IRON PILLAR , DELHI

Standing at the center of the Quwwatul Mosque the Iron Pillar is one of Delhi's most curious structures.Dating back to 4th century A.D, it highlights ancient India's achievements in metallurgy. The pillar is made of 98 per cent wrought iron and has stood 1,600 years without rusting or decomposing.

It stand 7.3 m tall, with one meter below the ground; the diameter is 48 centimeters at the foot, tapering to 29 cm at the top, just below the base of the wonderfully crafted capital; it weighs approximately 6.5 tones, and was manufactured by forged welding.It bears an inscription which states that it was erected as a flagstaff in honor of the Hindu god, Vishnu, and in the memory of the Gupta King Chandragupta II (375-413). How the pillar moved to its present location remains a mystery.

Mystery of Delhi's Iron Pillar

The pillar is now located in Delhi, although one knows almost for certain that it was moved to that place from somewhere in Madhya Pradesh about a thousand years ago. Who had the pillar moved to its present location, and why, is unknown. The most densely argued chapter however is on the corrosion-resistant nature of this iron pillar, the P-content and the S-content of the low carbon mild steel of which it is made, the process of rust protection, the color of whatever rust there is, spectroscopic analysis, are all themes, something that has led to its being widely regarded as a 'miracle' of technology, given the times in which the pillar was forged and erected.

Mystery unraveled

On July 18, Experts at the Indian Institute of 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.

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.

It has also come to light that the pillar was erected by Kumara Gupta of Gupta dynasty that ruled northern India in AD 320-540.