WHY is the iron column in Delhi almost rust-free in 16 centuries?

A 7-meter-high iron column near Delhi has hardly any corrosion since it was erected in 415. Numerous legends have been circulating to explain this phenomenon: ancient Indian craftsmen knew the secret of making stainless steel, used special meteorite iron and even aliens were involved.

In fact, as chemical analysis has shown, there is nothing special in the material of the column, and it corresponds to the technological capabilities of the time, and the main reason for its resistance to corrosion is a naturally formed oxide film on the metal surface.

High phosphorus content in the iron, which just increases the ability to form such a film, and low humidity in this area also contribute. But the underground part of the column is covered with a centimeter layer of rust.

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