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Lead stronger than steel? Yeah, it can be achieved with lasers!

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Posted November 19, 2019

Lead is a widely used soft metal with an atomic number 82. It is easily malleable, but rather dense – one cubic centimetre of lead weighs 11.34 grams. It is so soft that it cannot really be used in any sort of structural construction areas. However, scientists at the Lawrence Livermore National Laboratory thought of a way to make it stronger than steel.

Lead is soft and easily malleable, unless put under extreme pressure. Image credit: Alchemist-hp via Wikimedia

If you ever handled one of those bbs or a lead fishing weight you know how soft this metal is. In fact, you can easily scratch it with your fingernails, which you can never do to any harder metal. This, of course, limits the potential applications of lead, but it has many redeeming features and no one really paid attention to its structural capabilities. At least until now, when scientists at the Lawrence Livermore National Laboratory managed to condense lead increasing its strength by 250 times.

Well, ok, when you compare this laser-condensed lead to steel you only get a 10-fold increase in strength. And by “strength” we mean resistance to deformation when some kind of a stress is applied. Scientists have managed to achieve that by using a laser, which allowed reaching about 400 gigapascals of pressure within the sample. This is unbelievably huge pressure – scientists are comparing it to the core of the Earth, which is exaggeration, of course, but not as big as you think. And this kind of an immense pressure did change the properties of the lead, as we said. But why?

You see, properties of certain metal parts heavily depend on the structure of the piece. In short, each metal piece is made of crystals entangled with one another. When these crystals have weak elastic bond and can slide in relation to one another, metal is pliable. And when these bonds between crystals are very hard, the metal is hard and brittle. Changes to this crystalline structure can be introduced in many ways. For example, copper work-hardens. This means that if you bend it many times or beat on it with a hammer, it will rearrange its crystals making it harder and more brittle. Gold acts in a very similar way as well, while steal can be hardened by heating it and then shocking it by putting it into an ice-cold water.

So laser creates such an immense pressure that crystalline structure within that piece of lead had changed making it very hard. But does that mean lead can be used in construction now? Well, no, and not just because it is toxic.

Laser-condensed lead may be hard, but it is very expensive. Also, we are not running short on steel – it is the most recycled material in the world. More than anything this study shows what kind of weird properties can be achieved through pressure. Also, it shows that pressure can be created and concentrated using laser, which is also rather interesting.

 

Source: Extreme Hardening of Pb at High Pressure and Strain Rate

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