Difference between revisions of "Cerium" - New World Encyclopedia

Vapor pressure
58	lanthanum ← cerium → praseodymium
	periodic table
General
Name, Symbol, Number	cerium, Ce, 58
Chemical series	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	silvery white ;
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)
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

Revision as of 21:14, 19 February 2007

Cerium (chemical symbol Ce, atomic number 58) is a silvery metallic element that belongs to the lanthanide group. It is used in some rare-earth alloys.

Although cerium belongs to chemical elements group called rare earth metals, it is not rare at all. Cerium is available in relatively large quantities (68 ppm in Earth’s crust); in fact it is more common than lead.

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.

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 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 oxidizes slowly in cold water and rapidly in hot water.

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% 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 4 days, and the majority of these have half-lives under 10 minutes. This element also has 2 meta states. The isotopes of cerium range in atomic weight from 119 atomic mass units (u) to 157 u.

Compounds

Cerium(IV)-sulfate

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).

Applications

Uses of cerium:

In metallurgy:
- Cerium is used in making aluminium alloys.
- Adding cerium to cast irons opposes 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.
- 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 as an alloying element in tungsten electrodes for gas tungsten arc welding.
- Cerium 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 in carbon-arc lighting, especially in the motion picture industry.
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.
- 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.
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.
Cerium(III) and cerium(IV) compounds such as cerium(III) chloride have uses as catalysts in organic synthesis.

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. 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.

References
ISBN links support NWE through referral fees

Cerium Los Alamos National Laboratory.

Chang, Raymond (2006). Chemistry (ninth ed.) New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.

Greenwood, N.N.; and Earnshaw, A. (1998). Chemistry of the Elements (2nd Edition). Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654. Online version.

Cotton, F. Albert; and Wilkinson, Geoffrey (1980). Advanced Inorganic Chemistry (4th ed.), New York:Wiley. ISBN 0-471-02775-8.

Stwertka, Albert (1998). Guide to the Elements, Revised Edition. Oxford, UK: Oxford University Press. ISBN 0-19-508083-1.

Lattice and spin dynamics of gamma-Ce

External links

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@@ Line 60: / Line 60: @@
 '''Cerium''' (chemical symbol '''Ce''', [[atomic number]] 58) is a silvery metallic element that belongs to the [[lanthanide]] group. It is used in some rare-earth alloys.
+Although cerium belongs to chemical elements group called [[rare earth metals]], it is not rare at all. Cerium is available in relatively large quantities (68 ppm in Earth’s crust); in fact it is more common than [[lead]].
 == Occurrence ==
@@ Line 76: / Line 78: @@
 Cerium 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 oxidizes slowly in cold water and rapidly in hot water.
-Although cerium belongs to chemical elements group called [[rare earth metals]], it is not rare at all. Cerium is available in relatively large quantities (68 ppm in Earth’s crust); in fact it is more common than [[lead]].
 In forming compounds, cerium has two common [[oxidation state]]s, +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.