JP2012052209A - Device and method for continuously manufacturing nanoscale conductive particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for continuously manufacturing a nanoscale conductive particles, which can manufactures nanoscale conductive particles continuously for long periods of time.SOLUTION: The device includes: a first vessel 10 storing a conductive liquid; a liquid feeding path 20 for feeding the conductive liquid into the first vessel; a cathode 30 disposed in the conductive liquid in the first vessel and formed of an electrically-conductive material; an anode 40 disposed in the conductive liquid, while taking a predetermined distance from the cathode; an electric power source 50 for applying a voltage that generates a glow discharge plasma in the proximity of the cathode between the cathode and the anode; one or more second vessels 60 storing the liquid; and a liquid flow path 70 for communicating the first vessel with the one or more second vessels.

Description

  The present invention relates to the production of conductive fine particles, and more particularly, to an apparatus and method for continuously producing nanoscale conductive fine particles of the same quality for a long time.

  In recent years, nanoscale conductive fine particles having a particle size of several nanometers to several hundred nanometers, for example, have emerged chemical, optical, and electromagnetic functions that are not found in microscale particles having a particle diameter larger than about 1 μm. , Attracting attention. Nanoscale conductive fine particles are expected to be applied to, for example, chemical reaction catalyst materials, magnetic powders for magnetic recording media, semiconductor element materials, conductive ink materials for wiring, and pharmaceutical and cosmetic materials. .

  Nanoscale conductive fine particles are generally manufactured using a gas phase method or a liquid phase method, which is a build-up process in which a raw material at a molecular level is grown and generated. In any of these methods, improvement in the quality and productivity of the conductive fine particles are a problem. The gas phase method is mainly a method of vaporizing a pure substance and aggregating the vapor, and it is easy to obtain fine particles having a high purity and a small particle diameter. However, there are drawbacks in that a large-scale apparatus is required for vaporization, aggregation, and collection of the generated conductive fine particles, and that production efficiency and energy efficiency are low. The liquid phase method is a method of synthesizing fine particles mainly using a chemical reaction in a liquid phase. The liquid phase method can easily produce a large amount of fine particles, and has the advantage that a substrate is not necessary for the production of fine particles, but it is easy to introduce impurities, the particle shape is difficult to control, and a few nanometers or less. There are drawbacks such as difficulty in producing fine particles.

  For these techniques, a technique disclosed in Patent Document 1 has been proposed. In the technique in Patent Document 1, conductive fine particles using a cathode material as a raw material are generated using plasma generated using a counter electrode arranged in a conductive liquid. The cathode is locally dissolved by the glow discharge plasma in liquid, which is a non-thermal plasma generated only in the vicinity of the cathode, and the dissolved cathode material is released into the liquid and solidified into a spherical shape by surface tension. Conductive fine particles are produced. This method uses the reaction process in the coexistence region of the liquid phase and the gas phase converted to plasma by discharge in the vicinity of the cathode in the liquid, and thus has the advantages of the conventional liquid phase method and the gas phase method. Technology. According to the technique of Patent Document 1, high-quality nanoscale conductive fine particles can be generated in a short time in a stably controlled state.

International Publication No. 2008/099618

  The technique of Patent Document 1 has the following problems. The technology disclosed in Patent Document 1 is a batch technology using a single container. Therefore, the concentration of fine particles in the conductive liquid increases with the passage of time, causing aggregation, and the average particle size of the produced fine particles increases. In order to prevent agglomeration, a thin electrode, for example, a cathode having a cross-sectional diameter of about 1 mm must be used, or a single container must have a large capacity. When a thin cathode is used, the current density of the cathode continues to increase with the passage of time, and fine particles having a large particle diameter begin to be generated, so that the particle size distribution width of the finally obtained particles becomes wide. Further, when such a thin cathode is used, the electrodes are consumed and disconnected in a short time, so that the fine particles can be produced only for a short time and the yield is low. On the other hand, even if a large-capacity container is used, it is not possible to increase the distance between the electrodes without restriction depending on the capacity of the container. Aggregation occurs. In addition, when a large-capacity container is used, the amount of conductive liquid increases, which causes inconvenience in terms of handling.

  Furthermore, since the technique of Patent Document 1 uses a single container, another operation is required to collect and classify the generated fine particles, and conductive fine particles having different properties are generated at a time. It is difficult.

  In view of such circumstances, an object of the present invention is to provide a continuous production apparatus for nanoscale conductive fine particles capable of continuously producing nanoscale conductive fine particles having a small average particle diameter over a long period of time. .

  In producing nano-scale conductive fine particles using glow discharge plasma in a conductive liquid, the inventors have set the concentration of the conductive fine particles contained in the conductive liquid to prevent aggregation of the conductive fine particles. By providing a mechanism for maintaining the size of the cathode, the present invention is completed based on the knowledge that conductive fine particles can be continuously produced without causing aggregation in the liquid. I let you.

  The first aspect of the present invention provides an apparatus for continuously producing nanoscale conductive fine particles. The apparatus includes a first container containing a conductive liquid, a liquid supply path for supplying the conductive liquid to the first container, and a conductive material disposed in the conductive liquid in the first container. A cathode made of a conductive material, an anode arranged in a conductive liquid at a predetermined distance from the cathode, and a power source for applying a voltage between the cathode and the anode to generate a glow discharge plasma in the vicinity of the cathode One or a plurality of second containers that contain liquid, and a liquid flow path that communicates the first container and the one or more second containers. By applying a voltage between the cathode and the anode, conductive fine particles are generated in the conductive liquid in the first container. The concentration of the conductive fine particles in the first container is such that the conductive liquid is supplied from the liquid supply path to the first container, and moves from the first container to one or more second containers through the flow path. By doing so, the concentration is maintained such that the conductive fine particles do not aggregate.

  In one embodiment of the present invention, each of the first container and the one or more second containers is connected in series via a flow path, and the conductive liquid overflows the first container. Move to one of the one or more second containers. Furthermore, the liquid overflowing the container moves to the next one of the one or more second containers. In another embodiment of the invention, the one or more second containers are connected in parallel, and the first container is connected in series with one of the containers. Therefore, the liquid overflowing from the first container moves to one or more second containers connected in parallel. As described above, the conductive liquid sequentially moves from the first container to the next container, so that the amount of liquid in each container is maintained substantially constant. The concentration of the conductive fine particles is maintained at a concentration at which aggregation does not occur.

