Chromium 5669 225275576 2008-07-12T20:57:07Z SmackBot 433328 Date the maintenance tags or general fixes {{Infobox chromium}} '''Chromium''' ({{pronEng|ˈkroʊmiəm}}) is a [[chemical element]] which has the symbol '''Cr''' and [[atomic number]] 24. It is a steel-gray, [[Lustre (mineralogy)|lustrous]], hard [[metal]] that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable. Chromium was named after the Greek word "Chrôma" meaning [[color]], because of the many colorful compounds made from it.{{Fact|date=July 2008}} == History == On [[26 July]] [[1761]], [[Johann Gottlob Lehmann]] found an orange-red mineral in the [[Ural Mountains]] which he named ''Siberian red lead''. Though misidentified as a [[lead]] compound with [[selenium]] and [[iron]] components, the material was in fact ''lead chromate'' with a formula of PbCrO<sub>4</sub>, now known as the mineral [[crocoite]]. In 1770, [[Peter Simon Pallas]] visited the same site as Lehmann and found a red "lead" mineral that had very useful properties as a [[pigment]] in [[paint]]s. The use of Siberian red lead as a paint pigment developed rapidly. A bright [[yellow]] made from crocoite also became fashionable. In 1797, [[Louis Nicolas Vauquelin]] received samples of crocoite [[ore]]. He was able to produce [[chromium oxide]] with a chemical formula of CrO<sub>3</sub>, by mixing crocoite with [[hydrochloric acid]]. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious [[gemstone]]s, such as [[ruby]], or [[emerald]]. Later that year he successfully isolated elemental chromium. During the 1800s chromium was primarily used as a component of paints and in [[tanning]] salts but now metal alloys account for 85% of the use of chromium. The remainder is used in the [[chemical industry]] and [[refractory]] and [[foundry]] industries. A multitude of weapons found in the late 3rd century BC [[Qin Dynasty]] burial pits of the [[Terracotta Army]] near [[Xi'an]], [[China]] have been analyzed by archaeologists. Remarkably, after more than 2,000 years, the ancient bronze tips of [[crossbow]] bolts found at the site showed no sign of corrosion over time, the reason being that the Qin era Chinese had coated the bronze in chromium.<ref>Cotterell, Maurice. (2004). ''The Terracotta Warriors: The Secret Codes of the Emperor's Army''. Rochester: Bear and Company. ISBN 159143033X. Page 102.</ref> == Occurrence and production== [[Image:Chromium - world production trend.svg|thumb|left|World production trend]] Chromium is mined as [[chromite]] (FeCr<sub>2</sub>O<sub>4</sub>) ore. About two-fifths of the chromite ores and concentrates in the world are produced in [[South Africa]], while [[Kazakhstan]], [[India]], [[Russia]], and [[Turkey]] are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa. Approximately 15 million tons of marketable chromite ore were produced in 2000, and converted into approximately 4 million tons of ferro-chrome with an approximate market value of 2.5 billion [[United States dollar]]s. Though native chromium deposits are rare, some native chromium metal has been discovered. The Udachnaya Mine in [[Russia]] produces samples of the native metal. This mine is a [[kimberlite]] pipe rich in diamonds, and the reducing environment so provided helped produce both elemental chromium and diamond. (See also [[:category:Chromium minerals|chromium minerals]]) Chromium is obtained commercially by heating the [[ore]] in the presence of [[aluminium]] or [[silicon]]. ==Chemical properties== [[Image:Chrom 1.jpg|thumb|left|Chromium]] Chromium is a member of the [[transition metal]]s, in group 6. Chromium(0) has an electronic configuration of 4s<sup>1</sup>3d<sup>5</sup>, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common [[oxidation state]]s of chromium are +2, +3, and +6, with +3 being the most stable. +1, +4 and +5 are rare. Chromium compounds of oxidation state +6 are powerful oxidants. Chromium is [[passivation|passivated]] by oxygen, forming a thin (usually a few atoms thick being transparent because of thickness) protective oxide surface layer with another element such as nickel, and/or iron. It forms a compound called a [[spinel]] structure which, being very dense, prevents diffusion of oxygen into the underlying layer. (In iron or plain carbon steels the oxygen actually migrates into the underlying material.) Chromium is usually plated on top of a nickel layer which may or may not have been copper plated first. Chromium as opposite to most other metals such as iron and nickel does not suffer from [[hydrogen embrittlement]]. It does though suffer from nitrogen embrittlement and hence no straight chromium alloy has ever been developed. Below the [[pourbaix diagram]] can be seen, it is important to understand that the diagram only displays the thermodynamic data and it does not display any details of the rates of reaction. [[Image:Chromium in water pourbiax diagram.png|thumb|left|240px|The [[Pourbaix diagram]] for chromium in pure water, perchloric acid or sodium hydroxide<ref name="medusa">Ignasi Puigdomenech, ''Hydra/Medusa Chemical Equilibrium Database and Plotting Software'' (2004) KTH Royal Institute of Technology, freely downloadable software at [http://www.kemi.kth.se/medusa/]</ref>]] == Compounds == {{main|:Category:Chromium compounds|l1=Chromium compounds}} [[Potassium dichromate]] is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any trace organics. It is used as a saturated solution in concentrated sulfuric acid for washing the apparatus. For this purpose, however, [[sodium dichromate]] is sometimes used because of its higher solubility (5 g/100 ml vs. 20 g/100 ml respectively). [[Chrome green]] is the green oxide of chromium, Cr<sub>2</sub>O<sub>3</sub>, used in [[enamel paint]]ing, and glass staining. [[Chrome yellow]] is a brilliant yellow pigment, PbCrO<sub>4</sub>, used by painters. [[Chromic acid]] has the hypothetical structure H<sub>2</sub>CrO<sub>4</sub>. Neither chromic nor dichromic acid is found in nature, but their anions are found in a variety of compounds. Chromium trioxide, CrO<sub>3</sub>, the acid [[anhydride]] of chromic acid, is sold industrially as "chromic acid". === Chromium and the quintuple bond === [[Image:5-fold chromium.png|left|thumb|The compound synthesized by Nguyen, which was determined experimentally to contain a Cr-Cr quintuple bond]] Chromium is notable for its ability to form quintuple [[covalent bond]]s. The synthesis of a compound of chromium(I) and a [[hydrocarbon]] [[Radical (chemistry)|radical]] was shown via [[X-ray diffraction]] to contain a [[quintuple bond]] of length 183.51(4) pm (1.835 angstroms) joining the two central chromium atoms.<ref>{{cite journal | author = T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long and P. P. Power | title = Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers | year = 2005 | journal = [[Science (journal)|Science]] | volume = 310 | issue = 5749 | pages = 844–847 | doi =10.1126/science.1116789 | pmid = 16179432}}</ref> This was accomplished through the use of an extremely bulky monodentate ligand which through its sheer size prevents further coordination. Chromium currently remains the only element for which [[quintuple bond]]s have been observed. {{-}} == Applications == Uses of chromium: * In [[metallurgy]], to impart corrosion resistance and a shiny finish: ** as an [[alloy]] constituent, such as in [[stainless steel]] in [[cutlery]] ** in [[chrome plating]], ** in [[anodising|anodized]] [[aluminium]], literally turning the surface of aluminium into [[ruby]]. * As dyes and [[paint]]s: ** [[Chromium(III) oxide]] is a metal polish known as [[green rouge]]. ** Chromium salts color glass an [[emerald]] green. ** Chromium is what makes a [[ruby]] red, and therefore is used in producing synthetic rubies. ** also makes a brilliant yellow for painting * As a [[catalyst]]. * [[Chromite]] is used to make molds for the firing of [[brick]]s. * Chromium salts are used in the [[tanning]] of [[leather]]. * Potassium dichromate is a chemical [[reagent]], used in cleaning [[laboratory glassware]] and as a titrating agent. It is also used as a [[mordant]] (i.e., a fixing agent) for dyes in fabric. * [[Chromium(IV) oxide]] (CrO<sub>2</sub>) is used to manufacture [[magnetic tape]], where its higher [[coercivity]] than [[iron]] oxide tapes gives better performance. * In well drilling muds as an anti-corrosive. * In medicine, as a dietary supplement or slimming aid, usually as chromium(III) chloride, [[chromium(III) picolinate]], [[chromium(III) polynicotinate]] or as an amino acid chelate, such as [[chromium(III) D-phenylalanine]].