Springy ceramics bounce back when squeezed

[Nipuna]

Alumina nano-lattices can be compressed without going to bits (Image: L. R. Meza, S. Das, J. R. Greer)

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Put the squeeze on a ceramic mug and you'll crush it to powder. But ultra-tiny ceramic scaffolds can now be made that bounce back under pressure. Such materials can be made so light that they approach density of air, and might serve as shock absorbers in cellphones and other fragile devices.

"This, for ceramics, is unheard of," says Peter Fratzl at the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, who was not involved in the work. "They are usually brittle and will fracture."

Such brittle materials typically contain tiny defects – little cracks or holes – that lead to cracking under pressure. To tackle this problem, researchers led by Julia Greer at the California Institute of Technology in Pasadena built tiny lattices out of superthin ceramic tubes with walls just 5 to 60 nanometres thick. This thinness leaves little room for defects that might otherwise send cracks throughout the lattice.

Stress tests revealed that some of the lattices with tube walls 10 nanometre thick bounced back to more than 95 per cent of their original height after being compressed by more than 50 per cent.

Striking strength
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"The strength is the most striking," says materials scientist Sylvain Deville of the National Centre for Scientific Research in Cavaillon, France. Ceramics usually break after being compressed by 1 per cent, he notes, "so 50 per cent strain is really huge".

The tube walls wrinkle and warp under compression, then the tubes bend under the stress. Any cracks that appear in the lattice seem unable to propagate past these stressed bends in the tubes, so they are stopped in their tracks. When the research team made lattices with tubes with walls 60 nanometres thick, the lattices behaved like a normal brittle material and were crushed to dust.

"Elastic ceramics is a holy grail in materials science," says Fratzl. "With the thinness, they've achieved a very unusual effect." But he cautions that the technique may be difficult and expensive to scale up.

Journal reference: Science, DOI: 10.1126/science.1255908