  In one embodiment, the flow path connecting each container is a pipe, both ends of which are located in the liquid of another container. The pipe is provided with a mechanism for adjusting the vertical position in the liquid at both ends of the pipe. By adjusting the position of the end using this mechanism, the concentration and particle size of the conductive fine particles in the liquid can be controlled.

  In one embodiment, it is preferred that at least the portion of the cathode disposed in the conductive liquid does not have an edge. For example, in the case of a columnar electrode having a polygonal cross section, an edge corresponding to the apex of the polygon in the cross section exists on the side surface of the electrode along the major axis direction of the electrode. Further, in the case of a cylindrical electrode, there is no edge on the side surface, but there are edges on both ends unless both ends are rounded. In one embodiment of the present invention, a cylindrical cathode is used, and it is preferable that an insulating cover that covers the tip of the cathode is attached at least in the portion of the cathode disposed in the conductive liquid.

  In one embodiment, there are two or more anodes, in which case the distance between the cathode and each anode is equal.

  In one embodiment, the apparatus further comprises a partition disposed between the cathode and the anode. With this partition wall, the conductive fine particles generated from the cathode can be made difficult to diffuse inside the first container.

  The second aspect of the present invention provides a method for continuously producing nanoscale conductive fine particles. In this method, a predetermined voltage is applied to an anode disposed in a conductive liquid in a first container and a cathode made of a conductive material, glow discharge plasma is generated in the vicinity of the cathode, and nanoscale Generating conductive fine particles, supplying a conductive liquid into the first container, and moving the conductive liquid from the first container to one or a plurality of second containers via the flow path. Including. By these steps, the concentration of the conductive fine particles in the conductive liquid in the first container is maintained at a concentration at which the aggregation of the conductive fine particles does not occur.

  According to the present invention, a plurality of containers containing conductive liquids are connected in multiple stages, and the conductive liquid containing the generated conductive fine particles is sequentially overflowed from the preceding container to the subsequent container, thereby The concentration of the conductive fine particles contained in the conductive liquid in the container can be maintained at a concentration at which no aggregation occurs. Therefore, according to the present invention, the conductive fine particles can be continuously produced over a long time without aggregation of the conductive fine particles. In addition, since a large-sized cathode can be used, the current density of the cathode can be maintained almost constant over time, and the yield of conductive fine particles is large. Accordingly, fine particles having a small particle size can be produced for a long time, and a large amount of fine particles having a narrow particle size distribution range can be obtained.

  Furthermore, according to the present invention, since no edge is present in the cathode disposed in the conductive liquid, the current concentration phenomenon in the vicinity of the cathode surface can be uniformly generated over the entire cathode. It is possible to continuously produce conductive fine particles having a uniform and small particle diameter.

  Furthermore, according to the present invention, since a plurality of containers are connected continuously, it is possible to collect conductive fine particles having different particle diameters for each container, and without conducting a separate operation. Classification of conductive fine particles becomes possible. If the liquids stored in the plurality of containers are different from each other, conductive fine particles having different properties can be generated at a time.

  Furthermore, in the conventional liquid phase method or gas phase method, since the running cost increases, it is not preferable to stop the apparatus. On the other hand, according to the present invention, the operation of the main container can be stopped to easily stop the apparatus, and plasma can be generated as long as the temperature of the conductive liquid does not greatly decrease. As long as it can be restarted easily. Therefore, another electroconductive fine particle can be easily manufactured continuously by stopping the apparatus, cleaning the container and the anode, and replacing the cathode with another material.

It is the schematic of one Embodiment of the apparatus which manufactures the nanoscale electroconductive fine particle which concerns on one Embodiment of this invention continuously. FIG. 2 is a perspective view of the apparatus of FIG. It is a longitudinal cross-sectional view of an example of the electrode which does not have an edge based on one Embodiment of this invention. It is the electrode used in the Example. It is a SEM image of silver fine particles manufactured by the device concerning one embodiment of the present invention. It is a SEM image of silver fine particles manufactured by the device concerning one embodiment of the present invention. It is a SEM image of silver fine particles manufactured by the device concerning one embodiment of the present invention. It is a SEM image of silver fine particles manufactured by the device concerning one embodiment of the present invention. It is a SEM image of the copper particulates manufactured by the device concerning one embodiment of the present invention. It is a SEM image of the copper particulates manufactured by the device concerning one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
The present invention provides an apparatus for continuously producing nanoscale conductive fine particles. The nano-scale conductive fine particles refer to conductive fine particles having a particle size of a nanometer order lower than a micrometer order, that is, conductive fine particles having a particle diameter of about several nm to several hundred nm.

(Generation principle of nano-scale conductive fine particles)
First, the principle of producing nanoscale conductive fine particles will be described. This principle is described in detail in Patent Document 1. Nanoscale conductive fine particles are prepared by placing an anode and a cathode made of a conductive material to be generated in a conductive liquid and applying a voltage between the cathode and the anode to generate glow discharge plasma near the cathode. It can be formed by generating. Specifically, a voltage is applied to the counter electrode composed of the cathode and the anode, the temperature of the conductive liquid around the cathode is raised to the boiling point or higher, and vaporization is performed in the gas phase generated in the vicinity of the cathode. Is generated. This plasma locally melts the cathode, and the melted material re-solidifies in the conductive liquid, thereby generating conductive fine particles.

  By applying a voltage to the counter electrode, the electrode temperature rises due to power loss at the cathode surface, and when the conductive liquid around the cathode rises above the boiling point, a sheath (sheath) -like gas containing water vapor around the cathode. A phase occurs. When a voltage is further applied, continuous ionization occurs in the generated gas phase, and glow discharge plasma is generated in the gas phase around the cathode. When the plasma is generated, a current concentration phenomenon occurs in the sheath plasma at the interface between the cathode and the conductive liquid. Thereby, the temperature of the surface of the conductive material constituting the cathode locally exceeds the melting point of the material, and the material is locally melted. The material that is melted and released from the cathode surface in the form of droplets enters the conductive liquid, is formed into a substantially spherical shape by surface tension, and is then rapidly cooled to become nanoscale conductive fine particles.

