Figure 2. High-resolution scanning electron micrographs of the graphene that solves the problems regarding insufficient exfoliation of the graphite powder and deterioration in the electrical conductivity and thermal conductivity.
The high-resolution transmission electron micrographs are illustrated in Figure 3 for the graphene that solves the problems regarding insufficient exfoliation of the graphite powder and deterioration in the electrical conductivity and thermal conductivity. The organic solvent preferably has a viscosity of less than 80 Sabol seconds. Non-limiting examples include nonpolar organic solvents. The metal cylinder may be pressed against the flat metal plate by an extreme pressure. The pressure applied on the metal cylinder may be in the range of about 2000-6000 psi. This high pressure ensures graphene sheers to a stable form in the resultant nonpolar liquid dispersion. A pressure of below about 2000 psi leads to a wider platelet particle size distribution curve and larger stacks of graphene platelets, which will settle in the non-polar dispersion. The liquid precursor may be forced through an opening on the flat metal plate. The liquid precursor may then pass between the metal cylinder and the flat metal plate. The pumping pressure applied on the liquid precursor may be higher than the pressure between the metal plate and metal cylinder such that the feed of the liquid precursor can be directed through the opening and then between the metal cylinder and the flat metal plate. When the liquid precursor passes between the metal cylinder and the flat metal plate, the thick layers of graphene may be broken into thin layers by the high shear pressure between the metal cylinder and the flat metal plate. The greater the pressure between the metal cylinder and the flat metal plate, the smaller the graphene platelet particle size. When the liquid precursor is directed, for example, forced by the pumping pressure, through the opening on the flat metal plate and between the metal cylinder and the flat metal plate, and then exits from between the metal cylinder and the flat metal plate, the pressure on the liquid precursor drops significantly. This pressure drop allows the liquid precursor to flow and homogenizes the pass-through liquid of the liquid precursor that contains thin layers of graphene such that the smaller graphene platelet particle is well dispersed in the resultant fluid product. The greater the pressure drop is, the greater the level of homogenization. The process thus reduces the particle size of the graphene and creates more uniform graphene platelets. Further, when the liquid precursor passes between the metal cylinder and the flat metal plate, fumed silica undergoing sheer pressure may swell and expand in the nonpolar solvent to form a gel comprising a three-dimensional structure and with a higher rheology and viscosity than the organic solvent. The viscosity of the resultant silica gel can range from about 200,000 to about 600,000 centistokes. The graphene platelet particles are dispersed in the three-dimensional network of the silica gel and held therein stably in the silica gel matrix. The organic solvent keeps the graphene particles apart from each other in the silica web, breaking up the Van der Waals forces between them, so that the graphene particles do not aggregate and maintain their thin layers of two-dimensional configuration. When the graphene suspension additive is added to a product, such as a painting or coating, and when the product is applied on to a surface and allowed to dry, the organic solvent may evaporate, and upon evaporation of the solvent, the graphene nanoparticles can come together in the polymeric matrix of the silica gel and other components, thus strengthening the coating. The graphene can keep metals at uniform temperatures.