Iridium (Ir) - Properties, Applications

Topics Covered

Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties


Iridium is a chemical element with ‘Ir’ as its symbol. It belongs to group 9 of the periodic table and its atomic number is 77.

Iridium, palladium, platinum, ruthenium, rhodium, and osmium are a group of elements that are referred to as the platinum group metals (PGM).

Iridium is silvery white in color and is the most corrosion-resistant metal known. It can be obtained from platinum ores and as a by-product of mining nickel. It has a face centered cubic structure. This metal is very hard and brittle and hence quite difficult to machine and work. It remains unaffected by air, water and acids.

Chemical Properties

The chemical properties of iridium are provided in the table below.

Chemical Data
CAS number 7439-88-5
Thermal neutron cross section 440 barns/atom
Electrode potential 1.0 V
Ionic radius 0.680 Å
Electronegativity 2.2
X-ray absorption edge 0.16286 Å

Physical Properties

The following table discusses the physical properties of iridium.

Properties Metric Imperial
Density 22.65 g/cm3 0.8183 lb/in3
Melting point 2450 °C 4442°F
Boiling point 4527 °C 8181°F

Mechanical Properties

The mechanical properties of iridium are tabulated below.

Properties Metric Imperial
Tensile strength 2000 MPa 290000 psi
Poisson’s ratio 0.26 0.26
Modulus of elasticity 524 GPa 76000 ksi
Shear modulus 208 GPa 30200 ksi
Hardness, Brinell 565 565
Hardness, Vickers 650 650
Hardness, Rockwell A 80 80
Hardness, Rockwell C 56 56

Thermal Properties

The thermal properties of iridium are tabulated below.

Properties Metric Imperial
Thermal expansion co-efficient (@20-100°C/68-212°F) 6.80 µm/m°C 3.78 µin/in°F
Thermal conductivity 147 W/mK 1020 BTU in/hr.ft².°F


Iridium is mainly consumed by the automotive, electronic, and chemical industries.

The following are the other application areas of iridium:

  • In alloys
  • Pivot bearings
  • In tipping fountain pen nibs
  • for compass bearings
  • In scientific and other special equipment
  • Long-life aircraft engine parts are made of an iridium alloy

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