Graphite is a mineral that the average human being interacts with on a daily, to say the least. This silvery-black material is renowned for its use in pencils and technological devices like mobile phones.
But are you aware of the many distinct types of graphite available today?
Below, we traverse the world of graphite, dissecting its different types and their roles in shaping the modern world.
Types of Graphite Based on the Manufacturing Process
Despite all graphite having a dark, glossy aesthetic, it comes in distinct forms. How it is formed tremendously impacts its attributes and this gives rise to two main categories of graphite. They are;
Types of Natural Graphite
Natural graphite is defined by its soft and shiny appearance, proving its unique source. It is sourced from metamorphic rocks and its carbon atoms are aligned in a hexagonal lattice.
This organic type of graphite does not burn easily and is exceptional at conducting both heat and electricity. It is mined in distinct forms differentiated by composition and crystal structure. They include;
1. Crystalline Graphite
This natural graphite type is renowned for its high degree of crystallinity, which ultimately endows it with impeccable lubricity, electrical conductivity, and thermal resistance. It is also characterized by a hexagonal crystal structure with multiple layers loosely interlinked. Crystalline graphite thrives in lubricating components thanks to its comparatively low friction coefficient.
Its typical carbon concentration starts at 85% and is capped at 99%. A higher carbon content translates into better heat resistance and chemical resistance. Its formation is a result of the reaction carbon undergoes over millions of years under heat and pressure. It is primarily utilized as the anode material in Lithium-ion batteries and some of its other applications include;
- Lubricants
- Refractories
- Expandable graphite
- Steelmaking
- Pigments and fillers
2. Flake Graphite
This is a soft and thin type of natural graphite renowned for its high carbon composition which ranges between 85% and 98%. It boasts comparatively high crystallinity meaning it is impeccable at conducting heat and electricity.
Flake graphite is often sourced from marble and gneiss among other forms of metamorphic rocks. It is commonly sourced from underground mines or open-pit mines. Its unique properties have seen it become a household material in batteries and specialized lubricants.
3. Vein Graphite
This is arguably the most advanced and sophisticated form of natural graphite revered for its superior carbon purity at 90%-99%. It boasts of a highly crystalline structure, which is impeccably aligned making it highly conductive and chemical resistant.
Vein graphite commands a comparatively higher price, which is a testament to its quality and appeal. It is however quite rare and can only be sourced from metamorphic rock fissures.
Mining it is relatively more demanding further explaining its comparatively higher price points. It is commonly exploited in electric arc furnaces and nuclear reactors thanks to its high crystallinity.
4. Amorphous Graphite
Despite having a comparatively more granular and finer appearance, amorphous graphite ranks last when it comes to the crystallinity of natural graphite. You can tell apart amorphous graphite by its relatively black or dark gray color, which gives it a non-metallic feel. Its carbon content is comparatively lower ranging between 70%-85%.
Amorphous graphite is commonly found in coal beds and seams. You can extract it using either strip mining or surface mining. It is competent at conducting electricity although its conductivity is comparatively lower. It is primarily used to make pencils, carbon brushes, refractory coatings, and steelmaking.
5. Expanded Graphite
Although this is a category of natural graphite, it exhibits key differences in its properties due to the special treatment it is taken through. Expanded graphite is characteristically porous and it exhibits all the key attributes of natural graphite. It is simply flaked graphite reinforced with elements such as heat to fine-tune some of its key attributes.
Expanded graphite is often generated by heating intercalated graphite flakes at temperatures in the range of 800°C to 1000°C. This consequently leads to the enlargement of these flakes 100-300 times. This reinforcement makes it highly beneficial in the manufacturing of gaskets, flame retardants, and batteries among others.
Types of Synthetic Graphite
Even though the vast grades of natural graphite available come endowed with impressive attributes, you might find yourself in need of a high-tech and unique grade.
Synthetic graphite promises to address all your advanced graphite demands. It comes in a myriad of forms including;
1. Isostatic Graphite
Produced through isostatic pressing, this grade of synthetic graphite shines where other grades struggle. Its production began in the 1960s and it boasts of ultra-fine grains making it denser and more robust.