(Structure of the apparatus 1 for continuously producing nanoscale conductive fine particles)
<Main container, sub container, flow path>
FIG. 1 is a schematic view showing an embodiment of an apparatus 1 for continuously producing nanoscale conductive fine particles according to the present invention. The right side of FIG. 1 is a front view, and the left side is a side view. FIG. 2 is a perspective view of the device 1 shown in FIG. By the apparatus 1 according to the present invention, it is possible to continuously produce conductive fine particles having a small average particle diameter without any post-treatment such as spheroidization. The apparatus 1 comprises a main container 10 and one or more sub-containers 60 connected to the main container 10 by a fluid flow path 70. In FIG. 1, two sub-containers 60a and 60b are shown. In this case, the sub-container 60b is the final container. For this reason, fine particles having a small particle size distribution width and a small particle size can be recovered from the final container. The main container 10 contains a conductive liquid CL. The one or more sub-containers 60 contain the conductive liquid CL or other liquid depending on the properties of the generated conductive fine particles. The main container 10 is supplied with a conductive liquid CL from an external conductive liquid supply source (not shown) via a liquid feeding path 20 by a pump (not shown). The lower end of the liquid feeding path 20, that is, the vertical position of the conductive liquid outlet 21 is preferably near the bottom surface of the main container 10. When the outlet 21 is supplied to the main container 10 from near the liquid level of the conductive liquid, the conductive liquid in the main container 10 is agitated, and as a result, the generated conductive fine particles in the main container 10 are appropriately There are cases where classification is not possible.

<Material and capacity of container>
The material of the main container 10 and the one or more sub-containers 60 is not particularly limited as long as it is stable with respect to the liquid to be stored, and may be, for example, glass or plastic. The size of the main container 10 and the one or more sub-containers 60 is not particularly limited as long as it can accommodate an amount of liquid necessary to realize the present invention and does not become difficult to handle. Good. Moreover, the size of each container may be the same or different from each other.

<Connection between containers>
In one embodiment of the present invention, the main container 10 and each of the one or more sub-containers 60 are preferably connected in series by a flow path 70 that communicates each of the containers. That is, as shown in FIGS. 1 and 2, the main container 10 and the first sub container 60 a among the one or more sub containers 60 are connected by the flow path 70. In addition, the first sub container 60a and the second sub container 60b of the one or more sub containers 60 are also connected by the flow path 70. Similarly, the one or more containers 60 are respectively Are connected in series by a flow path 70. In another embodiment of the present invention, the main container 10 and one of the one or more sub-containers 60 are connected by a flow path 70, and the one container and the one or more sub-containers 60 are connected. The other container can be connected in parallel by the flow path 70. In yet another embodiment of the present invention, the main container 10 and one or more sub-containers 60 may be connected in part in series and part in parallel. In this way, the main container 10 and the one or more sub-containers 60 are connected in series and / or parallel in multiple stages, and the liquid overflowed from the preceding container is sent to the succeeding container. Therefore, the concentration of the conductive fine particles in each container can be maintained at a concentration at which aggregation does not occur, and the conductive fine particles can be classified according to the particle diameter using multistage connection.

  As shown in FIGS. 1 and 2, the channel 70 may be a hollow pipe in one embodiment. Both ends of the flow path 70 serving as the liquid inlet / outlet are disposed in the liquid in different containers. Accordingly, when the conductive liquid CL in the preceding container, for example, the main container 10 exceeds a certain amount, that is, when the level of the conductive liquid in the main container 10 exceeds the height of the inlet 71 of the flow path 70. In addition, the excess amount of the conductive liquid CL moves through the flow path 70 to the subsequent container, for example, the sub container 60a. The number of the flow paths 70 that connect the former container and the latter container may be one or plural. For example, the main container 1 and the sub container 60 a can be connected by five flow paths 70.

  The vertical position of the inlet 71 of the conductive liquid in the flow path 70, that is, the distance from the bottom surface of the container to the inlet 71 is the concentration of the conductive fine particles contained in the conductive liquid maintained in each container. Can be changed according to the condition of how much concentration is kept. For example, when the position of the inflow port 71 is lowered, the amount of the conductive liquid CL in the main container 10 is reduced, so that the concentration of the conductive fine particles in the conductive liquid CL is increased when the other conditions are the same. . Conversely, when the position of the inflow port 71 is increased, the concentration of the conductive fine particles in the conductive liquid CL is decreased. Note that if the concentration of the conductive fine particles in the conductive liquid CL is too high, the conductive fine particles are aggregated. Therefore, the lower limit of the position of the inlet 71 is a concentration at which the conductive fine particles are not aggregated. Must be in a position to be maintained.

  Further, the size of the conductive fine particles flowing out to the lower container 60 can be controlled by changing the position of the inflow port 71 in the vertical direction. That is, the conductive fine particles generated in the main container 10 include fine particles of various sizes, and those having a large particle size sink below the main container 10 and those having a small particle size float upward. Become. Therefore, as the vertical position of the inlet 71 is lowered, the conductive fine particles having a large particle size flow out into the lower container 60, and as a result, the particle size distribution width of the conductive fine particles accommodated in the lower container 60 becomes wider. . Conversely, as the vertical position of the inflow port 71 is increased, the conductive fine particles having a small particle size preferentially flow out to the lower container 60, and as a result, the particle size distribution of the conductive fine particles accommodated in the lower container 60. The width becomes narrower. The vertical position of the conductive liquid outlet 72 in the flow path 70, that is, the distance from the bottom surface of the container to the outlet 72 can be arbitrarily set.

  The position of the inflow port 71 of the conductive liquid in the flow path 70 in the horizontal direction, that is, the position of the inflow port 71 when the container is viewed from above is not particularly limited. In the embodiment of the present invention shown in FIGS. 1 and 2, the flow path 70 is located at the center of the container end, which is considered to connect the main container 10 and the plurality of containers 60. This is because. That is, for example, considering the next container 60a after the main container 10, the position 72 where the liquid from the preceding container 10 flows into the container 60a and the position 71 where the liquid flows out into the succeeding container 60b are within the container 60a. In order to maintain a uniform concentration of liquid in In consideration of such a state, in the present embodiment, the flow path 70 is installed at the center of the end of the container.

  In one embodiment of the present invention, the flow path 70 includes a plurality of hollow pipes 70a, 70b, and 70c and a connection member 75 such as a joint made of silicon rubber that connects the plurality of hollow pipes 70a to 70c. can do. The height of the liquid inflow port 71 or the outflow port 72 in the container can be adjusted by moving the end portions of the hollow pipes apart from or close to each other inside the connecting member 75. The material of the hollow pipes 70a to 70c is not particularly limited as long as it is stable with respect to the conductive liquid passing through the inside, and for example, glass, plastic or the like can be used.

