JP7114039B2 - METHOD FOR MANUFACTURING METAL NANOPARTICLES - Google Patents

Description

The present invention relates to a method for producing metal nanoparticles.

Metal nanoparticles are expected to have many advantages such as high specific surface area, high chemical activity, high hardness, high strength, low temperature sintering, new electronic state, etc., by reducing the particle size, especially 10 nm or less. It is thought that many new applications will be developed if the particle size is set to For example, metal nanoparticles made of ZnO (zinc oxide) have an excellent ultraviolet shielding function, antibacterial properties, small modifications, and high transparency. Therefore, it is applied in various fields such as pharmaceuticals, cosmetics, photocatalysts, plastics, etc., and is now indispensable to our lives.

Conventionally, metal nanoparticles are produced using crushing methods, liquid phase methods, pulsed wire discharge methods, and the like, but all of these methods have demerits. That is, the crushing method is a method in which a substance ejected using a high-pressure gas collides with a target member and is crushed to obtain target fine particles, and the particle size of the obtained fine particles is about 3 μm. . In addition, the liquid phase method is a method of obtaining target fine particles by precipitating ions and molecules present in a liquid. The cost is high due to the equipment required. In addition, the pulse wire discharge method is a method of obtaining target fine particles by evaporating, plasmatizing, and cooling a fine metal wire heated by applying a large pulse current. The cost is high by producing less and desired quantities.

Non-Patent Documents 1 and 2 report several examples in which ZnO fine particles with a particle size of several tens of nm were obtained using pulsed arc discharge. However, in these examples, ZnO and ZnO precursors are produced at a high rate, and they are in a mixed state, so that desired crystallinity is not obtained.

Kunisuke Fujii, Hirokazu Sato, Tsuyoshi Wang, Takao Namihira, Hidenori Akiyama, Kenji Shida, "Generation of ZnO Fine Particles Using Pulsed Arc Discharge Plasma", The 39th Annual Conference of the Institute of Electrostatics, Japan, 25pB-4, 2015.09.24-25 . Kunisuke Fujii, Hirokazu Sato, Tsuyoshi Wang, Takao Namihira, Hidenori Akiyama, "Generation of fine zinc oxide particles using microsecond pulse discharge plasma", Plasma/Pulse Power/Discharge Joint Study Group, PST-14-086, PPT-14 -070, ED-14-156, 2014.10.24-26.

The present invention has been made in view of the above circumstances, and provides a method for producing metal nanoparticles that enables easy production of metal nanoparticles having a desired particle size and crystallinity at low cost. intended to

In order to solve the above problems, the present invention provides the following means.

(1) A method for producing metal nanoparticles according to an aspect of the present invention is a method for producing metal nanoparticles composed of a metal element and a non-metal element, wherein between two electrodes containing the metal element, the A pulsed arc discharge is generated in a state in which the atmosphere gas containing the nonmetallic element is introduced. In the pulsed arc discharge, the arc current value is set to 100 A or more and the arc discharge generation time is set to 1 μs or less.

(2) In the method for producing metal nanoparticles according to (1) above, it is preferable that the pulsed arc discharge is generated using a Blumlein discharge circuit.

(3) In the Blumlein discharge circuit of the method for producing metal nanoparticles according to (2) above, one of the electrodes and the Blumlein line are connected via a matching resistance element having an electrical resistance of 1 kΩ or less. preferably.

(4) In the method for producing metal nanoparticles according to either (2) or (3) above, in the Blumlein discharge circuit, the length of the Blumlein line is preferably 0.1 m or more.

(5) In the method for producing metal nanoparticles according to any one of (1) to (4) above, it is preferable that the ambient gas is in a flow state in which it continues to flow in a predetermined direction.

The method for producing metal nanoparticles of the present invention generates a pulse arc discharge between electrodes containing a target substance, and is a simple process compared to conventional methods such as liquid phase methods that require expensive reagents. can be carried out and the manufacturing cost can be kept low.

In the pulsed arc discharge, the arc discharge formation time is a parameter that controls the particle size of the metal nanoparticles generated. particles can be obtained. In the pulsed arc discharge, the arc current value is a parameter for controlling the crystallinity of the particles generated. High metal nanoparticles can be obtained.

Thus, according to the method for producing metal nanoparticles of the present invention, it is possible to easily produce metal nanoparticles having a desired particle size and crystallinity at low cost.

