Samarium

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Samarium,  62Sm
Samarium-2.jpg
Samarium
Pronunciation /səˈmɛəriəm/ (sə-MAIR-ee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Sm)150.36(2) [1]
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
promethiumsamariumeuropium
Atomic number (Z)62
Group group n/a
Period period 6
Block f-block
Element category   Lanthanide
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 (near r.t.)7.52 g/cm3
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)1101001 k10 k100 k
at T (K)100111061240(1421)(1675)(2061)
Atomic properties
Oxidation states 0, [2] +1, +2, +3 (a mildly basic oxide)
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
Color lines in a spectral range Samarium spectrum visible.png
Color lines in a spectral range
Spectral lines of samarium
Other properties
Natural occurrence primordial
Crystal structure rhombohedral
Rhombohedral.svg
Speed of sound thin rod2130 m/s(at 20 °C)
Thermal expansion (r.t.) (α, poly) 12.7 µm/(m·K)
Thermal conductivity 13.3 W/(m·K)
Electrical resistivity (r.t.) (α, poly) 0.940 µΩ·m
Magnetic ordering paramagnetic [3]
Magnetic susceptibility +1860.0·10−6 cm3/mol(291 K) [4]
Young's modulus α form: 49.7 GPa
Shear modulus α form: 19.5 GPa
Bulk modulus α form: 37.8 GPa
Poisson ratio α form: 0.274
Vickers hardness 410–440 MPa
Brinell hardness 440–600 MPa
CAS Number 7440-19-9
History
Namingafter the mineral samarskite (itself named after Vassili Samarsky-Bykhovets)
Discovery and first isolation Lecoq de Boisbaudran (1879)
Main isotopes of samarium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
144Sm3.08% stable
145Sm syn 340 d ε 145Pm
146Smsyn6.8×107 y α 142Nd
147Sm15.00%1.06×1011 yα 143Nd
148Sm11.25%7×1015 yα144Nd
149Sm13.82%stable
150Sm7.37%stable
151Smsyn90 y β 151Eu
152Sm26.74%stable
153Smsyn46.284 hβ 153Eu
154Sm22.74%stable
| references

Samarium is a chemical element with the 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 assumes 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. The last compound is a common reducing agent in chemical synthesis. Samarium has no significant biological role but is only slightly toxic.

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

Symbol (chemistry) an arbitrary or conventional sign used in chemical science to represent a chemical element

In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

Atomic number number of protons found in the nucleus of an atom

The atomic number or proton number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons.

Contents

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 Vassili 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 metals such 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.

Paul-Émile Lecoq de Boisbaudran French chemist

Paul-Émile Lecoq de Boisbaudran, also called François Lecoq de Boisbaudran, was a French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium.

Vasili Yevgrafovich Samarsky-Bykhovets was a Russian mining engineer and the chief of Russian Mining Engineering Corps between 1845 and 1861. The mineral samarskite, and chemical element samarium are named after him. He was the first person whose name was given to a chemical element.

Rare-earth element Any of the fifteen lanthanides plus scandium and yttrium

A rare-earth element (REE) or rare-earth metal (REM), as defined by the International Union of Pure and Applied Chemistry, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are considered rare-earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties, but have different electronic and magnetic properties. Rarely, a broader definition that includes actinides may be used, since the actinides share some mineralogical, chemical, and physical characteristics.

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 (1,292 °F), without losing their magnetic properties, due to the alloy's higher Curie point. The radioactive isotope samarium-153 is the active 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 X-ray lasers.

A samarium–cobalt (SmCo) magnet, a type of rare earth magnet, is a strong permanent magnet made of two basic elements samarium and cobalt. Actually, samarium is substituted by a portion of other rare earth elements including praseodymium, cerium and gadolinium, and cobalt is substituted by a portion of other transition metals including iron, copper and zirconium. They are available in two "series", namely SmCo5 magnets and Sm2Co17 magnets. They were developed in the early 1960s based on work done by Karl Strnat and Alden Ray at Wright-Patterson Air Force Base and the University of Dayton, respectively. In particular, Strnat and Ray developed the first formulation of SmCo5. They are generally ranked similarly in strength to neodymium magnets, but have higher temperature ratings and higher coercivity. They are brittle, and prone to cracking and chipping. Samarium–cobalt magnets have maximum energy products (BHmax) that range from 14 megagauss-oersteds (MG·Oe) to 33 MG·Oe, that is approx. 112 kJ/m3 to 264 kJ/m3; their theoretical limit is 34 MG·Oe, about 272 kJ/m3.

