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   Sm

SAMARIUM

(Samarskite, a mineral.)

Sm   at. wt. 150.35
     at. no. 62
     m.p.  1072°C
     b.p.  1778°C
     sp. gr. (α)7.536 (β) 7.40   
     valence 2 or 3.

Samarium was discovered spectroscopically by its sharp absorption lines in 1879 by Lecoq de Boisbaudran in the mineral samarskite, named in honor of a Russian mine official, Col. Samarski. Samarium is found along with other members of the rare-earth elements in many minerals, including nionazite and bastnasite, which are commercial sources. It occurs in misch metal to the extent of 2.8%. While misch metal, containing about 1% of samarium metal, has long been used, samarium has not been isolated in relatively pure form until recent years. Ion exchange and solvent extraction techniques have recently simplified separation of the rare earths from one another; more recently, electrochemical deposition, using an electrolytic solution of lithium citrate and a mercury electrode, is said to be a simple, fast, and highly specific way to separate the rare earths. Samarium metal can be produced by reducing the oxide with barium or lanthanum. Samarium has a bright silver luster and is reasonably stable in air. Two crystal modifications of the metal exist, with a transformation point at 91 7°C. The metal ignites in air at about 150 °C. Sixteen isotopes of samarium exist. Natural samarium is a mixture of seven isotopes, four of which are unstable with long half-lives. Samarium, along with other rare earths, is used for carbon-arc lighting for the motion-picture industry. The sulfide has excellent high-temperature stability and good thermoelectric efficiencies up to 1100°C. SmCO5 has been used in making a new permanent magnet material with the highest resistance to demagnetization of any known material. It is said to have an intrinsic coercive force as high as 28,000 oersteds. Samarium oxide has been used in optical glass to absorb the infrared. Sarnarium is used to dope calcium fluoride crystals for use in optical masers or lasers. Compounds of the metal act as sensitizers for phosphors excited in the infrared; the oxide exhibits catalytic properties in the dehydration and dehydrogenation of ethyl alcohol. It is used in infrared absorbing glass and as a, neutron absorber in nuclear reactors. The metal is priced at about $1/gm or $250/lb. Little is known of the toxicity of samarium; therefore it should be handled carefully.

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