  The physical positional relationship between each of the main container 10 and the one or more sub-containers 60 is not particularly limited, and the liquid in the container may flow from the preceding container to the succeeding container through the flow path 70 without delay. Any arrangement can be used.

  In the present specification, the case where there is only one main container is described, but naturally, it is also possible to produce conductive fine particles using a plurality of main containers. In this case, the concept of connection between the main container and the sub-container described in this specification is expanded, and an apparatus for continuously producing the conductive fine particles of the present invention includes a plurality of main containers and each main container. It can be thought of as a system using one or more sub-containers connected to the container. According to such a system, a larger amount of conductive fine particles can be continuously produced.

<Conductive liquid>
The solvent of the conductive liquid CL may be any liquid that can dissolve the electrolyte substance. Examples thereof include organic solvents such as ethylene carbonate, diethyl carbonate, propylene carbonate, and dimethyl carbonate, water, and ionic liquid. It is not limited to these. Further, the conductive liquid CL may be an electrolytic aqueous solution containing an electrolyte as a solute, or may be a molten salt having conductivity. The electrolyte may be neutral, alkaline, or acidic, and examples of the alkaline electrolyte include carbonates such as potassium carbonate and sodium carbonate.

  The temperature of the conductive liquid CL may be equal to or lower than the boiling point at which the liquid is completely gasified, but may be about room temperature. When the conductive liquid CL is an electrolytic aqueous solution, the temperature of the conductive liquid is preferably about 70 to 90 ° C. under atmospheric pressure, and may exceed 100 ° C. under a pressurized environment.

  The liquid stored in the one or more sub containers 60 may be different from the conductive liquid CL stored in the main container 10. For example, the conductive liquid CL is accommodated in the main container 10 and the reducing liquid is accommodated in the second-stage sub-container 60a, so that the conductive fine particles generated in the main container 10 are contained in the second-stage sub-container 60a. Can be reduced. Further, as described above, a case where a plurality of sub containers 60 after the second stage are connected in parallel is also conceivable. In this case, it is also possible to store different liquids in the respective sub-containers 60 to generate conductive fine particles having different properties.

<Electrode>
In the conductive liquid stored in the main container 10, a cathode 30 made of a conductive material and an anode 40 are arranged at a predetermined distance from the cathode 30. The conductive material used for the cathode 30 is a raw material for the generated nanoscale conductive fine particles, and the material and composition can be appropriately selected according to the properties of the conductive fine particles to be generated. As the cathode 30, a single source material such as various metals and semiconductors can be used, and an alloyed composite source material can also be used.

  The shape of the cathode 30 is not particularly limited, but is preferably a shape having symmetry from the viewpoint of uniformity of the average electric field, and is preferably a columnar shape, a cylindrical shape, a spherical shape, or a conical shape. More preferably, it is cylindrical. When the cathode 30 is cylindrical, the shape of the tip is preferably changed according to the material used. For example, when the material used for the cathode 30 is a low melting point material, the tip is preferably flat, and when the material is a high melting point, the tip is preferably acute. In particular, when the material of the cathode 30 is zinc or aluminum, it is preferable that the tip portion is formed flat rather than formed at an acute angle because it is more difficult to break. Even in the case of a high melting point material, the shape of the tip can be made flat, but in order to generate plasma also on the side surface of the cathode 30, it is necessary to apply a higher voltage.

  Further, in order to continuously generate conductive fine particles having a more uniform particle diameter, at least a portion of the cathode 30 existing in the conductive liquid CL does not have an edge ( In other words, the portion of the electrode 30 that contacts the conductive liquid CL is preferably uniform in shape). For example, the cathode 30 having a polygonal cross-sectional shape has an edge extending along the long axis direction. One embodiment for obtaining an electrode 30 with no edges is shown in FIG. 3 expressed as a cross-sectional view. In the embodiment shown in FIG. 3, the shape of the cathode 30 is made cylindrical so that no edge is present in the electrode 30 in the conductive liquid CL, and the tip portion 31 does not contact the conductive liquid CL. Thus, a cover 35 that covers the tip 31 is attached. The cover 35 is a hollow cap-shaped cover with one end closed, formed using an insulating material such as glass or Teflon (registered trademark). By attaching the cover 35 to the cathode 30 so as to cover the tip portion 31 of the cathode 30, at least a portion (“L” portion in FIG. 3) in contact with the conductive liquid CL of the cathode 30 is, for example, the tip in FIG. 3. In the cathode 31 having the polygonal section 31 or the cross-sectional shape, there is no edge such as an edge extending along the long axis direction.

  In the case where an edge such as the tip 31 in FIG. 3 is present in the portion of the cathode 30 that contacts the conductive liquid CL, a current concentration phenomenon occurs particularly frequently at the edge compared to other portions. . When current concentration occurs in a part of the electrode, the generation of conductive fine particles from the part increases, and the particle diameter of the generated conductive fine particles gradually increases. On the other hand, when the electrode has no edge, for example, as shown in FIG. 3, when the portion L of the electrode 30 that is in contact with the conductive liquid CL is composed of only a surface, the current concentration phenomenon may occur on the surface of the electrode 30. Since there is no place where the current concentration occurs uniformly and current concentration is particularly frequent, conductive fine particles having a uniform particle diameter are generated from the entire surface. The above is considered to be the reason why conductive fine particles having a uniform particle diameter can be obtained due to the absence of an edge in the electrode 30.

  The size (size or thickness) of the cathode 30 is appropriately selected in consideration of the conditions such as the amount of the conductive liquid CL, the yield of the conductive fine particles to be generated, the generation duration, and the current density. In general, the larger the size of the cathode 30, the larger the amount of conductive fine particles generated, the longer the generation duration, and the smaller the current density variation, the smaller the average particle size. However, for example, in the case of a batch-type production apparatus as in the prior art, when the size of the cathode 30 is increased, the concentration of the conductive fine particles in the conductive liquid increases in a short time, and aggregation occurs. On the other hand, in the continuous manufacturing apparatus 1 according to the present invention, the conductive liquid CL containing the conductive fine particles overflowing the main container 10 moves to the sub container 60 in the subsequent stage through the flow path 70, so that the main container 10 can be maintained at a concentration at which aggregation does not occur, so that a large cathode 30 can be used. Therefore, when this apparatus 1 is used, it becomes possible to produce conductive fine particles having a small average particle diameter over a long period of time.

