Rhenium
Overview
 
Rhenium is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Re and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 75. It is a silvery-white, heavy, third-row transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

 in group 7
Group 7 element
A Group 7 element is one in the series of elements in group 7 in the periodic table, which consists of manganese , technetium , rhenium , and bohrium...

 of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

. With an average concentration of 1 part per billion
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...

 (ppb), rhenium is one of the rarest elements in the Earth's crust. The free element has the third-highest melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 and highest boiling point of any element. Rhenium resembles manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 chemically and is obtained as a by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....

 of molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

 and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 refinement.
Encyclopedia
Rhenium is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Re and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 75. It is a silvery-white, heavy, third-row transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

 in group 7
Group 7 element
A Group 7 element is one in the series of elements in group 7 in the periodic table, which consists of manganese , technetium , rhenium , and bohrium...

 of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

. With an average concentration of 1 part per billion
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...

 (ppb), rhenium is one of the rarest elements in the Earth's crust. The free element has the third-highest melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 and highest boiling point of any element. Rhenium resembles manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 chemically and is obtained as a by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....

 of molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

 and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 refinement. Rhenium shows in its compounds a wide variety of oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

s ranging from −1 to +7.

Discovered in 1925, rhenium was the last stable element to be discovered. It was named after the river Rhine in Europe.

Nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

-based superalloys for use in jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

s contain up to 6% rhenium, making jet engine construction the largest use for the element, with chemical industry catalytic uses being next-most important. Because of the low availability relative to demand, rhenium is among the most expensive industrial metals, with an average price of approximately US$4,575 per kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

, on 1 August 2011.http://www.metalprices.com/FreeSite/metals/re/re.asp

History

Rhenium ( meaning: "Rhine") was the last element to be discovered having a stable isotope (other new radioactive elements have been discovered in nature since then, such as (neptunium
Neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metal, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, 237Np, is a by-product of nuclear reactors and plutonium production and it can be used as a...

 and plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

). The existence of a yet undiscovered element at this position in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

 had been first predicted by Dmitry Mendeleev. Other calculated information was obtained by Henry Moseley
Henry Moseley
Henry Gwyn Jeffreys Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra...

 in 1914. It is generally considered to have been discovered by Walter Noddack
Walter Noddack
Walter Noddack was a German chemist. He, Ida Tacke , and Otto Berg reported the discovery of element 43 and element 75 in 1925.-Rhenium:...

, Ida Tacke, and Otto Berg
Otto Berg (scientist)
Otto Berg was a German scientist. He is one of the scientists credited with discovering rhenium, the next-to-last naturally occurring element to be discovered and the last element to be discovered having a stable isotope.-Rhenium:...

 in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. In 1925 they reported that they detected the element in platinum ore and in the mineral columbite
Columbite
Columbite, also called niobite, niobite-tantalite and columbate [2O6], is a black mineral group that is an ore of niobium and tantalum. It has a submetallic luster and a high density and is a niobate of iron and manganese, containing tantalate of iron. This mineral group was first found in Haddam,...

. They also found rhenium in gadolinite
Gadolinite
Gadolinite, sometimes also known as Ytterbite, is a silicate mineral which consists principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with the formula 2FeBe2Si2O10...

 and molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...

. In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite. The process was so complicated and expensive that production was discontinued until early 1950 when tungsten-rhenium and molybdenum-rhenium alloys were prepared. These alloys found important applications in industry that resulted in a great demand for the rhenium produced from the molybdenite fraction of porphyry copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 ores.

In 1908, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

ese chemist Masataka Ogawa
Masataka Ogawa
was a Japanese chemist known for the discovery of rhenium, which he named nipponium.After graduating from the University of Tokyo, he studied under William Ramsay in London, where he worked on the analysis of the rare mineral thorianite...

 announced that he discovered the 43rd element and named it nipponium (Np) after Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 (which is Nippon in Japanese). However, later analysis indicated the presence of rhenium (element 75), not element 43
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...

. The symbol Np was later used for the element neptunium
Neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metal, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, 237Np, is a by-product of nuclear reactors and plutonium production and it can be used as a...

.

Characteristics

Rhenium is a silvery-white metal with one of the highest melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

s of all elements, exceeded by only tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

 and carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

. It is also one of the densest, exceeded only by platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...

, iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...

 and osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...

.

