Samarium

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.

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Samarium, ₆₂Sm

Samarium
Pronunciation	/səˈmɛəriəm/ ​(sə-MAIR-ee-əm)
Appearance	silvery white
Standard atomic weight Ar°(Sm)
	150.36±0.02[1] 150.36±0.02 (abridged)[2]
Samarium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ Sm ↓ Pu promethium ← samarium → europium
Atomic number (Z)	62
Group	f-block groups (no number)
Period	period 6
Block	f-block
Electron configuration	[Xe] 4f6 6s2
Electrons per shell	2, 8, 18, 24, 8, 2
Physical properties
Phase at STP	solid
Melting point	1345 K ​(1072 °C, ​1962 °F)
Boiling point	2173 K ​(1900 °C, ​3452 °F)
Density (at 20° C)	7.518 g/cm3 [3]
when liquid (at m.p.)	7.16 g/cm3
Heat of fusion	8.62 kJ/mol
Heat of vaporization	192 kJ/mol
Molar heat capacity	29.54 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1001 1106 1240 (1421) (1675) (2061)
Atomic properties
Oxidation states	common: +3 0,[4] +1,[5] +2[6]
Electronegativity	Pauling scale: 1.17
Ionization energies	1st: 544.5 kJ/mol 2nd: 1070 kJ/mol 3rd: 2260 kJ/mol
Atomic radius	empirical: 180 pm
Covalent radius	198±8 pm
Spectral lines of samarium
Other properties
Natural occurrence	primordial
Crystal structure	​rhombohedral (hR3)
Lattice constants	ar = 0.89834 nm α = 23.307° ah = 0.36291 nm ch = 2.6207 nm (at 20 °C)[3]
Thermal expansion	poly: 12.7 (at r.t.) µm/(m⋅K)
Thermal conductivity	13.3 W/(m⋅K)
Electrical resistivity	α, poly: 0.940 (at r.t.) µΩ⋅m
Magnetic ordering	paramagnetic[7]
Molar magnetic susceptibility	+1860.0×10−6 cm3/mol (291 K)[8]
Young's modulus	49.7 GPa
Shear modulus	19.5 GPa
Bulk modulus	37.8 GPa
Speed of sound thin rod	2130 m/s (at 20 °C)
Poisson ratio	0.274
Vickers hardness	410–440 MPa
Brinell hardness	440–600 MPa
CAS Number	7440-19-9
History
Naming	after the mineral samarskite (itself named after Vassili Samarsky-Bykhovets)
Discovery and first isolation	Lecoq de Boisbaudran (1879)
Isotopes of samarium v e
Main isotopes[9] Decay abun­dance half-life (t1/2) mode pro­duct 144Sm 3.08% stable 145Sm synth 340 d ε 145Pm 146Sm trace 9.20×107 y[10] α 142Nd 147Sm 15% 1.066×1011 y α 143Nd 148Sm 11.3% 6.3×1015 y α 144Nd 149Sm 13.8% stable 150Sm 7.37% stable 151Sm synth 94.6 y β− 151Eu 152Sm 26.7% stable 153Sm synth 46.2846 h β− 153Eu 154Sm 22.7% stable
Category: Samarium view talk edit | references

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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 itself was named after a Russian mine official, Colonel 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. The radioisotope samarium-153 is the active component of the drug samarium (¹⁵³Sm) lexidronam (Quadramet), which kills cancer cells in lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and so is added to control rods of nuclear reactors. It also forms as a decay product during the reactor operation and is one of the important factors considered in the reactor design and operation. Other uses of samarium include catalysis of chemical reactions, radioactive dating and X-ray lasers. Samarium(II) iodide, in particular, is a common reducing agent in chemical synthesis.

Samarium has no biological role; some samarium salts are slightly toxic.^[11]

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.^[12][13] 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.^[14]

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),; it has actual transition temperature depending on 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.^[15] 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. Thin films of samarium obtained by vapor deposition may contain the hcp or dhcp phases in ambient conditions.^[15]

Samarium and its sesquioxide are paramagnetic at room temperature. Their corresponding effective magnetic moments, below 2 bohr magnetons, are the third-lowest among lanthanides (and their oxides) after lanthanum and lutetium. The metal transforms to an antiferromagnetic state upon cooling to 14.8 K.^[16][17] Individual samarium atoms can be isolated by encapsulating them into fullerene molecules.^[18] They can also be intercalated into the interstices of the bulk C₆₀ to form a solid solution of nominal composition Sm₃C₆₀, which is superconductive at a temperature of 8 K.^[19] Samarium doping of iron-based superconductors – a class of high-temperature superconductor – increases their transition to normal conductivity temperature up to 56 K, the highest value achieved so far in this series.^[20]

In air, samarium slowly oxidizes at room temperature and spontaneously ignites at 150 °C (302 °F).^[11][13] Even when stored under mineral oil, samarium gradually oxidizes and develops a grayish-yellow powder of the oxide-hydroxide mixture at the surface. The metallic appearance of a sample can be preserved by sealing it under an inert gas such as argon.

