Iridium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol Ir 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 every ...
77. A very hard, brittle, silvery-white
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 ca ...
of the
platinum group
The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered t ...
, it is considered the second-densest naturally occurring metal (after
osmium) with a density of as defined by experimental
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. It is one of the most
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
-resistant metals, even at temperatures as high as . However, corrosion-resistance is not quantifiable in absolute terms; although only certain molten salts and
halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable, whereas gold dust is not flammable but can be attacked by substances that iridium resists, such as
aqua regia.
Iridium was discovered in 1803 among insoluble impurities in natural
platinum.
Smithson Tennant
Smithson Tennant FRS (30 November 1761 – 22 February 1815) was an English chemist. He is best known for his discovery of the elements iridium and osmium, which he found in the residues from the solution of platinum ores in 1803. He also con ...
, the primary discoverer, named it after the Greek goddess
Iris
Iris most often refers to:
*Iris (anatomy), part of the eye
*Iris (mythology), a Greek goddess
* ''Iris'' (plant), a genus of flowering plants
* Iris (color), an ambiguous color term
Iris or IRIS may also refer to:
Arts and media
Fictional ent ...
, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is
one of the rarest elements in
Earth's crust, with annual production and consumption of only .
191Ir and
193Ir are the only two naturally occurring
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...
s of iridium, as well as the only
stable isotope
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
s; the latter is the more abundant.
The dominant uses of iridium are the metal itself and its alloys, as in high-performance
spark plugs,
crucible
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
s for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the
chloralkali process
The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodit ...
. Important compounds of iridium are chlorides and iodides in industrial
catalysis. Iridium is a component of some OLEDs.
Iridium is found in
meteorites in much higher abundance than in the Earth's crust.
For this reason, the unusually high abundance of iridium in the clay layer at the
Cretaceous–Paleogene boundary gave rise to the
Alvarez hypothesis that the impact of a massive extraterrestrial object caused the
extinction of dinosaurs and many other species 66 million years ago, now known to be produced by the impact that formed the
Chicxulub crater. Similarly, an iridium anomaly in core samples from the
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...
suggested the
Eltanin impact of about 2.5 million years ago.
It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum-group metals, the high density and
tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten.
Characteristics
Physical properties
![iridium2](https://upload.wikimedia.org/wikipedia/commons/4/46/Iridium2.jpg)
A member of the
platinum group
The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered t ...
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
s, iridium is white, resembling
platinum, but with a slight yellowish cast. Because of its
hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
,
brittleness, and very high
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 ...
, solid iridium is difficult to machine, form, or work; thus
powder metallurgy
Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and ...
is commonly employed instead.
It is the only metal to maintain good mechanical properties in air at temperatures above .
It has the 10th highest
boiling point among all elements and becomes a
superconductor at temperatures below .
Iridium's
modulus of elasticity
An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...
is the second-highest among the metals, being surpassed only by
osmium.
This, together with a high
shear modulus
In materials science, shear modulus or modulus of rigidity, denoted by ''G'', or sometimes ''S'' or ''μ'', is a measure of the elastic shear stiffness of a material and is defined as the ratio of shear stress to the shear strain:
:G \ \stackre ...
and a very low figure for
Poisson's ratio
In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Po ...
(the relationship of longitudinal to lateral
strain
Strain may refer to:
Science and technology
* Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes
* Strain (chemistry), a chemical stress of a molecule
* Strain (injury), an injury to a mu ...
), indicate the high degree of
stiffness and resistance to deformation that have rendered its fabrication into useful components a matter of great difficulty. Despite these limitations and iridium's high cost, a number of applications have developed where mechanical strength is an essential factor in some of the extremely severe conditions encountered in modern technology.
The measured
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
of iridium is only slightly lower (by about 0.12%) than that of osmium, the
densest metal known. Some ambiguity occurred regarding which of the two elements was denser, due to the small size of the difference in density and difficulties in measuring it accurately,
but, with increased accuracy in factors used for calculating density,
X-ray crystallographic data yielded densities of for iridium and for osmium.
Iridium is extremely brittle, to the point of being hard to weld because the heat-affected zone cracks, but it can be made more ductile by addition of small quantities of
titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
and
zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
(0.2% of each apparently works well).-
The
Vickers hardness of pure platinum is 56 HV, whereas platinum with 50% of iridium can reach over 500 HV.
Chemical properties
Iridium is the most
corrosion-resistant
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engin ...
metal known:
it is not attacked by
acids, including
aqua regia. In the presence of oxygen, it reacts with
cyanide salts.
