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Thorium - Wikipedia, the free encyclopedia /**/ /**/ if (wgNotice != '') document.writeln(wgNotice); Thorium From Wikipedia, the free encyclopedia Jump to: navigation, search 90actinium ← thorium → protactiniumCe↑Th↓(Uqn) Periodic Table - Extended Periodic TableGeneralName, Symbol, Numberthorium, Th, 90Element categoryActinidesGroup, Period, Blockn/a, 7, fAppearancesilvery whiteStandard atomic weight232.0381(2) g·mol−1Electron configuration[Rn] 6d2 7s2Electrons per shell2, 8, 18, 32, 18, 10, 2Physical propertiesPhasesolidDensity (near r.t.)11.7 g·cm−3Melting point2115 K(1842 °C, 3348 °F)Boiling point5061 K(4788 °C, 8650 °F)Heat of fusion13.81 kJ·mol−1Heat of vaporization514 kJ·mol−1Specific heat capacity(25 °C) 26.230 J·mol−1·K−1Vapor pressureP(Pa)1101001 k10 k100 kat T(K)263329073248368342595055Atomic propertiesCrystal structurecubic face centeredOxidation states4(weakly basic oxide)Electronegativity1.3 (Pauling scale)Ionization energies(more)1st: 587 kJ·mol−12nd: 1110 kJ·mol−13rd: 1930 kJ·mol−1Atomic radius180 pmMiscellaneousMagnetic orderingno dataElectrical resistivity(0 °C) 147 nΩ·mThermal conductivity(300 K) 54.0 W·m−1·K−1Thermal expansion(25 °C) 11.0 µm·m−1·K−1Speed of sound (thin rod)(20 °C) 2490 m/sYoung's modulus79 GPaShear modulus31 GPaBulk modulus54 GPaPoisson ratio0.27Mohs hardness3.0Vickers hardness350 MPaBrinell hardness400 MPaCAS registry number7440-29-1Most-stable isotopesMain article: Isotopes of thoriumisoNAhalf-lifeDMDE (MeV)DP228Thsyn1.9116 yearsα5.520224Ra229Thsyn7340 yearsα5.168225Ra230Thsyn75380 yearsα4.770226Ra231Thtrace25.5 hoursβ0.39231Pa232Th100%1.405×1010 yearsα4.083228Ra234Thtrace24.1 daysβ0.27234PaReferencesThorium (pronounced /ˈθɔːriəm/) is a chemical element with the symbol Th and atomic number 90. As a naturally occurring, slightly radioactive metal, it has been considered as an alternative nuclear fuel to uranium.Contents1 Characteristics2 Applications3 History4 Occurrence4.1 Distribution5 Thorium as a nuclear fuel6 Isotopes7 Precautions8 Thorium extraction9 See also10 Footnotes11 References12 External links//[edit] CharacteristicsWhen pure, thorium is a silvery-white metal that retains its luster for several months. However, when it is exposed to oxygen, thorium slowly tarnishes in air, becoming grey and eventually black. Thorium dioxide (ThO2), also called thoria, has the highest melting point of any oxide (3300°C).[1] When heated in air, thorium metal turnings ignite and burn brilliantly with a white light.Thorium has the largest liquid range of any element: 2946 K between the melting point and boiling point.See Actinides in the environment for details of the environmental aspects of thorium.[edit] ApplicationsApplications of thorium:As an alloying element in magnesium, used in aircraft engines, imparting high strength and creep resistance at elevated temperatures.Thorium is used to coat tungsten wire used in electronic equipment, improving the electron emission of heated cathodes.Thorium is an alloying agent used in GTAW ("Gas Tungsten Arc Welding") to increase the melting temperature of tungsten electrodes and improve arc stability.Uranium-thorium age dating has been used to date hominid fossils.As a fertile material for producing nuclear fuel. In particular, the proposed energy amplifier reactor design would employ thorium. Since thorium is more abundant than uranium, some nuclear reactor designs incorporate thorium in their fuel cycle.Thorium is a very effective radiation shield, although it has not been used for this purpose as much as lead or depleted uranium.Thorium may be used in nuclear reactors instead of uranium as fuel. This produces less transuranic waste.Applications of thorium dioxide (ThO2):Mantles in portable gas lights. These mantles glow with a dazzling light (unrelated to radioactivity) when heated in a gas flame.Used in gas tungsten arc welding electrodes.Used to control the grain size of tungsten used for electric lamps.Used in heat-resistant ceramics like high-temperature laboratory crucibles.Added to glass, it helps create glasses of a high refractive index and with low dispersion. Consequently, they find application in high-quality lenses for cameras and scientific instruments.Has been used as a catalyst:In the conversion of ammonia to nitric acid.In petroleum cracking.In producing sulfuric acid.Thorium dioxide is the active ingredient of Thorotrast, which was used as part of X-ray diagnostics. This use has been abandoned due to the carcinogenic nature of Thorotrast.