Diamonds are not forever
Aug 26, 2005
Physicists in Germany have created a material that is harder than diamond. Natalia Dubrovinskaia and colleagues at the University of Bayreuth made the new material by subjecting carbon-60 molecules to immense pressures. The new form of carbon, which is known as aggregated diamond nanorods, is expected to have many industrial applications (App. Phys. Lett. 87 083106).
The hardness of a material is measured by its isothermal bulk modulus. Aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), compared with 442 GPa for conventional diamond. Dubrovinskaia and two of her co-workers - Leonid Dubrovinky and Falko Langenhorst - have patented the process used to make the new material.
Diamond derives its hardness from the fact that each carbon atom is connected to four other atoms by strong covalent bonds. The new material is different in that it is made of tiny interlocking diamond rods. Each rod is a crystal that has a diameter of between 5 and 20 nanometres and a length of about 1 micron.
The group created the ADNRs by compressing the carbon-60 molecules to 20 GPa, which is nearly 200,000 times atmospheric pressure, while simultaneously heating to 2500 Kelvin. "The synthesis was possible due to a unique 5000-tonne multianvil press at Bayerisches Geoinstitut in Bayreuth that is capable of reaching pressures of 25 GPa and temperatures of 2700 K at the same time," Dubrovinskaia told PhysicsWeb.
The Bayreuth team measured the properties of the samples with a diamond anvil cell at the European Synchrotron Radiation Facility at Grenoble in France. These measurements indicated that ADNRs are about 0.3% denser than diamond, and that the new material has the lowest compressibility of any known material.
In addition to working out why the new material is so hard, the Bayreuth team also hope to exploit its industrial potential. "We have developed a concept for innovative technology to produce the novel material in industrial-scale quantities and now we are looking for partners in order to realize our ideas," said Dubrovinskaia.
About the author
Michelle Jeandron is a placement student on Physics World magazine.