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| The Iron pillar stands within the courtyard of Quwwat-ul-Islam Mosque | Wikipedia |
The iron pillar of Delhi, India is a 7 meter (22 feet) high pillar next to the Qutub Minar. The pillar was apparently erected at the time of Chandragupta II and is a curiosity because of the composition of the metals used in its construction.
The pillar—almost seven meters (22 feet) high and weighing more than six tons - was allegedly erected at the time of Chandragupta II Vikramaditya (375–413), though other authorities give dates as early as 912 BCE. It is the only remaining piece of a Hindu and Jain temple complex which stood there from the ruins of the temple. The temple is assumed to be destroyed by Qutb-ud-din Aybak who built the Qutub Minar and Quwwat-ul-Islam mosque around it. The pillar and ruins of the temple stand as still preserved and were not taken in consideration to be demolished by him.
The pillar is 98% wrought iron of pure quality, and is a testament to the high level of skill achieved by ancient Indian ironsmiths. It has attracted the attention of both archaeologists and metallurgists, as it has withstood corrosion for 1600 years, despite harsh weather.
The height of the pillar, from the top of its capital to the bottom of its base, is 7.21 m (23 ft 8 in), 1.12 m (3 ft 8 in) of which is below ground. Its bell pattern capital is 1.07 m (3 ft 6 in) in height, and its bulb-shaped base is 0.71 m (2 ft 4 in) high. The base rests on a grid of iron bars soldered with lead into the upper layer of the dressed stone pavement. The pillar's lower diameter is 420 mm (17 in), and its upper diameter 306 mm (12 in). It is estimated to weigh more than six tonnes (13,228 lb, over 6,000kg).
A fence was erected around the pillar in 1997 in response to damage caused by visitors. There is a popular tradition that it was considered good luck if one could stand with one's back to the pillar and make one's hands meet behind it. The practice led to significant wear and visible discoloration on the lower portion of the pillar.
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| Text and translation of the inscription in English at the site | Wikipedia |
The pillar bears a number of inscriptions and graffiti of different dates which have not been studied systematically despite the pillar's prominent location and easy access. The oldest inscription on the pillar is in Sanskrit which states that it was erected as a standard in honour of Lord Vishnu. It also praises the valor and qualities of a king referred to simply as Chandra, who has been identified with the Gupta King Chandragupta II Vikramaditya (375-413). The inscription reads (in the translation given in the tablets erected by Pandit Banke Rai in 1903):
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| Detail showing the inscription of King Chandragupta II |
(Line 3.)-He, the remnant of the great zeal of whose energy, which utterly destroyed (his) enemies, like (the remnant of the great glowing heat) of a burned-out fire in a great forest, even now leaves not the earth; though he, the king, as if wearied, has quit this earth, and has gone to the other world, moving in (bodily) from to the land (of paradise) won by (the merit of his) actions, (but) remaining on (this) earth by (the memory of his) fame;- (L. 5.)-By him, the king,-who attained sole supreme sovereignty in the world, acquired by his own arm and (enjoyed) for a very long time; (and) who, having the name of Chandra, carried a beauty of countenance like (the beauty of) the full-moon,-having in faith fixed his mind upon (the god) Vishnu, this lofty standard of the divine Vishnu was set up on the hill (called) Vishnupada.
In a report published in the journal Current Science, R. Balasubramaniam of the IIT Kanpur explains how the pillar's resistance to corrosion is due to a passive protective film at the iron-rust interface. The presence of second phase particles (slag and unreduced iron oxides) in the microstructure of the iron, that of high amounts of phosphorus in the metal, and the alternate wetting and drying existing under atmospheric conditions, are the three main factors in the three-stages formation of that protective passive film.
Lepidocrocite and goethite are the first amorphous iron oxyhydroxides that appear upon oxidation of iron. High corrosion rates are initially observed. Then an essential chemical reaction intervenes: slag and unreduced iron oxides (second phase particles) in the iron microstructure alter the polarization characteristics and enrich the metal–scale interface with P, thus indirectly promoting passivation of the iron(cessation of rusting activity). The second phase particles act as a cathode, and the metal itself serves as anode, for a mini-galvanic corrosion reaction during environment exposure. Part of the initial iron oxyhydroxides is also transformed into magnetite, which somewhat slows down the process of corrosion. But the ongoing reduction of lepidocrocite, and the diffusion of oxygen and complementary corrosion through the cracks and pores in the rust, still contribute to the corrosion mechanism from atmospheric conditions.
