JP5991645B2 - Method for producing metal powder - Google Patents

Description

  The present invention relates to an ultrafine metal powder called a so-called nano powder and a method for producing the same. In particular, the present invention relates to a method for producing metal powder capable of producing nanopowder with high productivity.

  Ultra fine powder having a particle size of nano order, typically, powder called nano powder is used in various fields. For example, Patent Document 1 discloses nano iron powder. Patent Document 2 discloses nanopowder made of an alloy such as silver-copper. Nano iron powder is used for the raw material of magnetic members, such as a magnetic recording medium, using the magnetic characteristic. Nano-powder such as silver-copper is expected to be used for conductive pastes used to form circuits by utilizing its conductivity.

  Patent Document 1 discloses a method using organic iron such as pentacarbonyl iron as a raw material as a method for producing nano iron powder. More specifically, a liquid in which a solvent such as benzyl ether, a colloid stabilizer such as oleic acid and pentacarbonyl iron are added is prepared, the liquid is heated to a predetermined temperature, and the resulting precipitate is retained. Nano iron powder is formed by drying. In Patent Document 2, an alloy is produced and subjected to a homogenization heat treatment, and then processed into a thin piece. The thin piece is further subjected to a heat treatment and then exposed to a leaching agent to remove a specific metal element in the alloy by leaching. Thus, a method of forming metal nanopowder having a desired composition is disclosed.

  Other methods for producing metal and metal oxide nanoparticles include using compounds such as metal chlorides and metal-containing salts as raw materials, using microwaves, using plasma, and using supercritical water. There is a way to do it.

Special Table 2010-512463 JP 2005-530048 Publication

  However, with the conventional manufacturing method, it is difficult to improve the productivity of the nanopowder.

  The synthesis of organic iron such as pentacarbonyl iron requires a complicated process such as CO treatment under a high pressure and high temperature environment, so that the raw material itself is inferior in productivity. Moreover, since such a complicated process is required, the raw material cost becomes high, resulting in an increase in cost. Metal chlorides such as iron chloride and colloidal stabilizers such as oleic acid are also generally expensive. Furthermore, iron pentacarbonyl and iron chloride are thermally unstable and easily decompose or react in a thermal environment, and also react significantly with oxygen and moisture in the atmosphere. That is, they are likely to deteriorate over time and are difficult to store for a long time. In addition, organic iron such as pentacarbonyl iron is highly toxic and difficult to handle. Therefore, these organic metals, inorganic compounds, metal salts, etc. need to be prepared not only in the environment during the production of nanopowder, but also in the raw material storage facilities and storage environment, and are difficult to handle, resulting in reduced workability. . As described in Patent Document 2, in order to produce metal nanopowder having a desired composition, a method of using a metal that is removed during production as a raw material also causes an increase in cost. Therefore, it is difficult to improve the productivity of nanopowder if these are used as raw materials.

  In the manufacturing method using microwaves, plasma, and supercritical water, the manufacturing equipment is special and large-scale, and the workability is inferior, resulting in a decrease in productivity. Further, in the production method using plasma or supercritical water, since the raw material liquid is diluted and used, the productivity is inferior from the viewpoint that the amount of powder that can be produced at one time is small. Further, in the manufacturing method using plasma, the liquid of the raw material is exposed to a high temperature by plasma to volatilize the solvent instantaneously, and the metal or metal oxide is crystallized, so that the metal is rapidly cooled. As a result, the resulting metal or metal oxide has poor crystallinity and may become amorphous. Even if such a metal oxide is reduced, a desired metal nanopowder may not be obtained. Therefore, it is difficult to improve the productivity of nanopowder using these manufacturing facilities.

  Then, one of the objectives of this invention is providing the manufacturing method of the metal powder which can manufacture metal powder with sufficient productivity. Another object of the present invention is to provide a metal powder having excellent productivity.

  The present inventors dissolved a metal powder such as iron powder (hereinafter, a powder used as a raw material may be referred to as a raw metal powder) in a carboxylic acid solution to prepare a precursor solution (sol) containing a metal complex. This precursor solution is dried to form a gel-like solid, metal oxide particles are generated from the gel-like solid, and the metal oxide particles are reduced. The inventors have obtained knowledge that metal powder (hereinafter referred to as metal nanopowder) can be obtained. In particular, the present inventors, when active carbonic acid such as free carbonic acid is present in the carboxylic acid solution, can enhance the dissolution reactivity of the metal with the carboxylic acid and the binding reactivity with the free carbonic acid, and the metal carbonate complex It was found that a precursor solution in which a stable presence can be produced. That is, the production time of the precursor solution can be shortened, and consequently the production time of the metal nanopowder can be shortened. Moreover, it is expected that the amount of carboxylic acid used can be reduced by increasing the reactivity. As described above, (1) raw materials that can be manufactured relatively easily such as metal powder, and those that are easy to handle such as carboxylic acid, carbonate capable of generating free carbonic acid, or carbon dioxide gas are used. The amount of use can be reduced, (3) because the production time can be shortened, the production method using the above-mentioned raw material metal powder, carboxylic acid solution, and free carbonic acid can improve the productivity of metal nanopowder, I can say that. The present invention is based on these findings.