[edit] HistoryM. T. Esmark found a black mineral on Løvøy Island, Norway and gave a sample to Professor Jens Esmark, a noted mineralogist who was not able to identify it, so he sent a sample to the Swedish chemist Jöns Jakob Berzelius for examination in 1828.[2] Berzelius analysed it and named it after Thor, the Norse god of thunder. The metal had virtually no uses until the invention of the gas mantle in 1885.Between 1900 and 1903 Ernest Rutherford and Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements. This observation led to the identification of half life as one of the outcomes of the alpha particle experiments that led to their disintegration theory of radioactivity.[3]The crystal bar process (or Iodide process) was discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925 to produce high-purity metallic thorium.[4]The name ionium was given early in the study of radioactive elements to the 230Th isotope produced in the decay chain of 238U before it was realized that ionium and thorium were chemically identical. The symbol Io was used for this supposed element.[edit] Occurrence  Monazite, a rare-earth-and-thorium phosphate mineral, is the primary source of the world's thoriumThorium is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium, and is about as common as lead. Soil commonly contains an average of around 12 parts per million (ppm) of thorium. Thorium occurs in several minerals, the most common being the rare-earth thorium-phosphate mineral monazite, which may contain up to about 12% thorium oxide. Thorium-containing monazite(Ce) occurs in Africa, Antarctica, Australia, Europe, India, North America, and South America.[5]232Th decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in the thorium and uranium decay chains. Most of these are short-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible.See also thorium minerals.[edit] DistributionPresent knowledge of the distribution of thorium resources is poor because of the relatively low-key exploration efforts arising out of insignificant demand.[6] There are two sets of estimates that define world thorium reserves, one set by the US Geological Survey (USGS) and the other supported by reports from the OECD and the International Atomic Energy Agency (the IAEA). Under the USGS estimate, Australia and India have particularly large reserves of thorium. India and Australia are believed to possess approx 300,000 metric tonnes each; i.e. each country possessing 25% of the world's thorium reserves.[7] However, in the OECD reports, estimates of Australian's Reasonably Assured Reserves (RAR) of Thorium indicate only 19,000 metric tonnes and not 300,000 tonnes as indicated by USGS. The two sources vary wildly for countries such as Brazil, Turkey, and Australia. However, both reports appear to show some consistency with respect to India's thorium reserve figures, with 290,000 metric tonnes (USGS) and 319,000 metric tonnes (OECD/IAEA). Furthermore the IAEA report mentions that India possesses two thirds (67%) of global reserves of monazite, the primary thorium ore:The world’s reserve of monazite is estimated to be in the range of 12 million tonnes of which nearly 8 million tonnes occur with the heavy minerals in the beach sands of India in the States of Kerala, Tamil Nadu, Andhra Pradesh and Orissa.[8]The IAEA also states that recent reports have upgraded India's thorium deposits up from approximately 300,000 metric tonnes to 650,000 metric tonnes:In the RAR category, the deposits in Brazil, Turkey and India are in the range of 0.60, 0.38 and 0.32 million tonnes respectively. The thorium deposits in India has recently been reported to be in the range 0.65 million tonnes.