JP2008106309A - Method for producing particulate by plasma-induced electrolysis, and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing particulate by plasma-induced electrolysis with which growth and flocculation of the produced particulate are suppressed, and to provide a device therefor. <P>SOLUTION: The invention is a method with which molten salt is subjected to plasma-induced electrolysis so as to produce particulate. Plasma is emitted to the surface of a molten salt bath held onto a rotating substantially flat face so as to produce particulate and also, the produced particulate is moved to the outside of the molten salt bath by centrifugal force. The device uses the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention continuously produces metal fine particles and / or metal compound fine particles by performing plasma irradiation on the surface of the molten salt on the rotating disk, and recovers the particles by moving them to the outside of the disk using centrifugal force. The present invention relates to a method for producing fine particles by plasma-induced electrolysis and an apparatus therefor.

By irradiating the surface of a molten salt bath containing a metal halide under plasma in an inert gas atmosphere such as argon, metal ions are reduced by discharge electrons to obtain micron-to-nanosized metal particles and metal compound particles. A method (plasma induced electrolysis) is known (for example, Non-Patent Documents 1, 2, 3, and Patent Document 1). The fine particles generated by this plasma-induced electrolysis are conventionally held in the molten salt bath for a long time until the end of discharge, and after the end of discharge, the entire molten salt bath is cooled and solidified, then repeatedly washed with distilled water and vacuum dried. After that, it was recovered as a dry powder.

However, in this recovery method, the time during which the generated particles are retained in the molten salt, particularly in the high temperature portion immediately below the discharge portion, becomes long, and fine particles may grow or secondary agglomerate. Furthermore, in this recovery method, since the entire molten salt subjected to plasma-induced electrolysis is cooled and solidified, there is a limit to developing it into a continuous mass production method. In order to recover continuously from molten salt as dispersed or loosely agglomerated fine particles, the fine particles generated in the molten salt are collected preferentially and continuously, while unintentional fine particle growth or secondary It is necessary to develop a method for producing fine particles capable of preventing aggregation and an apparatus therefor.

As such a recovery method, the present inventors disclosed in Japanese Patent Application No. 2005-121737 the flow of the molten salt in the portion where the fine particles are generated and the fine particles are moved out of the molten salt bath and recovered to recover the fine particles by plasma-induced electrolysis. A manufacturing method and apparatus were proposed. (Patent Document 2)

In the method in which the bath surface layer portion containing a large amount of fine particles immediately after the fine particles are formed is flowed or cooled and solidified, and this is selectively collected, the diameter of the collected fine particles is much smaller than the conventional one, and its particle size distribution Was also relatively uniform. However, in any of the methods in Patent Document 2, it is difficult to recover all the formed fine particles immediately after generation, and they are circulated in the molten salt bath. As a result, the growth and secondary agglomeration of the fine particles progress while circulating in the bath, making it difficult to control the particle size and dispersion of the recovered particles and lowering the yield. It was a problem.

In particular, when a recovery mechanism such as a rotating drum or a conveyor is used, salt may solidify in the recovery unit and interfere with the operation of a drive unit such as a motor, which again becomes a problem for long-term continuous electrolysis.

In addition, in the method of recovering the bath surface layer portion containing a large amount of fine particles to the outside of the bath, the amount of molten salt in the bath decreases with the recovery of the molten salt, resulting in a change in bath composition or a decrease in bath surface. In this case, the discharge cannot be maintained, so that it is necessary to add to the bathtub in an amount corresponding to the amount of the molten salt recovered. For this reason, in order to perform continuous electrolysis for a long time in a stable state, an auxiliary tub for supplying molten salt separately to the outside of the tub, a heated pipe, and a rod-like or box-like spacer are melted at a constant speed. The structure of the device, such as a mechanism that adjusts by sunk in a salt bath and linked to a sensor that monitors the height of the bath surface, has become very complex, leading to increased manufacturing costs.

On the other hand, in Patent Document 2, the generated fine particles are settled at the bottom of the molten salt bath by the flow of the bath, etc., and the molten salt containing the fine particles is discharged out of the bath and recovered from the discharge path installed at the bottom of the molten salt bath. Also suggested. Although it was necessary to add a salt corresponding to the amount of the molten salt discharged as described above, there was almost no mechanical drive, so there was no problem in the operation of the apparatus even during long-term continuous electrolysis. However, the fine particles settled on the bottom of the bath have a larger particle size than those collected at the surface layer portion, and there is a problem in forming uniform and dispersed fine particles having a smaller particle size.

Therefore, in order to continuously produce finer particles having a smaller particle size that are uniformly dispersed for a long time, the fine particles are generated under the same conditions as the recovery from the surface layer part in Patent Document 2, and the fine particles immediately after the generation are continuously produced. Therefore, it was necessary to develop a new and simple method and apparatus that can be recovered.

In Patent Documents 1 and 2, an electric resistance of several hundred to several thousand ohms is used between the power source and the electrode in order to stably maintain the discharge. Therefore, most of the applied power is consumed by the resistance, which leads to a large energy loss. By reducing the resistance value, the energy loss in the resistance could be reduced, but the current became unstable and it was difficult to keep the discharge stable for a long time.