The method for producing a metal powder of the present invention includes the following solution preparation step, drying step, separation step, and reduction step.
Solution preparation step A step of mixing a raw material metal powder of at least one kind of material, a carboxylic acid solution, and a free carbonic acid generation source, and dissolving the raw material metal powder in the carboxylic acid solution to prepare a precursor solution. .
Drying step The step of drying the precursor solution and removing the carbonic acid component to obtain a dried product.
Separation step A step of heat-treating the dried body to remove organic components in the dried body to produce a metal oxide powder.
Reduction step A step of reducing the metal oxide powder to produce a metal powder finer than the raw metal powder.

  The metal powder production method of the present invention produces metal oxide particles from a dried product (gel solid) obtained by drying a precursor solution (sol) by a technique similar to the so-called sol-gel method, and reduces the metal oxide. By doing so, fine metal particles are generated. In particular, in the method for producing a metal powder of the present invention, the reaction between a metal and an acid can proceed relatively gently by using a carboxylic acid having the properties of a weak acid and a chelating action when producing a sol. Therefore, each particle constituting the raw metal powder (hereinafter referred to as raw metal particle) can reach the inside from its surface and completely react with the acid, and a metal complex can be formed from each raw metal particle. Here, when strong acids such as nitric acid, hydrochloric acid, and sulfuric acid are used, since these strong acids are highly reactive with metals, the entire surface of the raw metal particles reacts in a very short time, and an oxide film is formed on the surface layer of the raw metal particles. Is formed. As a result, the reaction does not tend to proceed completely to the inside of the raw metal particles. It is difficult to produce fine metal oxide particles having a nano-order particle size from particles in which only the surface layer is oxidized to provide an oxide film, and as a result, metal nanopowder cannot be produced with high productivity. On the other hand, when carboxylic acid is used, metal oxide particles can be sufficiently generated from a metal complex, and fine particles can be easily generated by confining metal ions by chelating action. By using these fine metal oxide particles, metal nanopowder can be produced with high productivity.

  In addition, in the method for producing a metal powder of the present invention, in the production of the sol, by allowing free carbonic acid to be present in the carboxylic acid solution, the dissolution reactivity of the metal by the carboxylic acid can be enhanced and the binding reactivity with carbonic acid can be enhanced. As compared with the case where no free carbonic acid is used, the (carbonic acid) metal complex formation time can be shortened. Here, in the production of metal nanopowder using carboxylic acid, the present inventors have made various studies in order to increase the reactivity between the metal and carboxylic acid. For example, it is conceivable to adjust the pH, but a good reaction could not be obtained because it approaches the above-mentioned strong acid. On the other hand, when the metal and carbonic acid are simply reacted, precipitation of the metal carbonate occurs. It was examined to remove the carbonic acid from the precipitate to produce nanopowder, but the metal carbonate precipitate was chemically stable and it was difficult to remove the carbonic acid. On the other hand, when carbon dioxide gas was blown into a solution containing a metal and a carboxylic acid, the metal carbonate was not precipitated, and it was found that the state of the solution in which the metal was dissolved could be maintained. The reason for this is thought to be because precipitation was suppressed by the chelating action of the carboxylic acid. Moreover, in the state which the metal melt | dissolved completely, this solution was excellent in stability, for example, also acquired knowledge that long-term storage in air | atmosphere was possible. Furthermore, from this solution, metal oxide particles of uniform size can be produced, and by using such metal oxide particles, metal nanopowder of uniform size can be produced, preferably in mass production. The knowledge that it was possible was also obtained.

  Furthermore, the method for producing a metal powder of the present invention uses a relatively large metal powder as a raw material, typically a micro-order powder, which is excellent in the productivity of the raw material itself and easy to handle the raw material, It is also relatively inexpensive.

  As described above, the method for producing the metal powder of the present invention is (1) the production process is complicated, toxic, easily deteriorated over time, difficult to handle, and more expensive, There is no need to use raw materials that can increase costs, (2) there is no need to use special equipment that handles microwaves, plasma, or supercritical water, (3) production time can be shortened, (4) Since metal nanopowder of uniform size can be mass-produced, metal nanopowder can be stably produced with high productivity. Further, in the method for producing metal powder of the present invention, the precursor solution produced in the solution production process is easy to handle and the metal carbonate complex is stable, so that it can be stored for a long time in the atmosphere. Therefore, if this precursor solution is prepared, a desired amount of metal nanopowder can be produced at any time. Also from this point, the manufacturing method of the metal powder of the present invention has high industrial significance.

  As one form of the method for producing a metal powder of the present invention, the raw metal powder is one metal powder selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn and Cr, or two or more metals The form which is a powder.

  In the above-mentioned form, by preparing one or more raw metal powders having a desired composition, pure metal nanopowder made of a single metal element, or alloy nanopowder containing multiple kinds of metal elements is prepared. Can be manufactured. In particular, in the production of alloy nanopowder, it is not necessary to prepare an alloy or a compound containing a plurality of types of metal elements as raw materials, and the above form is also excellent in metal nanopowder productivity in this respect.

  As one form of the manufacturing method of the metal powder of this invention, the form whose average particle diameter of the said raw material metal powder is 1 micrometer or more and 100 micrometers or less is mentioned.

