Osmium

Osmium is the densest substance known and the hardest of all platinum group metals (PGMs). It is ten times harder than platinum itself. Osmium also has a higher melting point than the other platinum group metals.

Osmium's extraordinary qualities allow for its use in a range of applications in which frictional wear must be avoided, including fountain pen nibs, styluses, and instrument pivots. It is often alloyed with other PGMs such as platinum and iridium. 

Its conductivity means it can be used as a more effective and durable alternative to gold as plating in electronic products.

Like the other PGMs it is an extremely efficient oxidation catalyst and contributes to the environment through use in fuel cells. This quality is also uniquely applied in forensic science for staining fingerprints and DNA (as osmium tetroxide).

Properties

Electrical conductivity* 0.109 106 cm-1 Ohm-1
Density* 22.61 g/cc
Hardness (Brinell value)*   3920 MN m-2
Melting point* 3050 ºC
Chemical element of Group VIII (Mendeleev)
Atomic number 76
Atomic weight 190.23
Thermal conductivity 87 watts/metre/°C
Tensile strength - (annealed condition kg/mm2)

History

The densest substance known and the hardest of all platinum group metals, osmium has become a central material in many everyday and innovative items.

Having discovered platinum and palladium, William Hyde Wollaston handed over the remaining residues of ore to his commercial partner Smithson Tennant, a fellow Cambridge graduate with whom he had forged a partnership in 1800.

In 1804, Tennant isolated osmium (and iridium) from the residues and, due to the distinctive chlorine-like odour of its oxide, named it after the Greek for smell, "osme".

Originally, it was osmium's density and hardness that led to its widespread use - in everyday objects such as fountain pen nibs, styluses, electrical contacts and other tools where frictional erosion is likely to occur. By 1906, it was used in the filaments for incandescent lighting and is from where the company Osram derives it name.

In metal form, osmium's brittleness and hardness made it extremely difficult to work with and it is usually produced as a powder. This powder emits osmium tetroxide which is used in the detection of fingerprints and as a forensic stain for DNA samples.

Osmium occurs in a natural alloy with iridium called iridosule, in the platinum-bearing river sands of the Urals and North and South America, and as a by-product of nickel mining in Ontario's copper-nickel sulfide region, Sudbury.