Graphite is a crystalline form of carbon. It has a layered structure that consists of rings of six carbon atoms arranged in widely spaced horizontal sheets. Graphite crystallizes in the hexagonal system, in contrast to diamond, another form of carbon, which crystallizes in the tetrahedral system. Graphite is dark gray to black, opaque, and very soft (with a Mohs scale hardness of 1.5)

In this article, we will read in detail about Graphite, its structure, occurrence, properties, and uses.

What is Graphite

Graphite is a form of carbon that has a hexagonal structure. It is crystalline allotrope of carbon. It is formed when carbon is subjected to the intense heat and pressure of the earth crust and upper mantle. The most common use of graphite is in pencil with which we draw and write. The lead filling is a mixture of graphite and clay. It is also a common ingredient in the lubricant. Graphite has the same chemical composition as a diamond, which is also a pure carbon. It is the different molecular structure that gives each they are almost opposite characteristics. The countries that produces graphite include China, India Brazil, North Korea and Canada.

Structure of Graphite

• This crystal carbon has a structure that is planar and layered. Each layer of the graphite is termed as Graphene
• Every layer has atoms of carbon arranged in a honeycomb-like network with the division of 0.142 nm with 0.335 nm distance between planes.
• There is a covalent bonding for atoms in the plane bonding with the three neighboring atoms while one atom out of four remain free.
• This free fourth electron is able to move and provide conducting ability and slippery texture to Graphite
• The layers of the carbon crystal move past each other and are held together by weak van der Waals bonds.

Crystal Structure of Graphite

Graphite has a hexagonal crystal structure. The details of the crystal structure of graphite is discussed below:

Hexagonal Lattice: Graphite is made up of the carbon atoms arranged in the carbon hexagonal structure. Each carbon atom bonds with three neighboring carbon atoms with a strong covalent bond, which creates a single, two-dimensional sheet.

Sp2 Hybridization: Carbon atoms from each layer bind with three adjacent carbons using a sigma (σ) bond in a sp2 hybridization. This hybridization causes a planar structure with three substituted atoms in trigonal planar geometry around each carbon atom.

Weak Van der Waals Forces: One of the forces that hold the graphite crystal together is the weak van der Waals force, which lies between the layers of the hexagonal lattice.

π-Electron Delocalization: The pi (π) electrons in the carbon-carbon double bonds is able to delocalize making the graphite electrically conductive.

Interlayer Spaces: Interlayer spaces refers to the gaps or spaces between these stacked layers of carbon atoms. The interlayer spacing in graphite is approximately 0.335 nanometers (nm).

Occurrence of Graphite

Graphite is a form of carbon that is found naturally in the world and is characterized by its uniquely crystalline structure. It is mostly often found in metamorphic rocks i.e. marble, schist and gneiss among others including igneous rocks such as granite. Graphite, commonly if pressure and/or temperature are high, occur within the Earth’s crust. It is frequently found along with the duo of minerals such as quartz, mica, and feldspar.

Significant graphite deposits can be found in various parts of the world, including:

• China: Graphite is one of the most extensively produced minerals worldwide and China holds vast resources in Heilongjiang’s, Inner Mongolia’s, and Shandong’s provinces respectively.
• India: India with its significant graphite deposits concentrated in the states of Jharkhand, Odisha, Tamil Nadu and Karnataka is the country that holds those.
• Brazil: Brazil is famous for graphite ores located in Minas Gerais and Bahia states.
• Canada: Canadian graphite reserves are located in two main provinces namely Quebec, Ontario.
• Madagascar: Madagascar produces some of the world-class graphite, together with deposits scattered in various areas of the country.
• Other countries: Russia, Mozambique, Norway, Sri Lanka and the states of the US have the gas deposits of graphite

Natural Sources of Graphite

Graphite is found in various natural sources. These natural sources of Graphite is discussed below:

Metamorphic Rocks: Graphite often occurs in metamorphic rock types where there are carbon-rich minerals that have been subjected to high temperatures and pressures due to their geologic setting. Schist and gneiss-type rocks usually have graphite hidden within them as the result of this type of metamorphism from “organic-rich” sediments.