Therefore, in order to produce fine particles continuously for a long time by plasma-induced electrolysis with low energy consumption, a method capable of maintaining a stable discharge for a long time using a smaller electric resistance or without using a resistance, and Development of the device was necessary.
Formation of Ni fine particles by discharge electrolysis in molten chloride system, Hiroyuki Kawamura, Koichi Moriya, Yasuhiko Ito, Powder and Powder Metallurgy, Vol. 45, No. 12, p1142, 1998 Discharge electrolysis in molten chloride: formation of fine silver particles, H. Kawamura, K. Moritani and Y. Ito, Plasmas & Ions, 1, p29, 1998 Formation of Metal Oxide Particles by Anode-Discharge Electrolysis of Molten LiCl-KCl-CaO System, T. Oishi, T. Goto, and Y. Ito, J. Electrochemical. Soc., 149 (11) D155-D159 (2002) WO2005 / 111272 publication Japanese Patent Application No. 2005-121737

The present invention is simple and convenient for continuously collecting fine particles in a molten salt by plasma-induced electrolysis on the surface of the molten salt, and continuously collecting while suppressing the growth and aggregation of the produced fine particles. An object of the present invention is to provide a fine particle production and recovery apparatus and a method thereof. Another object of the present invention is to provide an apparatus and a method for stably maintaining a discharge for a long time using a small electric resistance or without using a resistance when performing plasma-induced electrolysis on a molten salt surface.

As a result of intensive studies in view of the problems of the prior art described above, the present inventor generates fine particles in the retained molten salt by performing plasma-induced electrolysis on the molten salt retained on the disk. It has been found that fine particles having a smaller particle diameter can be continuously produced and recovered by moving the molten salt containing the fine particles formed by the rotation of the disk to the outside of the disk using centrifugal force and collecting the molten salt. The present invention has been completed (see claims 1 and 9). Further, it has been found that by inserting a coil between a power source and an electrode, discharge can be stably maintained for a long time without using a large resistance, and the present invention has been completed (see claim 22). .

Specifically, the invention described in claim 1 is a method for producing fine particles by plasma-induced electrolysis of molten salt, wherein the molten salt bath is held on a rotating substantially flat surface. In the production method, fine particles are generated by performing plasma irradiation on the surface, and the fine particles generated by centrifugal force are moved out of the molten salt bath.

According to the first aspect of the present invention, there is provided a simple and simple method for producing fine particles that can be continuously collected while suppressing the growth and aggregation of fine particles produced by plasma-induced electrolysis. The substantially flat surface that is rotationally driven may be a surface that can generate centrifugal force that can move the fine particles generated by the rotation out of the molten salt bath, and is inclined downward. It is not limited to a two-dimensional plane as long as it is a surface that can form a smooth flow of molten salt by centrifugal force as a whole, such as a curved surface such as a conical surface or a surface on which a plurality of grooves are formed. Absent.

The invention described in claim 2 is the manufacturing method according to claim 1, wherein the fine particles are manufactured in an inert gas atmosphere.

According to the second aspect of the present invention, oxidation of the produced fine particles can be effectively prevented.

A third aspect of the present invention is the manufacturing method according to the first or second aspect, wherein the particle diameter of the fine particles is controlled by the number of rotations of the surface to be rotationally driven.

According to the third aspect of the present invention, it is possible to combine the factors that control the particle diameter of the manufactured fine particles into the rotational speed of the surface to be rotationally driven, so that the particle diameter of the fine particles can be easily controlled with high accuracy. become.

The invention according to claim 4 is characterized in that the rotation of the surface to be rotated is controlled so that the thickness of the molten salt bath is substantially maintained at 0.01 mm to 5 mm. It is a manufacturing method.

According to the fourth aspect of the present invention, the movement path of the fine particles in the molten salt generated by thinning the molten salt bath is simplified approximately two-dimensionally, and stable with little variation while suppressing the aggregation of the fine particles. Fine particles having a reduced particle diameter can be obtained.

The invention according to claim 5 is the manufacturing method according to any one of claims 1 to 4, wherein the surface on which the molten salt is held is heated to a predetermined temperature by an external heating means.

According to the invention described in claim 5, in particular, the molten salt bath can be prevented from solidifying by the cooling effect of the rotatable surface at the initial stage of the molten salt supply, and the temperature segregation of the molten salt bath is reduced and stable. Fine particles having a particle size can be obtained.

The invention described in claim 6 is to use an electrode material containing a fine metal component generated in the anode as the counter electrode in order to continuously supply metal ions consumed in the cathode discharge into the molten salt bath. 6. The manufacturing method according to claim 1, wherein the manufacturing method is characterized in that:

According to the sixth aspect of the invention, in the cathode discharge, metal ions having the same components as the metal fine particles generated from the anode into the molten salt bath are supplied, so that desired metal fine particles can be obtained continuously. it can.

The invention according to claim 7 uses an electrode material containing a metal component of a metal compound generated on an anode as a discharge electrode and generates a counter ion for generating fine particles of the metal compound in an anode discharge. The manufacturing method according to any one of claims 1 to 5, wherein a molten salt is used.

According to the seventh aspect of the present invention, in anodic discharge, metal ions different from the ions present in the molten salt bath can be supplied from the anode into the molten salt bath, so that the metal oxide, Fine particles made of a desired metal compound such as nitride can be obtained.

The invention according to claim 8 further includes the step of cooling the molten salt containing the fine particles moved out of the molten salt bath to below the melting point of the molten salt by an external cooling means. Or the production method according to any one of 7 to 7.

According to the invention described in claim 8, since it becomes possible to rapidly cool the molten salt containing fine particles moved out of the molten salt bath, further growth and aggregation of the produced fine particles can be suppressed, This greatly contributes to stably obtaining nano-sized fine particles.

