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A new compressed form of glassy carbon opens up possibilities for applications requiring low weight and high strength — from aerospace parts to football helmets.

The super-strong, elastic, electrically-conductive carbon was created by researchers at the Carnegie Institute for Science, using high pressure and temperatures.

The findings were published in June’s Science Advances publication.

A visualization of the different types of diamond-like linkages (red spheres) formed at curved surfaces or between the layers of graphene (black spheres) in this new type of compressed glassy carbon. (Credit: Timothy Strobel)

What Makes Carbon Special

Carbon’s unique electron configuration and ability to therefore bond in various states allows the formation of a range of materials: from three-dimensional, super-hard diamonds to the two-dimensional opaque graphite used in pencils. The Carnegie creation features a network of bonds that are both diamond-like and graphite-like.

The scientists, in collaboration with China’s Yanshan University, began with a rod of structurally disordered carbon: a material that looks like black glass. After compressing the “sp2-hybridized glassy carbon” to about 250,000 times normal atmospheric pressure and heating the rod to 1800 °F, the team developed the high-strength, elastic form of carbon.

According to researcher Tim Strobel, the compressed glassy carbons have “extraordinary” compressive strengths—more than two times that of commonly used ceramics.

“The material has comparable hardness to silicon carbide,” said Strobel. “It’s harder than sapphire or ruby.”

The glassy carbon maintains its strength while simultaneously demonstrating elastic recovery in response to local deformations.

The Carnegie team’s method of applying high pressure causes the graphene sheets to buckle, forming interpenetrating graphene structures. The networks create an overall structure that lacks a long-range spatial order, but achieves a short-range spatial order on the nanometer scale.

“If you imagine a perfectly planar graphite structure, you have these sheets of hexagons bonded to one another, and they’re only bonded in two dimensions,” said Strobel. “Here we’re seeing those crosslinks and we can actually visualize those images. I think that’s phenomenal.”

Making New Materials

Visualization of ultra-strong, hard and elastic compressed glassy carbon. The illustrated structure is overlaid on an electron microscope image of the material. (Credit: Timothy Strobel)

Strobel’s team, headquartered at Carnegie in Washington, D.C., is broadly interested in synthesizing new materials, often controlling the structure of matter by using extreme pressure and temperature to access states that scientists have not achieved before.

The researchers had previously tried to subject the glassy carbon to high pressures at both room temperature, known as cold compression, and extremely high temperatures. The so-called cold-synthesized material, however, could not maintain its structure when brought back to ambient pressure.

The newly made carbon, made of both graphite-like and diamond-like bonds, offers a unique combination of properties — and possibilities.

“Light materials with high strength and robust elasticity like this are very desirable for applications where weight savings are of the utmost importance, even more than material cost,” said Zhisheng Zhao, former Carnegie fellow and current Yanshan University professor, in a university press release.

“What’s more, we believe that this synthesis method could be honed to create other extraordinary forms of carbon and entirely different classes of materials.”

Although careful to speculate too much on applications, Strobel says the material offers potential for applications requiring light weight and high strength, including aircraft parts, car bumpers, military armor, and even American football helmets.

“Our material is the best of both worlds: both graphite-like and diamond-like,” said Strobel. “We’re mixing the properties. We increased the hardness. We increased the strength an extraordinary amount. We maintained the electrical conductivity. And it’s still an all-carbon material.”

What do you think? Will compressed glassy carbon support new kinds of real-world applications? Write your comments in the form below.

Additional team members included Meng Hu, Julong He, Wentao Hu, Dongli Yu, Hao Sun, Lingyu Liu, Zihe Li, Mengdong Ma, Jian Yu Huang, Zhongyuan Liu, Bo Xu, Yongjun Tian of the State Key Laboratory of Metastable Materials Science and Technology; Yanbin Wang of the University of Chicago; and Stephen J. Juhl of Penn State University.

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