WO2007117103A1

WO2007117103A1 - Method of preparing carbon nano colloidial solution using sono-chemistry and electro-chemistry, and carbon nano colloidal solution

Info

Publication number: WO2007117103A1
Application number: PCT/KR2007/001715
Authority: WO
Inventors: Kyu-Sung Park; Hee-Chang Oh; Sang-Ha Yun; Seong-Yong Moon; Cheol-Min Shin
Original assignee: N-Baro Tech Co., Ltd.
Priority date: 2006-04-10
Filing date: 2007-04-09
Publication date: 2007-10-18
Also published as: KR20070101449A; KR100843666B1

Abstract

A carbon nano colloidal solution is disclosed, which is useful for a black coating to be applied on a surface a cathode-ray tube to improve a contrast of an image display device. The method of preparing the carbon nano colloidal solution includesdisposing a carbon electrode and an opposite electrode in a pure water, and applying electricity to the electrodes and applying supersonic waves to the pure water to synthesize carbon nano particles. The carbon nano particles are hydrophilic and are homogenously dispersed in the pure water, and aldehyde radical and/or carboxyl radial are formed on a surface of the carbon nano particle.

Description

METHOD OF PREPARING CARBON NANO COLLOIDIAL SOLUTION USING SONO-CHEMISTRY AND ELECTRO-CHEMISTRY, AND CARBON NANO COLLOIDAL SOLUTION

Technical Field

The present invention relates to a carbon nano colloidal solution with excellent dispersion stability and a method of preparing the same, and more particularly, to a carbon nano colloidal solution useful for a black coating to be applied on a surface a cathode-ray tube to improve a contrast of an image display device.

Background Art

Many scientists have been making efforts to prepare existing graphite particles or carbon particles into particles of nano size. As a result, a carbon nano tube, which is called as the best material in a human history, and carbon particles, such as fluorene, have been successively developed. The carbon nano tube particles are used to create an optimum display up to now. In particular, a carbon black is widely used to improve the contrast of the image display device.

The carbon black is a natural black powder derived from the incomplete combustion of natural gas, acetylene, anthracene, naphthalene, coal tar, and aromatic petroleum residues. Also, the carbon nano tube and the fluorene are carbon nano particles which are dispersed in a dispersive medium, such as water or alcohol, to prepare a colloidal solution. It makes an attempt to coat the surface of the cathode-ray tube with the colloidal solution.

Since all the carbon nano particles are hydrophobic in nature, they are dispersed in the water of a common dispersive medium by using a specific dispersing agent, or are dispersed in alcohol or acid solution, instead of the water of the common dispersive medium, in order to prepare the colloidal solution which is coated on the surface of the cathode-ray tube.

More specifically, the process of preparing the carbon black is generally summarized as the following. First, the carbon black and a surfactant are input in a dispersive medium such as water, and are then subjected to a pulverizing process to mill the carbon black powder into micro particles, thereby obtaining a carbon black colloidal solution. The colloids are very unstable and tend to aggregate. That is, the stability of the colloids becomes weak due to the aggregation between carbon particles, with the lapse of time. Since the carbon nano tube is also hydrophobic in nature, a method of providing the surfaces of the particles with a hydrophilic characteristic by using an excellent surfactant

(e.g., gum Arabic) in a strong acid substance or dispersing agent, such as solution is used. However, it has to be subjected to a separate specific process. There are some problems of causing environmental pollution in process in order to treat the strong acid solution such as nitric acid or sulfuric acid or eliminate the dispersing agent.

Also, according to the conventional colloidal solution and the method of preparing the same, it should be subjected to a two-step process. In other words, first of all, carbon creates nano-sized particulates, and the particulates are dispersed in the solution to prepare the colloid solution.

Disclosure of the Invention Technical Problem Therefore, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a method of preparing a carbon nano colloid solution with good dispersion stability through a one-step process, without using additives such as dispersing agent.

Another object of the present invention is to provide a carbon nano colloid solution prepared by the above method.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Technical Solution In order to accomplish the above-mentioned objects, the present invention provides a method of preparing a carbon nano colloidal solution, including disposing a carbon electrode and an opposite electrode in a pure water, and applying electricity to the electrodes and applying supersonic waves to the pure water to synthesize carbon nano particles, wherein the carbon nano particles are hydrophilic and are homogenously dispersed in the pure water, aldehyde groups and/or carboxyl groups being formed on a surface of the carbon nano particle.