The invention according to claim 9 is a supply means for supplying a molten salt, a holding means for holding the supplied molten salt on a rotatable substantially flat surface, and a held molten salt. An electrode including a discharge electrode and a counter electrode for performing plasma irradiation on the bath surface, and fine particles generated by the plasma irradiation are moved out of the molten salt bath by centrifugal force generated by the rotation of the holding means. An apparatus for producing fine particles by plasma-induced electrolysis of a molten salt comprising:

According to the ninth aspect of the present invention, there is provided an apparatus capable of producing simple and simple microparticles that can be continuously collected while suppressing the growth and aggregation of the microparticles generated by plasma-induced electrolysis. Is done. The substantially flat surface that is rotationally driven may be a surface that can generate centrifugal force that can move the fine particles generated by the rotation out of the molten salt bath, and is inclined downward. It is not limited to a two-dimensional plane as long as it is a surface that can form a smooth flow of molten salt by centrifugal force as a whole, such as a curved surface such as a conical surface or a surface on which a plurality of grooves are formed. Absent.

A tenth aspect of the present invention is the apparatus according to the ninth aspect, wherein the molten salt supply port of the supply means is disposed on the rotating shaft of the holding means.

According to the invention described in claim 10, since the molten salt bath is supplied to the most static region in the molten salt bath, it has an extremely high purity without involving the molten salt of other regions having a dynamic flow. Thus, fine particles having a stable particle diameter can be obtained.

The invention according to claim 11 is the apparatus according to claim 9 or 10, further comprising an external heating means for maintaining the temperature of the molten salt in the supply means.

According to the eleventh aspect of the invention, in particular, the molten salt bath can be prevented from solidifying by the cooling effect of the molten salt supply initial stage and the supply means, and the temperature segregation of the molten salt bath is reduced, and the stable particle diameter is small. Can be obtained.

The invention according to claim 12 is characterized in that the holding means is provided with a disk-like or ring-shaped weir for forming a substantially circular molten salt bath on the outer periphery. It is an apparatus in any one.

According to the twelfth aspect of the present invention, the centrifugal force generated by rotating the holding means is uniformly distributed in the molten salt bath along the rotation direction, so that the fine particles in the generated molten salt are dispersed. The movement time and the movement path can be stabilized, and fine particles having an extremely stable particle diameter can be obtained.

The invention according to claim 13 is characterized in that the holding means is provided with a conical surface inclined downward toward the rotation axis so as to keep the thickness of the molten salt bath substantially constant. The apparatus according to any one of 9 to 11.

According to the thirteenth aspect of the present invention, the movement path of the fine particles in the molten salt generated by making the thickness of the molten salt bath uniform and thin is simplified approximately two-dimensionally to suppress the aggregation of the fine particles. In addition, fine particles having a stable particle diameter with little variation can be obtained.

The invention according to claim 14 is the apparatus according to any one of claims 9 to 13, further comprising an external heating means for maintaining the temperature of the molten salt in the holding means.

According to the invention described in claim 14, in particular, the molten salt bath can be prevented from solidification by the cooling effect of the rotatable surface at the initial stage of the molten salt supply, and the temperature segregation of the molten salt bath is reduced and stable with little variation. Fine particles having a particle size can be obtained.

The invention according to claim 15 is the apparatus according to any one of claims 9 to 14, wherein the discharge electrode is disposed outside the rotation axis of the holding means. The invention described in claim 16 is the apparatus according to any one of claims 9 to 15, characterized in that the counter electrode is disposed on the rotating shaft of the holding means, and further according to claim 17, The invention according to any one of claims 9 to 16, wherein at least a part of the counter electrode is brought into contact with a molten salt bath.

According to the invention described in claims 15, 16 and 17, it is possible to obtain a stable plasma with very little electrical interference with the counter electrode between the discharge electrode and the surface of the molten salt bath, and efficient plasma-induced electrolysis. Can be performed.

The invention according to claim 18 is the apparatus according to any one of claims 9 to 17, characterized in that it is made of a material containing a fine-particle metal component that generates an anode as a counter electrode in cathode discharge.

According to the eighteenth aspect of the invention, in the cathode discharge, metal ions having the same components as the metal fine particles generated from the anode into the molten salt bath are supplied, so that desired metal fine particles can be obtained continuously. it can.

The invention according to claim 19 is the apparatus according to claim 18, further comprising a metal scrap holder on the anode as the counter electrode.

According to the invention described in claim 19, in the cathode discharge, by inserting metal scrap having the same component as the metal fine particles generated in the metal scrap holder provided in the anode, Since it can function as an anode, a recyclable fine particle production apparatus by plasma induced electrolysis can be provided.

The invention according to claim 20 is constituted by a material containing a particulate metal component that generates an anode which is a discharge electrode in anode discharge, and the apparatus according to any one of claims 9 to 17.

According to the invention described in claim 20, in anodic discharge, metal ions different from ions present in the molten salt bath can be supplied from the anode into the molten salt bath. Fine particles made of a desired metal compound such as nitride can be obtained.

The invention according to claim 21 is characterized in that the apparatus according to the present invention is further provided with an external cooling means for cooling the molten salt containing fine particles moved out of the molten salt bath below the melting point of the molten salt. An apparatus according to any one of claims 9 to 20.

According to the invention of claim 21, since it becomes possible to rapidly cool the molten salt containing fine particles moved out of the molten salt bath, further growth and aggregation of the produced fine particles can be suppressed, This greatly contributes to stably obtaining nano-sized fine particles.

The invention according to claim 22 is characterized in that a coil for stabilizing discharge is arranged between a circuit connecting at least one electrode of the discharge electrode or counter electrode of the apparatus according to the present invention and a power source. Item 22. The device according to any one of Items 9 to 21.

According to the twenty-second aspect of the present invention, it is possible to maintain a stable discharge for a long time in a relatively wide inductance region even when the applied voltage is lowered after the discharge is stabilized. .