  The above form is uniform because the raw metal powder is easy to handle, and the reaction with the carboxylic acid proceeds sufficiently from the surface of the raw metal particles to the inside so that the raw metal powder can be dissolved well. A stable metal carbonate complex can be formed. As a result, the above-described embodiment can stably produce a metal powder finer than the raw metal powder with high productivity.

  As one form of the metal powder production method of the present invention, the free carbonic acid generation source is selected from the group consisting of carbonated water, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, potassium carbonate, and potassium bicarbonate. The form which is 1 type or 2 types or more is mentioned.

  The carbonated water or carbonate reacts with carboxylic acid to generate free carbonic acid. In other words, in the above form, the carboxylic acid functions as a decomposition agent that generates free carbonic acid in addition to the formation and maintenance of the complex by chelating action (suppression of precipitation). Free carbonic acid is excellent in reactivity with (dissolved) metal, and the above-described form can satisfactorily produce a metal carbonate complex solution, and thus is excellent in productivity of metal nanopowder.

  As a form using the carbonated water or carbonate, the ratio of the number of moles of the free carbonic acid source and the number of moles of the raw metal powder (hereinafter referred to as carbonic acid mole ratio) is a free carbonic acid source: metal = 2: 1. The form which is set to -9: 1 is mentioned.

  When the carbonic acid molar ratio satisfies the above-mentioned range, the bonding reaction between the metal and the free carbonic acid can be carried out without excess or deficiency, and the reaction between the carboxylic acid and the free carbonic acid, or when the solvent of the solution is water, And the precipitation of metal carbonate can be suppressed, and a homogeneous and stable metal carbonate complex can be produced satisfactorily. Therefore, since the said form can manufacture a precursor solution favorably and stably, it is excellent in productivity of metal nanopowder by extension.

  As one form of the method for producing metal powder of the present invention, the free carbonic acid generation source is one gas selected from the group consisting of carbon dioxide gas, carbon dioxide gas, and carbon monoxide gas, or a mixed gas of two or more. In the solution preparation step, there may be mentioned a form in which the one kind of gas or the mixed gas is mixed by bubbling.

  By bubbling the gas or the mixed gas, free carbon dioxide can be easily present in the solution and free carbon dioxide having excellent binding reactivity with (dissolved) metal can be continuously supplied into the solution. The metal and free carbonic acid can be reacted sequentially. Further, it is expected that the solution can be stirred to some extent by bubbling, and the binding reaction between the metal and free carbonic acid can be promoted. Therefore, the said form can manufacture a metal carbonate complex solution favorably and efficiently, and is excellent in the productivity of metal nanopowder by extension.

  As one form of the method for producing the metal powder of the present invention, the carboxylic acid is one acid selected from the group consisting of citric acid, malic acid, tartaric acid, malonic acid, phthalic acid, succinic acid, maleic acid, and gluconic acid. Or a form that is two or more acids.

  Each of the acids listed has the above-mentioned chelating action and weak acid properties, and can form a metal carbonate complex solution well and stably. Each of the listed acids is easy to handle and is commercially available and can be easily obtained. Therefore, the above form is excellent in productivity of metal nano powder.

  As one embodiment of the method for producing a metal powder of the present invention, the ratio of the number of moles of the carboxylic acid and the number of moles of the raw metal powder (hereinafter referred to as carboxylic acid mole ratio) is carboxylic acid: metal = 2: 1 to A form of 8: 1 is mentioned.

  When the carboxylic acid molar ratio satisfies the above range, the metal dissolution reaction by the carboxylic acid and the bonding reaction between the metal and free carbonic acid can be satisfactorily performed, and a homogeneous metal carbonate complex can be stably formed. Therefore, since the said form can manufacture a homogeneous precursor solution favorably and stably, it is excellent in productivity of metal nanopowder.

  As one form of the metal powder production method of the present invention, the solution preparation step includes an inert gas flow atmosphere, and the inert gas flow rate is 3 liter / min to 10 liter / min. .

In the state before the raw material metal powder is dissolved to form a metal carbonate complex, it easily reacts with oxygen and moisture in the atmosphere, and a metal oxide is generated by the reaction or precipitation of the metal carbonate is caused. Since the inert gas is a gas that does not react with the above-described dissolved metal and typically does not contain oxygen, the above-described form can produce a metal oxide or a metal carbonate during the preparation of the precursor solution. Precipitation can be prevented and a metal carbonate complex solution can be produced satisfactorily. In particular, when the flow rate of the inert gas satisfies the above range, CO ₂ gas generated by the reaction and released to the outside of the solution, oxygen in the atmosphere, and unreacted free carbonic acid are efficiently removed out of the atmosphere. it can. For this reason, it can suppress that these gas re-dissolves in a solution, or precipitation of a coarse metal oxide or metal carbonate arises by re-dissolution.

  Examples of the inert gas include one gas selected from the group consisting of Ar, He, Ne, and nitrogen, or a mixed gas of two or more.

  Any of rare gases such as Ar, He and Ne, nitrogen gas, and mixed gas thereof are excellent in stability and do not substantially react with the above-described dissolved metal. Therefore, the above-described form using the rare gas or nitrogen gas can suppress the formation of coarse metal oxide or metal carbonate precipitates, so that a solution of a metal carbonate complex can be produced satisfactorily and stably. Excellent powder productivity.

  As one form of the manufacturing method of the metal powder of this invention, in the said solution preparation process, the form which makes oxygen amount in atmosphere 100 ppm or less by volume ratio is mentioned.

