Expansible graphite crystals are a typical layered carbon material, where other unlike particles such as atoms, molecules, ions, or even atomic clusters are inserted between the crystal graphite layers by physical or chemical means, forming a new layered compound known as intercalated graphite, or expandable graphite. Expandable graphite is different from expanded graphite; for sealing strips, expanded graphite should be selected.
Expandable Graphite is natural flake graphite (or highly graphitized artificial graphite), a layered compound treated with acidic oxidizing agents (sulfuric acid, nitric acid, hydrogen peroxide, potassium permanganate). Also known as Graphene Oxide, the immersion of the oxidizing agents also causes the original graphite to exhibit slight expansion, increasing the interlayer spacing from the original 3.35A to 6-11A. A significant characteristic of Graphene Oxide is its unusual expandability, which allows it to expand at high temperatures, hence the name Expandable Graphite.
Unlike graphite, oxidized graphite can form a stable graphene oxide colloid or suspension in water or alkaline water under the action of external forces such as ultrasonic waves. Simultaneously, due to the electrostatic repulsion from interlayer charges, the layers of oxidized graphite undergo layer-by-layer exfoliation.
Expanding graphite is produced through the high-temperature treatment of graphitic oxide at 960-980°C. Under this heat, the interlayer compounds of graphite rapidly vaporize and decompose, generating a certain amount of thrust that disrupts the molecular forces holding the graphite layers together. This causes the C-C bonds within the graphite lattice to break, leading to a rapid expansion along the c-axis, with the interlayer spacing increasing by 50-500 times. The dense, scale-like graphite transforms into fibrous, worm-like graphite.
Expanding Graphite primarily produces graphite paper and processes various types of graphite gaskets and sealing materials, also known as flexible graphite. It boasts advantages such as high-temperature resistance, high-pressure resistance, excellent sealing properties, and resistance to corrosion by a variety of media, making it a novel and advanced sealing material. Expanding Graphite has a high thermal conductivity. Leveraging this characteristic of flexible graphite, it can be used as both thermal and conductive materials. Therefore, it is not suitable for manufacturing the sealing strips of fire doors.
Expanding graphite typically carries a certain charge on its surface. Utilizing its charged properties, Bai Wushen synthesized a poly(methyl methacrylate)-graphite composite by using H2SO3 aqueous solution as an initiator. Moreover, this polymerization method can also avoid the adverse effects of factors such as blending time and temperature during mechanical blending, which negatively impact the conductivity.
