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Material World
Element · Ir

Iridium

The most corrosion-resistant metal known, and the fingerprint of the asteroid that ended the Cretaceous.

Iridium resists corrosion better than any other metal — no acid attacks it, and it holds its structure above 2,000 °C. Spark plug electrodes and crucibles for growing sapphire and silicon crystals are made of it because nothing else survives the conditions.

It is also vanishingly rare in the Earth's crust and comparatively common in asteroids, most of the planet's original supply having sunk into the core. The worldwide iridium layer at the Cretaceous-Palaeogene boundary is the evidence that identified an impact as the cause of the extinction.

Uses

Iridium is used where conditions destroy everything else. It is the most corrosion-resistant metal known and melts above 2400 °C, so iridium crucibles grow the single crystals that lasers and semiconductors are cut from.

Iridium-tipped spark plug electrodes survive far longer than nickel ones. Iridium is a component of the electrodes used in chlorine production, and iridium-192 is a portable gamma source for industrial radiography — checking welds in pipelines without cutting them open.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is used as

  • Catalysis — application · spark plug electrodes and crucibles, where nothing else survives the conditions

is produced by

  • Electrorefining — process · from platinum-group concentrate, and among the rarest elements in the crust that is produced at all

is an alternative to

  • Platinum — element · in crucibles and electrodes, where iridium's higher melting point and resistance to attack are worth its greater scarcity

is a component of

  • Osmiridium — alloy · 20–80% · the other, in whatever ratio the deposit happened to deliver — it is a natural alloy, not a specification

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • PubChem
    US National Library of Medicine · Mixed — aggregated third-party content, rights retained by depositors
  • NIST — National Institute of Standards and Technology
    United States Department of Commerce · US Government work — public information, credit requested

Questions this page answers

Where it comes from, and what it becomes

Follow Iridium back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite
  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (reduced with carbon to metallic tin) → Cassiterite
  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (reduced with coke in a blast furnace) → Hematite
  • Iridium → is produced by (from platinum-group concentrate, and among the rarest elements in the crust that is produced at all) → Electrorefining → takes as input (as impure smelted anodes, around 99% copper, which is not pure enough for wire) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (the phosphate rock charged to the electric furnace, with coke to reduce it and silica to take up the calcium) → Apatite

These are the most distinct paths back. Iridium can be traced through others besides.

Downstream — what it becomes

  • Iridium → is used as (spark plug electrodes and crucibles, where nothing else survives the conditions) → Catalysis
  • Iridium → is a component of (the other, in whatever ratio the deposit happened to deliver — it is a natural alloy, not a specification) → Osmiridium