Magnet material or object that produces a magnetic field

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.

Neodymium magnet type of magnet

A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed independently in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. Due to different manufacturing processes, they are also divided into two subcategories, namely sintered NdFeB magnets and bonded NdFeB magnets. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners.

Physical properties

Samarium is a rare earth metal having a hardness and density similar to those of zinc. With the boiling point of 1794 °C, samarium is the third most volatile lanthanide after ytterbium and europium; this property facilitates separation of samarium from the mineral ore. At ambient conditions, samarium normally assumes a rhombohedral structure (α form). Upon heating to 731 °C, its crystal symmetry changes into hexagonally close-packed (hcp), however the transition temperature depends on the metal purity. Further heating to 922 °C transforms the metal into a body-centered cubic (bcc) phase. Heating to 300 °C combined with compression to 40  kbar results in a double-hexagonally close-packed structure (dhcp). Applying 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. [5] In one study, the dhcp phase could be produced without compression, using a nonequilibrium annealing regime with a rapid temperature change between about 400 and 700 °C, confirming the transient character of this samarium phase. Also, thin films of samarium obtained by vapor deposition may contain the hcp or dhcp phases at ambient conditions. [5]

Zinc Chemical element with atomic number 30

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. It is the first element in group 12 of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).

Ytterbium Chemical element with atomic number 70

Ytterbium is a chemical element with the symbol Yb and atomic number 70. It is the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. However, like the other lanthanides, its most common oxidation state is +3, as in its oxide, halides, and other compounds. In aqueous solution, like compounds of other late lanthanides, soluble ytterbium compounds form complexes with nine water molecules. Because of its closed-shell electron configuration, its density and melting and boiling points differ significantly from those of most other lanthanides.

Europium Chemical element with atomic number 63

Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanthanide, as it can be dented with a finger nail and easily cut with a knife. When oxidation is removed a shiny-white metal is visible. Europium was isolated in 1901 and is named after the continent of Europe. Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3, but the oxidation state +2 is also common. All europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the rarest of the rare earth elements on Earth.

Samarium (and its sesquioxide) are paramagnetic at room temperature. Their corresponding effective magnetic moments, below 2μB, are the 3rd lowest among the lanthanides (and their oxides) after lanthanum and lutetium. The metal transforms to an antiferromagnetic state upon cooling to 14.8 K. [6] [7] Individual samarium atoms can be isolated by encapsulating them into fullerene molecules. [8] They can also be doped between the C60 molecules in the fullerene solid, rendering it superconductive at temperatures below 8 K. [9] Samarium doping of iron-based superconductors – the most recent class of high-temperature superconductors – allows enhancing their transition temperature to 56 K, which is the highest value achieved so far in this series. [10]

A sesquioxide is an oxide containing three atoms of oxygen with two atoms (or radicals) of another element. For example, aluminium oxide (Al2O3) is a sesquioxide. Many sesquioxides contain the metal in the +3 oxidation state and the oxide ion, e.g., Al2O3, La2O3. The alkali metal sesquioxides are exceptions and contain both peroxide, (O2−
2
) and superoxide, (O
2
) ions, e.g., Rb2O3 is formulated [(Rb+
)
4
(O2−
2
)(O
2
)
2
]. Sesquioxides of iron and aluminium are found in soil.

Paramagnetism Magnetic ordering

Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Paramagnetic materials include most chemical elements and some compounds; they have a relative magnetic permeability slightly greater than 1 and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer.

In atomic physics, the Bohr magneton is a physical constant and the natural unit for expressing the magnetic moment of an electron caused by either its orbital or spin angular momentum.

Chemical properties

Freshly prepared samarium has a silvery luster. In air, it slowly oxidizes at room temperature and spontaneously ignites at 150 °C. [11] [12] 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.

Mineral oil liquid mixture of higher alkanes from a mineral source, particularly a distillate of petroleum

Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils.

Oxide chemical compound with at least one oxygen atom

An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– atom. Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 (called a passivation layer) that protects the foil from further corrosion. Individual elements can often form multiple oxides, each containing different amounts of the element and oxygen. In some cases these are distinguished by specifying the number of atoms as in carbon monoxide and carbon dioxide, and in other cases by specifying the element's oxidation number, as in iron(II) oxide and iron(III) oxide. Certain elements can form many different oxides, such as those of nitrogen. other examples are silicon, iron, titanium, and aluminium oxides.

