Iridium and it
Iridium and its applications:


Iridium is a rare, hard, lustrous, brittle, very dense platinum-like metal. Chemically it is very unreactive. It is the most corrosion-resistant metal known and it resists attack by any acid. Iridium is attacked by molten salts such as sodium chloride (NaCl) and sodium cyanide (NaCn). Iridium is generally credited with being the second dense element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser.

Atomic Weight: 192.9

Density: 22.65 g/cm3 at 20 oC

Melting Point: 2447 oC

Boiling Point: 4500 oC

Coefficient of Linear Thermal Expansion: 6.8 µm/m . K at 20oC

Specific Heat: 0.130 kJ/kg

Thermal Conductivity: 147 W/m K at 0 to 100 oC

Electrical Resistivity: 47.1 nΩ m at 0 oC; 53 nΩ m at 20 oC

Temperature Coefficient: 0.00427 nΩ per oC at 0 to 100 oC

Thermal Electromotive Force: Pt 67 (reference junction at 0 oC):

                                                +3.626 mV at 400 oC

                                                +6.271 mV at 600 oC

                                                +12.741 mV at 1000 oC  

Tensile Properties of Iridium Annealed at 1500 oC:

Temperature Tensile Strength  0.2% Yield Strength  Reduction in Area  

oC MPa MPa %
24 623 234 6.8
500 530 234 12.7
750 450 142 51.0
1000 331 43.4 80.6  

Magnetic Susceptibility Mass: 0.19 x 10-8 mks at 18 oC

Reflectivity:    64% at λ = 0.45 um

                       70% at λ = 0.55 um

                       78% at λ = 0.75 um 

Emissivity: 0.30 at 0.65 micron for solid unoxidized metal.

General Corrosion Behavior:

 Iridium is the most corrosion-resistant element. It is not affected by common acids, including hot sulfuric acid. It is slightly attacked by sodium hypochlorite solutions but not by aqua regia at ordinary temperatures. However, at elevated temperatures and pressures, aqua regia does attack iridium, and it may be used under these conditions for dissolving iridium and its refractory alloys for analysis. Iridium is virtually insoluble in lead even at high temperatures, and use is often made of this fact in preliminary steps in chemical analysis.

Fabrication Characteristics:

 Iridium can be arc melted (inert-gas cover), electron beam melted, or consolidated by powder metallurgy techniques. It is hot worked using procedures similar to those used for tungsten. Final working is done at warm temperatures, which produce a fibrous structure. Iridium has limited malleability at room temperature.

Tensile Properties (of 0.5 mm wire):

              Tensile Strength:    Annealed at 1000 oC: 1100 to 1240 MPa

                                                              Hot Drawn: 2070 to 2480 MPa

              Elongation:                                Annealed: 20 to 22%

                                                                Hot Drawn: 13 to 18%


Annealed at 1000 o: 200 to 240 HV

                               As-Cast: 210 to 240 HV

                           Hot Drawn: 600 to 700 HV

Modulus of Elasticity:

    Tension: 517 GPa (Static); 527 GPa (Dynamic) 

     Compression: 210 GPa

     Poisson's Ratio: .26


The main use of iridium is as a hardening agent for platinum alloys. With osmium, it forms an alloy that is used for tipping pens, and compass bearings. Iridium is used in making crucibles and other equipment that is used at high temperatures. It is also used to make heavy-duty electrical contacts. Iridium was used in making the international standard kilogram, which is an alloy of 90% platinum and 10% iridium. Radioactive isotopes of iridium are used in radiation therapy for the treatment of cancer.



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