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Ceramic or Silly Putty?

Materials scientists have developed a new ceramic that's closer to melted mozzarella than bathroom tiles. As reported in the 20 September issue of Nature, when heated the new material can be stretched to at least 10 times its original length without snapping. The ceramic is cheap to make and can be molded into shapes useful in engine parts and other industrial applications.

Fire clay in a kiln and the clay mineral crystals fuse, or sinter, together to form the characteristically hard, heat-resistant, and--oops!--tragically brittle stuff of pots, tiles, and teacups. Materials scientists have struggled to devise novel, malleable ceramics, but all attempts so far either crack when stretched or are impossibly slow to distort.

By homing in on how ceramics behave when stretched, Byung-Nam Kim and his colleagues at the National Institute for Materials Science in Tsukuba, outside Tokyo, hit on a new formulation using roughly equal amounts of powdered zirconium oxide, magnesium aluminate, and alumina. They mixed the three ingredients and heated them until they sintered. The resultant ceramic has a grainy structure that close-up looks like a honeycomb, which is central to the material's properties. With additional heating, the material can be stretched, because the 0.2-micrometer grains easily slide over one another without combining to form larger grains. "We think other kinds of ceramic powders ... will give the same results," says Kim.

The "sales point" of Kim's work is this huge extension, says the University of Tokyo's Taketo Sakuma. The new ceramic stretches about as easily as a typical heated metal and can be reshaped 3000 times faster than what had, until now, been the world's stretchiest ceramic, created by Sakuma. Because Kim's ceramic uses commercial materials and methods, it will be cheap to produce in bulk. It should be possible to use this and comparable ceramics to make ball bearings, valves, and rotor arms, Kim says.

Related sites

The National Institute for Materials Science
The University of Tokyo Ceramic Materials Laboratory