1 is a diagram showing the configuration of an apparatus for producing metal nanoparticles according to an embodiment of the present invention; FIG. 2 is a diagram showing a configuration example of a pulsed power generator in the metal nanoparticle manufacturing apparatus of FIG. 1. FIG. 2 is a diagram showing another configuration example of a pulsed power generator in the metal nanoparticle manufacturing apparatus of FIG. 1. FIG. 1 is a graph showing the results of X-ray diffraction analysis of ZnO particles obtained under the conditions of Example 1 of the present invention. It is an X-ray diffraction pattern of ZnO of PDF card number: 01-080-0074 (crystal system: hexagonal space group: P63mc(186)) registered in the Inorganic Crystal Structure Database. 1 is an SEM image of ZnO particles obtained in Example 1. FIG. FIG. 3 is a diagram showing a configuration example of a pulsed power generator in a metal nanoparticle manufacturing apparatus according to a comparative example of the present invention. 4 is a graph showing the results of X-ray diffraction analysis of ZnO particles obtained under the conditions of Comparative Example 1 of the present invention. 4 is a graph showing the results of X-ray diffraction analysis of ZnO particles obtained under the conditions of Comparative Example 2 of the present invention. (a) and (b) are SEM images of ZnO particles obtained in Comparative Examples 1 and 2. FIG.

Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. In the drawings used in the following explanation, in order to make it easier to understand the features of the present invention, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios and the like of each component are different from the actual ones. There is The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate changes within the scope of the present invention.

<First embodiment>
[Device for producing metal nanoparticles]
TECHNICAL FIELD The present invention relates to a method for producing metal nanoparticles composed of a metal element and a non-metal element. A configuration of a metal nanoparticle manufacturing apparatus 100 according to a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram showing a schematic configuration of an apparatus 100 for producing metal nanoparticles. An apparatus 100 for producing metal nanoparticles includes a sealed container (reactor) 101, two metal electrodes 102 (102A, 102B) arranged in the container 101, and means for regulating the pressure inside the container 101 (pressure regulating means). 103, means (gas supply means) 104 for supplying atmospheric gas between the metal electrodes 102A and 102B, means (not shown) for evacuating the inside of the container 101, and means for controlling the temperature inside the container 101 (temperature control means). means) 105 and a pulse power generator 106 for applying a voltage between the metal electrodes 102A and 102B.

As the container 101, one made of an insulating material such as polyphenylene sulfide (PPS) resin, polyetheretherketone (PEEK) resin, or ceramics can be used. The shape of the container 101 is not limited as long as the inside can be sealed.

As the metal electrodes 102A and 102B, those containing as a main component a metal element constituting the target metal nanoparticles are used. Examples of metal elements here include Zn, Cu (copper), Ti (titanium), Li (lithium), Be (beryllium), Na (sodium), Mg (magnesium), Al (aluminum), Si (silicon ), K (potassium), Ca (calcium), Sc (scandium), V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Ga (gallium ), Rb (rubidium), Sr (strontium), Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Ru (ruthenium), Rh (rhodium), Pd (palladium), Ag (silver ), Cd (cadmium), In (indium), Sn (tin), Sb (antimony), Te (tellurium), Ba (barium), Hf (hafnium), Ta (tantalum), W (tungsten), Re (rhenium ), Os (osmium), Ir (iridium), Pt (platinum), Au (gold), Tl (thallium), Pb (lead), Bi (bismuth), Po (polonium), La (lanthanum), Ce (cerium ), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium) ), Tm (thulium), Yb (ytterbium), Lu (lutetium), Ac (actinium), Th (thorium), and alloys of these metals. For example, when producing ZnO (zinc oxide) particles, Zn is used as the metal element.

Both of the metal electrodes 102A and 102B are flat plate-shaped, and are arranged so that their main surfaces face each other. Practically, from the viewpoint of generating more metal nanoparticles, the larger the area of the main surfaces (opposing surfaces) of the metal electrodes 102A and 102B, the better. Moreover, from the viewpoint of reducing the frequency of electrode replacement, the thicker the metal electrodes 102A and 102B, the better.

The atmosphere gas supplied by the gas supply means 104 contains, as a main component, a non-metallic element that constitutes the target metal nanoparticles. Examples of nonmetallic elements in this case include O ₂ (oxygen), N ₂ (nitrogen), F ₂ (fluorine), PH ₃ (phosphine), Cl ₂ (chlorine), CO ₂ (carbon dioxide), CO ( carbon monoxide), H ₂ (hydrogen), BCl ₃ (boron trichloride), and the like. For example, when producing ZnO (zinc oxide) particles, O ₂ is used as the nonmetallic element.

