Scientists unravel secrets of mother of pearl

December 22nd, 2008 - 5:07 pm ICT by IANS  

Washington, Dec 22 (IANS) The inner lining of the shells of mother of pearl known as nacre and certain other molluscs is renowned for an amazing strength and toughness that has been a long-standing mystery. Now, scientists have uncovered a new aspect of nacre’s nanostructural architecture, using the polarized x-ray beams and nanoscale imaging capabilities of the Advanced Light Source (ALS), a national synchrotron facility at the Berkeley Lab.

Pupa Gilbert, physics professor at the University of Wisconsin-Madison who led this research said “nacre is a biomineral composed of thin layers of crystalline aragonite tablets separated by even thinner layers of organic material.”

“Our studies have revealed that the aragonite tablet crystals in nacre are misoriented with respect to each other. This unique structural arrangement was a surprise and could play a role in nacre’s remarkable resistance to fracture.”

Approximately 95 percent of nacre’s composition is aragonite, a hard but brittle calcium carbonate mineral, yet nacre is 3,000 times tougher than aragonite.

No human-synthesized composite can outperform its component materials by such a wide margin. Hence nacre has been intensely studied, particularly in the ceramics and nanotechnology industries where brittleness remains a major limitation.

The goal is to learn how nacre formation occurs in nature so that new microstructures might be engineered for ceramics and other materials that would increase their toughness, said a Wisconsin-Madison release.

However, researchers in the past lacked the tools needed to study the dynamics of nacre formation at the nanoscale. Now, new capabilities at the ALS, including polarised beams of x-rays, have made this possible.

Pupa Gilbert, of the University of Wisconsin-Madison, is a leading authority on the dynamics of nacre formation and other aspects of biomineralisation.

These findings were reported in the Journal of the American Chemical Society.

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