Graphite Mechanical Properties Guide: Everything You Need to Know

Graphite mechanical properties are various properties which emerged under the action of force. These properties can be clearly derived from graphite’s structural particularity-the carbon atoms within every layer have a firm covalent bond but in between the layers, the bonding is weak.

Graphite’s Mechanical Properties

Graphite Compressive Strength

The compressive strength of graphite is anisotropic, and the strength parallel to the plane is much higher than that in the vertical direction. For instance, the compressive strength of carbon electrodes in the parallel direction is 21.6~49.0 MPa, while the vertical direction is only 11.7~29.4 MPa. Besides, the compressive strength of pyrolytic graphite is greatly improved at high temperature up to 137.3 MPa.

Graphite Flexural Strength

Graphite’s flexural strength has differences in direction: 4.9~12.7MPa in the parallel direction and 5.8~15.7MPa in the vertical direction. The flexural strength of graphite increases with the rise in temperature, hence indicating very excellent high-temperature mechanical properties.

Graphite Elastic Modulus

Graphite elastic modulus reflects the relationship between stress and strain, parallel direction more than vertical direction, room temperature is particularly critical. With the temperature rise, the change of its elastic modulus is very important for forecasting mechanics performance.

Graphite Thermal Expansion Coefficient

Graphite changes with temperature, and the difference of thermal expansion coefficient is obvious among different directions. Pyrolytic グラファイト has excellent structure and good dimension stability at high temperature.

Graphite Yield Strength

Yield strength reflects the ability of graphite to transform from elastic deformation into plastic deformation, and its size is influenced much by direction and temperature. The yield strength is improved greatly at high temperature, which accords with high temperature environment.

Hardness of Graphite

The hardness of graphite is anisotropic and depends on the test method; it can be determined by indentation hardness or rebound hardness. Pyrolytic graphite has a relatively high hardness and is particularly suitable for applications with high precision. Hardness depends on the direction and how the load is applied.

Application Based on Mechanical Properties of Graphite

High-Temperature Applications

Commonly utilized in furnace parts, crucibles, and molds for metal casting, the material can retain its structural integrity and resist deformation at extremely high temperatures. Besides that, its low coefficient of thermal expansion effectively reduces thermal stress and exhibits excellent durability in rapid temperature changes.

Aerospace and Defense

Due to its lightweight, high strength-to-weight ratio, and very temperature-resistant properties, it has wide applications in the manufacture of rocket nozzles, thermal protection systems, and structural components. With its high-temperature mechanical properties, graphite can realize very good stability in extreme environments. Moreover, its anisotropy can be optimized by design to meet the various performance requirements of components.

Nuclear Industry

Good mechanical properties and chemical stability enable graphite to act both as moderator and structural material in nuclear reactors. Graphite has low neutron absorption cross-sectional area and high compressive strength, enabling this material to operate steadily for very long period of time in high radiation and high-temperature conditions.

Lubrication and Sealing

Graphite has low hardness, good self-lubricating properties and high compressive strength. It can be widely used in bearings, gaskets and seals of industrial equipment. Its low friction coefficient and excellent wear resistance are particularly suitable for sealing needs in high pressure, high temperature and chemical corrosion environments.

Impact on graphite mechanical properties

Graphite crystal structure

The grain boundaries of the Stone-Wales defects mark a massive impact on the tensile strength and fracture behavior. The areas where the defects have a high-density structure could also have lower mechanical strength, since local stress may be concentrated.

Graphite production method

Polycrystalline graphite synthesized by CVD typically involves grain boundaries which provides lower tensile strength. However, single-crystal graphites have better mechanical properties simply because there are fewer defects.

Graphite grain size and orientation

This is because larger grains may offer a more continuous route for the distribution of stress, hence increasing strength. However, smaller grains would lead to increased brittleness and further reduction in overall strength due to increased grain boundaries.

Graphite surface modification and functionalization

Surface modification and functionalization allow the improvement of interactions at the surface and a more homogeneous distribution of stresses, reducing failures by defects. For instance, functionalized surfaces may be tougher and resistant to crack growth.

結論

As a non-metallic material, the structure and morphology of graphite usually determine its mechanical properties. The excellent mechanical properties of graphite are also widely used in many industrial fields. In the future, the application of the mechanical properties of graphite will be even more extensive and in-depth with the continuous progress and improvement of science and technology. This will provide a new direction for the development of industry and science and technology.