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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%
Hardness:
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
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