Graphite is a crystalline allotrope of carbon, consisting of stacked sheets of carbon atoms arranged in hexagonal networks. It occurs naturally as a mineral and is also manufactured as synthetic graphite material. Typically gray to black, opaque, and soft, it combines electrical and thermal conductivity with lubricity and resistance to high temperatures under suitable conditions. These properties make it useful in writing materials, metallurgy, electrical equipment, and batteries. Unlike diamond, another crystalline form of carbon, graphite has a layered rather than a three-dimensional tetrahedral bonding structure. (goldbook.iupac.org)
Structure and bonding
Within each graphite layer, every carbon atom is bonded to three neighboring atoms. The bonding is described by sp² orbital hybridization: strong covalent bonds form a planar network, while the remaining p orbitals contribute to a delocalized electronic system. The carbon–carbon distance is approximately 0.142 nanometers. An isolated sheet with this arrangement is graphene; graphite requires parallel sheets stacked with three-dimensional crystalline order. The interaction between layers is much weaker than the bonding within them and is commonly described in terms of van der Waals forces. (goldbook.iupac.org)
The most common structure is hexagonal, or Bernal, graphite, with an ABAB stacking sequence: alternate layers occupy equivalent positions. Its layer spacing is approximately 0.335 nanometers. Rhombohedral graphite instead has an ABCABC sequence. These arrangements differ in the lateral displacement of successive sheets, not in the basic hexagonal network within each sheet. Hexagonal graphite has four carbon atoms in its unit cell. Carbon containing approximately parallel sheets with rotational or translational disorder is termed turbostratic carbon and lacks graphite’s complete stacking order. (goldbook.iupac.org)
Physical and chemical properties
Graphite’s softness and ability to leave marks arise from its layered structure. Thin flakes detach and adhere to paper when graphite is drawn across it. Its gray-black appearance and metallic luster coexist with properties unlike those of ordinary metals: individual flakes are flexible but not elastic, and the material readily cleaves along its layers. These characteristics distinguish a graphite crystal from manufactured graphite components, whose behavior also depends on grain arrangement and processing. (books.rsc.org)
Graphite is an electrical conductor, with delocalized electrons contributing to charge transport. Its properties are strongly directional, or anisotropic. In particular, thermal conductivity is much greater along the sheets than perpendicular to them. Consequently, a single crystal, an oriented graphite sheet, and a manufactured component containing differently aligned grains need not show the same bulk performance. Graphite’s combination of conductivity and thermal resistance is central to its electrical and high-temperature uses. (edu.rsc.org)
Chemical inertness does not mean that graphite is unreactive under all conditions. Oxidation by oxygen and other gases can damage graphite crucibles, electrodes, and nuclear components. Reactions frequently begin at defects and exposed edges, which are more reactive than intact basal surfaces. Its high-temperature usefulness therefore depends on the surrounding atmosphere as well as temperature, material quality, and component design. (books.rsc.org)
Natural occurrence and commercial types
Natural graphite commonly occurs in metamorphic rocks, where carbon-bearing precursors have been transformed by heat and pressure. Commercial deposits are conventionally divided into three types according to crystal size, morphology, and geological setting:
- Flake graphite consists of recognizable crystals dispersed through carbonaceous metamorphic rocks.
- Amorphous graphite is microcrystalline material, commonly associated with thermally metamorphosed coal. Despite its commercial name, it is not structurally amorphous.
- Vein or lump graphite occurs in concentrated veins in high-grade metamorphic regions. (usgs.gov)
These categories describe ore materials rather than separate chemical substances. Crystal size and the minerals accompanying graphite influence both beneficiation and suitability for particular products. Natural graphite must generally be separated from its host rock and upgraded before use; a mined concentrate is not automatically equivalent to a high-purity electrode or battery material. (usgs.gov)
Production and processing
Natural graphite processing can include crushing, grinding, screening, froth flotation, and dewatering. Further purification and particle shaping depend on the intended application. For battery production, natural flake graphite is commonly processed into high-purity spherical particles. Thus, mining, concentration, purification, and production of finished active material are distinct stages of the supply chain. (ukcmic.org)
Synthetic graphite is manufactured from carbon-rich precursors through high-temperature treatment. Petroleum coke and pitch are important feedstocks, and graphitization commonly involves temperatures around 2,500–3,000 °C. Processing develops an increasingly ordered graphitic structure, although commercial materials may retain defects and imperfectly aligned crystallites. In strict terminology, IUPAC reserves unqualified graphite for the carbon allotrope and uses qualified expressions, such as graphite material or graphite electrode, for processed products consisting essentially of graphitic carbon. (usgs.gov)
Applications
Graphite is used in lubricants, refractory products, foundry materials, brake linings, and steelmaking. Manufactured graphite electrodes exploit its electrical conductivity and high-temperature performance, while brushes in electrical machines maintain conductive contact with moving parts. Expanded graphite can be formed into flexible foils for seals and gaskets. Selection among natural and synthetic materials depends on purity, particle form, thermal behavior, and the requirements of the finished component. (usgs.gov)
In a lithium-ion battery, graphite commonly forms the negative electrode. Lithium enters spaces between its carbon sheets through intercalation and leaves them during discharge. The conventional fully lithiated composition, LiC₆, corresponds to a theoretical specific capacity of approximately 372 milliampere-hours per gram of graphite. This is a limit for the active material, not the energy capacity of an entire battery. Graphite’s layered host structure therefore serves a different function here from its role as a lubricant or refractory material. (arxiv.org)