The historic Qutub Minar in New Delhi, has been a mystery to scientists for more than decades. The iron pillar stands 7 meters high, weighs 6 tonnes, and is even older than the building complex that houses it. For more than 1600 years, the pillar has remained unaffected by rust. It was not until 2003 that a study by scientists from IIT Kanpur explained this phenomenon.
As per the findings of the Archaeological Survey of India, the iron pillar is made of wrought iron and is known to have garnered much scientific attention due to the fact that iron structures corrode when they come into contact with water. According to reports, the structure carries inscriptions for Chandragupta Vikramaditya from the Gupta dynasty.
Qutub Minar has been studied by scientists since 1912. Murray Thompson and Percy of Roorkee Engineering College and the School of Mines analysed the chemical structure of the pillar. It revealed that the pillar was composed of wrought iron with a specific gravity of 7.66. But the cause for its high corrosion resistance was still unknown.
The breakthrough finally came in 2003. Scientists at the Indian Institute of Technology in Kanpur took a closer look at the pillar. The discovery showed that the iron used in the pillar has a high content of phosphorus. This is believed to be the cause of its longevity.
Another finding from the study was the presence of a very thin protective coating known as 'misawite.' This substance is composed of iron, oxygen, and hydrogen. It helps create a passive guard to prevent further corrosion of the metal.
Another significant discovery talks about the making process of Qutub Minar. The ancient artisans employed the forge-welding method, whereby hot pieces of iron were hammered together. This technique preserved the high phosphorus content in the metal.
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