Researchers explain the science behind the extraordinary pillar that hasn't rusted for 1,600 years
It is common knowledge that iron is supposed to rust and fall apart over time after prolonged exposure to oxygen and water, which is why the iconic iron pillar near Delhi's Qutub Minar which hasn't rusted for 1,600 years, remains an object of intrigue. The fine work of old architecture is situated in the Mehrauli district of Delhi, but its ability to withstand damage for such a long time remains a secret.
There are various theories surrounding the origins and the creation of the pillar and Britannica mentions that "the six-ton pillar was made during the Gupta period, likely at Udayagiri in what is now the state of Madhya Pradesh." The pillar stands at 7.2 meters tall if the section of it that is buried beneath the surface is counted. The stone platform on which it sits was most likely added to the structure between 1871 and 1872. There are Sanskrit and Pali language inscriptions found on the pillar that state how the pillar was "created for a temple dedicated to Lord Vishnu following the order of a king named Chandra." But it is still not certain who theis king actually was.
Qutb Minar and the complex around it is owned by the Government of India and managed by the Archaeological Survey of India (ASI). Its surrounding area is managed by multiple stakeholders, including the ASI, the Delhi Development Authority, the Municipal Corporation of Delhi, and the Government of the National Capital Territory of Delhi. So far, UNESCO has been tasked with maintaining the Qutb Minar and its monuments complex. The area is also monitored and managed by the ASI Acts and Rules through an annual conservation and development plan, per the UNESCO World Heritage Convention.
Now the real question is, why has the Iron Pillar not rusted in thousands of years? "The most superior and most important chemical corrosion resistance agent found for the Iron Pillar of Delhi results from a protective layer that is evenly distributed throughout the entire length of the pillar of a crystalline form of iron hydrogen phosphate hydrate (FePO4H3PO4-4H2O). The high phosphorus composition found within the pillar protects it from the effects of the local Delhi climate," Brett Cohen from the Institute for Advanced GABA Studies wrote, as per ResearchGate. He also called it "a remarkable achievement which deserves to be considered one of mankind's greatest technological accomplishments."
"Powder metallurgists claim it is a living example of an object manufactured by the powder metallurgical route. Corrosion scientists are aware of the remarkable corrosion resistance of the pillar," Professor Ramamurthy Balasubramaniam from IIT Kanpur said, per the International Union of Pure and Applied Chemistry. He also mentioned that the iron was obtained by the direct reduction process rather than casting. "The ideas proposed in this regard are the relatively pure composition of the iron used, the presence of phosphorus, and absence of sulfur and manganese in the iron, its slag particles, and the formation of a protective passive film. The large mass of the pillar also plays a contributory role,” he added.
