Expandable graphite is a kind of graphite intercalation compound, which was prepared by the method of chemical oxidation. It belongs to a group of products called «intumescents»; the main property of which is the ability to expand when heated. Expandable graphite, also called flexible graphite, is made from high quality natural flake graphite by chemical treatment. The material has the characteristics of high temperature resistance, thermal conductivity, lubricity, stable chemistry, heat shock resistance etc.
Crystalline graphite flake is the starting material for the manufacture of expandable graphite. Deposits of crystalline graphite are found throughout the world. The graphite is usually found either as inclusions in various metamorphic rocks, or concentrated in the silts and clays that result from their erosion. Graphite is recovered from the ore by crushing and flotation. Crystalline graphite consists of stacks of parallel planes of carbon atoms. Because no covalent bonding exists between the planes, other molecules can be inserted between them. This process, known as intercalation, is essential for the production of expandable graphite. In the commercial process, sulfuric acid is inserted into the graphite, after which the flake is washed and dried. During the expansion, the graphite flakes increase in volume by a factor of 200 to 400. When the intercalated graphite is exposed to heat or flame, the inserted molecules decompose to generate gas. The graphite layer planes are forced apart by the gas and the graphite expands. Since the intercalant is sealed within the graphite lattice, the expandable graphite is a dry, pourable material with only minimal acidity.
The unique properties of natural graphite are captured in expanded graphite for use in a variety of applications. During the expansion process, the graphite retains its excellent inherent properties such as electrical and thermal conductivity and chemical resistivity. Expandable graphite is used as a fire suppressant intumescent additive, as a raw material to manufacture graphite gasket products, as an electrically conductive filler, as a foundry additive.
The main fields of expanded graphite applications:
1. Chemical and Petrochemical Industry.
2. Energy Storage.
3. High-Temperature Furnaces.
4. Automotive Industry.
5. Mechanical Engineering