Samarium is a chemical element with symbols Sm and atomic number 62. It is a hard enough silver metal that is slowly oxidized in the air. Being a typical member of the lanthanide series, the samarium usually assumes an oxidation state 3. The samarium (II) compound is also known, especially the SmO monoxide, the SmSe monochalcogenides, SmSe and SmTe, as well as the 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.
Samarium was discovered in 1879 by the French chemist Paul-ÃÆ' â € ° mil Lecoq de Boisbaudran and named after the mineral samarsite from which it was isolated. The mineral itself was previously named a Russian mining official, Colonel Vassili Samarsky-Bykhovets, who thus 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 lead. Samarium occurs with concentrations of up to 2.8% in some minerals including cerite, gadolinite, samarskite, monazite and bastnÃÆ'¤site, the latter two being the most common commercial sources of the elements. These minerals are found in China, the United States, Brazil, India, Sri Lanka and Australia; China has so far been a world leader in mining and samarium production.
The main commercial application of a samarium is a samarium-cobalt magnet, which has a second permanent magnetization after a neodymium magnet; Nevertheless, the samarium compound can survive at significantly higher temperatures, above 700 ° C (1,292 ° F), without losing its magnetic properties, due to the higher Curie point of the alloy. The radioactive isotope samarium-153 is an active component of the samarium drug ( 153 Sm) lexidronam (Quadramet), which kills cancer cells in the treatment of lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a powerful neutron absorber and is therefore added to the nuclear reactor control rod. It is also formed as a decay product during reactor operation and is one of the important factors considered in the design and operation of the reactor. Other applications of samarium include chemical reaction catalysis, radioactive dating and X-ray lasers.
Video Samarium
Physical properties
Samarium is a rare earth metal that has a hardness and a density similar to zinc. With boiling point of 1794 Â ° C, samarium is the third most volatile lanthanide after ytterbium and europium; this property facilitates the separation of samarium from mineral ores. In ambient conditions, a samarium usually assumes a rhombohedral (? Shape) structure. After heating up to 731 Â ° C, the crystal symmetry changes to a closed hexagonal ( hcp ), but the transition temperature depends on the purity of the metal. Further heating to 922 Â ° C converts the metal into a cubic centered body phase ( bcc ). Heating up to 300 ° C is combined with compression for a 40 kbar result in a hexagonally closed double structure ( dhcp ). Applying a higher pressure of the order of hundreds or thousands of kilobars induces a series of phase transformations, in particular with the tetragonal phase that appears at about 900 kbar. In one study, the dhcp phase can be produced without compression, using an unqualibrium annealing regime with rapid temperature changes between about 400 and 700Ã, Â ° C, confirming the temporary character of this samarium phase. Also, thin films of samarium obtained by vapor deposition may contain a hcp or dhcp phase under ambient conditions.
Samarium (and sesquioxide) are paramagnetic at room temperature. The corresponding effective magnetic moment, below 2Âμ B , is the third lowest among the lanthanides (and their oxides) after lanthanum and luteium. The metal turns into an antiferromagnetic state after cooling to 14.8 K. The individual samarium atoms can be isolated by encapsulating them into fullerene molecules. They can also be doped between C 60 molecules in solid fullerenes, rendering it superconductive at temperatures below 8Ã, K. The latest iron-grade superconducting doping sagas of the newest high-temperature superconductors - allowing their transition temperature increases to 56  ° K, which is the highest score achieved so far in this series.
Maps Samarium
Chemical properties
The newly prepared Samarium has a silver luster. In the air, it slowly oxidizes at room temperature and spontaneously lights up at a temperature of 150 ° C. Even when deposited beneath mineral oil, the samarium gradually oxidizes and develops a grayish powder from a mixture of surface-hydroxides. The sample metallic appearance can be maintained by sealing it under an inert gas such as argon.
