons | journal =Zeitschrift Hyperfine Interactions | volume =109| year = 1997 |doi = 10.1023/A:1012680728257 | pages = 33&ndash;41 | first = D. | last =Möhl}}</ref>

[[Image:CHactivationGraham1982.svg|450px|left |thumb|An example of oxidative addition to hydrocarbons discovered in 1982 (Cp* = [[pentamethylcyclopentadienyl]])<ref>{{cite journal |title=Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex |author=Hoyano, J. K.; Graham, W. A. G. |journal=Journal of the American Chemical Society |year=1982 |volume=104 |issue=13 |pages=3723–3725 |doi=10.1021/ja00377a032}}</ref>]]
[[C-H bond activation|Carbon–hydrogen bond activation]] (C–H activation) is an active area of research that investigates reactions that cleave [[carbon–hydrogen bond]]s, a type of bond traditionally regarded as unreactive. The first reported successes at activating C–H bonds in [[saturated hydrocarbon]]s, published in 1982,<ref>{{cite journal |title=Carbon-hydrogen activation in completely saturated hydrocarbons: direct observation of M + R-H -> M(R)(H) |author=Janowicz, A. H.; Bergman, R. G. |journal=Journal of the American Chemical Society |year=1982 |volume=104 |issue=1 |pages=352–354 |doi=10.1021/ja00365a091}}</ref> used organometallic iridium complexes that undergo an [[oxidative addition]] with the hydrocarbon.

Iridium complexes are also being investigated as catalysts for [[asymmetric hydrogenation]]. These catalysts have been used in the synthesis of [[natural product]]s and able to hydrogenate certain difficult substrates, such as unfunctionalized alkenes, enantioselectively.<ref>{{cite journal |doi=10.1002/chem.200500755 |year=2006 |author=Källström, K; Munslow, I; Andersson, P. G. |title=Ir-catalysed asymmetric hydrogenation: Ligands, substrates and mechanism |volume=12 |issue=12 |pages=3194–3200 |pmid=16304642 |journal=Chemistry – A European Journal}}</ref><ref>{{cite journal |doi=10.1021/ar700113g |year=2007 |author=Roseblade, S. J.; Pfaltz, A. |title=Iridium-catalyzed asymmetric hydrogenation of olefins |volume=40 |issue=12 |pages=1402–1411 |pmid=17672517 |journal=[[Accounts of Chemical Research]]}}</ref>

The radioisotope [[iridium-192]] is used as a [[radiography]] source for non-destructive testing of materials.<ref>{{cite journal |title= The use and scope of Iridium 192 for the radiography of steel | first = R. | last = Halmshaw | year = 1954 | journal = Br. J. Appl. Phys. | volume = 5 | pages = 238&ndash;243 | doi = 10.1088/0508-3443/5/7/302}}</ref> Additionally, <sup>192</sup>Ir is used as a source of [[gamma-ray]] radioactivity for the treatment of cancer using [[brachytherapy]], a form of radiotherapy where a sealed radioactive source is placed inside or next to the area requiring treatment. Specific treatments include high dose rate prostate brachytherapy, bilary duct brachytherapy, and intracavitary cervix brachytherapy.<ref name="Emsley"/>

===Historical===
[[Image:Fountain-pen-nib.jpg| right|150px | thumb | Fountain pen nib labeled ''Iridium Point'']]
Iridium–osmium alloys were used to tip [[fountain pen]] nibs. The first major use of iridium was in 1834 in nibs mounted on gold.<ref name="hunt" /> Since 1944, the famous [[Parker 51]] fountain pen was fitted with a nib tipped a ruthenium and iridium alloy (with 3.8% iridium). The tip material in modern fountain pens is still conventionally called "iridium," although there is seldom any iridium in it; other metals such as tungsten have taken its place.<ref>{{cite journal |url=http://www.pencollectors.com/nib-corner.html |journal=The PENnant |volume=XIII |issue=2 |year=1999 |title=Notes from the Nib Works—Where's the Iridium? |author=Mottishaw, J.}}</ref>

An iridium–platinum alloy was used for the [[touch hole]]s or vent pieces of [[cannon]]s. According to a report of the [[Exposition Universelle (1867)|Paris Exhibition of 1867]], one of the pieces being exhibited by [[Johnson and Matthey]] "has been used in a Withworth gun for more than 3000 rounds, and scarcely shows signs of wear yet. Those who know the constant trouble and expense which are occasioned by the wearing of the vent-pieces of cannon when in active service, will appreciate this important adaptation".<ref>{{cite journal |editor=Crookes, W. |volume=XV |year=1867 |journal=The Chemical News and Journal of Physical Science |title=The Paris Exhibition |pages=182 | doi=<!--This comment stops DOI bot adding the incorrect DOI-->}}</ref>

The pigment ''iridium black'', which consists of very finely divided iridium, is used for painting [[porcelain]] an intense black; it was said that "all other porcelain black colors appear grey by the side of it".<ref>{{cite book |title=The Playbook of Metals: Including Personal Narratives of Visits to Coal, Lead, Copper, and Tin Mines, with a Large Number of Interesting Experiments Relating to Alchemy and the Chemistry of the Fifty Metallic Elements |author=Pepper, J. H. |publisher=Routledge, Warne, and Routledge |year=1861 |pages=455}}</ref>