FIG. 2 is a diagram showing a specific circuit configuration including a pair of metal electrodes 102A and 102B in the pulsed power generator 106 used in this embodiment. The pulse power generator 106 is a discharge circuit element using a Blumlein line, and mainly includes a power supply 107, a switch element 108, two pairs (four in total) of the Blumlein line 109, a charging resistance element 110, and a matching resistance element 111. and A thyratron switch, a self-explosive spark gap switch, a semiconductor switch, or the like is used as the switch element 108 . It is assumed that each Blumlein line 109 is charged in advance.

The Blumlein line 109 is composed of a coaxial line or a parallel plate line made of a metal and an insulator called a distributed constant line. In this embodiment, the case where the two pairs of Blumlein lines 109 are configured as coaxial lines is illustrated. The two pairs of Blumlein lines 109 each consist of a rod-shaped inner conductor 109A, a cylindrical outer conductor 109B surrounding it, and an insulator (not shown) filling between the two conductors. As the inner conductor 109A and the outer conductor 109B, a known metal material such as copper can be used. As the insulator, one made of crosslinked polyethylene or the like can be used.

The length of the Blumlein line 109 is preferably 0.1 m or more and 100 m or less. When the length of the Blumlein line is extended, the pulse width is widened and the heat treatment time is increased, so that the sintering proceeds and, as a result, the existence ratio of the precursor decreases. If the pulse width is short, the heat treatment time will be shortened, and particles that cannot be completely converted to ZnO will be produced as a precursor. Since the pulse width is a parameter that changes the size of the metal nanoparticles, metal nanoparticles of a desired size can be obtained by adjusting the pulse width by changing the length of the Blumlein line.

A power source 107 and a switch element 108 are electrically connected to the inner conductor 109A of each Blumlein line. That is, the four inner conductors 109A are equipotential. The outer conductor 109B 1 of one of the two pairs (the upper two in FIG. 2) of the Blumlein line and the outer conductor 109B ₂ of the other (the lower _two in FIG. 2) of the Blumlein line are They are electrically connected with the pair of metal electrodes 102A and 102B interposed therebetween.

The inner conductor 109A and the outer conductor 109B are connected via a switch element 108, and are configured such that their conduction states are switched by turning the switch element 108 on and off. When the switch element is turned on, a large amount of current flows from the Blumlein line in a short time due to a discharge phenomenon, a high voltage is applied between the metal electrodes 102A and 102B, and a pulse arc discharge is induced.

The outer conductor 109B of the Blumlein line and the power supply 107 are connected via a charging resistance element 110 that protects the DC power supply. As the charging resistance element 110, one having an appropriate resistance value corresponding to the DC power supply to be used is selected. Also, the outer conductor 109B of the Blumlein line and the metal electrode 102B are connected via a matching resistance element 111. FIG. The resistance of the matching resistance element 111 is preferably 0.1Ω or more and 1 kΩ or less.

[Method for producing metal nanoparticles]
A procedure for producing desired metal nanoparticles using the metal nanoparticle production apparatus 100 of FIG. 1 will be described.

First, using the pressure regulating means 103 and the temperature control means 105, the inside of the container 101 is regulated to a range of approximately 0.01 MPa or more and 1.0 MPa or less, and the heat resistant temperature range of the material of the container 101 (0 in the case of ceramics) °C to 2000 °C). As the pressure regulating means 103, a suitable combination of decompressing means such as a pump and pressurizing means such as a gas cylinder is assumed.

Next, the gas supply means 104 is used to introduce into the container 101 an atmospheric gas (raw material gas) containing a non-metallic element that constitutes the target metal nanoparticles. The inside of the container 101 after introduction is approximately 99.9 vol. % or more 99.99995 vol. % or less is preferably filled with atmospheric gas.

The atmospheric gas may be introduced before the pulse arc discharge process or intermittently at a predetermined timing, but from the viewpoint of keeping the amount of the atmospheric gas more constant, it saves the trouble of managing the amount of the atmospheric gas. From the point of view, etc., it is preferable to keep the liquid flowing continuously in a predetermined direction so as to continuously supply the liquid.

Next, using the pulse power generator 106, a high voltage is applied between the metal electrodes 102A and 102B to generate arc discharge. As a result, the electrons responsible for the arc discharge collide with the non-metallic element in the atmosphere gas, and the ions of the non-metallic element turned into plasma come into contact with the ions of the metallic element turned into plasma in the metal electrodes 102A and 102B. reacts to form metal nanoparticles.

In order to obtain smaller metal nanoparticles, the shorter the arc discharge generation time (arc discharge generation time), the better. For example, if the arc discharge generation time is set to 1 μs or less, small particles having a particle size of 10 nm or less can be obtained.

