Carbon, graphite and diamond materials include vitreous, amorphous, or glassy carbon; hexagonal and pyrolytic graphite (PG); and naturally-occurring and synthetic diamonds, diamond-like carbon (DLC) materials, and diamond-like coatings.

Carbon is a non-metallic element with graphite and diamond forms. Graphite is a gray, crystalline, carbon allotrope that is used as a solid lubricant and in nuclear reactors. Diamonds are formed by the crystallization of carbon under tremendous pressure, and are the hardest of all naturally-occurring materials. Synthetic diamonds are often used in industrial applications.

Materials

The Engineering360 SpecSearch database contains information about different types of carbon, graphite and diamond materials.

Carbon

Carbon that is amorphous, vitreous, or glassy lacks a crystalline structure. Vitreous carbon is produced by mixing a resin, usually furan, with a pore forming agent, casting it to a near net shape, and then pyrolizing it to drive out the volatile content. This process, pyrolysis, occurs under pressure and is a thermochemical decomposition of organic material at elevated temperatures in absence of oxygen.

Graphite

Graphite may have a hexagonal or anisotropic crystal structure.

Hexagonal graphite or flake graphite has a weak, platelet structure that flakes or wears away quickly, providing a lubricating action. Flake graphite is used in powder metallurgy, fuel cell bipolar plates, thermal materials, friction moderators, and electrically conductive materials. 

Pyrolytic graphite (PG) is layered and has a high density and highly anisotropic crystal structure. PG is produced by cracking methane at a very high temperature and allowing the carbon to be deposited on a substrate or mandrel. The resulting material has no grain structure and virtually no porosity. It has extremely large crystallographic planes and can approach a single crystal structure. Generally, PG’s mechanical, thermal, and electrical properties are far superior to conventional hexagonal (flake) structured or bonded materials.

Other types of graphite include vein, synthetic, and expandable.

Diamond

Diamond and diamond-like carbon (DLC) materials have high hardness and excellent wear resistance, which makes them useful in wear-part and tooling applications. They also provide high thermal conductivity and low electrical resistivity, which makes diamond suitable for use as a heat-dissipating, dielectric substrate in both electronic and semiconductor applications.

Products may be divided into diamonds (natural and synthetic) and diamond-like.

Diamonds have a face-centered, cubic structure in which the carbon atoms form tetrahedral bonds. Diamonds occur naturally but are also man-made.

Diamond-like carbon or coatings have an amorphous structure that still exhibit high-hardness levels. Often, diamond-like carbon materials are made using a chemical vapor deposition (CVD) process. Polycrystalline diamond (PCD) materials are made by consolidating or sintering fine diamond particles together using heat and pressure. PCD can also be manufactured through a CVD process.

Specialized and proprietary graphite and diamond-like materials are also available from some suppliers.

References

Eastern New Mexico State University: Diamond and Graphite

Asbury Carbons

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