Structure of expandable graphite Expandable graphite is […]
Structure of expandable graphite Expandable graphite is currently widely used in fireproof coatings for steel structures. Its chemical formula is C, which belongs to the hexagonal crystal system. The crystals are in the shape of hexagonal plates and flakes, and the appearance is scaly iron black. /cmз, the bulk density is 0.1002 to 0.1004g/cm3, the surface is smooth, with conductivity, corrosion resistance, and inactive chemical properties. Expandable graphite is made of natural flake graphite as raw material, and sulfuric acid is used as an intercalating agent. Sulfuric acid inserted between layers plays a key role in the expansion of expandable graphite.
Flame-retardant mechanism of expandable graphite When the expandable graphite is subjected to high temperature above 200℃, the compound stored in the layered lattice starts to decompose. The expandable graphite will exhibit hundreds of times of expansion along the C axis of the structure. The volume reaches its maximum at 1100°C. The gas phase product produced by the decomposition of the compound is composed of S02, C02 and water. Expandable graphite is used in fireproof coatings for steel structures. When a fire occurs, the volume instantly blocks the flame. After expansion, the graphite becomes very low-density worm-like. Its structure is loose, porous and curved, with large specific surface area, strong adsorption force, low thermal conductivity, excellent oxidation resistance and high temperature resistance.
The structural characteristics of expandable graphite determine that it will absorb a lot of heat during the expansion process, its mass loss is small, low smoke, non-toxic, high performance, environmentally friendly, will not react with other polymers, but it forms an expanded carbon layer Thermal insulation and oxygen barrier are also beneficial for the cross-linking of other polymers in the coating to carbon.
Studies have shown that about 0.8% of SO2 is produced during the thermal decomposition of expandable graphite, which is equivalent to 16% of the total sulfuric acid inserted into the graphite layer. The thermal decomposition residue still contains a large amount of sulfur-containing substances, indicating that only part of the sulfuric acid Participating in the reaction of the expandable graphite expansion process, the large amount of redox gas is the main reason for the expansion.
The application of expandable graphite still maintains the properties of natural graphite, the use is not restricted by the environment, and the plasticity, ductility and sealing are good. It is used to produce flexible graphite sheets, fire extinguishing agents for seals, fire retardant materials, etc. At present, it is widely used in high-tech industrial fields such as petroleum, chemical industry, light industry, metallurgy, power, machinery, pharmaceutical, medical, automobile, shipbuilding, aerospace, military, nuclear energy and so on.