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Mother of pearl, or nacre, makes up the inner shell layer of mussels and other mollusks. Its strength comes from its structural makeup, which includes a range of lengths from nanometers to micrometers.
By finding a way to replicate nacre's internal architecture, researchers have made a hybrid ceramic-based material that, with further research to make it lighter and stronger, could be beneficial to the energy and transportation industries.
The recent research built off work from two years ago, when researchers Antoni Tomsia and Eduardo Saiz made a ceramic four times stronger than artificial bone with a technique involving freezing seawater. When seawater is frozen, ice crystals form thin layers with impurities like salt trapped between them - a structure resembling the inner workings of nacre.
Robert Ritchie led the team, including Tomsia and Saiz, that further refined that process, making thin layers of ice to serve as templates for creating scaffold-like layers of aluminum oxide (alumnia). After removing the ice, they filled in the rest of the structure with a polymer.
“The key to material toughness is the ability to dissipate strain energy,” Ritchie said. “Infiltrating the spaces between the alumina layers with polymer allows the hard alumina layers to slide (by a small amount) over one another when load is applied, thereby dissipating strain energy. The polymer acts as a lubricant, like the oil in an automobile engine.”
The resulting ceramic is 300 times tougher than its components, with strength and fracture toughness comparable to that of aluminum alloys.
The researchers reported their findings in the journal Science. They hope to make even tougher materials by increasing the proportion of ceramic to polymer, increasing the ceramic content, making the layers even thinner and eventually replacing the polymer with metal to bear loads better.