Samarium is quite electropositive and reacts slowly with cold water and rapidly with hot water to form samarium hydroxide:^[21]

2Sm_(s) + 6H₂O_(l) → 2Sm(OH)_3(aq) + 3H_2(g)

Samarium dissolves readily in dilute sulfuric acid to form solutions containing the yellow^[22] to pale green Sm(III) ions, which exist as [Sm(OH₂)₉]³⁺ complexes:^[21]

2Sm_(s) + 3H₂SO_4(aq) → 2Sm³⁺_(aq) + 3SO2−4_(aq) + 3H_2(g)

Samarium is one of the few lanthanides with a relatively accessible +2 oxidation state, alongside Eu and Yb.^[23] Sm²⁺ ions are blood-red in aqueous solution.^[24]

Naturally occurring samarium is composed of five stable isotopes: ¹⁴⁴Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and two extremely long-lived radioisotopes, ¹⁴⁷Sm (half-life t_1/2 = 1.06×10¹¹ years) and ¹⁴⁸Sm (7×10¹⁵ years), with ¹⁵²Sm being the most abundant (26.75%).^{[9] 149}Sm is listed by various sources as being stable,^[9][62] but some sources state that it is radioactive,^[63] with a lower bound for its half-life given as 2×10¹⁵ years.^[9] Some observationally stable samarium isotopes are predicted to decay to isotopes of neodymium.^[64] The long-lived isotopes ¹⁴⁶Sm, ¹⁴⁷Sm, and ¹⁴⁸Sm 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.^[9] The known isotopes range from ¹²⁹Sm to ¹⁶⁸Sm.^[9][65] The half-lives of ¹⁵¹Sm and ¹⁴⁵Sm are 90 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. Samarium also has twelve known nuclear isomers, the most stable of which are ^141mSm (half-life 22.6 minutes), ^143m1Sm (t_1/2 = 66 seconds), and ^139mSm (t_1/2 = 10.7 seconds).^[9] Natural samarium has a radioactivity of 127 Bq/g, mostly due to ¹⁴⁷Sm,^[66] which alpha decays to ¹⁴³Nd with a half-life of 1.06×10¹¹ years and is used in samarium–neodymium dating.^{[67][68] 146}Sm is an extinct radionuclide, with the half-life of 9.20×10⁷ years.^[10] 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.^[69] It can be used in radiometric dating.^[70]

Samarium-149 is an observationally stable isotope of samarium (predicted to decay, but no decays have ever been observed, giving it a half-life at least several orders of magnitude longer than the age of the universe), and a product of the decay chain from the fission product ¹⁴⁹Nd (yield 1.0888%). ¹⁴⁹Sm is a decay product and neutron-absorber in nuclear reactors, with a neutron poison effect that is second in importance for reactor design and operation only to ¹³⁵Xe.^[71][72] Its neutron cross section is 41000 barns for thermal neutrons.^[73] Because samarium-149 is not radioactive and is not removed by decay, it presents problems somewhat different from those encountered with xenon-135. The equilibrium concentration (and thus the poisoning effect) builds to an equilibrium value during reactor operations in about 500 hours (about three weeks), and since samarium-149 is stable, its concentration remains essentially constant during reactor operation.^[74]

Samarium-153 is a beta emitter with a half-life of 46.3 hours. It is used to kill cancer cells in lung cancer, prostate cancer, breast cancer, and osteosarcoma. For this purpose, samarium-153 is chelated with ethylene diamine tetramethylene phosphonate (EDTMP) and injected intravenously. The chelation prevents accumulation of radioactive samarium in the body that would result in excessive irradiation and generation of new cancer cells.^[11] The corresponding drug has several names including samarium (¹⁵³Sm) lexidronam; its trade name is Quadramet.^[75][76][77]

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.^[78][79] 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.^[13] Swiss chemist Marc Delafontaine announced a new element decipium (from Latin: decipiens meaning "deceptive, misleading") in 1878,^[80][81] but later in 1880–1881 demonstrated that it was a mix of several elements, one being identical to Boisbaudran's samarium.^[82][83] 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 element was produced only in 1901 by Eugène-Anatole Demarçay.^{[84][85][86][87][88]}

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.^[89][90][91] Samarium was thus the first chemical element to be named after a person.^[84][92] The word samaria is sometimes used to mean samarium(III) oxide, by analogy with yttria, zirconia, alumina, ceria, holmia, etc. The symbol Sm was suggested for samarium, but an alternative Sa was often used instead until the 1920s.^[84][93]

Before the advent of ion-exchange separation technology in the 1950s, pure samarium had no commercial uses. However, a by-product of fractional crystallization purification of neodymium was a mix of samarium and gadolinium that got the name "Lindsay Mix" after the company that made it, and was used for nuclear control rods in some early nuclear reactors.^[94] Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate.^[92] It is prepared by solvent extraction from the mixed lanthanides isolated from bastnäsite (or monazite). Since heavier lanthanides have more affinity for the solvent used, they are easily extracted from the bulk using relatively small proportions of solvent. Not all rare-earth producers who process bastnäsite do so on a large enough scale to continue by separating the components of SEG, which typically makes up only 1–2% of the original ore. Such producers therefore make SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium in the ore is rescued for use in making phosphor. Samarium purification follows the removal of the europium. As of 2012^[update], being in oversupply, samarium oxide is cheaper on a commercial scale than its relative abundance in the ore might suggest.^[95]

Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion.^[11] The median value for its abundance in the Earth's crust used by the CRC Handbook is 7 parts per million (ppm)^[96] and is the 40th most abundant element.^[97] 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.^[98]

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%)^[13] 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.^[11] 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)^[98] and India (2,700 tonnes).^[99] Samarium is usually sold as oxide, which at the price of about US$30/kg is one of the cheapest lanthanide oxides.^[95] 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).^[79]

Very few minerals have samarium being the most dominant element. Minerals with essential (dominant) samarium include monazite-(Sm) and florencite-(Sm). These minerals are very rare and are usually found containing other elements, usually cerium or neodymium.^{[100][101][102][103]} It is also made by neutron capture by samarium-149, which is added to the control rods of nuclear reactors. Therefore, ¹⁵¹Sm is present in spent nuclear fuel and radioactive waste.^[98]

Quick Facts Hazards ...

Samarium

Hazards[126]
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H261
Precautionary statements	P231+P232, P280, P370+P378, P501
NFPA 704 (fire diamond)	[127] 2 3 2 W

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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.^[11][128] 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.^[98]