Preferably, the carbon electrode is a graphite plate, and the carbon electrode is immersed in the pure water during a certain time so that the pure water infiltrates into an internal structure of graphite having a laminated structure. The carbon nano colloidal solution is pH 3 or less. The carbon nano colloidal solution comprises carbon nano particles of 0.1 to 5wt% of the whole solution. According to another aspect of the present invention, there is provided a carbon nano colloidal solution prepared by any one of the above claims 1 to 5. The carbon nano colloidal solution is pH 3 or less, and the carbon nano colloidal solution comprises carbon nano particles of 0.1 to 5wt% of the whole solution.

The present invention teaches a method of preparing a carbon nano colloidal solution with excellent dispersion stability which is useful for a black coating to be applied on a surface a cathode-ray tube of an image display device, by using a graphite plate (300x500x50) of 99.97% purity. In case of being used as a surface coating of the cathode-ray tube, a metal oxide should be provided as a colloidal solution which is dispersed in a dispersive medium such as pure water or alcohol. The inventor has researched that a colloidal solution with high dispersion stability is prepared in a solution, preferably, a pure water, without using any additives, while manufacturing the carbon nano particles. It means that the present invention prepares the carbon nano colloidal solution by one-step process. In other words, the present invention can obtain the colloidal solution with the dispersion stability which is secured only in the one-step process, instead of the conventional two-step preparing method thereof, in which carbon firstly creates nano-sized particulates, and the particulates are dispersed in the solution to prepare the colloid solution.

Advantageous Effects

As apparent from the above description, the carbon nano colloidal solution with dispersion stability is prepared by using nano-sized carbon particles as a dispersoin in the pure water of a dispersive medium, without using any dispersing agent or additives to disperse the carbon particles. In addition, the colloidal solution with the high dispersion stability is prepared in the solution in the one-step process, while manufacturing the carbon nano particles. The carbon nano colloidal solution of the present invention obtains the colloid homogeneously dispersed with dispersoid which is the carbon nano particle having pH 2 to pH 3 at room temperature and atmospheric pressure, the high electromotive force (28OmV or more) , and the high electric conductivity (1600ms/cm) . Also, the present invention can mass produce the carbon nano colloid stably dispersed in the dispersive medium of the pure water above 1 ton per day. The carbon nano colloidal solution of pH 2 to pH 3 is especially useful for a black coating to be applied on the surface the cathode- ray tube to improve the contrast of the image display device.

Description of the Drawings The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view illustrating an apparatus of preparing a carbon nano colloidal solution according to a preferred embodiment of the present invention;

FIG. 2a is a photograph of a carbon nano colloidal solution prepared by the present invention;

FIG. 2b is a TEM (Transmission Electron Microscope) photograph of particulates contained in a carbon nano colloidal solution prepared by the present invention;

FIG. 2c is an AFM (Atomic Force Microscope) photograph of a carbon nano colloidal solution prepared by the present invention; and FIG. 3 is a zeta potential graph depicting the dispersion stability of particles contained in the carbon nano colloidal solution. Best Mode

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the whole description of the present invention, the same drawing reference numerals are used for the same elements among/across various figures.

A method of preparing a carbon nano colloidal solution according to the present invention utilizes the electrochemical reaction occurring by applying supersonic waves to a pure water. FIG. 1 shows an apparatus of preparing the carbon nano colloidal solution. Referring to FIG. 1, a carbon electrode 11 and an opposite electrode 12 are disposed in an electrolytic cell 10 filled with a pure water 13, by which supersonic waves are applied by a supersonic generator (not shown) when carrying out the electrolysis. In this instance, the preparing method of the present invention uses only the pure water no containing any additives as an electrolyte. The pure water 13 serves as a dispersive medium no containing any dispersing agent.

The pure water 13 used in the present invention has an electric conductivity of about 10 MΩ/cm, metal ion components being eliminated from the pure water. There is a problem in that, if a solvent having electric permittivity lower than the pure water (e.g., alcohol) is added, the dispersion stability is deteriorated due to a metallic anion resulted from the ionic dispersing agent, for example, Na⁺ or K⁺. More specifically, an acid ion is adhered on a surface of a colloidal particle, which appears in a negative charge. Anions are gathered together around the surface of the particle according to electrostatic attraction so as to offset a potential difference generated thereby, which deteriorates the dispersion stability. As a result, there is a problem in that the anions should be eliminated. The present invention is characterized in that the carbon nano colloid with excellent dispersion stability is synthesized in a pure state under room temperature and atmospheric pressure, without using any dispersing agent described above.

It is preferable that the carbon electrode 11 is a graphite plate of 99.97% purity. In general, carbon is made by carbonizing a mixed coke and a binding pitch at a temperature of 1100 to 1300^°C. Since then, if it is graphitized by an electric resistance at 2500 to 3000^°C, amorphous carbon organization is changed into graphite having a crystal structure.