Traditional oxidants also react, including the
halogens and oxygen
at higher temperatures.
Iridium also reacts directly with
sulfur at atmospheric pressure to yield
iridium disulfide.
[
]
Isotopes
Iridium has two naturally occurring, stable
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...
s,
191Ir and
193Ir, with
natural abundances of 37.3% and 62.7%, respectively.
At least 37
radioisotope
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; transferr ...
s have also been synthesized, ranging in
mass number
The mass number (symbol ''A'', from the German word ''Atomgewicht'' tomic weight, also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approxima ...
from 164 to 202.
192Ir, which falls between the two stable isotopes, is the most stable radioisotope, with a
half-life of 73.827 days, and finds application in
brachytherapy and in industrial
radiography
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeu ...
, particularly for nondestructive testing of welds in steel in the oil and gas industries; iridium-192 sources have been involved in a number of radiological accidents. Three other isotopes have half-lives of at least a day—
188Ir,
189Ir, and
190Ir.
Isotopes with masses below 191 decay by some combination of
β+ decay,
α decay, and (rare)
proton emission
Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case t ...
, with the exception of
189Ir, which decays by
electron capture. Synthetic isotopes heavier than 191 decay by
β− decay, although
192Ir also has a minor electron capture decay path.
All known isotopes of iridium were discovered between 1934 and 2008, with the most recent discoveries being
200–202Ir.
At least 32
metastable isomers have been characterized, ranging in mass number from 164 to 197. The most stable of these is
192m2Ir, which decays by
isomeric transition with a half-life of 241 years,
making it more stable than any of iridium's synthetic isotopes in their ground states. The least stable isomer is
190m3Ir with a half-life of only 2 μs.
The isotope
191Ir was the first one of any element to be shown to present a
Mössbauer effect. This renders it useful for
Mössbauer spectroscopy
Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer (sometimes written "Moessbauer", German: "Mößbauer") in 1958, consists of the nearly recoil-free emission and abs ...
for research in physics, chemistry, biochemistry, metallurgy, and mineralogy.
Chemistry
Oxidation states
Iridium forms compounds in
oxidation states between −3 and +9, but the most common oxidation states are +1, +3, and +4.
Well-characterized compounds containing iridium in the +6 oxidation state include
and the oxides and .
iridium(VIII) oxide () was generated under matrix isolation conditions at 6 K in
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
. The highest oxidation state (+9), which is also the highest recorded for ''any'' element, is found in gaseous .
Binary compounds
Iridium does not form
binary
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
hydride
In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
s. Only one
binary oxide is well-characterized:
Iridium dioxide, . It is a blue black solid that adopts the
fluorite structure In solid state chemistry, the fluorite structure refers to a common motif for compounds with the formula MX2. The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structur ...
.
A
sesquioxide, , has been described as a blue-black powder, which is oxidized to by .
The corresponding disulfides, diselenides, sesquisulfides, and sesquiselenides are known, as well as .
Binary trihalides, are known for all of the halogens.
For oxidation states +4 and above, only the
tetrafluoride,
pentafluoride and
hexafluoride are known.
Iridium hexafluoride, , is a volatile yellow solid, composed of octahedral molecules. It decomposes in water and is reduced to ,.
Iridium pentafluoride is also a strong oxidant, but it is a
tetramer, , formed by four corner-sharing octahedra.
Complexes
![IrCl3(aq)x](https://upload.wikimedia.org/wikipedia/commons/9/9e/IrCl3%28aq%29x.jpg)
The
coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...
es of iridium are extensive.
Iridium in its complexes is always
low-spin). Ir(III) and Ir(IV) generally form
octahedral complexes.
Polyhydride complexes are known for the +5 and +3 oxidation states. One example is . The ternary hydride is believed to contain both the and the 18-electron anion.
Iridium also
oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...
s with oxidation states +4 and +5. and can be prepared from the reaction of
potassium oxide
Potassium oxide ( K O) is an ionic compound of potassium and oxygen. It is a base. This pale yellow solid is the simplest oxide of potassium. It is a highly reactive compound that is rarely encountered. Some industrial materials, such as fertili ...
or
potassium superoxide with iridium at high temperatures. Such solids are not soluble in conventional solvents.
As for many elements, the chlorides are key complexes. Hexachloroiridic (IV) acid, , and its ammonium salt are the most common iridium compounds from an industrial and preparative perspectives.