However, when the arc discharge generation time is shortened, the sintering does not proceed, so the formed metal nanoparticles contain a high proportion of particles (precursors) that are not completely crystallized, and have sufficient crystallinity. It will be something that has not been done. Therefore, the voltage applied between the metal electrodes 102A and 102B is adjusted so that the value of the current flowing between the metal electrodes 102A and 102B due to arc discharge (arc current value) is 100A or more. When the arc current value is 100 A or more, the proportion of crystallized particles increases, and the formed metal nanoparticles have sufficient crystallinity.

Finally, the voltage application between the metal electrodes 102A and 102B is stopped, the atmosphere gas in the container 101 is exhausted, and the formed metal nanoparticles are recovered using a brush or the like.

As described above, the method for producing metal nanoparticles according to the present embodiment generates a pulsed arc discharge between electrodes containing a target substance, and is a conventional method such as a liquid phase method that requires an expensive reagent. It can be carried out in a simpler process than in , and the manufacturing cost can be kept low.

In the pulsed arc discharge, the arc discharge formation time is a parameter that controls the particle size of the metal nanoparticles to be generated. Nanoparticles can be obtained. Further, in the pulsed arc discharge, the arc current value is a parameter for controlling the crystallinity of the particles generated. high metal nanoparticles can be obtained.

As described above, according to the method for producing metal nanoparticles according to the present embodiment, it is possible to easily produce metal nanoparticles having a desired particle size and crystallinity at low cost.

<Second embodiment>
An apparatus and method for producing metal nanoparticles according to a second embodiment of the present invention will be described. FIG. 3 is a diagram showing the circuit configuration of the pulse power generator 126 used in this embodiment. The pulsed power generator 126 differs from the pulsed power generator 106 of the first embodiment only in that no matching resistance element is connected to the metal electrode 122B.

The apparatus for producing metal nanoparticles used in this embodiment is the same as the apparatus for producing metal nanoparticles 100 of the first embodiment except for the configuration of the pulsed power generator 126 . In addition, the method for producing metal nanoparticles used in this embodiment is the same as the method for producing metal nanoparticles in the first embodiment except that the pulsed arc discharge is generated using the pulsed power generator 126 .

In the pulsed power generator 126 of the present embodiment, since the matching resistance element is not connected, more current flows between the metal electrodes 122A and 122B, and the discharge duration becomes longer. Since the firing proceeds, the ratio of crystallized particles, that is, the crystallinity can be further increased.

It should be noted that the same effects as in the first embodiment can be obtained in terms of process simplification, production cost reduction, and miniaturization of the obtained metal nanoparticles.

The effects of the present invention will be made clearer by the following examples. It should be noted that the present invention is not limited to the following examples, and can be modified as appropriate without changing the gist of the invention.

(Example 1)
Metal nanoparticles were produced using the apparatus and method for producing metal nanoparticles according to the first embodiment.

The pressure (gauge pressure) and temperature inside the vessel 101 were set to 0.05 MPa and 25° C., respectively, and a gas containing 99.7% of O ₂ (oxygen) was introduced as the atmospheric gas.

A pulsed power generator 106 having the circuit configuration of FIG. 3 was used. The power source 127 was a constant current source of 152A. A thyratron switch was used as the switch element 128 . The length of the Blumlein line 129 was set to 10 m, and the pulse width was set to 100 ns. The resistance of charging resistance element 120 was set to 900Ω.

A flat member containing 99.8% of Zn (zinc) was used as the metal electrodes 122A and 122B. The metal electrodes 122A and 122B had a thickness of 10 mm and an area of the facing surfaces of π×30×30 mm ² .

The distance between the metal electrodes 122A and 122B was set to 1 mm, the output voltage and frequency of the power supply 127 were set to 24 kV and 500 Hz, respectively, and pulsed arc discharge was generated between the metal electrodes. The arc current maximum value at this time was 350A. The arc discharge generation time was set to 0.5 μs.

The sample obtained in Example 1 was analyzed by XRD (X-ray diffraction). FIG. 4 is a graph showing the analysis results. FIG. 5 is an X-ray diffraction pattern of ZnO of PDF card number: 01-080-0074 (crystal system: hexagonal space group: P63mc(186)) registered in the Inorganic Crystal Structure Database. In each graph, the horizontal axis indicates the diffraction angle, and the vertical axis indicates the diffraction intensity. In addition, the peaks indicated by circles (○) and the peaks indicated by squares (◇) in the graph correspond to ZnO and Zn ₅ (OH) ₈ (NO ₃ ) ₂ (H ₂ O) ₂ , respectively. .

