About Pyrolytic Graphite

Pyrolytic graphite is a polycrystalline graphite that is made of the decomposition of a hydrocarbon gas. This man-made compound looks similar to 흑연. However, it has numerous unique properties. As a result, individuals use it in various industries for diverse applications. This post provides you with complete knowledge about pyrolytic graphite, its characteristics, and applications. Let us start.

The Overview of Pyrolytic Graphite Compound

Pyrolytic graphite is a form of graphite produced by the decomposition of a hydrocarbon gas.

When the temperature of hydrocarbon gas reaches the stage of decomposition in a vacuum atmosphere, it forms highly oriented graphite layers.

What makes it different from ordinary graphite is its crystalline structure. Unlike natural graphite, it has organized carbon atoms. Moreover, it is extremely anisotropic.

Let us learn about the characteristics of it.

Characteristics/Properties of Pyrolytic Graphite

Pyrolytic graphite features a diverse range of characteristics. Due to the following properties, this graphite has applications in numerous industries.

High Thermal Conductivity

Pyrolytic graphite is renowned for its high in-plane thermal conductivity, thanks to its strong covalent bonding.

At room temperature, it can reach up to 2000 W/m-K. This quality makes this material ideal for products like heat spreaders and heat sinks.

High Electrical Conductivity

Pyrolytic graphite is anisotropic, featuring a layered structure. As a result, it supports an excellent flow of electricity. The electrons of this graphite move easily along the bonded carbon atoms.

High-Temperature Resistant

Pyrolytic graphite can endure extremely high temperatures. It is a thermodynamically stable carbon. As a result, it retains its chemical structure at high temperatures. The compound works fine even at 3500°C temperature in a non-oxidizing atmosphere.

Chemical Stability

Pyrolytic graphite is chemically inert. It does not react to most acids, alkalis, and solvents at room temperature. It can resist a wide range of chemical attacks. As a result, nuclear engineers use it in nuclear reactors.

기계적 강도

While pyrolytic graphite is light in weight, it has decent mechanical strength. Its in-plane tensile strength ranges between 20 to 40 MPa.

Coefficient of Friction

Pyrolytic Graphite has a negligible coefficient of friction, particularly in unlubricated conditions. Consequently, individuals employ it in applications where reduced friction is crucial.

You can notice its use in sealing, bearings, and various sliding components.

How Is Pyrolytic Graphite Made?

Pyrolytic graphite is made through a chemical vapor deposition process. Engineers deposit carbon atoms onto a substrate at extreme temperatures in thin layers.

Let us learn the complete process step-by-step.

Hydrocarbon Source Selection

First, manufacturers select a carbon-containing gas for making pyrolytic graphite. This gas can be methane, acetylene, and propane. It works as a carbon source to create graphite structures.

Formation of the Substrate

Once the gas is chosen, it is time to find a suitable substrate. Generally, manufacturers prefer graphite for substrate. After all, it can endure high temperatures. The substrate lets carbon atoms settle in a graphitic structure.

CVD (Chemical Vapor Deposition) Process

The hydrocarbon gas is released into a furnace. The temperature of the furnace ranges between 200 and 300°C.

This extreme temperature decomposes the gas into carbon and hydrogen components. The hydrogen is released as a waste product, while carbon atoms accumulate on the substrate surface.

Deposition

The deposition of carbon atoms happens in a thin layer because of controlled pressure. These carbon atom layers create an ordered structure of pyrolytic graphite.

Since the atoms are well-aligned in layers, pyrolytic graphite becomes anisotropic.

Cooling

Layer-by-layer deposition of carbon atoms is followed by a cooling process.

Now manufacturers can extract the graphite from the furnace to give it a desired shape

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The entire making process undergoes strict quality control. It ensures that the pyrolytic graphite has needed electrical and thermal properties.

Applications 

Nuclear Reactors

Power generation and nuclear energy companies worldwide use pyrolytic graphite as a moderator material in nuclear reactor designs.

The AGR and MAGNOX gas-cooled reactors of the United Kingdom are a perfect example of it.

As pyrolytic graphite is an anisotropic carbon form, it is used in HTGRs (High-Temperature Gas-Cooled Reactors) and fast reactors. The graphite’s resistance against thermal shock and chemicals makes it suitable for the nuclear industry.

As a moderator, the graphite slows down neutrons during fission reactions, helping the reactor to operate perfectly.

Nuclear engineers also use pyrolytic graphite to make structural material. It coats nuclear fuel particles.