It is highly utilized in industries spanning from aerospace to electrical applications due to its impressive properties. Isostatic graphiterepresents a plausible solution for anyone looking for the following properties;
- Excellent chemical resistance
- High thermal resistance
- Easy machinability
- Excellent electrical conductivity
- Excellent thermal conductivity
- Purity of up to 5 ppm
2. Extruded Graphite
This graphite type is often available in the form of long tubes and rods. It is often produced in bulk making it comparatively economical. Extruded graphite demonstrates a modest level of density and strength making it ideal for manufacturing casting molds.
To produce extruded graphite, you are simply required to mix your raw materials thoroughly before injecting your mixture into an extrusion die for shaping.
Consequently, bake the mixture using extremely high heat until the binder carbonizes. The impressive thermal conductivity of this graphite means that you can exploit it to produce high-quality foundry components. It also means that you can utilize it to produce heat exchangers.
3. Vibrated Graphite
This is a low-density version of synthetic graphite and it is characterized by uniformly aligned graphite particles. It is typically exploited to produce comparatively large components with less quality demands. Its production is centered on the vibration compression process, which simply mixes graphite powder and a specific binder in a mold.
Vibrated graphite comes with a grain size that is approximately larger than that of isostatic graphite. In the aerospace industry, vibrated graphite plays a key role in the production of brake linings, and rocket nozzles.
It also comes in handy in the automotive industry where it is exploited to produce engine components and seals. Vibrated graphite comes with the following traits:
- Thermally conductive
- Electrically conductive
- Bending resistant
- Chemically resistant
- High thermal resistance
- Superior thermal shock resistance
4. Molded Graphite
Typically manufactured from pitch coke and coal tar, molded graphite comes with an array of breathtaking attributes including; robustness, high density, and a consistent grain structure. The molded mixture is then subjected to temperatures in the range of 1000-3000 °C leading to carbonization.
Furthermore, the molded graphite is formed after the carbonized material is further heated at temperatures close to 3000 °C.
Molded graphite is broadly used in the production of electrodes due to its remarkable thermal stability and conductivity. It is also mainly exploited to manufacture piping and linings used in corrosive settings. If you are looking for either of the following attributes, consider using molded graphite;
- Low friction
- Excellent temperature resistance
- Porosity
- Lightweight
- Dimensional stability
- Electrical conductivity
- Thermal conductivity
Classification Depending on the Form Graphite Exists
Are you aware that one of the key ingredients in your batteries, pencils, or car is graphite? Well, graphite comes in varying forms thus ensuring that all your demands are adequately met. Some of these essential forms include;
1. Pyrolytic Graphite
This type of graphite exists in the form of slender, crystalline layers formed as a result of the decomposition of hydrocarbon gases. For this decomposition to occur, temperatures of 2200-3000°C are mandatory. Pyrolytic graphite boasts one of the best thermal conductivities. Which often surpasses 1000 W/m·K.
It exhibits anisotropic properties making it indispensable in high-temperature furnaces, nuclear reactors, and other heat management applications. Pyrolytic graphite often tramps natural graphite when it comes to electrical and thermal conductivity. Its broad array of beneficial properties include;
- Strong lubricating capabilities
- Low thermal expansion coefficient
- Strong anisotropic properties
- High purity
- Strong thermal conductivity
- Resistance to radiation
2. Graphite Block
This is simply compressed graphite powder and it is renowned for its high density, which endows it with a relatively superior thermal conductivity. To produce graphite blocks, simply dispense powdered graphite into a mold then apply pressure evenly.
This isostatic pressing gives birth to extremely dense blocks of graphite characterized by a uniform structure and impressive electrical conductivity.
The graphite powder used can be synthetic or natural meaning that your blocks can either be man-made or organic. Graphite blocks are highly sought after as key ingredients in the manufacturing of;
- Heating elements
- Foundaries
- Heat exchangers
- Nuclear reactors
- Crucibles
- Molds and dies
3. Compacted Graphite Iron
This graphite type exists in the form of nodules, which demonstrate stronger properties compared to cast iron. Its production involves the addition of precise amounts of nucleating agents such as magnesium and cerium.
It comes with an extremely high tensile strength at approximately 75% while its fatigue strength can be twice as high as that of cast iron.
The lightweight nature of CGI, coupled with its impressive thermal capabilities has prompted its extensive use in the production of high-quality engine blocks. Its strength is also heavily exploited to construct structural components of heavy-duty machinery like marine engines and powertrain components. It boasts of;
- A higher density.
- High strength.
- Excellent castability.
- A graphite structure.
- Damping capacity.
- Excellent thermal conductivity.
