Rhenium is a chemical element with symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Rhenium has the third-highest melting point and second-highest boiling point of any element at 5903 K. Rhenium resembles manganese and technetium chemically and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores. Rhenium shows in its compounds a wide variety of oxidation states ranging from −1 to +7.
Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization, and is used for example in catalytic reforming of naphtha for use in gasoline (rheniforming process). Because of the low availability relative to demand, rhenium is expensive, with price reaching an all-time high in 2008/2009 US$10,600 per kilogram (US$4,800 per pound). Due to increases in rhenium recycling and a drop in demand for rhenium in catalysts, the price of rhenium has dropped to US$2,844 per kilogram (US$1,290 per pound) as of July 2018.
|Standard atomic weight Ar, std(Re)||186.207(1)|
|Rhenium in the periodic table|
|Atomic number (Z)||75|
|Element category||transition metal|
|Electron configuration||[Xe] 4f14 5d5 6s2|
Electrons per shell
|2, 8, 18, 32, 13, 2|
|Phase at STP||solid|
|Melting point||3459 K (3186 °C, 5767 °F)|
|Boiling point||5903 K (5630 °C, 10,170 °F)|
|Density (near r.t.)||21.02 g/cm3|
|when liquid (at m.p.)||18.9 g/cm3|
|Heat of fusion||60.43 kJ/mol|
|Heat of vaporization||704 kJ/mol|
|Molar heat capacity||25.48 J/(mol·K)|
|Oxidation states||−3, −1, 0, +1, +2, +3, +4, +5, +6, +7 (a mildly acidic oxide)|
|Electronegativity||Pauling scale: 1.9|
|Atomic radius||empirical: 137 pm|
|Covalent radius||151±7 pm|
Spectral lines of rhenium
|Crystal structure|| hexagonal close-packed (hcp)|
|Speed of sound thin rod||4700 m/s (at 20 °C)|
|Thermal expansion||6.2 µm/(m·K)|
|Thermal conductivity||48.0 W/(m·K)|
|Electrical resistivity||193 nΩ·m (at 20 °C)|
|Magnetic susceptibility||+67.6·10−6 cm3/mol (293 K)|
|Young's modulus||463 GPa|
|Shear modulus||178 GPa|
|Bulk modulus||370 GPa|
|Vickers hardness||1350–7850 MPa|
|Brinell hardness||1320–2500 MPa|
|Naming||after the river Rhine (German: Rhein)|
|Discovery||Masataka Ogawa (1908)|
|First isolation||Masataka Ogawa (1919)|
|Named by||Walter Noddack, Ida Noddack, Otto Berg (1925)|
|Main isotopes of rhenium|
Rhenium (Latin: Rhenus meaning: "Rhine") was the second last-discovered of the elements that have a stable isotope (other new elements discovered in nature since then, such as francium, are radioactive). The existence of a yet-undiscovered element at this position in the periodic table had been first predicted by Dmitri Mendeleev. Other calculated information was obtained by Henry Moseley in 1914. In 1908, Japanese chemist Masataka Ogawa announced that he had discovered the 43rd element and named it nipponium (Np) after Japan (Nippon in Japanese). However, recent analysis indicated the presence of rhenium (element 75), not element 43, although this reinterpretation has been questioned by Eric Scerri. The symbol Np was later used for the element neptunium, and the name "nihonium", also named after Japan, along with symbol Nh, was later used for element 113. Element 113 was also discovered by a team of Japanese scientists and was named in respectful homage to Ogawa's work.
Rhenium is generally considered to have been discovered by Walter Noddack, Ida Noddack, and Otto Berg in Germany. In 1925 they reported that they had detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite. It was estimated in 1968 that 75% of the rhenium metal in the United States was used for research and the development of refractory metal alloys. It took several years from that point before the superalloys became widely used.
Rhenium is a silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten and carbon. It also has one of the highest boiling points of all elements. It is also one of the densest, exceeded only by platinum, iridium and osmium. Rhenium has a hexagonal close-packed crystal structure, with lattice parameters a = 276.1 pm and c = 445.6 pm.
