Aggregated diamond nanorod

Discovery

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. 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. 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'".

Hardness

A 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. 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. In another method, fullerite is compressed to lower pressures (2–20 GPa) and then heated to a temperature in the range of 300 to. Extreme hardness of what now appears likely to have been nanodiamonds was reported by researchers in the 1990s. The material is a series of interconnected diamond nanorods, with diameters of between 5 and 20 nanometres and lengths of around 1 micrometre each.

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.

References

References

1. (2015). "Natural occurrence of pure nano-polycrystalline diamond from impact crater". Scientific Reports.
2. (2003). "Materials: Ultrahard polycrystalline diamond from graphite". Nature.
3. (2005). "Aggregated diamond nanorods, the densest and least compressible form of carbon". Applied Physics Letters.
4. (2006). "Superior Wear Resistance of Aggregated Diamond Nanorods". Nano Letters.
5. (1998). "Ultrahard and superhard phases of fullerite C₆₀: Comparison with diamond on hardness and wear". Diamond and Related Materials.
6. (1994). "Is C₆₀ fullerite harder than diamond?". Physics Letters A.
7. (1995). "Superhard form of carbon obtained from C₆₀ at moderate pressure". Synthetic Metals.
8. (1995). "Ultrahard and superhard carbon phases produced from C₆₀ by heating at high pressure: structural and Raman studies". Physics Letters A.
9. (1996). "Chemical modifications of C under the influence of pressure and temperature: from cubic C to diamond". Synthetic Metals.
10. (1996). "Phase transformations in solid C₆₀ at high-pressure-high-temperature treatment and the structure of 3D polymerized fullerites". Physics Letters A.