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Home | Edit | Index | Recent ChangesJust visited: Food Diary 2008-04-15 | About The Hive Wiki | Selenium | Food Diary 2008-04-14 | Cryptozoology Cerium () is a chemical element with the symbol Ce and atomic number 58. Notable characteristicsCerium 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.
ApplicationsUses of cerium:
HistoryCerium 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 , 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!OccurrenceCerium 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 ([ZrSiO]Create?4), 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. See also :Category:Lanthanide minerals CompoundsCerium 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, [CeCl]Create?3 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:
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. See also :Category:Cerium compounds IsotopesNaturally-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. PrecautionsCerium, 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. ReferencesExternal linksCategory:Chemical elements Category:Lanthanides Category:cerium compounds ar:سيريوم bn:সিরিয়াম be:Цэрый bs:Cerijum ca:Ceri cs:Cer co:Ceriu da:Cerium de:Cer et:Tseerium el:Δημήτριο es:Cerio eo:Cerio eu:Zerio (elementua) fr:Cérium fur:Ceri gv:Kerrium gl:Cerio ko:세륨 hy:Ցերիում hr:Cerij io:Cerio id:Serium it:Cerio he:צריום ht:Seryòm la:Cerium lv:Cērijs lb:Cer lt:Ceris jbo:jinmrseri hu:Cérium ml:സെറിയം nl:Cerium ja:セリウム no:Cerium nn:Cerium oc:Cèri pl:Cer pt:Cério ro:Ceriu qu:Seryu ru:Церий scn:Ceriu sk:Cér sl:Cerij sr:Церијум sh:Cerijum fi:Cerium sv:Cerium ta:சீரியம் th:ซีเรียม vi:Xeri tr:Seryum uk:Церій ur:Cerium zh-yue:鈰 zh:铈
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