Hydroxide family of the hydroxide salts

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

Samarium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form samarium hydroxide: [13]

2 Sm (s) + 6 H2O (l) → 2 Sm(OH)3 (aq) + 3 H2 (g)

Samarium dissolves readily in dilute sulfuric acid to form solutions containing the yellow [14] to pale green Sm(III) ions, which exist as [Sm(OH2)9]3+ complexes: [13]

2 Sm (s) + 3 H2SO4 (aq) → 2 Sm3+ (aq) + 3 SO2−
4
(aq) + 3 H2 (g)

Samarium is one of the few lanthanides that exhibit the oxidation state +2. The Sm2+ ions are blood-red in aqueous solution. [15]

Compounds

Oxides

The most stable oxide of samarium is the sesquioxide Sm2O3. As many other samarium compounds, it exists in several crystalline phases. The trigonal form is obtained by slow cooling from the melt. The melting point of Sm2O3 is rather high (2345 °C) and therefore melting is usually achieved not by direct heating, but with induction heating, through a radio-frequency coil. The Sm2O3 crystals of monoclinic symmetry can be grown by the flame fusion method (Verneuil process) from the Sm2O3 powder, that yields cylindrical boules up to several centimeters long and about one centimeter in diameter. The boules are transparent when pure and defect-free and are orange otherwise. Heating the metastable trigonal Sm2O3 to 1900 °C converts it to the more stable monoclinic phase. [18] Cubic Sm2O3 has also been described. [19]

Samarium is one of the few lanthanides that form a monoxide, SmO. This lustrous golden-yellow compound was obtained by reducing Sm2O3 with samarium metal at elevated temperature (1000 °C) and pressure above 50 kbar; lowering the pressure resulted in an incomplete reaction. SmO has the cubic rock-salt lattice structure. [17] [37]

Chalcogenides

Samarium forms trivalent sulfide, selenide and telluride. Divalent chalcogenides SmS, SmSe and SmTe with cubic rock-salt crystal structure are also known. They are remarkable by converting from semiconducting to metallic state at room temperature upon application of pressure. Whereas the transition is continuous and occurs at about 20–30 kbar in SmSe and SmTe, it is abrupt in SmS and requires only 6.5 kbar. This effect results in spectacular color change in SmS from black to golden yellow when its crystals of films are scratched or polished. The transition does not change lattice symmetry, but there is a sharp decrease (~15%) in the crystal volume. [38] It shows hysteresis, that is when the pressure is released, SmS returns to the semiconducting state at much lower pressure of about 0.4 kbar. [11] [39]

Halides

Samarium metal reacts with all the halogens, forming trihalides: [40]

2 Sm (s) + 3 X2 (g) → 2 SmX3 (s) (X = F, Cl, Br or I)

Their further reduction with samarium, lithium or sodium metals at elevated temperatures (about 700–900 °C) yields dihalides. [30] The diiodide can also be prepared by heating SmI3, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature: [41]

Sm (s) + ICH2-CH2I → SmI2 + CH2=CH2.

In addition to dihalides, the reduction also produces numerous non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm3F7, Sm14F33, Sm27F64, [29] Sm11Br24, Sm5Br11 and Sm6Br13. [42]

As reflected in the table above, samarium halides change their crystal structures when one type of halide atoms is substituted for another, which is an uncommon behavior for most elements (e.g. actinides). Many halides have two major crystal phases for one composition, one being significantly more stable and another being metastable. The latter is formed upon compression or heating, followed by quenching to ambient conditions. For example, compressing the usual monoclinic samarium diiodide and releasing the pressure results in a PbCl2-type orthorhombic structure (density 5.90 g/cm3), [43] and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm3). [44]

Borides

Sintering powders of samarium oxide and boron, in vacuum, yields a powder containing several samarium boride phases, and their volume ratio can be controlled through the mixing proportion. [45] The powder can be converted into larger crystals of a certain samarium boride using arc melting or zone melting techniques, relying on the different melting/crystallization temperature of SmB6 (2580 °C), SmB4 (about 2300 °C) and SmB66 (2150 °C). All these materials are hard, brittle, dark-gray solids with the hardness increasing with the boron content. [25] Samarium diboride is too volatile to be produced with these methods and requires high pressure (about 65 kbar) and low temperatures between 1140 and 1240 °C to stabilize its growth. Increasing the temperature results in the preferential formations of SmB6. [23]

