Posted on 03/13/2005 1:55:06 PM PST by blam
Mystery of Delhi's Iron Pillar unraveled
Press Trust Of India
Thursday, July 18, 2002
New Delhi, July 18: Experts at the Indian Instituteof Technology have resolved the mystery behind the 1,600-year-old iron pillar in Delhi, which has never corroded despite the capital's harsh weather.
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 erection of the pillar and has been growing ever so slowly since then. After 1,600 years, the film has grown just one-twentieth of a millimeter thick, according to R. Balasubramaniam of the IIT.
In a report published in the journal Current Science Balasubramanian says, the protective film was formed catalytically by the presence of high amounts of phosphorous in the iron—as much as one per cent against less than 0.05 per cent in today's iron.
The high phosphorous content 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.
Modern blast furnaces, on the other hand, use limestone in place of charcoal yielding molten slag and pig iron that is later converted into steel. In the modern process most phosphorous is carried away by the slag.
The pillar—over seven metres high and weighing more than six tonnes—was erected by Kumara Gupta of Gupta dynasty that ruled northern India in AD 320-540.
Stating that the pillar is "a living testimony to the skill of metallurgists of ancient India", Balasubramaniam said the "kinetic scheme" that his group developed for predicting growth of the protective film may be useful for modeling long-term corrosion behaviour of containers for nuclear storage applications.
Yes, but rust greatly helps to enhance 'planned obsolescence'. The economy would take a deep dive if our cars didn't rust or wear out. sarcasm/off
agreed - but isnt beryllium nasty stuff ?
BTTT
US Steel has been producing "non-rusting" steel for years for structural purposes. The process involves a stable corrosion that turns the surface a deep brown and doesn't need painting. Some provisional needs for run off stain though as it does "bleed" some with rain. A good percentage of highway bridge beams are made of it. Look for it.. : USA is no. 1..
Cold rust bluing, which is a process applied to gun metal, works on a similar principle. Essentially, it is a fixed film of corrosion that prevents further rust from forming. Parkerization (used on Garand M1s) used a phosphate based process to achieve similar result.
uh huh huh huh huh huh huh huh, he said "erection"....
Keep in mind that this is not a casting but a forging
weighing 6.5 tons.
The skill level is amazing, I have had an interest in the
Pillar for over thirty years as a blacksmith.
That probably should read "removed the charcoal."
Cast iron is about 3 1/2% carbon, high carbon steel is about 1% carbon, mild steel is 0.2% carbon or less.
The iron pillar has longevity in spite of the high amount of phosphorus in the iron because it is loaded in compression instead of tension where the brittleness will show up.
Probably. That depends on the permeability of the film to oxygen. Some films are very impermeable (oxides of aluminum and titanium). Some are less impermeable (other iron oxides, copper oxide, and the like).
From the situation, I'd guess that this particular film is one of the highly impermeable ones.
Yup---VERY toxic.
I think you're talking about Cor-Ten steel. This steel is alloyed a little bit to make a rust stain that is supposed to be protective. However, this stuff hasn't always worked as well as planned. In some places, the local atmosphere is too aggressive for the steel, and the film isn't protective. Instead, the steel just keeps making a fine rust that falls from every surface and covers everyone and everything underneath.
Bill
Oh...It's right next to the Leaning Tower of Pizza...I'd wondered where it was at...
Thanks Blam, will add it to the GGG catalog. Welcome to RightOnTheLeftCoast.
similar thread:
Mystery of Delhi's Iron Pillar unraveled
Press Trust of India | Sunday, July 21, 2002 | Editorial Staff
Posted on 07/21/2002 1:15:49 PM PDT by vannrox
http://www.freerepublic.com/focus/f-news/719966/posts
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Every steel surface is coated with a layer of iron, oxygen, and hyrdogen. Rust is nothing but iron, oxygen, and hydrogen. Some of the iron oxides and hydroxides are more protective than others. Apparently, the phosphorus in this steel caused the surface to be coated with one of the more protective minerals.
It will be interesting to see whether the corrosion performance of this piece changes with time. If India gets enough industry to get a little acid rain, the whole surface could become active and start corroding rapidly in a very short period of time.
Bill
"The skill level is amazing, I have had an interest in the
Pillar for over thirty years as a blacksmith."
I started forging knives when I was 16 and until I moved to Colorado I had a nice forge. Can't do it in this subdivision I live in now. Have you ever been to the Ornamental Metal Museum in Memphis, Tn?
Maybe you should inform US Steel (Now USX) about it. People in Pittsburgh, PA should be warned that the USX Corporate Headquarters skyscraper, downtown, is an enviornmental hazard since it is primarily constructed of the stuf.. :)
I believe they called it Core 10 steel.
I cook with cast iron. My biceps are large, too.
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