Aggregated diamond nanorods, or ADNRs, are a nanocrystalline form of diamond, also known as nanodiamond or hyperdiamond.
Aggregated diamond nanorods, or ADNRs, are a nanocrystalline form of diamond, also known as nanodiamond or hyperdiamond.
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]
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.
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 300 to 2,500 K (27 to 2,227 °C). [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.[ 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]
Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexagonal form corresponding to graphite is the most stable and soft among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic variety analogous to diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior. The rare wurtzite BN modification is similar to lonsdaleite but slightly softer than the cubic form.
Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up about 0.025 percent of Earth's crust. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, but diamond is metastable and converts to it at a negligible rate under those conditions. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are used in major industrial applications such as cutting and polishing tools. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth.
Lonsdaleite, also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond. It is found in nature in meteorite debris; when meteors containing graphite strike the Earth, the immense heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with ordinary diamond.
β-Carbon nitride (beta-carbon nitride), β-C3N4, is a superhard material predicted to be harder than diamond.
Lab-grown diamond is diamond that is produced in a controlled technological process. Unlike diamond simulants, synthetic diamonds are composed of the same material as naturally formed diamonds – pure carbon crystallized in an isotropic 3D form – and share identical chemical and physical properties.
Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes have been discovered and researched, including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3‑periodic allotropes of carbon are known at the present time, according to the Samara Carbon Allotrope Database (SACADA).
The Popigai impact structure is the eroded remnant of an impact crater in northern Siberia, Russia. It is tied with the Manicouagan structure as the fourth largest verified impact structure on Earth. A large bolide impact created the 100-kilometre (62 mi) diameter crater approximately 35 million years ago during the late Eocene epoch. It might be linked to the Eocene–Oligocene extinction event.
Amorphous carbon is free, reactive carbon that has no crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed. Amorphous carbon is often abbreviated to aC for general amorphous carbon, aC:H or HAC for hydrogenated amorphous carbon, or to ta-C for tetrahedral amorphous carbon.
Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic, a covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers hardness of >30 GPa, it is one of the hardest known materials, behind cubic boron nitride and diamond.
A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their unique properties, these materials are of great interest in many industrial areas including, but not limited to, abrasives, polishing and cutting tools, disc brakes, and wear-resistant and protective coatings.
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. It is a crystal that is transparent to opaque and which is generally isotropic. Diamond is the hardest naturally occurring material known. Yet, due to important structural brittleness, bulk diamond's toughness is only fair to good. The precise tensile strength of bulk diamond is little known; however, compressive strength up to 60 GPa has been observed, and it could be as high as 90–100 GPa in the form of micro/nanometer-sized wires or needles, with a corresponding maximum tensile elastic strain in excess of 9%. The anisotropy of diamond hardness is carefully considered during diamond cutting. Diamond has a high refractive index (2.417) and moderate dispersion (0.044) properties that give cut diamonds their brilliance. Scientists classify diamonds into four main types according to the nature of crystallographic defects present. Trace impurities substitutionally replacing carbon atoms in a diamond's crystal structure, and in some cases structural defects, are responsible for the wide range of colors seen in diamond. Most diamonds are electrical insulators and extremely efficient thermal conductors. Unlike many other minerals, the specific gravity of diamond crystals (3.52) has rather small variation from diamond to diamond.
Heterodiamond is a superhard material containing boron, carbon, and nitrogen (BCN). It is formed at high temperatures and high pressures, e.g., by application of an explosive shock wave to a mixture of diamond and cubic boron nitride (c-BN). The heterodiamond is a polycrystalline material coagulated with nano-crystallites and the fine powder is tinged with deep bluish black. The heterodiamond has both the high hardness of diamond and the excellent heat resistance of cubic BN. These characteristic properties are due to the diamond structure combined with the sp3 σ-bonds among carbon and the hetero atoms.
Natalia Dubrovinskaia is a Swedish geologist of Russian origin.
Linear acetylenic carbon (LAC), also known as carbyne or Linear Carbon Chain (LCC), is an allotrope of carbon that has the chemical structure (−C≡C−)n as a repeat unit, with alternating single and triple bonds. It would thus be the ultimate member of the polyyne family.
The mechanical properties of carbon nanotubes reveal them as one of the strongest materials in nature. Carbon nanotubes (CNTs) are long hollow cylinders of graphene. Although graphene sheets have 2D symmetry, carbon nanotubes by geometry have different properties in axial and radial directions. It has been shown that CNTs are very strong in the axial direction. Young's modulus on the order of 270 - 950 GPa and tensile strength of 11 - 63 GPa were obtained.
Aluminium magnesium boride or Al3Mg3B56, colloquially known as BAM, is a chemical compound of aluminium, magnesium and boron. Whereas its nominal formula is AlMgB14, the chemical composition is closer to Al0.75Mg0.75B14. It is a ceramic alloy that is highly resistive to wear and has an extremely low coefficient of sliding friction, reaching a record value of 0.04 in unlubricated and 0.02 in lubricated AlMgB14−TiB2 composites. First reported in 1970, BAM has an orthorhombic structure with four icosahedral B12 units per unit cell. This ultrahard material has a coefficient of thermal expansion comparable to that of other widely used materials such as steel and concrete.
Nanodiamonds, or diamond nanoparticles, are diamonds with a size below 100 nanometers. They can be produced by impact events such as an explosion or meteoritic impacts. Because of their inexpensive, large-scale synthesis, potential for surface functionalization, and high biocompatibility, nanodiamonds are widely investigated as a potential material in biological and electronic applications and quantum engineering.
Boron can be prepared in several crystalline and amorphous forms. Well known crystalline forms are α-rhombohedral (α-R), β-rhombohedral (β-R), and β-tetragonal (β-T). In special circumstances, boron can also be synthesized in the form of its α-tetragonal (α-T) and γ-orthorhombic (γ) allotropes. Two amorphous forms, one a finely divided powder and the other a glassy solid, are also known. Although at least 14 more allotropes have been reported, these other forms are based on tenuous evidence or have not been experimentally confirmed, or are thought to represent mixed allotropes, or boron frameworks stabilized by impurities. Whereas the β-rhombohedral phase is the most stable and the others are metastable, the transformation rate is negligible at room temperature, and thus all five phases can exist at ambient conditions. Amorphous powder boron and polycrystalline β-rhombohedral boron are the most common forms. The latter allotrope is a very hard grey material, about ten percent lighter than aluminium and with a melting point (2080 °C) several hundred degrees higher than that of steel.
Superdense carbon allotropes are proposed configurations of carbon atoms that result in a stable material with a higher density than diamond.