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| Iron pillar seen with Qutub minar in background Wikipedia |
The next main agent to intervene in protection from oxidation is phosphorus, enhanced at the metal–scale interface by the same chemical interaction previously described between the slags and the metal. The ancient Indian smiths did not add lime to their furnaces. The use of limestone as in modern blast furnaces yields pig iron that is later converted into steel; in the process most phosphorus is carried away by the slag. The absence of lime in the slag, and the deliberate use of specific quantities of wood with high phosphorus content (for example Cassia auriculata) during the smelting, induces a higher P content (> 0.1%, average 0.25%) than in modern iron produced in blast furnaces (usually less than 0.05 per cent). There is also more phosphorus as solid solution throughout the metal than in the slags (one analysis gives 0.10% in the slags for 18% in the iron itself, for a total P content of 0.28% in the metal). This high P content and particular repartition are essential catalysts in the formation of a passive protective film of “misawite” (d-FeOOH), an amorphous iron oxyhydroxide that forms a barrier by adhering next to the interface between metal and rust. Misawite, the initial corrosion-resistance agent, was thus named because of the pioneering studies of Misawa and co-workers on the effects of P and Cu and those of alternating atmospheric conditions, in rust formation.
The most critical corrosion-resistance agent is iron hydrogen phosphate hydrate (FePO4-H3PO4-4H2O) under its crystalline form and building up as a thin layer next to the interface between metal and rust. Rust initially contains iron oxide/oxyhydroxides in their amorphous forms. Due to the initial corrosion of metal, there is more P at the metal–scale interface than in the bulk of the metal. Alternate environmental wetting and drying cycles provide the moisture for phosphoric acid formation. Over time the amorphous phosphate is precipitated into its crystalline form (the latter being therefore an indicator of old age, as this precipitation is a rather slow happening). The crystalline phosphate eventually forms a continuous layer next to the metal, which results in an excellent corrosion resistance layer. In 1,600 years the film has grown just one-twentieth of a millimetre thick.
Balasubramaniam states that the pillar is "a living testimony to the skill of metallurgists of ancient India". An interview with Balasubramaniam and his work can be seen in the recent article by Veazy.
It was claimed in the 1920s that iron manufactured in Mirjati near Jamshedpur is similar to the iron of the Delhi pillar. Further work on Adivasi (tribal) iron by the National Metallurgical Laboratory in the 1960s did not verify this claim.
According to INTACH, further research has been proposed on the Iron Pillar to study the ancient metallurgy of India. The ASI is reported to have has concurred for the proposed studies that would make comparisons by testing other ancient iron objects like the pillar at Dhar, the iron beams at Konarak, and so forth. The present research using non– intrusive technique as proposed by Dr.Baldev Raj who is the Director of the Indira Gandhi Centre for Atomic Research and a member of the panel of architects and scientists.
Evidence of cannonball strike
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| Upper half of pillar, demonstrating horizontal fissuring thought to be caused by cannonball strike | Wikipedia |
While no contemporaneous records, inscriptions, or documents describing the event are known to exist, historians generally agree that Nadir Shah is likely to have ordered the pillar's destruction during his invasion of Delhi in 1739 CE, as he would have considered a Hindu temple monument undesirable within an Islamic mosque complex.
Alternatively, he may have sought to dislodge the decorative top portion of the pillar in search of hidden precious stones or other items of value.
No additional damage attributable to cannon fire has been found on the pillar, suggesting that no further shots were taken.
Historians have speculated that ricocheting fragments of the cannonball may have damaged the nearby Quwwat-ul-Islam mosque - which is known to have suffered damage to its southwestern portion during the same period - and the assault on the pillar might have been abandoned as a result.
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Source: wikipedia
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