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Osmium (Os), is a metal found in IUPAC group 8, with a relative atomic mass of 190.2. Just over 12 years ago the BBC1 announced that intelligence agents in the UK and USA had foiled a plot to make a ‘dirty bomb’ that would have involved the explosion of Osmium Oxide (OsO4).
What was slightly unusual about this new article was that it did acknowledge that Osmium Oxide was extremely expensive and only really available to research institutions. In other words, it would be very hard to get hold of, especially in large quantities as it was so expensive. That said, I believe some context is needed to the article as the Madrid bombings had only just happened and most of the world was on a state of heightened terror alert.
When I came across this report recently, it did make me think how little I knew about Osmium so I thought I would do a little digging and inform you of my findings!
Firstly, it’s name – it comes from the Greek word for ‘smell’, osme. as when it was first discovered (by Smithson Tennant in 1803 2) is gave off a strong odour (on account of the acid and alkali treatments that were used to obtain it). Tennant also discovered Irridium at the same time …. but that is another story for another time).
It is a blueish-white metal that is very hard and brittle. Alloys of it are used in fountain pen nibs or gramophone needles due to its strength. The metal itself does not easily oxidise and it is shiny, even at high temperatures.
Osmium also has one of the highest melting points of the elements (the 4th greatest)3 at over 3000 oC. Due to its position in the periodic table, it has a wide range of oxidation states, ranging from -2 to +8. Osmium forms seven isotopes, with one of these being radioactive (186 Os which emits alpha radiation) 3.
It is also rare and typically found in rocks at a concentration of 0.2 ppb (parts per billion) 4. The oxide OSO4 (correctly called Osmium Tetroxide) is very very toxic to us (presumably to most animals) and causes lung skin and eye damage at very low concentrations (around 10-7g m3).
Osmium was originally used by Robert Bosch as a catalyst (with Uranium!) in the Haber Process. Bosch actually bought up the worlds supply of Osmium at the time. Osmium was, hover, replaced by Iron which was less effective but much cheaper and plentiful.
So next time you use a fountain pen, please spend a moment thinking about the element in the pen nib that is allowing you to write!
1 http://news.bbc.co.uk/1/hi/uk/3603961.stm
2 http://www.rsc.org/periodic-table/element/76/osmium
