Cerium

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Notable Characteristics

Cerium is a silvery metallic element, belonging to the lanthanide group. It is used in some rare-earth alloys. The oxidized form is used in the glass industry. It resembles iron in color and luster, but is soft, and both malleable and ductile. It tarnishes readily in the air.

Only europium is more reactive than cerium among rare earth elements. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife. Cerium decomposes slowly in cold water and rapidly in hot water.

Because of the relative closeness of the 4f and outer shell orbitals in cerium, it exhibits an interestingly variable chemistry. For example, compression or cooling of the metal can change its oxidation state from about 3 to 4.

Cerium in the +3 oxidation state is referred to as cerous, while the metal in the +4 oxidation state is called ceric.

Cerium (IV) salts are orange red or yellowish, whereas cerium (III) salts are usually white.

Applications

Uses of cerium:

• In metallurgy:
  • Cerium is used in making aluminium alloys and some steels and irons.
  • Adding cerium to cast irons opposes graphitisation and produces a malleable iron.
  • In steels cerium can help reduce sulfides and oxides and degasifies.
  • Cerium is used in stainless steel as a precipitation-hardening agent.
  • 3 to 4% cerium added to magnesium alloys, along with 0.2 to 0.6% zirconium, helps refine the grain and give sound casting of complex shapes. It also adds heat resistance to magnesium castings.
  • Cerium is used in alloys that are used to make permanent magnets.
• Cerium is used in carbon-arc lighting[?], especially in the motion picture industry.
• Cerium is a component of Mischmetal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters.
• The oxide is used in incandescent gas mantles.
• The oxide is emerging as a hydrocarbon catalyst in self cleaning ovens, incorporated into oven walls.
• Ceric sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis.
• Cerium compounds are used in the manufacture of glass, both as a component and as a decolorizer.
• Cerium compounds are used for the coloring of enamel.
• The oxide is finding increased use as a glass polishing agent.
• In glass, cerium oxide allows for selective absorption of ultraviolet light.
• Cerium oxide is finding use as a petroleum cracking catalyst in petroleum refining.
• Cerium(III) and Cerium(IV) compounds have uses as catalysts in organic synthesis.

History

Cerium was discovered in Sweden by Jöns Jacob Berzelius and Wilhelm von Hisinger[?], and independently in Germany by Martin Heinrich Klaproth[?], both in 1803. Cerium was so named by Berzelius after the asteroid Ceres, discovered two years earlier (1801).

Biological Role

Cerium serves no known biological function.

Occurrence

Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust. 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, 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

Isotopes

Naturally occurring cerium is composed of 3 stable isotopes and 1 radioactive isotope; 136-Ce, 138-Ce, 140-Ce, and 142-Ce with 140-Ce being the most abundant (88.48% natural abundance). 27 radioisotopes have been characterized with the most {abundant and/or stable} being 142-Ce with a half-life of >5E16 years, 144-Ce with a half-life of 284.893 days, 139-Ce with a half-life of 137.640, and 141-Ce with a half-life of 32.501 days. All of the remaining radioactive isotopes have half-lifes that are less than 4 days and the majority of these have half lifes that are less than 10 minutes. This element also has 2 meta states.

The isotopes of cerium range in atomic weight from 123 amu (123-Ce) to 152 amu (152-Ce).

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 65-80 degrees C. Cerium may react explosively with zinc, and its reactions with bismuth and antimony are very exothermic. 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 isn't radioactive, the impure commercial grade may contain traces of thorium, which is radioactive.

External Links

• WebElements.com - Cerium (http://www.webelements.com/webelements/elements/text/Ce/index.html)
• EnvironmentalChemistry.com - Cerium (http://environmentalchemistry.com/yogi/periodic/Ce.html)
• It's Elemental - The Element Cerium (http://education.jlab.org/itselemental/ele058.html)
• Cerium Properties and Applications (http://www.azom.com/details.asp?ArticleID=592)

Common misspelling and questions (FAQ)

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