A team of researchers at MIT has designed a three-dimensional (3D) form of graphene with a density of just five percent but a strength 10 times that of steel. Two-dimensional graphene is thought to be the strongest of all known materials.

The new, sponge-like material was developed by compressing and fusing flakes of graphene, a two-dimensional form of carbon.  Until now, however, researchers have had a hard time translating the strength of two-dimensional graphene into useful three-dimensional materials.

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The new findings show the crucial aspect of the new 3D forms has more to do with their unusual geometrical configuration than with the material itself. This finding suggests that similar strong, lightweight materials could be made from a variety of materials by creating similar geometric features.

The findings were just reported in the journal Science Advances, in a paper by Markus Buehler, the head of MIT's Department of Civil and Environmental Engineering (CEE) and the McAfee Professor of Engineering; Zhao Qin, a CEE research scientist; Gang Seob Jung, a graduate student and Min Jeong Kang Meng, a recent graduate.

Other groups had suggested the possibility of such lightweight structures, but lab experiments so far had failed to match predictions, with some results exhibiting several orders of magnitude less strength than expected.

The MIT team decided to solve the mystery by analyzing the material's behavior down to the level of individual atoms within the structure. They were able to produce a mathematical framework that very closely matches experimental observations.

Two-dimensional materials are basically flat sheets just one atom in thickness but can be indefinitely large in the other dimensions. They have exceptional strength as well as unique electrical properties.

But because of their extraordinary thinness, "they are not very useful for making 3D materials that could be used in vehicles, buildings, or devices," said Buehler.

"What we've done is to realize the wish of translating these 2D materials into three-dimensional structures."

The team was able to compress small flakes of graphene using a combination of heat and pressure.

This process produced a strong, stable structure whose form resembles that of some corals and microscopic creatures called diatoms. These shapes, which have an enormous surface area in proportion to their volume, proved to be remarkably strong.

"Once we created these 3D structures, we wanted to see what's the limit -- what's the strongest possible material we can produce," said Qin.

"To do that, they created a variety of 3D models and then subjected them to various tests. In computational simulations, which mimic the loading conditions in the tensile and compression tests performed in a tensile loading machine, "one of our samples has 5 percent the density of steel, but 10 times the strength."

Buehler said that what happens to their 3D graphene material, which consists of curved surfaces under deformation, resembles what would happen with sheets of paper.

Paper has little strength along its length and width, and can be easily crumpled up. But when made into certain shapes, for example rolled into a tube, suddenly the strength along the length of the tube is much greater and can support substantial weight.

Similarly, the geometric arrangement of the graphene flakes after treatment naturally forms a very strong configuration.

TagsMIT, Graphene, 3D graphene, three-dimensiona graphene, two-dimensional graphene