Samarium is quite electropositive and reacts slowly with cold water and fast enough with hot water to form the samarium hydroxide: (a) 3 H 2 <3 (g)
Samarium is easy to dissolve in dilute sulfuric acid to form a solution containing yellow Sm (III) ions to pale green, which is present as 9 3 complex:
- 2 Sm (s) 3 H 2 SO 4 (aq) -> 2 Sm 3 (aq) 3 SO 2 -
​​Compound
Oxide
The most stable oxide of the samarium is the sesquioxide Sm 2 O 3 . Like many other samarium compounds, it exists in several phases of crystals. The trigonal form is obtained by slow cooling of the melt. The melting point of Sm 2 O 3 is rather high (2345 Â ° C) and therefore melting is usually achieved not by direct heating, but by induction heating, via radio coil frequency. The crystal sm 2 O 3 of the monoclinic symmetry can be grown by the flame method (Verneuil process) of Sm 2 O 3 powder, which produces a cylindrical boule up to several centimeters in length and about one centimeter in diameter. The boule is transparent when pure and defect-free and orange otherwise. Metastable trigonal heating Sm 2 O 3 to 1900 ° C transforms it into a more stable monoclinic phase. Cubic Sm 2 O 3 has also been described.
Samarium is one of several lanthanides that make up monoxide, Smo. This sparkling gold-yellow compound is obtained by subtracting Sm 2 O 3 by metallic samarium at high temperature (1000 Â ° C) and pressures above 50 kbar; lowering the pressure produces an incomplete reaction. Smo has a cubic-rock lattice grid structure.
Chalcogenides
Samarium forms trivalent sulfide, selenide and telluride. Chalcogenides divalent SmS, SmSe and SmTe with crystal-rock crystal-rock structures are also known. They are remarkable by converting from semiconductors to metal states at room temperature at the time of application of pressure. While the transition takes place continuously and occurs at about 20-30 kbar in SmSe and SmTe, it's suddenly in SmS and it only takes 6.5 kbar. This effect produces spectacular color changes in SmS from black to golden yellow when the film crystal is scratched or polished. The transition does not change the symmetry of the lattice, but there is a sharp decrease (~ 15%) in the crystal volume. This indicates hysteresis, ie when pressure is released, SmS returns to a semiconductor state at a much lower pressure of about 0.4 kbar.
Halide
Samarium metals react with all halogen, forming trihalides: 2
Their further reduction with samarium, lithium or sodium metal at high temperatures (around 700-900 ° C) produces dihalides. Diiodide may also be prepared by heating Smi 3 , or by reacting the metal with 1,2-diodoethane in anhydrous tetrahydrofuran at room temperature:
- Sm (s) ICH 2 -CH 2 I -> SmI 2 CH 2 = CH 2 .
In addition to dihalides, the reduction also produces many non-stoichiometric halide halides with a well-defined crystal structure, such as Sm 3 F 7 , Sm 14 F 33 , sm 27
sub 24 > 5 Br 11 and Sm 6 Br 13 .
As reflected in the above table, samarium halides change their crystal structure when one type of halide atom is replaced with another, which is a behavior that is not common to most elements (eg actinides). Many halides have two main crystal phases for one composition, one being significantly more stable and the other metastable. The latter is formed on compression or heating, followed by quenching to ambient conditions. For example, compressing the usual monoclinic samarium diiodide and releasing the pressure yields an orthorhombic structure of PbCl 2 -type (density 5,90 g/cm 3 ), and similar treatment results in a new phase of samarium triiodide (density 5,97 g/cm 3 ).
Borides
The sintering powder of samarium oxide and boron, in a vacuum, produces a powder containing several phases of boram samarium, and their volume ratio can be controlled through the proportion of mixing. The powder can be converted to a larger crystal of a particular boram samarium using arc smelting or fusion techniques, depending on the melting/crystallization temperature different from SmB 6 (2580 Â ° C), SmB 4 (about 2300 ° C) and SmB 66 (2150 ° C). All of these ingredients are hard, brittle, dark gray solids with hardness increasing with boron content. Samarium diboride is too volatile to produce with this method and requires high pressure (about 65 kbar) and low temperatures between 1140 and 1240 ° C to stabilize its growth. Increases temperature results in preferential formations from smb 6 .
