Difference between revisions of "Iridium" - New World Encyclopedia

Vapor pressure
77	osmium ← iridium → platinum
	periodic table
General
Name, Symbol, Number	iridium, Ir, 77
Chemical series	transition metals
Group, Period, Block	9, 6, d
Appearance	silvery white ;
Atomic mass	192.217(3) g/mol
Electron configuration	[Xe] 4f14 5d7 6s2
Electrons per shell	2, 8, 18, 32, 15, 2
Physical properties
Phase	solid
Density (near r.t.)	22.65 g/cm³
Liquid density at m.p.	19 g/cm³
Melting point	2719 K; (2446 °C, 4435 °F)
Boiling point	4701 K; (4428 °C, 8002 °F)
Heat of fusion	41.12 kJ/mol
Heat of vaporization	231.8 kJ/mol
Heat capacity	(25 °C) 25.10 J/(mol·K)
Atomic properties
Crystal structure	cubic face centered
Oxidation states	2, 3, 4, 6; (mildly basic oxide)
Electronegativity	2.20 (Pauling scale)
Ionization energies	1st: 880 kJ/mol
	2nd: 1600 kJ/mol
Atomic radius	135 pm
Atomic radius (calc.)	180 pm
Covalent radius	137 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(20 °C) 47.1 nΩ·m
Thermal conductivity	(300 K) 147 W/(m·K)
Thermal expansion	(25 °C) 6.4 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 4825 m/s
Speed of sound (thin rod)	(r.t.) 528 m/s
Shear modulus	210 GPa
Bulk modulus	320 GPa
Poisson ratio	0.26
Mohs hardness	6.5
Vickers hardness	1760 MPa
Brinell hardness	1670 MPa
CAS registry number	7439-88-5
Notable isotopes

Revision as of 04:36, 24 October 2006

This article is about the chemical element. For the satellite phone service, see Iridium (satellite).

Iridium (chemical symbol Ir, atomic number 77) is a dense, hard, brittle, silvery-white transition metal of the platinum family. It occurs in natural alloys with platinum or osmium and is notable for being the most corrosion-resistant element known. Researchers have associated it with a meteorite strike that is thought to have caused the demise of dinosaurs. It is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum alloys.

Occurrence

Iridium is rare on Earth, but relatively common in meteorites. The element is found uncombined in nature with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.

History

Iridium was discovered in 1803 by Smithson Tennant in London, England along with osmium in the dark-colored residue of dissolving crude platinum in aqua regia (a mixture of hydrochloric and nitric acid). The element was named after the Latin word for rainbow (iris; iridium means "of rainbows") because many of its salts are strongly colored.

An alloy of 90% platinum and 10% iridium was used in 1889 to construct the standard metre bar and kilogram mass, kept by the International Bureau of Weights and Measures near Paris. The metre bar was replaced as the definition of the fundamental unit of length in 1960 (see krypton), but the kilogram prototype is still the international standard of mass.

The KT event of 65 million years ago, marking the temporal border between the Cretaceous and Tertiary eras of geological time, was identified by a thin stratum of iridium-rich clay. A team led by Luis Alvarez (1980) proposed an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact near what is now Yucatán Peninsula. Their theory is widely accepted to explain the demise of the dinosaurs. Dewey M. McLean and others argue that the iridium may have been of volcanic origin instead. The Earth's core is rich in iridium, and Piton de la Fournaise on Réunion, for example, is still releasing iridium today.

Notable characteristics

A platinum group metal, iridium is white, resembling platinum, but with a slight yellowish cast. Due to its extreme hardness and brittle properties, iridium is difficult to machine, form, or work. Iridium is the most corrosion-resistant metal known. Iridium cannot be attacked by any acids or by aqua regia, but it can be attacked by molten salts, such as NaCl and NaCN.

It is used in high-strength alloys that can withstand high temperatures.

The measured density of this element is only slightly lower than that of osmium, which is often listed as the most dense element known. However, calculations of density from the space lattice may produce more reliable data for these elements than actual measurements and give a density of 22650 kg/m³ for iridium versus 22610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time.

Isotopes

There are two natural isotopes of iridium, and many radioisotopes, the most stable radioisotope being Ir-192 with a half-life of 73.83 days. Ir-192 beta decays into platinum-192, while most of the other radioisotopes decay into osmium.

