Chemistry

An Overview of the Element Samarium



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Samarium

Symbol: Sm

Atomic Number: 62

Atomic Mass: 150.36 amu (atomic mass units)

Melting Point: 1072.0°C (1345.15 K, 1961.6°F)

Boiling Point: 1900.0°C (2173.15 K, 3452.0°F)

Number of Protons: 62

Number of Electrons: 62

Number of Neutrons: 88

Classification: Rare Earth Metal

Crystal Structure: Rhombohedral

Density @ 293 K: 7.54 grams per cubic centimeter

Color: silver

Samarium is a rare earth element of the Lanthanide or Lathanoid series. It was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1879 while working with the mineral Samarskite from which the element gets its name. Samarskite was named after Colonel Vasili Samarsky-Bykhovets of the Russian Corp on mining engineers.

Samarium has never been found in its pure form naturally. The purified metal has a silvery luster which develops a grey oxide coating in moist air but it is relatively stable in dry air. It can be ignited, in air, at about 150°C. Samarium has been found to have three crystal modifications which are heat dependant. Transformations to the different crystal forms take place at 734°C and 922°C.

Samarium currently has twenty one known isotopes some of which are man made. Naturally occurring Samarium is a mixture of seven isotopes including three which are unstable with very long half lives. In order of abundance these isotopes are samarium-152 (26.75%, stable), samarium-154 (22.75%, stable), samarium-147 (14.99%, unstable), samarium-149 (13.82%, unstable), samarium-148 (11.24%, unstable), samarium-150 (7.38%, stable) and samarium-144 (3.07%, stable).

The main source mineral ores from which it is now extracted commercially along with Samarskite are Monazite and Bastnasite. The chemical methods of ion exchange and solvent extraction which were developed in the 1950s have allowed pure Samarium to be extracted from its' ores. Prior to the development these techniques Samarium was used in misch metal, this is an alloy of various naturally occurring rare earth metals which is commonly used to make the flints used in cigarette lighters. The term misch metal is derived from the German for mixed metals.

Now pure samarium is available it has found a number of commercial and scientific uses. The toxicity or otherwise of samarium has not yet been established because of this it is recommended that the pure metal be handled with caution.

* Along with a number of other rare earth minerals it is used to provide carbon-arc lighting for the film industry.

* Within the field of physics it is used as a neutron absorber in nuclear rectors and to produce infra-red absorbing optical quality glass.

* It has also proved valuable in the field of laser technology where it is commonly used to dope calcium fluoride crystals.

* The chemistry industry uses samarium oxide as a catalyst in the dehydration and dehydrogenation of ethyl alcohol.

* In a recent development samarium has been combined with cobalt to form the compounds SmCo5 and Sm2Co17. These samarium-cobalt compounds have been found to be permanent magnets with the strongest resistance to demagnetization of any known material. Samarium-cobalt magnets are now being used as high-end magnetic pickups in musical instruments such as guitars.

Reference Sources:

National nuclear data center http://www.nndc.bnl.gov/

Los Alamos National Laboratory Chemistry Division http://periodic.lanl.gov/elements/62.html

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