4. Graphite Sheets
These slender graphite panels are primarily designed to undertake thermal management in a range of distinct industries. They boast exceptional thermal conductivity at approximately 100 to 350 W/m-K, meaning you can utilize them as heat spreaders. However, certain grades of these sheets can achieve thermal conductivities of up to 1500 W/m-K.
Graphite sheets can be products of both synthetic and organic graphite. Their unique attributes have prompted their extensive use in high-power applications such as LED lighting and electrical insulation. They have essentially replaced traditional thermal interface components.
5. Graphite Rods
These graphite components feature a straightforward construction and they boast stability and resistance to wear, high temperatures, and thermal shock. They have a compressive strength range of approximately 11,000 to 38,000 psi making them ideal for manufacturing electronics, battery electrodes, and nuclear reactors. They are available in distinct forms including;
- Fine-grained graphite rods.
- Superfine graphite rods.
- Higher density graphited rods.
- Medium-grained graphite rods.
- Coarse-grained graphite rods.
6. Graphite Tubes
These hollow and spherical components are known and revered for their chemical inertness and exceptional thermal conductivity. This is mainly a consequence of their parent material (graphite), which possesses a myriad of impressive traits including electrical conductivity and electrical stability.
This has greatly ballooned the demand for graphite tubes in demanding applications and industries including chemical processing and thermocouple protection. They come in distinct varieties including;
- Resin graphite tubes.
- Pyrolytic graphite tubes.
- Carbon-bonded tubes.
- Fully graphitized tubes.
7. Graphite Powder
For decades graphite powder has thrived as a dry lubricant since it possesses all the primary attributes of conventional or solid graphite. This finely ground form of graphite is primarily formed by crushing naturally solid graphite into fine particles. Alternatively, it is manufactured using synthetic processes.
In addition to being a highly effective lubricant, powdered graphite is also prominently exploited in the manufacturing of lithium-ion batteries due to its impeccable electrical conductivity. It is also commonly injected into paints and coatings especially when the intention is to prevent friction and corrosion.
8. Nano Graphite Powder
Imagine the particle size of regular powdered graphite. It is extremely small. Then, imagine how small nano powdered graphite is. It features particles measuring approximately 10-100 nanometers and this gives this form of graphite an unmatched surface area.
This ultimately translates into impeccable conductivity both thermally and electrically.
The use of nano graphite powder transcends energy storage where it acts as the primary material for the anode and the world of lubrication where it thrives as a dry lubricant. It boasts of unique features such as;
- Enhanced mechanical features.
- Relatively higher surface area.
- Great lubrication.
- Chemical stability.
- Great electrical conductivity.
9. Graphite Paste
This graphite emulsion is a semi-liquefied version of graphite powder featuring a solvent and binding agent.
Due to its pasty feel, graphite paste reigns supreme in minimizing friction hence it finds extreme usage as a lubricant. Its strong thermal properties mean that you can exploit it to lubricate machines or components in high-heat environments including gears and bearings.
Using graphite emulsions will significantly shrink your lubrication budget since it offers long-lasting lubrication. It will also safeguard your valuable machinery and components against rusting or corrosion. You must however be wary that its use in certain applications may be limited. For instance, you cannot utilize it where a less viscous lubricant is needed.
10. Flexible Graphite
More commonly known as graphite foil, this graphite form is sourced from processed organic graphite. It exists as a porous sheet equipped with the unique property of expandability. To generate flexible graphite, simply treat graphite flakes using specified acids and heating parameters.
It is essentially known for its role in the production of sealing materials particularly gaskets. Flexible graphite conforms easily making it essential when sealing irregularly shaped surfaces. Unmounting flexible graphite seals is essentially just as simple as mounting them. Its prominence in multiple industries is down to its notable attributes including;
- Chemically compatible with most chemicals.
- Thermal conductivity.
- Electrical conductivity.
- Conformable nature.
- Heat resistance.
- Low creep relaxation.
Types of Graphite Based on Application
Given the exceptional qualities harbored by graphite, it is no surprise that this material is one of the world’s most prominently exploited raw materials. For ages, graphite has spearheaded the production of pencil leads.
However, as the years have gone by, its demand has grown exponentially resulting in its exploitation in battery production and other demanding components. With a little customization graphite can be tailored to fulfill just about any of your demands.
1. Nuclear Graphite
Graphite, especially synthetic graphite demonstrates an unrivaled degree of purity and resistance to heat and radiation, making it perfect for use in nuclear reactors.
