Thorium
30044
226119526
2008-07-16T22:13:44Z
Arkuat
29003
/* Characteristics */ section title according to [[WP:WikiProject Elements]]
{{Elementbox_header | number=90 | symbol=Th | name=thorium | left=[[actinium]] | right=[[protactinium]] | above=[[cerium|Ce]] | below=(Uqn) | color1=#ff99cc | color2=black }}
{{Elementbox_series | [[Actinide]]s }}
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{{Elementbox_atomicmass_gpm | [[1 E-25 kg|232.0381]][[List of elements by atomic mass|(2)]] }}
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{{Elementbox_epershell | 2, 8, 18, 32, 18, 10, 2 }}
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{{Elementbox_phase | [[solid]] }}
{{Elementbox_density_gpcm3nrt | 11.7 }}
{{Elementbox_meltingpoint | k=2115 | c=1842 | f=3348 }}
{{Elementbox_boilingpoint | k=5061 | c=4788 | f=8650 }}
{{Elementbox_heatfusion_kjpmol | 13.81 }}
{{Elementbox_heatvaporiz_kjpmol | 514 }}
{{Elementbox_heatcapacity_jpmolkat25 | 26.230 }}
{{Elementbox_vaporpressure_katpa | 2633 | 2907 | 3248 | 3683 | 4259 | 5055 | comment= }}
{{Elementbox_section_atomicprop | color1=#ff99cc | color2=black }}
{{Elementbox_crystalstruct | cubic face centered }}
{{Elementbox_oxistates | 4<br />(weakly [[base (chemistry)|basic]] oxide) }}
{{Elementbox_electroneg_pauling | 1.3 }}
{{Elementbox_ionizationenergies4 | 587 | 1110 | 1930 }}
{{Elementbox_atomicradius_pm | [[1 E-10 m|180]] }}
{{Elementbox_section_miscellaneous | color1=#ff99cc | color2=black }}
{{Elementbox_magnetic | no data }}
{{Elementbox_eresist_ohmmat0 | 147 n}}
{{Elementbox_thermalcond_wpmkat300k | 54.0 }}
{{Elementbox_thermalexpansion_umpmkat25 | 11.0 }}
{{Elementbox_speedofsound_rodmpsat20 | 2490 }}
{{Elementbox_youngsmodulus_gpa | 79 }}
{{Elementbox_shearmodulus_gpa | 31 }}
{{Elementbox_bulkmodulus_gpa | 54 }}
{{Elementbox_poissonratio | 0.27 }}
{{Elementbox_mohshardness | 3.0 }}
{{Elementbox_vickershardness_mpa | 350 }}
{{Elementbox_brinellhardness_mpa | 400 }}
{{Elementbox_cas_number | 7440-29-1 }}
{{Elementbox_isotopes_begin | color1=#ff99cc | color2=black }}
{{Elementbox_isotopes_decay | mn=228 | sym=Th
| na=[[synthetic radioisotope|syn]] | hl=1.9116 [[years]]
| dm=[[alpha decay|α]] | de=5.520 | pn=224 | ps=[[radium|Ra]] }}
{{Elementbox_isotopes_decay | mn=229 | sym=Th
| na=[[synthetic radioisotope|syn]] | hl=7340 [[years]]
| dm=[[alpha decay|α]] | de=5.168 | pn=225 | ps=[[radium|Ra]] }}
{{Elementbox_isotopes_decay | mn=230 | sym=Th
| na=[[synthetic radioisotope|syn]] | hl=75380 [[years]]
| dm=[[alpha decay|α]] | de=4.770 | pn=226 | ps=[[radium|Ra]] }}
{{Elementbox_isotopes_decay | mn=231 | sym=Th
| na=[[trace radioisotope|trace]] | hl=25.5 [[hour]]s
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{{Elementbox_isotopes_decay | mn=232 | sym=Th
| na=100% | hl=1.405×10<sup>10</sup> [[years]]
| dm=[[alpha decay|α]] | de=4.083 | pn=228 | ps=[[radium|Ra]] }}
{{Elementbox_isotopes_decay | mn=234 | sym=Th
| na=[[trace radioisotope|trace]] | hl=24.1 [[days]]
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{{Elementbox_isotopes_end}}
{{Elementbox_footer | color1=#ff99cc | color2=black }}
'''Thorium''' ({{pronEng|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]].
==Characteristics==
When 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]] (ThO<sub>2</sub>), also called thoria, has the highest melting point of any oxide (3300°C).<ref> {{cite book | last = Emsley | first = John | title = Nature's Building Blocks | edition = (Hardcover, First Edition) | publisher = [[Oxford University Press]] | date = 2001 | pages = page 441 | id = ISBN 0198503407 }}</ref> When heated in air, thorium metal [[swarf|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.
