Zirconium

Zirconium (pronEng|zɚˈkoʊniəm, IPA|/ˌzɝˈkoʊniəm/) is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium. Zirconium is used as an alloying agent due to its high resistance to corrosion. It is never found as a native metal, but is instead obtained mainly from the mineral zircon, which can be purified by chlorine. Zirconium was first isolated in an impure form in 1824 by Jöns Jakob Berzelius.

Zirconium has no known biological role. Zirconium forms both inorganic and organic compounds, such as zirconium dioxide and zirconocene dibromide, respectively. There are five naturally-occurring isotopes, three of which are stable. Short-term exposure to zirconium powder causes minor irritation, and inhalation of zirconium compounds can cause skin and lung granulomas.

Characteristics

Zirconium is a lustrous, grayish-white, soft, ductile, and malleable metal which is solid at room temperature, though it becomes hard and brittle at lower purities. In powder form, zirconium is highly flammable, but the solid form is far less prone to igniting. Zirconium is highly resistant to corrosion by alkalis, acids, salt water, and other agents.cite web |title=Zirconium|publisher=Los Alamos Chemistry Division|date=2003-12-15|url=http://periodic.lanl.gov/elements/40.html| accessdate = 2008-02-12] However, it will dissolve in hydrochloric and sulfuric acid, especially when fluorine is present.Citation|contribution=Zirconium|year=2005|title=Van Nostrand's Encyclopedia of Chemistry| editor-last = Considine| editor-first = Glenn D.|pages=1778–1779|place=New York|publisher=Wylie-Interscience|isbn=0-471-61525-0 ] Alloys with zinc become magnetic below 35 K.

The melting point of zirconium is at 1855°C, and the boiling point is at 4409°C.Citation|contribution=Zirconium|year=2007–2008|title=CRC Handbook of Chemistry and Physics|editor-last=Lide|editor-first=David R.|volume=4|pages=42|place=New York|publisher=CRC Press|id=978-0-8493-0488-0] Zirconium has an electronegativity of 1.33 on the Pauling scale. Of the elements within d-block, Zirconium has the fourth lowest electronegativity after yttrium, lutetium, and hafnium. [cite web|last=Winter|first=Mark|title=Electronegativity (Pauling)|publisher=University of Sheffield| year = 2007| url = http://www.webelements.com/webelements/properties/text/image-flash/electroneg-pauling.html| accessdate = 2008-03-05]

Applications

Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to corrosive agents, such as surgical appliances, explosive primers, vacuum tube getters and filaments. Zirconium dioxide (ZrO₂) is used in laboratory crucibles, metallurgical furnaces, and as a refractory material. Zircon (ZrSiO₄) is cut into gemstones for use in jewelry. Zirconium carbonate (3ZrO₂·CO₂·H₂O) was used in lotions to treat poison ivy, but this was discontinued as it caused bad skin reactions in some cases.cite book| last = Emsley| first = John| title = Nature's Building Blocks| publisher = Oxford University Press| year = 2001| location = Oxford| pages = 506–510| isbn = 0-19-850341-5 ] 90% of all zirconium produced is used in nuclear reactors because of its low neutron-capture cross-section and resistance to corrosion.cite web| title = Zirconium| work = How Products Are Made| publisher = Advameg Inc.| year = 2007| url = http://www.madehow.com/Volume-1/Zirconium.html| accessdate = 2008-03-26] Zirconium alloys are used in space vehicle parts for their resistance to heat, an important quality given the extreme heat associated with atmospheric reentry.cite book|last=Stwertka|first=Albert|title=A Guide to the Elements|publisher=Oxford University Press|year=1996|pages=117–119| isbn = 0-19-508083-1] Zirconium is also a component in some abrasives, such as grinding wheels and sandpaper.cite book|last=Krebs|first=Robert E.|title=The History and Use of our Earth's Chemical Elements|publisher=Greenwood Press|year=1998|location=Westport, Connecticut|pages=98–100|isbn=0-313-30123-9] Zirconium is used in weapons such as the BLU-97/B Combined Effects Bomb for incendiary effect. Zirconium in the oxidized form is also used in dentistry for crowning of the teeth because of its biocompatibility, strength and appeareance.

Refining

Upon being collected from coastal waters, the solid mineral zircon is purified by spiral concentrators to remove excess sand and gravel and by magnetic separators to remove ilmenite and rutile. The byproducts can then be dumped back into the water safely, as they are all natural components of beach sand. The refined zircon is then purified into pure zirconium by chlorine or other agents, then sintered until sufficiently ductile for metalworking. Zirconium and hafnium are both contained in zircon and they are quite difficult to separate due to their similar chemical properties.