Its usual commercial form is a powder, but this element can be consolidated by pressing and sintering
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...

 in a vacuum or hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atmosphere. This procedure yields a compact solid having a density above 90% of the density of the metal. When annealed
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...

 this metal is very ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

s are superconductive
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

 at 10 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

; tungsten-rhenium alloys are also superconductive around 4-8 K, depending on the alloy. Rhenium metal superconducts at 2.4 K.

Isotopes

Rhenium has a stable isotope, rhenium-185, which nevertheless occurs in minority abundance, a situation found only in one other element (indium
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

). Naturally occurring rhenium is 37.4% 185Re, which is stable
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...

, and 62.6% 187Re, which is unstable
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...

 but has a very long half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 (~1010 years). This lifetime is affected by the charge state of rhenium atom. The beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...

 of 187Re is used for rhenium-osmium dating
Rhenium-osmium dating
Rhenium-Osmium dating is a form of radiometric dating based on the beta decay of the isotope 187Re to 187Os. This normally occurs with a half-life of 41.6 × 109 y, but studies using fully ionised 187Re atoms have found that this can decrease to only 33 y...

 of ores. The available energy for this beta decay (2.6 keV
Kev
Kev can refer to:*Kev Hawkins, a fictional character.*Kevin, a given name occasionally shortened to "Kev".*Kiloelectronvolt, a unit of energy who symbol is "KeV".* Krefelder Eislauf-VereinKEV can refer to:...

) is one of the lowest known among all radionuclide
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...

s. There are twenty-six other recognized radioactive isotopes of rhenium.

Compounds

Rhenium has nine known oxidation states: −1, 0, +1, +2, +3, +4, +5, +6 and +7. The oxidation states +7, +6, +4, and +2 are the most common.

The most common rhenium compounds are the oxides and the halides exhibiting a broad oxidation number spectrum: Re2O7
Rhenium(VII) oxide
Rhenium oxide is the chemical compound with the formula Re2O7. It is the anhydride of the hypothetical acid . Perrhenic acid, Re2O7·2H2O, however is closely related structurally to Re2O7. Solid Re2O7 is polymeric consisting, unusually, of the metal centers in two coordination environments...

, ReO3, Re2O5, ReO2
Rhenium(IV) oxide
Rhenium oxide or rhenium dioxide is the chemical compound composed of rhenium and oxygen with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It form perrhenates with alkaline hydrogen peroxide and oxidizing acids. It disproportionates...

, and Re2O3 are the known oxides, and ReF7
Rhenium heptafluoride
Rhenium heptafluoride is the compound with the formula ReF7. It is a yellow low melting solid, and is the only thermally stable metal heptafluoride. It has a distorted pentagonal bipyramidal structure similar to IF7, which was confirmed by neutron diffraction at 1.5K. The structure is non-rigid as...

, ReCl6, ReCl5
Rhenium pentachloride
Rhenium pentachloride is an inorganic compound of chlorine and rhenium. The compound has the formula Re2Cl10 but it is usually referred to as the pentachloride. It is a red-brown solid. It is the highest chloride of rhenium.-Structure and preparation:...

, ReCl4 and ReCl3
Rhenium trichloride
Rhenium trichloride is a compound of rhenium and chlorine. It was first discovered in 1932 by Geilnann, Wriuce, and Biltz.-Structure and physical properties:...

 are a few of the known halogen derivatives. Known sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...

s are ReS2 and Re2S7.
Reaction of rhenium with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 produces the negatively charged hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

 [ReH9]2− ion, which is isostructural with [TcH9]2−. It consists of a trigonal prism with Re atom in the center and six hydrogen atoms at the corners. Three more hydrogens make a triangle lying parallel to the base and crossing the prism in its center (see figure). Although those hydrogen atoms are not equivalent geometrically, their electronic structure is almost the same. The coordination number 9 in this complex is the highest for a rhenium complex. Two protons in it can be replaced by sodium (Na+) or potassium (K+) ions.

Rhenium is most available commercially as the sodium
Sodium perrhenate
Sodium perrhenate is a white crystalline solid. It is a commonly available precursor for rhenium compounds....

 and ammonium perrhenate
Ammonium perrhenate
Ammonium perrhenate is the ammonium salt of perrhenic acid, NH4ReO4. This is the most common form in which rhenium is traded. Prices are quoted in US Dollars per kg Rhenium content. Rhenium content of APR is typically 69.0 - 69.4%.-Structure:...

s. It is also readily available as dirhenium decacarbonyl
Dirhenium decacarbonyl
Dirhenium decacarbonyl is an inorganic compound with the formula Re210. Commercially available, it is used as a starting point for the synthesis of many rhenium carbonyl complexes. It was first reported in 1941 by Walter Hieber who prepared it by carbonylation of Re2O7. The compound consists of a...