==Applications==
Applications of thorium:
* As an [[alloying]] element in [[magnesium]], used in aircraft engines, imparting high [[strength of materials|strength]] and [[creep (deformation)|creep]] resistance at elevated temperatures.
* Thorium is used to coat [[tungsten]] wire used in electronic equipment, improving the [[electron]] [[thermionic emission|emission]] of heated [[cathode]]s.
* 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 dating|Uranium-thorium age dating]] has been used to date hominid [[fossil]]s.
* 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 [[nuclear fuel cycle|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 reactor]]s instead of uranium as fuel. This produces less [[transuranic waste]].
Applications of [[thorium dioxide]] (ThO<sub>2</sub>):
* [[Gas mantle|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 [[refraction (metallurgy)|heat-resistant]] [[ceramic]]s like high-temperature laboratory [[crucible]]s.
* Added to [[glass]], it helps create glasses of a high [[refractive index]] and with low [[dispersion (optics)|dispersion]]. Consequently, they find application in high-quality [[lens (optics)|lens]]es for cameras and scientific instruments.
* Has been used as a [[catalyst]]:
** In the conversion of [[ammonia]] to [[nitric acid]].
** In [[petroleum]] [[cracking (chemistry)|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.
==History==
M. 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.<ref>{{cite web
|url=http://www.bbc.co.uk/dna/h2g2/A3768861
|title=Thorium
|publisher=BBC.co
|accessdate=2007-01-18
}}</ref>
Berzelius analysed it and named it after [[Thor]], the [[norse mythology|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]].<ref>{{cite book|last=Simmons|first=John Galbraith|title=The Scientific 100|page=19|date=1996|publisher=Seacaucus NJ: Carol}}</ref>
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.<ref>{{cite journal|last=van Arkel|first=A.E.|coauthors=de Boer, J.H.|title=Preparation of pure titanium, zirconium, hafnium, and thorium metal|journal=Zeitschrift für Anorganische und Allgemeine Chemie|volume=148|pages=345–350|date=1925}}</ref>
The name '''ionium''' was given early in the study of radioactive elements to the <sup>230</sup>Th [[isotope]] produced in the [[decay chain]] of [[Uranium-238|<sup>238</sup>U]] before it was realized that ionium and thorium were chemically identical. The symbol '''Io''' was used for this supposed element.
==Occurrence==
[[Image:MonaziteUSGOV.jpg|thumb|left|Monazite, a rare-earth-and-thorium phosphate mineral, is the primary source of the world's thorium]]
Thorium is found in small amounts in most rocks and [[soil]]s, 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 [[mineral]]s, 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, North America, and South America.<ref>http://www.mindat.org/min-2751.html</ref>
<sup>232</sup>Th decays very slowly (its [[half-life]] is about three times the age of the earth) but other thorium [[isotope]]s occur in the thorium and [[uranium]] decay chains. Most of these are short-lived and hence much more radioactive than <sup>232</sup>Th, though on a mass basis they are negligible.
''See also [[:Category:Thorium minerals|thorium minerals]].''
===Distribution===
Present knowledge of the distribution of thorium resources is poor because of the relatively low-key exploration efforts arising out of insignificant demand.<ref>{{cite web|url=http://www.iaea.org/inis/aws/fnss/fulltext/0412_1.pdf|title=An Overview of World Thorium Resources, Incentives for Further Exploration and Forecast for Thorium Requirements in the Near Future|author=K.M.V. Jayaram}}</ref> Under the prevailing estimate, [[Australia]] and [[India]] have particularly large reserves of thorium. India is believed to have 25% of the world's thorium reserves.<ref name="bbc">{{cite web|title=US approves Indian nuclear deal|publisher=BBC News|date=2006-12-09|url=http://news.bbc.co.uk/2/hi/south_asia/6219998.stm}}</ref>
* The prevailing estimate of the economically available thorium reserves comes from the US Geological Survey, Mineral Commodity Summaries (1997-2006):<ref>{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/thorium/index.html#mcs|title=U.S. Geological Survey, Mineral Commodity Summaries - Thorium}}</ref><ref>{{cite web|url=http://www.world-nuclear.org/info/inf62.htm|title=Information and Issue Briefs - Thorium|publisher=World Nuclear Association|accessdate=2006-11-01}}</ref>
{| border="0"
! Country !!colspan=2| Th Reserves (tonnes) !!colspan=2| Th Reserve Base (tonnes)
|-
| Australia
|align=right| 300,000 ||
|align=right| 340,000 ||
|-
| India ||align=right| 290,000 || ||align=right| 300,000
|-
| Norway ||align=right| 170,000 || ||align=right| 180,000
|-
| United States ||align=right| 160,000 || ||align=right| 300,000
|-
| Canada ||align=right| 100,000 || ||align=right| 100,000
|-
| South Africa ||align=right| 35,000 || ||align=right| 39,000
|-
| Brazil ||align=right| 16,000 || ||align=right| 18,000
|-
| Malaysia ||align=right| 4,500 || ||align=right| 4,500
|-
| ''Other Countries'' ||align=right| 95,000 || ||align=right| 100,000
|-
| ''World Total'' ||align=right| 1,200,000 || ||align=right| 1,400,000
|}
* 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).<ref>{{cite book|url=http://www-pub.iaea.org/MTCD/publications/PDF/TE_1450_web.pdf|title=IAEA: Thorium fuel cycle — Potential benefits and challenges|pages=pp 45(table 8), 97(ref 78)}}</ref>
{| border="0"
! Country !!colspan=2| RAR Th (tonnes) !!colspan=2| EAR Th (tonnes)
|-
| Brazil
|align=right| 606,000 ||
|align=right| 700,000 ||
|-
| Turkey
|align=right| 380,000 || ||align=right| 500,000
|-
| India ||align=right| 319,000 || ||align=center| —
|-
| United States ||align=right| 137,000 || ||align=right| 295,000
|-
| Norway ||align=right| 132,000 || ||align=right| 132,000
|-
| Greenland ||align=right| 54,000 || ||align=right| 32,000
|-
| Canada ||align=right| 45,000 || ||align=right| 128,000
|-
| Australia ||align=right| 19,000 || ||align=center| —
|-
| South Africa ||align=right| 18,000 || ||align=center| —
|-
| Egypt ||align=right| 15,000 || ||align=right| 309,000
|-
| ''Other Countries'' ||align=right| 505,000 || ||align=center| —
|-
| ''World Total'' ||align=right| 2,230,000 || ||align=right| 2,130,000
|}
The two sources vary wildly for countries such as Brazil, Turkey, and Australia.
==Thorium as a nuclear fuel==
[[Image:Thorium.jpg|thumb|150px|left|Thorium metal foil (approximately 0.5 mm thick) sealed in a glass ampoule under an argon atmosphere to prevent oxidation]]
Thorium, as well as [[uranium]] and [[plutonium]], can be used as fuel in a [[nuclear reactor]]. Although not [[fissile]] itself, <sup>232</sup>Th will absorb [[slow neutron]]s to produce [[uranium-233 | (<sup>233</sup>U]]), which is fissile. Hence, like [[Uranium-238 | <sup>238</sup>U]], it is [[Fertile material | fertile]].
In one significant respect <sup>233</sup>U is better than the other two fissile isotopes used for nuclear fuel, [[Uranium-235 | <sup>235</sup>U]] and [[plutonium-239]] (<sup>239</sup>Pu), because of its higher neutron yield per neutron absorbed. Given a start with some other fissile material (<sup>235</sup>U or <sup>239</sup>Pu), a [[Breeder reactor | breeding cycle]] similar to, but more efficient than that currently possible with the <sup>238</sup>U-to-<sup>239</sup>Pu cycle (in [[Thermal reactor|slow-neutron reactors]]), can be set up. The <sup>232</sup>Th absorbs a neutron to become <sup>233</sup>Th which normally emits an [[electron]] and an [[antineutrino|anti-neutrino]] (<math>\bar{\nu}_e</math>) by [[beta decay|β<sup>−</sup> decay]] to become [[protactinium]]-233 (<sup>233</sup>Pa) and then emits another electron and anti-neutrino by a second β<sup>−</sup> decay to become <sup>233</sup>U:
:<math>\mathrm\hbox{n}+{{}^2{}^{32}_{90}\mathrm{Th}}\rightarrow\mathrm{{}^2{}^{33}_{90}\mathrm{Th}}\rightarrow\mathrm{{}^2{}^{33}_{91}Pa}+ e^- + \bar{\nu}_e</math>
:<math>\mathrm{{}^2{}^{33}_{91}Pa}\rightarrow\mathrm{{}^2{}^{33}_{92}U}+ e^- + \bar{\nu}_e</math>
The irradiated fuel can then be unloaded from the reactor, the <sup>233</sup>U separated from the thorium (a relatively simple process since it involves chemical instead of [[Isotope separation | isotopic separation]]), and fed back into another reactor as part of a closed [[nuclear fuel cycle]].