==Precautions==
Iridium in bulk metallic form is not biologically important or hazardous to health due to its lack of reactivity with tissues; there are only about 20&nbsp;[[parts per notation|parts per trillion]] of iridium in human tissue.<ref name="Emsley"/> However, finely divided iridium powder can be hazardous to handle, as it is an irritant and may ignite in air.<ref name="kirk-pt">{{cite book |title=Kirk Othmer Encyclopedia of Chemical Technology |first =R. J. | last = Seymour | coauthors = O'Farrelly, J. I. |chapter=Platinum-group metals |doi=10.1002/0471238961.1612012019052513.a01.pub2 |year=2001 |publisher=Wiley}}</ref>
Very little is known about the toxicity of iridium compounds because they are used in very small amounts, but soluble salts, such as the iridium halides, could be hazardous due to elements other than iridium or due to iridium itself.<ref name="mager"/> However, most iridium compounds are insoluble, which makes absorption into the body difficult.<ref name="Emsley"/>

A radioisotope of iridium, <sup>192</sup>Ir, is dangerous like other radioactive isotopes. The only reported injuries related to iridium concern accidental exposure to radiation from <sup>192</sup>Ir used in brachytherapy.<ref name="mager">{{cite book |title=Encyclopaedia of Occupational Health and Safety |first =J. | last = Mager Stellman | coauthors = |chapter=Iridium |isbn=9789221098164 |year=1998|publisher=International Labour Organization| pages =63.19 | url = http://books.google.de/books?id=nDhpLa1rl44C |oclc=35279504 45066560}}</ref> High-energy gamma radiation from <sup>192</sup>Ir can increase the risk of cancer. External exposure can cause burns, [[radiation poisoning]], and death. Ingestion of <sup>192</sup>Ir can burn the linings of the stomach and the intestines.<ref>{{cite web| title = Radioisotope Brief: Iridium-192 (Ir-192)| work = Radiation Emergencies| publisher = Center for Disease Control and Prevention| date = 2004-08-18| url = http://emergency.cdc.gov/radiation/isotopes/pdf/iridium.pdf| format = [[PDF]]| accessdate = 2008-09-20}}</ref> <sup>192</sup>Ir, <sup>192m</sup>Ir, and <sup>194m</sup>Ir tend to deposit in the [[liver]], and can pose health hazards from both gamma and beta radiation.<ref name="argonne">{{cite web| title = Iridium| work = Human Health Fact Sheet| publisher = Argonne National Laboratory| date = March 2005| url = http://www.ead.anl.gov/pub/doc/Iridium.pdf| format = PDF| accessdate = 2008-09-20}}</ref>

==Notes==
<references group="note" />

==References==
{{reflist|2}}

==External links==
{{Commons|Iridium}}
{{wiktionary|iridium}}

{{clear}}
{{Compact periodic table}}

<!--Categories-->
[[Category:Chemical elements]]
[[Category:Precious metals]]
[[Category:Transition metals]]
[[Category:Meteorite minerals]]
[[Category:Impact event minerals]]
[[Category:Iridium|*]]

<!--Interwiki-->
[[ar:إريديوم]]
[[bn:ইরিডিয়াম]]
[[be:Ірыдый]]
[[bs:Iridijum]]
[[ca:Iridi]]
[[cs:Iridium]]
[[co:Iridiu]]
[[cy:Iridiwm]]
[[da:Iridium]]
[[de:Iridium]]
[[et:Iriidium]]
[[el:Ιρίδιο]]
[[es:Iridio]]
[[eo:Iridio]]
[[eu:Iridio]]
[[fa:ایریدیوم]]
[[fr:Iridium]]
[[fur:Iridi]]
[[gv:Iriddjum]]
[[gl:Iridio]]
[[ko:이리듐]]
[[hy:Իրիդիում]]
[[hr:Iridij]]
[[io:Iridio]]
[[id:Iridium]]
[[ia:Iridium]]
[[is:Iridín]]
[[it:Iridio]]
[[he:אירידיום]]
[[jv:Iridium]]
[[kn:ಇರಿಡಿಯಮ್]]
[[ht:Iridyòm]]
[[ku:Îrîdyûm]]
[[la:Iridium]]
[[lv:Irīdijs]]
[[lb:Iridium]]
[[lt:Iridis]]
[[li:Iridium]]
[[jbo:jinmrdiridi]]
[[hu:Irídium]]
[[ml:ഇറിഡിയം]]
[[mr:इरिडियम]]
[[nl:Iridium (element)]]
[[ja:イリジウム]]
[[no:Iridium]]
[[nn:Iridium]]
[[oc:Iridi]]
[[pl:Iryd]]
[[pt:Irídio]]
[[ro:Iridiu]]
[[ru:Иридий]]
[[scn:Irìdiu]]
[[simple:Iridium]]
[[sk:Irídium]]
[[sl:Iridij]]
[[sr:Иридијум]]
[[sh:Iridijum]]
[[fi:Iridium]]
[[sv:Iridium]]
[[ta:இரிடியம்]]
[[th:อิริเดียม]]
[[vi:Iridi]]
[[tr:İridyum]]
[[uk:Іридій]]
[[zh:铱]]

Revision as of 14:24, 12 October 2008

The Outer Ring Road in Tianjin, China is a city express road, 71.322 kilometres in length, which encircles Tianjin municipality.

Although its distance markers indicate its status as an expressway-grade road, it is not, strictly speaking, an expressway, as it has at-grade crossings, a low speed limit (60 km/h or 80 km/h), and even traffic lights.

The Jinghu, Jinbin, Jingjintang, Baojin and Jinji Expressways are all linked by this ring road. Major China National Highways and roads to Zibo, Tangshan, Wuxi and other nearby localities, as well as to other regions in the municipality, are also linked.

Retrieved from "https://en.wikipedia.org/w/index.php?title=Iridium&oldid=244777838"