Nanodiamond or hyperdiamond was produced by compression of graphite in 2003 by a group of researchers in Japan and in the same work, published in Nature, it was shown to be much harder than bulk diamond.[2] Later, it was also produced by compression of fullerene and confirmed to be the hardest and least compressible known material, with an isothermal bulk modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442–446 GPa; these results were inferred from X-ray diffraction data, which also indicated that ADNRs are 0.3% denser than regular diamond.[3] The same group later described ADNRs as "having a hardness and Young's modulus comparable to that of natural diamond, but with 'superior wear resistance'".[4]
Hardness
A <111> surface (normal to the largest diagonal of a cube) of pure diamond has a hardness value of 167±6 GPa when scratched with a nanodiamond tip, while the nanodiamond sample itself has a value of 310 GPa when tested with a nanodiamond tip. However, the test only works properly with a tip made of harder material than the sample being tested due to cracking. This means that the true value for nanodiamond is likely lower than 310 GPa.[5] Due to its hardness, a hyperdiamond could possibly exceed 10 on the Mohs scale of mineral hardness.
Synthesis
ADNRs (hyperdiamonds/nanodiamonds) are produced by compressing fullerite powder—a solid form of allotropic carbon fullerene—by either of two somewhat similar methods. One uses a diamond anvil cell and applied pressure ~37 GPa without heating the cell.[6] In another method, fullerite is compressed to lower pressures (2–20 GPa) and then heated to a temperature in the range of Шаблон:Convert.[7][8][9][10] Extreme hardness of what now appears likely to have been nanodiamonds was reported by researchers in the 1990s.[5][6] The material is a series of interconnected diamond nanorods, with diameters of between 5 and 20 nanometres and lengths of around 1 micrometre each.Шаблон:Citation needed
Nanodiamond aggregates ca. 1 mm in size also form in nature, from graphite upon meteoritic impact, such as that of the Popigai impact structure in Siberia, Russia.[1]
