AskDefine | Define cerium

Dictionary Definition

cerium n : a ductile gray metallic element of the lanthanide series; used in lighter flints; the most abundant of the rare-earth group [syn: Ce, atomic number 58]

User Contributed Dictionary

English

Alternative spellings

  • cererium (a name proposed (but not accepted) to indicate "cerium" does not come from the Greek word for "wax")

Noun

  1. A metallic chemical element (symbol Ce) with an atomic number of 58.

Related terms

Translations

chemical element

External links

For etymology and more information refer to: http://elements.vanderkrogt.net/elem/ce.html (A lot of the translations were taken from that site with permission from the author)

Finnish

Noun

  1. cerium

Swedish

Noun

cerium

Extensive Definition

Cerium () is a chemical element with the symbol Ce and atomic number 58.

Notable characteristics

Cerium is a silvery metal, belonging to the lanthanide group. It resembles iron in color and luster, but is soft, and both malleable and ductile. Cerium has the longest liquid range of any non-radioactive element: 2648 °C (795 °C to 3443 °C) or 4766 °F (1463 °F to 6229 °F). (Thorium has a longer liquid range.)
Although cerium belongs to chemical elements group called rare earth metals, it is in fact more common than lead. Cerium is available in relatively large quantities (68 ppm in Earth’s crust). It is used in some rare-earth alloys.
Among rare earth elements only europium is more reactive. It tarnishes readily in the air. Alkali solutions and dilute and concentrated acids attack the metal rapidly. Cerium oxidizes slowly in cold water and rapidly in hot water. The pure metal can ignite if scratched.
Cerium(IV) (ceric) salts are orange red or yellowish, whereas cerium(III) (cerous) salts are usually white or colorless. Both oxidation states absorb ultraviolet light strongly. Cerium(III) can be used to make glasses that are colorless, yet absorb ultraviolet light almost completely. Cerium can be readily detected in rare earth mixtures by a very sensitive qualitative test: addition of ammonia and hydrogen peroxide to an aqueous solution of lanthanides produces a characteristic dark brown color if cerium is present.

Applications

Uses of cerium:
  • In metallurgy:
  • Cerium oxalate is an anti-emetic drug.
  • Cerium(IV) oxide
    • The oxide is used in incandescent gas mantles, such as the Welsbach mantle, where it was combined with thorium, lanthanum, magnesium or yttrium oxides .
    • The oxide is emerging as a hydrocarbon catalyst in self cleaning ovens, incorporated into oven walls.
    • Cerium(IV) oxide has largely replaced rouge in the glass industry as a polishing abrasive.
    • Cerium(IV) oxide is finding use as a petroleum cracking catalyst in petroleum refining.
    • Cerium(IV) additives to diesel fuel cause that to burn more cleanly, with less resulting air-pollution.
    • In glass, cerium(IV) oxide allows for selective absorption of ultraviolet light.
  • Cerium(IV) sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis.
  • Ceric ammonium nitrate is a useful one-electron oxidant in organic chemistry, used to oxidatively etch electronic components, and as a primary standard for quantitative analysis.
  • Cerium compounds are used in the manufacture of glass, both as a component and as a decolorizer.
  • Cerium in combination with titanium gives a golden yellow color to glass.
  • Cerium compounds are used for the coloring of enamel.
  • Cerium(III) and cerium(IV) compounds such as cerium(III) chloride have uses as catalysts in organic synthesis.

History

Cerium was discovered in Bastnäs in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently in Germany by Martin Heinrich Klaproth, both in 1803. Cerium was so named by Berzelius after the dwarf planet dp Ceres, discovered two years earlier (1801). As originally isolated, cerium was in the form of its oxide, and was named ceria, a term that is still used. The metal itself was too electropositive to be isolated by then-current smelting technology, a characteristic of earth metals in general. However, the development of electrochemistry by Humphry Davy was only five years into the future, and then the earths were well on their way to yielding up the metals they contained. Ceria, as isolated in 1803, contained all of the lanthanides present in the cerite ore from Bastnaes, Sweden, and thus only contained about 45% of what is now known to be pure ceria. It was not until Mosander succeeded in removing lanthana and "didymia" in the late 1830s, that ceria was obtained pure. As an historical aside: Wilhelm Hisinger was a wealthy mine owner and amateur scientist, and sponsor of Berzelius. He owned or controlled the mine at Bastnaes, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungstein of Bastnaes"), now known as cerite, that he had in his mine. Mosander and his family lived for many years in the same house as Berzelius, and the former was undoubtedly persuaded by the latter to investigate ceria further. When the rare earths were first discovered, since they were strong bases like the oxides of calcium or magnesium, they were thought to be divalent. Thus, "ceric" cerium was thought to be trivalent, and the oxidation state ratio was therefore thought to be 1.5. Berzelius was extremely annoyed to keep on getting the ratio 1.33. He was after all one of the finest analytical chemists in Europe. But he was a better analyst than he thought, since 1.33 was the correct answer!

