Osmium

Osmium is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, blue-gray or blue-black transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with a density of 22.59 g/cm3.

Characteristics

Osmium has a blue-gray tint and is the densest stable element; it is approximately twice as dense as lead. The high density of osmium is a consequence of the lanthanide contraction. People not familiar with osmium often mistake it for platinum. Osmium is a hard but brittle metal that remains lustrous even at high temperatures.

Applications

Osmium is used in high-strength alloys. Pen nibs, electrical contacts, and other applications that require extreme durability and hardness have been made from osmium alloys. Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for microscope slides. As a pure element, osmium is toxic and can cause lung damage if inhaled.

History

Osmium was discovered in 1803 by Smithson Tennant and William Hyde Wollaston in London, England. The discovery of osmium was followed shortly by the discovery of other platinum group metals. Osmium was named after the Greek word for "smell", because of the strong odor of its oxide.

Occurrence and production

Osmium is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper and nickel, noble metals such as silver, gold and the platinum group metals, including osmium, settle to the bottom of the cell as anode mud, which forms the starting material for their extraction.

Precautions

Osmium tetroxide, OsO4, is highly toxic. Airborne low concentrations of osmium tetroxide vapor can cause lung congestion and skin or eye damage, and should therefore be used in a fume hood. Osmium powder can form the highly volatile and poisonous osmium tetroxide on exposure to air, and care should be taken to avoid contact with the skin and eyes.

See also

• Platinum group
• Transition metal
• Chemical element
• Smithson Tennant

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