Hear mention of tin and your thoughts instantly turn to cans stuffed with limp vegetables. But while the metal has become ubiquitous thanks to its use in convenience food packaging, it actually serves all manner of exotic purposes — and it could just change the future of electronics.
Tin — or Sn to its buddies in the periodic table — has been a part of humanity’s arsenal for eons. Usually found within the mineral cassiterite, where it occurs as tin dioxide, it was first extracted some time in the Bronze Age, around 3000 BC. In fact, that entire period is named after an alloy in which tin is present: bronze, while primarily made up of copper, contains a few per cent of the stuff.
The general assumption is that the first tin usage was a happy fireside accident, where early man found himself with copper ore containing trace quantities of the stuff, and it soon became obvious that a little extra could increase bronze’s hardness, as well as decreasing its melting point, making it far easier to cast into rudimentary tools.
Tin took center stage a few centuries later in pewter. Made up of 85 — 99 per cent tin, with some copper, antimony, silver, lead or bismuth thrown into the mix, pewter was employed by everyone from the Egyptians to the Romans, and came into extensive use in Europe from the Middle Ages. Why so popular? Primarily because it was so easy to work with. Simple to shape and craft, it was used to make plates, bowls, tankards and all manner of other kitchenware — affectionately referred to as flatware — before ceramics really took hold.
But enough history. In the modern age, you probably know about two major uses of tin. First, alloyed with lead, it’s used as solder, which has held together millions of circuits over the years because it can melt at sufficiently low temperatures. The second usage is to stop things rusting. Because tin doesn’t readily oxidise — the process that makes steel and iron rust — it can be used to coat other metals to prevent corrosion. Hence the tin can’s moniker: usually made of steel, the food-carrying cylinders are actually coated with a little tin to keep them in tip-top shape. But there is way, way more to tin than that.
You may not know it, since it happened in a lab and not a grocery store shelf, but tin just happened to be one of first ever superconductors to be studied. Take crystals of it down to below 3.72 Kelvin and it starts superconducting, allowing electricity to pass through it with zero resistance. In fact, it was the material in which the Meissner effect — where superconductors expel magnetic field — was first observed. Research into using tin as a superconductor in its pure form has seen a resurgence recently — more on that later — but in the meantime it’s been the basis of many superconducting magnets: a 5-pound magnet made from niobium-tin, for instance, can produce the same strength of field as a conventional electromagnet weighing tons.
Elsewhere, tin is, weirdly, increasingly cropping up in plastic. Usually, PVC plastics degrade with heat, light and even just exposure to oxygen, becoming discolored and brittle. Both aesthetically and structurally, that’s bad news. But throw a little tin in the mix, and it bonds with chloride ions — which otherwise cause the plastic to degrade — to form new, inert compounds which stops things going bad.
That’s not the only place a sprinkle of the stuff can transform another material, either. The zirconium alloys used to clad nuclear fuel rods in reactors now include a few per cent of metal, which is included to improve the corrosion resistance of the wrapper. Essentially, you can thank it for keeping those rods safely sealed.
But tin isn’t confined to a role as supporting player; if current research is anything to go by, tin could be one of the most important materials of the electronic age.
Anyone who uses a smartphone knows that perhaps the biggest limiting factor in current technology is battery life. There’s no denying that li-on batteries have improved with time, but not at a rate that can keep up the the quantum leaps in performance that we’ve come to expect. Researchers at the Washington State University, though, have discovered that tin could help boost capacity of the li-on batteries that sit in our phones, laptops and cars.
Instead of using graphite at the anode — the electrode of a battery into which electric current flows — they have been experimenting with tin instead. By choosing different anode materials carefully, it’s possible to increase the density of lithium ions that a battery stores — which is what provides the potential charge of a battery, and let loose electrons during use as they move to the cathode. Turns out that coating an anode in 50 nanometer needles of tin instead of graphite triples the density of the ions on the anode. Now, those same scientists are just working out how to make tin electrodes cheaply in bulk, so we can expect way better batteries in the coming years.
Even more recently, a team of researchers has developed something called stanene: a single layer of tin atoms that could just be the world’s first material to conduct electricity with 100 per cent efficiency at the temperatures at which computers work. Scientists from the SLAC National Accelerator Laboratory and Stanford University have long been thinking about topological insulators, which should conduct electricity just through their outside edges or surfaces, but not through their interiors. Make those materials one atom thick, and theoretically they can conduct electricity with 100 per cent efficiency.
New calculations led the researchers to realise that a single layer of tin would be a topological insulator at and above room temperature. Not just that, they reckoned that adding some fluorine atoms the mix would extend its 100 per cent efficiency operating range to at least 100C. In practical terms, the implications of such a material would be amazing: computers could run with zero electrical loss; smartphone batteries could last way longer.
Amazingly, their theoretical modelling has confirmed the hunch: stanene really could deliver. So far, it remains bound to the lab, a prototype material that needs to undergo a hell of a lot of testing before we’re certain it’s the winner that the researchers claim it is. But if the team can overcome the manufacturing challenges — like ensuring only a single layer of tin is deposited and making sure it remains in tact when it’s used to manufacture components — then it might just be super conductor to beat them all. And there should be enough juice, thanks to tin in the batteries to take advantage of it, too.