Its usual commercial form is a powder, but this element can be consolidated by pressing and sintering in a vacuum or hydrogen atmosphere. This procedure yields a compact solid having a density above 90% of the density of the metal. When annealed this metal is very ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloys are superconductive at 10 K; tungsten-rhenium alloys are also superconductive around 4–8 K, depending on the alloy. Rhenium metal superconducts at 1.697±0.006 K.
Rhenium has one stable isotope, rhenium-185, which nevertheless occurs in minority abundance, a situation found only in two other elements (indium and tellurium). Naturally occurring rhenium is only 37.4% 185Re, and 62.6% 187Re, which is unstable but has a very long half-life (≈1010 years). This lifetime can be greatly affected by the charge state of rhenium atom. The beta decay of 187Re is used for rhenium-osmium dating of ores. The available energy for this beta decay (2.6 keV) is one of the lowest known among all radionuclides. The isotope rhenium-186m is notable as being one of the longest lived metastable isotopes with a half-life of around 200,000 years. There are twenty-five other recognized radioactive isotopes of rhenium.
Rhenium compounds are known for all the oxidation states between −3 and +7 except −2. The oxidation states +7, +6, +4, and +2 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds.
The most common rhenium chlorides are ReCl6, ReCl5, ReCl4, and ReCl3. The structures of these compounds often feature extensive Re-Re bonding, which is characteristic of this metal in oxidation states lower than VII. Salts of [Re2Cl8]2− feature a quadruple metal-metal bond. Although the highest rhenium chloride features Re(VI), fluorine gives the d0 Re(VII) derivative rhenium heptafluoride. Bromides and iodides of rhenium are also well known.
Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of oxyhalides. The oxychlorides are most common, and include ReOCl4, ReOCl3.
The most common oxide is the volatile colourless Re2O7. Rhenium trioxide ReO3 adopts a perovskite-like structure. Other oxides include Re2O5, ReO2, and Re2O3. The sulfides are ReS2 and Re2S7. Perrhenate salts can be converted to tetrathioperrhenate by the action of ammonium hydrosulfide.
Dirhenium decacarbonyl is the most common entry to organorhenium chemistry. Its reduction with sodium amalgam gives Na[Re(CO)5] with rhenium in the formal oxidation state −1. Dirhenium decacarbonyl can be oxidised with bromine to bromopentacarbonylrhenium(I):
Methylrhenium trioxide ("MTO"), CH3ReO3 is a volatile, colourless solid has been used as a catalyst in some laboratory experiments. It can be prepared by many routes, a typical method is the reaction of Re2O7 and tetramethyltin:
Analogous alkyl and aryl derivatives are known. MTO catalyses for the oxidations with hydrogen peroxide. Terminal alkynes yield the corresponding acid or ester, internal alkynes yield diketones, and alkenes give epoxides. MTO also catalyses the conversion of aldehydes and diazoalkanes into an alkene.
A distinctive derivative of rhenium is nonahydridorhenate, originally thought to be the rhenide anion, Re−, but actually containing the ReH2−
9 anion in which the oxidation state of rhenium is +7.
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 (which is primarily molybdenum disulfide), the major commercial source, although single molybdenite samples with up to 1.88% have been found. Chile 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 was found and described (in 1994), a rhenium sulfide mineral (ReS2) condensing from a fumarole on Kudriavy volcano, Iturup island, in the Kuril Islands. Kudriavy discharges up to 20–60 kg rhenium per year mostly in the form of rhenium disulfide. Named rheniite, this rare mineral commands high prices among collectors.
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 and perrhenic acid readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified by recrystallization. Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Poland. 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 in 2003–2006 to over $10,000 in February 2008. The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures:
Rhenium is added to high-temperature superalloys that are used to make jet engine parts, using 70% of the worldwide rhenium production. Another major application is in platinum–rhenium catalysts, which are primarily used in making lead-free, high-octane gasoline.
The nickel-based superalloys have improved creep strength 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 for the F-15 and F-16, whereas the newer single-crystal third-generation alloys contain 6% of rhenium; they are used in the F-22 and F-35 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 engines like the GE 7FA. Rhenium can cause superalloys to become microstructurally unstable, forming undesirable TCP (topologically close packed) phases. In 4th- and 5th-generation superalloys, ruthenium is used to avoid this effect. Among others the new superalloys are EPM-102 (with 3% Ru) and TMS-162 (with 6% Ru), as well as TMS-138 and TMS-174.
