JP5826204B2 - Method for producing metal fine particles - Google Patents

Description

The present invention relates to the production how of the fine metal particles using a burner.

  In recent years, the density of semiconductor packaging technology used for electronic devices such as portable terminals has been increased. There are various needs for the metal fine particles used in the semiconductor packaging technology. Specifically, there are various requirements for the particle size, particle size distribution, shape, and the like of the metal fine particles depending on the use of the metal fine particles.

  In Patent Document 1, a nickel chloride gas obtained by sublimating solid nickel chloride using a gas phase chemical reaction method is diluted with an inert gas and sent to a reduction furnace, and hydrogen gas is brought into contact therewith for a reduction reaction. A method for producing nickel ultrafine powder is disclosed.

  In Patent Document 2, a fuel is partially burned using oxygen or oxygen-enriched air to form a high-temperature reducing atmosphere in the furnace, the oxygen ratio of the burner is adjusted, and the high-temperature reducing airflow generated by the burner A method for producing ultrafine metal powder is disclosed in which a spherical metal ultrafine powder having a controlled particle size is produced by ejecting a powdery metal compound and heating and reducing the metal compound.

  In Patent Document 3, a metal powder as a raw material is blown into a reducing flame formed in a furnace by a burner, and the metal powder is melted in a flame to be in an evaporated state to obtain a spherical metal ultrafine powder. A manufacturing method is disclosed.

  Compared with the method disclosed in Patent Document 1, the method for producing ultrafine metal powder disclosed in Patent Documents 2 and 3 does not use chloride as a raw material or is directly heated by a flame. It becomes possible to produce ultrafine metal powder at low cost and safety.

  By the way, the nickel powder used for the internal electrode for multilayer ceramic capacitors (hereinafter referred to as “MLCC”) is to make the internal electrode layer thinner and more multilayered as MLCC becomes smaller and higher in capacity. In order to realize this, a particle diameter of 0.1 μm or less is required.

  MLCC is formed by alternately laminating a dielectric layer made of a dielectric green sheet containing barium titanate and an internal electrode layer made of a conductive paste containing nickel powder, and then included in each layer by heat treatment. The organic component is removed and then heated to high temperature and sintered.

  Sintering when manufacturing MLCC is generally performed in a reducing atmosphere containing hydrogen or the like. During sintering, the nickel powder composing the internal electrode layer and the barium titanate composing the dielectric layer shrink in volume, but the nickel powder has a lower sintering start temperature than the barium titanate and heat Since the shrinkage rate is also large, there is a difference in shrinkage behavior between the dielectric layer and the internal electrode layer, which may result in structural defects such as cracks and delamination.

  Furthermore, since the sintering start temperature of the internal electrode layer starts at a lower temperature as the nickel powder becomes smaller, the difference in shrinkage behavior between the dielectric layer and the internal electrode layer becomes larger.

For the above reasons, the reduction in the particle size of nickel powder makes the sintering process in MLCC production difficult. That is, the reduction in the particle size of nickel powder makes it difficult to improve the yield of MLCC.
For this reason, the nickel powder has a small particle size (for example, 0.1 μm or less) and a sintering behavior close to that of barium titanate in order to reduce the difference in shrinkage behavior between the dielectric layer and the internal electrode layer. It is desirable to have The technology for improving the sintering characteristics of nickel powder is considered to be of great industrial value.

  As a technique that can solve the problems in the sintering process as described above, for example, in Patent Documents 4 and 5, there is a method that can improve the sintering characteristics of nickel powder by adding a sulfur content to the nickel powder. It is disclosed.

Specifically, in Patent Document 4, a nickel powder having a surface coated with 0.02 to 0.20% by weight of sulfur or a sulfate group in terms of sulfur, and nickel powder are added to the nickel powder in an amount of 0.0. Disclosed is a method for producing nickel powder which is contact-treated with a gas containing sulfur in the form of 02 to 0.30% by weight of hydride and / or oxide.
Patent Document 4 discloses that nickel powder and sulfur-containing gas are sealed in a sealed container and held for several minutes, so that sulfur reacts with nickel and is adsorbed on the particle surface. .

Patent Document 5 discloses a method for producing nickel fine particles in which nickel fine particles are wet-treated with a solution of a sulfur compound to contain a sulfur content in the range of 0.05 to 1.0% by weight with respect to the nickel fine particles. Yes.
Patent Document 5 discloses that nickel powder is added to an ammonium sulfate aqueous solution corresponding to the sulfur content to be added to form a slurry, followed by heating and drying.

JP-A-4-365806 Japanese Patent No. 4304212 Japanese Patent No. 4304221 JP 2004-24465 A JP 2007-191771 A

However, in the method for producing nickel powder disclosed in Patent Document 4, when a large amount of nickel powder is produced, there is a problem that it is difficult to uniformly coat the surface of nickel powder with sulfur. There was a problem that productivity of nickel powder was low.
In addition, in the sulfur coating step on nickel powder, since a large amount of hydrogen sulfide is used, exhaust gas treatment is indispensable, so that there is a problem of safety and a complicated manufacturing method of nickel powder. .