1. Plasma-induced electrolysis In the present specification, a method of producing metal fine particles and / or metal compound fine particles by irradiating plasma induced by arc discharge or the like on the surface of the molten salt may be referred to as plasma-induced electrolysis. . There are roughly two methods for producing fine particles by plasma-induced electrolysis. One is cathodic discharge and the other is anodic discharge. This is the difference between whether the electrode that causes discharge functions as a cathode or an anode.

The discharge electrode is installed in the vicinity of the electrolytic bath so as not to be in contact with or immersed in the molten salt bath (electrolytic bath). The installation location is not particularly limited as long as it is a location where fine particles are generated in the molten salt by the plasma generated by the discharge electrode, but it is preferably installed on the upper surface of the molten salt liquid surface. By doing so, plasma is induced from the discharge electrode, and fine metal particles and / or fine metal compound particles are generated in the electrolytic bath.

In the case of cathode discharge, ions of metal fine particle components to be manufactured exist in the molten salt bath, and electrons supplied to the bath by the cathode discharge reduce metal ions near the surface of the molten salt bath, Form fine particles. By controlling the type and concentration of metal ions present in the bath, multi-component alloy fine particles composed of two or more metals can be formed. It is preferable to use the electrode containing the metal component made into the counter electrode (anode) at the time of performing electrolysis.

On the other hand, in anodic discharge, the object of manufacture is fine particles of metal compounds, such as metal oxides, nitrides, oxynitrides, sulfides, and carbides. As an example, in the case of a metal compound, when an anode containing a metal component constituting the metal compound to be manufactured is used and anodic discharge is performed, the metal component is ionized and supplied to the surface of the molten salt bath.

On the other hand, in the molten salt bath, there are ions on the other side forming a compound with the metal. For example, when forming metal oxide fine particles, oxide ions from CaO added to the bath Existing. Metal ions supplied by anodic discharge react with partner ions in the molten salt near the bath surface to form metal compound fine particles. It is preferable to use an Al electrode or a gas diffusion electrode as a counter electrode (cathode) for electrolysis.

As described above, depending on whether fine particle formation is performed by cathode discharge or anode discharge, the components constituting the cathode and anode and the types of source ions added to the molten salt are different. However, since both are the same from the viewpoint of forming fine particles on the surface of the molten salt immediately below the discharge, the same method can be used to recover the fine particles generated on the surface of the molten salt.

In the following, the case of cathode discharge is mainly shown as an example. In the case of cathodic discharge, the produced fine particles are metal fine particles, but the same recovery method, apparatus, etc. can be adopted even when the metal compound fine particles are produced by anodic discharge. For this reason, the following example is applicable also as a collection | recovery method and apparatus of the metal compound fine particle manufactured by anode discharge. In the case of anodic discharge, when there is a matter to be noted, it will be described as appropriate at a necessary place.

2. Fine particle production and recovery method according to the present invention An example of the fine particle production and recovery method according to the present invention is schematically shown in FIG. This apparatus 1 includes a rotating disk 10, a cathode 11 (discharge electrode, anode in the case of anode discharge) installed on the disk, and a supply for supplying molten salt 12 (raw material salt) on the disk. To recover a salt containing a salt bath 13, an anode 14 (counter electrode, cathode in the case of anode discharge) in contact with the molten salt supplied on the disc, and fine particles 15 moving out of the disc by centrifugal force It consists of the collection container 16 of this.

2-1. Rotating disc The rotating disc 10 is rotated by being directly connected to a motor 100 or the like installed on the upper or lower portion of the disc. You may drive via a gear, a belt, etc., without connecting directly with a motor. Fine particles 15 are generated directly under the discharge electrode 11, and the particles 15 grow until they reach the outside of the disk. Therefore, the particle diameter can be controlled by controlling the rotation speed.

The number of rotations may be appropriately adjusted according to the components of the fine particles 15 to be generated, the desired particle diameter, or the disk diameter to be used, but as an example, it may be in the range of 0.1 to 3,000 rpm, preferably 1 to 1,500 rpm. It ’s fine.

Further, when the supply of the molten salt 12 onto the disk 10 is started, the disk temperature is reduced to the temperature of the supplied molten salt in order to prevent the molten salt 12 held on the disk 10 from being cooled. Is preferably raised in advance, and preheating may be performed from the heater 130 installed in a contact or non-contact manner inside, below, or on the side of the disk. When the disk temperature is maintained by the supplied molten salt 12 or internal heating by discharge after the supply starts, it is not particularly necessary to heat the disk 10.

As for the material of the disk 10, it dissolves in the molten salt 12 supplied on the disk or reacts with ions in the molten salt 12, which does not adversely affect the formation of the fine particles 15 as impurities. As long as it is not particularly limited, it is preferable to use ceramics with high insulating properties (Al ₂ O ₃ , SiO _2, etc.), or those composed of the same or a part of the metal elements of the fine particles 15 to be generated. . In the latter case, particularly in the case of cathode discharge, this rotating disk itself can be used as the anode.

The cross-sectional shape of the disk 10 is not particularly limited as long as the molten salt 12 can be kept thin on the rotating disk. The molten salt 12 to be held has a thickness of 0.01 mm to 5 mm, preferably 0.1 mm to 3 mm. In order to achieve this, the disk has a concave cross section or has an edge on the outer periphery, etc. The outer periphery may be higher than the surface (see FIG. 1b). Further, for the purpose of controlling the flow of the molten salt 12 on the disk 10 to the outer periphery, there may be grooves or projections on the upper part of the disk from the center of the disk to the outer periphery or concentrically. good.