  The above-described form in which the atmosphere of the solution preparation process is the above-described low oxygen atmosphere, preferably a non-oxygen atmosphere, indicates that precipitation of (coarse) metal oxide or metal carbonate occurs during preparation of the precursor solution as described above. The solution of the metal carbonate complex can be produced satisfactorily and stably, and as a result, the productivity of the metal nanopowder is excellent.

  As one form of the manufacturing method of the metal powder of this invention, the form which makes the temperature of a liquid mixture 40 to 100 degreeC in the said solution preparation process is mentioned.

  In the method for producing a metal powder of the present invention, the reactivity can be enhanced by utilizing free carbonic acid in addition to carboxylic acid, so there is no need to make the precursor solution high in temperature. The temperature of the mixed solution of the carboxylic acid solution and the free carbonic acid source can be set to room temperature (about 25 ° C.). However, by increasing the temperature of the mixed solution, it is possible to promote the dissolution of the raw metal powder and the binding reaction with free carbonic acid. Moreover, it can prevent that a film | membrane is produced | generated on the metal surface and the dissolution reaction is inhibited by making the temperature of the said liquid mixture into 100 degrees C or less. Therefore, the said form can manufacture the solution of a metal carbonate complex favorably and stably, and also can shorten the manufacturing time of a precursor solution, and contributes to the improvement of productivity of metal nanopowder.

  As one form of the manufacturing method of the metal powder of this invention, the form which makes pH of a liquid mixture 1 to 5 or less in the said solution preparation process is mentioned.

  In the above form, the pH of the mixed solution of the raw metal powder, the carboxylic acid solution and the free carbonic acid source satisfies the above range, thereby suppressing recombination with hydrogen in free carbonic acid and stabilizing the metal carbonate complex solution. And thus excellent in productivity of metal nanopowder.

  As one form of the method for producing the metal powder of the present invention, the heat treatment includes a form in which the heating temperature is 320 ° C. or more and 500 ° C. or less and the holding time is 20 minutes or more and 4 hours or less.

  In the above-mentioned form in which the heat treatment conditions are in the above range, the organic component can be removed well, and the metal oxide powder can be made fine by suppressing the growth of the metal oxide particles. Can be manufactured well.

  As one form of the method for producing the metal powder of the present invention, the reduction treatment includes a form in which the heating temperature is 300 ° C. or more and 550 ° C. or less, and the holding time is 10 minutes or more and 3 hours or less.

  The above-described embodiment in which the reduction condition is in the above range can remove oxygen well, suppress the growth of metal particles, and favorably produce fine metal powder.

  As one form of the manufacturing method of the metal powder of this invention, the said reduction process has the form performed in a hydrogen atmosphere.

Since the hydrogen (H ₂ ) atmosphere is excellent in reducibility, the above form can sufficiently remove oxygen and produce metal nanopowder satisfactorily.

  Examples of the metal powder of the present invention obtained by the method for producing a metal powder of the present invention include those having an average particle diameter of 8 nm to 200 nm.

  In the method for producing a metal powder of the present invention, a metal powder having an average particle size of 200 nm or less can be produced. A powder having an average particle size satisfying the above range is generally called a nanopowder and can be used for various raw materials. The metal constituting the powder can be both a pure metal consisting essentially of one kind of metal element and an alloy containing two or more kinds of metal elements.

  As one form of the metal powder of the present invention, there is a form in which the metal is an alloy containing Fe and one or more elements selected from the group consisting of Co, Ni, Zn, Cu, Mn, and Cr.

  Many of the above alloys have excellent magnetic properties such as high saturation magnetization, and the above-described form can be suitably used as a raw material for magnetic members.

  The method for producing a metal powder of the present invention can produce an ultrafine metal powder having a particle size of nano order with high productivity. The metal powder of the present invention is excellent in productivity.

Hereinafter, the present invention will be described in more detail.
[Production method of metal powder]
(Solution preparation process)
In the present invention, in producing ultrafine metal powder, first, a solution of a metal carbonate complex is prepared. In this solution, a metal carbonate precipitate is substantially absent, and a metal carbonate complex is present. In particular, one feature of the present invention is that metal powder is used as a raw material in the production of a metal carbonate complex solution. The material of the raw metal powder is appropriately selected according to the material of the metal to be manufactured. By using one kind of metal powder as a raw material, a pure metal fine powder consisting essentially of a single metal element can be obtained, and by using two or more kinds of metal powder as a raw material, 2 A fine powder composed of a seed or an alloy (binary alloy, ternary alloy, or higher alloy) containing three or more metal elements is obtained. That is, when producing an alloy powder containing a plurality of metal elements, it is preferable to prepare metal powders of a plurality of types of materials according to the number of metal elements in the alloy. It is not necessary to use as a raw material a metal that can be removed during the production. The raw metal powder is, for example, one type of metal powder selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn, and Cr, or two types of metal powders, or three or more types of metal powders. Can be mentioned. Each raw metal powder is preferably made of a so-called pure metal having a metal element content of 99.99% by mass or more. The form of the powder (difference due to shape and manufacturing method) is not particularly limited. Any of reduced metal powder, metal fiber, cast metal powder, spongy metal powder and the like can be used. Of course, commercially available metal powder can also be used. Further, a plurality of powders having different forms (such as shapes) can be used in combination. Although alloy powder can be used as a raw material, it is easier to obtain nano-powder made of an alloy whose blending ratio satisfies a desired value by using multiple kinds of pure metal powder as a raw material as described above. It is thought that it is excellent in property.

