Samarium
Samarium was discovered in 1879 by the French chemist Paul Émile Lecoq de Boisbaudran and named after the mineral samarskite from which it was isolated. The mineral itself was earlier named after a Russian mine official, Colonel Vasili Samarsky-Bykhovets, who thereby became the first person to have a chemical element named after him, albeit indirectly. Although classified as a rare earth element, samarium is the 40th most abundant element in the Earth's crust and is more common than such metals as tin. Samarium occurs with 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 major commercial application 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, without losing their magnetic properties. The radioactive isotope samarium-153 is the major component of the drug samarium (153Sm) lexidronam (Quadramet), which kills cancer cells in the treatment of lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and is therefore added to the control rods of nuclear reactors. It is also formed as a decay product during the reactor operation and is one of the important factors considered in the reactor design and operation. Other applications of samarium include catalysis of chemical reactions, radioactive dating and an X-ray laser.
Occurrence and production
With the average concentration of about 8 parts per million (ppm), samarium is the 40th most abundant element in the Earth's crust. It is the fifth most abundant lanthanide and is more common than such element as tin. Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion. Distribution of samarium in soils strongly depends on its chemical state and is very inhomogeneous: in sandy soils, samarium concentration is about 200 times higher at the surface of soil particles than in the water trapped between them, and this ratio can exceed 1,000 in clays.
Samarium is not found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnäsite, cerite, gadolinite and samarskite; monazite (in which samarium occurs at concentrations of up to 2.8%)[9] and bastnäsite are mostly used as commercial sources. World resources of samarium are estimated at two million tonnes; they are mostly located in China, US, Brazil, India, Sri Lanka and Australia, and the annual production is about 700 tonnes.[8] Country production reports are usually given for all rare-earth metals combined. By far, China has the largest production with 120,000 tonnes mined per year; it is followed by the US (about 5,000 tonnes) and India (2,700 tonnes). Samarium is usually sold as oxide, which at the price of about 30 USD/kg is one of the cheapest lanthanide oxides. Whereas mischmetal – a mixture of rare earth metals containing about 1% of samarium – has long been used, relatively pure samarium has been isolated only recently, through ion exchange processes, solvent extraction techniques, and electrochemical deposition. The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing its oxide with lanthanum. The product is then distilled to separate samarium (boiling point 1794 °C) and lanthanum (b.p. 3464 °C).
Samarium-151 is produced in nuclear fission of uranium with the yield of about 0.4% of the total number of fission events. It is also synthesized upon neutron capture by samarium-149, which is added to the control rods of nuclear reactors. Consequently, samarium-151 is present in spent nuclear fuel and radioactive waste.
| Symbol | Sm | |
| Atomic Number | 62 | |
| Atomic Weight | 150.36 | |
| Oxidation States | +2, +3 | |
| Electronegativity, Pauling | 1.17 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 1350 | |
| Boiling Point, K | 2064 |
Appearance and Characteristics
Harmful effects:
Samarium is considered to be moderately toxic.
Characteristics:
- Samarium is a bright, fairly hard, silvery white metal. It is one of the lanthanide rare earth metals.
- It is stable in air at normal temperatures, but ignites in air when the temperature is 150 oC or higher. In moist air it tarnishes to the oxide.
- In its compounds Samarium usually exists as a trivalent ion, Sm3+. Most of its salts are pale yellow in color.
Uses of Samarium
- Samarium’s main use is in samarium-cobalt alloy magnets for headphones, small motors and pickups for some electric guitars. These magnets have a high resistance to demagnetization. They keep their ferromagnetism at temperatures up to 700 oC. As a result of their ability to operate at high temperatures, SmCo magnets are used in precision-guided weapons.
- Samarium oxide (samaria) is used as a catalyst for the dehydration and dehydrogenation of ethanol. Samarium oxide is also used in infrared absorbing glass.
- Radioactive 153Sm is used in the treatment of cancers.
- Samarium is also used as an absorber in nuclear reactors.
