Samarium (Sm)

• Element Symbol: Sm
• Atomic Number: 62
• Atomic Mass: 150.36
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Paul-Émile Lecoq de Boisbaudran (1879)

Samarium is a metallic chemical element in the periodic table. It is a rare earth element, belonging to the lanthanide group of elements, which includes fourteen other rare earth elements, such as lanthanum and neodymium. Rare earth elements, also known as rare earth metals, typically occur together in nature and are oftentimes difficult to separate.

The element cerium, the most abundant of all the rare earth elements, was discovered in its oxide form in 1803. Cerium oxide, also known as ceria, was believed to contain other metals, but it was not until 1839 that Swedish chemist Carl Mosander successfully obtained and isolated the first pure form of lanthanum from it. Forty years later, French chemist Paul-Émile Lecoq de Boisbaudran began experimenting with the mineral samarskite and successfully extracted didymium. In 1879 Boisbaudran created a solution of didymium nitrate and ammonium hydroxide, which yielded two solids. After he had performed a spectroscopic analysis, the strong absorption lines revealed the element to be samarium. Boisbaudran’s isolated portion of samarium was impure, however, because it contained other rare earth elements, namely gadolinium and europium, which were subsequently separated over the next twenty years. It was not until 1901 that Eugène-Anatole Demarçay isolated the first pure samarium sample. Samarium was named after samarskite, the mineral from which it was extracted, which in turn was named in honor of Russian mining chief of staff Vasili Samarsky-Bykhovets; thus, the newly discovered element was named for him as well. Samarium was the first element to be named in honor of a public figure.

Samarium is used in the creation of powerful magnets and nuclear reactors, and it has substantial use in the field of medicine.

Physical Properties

Samarium has a silvery-white, metallic color. At 298 kelvins (K), samarium’s standard state is a fairly hard solid, with a density of 7.52 grams per cubic centimeter (g/cm³). Many rare earth elements are particularly susceptible to corrosion when exposed to air, and samarium is no exception, slowly beginning to oxidize at room temperature. Most rare earth metals are stored in mineral oil to prevent oxidation, but even when kept under these conditions, samarium will continue to oxidize until its silvery-white sheen is covered in a gray-yellow powder. Its natural metallic color can only be preserved if sealed in a nonreactive gas, such as argon. At 298 K, in dry conditions, samarium is stable, but it can be extremely volatile if not kept in the right conditions. It begins to oxidize in humid air, and upon reaching temperatures of 150 degrees Celsius (°C) or above, it will ignite.

The melting point of samarium is 1074 °C, and its boiling point is 1794 °C. This high boiling point makes samarium the third most volatile rare earth element, after europium and ytterbium. The specific heat of samarium at 298 K is 196 joules per kilogram-kelvin (J/kg·K). Samarium has an electrical conductivity of 1.1 × 10⁶ siemens per meter (S/m) and a thermal conductivity of 13 watts per meter-kelvin (W/m·K).

Chemical Properties

Common oxidation states of samarium are +3 and +2. Naturally occurring samarium is made up of four stable isotopes (samarium-144, samarium-150, samarium-152, and samarium-154) as well as three long-lasting radioactive isotopes (samarium-147, samarium-148, and samarium-149). Many of samarium’s isotopes have extremely long half-lives, including samarium-151, which has a half-life of 88.8 years. However, most of the remaining radioactive isotopes have half-lives of less than two days. Unstable samarium isotopes most commonly undergo alpha decay, a form of radioactivity in which an alpha particle (two neutrons and two protons) is released, resulting in isotopes of neodymium. At room temperature samarium has a rhombohedral crystal structure, but it undergoes crystal transformations at 734 °C and 922 °C, at which temperatures it becomes hexagonally close-packed and body-centered cubic, respectively.

Applications

Despite its classification as a rare earth element, which may appear to suggest its scarcity, samarium actually occurs naturally in many different sources on Earth. Samarium is not found freely in nature, but it is the fortieth most abundant element in Earth’s crust; it is even more abundant than elements such as tin. Samarium is also found alongside its fellow rare earth elements in many minerals, such as monazite and bastnaesite. It is from these minerals that samarium is generally acquired via the process of ion exchange. China is the world’s leading producer of samarium, mining approximately 120,000 metric tons annually. Additionally, samarium makes up about 1 percent of misch metal, a material that is used in lighter flints.

Samarium is considered to have low toxicity, and it does not pose any major threats to humans. No biological roles of samarium have been noted, except as a potential metabolism stimulant. However, it is unclear whether this effect, achieved by ingesting samarium salts, can be attributed to samarium or to one of the other rare earth elements that are present.

When combined with cobalt, samarium creates an extremely powerful permanent magnet, one that is ten thousand times more powerful than iron magnets. Samarium-cobalt magnets are second only to neodymium magnets in strength, and they are able to resist demagnetization at very high temperatures. This has made such magnets useful in the motor of the Solar Challenger, a solar-powered electric aircraft, as well as in precision weapons. Samarium-cobalt magnets are also used in other motors, in headphones, and in the pickups of certain electric guitars.

The radioactive isotope samarium-149 is a very effective neutron absorber, which has made its use in the control rods of nuclear reactions important. Additionally, samarium is used in glass and ceramics in order to absorb light in the infrared range. Samarium-153, another radioactive isotope, is a beta emitter with a half-life of 46.3 hours. It is an important ingredient in the drug samarium lexidronam, which is commonly used in the treatment of breast, prostate, lung, and bone cancers.

Bibliography

Atwood, David A., ed. The Rare Earth Elements: Fundamentals and Applications. Hoboken: Wiley, 2012. Print.

"Facts about Samarium." LiveScience. Purch, 12 July 2013. Web. 5 Aug. 2015.

Haynes, William M., ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

Lucas, Jacques, et al. Rare Earths: Science, Technology, Production and Use. Waltham: Elsevier, 2015. Print.

"Samarium (Sm)." Encyclopaedia Britannica. Encyclopaedia Britannica, 4 May 2014. Web. 5 Aug. 2015.

"Technical Data for Samarium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 5 Aug. 2015.