30 Sep The Iron Pillar of Delhi
The Vedic literature contains descriptions of advanced scientific techniques, sometimes even more sophisticated than those used in our modern technological world.
Modern metallurgists have not been able to produce iron of comparable quality to the 22 foot high Iron Pillar of Delhi, which is the largest hand forged block of iron from antiquity.
This pillar stands at mute testimony to the highly advanced scientific knowledge of metallurgy that was known in ancient India. Cast in approximately the 3rd century B.C., the six and a half ton pillar, over two millennia has resisted all rust and even a direct hit by the artillery of the invading army of Nadir Shah during his sacking of Delhi in 1737.
The pillar is 7.3 metres tall and is one metre below the ground with a diameter of 48 centimetres at the foot, tapering to 29 cm at the top. It has a weight of approximately 6.5 tonnes and it was manufactured by ‘forged welding’. But it raises more questions than it answers. What was the reason for its construction? What is the true meaning of long inscription in Brahmi characters engraved upon it? What were exact processes followed in making it?
According to a popular translation of the Brahmi script upon the Iron Pillar of Delhi, the pillar was made for a king (presumably of the Gupta period, given the era of its creation). It was also made to honor one of the most important Hindu gods – Vishnu. Which Gupta king the Iron Pillar was made for is not made clear by the inscription. However, it is widely believed that the king to which the inscription refers is Chandragupta Vikramaditya.
The purpose of the Iron Pillar of Delhi is one of its many mysteries. Some say it was a flagstaff made for the king mentioned in the inscription. Others say it was a sundial at its original home in Madhya Pradesh. Why it is no longer in Madhya Pradesh is yet another mystery. There is no evidence of who moved the pillar 1,000 years ago, how it was moved or even why it was moved. All we can say for certain about this aspect of the history of the pillar is that the mysterious Iron Pillar has been part of the Delhi landscape for a very long time.
How is it non-rusting?
Metallurgists at Kanpur IIT 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 the erection of the pillar and has been growing ever so slowly since then. This layer was formed due to the high amounts of phosphorous in iron. This is a result of the unique iron-making process practiced by ancient Indians, who reduced iron ore into steel in one step by mixing it with charcoal.
According to another theory, the protective oxide could have formed from atmospheric exposure. Examination of small pieces of scale obtained from the iron pillar reveals that it consists of approximately 80% of an oxide of iron having the properties of the solution phase of mixtures of FeO and Fe2O3. Hence it can be concluded that the scale was apparently formed under conditions of heating with a large amount of atmospheric oxidation taking place at the surface and penetrating along cracks.
Initially, the corrosion of the metal leads to the formation of a- and g-FeOOH. However, the presence of slag particles accelerates the corrosion of iron thereby enhancing the P concentration on the surface. This enhancement of P on the surface catalyzes the formation of amorphous d-FeOOH as a compact layer next to the surface and this results in atmospheric corrosion resistance of the Delhi iron pillar. With time, conversion of this d-FeOOH to a stable form of iron oxide, i.e., magnetite, is possible. The magnetite could be doped with ions. This would further enhance the corrosion resistance of the surface film on the surface. The FTIR and Mössbauer spectra indicate the presence of iron phosphates. The presence of these phosphates would provide further corrosion resistance to the passive film by lowering ionic diffusion in the oxide and also by blocking the pores in the oxide. The golden hue of the pillar, when viewed in certain orientations, is due to the presence of iron phosphates. We hope to compositionally map the rust on the entire exposed surface of the pillar in the near future.
What man can make, man can also destroy? In 1997, a fence was erected around the pillar as a response to the damage caused by visitors. According to a popular belief, it is considered good luck if one could stand with one’s back to the pillar and make one’s hands meet behind it. Consequently, the protective passive layer of rust on the surface of the iron would have been inadvertently removed by visitors over time, leading to significant wear and visible discoloration on the lower portion of the pillar. It would be a great shame indeed if such monuments that reflect mankind’s ingenuity fall victim not to the ravages of time, but to the actions of man himself.
By Prachodayat Team