Applications

The principal use of iridium is as a hardening agent in platinum alloys. Other uses:

For making crucibles and devices that require high temperatures.
Electrical contacts (notable example: Pt/Ir sparkplugs).
Osmium/iridium alloys are used for compass bearings.
Iridium is commonly used in complexes like Ir(mppy)₃ and other complexes in polymer LED technology to increase the efficiency from 25% to almost 100% due to triplet harvesting.
Used in high-dose-radiation therapy for the treatment of prostate and other forms of cancer

Iridium is used as a catalyst for carbonylation of methanol to produce acetic acid

At one time iridium, as an alloy with platinum, was used in bushing the vents of heavy ordnance and, in a finely powdered condition (iridium black), for painting porcelain black.

Iridium was used to tip some early twentieth century fountain pen nibs. The tip material in modern pens is still conventionally called "iridium," although there is seldom any iridium in it.

Precautions

Iridium metal is mostly non-toxic due to its relative unreactivity, but iridium compounds should be considered highly toxic.

References
ISBN links support NWE through referral fees

Los Alamos National Laboratory - Iridium

External links

Credits

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History of "Iridium"

Note: Some restrictions may apply to use of individual images which are separately licensed.

@@ Line 64: / Line 64: @@
 {{Elementbox_footer | color1=#ffc0c0 | color2=black }}
-'''Iridium''' ([[International Phonetic Alphabet|IPA]]: {{IPA|/ɪˈrɪdiəm/}}) is a [[chemical element]] in the [[periodic table]] that has the symbol '''Ir''' and [[atomic number]] 77. A dense, very hard, brittle, silvery-white [[transition metal]] of the [[platinum group|platinum family]], iridium is used in high strength [[alloy]]s that can withstand high temperatures and occurs in natural alloys with [[platinum]] or [[osmium]]. Iridium is notable for being the most corrosion resistant element known and for its association with the [[Cretaceous-Tertiary extinction event#Impact event and iridium|demise]] of the [[dinosaur]]s, in the form of a meteorite strike. It is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum.
+'''Iridium''' (chemical symbol '''Ir''', [[atomic number]]* 77) is a dense, hard, brittle, silvery-white [[transition metal]] of the [[platinum]] family. It occurs in natural alloys with [[platinum]] or [[osmium]] and is notable for being the most corrosion-resistant element known. Researchers have associated it with a meteorite strike that is thought to have caused the demise of [[dinosaur]]s. It is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum [[alloy]]s.
+== Occurrence ==
+Iridium is rare on [[Earth]], but relatively common in [[meteorite]]s. The element is found uncombined in nature with platinum and other platinum group metals in [[alluvium|alluvial]] deposits. Naturally occurring iridium alloys include [[osmiridium]] and [[iridiosmium]], both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from [[nickel]] mining and processing.
+== History ==
+Iridium was discovered in 1803 by [[Smithson Tennant]]* in London, England along with [[osmium]] in the dark-colored residue of dissolving crude [[platinum]] in [[aqua regia]] (a mixture of [[hydrochloric acid|hydrochloric]] and [[nitric acid]]). The element was named after the Latin word for [[rainbow]] (''iris''; ''iridium'' means "of rainbows") because many of its salts are strongly colored.
+An alloy of 90% platinum and 10% iridium was used in [[1889]] to construct the standard [[metre]] bar and [[kilogram]] mass, kept by the [[Bureau International des Poids et Mesures|International Bureau of Weights and Measures]] near [[Paris]]. The metre bar was replaced as the definition of the fundamental unit of length in [[1960]] (see [[krypton]]), but the kilogram prototype is still the international standard of mass.
+The [[Cretaceous-Tertiary extinction event|KT event]] of 65 million years ago, marking the temporal border between the [[Cretaceous]] and [[Tertiary]] eras of [[Geologic Timescale|geological time]], was identified by a thin [[stratum]] of iridium-rich clay. A team led by [[Luis Alvarez]] ([[1980]]) proposed an extraterrestrial origin for this iridium, attributing it to an [[asteroid]] or [[comet]] impact near what is now [[Yucatán Peninsula]]. Their theory is widely accepted to explain the demise of the [[dinosaur]]s. Dewey M. McLean and others argue that the iridium may have been of [[volcano|volcanic]] origin instead. The [[Earth]]'s core is rich in iridium, and [[Piton de la Fournaise]] on [[Réunion]], for example, is still releasing iridium today.