They are intermediates in the purification of iridium and used as precursors for most other iridium compounds, as well as in the preparation of
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...
coatings. The ion has an intense dark brown color, and can be readily reduced to the lighter-colored and vice versa.
Iridium trichloride, , which can be obtained in anhydrous form from direct oxidation of iridium powder by
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
at 650 °C,
or in hydrated form by dissolving in
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
Acid strength is the tendency of an acid, symbol ...
, is often used as a starting material for the synthesis of other Ir(III) compounds.
Another compound used as a starting material is ammonium hexachloroiridate(III), .
In the presence of air, iridium metal dissolves in molten alkali-metal cyanides to produce the (hexacyanoiridate) ion.
Organoiridium chemistry
Organoiridium compounds contain iridium–
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 mak ...
bonds. Early studies identified the very stable
tetrairidium dodecacarbonyl
Tetrairidium dodecacarbonyl is the chemical compound with the formula Ir4(CO)12. This tetrahedral cluster is the most common and most stable "binary" carbonyl of iridium. This air-stable species is only poorly soluble in organic solvents.
It ha ...
, .
In this compound, each of the iridium atoms is bonded to the other three, forming a tetrahedral cluster. The discovery of
Vaska's complex
Vaska's complex is the trivial name for the chemical compound ''trans''-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO) (C6H5)3sub>2. This square planar diamagnetic organometallic complex consists of a central iridi ...
() opened the door for
oxidative addition
Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxid ...
reactions, a process fundamental to useful reactions. For example,
Crabtree's catalyst
Crabtree's catalyst is an organoiridium compound with the formula 1,5-Cyclooctadiene.html" ;"title="/nowiki> C8H12IrTricyclohexylphosphine.html" ;"title="1,5-Cyclooctadiene">C8H12Ir P(C6H11)3 P(C6H11)3pyridine">C5H5N.html" ;"title="pyridine.html" ...
, a
homogeneous 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 organ ...
reactions.
![C-HactnBergGrah](https://upload.wikimedia.org/wikipedia/commons/c/c4/C-HactnBergGrah.png)
Iridium complexes played a pivotal role in the development of
Carbon–hydrogen bond activation (C–H activation), which promises to allow functionalization of hydrocarbons, which are traditionally regarded as unreactive.
History
Platinum group
![Winged goddess Cdm Paris 392](https://upload.wikimedia.org/wikipedia/commons/a/aa/Winged_goddess_Cdm_Paris_392.jpg)
The discovery of iridium is intertwined with that of platinum and the other metals of the platinum group.
The first European reference to platinum appears in 1557 in the writings of the
Italian
Italian(s) may refer to:
* Anything of, from, or related to the people of Italy over the centuries
** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom
** Italian language, a Romance language
*** Regional Ita ...
humanist
Julius Caesar Scaliger
Julius Caesar Scaliger (; April 23, 1484 – October 21, 1558), or Giulio Cesare della Scala, was an Italian scholar and physician, who spent a major part of his career in France. He employed the techniques and discoveries of Renaissance humanism ...
as a description of an unknown noble metal found between
Darién and Mexico, "which no fire nor any Spanish artifice has yet been able to liquefy".
From their first encounters with platinum, the Spanish generally saw the metal as a kind of impurity in gold, and it was treated as such. It was often simply thrown away, and there was an official decree forbidding the
adulteration
An adulterant is caused by the act of adulteration, a practice of secretly mixing a substance with another. Typical substances that are adulterated include but are not limited to food, cosmetics, pharmaceuticals, fuel, or other chemicals, that ...
of gold with platinum impurities.
![Platinum symbol](https://upload.wikimedia.org/wikipedia/commons/c/ce/Platinum_symbol.svg)
In 1735,
Antonio de Ulloa and
Jorge Juan y Santacilia saw Native Americans mining platinum while the Spaniards were travelling through Colombia and Peru for eight years. Ulloa and Juan found mines with the whitish metal nuggets and took them home to Spain. Antonio de Ulloa returned to Spain and established the first mineralogy lab in Spain and was the first to systematically study platinum, which was in 1748. His historical account of the expedition included a description of platinum as being neither separable nor
calcinable. Ulloa also anticipated the discovery of platinum mines. After publishing the report in 1748, Ulloa did not continue to investigate the new metal. In 1758, he was sent to superintend mercury mining operations in
Huancavelica
Huancavelica () or Wankawillka in Quechua is a city in Peru. It is the capital of the department of Huancavelica and according to the 2017 census had a population of 49,570 people. The city was established on August 5, 1572 by the Viceroy ...
