Expandable graphite or exfoliated graphite is made from the naturally occurring mineral graphite. The layered structure of graphite allows molecules to be inserted between the graphite layers. By adding acid, graphite sulfate can usually be converted into expandable graphite.
If expandable graphite is heated, the graphite sheet will expand to a multiple of its initial volume. The starting temperature of the main products on the market is in the range of 200 °C. Inflated flakes have a "worm-like" appearance and are usually several millimeters long.
What is expandable graphite used for?
Flame retardant agent
One of the main applications of expandable graphite is as a flame retardant. When exposed to heat, expandable graphite expands and forms an expansion layer on the surface of the material. This slows down the spread of the fire and offsets the most dangerous consequences of the fire to humans, namely the formation of toxic gases and smoke.
By compressing expanded graphite, pure graphite can be used to produce foil. These are mainly used as seals or radiators with high heat resistance and chemical resistance in the construction of chemical plants.
Expandable graphite for metallurgy
Expandable graphite is also used in metallurgy to cover melts and molds. The material is used here as oxidation protection and insulators.
Expandable graphite for chemical industry
Expandable graphite is included in the chemical process of paints and varnishes.
How do you make graphite expandable?
In order to produce expandable graphite, natural graphite slices are treated in acid and oxidant baths. The commonly used oxidants are hydrogen peroxide, potassium permanganate or chromic acid. Concentrated sulfuric acid or nitric acid is usually used as the compound to be added, and the reaction takes place at a temperature of 30 °C to 130 °C for up to 4 hours. After the reaction time, the flakes are washed with water and then dried. The initial temperature and expansion rate depend on the production conditions and particle size of graphite. The temperature and expansion rate depend on the fineness of the graphite used.
What are the three types of graphite?
Graphite is divided into natural graphite and synthetic graphite.
There are three forms of natural graphite, all of which are processed from graphite materials of natural origin. These three forms are amorphous graphite, flake graphite and crystalline veined graphite, which have their own unique characteristics, which make them very suitable for some applications.
Why can expandable graphite be expanded?
The layered structure of graphite allows molecules to be inserted between the graphite layers. Sulfur compounds or nitrogen compounds are usually used as intercalation agents. Under the influence of heat, these layers separate like an accordion and the graphite sheets expand.
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