2-2. Discharge electrode The discharge electrode 11 is installed in the vicinity of the electrolytic bath so as not to be in contact with or immersed in the molten salt bath (electrolytic bath). The installation location is not particularly limited as long as the fine particles 15 are generated in the molten salt 12 by the plasma generated by the discharge electrode 11, but it is preferably installed at the upper part of the molten salt bath surface. By doing so, plasma is induced by the discharge electrode 11, and metal fine particles and / or metal compound fine particles are generated in the electrolytic bath. The distance from the surface of the electrolytic bath to the lowest part of the discharge electrode 11 is not limited as long as the plasma is stably maintained.

In the case of cathode discharge, the material of the discharge electrode 11 is generally used for molten salt electrolysis and can generate plasma, and is not particularly limited. For example, various high melting point metals such as molybdenum, tantalum, and tungsten, alloys thereof, carbon materials such as glassy carbon and conductive diamond, conductive ceramics, and semiconductive ceramics can be used. Moreover, what formed these in the thin film form on the dissimilar material can also be used as a cathode. Among them, it is preferable to use a refractory metal such as tungsten or tantalum which is not easily consumed when plasma is induced.

On the other hand, in the case of anodic discharge, since the anode itself is a raw material for the fine particles 15, it is sufficient to use only the desired fine particle 15 component or a part of the fine particle component. There are no particular restrictions on the shape and size of the discharge electrode, but a rod shape such as a round bar shape or a square bar shape is preferable. In order to maintain a stable discharge, the anode is consumed evenly, particularly in the case of anodic discharge. Therefore, it is better if the discharge electrode side surface is covered with insulating ceramics such as alumina or silica.

Electrolysis conditions in plasma-induced electrolysis can be generally performed under conditions for performing plasma-induced electrolysis, and can be appropriately selected according to the composition of the solvent, the type of the target metal fine particles 15 and the like. For example, the applied voltage may be about 100 to 2,000 V, but is preferably about 100 to 400 V in consideration of reducing the burden on the electric circuit. When the discharge is stable, the voltage can be lowered to 10 to 200 V, preferably 20 to 150 V. The type of current is preferably direct current, and the current per discharge electrode is about 0.05 to 50A, preferably about 0.1 to 20A.

In order to induce plasma stably, it is preferable to ensure the stability of discharge by inserting an electric resistance or a coil in series between the power source and the electrode. The electrical resistance can be inserted on the cathode side, the anode side, or both. The type of the electrical resistance is not limited as long as it is a resistor having a capacity capable of withstanding the current during electrolysis. For example, a cement resistor, a hollow resistor, a non-combustible wire fixed resistor, etc. can be used, and a non-combustible wire is used. A fixed resistor is more preferred.

The value of the resistance is usually about 1Ω to 5kΩ, preferably 3Ω to 500Ω. When using a small resistance of several tens to several tens of ohms, the power consumption in the resistance part becomes extremely small and the applied voltage can be lowered to several tens of volts. Becomes difficult. When such a small resistance is used, the discharge can be stabilized by using a combination of coils, and it is not necessary to use a resistance.

As the resistance value of the discharge part fluctuates, the current flowing through the system changes. When the inductance is too large, the time constant (τ = R / L) becomes very small with respect to the time width, and thus it becomes impossible to suppress a change in current. On the other hand, when the inductance is too small, magnetic energy (W = (1/2) LI ² ) sufficient to reduce the current change cannot be stored. Therefore, in the case of the plasma induced electrolysis performed in the present invention, it is preferable to use one having an inductance of 0.05 μH to 100 mH, preferably 0.2 μH to 10 mH. A coil and a smoothing capacitor may be used in combination.

The electrolysis is usually performed under atmospheric pressure, but can be performed under pressure or under reduced pressure. Moreover, in order to suppress the oxidation of the generated particles 15, the electrolysis is preferably performed in an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, neon, and the like, and argon is preferable.

2-3. Supply of molten salt on the disk The supply of the molten salt 12 on the disk 10 is performed from a molten salt bath 13 installed at the upper part of the disk through a supply path 17 connected to the lower part of the molten salt bath. Is preferred. The molten salt bath 13 has a heater 130 and a heat insulating material for melting and holding the salt. In order to prevent moisture, air and the like from being mixed into the molten salt 12, the molten salt bath 13 is preferably installed in an inert gas atmosphere, or the inside of the bathtub 13 is preferably set to an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, neon and the like, and argon is preferable.

You may install this molten salt bathtub 13 in a disk lower part. In this case, in order to perform continuous electrolysis for a long time, a mechanism for pumping the molten salt 12 onto the disc is necessary. Moreover, the molten salt bath 13 can be installed in the lower part of the disk, and the molten salt 12 can be pumped by moving the disk up and down. In this case, a series of operations of intermittently pumping the bath, performing electrolysis for a certain time while rotating the disk at a low rotation speed, and moving the salt 12 containing the fine particles 15 to the outside of the disk by increasing the rotation speed are intermittent. By performing the step, electrolysis can be performed for a long time. However, care must be taken so that the molten salt 12 containing the fine particles 15 moved to the outside of the disk does not enter the molten salt bath 13 below.

The material of the molten salt bath 13 and the supply path 17 is dissolved in the molten salt 12 supplied on the disk 10 or reacts with ions in the molten salt 12. Although it is not particularly limited as long as it does not adversely affect the formation, ceramics (Al ₂ O ₃ , SiO _2, etc.), or those made of the same or a part of the metal component of the fine particles 15 are used. Preferably, stainless steel or the like is used as a structural material, and ceramic coating may be applied to the inside.