Samarium hexaboride

Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm2+ and Sm3+ ions at the ratio 3:7. [45] It belongs to a class of Kondo insulators, that is at high temperatures (above 50 K), its properties are typical of a Kondo metal, with metallic electrical conductivity characterized by strong electron scattering, whereas at low temperatures, it behaves as a non-magnetic insulator with a narrow band gap of about 4–14 meV. [46] The cooling-induced metal-insulator transition in SmB6 is accompanied by a sharp increase in the thermal conductivity, peaking at about 15 K. The reason for this increase is that electrons themselves do not contribute to the thermal conductivity at low temperatures, which is dominated by phonons, but the decrease in electron concentration reduced the rate of electron-phonon scattering. [47]

New research seems to show that it may be a topological insulator. [48] [49] [50]

Other inorganic compounds

Samarium sulfate, Sm2(SO4)3 Samarium-sulfate.jpg
Samarium sulfate, Sm2(SO4)3

Samarium carbides are prepared by melting a graphite-metal mixture in an inert atmosphere. After the synthesis, they are unstable in air and are studied also under inert atmosphere. [27] Samarium monophosphide SmP is a semiconductor with the bandgap of 1.10 eV, the same as in silicon, and high electrical conductivity of n-type. It can be prepared by annealing at 1100 °C an evacuated quartz ampoule containing mixed powders of phosphorus and samarium. Phosphorus is highly volatile at high temperatures and may explode, thus the heating rate has to be kept well below 1 °C/min. [35] Similar procedure is adopted for the monarsenide SmAs, but the synthesis temperature is higher at 1800 °C. [36]

Numerous crystalline binary compounds are known for samarium and one of the group-14, 15 or 16 element X, where X is Si, Ge, Sn, Pb, Sb or Te, and metallic alloys of samarium form another large group. They are all prepared by annealing mixed powders of the corresponding elements. Many of the resulting compounds are non-stoichiometric and have nominal compositions SmaXb, where the b/a ratio varies between 0.5 and 3. [51] [52] [53]

Organometallic compounds

Samarium forms a cyclopentadienide Sm(C5H5)3 and its chloroderivatives Sm(C5H5)2Cl and Sm(C5H5)Cl2. They are prepared by reacting samarium trichloride with NaC5H5 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Sm(C5H5)3 some C5H5 rings bridge each other by forming ring vertexes η1 or edges η2 toward another neighboring samarium atom, thereby creating polymeric chains. [15] The chloroderivative Sm(C5H5)2Cl has a dimer structure, which is more accurately expressed as (η5-C5H5)2Sm(μ-Cl)25-C5H5)2. There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups. [54]

The (C5H5) ion in samarium cyclopentadienides can be replaced by the indenide (C9H7) or cyclooctatetraenide (C8H8)2− ring, resulting in Sm(C9H7)3 or KSm(η8-C8H8)2. The latter compound has a similar structure to that of uranocene. There is also a cyclopentadienide of divalent samarium, Sm(C5H5)2 – a solid that sublimates at about 85 °C. Contrary to ferrocene, the C5H5 rings in Sm(C5H5)2 are not parallel but are tilted by 40°. [54] [55]

Alkyls and aryls of samarium are obtained through a metathesis reaction in tetrahydrofuran or ether: [54]

SmCl3 + 3 LiR → SmR3 + 3 LiCl
Sm(OR)3 + 3 LiCH(SiMe3)2 → Sm{CH(SiMe3)2}3 + 3 LiOR

Here R is a hydrocarbon group and Me stands for methyl.

Isotopes

Naturally occurring samarium has a radioactivity of 128  Bq/g. It is composed of four stable isotopes: 144Sm, 150Sm, 152Sm and 154Sm, and three extremely long-lived radioisotopes, 147Sm (half-life t1/2 = 1.06×1011 years), 148Sm (7×1015 years) and 149Sm (>2×1015 years), with 152Sm being the most abundant (natural abundance 26.75%). [56] 149Sm is listed by various sources either as stable [56] [57] or radioactive isotope. [58]

The long-lived isotopes,146Sm, 147Sm, and 148Sm, primarily decay by emission of alpha particles to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones convert through beta decay to isotopes of europium. [56]

The alpha decay of 147Sm to 143Nd with a half-life of 1.06×1011 years serve for samarium–neodymium dating.