In gas-cooled reactors, fuel gets encapsulated in tristructural-isotropic particles. The coating of this graphite protects the fuel.

It also acts as a barrier and protects reactors against radioactive materials. This graphite does not lose its structural integrity even in temperatures exceeding 1,000°C.

Batteries

Battery manufacturers use pyrolytic graphite in multiple ways. It has a great role in modern battery technologies. 

Lithium-ion batteries also employ this graphite due to its excellent electrical conductivity and thermal stability.

These batteries use this graphite as a host for lithium ions while charging and discharging cycles.

Moreover, manufacturers use this graphite as a negative electrode in rechargeable lithium batteries.

The layered structure of pyrolytic graphite lets lithium ions intercalate between its layers. As a result, it creates a reversible mechanism for energy storage.

Unlike other anode materials, this graphite form can endure high temperatures and chemical reactions. It helps the battery to function in extreme conditions. Such batteries are common in EVs and aerospace.

Fuel Cell Technology

It has been playing a crucial role in fuel cell technology. Pyrolytic graphite sheets are one good example of it.

These sheets in the fuel cell maintain temperature and dissipate waste heat. Solid oxide fuel cells with high temperatures depend on this graphite to manage heat.

Graphene Transistors

A graphene transistor is a nanoscale device used in wireless communication devices, electronic textiles, radar systems, and foldable smartphones.

The transistor uses graphene as the semiconducting material. Pyrolytic graphite plays an important role in making graphene. It serves as a precursor material for graphene production.

The graphite also ensures efficient heat management in graphene transistors.

Rocket Nozzle

Rocket scientists use pyrolytic graphite in rocket nozzles because of its excellent structural integrity and thermal properties.

The pyrolytic graphite-coated throat and chambers of the rocket can withstand temperatures exceeding 3,000°C. Furthermore, this graphite does not erode by hot gasses expelled from the nozzle.

Air Force Rocket Propulsion Laboratory also used pyrolytic graphite-coated throat inserts in their rocket in 1974.

Medical Diagnostic Tools

You can also notice the use of pyrolytic graphite in numerous diagnostic equipment.

It minimizes the field of inhomogeneities in MRI machines. Therefore, it naturally improves the clarity and detail of magnetic fields.

Due to its biocompatibility, the graphite compound is also used in pacemaker components.

Pyrolytic graphite does not react with body tissues and fluids. Consequently, you do not need to worry about complications.

Electrochemical sensors help to check cholesterol and glucose. Did you know, these sensors also use pyrolytic graphite?

This graphite form features a highly conductive surface. Therefore, it ensures proficient electron transfer and gives reliable reading every time.

Additionally, its corrosion-resistant capability helps electrochemical sensors to sustain different biological environments.

Electrochemical

Outstanding chemical stability and electrical conductivity make pyrolytic graphite suitable for various electrochemical applications. It serves as electrode material in various electrochemical cells, such as capacitors and batteries.

This graphite supports the quick transfer of electrons between the electrode and the analyte. As a result, it helps in the detection of neurotransmitters.

X-ray Tubes

An X-ray tube has uses in industrial inspection and medical imaging. These tubes utilize pyrolytic graphite as the target anode backing material. The anode aims to turn the kinetic energy of accelerated electrons into X-rays.

During this process, the anode might overheat. Thankfully, the high thermal conductivity of pyrolytic graphite disperses the heat generated during X-ray production. Therefore, it increases the lifespan of the tube.

Laser Light

Several companies have been using pyrolytic graphite in laser light systems. This compound features distinctive optical and thermal properties allowing it to endure the intense laser beam.

In 2012, a research group in Japan demonstrated that pyrolytic graphite responds to laser light. They also investigated that the compound responds to natural sunlight by moving in the direction of the field gradient.

Laser beam dumps employ this graphite to absorb laser energy and dispel heat rapidly. The device is used to absorb excessive energy from laser beams.

Laser engraving systems also use pyrolytic graphite as a substrate. Since this graphite is resistant to laser ablation, it ensures precise laser marking and cutting.

In addition to this, you can also notice the use of pyrolytic graphite mirrors in powerful laser setups. These mirrors reflect laser beams without getting affected by high temperatures.

결론

This is an in-depth guide on pyrolytic graphite. Considering everything together, we can say that this graphite form is a versatile material. Its anisotropic electrical properties, thermal conductivity, and high-temperature resistance make it ideal for a wide range of applications. 

Different industries have been using it differently. In upcoming years, we may see its usage in various other modern technologies and innovations

We hope this comprehensive guide provides you with adequate information on pyrolytic graphite.