.
In 1741, Charles Wood, a British
metallurgist, found various samples of Colombian platinum in Jamaica, which he sent to
William Brownrigg
William Brownrigg ( – 6 January 1800) was a British doctor and scientist, who practised at Whitehaven in Cumberland. While there, Brownrigg carried out experiments that earned him the Copley Medal in 1766 for his work on carbonic acid gas. He ...
for further investigation.
In 1750, after studying the platinum sent to him by Wood, Brownrigg presented a detailed account of the metal to the
Royal Society
The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
, stating that he had seen no mention of it in any previous accounts of known minerals. Brownrigg also made note of platinum's extremely high melting point and refractoriness toward
borax. Other chemists across Europe soon began studying platinum, including
Andreas Sigismund Marggraf,
Torbern Bergman
Torbern Olaf (Olof) Bergman (''KVO'') (20 March 17358 July 1784) was a Swedish chemist and mineralogist noted for his 1775 ''Dissertation on Elective Attractions'', containing the largest chemical affinity tables ever published. Bergman was the ...
,
Jöns Jakob Berzelius,
William Lewis, and
Pierre Macquer. In 1752,
Henrik Scheffer published a detailed scientific description of the metal, which he referred to as "white gold", including an account of how he succeeded in fusing platinum ore with the aid of
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
. Scheffer described platinum as being less pliable than gold, but with similar resistance to corrosion.
Discovery
Chemists who studied platinum dissolved it in
aqua regia (a mixture of
hydrochloric
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 digestiv ...
and
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 nitri ...
s) to create soluble salts. They always observed a small amount of a dark, insoluble residue.
Joseph Louis Proust thought that the residue was
graphite.
The French chemists
Victor Collet-Descotils,
Antoine François, comte de Fourcroy, and
Louis Nicolas Vauquelin
Prof. Louis Nicolas Vauquelin FRS(For) HFRSE (16 May 1763 – 14 November 1829) was a French pharmacist and chemist. He was the discoverer of both chromium and beryllium.
Early life
Vauquelin was born at Saint-André-d'Hébertot in Normandy, F ...
also observed the black residue in 1803, but did not obtain enough for further experiments.
In 1803, British scientist
Smithson Tennant
Smithson Tennant FRS (30 November 1761 – 22 February 1815) was an English chemist. He is best known for his discovery of the elements iridium and osmium, which he found in the residues from the solution of platinum ores in 1803. He also con ...
(1761–1815) analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids
and obtained a volatile new oxide, which he believed to be of this new metal—which he named ''ptene'', from the Greek word ''ptēnós'', "winged".
Tennant, who had the advantage of a much greater amount of residue, continued his research and identified the two previously undiscovered elements in the black residue, iridium and osmium.
He obtained dark red crystals (probably of ]·''n'') by a sequence of reactions with
sodium hydroxide and
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
Acid strength is the tendency of an acid, symbol ...
.
He named iridium after
Iris
Iris most often refers to:
*Iris (anatomy), part of the eye
*Iris (mythology), a Greek goddess
* ''Iris'' (plant), a genus of flowering plants
* Iris (color), an ambiguous color term
Iris or IRIS may also refer to:
Arts and media
Fictional ent ...
(), the Greek winged goddess of the rainbow and the messenger of the Olympian gods, because many of the
salts
In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...
he obtained were strongly colored. Discovery of the new elements was documented in a letter to the
Royal Society
The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
on June 21, 1804.
Metalworking and applications
British scientist
John George Children was the first to melt a sample of iridium in 1813 with the aid of "the greatest galvanic battery that has ever been constructed" (at that time).
The first to obtain high-purity iridium was
Robert Hare in 1842. He found it had a density of around and noted the metal is nearly immalleable and very hard. The first melting in appreciable quantity was done by
Henri Sainte-Claire Deville and
Jules Henri Debray
Jules Henri Debray (26 July 1827, in Amiens – 19 July 1888, in Paris) was a French chemist.
In 1847 he began his studies at the École Normale Supérieure in Paris, and several years later became an instructor at the Lycée Charlemagne (185 ...
in 1860. They required burning more than of pure and gas for each of iridium.
These extreme difficulties in melting the metal limited the possibilities for handling iridium.
John Isaac Hawkins
John Isaac Hawkins (1772–1855) was an inventor who practised civil engineering.
He was known as the co-inventor of the ever-pointed pencil, an early mechanical pencil, and of the upright piano.