The half-lives of 151Sm and 145Sm are 90 years and 340 days, respectively. All the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives that are less than 48 seconds. Samarium also has five nuclear isomers with the most stable being 141mSm (half-life 22.6 minutes), 143m1Sm (t1/2 = 66 seconds) and 139mSm (t1/2 = 10.7 seconds). [56]

History

Paul Emile Lecoq de Boisbaudran, the discoverer of samarium Lecoq de Boisbaudran.jpg
Paul Émile Lecoq de Boisbaudran, the discoverer of samarium

Detection of samarium and related elements was announced by several scientists in the second half of the 19th century; however, most sources give the priority to the French chemist Paul Émile Lecoq de Boisbaudran. [59] [60] 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. [12] The Swiss chemist Marc Delafontaine announced a new element decipium (from Latin : decipiens meaning "deceptive, misleading") in 1878, [61] [62] but later in 1880–1881 demonstrated that it was a mixture of several elements, one being identical to the Boisbaudran's samarium. [63] [64] Although samarskite was first found in the remote Russian region of Urals, by the late 1870s its deposits had been located in other places making the mineral available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impure and contained comparable amount of europium. The pure element was produced only in 1901 by Eugène-Anatole Demarçay. [65]

Boisbaudran named his element samaria 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 Rose and Heinrich Rose, to study the mineral samples from the Urals. [66] [67] [68] In this sense samarium was the first chemical element to be named after a person. [65] [69] Later the name samaria used by Boisbaudran was transformed into samarium, to conform with other element names, and samaria nowadays is sometimes used to refer to samarium oxide, by analogy with yttria, zirconia, alumina, ceria, holmia, etc. The symbol Sm was suggested for samarium; however an alternative Sa was frequently used instead until the 1920s. [65] [70]

Prior to the advent of ion-exchange separation technology in the 1950s, samarium had no commercial uses in pure form. However, a by-product of the fractional crystallization purification of neodymium was a mixture of samarium and gadolinium that acquired the name of "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some early nuclear reactors. Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate. [69] It is prepared by solvent extraction from the mixed lanthanides isolated from bastnäsite (or monazite). Since the heavier lanthanides have the greater 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 onward with the separation of the components of SEG, which typically makes up only one or two percent of the original ore. Such producers will therefore be making SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium content of the ore is rescued for use in phosphor manufacture. Samarium purification follows the removal of the europium. As of 2012, being in oversupply, samarium oxide is less expensive on a commercial scale than its relative abundance in the ore might suggest. [71]

Occurrence and production

Samarskite Samarskite-fresh.jpg
Samarskite

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 elements such as tin. Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion. [11] 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. [72]

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%) [12] 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) [72] and India (2,700 tonnes). [73] Samarium is usually sold as oxide, which at the price of about 30 USD/kg is one of the cheapest lanthanide oxides. [71] 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). [60]

Domination of samarium in minerals is unique. Minerals with essential (dominant) samarium include monazite-(Sm) and florencite-(Sm). They are very rare. [74] [75] [76] [77]

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. [72]

Applications

Barbier reaction using SmI2 Samariumiodide.jpg
Barbier reaction using SmI2

One of the most important applications of samarium is in samarium–cobalt magnets, which have a nominal composition of SmCo5 or Sm2Co17. They have high permanent magnetization, which is about 10,000 times that of iron and is second only to that of neodymium magnets. However, samarium-based magnets have higher resistance to demagnetization, as they are stable to temperatures above 700 °C (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. [11] 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.

Another important application of samarium and its compounds is as catalyst and chemical reagent. Samarium catalysts assist decomposition of plastics, dechlorination of pollutants such as polychlorinated biphenyls (PCBs), as well as the dehydration and dehydrogenation of ethanol. [12] 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. [78] Samarium(II) iodide is a very common reducing and coupling agent in organic synthesis, for example in the desulfonylation reactions; annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total syntheses; strychnine total synthesis; Barbier reaction and other reductions with samarium(II) iodide. [79]

In its usual oxidized form, samarium is added to ceramics and glasses where it increases absorption of infrared light. As a (minor) part of mischmetal, samarium is found in "flint" ignition device of many lighters and torches. [11] [12]

Chemical structure of Sm-EDTMP 153Sm-lexidronam structure.svg
Chemical structure of Sm-EDTMP

