METHOD OF OBTAINING GRAPHENE
Patent RU 2 632 688 C1
C01B 32/19
B82Y 40/00
B82B 3/00
Application: 2016143665, priority from 11/07/2016
Application PCT / RU2017 / 000304. An international search report and a written report from the international search authority have been received with a valid statement of the invention's compliance with the criteria of novelty, inventive step and industrial applicability.
Date of the beginning of the patent validity period: 11/07/2016
The author and patent owner: Zhebelev S.I. (RU)
Date of registration: 10/9/2017
Published: 10/09/2017 Boul. № 28.
E-mail address: SIZHEB@YANDEX.RU
The invention relates to the production of carbon nanomaterials, for example graphene, and can be used to produce graphene for use in nanoelectronics.
The essence of the proposed invention is as follows.
The process is performed in the regime of electrodynamic fluidization of graphite particles in a vacuum, and conditions are created for which the energy of the graphite particles exceeds the work necessary for their separation into layers during brittle fracture along cleavage planes resulting from impacts of particles on the electrodes.
The method is carried out as follows. As a source for the production of graphene, a graphite grain is used, the particles of which are placed in an electric field between two electrodes in a vacuum, with a potential difference sufficient to liquefy the particles (moving the particles between the electrodes with their charge exchange at the electrodes), when qU / d> mg , where q is the charge of the particle, U is the potential difference of the electrodes, d is the interelectrode distance, m is the particle mass, and g is the acceleration due to gravity. At each passage of the interelectrode gap without the medium's resistance in vacuum, the particle acquires energy qU. In this case, the particles experience point impacts against the electrodes, which leads to their brittle fracture along the cleavage planes perfect for graphite, that is, along the boundaries of the layers of graphene. A necessary condition for this process is the sufficiency of the energy accumulated by the particle before impact on the electrode qU, for the work on the splitting of the particle Esplit. To fulfill this condition, adjust the value U - the potential difference of the electrodes. The consecutive split of particles and their parts leads to the fact that the final product of the process are single sheets of graphene. The condition of carrying out the process in a vacuum provides sufficient energy for the particles to split and the purity of the product. It should also be noted that graphene in its free state is not rigid and folds into a ball. However, in an electric field having a charge, a sheet of graphene unfolds and is suitable for further processing (moving, separating in size and other operations) in the same vacuum space.
As a starting material, graphite grains obtained by crushing pyrolytic graphite up to a millimeter in size can be used. A promising material can be graphite grains obtained by carbonization and graphitization of fine anthracite fractions (less than 6 mm - shtyb) in electrocalcinators.
Mechanisms of Particle Splitting
1. Shock split
In an electric field, a graphite particle consisting of conductive layers of graphene and a bundle of dipoles is oriented along the electric field. Therefore, when the electrode strikes, the direction of the shock coincides with the direction of the layers. The impact is central, that is, the direction of impact passes through the center of mass of the particle and point. A point strike causes a displacement of adjacent layers of the particle, a weakening of the bond between adjacent layers due to van der Waals forces, splitting along the boundary of the layers, and separation of the particle into fragments. The same mechanism works in other ways of micromechanical production of graphene. The difference between the known methods and the proposed method for producing graphene from graphite is that if external methods for applying graphite, for example a rough surface, are used in the known methods, then the graphite particle itself is an instrument of its cleavage in the proposed method.
2. Splitting of particles due to their loss of longitudinal stability upon impact against the electrode.
As the thickness of the particles decreases as a result of the split, less than a certain limit upon impact, the particles begin to lose longitudinal stability, which leads to their bending. When bending occurs, the adjacent layers of the particle are displaced, the bond between adjacent layers due to van der Waals forces is cut, the layers are split along the boundary, and the particle is divided into fragments. An analog of this mechanism is the splitting of poorly glued laminated materials in bending.
3. Mechanism of electrostatic separation of particles into graphene layers
In the process of particle motion during electrodynamic fluidization, another mechanism of its cleavage is possible. This mechanism is due to the electrostatic repulsion of external charged layers of a particle having a charge of the same sign.
Implementation of the method
To implement the method, it is necessary to have a device having two electrodes and the possibility of creating the necessary electrode potential difference in accordance with the particle size of the starting material. The starting material is loaded into the interelectrode space, in which the material particles enter the electrodynamic liquefaction regime, in which the particles are struck against the electrodes. The fragmentation of particles to graphene occurs in several stages. At the initial stage large particles are divided into fragments with a relatively large thickness. Further, these fragments are split into thin particles. The last stage is the splitting of fine particles into graphene layers. The first mechanism of the split is a shock split, acts at all stages. The second mechanism is the loss of longitudinal stability and bending of thin particles, acts at the stage of splitting of thin particles into even thinner ones and into layers of graphene. The third mechanism of the split is the electrostatic splitting acting at the stage of splitting the fine particles into layers. Thus, the creation of conditions for the electrodynamic fluidization of graphite particles and the sufficiency of their energy for the split, the action of the split mechanisms, provides the solution to the technical problem of obtaining graphene from graphite
Simple experimental setup for studying the process of obtaining graphene from a single particle
must contains electrodes, a vacuum system and a power source. Besides
this should provide for the presence of a trap for the products of the split,
which settle on the lower electrode after the current is turned off. A trap can
represent the upper metal electrode with an insulating coating.
When removing the vacuum and replacing the upper electrode with a trap after a short time
The inclusion of voltage products charged positively settle on the trap.
The insulating coating can have the properties necessary for visualization
nanolayers using Raman scattering.
