JP2006063445A - Metal particle and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing metal particles, by which fine carbon fibers can be dispersed in an electrolyte solution without using any dispersant and to provide metal particles produced without using any dispersant. <P>SOLUTION: The method for producing the fine metal particles comprises a step of electrolyzing an electrolyte solution in which fine carbon fibers are dispersed to deposit metal particles mixed with the fine carbon fibers on a cathode and a step of separating the deposited metal particles from the cathode, wherein vibrations or impacts are applied to the electrolyte solution. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal material that can be suitably used as a material such as powder metallurgy, an electrical contact, a battery, an electromagnetic wave shield, a conductive material, a friction material contact, and a sliding material, and a manufacturing method thereof.

A composite material in which carbon nanotubes or carbon nanofibers (hereinafter referred to as fine carbon fibers) are dispersed in a metal is known.
The composite material disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-220304) is obtained by mixing fine carbon fibers and metal powder and sintering them into a block shape.
By the way, the fine carbon fiber has a very fine diameter of about 5 to 300 nm, while the metal powder generally has a diameter in the range of 1 μm to several hundred μm, which is larger than the diameter of the fine carbon fiber. One digit larger. If these two materials are simply mixed, uniform mixing is difficult.
Therefore, in the conventional one, first, the metal powder is dissolved in an acid solution. For example, copper powder is dissolved in hydrochloric acid, sulfuric acid, or nitric acid. Then, fine carbon fibers are dispersed in this solution, and then dried and sintered to obtain a composite material.

However, in the above conventional method, the process of dissolving the metal powder and further drying and sintering the acid solution in which fine carbon fibers are dispersed is extremely troublesome, has a long time, and is expensive. Furthermore, when manufacturing in large quantities, there existed a subject that it was difficult to disperse | distribute fine carbon fiber uniformly.
Accordingly, the present inventors have conceived that an electrolytic solution in which fine carbon fibers are dispersed is electrolyzed to deposit metal particles mixed with fine carbon electrons on the cathode electrode (Japanese Patent Application No. 2003-40308).

Japanese Patent Laid-Open No. 2000-220304

However, in order to disperse the fine carbon fibers in the electrolytic solution, it is necessary to add a dispersant made of an organic compound such as polyacrylic acid to the electrolytic solution, and a small amount of the dispersant is added to the metal particles mixed with the fine carbon fibers. There was also the possibility of being taken in.
As described above, when the dispersant is incorporated into the metal particles, the performance such as electrical conductivity and thermal conductivity may be deteriorated.
In addition, since the optimum dispersant differs depending on the type of electrolyte and the type of fine carbon electrons, it is necessary to repeat experiments to find the optimum dispersant, and it is difficult to find the optimum dispersant. There is also.

  Accordingly, the present invention has been made to solve the above-mentioned problems, and the object of the present invention is a method for producing metal particles that can disperse fine carbon fibers in an electrolyte without using a dispersant, and dispersion. It is providing the metal particle manufactured without using an agent.

According to the method for producing metal particles according to the present invention, a step of electrolyzing an electrolytic solution in which fine carbon fibers are dispersed to deposit metal particles mixed with the fine carbon fibers on the cathode electrode, and the deposited metal particles In the method for producing metal particles, including the step of separating from the cathode electrode, vibration or impact is applied to the electrolytic solution.
According to this method, since fine carbon fibers are dispersed in the electrolyte solution by vibration or impact, metal particles mixed with fine carbon fibers having high performance such as electrical conductivity and thermal conductivity are used without using a dispersant. Can be manufactured.

Further, the vibration or impact may be applied constantly during electrolysis or may be applied temporarily (including application at predetermined time intervals).
Furthermore, the vibration or impact may be characterized in that metal particles mixed with fine carbon fibers separated from the cathode electrode into the electrolyte are crushed. According to this, even if the metal particles once deposited on the cathode electrode are separated from the cathode electrode into the electrolytic solution, the metal particles and fine carbon fibers are aggregated in the electrolytic solution by crushing the separated metal particles. Can be prevented.

The vibration or impact may be caused by ultrasonic waves. At this time, the ultrasonic wave may have a frequency of 20 kHz or more and an intensity of 8 kW or less per liter of the electrolytic solution. The number 8 kW / L was obtained based on the results of Example 4. More preferably, the frequency is 20 kHz to 1 MHz and the strength is 4 kW or less per liter of the electrolyte.
In some cases, the electrolytic solution may be agitated. That is, the concentration and temperature in the electrolyte solution can be made uniform by performing stirring in the same manner as in the past in addition to vibration and impact.

