The Secret of a Conch Shell’s Hardest Material:

Domestic Joint Research Team Observes a Nanoscale Process of Change

A domestic joint research team revealed why conch shells rarely become brittle or tear.  On February 18th, a research team led by Prof. Oh, Sang Ho in the Dept. of Energy Science at Sungkyunkwan University (SKKU), and researchers from the Institute for Basic Science (IBS) in Pohang University of Science and Technology reported that conches have strong outer shell thanks to their structure in which nanosized crystals are arranged vertically.

A conch’s outer shell is considered to be one of the hardest materials in nature.  So far, even though scientists have strived to find out the secret of its hardness in order to utilize the quality in other materials, it remained a mystery.
 
(A conch’s structure observed by transmission electronic microscopy)

Researchers discovered that when a crack is applied to the shell (right top), the interfacial plane’s crystal arrangement changes, blocking the crack (right bottom).
– provided by SKKU

The research team focused on the special crystalline structure of conches.  On a conch’s shell, calcium carbonate crystal, which is uniformly arranged at a nanoscale interval, is piled up into a layer.  Interface between layers consists of a ‘twin crystal’ structure with an arrangement direction that seems to have a form like mirrors facing each other.

The research team observed how a conch shell changes when it is cracked using a transmission electronic microscope which enables scientists to observe the change in nanoscale.  It was revealed that when a crack occurs, interface of twin crystal plays a role in blocking the spread and change in direction of the crack.  Since the external force is all used up to block the crack from spreading, a conch shell is rarely destroyed.

The energy required to destroy a conch shell is ten times higher than the energy needed for the destruction of ‘aragonite’, a mineral composed of calcium carbonate. 
Prof. Oh said, “If we imitate the structure of a conch shell, we will be able to develop new light and strong materials which would be apt for aviation or military uses.”  He also added, “It is meaningful that we were able to make these discoveries by observing what happened in nanoscale with an electronic microscope.”

The research results were published online in ‘Nature Communications’ on February 17th.