The legendary Damascene swords were strong, flexible and never broke. German research shows that in 1200 the Eastern blacksmiths were already using nanotubes to amplify their weapons without knowing it.
The crusaders traveled to Jerusalem for it:an unbreakable Saracen sword. The swords of the "heathens" proved to be much stronger and more flexible than their western counterparts. That the Damascene swords did not break on stone or hostile shields meant that they were raised to mythical proportions in Europe. Blacksmiths all over Europe tried to imitate the stuff, without success. Now, German research shows that nanotechnology was responsible for the steel's unique properties. The carbon contaminants in the iron were transformed into nanotubes during the forging process. Nanotechnology avant la lettre !
Wonder Ore
So unknowingly, the Eastern blacksmiths were already using nanotechnology. This has already been discovered before:the golden glow in stained glass windows also turned out to be an early application of nanoparticles. People at the time sought the explanation for the mythical steel a little closer to home:all real Damascene steel came from the same mine in India. The ore from that mine is called wootz.
All steel consists of an alloy of iron and carbon. The percentage of carbon is very important here:1-2% carbon provides a very strong material, but also makes it 'brittle'. Cast iron is an example of this:it is very strong but not very flexible, so it does not bend but breaks if the force on it is too great. Not so useful for swords, which normally contain less than 1% carbon. Wootz iron contains 1.5% carbon, so much too much. How did these swords become so flexible?
German researchers at the University of Dresden solved this paradox by dissolving a very small piece of a Damascene sword in strong acid and examining its composition. The carbon in wootz was found to be primarily iron carbide, a very strong yet brittle material. The iron also contained traces of rare metals such as vanadium, chromium, magnesium, cobalt and nickel. They then looked at the structures in the material under the electron microscope. It turned out to be ordered down to the nanoscale. Tiny nanotubes half a nanometer long protected a core of iron carbide. The combination of the flexible nanotubes with the strong iron carbide is probably the reason the swords were so strong.
Contaminations
The researchers can only guess how the nanotubes were formed. In any case, different from how we do it now, probably it happened during the forging. During that process, the steel was heated to extremes several times and then quickly cooled again. When the steel was hot and soft, the smith 'folded' the steel and hammered it out again. As a result, layers formed within the metal which made the steel harder. This method in itself was nothing special.
But the contaminants in the wootz were forced out of the iron in intermediate layers and probably took on a life of their own. The trace elements catalyzed the formation of the nanotubes, which in turn stimulated the formation of iron carbide nanowires. When the sword was finished, these layers remained visible in steel. The stripe pattern was even considered a quality mark.
These swords have been made in India since 1200. They were traded west through Damascus, which is why we call them that. But the other side of the world was also interested in super strong super sharp swords. And there too, legendary powers were attributed to them:the katanas of the Samurai also showed the characteristic drawing of the Damascene steel. Unfortunately, the mine became exhausted around 1800. So you can no longer have a Damascene kitchen knife made, but only admire them in the museum.
What do you think of the promising new applications of nanotechnology? Does nanotechnology bring a better world, or are the risks too great? Give your opinion in the NanoDiscussion from Kennislink!