Lanthanide
Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide.
Discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, samarium was named after the mineral samarskite from which it was isolated. The mineral was named after a Russian mine official, Vassili Samarsky-Bykhovets, who thus became the first person to have a chemical element named after him, though the name was indirect.
Samarium occurs in 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 main commercial use 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 (1,292 °F), without losing their permanent magnetic properties. …
Detection of samarium and related elements was announced by several scientists in the second half of the 19th century; however, most sources give priority to French chemist Paul-Émile Lecoq de Boisbaudran. Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16) and identified a new element in it via sharp optical absorption lines. Swiss chemist Marc Delafontaine announced a new element decipium (from Latin: decipiens meaning "deceptive, misleading") in 1878, but later in 1880–1881 demonstrated that it was a mix of several elements, one being identical to Boisbaudran's samarium. Though samarskite was first found in the Ural Mountains in Russia, by the late 1870s it had been found in other places, making it available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impure and had a comparable amount of europium. The pure samarium(III) oxide was produced only in 1901 by Eugène-Anatole Demarçay, and in 1903 Wilhelm Muthmann isolated the element.
Boisbaudran named his element samarium after the mineral samarskite, which in turn honored Vassili Samarsky-Bykhovets (1803–1870). Samarsky-Bykhovets, as the Chief of Staff of the Russian Corps of Mining Engineers, had granted access for two German mineralogists, the brothers Gustav and Heinrich Rose, to study the mineral samples from the Urals. Samarium was thus the first chemical element to be named after a person. …
Samarium is a rare earth element with a hardness and density similar to zinc. With a boiling point of 1,794 °C (3,261 °F), samarium is the third most volatile lanthanide after ytterbium and europium and comparable in this respect to lead and barium; this helps separation of samarium from its ores. When freshly prepared, samarium has a silvery lustre, and takes on a duller appearance when oxidized in air. Samarium is calculated to have one of the largest atomic radii of the elements; with a radius of 238 pm, only potassium, praseodymium, barium, rubidium and caesium are larger.
In ambient conditions, samarium has a rhombohedral structure (α form). Upon heating to 731 °C (1,348 °F), its crystal symmetry changes to hexagonal close-packed (hcp), though its actual transition temperature depends on the metal purity. Further heating to 922 °C (1,692 °F) transforms the metal into a body-centered cubic (bcc) phase. Heating to 300 °C (572 °F) plus compression to 40 kbar results in a double-hexagonally close-packed structure (dhcp). Higher pressure of the order of hundreds or thousands of kilobars induces a series of phase transformations, in particular with a tetragonal phase appearing at about 900 kbar. In one study, the dhcp phase could be produced without compression, using a nonequilibrium annealing regime with a rapid temperature change between about 400 °C (752 °F) and 700 °C (1,292 °F), confirming the transient character of this samarium phase. …
Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion. The median value for its abundance in the Earth's crust used by the CRC Handbook is 7 parts per million (ppm) and is the 40th most abundant element. 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%) 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. 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 US$30/kg is one of the cheapest lanthanide oxides. …
An important use of samarium is samarium–cobalt magnets, which are nominally SmCo5 or Sm2Co17. They have high permanent magnetization, about 10,000 times that of iron and second only to neodymium magnets. However, samarium magnets resist demagnetization better; they are stable to temperatures above 700 °C (1,292 °F) (cf. 300–400 °C for neodymium magnets). These magnets are found in small motors, headphones, and high-end magnetic pickups for guitars and related musical instruments. For example, they are used in the motors of a solar-powered electric aircraft, the Solar Challenger, and in the Samarium Cobalt Noiseless electric guitar and bass pickups.
Due to their heat resistance, samarium magnets are also used for military applications and are needed to manufacture modern aircraft and missiles. A single F-35 fighter jet contains about 50 pounds (23 kg) of samarium magnets.
Samarium and its compounds are important as catalysts and chemical reagents. Samarium catalysts help the decomposition of plastics, dechlorination of pollutants such as polychlorinated biphenyls (PCB), as well as dehydration and dehydrogenation of ethanol. Samarium(III) triflate Sm(OTf)3, that is Sm(CF3SO3)3, is one of the most efficient Lewis acid catalysts for a halogen-promoted Friedel–Crafts reaction with alkenes. …
Naturally occurring samarium is composed of five stable isotopes: 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half-life t1/2 = 1.066×1011 years) and 148Sm (6.3×1015 years), with 152Sm being the most abundant (26.75%). 149Sm is listed by various sources as being stable, but some sources state that it is radioactive; the lower bound on its half-life is 2×1015 years. Some observationally stable samarium isotopes are predicted to decay to isotopes of neodymium. The long-lived isotopes 146Sm, 147Sm, and 148Sm (and 149Sm if it decays) undergo alpha decay to neodymium isotopes. Lighter unstable isotopes of samarium mainly decay by electron capture to promethium, while heavier ones beta decay to europium. The known isotopes range from 129Sm to 168Sm. The half-lives of 151Sm and 145Sm are 94.6 years and 340 days, respectively. All remaining radioisotopes have half-lives that are less than 2 days, and most these have half-life less than 48 seconds. Natural samarium has a radioactivity of 127 Bq/g, mostly due to 147Sm, whose alpha decay to 143Nd is used in samarium–neodymium dating. 146Sm is an extinct radionuclide, with the half-life of 9.20×107 years. There have been searches of samarium-146 as a primordial nuclide, because its half-life is long enough such that minute quantities of the element should persist today. It can be used in radiometric dating. …
Samarium salts stimulate metabolism, but it is unclear whether this is from samarium or other lanthanides present with it. The total amount of samarium in adults is about 50 μg, mostly in liver and kidneys and with ~8 μg/L being dissolved in blood. Samarium is not absorbed by plants to a measurable concentration and so is normally not part of human diet. However, a few plants and vegetables may contain up to 1 part per million of samarium. Insoluble salts of samarium are non-toxic and the soluble ones are only slightly toxic. When ingested, only 0.05% of samarium salts are absorbed into the bloodstream and the remainder are excreted. From the blood, 45% goes to the liver and 45% is deposited on the surface of the bones where it remains for 10 years; the remaining 10% is excreted.