The metal particles are manufactured by any one of the above manufacturing methods.
Moreover, various composite materials containing metal particles can be obtained by melting or firing the aggregate of metal particles.
Examples of such a composite material include an aggregate of the metal particles, a mixture of the metal particles and metal particles composed of other elements, or a mixture of the metal particles and a polymer or ceramic. These aggregates or mixtures include composites by melting (including sintering) or by binders such as metals and polymers.

According to the method for producing metal particles of the present invention, fine carbon fibers can be dispersed in the electrolytic solution without using a dispersant. For this reason, a dispersing agent is not taken in into the obtained metal particle, and a high performance metal particle can be manufactured. Moreover, contamination of the production process due to the decomposition of the dispersant can be prevented.
Moreover, since the metal particle of this invention has not taken in the dispersing agent, its performance, such as electrical conductivity and thermal conductivity, is high.

Hereinafter, preferred embodiments of the present invention will be described.
As described above, the metal particle manufacturing method according to the present invention electrolyzes an electrolytic solution in which fine carbon fibers (carbon nanotubes: CNT, carbon nanofibers: CNF) are dispersed, and fine carbon fibers are formed on the cathode electrode. During the process of depositing the mixed metal particles, ultrasonic vibration is applied to the electrolytic solution to disperse the fine carbon fibers.
In addition, when the metal particles deposited on the cathode electrode are separated from the cathode electrode into the electrolytic solution, the ultrafine carbon fibers are dispersed so that the metal particles and the fine carbon fibers are not aggregated in the electrolytic solution. The sound vibration also acts to crush away the separated metal particles.

In FIG. 1, the outline of the manufacturing apparatus for performing the manufacturing method of a metal particle is shown.
The electrolytic solution X is put into an electrolytic cell 20 including an anode electrode 21 and a cathode electrode 22. A DC power source 24 is connected between the anode electrode 21 and the cathode electrode 22 so as to apply a predetermined voltage to both electrodes.
The electrolytic bath 20 is provided with a stirring device 26 so that the electrolytic solution X can be stirred.
In addition, the electrolytic cell 20 is provided with a temperature regulator 30 for regulating the temperature of the electrolytic solution X placed therein. Specifically, the temperature controller 30 includes a thermocouple 31 that is a temperature sensor disposed in the electrolytic cell 20, a heating / cooling device 32 that actually heats and cools the temperature of the electrolytic solution X in the electrolytic cell 20, The temperature controller 34 is configured to control the heating / cooling device 32 based on the temperature measured by the thermocouple 31.

  The electrolytic cell 20 is provided with a vibration generator 36 for applying vibration to the electrolytic solution X in the electrolytic cell 20. A specific example of the vibration generator 36 is an ultrasonic generator. The ultrasonic generator has an ultrasonic generator 38 and a vibrator 39, and the vibrator 39 vibrates the electrolyte X in the electrolytic cell 20 by the ultrasonic waves generated by the ultrasonic generator 38. give. Further, the metal particles separated from the cathode electrode 22 in the electrolytic solution X are crushed by the ultrasonic waves so that the metal particles and the fine carbon fibers do not aggregate in the electrolytic solution X.

By using the manufacturing apparatus as described above and adjusting electrolysis conditions such as current density and electrolysis time, metal particles having an average particle size in the range of several hundred nm to several tens of μm can be deposited. The optimum current density is selected in consideration of the particle size and productivity.
For example, in the case of a copper electrolytic solution, an electrolytic solution containing a copper sulfate aqueous solution and sulfuric acid as main components is placed in the electrolytic bath 20, and CNT or CNF is placed in the electrolytic solution.
In the electrolytic cell 20, electrolytic copper is used as the anode electrode 21 to replenish copper ions during electrolysis. The supply of copper ions to the electrolytic solution X may be performed by using a metal other than copper, for example, lead as the anode electrode 21 and supplying copper ions from the outside.
In some cases, the electrolytic solution X being electrolyzed is stirred by the stirring device 26, and at the same time, the electrolytic solution concentration and the component amount are controlled to have a predetermined ratio.

  The ultrasonic vibration may be applied to the electrolytic solution X during the electrolysis or may not always be performed. When vibration is not always applied, it may be at predetermined time intervals.

  When the deposited metal particles are separated from the cathode electrode 22, the metal particles can be mechanically separated from the cathode electrode 22 on which the metal particles are deposited using a blade or the like.

