Vidyarthi Vigyan Manthan: A national programme to ... - Vigyan Prasar

Experts at the Indian Institute of Technology, Kanpur resolved the mystery behind 1600-year-
old iron pillar in the year 2002. Metallurgists at IIT-Kanpur 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 1600 years, the film has grown just one-
twentieth of a millimetre thick. The protective layer was formed in the presence of high
amounts of phosphorus that acted as a catalyst. It was a unique iron-making process
practised by ancient ironsmiths in India who reduced iron 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 process, most
phosphorous content is carried away by the slag.
The pillar, weighing more than six tonnes, was erected by Chandragupta II Vikramaditya (375–
414 CE) (interpretation based on careful analysis of the archer-type Gupta gold coins) of the
Gupta dynasty that ruled northern India during 320–540 CE.
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