SPI-CHEM™ Osmium Tetroxide
Interesting facts about osmium metal
Osmium metal is found only in a limited number of locations in the world and if ever there
was a non-renewable resource that should be conserved for future generations and recycled,
osmium would have to be it. Osmium is found in the mineral iridosmine (Os, Ir) and in
platinum bearing river sands of the Urals, and North and South America. When found, it is
always present as an impurity for either platinum or some other precious metal bearing ore.
It is also found in nickel-bearing ores and while the concentration of the osmium metal is
extremely low, the very large volumes of nickel ore that are processed does result in yet
additional osmium metal.
Physically, the metal is a lustrous, bluish white, color and also, is extremely hard. And
it remains brittle even at high temperatures that begin to approach the melting point. It
is a member of the six element "platinum group", and among those elements, it has the highest
melting point yet the lowest vapor pressure.
Osmium metal is extremely difficult to fabricate, but the powder can be sintered in a hydrogen
atmosphere at a temperature of 2000°C. The solid metal is inert in air at room temperature,
but the powdered or "spongy" form of the metal slowly gives off
osmium tetroxide, which is a powerful oxidizing agent and has a strong smell.
Osmium tetroxide is highly toxic, and boils at 130°C (760 mm). Concentrations in air as
low as 10-7 g/m3 can cause lung
congestion, skin damage, or eye damage. The tetroxide is used as an outstanding electron dense
stain for electron microscopy. It has been used by forensic laboratories to detect fingerprints
and to stain fatty tissue for histology applications.
The measured densities of iridium and osmium seem to indicate that osmium is slightly more
dense than iridium, so osmium has generally been credited with being the heaviest known
element. Calculations of the density from the space lattice, which may be more reliable for
these elements than actual measurements, however, give a density of 22.65 for iridium compared
to 22.61 for osmium. At present, therefore, we know either iridium or osmium is the heaviest
element, but the data do not allow selection between the two.
Reference:
See Schenectady County Community College
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Sunday March 21, 2010
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