In order to adjust the particle size and strength of the precipitated particles and the separability from the cathode electrode 22, an organic or inorganic compound such as thiourea, gelatin, tungsten, or chloride may be added to the electrolytic solution X.
For the cathode electrode 22, it is preferable to use titanium which has poor adhesion to the deposited metal and can easily separate the deposited particles. Further, it is desirable that the surface of the cathode electrode 22 is roughened in order to make the deposited metal into particles. For example, a cathode electrode 22 in which niobium, tantalum, or platinum is fixed on the surface of titanium in the form of minute protrusions can be suitably used.

The particle size of the metal particles modified with CNT or CNF to be produced is determined in relation to the size and shape of protrusions on the cathode surface, the electrolytic current density, and the period of impact or vibration applied to the cathode.
Note that the metal type of the metal particles is not limited to copper.

Various composite materials can be obtained by melting the aggregate of metal particles. In this case, various additives may be added to the metal particles to form a composite material.
For example, the composite material which controlled the compounding quantity of the fine carbon fiber is realizable by controlling suitably and the mixing ratio of the metal particle which mixed the said fine carbon fiber, and the metal particle which does not contain a fine carbon fiber.
In addition, it can be used as a material for various composite materials such as mixed with a resin.
As means for producing these composite materials, means such as resin molding, sintering and metal injection molding can be used.

  The metal particles obtained as described above are extremely fine particles of several hundred nm to several tens of μm, and fine carbon fibers are mixed in each metal particle. Therefore, fine carbon fibers are uniformly mixed in the composite material obtained by melting the aggregate of these metal particles.

In addition, by changing the amount of fine carbon fibers dispersed in the electrolytic solution X, the electrolysis conditions, and the like, metal particles having various fine carbon fibers mixed in and particle sizes can be obtained. Therefore, the aggregate of these metal particles is melted. Thus, the amount of fine carbon fibers in the composite material obtained can be arbitrarily controlled.
Such composite materials can be used in various applications such as bearings that require slidability, electrodes and electrical contacts that require high electrical conductivity, and heat dissipation mechanisms that require high thermal conductivity, taking advantage of the characteristics of CNT or CNF. Is available.

  Hereinafter, examples will be described. The output of the ultrasonic wave applied to the electrolyte solution X in each example is slightly weak in Example 2 and strong in Example 4 in Example 1 and Example 3. Explains. This ultrasonic intensity is a relative intensity between each example. Further, after the intensity of the ultrasonic output, a specific ultrasonic frequency and the ultrasonic intensity per 1 L of the electrolytic solution are described.

Electrolytic solution CuSO ₄ · 5H ₂ O 160 g / L
H ₂ SO ₄ 100 g / L
CNT 1g / L
Ultrasonic intensity Medium (20 kHz, 4 kW / L)
When electrolysis was performed for 15 minutes at a liquid temperature of 25 ° C. and a current density of 40 A / dm ² while applying an ultrasonic vibration of a medium intensity with an ultrasonic generator while stirring using the above electrolytic solution, A scanning electron micrograph of the film deposited on the surface of the electrode is shown in FIG.
As seen in FIG. 2, a Cu—CNT composite is formed in which a large number of CNTs are incorporated into extremely fine spherical copper particles having a particle size of about 10 μm or less.
These composites could be mechanically stably separated from the cathode electrode and granulated.

Electrolyte CuSO ₄ · 5H ₂ O 40g / L
H ₂ SO ₄ 100 g / L
CNT 1g / L
Ultrasonic intensity Somewhat weak (38kHz, 400W / L)
When electrolysis was performed for 15 minutes at 25 ° C. and a current density of 40 A / dm ² using the above electrolytic solution while stirring and applying ultrasonic vibration of slightly weaker strength with an ultrasonic generator, the surface of the cathode electrode A scanning electron micrograph of the deposited film is shown in FIG.
As seen in FIG. 3, a Cu—CNT composite is formed in which a large number of CNTs are incorporated into fine spherical copper particles having a particle size of about 10 μm.
These composites could be mechanically stably separated from the cathode electrode and granulated.

Electrolyte CuSO ₄ · 5H ₂ O 40g / L
H ₂ SO ₄ 100 g / L
CNT 1g / L
Ultrasonic intensity Medium (20 kHz, 4 kW / L)
The surface of the cathode electrode was obtained when electrolysis was performed for 15 minutes at 25 ° C. and a current density of 40 A / dm ² using the above electrolyte solution while stirring and applying an ultrasonic vibration of medium intensity with an ultrasonic generator. 4 and 5 show scanning electron micrographs of the film deposited on the substrate. 4 and 5 have different magnifications. FIG. 5 is a photograph of FIG. 4 enlarged five times.
As can be seen in FIG. 4, a spherical Cu—CNT composite having a uniform particle size as a whole is formed. As shown in FIG. 5, a Cu—CNT composite is formed in which a large number of CNTs are incorporated into fine spherical copper particles having a particle diameter of about 10 to 30 μm.
These composites could be mechanically stably separated from the cathode electrode and granulated.

