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Cerium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                58            lanthanum ← cerium → praseodymium
                 -
                ↑
                Ce
                ↓
                Th

                                  Periodic Table - Extended 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] 4f^1 5d^1 6s^2
                                    Electrons per shell 2, 8, 18, 19, 9, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 6.770 g·cm^−3
                                    Liquid density at m.p. 6.55 g·cm^−3
                                                     Melting point 1068  K
                                                     (795 ° C, 1463 ° F)
                                                      Boiling point 3716 K
                                                    (3443 ° C, 6229 ° F)
                                          Heat of fusion 5.46 kJ·mol^−1
                                     Heat of vaporization 398 kJ·mol^−1
                          Heat capacity (25 °C) 26.94 J·mol^−1·K^−1

   CAPTION: 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^−1
                                                    2nd: 1050 kJ·mol^−1
                                                    3rd: 1949 kJ·mol^−1
                                                      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^−1·K^−1
                                      Thermal expansion ( r.t.) (γ, poly)
                                                            6.3 µm/(m·K)
                               Speed of sound (thin rod) (20 °C) 2100 m/s
                                        Young's modulus (γ form) 33.6 GPa
                                          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
                                                         Selected isotopes

                  CAPTION: 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% > 5×10^16 years β^- unknown   ^142Nd
                        ^144Ce syn    284.893 days    β^- 0.319     ^144Pr

                                                                References

   Cerium ( IPA: /ˈsiːriəm, ˈsɪəriəm/) is a chemical element in the
   periodic table that has the symbol Ce and atomic number 58.

Notable characteristics

   Cerium is a silvery metallic element, belonging to the lanthanide
   group. It is used in some rare-earth alloys. It resembles iron in
   colour 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.

   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.
          + 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.

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 asteroid
   Ceres, discovered two years earlier ( 1801).

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](SiO[4])[3](OH), monazite (Ce, La, Th, Nd, Y)PO[4],
   bastnasite(Ce, La, Y)CO[3]F, hydroxylbastnasite (Ce, La, Nd)CO[3](OH,
   F), rhabdophane (Ce, La, Nd)PO[4]-H[2]O, zircon (ZrSiO[4]), and
   synchysite Ca(Ce, La, Nd, Y)(CO[3])[2]F. 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 h

Compounds

   Cerium(IV)-sulfate
   Enlarge
   Cerium(IV)-sulfate

   Cerium has two common oxidation states, +3 and +4. The most common
   compound of cerium is cerium(IV) oxide (CeO[2]), 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, (NH[4])[2]Ce(SO[4])[3]) and ammonium
   cerium(IV) nitrate (ceric ammonium nitrate or CAN,
   (NH[4])[2]Ce(NO[3])[6]). Cerium also forms a chloride, CeCl[3] or
   cerium(III) chloride, used to facilitate reactions at carbonyl groups
   in organic chemistry. Other compounds include cerium(III) carbonate
   (Ce[2](CO[3])[3]), cerium(III) fluoride (CeF[3]), cerium(III) oxide
   (Ce[2]O[3]), as well as cerium(IV) sulfate (ceric sulfate,
   Ce(SO[4])[2]) and cerium(III) triflate (Ce(OSO[2]CF[3])[3]).

   See also Category:Cerium compounds

Isotopes

   Naturally occurring cerium is composed of 3 stable isotopes and 1
   radioactive isotope; ^136Ce, ^138Ce, ^140Ce, and ^142Ce with ^140Ce
   being the most abundant (88.48% natural abundance). 27 radioisotopes
   have been characterized with the most {abundant and/or stable} being
   ^142Ce with a half-life of greater than 5×10^16 years, ^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 isotopes of cerium range in atomic weight from 123 u (^123Ce) to
   152 u (^152Ce).

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.
   Retrieved from " http://en.wikipedia.org/wiki/Cerium"
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   with only minor checks and changes (see www.wikipedia.org for details
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