Process for producing graphene

Abstract

The invention relates to the production of carbon nanomaterials, for example graphene, and can be used to produce graphene for use in nanoelectronics. Graphene is produced by stratifying graphite particles, differing in that graphite particles undergo electrodynamic fluidization in a vacuum in which the energy of the graphite particles exceeds the work necessary for their cleavage along the cleavage planes on graphene layers during brittle fracture when striking against the electrodes. The method makes it possible to obtain graphene with high productivity, economy and purity of the product.

Claims

1. A method for producing graphene by graphite stratification, characterized in that the graphite particles are subjected to electrodynamic fluidization in a vacuum in which the energy of the graphite particles exceeds the work necessary to split them upon impact of particles on the electrodes.

Description

EXAMPLE

(1) According (CRC Handbook of chemistry and physics. 86 h edition. 2005-2006.) graphite consists of two-dimensional layers of graphene. Spacing between layers 0.3354 nm with a binding energy in the layer of graphene 7.8 eV/atom, and considerably weaker bonds between 0.056 eV/atom layers, determined by Van der Waals forces. The values of the binding energy between layers obtained experimentally lie in the range from 0.043 to 0.061 eV/atom (Zacharia R., Ulbricht H., Hertel T. Interlayer cohesive energy of graphite from thermal desorption of polyaromatic hedrocarbons//Phys.Rev. 2004 V.B69, P.155406.). A two-dimensional lattice of graphene consists regular hexagons with sides dl=0.1418 nm and an area of (3).sup.3/2×dl.sup.2=5, 35×10.sup.−20 m.sup.2 by two carbon atoms per cell. Then the specific binding energy of the layers per unit area of the particle split surface is
e.sub.split=2.Math.(0.056 eV/atom.Math.1,602.Math.10.sup.−18 J/eV)/5, 35×10.Math..sup.20m.sup.2=0.335 J/m.sup.2

(2) The energy required to split a particle with an area of split S.sub.split into two parts is equal to E.sub.split=2S.sub.splite.sub.split, J.

(3) The process of electrodynamic fluidization consists in vibrational motion of conducting particles between electrodes when they are recharged on electrodes. When finding on the electrode particles acquire a charge q, which depends on the intensity of U/d field, the charge is proportional to the surface area of the particle, in vacuum (not experiencing resistance of environment), moving under the force qU/d, where U is the difference of the electrode potentials, d—the interelectrode distance, the particle acquires energy qU.

(4) The electrical conductivity of graphite over layers is close to metallic, while at the same time the electrical conductivity across the layers is hundreds of times smaller (Eletskii A V, Iskandarova I M, Knizhnik A A, Krasikov D N “Graphene: fabrication methods and thermophysical properties” Phys. Usp. 54 233-250 (2011); DOI:10.3367/UFNe.0181.201103a.0233).

(5) Therefore, a charged graphite particle is a stack of dipoles (graphene layers) oriented along the field. Upon impact, the particle undergoes a shear stress, parallel to the layers of graphite.

(6) With sufficient energy, this leads to a split of the particle. Since the particle charge q is proportional to surface area of the particle, and the work on splitting the particle proportional to the area of its section, the ratio qU/E.sub.split does not depend on the particle size and regulated by value U. To implement splitting of particle is necessary that the ratio of energy of the particle before to impacts on electrodes to split energy (energy reserve) was greater than unity: qU/E.sub.split>1. For spherical particles q=⅔π.sup.3r.sup.2ε.sub.0 U/d, where r—radius of the particle, ε.sub.0=8.85.Math.10.sup.−12 F/m—the permittivity.

(7) In the case of a split in the maximum cross section, that is, half, S.sub.split=π r.sup.2 and the energy reserve equals
qU/E.sub.split=(⅔π.sup.3r.sup.2ε.sub.0U.sup.2/d)/(2πr.sup.2e.sub.split)=(⅓π.sup.2)(ε.sub.0U.sup.2/d)/e.sub.split.

(8) It is important to emphasize that this ratio does not depend on the particle size, but depends only on their shape (the first factor). For the usual conditions of electrodynamic fluidization d=1.Math.10.sup.−2 m and U=3.Math.10.sup.4 V the energy reserve for spherical particles is 7.74. For asymmetric particles such as a hemisphere, and the charge q=3π r.sup.2 ε.sub.0 U/d the energy reserve is 3.6.

(9) For thin particles lying on the electrode, in which the thickness is much smaller than the other dimensions, the charge density is equal to the electrode charge density Σ.sub.0 U/d, and the charge is determined by the area of the exposed surface S, q=Sε.sub.0 U/d. For thin disks q=πr.sup.2ε.sub.0 U/d. Accordingly, the energy reserve is 1.19. Since for fine particles the value of the surface is close in the size of the cleavage area, this value will be the same for thin particles of a different shape. Since the particle charge q is proportional to the surface area of the particle, and the work on the particle splitting is proportional to the area of its cross section, the ratio qU/E.sub.t does not depend on the particle size and is regulated by the value of U.

(10) Since for fine particles the value of the surface is close in the size of the cleavage area, this value will be the same for thin particles of a different shape.

(11) When 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 bending stresses This further contributes to the stratification of particles. Conditions electrodynamic fluidization qU/d>>mg performed for particles smaller than 1 mm under the graphite density of 2.3×10.sup.3 kg/m.sup.3. Thus all particles of any size and shape smaller than 1 mm for the accepted conditions d=10.sup.−2 m and U=3.Math.10.sup.4 V there is enough energy to split.

(12) Therefore, the process goes on until the end, that is, before the particles split into single layers. It should be noted that the splitting of particles across the layers requires two orders of magnitude more energy. When taking into account the conservation of part of the energy when a particle bounces off electrodes, the maximum energy of a particle is qU/(1−k.sup.2), where k—the coefficient of conservation of momentum on impact. To improve the economics of the process, it is advisable to use hard electrodes, for which a large momentum conservation factor is observed upon impact. Thus, the proposed method allows to increase efficiency and productivity of obtaining graphene from graphite.