  Examples of the material of the anode 40 include platinum, but the material is not limited to this, and any material that is stable in the conductive liquid CL may be used. The shape of the anode 40 is not particularly limited, but it is preferable to increase the surface area as much as possible. The surface area of the anode 40 is preferably about 25 to about 1000 times the surface area of the cathode 30. By increasing the surface area of the anode 40, a uniform electric field can be generated around the cathode 30, and voltage drop, power loss and temperature increase can be concentrated in the vicinity of the cathode 30. In order to increase the surface area of the anode 40, for example, the size of the anode 40 itself may be increased, or the anode 40 may be a mesh electrode surrounding the cathode 30.

  Although only one cathode 30 is shown in FIGS. 1 and 2, the number of the cathodes 30 is not limited to this. When the number of the cathodes 30 is two or more, the anodes 40 corresponding to the cathodes 30 may be provided so as to form a counter electrode. Moreover, in FIG.1 and FIG.2, although the two anodes 40 are shown, the number of the anodes 40 is not limited to this. If the anode 40 with a large area can be used, the number of the anodes 40 may be one. Further, the number of anodes 40 may be three or more as required. When the number of anodes 40 is two or more, the arrangement of the anodes 40 is preferably such that the distances between the cathodes 30 and the anodes 40 are equal. When the main container 10 having a large capacity is used, a plurality of pairs of counter electrodes each composed of the cathode 30 and the anode 40 can be used according to the capacity.

  The cathode 30 and the anode 40 are disposed in the conductive liquid CL without contacting each other. It is preferable that only the conductive liquid CL exists between the cathode 30 and the anode 40. It is preferable to arrange the anodes 40 concentrically so as to evenly surround the cathode 30.

  The distance between the cathode 30 and the anode 40 is that a stable glow discharge plasma is generated in the vicinity of the surface of the cathode 30 by the application of a voltage, but the cathode 30 and the anode 40 are directly connected by a high current density discharge path. It adjusts suitably so that discharge may not arise. The appropriate distance between the cathode 30 and the anode 40 is determined in relation to the concentration of the conductive liquid. In the case of other than neutral, the conductive liquid preferably has a lower concentration from the viewpoint of handling. However, in the case of using a low-concentration conductive liquid, if the distance between the cathode 30 and the anode 40 is too long, no current flows between the electrodes, so it is necessary to apply a higher voltage. It is not preferable from the viewpoint of environmental load. On the other hand, if the distance between the cathode 30 and the anode 40 is too short, arc discharge is likely to occur, making it difficult to control the conditions for generating conductive fine particles. Therefore, for example, the distance between the cathode 30 and the anode 40 is preferably about 20 to about 1000 mm, and more preferably about 50 mm. When the capacity of the main container 10 is large, it is preferable to use a plurality of pairs of the cathode 30 and the anode 40 separated by a predetermined distance. Such a configuration, for example, connects the cathode 30 and the anode 40 to a predetermined distance. This can be realized by arranging them alternately.

<Applied voltage>
The voltage to be applied is preferably higher than the lower limit voltage at which glow discharge plasma can be generated in the vicinity of the cathode 30 and lower than the voltage at which the cathode 30 glows red. When the cathode 30 is red hot, the material melts and the conductive fine particles are not continuously generated. The voltage at which the cathode 30 glows red is, for example, about 200 V for copper, about 180 V for silver, and about 300 V for tungsten. The voltage to be applied is preferably a voltage lower than the voltage at which the cathode 30 glows red. By applying a voltage of this level, the vicinity of the cathode 30 is close to the complete plasma but does not reach the complete plasma, so that the plasma unevenness is reduced and conductive fine particles are continuously generated. When the voltage is too low, glow discharge plasma is not generated in the vicinity of the cathode 30 and conductive fine particles cannot be obtained. Even if plasma is generated, the yield of conductive fine particles is extremely small. On the other hand, if the voltage is too high, arc discharge occurs between the anode and the cathode, so that desired conductive fine particles cannot be obtained. When the conductive liquid is an electrolytic aqueous solution, the voltage to be applied is preferably about 65 V to about 200 V, more preferably about 80 V to about 140 V.

<Partition wall>
In one embodiment of the present invention, a partition wall 80 can be provided between the cathode 30 and the anode 40. The partition wall 80 may be made of a material that does not inhibit the movement of electrons in the conductive liquid CL. For example, the partition wall 80 may be made of a material such as a porous film of zirconia (zirconium oxide) or Teflon (registered trademark) mesh. Is preferred. By providing the partition wall 80, the conductive fine particles generated from the cathode 30 can be made difficult to diffuse inside the main container 10. In addition, when an electrolytic aqueous solution is used as the conductive liquid CL, hydrogen is generated from the vicinity of the cathode 30 by electrolysis of water, but by providing a cover 90 for recovering hydrogen on the partition wall 80, The generated hydrogen can be efficiently recovered. The shape of the partition wall 80 is not particularly limited, but a shape that can cover as much area as possible around the cathode 30 is preferable.

(Method of continuously producing nanoscale conductive particles)
Here, an embodiment of a method for continuously producing nanoscale conductive fine particles using the apparatus 1 will be described. First, the conductive liquid CL is accommodated in the main container 10. A conductive liquid having the same composition as that of the conductive liquid CL stored in the main container 10 is also stored in one or a plurality of sub-containers 60. As shown in FIG. 1, here, two sub-containers 60a and 60b are connected in series. In another embodiment, the one or more sub-containers 60 can contain a liquid other than the main container 10. Moreover, the one or several sub container 60 can also be connected in parallel. A voltage is applied by a power supply 50 to the counter electrode composed of the cathode 30 and the anode 40 disposed in the conductive liquid in the main container 10.

  When a voltage is applied to the counter electrode, the temperature of the cathode 30 rises due to power loss at the surface of the cathode 30, and accordingly, the temperature of the conductive liquid around the cathode 30 also rises. When the temperature of the conductive liquid exceeds the boiling point, a sheath-like gas phase containing water vapor is formed in the vicinity of the cathode 30, and glow discharge plasma is generated in the gas phase. After the glow discharge plasma is established, the voltage is further increased, and the glow discharge plasma is continuously formed in the vicinity of the cathode 30.

