Rust-resistant alloys, Galvanization, Cathodic protection, paint coating, Bluing, Inhibitors, Humidity control, etc.. None of these terms were available in this world a millennium ago, But Still Iron pillar of Delhi stand for 1600 year without rusting and Corrosion free still a Mystery.
The 23 feet Iron pillar of Delhi which weighs approximately 6.5 tones stands as Symbol of Excellence in metallurgy of ancient Indian. Iron pillar of Delhi is called as called “a testament to the skill of ancient Indian blacksmiths”.
It is believed that the iron pillar of Delhi was originally erected by Chandragupta II Vikramaditya (374-413 AD) of the Gupta dynasty in Udayagiri and Later King Iltutmish (1210-36 AD) of slave dynasty brought it to Delhi and erected it.
Metallurgists of IIT Kanpur later discovered that, a thin layer of “misawite”, a compound of iron, oxygen and hydrogen, is protecting the cast iron pillar of Delhi 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 millimetre thick. It is also believed that protective film was formed catalytically by the presence of high amounts of phosphorous in the iron.
But still iron pillar od Delhi remains as an unsolved mystery that exposes the advanced techniques of Indian craftsmanship in ancient India.