Rhenium
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Rhenium | |||||||||||||||||||||||||||||||||||
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Pronunciation | /ˈriːniəm/ | ||||||||||||||||||||||||||||||||||
Appearance | silvery-grayish | ||||||||||||||||||||||||||||||||||
Standard atomic weight Ar°(Re) | |||||||||||||||||||||||||||||||||||
Rhenium in the periodic table | |||||||||||||||||||||||||||||||||||
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kJ/mol | |||||||||||||||||||||||||||||||||||
Heat of vaporization | 704 kJ/mol | ||||||||||||||||||||||||||||||||||
Molar heat capacity | 25.48 J/(mol·K) | ||||||||||||||||||||||||||||||||||
Vapor pressure
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Atomic properties | |||||||||||||||||||||||||||||||||||
Oxidation states | common: +4, +7 −3, Discovery Masataka Ogawa (1908) | | |||||||||||||||||||||||||||||||||
First isolation | Masataka Ogawa (1919) | ||||||||||||||||||||||||||||||||||
Named by | Walter Noddack, Ida Noddack, Otto Berg (1925) | ||||||||||||||||||||||||||||||||||
Isotopes of rhenium | |||||||||||||||||||||||||||||||||||
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Rhenium is a
Rhenium was originally discovered in 1908 by Masataka Ogawa, but he mistakenly assigned it as element 43 (now known as technetium) rather than element 75 and named it nipponium. It was rediscovered in 1925 by Walter Noddack, Ida Tacke and Otto Berg,[10] who gave it its present name. It was named after the river Rhine in Europe, from which the earliest samples had been obtained and worked commercially.[11]
Nickel-based superalloys of rhenium are used in 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: it 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 2008–09 of US$10,600 per kilogram (US$4,800 per pound). As of 2018, its price had dropped to US$2,844 per kilogram (US$1,290 per pound) due to increased recycling and a drop in demand for rhenium catalysts.[12]
History
In 1908,
Rhenium (
The original mischaracterization by Ogawa in 1908 and final work in 1925 makes rhenium perhaps the last stable element to be understood. Hafnium was discovered in 1923[21] and all other new elements discovered since then, such as francium, are radioactive.[22]
Characteristics
Rhenium is a silvery-white metal with one of the highest
Its usual commercial form is a powder, but this element can be consolidated by pressing and
In bulk form and at room temperature and atmospheric pressure, the element resists alkalis, sulfuric acid, hydrochloric acid, nitric acid, and aqua regia. It will however, react with nitric acid upon heating.[27]
Isotopes
Rhenium has one
Compounds
Rhenium compounds are known for all the
Halides and oxyhalides
The most common rhenium chlorides are ReCl6,
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.
Oxides and sulfides

The most common oxide is the volatile yellow
Other compounds
Rhenium diboride (ReB2) is a hard compound having a hardness similar to that of tungsten carbide, silicon carbide, titanium diboride or zirconium diboride.[37]
Organorhenium compounds
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.[38] Dirhenium decacarbonyl can be oxidised with bromine to bromopentacarbonylrhenium(I):[39]
- Re2(CO)10 + Br2 → 2 Re(CO)5Br
Reduction of this pentacarbonyl with zinc and acetic acid gives pentacarbonylhydridorhenium:[40]
- Re(CO)5Br + Zn + HOAc → Re(CO)5H + ZnBr(OAc)
- Re2O7 + (CH3)4Sn → CH3ReO3 + (CH3)3SnOReO3
Analogous alkyl and aryl derivatives are known. MTO catalyses for the oxidations with
Nonahydridorhenate

9.
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.
Occurrence

Rhenium is one of the rarest elements in
Production

Approximately 80% of rhenium is extracted from porphyry molybdenum deposits.[49] Some ores contain 0.001% to 0.2% rhenium.[35] Roasting the ore volatilizes rhenium oxides.[43] 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.[35] Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Poland.[50] 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.[51][52] The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures:[33]
- 2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3
There are technologies for the associated extraction of rhenium from productive solutions of underground leaching of uranium ores.[53]
Applications

Rhenium is added to high-temperature superalloys that are used to make
Alloys
The nickel-based superalloys have improved creep strength with the addition of rhenium. The alloys normally contain 3% or 6% of rhenium.[57] 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.[56][58] 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 topologically close packed (TCP) 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),[59] as well as TMS-138[60] and TMS-174.[61][62]

For 2006, the consumption is given as 28% for
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.[65] 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.[66] 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.[67] Rhenium tungsten alloys are also applied as thermocouples to measure temperatures up to 2200 °C.[68]
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 that occurs during electrical switching oxidizes the contacts. However, rhenium oxide Re2O7 is volatile (sublimes at ~360 °C) and therefore is removed during the discharge.[55]
Rhenium has a high melting point and a low vapor pressure similar to
Catalysts
Rhenium in the form of rhenium-platinum alloy is used as catalyst for
Other uses
The isotopes 186Re and 188Re 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 the advantage of a longer half life (90 hours vs. 17 hours).[76][77]
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 technetium-99m isotope used in medicine – due to its expense and short half-life.[76][80]
Rhenium is used in manufacturing high precision equipment like
Rhenium is used in aerospace, nuclear, and electronic industries, and it shows potential for application in medical instrumentation.[84] In the rocket industry, it is used in engine components for booster rockets.[85][86] Additionally, rhenium was employed in the SP-100 program due to its low-temperature ductility.[87]
Rhenium's stiffness and high melting point makes it a common gasket material for
Precautions
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.[90] 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.[91]
Notes
- ^ The thermal expansion of Rh is anisotropic: the parameters for each crystal axis (at 20 °C) are αa = 6.07×10−6/K, αc = 4.69×10−6/K, and αaverage = αV/3 = 5.61×10−6/K.[4]
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Further reading
- Scerri, Eric (2013). A Tale of Seven Elements. Oxford University Press, ISBN 9780195391312.
External links
- Rhenium at The Periodic Table of Videos(University of Nottingham)