How has the iron pillar in Delhi not rusted inspite of being made of 98% impure iron?

Question

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Answer 1

The Delhi Iron Pillar is a classical example of massive production of high class iron and is the biggest hand-forged block of iron from antiquity. It is a demonstration of the high degree of accomplishment in the art of iron making by ancient Indian iron and steel makers. It has been said that the Indians were the only non-European people who manufactured heavy forged pieces of iron and the pieces were of the size that the European smiths did not learn to make more than one thousand years later.

Many theories have been put forward from time to time to explain the rust-free state of the pillar. For example, the site of the pillar is away from industrial areas and the climate of Delhi is fairly dry. It is known that serious corrosion of iron does not take place if critical value of relative humidity is less than 80%. At Delhi, the relative humidity exceeds 80% for only about 20 days in a year and exceeds 70% for only about 65 days in a year. Therefore, although the total rainfall annually is about 15-30 inches the atmosphere in Delhi is not very conducive to rusting of iron.

Besides a dry environment, there appears to be no doubt that the protective scale on the pillar has played a major role in protecting this monument. There are two major theories of formation of this protective scale. It is quite possible that both the factors have played equally important roles in formation of this scale.

Protective Coating:

The heterogeneous nature of the structure of the monument reveals two important points, namely, no heat treatment has been applied and the metal of the pillar has never been in the molten state, probably the last stage in the construction of so large a piece of iron at that date would almost certainly have consisted of the hammer forging together of balls of iron and thereafter repeated re-heating and hammering process to create smooth surface. This must have taken a considerable time to complete. During this time an oxide film would have formed some of which could get hammered into the surface. Slag too would have oozed out and would have joined the scale. Owing to its high heat capacity and high ambient temperature the finished iron would have taken relatively long time to cool leading to a somewhat non-homogenous normalization, the quality of the oxide layer produced by this sequence of operation would in all probability greatly promote the preservation of the pillar in pure and dry climate.

According to the second 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 solid solution phase of mixtures of FeO and Fe2O3. About 10% of this hydrated oxide of iron, approaching Limonite (Fe2O3.3H2O) has also been reported. From the above reports it can be concluded that the scale was apparently formed under conditions of heating with significant extent of atmospheric oxidation occurring at the surface and penetrating along cracks running longitudinally in the scale.

There have also been suggestions that in the past pillar was ceremonially anointed with purified butter. Tghee obtained from the milk of cow would have had a marked effect. A thin coating of linseed oil or lanoline or wool grease is well known to give good protection to steel for some months. If applied regularly and reinforced b the dust and sand which settle on it, it gives a good protective coating to the material underneath. However, the practice of ceremonial anointing would probably have been discontinued during Muslim occupation of the area in 12th century AD.

The great mass of metal might act as a temperature stabilizer, thus reducing condensation of moisture on it. It has already been mentioned that corrosion proceeds during those time when the effective relative humidity on the surface of the metal exceeds the critical value (e.g. 80%). In Delhi, this cannot normally occur during the day or early in the night because the air is very dry, except of course when it rains. During the remainder of the night the temperature slowly drops and because of its high heat capacity, the pillar remains warm and less liable to corrode than the relative humidity of the air would indicate. Just before day break the pillar is for a very short time cooler than air as dry, daytime conditions are quickly reestablished.

So, in brief, it can be concluded that the corrosion resistance property of the Delhi Pillar is due to: (i) the purity of its iron; (ii) high phosphorus; (iii) low sulphur; (iv) absence of any other metal; (v) cinder coating formed on the surface; (vi) better forge welding; (vii) drier and uncontaminated atmospheric condition; and (viii) mass metal effect.

Answer 2

This pillar stands in the courtyard of the Jama Masjid but it has been there since long before the mosque's construction. A six - line Sanskrit inscription indicates that it was initially erected outside a Vishnu temple, and was raised in memory of the Gupta King Chandragupta Vikramaditya. This is a seven-metre-high pillar. What the inscription does not tell is how it was made. Scientists have never discovered how this iron, which is of such purity that it has not rusted after 2000 years, could be cast with the technology of the time. It’s a wonder.
The answer for such a mystery is as follows:
==============================================
The iron was protected by a layer of "misamite" which had been formed catalytically around the pillar due to a higher amount of phosphorous in the iron (about 1% compared to today's usual 0.5%). The ancient Indians did this by using charcoal at one point of iron extraction whereas today mainly limestone is used. Does this mean everything is now "hunky-dory" and we can relax and think of the ancients a "just" brilliant metallurgist? It may help to remind us that they figured this out a long time ago (and it worked), whereas we never developed this technique and have to make do with rusty iron.