; these three compounds are common entry points to rhenium chemistry. Various perrhenate salts may be easily converted to tetrathioperrhenate by the action of ammonium hydrosulfide. It is possible to reduce the dirhenium decacarbonyl
Dirhenium decacarbonyl
Dirhenium decacarbonyl is an inorganic compound with the formula Re210. Commercially available, it is used as a starting point for the synthesis of many rhenium carbonyl complexes. It was first reported in 1941 by Walter Hieber who prepared it by carbonylation of Re2O7. The compound consists of a...

 Re2(CO)10 by reacting it with sodium amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

 to Na[Re(CO)5] with rhenium in the formal oxidation state −1. Dirhenium decacarbonyl may be oxidatively cleaved with bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 to give bromopentacarbonylrhenium(I)
Bromopentacarbonylrhenium(I)
Bromopentacarbonylrhenium is an inorganic compound of rhenium, commonly used for the syntheses of other rhenium complexes.-Preparation:Bromopentacarbonylrhenium is commercially available...

, then reduced with zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 and acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

 to pentacarbonylhydridorhenium
Pentacarbonylhydridorhenium
Pentacarbonylhydridorhenium is a chemical compound with the formula ReH5. This colorless liquid is a weak acid and represents one of the most important derivatives of dirhenium decacarbonyl...

:
Re2(CO)10 + Br2 → 2 Re(CO)5Br
Re(CO)5Br + Zn + HOAc → Re(CO)5H + ZnBr(OAc)


Bromopentacarbonylrhenium(I) may be decarbonylated to give the rhenium tricarbonyl fragment either by refluxing in water:
Re(CO)5Br + 3 H2O → [Re(CO)3(H2O)3]Br + 2 CO


or by reacting with tetraethylammonium bromide
Tetraethylammonium bromide
Tetraethylammonium bromide is a quaternary ammonium salt. It is a common source for the tetraethylammonium cation. Currently, no NFPA 704 for TEABr has been established. Industrially, it can be used to determine the epoxide value of various adhesives....

:
Re(CO)5Br + 2 NEt4Br → [NEt4]2[Re(CO)3Br3] + 2 CO


Rhenium diboride
Rhenium diboride
Rhenium diboride is a synthetic superhard material. It was first synthesized in 1962 and re-emerged recently due to hopes of achieving high hardness comparable to that of diamond...

 (ReB2) is a hard compound having the hardness similar to that of tungsten carbide
Tungsten carbide
Tungsten carbide is an inorganic chemical compound containing equal parts of tungsten and carbon atoms. Colloquially, tungsten carbide is often simply called carbide. In its most basic form, it is a fine gray powder, but it can be pressed and formed into shapes for use in industrial machinery,...

, silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...

, titanium diboride or zirconium diboride
Zirconium diboride
Zirconium diboride is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an Ultra High Temperature Ceramic with a melting point of 3246 °C...

.

Rhenium was originally thought to form the rhenide anion, Re, in which it has the −1 oxidation state. This was based on the product of the reduction of perrhenate
Perrhenate
The perrhenate ion is ReO4− and a perrhenate is a compound containing this ion. Salts of perrhenic acid are known as perrhenates. The perrhenate anion is tetrahedral, as shown by IR and Raman spectroscopy...

 salts, such as the reduction of potassium perrhenate by potassium metal. "Potassium rhenide" was shown to exist as a tetrahydrated complex, with the postulated chemical formula . This compound exhibits strongly reducing properties, and slowly yields hydrogen gas when dissolved in water. The lithium and thallous
Thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...

 salts were also reported. Later research, however, indicates that the "rhenide" ion is actually a hydridorhenate complex. "Potassium rhenide" was shown to be in fact the nonahydridorhenate
Potassium nonahydridorhenate
Potassium nonahydridorhenate is an inorganic compound with the formula K2ReH9. This colourless salt features the ReH92− anion, a rare example of a coordination complex bearing only hydride ligands....

, , containing the ReH92− anion in which the oxidation state of rhenium is actually +7. Other methods of reduction of perrhenate salts yield compounds containing other hydrido- complexes, including .

Occurrence

Rhenium is one of the rarest elements in Earth's crust with an average concentration of 1 ppb; other sources quote the number of 0.5 ppb making it the 77th most abundant element in Earth's crust. Rhenium is probably not found free in nature (its possible natural occurrence is uncertain), but occurs in amounts up to 0.2% in the mineral molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...