  When the raw metal powder has a size that can be easily dissolved in a carboxylic acid solution of a weak acid, the production time of the precursor solution can be shortened, and the precursor solution can be produced with high productivity. If the raw material metal powder is too large, it may not be completely dissolved or difficult to dissolve even if free carbonic acid is used. Therefore, the average particle diameter of the raw metal powder (or each metal powder when a plurality of metal powders are used) is preferably 100 μm or less. If it is this magnitude | size, raw material metal powder can fully be melt | dissolved and the fine metal powder called nano order can be manufactured favorable using micro order raw material metal powder. The smaller the average particle size of the raw metal powder, the easier the dissolution proceeds and the shorter the dissolution time, and the easier it is to produce fine metal oxide particles. As a result, the metal powder is sufficiently finer than the raw metal powder. Since it is easy to obtain, 50 μm or less is more preferable. However, if it is too small, (1) an oxide film is formed on the surface of the raw metal particles, and the presence of this oxide film lowers the dissolution reactivity, (2) it becomes bulky and difficult to handle, and the workability decreases. As a result, the productivity of metal nanopowder is reduced. Therefore, the average particle size of the raw metal powder is preferably 1 μm or more, and more preferably 10 μm or more. When using several metal powder for a raw material, the average particle diameter of each metal powder may be the same, and may differ.

  The average particle diameter of the raw metal powder may be measured with a commercially available device. In the case of fibrous metal powder, a cross section (transverse section) in a direction orthogonal to the longitudinal direction of the fiber is taken, the equivalent circle diameter of this cross-sectional area is taken as the diameter, and the average of the diameters is taken as the average particle diameter. A metal wire having both a diameter and a length of 100 μm or less may be used as a raw material.

  One feature of the present invention is that a free carbonic acid source is used in the production of a solution of a metal carbonate complex. For example, when carbonated water or the like is simply brought into contact with a metal, a metal carbonate is formed as described above, and this metal carbonate generally precipitates. However, as will be described later, in the present invention, by adding carboxylic acid, this precipitation can be suppressed and a solution in which the metal carbonate exists in a complex state can be produced. Then, by removing the solvent of the solution, the carbonic acid component, and the organic component (carboxylic acid) from the metal carbonate complex solution (sol), fine particles made of metal oxide are obtained, and the particles are reduced. By doing so, fine metal particles can be obtained. Therefore, in the present invention, a material capable of generating free carbonic acid is used as a raw material.

  As the free carbonic acid generation source, various sources capable of generating free carbonic acid in a solution can be used. For example, one type of gas selected from the group consisting of carbon dioxide gas, carbon dioxide gas, and carbon monoxide gas, or a mixed gas of two or more types can be given. The one type of gas and the two or more types of mixed gas can be easily generated in the mixed solution by bubbling and mixing in the mixed solution of the raw metal powder and the carboxylic acid solution described later. In such a gas-utilizing form, the amount of free carbon dioxide can be adjusted easily and accurately by adjusting the gas supply amount because the amount of gas supplied and the amount of free carbon dioxide produced are substantially proportional. Can be adjusted. Moreover, in this form, since continuous supply of gas is possible, free carbonic acid can be supplied continuously and a free carbonic acid and a metal can react sequentially. In particular, since the solution can be stirred by bubbling, it is easy to react free carbonic acid and metal. From these points, this form is expected to be able to produce a metal carbonate complex solution satisfactorily and efficiently, and to further improve the productivity of metal nanopowder.

  Another example of the free carbonic acid generating source is one that reacts with a carboxylic acid described later to produce free carbonic acid. Specific examples include one or more selected from the group consisting of carbonated water, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, potassium carbonate, and potassium bicarbonate. Both carbonated water and the above carbonates are added to the carboxylic acid solution after adjusting the addition amount so as to obtain the desired free carbonic acid. In particular, when carbonate is used, one or a plurality of two or more may be mixed. In this form using carbonated water or carbonate, once a fixed amount is added to the carboxylic acid solution, it may not be added until the completion of the reaction, and the preparation atmosphere of the precursor solution can be easily maintained in a desired atmosphere. Carbonated water can contain free carbonic acid, but more carbonic acid can be generated more reliably by reaction with carboxylic acid.

