Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Iridium

Iridium

Iridium is a chemical element with the symbol Ir and atomic number 77. It is a very dense, hard, brittle, silvery-white transition metal and is sometimes used as a contact material in reed switches due to its resistance to arc erosion. Reed Switches contacts coated with Iridium are durable and more expensive.


Iridium (Wikipedia)

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 of 22.56 g/cm3 (0.815 lb/cu in) as defined by experimental X-ray crystallography. It is one of the most corrosion-resistant metals, even at temperatures as high as 2,000 °C (3,630 °F). 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, 77Ir
Pieces of pure iridium
Iridium
Pronunciation/ɪˈrɪdiəm/ (i-RID-ee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Ir)
  • 192.217±0.002
  • 192.22±0.01 (abridged)
Iridium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Rh

Ir

Mt
osmiumiridiumplatinum
Atomic number (Z)77
Groupgroup 9
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d7 6s2
Electrons per shell2, 8, 18, 32, 15, 2
Physical properties
Phase at STPsolid
Melting point2719 K ​(2446 °C, ​4435 °F)
Boiling point4403 K ​(4130 °C, ​7466 °F)
Density (near r.t.)22.56 g/cm3
when liquid (at m.p.)19 g/cm3
Heat of fusion41.12 kJ/mol
Heat of vaporization564 kJ/mol
Molar heat capacity25.10 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2713 2957 3252 3614 4069 4659
Atomic properties
Oxidation states−3, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8, +9
ElectronegativityPauling scale: 2.20
Ionization energies
  • 1st: 880 kJ/mol
  • 2nd: 1600 kJ/mol
Atomic radiusempirical: 136 pm
Covalent radius141±6 pm
Color lines in a spectral range
Spectral lines of iridium
Other properties
Natural occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for iridium
Speed of sound thin rod4825 m/s (at 20 °C)
Thermal expansion6.4 µm/(m⋅K)
Thermal conductivity147 W/(m⋅K)
Electrical resistivity47.1 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic
Molar magnetic susceptibility+25.6 × 10−6 cm3/mol (298 K)
Young's modulus528 GPa
Shear modulus210 GPa
Bulk modulus320 GPa
Poisson ratio0.26
Mohs hardness6.5
Vickers hardness1760–2200 MPa
Brinell hardness1670 MPa
CAS Number7439-88-5
History
Discovery and first isolationSmithson Tennant (1803)
Isotopes of iridium
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
188Ir synth 1.73 d ε 188Os
189Ir synth 13.2 d ε 189Os
190Ir synth 11.8 d ε 190Os
191Ir 37.3% stable
192Ir synth 73.827 d β 192Pt
ε 192Os
192m2Ir synth 241 y IT 192Ir
193Ir 62.7% stable
193mIr synth 10.5 d IT 193Ir
194Ir synth 19.3 h β 194Pt
194m2Ir synth 171 d IT 194Ir
 Category: Iridium
| references

Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named it after the Greek goddess Iris, 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 estimated annual production and consumption of only 7.3 tonnes (16 thousand pounds) in 2018. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant.

The dominant uses of iridium are the metal itself and its alloys, as in high-performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. 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 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.


« Back to Glossary Index