Electrolyte CuSO ₄ · 5H ₂ O 40g / L
H ₂ SO ₄ 100 g / L
CNT 1g / L
Ultrasonic strength Strong (20kHz, 7.5kW / L)
When electrolysis is performed for 15 minutes at 25 ° C. and a current density of 40 A / dm ² while applying strong ultrasonic vibration with an ultrasonic generator with stirring using the above electrolytic solution, it is deposited on the surface of the cathode electrode. Scanning electron micrographs of the coated film are shown in FIGS. FIG. 7 is an enlargement of the photograph of FIG. 6 by 25 times.
Although it is difficult to understand in FIG. 6, as seen in FIG. 7, Cu—CNT composites are formed in which a large number of CNTs are incorporated into fine spherical copper particles having a particle diameter of about 20 to 40 μm. As for the grain of a thing, one grain is not separated compared with each example mentioned above. That is, when the ultrasonic intensity is strong as in the present example, the formed Cu—CNT composite becomes a lump or plate, and it is difficult to separate from the cathode electrode to form particles.

In this way, by irradiating the electrolyte with ultrasonic waves having a predetermined intensity, the fine carbon fibers can be dispersed well in the electrolyte X without using a dispersant, and the metal particles mixed with the fine carbon fibers can be dispersed. It was possible to form.
In addition, when the ultrasonic intensity is too strong as in Example 4 described above, the metal incorporating the fine carbon fibers is not a fine particle but a lump or plate, which is considered undesirable.

  Therefore, it is considered preferable for the ultrasonic wave to have an intensity of 4 kW or less with respect to 1 L of the electrolytic solution. Moreover, the frequency of the ultrasonic wave at this time is 20 kHz or more, and preferably 20 kHz to 1 MHz.

In the above-described embodiment, only the vibration due to the ultrasonic wave has been described, but an impact due to the ultrasonic wave may be used.
Furthermore, the vibration or impact applied to the electrolytic solution is not limited to that by ultrasonic waves.

  While the present invention has been described in detail with reference to a preferred embodiment, the present invention is not limited to this embodiment, and it goes without saying that many modifications can be made without departing from the spirit of the invention. .

It is explanatory drawing shown about schematic structure of the manufacturing apparatus which can perform the manufacturing method of the metal particle of this invention. 2 is a scanning electron micrograph of metal particles deposited on a cathode electrode in Example 1. FIG. 2 is a scanning electron micrograph of metal particles deposited on a cathode electrode in Example 2. FIG. 4 is a scanning electron micrograph of metal particles deposited on a cathode electrode in Example 3. FIG. 6 is an enlarged view of Example 3. FIG. 4 is a scanning electron micrograph of metal particles deposited on a cathode electrode in Example 4. FIG. 10 is an enlarged view of Example 4. FIG.

Explanation of symbols

20 Electrolysis Cell 21 Anode Electrode 22 Cathode Electrode 24 DC Power Supply 26 Stirrer 30 Temperature Controller 31 Thermocouple 32 Heating / Cooling Device 34 Temperature Controller 36 Vibration Generator 38 Ultrasonic Generator 39 Vibrator

Claims (8)

Electrolyzing an electrolytic solution in which fine carbon fibers are dispersed, and depositing metal particles mixed with fine carbon fibers on the cathode electrode;
Separating the deposited metal particles from the cathode electrode, and a method for producing the metal particles,
A method for producing metal particles, wherein vibration or impact is applied to the electrolytic solution. 2. The method for producing metal particles according to claim 1, wherein the vibration or impact is applied constantly or temporarily during electrolysis. 3. The method for producing metal particles according to claim 1, wherein the vibration or impact crushes metal particles mixed with fine carbon fibers separated from the cathode electrode into the electrolyte. The method for producing metal particles according to claim 1, wherein the vibration or impact is caused by ultrasonic waves. 5. The method for producing metal particles according to claim 4, wherein the ultrasonic wave has an intensity of 8 kW or less per liter of the electrolytic solution. The method for producing metal particles according to claim 1, wherein the electrolytic solution is stirred. The metal particle manufactured by the manufacturing method of the metal particle of any one of Claims 1-6. A composite material obtained by melting or firing the aggregate of metal particles according to claim 7.