What is the elasticity of materials

Hard as stone, elastic as rubber

Diamond, graphite, graphene or nanotubes - pure carbon offers a wide variety of materials with the most varied of properties. With a high-pressure experiment, researchers have now expanded the range of versatile carbon compounds. They created a light material that is hard like stone or ceramic and elastic like a plastic at the same time. As the group reports in the journal “Science Advances”, the new vitreous carbon is also electrically conductive and thus offers many possible applications.

The basis of the new compound is the unique property of carbon atoms to be able to combine with two, three or four other atoms. As the starting material, Meng Hu from Yanshan University in Qinhuangdao, China, and colleagues chose a special carbon compound in which bent, atomically thin layers of graphene irregularly agglomerate to form a solid. The researchers pressed a sample of this vitreous carbon measuring just a few millimeters between two diamonds at a pressure of up to 25 gigapascals. In addition, they quickly heated their sample to up to 1,100 degrees Celsius. After about two hours, the previously unknown hard and elastic variants of carbon were created, which are resistant to pressure and chemicals and which deform elastically under strong bending forces and do not break. "Simply put, the material combines the best properties of graphite- and diamond-like carbon compounds," says co-author Zhisheng Zhao from Yanshan University.

Structural model of the compressed glassy carbon

Using several methods - such as electron microscopy, X-ray diffraction and Raman spectroscopy - the researchers analyzed the internal structure of the compressed glassy carbon. In doing so, they recognized that the atoms in the immediate vicinity had been arranged strictly symmetrically at a distance of up to five nanometers. Over greater distances, however, a rather disordered atomic structure dominates. In the connection, the atoms are linked on the one hand with four other atoms as in diamond, but sometimes only with three neighboring atoms as in graphite or graphene.

This experiment shows that new materials can be created from carbon. "In the future, we want to use our process to create more new materials," says Zhao. Your goal is extremely strong, ultra-hard and at the same time super-elastic materials. These could be used, for example, for the construction of bridges, rotor blades or aircraft hulls. In order to be able to produce large quantities of these carbon compounds, the synthesis process would also have to be significantly optimized. Because the samples created so far were hardly bigger than the head of a pin.