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Samarium (revised)

SAMARIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Samarium is one of the rare earth elements found in Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The rare earth metals are not really very rare in the Earth's surface. The name comes from the fact that these elements are very difficult to separate from each other. For a long time, chemists knew very little about the individual elements. A more correct name for the rare earth elements is the lanthanide series. It is named after the element lanthanum, a transition metal also often considered a lanthanide.

Samarium looks and behaves like most other metals, but it has relatively few uses. One of the most important is in the manufacture of very powerful magnets. Compounds of samarium are also used to color glass and in television tubes.

SYMBOL
Sm

ATOMIC NUMBER
62

ATOMIC MASS
150.4

FAMILY
Lanthanide
(rare earth metal)

PRONUNCIATION
suh-MARE-ee-um

Discovery and naming

The study of chemical elements during the nineteenth century was frustrating. Each time a new element was announced, questions were immediately raised. Was the element really a new element? Or was it a mixture of two or more new elements?

The discovery of samarium grew out of this kind of frustration. In 1880, French chemist Paul-Émile Lecoq de Boisbaudran (1838-1912) was studying a substance known as didymium. Earlier chemists believed didymium might be a new element. Boisbaudran said that at least two new elements were present in didymium.

At nearly the same time, French chemist Jean-Charles-Galissard de Marignac (1817-94) was also studying didymium. He was able to separate didymium into two parts, which he called didymium and samarium. He announced that samarium was a new element.

Marignac's research appeared to be satisfactory for nearly twenty years. Then, another French chemist, Eugène-Anatole Demarçay (1852-1904), found that samarium could itself be broken into two parts. He called the new elements samarium and europium. Because of this long history, credit for the discovery of samarium is usually given to Boisbaudran, Marignac, Demarçay, or to all three chemists.

The name samarium was taken from a mineral in which it occurs, samarskite. The name of the mineral, in turn, comes from the last name of a Russian mine official, Colonel Samarski.

Physical properties

Samarium is a yellowish metal with a melting point of 1,072°C (1,962°F) and a boiling point of about 1,900°C (3,450°F). Its density is 7.53 grams per cubic centimeter. Samarium is the hardest and most brittle of the rare earth elements.

Chemical properties

Samarium is a fairly reactive metal. It tends to combine with many other substances under relatively mild conditions. For example, it reacts with water to release hydrogen gas. It also combines easily with oxygen and will ignite (catch fire) at about 150°C (300°F).

Occurrence in nature

As with other rare earth elements, the primary sources of samarium are the mineral monazite and bastnasite. It is also found in samarskite, cerite, orthite, ytterbite, and fluorspar.

Samarium is regarded as a relatively abundant lanthanide. It occurs to the extent of about 4.5 to 7 parts per million in the Earth's crust. That makes it about as common as boron and two other lanthanides, thulium and gadolinium.

Isotopes

There are seven naturally occurring isotopes of samarium, samarium-144, samarium-147, samarium-148, samarium-149, samarium-150, samarium-152, and samarium-154. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Three of samarium's naturally occurring isotopes are radioactivesamarium-147, samarium-148, and samarium-149. A radioactive isotope is one that breaks apart and gives off some form of radiation.

One radioactive isotope of samarium, samarium-153, is used in medicine. Patients with bone cancer often have very severe pain. The isotope samarium-153, can help relieve that pain. It in injected in the form of a drug known as Quadramet. Quadramet was approved by the U.S. Food and Drug Administration (FDA) for this purpose in March 1997.

Extraction

Samarium can be obtained by heating samarium oxide (Sm2O3) with barium or lanthanum metal:

Uses

Samarium has some uses similar to those of other rare earth elements. For example, it can be added to glass for color or special optical (light) properties. It is also used to make lasers for special applications. A laser is a device for producing very bright light of a single color. The color produced by the laser depends on the elements it contains.

One of the most important uses of samarium is in the manufacture of very powerful magnets. Samarium is combined with the metal cobalt to make samarium-cobalt, or SmCo, magnets. They are among the strongest magnets known. They also have other desirable properties. For example, they can be used at high temperatures and do not react easily with substances around them. SmCo magnets are widely used in motors, such as those used to power specialized kinds of airplanes.

Compounds

The only compound of samarium with any commercial applications is samarium oxide (Sm2O3). This compound is used in the manufacture of special kinds of glass, as a catalyst in the manufacture of ethanol (ethyl alcohol), and in nuclear power plants as a neutron absorber.

