Expandable graphite (also known as exfoliated graphite) is produced from the naturally occurring mineral

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

. The layered structure of graphite allows molecules to be

intercalate Intercalation may refer to: *Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite * Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar foll ...

d in between the graphite layers. Through incorporation of acids, usually sulfuric acid graphite can be converted into expandable graphite.Vijay J. Bhagat: Behaviour of expandable graphite as a flameretardant in flexible polyurethane foam Presented at: Polyurethane Foam Association (PFA)Arlington, Virginia, USA, May 10, 2001

Characteristics

If expandable graphite is heated, the graphite flakes will expand to a multiple of their starting volume. The main products in the market have a starting temperature in the range of 200 °C. The expanded flakes have a “worm-like” appearance and are generally several millimeters long.Vijay J. Bhagat: Behaviour of expandable graphite as a flameretardant in flexible polyurethane foam Presented at: Polyurethane Foam Association (PFA)Arlington, Virginia, USA, May 10, 2001

Production

To produce expandable graphite, natural graphite flakes are treated in a bath of

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...

and

oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...

.Usually used oxidizing agents are hydrogen peroxide, potassium permanganate or chromic acid. Concentrated sulphuric acid or nitric acid are usually used as the compound to be incorporated, with the reaction taking place at temperatures of 30 °C to 130 °C for up to four hours. After the reaction time, the flakes are washed with water and then dried. Starting temperature and expansion rate depend on the production conditions and particle size of the graphite. temperature and expansion rate are depending on the degree of fineness of the graphite used.

Applications

Flame retardant

One of the main applications of expandable graphite is as a flame retardant. When exposed to heat, expandable graphite expands and forms an intumescent layer on the material surface. This slows down the spread of fire and counteracts the most dangerous consequences of fire for humans, the formation of toxic gases and smoke. Mineralischer Flammschutz mit Blähgraphit – Der hochwirksame und REACH-konforme Intumeszenzbildner
Pressemitteilung Georg H. Luh GmbH.

Graphite foil

By compressing expanded graphite, foils can be produced from pure graphite. These are mainly used as thermally and chemically highly resistant seals in chemical plant construction or as heat spreaders.

Expandable graphite for metallurgy

Expandable graphite is also used in metallurgy to cover melts and moulds. The material serves here as an oxidation protection and insulator.

Expandable graphite for the chemical industry

Expandable graphite is included in the chemical processes for paints and varnishes.

References

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