Although there is no restriction | limiting in particular also about the internal diameter of the supply path 17, 0.05-10 mm as an example, Preferably it should just be 0.5-5 mm. Moreover, about the location which has the said internal diameter in the supply path 17, it is not necessary to have the same diameter over the whole supply path, and the spacer etc. which have the hole of the said diameter may be installed in a part of flow path. In this case, when it is necessary to optimize the inner diameter of the supply path 17 according to the desired diameter and composition of the fine particles 15 and the production rate, it is convenient because a common flow path can be used. Moreover, you may use the porous spacer from which the flow velocity equivalent to the supply path 17 of said diameter is obtained.

Further, the lower end of the supply path 17 is preferably installed near the center of the rotating disk 10 so as not to be fixed to the rotating disk but in contact with the molten salt 12 on the rotating disk. The lower end of 17 may be fixed to the rotating disk 10 itself, and the installation position may not be the center of the rotating disk 10 but may be installed at an eccentric position. Further, the molten salt 12 may be supplied in the form of droplets by being installed further above the lower end of the supply path 17 so as not to contact the molten salt 12 on the rotating disk 10.

As the molten salt 12 bath (electrolytic bath) used in plasma-induced electrolysis, a bath generally used in molten salt electrolysis can be used. For example, alkali metal halide, alkaline earth metal halide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal sulfate, alkaline earth metal sulfate, alkali metal nitrate, alkaline earth metal nitrate, etc. It is preferable to use a molten salt obtained by singly or in combination of two or more as a solvent for an electrolytic bath.

As alkali metal halides, LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, etc. are used. can, halides of alkaline earth _{metals, MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr 2, MgI 2 , CaI ₂ , SrI ₂ , BaI _{2 and the} like can be used. The said compound can also be used independently and can also be used in combination of 2 or more type. The combination of these compounds, the number of compounds to be combined, the mixing ratio, and the like are not limited, and can be appropriately selected according to the desired components, types, and the like of the fine particles 15.

The metal fine particles 15 can be obtained by dissolving a metal compound or the like as a raw material for the metal fine particles in such a solvent and performing plasma-induced electrolysis.

The metal element-containing raw material is a raw material of metal fine particles or metal compound fine particles for production purpose, and exists as ions in the electrolytic bath. When the metal type of the metal element-containing raw material to be used is one kind, the metal fine particles 15 made of a single metal atom can be obtained, and when the metal element-containing raw material to be used is two or more kinds, It is also possible to obtain metal fine particles 15 (consisting of a plurality of metals) of an alloy. Therefore, the metal fine particles 15 include alloy fine particles.

In addition, when the metal or metal compound used as the raw material of the metal microparticle 15 is contained in the anode, since the anode 11 becomes the metal element-containing raw material, the addition of the metal element-containing raw material to the molten salt 12 is optional. .

The metal element-containing raw material is a metal oxide (as titanium oxide, TiO, TiO ₂ , Ti ₂ O ₃ etc .; as zirconium oxide, ZrO ₂ etc .; as vanadium oxide, VO, VO ₂ , V ₂ O ₃ , V ₂ O ₄ , V ₃ O _5, etc .; niobium oxides such as NbO, NbO ₂ , Nb ₂ O _5, etc .; tantalum oxides such as TaO, Ta ₂ O _5, etc .; molybdenum As oxides of MoO ₂ , MoO ₃ etc .; as tungsten oxides WO ₂ , WO ₃ etc .; as chromium oxides CrO, CrO ₂ , Cr ₂ O ₃ etc .; as platinum oxides PtO , Pt ₃ O ₄ , PtO _{2 and the} like; CoO as the cobalt oxide, Co ₃ O _4, etc .; NiO as the oxide of nickel, Ni _1-x O (0.003 <x <0.17); oxidation of silicon Examples of such materials include SiO, SiO ₂ , metal sulfates, nitrates, phosphates, halides (chlorides, fluorides, bromides, iodides, etc.).

The amount of the metal element-containing raw material added to the molten salt 12 bath is not limited, and can be appropriately selected according to the electrolysis time and the amount and size of the fine particles. For example, the metal element-containing material relative to the amount of solvent in the electrolytic bath may be dissolved so as to be about 0.0001 to 20 mol / L, preferably about 0.1 to 5.0 mol / L.

The temperature of the molten salt 12 to be supplied is not limited, and can be appropriately selected according to the melting point of the solvent, the melting point of the ion source, and the like. A heat source such as a heat insulating material or an auxiliary heater may be installed outside the flow path so that the supplied molten salt 12 does not solidify in the flow path. On the contrary, a cooling part by air cooling or the like may be installed. In this case, the solidified salt itself can serve as a valve by positively solidifying the molten salt 12 in the flow path.

2-4. Counter electrode The counter electrode 14 according to the present invention is used in contact with the molten salt 12 supplied on the disk 10, so that it is installed near the lower part of the molten salt supply path 17 in the center of the rotating disk 10. To do. When the molten salt 12 in the molten salt bath and the molten salt 12 on the disc 10 are always connected, the counter electrode 14 can be installed in the molten salt bath.

As the counter electrode, an electrode generally used as an anode in molten salt electrolysis can be used and is not particularly limited. For example, carbon materials such as glassy carbon, graphite, and conductive diamond, tantalum, tungsten, molybdenum, platinum, and the like can be used as electrodes. In addition, a material in which a metal such as tantalum, tungsten, molybdenum, or platinum is coated on a different material can be used as the anode. Moreover, a used metal can also be used as an anode material. Moreover, when it is calculated | required that generation | occurrence | production of chlorine gas is calculated | required, it can suppress by making a fine particle raw material metal or the compound of this metal contain in an anode. The shape, size, etc. of the electrode 14 to be used are not limited.