  In the method for producing nickel fine particles disclosed in Patent Document 5, nickel fine particles are added to an aqueous ammonium sulfate solution corresponding to the sulfur content to be added to form a slurry, and then heated and dried. Since the nickel fine particles are dry and agglomerated, the dispersibility is poor, and when the paste is applied as a paste to form the MLCC internal electrode layer, the nickel fine particles behave as large particles when pressed, and the upper and lower There was a problem of causing a short circuit by breaking through the dielectric layer.

  Further, Patent Documents 4 and 5 are methods in which sulfur is added to nickel powder (nickel fine particles) in a process different from the nickel powder production process (nickel fine particle production process). There was a problem of becoming complicated.

Accordingly, the present invention is, while securing safety, by a simple method, sulfur surface layer and to provide a manufacturing how possible metal particles produce a concentrated metal particles

  In order to solve the above-mentioned problem, according to the invention according to claim 1, a raw material and a sulfur compound which are charged with a metal compound powder as a raw material of metal fine particles and a sulfur compound into a flame formed at the tip of the burner And a metal fine particle forming step of forming metal fine particles enriched with sulfur on the surface layer by heating and reducing the metal compound powder by the flame and thermally decomposing the sulfur compound. A method for producing metal fine particles is provided.

  According to the invention of claim 2, in the raw material and sulfur compound charging step, a mixture of the metal compound powder and the sulfur compound is charged into the flame from the tip of the burner. The manufacturing method of the metal microparticle of claim | item 1 is provided.

  According to the invention of claim 3, the metal fine particles according to claim 1 or 2, wherein in the raw material and sulfur compound charging step, the metal compound powder and the sulfur compound are separately charged. A manufacturing method is provided.

 According to the invention of claim 4, in the raw material and sulfur compound charging step, the metal compound powder and the sulfur compound powder are charged into the flame using a combustible gas. A method for producing metal fine particles according to any one of claims 1 to 3 is provided.

  According to the invention according to claim 5, in the raw material and sulfur compound charging step, a sulfur compound-containing solution in which the sulfur compound is dissolved in a solvent is charged into the flame. A method for producing the described metal microparticles is provided.

  Further, according to the invention according to claim 6, the flame formed at the tip of the burner is charged with a metal compound powder and sulfur as raw materials for the metal fine particles, and the sulfur charging step, And a metal fine particle forming step of forming metal fine particles in which the sulfur is concentrated on a surface layer by heating and reducing the metal compound powder and sublimating the sulfur. Provided.

  Moreover, according to the invention concerning Claim 7, in the said raw material and sulfur injection | throwing-in process, the said metal compound powder and the mixture of the said sulfur are thrown into the said flame from the front-end | tip of the said burner. A method for producing the described metal microparticles is provided.

  Moreover, according to the invention concerning Claim 8, in the said raw material and sulfur addition process, the said metal compound powder and the said sulfur are thrown in separately, The manufacture of the metal microparticle of Claim 6 or 7 characterized by the above-mentioned. A method is provided.

  According to a ninth aspect of the present invention, in the raw material and sulfur charging step, the metal compound powder and the sulfur powder are charged into the flame using a combustible gas. Item 9. A method for producing metal fine particles according to any one of Items 6 to 8.

  According to the invention of claim 10, nickel oxide powder is used as the metal compound powder, and in the metal fine particle production step, the particle diameter is 0.1 μm or less and sulfur is concentrated in the surface layer. The method for producing fine metal particles according to any one of claims 1 to 9, wherein the fine nickel particles are formed.

According to the method for producing fine metal particles of the present invention, in the sulfur compound charging step, a metal compound powder that is a raw material for the metal fine particles and a sulfur compound or sulfur are charged into a flame formed at the tip of the burner, In the metal particle formation process, the metal compound powder is heated and reduced by a flame and the sulfur compound is thermally decomposed to form metal particles concentrated in the surface layer. It is not necessary to provide a process for making
Therefore, metal fine particles having sulfur concentrated on the surface layer can be produced by a simple method.

Further, by using a powder containing sulfur instead of a gas containing sulfur, metal fine particles having sulfur concentrated on the surface layer can be produced while ensuring safety.
Furthermore, the metal fine particles obtained by the method for producing metal fine particles of the present invention can be used as an MLCC material. In this case, when the metal fine particles are pasted and sintered on the electrode layer, the shrinkage start temperature can be improved to the high temperature side, and the shrinkage rate can be reduced.

  In addition, since the method for producing metal fine particles of the present invention is a dry method, the metal fine particles obtained by the method for producing metal fine particles of the present invention have improved dispersibility compared to metal fine particles produced by a wet method. Can be made.

It is a figure which shows typically schematic structure of the metal microparticle manufacturing apparatus used in the manufacturing method of the metal microparticle which concerns on embodiment of this invention. It is the figure (front view) which looked at the burner shown in FIG. It is sectional drawing of the BB line direction of the burner shown in FIG. It is a figure which shows the photograph (SEM photograph) of the metal microparticle of Example 1 image | photographed with the field emission type scanning electron microscope. It is a figure which shows the sintering characteristic of the nickel fine particle of a reference example and Example 8. FIG. It is a figure which shows the result which arranged the shrinkage | contraction rate and shrinkage | contraction start temperature regarding Examples 1-10 and the nickel fine particle of a reference example by sulfur concentration. It is a figure which shows the relationship between the shrinkage | contraction rate regarding the nickel fine particles of Examples 1-10 and a reference example, and sulfur concentration.

  Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. The drawings used in the following description are for explaining the configuration of the embodiment of the present invention, and the size, thickness, dimensions, etc. of the respective parts shown in the drawings are the dimensional relationships between the actual metal fine particle manufacturing apparatus and the burner. May be different.

(Embodiment)
FIG. 1 is a diagram schematically showing a schematic configuration of a metal fine particle production apparatus used in a method for producing metal fine particles according to an embodiment of the present invention.
Before describing the method for producing metal fine particles of the present embodiment, the metal fine particle production apparatus 10 (see FIG. 1) according to the present embodiment will be described.

  Referring to FIG. 1, the metal fine particle manufacturing apparatus 10 includes a burner 11, a combustible gas supply source 13, a raw material and sulfur compound supply source 14, a combustion-supporting gas supply source 15, a water-cooled furnace 18, nitrogen A supply source 21, a nitrogen supply line 22, a line 24, a bag filter 26, an exhaust line 27, and a blower 28 are included.

The burner 11 is arranged so that the front end surface 11A forming the flame 12 (high temperature reducing flame) is the lower surface. The tip of the burner 11 is accommodated in the upper end of the water-cooled furnace 18.
The high-temperature reducing flame refers to a flame formed in a combustion state containing a large amount of hydrogen and carbon monoxide by partially burning fuel. In addition, partial combustion means that oxidation reaction (combustion) is partially performed under the condition of insufficient oxygen amount.

  FIG. 2 is a view (front view) of the burner shown in FIG. 3 is a cross-sectional view of the burner shown in FIG. 2 in the BB line direction. In FIG. 3, only the tip of the burner 11 is shown.

  2 and 3, the burner 11 includes a raw material and sulfur compound supply pipe 32, a ring-shaped member 33, an annular member 34, a first combustion-supporting gas supply path 35, and a combustion chamber 36. The outer cylinder 37, the second combustion-supporting gas supply path 39, the raw material and sulfur compound supply path 41, the plurality of raw material and sulfur compound ejection holes 42, and the plurality of first combustion-supporting gas ejection holes 44. And a plurality of second combustion-supporting gas ejection holes 46.

The raw material and sulfur compound supply pipe 32 is a cylindrical member. The raw material and sulfur compound supply pipe 32 is arranged so that the central axis thereof coincides with the central axis C of the burner 11.
The raw material and sulfur compound supply pipe 32 has a tip 32A. The tip portion 32 </ b> A has a tip surface 32 a that defines the combustion chamber 36 and is perpendicular to the central axis C of the burner 11.

The ring-shaped member 33 is provided on the outer wall of the raw material and sulfur compound supply pipe 32 located in the vicinity of the front end portion 32 </ b> A and between the front and rear ends of the raw material and sulfur compound supply pipe 32. ing. The ring-shaped member 33 is disposed between the raw material and sulfur compound supply pipe 32 and the annular member 34, and is in contact with the inner wall of the annular member 34.
The ring-shaped member 33 is arranged so that the central axis thereof coincides with the central axis C of the burner 11.

The annular member 34 is a cylindrical member, and is provided outside the raw material and sulfur compound supply pipe 32 so that the inner wall thereof is in contact with the ring-shaped member 33. The annular member 34 is arranged so that its central axis coincides with the central axis C of the burner 11.
The annular member 34 has a distal end portion 34 </ b> A that protrudes in an oblique direction away from the raw material and sulfur compound supply pipe 32. The tip portion 34 </ b> A has an inclined surface 34 a that constitutes the combustion chamber 36.

The first combustion-supporting gas supply path 35 is a cylindrical space formed between the raw material and sulfur compound supply pipe 32 and the annular member 34. The first combustion-supporting gas supply path 35 is connected to the combustion-supporting gas supply source 15 shown in FIG.
The first combustion-supporting gas supplied from the combustion-supporting gas supply source 15 is introduced into the first combustion-supporting gas supply path 35. The first combustion-supporting gas supply path 35 is a path for supplying the first combustion-supporting gas to the plurality of first combustion-supporting gas ejection holes 44.
For example, oxygen or oxygen-enriched air can be used as the first combustion-supporting gas.

  The combustion chamber 36 is a space defined by a front end surface 32 a of the raw material and sulfur compound supply pipe 32 and a front end surface 32 a of the raw material and sulfur compound supply pipe 32. The combustion chamber 36 has a truncated cone shape whose opening diameter increases as the distance from the front end surface 32a in the axial direction of the burner 11 increases.

The outer cylinder 37 is provided on the outer side of the annular member 34 so that the inner wall at the distal end thereof is connected to the distal end portion 34 </ b> A of the annular member 34.
The outer cylinder 37 has a cooling water path 37 </ b> A through which cooling water for cooling the tip of the burner 11 flows.

The second combustion-supporting gas supply path 39 is a cylindrical space formed between the annular member 34 and the outer cylinder 37. The second combustion-supporting gas supply path 39 is connected to the combustion-supporting gas supply source 15 shown in FIG.
The second combustion-supporting gas supplied from the combustion-supporting gas supply source 15 is introduced into the second combustion-supporting gas supply path 39. The second combustion-supporting gas supply path 39 is a path for supplying the second combustion-supporting gas to the plurality of second combustion-supporting gas ejection holes 46. As the second combustion-supporting gas, the same gas as the first combustion-supporting gas is used.

