Cerium

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58 lanthanumceriumpraseodymium
-

Ce

Th
Ce-TableImage.png
General
Name, Symbol, Number cerium, Ce, 58
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance silvery white
Ce,58.jpg
Atomic mass 140.116(1) g/mol
Electron configuration [Xe] 4f1 5d1 6s2
Electrons per shell 2, 8, 18, 19, 9, 2
Physical properties
Phase solid
Density (near r.t.) 6.770 g/cm³
Liquid density at m.p. 6.55 g/cm³
Melting point 1068 K
(795 °C, 1463 °F)
Boiling point 3716 K
(3443 °C, 6229 °F)
Heat of fusion 5.46 kJ/mol
Heat of vaporization 398 kJ/mol
Heat capacity (25 °C) 26.94 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1992 2194 2442 2754 3159 3705
Atomic properties
Crystal structure cubic face centered
Oxidation states 3, 4
(mildly basic oxide)
Electronegativity 1.12 (Pauling scale)
Ionization energies
(more)
1st: 534.4 kJ/mol
2nd: 1050 kJ/mol
3rd: 1949 kJ/mol
Atomic radius 185 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (r.t.) (β, poly) 828 nΩ·m
Thermal conductivity (300 K) 11.3 W/(m·K)
Thermal expansion (r.t.) (γ, poly)
6.3 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2100 m/s
Speed of sound (thin rod) (r.t.) (γ form) 33.6 m/s
Shear modulus (γ form) 13.5 GPa
Bulk modulus (γ form) 21.5 GPa
Poisson ratio (γ form) 0.24
Mohs hardness 2.5
Vickers hardness 270 MPa
Brinell hardness 412 MPa
CAS registry number 7440-45-1
Notable isotopes
Main article: Isotopes of cerium
iso NA half-life DM DE (MeV) DP
134Ce syn 3.16 days ε 0.500 134La
136Ce 0.19% Ce is stable with 78 neutrons
138Ce 0.25% Ce is stable with 80 neutrons
139Ce syn 137.640 days ε 0.278 139La
140Ce 88.48% Ce is stable with 82 neutrons
141Ce syn 32.501 days β- 0.581 141Pr
142Ce 11.08% > 5×1016 years β- unknown 142Nd
144Ce syn 284.893 days β- 0.319 144Pr

Cerium (chemical symbol Ce, atomic number 58) is a silvery metallic element that is a member of the lanthanide series of chemical elements. It is considered one of the "rare earth metals," but it is not rare at all.[1] It is, in fact, more common than lead.

Contents

Cerium, its alloys, and its compounds are valuable for a variety of applications. For example, cerium is used in carbon-arc lighting in the motion picture industry and is an alloying agent in tungsten electrodes for gas tungsten arc welding. It is used in alloys for permanent magnets and is a major component of ferrocerium, also known as "lighter flint." It degasifies steels, reducing sulfides and oxides in them. Cerium(IV) oxide is used in incandescent gas mantles, and has largely replaced rouge in the glass industry as a polishing abrasive. The oxide is also useful as a catalyst for petroleum refining and for self cleaning ovens. Cerium(IV) sulfate is an oxidizing agent for quantitative chemical analyses, and cerium(III) chloride is a catalyst in organic synthetic reactions.

Occurrence

Cerium is the most abundant of the rare earth elements, making up about 0.0046 percent 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. The existence of large deposits of monazite, allanite, and bastnasite will supply cerium, thorium, and other rare-earth metals for many years to come. Cerium is most often prepared via an ion exchange process that uses monazite sands as its cerium source.

History

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

Notable characteristics

Cerium is an inner transition metal (or lanthanide) that lies in period six of the periodic table, between lanthanum and praseodymium. It resembles iron in color and luster, but it is soft, malleable, and ductile. It tarnishes readily in the air. Only europium is more reactive than cerium among rare earth elements. The pure metal is likely to ignite if scratched with a knife. It oxidizes slowly in cold water and rapidly in hot water. It is rapidly attacked by alkali solutions and acids.

In forming compounds, cerium has two common oxidation states, +3 and +4. The metal in the +3 oxidation state is referred to as cerous, that in the +4 oxidation state is called ceric. Cerium(IV) salts are orange red or yellowish, whereas cerium(III) salts are usually white.

Isotopes

Naturally occurring cerium is composed of three stable isotopes (136Ce, 138Ce, 140Ce) and one radioactive isotope (142Ce). Of these, 140Ce is the most abundant (88.48 percent natural abundance). The radioisotope 142Ce has a half-life of greater than 5×1016 years.

Many additional radioisotopes have been characterized, including 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 the remaining radioactive isotopes have half-lives that are less than four days, and the majority of these have half-lives under ten minutes. This element also has two meta states. The isotopes of cerium range in atomic weight from 119 atomic mass units (u) to 157 u.

