Corrosion Resistance of the Iron Pillar of Delhi

The celebrated Iron Pillar of Delhi is widely regarded an architectural wonder for the way it has defied rust through the last 1600 years. The Iron Pillar has long been an enigma for metallurgists who have been unable to unravel the reason behind this stubborn resistance to corrosion. Made of 98% wrought iron, this tall, sleek pillar is a bona fide proof of the mastery Indian ironsmiths achieved in the extraction and processing of iron.

However, in 2002, a report published in the Current Science journal by experts of IIT, Kanpur offered a scientific explanation to the rust-resilient nature of the Iron Pillar at Delhi. The scientists, led by noted metallurgist R. Balasubramaniam, found that the pillar's anti-corrosion ability stems from the presence of a thin layer of "misawite", a compound of iron, oxygen and hydrogen. This protective layer took form within three years after erection of the pillar and has been growing slowly since.

The film was created by a catalytic reaction triggered off by the high phosphorous content in the iron-as much as one per cent against less than 0.05 per cent in today's iron. This substantial presence of phosphorous content results from the unique iron-making process practiced by ancient Indians, who reduced iron ore into steel in one step by mixing it with charcoal.