The raw material and sulfur compound supply path 41 is a cylindrical space formed in the raw material and sulfur compound supply pipe 32. The raw material and sulfur compound supply path 41 is connected to the raw material and sulfur compound supply source 14 shown in FIG.
A mixture D (described later) transported by a combustible gas is introduced into the raw material and sulfur compound supply path 41. The raw material and sulfur compound supply path 41 is a path for supplying the mixture D transported by the combustible gas to the plurality of raw material and sulfur compound ejection holes 42.

A plurality of raw material and sulfur compound ejection holes 42 (in the case of FIG. 2, as an example, four raw materials and sulfur compound ejection holes 42) are provided so as to penetrate the tip 32 </ b> A of the raw material and sulfur compound supply pipe 32. Yes.
The axial directions of the plurality of raw materials and the sulfur compound ejection holes 42 are inclined with respect to the central axis C of the burner 11. The plurality of raw material and sulfur compound ejection holes 42 are integrated with the raw material and sulfur compound supply path 41.
The plurality of raw material and sulfur compound ejection holes 42 eject the combustible gas and the mixture D in the direction away from the central axis C of the burner 11 with respect to the combustion chamber 36.

  The plurality of first combustion-supporting gas ejection holes 44 (eight first combustion-supporting gas ejection holes 44 as an example in the case of FIG. 2) are arranged in a direction parallel to the central axis C of the burner 11. It is provided so as to penetrate the shaped member 33. The plurality of first combustion-supporting gas ejection holes 44 are integrated with the first combustion-supporting gas supply path 35. The plurality of first combustion-supporting gas ejection holes 44 cause the combustion chamber 36 to eject the first combustion-supporting gas.

The plurality of second combustion-supporting gas ejection holes 46 (in the case of FIG. 2, as an example, twelve second combustion-supporting gas ejection holes 46) are provided so as to penetrate the distal end portion 34 </ b> A of the annular member 34. It has been.
The axial direction of the plurality of second combustion-supporting gas ejection holes 46 is inclined with respect to the central axis C of the burner 11. The plurality of second flammable gas ejection holes 46 are integrated with the second flammable gas supply path 39.
The plurality of second combustion-supporting gas ejection holes 46 eject the second combustion-supporting gas in the direction toward the central axis C of the burner 11.

  The plurality of raw material and sulfur compound ejection holes 42, the plurality of first combustion-supporting gas ejection holes 44, and the plurality of second combustion-supporting gas ejection holes 46 described above are in relation to the central axis C of the burner 11. They are arranged concentrically.

  Referring to FIG. 1, the combustible gas supply source 13 is connected to a raw material and a sulfur compound supply source 14. The combustible gas supply source 13 supplies a combustible gas (for example, methane) to the raw material and the sulfur compound supply source 14.

The raw material and sulfur compound supply source 14 are connected to the raw material and sulfur compound supply path 41 of the burner 11 (see FIG. 3). The raw material and sulfur compound supply source 14 maintains a state in which the metal compound powder as the raw material and the sulfur compound in the powder are sufficiently mixed (mixed uniformly).
When the combustible gas is supplied from the combustible gas supply source 13, the raw material and the sulfur compound supply source 14 are sufficiently mixed with the metal compound powder and the sulfur compound in the raw material and sulfur compound supply path 41 of the burner 11. Feed the mixture D.

  In order to sufficiently stir the mixture D, for example, a mixer for stirring powder can be used. When the metal compound powder and the sulfur compound are mixed in a non-uniform state, the concentration of sulfur contained in the surface layer of the generated metal fine particles becomes non-uniform. Therefore, it is important to sufficiently mix the metal compound powder and the sulfur compound so that they are uniform.

Examples of the metal compound powder constituting the mixture D include nickel powder (for example, nickel oxide powder) having an average particle diameter of about 5 to 20 μm, cobalt powder, copper powder, silver powder, and iron. Powder or the like can be used.
Moreover, as a sulfur compound which comprises the mixture D, a sulfuric acid, a sulfate, sulfide, etc. can be used, for example.

As the sulfate, for example, iron sulfate, copper sulfate, aluminum sulfate, nickel sulfate and the like can be used. Moreover, as a sulfide, sodium sulfide, sodium hydrogen sulfide, etc. can be used, for example.
The particle size of the sulfur compound can be appropriately selected within a range of 1 to 50 μm, for example.

  In the case where it is not desired that the metal fine particles contain a metal component different from the metal constituting the generated metal fine particles, a sulfate or sulfide having the same metal ions as the metal fine particles may be used. .

  The combustion-supporting gas supply source 15 is connected to the first and second combustion-supporting gas supply paths 35 and 39 shown in FIG. The combustion-supporting gas supply source 15 supplies the first combustion-supporting gas (for example, oxygen or oxygen-enriched air) to the first combustion-supporting gas supply path 35 and the second combustion-supporting gas supply. A second combustion-supporting gas (for example, oxygen or oxygen-enriched air) is supplied to the passage 39.