Health effects

The health effects of samarium are not well studied. In such a case, chemists treat the element as toxic and handle it with great caution.

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Samarium

Samarium


melting point: 1,072°C
boiling point: 1,900°C
density: 7.536 g/cm3
most common ions: Sm2+, Sm3+

In 1886, French chemist P. E. Lecoq de Boisbaudran, working with the mixture of oxides known as didymia, isolated the element gadolinium and, three years later, a mixture known as samaria. Working with this mixture, Eugene-Anatole Demarçay (1901) discovered the elements europium and samarium (getting its name from the mineral samarskite). The element comprises 6.47 × 104 percent of the igneous rocks of Earth's crust. The important minerals are bastnasite (in which are found fluorocarbonates of the cerium group), and monazite and xenotime (in which are found phosphates of the cerium and yttrium group, respectively). Two crystal structures exist: α -Sm (at room temperature to 917°C) and β -Sm (at >917°C, body-centered cubic).

The chemistry of samarium(III) is essentially that of all the lanthanide (III) ions. Sm(III) can be reduced to Sm(II) under special conditions, but in solution it is rapidly oxidized to the +3 state. With respect to the solid state, the halides (SmX2) and some chalogenides(II) (oxide, sulfide, selenide, and telluride compounds) have been obtained. SmF3, together with the oxide, hydroxide, carbonate, oxalate, and phosphate compounds are insoluble in aqueous solution . The halide, perchlorate, nitrate, and acetate compounds are water-soluble.

The commercially important samarium-containing minerals are treated with concentrated sulfuric acid or, in the case of monazite, with a solution of sodium hydroxide (73%) at approximately 40°C (104°F) and under pressure. The element is separated from the solutions via solvent extraction or ion exchange. Sm3+ salts are weakly yellow and may exhibit ion emission. Sm2+ ions show luminescence and are sometimes used to generate lasers. Samarium is used in the manufacture of headphones and tape drivers.

see also Cerium; Dysprosium; Erbium; Europium; Gadolinium; Holmium; Lanthanum; Lutetium; Neodymium; Praseodymium; Promethium; Terbium; Ytterbium.

Lea B. Zinner

Bibliography

Moeller, Therald (1973). "The Chemistry of the Lanthanides." In Comprehensive Inorganic Chemistry, ed. J. C. Bailar Jr.; H. J. Emeléus; Sir Ronald Nyholm; and A.F. Trotman-Dickenson. Oxford, UK: Pergamon Press. 10

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samarium

samarium (səmâr´ēəm), metallic chemical element; symbol Sm; at. no. 62; at. wt. 150.36; m.p. 1,072°C; b.p. 1,791°C; sp. gr. 7.54 at 20°C; valence +2 or +3. Samarium is a lustrous silver-white metal. It is one of the rare-earth metals of the lanthanide series in Group 3 of the periodic table. It has two crystalline forms (see allotropy). The metal does not oxidize at room temperature but ignites when heated above 150°C. Samarium is found widely distributed in nature; it is obtained commercially from the minerals monazite and bastnasite. Naturally occurring samarium is a mixture of seven isotopes, three of which are radioactive with extremely long half-lives. The metal was not isolated in relatively pure form until recently, although it has long been used in pyrophoric alloys used in cigarette lighter flints. Samarium is used as a catalyst in certain organic reactions. A samarium-cobalt compound, SmCo5, is used to make magnets for use in computer memories. The oxide, samaria, is used in special infrared absorbing glass and cores of carbon arc-lamp electrodes. Since one isotope of samarium is a good neutron absorber, the element has found use in nuclear reactor control rods. Samarium was discovered in 1879 by P. E. Lecoq de Boisbaudran by spectroscopic analysis of the mineral samarskite.

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samarium

samarium (symbol Sm) Grey-white, metallic element of the lanthanide series (rare-earth metals). First identified spectroscopically in 1879 by French chemist Paul Lacoq de Boisbaudran (1838–1912), its chief ores are monazite and bastnasite. Samarium is used in carbon-arc lamps, as a neutron absorber in nuclear reactors, and as a catalyst. Some samarium alloys are used in making powerful permanent magnets. Properties: at.no. 62; r.a.m. 150.35; r.d 7.52; m.p. 1072°C (1962°F); b.p. 1791°C (3256°F); most common isotope Sm152 (26.72%).

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samarium

sa·mar·i·um / səˈme(ə)rēəm/ • n. the chemical element of atomic number 62, a hard, silvery-white metal of the lanthanide series. (Symbol: Sm)

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