Samarium hexaboride
Samarium hexaboride is a typical intermediate-valence compound in which the samarium is present both as Sm 2 and Sm 3 ion at a ratio of 3: 7. This includes a condo insulator class, which at high temperature (above 50 °), its properties are typical of the condo metal, with metal electrical conductivity characterized by strong electron scattering, whereas at low temperatures, it behaves as a magnetic insulator with a narrow band gap of about 4-14 °, meV. Transition-induced metal-induced cooling in SmB 6 is accompanied by a sharp increase in thermal conductivity, peaking at about 15 ° C. The reason for this increase is that the electron itself does not contribute to heat. conductivity at low temperatures, which is dominated by phonons, but the decrease in electron concentration reduces the rate of electron-phonon scattering.
New research seems to suggest that it may be a topological isolator.
Other inorganic compounds
Samarium carbide is prepared by fusing a mixture of graphite-metal in an inert atmosphere. After synthesis, they are unstable in the air and studied also under an inert atmosphere. Samarium monophosphide SmP is a semiconductor with band gap of 1.10 eV, the same as in silicon, and high electrical conductivity of the n-type. It can be prepared with anchoring at 1100 ° C Evacuated quartz ampoules containing a mixture of phosphorus and samarium mixtures. Phosphorus is highly volatile at high temperatures and can explode, so the heating rate should be kept below 1 Ã, Â ° C/min. A similar procedure was adopted for SM monarsenide, but the synthesis temperature was higher at 1800 ° C.
Many crystalline binary compounds are known for samariums and one of the 14, 15 or 16 element X, where X is Si, Ge, Sn, Pb, Sb or Te, and samarium metal alloys form other large groups. They are all prepared by mixing the mixed powders of the appropriate elements. Many of the resulting compounds are non-stoichiometric and have the nominal composition of Sm a X b , where b/a ratios vary between 0.5 and 3.
Organometallic compound
Samarium forms cyclopentadienide Sm (C 5 H 5 ) 3 and chloroderivatives Sm (C 5 H 5 ) 2 Cl and Sm (C 5 Cl 2 . They are prepared by reacting samarium trichloride with NaC 5 H 5 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Sm (C 5 H 5 ) 3 some C 5 H < sub> 5 ring bridging each other by forming a ring node? 1 or edge? 2 toward the adjacent samarium atom, thus creating a polymeric chain. The chloroderivative Sm has a dimer structure, which is more accurately expressed as (? 5 5 2 > 5 Sm (Ã,Âμ-Cl) 2 (? 5 -C 5 H 5 ) 2 . There, the chlorine bridge may be replaced, for example, by an iodine, hydrogen or nitrogen atom or by a CN group.
Ion (C 5 H 5 ) - in samarium cyclopentadienides can be replaced by indenide (C 9 H 7 ) - <-> rings, resulting in Sm ( C 9 H 7 ) 3 or KSm (? 8 -C 8 H 8 ) 2 . The last compound has a structure similar to uranocene. There is also a cyclopentadienide of divalent samarium, Sublime solids about 85 ° C. Contrary to ferrocene, ring C 5 H 5 in Sm (C 5 H 5 ) 2 no parallel but tilted by 40 Â °.
The alkyl and aryl of the samarium are obtained by metathesis reaction in tetrahydrofuran or ether:
- SmCl 3 3 LiR -> SmR 3 3 LiCl
- Sm (OR) 3 3 LiCH (SiMe 3 ) 2 -> Sm {CH (SiMe 3 ) 2 } 3 3 LiOR
Here R is a hydrocarbon group and Me is an abbreviation of methyl.
Isotope
Samarium that occurs naturally has a radioactivity of 128 Bq/g. It consists of four stable isotopes: 144 Sm, 150 Sm, 152 Sm and 154 Sm, and three radioisotopes which is very long-lived, 147 Sm (half-life t 1/2 = 1.06 ÃÆ' - 10 11 year), 148 Sm (7 ÃÆ' - 10 15 year) and 149 Sm (& gt; 2 ÃÆ' - 10 15 year), with 152 Sm being the most abundant (natural abundance 26.75%). 149 Sm is listed by various sources either as a stable or radioactive isotope.
