Graphite Structure : A Complete Guide

Graphite, as a key allotrope of carbon, plays an important role in many fields. The in-depth exploration of its structure is the key to unlock the wide application potential of graphite and the development of new materials.

Qu'est-ce que le graphite ?

Graphite, a mineral made of carbon atoms, is widely distributed in nature. It has a metallic luster and a soft and smooth feel. This makes it an ideal material for pencil leads. The color of graphite is mostly black or dark gray. And its purity and crystallization degree vary according to the formation environment.

Atomic and Molecular structure of graphite

Atomic structure of graphite

The mainly composition of graphite is carbon. The carbon atoms in graphite are connected by covalent bonds. And each carbon atom and the surrounding three carbon atoms form a stable hexagonal ring structure, which extends indefinitely in the plane to form a solid atomic skeleton.

Molecular structure of graphite

At the molecular level, graphite is made up of layers of carbon atoms stacked on top of each other. The interlayer carbon atoms are maintained by relatively weak van der Waals forces. And this layered structure explains why the graphite excellent lubricity and easy sliding between layers.

Two key elements of graphite structure

Graphite hexagonal crystal structure

Arrangements

Graphite has a hexagonal crystal structure, carbon atoms are closely arranged in hexagons in the plane, including an Angle of 120 degrees. The arrangement is regular and stable, conducive to electron conduction, is the basis of its good electrical conductivity.

Layering

The carbon atoms are stacked in parallel planes, the layer spacing is about 0.335nm. And the van der Waals force between the layers is weak, which makes the graphite easy to slide between the external layers and has lubricability. This is commonly used as a lubricant in the field of mechanical manufacturing.

Layers of crystal structure

Each layer of carbon atoms forms a network plane through covalent bonds. This is arranged in an orderly manner in space, giving the macroscopic crystal characteristics and anisotropy of graphite. The strong covalent bond in the layer makes the graphite have high strength and hardness in plane. The vertical plane direction has low strength due to weak interlayer force.

Bonds within carbon atoms

 Van der Waal Forces

The interlayer carbon atoms rely on the van der Waals force, which is weak, resulting in easy sliding separation between graphite layers and lubricity. But it also makes the interlayer structure of graphite variable under certain conditions (such as high temperature and pressure). Such as it can be transformed into a diamond structure.

Layer separation

Due to the weak van der Waals force, the graphite layer can be separated by applying a small shear force. This is not only reflects lubricity, but also creates the possibility of intercalation reactions, through which the physical and chemical properties of graphite can be changed to prepare special composite materials. Such as negative electrode materials for lithium-ion batteries.

Covalent bonds

The carbon atoms in the layer are tightly connected by covalent bonds to form a stable hexagonal structure. This determines the high hardness and strength of graphite in the plane, guarantees its structural stability in the application of electrode materials. And it limits the movement of electrons, affecting the anisotropy in the plane.

 Sp2 hybridization

 Bond Angle

Carbon atoms adopt sp2 hybridization, one 2s and two 2p orbitals hybridize to form three equivalent sp2 hybridization orbitals. These are distributed in a plane triangle with an Angle of about 120 degrees. So that carbon atoms form stable covalent bonds with three adjacent carbon atoms to build a hexagonal structure, which is conducive to electron delocalization conduction and good electrical conductivity.

Carbon atoms

The carbon atom constructs a planar skeleton with three surrounding carbon atoms through sp2 hybrid orbitals. And the vertical planes of non-hybrid 2p orbitals overlap to form delocalized π-electron clouds. π-electron clouds give graphite good electrical conductivity, in which electrons can move freely in response to changes in electric fields. And make graphite active in chemical reactions and participate in electrochemical processes. Such as as an electron transfer medium in lithium-ion batteries.

Anisotropy

In-plane attributes and out-of-plane attributes

The graphite shows significant anisotropy in different directions. In the plane, the covalent bond is strong, with high hardness, strength and good electrical conductivity. Such as you can use graphite fiber reinforced composite materials as a reinforcement phase to use its in-plane tensile strength. In the vertical plane direction, due to the weak inter-layer van der Waals force, low strength and poor conductivity. This characteristic makes it play a targeted advantage in different application scenarios.

Atomic Energy arrangements

The graphite carbon atoms are arranged according to a specific law, forming hexagons in the plane and stacking layers in space. This arrangement determines the crystal structure and physical and chemical properties. X-ray diffraction can determine the crystallinity and structural parameters according to the specific pattern presented by its ordered arrangement. And the stability of the atomic arrangement makes the graphite maintain stable performance in a certain temperature and pressure range. Such as graphite as a refractory material at high temperature can ensure the integrity of the structure, providing protection for the reliability of industrial applications.