<ref>[http://www.freepatentsonline.com/7271278.html United States Patent 7271278]</ref> * [[Chromium hexacarbonyl]] (Cr(CO)<sub>6</sub>) is used as a [[gasoline]] additive. * Chromium boride (CrB) is used as a high-temperature electrical conductor. * Chromium(III) sulfate (Cr<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) is used as a green [[pigment]] in [[paint]]s, in [[ceramic]], [[varnish]]es and [[ink]]s as well as in [[chrome plating]]. * Chromium(VI) is used in the post Ballard preparation of Gravure (rotogravure) printing Forme Cylinders. By electroplating the metal onto the second coat of copper (after the Ballard skin), the longevity of the printing cylinder is increased. == Biological role == Trivalent chromium (Cr(III), or Cr<sup>3+</sup>) is required in trace amounts for [[sugar]] [[metabolism]] in humans ([[GTF|Glucose Tolerance Factor]]) and its deficiency may cause a disease called [[chromium deficiency]]. In contrast, [[hexavalent chromium]] is very toxic and [[mutagen]]ic when inhaled as publicized by the film [[Erin Brockovich (film)|Erin Brockovich]]. Cr(VI) has not been established as a carcinogen when not inhaled but in solution it is well established as a cause of allergic [[contact dermatitis]] (ACD).<ref>{{cite web| publisher = Agency for Toxic Substances & Disease Registry, [[Centers for Disease Control and Prevention]] | title = ToxFAQs: Chromium | url = http://www.atsdr.cdc.gov/tfacts7.html | date = February 2001|accessdate=2007-10-02}}</ref> Recently it was shown that the popular dietary supplement [[chromium picolinate]] complex generates chromosome damage in hamster cells. In the United States the dietary guidelines for daily chromium uptake were lowered from 50-200 [[microgram|µg]] for an adult to 35 µg (adult male) and to 25 µg (adult female).<ref>{{cite journal | author = Vincent, J.B. | year = 2007 | title = Recent advances in the nutritional biochemistry of trivalent chromium | journal = Proceedings of the Nutrition Society | volume = 63 | issue = 01 | pages = 41–47 | doi = 10.1079/PNS2003315 }}</ref> == Isotopes == {{main|Isotopes of chromium}} Naturally occurring chromium is composed of three stable [[isotope]]s; <sup>52</sup>Cr, <sup>53</sup>Cr, and <sup>54</sup>Cr with <sup>52</sup>Cr being the most abundant (83.789% [[natural abundance]]). Nineteen [[radioisotope]]s have been characterized with the most stable being <sup>50</sup>Cr with a [[half-life]] of (more than) 1.8x10<sup>17</sup> years, and <sup>51</sup>Cr with a half-life of 27.7 days. All of the remaining [[radioactive]] isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 [[meta state]]s. <sup>53</sup>Cr is the [[radiogenic]] decay product of <sup>53</sup>[[manganese|Mn]]. Chromium [[isotope|isotopic]] contents are typically combined with [[manganese]] isotopic contents and have found application in [[isotope geology]]. [[manganese|Mn]]-Cr isotope ratios reinforce the evidence from <sup>26</sup>[[Aluminium|Al]] and <sup>107</sup>[[Palladium|Pd]] for the early history of the [[solar system]]. Variations in <sup>53</sup>Cr/<sup>52</sup>Cr and Mn/Cr ratios from several meteorites indicate an initial <sup>53</sup>Mn/<sup>55</sup>Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of <sup>53</sup>Mn in differentiated planetary bodies. Hence <sup>53</sup>Cr provides additional evidence for [[nucleosynthesis|nucleosynthetic]] processes immediately before coalescence of the solar system. The isotopes of chromium range in [[atomic weight]] from 43 [[atomic mass unit|u]] (<sup>43</sup>Cr) to 67 u (<sup>67</sup>Cr). The primary [[decay mode]] before the most abundant stable isotope, <sup>52</sup>Cr, is [[electron capture]] and the primary mode after is [[beta decay]]. == Precautions == Chromium metal and chromium(III) compounds are not usually considered health hazards; chromium is an essential trace mineral.