Feb 11 2003
Background
Osmium (Os) was discovered in 1803 by Smithson Tennant in London, England.
Pure Osmium is silver in colour and is the densest of all metals. It has a pungent smell, due to the formation of osmium tetroxide
Abundance and Occurrence
Osmium is a member of the platinum group of metals and is commonly found in conjunction with these elements (abundancy is 1 x 10-4 ppm in the earth’s crust).
Extraction
The mixed metals can be extracted from the ore with aqua regia, followed by treatment of the soluble and insoluble portions in various ways. Osmium is found in both portions and is removed as the volatile tetroxide, which can then be reduced.
Applications
Applications for Osmium include its use as an alloying constituent with other group metals, the resultant alloys being extremely hard (e.g. osmiridium, a naturally occurring alloy of osmium and iridium which is extremely hard and is used for the tips of pen nibs).
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Osmium is an extremely hard material and can be used for the tips of pens. Image Credit: ShutterStock/tantawat
Osmium can also be used as a powerful catalyst in gas reactions.
Key Properties
The key properties of Osmium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
76 |
| Atomic radius - Goldschmidt ( nm ) |
0.135 |
| Atomic weight ( amu ) |
190.2 |
| Crystal structure |
Hexagonal close packed |
| Electronic structure |
Xe 4f14 5d6 6s2 |
| Photo-electric work function ( eV ) |
4.8 |
| Thermal neutron absorption cross-section ( Barns ) |
15.3 |
| Valences shown |
0, 1, 2, 3, 4, 5, 6, 7, 8 |
| Ionisation Potential |
No. |
eV |
| |
1 |
8.7 |
| |
2 |
16 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
184 |
0.02 |
| |
186 |
1.58 |
| |
187 |
1.6 |
| |
188 |
13.3 |
| |
189 |
16.1 |
| |
190 |
26.4 |
| |
192 |
41.0 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
8.8 |
| Temperature coefficient @ 0-100 °C ( K-1 ) |
0.0041 |
| Superconductivity critical temperature ( K ) |
0.66 |
| Mechanical Properties |
| Material condition |
Soft |
Hard |
Polycrystalline |
| Bulk modulus ( GPa ) |
|
|
373 |
| Hardness - Vickers |
300-350 |
670-1000 |
|
| Poisson’s ratio |
|
|
0.25 |
| Tensile modulus ( GPa ) |
|
|
559 |
| Physical Properties |
| Boiling point ( °C ) |
5027 |
| Density @ 20 °C ( g.cm-3 ) |
22.5 |
| Melting point ( °C ) |
3045 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
4.57 |
| Latent heat of evaporation ( J.g-1 ) |
3305 |
| Latent heat of fusion ( J.g-1 ) |
154 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
131 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
87.6 |
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