Graphite fillers, as high-performance solid lubricants, are widely used in mechanical seals, aerospace, and industrial lubrication due to their excellent high-temperature resistance, chemical stability, and low friction coefficient. Their synthesis methods are diverse, primarily including natural graphite modification, chemical vapor deposition (CVD), redox methods, and polymer-based composite preparation techniques.
Natural graphite, after purification, pulverization, and surface modification, can be used as a base filler. High-temperature expanded graphite is a common modification. The interlayer structure of graphite is treated with intercalating agents (such as sulfuric acid and nitric acid), followed by rapid heating to expand it dozens of times, forming a loose, porous, worm-like material, significantly improving lubrication and filling properties. Chemical vapor deposition is suitable for preparing high-purity nanographite fillers. Methane or acetylene is typically used as a carbon source. Under high temperatures (800–1200°C) and the presence of a metal catalyst, carbon atoms are decomposed to form carbon atoms, which are then deposited on the substrate surface to form a graphite coating or particles. This method offers high controllability but is relatively costly and is primarily used in precision devices.
The redox method involves oxidizing graphite to graphene oxide (GO) using a strong oxidant (such as potassium permanganate). The graphite structure is then restored by treatment with a reducing agent (such as hydrazine hydrate), resulting in reduced graphene oxide (rGO). This product combines the electrical conductivity of graphite with the high surface area of nanosheets, making it suitable for composites with other materials to enhance mechanical properties. Furthermore, polymer-based graphite composites are prepared by melt blending or solution dispersion, uniformly dispersing graphite fillers in matrices such as polyethylene and polytetrafluoroethylene to improve the material's wear resistance and self-lubrication.
In the future, with the advancement of nanotechnology and green chemistry, the synthesis of graphite fillers will place greater emphasis on environmental friendliness and functional design, such as through microwave-assisted reduction or bioreduction to reduce energy consumption, and exploring their potential applications in new energy devices.