The water-cooled furnace 18 accommodates the tip of the burner 11 at its upper end. The water cooling furnace 18 suppresses the metal wall powder and metal fine particles from adhering to or growing on the inner wall by water cooling the furnace wall.
The water cooling furnace 18 has a plurality of nitrogen introduction holes (not shown) for introducing nitrogen supplied from the nitrogen supply source 21 into the water cooling furnace 18.

  The nitrogen supply source 21 is connected to one end of the nitrogen supply line 22. The nitrogen supply source 21 supplies nitrogen into the water cooling furnace 18 through the nitrogen supply line 22, thereby forming a swirling flow in the water cooling furnace 18.

  One end of the nitrogen supply line 22 is connected to the nitrogen supply source 21, the other end is branched into a plurality, and the other branched end is connected to a nitrogen introduction hole (not shown) of the water-cooled furnace 18. ing. The nitrogen supply line 22 is a line for introducing nitrogen supplied from the nitrogen supply source 21 into the water-cooled furnace 18.

One end of the line 24 is connected to the lower end of the water-cooled furnace 18, and the other end is connected to the upper end of the bag filter 26. The line 24 is a line for transporting the generated metal fine particles to the upper end of the bag filter 26.
The bag filter 26 is a filter for collecting metal fine particles having a desired size among the metal fine particles transported through the line 24.

One end of the exhaust line 27 is connected to the upper end of the bag filter 26. The exhaust line 27 is a line for exhausting gas from the upper end of the bag filter 26.
The blower 28 is provided in the exhaust line 27. The blower 28 exhausts gas from the upper end of the bag filter 26 through the exhaust line 27.

  Next, with reference to FIGS. 1-3, the manufacturing method of the metal microparticle which concerns on this Embodiment at the time of using the metal microparticle manufacturing apparatus 10 shown in FIG. 1 is demonstrated. Here, as an example, a case where the mixture D in which the metal compound powder and the sulfur compound of the powder are sufficiently mixed (uniformly mixed) is ejected to the flame 12 through the raw material and the sulfur compound ejection hole 42 is an example. The following explanation will be given.

  In the raw material and sulfur compound supply source 14, a mixture (not shown) is used to form a mixture D in which the metal compound powder and the sulfur compound in the powder are uniformly mixed. The mixture D is always in a state where the metal compound powder and the sulfur compound of the powder are uniformly mixed.

The first and second combustion-supporting gas ejection holes 44 and 46 eject the first and second combustion-supporting gas, and the fuel from the raw material and sulfur compound ejection hole 42 (in other words, the tip 11A of the burner 11). The mixture D transported by the gas is ejected.
A flame 12 is formed by the combustion-supporting gas and the combustible gas, and when the mixture D is put into the flame 12, the metal compound powder is heated and reduced, and the sulfur compound is thermally decomposed.

At this time, in the water-cooled path furnace 18, the metal compound powder is heated and reduced to become metal fine particles, and sulfur generated by thermal decomposition of the sulfur compound is concentrated on the surface layer of the metal fine particles. .
In the water-cooled path furnace 18, the generated metal fine particles are transported to the bag filter 26 via the line 24.

  The metal fine particles having sulfur concentrated on the surface layer may be formed so that the total sulfur concentration of the metal fine particles is 0.15% or more. Thus, when the nickel fine particles in which sulfur is concentrated on the surface layer so that the concentration of sulfur is 0.15% or more are used as, for example, an internal electrode for MLCC, the sintering characteristics are improved.

  Further, by using the method for producing fine metal particles according to the present embodiment, when nickel oxide powder is used as the metal compound powder, the nickel powder having a particle size of 0.1 μm or less and containing sulfur The body can be formed.

  The bag filter 26 collects metal particles of a desired size from the lower end. The gas in the bag filter 26 is exhausted through the exhaust line 27 from above.

  According to the method for producing metal fine particles according to the present embodiment, a metal compound powder that is a raw material for metal fine particles and a sulfur compound are introduced into a flame 12 formed at the tip of burner 11, and then a flame. 12 to heat and reduce the metal compound powder and thermally decompose the sulfur compound to form metal fine particles in which sulfur is concentrated on the surface layer. Therefore, it is necessary to provide a separate step of adding sulfur to the metal fine particles. Absent.

  Further, by using a sulfur compound instead of a gas containing sulfur, metal fine particles in which sulfur is concentrated on the surface layer can be formed while ensuring safety.

  In this embodiment, as an example, a case where the metal compound powder and the sulfur compound of the powder are sufficiently mixed, and then the sulfur compound is supplied to the flame 12 as a mixture D as a powder is taken as an example. As described above, these may be ejected into the flame via separate ejection holes (ejection holes provided in a burner not shown).

  Further, instead of providing the burner 11 with a sulfur compound ejection hole (not shown) for ejecting a sulfur compound, a sulfur compound supply unit (not shown) capable of supplying powdery sulfur compounds to the flame 12 is provided. The sulfur compound may be supplied to the flame 12 from the sulfur compound supply unit.

In this case, the said sulfur compound supply part can be arrange | positioned at the outer peripheral part of the front-end | tip of the burner 11 shown in FIG. 1, for example.
Furthermore, in the case where the metal compound powder and the powdered sulfur compound are ejected from separate ejection holes, the sulfur compound may be conveyed by air flow using an inert gas such as nitrogen.