The carbon electrode 11 is immersed in the pure water 13 during a certain time, preferably, 20 to 30 hours. The reason is that the pure water infiltrates into an internal structure of the graphite having a laminated structure to lead to an electric/chemical reaction, so that the electrolysis of the water is sufficiently induced in the inside of the graphite plate which is the carbon electrode 11.

The opposite electrode 12 is made of a stainless steel. In FIG. 1, reference numeral 14 denotes a power supply apparatus for supplying electricity to the electrolytic cell, 15 denotes a pure water supply line, 16 denotes a drain line for draining the colloidal solution, and 17 denotes a circulation line. The circulation of the solution through the circulation line 17 in the process allows the solution to flow between the electrodes, thereby supplying carbon particles, and allows the gas generated by the electrolysis to be eliminated between the electrodes. The process using the sono-chemistry and electrochemistry is carried out as the followings.

First step: constant voltage combining step (fixed voltage: 0 to 50V) (low frequency, middle frequency, and high frequency are alternatively applied) Second step: constant voltage combining step (fixed voltage: 0 to 50V) (low frequency, middle frequency, and high frequency are alternatively applied)

Third step: constant voltage combining step (fixed voltage: 0 to 50V) (low frequency, middle frequency, and high frequency are alternatively applied)

After the sono-chemistry and electro-chemistry process, the graphite plate of the positive carbon electrode 11 starts to be damaged due to attack of the oxygen generated by the electrolysis of the water. It can be described as the onion theory which is new technology of manufacturing carbon nano. The structure of the graphite plate having the laminated structure has a shape similar to onion skins. According to the carbon nano synthesis, in which the onion skins are peeled off repeatedly, the carbon creates continuously nano- sized particulates in the solution by the sono-chemistry and electro-chemistry process. The laminated structure of which the outermost layer of the graphite plate is damaged creates particulates of several nm to 200 nm by the electrochemical method in which a voltage and a current are fixed.

The mechanism of the electrochemical oxidation is as follows. That is, the chemical oxidation is started by a reduction reaction of oxygen. e^" + O₂ → O₂ ^"

Specifically, the oxygen is a product resulted from the electrolysis occurring at the anode. Oxygen atoms are moved from the anode to the cathode. The reaction product, that is, O₂ ^", is finally changed into OH^".

O₂ + 2 H₂O + 4 e^" → 4OH^"

OH^" is reacted with the carbon anode to generate OH^" radical on the surface of the carbon.

Also, the OH radical is changed into aldehyde (-COH) and carboxyl ( -COOH) through the continuous oxidation reaction. The evidence, in which the oxygen is existed on the surface of the carbon, is that the carbon nano particles are hydrophilic and are dispersed in a stable solution state so that the carbon is not permanently cohered and thus is not precipitated. In case of the carbon graphite, a split is occurring in the laminated structure of the graphite particle, when the graphite is oxidized by the electrolysis, and thus, the graphite particle is changed into the carbon particulates according to the electric-chemistry reaction. In addition, this process contributes to the dispersion of the particles and the solution of the stable colloidal state. The supersonic wave applied to the electrolyte serves to split the carbon particulate and accelerate the oxidation of the surface. Also, the supersonic wave contributes to the homogeneous dispersion. Preferably, the low frequency, the middle frequency, and the high frequency are alternatively applied. The supersonic wave of high frequency has high penetrability and low cavitation intensity, while the supersonic wave of low frequency has low penetrability and high cavitation intensity. That is, since the penetrability and cavitation intensity of the supersonic wave are varied depending upon a pitch of the frequency, the carbon particle can be effectively split if the supersonic waves of high frequency, middle frequency, and low frequency are alternatively applied. Also, the supersonic wave disaggregates the cohered carbon particles to disperse the particles in the electrolyte, so that the electrolyte is homogeneously dispersed.

Since oxidation and reduction resulted from the sono- chemistry and electro-chemistry are occurring in each process, an electromotive force, pH of the colloidal solution, and the electric conductivity due to the carbon nano particles are varied. It is a base material to explain the state of the carbon nano particle. The technology, that the nano-sized particles are synthesized as the colloidal solution in the pure water by using sono-chemistry and electro-chemistry under room temperature and atmospheric pressure, without using any dispersing agent described above, is the first in the world. The particles are synthesized as the carbon nano colloidal solution of pH 2 to pH 3. It appears the very high electromotive force, for example, the surface of the carbon particle has high negative charge, and the electric conductivity is high in the colloidal solution.