  When the carbonated water or carbonate is used as a free carbonic acid generation source, it is preferable to select a sufficient amount capable of forming a metal carbonate complex. Specifically, when the number of moles of the raw metal powder (the total number of moles when plural kinds of materials are used) is 1, the number of moles of the free carbonic acid generation source (the total number of moles when plural kinds of materials are used). The number) is 2 to 9 times. That is, the above-mentioned carbonic acid molar ratio is set to free carbonic acid generation source: metal = 2: 1 to 9: 1. By setting the number of moles of the free carbonic acid generating source to be twice or more the number of moles of the raw metal powder, free carbonic acid is sufficiently present, and the bonding reaction between the metal and the free carbonic acid can be satisfactorily performed without excess or deficiency. In addition, the presence of sufficient free carbonic acid makes the precipitation of metal carbonate predominate, and when the solvent in the solution is water, the oxidation reaction between water and the metal predominates, thereby dissolving the metal. A decrease in reactivity can also be suppressed. The more the number of moles of free carbonic acid source, the better the metal dissolution reaction and the metal binding reaction, but if too much, the reaction between carboxylic acid and free carbonic acid becomes prominent and the metal dissolution reactivity There is a risk of lowering. Accordingly, the number of moles of the free carbonic acid generating source is preferably 9 times or less the number of moles of the raw metal powder. When the carbonic acid molar ratio is in the range of 2: 1 to 9: 1, it is possible to satisfactorily produce a precursor solution that is homogeneous and stably contains a metal carbonate complex. The carbonic acid molar ratio is more preferably a free carbonic acid source: metal = 2: 1 to 6: 1.

  One feature of the present invention is that carboxylic acid is used in the production of a solution of a metal carbonate complex. Since the carboxylic acid is a weak acid, when the raw metal powder is mixed with the carboxylic acid solution, it can react gently with each raw metal particle constituting the raw metal powder and has a chelating action. The reaction can proceed from the inside to the inside, and the raw metal powder can be dissolved. That is, unlike the case of using a strong acid, in the present invention using a carboxylic acid, the raw metal powder and the acid can be completely reacted. And in this invention, the above-mentioned free carbonic acid exists in a carboxylic acid solution, The metal and free carbonic acid which were melt | dissolved by carboxylic acid react rapidly, A metal carbonate complex can be produced | generated, and a metal carbonate complex Can be maintained stably. Therefore, in the present invention using both the carboxylic acid and the free carbonic acid source, precipitation of the metal carbonate can be suppressed, and a precursor solution in which the metal carbonate complex exists stably can be produced. In addition, ultrafine metal oxide particles having a particle size of nano order can be produced from the metal carbonate complex in the precursor solution, and fine metal particles can be produced by reducing the metal oxide particles.

  The carboxylic acid is preferably various ones other than unsaturated carboxylic acid such as oleic acid. In particular, at least one acid selected from the group consisting of citric acid, malic acid, tartaric acid, malonic acid, phthalic acid, succinic acid, maleic acid, and gluconic acid (sometimes referred to as fruit acid) can be suitably used. . All of the listed acids are commercially available and are readily available. A plurality of different carboxylic acids may be used in combination.

  Typical examples of the carboxylic acid solution include an aqueous solution using distilled water as a solvent, and an alcohol solution.

  The content of the carboxylic acid in the carboxylic acid solution is preferably adjusted according to the amount of the raw metal powder added. For example, when the number of moles of the raw metal powder (total number of moles when using multiple types of materials) is 1, the number of moles of carboxylic acid (total number of moles when using multiple types of materials) is doubled. It is mentioned that it is 8 times or less. That is, the carboxylic acid molar ratio is set to carboxylic acid: metal = 2: 1 to 8: 1. By making the number of moles of carboxylic acid more than twice the number of moles of the raw metal powder, the carboxylic acid is sufficiently present, so that the raw metal powder can be dissolved satisfactorily and in addition, and the metal carbonate complex is stable. To be present. In addition, since the carboxylic acid is sufficiently present, when the above-mentioned carbonated water or carbonate is used as the free carbonic acid generating source, the free carbonic acid can be generated satisfactorily by the carboxylic acid. Furthermore, as the amount of carboxylic acid increases to some extent, the particle size of the metal oxide tends to be reduced. In addition, since sufficient free carboxylic acid can be generated as described above due to the sufficient presence of carboxylic acid, as a result, precipitation of metal carbonate is dominant, and when the solvent is water, It can also be suppressed that the oxidation reaction becomes dominant and the dissolution of the raw metal powder and the binding reaction with free carbonic acid decrease. However, if there is too much carboxylic acid, the reaction between carboxylic acid and free carbonic acid becomes prominent, which may lead to a decrease in metal dissolution reactivity. Therefore, the number of moles of carboxylic acid is preferably 8 times or less of the number of moles of the raw metal powder. When the carboxylic acid molar ratio is in the range of 2: 1 to 8: 1, it is possible to satisfactorily produce a precursor solution that is homogeneous and stably contains a metal carbonate complex. Further, in the present invention, by using a free carbonic acid generation source in combination, the metal dissolution reactivity and the binding reactivity with free carbonic acid can be improved, so the formation time (reaction time) of the metal carbonate complex can be shortened, Time can be shortened. For example, it is expected that the production time per 1 kg of metal powder can be shortened to about 1/2 to 1/3 as compared with the case where no free carbonic acid generating source is used. Furthermore, the use of the carboxylic acid can be reduced and the raw material cost can be reduced by improving the reactivity described above. From these points, the present invention is expected to contribute to the improvement of the productivity of the metal nanopowder. The carboxylic acid molar ratio is more preferably carboxylic acid: metal = 2: 1 to 6: 1. Note that either the addition of the carboxylic acid or the addition of the free carbonic acid generation source may be performed first.

