KR20140097650A - manufacturing method of cobalt nano fluid using liquid phase plasma reaction - Google Patents

Abstract

The present invention relates to a method for manufacturing a cobalt nanofluid using a liquid phase plasma reaction and, more specifically, to a method for manufacturing a cobalt nanofluid, wherein the manufacture and dispersion of the cobalt nanofluid are continuously conducted in a single process by generating plasma inside a liquid containing cobalt ions. The method for manufacturing a cobalt nanofluid using a liquid phase plasma reaction according to the present invention includes a precursor solution manufacturing step for manufacturing a precursor solution containing cobalt ions by dissolving cobalt chloride in water; a surfactant addition step for adding a surfactant into the precursor solution; and a liquid phase plasma reaction step for generating plasma inside the precursor solution added with the surfactant to generate cobalt nanoparticles.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a cobalt nanofluid using a liquid-phase plasma reaction,

The present invention relates to a process for producing a cobalt nanofluid by using a liquid-phase plasma reaction, and more particularly, to a process for producing a cobalt nanofluid by a plasma in which a process for producing and dispersing cobalt nano- The present invention relates to a method for producing a cobalt nanofluid.

Nanoparticles have been studied in recent years because of their optical, electrical, and catalytic properties, which are different from bulk materials. The properties of the nanofluids are determined by various factors such as the size and shape of the nanoparticles and the dispersibility. Because of the nature of these nanoparticles, they are used in many applications. For example, when nanoparticles are dispersed in a common fluid, the thermal conductivity and convective heat transfer effect are increased.

The concept of nanofluids was first introduced by the American ANL (Argonne National Laboratory). Nanofluids have a high thermal conductivity that conventional liquids do not have due to the uniform dispersion of solid nanoparticles with thermal conductivity of several hundred to several tens of times greater than liquids.

 A conventional nanofluid manufacturing method uses a two step method in which two steps are sequentially performed. The two step method is a method of manufacturing a nanofluid by performing a process of producing nanoparticles in a gas phase and a process of dispersing the produced nanoparticles in a liquid.

The two-step method is a domestic nanofluid-related research project that is designed and developed for the reactor design and safety analysis of a nuclear power plant. It is a technology to develop a fluid mixed with nanoparticles for improving the heat transfer coefficient in the cooling furnace. (Supporting institution: Ministry of Science and Technology, Basic Research Project, 2002.10 - 2003.09). In this study, the basic fluid was water and mechanical dispersion using ultrasonic wave was applied for dispersion stability of nanoparticles.

A method for producing a nanoparticle compound with a patented technique, a method for manufacturing a nanoparticle dispersion, and a device therefor are disclosed in Patent Publication No. 2010-0019599. The patented technique involves suspending the prepared nanoparticles with a carrier gas, subjecting the suspended nanoparticles to hydrophilization by atmospheric plasma treatment, mixing the nanoparticles with a liquid material, stirring the nanoparticles, and filtering the nanoparticles to produce a nanoparticle dispersion.

Thus, the conventional techniques use a two step method for producing nanofluids through a separate process of dispersing the nanoparticles produced after the process of manufacturing nanoparticles in a gas phase.

However, the conventional two-step method has advantages in that it can be mass-produced. However, since each step needs to be carried out in a separate process and apparatus, the production efficiency is low, and when the surface properties and fluid characteristics of the nanoparticles are different from each other, There are disadvantages.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for producing nanoparticles, which comprises generating plasma in a liquid containing nanoparticles in ionic form, The present invention provides a method for manufacturing nanofluids and cobalt nanoparticles using the same.

According to another aspect of the present invention, there is provided a method of preparing a cobalt nanofluid using a liquid-phase plasma reaction, the method comprising the steps of: preparing a precursor solution containing cobalt ions by dissolving cobalt chloride in water; A surfactant addition step of adding a surfactant to the precursor solution; And a liquid-phase plasma reaction step of generating cobalt nanoparticles by generating plasma in the precursor solution to which the surfactant is added.

Wherein the surfactant in the surfactant addition step is an anionic surfactant.

The anionic surfactant is sodium dodecyl sulfate.

The cobalt chloride in the precursor solution is 2.2 mM and the surfactant addition step is characterized by adding 20 to 30% of the anionic surfactant to the precursor solution in a molar ratio to the cobalt chloride.

The liquid-phase plasma reaction step is characterized in that the power supplied to the electrode exposed to the precursor solution is a voltage of 250 V, a pulse width of 1 to 5 μs, and a frequency of 30 kHz.

As described above, the plasma is generated in the precursor solution containing the cobalt ions, and the production and dispersion of the cobalt nanoparticles are continuously performed in the liquid, so that the nanofluid can be easily manufactured in one process.

In addition, the present invention can produce nano-sized cobalt particles by reducing cobalt ions in water using a liquid-phase plasma reaction.