For 2006, the consumption is given as 28% for General Electric, 28% Rolls-Royce plc and 12% Pratt & Whitney, all for superalloys, whereas 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 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-rhenium alloys are more ductile at low temperature, allowing them to be more easily machined. 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. Tungsten-rhenium wire was originally created in efforts to develop a wire that was more ductile after recrystallization. This allows the wire to meet specific performance objectives, including superior vibration resistance, improved ductility, and higher resistivity. One application for the tungsten-rhenium alloys is X-ray sources. The high melting point of both elements, together with their high atomic mass, makes them stable against the prolonged electron impact. Rhenium tungsten alloys are also applied as thermocouples to measure temperatures up to 2200 °C.
The high temperature stability, low vapor pressure, good wear resistance 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 (sublimes 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. 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.
Rhenium in the form of rhenium-platinum alloy is used as catalyst for catalytic reforming, which is a chemical process to convert petroleum refinery naphthas with low octane ratings into high-octane liquid products. Worldwide, 30% of catalysts used for this process contain rhenium. The olefin metathesis 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 from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions.
The isotopes 188Re and 186Re are radioactive and are used for treatment of liver cancer. 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).
188Re is also being used experimentally in a novel treatment of pancreatic cancer where it is delivered by means of the bacterium Listeria monocytogenes.
Related by periodic trends, rhenium has a similar chemistry to that of technetium; 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.
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.
Bohrium is a synthetic chemical element with symbol Bh and atomic number 107. It is named after Danish physicist Niels Bohr. As a synthetic element, it can be created in a laboratory but is not found in nature. It is radioactive: its most stable known isotope, 270Bh, has a half-life of approximately 61 seconds, though the unconfirmed 278Bh may have a longer half-life of about 690 seconds.
In the periodic table of the elements, it is a d-block transactinide element. It is a member of the 7th period and belongs to the group 7 elements as the fifth member of the 6d series of transition metals. Chemistry experiments have confirmed that bohrium behaves as the heavier homologue to rhenium in group 7. The chemical properties of bohrium are characterized only partly, but they compare well with the chemistry of the other group 7 elements.Group 7 element
Group 7, numbered by IUPAC nomenclature, is a group of elements in the periodic table. They are manganese (Mn), technetium (Tc), rhenium (Re), and bohrium (Bh). All known elements of group 7 are transition metals.
Like other groups, the members of this family show patterns in their electron configurations, especially the outermost shells resulting in trends in chemical behavior.Isotopes of rhenium
Naturally occurring rhenium (75Re) is 37.4% 185Re, which is stable, and 62.6% 187Re, which is unstable but has a very long half-life (41.2×109 years). Among elements with a known stable isotope, only indium and tellurium similarly occur with a stable isotope in lower abundance than the long-lived radioactive isotope.
There are 33 other unstable isotopes recognized, the longest-lived of which are 183Re with a half-life of 70 days, 184Re with a half-life of 38 days, 186Re with a half-life of 3.7186 days, 182Re with a half-life of 64.0 hours, and 189Re with a half-life of 24.3 hours. There are also numerous isomers, the longest-lived of which are 186mRe with a half-life of 200,000 years and 184mRe with a half-life of 169 days. All others have half-lives less than a day.Organorhenium chemistry
Organorhenium chemistry describes the compounds with Re−C bonds. Because rhenium is a rare element, relatively few applications exist, but the area has been a rich source of concepts and a few useful catalysts.Osmium (album)
Osmium is the debut album of American funk band Parliament, led by George Clinton. The album has a psychedelic soul sound with a spirit of experimentation that is more similar to early Funkadelic than the later R&B-inspired Parliament albums. It was originally released in September 1970 on Invictus Records. The original vinyl release contained a glossy lyric sheet.
Since its re-release in 1990, Osmium has been distributed numerous times by various labels in the U.S., Europe and Japan, sometimes under alternate titles that have included Rhenium and First Thangs. A number of these reissues have featured material that was not included on the original album, such as unreleased tracks and singles that were recorded around the same time as Osmium.
