Monday, April 2, 2012

Element of the Month: Osmium!

April's Element of the Month:


Atomic Mass: 190.23 amu
Melting Point: 3045 °C
Boiling Point: 5027 °C

Osmium, like Iridium, was first discovered in the weird sludge that always seemed to be left over if you did a really good job of smelting your Platinum. It is, needless to say, a silvery metal.

Now, when Iridium took its turn upon the stage in January, I said that there were only three elements -- Rhenium, Ruthenium, and Rhodium -- that were less common in the Earth's crust. Except, it says here that "Osmium is the least abundant stable element in the Earth's crust." This kind of contradiction seems sloppy, but I think there is genuine scientific uncertainty about it. At any event, there seem to be some fairly broad discrepancies among various sources as to just exactly how rare the rarer elements are. And when you think about it, that's fair. There are many, many different kinds of dirt, sediments, and rocks all three dimensionally intermixed within our lovely planet, and although we've got decent geological maps we don't have anything remotely like a cubic-meter-by-cubic-meter breakdown of the crust, let alone a molecular census. Is there more Rhenium or more Ruthenium on this planet? There are probably some chemists and geologists who can support an educated guess, but if someone ever professes to know with total certainty, you should laugh in his or her face! Because there could very, very conceivably be a vast undiscovered Rhenium-rich belt deep under the Urals, or Vanuatu, or anyplace else, that nobody knows about. And that would throw everybody's calculations off, wouldn't it.

Basically, Osmium is quite rare. It's also the densest natural element (twice as dense as lead!) and the fourth highest melting point. These facts are much easier to check up on, so there's not much diagreement about them.

The Centerfold!

Element of the Month is a humane and practical feature that likes to note the practical human applications of the molecules under consideration. In the case of Osmium, the practical human applications are few. It actually used to have more uses. They made early record needles from it, made it the filament of early light bulbs, and used as a catalyst in the production of ammonia. As the 20th Century got into full swing, however, it was found that saphires and diamonds gave you better sound, that Tungsten was a better and cheaper filament, and that you can use cheap iron compounds to catylize ammonia. That leaves Osmium out on the fringes of metalurgy, not used for much except alloying palladium to make it more durable (for instance in pacemakers, artificial blood valves).

Osmium might be a little more popular if it didn't react to oxygen at room temperature to form a highly toxic compound that can zip right through your skin, lungs, or eyeballs. This also keeps it from being a real popular collector's element. As it is, global yearly production of Osmium is apparently somewhat less than my own body weight.

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