[9]Therefore, the IAEA and OECD appear to conclude that Brazil and India may actually possess the lion's share of world's thorium deposits.The prevailing estimate of the economically available thorium reserves comes from the US Geological Survey, Mineral Commodity Summaries (1997-2006):[10][11]CountryTh Reserves (tonnes) Th Reserve Base (tonnes)Australia300,000 340,000 India290,000300,000Norway170,000180,000United States160,000300,000Canada100,000100,000South Africa35,00039,000Brazil16,00018,000Malaysia4,5004,500Other Countries95,000100,000World Total1,200,0001,400,000Note: The Australian figures are based on assumptions and not on actual geological surveys, therefore the figures cited for Australia may be misleading, should be treated with caution and could possibly indicate inflated values for Australia's actual reserves of thorium; note the OECD estimates of Australian's Reasonably Assured Reserves (RAR) of Thorium (listed below) indicate only 19,000 metric tonnes and not 300,000 tonnes as listed above.Another estimate of Reasonably Assured Reserves (RAR) and Estimated Additional Reserves (EAR) of thorium comes from OECD/NEA, Nuclear Energy, "Trends in Nuclear Fuel Cycle", Paris, France (2001).[12]CountryRAR Th (tonnes) EAR Th (tonnes)Brazil606,000 700,000 Turkey380,000500,000India319,000 —United States137,000295,000Norway132,000132,000Greenland54,00032,000Canada45,000128,000Australia19,000 —South Africa18,000 —Egypt15,000309,000Other Countries 505,000 —World Total2,230,0002,130,000[edit] Thorium as a nuclear fuelMain article: Thorium fuel cycleThorium, as well as uranium and plutonium, can be used as fuel in a nuclear reactor. Although not fissile itself, 232Th will absorb slow neutrons to produce 233U, which is fissile. Hence, like 238U, it is fertile.Problems include the high cost of fuel fabrication due partly to the high radioactivity of 233U which is a result of its contamination with traces of the short-lived 232U; the similar problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk of 233U; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialised, and the effort required seems unlikely while (or where) abundant uranium is available.Nevertheless, the thorium fuel cycle, with its potential for breeding fuel without fast neutron reactors, holds considerable potential long-term benefits. Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy. Perhaps more importantly, thorium produces several orders of magnitude less long-lived radioactive waste.One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental reactor was built based on molten salt reactor technology to study the feasibility of such an approach, using thorium-fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used 232Th as the fertile material and 233U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976.In 2007, Norway was debating whether or not to focus on thorium plants, due to the existence of large deposits of thorium ores in the country, particularly at Fensfeltet, near Ulefoss in Telemark county.The primary fuel of the HT3R Project near Odessa, Texas, USA will be ceramic-coated thorium beads.[edit] IsotopesMain article: isotopes of thoriumNaturally occurring thorium is composed of one isotope: 232Th. Twenty-seven radioisotopes have been characterized, with the most abundant and/or stable being 232Th with a half-life of 14.05 billion years, 230Th with a half-life of 75,380 years, 229Th with a half-life of 7340 years, and 228Th with a half-life of 1.92 years. All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. One isotope, 229Th, has a nuclear isomer (or metastable state) with a remarkably low excitation energy of 7.6 eV.[13]The known isotopes of thorium range in atomic weight from 210 u (210Th) to 236 u (236Th).[14][edit] PrecautionsPowdered thorium metal is often pyrophoric and should be handled carefully.Natural thorium decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin. Owning and handling small amounts of thorium, such as a gas mantle, is considered safe if care is taken not to ingest the thorium -- lungs and other internal organs can be penetrated by alpha radiation. Exposure to an aerosol of thorium can lead to increased risk of cancers of the lung, pancreas and blood. Exposure to thorium internally leads to increased risk of liver diseases. This element has no known biological role. See also Thorotrast.