Graphite is a crystalline allotrope of carbon, composed solely of carbon atoms arranged in planar, hexagonal rings. Each layer is often referred to as a sheet of graphene. Within these layers, carbon atoms are strongly bonded, but the layers themselves are held by much weaker Van der Waals forces. This layered lattice gives graphite a combination of properties: it is an excellent electrical conductor due to its delocalized electrons, yet it is soft and slippery, and it maintains stability at extremely high temperatures.
Applications in Energy Storage and Electronics
Graphite’s electrical conductivity and layered structure make it the material of choice for the anode, or negative electrode, in nearly all commercial lithium-ion batteries. During charging, lithium ions travel from the cathode and intercalate between the hexagonal sheets of the graphite anode. This reversible process allows the battery to store and release energy efficiently, contributing to the long cycle life of lithium-ion cells.
The material used can be either natural graphite, which is mined and purified, or synthetic graphite, produced from petroleum coke and coal tar pitch. Graphite often accounts for 10% to 20% of a battery cell’s total weight. Beyond batteries, its high electrical conductivity is exploited in large-scale industrial processes, particularly in the manufacture of electrodes for electric arc furnaces and for use in electrolysis. These applications leverage graphite’s ability to conduct intense electrical current while resisting the high temperatures generated by the processes.
High-Temperature Industrial Applications
The ability of graphite to withstand extreme heat without melting or deforming is utilized in various refractory and metallurgical processes. Graphite has an exceptionally high melting point, reaching around 3,600°C. This property is central to its use in manufacturing crucibles, which are specialized containers for melting and alloying precious metals like gold, silver, and aluminum.
These crucibles and molds are highly valued in foundries because graphite exhibits excellent thermal shock resistance, remaining structurally stable even when subjected to rapid heating and cooling cycles. Furthermore, graphite is chemically inert, meaning it does not react with the molten metals it contains, which helps ensure the purity of the cast product. Graphite is also incorporated into refractory materials, such as bricks and linings for blast furnaces and kilns, where it provides structural integrity and insulation under continuous high-temperature operation.
Friction Reduction and Writing Tools
Graphite’s softness and layered structure allow its sheets to slide past one another easily, giving it a low coefficient of friction that is harnessed for lubrication. It functions as a dry lubricant, often powdered, in industrial settings where liquid oils would fail, such as in high-temperature or dusty environments.
In a more common application, graphite is the primary component in “pencil lead,” which is actually a mixture of graphite powder and clay binder. Varying the ratio of graphite to clay allows manufacturers to control the hardness and blackness of the mark left on paper. The material is also included in friction materials, such as automotive brake pads and clutch facings, where its flakes help to stabilize the friction coefficient, reduce noise, and efficiently dissipate the intense heat generated during braking.
Specialized Structural and Chemical Uses
In the nuclear energy sector, graphite is employed as a neutron moderator in certain types of reactors, such as High-Temperature Gas-Cooled Reactors. Its function is to slow down the fast neutrons released during nuclear fission to a thermal energy level, which increases the probability of sustaining a nuclear chain reaction. Graphite is particularly effective because it has a low probability of absorbing these neutrons, ensuring they remain available to split other atoms.
In metallurgy, graphite is widely used as a recarburizer, a high-carbon additive introduced to molten steel or iron to precisely adjust the final carbon content. High-purity graphite recarburizers are favored because they dissolve quickly into the molten metal and introduce minimal impurities, such as sulfur or nitrogen. Furthermore, graphite is processed into graphite fibers, which are then combined with resins to create advanced composites known for their high stiffness and exceptional strength-to-weight ratio, commonly used in aerospace structures.