Iridium

Iridium is a rare, precious metal which is hard, brittle and has a low ductility, which makes it a difficult material to work. In appearance, it is a lustrous, silvery metal. It has an abundance in the earth’s crust of approximately 3x10^-6 ppm. As might be expected from its position in the periodic table, iridium is stable to air and water and is not attacked by any acids, including "aqua regia" (this acid is used to separate iridium from the other platinum group metals). However, fused NaOH will attack iridium. It is extremely corrosion resistant and is used as group metals). However, fused NaOH will attack iridium. It is extremely corrosion resistant and is used as an alloying agent with metals such as gold and osmium to produce alloys which are extremely hard and have good corrosion resistance. Iridium is also used in spark plugs, and its radioactive isotope, ¹⁹²Ir is a medium energy gamma emitter used for industrial radiography.

Symbol

Ir

Discovered

1803 in London by S. Tennant.

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Atomic number	77		Clip
Atomic / Molecular Weight	192.22	gmol-1	Clip
Density	22550	kgm-3	Clip
Crystal Structure	fcc		Clip
Lattice constant	384	fm	Clip
Melting Point	2720	K	Clip
Boiling Point	4803	K	Clip
Linear expansivity	0.0000064	K-1	Clip
Specific heat capacity	134	Jkg-1K-1	Clip
Thermal conductivity	147	Wm-1K-1	Clip

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See also: Osmiridium, Periodic Table, Platinum.