Damascus sabres may get their famed pattern and strength from nanotubes in the steel:
Sabres from Damascus, now in Syria, date back as far as 900 AD. Strong and sharp, they are made from a type of steel called wootz.Their blades bear a banded pattern thought to have been created as the sword was annealed and forged. But the secret of the swords’ manufacture was lost in the eighteenth century.
Materials researcher Peter Paufler and his colleagues at Dresden University, Germany, have taken electron-microscope pictures of the swords and found that wootz has a microstructure of nano-metre-sized tubes, just like carbon nanotubes used in modern technologies for their lightweight strength.
The tubes were only revealed after a piece of sword was dissolved in hydrochloric acid to remove another microstructure in the swords: nanowires of the mineral cementite.
Wootz’s ingredients include iron ores from India that contain transition-metal impurities. It was thought that these impurities helped cementite wires to form, but it wasn’t clear how. Paufler thinks carbon nanotubes could be the missing piece of the puzzle.
At high temperatures, the impurities in the Indian ores could have catalysed the growth of nanotubes from carbon in the burning wood and leaves used to make the wootz, Paufler suggests. These tubes could then have filled with cementite to produce the wires in the patterned blades, he says.