  In the production of the precursor solution, the mixed solution of the raw material metal powder, the carboxylic acid solution and the free carbonic acid source can dissolve the raw material metal powder to form a metal carbonate complex even at room temperature (for example, about 25 ° C.). . However, when the temperature of the mixed solution is increased, the progress of dissolution of the raw metal powder and the bonding between the dissolved metal and free carbonic acid can be promoted, and the production time of the precursor solution can be shortened. In particular, when the temperature of the mixed solution is 40 ° C. or higher, the above-described dissolution and bonding are likely to proceed. The higher the temperature of the mixed solution, the more the dissolution and bonding described above can be promoted. By setting the temperature to 50 ° C. or higher, and further 60 ° C. or higher, the production time can be further shortened, and the productivity of the metal nanopowder can be improved. However, when the carboxylic acid solution is an aqueous solution, if the temperature of the mixed solution exceeds 100 ° C., a film (oxide film) is formed on the surface of the raw metal particles by oxygen generated when water evaporates. This may hinder the reaction with the carboxylic acid up to the inside of the raw metal particles. Moreover, if the temperature of the said liquid mixture is made low, a heating energy can also be reduced and it can contribute to the improvement of productivity. Accordingly, the temperature of the mixed solution is preferably 100 ° C. or lower, and more preferably 85 ° C. or lower. Moreover, if it is 100 degrees C or less, it will be easy to handle the said liquid mixture in industrial mass production.

In the production of the precursor solution, the mixture of the raw metal powder, the carboxylic acid solution and the free carbonic acid source has a hydrogen ion index (pH) of more than 1 and less than 5 (1 × 10 ⁻¹ mol / liter above 1 × 10 ^{− 5} mol / liter or less) can be adjusted. In this range, recombination with hydrogen in free carbonic acid can be suppressed, and dissolution of raw metal powder and binding reaction with free carbonic acid can be performed satisfactorily, so that a metal carbonate complex solution can be produced stably. If the pH is too high, the raw material metal powder may not be sufficiently dissolved, or the complex may be stabilized by the carboxylic acid. When the pH is 2 or more and 4 or less, it is expected that the metal carbonate complex can be obtained more stably and more easily used. Typically, pH adjustment includes adding an alkali salt such as sodium hydroxide or ammonium salt. Increasing the amount of alkali salt added increases the pH.

  The atmosphere for producing the precursor solution is preferably an inert gas atmosphere. Further, a low oxygen atmosphere, particularly a non-oxygen atmosphere, in which the oxygen concentration in the atmosphere is 100 ppm or less by volume and 80 ppm or less is preferable. By making the inert gas atmosphere, it is possible to prevent the dissolved metal and the atmosphere gas itself from reacting as well as the raw metal powder. It is also possible to prevent the dissolved metal from reacting with oxygen in the atmosphere, oxygen in the atmosphere, and moisture. As a result, it is possible to prevent the formation of a metal oxide or metal carbonate precipitate during the preparation of the precursor solution.

  As a more specific inert gas atmosphere, one kind of gas selected from the group consisting of rare gases such as Ar, He, and Ne, and nitrogen, or a mixture of two or more kinds of gases can be given. None of the rare gas, nitrogen gas, and mixed gas thereof substantially react with the raw metal powder, dissolved metal, or metal carbonate. Therefore, by using the atmosphere gas as these gases, the metal carbonate complex can be stably formed, and thus the precursor solution can be manufactured satisfactorily. If it is a single kind of gas atmosphere, it is easy to control and use.

In producing the precursor solution, for example, a desired atmospheric gas can be sealed in a sealed container. When a flow atmosphere is used in which an atmosphere gas is circulated in the sealed container, oxygen from the outside hardly enters the sealed container, and the above-described low oxygen atmosphere, preferably a non-oxygen atmosphere is easily maintained. The gas flow rate in the case of a flow atmosphere is, for example, 3 liters / min or more and 10 liters / min or less. By setting the above flow rate to 3 liters / min or more, CO ₂ gas generated by the reaction and released to the outside of the solution and oxygen in the atmosphere that can enter from the outside can be efficiently removed out of the atmosphere. Since the gas can be dissolved or redissolved in the solution and precipitation of (coarse) metal oxide or metal carbonate can be suppressed, a metal carbonate complex solution can be produced satisfactorily. By setting the rate to 10 liters / min or less, unreacted free carbonic acid can be removed out of the solution and further out of the atmosphere, so that the metal carbonate by re-reaction of excess free carbonic acid and metal carbonate complex remaining in the solution. Can prevent precipitation. The flow rate is more preferably 4 liter / min or more and 8 liter / min or less.

  In addition, in a solution preparation process, when the metal which comprises raw material metal powder is a magnetic body, and the metal to manufacture is also a magnetic body, a magnetic field can be applied. By applying a magnetic field, metal components can be elongated in the direction in which the magnetic field is applied, resulting in metal oxide particles with a large aspect ratio, that is, elongated particles. By reducing the metal oxide particles, the aspect ratio is large. Metal particles are obtained. Metal particles having a large aspect ratio have excellent magnetic properties due to shape anisotropy. Therefore, the metal nanopowder having such shape anisotropy can be suitably used as a raw material for the magnetic member. In order to obtain particles having a large aspect ratio, the applied magnetic field is preferably 3 T or more, and more preferably 5 T or more. For applying the magnetic field, a pulsed magnetic field generated by a normal conducting coil or a superconducting coil can be used.