Early life
Hawkins was born 14 March 1772 at Taun ...
was looking to obtain a fine and hard point for fountain pen nibs, and in 1834 managed to create an iridium-pointed gold pen. In 1880,
John Holland and
William Lofland Dudley
William Lofland Dudley (April 16, 1859 – September 8, 1914) was an American chemistry professor at both the University of Cincinnati and Vanderbilt University and an athletics pioneer during the Progressive Era. At Vanderbilt, he was appoint ...
were able to melt iridium by adding
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
and patented the process in the United States; British company
Johnson Matthey
Johnson Matthey is a British multinational speciality chemicals and sustainable technologies company headquartered in London, England. It is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index.
History Early years
Jo ...
later stated they had been using a similar process since 1837 and had already presented fused iridium at a number of
World Fairs.
The first use of an alloy of iridium with ruthenium in
thermocouples was made by Otto Feussner in 1933. These allowed for the measurement of high temperatures in air up to .
In Munich, Germany in 1957
Rudolf Mössbauer, in what has been called one of the "landmark experiments in twentieth-century physics", discovered the resonant and
recoil
Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, as according to Newton's third law the force r ...
-free emission and absorption of
gamma rays by atoms in a solid metal sample containing only
191Ir. This phenomenon, known as the
Mössbauer effect resulted in the awarding of the
Nobel Prize in Physics in 1961, at the age 32, just three years after he published his discovery.
Occurrence
Along with all elements having
atomic weight
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
s higher than that of
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
, iridium is only naturally formed by the
r-process (rapid neutron capture) in
supernovae and
neutron star merger
A neutron star merger is a type of stellar collision.
It occurs in a fashion similar to the rare brand of type Ia supernovae resulting from merging white dwarf stars.
When two neutron stars orbit each other closely, they gradually spiral i ...
s.
![Elemental abundances](https://upload.wikimedia.org/wikipedia/commons/0/09/Elemental_abundances.svg)
Iridium is one of the nine least abundant stable elements in Earth's crust, having an average mass fraction of 0.001
ppm in crustal rock;
platinum is 10 times more abundant,
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
is 40 times more abundant, and
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
and
mercury are 80 times more abundant.
Tellurium is about as abundant as iridium.
In contrast to its low abundance in crustal rock, iridium is relatively common in
meteorites, with concentrations of 0.5 ppm or more.
The overall concentration of iridium on Earth is thought to be much higher than what is observed in crustal rocks, but because of the density and
siderophilic ("iron-loving") character of iridium, it descended below the crust and into
Earth's core
The internal structure of Earth is the solid portion of the Earth, excluding its atmosphere and hydrosphere. The structure consists of an outer silicate solid crust, a highly viscous asthenosphere and solid mantle, a liquid outer core whose ...
when the planet was still molten.
Iridium is found in nature as an uncombined element or in natural
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, ductilit ...
s; especially the iridium–osmium alloys,
osmiridium (osmium-rich), and
iridosmium (iridium-rich).
In the
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 ...
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 pinkis ...
deposits, the platinum group metals occur as
sulfides (i.e. (),
tellurides (i.e. PtBiTe),
antimonide Antimonides (sometimes called stibnides) are compounds of antimony with more electropositive elements. The antimonide ion is Sb3−.
Reduction of antimony by alkali metals or by other methods leads to alkali metal antimonides of various types. K ...
s (PdSb), and
arsenide
In chemistry, an arsenide is a compound of arsenic with a less electronegative element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many stoichiometries, and in this respect a ...
s (i.e. ). In all of these compounds, platinum is exchanged by a small amount of iridium and osmium. As with all of the platinum group metals, iridium can be found naturally in alloys with raw nickel or
raw copper. A number of iridium-dominant minerals, with iridium as the species-forming element, are known. They are exceedingly rare and often represent the iridium analogues of the above-given ones. The examples are irarsite and cuproiridsite, to mention some. Within Earth's crust, iridium is found at highest concentrations in three types of geologic structure: igneous deposits (crustal intrusions from below), impact craters, and deposits reworked from one of the former structures. The largest known primary reserves are in the
Bushveld igneous complex
The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It i ...
in
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
,
(near the largest known impact structure, the
Vredefort impact structure
The Vredefort impact structure is the largest verified impact structure on Earth. The crater, which has since been eroded away, was around across when it was formed. The remaining structure, comprising the deformed underlying bedrock, is loca ...