Answer 3

First off the humidity in that region does not exceed 70%. This equates to a relatively dry climate. As anyone who has ever lived in Yuma Arizona will confirm, you can beat your jeep up all day over the rocks and it will never rust. The second and probably most important factor is the way the iron was forged. Apparently the iron that was produced in India is rich in phosphorous. The pressure it was exposed to during it’s hammering at the forge caused a heavy concentration of phosphorous to the surface. This caused the iron to be less susceptible to rusting. Additionally it is an erroneous statement to claim that the structure has no rust. The pillar does have some surface rust that is what Dr. R. Balasubramaniam of the Department of Materials and Metallurgical Engineering in Kanpur, Kanpur analyzed to determine why the pillar is so rust resistant.

Answer 4

There are two factors that explain why the Delhi iron pillar has withstood corrosion so well. First off the humidity in that region does not exceed 70%. This equates to a relatively dry climate. As anyone who has ever lived in Yuma Arizona will confirm, you can beat your jeep up all day over the rocks and it will never rust. The second and probably most important factor is the way the iron was forged. Apparently the iron that was produced in India is rich in phosphorous. The pressure it was exposed to during it’s hammering at the forge caused a heavy concentration of phosphorous to the surface. This caused the iron to be less susceptible to rusting. Additionally it is an erroneous statement to claim that the structure has no rust. The pillar does have some surface rust that is what Dr. R. Balasubramaniam of the Department of Materials and Metallurgical Engineering in Kanpur, Kanpur analyzed to determine why the pillar is so rust resistant.

Answer 5

As anyone who has ever lived in Yuma Arizona will confirm, you can beat your jeep up all day over the rocks and it will never rust. The second and probably most important factor is the way the iron was forged. Apparently the iron that was produced in India is rich in phosphorous. The pressure it was exposed to during it’s hammering at the forge caused a heavy concentration of phosphorous to the surface. This caused the iron to be less susceptible to rusting. Additionally it is an erroneous statement to claim that the structure has no rust. The pillar does have some surface rust that is what Dr. R. Balasubramaniam of the Department of Materials and Metallurgical Engineering in Kanpur, Kanpur analyzed to determine why the pillar is so rust resistant.

Answer 6

. It is a demonstration of the high degree of accomplishment in the art of iron making by ancient Indian iron and steel makers. It has been said that the Indians were the only non-European people who manufactured heavy forged pieces of iron and the pieces were of the size that the European smiths did not learn to make more than one thousand years later.

Many theories have been put forward from time to time to explain the rust-free state of the pillar. For example, the site of the pillar is away from industrial areas and the climate of Delhi is fairly dry. It is known that serious corrosion of iron does not take place if critical value of relative humidity is less than 80%. At Delhi, the relative humidity exceeds 80% for only about 20 days in a year and exceeds 70% for only about 65 days in a year. Therefore, although the total rainfall annually is about 15-30 inches the atmosphere in Delhi is not very conducive to rusting of iron.

Answer 7

This pillar stands in the courtyard of the Jama Masjid but it has been there since long before the mosque's construction. A six - line Sanskrit inscription indicates that it was initially erected outside a Vishnu temple, and was raised in memory of the Gupta King Chandragupta Vikramaditya. This is a seven-metre-high pillar. What the inscription does not tell is how it was made. Scientists have never discovered how this iron, which is of such purity that it has not rusted after 2000 years, could be cast with the technology of the time. It’s a wonder.
The answer for such a mystery is as follows:

Answer 8

Iron Pillar Of Delhi

Answer 9

Many theories have been put forward from time to time to explain the rust-free state of the pillar. For example, the site of the pillar is away from industrial areas and the climate of Delhi is fairly dry. It is known that serious corrosion of iron does not take place if critical value of relative humidity is less than 80%. At Delhi, the relative humidity exceeds 80% for only about 20 days in a year and exceeds 70% for only about 65 days in a year. Therefore, although the total rainfall annually is about 15-30 inches the atmosphere in Delhi is not very conducive to rusting of iron.

Answer 10

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How has the iron pillar in Delhi not rusted inspite of being made of 98% impure iron?
Yahoo! Answers India Team was on the look out for India’s unsolved, mysterious question. The response was overwhelming and we picked out 5 questions with the highest curiosity value.
We now bring you 'India’s Mysterious 5 Contest' where we feature these questions.
Answer today’s...

Answer 11

This Delhi Iron Pillar has not rusted because it is made of impure IRON !!
its pure iron that rusts. This Iron Pillar has a high level of phosphorous content making it impure. Phosphorous is resistive to corrosion and thus this iron pillar has not rusted.
but still the other thing to be noted is that a process callled "oxidation" ( which results in corrosion ) has taken place on the outer surface of the pillar thus preventing it from "furthur" rusting in the inside.
Lastly some other things have to be noted which is - for iron to rust it needs moisture and if there is no moisture it wont rust. So if the intensity of sunlight falling on the pilar is more the pillar wont rust.
so you see there are a lot of mysteries and predictions behind this iron pillar. more predictions will come in the near future. Thus the real reason behind the resistive properety of this iron pillar is known only by the creators...........