Long-lived isotopes, 146 Sm, 147 Sm, and 148 Sm, mainly decays by emission of alpha particles into neodymium isotopes. The lighter isotope is unstable from decay primarily by the capture of electrons to the promethium isotope, while the heavier ones convert through beta decay into the europium isotope.
Alfa decay 147 Sm to 143 Nd with half-life of 1.06 ÃÆ' - 10 11 years serving for dating samarium-neodymium.
Half life 151 Sm and 145 Sm is 90 years and 340 days, respectively. All remaining radioisotopes have a half-life of less than 2 days, and most have half-lives of less than 48 seconds. Samarium also has five nuclear isomers with the most stable is 141m Sm (half 22.6 min), 143m1 Sm ( t 1/2 = 66 seconds) and 139m Sm ( t 1/2 = 10.7 seconds).
History
Detection of samarium and related elements was announced by some scientists in the second half of the 19th century; However, most sources give priority to the French chemist Paul ÃÆ'â € ° mile Lecoq de Boisbaudran. Boisbaudran isolated the samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite (N, Y, Ce, U, Fe) 3 O 16 ) and identify new elements in it through a sharp optical absorption path. Swiss chemist Marc Delafontaine declared a new element of decipium (from Latin: decipiens meaning "deceptive, misleading") in the year 1878, but later in 1880-1881 showed that it was a mixture of several elements, one identical to the Boisbaudran samarium. Although samarskite was first discovered in Russia's remote Urals region, by the end of the 1870s its deposits had been placed elsewhere that made minerals available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impure and contained comparable amounts of europium. The pure element was only produced in 1901 by EugÃÆ'¨ne-Anatole DemarÃÆ'§ay.
Boisbaudran named its samaria after mineral samarskite, which in turn respects Vassili Samarsky-Bykhovets (1803-1870). Samarsky-Bykhovets, as Chief of Staff of the Russian Mining Corps, has given access to two German mineralogy, Gustav Rose's brother and Heinrich Rose, to study mineral samples from Ural. In this sense samarium is the first chemical element named under the name of a person. Then the name samaria used by Boisbaudran was changed to samarium , to match the name of another element, and today's samaria is sometimes used to refer to samarium oxide, in analogy with yttria , zirconia, alumina, cheerful, holmia, etc. Symbol Sm is recommended for samarium; However alternatives Sa are often used instead until the 1920s.
Prior to the advent of ion-exchange separation technology in the 1950s, samariums had no commercial use in pure form. However, a by-product of purifying the fractional crystallisation of neodymium is a mixture of samarium and gadolinium which gets the name "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some of the early nuclear reactors. Currently, similar commodity products have the name "samarium-europium-gadolinium" (SEG) concentrate. It is prepared by solvent extraction from a mixture of lanthanides isolated from bastnÃÆ'¤site (or monazite). Because the heavier lanthanides have a greater affinity for the solvents used, they are easily extracted from the bulk by a relatively small proportion of solvents. Not all rare-earth producers that process bastnÃÆ'¤site do so on a scale large enough to continue with SEG component separation, which typically reaches only one or two percent of the original ore. Manufacturers like that will make SEG with the intent to market it to a special processor. In this way, the valuable europium content of the ore is saved for use in the manufacture of phosphorus. Samarium purification follows the removal of europium. In 2012, due to oversupply, samarium oxide is cheaper on a commercial scale than its relative abundance in possible ore.
Genesis and production
With an average concentration of about 8 parts per million (ppm), samarium is the 40th most abundant element in the Earth's crust. This is the fifth most abundant lanthanide and is more common than tin-like elements. The concentration of samarium in the soil varies between 2 and 23 ppm, and the oceans contain about 0.5-0.8 parts per trillion. The distribution of samariums in the soil is highly dependent on their chemical state and is not very homogeneous: in sandy soil, the samarium concentration is about 200 times higher on the surface of the soil particles than in the water trapped between them, and this ratio can exceed 1,000 in clay.
