Tuesday, January 17, 2012

Element of the Month: Iridium!

January's Element of the Month:


Atomic Mass: 192.217  amu
Melting Point: 2466 °C
Boiling Point: 4428 °C

Iridium is among the Elements with the coolest names.  It is, however, very, very rare! Wikipedia will even tell you, in fact, that there are only three Elements (Rhenium, Ruthenium, and Rhodium) that are less common in the Earth's crust.   Naturally you won't fall for that old line, though: you are a savvy IAT(fL&TM5K) reader and know all about naturally-occurring Neptunium.  But the point is, there's not a whole lot of Iridium strewn about.  There's only about 1/40th as much of it as there is Gold, if that gives you a point of reference. There is only about a tenth as much of it as there is of Platinum.  Platinum is the Element that Iridium tends to hang out with most. In fact, Iridium was first discovered, along with Osmium, in the weird sludge that always seemed to be left over if you did a really good job of smelting your Platinum.

It's pretty impressive stuff, Iridium. It is very, very dense, and has one of the highest melting points of all the elements (2466°C, as compared with a relatively wussy 1668°C for big-shot Titanium). Machine parts made out of Iridium can remain functional at extremely high temperatures, and it is the most corrosion resistant of all the metals. You would think that engineers would be all over it, right? But there's a hitch! In addition to being so damn rare, it is also hella difficult to work with. Think about it: You want to make Iridium machine parts that would be resistant to the greatest extremes of heat. Great! So, you make your mould, then you melt down the Iridium, and -- d'oh! So that's why one of its uses is in cruciables used to melt other metals with high, but not quite as high, melting points. It is also used, as you might expect, in alloys for specialized things that you really, really want to hold up well to corrosion and wear, like jet engine parts and casings around plutonium fuel capsules and stuff like that.

The Centerfold!

An Iridium wedding band is unconventional, but practical if your spouse is
frequently subjected to corrosion or extremely high temperatures. 
Now, it's thought that there might be a lot more Iridium down in the Earth's interior than there up here on the crust. I was not able to check this out in person, but it seems reasonable enough. Iridium is a very heavy element -- #77! -- and some settling was bound to occur in shipping.  And if that doesn't get your futuristic mining fantasies going,  consider this: there is 500 times as much Iridium in your average meteorite than there is here on Crustal Earth.

There's actually a tie-in from this last little fact to the well-known hypothesis that a meteor impact caused the great age of extinctions after the dinosaurs. Wherever you go in the world, there's apparently this thin layer, right between your Cretacious and your Tertiary sedimentary rocks, that has way, way, way more Iridium than it ought to. This evidence is consistent with a scenario in which the Cretacious era was going along all fine and dandy, tra-la-la, and suddenly pow! there was a big, brief, sudden infusion of Iridium over the entire planet at the same time that the global environment changed so extensively that it would effect geology: the sedimentary rocks formed afterwards would be dramatically different. Wow! A nervous glance up at the sky would be appropriate at this point.

Like with a lot of the rare Elements, the price point for Iridium tends to flit all over the place. Without many sellers (the human community, in the average year, extracts from the planet a quantity of Iridium equal only to the mass of a blue whale's tongue) and without many buyers (see "hard to work with," above), the market is ripe for gaming by people in suits, and also for hoarding by users of Iridium who wish to protect themselves from gaming of the market by people in suits.


Voron X said...

I think Iridium might be my favorite element.

UnwiseOwl said...

Oh Michael. You are a card.

David Allan said...

In the mid XIXth century a French silversmith patented an iridium-nickel alloy for making cutlery (flatware) and small silverware...

BTW, who made the wedding band ?

Daniel He said...

Wow, I like this one.