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Researchers in Singapore, MIT develop flexible ceramics

Posted: 02 Oct 2013 ?? ?Print Version ?Bookmark and Share

Keywords:flexible ceramics? zirconia? ductility?

A research team has found a way to create minuscule ceramic objects that are not only flexible, but also have a "memory" for shape: when bent and then heated, they return to their original shapes. The discovery was revealed in a paper by Massachusetts Institute of Technology (MIT) graduate student Alan Lai and professor Christopher Schuh with the help of Zehui Du and Chee Lip Gan of Nanyang Technological University in Singapore.

Shape-memory materials, which can bend and then snap back to their original configurations in response to a temperature change, have been known since the 1950s, said Schuh, the Danae and Vasilis Salapatas professor of metallurgy and head of MIT's department of materials science and engineering. "It's been known in metals, and some polymers," he said, "but not in ceramics."

In principle, the molecular structure of ceramics should make shape memory possible, he notedbut the materials' brittleness and propensity for cracking has been a hurdle. "The concept has been there, but it's never been realised," Schuh stated. "That's why we were so excited."

The key to shape-memory ceramics, it turns out, was thinking small.

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Figure 1: When subjected to a load, the molecular structure of the ceramic material studied by the MIT-Singapore team deforms rather than cracking. When heated, it then returns to its original shape.

The team accomplished this in two key ways. First, they created tiny ceramic objects, invisible to the naked eye: "When you make things small, they are more resistant to cracking," Schuh indicated. Then, the researchers concentrated on making the individual crystal grains span the entire small-scale structure, removing the crystal-grain boundaries where cracks are most likely to occur.

Those tactics resulted in tiny samples of ceramic materialsamples with deformability equivalent to about seven per cent of their size. "Most things can only deform about one per cent," Lai said, adding that normal ceramics can't even bend that much without cracking.

David Dunand, a professor of materials science and engineering at Northwestern University, said the MIT team "achieved something that was widely considered impossible," finding "a clever solution, based on fundamental materials-science principles, to the Achilles' heel of ceramics and other brittle materials."

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