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.