Iron pillar of Delhi
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Wikidas
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{{otheruses|Ashoka Pillar (Disambigition)}}
[[Image:QtubIronPillar.JPG|thumb|The iron pillar of Delhi.]]
[[Image:India-Qutb-Iron.jpg|right|thumb|Detail of the inscription.]]
The '''iron pillar''' of [[Delhi]], [[India]], located in the [[Qutb complex]], is an important testimony of the [[history of metallurgy in the Indian subcontinent]], and of the [[history of ferrous metallurgy]] in general.
The pillar—almost seven meters or 22 feet high and weighing more than six tons—was allegedly erected at the times of [[Chandragupta II]] Vikramaditya (375–413), <ref>Balasubramaniam, R. 2002</ref> The dating of it as given by various authorities to be as early as 912 [[BCE]].<ref name="WI">{{cite book
|author=Arnold Silcock; Maxwell Ayrton
|title=Wrought iron and its decorative use: with 241 illustrations
|publisher=Dover
|location=Mineola, N.Y
|year=2003
|pages=p. 4
|isbn=0-486-42326-3
}}</ref> It is the remaining piece of a [[Hindu]] and [[Jain]] temple complex which stood there before being destroyed by [[Qutb-ud-din Aybak]] to build the [[Qutub Minar]] and [[Quwwat-ul-Islam mosque]]. Qutub built around it when he constructed the mosque.
The pillar is made up of 98% [[wrought iron]] of pure quality, and is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron. It has attracted the attention of [[archaeology|archaeologists]] and [[metallurgy|metallurgists]] as it has withstood [[corrosion]] for the last 1600 years, despite harsh weather.
== Description ==
The pillar, almost seven metres high and weighing more than six tonnes, was erected by Chandragupta II Vikramaditya (375 AD–414 AD), (interpretation based on careful analysis of archer type Gupta gold coins) of the [[Gupta dynasty]] that ruled northern India 320–540.<ref> Identity of Chandra and Vishnupadagiri of the Delhi Iron Pillar Inscription: Numismatic, Archaeological and Literary Evidence, R Balasubramaniam, Bulletin of Metals Museum, 32 (2000) 42–64.</ref> The pillar with the idol of [[Chakra]] at the top was originally located at a place called [[Vishnupadagiri]] (meaning “hill with footprint of Vishnu”).<ref>On the Astronomical Significance of the Delhi Iron Pillar, R Balasubramaniam and Meera I Dass, Current Science, volume 86 (2004) pp. 1134–1142. [http://www.iisc.ernet.in/~currsci/apr252004/1134.pdf] </ref> This has been identified as modern [[Udayagiri]], situated in the vicinity of [[Besnagar]], [[Vidisha]] and [[Sanchi]]. These towns are located about 50 kilometres east of [[Bhopal]], in central India. There are several aspects to the original site of the pillar at Udayagiri. Vishnupadagiri is located on the [[Tropic of Cancer]] and, therefore, was a centre of astronomical studies during the Gupta period. The Iron Pillar served as a [[sundial]] when it was originally at Vishnupadagiri. The early morning shadow of the Iron Pillar fell in the direction of the foot of [[Anantasayin Vishnu]] (in one of the panels at Udayagiri) only around the [[summer solstice]] (June 21). The Udayagiri site in general, and the Iron Pillar location in particular, provide evidence of such [[Indian astronomy|astronomical knowledge]] as existed in [[Gupta period|Gupta India]].
The pillar bears an inscription in [[Sanskrit]] which states that it was erected as a standard in honour of [[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):
{{quote|He, on whose arm fame was inscribed by the sword, when, in battle in the Vanga countries (Bângal), he kneaded (and turned) back with (his) breast of the enemies who, uniting together, came against (him);-he, by whom, having crossed in warfare the seven mouths of the (river) Sindhu, the Vâhlikas were conquered;-he, by the breezes of whose prowess the southern ocean is even still perfumed;-
(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.}}
Made up of 98% [[wrought iron]] of pure quality, it is 7.21m (23 feet 8 inches) high, with 93cm buried below the present floor level,<ref>Iron Pillar - Qutab Minar - Forts & Monuments - Delhi [http://www.exploredelhi.com/qutub-minar/iron-pillar.html]</ref> and has a diameter of 41cm (16 inches) at the bottom which tapers towards the upper end. The pillar was manufactured by [[forge welding]]. The temperatures required to form such a pillar by [[forge welding]] can only be achieved by the combustion of [[coal]]. The pillar is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron.