In addition, the size and shape of the cobalt nanoparticles can be controlled using the concentration of the precursor, the discharge condition, and the surfactant.

FIG. 1 is a schematic view showing a liquid-phase plasma reactor applied to an embodiment of the present invention,
2 is a graph showing OES analysis results measured in pure distilled water,
FIG. 3 is a graph showing the OES analysis results (a) measured in the cobalt precursor solution and the OES analysis results (b) measured in the pure distilled water,
FIG. 4 is a TEM photograph of cobalt nanoparticles prepared by varying the discharge time and the concentration of cobalt chloride,
5 is a TEM photograph of cobalt nanoparticles prepared by varying the concentration of the surfactant and the discharge time,
6 is an EDX graph showing the results of chemical composition analysis of cobalt nanoparticles.

Hereinafter, a method for producing a cobalt nanofluid using a liquid-phase plasma reaction according to a preferred embodiment of the present invention will be described.

The method for producing a cobalt nanofluid using the liquid-phase plasma reaction of the present invention provides a nanofluid in which cobalt nanoparticles are uniformly dispersed in a liquid. The cobalt nanoparticles dispersed in the liquid may have an average size of 1 to 100 nm.

The method for preparing a cobalt nanofluid using a liquid-phase plasma reaction according to an embodiment of the present invention includes a step of preparing a precursor solution for preparing a cobalt ion-containing precursor solution, a step of adding a surfactant to the precursor solution, And a liquid-phase plasma reaction step of generating cobalt nanoparticles by generating a plasma in a precursor solution to which a surfactant is added. Hereinafter, each step will be described in detail.

1. Preparation of precursor solution

A precursor solution containing cobalt ions is prepared in the precursor solution preparation step.

An example of a precursor solution is obtained by dissolving a metal salt in water. The metal salt dissolved in water is a precursor of metal nanoparticles. Thus, the precursor solution means that the precursor metal salt is dissolved in water.

The type of metal salt depends on the type of metal to be nanostructured. For example, a cobalt salt, such as cobalt chloride (CoCl ₂ ), can be used to produce cobalt nanoparticles.

In the precursor solution obtained by dissolving cobalt chloride in water, cobalt exists in the form of a cation (Co ^{2 +} ). Cobalt chloride may be dissolved in water at a concentration of 0.5 to 10.0 mM. Depending on the molar concentration of dissolved cobalt chloride, the electric conductivity of the precursor solution changes. Electrical conductivity affects the properties of the resulting cobalt nanoparticles. The higher the electric conductivity, that is, the larger the molar concentration of cobalt chloride, the larger the number and size of the produced cobalt nanoparticles.

2. Add surfactant step

When the precursor solution is prepared, a surfactant addition step of adding a surfactant is performed.

By adding a surfactant to the precursor solution, it is possible to manufacture highly dispersed nanoparticles having a smaller particle size more efficiently.

When the solid particles (1 μm or less) are dispersed in an aqueous solution to form a suspension, the surface of the particles is positively or negatively charged. The mechanism of generating charges on the surface of such particles is not clearly defined not.

The metal nanoparticles prepared in the present invention have a charge at the interface with the solution except for special cases. If the charge value of the metal nanoparticle has a negative sign, it can be judged that it is charged with a negative charge such as a negative charge or a hydroxide ion. If the metal nanoparticles produced in solution are negatively charged, use a cationic surfactant. If the metal nanoparticles are charged positively, use an anionic surfactant to disperse the metal nanoparticles in solution. .

In the present invention, it can be experimentally confirmed that cobalt nanoparticles can be dispersed using an anionic surfactant.

As an ionic surfactant, sodium dodecyl sulfate (SDS) may be used. In addition, laurylbenzene sulfonate (LAS) and sodium polyoxyethylene lauryl ether sulfate can be used, but sodium dodecyl sulfate is effective.

The concentration of the surfactant may be from 5 to 50% (molar ratio of surfactant to cobalt chloride dissolved in water).

3. Liquid Phase Plasma Reaction Step

After the surfactant is added, a plasma is generated in the precursor solution to produce cobalt nanoparticles.

The liquid phase plasma (LPP) reaction applied to the present invention is a technique for synthesizing and dispersing nanoparticles in a single process by generating a high-density, high-energy plasma in a liquid, which is economical and secures productivity, Dispersed metal nanoparticles can be produced.

The flow of ions and electrons in response to the application of electrical energy in the liquid generates a plasma in the liquid. When the liquid is water, the main generating elements of the plasma are hydrogen and oxygen. As the amount of electric energy applied increases, the flow of ions and electrons increases, and the plasma intensity can be increased. Plasma generation is related to the flow of electrons, and thus electrons are provided to the metal ions present in the liquid to generate nanoparticles by reduction.

