Recently, formations of superhard amorphous carbon have been found by high-pressure compression of type-I GC 5, 6, 7, 8. Both low- and high-temperature GCs are composed of nearly 100% sp 2-bond at ambient condition 2. A “high-temperature” GC produced at ~2500–3000 ☌ (e.g., type II in Alfa Aesar and Sigradur G in HTW Hochtemperatur-Werkstoffe GmbH) contains broken or imperfect fullerene-like nanospheroids encased in a disordered multilayer graphene matrix 2, 3, 4. ![]() A “low-temperature” GC, which is produced by heat treatment at ~1000–2000 ☌ (e.g., type I in Alfa Aesar, USA, and Sigradur K in HTW Hochtemperatur-Werkstoffe GmbH, Germany), consists of discrete fragments of distorted graphene layer 2, 3, 4. Two types of GCs are commercially available at the moment. Glassy carbon (GC), which is an amorphous carbon allotrope, has attracted great interest in the fields of materials science, engineering, and industry, because of its unique physical and chemical properties such as low density, high-temperature stability, extreme resistance to chemical corrosion, and high impermeability to gases and liquids 1, 2. The unique structure of the compressed glassy carbon may be the key to the ultrahigh strength.Ĭarbon is known to display numerous allotropes, such as graphite, diamond, fullerenes, carbon nanotubes, and glassy carbon, because of its flexibility to form chemical bonds with sp-, sp 2-, and sp 3-hybridizations. ![]() Linkages between the graphene layers may be formed with such a short distance, but not in the form of tetrahedral sp 3 bond. In contrast, graphene interlayer distance decreases sharply with increasing pressure, approaching values of the second neighbor C-C distance above 31.4 GPa. Our data clearly indicate that the glassy carbon maintains graphite-like structure up to 49.0 GPa. Our results show that the C-C-C bond angle in the glassy carbon remains close to 120°, which is the ideal angle for the sp 2-bonded honey-comb structure, up to 49.0 GPa. Here we succeeded to experimentally determine pair distribution functions of a glassy carbon at ultrahigh pressures up to 49.0 GPa by utilizing our recently developed double-stage large volume cell. However, there is no direct experimental determination of the bond structure of the compressed glassy carbon, because of experimental challenges. Previous studies attributed the ultrahigh strength of the compressed glassy carbon to structural transformation from graphite-like sp 2-bonded structure to diamond-like sp 3-bonded structure. Amorphous diamond, formed by high-pressure compression of glassy carbon, is of interests for new carbon materials with unique properties such as high compressive strength.
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