In particular, in the case of performing cathode discharge, it is preferable to use, as the counter electrode (anode) 14, the same component as the target component of the fine particles 15 or a part of the metal component of the fine particle component. In this case, a bowl-shaped conductive anode material holder 140 is installed in the lower part of the molten salt supply path 17, and the metal 141 of the above-described component that functions as an anode is held therein (see FIG. 2). As long as the metal 141 held in the holder 140 is in contact with the molten salt 12 supplied from the flow path, it functions as a counter electrode (anode). Therefore, the entire anode or a part thereof may be immersed. You may install in a molten salt bath.

Thereby, it becomes easy to use a used metal etc. as an anode material. As a material of the conductive anode material holder 140, for example, a carbon material such as glassy carbon, graphite, conductive diamond, tantalum, tungsten, molybdenum, platinum, or the like can be used.

2-5. Recovery part The molten salt 12 containing the fine particles 15 generated on the disk 10 is moved to the outside of the disk by centrifugal force due to the rotation of the disk 10 and recovered by the collector 16. The shape and size of the collector 16 are not particularly limited as long as the molten salt 12 moved to the outside of the disk 10 can be captured. The material is not particularly limited as long as it does not adversely affect the formation of the fine particles 15 as impurities by reacting with the collected salt 12, but ceramics (Al ₂ O ₃ , SiO ₂ etc.), Metals such as stainless steel are preferred.

The molten salt 12 containing the collected fine particles 15 is preferably immediately solidified in order to suppress the growth and secondary aggregation of the fine particles in the molten salt. Therefore, the collector 16 is preferably kept below the melting point of the molten salt 12 to be used by water cooling, air cooling, etc., and may be cooled to 50 ° C. or less, preferably 100 ° C. or less of the melting point.

According to the recovery method of the present invention, the fine particles formed in the molten salt can be continuously recovered while suppressing the growth and secondary aggregation of the fine particles, and the continuous productivity compared to the conventional recovery method. And the efficiency of the recovery process is improved.

Next, examples of the present invention will be described. The present invention is not limited to the examples shown below, and various modifications can be made without departing from the technical idea of the present invention.

One embodiment of the present invention was made for the purpose of establishing a simple and simple new method capable of continuously collecting fine particles immediately after generation under the same conditions as in the recovery from the surface layer portion in Patent Document 2. (See claims 1 and 9).

Therefore, in the example, the production of Al fine particles is used as a model case, and based on the details of the invention described above, the case where the fine particles are generated and recovered by performing plasma induced electrolysis on the molten salt on the rotating disk (Example 1). In the case where only the surface layer portion is recovered by a method considered to be the simplest and most effective among the recovery methods of Patent Document 2 by performing plasma-induced electrolysis directly on the molten salt bath without using fine particles and a rotating disk ( The fine particles of Comparative Example 1) were prepared. These were compared, and it was confirmed that the fine particles were pure Al, and that the particle size thereof was as small or even as that of Comparative Example 1 and was uniform.

In another embodiment of the present invention, in the conventional plasma-induced electrolysis, a resistor is used to stably maintain a discharge, but this is added to the resistor or a coil is used without using the resistor. By doing so, the purpose is to maintain a stable discharge. Therefore, in Example 2, the induction of electrolysis was actually performed using coils having various inductances without using resistors, and an inductance value that can maintain a stable discharge was found (see claim 22).

As a molten salt, LiCl-KCl-CsCl (57.5: 13.3: 29.2mol%) mixed in the eutectic composition was vacuum dried at 200 ° C for several days and then melted at 300 ° C in an argon atmosphere. The aluminum ion concentration in the salt was adjusted to be 0.2 mol%, and the bath was kept thin on the rotating disk so that the bath thickness was about 2 mm.

A tungsten rod was placed on the top of the disc as the discharge electrode. The disc used was made of 70 mm diameter aluminum, and consumed aluminum ions were supplied from the disc by using the disc itself as a counter electrode. 150 V was applied between the discharge electrode and the disc holding the molten salt, and plasma was induced between the discharge electrode and the molten salt to discharge. When discharging, the disk is rotated at 25 rpm, and after discharging for 1 minute at 1 A, the rotational speed is increased to move the molten salt containing the fine particles on the disk to the outside of the disk for rapid cooling and solidification. And recovered.

The salt containing the collected fine particles was subjected to dissolution washing of the salt with deoxygenated water and filtration with a filter (both once) to obtain produced fine particles.

Comparative Example 1

As the molten salt, LiCl—KCl—CsCl containing 0.2 mol% of aluminum ions as in Example 1 was used, and this was held at 300 ° C. in a crucible in an argon atmosphere. After discharging the surface of the molten salt layer for 1 minute at 1A in the same manner as in Example 1, only the bath surface layer was cooled and solidified by bringing it into contact with a cooled Pyrex plate. Through the same washing process, produced fine particles were obtained. In the molten salt bath in the crucible after recovery, the presence of particles that could not be recovered by cooling and solidification was visually confirmed.

As a result of observing the collected fine particles by SEM, the particles in the case of using a rotating disk (Example 1) are nanoparticles having a particle size of about 30 to 50 nm and having a very uniform particle size, and secondary aggregation is also caused. It was hardly seen (see FIGS. 3A and 3B). As a result of analyzing the recovered particles by XRD, the generated fine particles were Al, and the presence of oxide or the like was not confirmed (see FIG. 4).

On the other hand, the fine particles collected from the surface layer without using the rotating disk were about 100 to 200 nm although the particle size was small, and it was confirmed that the particles were partially agglomerated compared with the case using the rotating disk. (See FIGS. 3C and D). From this result, the effectiveness of the present invention using a rotating disk was confirmed.