) though the large copper–nickel deposits near
Norilsk
Norilsk ( rus, Нори́льск, p=nɐˈrʲilʲsk, ''Norílʹsk'') is a closed city in Krasnoyarsk Krai, Russia, located south of the western Taymyr Peninsula, around 90 km east of the Yenisey River and 1,500 km north of Krasnoyarsk. Norilsk ...
in
Russia
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
, and the
Sudbury Basin (also an impact crater) in
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
are also significant sources of iridium. Smaller reserves are found in the United States.
Iridium is also found in secondary deposits, combined with platinum and other platinum group metals in
alluvial deposits. The alluvial deposits used by
pre-Columbian people in the
Chocó Department
Choco Department is a department of Western Colombia known for its large Afro-Colombian population. It is in the west of the country, and is the only Colombian department to have coastlines on both the Pacific Ocean and the Atlantic Ocean. It ...
of
Colombia are still a source for platinum-group metals. As of 2003, world reserves have not been estimated.
Marine oceanography
Iridium is found within marine organisms,
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s, and the water column. The abundance of iridium in seawater
and organisms
is relatively low, as it does not readily form
chloride complexes.
The abundance in organisms is about 20 parts per trillion, or about five
orders of magnitude
An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...
less than in
sedimentary rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
s at the
Cretaceous–Paleogene (K–T) boundary.
The concentration of iridium in seawater and marine sediment is sensitive to
marine oxygenation, seawater temperature, and various geological and biological processes.
Iridium in sediments can come from
cosmic dust, volcanoes,
precipitation from seawater, microbial processes, or
hydrothermal vents,
and its abundance can be strongly indicative of the source.
It tends to associate with other ferrous metals in
manganese nodule
Polymetallic nodules, also called manganese nodules, are mineral concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core. As nodules can be found in vast quantities, and contain valuable metals, de ...
s.
Iridium is one of the characteristic elements of extraterrestrial rocks, and, along with osmium, can be used as a tracer element for meteoritic material in sediment.
For example core samples from the
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...
with elevated iridium levels suggested the
Eltanin impact of about 2.5 million years ago.
Some of the
mass extinctions, such as the
Cretaceous extinction, can be identified by anomalously high concentrations of iridium in sediment, and these can be linked to major
asteroid impact
An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or me ...
s.
Cretaceous–Paleogene boundary presence
![K-T boundary](https://upload.wikimedia.org/wikipedia/commons/5/57/K-T_boundary.jpg)
The
Cretaceous–Paleogene boundary of 66 million years ago, marking the temporal border between the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
and
Paleogene periods of
geological time
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...
, was identified by a thin
stratum of
iridium-rich clay.
A team led by
Luis Alvarez proposed in 1980 an extraterrestrial origin for this iridium, attributing it to an
asteroid or
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
impact.
Their theory, known as the
Alvarez hypothesis, is now widely accepted to explain the extinction of the non-avian
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. A large buried impact crater structure with an estimated age of about 66 million years was later identified under what is now the
Yucatán Peninsula
The Yucatán Peninsula (, also , ; es, Península de Yucatán ) is a large peninsula in southeastern Mexico and adjacent portions of Belize and Guatemala. The peninsula extends towards the northeast, separating the Gulf of Mexico to the north ...
(the
Chicxulub crater). Dewey M. McLean and others argue that the iridium may have been of
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
origin instead, because
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's core is rich in iridium, and active volcanoes such as
Piton de la Fournaise, in the island of
Réunion, are still releasing iridium.
Production
Worldwide production of iridium is about . The price is high and varying (see table). Illustrative factors that affect the price include oversupply of Ir crucibles
and changes in
LED technology.
Platinum metals occur together as dilute ores. Iridium is one of the rarer platinum metals: for every 190 tonnes of platinum obtained from ores, only 7.5 tonnes of iridium is isolated.
To separate the metals, they must first be brought into
solution. Two methods for rendering Ir-containing ores soluble are (i) fusion of the solid with
sodium peroxide followed by extraction of the resulting glass in
aqua regia and (ii) extraction of the solid with a mixture of
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
with
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
Acid strength is the tendency of an acid, symbol ...
.
From soluble extracts, iridium is separated by precipitating solid
ammonium hexachloroiridate () or by extracting with organic amines. The first method is similar to the procedure Tennant and Wollaston used for their original separation. The second method can be planned as continuous
liquid–liquid extraction and is therefore more suitable for industrial scale production. In either case, the product, an iridium chloride salt, is reduced with hydrogen, yielding the metal as a powder or ''
sponge
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...