In the graph of FIG. 4, the distribution of peaks at the same diffraction angles as in the graph of FIG. 5 can be seen, and it can be seen that the ratio of the sizes of those peaks (peak ratio) is about the same as in the graph of FIG. . That is, the graph of FIG. 4 includes the ZnO peak shown in the graph of FIG. In addition, when the pressure during discharge is high, Zn ₅ (OH) ₈ (NO ₃ ) ₂ (H ₂ O) is added to ZnO due to the presence of OH, NO ₃ , etc. on the surface or inside of the electrode. Precursors such as ₂ may also be produced.

6 is an FE-SEM (Field Emission Scanning Electron Microscope) image of the sample obtained in Example 1. FIG. The primary particles of the metal nanoparticles in the sample have a particle size of 10 nm or less, and the aggregated average particle size is 34 nm.

(Comparative example 1)
As the pulsed power generator 206, one having a capacitor discharge circuit shown in FIG. 7 was used to produce metal nanoparticles. The conditions were the same as in Example 1, except that the configuration of the pulse power generator 206 was changed to set the arc discharge generation time to 20 μs.

The capacitor discharge circuit of FIG. 7 charges the capacitors 209A and 209B and reverses the polarity with the thyratron switch element 208 so that a voltage doubled between the metal electrodes 202A and 202B in the container 201 is applied. It is configured.

(Comparative example 2)
Metal nanoparticles were produced under the same conditions as in Comparative Example 1 except that the pressure in the container 201 was set to 0.10 MPa.

The samples obtained in Comparative Examples 1 and 2 were analyzed by XRD. 8 and 9 are graphs showing analysis results corresponding to Comparative Examples 1 and 2, respectively. The horizontal and vertical axes of each graph are the same as in FIGS. The peaks indicated by circles (○) and squares (◇) in the graph respectively correspond to ZnO and Zn ₅ (OH) ₈ (NO ₃ ) ₂ (H ₂ O) ₂ .

In the graphs of FIGS. 8 and 9 as well, the distribution of peaks at the same diffraction angles as in the graph of FIG. 5 can be seen, and it can be seen that their peak ratios are approximately the same as in the graph of FIG. That is, the graphs of FIGS. 8 and 9 also include the ZnO peak shown in the graph of FIG.

10(a) and (b) are FE-SEM images of the samples obtained in Comparative Examples 1 and 2, respectively.

For the samples obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the particle size (average particle size) and abundance ratio (content ratio) of the ZnO particles contained were measured. Table 1 shows the measurement results.

In Example 1 using the Blumlein discharge circuit, the arc current value was set to 100 A or more and the arc discharge generation time was set to 1 μs or less, so that ZnO particles having an average particle size of 34 nm were included in a ratio of 90% or more. A highly crystalline sample was obtained. The obtained ZnO particles include those with a particle size of 10 nm or less. On the other hand, in Comparative Examples 1 and 2 using a capacitor discharge circuit, the arc discharge generation time is longer than 1 μA due to the nature of the circuit. Samples larger than particles have been obtained.

REFERENCE SIGNS LIST 100 Metal nanoparticle production apparatus 101, 121 Containers 102, 102A, 102B, 122A, 122B Metal electrode 103 Pressure adjusting means 104 Gas supply means 105 Temperature Control means 106, 126 Pulse power generators 107, 127 Power sources 108, 128 Switch elements 109, 129 Blumlein line 109A Inner conductors 109B, 109B ₁ , 109B ₂ , 109B, 109B ₁ , 109B ₂ . . . Outer conductors 110, 111, 120 .

Claims (3)

A method for producing metal nanoparticles composed of a metal element and a non-metal element, comprising:
A step of generating a pulsed arc discharge using a Blumlein discharge circuit in a state in which the atmospheric gas containing the non-metallic element is introduced between the two electrodes containing the metallic element;
In the pulse arc discharge, the arc current value is set to 100 A or more, the arc discharge generation time is set to 1 μs or less,
In the Blumlein discharge circuit, the length of the Blumlein line is 0.1 m or more ,
The metallic element is zinc, the non-metallic element is oxygen,
Assuming that the metal nanoparticles are particles of zinc oxide,
A method for producing metal nanoparticles , wherein the pulsed arc discharge is generated in a container in which the pressure is adjusted to a range of 0.01 MPa or more and 0.05 MPa or less . 2. Production of metal nanoparticles according to claim 1, wherein in the Blumlein discharge circuit, one of the electrodes and the Blumlein line are connected via a matching resistance element having an electrical resistance of 1 kΩ or less. Method. 3. The method for producing metal nanoparticles according to claim 1, wherein the atmosphere gas is in a flow state in which it continues to flow in a predetermined direction.

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