 == Notable characteristics ==
 A [[platinum group]] [[metal]], iridium is white, resembling [[platinum]], but with a slight yellowish cast. Due to its extreme hardness and brittle properties, iridium is difficult to machine, form, or work. Iridium is the most [[corrosion]]-resistant metal known. Iridium cannot be attacked by any [[acid]]s or by [[aqua regia]], but it can be attacked by molten [[salt]]s, such as [[sodium chloride|NaCl]] and [[sodium cyanide|NaCN]].
+It is used in high-strength [[alloy]]s that can withstand high temperatures.
 The measured [[density]] of this element is only slightly lower than that of [[osmium]], which is often listed as the most dense element known. However, calculations of density from the [[space lattice]] may produce more reliable data for these elements than actual measurements and give a density of 22650 [[kilogram per cubic metre|kg/m³]] for iridium versus 22610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time.
+=== Isotopes ===
+There are two natural [[isotope]]s of iridium, and many [[radioisotope]]s, the most stable radioisotope being Ir-192 with a [[half-life]] of 73.83 days. Ir-192 [[beta decay]]s into platinum-192, while most of the other radioisotopes decay into osmium.
 == Applications ==
 The principal use of iridium is as a hardening agent in platinum alloys. Other uses:
 *For making [[crucible]]s and devices that require high temperatures.
@@ Line 83: / Line 102: @@
 Iridium was used to tip some early twentieth century fountain pen nibs.  The tip material in modern pens is still conventionally called "iridium," although there is seldom any iridium in it.
-== History ==
-Iridium was discovered in [[1803]] by [[Smithson Tennant]] in London, England along with [[osmium]] in the dark-colored residue of dissolving crude [[platinum]] in [[aqua regia]] (a mixture of [[hydrochloric acid|hydrochloric]] and [[nitric acid]]). The element was named after the Latin word for [[rainbow]] (''iris''; ''iridium'' means "of rainbows") because many of its salts are strongly colored.
-An alloy of 90% platinum and 10% iridium was used in [[1889]] to construct the standard [[metre]] bar and [[kilogram]] mass, kept by the [[Bureau International des Poids et Mesures|International Bureau of Weights and Measures]] near [[Paris]]. The metre bar was replaced as the definition of the fundamental unit of length in [[1960]] (see [[krypton]]), but the kilogram prototype is still the international standard of mass.
-The [[Cretaceous-Tertiary extinction event|KT event]] of 65 million years ago, marking the temporal border between the [[Cretaceous]] and [[Tertiary]] eras of [[Geologic Timescale|geological time]], was identified by a thin [[stratum]] of iridium-rich clay. A team led by [[Luis Alvarez]] ([[1980]]) proposed an extraterrestrial origin for this iridium, attributing it to an [[asteroid]] or [[comet]] impact near what is now [[Yucatán Peninsula]]. Their theory is widely accepted to explain the demise of the [[dinosaur]]s. Dewey M. McLean and others argue that the iridium may have been of [[volcano|volcanic]] origin instead. The [[Earth]]'s core is rich in iridium, and [[Piton de la Fournaise]] on [[Réunion]], for example, is still releasing iridium today.
-== Occurrence ==
-Iridium is found uncombined in nature with platinum and other platinum group metals in [[alluvium|alluvial]] deposits. Naturally occurring iridium alloys include [[osmiridium]] and [[iridiosmium]], both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from [[nickel]] mining and processing.
-Iridium is rare on [[Earth]], but relatively common in [[meteorite]]s.  <!-- Why is iridium rare on Earth?! —>
-== Isotopes ==
-There are two natural [[isotope]]s of iridium, and many [[radioisotope]]s, the most stable radioisotope being Ir-192 with a [[half-life]] of 73.83 days. Ir-192 [[beta decay]]s into platinum-192, while most of the other radioisotopes decay into osmium.
 == Precautions ==
@@ Line 107: / Line 111: @@
 == External links ==
-{{Commons|Iridium}}
-{{wiktionary|iridium}}
 *[http://www.webelements.com/webelements/elements/text/Ir/index.html WebElements.com - Iridium]
 *[http://www.pniok.de/ir.htm Picture in the element collection from Pniok.de]