Aggregated diamond nanorods

Aggregated diamond nanorods, or ADNRs, are an allotrope of carbon believed to be the hardest and least compressible known material, as measured by its isothermal bulk modulus; aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442 GPa. ADNRs are also 0.3% denser than regular diamond. The ADNR material is also harder than type IIa diamond and ultrahard fullerite.

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A process to produce the substance was discovered by physicists in Germany, led by Natalia Dubrovinskaia, at the University of Bayreuth in 2005. ADNRs are made by compressing allotropic carbon fullerene molecules (generally 60 carbon atoms per molecule) to a pressure of 20 GPa, while at the same time heating to 2500 kelvin, using a unique 5000-metric-ton multi anvil press. The resulting substance is a series of interconnected diamond nanorods, with diameters of between 5 and 20 nanometres and lengths of around 1 micrometre each.  

A diamond anvil cell, located at the European Synchrotron Radiation Facility at Grenoble, France, was used to measure the compressibility of the material.

Hardness

Carbon nanotubes have a hardness greater than 10 in the Mohs' hardness scale. Its absolute hardness is greater than 1500.

See also

• Carbon nanotube
• Fullerite
• Diamond
• Rhenium diboride
• Mohs scale of mineral hardness