 (which is primarily molybdenum disulfide), the major commercial source, although single molybdenite samples with up to 1.88% have been found. Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 has the world's largest rhenium reserves, part of the copper ore deposits, and was the leading producer as of 2005. It was only recently that the first rhenium mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 was found and described (in 1994), a rhenium sulfide mineral
Sulfide mineral
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...

 (ReS2) condensing from a fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...

 on Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

's Kudriavy volcano, Iturup
Iturup
Iturup is the largest island of the South Kuril Islands. It is the northernmost island in the southern Kuril/Chishima islands, and though it is presently controlled by Russia, Japan also claims this island...

 island, in the Kurile Islands. Kudryavy discharges up to 20–60 kg rhenium per year mostly in the form of rhenium disulfide. Named rheniite
Rheniite
Rheniite is a very rare rhenium sulfide mineral . It forms metallic, silver grey platey crystals in the Triclinic - pinacoidal class. It has a specific gravity of 7.5....

, this rare mineral commands high prices among collectors.

Production

Commercial rhenium is extracted from molybdenum roaster-flue gas obtained from copper-sulfide ores. Some molybdenum ores contain 0.001% to 0.2% rhenium. Rhenium(VII) oxide
Rhenium(VII) oxide
Rhenium oxide is the chemical compound with the formula Re2O7. It is the anhydride of the hypothetical acid . Perrhenic acid, Re2O7·2H2O, however is closely related structurally to Re2O7. Solid Re2O7 is polymeric consisting, unusually, of the metal centers in two coordination environments...

 and perrhenic acid
Perrhenic acid
Perrhenic acid is the chemical compound with the formula Re2O72. It is obtained by evaporating aqueous solutions of Re2O7. Conventionally, perrhenic acid is considered to have the formula HReO4, and a species of this formula forms when rhenium oxide sublimes in the presence of water or steam...

 readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium
Potassium chloride
The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...

 or ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...

 as the perrhenate
Perrhenate
The perrhenate ion is ReO4− and a perrhenate is a compound containing this ion. Salts of perrhenic acid are known as perrhenates. The perrhenate anion is tetrahedral, as shown by IR and Raman spectroscopy...

 salts, and purified by recrystallization
Recrystallization (chemistry)
-Chemistry:In chemistry, recrystallization is a procedure for purifying compounds. The most typical situation is that a desired "compound A" is contaminated by a small amount of "impurity B". There are various methods of purification that may be attempted , which includes recrystallization...

. Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Kazakhstan. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons per year. Prices for the metal rose rapidly in early 2008, from $1000–$2000 per kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

 in 2003-2006 to over $10,000 in February 2008. The metal form is prepared by reducing ammonium perrhenate
Ammonium perrhenate
Ammonium perrhenate is the ammonium salt of perrhenic acid, NH4ReO4. This is the most common form in which rhenium is traded. Prices are quoted in US Dollars per kg Rhenium content. Rhenium content of APR is typically 69.0 - 69.4%.-Structure:...

 with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 at high temperatures:
2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3

Applications

Rhenium is added to high-temperature superalloys that are used to make jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

 parts, making 70% of the worldwide rhenium production. Another major application is in platinum-rhenium catalysts, which are primarily used in making lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

-free, high-octane gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

.

Alloys

The nickel-based superalloys have improved creep strength
Creep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....

 with the addition of rhenium. The alloys normally contain 3% or 6% of rhenium. Second generation alloys contain 3%; these alloys were used in the engines of the F-16 and F-15, while the newer single-crystal third generation alloys contain 6% of rhenium; they are used in the F-22 and F-35
F-35 Lightning II
The Lockheed Martin F-35 Lightning II is a family of single-seat, single-engine, fifth generation multirole fighters under development to perform ground attack, reconnaissance, and air defense missions with stealth capability...

 engines. Rhenium is also used in the superalloys, such as CMSX-4 (2nd gen) and CMSX-10 (3rd gen) that are used in industrial gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 engines like the GE 7FA. Rhenium can cause superalloys to become microstructurally unstable, forming undesirable TCP (topologically close packed) phase
Phase (matter)
In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

s. In 4th and 5th generation superalloys, ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...

 is used to avoid this effect. Among others the new superalloys are EPM-102 (with 3 % Ru) and TMS-162 (with 6 % Ru), both containing 6 % rhenium, as well as TMS-138 and TMS-174.

For 2006, the consumption is given as 28% for General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

, 28% Rolls-Royce plc
Rolls-Royce plc
Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

 and 12% Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...