A fence was erected around the pillar in 1997 because visitors were damaging the pillar. There is a popular tradition that it was considered good luck if you could stand with your back to the pillar and make your hands meet behind it.
== Scientific analysis ==
[[Image:QutbIronInscription.jpg|thumb|right|Translation of the inscription in English.]]
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 [[Wrought iron#Coldshort wrought iron|'''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<ref>[http://home.iitk.ac.in/%7Ebala/journalpaper/journal/journalpaper_17.pdf ''On the Corrosion Resistance of the Delhi Iron Pillar''], R. Balasubramaniam, Corrosion Science, Volume 42 (2000) pp. 2103-2129.</ref>.
Lepidocrocite and goethite are the first amorphous iron oxyhydroxides that appear upon oxydation 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<ref>[http://www.iisc.ernet.in/currsci/jun102002/1357.pdf ''On the growth kinetics of the protective passive film of the Delhi Iron Pillar''], R. Balasubramaniam, Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur 208 016, India. Current Science, vol. 82, no. 11, 10 June 2002.</ref> (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.
The next main agent to intervene in protection from oxydation 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 furnace]]s yields [[pig iron]] that is later [[steelmaking|converted into steel]]; in the process most phosphorus is carried away by the slag<ref>[http://home.iitk.ac.in/~bala/journalpaper/journal/index.htm ''On the Origin of High Phosphorus Content in Ancient Indian Iron''], Vikas Kumar and R. Balasubramaniam, International Journal of Metals, Materials and Processes, vol. 14, pp. 1-14. 2002</ref>.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 thoughout 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<ref>''The mechanism of atmospheric rusting and the effect of Cu and P on the rust formation of low alloy steels'', T. Misawa, T. Kyuno, W. Suetaka, S. Shimodaira, Corrosion Science 11 (1971) 35-48.</ref>.
The most critical corrosion-resistance agent is '''iron hydrogen phosphate hydrate''' (FePO<sub>4</sub>-H<sub>3</sub>PO<sub>4</sub>-4H<sub>2</sub>O) 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<ref>[http://home.iitk.ac.in/%7Ebala/journalpaper/journal/journalpaper_17.pdf ''On the Corrosion Resistance of the Delhi Iron Pillar''], R. Balasubramaniam, Corrosion Science, Volume 42 (2000) pp. 2103-2129.] “Corrosion Science” is a publication specialized in corrosion science and engineering.</ref>. In 1,600 years the film has grown just one-twentieth of a millimetre thick<ref>[http://www.iisc.ernet.in/currsci/jun102002/1357.pdf ''On the growth kinetics of the protective passive film of the Delhi Iron Pillar''], R. Balasubramaniam, Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur 208 016, India. Current Science, vol. 82, no. 11, 10 June 2002.</ref>.
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<ref>[http://www.iupac.org/publications/ci/2005/2706/3_veazey.html 1600 Years Young, Materials Performance, July, 2005.]</ref>.
It was claimed in the 1920s that iron manufactured in Mirjati near [[Jamshedpur]] is similar to the iron of the Delhi pillar<ref>Andrew McWilliam 1920, cited in Chakrabarti 1992</ref>. Further work on Adivasi (tribal) iron by the National Metallurgical Laboratory in the 1960s did not verify this claim<ref>''Some Observations on Corrosion-Resistance of Ancient Delhi Iron Pillar and Present-time Adivasi Iron Made by Primitive Methods'', A.K. Lahiri, T. Banerjee and B.R. Nijhawan. NML Tech. J., 5 (1963) 46-5. Cited in [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWS-416C25N-6&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e6bad486cf7b00486fd8ee8fb2f99125 ''On the corrosion resistance of the Delhi iron pillar'', R. Balasubramaniam.]</ref>.