  After the continuous formation of the glow discharge plasma, the local temperature of the cathode 30 surface exceeds the melting point of the material due to the current concentration phenomenon in the sheath-shaped plasma at the interface between the cathode 30 and the conductive liquid CL, and the material is locally Melt. The material that is melted and released from the surface of the cathode 30 in the form of droplets enters the conductive liquid CL, is formed into a spherical shape by surface tension, and is then rapidly cooled to generate nanoscale conductive fine particles. In the present apparatus 1, since the cathode 30 having a size larger than that disclosed in Patent Document 1 can be used, the nanoscale conductive fine particles having the same quality can be used for a long time without the cathode 30 being consumed in a short time. Can be produced continuously.

  Before or after the generation of the nanoscale conductive fine particles, a pump (not shown) is operated, and the conductive liquid CL is supplied from the conductive liquid supply source (not shown) to the main container 10 via the liquid supply path 20. Start supplying. The supply flow rate of the conductive liquid CL is preferably constant, and is preferably substantially equal to the flow rate of the conductive liquid CL sent from the main container 10 to the sub container 60a via the flow path 70. Thus, by balancing the supply flow rate of the conductive liquid CL to the main container 10 and the outflow flow rate from the main container 10, the amount of the conductive liquid CL in the main container 10 can be maintained substantially constant. As a result, the concentration of the conductive fine particles in the conductive liquid CL can be maintained at a concentration at which aggregation does not occur. For example, in the case of a batch technique using a single container as in Patent Document 1, in our experiment, about 10 mg of conductive fine particles (stainless steel (SUS316) in about 300 cc of conductive liquid. ) Were present, the fine particles aggregated. Therefore, for example, in the case of stainless (SUS316) fine particles, the fine particle concentration in the conductive liquid CL needs to be maintained at least at a lower concentration.

  The supply flow rate of the conductive liquid CL is preferably small. When conductive fine particles having different particle diameters are generated, in the present apparatus and method, the fine particles having a large particle size are settled below the main container 10 as described above, and the fine particles having a small particle diameter are the main container 10. It rises inside and moves to the sub container 60. Therefore, if the supply flow rate of the conductive liquid CL is large, the liquid in the main container 10 and the sub-container 60 is agitated, and as a result, conductive fine particles having different particle diameters are mixed together, so that proper classification may not be performed. is there.

  As described above, the concentration of the conductive fine particles in the conductive liquid CL in the main container 10 can be changed by changing the vertical position of the inlet 71 of the flow path 70. For example, when the position of the inflow port 71 is lowered, the amount of the conductive liquid CL in the main container 10 is reduced. Therefore, when the other conditions are the same, the concentration of the conductive fine particles in the conductive liquid CL is high. Become. Conversely, when the position of the inflow port 71 is increased, the concentration of the conductive fine particles in the conductive liquid CL is decreased.

  The concentration of the conductive fine particles in the conductive liquid CL can also be adjusted by increasing the supply flow rate of the conductive liquid CL to the main container 10 and the outflow flow rate from the main container 10. By increasing the flow rate, the concentration of the conductive fine particles contained in the conductive liquid CL flowing out from the main container 10 decreases. In addition, by increasing the flow rate, large particles among the generated conductive fine particles flow out before settling in the conductive liquid. Therefore, particles having a large particle size are mixed with the collected conductive fine particles, and the width of the particle size distribution is widened.

  The conductive liquid CL containing the conductive fine particles flowing out from the main container 10 flows into the sub container 60a through the flow path 70. A container 60b is further connected to the sub container 60a via a flow path 70, and the conductive liquid CL containing conductive fine particles flowing out from the sub container 60a flows into the container 60b. In FIG. 1, only two sub-containers 60a and 60b are connected in series, but one or more sub-containers 60 can be connected in series and / or in parallel to the subsequent stage of the sub-container 60b. In this way, a plurality of containers are connected in series and / or in parallel, and the conductive liquid containing the conductive fine particles is sequentially moved from the preceding container to the subsequent container, whereby the conductivity in the conductive liquid in each container is determined. The concentration of the fine particles can be maintained at a concentration that does not aggregate. As a result, even when a larger size cathode is used as the cathode 30 disposed in the main container 10, conductive fine particles can be continuously produced over a long period of time.

  In the main container 10, with the passage of time, of the generated conductive fine particles, those having a large particle size settle downward in the conductive liquid. The conductive fine particles having a small particle diameter that do not easily settle move together with the conductive liquid CL flowing out from the main container 10 to the sub container 60a. Similarly, in the sub container 60a, with the passage of time, the conductive fine particles having a small particle size remain on the upper side, and the conductive fine particles having a large particle size settle on the lower side. The conductive fine particles having a small particle size on the upper side move to the sub container 60b together with the conductive liquid CL flowing out from the sub container 60a. Thus, according to the present apparatus 1, conductive fine particles having different particle size distributions can be collected for each container. Eventually, in the sub-container 60b, uniform conductive particles having a small particle size among the conductive particles are present.

  When the conductive fine particles are continuously generated and the cathode 30 is consumed, the voltage application is stopped, and the consumed cathode 30 is replaced with a new cathode 30 before the temperature of the conductive liquid CL is significantly reduced. If the voltage is applied again, the production of the conductive fine particles can be continued.

  A method of collecting the conductive fine particles remaining in the main container 10 and the sub-container 60 among the generated conductive fine particles from the liquid in these containers is not particularly limited. For example, the precipitated conductive fine particles can be collected by circulating the liquid around an axis perpendicular to the bottom surface of the container and precipitating the conductive fine particles on the bottom of the container. Alternatively, the conductive fine particles can be recovered from the liquid by treating the liquid in each container with a centrifuge. Furthermore, the conductive fine particles can be recovered by filtration, and can also be recovered by concentrating the conductive fine particles in the organic phase using a solvent extraction method.

  The physical properties such as the shape, size (diameter), particle size distribution, composition, crystallinity and the like of the generated conductive fine particles can be controlled by the conditions of glow discharge. Conditions for glow discharge include the magnitude of applied voltage and current, their fluctuations, discharge time, type of conductive liquid, concentration of conductive liquid, temperature of conductive liquid, composition of elements constituting the electrode, and electrode shape The initial surface roughness of the electrode, the temperature of the electrode, the type or concentration of impurities or additive elements in the electrode material. For example, when the applied voltage is increased, the particle diameter of the conductive fine particles can be reduced.