[edit] Thorium extractionThorium has been extracted chiefly from monazite through a multi-stage process. In the first stage, the monazite sand is dissolved in an inorganic acid such as sulfuric acid (H2SO4). In the second, the Thorium is extracted into an organic phase containing an amine. Next it is separated or "stripped" using an ion such as nitrate, chloride, hydroxide, or carbonate, returning the thorium to an aqueous phase. Finally, the thorium is precipitated and collected.[15][edit] See alsoDavid Hahn, who produced small quantities of fissionable material in his backyard.Periodic tableNuclear reactorDecay chainSylvania Electric Products explosion[edit] Footnotes^ Emsley, John (2001). Nature's Building Blocks, (Hardcover, First Edition), Oxford University Press, page 441. ISBN 0198503407. ^ "Thorium". BBC.co. Retrieved on 2007-01-18.^ Simmons, John Galbraith (1996). The Scientific 100. Seacaucus NJ: Carol, 19. ^ van Arkel, A.E.; de Boer, J.H. (1925). "Preparation of pure titanium, zirconium, hafnium, and thorium metal". Zeitschrift für Anorganische und Allgemeine Chemie 148: 345–350. ^ Monazite-(Ce): Monazite-(Ce) mineral information and data^ K.M.V. Jayaram. "An Overview of World Thorium Resources, Incentives for Further Exploration and Forecast for Thorium Requirements in the Near Future".^ "US approves Indian nuclear deal". BBC News (2006-12-09).^ IAEA: Thorium fuel cycle — Potential benefits and challenges, pp 45. ^ IAEA: Thorium fuel cycle — Potential benefits and challenges, pp 45. ^ "U.S. Geological Survey, Mineral Commodity Summaries - Thorium".^ "Information and Issue Briefs - Thorium". World Nuclear Association. Retrieved on 2006-11-01.^ IAEA: Thorium fuel cycle — Potential benefits and challenges, pp 45(table 8), 97(ref 78). ^ Phys. Rev. Lett. 98 142501 (April 2007)^ Phys. Rev. C 52, 113–116 (1995)^ Crouse, David; Brown, Keith (December 1959) "The Amex Process for Extracting Thorium Ores with Alkyl Amines".Industrial & Engineering Chemistry 51 (12): 1461. Retrieved on 2007-03-09[edit] ReferencesLos Alamos National Laboratory — ThoriumWebElements.com — ThoriumThe Uranium Information Centre provided some of the original material in this article.European Nuclear Society — Natural Decay Chains[edit] External links Wikimedia Commons has media related to:Thorium Look up thorium inWiktionary, the free dictionary.Thorium information pageNew Age Nuclear: article on thorium reactors | Cosmos MagazineATSDR ToxFAQs — ThoriumUSGS data — ThoriumThe Endless Refrigerator/Freezer Deodorizer, a commercial product which claimed to destroy odours 'forever.' Made with thorium-232.Is thorium the answer to our energy crisis?Thorium Energy Blog, discussion forum and document repositoryAnother thorium information pageMonazitev • d • ePeriodic tableH HeLiBe BCNOFNeNaMg AlSiPSClArKCa ScTiVCrMnFeCoNiCuZnGaGeAsSeBrKrRbSr YZrNbMoTcRuRhPdAgCdInSnSbTeIXeCsBaLaCePrNdPmSmEuGdTbDyHoErTmYbLuHfTaWReOsIrPtAuHgTlPbBiPoAtRnFrRaAcThPaUNpPuAmCmBkCfEsFmMdNoLrRfDbSgBhHsMtDsRgUubUutUuqUupUuhUusUuoUueUbn Alkali metalsAlkaline earth metalsLanthanoidsActinoidsTransition metalsOther metalsMetalloidsOther nonmetalsHalogensNoble gasesRetrieved from "http://en.wikipedia.org/wiki/Thorium" Categories: Chemical elements | Actinides | Nuclear materials | Carcinogens | Thorium Views Article Discussion Edit this page History Personal tools Log in / create account if (window.isMSIE55) fixalpha(); Navigation Main page Contents Featured content Current events Random article Search Interaction About Wikipedia Community portal Recent changes Contact Wikipedia Donate to Wikipedia Help Toolbox What links here Related changesUpload fileSpecial pages Printable version Permanent linkCite this page Languages العربية বাংলা Беларуская Bosanski Български Català Česky Corsu Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Furlan Gaelg Galego 한국어 Հայերեն हिन्दी Hrvatski Ido Bahasa Indonesia Interlingua Italiano עברית Kreyòl ayisyen Latina Latviešu Lëtzebuergesch Lietuvių Lojban Magyar മലയാളം Nederlands 日本語 Norsk (bokmål) Norsk (nynorsk) Polski Português Română Runa Simi Русский Sicilianu Simple English Slovenčina Slovenščina Српски / Srpski Srpskohrvatski / Српскохрватски Suomi Svenska ไทย Türkçe Українська 中文   This page was last modified on 21 November 2008, at 03:26. 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