==See also==
*[[History of metallurgy in the Indian subcontinent]]
*[[Wootz steel]]
*[[Heliodorus pillar]]
*[[Wolfsegg Iron]]
*[[Nine Unknown Men]]
*[[Serpent Column]]
*[[Qutb complex]]
==References==
{{reflist}}
== Further reading ==
* ''King Chandra and the Mehrauli Pillar'', M.C. Joshi, S.K. Gupta and Shankar Goyal, Eds., Kusumanjali Publications, Meerut, 1989.
* ''The Rustless Wonder – A Study of the Iron Pillar at Delhi'', [[T.R. Anantharaman]], Vigyan Prakashan, New Delhi, 1996.
* ''Delhi Iron Pillar: New Insights''. R. Balasubramaniam, Delhi: Aryan Books International and Shimla: Indian Institute of Advanced Studies, 2002, Hardbound, ISBN-81-7305-223-9. [http://www.infinityfoundation.com/mandala/t_rv/t_rv_agraw_delhi_frameset.htm] [http://home.iitk.ac.in/~bala/journalpaper/journal/index.htm]
* ''The Delhi Iron Pillar : Its Art, Metallurgy and Inscriptions'', M.C. Joshi, S.K. Gupta and Shankar Goyal, Eds., Kusumanjali Publications, Meerut, 1996.
* ''The World Heritage Complex of the Qutub,'' R Balasubramaniam, Aryan Books International, New Delhi, 2005, Hardbound, ISBN 81-7305-293-X.
* ''Story of the Delhi Iron Pillar'', R Balasubramaniam, Foundation Books, New Delhi, 2005, Paperback, ISBN-81-7596-278-X.
* ''Delhi Iron Pillar'' (in two parts), R. Balasubramaniam, IIM Metal News Volume 7, No. 2, April 2004, pp. 11-17. and IIM Metal News Volume 7, No. 3, June 2004, pp. 5-13. [http://home.iitk.ac.in/%7Ebala/journalpaper/popart_6_7/metalnews_2004.pdf]
* ''New Insights on the 1600-Year Old Corrosion Resistant Delhi Iron Pillar'', R. Balasubramaniam, ''Indian Journal of History of Science'', 36 (2001) 1-49. [http://home.iitk.ac.in/%7Ebala/journalpaper/journal/journalpaper_20.pdf]
*'' The Early use of Iron In India''. Dilip K. Chakrabarti. 1992. New Delhi: The Oxford University Press.
==External links==
{{commons2|iron pillar}}
*[http://home.iitk.ac.in/%7Ebala/journalpaper/journal/index.htm#journal_pub Detailed list of Publications on Delhi Iron Pillar by Balasubramaniam, IIT Kanpur]
*[http://www.hindu.com/thehindu/seta/2002/09/12/stories/2002091200090200.htm Corrosion resistance of Delhi iron pillar]
*[http://www.ias.ac.in/currsci/jun252005/1948.pdf Nondestructive evaluation of the Delhi iron pillar] ''Current Science'', Indian Academy of Sciences, Vol. 88, No. 12, 25 June 2005 (PDF)
*[http://www.iitk.ac.in/infocell/Archive/dirnov1/iron_pillar.html The Delhi Iron Pillar]
*[http://timesofindia.indiatimes.com/articleshow/1058320.cms IIT team solves the pillar mystery, 21 Mar 2005, Times of India (About Nondestructive evaluation of the Delhi iron pillar)]
*[http://www.indiaenews.com/technology/20071013/75049.htm Indians develop new iron using ancient technology]
[[Category:Delhi]]
[[Category:Monumental columns in India]]
[[Category:Buildings and structures in Delhi]]
[[Category:Visitor attractions in Delhi]]
[[Category:Mehrauli]]
{{coor title dms|28|31|28.76|N|77|11|6.25|E|type:landmark_region:IN}}
[[cs:Železný pilíř]]
[[da:Jernpillen i Delhi]]
[[de:Eiserne Säule]]
[[fr:Pilier de fer de Delhi]]
[[it:Colonna di Ashoka]]
[[ja:デリーの鉄柱]]
[[ru:Железная колонна]]
[[sv:Järnpelaren i Delhi]]