Samarium

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Samarium is a chemical element in the periodic table that has the symbol Sm and atomic number 62.

Contents 1 Notable characteristics 2 Applications 3 History 4 Biological role 5 Occurrence 6 Compounds 7 Isotopes 8 Precautions 9 References 10 External links

Notable characteristics

Samarium is a rare earth metal, with a bright silver luster, that is reasonably stable in air; it ignites in air at 150°C. Three crystal modifications of the metal also exist, with transformations at 734 and 922°C, respectively.

Applications

Uses of Samarium include:

• Carbon-arc lighting for the motion picture industry (together with other rare earth metals).
• Doping CaF₂ crystals for use in optical masers or lasers.
• As a neutron absorber in nuclear reactors.
• For alloys and headphones.
• Samarium-Cobalt magnets; SmCo₅ is used in making a new permanent magnet material with the highest resistance to demagnetization of any known material, and an intrinsic coercive force as high as 2200 kA/m.
• Samarium(II) iodide is used as a chemical reagent in organic synthesis, for example in the Barbier reaction.
• Samarium oxide is used in optical glass to absorb infrared light.
• Samarium compounds act as sensitizers for phosphors excited in the infrared.
• Samarium oxide is a catalyst for the dehydration and dehydrogenation of ethanol.

History

Samarium was first discovered spectroscopically in 1853 by Swiss chemist Jean Charles Galissard de Marignac by its sharp absorption lines in didymium, and isolated in Paris in 1879 by French chemist Paul Émile Lecoq de Boisbaudran from the mineral samarskite ((Y,Ce,U,Fe)₃(Nb,Ta,Ti)₅O₁₆). Like the mineral, it was named after a Russian mine official, Colonel Samarski.

Biological role

Samarium has no known biological role, but is said to stimulate the metabolism.

Occurrence

Samarium is never found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnasite and samarskite; monazite (in which it occurs up to an extent of 2.8%) and bastnasite are also used as commercial sources. Misch metal containing about 1% of samarium has long been used, but it was not until recent years that relatively pure samarium has been isolated through ion exchange processes, solvent extraction techniques, and electrochemical deposition. The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride^[1]. Samarium can also be obtained by reducing its oxide with lanthanum.

Compounds

Compounds of Samarium include:

• Fluorides
  • SmF₂
  • SmF₃
• Chlorides
  • SmCl₂
  • SmCl₃
• Bromides
  • SmBr₂
  • SmBr₃
• Iodides
  • SmI₂
  • SmI₃
• Oxides
  • Sm₂O₃
• Sulfides
  • Sm₂S₃
• Selenides
  • Sm₂Se₃
• Tellurides
  • Sm₂Te₃

See also samarium compounds.

Isotopes

Naturally occurring samarium is composed of 4 stable isotopes, ¹⁴⁴Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and 3 radioisotopes, ¹⁴⁷Sm, ¹⁴⁸Sm and ¹⁴⁹Sm, with ¹⁵²Sm being the most abundant (26.75% natural abundance). 32 radioisotopes have been characterized, with the most stable being ¹⁴⁸Sm with a half-life of 7x10¹⁵ years, ¹⁴⁹Sm with a half-life of more than 2x10¹⁵ years, and ¹⁴⁷Sm with a half-life of 1.06x10¹¹ years. All of the remaining radioactive isotopes have half-lifes that are less than 1.04x10⁸ years, and the majority of these have half lifes that are less than 48 seconds. This element also has 5 meta states with the most stable being ^141mSm (t_½ 22.6 minutes), ^143m1Sm (t_½ 66 seconds) and ^139mSm (t_½ 10.7 seconds).

The primary decay mode before the most abundant stable isotope, ¹⁵²Sm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before ¹⁵²Sm are element Pm (promethium) isotopes, and the primary products after are element Eu (europium) isotopes.

Precautions

As with the other lanthanides, samarium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.

References

• Los Alamos National Laboratory – Samarium

1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.

External links

Template:Commons Template:Wiktionary

• WebElements.com – Samarium
• It's Elemental – Samarium
• Chemical Elements.com – Samarium (Sm)
• Reducing Agents > Samarium low valentca:Samari

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