Thursday, January 11, 2007

Nano-Secret of Damascus Steel

Brief History of Tool-Making:
Stone Age: [sticks & stones] not easily shaped and not durable (pre - 4000 BC).
Copper Age: easily shaped but not durable (4000 BC - 3000 BC).
Bronze Age: [copper + tin] easily shaped and more durable (3000 BC - 1000 BC).
Iron Age: [wrought iron, steel, and cast iron] more difficult to shape, very durable (1000 BC - present).

There is new evidence that since the discovery of Iron, ancient blacksmiths were making cast iron and steel. Carbon (charcoal) is freely soluble in molten iron. The difference between wrought iron, steel, and cast iron is simply the carbon content. Wrought iron, or pure iron has less than 0.5% carbon. Iron is more mallible than cast iron and steel but lacks tensile strength. Consequently, it is easily worked and shaped, but not very durable. Ancient steel could be made by simply mixing the right amounts of molten wrought iron and cast iron.

Cast iron has a carbon content of greater than 2%. Carbon creates a crystaline matrix within the metal, giving iron structure and greater tensile strength. Due to cast iron's high carbon content, it is very hard. Cast iron is so hard that is is almost impossible to work and shape. Therefore, molten cast iron is poured into molds and tools are cast in their final shape. Unfortunately, although carbon makes cast iron hard, it also makes it brittle. Consequently, like diamonds, cast iron can be cut or sheer if struck in just the right way. Consequently, cast iron tools are not durable either. Steel is the perfect balance of strength and durability. Steel generally has a carbon content between 0.5% and 1.5%. Metallurgists have been experimenting for 3000 years to make steels with higher ductial or tensile strength by varying the carbon content and adding other metals (alloying).

Damascus or "wootz" steel is the literal holy grail of metallury. It has a carbon content greater than 2% but unlike cast iron, it retains its steel-like flexibility. During the first century AD, India was the world leader in steel making. They developed a recipe for steel called "wootz" which was exported all over the ancient world. Wootz was made in a ceramic crucible in a type of blast furnace which produced steel ingots about the size of a small loaf of bread. These ingots (billets) were exported and worked or forged into tools, swords, and machine parts. Damascus was a major importer of wootz which was used to make the legendary Damascus saber.

The Europeans experienced the superior strength and duribility of Damascus steel during the crusades. Demascus sabers had a mysterious grey swirl pattern on their blades. Unfortunally, the recipe for making wootz was lost some time in the 18th century. There are many knifes, swords, and rifle barrels which claim to be made from Demascus steel. These "knock-off" products reproduce the swirl pattern in the steel by a process of fold-lamination, forge-layering, and pattern-welding the steel on itself. Although this technique recreates the intricate swirl pattern, it usually makes the steel much weaker. This "Damask"or "bulat" steel should not be confused with true Damascus wootz steel.

An article in Nov, 06 in Nature finally unvails the secret behind Damascus steel. Scientists disolved samples of true Damascus steel in concentrated hydrochloric and sulfuric acid leaving only the carbon residue behind. They then studied the carbon residue using electron microscopy to discover that it was made up of carbon nano-tubes. So, unknowingly, the Muslims superior sabers advantage during the crusades came down to advanced nanotechnology. Instead of the high carbon content in wootz steel making it more brittle, the complex nano-structure within the metal served to make wootz steel 3-5 times more flexible and stronger than conventional steel.

Hobbiest and scientists are on the cusp of rediscovering how to produce wootz steel for the first time in hundreds of years. Several hobbiest have seridipitously discovered by adding impurities (vanadium, manganese, rare-earth, ect) and alternating heating and partial cooling during the the forging process is required to allow the carbon within the iron matrix to self-assemble in to these complex structures. Other researchers have sucessfully created and visuallized the formation of c60 or buckmisterfullerene structures. This metallofullerene-based or "rhondite" steel also exhibits superior strength and durability over coventional steels.