It is primarily customized to act as the nuclear reactor’s moderator serving pivotal roles including sustaining nuclear fission. This is a consequence of the deceleration of the reactor’s neutrons. Nuclear graphite is also pivotal in the construction of:
- Fuel matrix: The strength of nuclear graphite encourages its use in the production of fuel matrix, whose role is to provide structural support and enclose the reactor’s nuclear fuel.
- Reflectors: Its low neutron absorption rate also translates into better reflection of neutrons, which ultimately helps sustain the chain reaction.
- Control Rod: The control rod is tasked with regulating the reactor’s reaction and nuclear graphite ensures this is achieved by absorbing neutrons.
2. Electrode Graphite
Graphite naturally transmits electricity. Topping up this rare feature with its high purity levels, superior thermal resistance, and structural integrity makes it one of the best materials for manufacturing graphite electrodes.
This type of specialized graphite works best with fuel cells and lithium-ion batteries among others.
Although natural graphite is used to manufacture electrodes, synthetic graphite is the more advantageous option thanks to its higher purity levels. The resulting electrodes find extensive use in;
- Electric arc furnaces
- Submerged arc furnaces
- Aluminum production
- Steelmaking
- Metallurgical processes like titanium production
3. Crucible Graphite
Graphite crucibles are indispensable laboratory equipment. However, they are equally significant in jewelry making, metallurgy, and other high-heat applications.
Graphite is naturally capable of enduring high temperatures for prolonged periods and it can also conduct thermal heat making it the perfect material for manufacturing crucibles.
Crucible graphite possesses all the primary attributes of conventional graphite but with certain modifications or reinforcements to improve its thermal capabilities. This graphite form boasts superior corrosion resistance making it perfect for crucibles and stoppers designed to handle corrosive elements.
4. Battery Graphite
Batteries, be it the typical lithium-ion batteries or flow batteries depend on a highly conductive anode and graphite demonstrates a superior degree of electrical and thermal conductivity. Battery graphite is tailored to feature smaller particles and is further purified to avert side reactions.
It boasts of a layered structure, which permits the efficient preservation of energy. Battery graphite is also comparatively more stable and this ensures that the batteries you produce have a longer lifespan and can endure more charge and discharge cycles. It is primarily used in;
- Electric vehicle batteries.
- Lithium-ion batteries.
- Consumer electronics.
- Lead acid batteries.
5. Exchanger Graphite
Heat exchangers operate under the most extreme conditions hence the need for a robust and resilient material like graphite.
However, conventional graphite, despite its numerous impressive attributes needs reinforcement to prosper under these conditions. Exchanger graphite offers better thermal conductivity, is more heat resistant, and boasts superior corrosion resistance.
This specialized type of graphite is primarily made from isostatic and flexible graphite as well as graphene. It is also significantly lighter than metals, which are the only other alternative you have. With exchanger graphite, you can produce;
- Pharmaceutical heat exchangers.
- Chemical processing heat exchangers.
- Oil and gas heat exchangers.
- Nuclear reactors heat exchangers.
6. Brushes Graphite
Reinforced with an appropriate binder, this specialized type of graphite thrives in providing contact between immobile and moving electrical components. It retains the electrical conductivity of typical graphite hence its broad utilization in contactors, motors, and generators. Brushes graphite is characterized by;
- Low friction properties
- Exceptional electrical conductivity
- Wear resistance
- High-temperature stability
- Excellent thermal stability
- Impressive chemical resistance
7. Graphite Heat Spreaders
Despite graphite possessing inherently high thermal conductivity, its use in heat spreaders necessitates further reinforcement. The specialized type of graphite deployed in heat spreaders boasts thermal conductivity as high as 1500 W/m·K, making it perfect for distributing heat from the primary hotspots.
In addition to this tremendously high degree of thermal conductivity, the graphite heat spreader is also significantly resistant to corrosion and extreme heat. This graphite type flourishes in;
- LED lighting.
- Consumer electronics.
- Power modules.
- High-performance computers.
8. Furnace Graphite
A high heat tolerance is the minimum requirement for any heating furnace. Graphite can operate under exceptionally high temperatures but this type of graphite is capable of continually enduring extreme heat (3000°C).
It also demonstrates a high level of chemical inertness hence you can exploit it to produce chemical vapor deposition furnaces.