Radioactive samarium-153 is a beta emitter with a half-life of 46.3 hours. It is used to kill cancer cells in the treatment of 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. [80] [81] [82]

Samarium-149 has high cross-section for neutron capture (41,000  barns) and is therefore used in the control rods of nuclear reactors. Its advantage compared to competing materials, such as boron and cadmium, is stability of absorption – most of the fusion and decay products of samarium-149 are other isotopes of samarium that are also good neutron absorbers. For example, the cross section of samarium-151 is 15,000 barns, it is on the order of hundreds of barns for 150Sm, 152Sm, and 153Sm, and is 6,800 barns for natural (mixed-isotope) samarium. [12] [72] [83] Among the decay products in a nuclear reactor, samarium-149 is regarded as the second most important for the reactor design and operation after xenon-135. [84]

Samarium hexaboride, abbreviated SmB6, has recently been shown to be a topological insulator with potential applications to quantum computing. [85]

Non-commercial and potential applications

Samarium-doped calcium fluoride crystals were used as an active medium in one of the first solid-state lasers designed and constructed by Peter Sorokin (co-inventor of the dye laser) and Mirek Stevenson at IBM research labs in early 1961. This samarium laser emitted pulses of red light at 708.5 nm. It had to be cooled by liquid helium and thus did not find practical applications. [86] [87]

Another samarium-based laser became the first saturated X-ray laser operating at wavelengths shorter than 10 nanometers. It provided 50-picosecond pulses at 7.3 and 6.8 nm suitable for applications in holography, high-resolution microscopy of biological specimens, deflectometry, interferometry, and radiography of dense plasmas related to confinement fusion and astrophysics. Saturated operation meant that the maximum possible power was extracted from the lasing medium, resulting in the high peak energy of 0.3 mJ. The active medium was samarium plasma produced by irradiating samarium-coated glass with a pulsed infrared Nd-glass laser (wavelength ~1.05 μm). [88]

The change in electrical resistivity in samarium monochalcogenides can be used in a pressure sensor or in a memory device triggered between a low-resistance and high-resistance state by external pressure, [89] and such devices are being developed commercially. [90] Samarium monosulfide also generates electric voltage upon moderate heating to about 150 °C that can be applied in thermoelectric power converters. [91]

The analysis of relative concentrations of samarium and neodymium isotopes 147Sm, 144Nd, and 143Nd allows the determination of the age and origin of rocks and meteorites in samarium–neodymium dating. Both elements are lanthanides and have very similar physical and chemical properties. Therefore, Sm–Nd dating is either insensitive to partitioning of the marker elements during various geological processes, or such partitioning can well be understood and modeled from the ionic radii of the involved elements. [92]

The Sm3+ ion is a potential activator for use in warm-white light emitting diodes. It offers high luminous efficacy due to the narrow emission bands, however, the generally low quantum efficiency and insufficient absorption in the UV-A to blue spectral region hinders commercial application. [93]

In recent years it has been demonstrated that nanocrystalline BaFCl:Sm3+ as prepared by a co-precipitation can serve as a very efficient x-ray storage phosphor. [94] The co-precipitation leads to nanocrystallites of the order of 100-200 nm in size and their sensitivity as x-ray storage phosphors is increased an astounding ∼500,000 times because of the specific arrangements and density of defect centres in comparison with microcrystalline samples prepared by sintering at high temperature. [95] The mechanism is based on the reduction of Sm3+ to Sm2+ by trapping electrons that are created upon exposure to ionizing radiation in the BaFCl host. The 5 DJ-7 FJ f-f luminescence lines can be very efficiently excited via the parity allowed 4f6 →4f5 5d transition at around 417 nm. The latter wavelength is ideal for efficient excitation by blue-violet laser diodes as the transition is electric dipole allowed and thus relatively intense (400 l/(mol⋅cm)). [96] The phosphor has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging. [97]

Samarium is used for ionosphere testing. A rocket spreads it as a red vapor at high altitude, and researchers tests how the atmosphere disperses it and how it impacts radio transmissions. [98] [99]

Biological role

Samarium
Hazards
GHS pictograms GHS-pictogram-flamme.svg GHS-pictogram-silhouette.svg
GHS Signal word Danger
H228, H261, H373
P210, P231+232, P422 [100]
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acidSamarium
2
0
2
W

Samarium salts stimulate metabolism, but it is unclear whether this is the effect of 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 about 8 μg/L being dissolved in the blood. Samarium is not absorbed by plants to a measurable concentration and therefore is normally not a 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]

When ingested, only about 0.05% of samarium salts is absorbed into the bloodstream and the remainder is excreted. From the blood, about 45% goes to the liver and 45% is deposited on the surface of the bones where it remains for about 10 years; the balance 10% is excreted. [72]

Related Research Articles

Gadolinium Chemical element with atomic number 64

Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of 20 °C (68 °F) is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare-earths because of their similar chemical properties.

