Learn About Graphite Thermal Conductivity

Graphite is a high-profile carbonaceous material in materials science, with unique properties that play a key role in multiple industries. Its thermal conductivity characteristics determine heat dissipation, thermal management and other applications. And it provides a solid support for the development of modern science and technology.

Graphite structure and thermal conductivity basis

Graphite crystal structure

The graphite has a typical layered crystal structure, and each layer is connected by covalent bonds between carbon atoms to form a planar network structure of regular hexagons. This in-plane covalent bond makes the binding force between carbon atoms very strong. And the atoms are tightly arranged and regular. The layers interact with each other through weaker van der Waals forces. This weak force makes it relatively easy to slide between layers. The strong covalent bond in the layer provides an efficient channel for heat conduction. While the van der Waals force between the layers hinders the heat conduction to a certain extent. So the thermal conductivity of graphite shows obvious anisotropy.

Basic concept of thermal conductivity

Thermal conductivity, expressed in W/(m·K), refers to the heat passing through a unit vertical area in a unit time at a unit temperature gradient. Its physical significance is to quantify the ability of a material to conduct heat. And the higher the thermal conductivity, the easier it is for the material to conduct heat. In practical applications, thermal conductivity is crucial to the selection and design of materials. Such as in heat dissipation systems, which require materials with high thermal conductivity to quickly transfer heat.

Characteristics of graphite thermal conductivity

Differences in thermal conductivity in different directions

In graphite, the thermal conductivity within the plane (within the plane layers of carbon atoms) is much higher than the thermal conductivity between the planes (between layers). At room temperature, the in-surface thermal conductivity can reach 1500-2000W /(m·K). While the inter-surface thermal conductivity is only 5-10W /(m·K). This is because the carbon atoms within the layer are connected by strong covalent bonds. And phonons (the energy quanta of lattice vibration) can propagate efficiently in this ordered structure, carrying heat quickly. However, depending on the weak van der Waals force between layers, phonons will have strong scattering across the layers. This greatly hinders the transfer of heat and makes the inter-surface thermal conductivity extremely low. This anisotropic thermal conductivity makes it necessary to fully consider its direction in the application of graphite. In order to play the best heat conduction properties.

Comparison of thermal conductivity with other materials

From the table comparison, it can be seen that the internal thermal conductivity of graphite is far higher than that of common metals such as aluminum and copper. And it is directly forced by diamond with very high thermal conductivity. Compared with stainless steel, it has significant advantages, even when compared with high-conductivity metal silver, it is not inferior. In the face of harsh heat dissipation requirements, its anisotropic characteristics can efficiently conduct heat in a specific direction. Making it a highly competitive material. In contrast, for materials with low thermal conductivity such as ceramics, rubber and plastics, graphite has full advantages. And it has great application potential in the fields of heat dissipation and thermal management.

Factors affecting the thermal conductivity of graphite

Crystal defect

Point defects (vacancies, interstitial atoms) and line defects (dislocations) in graphite significantly affect the thermal conductivity. Point defects destroy atomic arrangement, increase phonon scattering, hinder heat conduction, such as vacancy, phonon propagation energy loss. When dislocation density is high, phonon scattering intensifies and thermal conductivity decreases significantly. The defect concentration is negatively correlated with thermal conductivity.

Impurity content

Impurities affect the thermal conductivity of graphite. Common metallic (iron, nickel) and non-metallic (silicon, oxygen) impurities destroy the crystal structure and interfere with phonon propagation. Due to their atomic size and chemical properties are different from carbon atoms. Its interaction with carbon atoms causes lattice distortion, forms scattering center, shortens phonon mean free path, reduces thermal conductivity. And it controls impurities to optimize thermal conductivity.

Temperature change

The influence of temperature on the thermal conductivity is complex. At low temperature, the phonon energy and mean free path increase and the thermal conductivity increases with the increase of temperature. When the temperature is too high, the phonon-phonon interaction is enhanced, the scattering is intensified. The mean free path of phonons is reduced, and the thermal conductivity is decreased. The internal thermal conductivity decreases slowly at high temperature, and the interfacial thermal conductivity is more sensitive to temperature change.

Application of graphite thermal conductivity

Electronic chips

With the continuous improvement of chip integration, the heat generated by chips during operation increases sharply. Because of its high in-plane thermal conductivity, you can widely use graphite in heat dissipation solutions for chips. By adding graphite material between the chip and the heat dissipation device, the heat generated by the chip can be quickly transmitted out. This effectively reduces the chip temperature, improves the performance and stability of the chip. And it also extends the service life of the chip.

Graphite heat sink

Graphite heat sink is a typical application using the thermal conductivity characteristics of graphite. It is thin, bendable and highly thermally conductive. And you can customize it for different electronic device shapes to fit on the surface of the heating element. For example, in mobile devices such as smartphones and tablets, graphite heat sinks can rapidly spread the heat generated by heating components. Such as processors to the entire device housing. Achieving efficient heat dissipation and ensuring that the device will not suffer performance degradation or failure due to overheating during long-term use.

Lithium-ion batteries

In lithium-ion batteries, thermal management is critical. As an important component of battery electrode material, the thermal conductivity of graphite has an important effect on the performance and safety of battery. The graphite electrode with high thermal conductivity helps to evenly dissipate heat during battery charging and discharging. Avoiding local overheating that leads to battery capacity attenuation, shortened life and even safety problems. At the same time, in the design of the battery pack, the use of graphite-based thermal management materials can effectively improve the overall thermal stability of the battery pack. Then improve the charge and discharge efficiency and cycle life of the battery.

Graphite heat exchanger

Due to its excellent thermal conductivity and high chemical resistance, graphite heat exchangers are mainly used in industrial applications that require heating or cooling of highly corrosive fluids. They are often used in chemical processing, pharmaceuticals, and the production of chemicals such as chlorine, fluorides, and titanium dioxide. For example, highly corrosive chemicals such as acids, alkalis, and chlorides are handled in processes such as chlor-alkali electrolysis, petrochemical production, and chloroacetic acid manufacturing.

Aerospace Field

In the aerospace field, equipment needs to work in extreme environments, which requires extremely high thermal properties of materials. You can use graphite materials in the manufacture of thermal control systems for aerospace components. Because of its high specific strength, low density and excellent thermal conductivity. For example, you can use graphite composites in the satellite’s electronic equipment compartment. To conduct and dissipate the heat generated by the equipment. Ensuring that the equipment can operate normally in the high and low temperature environment of space. In addition, you can also use it to manufacture the leading edge of the wings of aircraft, engine components, graphite nozzle etc.. It ensures the normal operation of key components in high temperature environments and ensures flight safety.

Conclusions

The unique crystal structure of graphite makes its thermal conductivity anisotropic, which has obvious advantages over other materials. And you can widely use it in many fields. Optimizing performance by controlling influencing factors is expected to help more thermal management scenarios as research progresses.