An example of a liquid-phase plasma reactor for generating a plasma in a liquid phase is shown in Fig.

The illustrated liquid-phase plasma reactor includes a cylindrical reactor 10, a cooling tank 40 for circulating the precursor solution in the reactor 10 to maintain a constant temperature, a circulation pump 50, And an electric power supply (bipolar pulse power supply) 20 for supplying electric power to the electrode 30. The electrode 30 is made of tungsten, and the outside of the electrode 30 is covered with an insulator 35 made of a ceramic material. The distance between the two electrodes 30 can be maintained at about 0.7 mm.

When power is supplied to the electrode 30 through the power supply 20, a plasma is formed in the liquid by electric discharge to synthesize nanoparticles. In order to prevent the temperature of the precursor solution due to the high temperature from rising when the plasma is generated by the electric discharge, the circulation pump 50 is used to circulate the precursor solution to the cooling bath 40 to adjust the temperature of the precursor solution to 20 to 25 캜 . The reactor (10) and the cooling bath (40) are connected to circulation lines (45) and (55).

It is preferable to supply pulses (pulse width 1 to 5)) rather than supplying power continuously to the electrodes at the time of power supply. Supplying the power as a pulse suppresses the dissolution of the electrode exposed to the precursor solution, thereby greatly reducing the elution of the electrode component into the precursor solution.

The power supply condition supplied to the electrode for generating the plasma may be 250 V, a pulse width of 1 to 5 μs, and a frequency of 30 kHz. The discharge time can be maintained for 1 to 120 minutes.

When the plasma is generated in the liquid, the cobalt ions in the precursor solution are reduced and the cobalt nanoparticles can be produced in which the cobalt nanoparticles are uniformly dispersed in the liquid. As described above, the present invention can produce and disperse cobalt nanoparticles in a continuous process by generating a plasma in a precursor solution. Nanofluids can be used in a variety of industrial applications, such as local heating fluid transport fluids, industrial heat exchangers, and automotive engine cooling systems. Further, the cobalt nanoparticles dispersed in the nanofluid can be used as a carbon material (activated carbon, carbon nanotube, graphene, fullerene) or TiO ₂ And can be used in various high-tech materials for production.

Hereinafter, the production method of the cobalt nanofluid of the present invention will be described by way of examples. However, the following experimental examples are intended to illustrate the present invention in detail, and the scope of the present invention is not limited to the following experimental examples.

≪ Production test of nanofluids >

1. Preparation of precursor solution

Cobalt chloride (CoCl ₂ .6H ₂ O, Junsei Chemical Co., Ltd.) was added as a precursor to distilled water as a solvent to prepare a cobalt precursor solution, and the mixture was stirred for 10 minutes. The electric conductivity of the precursor solution according to the molar concentration of cobalt chloride is shown in Table 1 below.

Concentration (mM) Conductivity (μS / cm) 0.9 250 2.2 500 3.0 750

SDS (sodium dodecyl sulfate, C ₁₂ H ₂₅ NaO ₄ S, Tokyo Chemical Co., Ltd.) was added as a surfactant to the prepared precursor solution at 20% (surfactant / cobalt chloride molar ratio) and stirred for 10 minutes.

2. Experimental apparatus

The schematic structure of the liquid-phase plasma reactor used in this experiment is shown in Fig. A high-frequency bipolar pulse power supply (NTI-500W) was used as a power supply to induce the liquid-phase plasma reaction. The generated power was supplied to a pair of cylindrical reactors (outer diameter 40 mm, height 80 mm) Tungsten electrode (diameter 2 mm, purity 99.95%, TTM Korea Co.). The outside of the tungsten electrode inside the reactor was covered with a ceramic insulator, and the distance between the two electrodes was maintained at 0.3 mm.

In order to prevent the temperature rise of the precursor solution due to the high temperature when the liquid plasma was generated by electric discharge, the precursor solution was circulated to the cooling bath at a rate of 200 cc / min by using a circulation pump, and the temperature was maintained at 20 to 25 ° C.

After the precursor solution was charged into the reactor, power was supplied to the electrode under conditions of 250V, 30KHz, and 5μs to conduct the experiment. In one experiment, the amount of the precursor solution was adjusted to 300 mL.

3. Experimental Results

(1) Optical Emission Spectrum (OES)

In order to analyze the type and intensity of the material that emits the light when the plasma is generated, the spectrum of the light source generated in the plasma was measured in the range of 200 nm to 900 nm using Optical Emission Spectroscopy (AvaSpec - 3648, Avantes).

FIG. 2 is a graph showing OES analysis results when plasma is generated in pure distilled water. Although the difference in magnitude of the element-by-element ionized while the plasma is generated, the main generating elements as in FIG. 2 is _{OH (309nm), H β (} 486.1 nm), H α (656.3 nm), O Ι (777.1, 844.34 nm) , And it was confirmed that the plasma generated by OH was most strongly occurred. Through this, the active species OH, H _β , H _α , It is believed that the metal ions are reduced by the excellent reactivity of the O _Ⅰ to _produce metal nanoparticles.

