THE mystery of an ancient iron pillar that has remained free of rust since the 5th century has finally been solved.
The 6-tonne pillar stands next to the famous Qutub Minaret in Delhi, and is legendary for showing hardly any signs of corrosion, despite being exposed to the elements for 1600 years. But now a researcher at the Indian Institute of Technology in Kanpur has worked out why.
After analysing part of the pillar’s surface, materials engineer Ramamurthy Balasubramaniam found it was made of a compound called iron hydrogen phosphate hydrate. The metal in the pillar contains an unusually high…