Some examples obtained by the embodiment of the present invention are shown in Table below.

As can be known from Table, there is no or little coherence in Examples 2 to 5, except for Example 1. That is, if the carbon nano particle is in the range of several nm to 200 nm, the coherence is weak or none. In case the carbon nano particle of up to ph 3 is 50 nm or less, the dispersion stability is very excellent. Also, contents of the carbon nano particulates are 0.1 to 5.0wt% of the whole weight of the colloidal solution.

The present invention prepares the carbon nano colloidal solution with dispersion stability without using any dispersing agent which is usually used as a surfactant, such as sodium polycarbonate, ammonium polycarbonate, sodium naphthalene sulfonate, or polyvinyl pyrrolidone, so as to secure the stability of the colloid. The carbon nano colloidal solution prepared by the present invention is useful for a black coating to be applied on a surface a cathode-ray tube to improve a contrast of an image display device. Also, the present invention provides a paste composition for emitting electrons in an electron emission display apparatus by using the carbon nano colloid with good electric conductivity and electron emission which is prepared by the present invention. The carbon nano colloidal solution may activate the high electric conductivity of an inert substance .

FIG. 2a is a photograph of the carbon nano colloidal solution prepared by the present invention, and FIG. 2b is a TEM (Transmission Electron Microscope) photograph of particulates contained in the carbon nano colloidal solution prepared by the present invention. As can be known from the photographs, a grain size of the particulate is in the range of several nm to 200 nm, in which a black point denotes the particulate, and the grain size can be verified by a scale bar illustrated on a left lower end of the photograph. FIG. 2c is an AFM (Atomic Force Microscope) photograph of the carbon nano colloidal solution prepared by the present invention and shows that the grain size of the carbon particulate is in the range of several nm to 200 nm and the particulates are homogeneously dispersed in the solution. The photograph is taken from a surface morphology of the particulates after the colloidal solution is dried, in which white points denote the shape of the particulates. It can be known from FIGs 2a to 2c that carbon nano particles are homogenously dispersed in the carbon nano colloidal solution of the present invention.

FIG. 3 is a zeta potential graph depicting the dispersion stability of particles contained in the carbon nano colloidal solution of the present invention (Model: Malvern Instruments Zetasizer Nano S in U.K.). As can be known from the graph, the carbon nano particle of the present invention proves the dispersion stability in the solution in that Z. P corresponds to -40.95mv (excellent).

The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.

Industrial Applicability As apparent from the above description, the carbon nano colloidal solution with dispersion stability is prepared by using nano-sized carbon particles as a dispersoid in the pure water of a dispersive medium, without using any dispersing agent or additives to disperse the carbon particles. In addition, the colloidal solution with the high dispersion stability is prepared in the solution in the one-step process, while manufacturing the carbon nano particles. The carbon nano colloidal solution of the present invention obtains the colloid homogeneously dispersed with dispersoid which is the carbon nano particle having pH 2 to pH 3 at room temperature and atmospheric pressure, the high electromotive force (28OmV or more) , and the high electric conductivity (1600ms/cm). Also, the present invention can mass produce the carbon nano colloid stably dispersed in the dispersive medium of the pure water above 1 ton per day. The carbon nano colloidal solution of pH 2 to pH 3 is especially useful for a black coating to be applied on the surface the cathode- ray tube to improve the contrast of the image display device.

Claims

1. A method of preparing a carbon nano colloidal solution, comprising the steps of: disposing a carbon electrode and an opposite electrode in a pure water; and applying electricity to the electrodes and applying supersonic waves to the pure water to synthesize carbon nano particles; wherein the carbon nano particles are hydrophilic and are homogenously dispersed in the pure water, aldehyde radical and/or carboxyl radial being formed on a surface of the carbon nano particle.

2. The method as claimed in claim 1, wherein the carbon electrode is a graphite plate.

3. The method as claimed in claim 1, wherein the carbon nano colloidal solution is pH 3 or less.

4. The method as claimed in claim 1, wherein the carbon nano colloidal solution comprises carbon nano particles of 0.1 to 5wt% of the whole solution.

5. The method as claimed in claim 1, wherein the carbon electrode is immersed in the pure water during a certain time so that the pure water infiltrates into an internal structure of graphite having a laminated structure.

6. A carbon nano colloidal solution prepared by any one of the above claims 1 to 5.

7. The carbon nano colloidal solution as claimed in claim 6, wherein the carbon nano colloidal solution is pH 3 or less.

8. The carbon nano colloidal solution as claimed in claim 6, wherein the carbon nano colloidal solution comprises carbon nano particles of 0.1 to 5wt% of the whole solution.