FIG. 3 shows the OES analysis results (a) measured in the precursor solution when plasma was generated, and the OES analysis results (b) measured in pure distilled water. In FIG. 3, it was observed that the active species produced by the plasma reacted with the precursor solution, and the cobalt elements were generated at 331, 347, 514 and 608 nm.

(2) Characterization of metal particles according to cobalt chloride concentration and discharge time

The size and shape of the cobalt nanoparticles were observed using a HR-TEM (JEM 2100F, JEOL) to examine the characteristics of the cobalt nanoparticles in the prepared nanofluid. For analysis, nanofluid was dropped on microgird B type 150-Cu (Japan) and dried.

4 is a photograph of cobalt nanoparticles prepared by varying the discharge time and the concentration of cobalt chloride.

Referring to FIG. 4, the higher the concentration of cobalt chloride, the larger the number and size of cobalt nanoparticles. Also, as the discharge time became longer, the size of the cobalt nanoparticles increased. It was confirmed that the discharge time gradually increased as the discharge time increased while keeping the spherical shape until 10 ~ 30 minutes.

(3) Characterization of nanoparticles by surfactant concentration

In order to analyze the characteristics of cobalt nanoparticles according to surfactant concentration, surfactant concentration was changed from 10 to 30% in a state where the molar concentration of cobalt chloride in the precursor solution was fixed to an electric conductivity of 500 μS / cm. And the discharge time was varied from 10 to 120 minutes to prepare the nanofluid.

5 is a photograph of cobalt nanoparticles prepared by varying the concentration of the surfactant and the discharge time.

Referring to FIG. 5, the morphology of the cobalt nanoparticles was found to be influenced by the surfactant concentration. When the surfactant concentration was low, the particle size was large and the particles were aggregated. As the concentration of surfactant increased, the particle size decreased and the dispersibility changed steadily.

Particularly, when the discharge time is 10 to 30 minutes and the surfactant concentration is 20 to 30%, spherical cobalt nanoparticles of small size are well dispersed.

(4) Analysis of components of nanoparticles

In order to analyze the chemical composition of the cobalt nanoparticles, the components were analyzed using EDX attached to HR-TEM (JEM 2100F, JEOL), and the results are shown in FIG.

Referring to FIG. 6, in the case of the cobalt nanoparticles, Co 83.07%, Cu 16.03% and W 0.82% were measured. Copper appears to be detected by a copper grid used to lift the TEM specimen, and tungsten appears to have eluted from the electrode during discharge. Thus, except for copper and tungsten, pure cobalt can be seen.

Through the above experimental results, it was possible to produce nano-sized cobalt particles in the liquid by generating plasma in the precursor solution. Further, it was confirmed that the production and dispersion of cobalt nanoparticles in a liquid can be continuously performed in one process. Also, it was confirmed that the size and shape of cobalt nanoparticles can be controlled by using precursor concentration, discharge condition, and surfactant.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, and that various modifications and equivalent embodiments may be made by those skilled in the art. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

The cobalt nanofluid produced by the present invention can be applied to various industrial fields such as a district heat transfer fluid for transportation, an industrial heat exchanger, an engine cooling system for a vehicle, and the like, and is excellent in economy due to energy efficiency improvement.

The cobalt nanoparticles thus prepared can be used for various carbon materials (activated carbon, carbon nanotubes, graphene, fullerene), TiO₂ It is very useful for developing high-tech materials having various functions.

10: reactor 20: power supply
30: electrode 40: cooling tank
50: circulation pump

Claims (5)

A precursor solution preparation step of dissolving cobalt chloride in water to prepare a precursor solution containing cobalt ions;
A surfactant addition step of adding a surfactant to the precursor solution;
And a liquid-phase plasma reaction step of generating a plasma in the precursor solution to which the surfactant is added to produce cobalt nanoparticles. The method of claim 1, wherein the surfactant in the surfactant addition step is an anionic surfactant. 3. The method of claim 2, wherein the anionic surfactant is sodium dodecyl sulfate. 2. The method of claim 1, wherein the anionic surfactant is sodium dodecyl sulfate. 4. The method according to claim 2 or 3, wherein the cobalt chloride in the precursor solution is 2.2 mM,
Wherein the surfactant addition step comprises adding 20 to 30% of the anionic surfactant to the precursor solution in a molar ratio to the cobalt chloride, to the precursor solution. The method as claimed in claim 1, wherein the liquid-phase plasma reaction step comprises the steps of: supplying power to the electrode exposed to the precursor solution at a voltage of 250 V, a pulse width of 1 to 5 μs, and a frequency of 30 KHz; Gt;

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