Moreover, in this Embodiment, although the case where the sulfur compound was supplied to the flame 12 as an example was described as an example, the sulfur compound may be supplied to the flame 12 in a liquid state.
In this case, a sulfur compound-containing solution in which sulfur compound powder is dissolved in a solvent (for example, water or ethanol) is prepared, and the sulfur compound-containing solution is put into the flame 12.
In order to mix the sulfur compound-containing solution better, for example, a mixture obtained by atomizing the sulfur compound-containing solution using a spray or the like may be mixed with a mixer or the like while spraying the metal compound as a raw material. In addition, when the sulfur compound-containing solution is directly put into the flame 12, for example, spray injection by pressure spray may be used.

  Furthermore, although the case where the water-cooled furnace 18 is used has been described as an example in the present embodiment, a furnace having a refractory structure may be used instead.

Further, in the present embodiment, as an example, the case where the metal compound powder and the sulfur compound are charged into the flame 12 formed at the tip of the burner 11 (raw material and sulfur compound charging step) has been described as an example. Instead of this, metal compound powder and sulfur may be charged into the flame 12 formed at the tip of the burner 11 (raw material and sulfur charging step).
In this case, the metal compound powder is heated / reduced by the flame 12 to sublimate sulfur, thereby forming metal fine particles enriched with sulfur on the surface layer (metal fine particle forming step).

In the raw material and sulfur charging step, a mixture of the metal compound powder and sulfur may be charged into the flame 12 from the tip of the burner 11.
Furthermore, in the raw material and sulfur charging step, the metal compound powder and sulfur may be charged separately.
In the raw material and sulfur charging step, the metal compound powder and the sulfur powder may be charged into the flame 12 using a combustible gas.
As described above, when sulfur is used instead of the sulfur compound, the same effect as when the sulfur compound is used can be obtained.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and within the scope of the present invention described in the claims, Various modifications and changes are possible.

(Experimental example 1)
In Experimental Example 1, nickel sulfate hexahydrate was put into a flame 12 in the form of powder under the following conditions using the metal fine particle production apparatus 10 shown in FIG. 1 including the burner 11 shown in FIGS. As a result, nickel fine particles E1 to E3 were formed.

As the metal compound powder as a raw material, nickel oxide having a particle size of 7 μm was used. As the sulfur compound, nickel sulfate hexahydrate powder having a particle size of 5 μm by pulverization was used.
Using a mixer for powder processing (manufactured by Nippon Coke Kogyo Co., Ltd., FM mixer), the above nickel oxide and nickel sulfate hexahydrate are sufficiently mixed so as to produce a mixture D1 to D3. did.

The mixture D1 was prepared by adjusting the amount of nickel sulfate hexahydrate relative to nickel oxide so that the concentration of sulfur relative to nickel oxide was 0.16%.
Similarly, the mixture D2 was prepared so that the concentration of sulfur relative to nickel oxide was 0.27%, and the mixture D3 was prepared such that the concentration of sulfur relative to nickel oxide was 0.37%.

In Example 1, the nickel fine particle E1 was created by throwing the mixture D1 into the flame 12 using the following conditions.
In Example 1, methane was supplied from the combustible gas supply source 13 at a supply rate of 3.0 Nm ³ / h. In addition, oxygen is used as the first and second combustion-supporting gas, and the amount of oxygen ejected from the first combustion-supporting gas ejection hole 44 is four times the amount of oxygen ejected from the first combustion-supporting gas ejection hole 44. Oxygen was blown out. At this time, the amount of oxygen ejected from the first combustion-supporting gas ejection hole 44 was set to 1.08 Nm ³ / h. The supply amount of nickel oxide was 1.0 kg / h.

  Thereafter, the average particle diameter (nm) of the nickel fine particles E1 (nickel fine particles), the sulfur concentration (%) with respect to the entire nickel fine particles E1, and the sulfur concentration (%) of the surface layer (about several nm deep from the surface) of the nickel fine particles E1 Were measured by the following method. The results are shown in Table 1.

The average particle diameter (nm) of the nickel fine particles E1 is obtained by observing a plurality of metal fine particles E1 by using a field emission scanning electron microscope (JSM-6700F manufactured by JEOL Ltd., also referred to as “FE-SEM”). It acquired by analyzing 20 field-of-view images 20000 times observed at random using image analysis software (Scandium made by Soft Imaging System GmbH).
At this time, a photograph (SEM photograph) of a plurality of nickel fine particles E1 taken with a field emission scanning electron microscope is shown in FIG.

The total sulfur concentration (%) of the nickel fine particles E1 was measured by a combustion-infrared absorption method using EMIA920 manufactured by Horiba, Ltd.
The sulfur concentration (%) of the surface layer portion of the metal fine particles E1 was measured by X-ray photoelectron spectroscopy using JPS-9200 manufactured by JEOL Ltd.

In Example 2, nickel fine particles E2 were formed under the same conditions as in Example 1 except that the mixture D2 was used instead of the mixture D1, and the same evaluation as in Example 1 was performed.
In Example 3, nickel fine particles E3 were formed under the same conditions as in Example 1 except that the mixture D3 was used in place of the mixture D1, and the same evaluation as in Example 1 was performed. The results of Examples 2 and 3 are shown in Table 1.