<ref>{{cite web | publisher = Wellness Letter | title = Chromium | url = http://www.berkeleywellness.com/html/ds/dsChromium.php}}</ref> However, [[hexavalent chromium]] (chromium VI) compounds can be [[toxic]] if orally ingested or inhaled. The lethal dose of poisonous chromium (VI) compounds is about one half teaspoon of material. Most chromium (VI) compounds are irritating to eyes, skin and mucous membranes. Chronic exposure to chromium (VI) compounds can cause permanent eye injury, unless properly treated. Chromium(VI) is an established human [[carcinogen]]. An investigation into hexavalent chromium release into drinking water formed the plot of the motion picture [[Erin Brockovich (film)|Erin Brockovich]]. [[World Health Organization]] recommended [[maximum allowable concentration]] in drinking water for chromium (VI) is 0.05 [[milligram]]s per [[liter]]. Hexavalent chromium is also one of the substances whose use is restricted by the European [[Restriction of Hazardous Substances Directive]]. Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives. Contact with products containing chromates leads to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers. <ref>{{cite web | publisher = DermNet NZ | title = Chrome Contact Allergy | url = http://dermnetnz.org/dermatitis/chrome-allergy.html}}</ref> As chromium compounds were used in [[dye]]s and [[paint]]s and the [[tanning]] of [[leather]], these compounds are often found in soil and [[groundwater]] at abandoned industrial sites, now needing [[environmental cleanup]] and [[remediation]] per the treatment of [[brownfield land]]. [[Primer (paint)|Primer paint]] containing hexavalent chromium is still widely used for [[aerospace]] and [[automobile]] refinishing applications. == See also == * [[:category:Chromium compounds|Chromium compounds]] * [[:Category:Chromium minerals|Chromium minerals]] * [[Chromium VI]] == References == * [http://periodic.lanl.gov/elements/24.html Los Alamos National Laboratory - Chromium] * [http://www.webelements.com/webelements/elements/text/Cr/index.html WebElements.com &ndash; Chromium] {{reflist}} == External links == {{Commons|Chromium}} {{wiktionary|chromium}} * [http://www-cie.iarc.fr/htdocs/monographs/vol49/chromium.html IARC Monograph "Chromium and Chromium compounds"] * [http://www.chromium-asoc.com/ International Chromium Development Association] * [http://education.jlab.org/itselemental/ele024.html It's Elemental &ndash; The Element Chromium] * [http://www.npi.gov.au/database/substance-info/profiles/24.html National Pollutant Inventory - Chromium (III) compounds fact sheet] * [http://www.merck.com/pubs/mmanual/section1/chapter4/4f.htm The Merck Manual &ndash; Mineral Deficiency and Toxicity] * [http://www.cdc.gov/niosh/topics/chromium/ National Institute for Occupational Safety and Health - Chromium Page] {{clear}} {{compact periodic table}} [[Category:Chemical elements]] [[Category:Transition metals]] [[Category:Chromium|*]] [[Category:Dietary minerals]] [[Category:Occupational safety and health]] <!-- interwiki --> [[af:Chroom]] [[ar:كروم]] [[ast:Cromu (elementu)]] [[az:Xrom]] [[bn:ক্রোমিয়াম]] [[be:Хром]] [[bs:Hrom]] [[bg:Хром]] [[ca:Crom]] [[cs:Chróm]] [[co:Cromu]] [[da:Krom]] [[de:Chrom]] [[et:Kroom]] [[el:Χρώμιο]] [[es:Cromo]] [[eo:Kromo]] [[eu:Kromo]] [[fa:کروم]] [[fr:Chrome]] [[fur:Crom]] [[gv:Cromium]] [[gl:Cromo]] [[ko:크로뮴]] [[hy:Քրոմ]] [[hi:क्रोमियम]] [[hr:Krom]] [[io:Kromio]] [[id:Kromium]] [[is:Króm]] [[it:Cromo]] [[he:כרום]] [[kn:ಕ್ರೋಮಿಯಮ್]] [[sw:Chromi]] [[ht:Kwòm]] [[ku:Krom]] [[la:Chromium]] [[lv:Hroms]] [[lb:Chrom]] [[lt:Chromas]] [[jbo:rogjinme]] [[hu:Króm]] [[mk:Хром]] [[ml:ക്രോമിയം]] [[mi:Konukita]] [[ms:Kromium]] [[nah:Tlapāltepoztli]] [[nl:Chroom (element)]] [[ja:クロム]] [[no:Krom]] [[nn:Krom]] [[oc:Cròme]] [[uz:Xrom]] [[nds:Chrom]] [[pl:Chrom]] [[pt:Crômio]] [[ro:Crom]] [[qu:Krumu]] [[ru:Хром]] [[sq:Kromi]] [[scn:Cromu]] [[simple:Chromium]] [[sk:Chróm]] [[sl:Krom]] [[sr:Хром]] [[sh:Hrom]] [[stq:Chrom]] [[fi:Kromi]] [[sv:Krom]] [[ta:குரோமியம்]] [[th:โครเมียม]] [[vi:Crom]] [[tr:Krom]] [[uk:Хром]] [[zh:铬]]