'', which is amenable to
powder metallurgy
Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and ...
techniques. Iridium is also obtained commercially as a by-product from
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 ...
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 pinkis ...
mining and processing. During
electrorefining of copper and nickel, noble metals such as silver, gold and the
platinum group metals as well as
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
and
tellurium settle to the bottom of the cell as ''anode mud'', which forms the starting point for their extraction.
Applications
The main areas of use of iridium are electrodes for producing chlorine and other aggressive products,
OLED
An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
s, crucibles,
catalysts
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 ...
(e.g.
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 component ...
), and ignition tips for spark plugs.
[
]
Ir metal and alloys
Resistance to heat and corrosion are the bases for several uses of iridium and its alloys.
Owing to its high melting point, hardness, and corrosion resistance
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
, iridium is used to make crucibles. Such crucible
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
s are used in the Czochralski process to produce oxide single-crystals (such as sapphire
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
s) for use in computer memory devices and in solid state lasers. The crystals, such as gadolinium gallium garnet
Gadolinium Gallium Garnet (GGG, ) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has a cubic lattice, a density of 7.08 g/cm3 and its Mohs hardness is v ...
and yttrium gallium garnet, are grown by melting pre-sintered charges of mixed oxides under oxidizing conditions at temperatures up to .
Certain long-life aircraft engine parts are made of an iridium alloy, and an iridium–titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
alloy is used for deep-water pipes because of its corrosion resistance. Iridium is used for multi-pored spinnerets
A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and are ...
, through which a plastic polymer melt is extruded to form fibers, such as rayon
Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose f ...
. Osmium–iridium is used for compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
bearings and for balances.
Because of their resistance to arc erosion, iridium alloys are used by some manufacturers for electrical contacts for spark plugs, and iridium-based spark plugs are particularly used in aviation.
Catalysis
Iridium compounds are used as catalysts
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 the Cativa process
The Cativa process is a method for the production of acetic acid by the carbonylation of methanol. The technology, which is similar to the Monsanto process, was developed by BP Chemicals and is under license by BP Plc. The process is based on an ...
for carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbon ...
of methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
to produce 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 component ...
.
Iridium complexes are often active for asymmetric hydrogenation
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from othe ...
both by traditional 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 organ ...
. and transfer hydrogenation
In chemistry, transfer hydrogenation is a chemical reaction involving the addition of hydrogen to a compound from a source other than molecular . It is applied in laboratory and industrial organic synthesis to saturate organic compounds and redu ...
. This property is the basis of the industrial route to the chiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from ...
herbicide
Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
(S)-metolachlor. As practiced by Syngenta on the scale of 10,000 tons/year, the complex _[Ir(COD)Clsub>2_in_the_presence_of_Josiphos_ligands.html" ;"title="r(COD)Cl.html" ;"title=" [Ir(COD)Cl"> [Ir(COD)Clsub>2 in the presence of Josiphos ligands">r(COD)Cl.html" ;"title=" [Ir(COD)Cl"> [Ir(COD)Clsub>2 in the presence of Josiphos ligands.
Medical imaging
The radioisotope iridium-192
There are two natural isotopes of iridium (77Ir), and 34 radioisotopes, the most stable radioisotope being 192Ir with a half-life of 73.83 days, and many nuclear isomers, the most stable of which is 192m2Ir with a half-life of 241 years. All othe ...
is one of the two most important sources of energy for use in industrial Industrial radiography#Radioisotope sources, γ-radiography for non-destructive testing of metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
s. Additionally, 192Ir is used as a source of gamma radiation
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...
for the treatment of cancer using brachytherapy, a form of radiotherapy where a sealed radioactive source is placed inside or next to the area requiring treatment. Specific treatments include high-dose-rate prostate brachytherapy, biliary duct brachytherapy, and intracavitary cervix brachytherapy. iridium-192
There are two natural isotopes of iridium (77Ir), and 34 radioisotopes, the most stable radioisotope being 192Ir with a half-life of 73.83 days, and many nuclear isomers, the most stable of which is 192m2Ir with a half-life of 241 years. All othe ...
is normally produced by neutron activation of isotop iridium-191
There are two natural isotopes of iridium (77Ir), and 34 radioisotopes, the most stable radioisotope being Iridium-192, 192Ir with a half-life of 73.83 days, and many nuclear isomers, the most stable of which is 192m2Ir with a half-life of 241 yea ...
in natural-abundance iridium metal
Photocatalysis and OLEDs
Iridium complexes are key components of white OLED
An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
s. Similar complexes are used in photocatalysis
In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abi ...