Furnace graphite hardly cracks even when subjected to continuously high heat. This is a testament to graphite’s low coefficient for thermal expansion. Furnaces made from this type of graphite will most likely endure rapid fluctuations in temperature. This type of graphite is ideal for;
- Sintering furnaces
- Induction furnaces
- Electric arc furnaces
- Steel Making
- Vacuum furnaces
9. Refractory Graphite
The refractory industry has benefited massively from graphite, particularly refractory graphite, which has been refined to exhibit superior oxidation resistance.
Refractory graphite is presently utilized to produce a broad range of refractories capable of surviving prolonged exposure to harsh conditions like extreme heat.
A good example is its use in the linings of furnaces used to produce magnesite bricks. Refractory graphite is primarily made from flake graphite thus it still exhibits the high temperature stability of flake graphite. Its most prominent applications include;
- Graphite crucibles
- Refractory mortars
- Furnace linings
- Steelmaking
- Graphite insulation
10. Graphite for Aerospace Industry
Components deployed in aircraft and other aerospace machinery must demonstrate robustness and great thermal stability while maintaining a lightweight. Finding a singular material offering a balance between these properties can be quite daunting. However, graphite possesses all these attributes in plenty hence it has become a staple in the aerospace industry.
But for regular graphite to qualify as a competent material for the manufacturing of aerospace components, it must be accorded further treatment. Graphite for the aerospace industry must bear the following qualities;
- High-temperature resistance (up to 3000°C)
- Lightweight
- Corrosion resistance
- Thermal stability
- Low density
- High mechanical strength
- Superior thermal shock resistance
11. Fireproofing Graphite
This special type of graphite prospers in the production of coatings meant to safeguard essential components and machinery from heat and fire flames. Fireproofing graphite has a very robust structural integrity, which remains intact even when exposed to temperatures exceeding 3000°C, particularly in an inert atmosphere.
This specialized graphite is subjected to treatment, which leaves it reinforced with fire-retardant chemicals like borates and silicates. You may elevate its fireproofing capabilities through;
- Intumescent Coating: This involves encapsulating raw graphite with an intumescent coating, which ultimately forms a fire barrier upon expansion when exposed to fire.
- Composite formation: This involves mixing graphite with inorganic fillers or other fire-resistant materials, consequently generating composites that are virtually flame-resistant.
Fireproofing graphite comes with a myriad of rewards, hence it has found usage in the aerospace industry, nuclear reactors, building, and construction. In addition to being non-flammable, this remarkable material exhibits the following traits;
- Low thermal expansion.
- Chemical stability.
- Superior thermal resistance.
- Smoke suppression.
- Non-flammability.
FAQs
In What Form Does Graphite Occur Naturally?
Organic or unprocessed graphite is primarily sourced from metamorphic or igneous rocks and its formation can take millions of years. It is found in multiple parts of the world and you can find it in the following forms;
- Vein Graphite: This form of natural graphite exists in the form of lumps, which resemble veins hence the name vein graphite. It is extremely rare and its formation is a consequence of magmatic activities.
- Amorphous Graphite: From a glance, you can tell that it is a dark gray powder made up of fine-grained particles. It takes millions of years to form since it is dependent on the transformation of coal under certain pressure and temperature parameters.
- Flake Graphite: This scaly form of natural graphite is not as rare as vein graphite nor is it as common as amorphous graphite. It has a flaky feel and texture explaining the extremely high pressure and temperatures involved in its formation.
Are there Different Grades of Graphite?
Yes. Graphite, whether synthetic or natural is made up of small particles and the size of these particles determines your graphite’s grade. Common grades include;
- Fine-grain graphite.
- Medium grain graphite.
- Coarse grain graphite.
- Ultrafine grain graphite.
What is the Most Common Form of Graphite?
Present in numerous geological settings spread out across the globe, amorphous graphite is the most prominent graphite form or type. Its bulky presence in countries like China, Brazil, and North America, makes it one of the most easily accessible types of graphite. In addition to being readily accessible, amorphous graphite also possesses a myriad of formidable traits including;
- High surface area.
- Great mechanical strength.
- High conductivity.
- Great thermal stability.
Conclusion
You can tell from the immense number of industries and applications reliant on graphite, that it exists in different forms and comes in distinct types. The type of graphite that works perfectly in pencils is not the type of graphite needed to manufacture aerospace components.
With this understanding, you can now find the right category of graphite for your respective factory.