Problems include the high cost of fuel fabrication due partly to the high radioactivity of <sup>233</sup>U which is a result of its contamination with traces of the short-lived <sup>232</sup>U; the similar problems in recycling thorium due to highly radioactive <sup>228</sup>Th; some weapons proliferation risk of <sup>233</sup>U; 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 [[Nuclear fuel cycle#Thorium cycle|thorium fuel cycle]], with its potential for breeding fuel without [[fast neutron reactor]]s, holds considerable potential long-term benefits. Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy.
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 (chemistry)|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 <sup>232</sup>Th as the fertile material and <sup>233</sup>U 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|HT<sup>3</sup>R]] Project near [[Odessa, Texas]], [[USA]] will be ceramic-coated thorium beads.
==Isotopes==
{{main|isotopes of thorium}}
Naturally occurring thorium is composed of one [[isotope]]: [[Thorium-232|<sup>232</sup>Th]]. Twenty-seven [[radioisotope]]s have been characterized, with the most abundant and/or stable being <sup>232</sup>Th with a [[half-life]] of 14.05 billion years, <sup>230</sup>Th with a half-life of 75,380 years, <sup>229</sup>Th with a half-life of 7340 years, and <sup>228</sup>Th 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, <sup>229</sup>Th, has a [[nuclear isomer]] (or metastable state) with a remarkably low excitation energy of 3.5 eV.<ref>Phys. Rev. C 73 044326 (April 2006)</ref>
The known isotopes of thorium range in [[atomic weight]] from 210 [[atomic mass unit|u]] (<sup>210</sup>Th) to 236 u (<sup>236</sup>Th).<ref>Phys. Rev. C 52, 113–116 (1995)</ref>
==Precautions==
Powdered 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 aerosolized thorium can lead to increased risk of [[cancer]]s 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]].
==Thorium Extraction==
Thorium 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 (H<sub>2</sub>SO<sub>4</sub>). 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.<ref> Crouse, David; Brown, Keith (December 1959) "[http://pubs.acs.org/cgi-bin/abstract.cgi/iechad/1959/51/i12/f-pdf/f_ie50600a030.pdf?sessid=6006l3 The Amex Process for Extracting Thorium Ores with Alkyl Amines]".''Industrial & Engineering Chemistry'' '''51''' (12): 1461. Retrieved on [[2007-03-09]] </ref>
==See also==
*[[David Hahn]], who produced small quantities of fissionable material in his backyard.
*[[Periodic table]]
*[[Nuclear reactor]]
*[[Decay chain]]
*[[Sylvania Electric Products explosion]]
<!--*Thorium's entries at [[fictional applications of real materials]].
DELETED [[Wikipedia:Articles_for_deletion/Fictional_applications_of_real_materials]] -->
==Footnotes==
{{reflist}}
==References==
*[http://periodic.lanl.gov/elements/90.html Los Alamos National Laboratory — Thorium]
*[http://www.webelements.com/webelements/elements/text/Th/index.html WebElements.com — Thorium]
*[http://www.uic.com.au/ The Uranium Information Centre] provided some of the original material in this article.
*[http://www.euronuclear.org/info/encyclopedia/d/decaybasinnatural.htm European Nuclear Society — Natural Decay Chains]
==External links==
{{Commons|Thorium}}
{{wiktionary|thorium}}
*[http://www.world-nuclear.org/info/inf62.htm Thorium information page]
*[http://www.cosmosmagazine.com/node/348/ New Age Nuclear: article on thorium reactors | ''Cosmos Magazine'']
*[http://www.atsdr.cdc.gov/tfacts147.html ATSDR ToxFAQs — Thorium]
*[http://minerals.usgs.gov/minerals/pubs/commodity/thorium/ USGS data — Thorium]
*[http://www.orau.org/ptp/collection/quackcures/endless.htm The Endless Refrigerator/Freezer Deodorizer], a commercial product which claimed to destroy odours 'forever.' Made with thorium-232.
*[http://news.independent.co.uk/sci_tech/article2070374.ece Is thorium the answer to our energy crisis?]
*[http://thoriumenergy.blogspot.com Thorium Energy] Blog, discussion forum and document repository
*[http://www.energyfromthorium.com/ Another thorium information page]
*[http://www.mindat.org/min-2751.html/ Monazite]
{{clear}}
{{Compact periodic table}}
[[Category:Chemical elements]]
[[Category:Actinides]]
[[Category:Nuclear materials]]
[[Category:Carcinogens]]
[[Category:Thorium]]
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