Rhenium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Re and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of ever ...
75. It is a silvery-gray, heavy, third-row
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
in
group 7 of the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
. With an estimated average concentration of 1
part per billion
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, t ...
(ppb), rhenium is one of the rarest elements in the
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
. Rhenium has the
third-highest melting point
The melting point (or, rarely, liquefaction point) of a substance 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 depen ...
and highest boiling point of any stable element at 5869 K. Rhenium resembles
manganese
Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
and
technetium chemically and is mainly obtained as a
by-product
A by-product or byproduct is a secondary product derived from a production process, 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 consid ...
of the extraction and refinement of
molybdenum and
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
ores. Rhenium shows in its compounds a wide variety of
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
s ranging from −1 to +7.
Discovered by
Walter Noddack
Walter Noddack (17 August 1893 – 7 December 1960) was a German chemist. He, Ida Tacke (who later married Noddack), and Otto Berg reported the discovery of element 43 and element 75 in 1925.
Rhenium
They named element 75 rhenium ( Latin ''R ...
,
Ida Tacke
Ida Noddack (25 February 1896 – 24 September 1978), ''née'' Tacke, was a German chemist and physicist. In 1934 she was the first to mention the idea later named nuclear fission. With her husband - Walter Noddack - and Otto Berg she discover ...
and
Otto Berg in 1925, rhenium was the last
stable element to be discovered. It was named after the river
Rhine
), Surselva, Graubünden, Switzerland
, source1_coordinates=
, source1_elevation =
, source2 = Rein Posteriur/Hinterrhein
, source2_location = Paradies Glacier, Graubünden, Switzerland
, source2_coordinates=
, source ...
in Europe, from which the earliest samples had been obtained and worked commercially.
Nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
-based
superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s of rhenium are used in combustion chambers, turbine blades, and exhaust nozzles of
jet engine
A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...
s. 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
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
: rhenium is an excellent catalyst for
hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
and isomerization, and is used for example in
catalytic reforming
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-oc ...
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 of US$10,600 per
kilogram
The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...
(US$4,800 per pound). Due to increases in rhenium recycling and a drop in demand for rhenium in catalysts, the price of rhenium had dropped to US$2,844 per
kilogram
The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...
(US$1,290 per pound) as of July 2018.
History
Rhenium ( la, Rhenus meaning: "
Rhine
), Surselva, Graubünden, Switzerland
, source1_coordinates=
, source1_elevation =
, source2 = Rein Posteriur/Hinterrhein
, source2_location = Paradies Glacier, Graubünden, Switzerland
, source2_coordinates=
, source ...
") was the last-discovered of the elements that have a stable isotope (other new elements discovered in nature since then, such as
francium
Francium is a chemical element with the symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain it appears in), has a half-life of only 22&n ...
, are radioactive).
The existence of a yet-undiscovered element at this position in the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
had been first predicted by
Dmitri Mendeleev
Dmitri Ivanovich Mendeleev (sometimes transliterated as Mendeleyev or Mendeleef) ( ; russian: links=no, Дмитрий Иванович Менделеев, tr. , ; 8 February Old_Style_and_New_Style_dates">O.S._27_January.html" ;"title="O ...
. Other calculated information was obtained by
Henry Moseley in 1914. In 1908,
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
ese chemist
Masataka Ogawa
was a Japanese chemist mainly known for the claimed discovery of element 43 (later known as technetium), which he named nipponium. In fact, he might have discovered, but misidentified, element 75 (later called rhenium).
After graduating from th ...
announced that he had discovered the 43rd element and named it ''nipponium'' (Np) after
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
(''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
Walter Noddack (17 August 1893 – 7 December 1960) was a German chemist. He, Ida Tacke (who later married Noddack), and Otto Berg reported the discovery of element 43 and element 75 in 1925.
Rhenium
They named element 75 rhenium ( Latin ''R ...
,
Ida Noddack
Ida Noddack (25 February 1896 – 24 September 1978), ''née'' Tacke, was a German chemist and physicist. In 1934 she was the first to mention the idea later named nuclear fission. With her husband - Walter Noddack - and Otto Berg she discov ...