History

The zirconium-containing mineral zircon, or its variations (jargoon, hyacinth, jacinth, ligure), were mentioned in biblical writings. The mineral was not known to contain a new element until 1789, when Klaproth analyzed a jargoon from the island of Ceylon in the Indian Ocean. He named the new element Zirkonerde (zirconia). Humphry Davy attempted to isolate this new element in 1808 through electrolysis, but failed. Zirconium (from Syriac "zargono", [cite web| last = Pearse| first = Roger| title = Syriac Literature| date = 2002-09-16| url = http://www.tertullian.org/rpearse/oriental/syriac.htm| accessdate = 2008-02-11] Arabic "zarkûn" from Persian "zargûn" "زرگون" meaning "gold like") was first isolated in an impure form in 1824 by Berzelius by heating a mixture of potassium and potassium-zirconium fluoride in a small decomposition process conducted in an iron tube.

The "crystal bar process" (or "Iodide process"), discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925, was the first industrial process for the commercial production of pure metallic zirconium. The process involved thermally decomposing zirconium tetraiodide. It was superseded in 1945 by a much cheaper process developed by William Justin Kroll, in which zirconium tetrachloride is broken down by magnesium.Citation|first=James B.|last=Hedrick|contribution=Zirconium|title=Metal Prices in the United States through 1998|year=1998|pages=175–178|publisher=US Geological Survey|url=http://minerals.usgs.gov/minerals/pubs/metal_prices/metal_prices1998.pdf|format=PDF|accessdate=2008-02-26]

Occurrence

Geological

Zirconium has a concentration of about 130 mg/kg within the earth's crust and about .026 μg/L in sea water, though it is never found in nature as a native metal. The principal commercial source of zirconium is the zirconium silicate mineral, zircon (ZrSiO₄), which is found primarily in Australia, Brazil, India, Russia, South Africa, and the United States, as well as in smaller deposits around the world. 80% of zircon mining occurs in Australia and South Africa. Zircon resources exceed 60 million metric tons worldwidecite journal| title = Zirconium and Hafnium| journal = Mineral Commodity Summaries| pages = 192–193| publisher = US Geological Survey| month = January | year = 2008| url = http://minerals.usgs.gov/minerals/pubs/commodity/zirconium/mcs-2008-zirco.pdf| format = PDF| accessdate = 2008-02-24] and annual worldwide zirconium production is approximately 900,000 metric tons.Citation|first=John|last=Peterson|first2=Margaret|last2=MacDonell| contribution=Zirconium|title=Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas|year=2007|pages=64–65|publisher=Argonne National Laboratory|format=PDF|url=http://www.evs.anl.gov/pub/doc/ANL_ContaminantFactSheets_All_070418.pdf|accessdate=2008-02-26]

Zircon is a by-product of the mining and processing of the titanium minerals ilmenite and rutile, as well as tin mining. [cite web|last=Callaghan|first=R.|title=Zirconium and Hafnium Statistics and Information|publisher=US Geological Survey|date=2008-02-21|url=http://minerals.usgs.gov/minerals/pubs/commodity/zirconium/|accessdate=2008-02-24] From 2003 to 2007, zircon prices have steadily increased from $360 to $840 per metric ton. Zirconium also occurs in more than 140 other recognized mineral species including baddeleyite and kosnarite. [cite web|last=Ralph|first=Jolyon|coauthors=Ida Ralph|title=Minerals that include Zr|publisher=Mindat.org| year=2008|url=http://www.mindat.org/chemsearch.php?inc=Zr%2C&exc=&sub=Search+for+Minerals|accessdate=2008-02-23] This metal is commercially produced mostly by the reduction of the zirconium(IV) chloride with magnesium metal in the Kroll process. Commercial-quality zirconium for most uses still has a content of 1% to 3% hafnium.

This element is relatively-abundant in S-type stars, and it has been detected in the sun and in meteorites. Lunar rock samples brought back from several Apollo program missions to the moon have a quite high zirconium oxide content relative to terrestrial rocks.

"See also ."

Biological

Zirconium has no known biological role, though zirconium salts are of low toxicity. The human body contains, on average, only 1 milligram of zirconium, and daily intake is approximately 50 μg per day. Zirconium content in human blood is as low as 10 parts per billion. Aquatic plants readily take up soluble zirconium, but it is rare in land plants. 70% of plants have no zirconium content at all, and those that do have as little as 5 parts per billion.

Compounds

As a transition metal, zirconium forms various inorganic compounds, such as zirconium dioxide (ZrO₂). This compound, also referred to as "zirconia", has exceptional fracture toughness and chemical resistance, especially in its cubic form.cite web|title=Zirconia| publisher = AZoM.com| year = 2008| url = http://www.azom.com/details.asp?ArticleID=133#_Key_Properties| accessdate=2008-03-17] These properties make zirconia useful as a thermal barrier coating, [cite journal|last=Gauthier| first=V.| last2=Dettenwanger|first2=F.|last3=Schütze|first3=M.|title=Oxidation behavior of γ-TiAl coated with zirconia thermal barriers| journal=Intermetallics| volume=10| issue=7|pages=667–674|publisher=Karl Winnacker Institut der Dechema|location= Frankfurt, Germany|date=2002-04-10| doi=10.1016/S0966-9795(02)00036-5] though it is also a common diamond substitute. Zirconium tungstate is an unusual substance in that it shrinks in all directions when heated, whereas other elements expand when heated. ZrZn₂ is one of only two substances to exhibit superconductivity and ferromagnetism simultaneously, with the other being UGe₂. [cite journal|last=Day|first=Charles|title=Second Material Found that Superconducts in a Ferromagnetic State|journal=Physics Today|volume=54|issue=9|pages=16| publisher=American Institute of Physics |month=September | year=2001| issn=0031-9228|doi=10.1063/1.1420499] Other inorganic zirconium compounds include zirconium(II) hydride, zirconium nitride, and zirconium tetrachloride (ZrCl₄), which is used in the Friedel-Crafts reaction. [cite journal | author= Bora U.|title=Zirconium Tetrachloride|journal=Synlett|year=2003|pages=1073–1074|doi=10.1055/s-2003-39323]

