Ceramics That Won't Shatter

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Uncushioned by the polymer, the bricks would be brittle like most ceramics. But the polymer permits the brick-like layers to slide over one another when stressed, making the material resistant to fractures. Indeed, this brick-and-mortar structure is tougher than any ceramic ever made in the lab. "High toughness and high strength are usually incompatible" in a ceramic, says Eric Stach, a materials engineer at Purdue University who was not involved with the Berkeley work. But the ceramics created at Berkeley have as much strength and toughness as aluminum alloys, which "you can fly planes with," says Stach.

Though they caution that the nacre-like ceramics are in their early stages of development, the Berkeley researchers say the materials should make possible applications of ceramics that have seemed unattainable. "You could use ceramics to make the frame of a car instead of steel, and save fuel," says Ritchie. Antoni Tomsia, a materials scientist at the Lawrence Berkeley Laboratory who co-led the research, says that tough ceramics, which are good insulators, could do double duty as structural elements in energy-efficient buildings. And they might also be used in lightweight bulletproof vests and vehicle armor for the military.

The new work, say materials scientists, shows the way forward for tough biomimetic materials. Paul Hansma, professor of physics at the University of California at Santa Barbara, calls the work "astonishing" and says the performance of the new ceramic "raises the bar in this important field."

Ritchie and Tomsia are confident they can make the material even better. Natural nacre has ceramic structures an order of magnitude smaller than those in the Berkeley material, as well as a higher ratio of brick to mortar. Ritchie says the group is working on making the ceramic bricks smaller and closer together, and decreasing the polymer content. They're also experimenting with different mortars. Because the newly developed ceramic contains a gluey polymer, it would fail in high-temperature environments like the inside of an engine. So the Berkeley researchers are experimenting with metal fillers, which can withstand higher temperatures.