  In order to control the shape of the conductive fine particles, the current concentration growth rate may be increased. In order to increase the current concentration growth rate, it is only necessary to prevent heat from escaping from the cathode or to increase the applied voltage. In order to prevent heat from escaping from the cathode, the shape and physical properties of the cathode may be selected as appropriate, and the connection method between the cathode and the cathode lead may be selected as appropriate. By increasing the applied voltage, the temperature (energy) of electrons can be increased, and the growth rate of current concentration can be increased.

(Example 1; silver fine particles / with cover)
An apparatus for continuously producing conductive fine particles comprising a main container and one sub-container (that is, main container 10 and sub-container 60a shown in FIG. 1) was used. Silver (Ag) was used as the cathode. As shown in FIG. 4, a terminal for connecting the cathode to a power source and a holder for installing the cathode on a gantry provided on the upper part of the main container were attached to the upper part of the cathode. Moreover, the cover which covers the front-end | tip part of a cathode was attached to the lower part of a cathode. Therefore, only the portion L not covered by the holder and the cover comes into contact with the liquid in the main container. The cathode had a cylindrical shape, a diameter of 4 mm, and the length of the portion L that contacted the liquid in the main container was 48 mm. On the other hand, an anode in which a platinum wire was wound around a set of anode holders having a shape similar to the anode 40 as shown in FIG. 1 was used. The platinum wire wound around one anode had a length of 1000 mm and a diameter of 0.5 mm.

  The main container and the sub container were made of glass. A potassium carbonate (K2CO3) aqueous solution (0.5M) was accommodated in the main container. The main container was provided with a glass overflow pipe (corresponding to the flow path 70 in FIG. 1) for overflowing the aqueous solution in the main container and sending it to the sub container. The diameter of the overflow pipe was 20 mm. The height of the liquid level of the aqueous solution (that is, the distance between the upper end of the overflow pipe and the bottom surface of the main container) was 70 mm, and the volume of the aqueous solution accommodated in the main container was 40 liters. Further, a liquid feeding pipe (corresponding to the liquid feeding path 20 in FIG. 1) for supplying an aqueous solution to the main container was installed in the main container. The flow rate of the aqueous solution supplied from the liquid feeding pipe to the main container was 1 liter / h. The above-described cathode and anode were placed in a main container containing an aqueous potassium carbonate solution. The distance between the cathode and the anode was 50 mm. In addition, the thermocouple for measuring the temperature of aqueous solution was also installed in the main container.

  A voltage of 95 V was applied between the cathode and the anode to continuously produce silver fine particles. About 30 minutes after the start of energization, the temperature of the aqueous solution reached about 88 ° C., and then the temperature was maintained. The production of silver fine particles could be carried out continuously for at least about 8 hours. In the main container, the produced silver fine particles are sent to the sub-container through the overflow pipe, so that the silver fine particle concentration is maintained at a concentration at which the silver fine particles do not aggregate, and as a result, it is continuously produced without agglomeration. It was possible. Further, the cathode did not break.

  5A and 5B are photographs in which the produced silver fine particles are observed with a scanning electron microscope (SEM; JSM-7001F thermal field emission scanning electron microscope manufactured by JEOL Ltd .; measured at an acceleration voltage of 15 kV). These are silver fine particles in the aqueous solution in the sub-container (that is, floated upward in the aqueous solution in the main container). FIG. 5A shows silver fine particles obtained about 1 hour after the start of energization, and FIG. 5B shows silver fine particles obtained about 6 hours after the start of energization. The particle diameters of the silver fine particles in FIGS. 5A and 5B were both about 70 to 80 nm from the scale in the figure. From FIG. 5, it can be seen that silver particles having a small particle size and substantially uniform were produced continuously for a long time. FIGS. 6A and 6B are photographs of silver fine particles collected from different locations in the conductive liquid in the main container. From these photographs, any location in the main container is shown. It is understood that silver fine particles having a substantially uniform particle diameter can be obtained.

(Example 2; silver fine particles / no cover)
7 (a) and 7 (b) and FIGS. 8 (a) and 8 (b) are manufactured using a silver cathode in which the cover for covering the tip portion is not attached in the apparatus having the same configuration and conditions as in the first embodiment. It is the photograph which observed the silver fine particle by SEM. FIG. 7A shows silver fine particles in the aqueous solution in the sub-container obtained after 1 hour from the start of energization (that is, floating upward in the aqueous solution of the main container), and FIG. Silver fine particles settled below the aqueous solution. FIG. 8A shows silver fine particles in the aqueous solution in the sub-container obtained after 4 hours from the start of energization (that is, floating upward in the aqueous solution of the main container), and FIG. Silver fine particles settled below the aqueous solution. In the present example, the voltage between the cathode and the anode was 140V. Similar to Example 1, also in Example 2, it was possible to produce silver fine particles continuously for a long time. However, it can be seen from FIGS. 7 and 8 that, unlike the case of Example 1 shown in FIG. 5, the produced silver fine particles have non-uniform particle sizes. For example, at the time of FIG. 7B, the particle size of the largest fine particle among silver fine particles settled below the aqueous solution in the main container was about 5 μm. The photograph in FIG. 7B does not show a fine particle having a particle diameter of 5 μm, but the largest fine particle among the fine particles contained in the same sample as the sample in FIG. It has been confirmed that the particle size is about 5 μm.

(Example 3; copper fine particles / no cover)
In the apparatus having the same configuration and conditions as in Example 1, copper fine particles were produced using a copper cathode to which a cover covering the tip portion was not attached. The shape of the copper cathode was a cylinder, the diameter was 4 mm, and the length in the liquid in the main container was 70 mm. The conductive liquid contained in the main container is phosphoric acid composed of L (+)-ascorbic acid (0.1M), dipotassium hydrogen phosphate (0.05M) and potassium dihydrogen phosphate (0.05M). A buffer solution (0.1 M) mixed at a ratio of 1: 6 was used. A voltage of 190 V was applied between the cathode and the anode.