, and
Otto Berg in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
. In 1925 they reported that they had detected the element in platinum ore and in the mineral
columbite
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
. They also found rhenium in
gadolinite
Gadolinite, sometimes known as ytterbite, is a silicate mineral consisting principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with the formula . It is called gadolinite-(Ce) or gadolinite-(Y), depending o ...
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
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
was used for research and the development of
refractory metal alloys. It took several years from that point before the superalloys became widely used.
Characteristics
Rhenium is a silvery-white metal with one of the highest
melting point
The melting point (or, rarely, liquefaction point) of a substance 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 depen ...
s of all elements, exceeded by only
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
. It also has one of the highest
boiling points of all elements, and the highest among stable elements. It is also one of the densest, exceeded only by
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Pla ...
,
iridium
Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density o ...
and
osmium
Osmium (from Greek grc, ὀσμή, osme, smell, label=none) is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, ...
. 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
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
in a vacuum or
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
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
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
s are
superconductive at 10
K; tungsten-rhenium alloys are also superconductive around 4–8 K, depending on the alloy. Rhenium metal superconducts at .
In bulk form and at room temperature and atmospheric pressure, the element resists alkalis,
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
,
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
,
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
, and
aqua regia. It will however, react with nitric acid upon heating.
Isotopes
Rhenium has one
stable
A stable is a building in which livestock, especially horses, are kept. It most commonly means a building that is divided into separate stalls for individual animals and livestock. There are many different types of stables in use today; the ...
isotope, rhenium-185, which nevertheless occurs in minority abundance, a situation found only in two other elements (
indium and
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
). Naturally occurring rhenium is only 37.4%
185Re, and 62.6%
187Re, which is
unstable but has a very long
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
(≈10
10 years). A kilogram of natural rhenium emits 1.07 MBq of radiation due to the presence of this isotope. This lifetime can be greatly affected by the charge state of the rhenium atom.
The
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
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
radionuclide
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...
s. 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 33 other unstable isotopes that have been recognized, ranging from
160Re to
194Re, the longest-lived of which is
183Re with a half-life of 70 days.
Compounds
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 The perrhenate ion is the anion with the formula , or a compound containing this ion. The perrhenate anion is tetrahedral, being similar in size and shape to perchlorate and the valence isoelectronic permanganate. The perrhenate anion is stable ove ...
, including
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
and
ammonium perrhenate
Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH4ReO4. It is the most common form in which rhenium is traded. It is a white salt; soluble in ethanol and water, and mildly soluble in NH4Cl. It was first described soon after the ...
s. These are white, water-soluble compounds.
[Glemser, O. (1963) "Ammonium Perrhenate" in ''Handbook of Preparative Inorganic Chemistry'', 2nd ed., G. Brauer (ed.), Academic Press, NY., Vol. 1, pp. 1476–85.] Tetrathioperrhenate anion
4">eS4sup>− is possible.
Halides and oxyhalides
The most common rhenium chlorides are ReCl
6,
ReCl5, ReCl
4, 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
2Cl8">e2Cl8sup>2− feature a
quadruple metal-metal bond. Although the highest rhenium chloride features Re(VI), fluorine gives the d
0 Re(VII) derivative
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 ...
. 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
In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), chlo ...
. The oxychlorides are most common, and include ReOCl
4, ReOCl
3.
Oxides and sulfides
The most common oxide is the volatile yellow
Re2O7. The red
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 that resembles copper in appearance. It is the only stable trioxide of the Group 7 elements ( Mn, Tc, Re).
Prepar ...
ReO
3 adopts a
perovskite
Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as (XIIA2+VIB4+X2−3), known a ...
-like structure. Other oxides include Re
2O
5,
ReO2, and Re
2O
3.
The
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
s are
ReS2 and
Re2S7. Perrhenate salts can be converted to
tetrathioperrhenate by the action of
ammonium hydrosulfide.
Other compounds
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, alth ...
