Thermo-Conductive Graphite Fillers for Polymer Composites
Thermo-conductive Graphite Fillers for Polymer Composites
Carbon fillers have attracted scientific and industrial attention in the recent decade, as they can increase the electrical and thermal conductivity of polymer composites. They are characterized by high aspect ratio, excellent heat-conducting properties, and good mechanical strength. These characteristics are highly attractive for the production of conductive composite materials, such as electric motors and generators, heat exchangers in power generation, and automotive applications.
Graphite is a crystalline form of carbon. It has a layered structure made up of stacked planes of carbon atoms organized in a hexagonal pattern. The crystalline structure of graphite is formed when the stacked carbon atoms are bonded by covalent bonds. The crystalline structure of graphite flakes is known to be thermally conductive, as the thermal conductivity of natural graphite flakes at room temperature is 129 W/m*K.
Natural graphite consists of large sheets (about 200-500 mm in diameter) with smooth and durable surfaces, as shown in Figure 1d. This material is used for the production of conductive composites and is often called exfoliated graphite.
Thermally Expanded Graphite, also called expanded graphite or EG, is produced from natural graphite flakes through the process of intercalation of a non-carbon compound containing a variety of molecules and atoms between the planes of the carbon flakes. This intercalation process creates a gas inside the graphite layers that decomposes and pushes the edges of the graphite layers open. The resulting chemically treated EG is a very useful conductive filler that can be used in the production of conductive composites, as it has a higher thermal conductivity and mechanical load transfer than natural graphite flakes.