  About 30 minutes after the start of energization, the temperature of the aqueous solution reached about 90 ° C., and the temperature was maintained thereafter. The production of copper fine particles could be carried out continuously for at least about 8 hours. In the main container, the produced copper fine particles are sent to the sub-container through the overflow pipe, so that the copper fine particle concentration is maintained at a concentration at which the copper fine particles are not aggregated. As a result, the copper fine particles are continuously produced without agglomeration. It was possible. Further, the cathode did not break.

  FIGS. 9A to 9C and FIGS. 10A and 10B are photographs of the collected copper fine particles observed with a scanning electron microscope (SEM). 9 (a) and 9 (b) are copper fine particles in the aqueous solution in the sub-container obtained after 1 hour from the start of energization (that is, floating upward in the aqueous solution of the main container). ) Are copper fine particles settled below the aqueous solution at that time. The magnification of the SEM in FIG. 9A is 5000 times, and the magnification of the SEM in FIGS. 9B and 9C is 20000 times. From FIG. 9, it can be seen that the produced copper fine particles are nanoscale copper fine particles although the uniformity of the particle diameter is inferior to the result of Example 1. FIG. 10A shows the copper fine particles in the aqueous solution in the sub-container obtained 8 hours after the start of energization (that is, the copper fine particles floating upward in the aqueous solution of the main container), and FIG. The copper fine particles settled below the aqueous solution. 10 (a) and 10 (b), the copper fine particles remaining in the main container (FIG. 10 (b)) and the copper fine particles moving to the sub container (FIG. 10 (a)) are classified according to the particle diameter. It can be seen that the diameter of the fine particles in FIG.

(Example 4: stainless fine particles / no cover)
In the apparatus having the same configuration as that of Example 1, stainless steel fine particles were manufactured using a stainless steel (SUS316 steel) cathode to which a cover covering the tip portion was not attached. The shape of the stainless cathode was a cylinder, the diameter was 4 mm, and the length in the liquid in the main container was 70 mm. As the conductive liquid contained in the main container, a phosphate buffer solution (0.1 M) composed of dipotassium hydrogen phosphate (0.05 M) and potassium dihydrogen phosphate (0.05 M) was used. A voltage of 140 V was applied between the cathode and the anode.

  About 30 minutes after the start of energization, the temperature of the aqueous solution reached about 90 ° C., and the temperature was maintained thereafter. The production of stainless fine particles could be carried out continuously for at least about 8 hours. In the main container, the produced stainless steel fine particles are sent to the sub-container through the overflow pipe, so that the stainless fine particle concentration is maintained at a concentration at which the stainless fine particles are not aggregated. It was possible. Further, the cathode did not break. The amount of stainless fine particles obtained 4 hours after the start of energization was about 900 mg.

DESCRIPTION OF SYMBOLS 1 Continuous production apparatus 10 of nanoscale electroconductive fine particles Main container 20 Liquid sending path 30 Cathode 40 Anode 50 Power supply 60, 60a, 60b Sub container 70, 70a, 70b, 70c Channel 71 Inlet 72 Outlet 75 Connecting member 80 Partition

Claims (15)

An apparatus for continuously producing nanoscale conductive fine particles,
A first container containing a conductive liquid;
A liquid feed path through which the conductive liquid supplied to the first container passes;
An anode disposed in a conductive liquid in the first container and a cathode made of a conductive material;
A power source for applying a voltage that generates glow discharge plasma in the vicinity of the cathode between the cathode and the anode;
A second container containing a liquid;
A liquid flow path communicating the first container and the second container;
With
The conductive liquid is supplied to the first container through the liquid supply path and moves from the first container to the second container through the liquid flow path, so that at least in the first container. An apparatus characterized in that the concentration of the conductive fine particles in the conductive liquid is maintained at a concentration at which the conductive fine particles do not aggregate in the first container.   One or more third containers containing liquid are further provided, and the second container and each of the one or more third containers are connected in series via a fluid channel. The apparatus according to claim 1, wherein:   One or more third containers containing liquid are further provided, and the second container and one of the one or more third containers are connected in series via a fluid flow path. The one container and the other container among the one or more third containers are connected in parallel to each other via a fluid flow path. The device described.   The flow path is a pipe having both ends positioned in the liquid in a separate container, and the pipe includes the end of the pipe and the bottom of the container in which each of the ends is disposed. The apparatus according to claim 1, further comprising a mechanism for adjusting the distance.   The apparatus according to claim 1, wherein the cathode is configured such that no edge exists in a portion of the cathode disposed in the conductive liquid.   The said cathode is a column shape, The insulating cover which covers the front-end | tip part of the said cathode is attached in the part of the said cathode arrange | positioned in the said electroconductive liquid, It is characterized by the above-mentioned. Equipment.   The apparatus of claim 1, wherein there are two or more anodes, and the distance between the cathode and each of the two or more anodes is approximately equal.   The apparatus according to claim 1, further comprising a partition wall disposed between the cathode and the anode. A method for continuously producing nanoscale conductive fine particles,
Applying a voltage to an anode disposed in a conductive liquid in a first container and a cathode made of a conductive material;
Generating glow discharge plasma in the vicinity of the cathode to produce conductive fine particles;
Supplying a conductive liquid into the first container;
Moving a conductive liquid from the first container to a second container;
And controlling the flow rate of the conductive liquid supplied to the first container, so that at least the concentration of the conductive fine particles in the conductive liquid in the first container is in the first container. The method is characterized in that it is maintained at a concentration at which no aggregation of the conductive fine particles occurs.   One or more third containers containing liquid are further provided, and the second container and each of the one or more third containers are connected in series via a fluid flow path, The method according to claim 9, wherein the liquid in each container is sequentially moved through the fluid flow path.   One or more third containers containing liquid are further provided, and the second container and one of the one or more third containers are connected in series via a fluid flow path. The one container and the other one of the one or a plurality of third containers are connected in parallel to each other via a fluid flow path, and are connected to each other via the fluid flow path. The method according to claim 9, wherein the liquid in the container is sequentially moved.   The method according to claim 9, wherein the cathode is configured such that an edge does not exist in a portion of the cathode disposed in the conductive liquid.   The method according to claim 12, wherein the cathode is cylindrical, and an insulating cover that covers a tip of the cathode is attached to a portion of the cathode disposed in the conductive liquid. .   10. The method of claim 9, wherein there are two or more anodes and the distance between the cathode and each of the two or more anodes is approximately equal. The method according to claim 9, further comprising a partition wall disposed between the cathode and the anode.