Muslim Metallurgists Way Ahead Now We Know Why

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Carbon nanotubes
are no longer the proud boast of 21st century materials scientists.
It appears their discovery was unwittingly pre-empted by mediaeval
Muslim sword-smiths whose tough Damascus blades taught the Crusaders
the true meaning of cold steel when they fought over the Holy Land.

Peter Paufler
and colleagues at Dresden’s Technical University discovered carbon
nanotubes in the microstructure of a 17th century Damascus sabre.
Intriguingly, the nanotubes could have encapsulated iron-carbide
nanowires that might give clues to the mechanical strength and sharpness
of these swords.

To Europeans,
Damascus steel blades seemed magical. Not only could they cut a
piece of silk in half as it fell to the floor, they could cleave
rocks and their own swords without losing sharpness. The problem
facing sword smiths was how to produce steel that was both hard
and malleable. Too much carbon and the steel is hard and brittle;
too little and it is too soft and malleable to hold an edge when
sharpened. Damascus steel blades were forged out of small pure cakes
of steel containing around 1.6-1.7 per cent carbon, called wootz.
Produced in India, wootz cakes were shipped to Damascus where expert
sword smiths fashioned them into blades.

Steel that
contains this amount of carbon forms plates of cementite (Fe3C)
which, on its own, makes the steel brittle. However, during the
forging process at around 800oC, small amounts of ‘impurities’ were
added containing many first-row transition elements (such as V,
Cr, Mn, Co, and Ni), tungsten, and some rare-earths. which together
had the effect of forming the cementite into bands. This gave the
blades great strength, malleability, and a distinctive wavy-band
pattern known as a damask. The skill had been lost by the 18th century,
when supplies of these ores and impurities ran out.

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30, 2009

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