Samarium

Samarium (pronounced /səˈmɛəriəm/) is a chemical element with the symbol Sm and atomic number 62.

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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. Even with long-term storage under mineral oil, samarium is gradually oxidized, with a grayish-yellow powder of the oxide-hydroxide being formed. Three crystal modifications of the metal also exist, with transformations at 734 and 922 °C.

Applications

Uses of Samarium include:

• Carbon-arc lighting for the motion picture industry (together with other rare earth metals).
• CaF₂ crystals for use in optical masers or lasers.
• As a neutron absorber in nuclear reactors.
• For alloys and headphones.
• Samarium-Cobalt magnets; SmCo₅ and Sm₂Co₁₇ are used in making permanent magnet materials that have high resistance to demagnetization when compared to other permanent magnet materials. These materials have high coercivities and intrinsic coercivities. Samarium-cobalt combinations have recently found use in high-end magnetic pickups for guitars and related musical instruments.
• 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.
• Radioactive Samarium-153 is used in medicine to treat the severe pain associated with cancers that have spread to bone. The drug is called "Quadramet".

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). Although samarskite was first found in the Urals, by the late 1870s a new deposit had been located in North Carolina, and it was from that source that the samarium-bearing didymium had originated.

The samarskite mineral was named after Vasili Samarsky-Bykhovets, the Chief of Staff (Colonel) of the Russian Corps of Mining Engineers in 1845–1861. The name of the element is derived from the name of the mineral, and thus traces back to the name Samarsky-Bykhovets. In this sense samarium was the first chemical element to be named after a living person.

Prior to the advent of ion-exchange separation technology in the 1950s, samarium had no commercial uses in pure form. However, a by-product of the fractional crystallization purification of neodymium was a mixture of samarium and gadolinium that acquired the name of "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some of the early nuclear reactors. Nowadays, a similar commodity product goes under the name of "Samarium-Europium-Gadolinium" concentrate (or SEG concentrate). This is prepared by solvent extraction from the mixed lanthanides extracted from bastnäsite (or monazite). Since the heavier lanthanides have the greater affinity for the solvent used, they are easily extracted from the bulk using relatively small proportions of solvent. Not all rare earth producers who process bastnäsite do so on large enough scale to continue onward with the separation of the components of SEG, which typically makes up only one or two percent of the original ore. Such producers will therefore be making SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium content of the ore is rescued for use in phosphor manufacture. Samarium purification follows the removal of the europium. Currently, being in oversupply, samarium oxide is less expensive on a commercial scale than its relative abundance in the ore might suggest.

Biological role

Samarium has no known biological role, but is said to stimulate the metabolism.^{[citation needed]}

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 bastnäsite 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

Main article: isotopes of samarium

Naturally occurring samarium is composed of 4 stable isotopes, ¹⁴⁴Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and 3 extremely long-lived radioisotopes, ¹⁴⁷Sm (1.06×10¹¹y), ¹⁴⁸Sm (7×10¹⁵y) and ¹⁴⁹Sm (>2×10¹⁵y), with ¹⁵²Sm being the most abundant (26.75% natural abundance).

¹⁵¹Sm has a halflife of 90 years, and ¹⁴⁵Sm has a halflife of 340 days. All of the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives 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.

Natural Samarium has an activity of 128 Bq/g.

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
• Centerwatch About drug Quadramet

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