Occurrence

Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals including allanite (also known as orthite)—(Ca, Ce, La, Y)2(Al, Fe)3(SiO4)3(OH), monazite (Ce, La, Th, Nd, Y)PO4, bastnasite (Ce, La, Y)CO3F, hydroxylbastnasite (Ce, La, Nd)CO3(OH, F), rhabdophane (Ce, La, Nd)PO4-H2O, zircon (ZrSiO4), and synchysite Ca(Ce, La, Nd, Y)(CO3)2F. Monazite and bastnasite are presently the two most important sources of cerium.
Cerium is most often prepared via an ion exchange process that uses monazite sands as its cerium source.
Large deposits of monazite, allanite, and bastnasite will supply cerium, thorium, and other rare-earth metals for many years to come.

Compounds

Cerium has two common oxidation states, +3 and +4. The most common compound of cerium is cerium(IV) oxide (CeO2), which is used as "jeweller's rouge" as well as in the walls of some self-cleaning ovens. Two common oxidising agents used in titrations are ammonium cerium(IV) sulfate (ceric ammonium sulfate, (NH4)2Ce(SO4)3) and ammonium cerium(IV) nitrate (ceric ammonium nitrate or CAN, (NH4)2Ce(NO3)6). Cerium also forms a chloride, CeCl3 or cerium(III) chloride, used to facilitate reactions at carbonyl groups in organic chemistry. Other compounds include cerium(III) carbonate (Ce2(CO3)3), cerium(III) fluoride (CeF3), cerium(III) oxide (Ce2O3), as well as cerium(IV) sulfate (ceric sulfate, Ce(SO4)2) and cerium(III) triflate (Ce(OSO2CF3)3).
The two oxidation states of cerium differ enormously in basicity: cerium(III) is a strong base, comparable to the other trivalent lanthanides, but cerium(IV) is weak. This difference has always allowed cerium to be by far the most readily isolated and purified of all the lanthanides, otherwise a notoriously difficult group of elements to separate. A wide range of procedures have been devised over the years to exploit the difference. Among the better ones:
  1. Leaching the mixed hydroxides with dilute nitric acid: the trivalent lanthanides dissolve in cerium-free condition, and tetravalent cerium remains in the insoluble residue as a concentrate to be further purified by other means. A variation on this uses hydrochloric acid and the calcined oxides from bastnaesite, but the separation is less sharp.
  2. Precipitating cerium from a nitrate or chloride solution using potassium permanganate and sodium carbonate in a 1:4 molar ratio.
  3. Boiling rare-earth nitrate solutions with potassium bromate and marble chips.
Using the classical methods of rare-earth separation, there was a considerable advantage to a strategy of removing cerium from the mixture at the beginning. Cerium typically comprised 45% of the cerite or monazite rare earths, and removing it early greatly reduced the bulk of what needed to be further processed (or the cost of reagents to be associated with such processing). However, not all cerium purification methods relied on basicity. Ceric ammonium nitrate [ammonium hexanitratocerate(IV)] crystallization from nitric acid was one purification method. Cerium(IV) nitrate (hexanitratoceric acid) was more readily extractable into certain solvents (e.g. tri-n-butyl phosphate) than the trivalent lanthanides. However, modern practice in China seems to be to do purification of cerium by counter-current solvent extraction, in its trivalent form, just like the other lanthanides.
Cerium(IV) is a strong oxidant under acidic conditions, but stable under alkaline conditions, when it is cerium(III) that becomes a strong reductant, easily oxidized by molecular dioxygen (or air). This ease of oxidation under alkaline conditions leads to the occasional geochemical parting of the ways between cerium and the trivalent light lanthanides under supergene weathering conditions, leading variously to the "negative cerium anomaly" or to the formation of the mineral cerianite. Air-oxidation of alkaline cerium(III) is the most economical way to get to cerium(IV), which can then be handled in acid solution.