As the molten salt, LiCl—KCl—CsCl (57.5: 13.3: 29.2 mol%) mixed in the eutectic composition was vacuum dried at 200 ° C. for several days and then melted at 300 ° C. in an argon atmosphere. Nickel ions were added to the molten salt to adjust the concentration to 0.1 mol%. 150 to 250 V was applied between the discharge electrode and the disc holding the molten salt, plasma was induced between the discharge electrode and the molten salt, and then the voltage was lowered to about 20 to 35 V to discharge. .

Table 1 shows the results of examining the inductance of the coil used in the system and the discharge sustaining time (set to 5 minutes at the longest) after the voltage was lowered.

When the coil was not used, it was difficult to maintain the discharge after the applied voltage was lowered, and the maintenance for several seconds was the limit. On the other hand, it was found that the discharge can be maintained for a long time in a relatively wide inductance region by inserting the coil into the system.

The fine particles produced according to the present invention can be used for capacitor materials, electrode catalysts, photocatalysts, abrasives, magnetic powders, pigments, paints, etc. after the attached salt is removed by washing or the like.

FIG. 2 is a schematic view (a) and a cross-sectional view (b) of an apparatus according to the present invention for producing fine particles by irradiating a molten salt on a rotating disk with plasma. FIG. 2 is a partially enlarged cross-sectional view of another embodiment of the apparatus shown in FIG. FIG. 3 shows SEM photographs (A) and (B) of Al fine particles produced by the apparatus of the present invention, and SEM photographs (C) and (D) of Al fine particles produced without using a rotating disk as a comparative example. (Photo A, C: × 50,000, Photo B, D: × 100,000). FIG. 4 is a diagram showing the results of analyzing Al fine particles produced by the apparatus of the present invention by XRD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fine particle manufacturing apparatus 10 ... Rotating disc 11 ... Discharge electrode 12 ... Molten salt 13 ... Molten salt bath 14 ... Counter electrode 15 ... Fine particle 16 ... Collection container 17 ... Supply path 100 ... Motor 130 ... Heater 140 ... Anode material holder 141 ... Metal waste

Claims (22)

A method for producing fine particles by plasma-induced electrolysis of a molten salt,
Fine particles are generated by irradiating the molten salt bath surface held on a rotating substantially flat surface with plasma, and the fine particles generated by centrifugal force are moved out of the molten salt bath. Said manufacturing method characterized by these.   The production method according to claim 1, wherein the production of the fine particles is performed in an inert gas atmosphere.   The method according to claim 1 or 2, wherein the particle diameter of the fine particles is controlled by the number of rotations of the surface.   The manufacturing method according to claim 1, wherein the surface is rotationally controlled so as to keep the thickness of the molten salt bath substantially 0.01 mm to 5 mm.   The manufacturing method according to claim 1, wherein the surface is heated to a predetermined temperature by an external heating unit.   6. The anode as a counter electrode contains a fine metal component to be produced in order to continuously supply metal ions consumed in the cathode discharge into the molten salt bath. The manufacturing method as described in.   The anode as a discharge electrode contains a metal component of the metal compound to be produced in order to produce fine particles of the metal compound in the anodic discharge, and the counter ion is contained in the molten salt. 6. The production method according to any one of 1 to 5.   The molten salt containing the fine particles moved out of the molten salt bath is further cooled by an external cooling means to a melting point or lower of the molten salt. Manufacturing method. Supply means for supplying molten salt;
Holding means for holding the supplied molten salt on a rotatable substantially flat surface;
An electrode including a discharge electrode and a counter electrode for performing plasma irradiation on the surface of the held molten salt bath, and fine particles generated by the plasma irradiation are melted by a centrifugal force generated by the rotation of the holding means. Rotational drive means for moving outwards;
An apparatus for producing fine particles by plasma-induced electrolysis of a molten salt comprising:   The apparatus according to claim 9, wherein the molten salt supply port of the supply unit is disposed on a rotation shaft of the holding unit.   The apparatus according to claim 9 or 10, wherein the supply means further includes an external heating means for maintaining the temperature of the molten salt.   12. The apparatus according to claim 9, wherein the holding means includes a disk-shaped or ring-shaped weir for forming a substantially circular molten salt bath on the outer periphery. .   The said holding | maintenance means is provided with the conical surface which inclines downward toward the rotating shaft so that the thickness of the said molten salt bath may be hold | maintained substantially constant. A device according to the above.   The apparatus according to any one of claims 9 to 13, wherein the holding means further includes an external heating means for holding the temperature of the molten salt.   15. The apparatus according to claim 9, wherein the discharge electrode is disposed outside a rotation axis of the holding means.   The apparatus according to claim 9, wherein the counter electrode is disposed on a rotation axis of the holding unit.   The apparatus according to claim 9, wherein at least a part of the counter electrode is in contact with a molten salt bath.   The device according to claim 9, wherein in the cathode discharge, the anode as the counter electrode contains a fine particle metal component to be generated.   The apparatus of claim 18, wherein the anode as the counter electrode further comprises a metal scrap holder.   The apparatus according to claim 9, wherein an anode as the discharge electrode contains a fine metal component to be generated in an anodic discharge.   21. The apparatus according to claim 9, further comprising an external cooling means for cooling the molten salt containing the fine particles moved out of the molten salt bath to a temperature below the melting point of the molten salt. The device described in 1.   The device according to any one of claims 9 to 21, wherein a coil for stabilizing discharge is disposed between a circuit connecting at least one electrode of the discharge electrode or the counter electrode and a power source. The device described in 1.

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