Expandable graphite - a special kind of graphite.
Due to the layered structure of graphite, atoms or small molecules can be introduced between the carbon layers (intercalation). During this process a so-called expandable graphite salt or GIC (Graphite Intercalation Compound) is produced. Outstanding expandable graphite grades have a high proportion of intercalated layers. Usually sulphur or nitrogen compounds are used as intercalation agents. Under the influence of heat the layers separate like an accordion, and the graphite flakes expand.
Depending upon the grade of material expansion can commence at as low as 180°C and can occur suddenly and rapidly. In the case of free expansion the final volume can be several hundred times greater than the initial volume. The properties of expandable graphite, i.e. initial expansion temperature and degree of expansion, are primarily defined by the quality of intercalation (proportion of intercalated layers) and by the intercalation agent.
expandable graphite as flame retardant.
One of the principal applications of expandable graphite is as a flame retardant. As a result of the heat of a fire the graphite expands and creates an intumescent layer on the surface of the material. This retards the spread of fire and minimises one of the most harmful effects of combustion, the creation of toxic gases and fumes.