Organozirconium chemistry is the study of compounds containing a carbon-zirconium bond. These organozirconium compounds are often employed as polymerization catalysts. The first such compound was zirconocene dibromide, prepared in 1952 by John M. Birmingham at Harvard University. [cite journal|last=Rouhi|first=A. Maureen|title=Organozirconium Chemistry Arrives|journal=Science & Technology| volume=82|issue=16|pages=36–39|publisher=Chemical & Engineering News|date=2004-04-19|url=http://pubs.acs.org/cen/nlw/8216sci1.html|issn=0009-2347| accessdate=2008-03-17] Schwartz's reagent, prepared in 1970 by P. C. Wailes and H. Weigold, [cite journal|author=P. C. Wailes and H. Weigold|title=Hydrido complexes of zirconium I. Preparation|journal=Journal of Organometallic Chemistry|year=1970|volume=24|pages=405–411|doi=10.1016/S0022-328X(00)80281-8] is a metallocene used in organic synthesis for transformations of alkenes and alkynes.cite journal | author=D. W. Hart and J. Schwartz| title=Hydrozirconation. Organic Synthesis via Organozirconium Intermediates. Synthesis and Rearrangement of Alkylzirconium(IV) Complexes and Their Reaction with Electrophiles| journal=J. Am. Chem. Soc.|volume=96 |issue=26|year=1974|pages=8115–8116|doi=10.1021/ja00833a048]

Isotopes

Naturally-occurring zirconium is composed of five isotopes. ⁹⁰Zr, ⁹¹Zr, and ⁹²Zr are stable. ⁹⁴Zr has a half-life of 1.10×10¹⁷ years. ⁹⁶Zr has half-life of 2.4×10¹⁹ years, making it the longest-lived radioisotope of zirconium. Of these natural isotopes, ⁹⁰Zr is the most common, making up 51.45% of all zirconium. ⁹⁶Zr is the least common, comprising only 2.80% of zirconium.cite journal|title=Nubase2003 Evaluation of Nuclear and Decay Properties|journal=Nuclear Physics A|volume=729|pages=3–128|publisher=Atomic Mass Data Center|year=2003|doi=10.1016/j.nuclphysa.2003.11.001|author=Audi, G]

28 artificial isotopes of zirconium have been synthesized, ranging in atomic mass from 78 to 110. ⁹³Zr is the longest-lived artificial isotope, with a half-life of 1.53×10⁶ years. ¹¹⁰Zr, the heaviest isotope of zirconium, is also the shortest-lived, with an estimated half-life of only 30 milliseconds. Radioactive isotopes at or above mass number 93 decay by β⁻, whereas those at or below 89 decay by β⁺. The only exception is ⁸⁸Zr, which decays by ε.

Zirconium also has six metastable isomers, ^83mZr, ^85mZr, ^89mZr, ^90m1Zr, ^90m2Zr, and ^91mZr. Of these, ^90m2Zr has the shortest halflife at 131 nanoseconds. ^89mZr is the longest lived with a half-life of 4.161 minutes.

Toxicity

Ingestion or inhalation of ⁹³Zr, a radioactive isotope, causes a slight increase in the likelihood of developing cancer. Short-term exposure to zirconium powder can cause irritation, but only contact with the eyes requires medical attention. [Citation| contribution=Zirconium|title=International Chemical Safety Cards|date=October 2004|publisher=International Labour Organization|url=http://www.oit.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc14/icsc1405.htm|accessdate=2008-03-30] Inhalation of zirconium compounds can cause skin and lung granulomas. Zirconium aerosols can cause pulmonary granulomas. Persistent exposure to zirconium tetrachloride resulted in increased mortality in rats and guinea pigs and a decrease of blood hemoglobin and red blood cells in dogs. OSHA recommends a 5 mg/m³ time weighted average limit and a 10 mg/m³ short-term exposure limit. [cite web|title=Zirconium Compounds|publisher=National Institute for Occupational Health and Safety|date=2007-12-17|url=http://www.cdc.gov/niosh/pel88/7440-67.html|accessdate=2008-02-17]

ee also

*

Notes

External links

* [http://webelements.com/zirconium/ WebElements.com: Zirconium]
* [http://periodic.lanl.gov/elements/40.html Los Alamos National Laboratory: Zirconium]