Isotopes

Naturally-occurring cerium is composed of 4 stable isotopes; 136Ce, 138Ce, 140Ce, and 142Ce with 140Ce being the most abundant (88.48% natural abundance). 136Ce and 142Ce are predicted to be double beta active but no signs of activity were ever observed (for 142Ce, the lower limit on half-life is 5×1016 years). 26 radioisotopes have been characterized with the most long-lived being 144Ce with a half-life of 284.893 days, 139Ce with a half-life of 137.640 days, and 141Ce with a half-life of 32.501 days. All of the remaining radioactive isotopes have half-lives that are less than 4 days and the majority of these have half-lives that are less than 10 minutes. This element also has 2 meta states.
The known isotopes of cerium range in atomic weight from 123 u (123Ce) to 152 u (152Ce).
Cerium 144 is a high-yield product of nuclear fission; the ORNL Fission Product Pilot Plant separated substantial quantities of cerium-144 from reactor waste, and it was used in the Aircraft Nuclear Propulsion and SNAP programs.

Precautions

Cerium, like all rare-earth metals, is of low to moderate toxicity. Cerium is a strong reducing agent and ignites spontaneously in air at 65 to 80 °C (150 to 175 °F). Fumes from cerium fires are toxic. Water should not be used to stop cerium fires, as cerium reacts with water to produce hydrogen gas. Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Animals injected with large doses of cerium have died due to cardiovascular collapse.
Cerium(IV) oxide is a powerful oxidizing agent at high temperatures and will react with combustible organic materials. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. Cerium serves no known biological function.

Popular culture references

One chapter in Primo Levi's book The Periodic Table called Cerium, the element saves the hero from starvation.

External links

cerium in Arabic: سيريوم
cerium in Bengali: সিরিয়াম
cerium in Belarusian: Цэрый
cerium in Bosnian: Cerijum
cerium in Catalan: Ceri
cerium in Czech: Cer
cerium in Corsican: Ceriu
cerium in Danish: Cerium
cerium in German: Cer
cerium in Estonian: Tseerium
cerium in Modern Greek (1453-): Δημήτριο
cerium in Spanish: Cerio
cerium in Esperanto: Cerio
cerium in Basque: Zerio (elementua)
cerium in French: Cérium
cerium in Friulian: Ceri
cerium in Manx: Kerrium
cerium in Galician: Cerio
cerium in Korean: 세륨
cerium in Armenian: Ցերիում
cerium in Croatian: Cerij
cerium in Ido: Cerio
cerium in Indonesian: Serium
cerium in Italian: Cerio
cerium in Hebrew: צריום
cerium in Haitian: Seryòm
cerium in Latin: Cerium
cerium in Latvian: Cērijs
cerium in Luxembourgish: Cer
cerium in Lithuanian: Ceris
cerium in Lojban: jinmrseri
cerium in Hungarian: Cérium
cerium in Malayalam: സെറിയം
cerium in Dutch: Cerium
cerium in Japanese: セリウム
cerium in Norwegian: Cerium
cerium in Norwegian Nynorsk: Cerium
cerium in Occitan (post 1500): Cèri
cerium in Polish: Cer
cerium in Portuguese: Cério
cerium in Romanian: Ceriu
cerium in Quechua: Seryu
cerium in Russian: Церий
cerium in Sicilian: Ceriu
cerium in Slovak: Cér
cerium in Slovenian: Cerij
cerium in Serbian: Церијум
cerium in Serbo-Croatian: Cerijum
cerium in Saterfriesisch: Cerium
cerium in Finnish: Cerium
cerium in Swedish: Cerium
cerium in Tamil: சீரியம்
cerium in Thai: ซีเรียม
cerium in Vietnamese: Xeri
cerium in Turkish: Seryum
cerium in Ukrainian: Церій
cerium in Urdu: Cerium
cerium in Contenese: 鈰
cerium in Chinese: 铈
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