Vein Deposits: Carbon-bearing liquid can be found in fissures and faults of rocks where it is gradually deposited in vein-type graphite. These veins are often present together with other minerals like quartz and mica, which are surrounded by walls of fractured rock.

Igneous Rocks: Some igneous rocks, especially those near intrusions, are known to contain graphite. In such cases, graphite is formed by the carbon-rich droplets that are released during the cooling of magma, and subsequently, the graphite crystals precipitate out.

Hydrothermal Deposits: With hydrothermal processes, hydrofluids rich in carbon can form the basis of graphite deposits. These fluids run through the earth’s crust, and as they get cooled down, the graphite gets precipitated. The hydrothermal deposits could be found alongside the other minerals.

Properties of Graphite

The properties of graphite can be studied under the following two headings:

• Physical Properties of Graphite
• Chemical Properties of Graphite

Let’s discuss these properties in detail

Physical Properties of Graphite

The physical properties of graphite are mentioned below:

• Luster: Graphite has a metallic luster, giving it a shiny appearance.
• Color: It’s generally black or dark argentine in color.
• Crystal Structure: Graphite has a hexagonal demitasse structure, conforming of layers of carbon tittles arranged in a honeycomb form.
• Softness: Graphite is soft and has a slippery in nature. This is due to its layered structure, which allows the layers to slide over each other fluently.
• Viscosity: The viscosity of graphite varies depending on its grade, but it’s generally around2.09 to2.23 grams per boxy centimeter.
• Electrical Conductivity: Graphite is an excellent conductor of electricity due to the delocalized electrons within its layers.
• Thermal Conductivity: It also exhibits high thermal conductivity, making it useful in operations where heat dispersion is important.

Chemical Properties of Graphite

The chemical properties of Graphite are mentioned below:

• Inertness: Graphite is chemically inert under normal conditions, meaning it doesn’t readily react with other substances.
• Oxidation Resistance: Graphite is largely resistant to oxidation, indeed at high temperatures. This is due to the defensive layer of carbon dioxide( CO₂) that forms on its face when exposed to oxygen.
• Response with Strong Oxidizing Agents: While graphite is resistant to utmost chemicals, it can react with strong oxidizing agents, such as concentrated nitric acid or hot concentrated sulfuric acid, especially at elevated temperatures.
• Interlayer Forces: Weak van der Waals forces hold the layers of graphite together.
• Carbon Content: Graphite consists nearly entirely of carbon, generally with further than 95 carbon content.
• Electrochemical Reactions: Graphite is frequently used as an electrode material due to its capability to conduct electricity and its stability in electrolytic results.
• Corrosion Resistance: Graphite exhibits excellent corrosion resistance in numerous surroundings, making it suitable for use in sharp chemical processes and as a material for lining holders and pipes.

Uses of Graphite

The applications of Graphite are mentioned below:

Refractories: The heat resistance and stability of graphite, which are essential properties for refractory uses, make it suitable as refractories. It is employed in the production refractory bricks, crucibles, and molds casting metals in the high-temperature environments like foundries and steelmaking while in service.

Lubricants: Graphite being soft and having less friction makes it great as not only a solid form but also powder form lubricant. It is widely used as a replacement of conventional lubricants in cases where the especially in high temperature environment or the presence of chemicals.

Pencil Cores: Graphite is most commonly used in pencil tip. It has two important characteristics, smoothness and brittleness, which are responsible for easy writing and sharpening.

Electrodes in Cells: The electrodes of graphite are applied in cells such as electrochemical cell and electrolytic cell.

Thermal Management: Graphite, with its high thermal conductivity, is useful for the efficient removal of heat in situations where the heat needs to be removed quickly such as in aircraft, heat sinks for electronic devices and as a thermal interface material.

Graphite vs. Diamond

Graphite and Diamond both are two crystalline form of carbon. A comparison between the two is tabulated below: