The principle of graphitization involves high-temperature heat treatment (2300–3000°C), which induces the rearrangement of amorphous, disordered carbon atoms into a thermodynamically stable three-dimensional ordered graphite crystal structure. The core of this process lies in the reconstruction of a hexagonal lattice through SP² hybridization of carbon atoms, which can be divided into three stages:
Microcrystalline Growth Stage (1000–1800°C):
Within this temperature range, impurities in the carbon material (such as low-melting-point metals, sulfur, and phosphorus) begin to vaporize and volatilize, while the planar structure of carbon layers gradually expands. The height of microcrystals increases from an initial ~1 nanometer to 10 nanometers, laying the foundation for subsequent ordering.
Three-Dimensional Ordering Stage (1800–2500°C):
As the temperature rises, misalignments between carbon layers decrease, and the interlayer spacing gradually narrows to 0.343–0.346 nanometers (approaching the ideal graphite value of 0.335 nanometers). The graphitization degree increases from 0 to 0.9, and the material begins to exhibit distinct graphite characteristics, such as significantly enhanced electrical and thermal conductivity.
Crystal Perfection Stage (2500–3000°C):
At higher temperatures, microcrystals undergo rearrangement, and lattice defects (such as vacancies and dislocations) are progressively repaired, with the graphitization degree approaching 1.0 (ideal crystal). At this point, the material’s electrical resistivity can decrease by 4–5 times, thermal conductivity improves by approximately 10 times, the coefficient of linear expansion drops by 50–80%, and chemical stability is significantly enhanced.
The input of high-temperature energy is the key driving force for graphitization, overcoming the energy barrier for carbon atom rearrangement and enabling the transition from a disordered to an ordered structure. Additionally, the addition of catalysts (such as boron, iron, or ferrosilicon) can lower the graphitization temperature and promote carbon atom diffusion and lattice formation. For example, when ferrosilicon contains 25% silicon, the graphitization temperature can be reduced from 2500–3000°C to 1500°C, while generating hexagonal silicon carbide to assist in graphite formation.
The application value of graphitization is reflected in the comprehensive enhancement of material properties:
- Electrical Conductivity: After graphitization, the material’s electrical resistivity decreases significantly, making it the only non-metallic material with excellent electrical conductivity.
- Thermal Conductivity: Thermal conductivity improves by approximately 10 times, making it suitable for thermal management applications.
- Chemical Stability: Oxidation resistance and corrosion resistance are enhanced, extending the material’s service life.
- Mechanical Properties: Although strength may decrease, pore structure can be improved through impregnation, increasing density and wear resistance.
- Purity Enhancement: Impurities volatilize at high temperatures, reducing product ash content by approximately 300 times and meeting high-purity requirements.
For instance, in lithium-ion battery anode materials, graphitization is a core step in the preparation of synthetic graphite anodes. Through graphitization treatment, the energy density, cycle stability, and rate performance of anode materials are significantly improved, directly impacting overall battery performance. Some natural graphite also undergoes high-temperature treatment to further enhance its graphitization degree, thereby optimizing energy density and charge-discharge efficiency.
Post time: Sep-09-2025