1. Field of Invention
The present invention relates to a method for making a highly thermally conductive composite and, more particularly, to a method for making a highly thermally conductive composite by melting and mixing modified paraffin wax with organic modified expandable graphite.
2. Related Prior Art
Paraffin wax is a potential heat-storing material that stores or releases heat via transformation of physical states. Paraffin wax stores heat when it transforms to liquid from solid and releases heat when it transforms to solid from liquid. This transformation is phase transformation. Paraffin wax however exhibits a poor thermal transfer coefficient. That is, the melting and solidification of paraffin wax are slow. In other words, heat transfer through paraffin wax is slow. Therefore, for storing heat, paraffin wax is often mixed with a highly thermally conductive material to increase the heat transfer rate. Graphite is a good choice as a highly thermally conductive material to be added into paraffin wax to this end.
Graphite includes a two-dimensional structure that consists of six carbon atoms. In graphite, layers and layers are bonded by van der Waal's forces.
Graphite is refractory, highly electrically conductive, highly thermally conductive and highly plastic. Graphite exhibits a low frictional coefficient but excellent viscosity for including scales and leaves, and this is why it is highly plastic. Graphite is not metal mineral but exhibits properties of metal organic compounds because its lattice includes layers of atoms are arranged in a compact manner and electrons can easily travel in the lattice for conducting electricity and heat between the atoms. Therefore, graphite exhibits excellent electrical conductivity and thermal conductivity. If paraffin wax is mixed with more graphite, the mixture exhibits better thermal conductivity. Moreover, at the normal temperature, graphite is chemically stable and stands strong acids, strong alkalis and organic solutions.
Expandable graphite (“EG”) exhibits a low density and a low thermal expansion coefficient, is refractory, and absorbs waves. Based on the ways the crystals build up and the foam structures, expandable graphite can be used as a thermally conductive or insulating material. In early days, expandable graphite was used in the aerospace industry. Expandable graphite is now used in the electronic industry because its carbon atoms build up perfectly and it exhibits an excellent heat transfer coefficient. Furthermore, expandable graphite includes open cells in communication with one another. Expandable graphite exhibits a high specific surface for heat dissipation via convection. Expandable graphite exhibits a high heat transfer coefficient and is therefore commonly used as a thermally conductive material. Paraffin wax and graphite are organic or inorganic, respectively. Hence, it is difficult to mix expandable graphite with paraffin wax evenly.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.