Referring to Table 1, by changing the sulfur concentration relative to nickel oxide (in other words, changing the amount of nickel sulfate hexahydrate), the total nickel fine particles E1 to E3 and the surface sulfur concentration can be adjusted. I was able to confirm.
Moreover, even if it changed the density | concentration of sulfur with respect to nickel oxide, it has confirmed that the difference was not produced in the average particle diameter of nickel fine particles E1-E3.

(Experimental example 2)
In Experimental Example 2, an aqueous solution of nickel sulfate hexahydrate was added to nickel oxide under the following conditions using the metal fine particle production apparatus 10 shown in FIG. 1 including the burner 11 shown in FIGS. Nickel fine particles E4 to E8 were prepared by throwing into a flame 12 what was kneaded so that nickel and nickel sulfate hexahydrate were uniform.
The same kind of nickel oxide and nickel sulfate hexahydrate as in Experimental Example 1 were used and dissolved in pure water to prepare a nickel sulfate aqueous solution F having a sulfur concentration of 4.6%.

In Example 4, nickel fine particles E4 were produced using a material in which the mixing ratio of nickel oxide and nickel sulfate was adjusted so that the concentration of sulfur with respect to nickel oxide was 0.05%.
Similarly, in Example 5, 0.16% in Example 6, 0.27% in Example 7, and 0.37% in Example 8 so that the concentration of sulfur with respect to nickel oxide is 0.11%. In this way, a mixture of nickel oxide and nickel sulfate hexahydrate aqueous solution was added to the flame 12 to prepare nickel fine particles E5 to E8.
Then, evaluation similar to the nickel fine particles E1-E3 of Examples 1-3 was performed with respect to the nickel fine particles E4-E8 of Examples 4-8. The results are shown in Table 2.

Referring to Table 2, even when nickel fine particles E4 to E8 are produced by introducing an aqueous solution of nickel sulfate hexahydrate mixed with nickel oxide into the flame 12, the nickel sulfate hexahydrate in the powder state is also produced. Similar to the case where the hydrate is mixed with nickel oxide and put into the flame 12, the concentration of sulfur with respect to nickel oxide is changed (in other words, the amount of nickel sulfate hexahydrate is changed), thereby forming nickel fine particles. It was confirmed that the concentration of sulfur in the whole E4 to E8 and the surface layer could be adjusted.
It was also confirmed that there was no difference in the average particle size of the nickel fine particles E4 to E8 even when the concentration of sulfur with respect to nickel oxide was changed.

(Experimental example 3)
As Example 9, nickel oxide was ejected from the raw material of the burner 11 and the sulfur compound ejection hole 42 shown in FIG. 3 to the flame 12, and the powder was supplied from a sulfur compound supply unit (not shown) disposed outside the burner 11. Nickel fine particles E9 were produced by putting the nickel sulfate hexahydrate in the body into the flame 12. In Example 9, except for the above, the metal fine particle production apparatus 10 shown in FIG. 1 was used.

In Example 9, the same kind of nickel oxide and nickel sulfate hexahydrate as the nickel oxide and nickel sulfate hexahydrate described in Experimental Example 1 were used.
The amount of nickel sulfate hexahydrate was set so that the concentration of sulfur relative to nickel oxide was 0.27%. Nickel oxide was air-flowed with 0.5 Nm ³ / h of nitrogen.
Thereafter, the nickel fine particle E9 was evaluated in the same manner as in Example 1 described above. The results are shown in Table 3.

  In Example 10, using the apparatus used in Example 9, nickel oxide was ejected from the raw material of the burner 11 and the sulfur compound ejection hole 42 shown in FIG. 3 to the flame 12 and arranged outside the burner 11. Nickel fine particles E10 were produced by introducing the nickel sulfate aqueous solution F described in Experimental Example 2 into the flame 12 from a sulfur compound supply unit (not shown).

At this time, the supply amount of the nickel sulfate aqueous solution F was adjusted so that the concentration of sulfur with respect to nickel oxide was 0.27%.
In Example 10, the same kind of nickel oxide and nickel sulfate hexahydrate as the nickel oxide and nickel sulfate hexahydrate described in Experimental Example 1 were used.
Thereafter, the same evaluation as in Example 1 described above was performed on the nickel fine particles E10. The results are shown in Table 3.

  Referring to Table 3, when nickel oxide and powdered or liquid nickel sulfate hexahydrate are separately added to the flame 12 without mixing with nickel oxide, sulfur is concentrated on the surface layer. It was confirmed that the produced nickel fine particles E9 and E10 could be produced.

(Experimental example 4)
As a reference example, using the fine metal particle production apparatus 10 shown in FIG. 1, the nickel oxide described in Experimental Example 1 is used, and nickel fine particles G having an average particle diameter of 100 nm are used without using nickel sulfate hexahydrate. Produced.
Thereafter, TMA measurement was performed on the nickel fine particles G of Reference Example and the nickel fine particles E8 of Example 8. The result is shown in FIG.

