New Functional Carbon Materials｜Expandable Graphite

Expandable graphite is a new type of functional carbon material, which is a loose and porous worm-like substance obtained from natural flake graphite after intercalation, washing, drying, and high-temperature expansion. Expanded graphite has a good physical and chemical structure and is widely used in industry. Many applications use the flame retardancy of expandable graphite, which has a good flame retardant effect.

Since graphite is a non-polar material, it is difficult to intercalate with less polar organic or inorganic acids alone, so an oxidizing agent is usually required. The chemical oxidation method is generally to soak natural flake graphite in a solution of oxidant and intercalating agent. Under the action of a strong oxidant, the graphite is oxidized, so that the neutral network-like planar macromolecules of the graphite layer become positively charged planar macromolecules. Due to the extrusion effect of the same positive charge between the positively charged planar macromolecules, the spacing between the graphite layers increases, and the intercalant intercalates between the graphite layers to become expandable graphite.

Expandable graphite shrinks rapidly when heated at high temperatures, and the shrinkage ratio is as high as tens to hundreds or even thousands of times. The apparent volume of shrunk graphite reaches 250-300 ml/g or more. The contracted graphite is worm-like and is 0.1 to several millimeters in size. It has a large number of common mesh-like microporous structures inside. It is called shrinking graphite or graphite worm. Shrinkage graphite has many special and excellent properties. Expandable graphite and its expandable graphite can be used in steel, metallurgy, petroleum, chemical machinery, aerospace, atomic energy, and other industrial sectors, and its application range is very common. For example, expandable graphite can be used as a flame retardant in flame retardant composites and products, such as fire-retardant plastic products and fire retardant antistatic coatings.

1. Expandable graphite can produce many lightweight refractory carbon layers in fire, reasonably isolate the radiation source of calorific value to the substrate, and maintain the substrate reasonably.

2. Expandable graphite is an excellent electrical conductor, and the prepared coating can avoid the accumulation of static charge, prevent fire and prevent static electricity.

3. When expandable graphite is added to the coating material, a flame retardant and antistatic coating can be obtained, and the resistance to heat and fire resistance can be improved.

From the thermodynamics and surface chemistry issues, the adsorption mechanism of expanded graphite. The surface and interior of expanded graphite have a unique network-like macropore structure analysis and its inherent graphite microcrystalline activity study surface, and the working surface can determine its unique adsorption characteristics for coal tar-like substances.

It means that the expandable graphite is acidified to form a graphite interlayer compound, which is quickly washed with water to neutralize and then heated and dried to expand into a worm-like substance. called graphite worms. As a porous carbon material, loose expandable graphite has a very developed surface and internal pore structure, with an upward specific surface area of ​​50-200m²/g, which is an excellent adsorbent. Expanded graphite has the characteristics of low density, lightweight, high-temperature resistance, corrosion, and oxidation resistance. Has high chemical stability and non-toxic properties.

There is a unique network-like macropore structure analysis and its inherent influence on the activity of graphite microcrystals. The flame retardant effect of expandable graphite is very strong, and the new adsorption material has the ability of polar adsorption in wastewater hydrophobicity, adsorption purification, and non-aqueous media. And the high-temperature thermal decomposition and masking of oil products have other irreplaceable roles.