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Samarium

Samarium

Gist

Samarium (Sm) is a chemical element, a silvery-white, moderately hard metal that is part of the lanthanide series on the periodic table. It has an atomic number of 62 and is represented by the symbol Sm. Discovered in 1879 by Paul-Émile Lecoq de Boisbaudran, samarium is known for its use in Samarium-Cobalt magnets.

Samarium has diverse applications, primarily in samarium-cobalt (SmCo) magnets, which are known for their high resistance to demagnetization and ability to function at high temperatures. It's also used in nuclear reactors as a neutron absorber, in catalysis, and in medical treatments for cancer pain.

Summary

Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide.

Discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, samarium was named after the mineral samarskite from which it was isolated. The mineral itself was named after a Russian mine official, Colonel Vassili Samarsky-Bykhovets, who thus became the first person to have a chemical element named after him, though the name was indirect.

Samarium occurs in concentration up to 2.8% in several minerals including cerite, gadolinite, samarskite, monazite and bastnäsite, the last two being the most common commercial sources of the element. These minerals are mostly found in China, the United States, Brazil, India, Sri Lanka and Australia; China is by far the world leader in samarium mining and production.

The main commercial use of samarium is in samarium–cobalt magnets, which have permanent magnetization second only to neodymium magnets; however, samarium compounds can withstand significantly higher temperatures, above 700 °C (1,292 °F), without losing their permanent magnetic properties. The radioisotope samarium-153 is the active component of the drug samarium (153Sm) lexidronam (Quadramet), which kills cancer cells in lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and so is added to control rods of nuclear reactors. It also forms as a decay product during reactor operation and is one of the important factors considered in reactor design and operation. Other uses of samarium include catalysis of chemical reactions, radioactive dating and X-ray lasers. Samarium(II) iodide, in particular, is a common reducing agent in chemical synthesis.

Samarium has no biological role; some samarium salts are slightly toxic.

Details

Samarium (Sm) is a chemical element, a rare-earth metal of the lanthanide series of the periodic table.

Samarium is a moderately soft metal, silvery white in colour. It is relatively stable in air, slowly oxidizing to Sm2O3. It rapidly dissolves in diluted acids—except hydrofluoric acid (HF), in which it is stable because of formation of a protective trifluoride (SmF3) layer. Samarium is a moderately strong paramagnet above 109 K (−164 °C, or −263 °F). Below 109 K, antiferromagnetic order develops for the cubic sites in the samarium lattice, and the hexagonal site atoms finally order antiferromagnetically below 14 K (−259 °C, or −434 °F).

Samarium was isolated as an impure oxide and spectroscopically identified as a new element in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran. Samarium occurs in many other rare-earth minerals but is almost exclusively obtained from bastnasite; it is also found in products of nuclear fission. In Earth’s crust, samarium is as abundant as tin.

The seven naturally occurring isotopes of samarium are samarium-144 (3.1 percent), samarium-147 (15.0 percent), samarium-148 (11.2 percent), samarium-149 (13.8 percent), samarium-150 (7.4 percent), samarium-152 (26.8 percent), and samarium-154 (22.0 percent). Samarium-144, samarium-150, samarium-152, and samarium-154 are stable, but the other three naturally occurring isotopes are alpha emitters. A total of 34 (excluding nuclear isomers) radioactive isotopes of samarium have been characterized. Their mass ranges from 128 to 165, and their half-life can be as short as 0.55 second for samarium-129 or as long as 7 × 1015 years for samarium-148.

Liquid-liquid and ion-exchange techniques are used for the commercial separation and purification of samarium. The metal is conveniently prepared by metallothermic reduction of its oxide, Sm2O3, with lanthanum metal, followed by distillation of the samarium metal, which is one of the most volatile rare-earth elements. Samarium exists in three allotropic (structural) forms. The α-phase (or Sm-type structure) is a rhombohedral arrangement that is unique among the elements, with a = 3.6290 Å and c = 26.207 Å at room temperature. (The unit cell dimensions are given for the non-primitive hexagonal unit cell of the primitive rhombohedral lattice.) The β-phase is hexagonal close-packed with a = 3.6630 Å and c = 5.8448 Å at 450 °C (842 °F). The γ-phase is body-centred cubic with a = 4.10 Å (estimated) at 922 °C (1,692 °F).

The most common use of samarium is with cobalt (Co) in high-strength SmCo5- and Sm2Co17-based permanent magnets suitable for high-temperature applications. The energy product of samarium-based permanent magnets is second to those based on neodymium, iron, and boron (Nd2Fe14B), but the latter have much lower Curie points than the samarium magnets and therefore are unsuitable for applications above approximately 300 °C (570 °F). Because of its high absorption cross section for thermal neutrons (samarium-149), samarium is used as an addition in nuclear reactor control rods and for neutron shielding. Other uses are in phosphors for displays and TV screens that use cathode-ray tubes, in special luminescent and infrared-absorbing glasses, in inorganic and organic catalysis, and in the electronics and ceramics industries.

In addition to its more stable +3 oxidation state, samarium, unlike most of the rare earths, has a +2 oxidation state. The Sm2+ ion is a powerful reducing agent that rapidly reacts with oxygen, water, or hydrogen ions. It can be stabilized by precipitation as the extremely insoluble sulfate SmSO4. Other salts of samarium in the +2 state are SmCO3, SmCl2, SmBr2, and Sm(OH)2; they are reddish brown in colour. In its +3 oxidation state, samarium behaves as a typical rare-earth element; it forms a series of yellow salts in solutions.

Element Properties

atomic number  :  62
atomic weight  :  150.36
melting point  :  1,074 °C (1,965 °F)
boiling point  :  1,794 °C (3,261 °F)
density  :  7.520 g/{cm}^{3} (24 °C, or 75 °F)
oxidation states  :  +2, +3.

Additional Information:

Appearance

A silvery-white metal.

Uses

Samarium-cobalt magnets are much more powerful than iron magnets. They remain magnetic at high temperatures and so are used in microwave applications. They enabled the miniaturisation of electronic devices like headphones, and the development of personal stereos. However, neodymium magnets are now more commonly used instead.

Samarium is used to dope calcium chloride crystals for use in optical lasers. It is also used in infrared absorbing glass and as a neutron absorber in nuclear reactors. Samarium oxide finds specialised use in glass and ceramics. In common with other lanthanides, samarium is used in carbon arc lighting for studio lighting and projection.

Biological role

Samarium has no known biological role. It has low toxicity.

Natural abundance

Samarium is found along with other lanthanide metals in several minerals, the principal ones being monazite and bastnaesite. It is separated from the other components of the mineral by ion exchange and solvent extraction.

Recently, electrochemical deposition has been used to separate samarium from other lanthanides. A lithium citrate electrolyte is used, and a mercury electrode. Samarium metal can also be produced by reducing the oxide with barium.

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