.
Scientific
An alloy of 90% platinum and 10% iridium was used in 1889 to construct the International Prototype Metre
The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of ''De revolutionibus orbium coelestium'' in 1543. Increasingly accurate measurements were required, and sc ...
and 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 ...
mass, kept by the International Bureau of Weights and Measures
The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation, through which its 59 member-states act together on measurement standards in four areas: chemistry, ...
near Paris
Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...
. The meter bar was replaced as the definition of the fundamental unit of length in 1960 by a line in the atomic spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a transition from a high energy state to a lower energy state. The photon energy o ...
of krypton
Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...
, but the kilogram prototype remained the international standard of mass until 20 May 2019, when the kilogram was redefined in terms of the Planck constant
The Planck constant, or Planck's constant, is a fundamental physical constant of foundational importance in quantum mechanics. The constant gives the relationship between the energy of a photon and its frequency, and by the mass-energy equivale ...
.
Historical
Iridium–osmium alloys were used in fountain pen
A fountain pen is a writing instrument which uses a metal nib to apply a water-based ink to paper. It is distinguished from earlier dip pens by using an internal reservoir to hold ink, eliminating the need to repeatedly dip the pen in an inkw ...
nib tips. The first major use of iridium was in 1834 in nibs mounted on gold. Since 1944, the famous Parker 51
The Parker 51 is a fountain pen first introduced in 1941. Parker marketed it as “The World’s Most Wanted Pen,” a slogan alluding to restrictions on production of consumer goods for civilian markets in the United States during World War II.
...
fountain pen was fitted with a nib tipped by a ruthenium and iridium alloy (with 3.8% iridium). The tip material in modern fountain pens is still conventionally called "iridium", although there is seldom any iridium in it; other metals such as ruthenium
Ruthenium is a chemical element with the Symbol (chemistry), 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 ...
, osmium, and 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 isolat ...
have taken its place.
An iridium–platinum alloy was used for the touch hole
A touch hole, also called a vent, is a small hole at the rear (breech) portion of the barrel of a muzzleloading gun or cannon. The hole provides external access of an ignition spark (fire), spark into the breech chamber of the barrel (where the ...
s or vent pieces of cannon
A cannon is a large- caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder ...
. According to a report of the Paris Exhibition of 1867, one of the pieces being exhibited by Johnson and Matthey
Johnson Matthey is a British Multinational corporation, multinational speciality chemicals and Sustainability, sustainable technologies company headquartered in London, England. It is listed on the London Stock Exchange and is a constituent of t ...
"has been used in a Whitworth gun for more than 3000 rounds, and scarcely shows signs of wear yet. Those who know the constant trouble and expense which are occasioned by the wearing of the vent-pieces of cannon when in active service, will appreciate this important adaptation".
The pigment ''iridium black'', which consists of very finely divided iridium, is used for painting porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises mainl ...
an intense black; it was said that "all other porcelain black colors appear grey by the side of it".
Precautions
Iridium in bulk metallic form is not biologically important or hazardous to health due to its lack of reactivity with tissues; there are only about 20 parts per trillion
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 ...
of iridium in human tissue. Like most metals, finely divided iridium powder can be hazardous to handle, as it is an irritant and may ignite in air. By 2015 very little is known about the toxicity of iridium compounds, primarily because it is used so rarely that few people come in contact with it and those who do only with very small amounts. However, soluble salts, such as the iridium halides, could be hazardous due to elements other than iridium or due to iridium itself. At the same time, most iridium compounds are insoluble, which makes absorption into the body difficult.
A radioisotope of iridium, , is dangerous, like other radioactive isotopes. The only reported injuries related to iridium concern accidental exposure to radiation from used in brachytherapy. High-energy gamma radiation from can increase the risk of cancer. External exposure can cause burns, radiation poisoning, and death. Ingestion of 192Ir can burn the linings of the stomach and the intestines. 192Ir, 192mIr, and 194mIr tend to deposit in the liver
The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...
, and can pose health hazards from both gamma
Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...
and beta
Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
radiation.
Notes
References
External links
Iridium
at ''The Periodic Table of Videos
''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...
'' (University of Nottingham)
Iridium in Encyclopædia Britannica
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Chemical elements
Transition metals
Precious metals
Noble metals
Impact event minerals
Meteorite minerals
Native element minerals
Chemical elements with face-centered cubic structure