  Specifically, using a thermal expansion and contraction behavior measuring apparatus (TMA8310, manufactured by Rigaku Corporation), PVA was applied to the nickel fine particles E8 and G under the conditions of a hydrogen 3% -nitrogen 97% reducing atmosphere and a heating rate of 10 ° C./min. The sintering start temperature was determined from the shrinkage behavior of the cylindrical pellets molded by adding 0.1% aqueous solution, and the sulfur characteristics were added to evaluate the sintering characteristics of the nickel fine particles E8 and G.

  Referring to FIG. 5, the nickel fine particles E8 enriched with sulfur on the surface move the shrinkage start to the high temperature side compared with the sintering behavior of the nickel fine particles G not containing sulfur, and the shrinkage rate is low. It was found that it can be reduced.

FIG. 6 shows the relationship between the concentration of sulfur contained in the nickel fine particles and the shrinkage start temperature. The data shown in FIG. 6 is a result of arranging the shrinkage rate and the shrinkage start temperature with respect to the nickel fine particles E1 to E10, G of Examples 1 to 10 and the reference example by the sulfur concentration. It was defined as the point at which the rate reached -1.5%.
Referring to FIG. 6, it was found that when the sulfur concentration is 0.15% or more, the shrinkage start temperature clearly moves to the high temperature side, and when the sulfur concentration is increased, the shrinkage start temperature becomes higher.

FIG. 7 shows the relationship between the sulfur concentration of nickel fine particles and the shrinkage rate. The data shown in FIG. 7 is the result of arranging the shrinkage ratios for the nickel fine particles E1 to E10, G of Examples 1 to 10 and Reference Example by the sulfur concentration.
Referring to FIG. 7, it was found that when the sulfur concentration was 0.15% or more, the shrinkage ratio was clearly reduced, and when the sulfur concentration was increased, the shrinkage reduction effect was increased.
From the results shown in FIGS. 5 to 7, it was confirmed that the method for producing fine metal particles of the present invention has a high effect on improving the sintering characteristics.

The present invention is applicable to the production how of the fine metal particles using a burner.

  DESCRIPTION OF SYMBOLS 10 ... Metal fine particle manufacturing apparatus, 11 ... Burner, 11A ... Front end surface, 12 ... Flame, 13 ... Combustible gas supply source, 14 ... Raw material and sulfur compound supply source, 15 ... Combustion gas supply source, 18 ... Water-cooled furnace , 21 ... Nitrogen supply source, 22 ... Nitrogen supply line, 24 ... Line, 26 ... Bag filter, 27 ... Exhaust line, 28 ... Blower, 32 ... Raw material and sulfur compound supply pipe, 32a ... Tip surface, 32A, 34A ... Tip 33, ring-shaped member, 34 ... annular member, 34a ... inclined surface, 35 ... first combustion-supporting gas supply path, 36 ... combustion chamber, 37 ... outer cylinder, 37A ... path for cooling water, 39 ... first 2 flammable gas supply paths, 41 ... raw material and sulfur compound supply path, 42 ... raw material and sulfur compound ejection holes, 44 ... first flammable gas ejection holes, 46 ... second flammable gas ejection holes , C ... central axis

Claims (10)

A raw material and a sulfur compound charging step for charging a metal compound powder as a raw material of metal fine particles and a sulfur compound into a flame formed at the tip of the burner,
A metal fine particle forming step of forming metal fine particles enriched with sulfur on the surface layer by heating and reducing the metal compound powder with the flame and thermally decomposing the sulfur compound;
The manufacturing method of the metal microparticle characterized by including.   2. The method for producing metal fine particles according to claim 1, wherein, in the raw material and sulfur compound charging step, a mixture of the metal compound powder and the sulfur compound is charged into the flame from the tip of the burner.   The method for producing fine metal particles according to claim 1 or 2, wherein in the raw material and sulfur compound charging step, the metal compound powder and the sulfur compound are separately charged.   4. The raw material and sulfur compound charging step, wherein the metal compound powder and the sulfur compound powder are charged into the flame using a combustible gas. The manufacturing method of the metal microparticle of description.   The method for producing fine metal particles according to claim 1 or 3, wherein, in the raw material and sulfur compound charging step, a sulfur compound-containing solution in which the sulfur compound is dissolved in a solvent is charged into the flame. A raw material and a sulfur charging step for charging a metal compound powder and sulfur as raw materials for the metal fine particles into a flame formed at the tip of the burner;
A metal fine particle forming step of forming metal fine particles in which the sulfur is concentrated on the surface layer by heating and reducing the metal compound powder by the flame and sublimating the sulfur;
The manufacturing method of the metal microparticle characterized by including.   The method for producing metal fine particles according to claim 6, wherein, in the raw material and sulfur charging step, the metal compound powder and the mixture of sulfur are charged into the flame from the tip of the burner.   The method for producing fine metal particles according to claim 6 or 7, wherein in the raw material and sulfur charging step, the metal compound powder and the sulfur are separately charged.   9. The method according to claim 6, wherein in the raw material and sulfur charging step, the metal compound powder and the sulfur powder are charged into the flame using a combustible gas. A method for producing metal fine particles. Using nickel oxide powder as the metal compound powder,
10. The metal according to claim 1, wherein in the metal fine particle generation step, nickel fine particles having a particle diameter of 0.1 μm or less and sulfur concentrated in a surface layer are formed. A method for producing fine particles.