Samarium is not found free in nature, but, like other rare earths, is contained in many minerals, including monasite, bastnÃÆ'¤site, cerite, gadolinite and samarskite; monasite (where samariums occur at concentrations of up to 2.8%) and bastnÃÆ'¤site is mostly used as a commercial source. The world's samarium resources are estimated at two million tons; they are mostly located in China, US, Brazil, India, Sri Lanka and Australia, and annual production of about 700 tons. Country production reports are usually provided for all rare earth metals combined. So far, China has the largest production with 120,000 tons mined annually; followed by the US (about 5,000 tons) and India (2,700 tons). Samarium is usually sold as oxide, which at a price of about 30 USD/kg is one of the cheapest lanthanide oxides. Whereas mischmetal - a rare earth metal mixture containing about 1% of samariums - has long been used, relatively pure samariums have been isolated only recently, through ion exchange processes, solvent extraction techniques, and electrochemical deposition. These metals are often made by electrolyzing a fused mixture of samarium (III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing the oxide by lanthanum. The product is then distilled to separate the samarium (boiling point 1794 Â ° C) and lanthanum (b.p. 3464 Â ° C).
The dominance of samarium in minerals is unique. Minerals with essential (dominant) samariums include monazite- (Sm) and florencite- (Sm). They are very rare.
Samarium-151 is produced in uranium nuclear fission with a yield of about 0.4% of the total number of fission events. It is also synthesized on the capture of neutrons by samarium-149, which is added to the nuclear reactor control rod. As a result, samarium-151 is present in spent fuel and radioactive waste.
Apps
One of the most important applications of samariums is the samarium-cobalt magnet, which has the nominal composition of SmCo 5 or Sm 2 Co 17 . They have a high permanent magnetization, which is about 10,000 times that of iron and only the second of neodymium magnets. However, samarium-based magnets have higher resistance to demagnetization, as they are stable at temperatures above 700 ° C (about 300-400 ° C for neodymium magnets). This magnet is found in small motors, headphones, and high-end magnetic pickups for guitars and related musical instruments. For example, they are used in motors from solar-powered electric planes, Solar Challenger, and in Samarium Cobalt Voice-guitar electric and bass pickups.
Other important applications of samarium and its compounds are as catalyst and chemical reagents. Samarium catalysts help with the decomposition of plastics, pollorine declorination such as polychlorinated biphenyls (PCBs), as well as dehydration and dehydrogenation of ethanol. Samarium (III) triflate (Sm (OTf) 3 , ie Sm (CF 3 SO 3 ) 3 ) , is one of the most efficient Lewis acid catalysts for Friedel-Crafts reactions that are promoted halogen with alkene. Samarium (II) iodide is a reducing agent and coupling which is very common in organic synthesis, for example in desulphonylation reactions; annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total synthesis; total synthesis of strychnine; Barbier reaction and other reduction with samarium (II) iodide.
In the usual oxidized form, the samarium is added to the ceramic and glass where it enhances the absorption of infrared light. As a (small) piece of mischmetal, the samarium is found in "stone" ignition devices of many matches and torches.
The radioactive Samarium-153 is a beta transmitter 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 is injected intravenously. Chelation prevents the accumulation of radioactive samarium in the body that will result in excessive irradiation and generation of new cancer cells. Appropriate drugs have several names including samarium ( 153 Sm) lexidronam; its trade name is Quadramet.
Samarium-149 has a high cross section for neutron capture (41,000 barns) and is therefore used in nuclear reactor control rods. The advantages compared to competing materials, such as boron and cadmium, are the stability of absorption - most of the fusion and decay of samarium-149 products are other isotopes of samarium that are also good neutron dampers. For example, the samarium-151 cross-section is 15,000 barns, it is in the order of hundreds of granaries for 150 Sm, 152 Sm, and 153 Sm, and 6,800 granaries for natural samarium (mixture-isotope). Among decay products in nuclear reactors, samarium-149 is considered the second most important for the design and operation of the reactor after xenon-135.