Holmium Chemical element with atomic number 67

Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare-earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare-earth ores in 1878. The element's name comes from Holmia, the Latin name for the city of Stockholm.

Lanthanum Chemical element with atomic number 57

Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals, which would put it in group 3, although lutetium is sometimes placed in this position instead. Lanthanum is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.

Promethium Chemical element with atomic number 61

Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of only two radioactive elements that are followed in the periodic table by elements with stable forms, the other being technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.

Terbium Chemical element with atomic number 65

Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime, and euxenite.

Mischmetal

Mischmetal (from German: Mischmetall – "mixed metal") is an alloy of rare-earth elements. It is also called cerium mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15-18% neodymium with other rare earth metals following. Its most common use is in the pyrophoric ferrocerium "flint" ignition device of many lighters and torches, although an alloy of only rare-earth elements would be too soft to give good sparks. For this purpose, it is blended with iron oxide and magnesium oxide to form a harder material known as ferrocerium. In chemical formulae it is commonly abbreviated as Mm, e.g. MmNi5.

Monazite phosphate mineral series

Monazite is a reddish-brown phosphate mineral containing rare-earth metals. It occurs usually in small isolated crystals. It has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3. There are at least four different kinds of monazite, depending on relative elemental composition of the mineral:

Bastnäsite bastnäsite mineral series

The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-(Ce) with a formula of (Ce, La)CO3F, bastnäsite-(La) with a formula of (La, Ce)CO3F, and bastnäsite-(Y) with a formula of (Y, Ce)CO3F. Some of the bastnäsites contain OH instead of F and receive the name of hydroxylbastnasite. Most bastnäsite is bastnäsite-(Ce), and cerium is by far the most common of the rare earths in this class of minerals. Bastnäsite and the phosphate mineral monazite are the two largest sources of cerium and other rare-earth elements.

Praseodymium Chemical element with atomic number 59

Praseodymium is a chemical element with the symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

Neodymium(III) chloride or neodymium trichloride is a chemical compound of neodymium and chlorine with the formula NdCl3. This anhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl3·6H2O. Neodymium(III) chloride is produced from minerals monazite and bastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-based lasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination, corrosion protection of aluminium and its alloys, and fluorescent labeling of organic molecules (DNA).

Samarium(III) chloride chemical compound

Samarium(III) chloride, also known as samarium trichloride, is an inorganic compound of samarium and chloride. It is a pale yellow solid that rapidly absorbs water to form a hexahydrate, SmCl3.6H2O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.

Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.06×1011 y) and 148Sm (7×1015 y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm is also fairly long-lived (6.8×107 y), but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an extinct radionuclide.

Yttrium Chemical element with atomic number 39

Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. 89Y is the only stable isotope, and the only isotope found in the Earth's crust.

Cerium Chemical element with atomic number 58

Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role in humans and is not very toxic.

Xikuangshan mine (simplified Chinese: 锡矿山; traditional Chinese: 錫礦山; pinyin: Xīkuàngshān) in Lengshuijiang, Hunan, China, contains the world's largest deposit of antimony. It is unique in that there is a large deposit of stibnite (Sb2S3) in a layer of Devonian limestone. There are three mineral beds which are between 2.5 and 8 m thick which are folded in an anticline that plunges to the south-west. The total mineralised area of the mine has a surface extent of 14 km2. There are two different units at the mine, the northern one produces mixed oxide and sulfide such as stibiconite (Sb3O6(OH)) and the southern one produces stibnite. Ore is concentrated and refined on site in a refinery with a capacity of 10,000 tonnes of antimony per year.

Samarium monochalcogenides are chemical compounds with the composition SmX, where Sm stands for the lanthanide element samarium and X denotes any one of three chalcogen elements, sulfur, selenium or tellurium, resulting in the compounds SmS, SmSe or SmTe. In these compounds, samarium formally exhibits oxidation state +2, whereas it usually assumes the +3 state, resulting in chalcogenides with the chemical formula Sm2X3.

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