(ReB
2) is a hard compound having a hardness similar to that of
tungsten carbide,
silicon carbide,
titanium diboride or
zirconium diboride.
Organorhenium compounds
Dirhenium decacarbonyl
Dirhenium decacarbonyl is the inorganic compound with the chemical formula Re2(CO)10 . 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 ...
is the most common entry to organorhenium chemistry. Its reduction with sodium
amalgam
Amalgam most commonly refers to:
* Amalgam (chemistry), mercury alloy
* Amalgam (dentistry), material of silver tooth fillings
** Bonded amalgam, used in dentistry
Amalgam may also refer to:
* Amalgam Comics, a publisher
* Amalgam Digital, an in ...
gives Na
5">e(CO)5with rhenium in the formal oxidation state −1. Dirhenium decacarbonyl can be oxidised with
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
to
bromopentacarbonylrhenium(I)
Bromopentacarbonylrhenium(I) is an inorganic compound of rhenium, commonly used for the syntheses of other rhenium complexes.
Preparation
Bromopentacarbonylrhenium(I) is commercially available. It is also easily and inexpensively synthesized by th ...
:
:Re
2(CO)
10 + Br
2 → 2 Re(CO)
5Br
Reduction of this pentacarbonyl with
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main componen ...
gives
pentacarbonylhydridorhenium
Pentacarbonylhydridorhenium is a chemical compound with the formula ReH(CO)5. This colorless liquid is a weak acid and represents one of the most important derivatives of dirhenium decacarbonyl (Re2(CO)10). It is synthesized by treating a methanol ...
:
:Re(CO)
5Br + Zn + HOAc → Re(CO)
5H + ZnBr(OAc)
Methylrhenium trioxide ("MTO"), CH
3ReO
3 is a volatile, colourless solid has been used as a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in some laboratory experiments. It can be prepared by many routes, a typical method is the reaction of Re
2O
7 and
tetramethyltin:
:Re
2O
7 + (CH
3)
4Sn → CH
3ReO
3 + (CH
3)
3SnOReO
3
Analogous alkyl and aryl derivatives are known. MTO catalyses for the oxidations with
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
. Terminal
alkynes yield the corresponding acid or ester, internal alkynes yield diketones, and
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s give epoxides. MTO also catalyses the conversion of
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
s and
diazoalkane
The diazo group is an organic moiety consisting of two linked nitrogen atoms ( azo) at the terminal position. Overall charge neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes ...
s into an alkene.
Nonahydridorhenate
A distinctive derivative of rhenium is
nonahydridorhenate
Potassium nonahydridorhenate(VII) is an inorganic compound having the formula K2ReH9. This colourless salt is soluble in water but only poorly soluble in most alcohols. The anion is a rare example of a coordination complex bearing only hydride ...
, originally thought to be the ''rhenide'' anion, Re
−, but actually containing the anion in which the oxidation state of rhenium is +7.
Occurrence
Rhenium is one of the rarest elements in
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
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
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...
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
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
was found and described (in 1994), a rhenium
sulfide mineral (ReS
2) condensing from a
fumarole on
Kudriavy
Medvezhya (russian: Медве́жий; ja, 茂世路岳, ''Moyoro-dake'') is a volcanic complex located at the northern end of Iturup Island, Kuril Islands, Russia.
Rheniite, a rhenium sulfide mineral (ReS2), was discovered and approved in 200 ...
volcano,
Iturup island, in the
Kuril Islands
The Kuril Islands or Kurile Islands (; rus, Кури́льские острова́, r=Kuril'skiye ostrova, p=kʊˈrʲilʲskʲɪjə ɐstrɐˈva; Japanese language, Japanese: or ) are a volcanic archipelago currently administered as part of Sakh ...
. Kudriavy discharges up to 20–60 kg rhenium per year mostly in the form of rhenium disulfide. Named
rheniite
Rheniite is a very rare rhenium sulfide mineral with the chemical formula ( ). It forms metallic, silver grey platey crystals in the triclinic - pinacoidal class. It has a specific gravity of 7.5.
