page_title: Iridium
section_title: Industrial and medical
hierarchical_section_title: Iridium / Applications / Industrial and medical
caption_attribution_description: English: Ir(mppy)3. see also [1]
context_page_description: 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, iridium is considered to be the second-densest metal with a density of 22.56 g/cm³ as defined by experimental X-ray crystallography. However, at room temperature and standard atmospheric pressure, iridium has been calculated to have a density of 22.65 g/cm³, 0.04 g/cm³ higher than osmium measured the same way. Still, the experimental X-ray crystallography value is considered to be the most accurate, as such iridium is considered to be the second densest element. It is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.
  Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium after the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts.
context_section_description: The high melting point, hardness and corrosion resistance of iridium and its alloys determine most of its applications. Iridium (or sometimes platinum alloys or osmium) and mostly iridium alloys have a low wear and are used, for example, for multi-pored spinnerets, through which a plastic polymer melt is extruded to form fibers, such as rayon. Osmium–iridium is used for compass bearings and for balances.
  Their resistance to arc erosion makes iridium alloys ideal for electrical contacts for spark plugs, and iridium-based spark plugs are particularly used in aviation.
  Pure 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 and zirconium (0.2% of each apparently works well).
  Corrosion and heat resistance makes iridium an important alloying agent. Certain long-life aircraft engine parts are made of an iridium alloy, and an iridium–titanium alloy is used for deep-water pipes because of its corrosion resistance. Iridium is also used as a hardening agent in platinum alloys. The Vickers hardness of pure platinum is 56 HV, whereas platinum with 50% of iridium can reach over 500 HV.
  Devices that must withstand extremely high temperatures are often made from iridium. For example, high-temperature crucibles made of iridium are used in the Czochralski process to produce oxide single-crystals (such as sapphires) for use in computer memory devices and in solid state lasers. The crystals, such as gadolinium gallium garnet and yttrium gallium garnet, are grown by melting pre-sintered charges of mixed oxides under oxidizing conditions at temperatures up to 2100 °C.
  Iridium compounds are used as catalysts in the Cativa process for carbonylation of methanol to produce acetic acid.
  The radioisotope iridium-192 is one of the two most important sources of energy for use in industrial γ-radiography for non-destructive testing of metals. Additionally, ¹⁹²Ir is used as a source of gamma radiation 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.
  In February 2019, medical scientists announced that iridium attached to albumin, creating a photosensitized molecule, can penetrate cancer cells and, after being irradiated with light (a process called photodynamic therapy), destroy the cancer cells.
  Iridium is a good catalyst for the decomposition of hydrazine (into hot nitrogen and ammonia), and this is used in practice in low-thrust rocket engines; there are more details in the monopropellant rocket article.
caption: Molecular structure of Ir(mppy)
  3
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