Monday, April 8, 2019

Element of the Month: Tin!

April's Element of the Month:


Atomic Mass: 118.710 amu
Melting Point: 231.93 °C
Boiling Point: 2602 °C

You have to love the prosaic elements, the ones that don't have names like Neodymium or Darmstadtium or Protactinium but, like, "Iron" or "Sulfur." Or "Tin." Tin is a great name, the shortest on the whole damn table. And it is abbreviated "Sn." Wait, what? Oh, apparently the Latin name is stannum, and there's a bit of a divide between Germanic forms (German Zinn, Swedish Tenn) and Romantic forms (Portuguese Estanho, Italian Stagno). That the kind of semantic trouble you run into with substances that were discovered back before the naming committee of the International Union of Pure and Applied Chemistry (IUPAC) arrived on the scene to keep things neat and tidy.

How long ago did people start messing about with Tin? To answer that, we need to go all the way back to the Bronze Age. After all, Bronze, which was the hot new tech about 5000 years ago, is basically Copper alloyed with Tin, right?  Since Bronze is much harder and more durable than unalloyed Copper, it could be used to make tools, weapons, and decorative obects that were absolutely state of the art. Since Copper ore and Tin ore are seldom found together, mind you, it took not only metallurgical sophistication but also control of a considerable supply chain in order to produce Bronze. In order to create the tools that would allow you to operate at a large scale, you had to operate at a large scale. For humanity, in other words, the Bronze Revolution was more or less the first day of the rest of our lives.

Now, a side note on Bronze: it's actually a pretty vague word, referring not only to Copper with Tin but also potentially with Aluminum, Manganese, Nickel, Zinc, Phosphorus, or what have you. "Wait," you say, "you said Zinc!  Isn't Copper alloyed with Zinc Brass?" Yes. Yes, it is. But Brass can also include Aluminum, Manganese, Phosphorus, and, um, Tin. Where are the IUPAC lads when you really need them? Actually, before Tin became what we shouldn't call the "Gold standard" of Bronze, the very earliest Bronzes alloyed Copper with Arsenic. This actually results in a lovely silvery product, but is rather tough on the people doing the mining and smelting, often causing health problems such as agonizing death. Also, remember how the Greek god of the forge, Hephaestus, was lame? There's a theory out there that lots of smiths in the early Bronze Age were lame, from the neurological problems caused by chronic exposure to Arsenic fumes.

The Centerfold!

Alpha-state Tin on the left, beta-state Tin on the right.  This is a still
from a nifty YouTube video that will convince you, if the next paragraph
doesn't, that you shouldn't keep your Tin ingots in the freezer.

But this isn't about Arsenic.  This is about Tin, which has two commonly occurring (and several more obscure) allotropes.  An allotrope is when an Element can take more than one form in a given physical state (ie. gas, liquid, solid) depending on its environment and mood.  This is generally a matter of how the molecules situate themselves geometrically relative to each other.  In the case of Tin, there's the silvery, metallic "beta" state we all know and love, but also a brittle grey "alpha" state which, for human uses, is often pretty problematic. The transformation, which can get started by cold conditions or exposure to Germanium, is called "Tin pest" or sometimes "Tin blight," "Tin disease," or "Tin leprosy," names that give you a feel for how popular this chemical phenomenon is among Tin users. Once the process gets rolling, it's "autocatylizing" -- the first areas of alpha-state Tin will actively recruit beta-state Tin to the dark side -- and, since alpha-state Tin takes up a lot more volume molecule to molecule, a manufactured item going through the transition will literally crumble to dust.

Human uses of Tin (outside of Bronze and other alloys) include its use in tin cans or "tins," which are generally made out of Iron, steel, or Aluminum. But they are often coated with Tin! A tin coating tends to protect other metals from decay, and to not react with food to create poisons the way a lot of things would. However, if you've been reading carefully you can probably work out why it is not a great idea to store your canned goods at sub-freezing temperatures. Well, there are actually a number of important reasons not to do that actually.

Tin has often been alloyed with Lead in electrical soldering. Lead is super malleable, and Tin conducts electricity well. With increased concern about Lead's toxicity, though, some electronics manufacturers have tried going the pure-Tin route. That works OK... unless the gadget gets too cold. But then, if the Tin pest sets in, those electrical connections turn to powder. If the gadget still has working parts, reheating it enough that the alpha-Tin converts back to beta-Tin can cause further damage, since the dust has likely drifted in the meantime and so you are creating new random electrical connections, and probably short circuits, wherever it ended up. So, this is something that they're trying to avoid in your higher-end gear.

I didn't think I'd have much to say about Tin, but I got kind of into it. Thanks for reading.

This cheerful guy is in the Mexican "Hojalata" tradition of painted tin.  The Spanish
word for Tin as an Element is
estaƱo, but as a sheet metal, it's Hojalata.


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