Standing at the center of the Quwwatul Mosque the Iron Pillar is one of Delhi’s most curious structures. Dating back to 4th century A.D., the pillar bears an inscription which states that it was erected as a flagstaff in honour of the Hindu god, Vishnu, and in the memory of the Gupta King Chandragupta II (375-413). How the pillar moved to its present location remains a mystery. The pillar also highlights ancient India’s achievements in metallurgy. The pillar is made of 98 per cent wrought iron and has stood 1,600 years without rusting or decomposing.
Well Established facts
It is 7.3 metres tall
one metre below the ground
diameter is 48 centimetres at the foot, tapering to 29 cm at the top
weighs approximately 6.5 tonnes
manufactured by forged welding
Mystery around the monument:
The present structure is believed to be originally located at some place in Madhya Pradesh, but its exact location is still not found out. It is believed to be shifted to its present location around 1000 years ago. But the most mysterious fact of the pillar is that it is almost corrosion free.
Reason for the corrosion free :
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 phosphorous in the iron—as much as one per cent against less than 0.05 per cent in today’s iron.
The high phosphorous 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 phosphorous is carried away by the slag.
The pillar—over seven metres high and weighing more than six tonnes—was erected by Kumara Gupta of Gupta dynasty that ruled northern India in AD 320-540.