Iron pillar
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The iron pillar of Delhi, the capital city of India, is one of the world's foremost metallurgical curiousities, standing in the famous Qutb complex.
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History
Iron-pillar.jpg
The pillar—almost seven metres high and weighing more than six tonnes—was erected by Kumara Gupta of the Gupta dynasty that ruled northern India in AD 320-540.
Built in the Mauryan dynasty around 6th century, it is the only piece of the Hindu temple remaining, which stood there before being destroyed by Qutb-ud-din Aybak to build Qutub Minar and Quwwat-ul-Islam mosque. Qutub built around it when he constructed the mosque.
The pillar is made up of 98% wrought iron of impure quality, and is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron. It has attracted the attention of archaeologists and metallurgists as it has withstood corrosion for the last 1600 years, despite harsh weather.
Scientific analysis
Metallurgists at Kanpur IIT have discovered that a thin layer of "misawite", a compound of iron, oxygen and hydrogen, has protected the cast iron pillar from rust.
The protective film took form within three years after erection of the pillar and has been growing ever so slowly since then. After 1,600 years, the film has grown just one-twentieth of a millimeter thick, according to R. Balasubramaniam of the IIT.
In a report published in the journal Current Science, Balasubramanian says the protective film was formed catalytically by the presence of high amounts of phosphorus in the iron— this phosphorus is as much as one per cent against less than 0.05 per cent in today's iron.
The high phosphorus content is a result of the unique iron-making process practiced by ancient Indians, who reduced iron ore into steel in one step by mixing it with charcoal.
Modern blast furnaces, on the other hand, use limestone in place of charcoal yielding molten slag and pig iron that is later converted into steel. In the modern process most phosphorus is carried away by the slag.
Stating that the pillar is "a living testimony to the skill of metallurgists of ancient India", Balasubramaniam said the "kinetic scheme" that his group developed for predicting growth of the protective film may be useful for modeling long-term corrosion behaviour of containers for nuclear storage applications.
See also
External link
- Corrosion resistance of Delhi iron pillar (http://www.hindu.com/thehindu/seta/2002/09/12/stories/2002091200090200.htm)fr:Pilier de fer de Delhi