The personnel for this album included the five Parliaments singers and the five backing musicians known as Funkadelic. The same personnel also recorded as Funkadelic, releasing that act's self-titled debut album also in 1970. After the release of Osmium, contractual difficulties prevented further recording under the name Parliament until 1974, when Clinton signed that act to Casablanca Records and positioned it as an R&B-inspired counterpoint to the more rock-oriented Funkadelic.
The yodeling that arguably uniquely identifies one of De La Soul's early hits, "Potholes in My Lawn" (which eventually appeared on De La Soul's 3 Feet High and Rising), comes from Osmium's "Little Ole Country Boy".This is the only Parliament album that Ruth Copeland worked on.Refractory metals
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period (niobium and molybdenum) and three of the sixth period (tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatures.Rhenium(IV) oxide
Rhenium(IV) oxide or rhenium dioxide is the inorganic compound with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure.Rhenium(VII) oxide
Rhenium(VII) oxide is the inorganic compound with the formula Re2O7. This yellowish solid is the anhydride of HOReO3. Perrhenic acid, Re2O7·2H2O, is closely related to Re2O7. Re2O7 is the raw material for all rhenium compounds, being the volatile fraction obtained upon roasting the host ore.Rhenium(VII) sulfide
Rhenium(VII) sulfide is a chemical compound with the formula Re2S7. It can be produced through the reaction of ReO4− and H2S in 4N HCl.Rhenium diboride
Rhenium diboride (ReB2) 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. The reported ultrahigh hardness has been questioned, although this is a matter of definition as in the initial test rhenium diboride was able to scratch diamond.The production method of this material does not involve high pressures as with other hard synthetic materials, such as cubic boron nitride, which makes production cheap. However, rhenium itself is an expensive metal.
The compound is formed from a mixture of rhenium, noted for its resistance to high pressure, and boron, which forms short, strong covalent bonds with rhenium.Rhenium diselenide
Rhenium diselenide is an inorganic compound with the formula ReSe2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material.Rhenium disulfide
Rhenium disulfide is an inorganic compound of rhenium and sulfur with the formula ReS2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material. It is a two-dimensional (2D) group VII transition metal dichalcogenide (TMD). Different to other TMDs, ReS2 has shown layer-independent electrical, optical, and vibrational properties.Nanostructured ReS2 can usually be achieved through mechanical exfoliation, chemical vapor deposition (CVD), and chemical and liquid exfoliations. It is widely used in electronic and optoelectronic device, energy storage, photocatalytic and electrocatalytic reactions.Rhenium ditelluride
Rhenium ditelluride is an inorganic compound of rhenium and tellurium with the formula ReTe2. Contrary to rhenium disulfide and diselenide, it does not have a layered structure.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 evidenced by electron diffraction studies.It can be prepared from the elements at 400 °C:
2Re + 7 F2 → 2 ReF7With fluoride donors such as CsF, the ReF8− anion is formed, which has a square antiprismatic structure. With antimony pentafluoride, SbF5, a fluoride acceptor, the ReF6+ cation is formed.Rhenium hexafluoride
Rhenium hexafluoride, also rhenium(VI) fluoride, (ReF6) is a compound of rhenium and fluorine and one of the seventeen known binary hexafluorides.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 rhenium pentachloride. It is a red-brown solid.Rhenium trioxide
Rhenium trioxide or rhenium(VI) oxide is an inorganic compound with the formula ReO3. It is a red solid with a metallic lustre, which resembles copper in appearance. It is the only stable trioxide of the Group 7 elements (Mn, Tc, Re).Sodium perrhenate
Sodium perrhenate (also known as sodium rhenate(VII)) is the inorganic compound with the formula NaReO4 It is a white solid that is soluble in water. It is a common precursor to other rhenium compounds. Its structure resembles that of sodium perchlorate and sodium permanganate.Trirhenium nonachloride
Trirhenium nonachloride is a compound with the formula ReCl3, sometimes also written Re3Cl9. It is a dark red hygroscopic solid that is insoluble in ordinary solvents. The compound is important in the history of inorganic chemistry as an early example of a cluster compound with metal-metal bonds. It is used as a starting material for synthesis of other rhenium complexes.