Samarium hexaboride, abbreviated SmB 6 , has recently proven to be a topological isolator with potential applications for quantum computing.
Non-commercial and potential applications
Calcium fluoride crystals used in samariums are used as an active medium in one of the first solid-state lasers designed and constructed by Peter Sorokin (inventor of the dye laser) and Mirek Stevenson at IBM's research laboratory in early 1961. This samarium laser emits a red light pulse at 708.5 n nm. It must be cooled by liquid helium and thus find no practical application.
Other samarium-based lasers become the first saturated X-ray laser to operate at wavelengths shorter than 10 nanometers. It provides 50-picosecond pulses at 7.3 and 6.8 nm suitable for applications in holography, high-resolution microscopy of biological specimens, deflectionometry, interferometry, and solid plasma radiography associated with adhesion and astrophysics. Saturation operation means that the maximum strength may be extracted from the reinforcing medium, producing a high peak energy of 0.3 mJ. The active medium is a samarium plasma produced by a glass of samarium coated with a pulsed infrared Nd-glass laser (wavelength ~ 1.05 Âμm).
The electrical resistivity changes in the samarium monocalcogenoid can be used in pressure sensors or in memory devices triggered between low resistance and high resistance by external pressure, and the device is being commercially developed. Samarium monosulfide also produces an electric voltage at moderate heating to about 150 Â ° C which can be applied in thermoelectric power converters.
Analysis of relative concentrations of samarium and neodymium isotope 147 Sm, 144 Nd, and 143 Nd allow the determination of age and origin of rocks and meteorites in the samarium datum -neodymium. Both elements are lanthanides and have very similar physical and chemical properties. Therefore, Sm-Nd dating is not sensitive to partition of marking elements during various geological processes, or such partitions can be understood and modeled from the ionic radius of the elements involved.
Ion Sm 3 is a potential activator for use in warm white light-emitting diodes. It offers high luminous efficacy because of narrow band emissions; however, quantum efficiencies are generally low and insufficient absorption in UV-A for blue spectrum areas precludes commercial applications.
In recent years it has been shown that nanocrystalline BaFCl: Sm 3 prepared by co-precipitation can serve as a highly efficient x-ray storage phosphor. Co-precipitation causes nanocrystallites from the order of 100-200 in size and their sensitivity as x-ray storage phosphorus increases surprisingly ~ 500,000 times due to special arrangement and defect center density compared to microcrystalline samples prepared by sintering at high temperatures. This mechanism is based on the reduction of Sm 3 to Sm 2 by trapping electrons created after exposure to ionizing radiation in BaFCl host. The line 5 D J - 7 F J ff luminescence can be very excited through permitted parity 4f 6 -> 4f 5 5d transitions around 417 nm. The last wavelength is ideal for efficient excitation by a blue-violet laser diode as an electric dipole transition is allowed and thus relatively intense (400 l/(mol? Cm)). Phosphorus has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging.
The role of biology
Samarium salts stimulate metabolism, but it is unclear whether this is the effect of the samarium or other lanthanides present with it. The total amount of samarium in adults is about 50 Âμg, mostly in the liver and kidneys and with about 8 Âμg/L dissolved in the blood. Samarium is not absorbed by plants to a measurable concentration and is therefore usually not part of the human diet. However, some plants and vegetables can contain up to 1 part per million samariums. The insoluble salt samarium is non-toxic and the soluble is only slightly toxic.
When ingested, only about 0.05% of the samarium salt is absorbed into the bloodstream and the rest is excreted. Of the blood, about 45% goes to the liver and 45% is deposited on the bone surface where it lasts for about 10 years; 10% balance is excreted.
References
Bibliography
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemical Elements (2nd ed.). Butterworth-Heinemann. ISBN: 0080379419.
External links
- Samarium in Curlie (based on DMOZ)
- This is Elemental - Samarium
- Reduce Agents & gt; Samarium valent low
Source of the article : Wikipedia
0 Comments