, all for superalloys, while the use for catalysts only accounts for 14% and the remaining applications use 18%. In 2006, 77% of the rhenium consumption in the United States was in alloys. The rising demand for military jet engines and the constant supply made it necessary to develop superalloys with a lower rhenium content. For example the newer CFM International CFM56
CFM International CFM56
The CFM International CFM56 series is a family of high-bypass turbofan aircraft engines made by CFM International , with a thrust range of . CFMI is a 50–50 joint-owned company of SNECMA, France and GE Aviation , USA. Both companies are responsible for producing components and each has its own...

  high-pressure turbine (HPT) blades will use Rene N515 with a rhenium content of 1.5 % instead of Rene N5 with 3 %.

Rhenium improves the properties of tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...

 and is therefore the most important alloying material for tungsten. Tungsten-rhenium alloys are more ductile at low temperature making them easier to machine, while the high-temperature stability is also improved. The effect increases with the rhenium concentration, and therefore tungsten alloys are produced with up to 27% of Re, which is the solubility limit. One application for the tungsten-rhenium alloys is X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 sources. The high melting point of both compounds, together with the high atomic mass, makes them stable against the prolonged electron impact. Rhenium tungsten alloys are also applied as thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...

s to measure temperatures up to 2200 °C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

.

The high temperature stability, low vapor pressure, good wear resistance
Wear
In materials science, wear is erosion or sideways displacement of material from its "derivative" and original position on a solid surface performed by the action of another surface....

 and ability to withstand arc corrosion of rhenium are useful in self-cleaning electrical contacts. In particular, the discharge occurring during the switching oxidizes the contacts. However, rhenium oxide Re2O7 has poor stability (sublimates at ~360 °C) and therefore is removed during the discharge.

Rhenium has a high melting point and a low vapor pressure similar to tantalum and tungsten, however, rhenium forms no volatile oxides. Therefore, rhenium filaments exhibit a higher stability if the filament is operated not in vacuum, but in oxygen-containing atmosphere. Those filaments are widely used in mass spectrometers, in ion gauges. and in photoflash lamps in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

.

Catalysts

Rhenium in the form of rhenium-platinum alloy is used as catalyst for catalytic reforming
Catalytic reforming
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline...

, which is a chemical process to convert petroleum refinery naphtha
Naphtha
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e., a component of natural gas condensate or a distillation product from petroleum, coal tar or peat boiling in a certain range and containing certain hydrocarbons. It is a broad term covering among the...

s with low octane rating
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

s into high-octane liquid products. Worldwide, 30% of catalysts used for this process contain rhenium. The olefin metathesis
Olefin metathesis
Olefin metathesis or transalkylidenation is an organic reaction that entails redistribution of alkylene fragments by the scission of carbon - carbon double bonds in olefins . Its advantages include the creation of fewer sideproducts and hazardous wastes. Yves Chauvin, Robert H. Grubbs, and Richard R...

 is the other reaction for which rhenium is used as catalyst. Normally Re2O7 on alumina is used for this process. Rhenium catalysts are very resistant to chemical poisoning
Catalyst poisoning
Catalyst poisoning refers to the effect that a catalyst can be 'poisoned' if it reacts with another compound that bonds chemically to its active surface sites. This effectively reduces the usefulness of the catalyst...

 from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions.

Other uses

188Re and 186Re isotopes are radioactive and are used for treatment of liver cancer
Liver cancer
Liver tumors or hepatic tumors are tumors or growths on or in the liver . Several distinct types of tumors can develop in the liver because the liver is made up of various cell types. These growths can be benign or malignant...

. They both have similar penetration depth in tissue (5 mm for 186Re and 11 mm for 188Re), but 186Re has advantage of longer lifetime (90 hours vs. 17 hours).

Related by periodic trends
Periodic trends
In Chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements.-Atomic radius:...

, rhenium has a similar chemistry with technetium
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...

; work done to label rhenium onto target compounds can often be translated to technetium. This is useful for radiopharmacy, where it is difficult to work with technetium – especially the 99m isotope used in medicine – due to its expense and short half-life.

Precaution

Very little is known about the toxicity of rhenium and its compounds because they are used in very small amounts. Soluble salts, such as the rhenium halides or perrhenates, could be hazardous due to elements other than rhenium or due to rhenium itself. Only a few compounds of rhenium have been tested for their acute toxicity; two examples are potassium perrhenate and rhenium trichloride, which were injected as a solution into rats. The perrhenate had an LD50 value of 2800 mg/kg after seven days (this is very low toxicity, similar to that of table salt) and the rhenium trichloride showed LD50 of 280 mg/kg.

External links

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