Lattice and crystal structure of graphite

Lattice structure of graphite

Graphite has hexagonal lattice structure, a axis and b axis are equal length. And the Angle is 120 degrees, c axis is perpendicular to the carbon atom plane. Its length reflects the periodic arrangement of the layered structure, belongs to the hexagonal crystal system, with specific symmetry and crystallographic characteristics.

Graphite crystal structure

The graphite crystal consists of numerous hexagonal lattice units arranged in an orderly manner in space. And the internal carbon atoms are arranged in a highly ordered manner. And it defects and impurities will significantly change its performance, affecting electron and phonon transport, chemical reactions and material uniformity.

Three common defects in graphite structure

The defects in graphite structure have a great influence on its performance.

Point defects, such as vacancy and clearance atoms, will destroy atomic integrity and affect electron conduction and mechanical properties.

Linear defects such as dislocation affect plastic deformation and strength.

Surface defects, such as grain boundary, hinder the transmission of electrons and phonons, reduce the conductivity and thermal conductivity. And it easily leads to chemical reactions and impurity aggregation.

Graphite structure related concepts

Graphite Lewis structure

The Lewis structure of graphite shows the electron sharing between carbon atoms, and satisfies the eight-electron stable structure by forming covalent bonds with neighboring carbon atoms. The uninvolved electrons form delocalized π electron clouds. This provides the basis for understanding chemical bonding and electron distribution.

Graphite hybridization

The sp2 hybridization of graphite carbon atoms is the root of its unique structure and properties. This results in a planar structure, delocalized π-electron cloud, giving graphite a variety of excellent properties.

Graphite symbols and formulae

The chemical symbol of graphite is “C”. Although it is difficult to express the macromolecular structure with a simple molecular formula, but in the chemical calculation and reaction formula. “C” can represent the reaction of graphite, reflecting the transformation and conservation of carbon.

Graphite structure and bonding

The layered structure and surface properties of graphite are of great significance to its bonding properties. The interlayer van der Waals force is weak, so it is necessary to modify the graphite surface or select a suitable binder to enhance the interaction. The surface modification can introduce functional groups or coarsening treatment. And the polar groups of the binder can bind strongly with the carbon atoms on the graphite surface. In composite materials, good bonding performance is the key to guarantee the overall mechanical and functional properties. And poor bonding is easy to cause interfacial stress concentration, resulting in material failure.

Explain the Structure of Graphite and Other Materials Difference

Graphite Structure vs. Graphene Structure

Actually,  graphène represents a one-atom-thick layer of graphite. In every 1-mm thick sheet of graphite that there are about 3 million layers of graphene stacked on top of each other. Graphene can be regarded as one layer of graphite whereas graphite consists of several layers of graphene on top of each other.

Comparison of graphite and diamond structure

Structural differences

The carbon atoms of diamond adopt sp3 hybridization to form tetrahedral space structure, and the covalent bonds between atoms are very strong. Graphite is sp2 hybrid planar hexagonal and layered, with weak van der Waals forces between layers.

Performance differences

Structural differences result in distinct performance differences. Diamond hardness is very high, used in machining; Graphite soft texture, good lubricity, used as a lubricant and pencil lead. Graphite conducts electricity, diamond hardly. Diamond with high refractive index and transparency, used in jewelry; Graphite is black and opaque.

Types of graphite structure

Natural Graphite

It typically occurs in graphite schist, graphite gneiss, graphite-bearing schist, and metamorphic shale. According to crystal form, natural graphite may simultaneously be divided into two varieties: crystalline graphite-which is further divided into flake graphite and cryptocrystalline graphite, also known as earthy graphite.

Synthetic Graphite

Synthetic graphite is a kind of chemical product. Its major ingredient is carbon. It is obtained through high-temperature pyrolysis and graphitization of organic polymers.

Special graphite structures such as expandable graphite and nanographite structures. Expandable graphite by special treatment, interlayer insert material, decomposition and expansion at high temperature, with good flame retardant, used for fireproof materials. Nano-graphite structures, such as nano-graphite sheets and nano-graphite fibers, have large specific surface area, high surface activity and excellent mechanical properties. And it has great potential in the fields of energy storage, catalyst carriers and high-performance composite materials.

Correlation between graphite structure and use

The unique structure of graphite determines its wide use. Good electrical conductivity makes it an electrode material, which is used in batteries and electrolytic cells. High temperature stability and chemical inertness make it a refractory for the steel industry. Lubricity enables it to act as a lubricant in machinery manufacturing. In the aerospace field, graphite composites are used in the manufacture of aircraft and rocket components due to their low density, high strength and thermal stability. In addition, graphite also plays an important role in pencil manufacturing, graphene preparation and other fields. And each application is closely linked to the graphite structure.

Conclusion

The structure of graphite shows its uniqueness and complexity from multiple dimensions, which profoundly affects the performance and application. The in-depth research and understanding of graphite structure opens up broad prospects for its innovative application in many fields such as materials science and energy. And this helps to overcome the material and energy problems in modern society.