Compounds

Cerium(IV)-sulfate
  • Cerium(IV) oxide, ceric oxide, or ceria (CeO2): This pale yellow oxide is the most common compound of cerium. It is used in lapidary as "jeweler's rouge" and in ceramics to polish glass. It is also used in the walls of some self-cleaning ovens as a catalyst during the high-temperature cleaning process. Ceria can conduct ions (oxide ions) and electrons, and it is therefore called a "mixed ionic electronic conducting material." At temperatures above 500 °C, it becomes a predominantly ionic conductor and is potentially useful as an electrolyte in solid-oxide fuel cells (SOFCs).
  • Cerium(III) chloride, cerous chloride, or cerium trichloride (CeCl3): This compound serves as a starting material for the preparation of other cerium salts. In addition, it is a catalyst for certain reactions in organic chemistry.[2]
  • Ammonium cerium(IV) nitrate or ceric ammonium nitrate (CAN) [(NH4)2Ce(NO3)6]: This orange-red compound is an oxidizing agent widely used in organic synthesis. It is also a standard oxidant used in quantitative analysis (titrations). Catalytic amounts of CAN in tap water can be used for the efficient synthesis of various quinoxaline derivatives, which in turn are useful for dyes, organic semiconductors, and DNA cleaving agents. Quinoxaline derivatives are also important components in antibiotics such as echinomycin and actinomycin.
  • Cerium(IV) sulfate or ceric sulfate (Ce(SO4)2): This compound is a common oxidizing agent used in quantitative analysis (titrations).

Additional compounds

  • Cerium(III) carbonate (Ce2(CO3)3)
  • Cerium(III) fluoride (CeF3)
  • Cerium(III) oxide (Ce2O3)
  • Cerium(III) triflate (Ce(OSO2CF3)3)
  • Ammonium cerium(IV) sulfate or ceric ammonium sulfate [(NH4)2Ce(SO4)3]

Applications

  • Uses of cerium:
    • Cerium is used in carbon-arc lighting, especially in the motion picture industry.
    • It is a major component of ferrocerium, also known as "lighter flint." Although modern alloys of this type generally use Mischmetal rather than purified cerium, it still is the most prevalent constituent.
    • Cerium is used as an alloying element in tungsten electrodes for gas tungsten arc welding.
    • Cerium is used in alloys that are used to make permanent magnets.
    • Cerium is used in making aluminum alloys.
    • Addition of cerium to cast iron counters graphitization and produces a malleable iron.
    • In steels, cerium degasifies and can help reduce sulfides and oxides.
    • Cerium is used in stainless steel as a precipitation hardening agent.
    • Addition of three to four percent cerium to magnesium alloys, along with 0.2 to 0.6 percent zirconium, helps refine the grain and allows sound casting in complex shapes. It also enhances heat resistance of magnesium castings.
  • Uses of Cerium(IV) oxide:
    • The oxide is used in incandescent gas mantles, such as the Welsbach mantle, where it has been combined with thorium, lanthanum, magnesium or yttrium oxides.
    • This oxide has largely replaced rouge in the glass industry as a polishing abrasive.
    • It is finding use as a petroleum cracking catalyst in petroleum refining.
    • It is also emerging as a catalyst in self cleaning ovens, incorporated into oven walls.
    • In glass, cerium(IV) oxide allows for selective absorption of ultraviolet light.
  • Cerium(IV) sulfate is used extensively as an oxidizing agent in quantitative chemical analysis.
  • Cerium(III) and cerium(IV) compounds, such as cerium(III) chloride, are useful as catalysts in organic synthetic reactions.
  • Cerium compounds are used as components and decolorizers of glass. Cerium compounds are used for the coloring of enamel.

Precautions

Cerium, like all rare earth metals, has low-to-moderate toxicity. It is a strong reducing agent and ignites spontaneously in air at 65 to 80 °C. 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.

See also

Notes

  1. The term "rare earth metals" (or "rare earth elements") is a trivial name applied to 16 chemical elements: scandium, yttrium, and 14 of the 15 lanthanides (excluding promethium), which occur naturally on Earth. Some definitions also include the actinides. The word "earth" is an obsolete term for oxide. The term "rare earth" is discouraged by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are relatively abundant in the Earth's crust.
  2. Cerium(III) chloride is a catalyst for Friedel-Crafts alkylation reactions and for reactions at carbonyl groups in organic compounds.

References

  • "Cerium" Los Alamos National Laboratory, Chemistry Division. Retrieved December 9, 2007.
  • Chang, Raymond. 2006. Chemistry. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
  • Cotton, F. Albert, and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry. 4th ed. New York: Wiley. ISBN 0-471-02775-8
  • Greenwood, N.N. and A. Earnshaw. 1998. Chemistry of the Elements. 2nd ed. Oxford, U.K.; Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
  • Jones, Adrian P., Frances Wall, and C. Terry Williams, eds. 1996. Rare Earth Minerals: Chemistry, Origin and Ore Deposits. The Mineralogical Society Series. London: Chapman and Hall. ISBN 0412610302
  • Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford: Oxford University Press.

External links

All links retrieved April 28, 2013.

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