It was discovered at the Kudriavy Volcano, Ituru ...
, this rare mineral commands high prices among collectors.
Production
Approximately 80% of rhenium is extracted from
porphyry molybdenum deposits. Some ores contain 0.001% to 0.2% rhenium.
Roasting the ore volatilizes rhenium oxides.
Rhenium(VII) oxide and
perrhenic acid
Perrhenic acid is the chemical compound with the formula . It is obtained by evaporating aqueous solutions of . Conventionally, perrhenic acid is considered to have the formula , and a species of this formula forms when rhenium(VII) oxide sublime ...
readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
or
ammonium chloride as the
perrhenate The perrhenate ion is the anion with the formula , or a compound containing this ion. The perrhenate anion is tetrahedral, being similar in size and shape to perchlorate and the valence isoelectronic permanganate. The perrhenate anion is stable ove ...
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
Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH4ReO4. It is the most common form in which rhenium is traded. It is a white salt; soluble in ethanol and water, and mildly soluble in NH4Cl. It was first described soon after the ...
with
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
at high temperatures:
:2 NH
4ReO
4 + 7 H
2 → 2 Re + 8 H
2O + 2 NH
3
There are technologies for the associated extraction of rhenium from productive solutions of underground leaching of uranium ores.
Applications
Rhenium is added to high-temperature superalloys that are used to make
jet engine
A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...
parts, using 70% of the worldwide rhenium production.
Another major application is in platinum–rhenium
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s, which are primarily used in making
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
-free, high-octane
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
.
Alloys
The nickel-based
superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s 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
superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s to become microstructurally unstable, forming undesirable topologically close packed (TCP)
phases. In 4th- and 5th-generation
superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s,
ruthenium is used to avoid this effect. Among others the new
superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s 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
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable ene ...
, 28%
Rolls-Royce plc and 12%
Pratt & Whitney
Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military av ...
, all for superalloys, whereas the use for catalysts only accounts for 14% and the remaining applications use 18%.
In 2006, 77% of 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
The CFM International CFM56 (U.S. military designation F108) series is a Franco-American family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of . CFMI is a 50–50 joint-owned company of Saf ...
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, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
. 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
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
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
An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they ...
. In particular, the discharge that occurs during electrical switching oxidizes the contacts. However, rhenium oxide Re
2O
7 is volatile (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
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that ...
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,
ion gauges and
photoflash lamps in
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...
.
Catalysts
Rhenium in the form of rhenium-platinum alloy is used as catalyst for
catalytic reforming
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-oc ...
, which is a chemical process to convert petroleum refinery
naphthas with low
octane rating
An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonatin ...
s 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 Re
2O
7 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.
Other uses
The isotopes
188Re and
186Re are radioactive and are used for treatment of
liver cancer
Liver cancer (also known as hepatic cancer, primary hepatic cancer, or primary hepatic malignancy) is cancer that starts in the liver. Liver cancer can be primary (starts in liver) or secondary (meaning cancer which has spread from elsewhere to th ...
. 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''. The
188Re isotope is also used for the rhenium-SCT (
skin cancer therapy). The treatment uses the isotope's properties as a
beta emitter for
brachytherapy
Brachytherapy is a form of radiation therapy where a sealed radiation source is placed inside or next to the area requiring treatment. ''Brachy'' is Greek for short. Brachytherapy is commonly used as an effective treatment for cervical, pro ...
in the treatment of
basal cell carcinoma and
squamous cell carcinoma
Squamous-cell carcinomas (SCCs), also known as epidermoid carcinomas, comprise a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the ...
of the skin.
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
Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medica ...
isotope used in medicine – due to its expense and short half-life.
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.
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 LD
50 of 280 mg/kg.
References
External links
Rheniumat ''
The Periodic Table of Videos'' (University of Nottingham)
{{Good article
Chemical elements
Transition metals
Noble metals
Refractory metals
Chemical elements predicted by Dmitri Mendeleev
Chemical elements with hexagonal close-packed structure
Native element minerals