Iron pillar of Delhi

The Iron Pillar located in Delhi, in the Qutb complex, notable for the rust-resistant composition of the metals used in its construction has attracted the attention of archaeologists and materials scientists and has been called "a testament to the skill of ancient Indian blacksmiths" because of its high resistance to corrosion.

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, 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.

Source: http://expressindia.indianexpress.com/news/fullstory.php?newsid=12824

(Press Trust of India)

Further Reading:

1. On the Corrosion Resistance of the Delhi Iron Pillar, R. Balasubramaniam, Corrosion Science, Volume 42 (2000) pp. 2103–2129.
2. Story of the Delhi Iron Pillar,Balasubramaniam, Ramamurthy (2005). Pg.1 (Foundation Books). ISBN 81-7596-278-X.

The Titanic: What made it sink?

When the "unsinkable" ship, the largest, most luxurious ocean liner of its time, crashed into an iceberg on its maiden voyage in 1912, it took more than 1,500 of its 2,200 passengers to the bottom. As the ship slipped into the North Atlantic, so, too, did the secret of how and why it sank.

Investigations conducted immediately after the disaster agreed it was the iceberg, not any weakness in the ship itself, that caused the Titanic to sink. Both inquiries concluded the vessel had gone to the bottom intact. But lingering questions about what might have sunk the seemingly indestructible ship never completely disappeared. In 1985, when oceanographer Robert Ballard, after years of searching, finally located the ship's remains 2.5 miles down on the ocean bottom, he discovered that it had, in fact, broken in two on the surface before sinking.

A few years after Ballard discovered the wreck, the first pieces of the ship were brought to the surface, raising even more eyebrows when they seemed to offer physical evidence that low-quality steel might have caused the disaster.

Jennifer Hooper McCarty, a materials scientist at Oregon Health and Science University, and Tim Foecke, a scientist at the National Institute of Standards and Technology, make the case that it wasn't the ship's steel that was weak; it was the rivets, the all-important metal pins that held the steel hull plates together. When the Titanic hit the iceberg, McCarty and Foecke say, the weaker iron rivets in the bow popped, opening seams in the hull—and hurrying the ship's demise.

There were more than 3 million rivets holding the ship together. McCarty and Foecke began examining 48 rivets brought up from the wreck and found they contained high concentrations of "slag," a residue of smelting that can make metal fracture prone.

Source: http://www.usnews.com/news/national/articles/2008/09/25/the-secret-of-how-the-titanic-sunk

(Image: RMS Titanic departing Southampton on April 10, 1912.)