(Drying process)
The precursor solution is in a wet state containing a solvent (such as water) of a carboxylic acid solution. Further, the metal carbonate complex in the precursor solution is in a state containing carbonic acid. Therefore, in the drying step, the solvent is mainly removed from the precursor solution, and the carbonic acid component (typically carbon dioxide) is removed. When drying is performed while placing the precursor solution in a heat treatment furnace maintained at a predetermined temperature and exhausting, a solvent such as water and a carbonic acid component can be efficiently removed. Drying conditions include a temperature of 140 ° C. or higher (preferably 145 ° C. or higher) 270 ° C. or lower and a holding time of 1 hour or longer and 3 hours or shorter. The atmosphere of the drying process includes an air atmosphere, a vacuum atmosphere, and a nitrogen atmosphere. If the drying step and the separation step described later are in an air atmosphere, the control is easy and the workability is excellent. In addition, the precursor solution in which the reaction is completely completed does not substantially react with oxygen, moisture, or the like in the atmosphere. Therefore, the precursor solution can be stored in the atmosphere, for example, and the drying step, the separation step and the reduction step described later can be performed as desired.

(Separation process)
Through the drying step, a dried product (gel solid) containing the metal complex from which the carbonic acid component has been removed is obtained. This dried product is in a state containing an organic component of carboxylic acid. Therefore, in the separation step, mainly the organic component (complex) is removed to convert the metal complex into a metal oxide. The organic component can be efficiently removed by removing the organic component while placing the dry body in a heat treatment furnace maintained at a predetermined temperature and exhausting it. Examples of the heat treatment conditions in the separation step include a heating temperature of 320 ° C. or more and 500 ° C. or less and a holding time of 20 minutes or more and 4 hours or less. By setting it as said range, while being able to remove an organic component completely, the remaining solvent and a carbonic acid component can also be removed reliably. The higher the heating temperature or the longer the holding time, the higher the certainty of removing the organic component, but the generated particles tend to grow and become coarse due to heat. Considering that the particles are also heated in the reduction step described later, in the separation step, the heating temperature is preferably 500 ° C. or less and the holding time is preferably 4 hours or less as described above. The heat treatment conditions for the separation step are more preferably a heating temperature of 350 ° C. or higher and 460 ° C. or lower and a holding time of 30 minutes or longer and 2 hours or shorter. The atmosphere of the separation process includes an air atmosphere, an argon atmosphere, and a nitrogen atmosphere. Depending on the size of the dried body, it is preferable to pulverize it in advance so that the heat treatment can be uniformly applied, and the mass productivity is excellent.

  The metal oxide particles obtained through the separation step are ultrafine particles having a nano-order particle size. In particular, in the present invention, in addition to the carboxylic acid, by using a free carbonic acid source, the dissolution of the raw metal powder and the binding with the free carbonic acid are uniformly compared with the case of not using the free carbonic acid source. Easy to do. Therefore, a metal oxide powder having a uniform particle size distribution can be produced by the above process.

(Reduction process)
In this step, the metal oxide obtained through the separation step is subjected to a reduction treatment to remove oxygen in the metal oxide, thereby converting the metal oxide into a metal. The reducing conditions include a heating temperature of 300 ° C. to 550 ° C., a holding time of 10 minutes to 3 hours, and a reducing atmosphere. When the reduction treatment is performed under the above conditions, oxygen can be removed and remaining organic components can be completely removed. The higher the heating temperature or the longer the holding time, the higher the certainty of removing oxygen, but the particles tend to grow and become coarse due to heat. Therefore, as described above, the reduction conditions are preferably a heating temperature of 550 ° C. or lower and a holding time of 3 hours or shorter. The reduction conditions are more preferably a heating temperature of 350 ° C. or higher and 440 ° C. or lower and a holding time of 20 minutes or longer and 2 hours or shorter. The reducing atmosphere is preferably an atmosphere containing hydrogen having high reducibility. For example, an atmosphere containing only hydrogen or a mixed atmosphere of hydrogen and the above-described inert gas (hydrogen ratio is 30% by volume or more) can be given. In particular, in an atmosphere containing only hydrogen, the reductivity is very high. By this reduction step, metal nanopowder, preferably metal nanopowder having a uniform particle size distribution can be produced. Further, the metal powder formed through the reduction process may be slightly smaller due to the removal of oxygen compared to the metal oxide before the reduction.

[Metal powder]
As for the metal powder of this invention, the particle size of each metal particle which comprises is nano order as above-mentioned, and the average particle diameter is typically 200 nm or less. By adjusting the size of the raw metal powder, the above-mentioned carbonic acid molar ratio and carboxylic acid molar ratio, the temperature of the liquid mixture in the solution preparation process, the heating temperature and the holding time in the separation process and the reduction process, the average particle diameter is 180 nm. Hereinafter, finer metal nanopowder such as 160 nm or less, 100 nm or less, or 60 nm or less can be obtained. In addition, when the average particle size is 8 nm or more, further 9 nm or more, 10 nm or more, or 15 nm or more, it is expected that the preparation of raw materials and the adjustment / control of manufacturing conditions are easy and the productivity is excellent.

  The metal constituting the metal powder of the present invention is a pure metal consisting essentially of only one kind of metal element, an alloy containing two or more kinds of metal elements (a binary alloy, a ternary alloy, or more Alloy). Specific metal elements include one or more selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn, and Cr. Of these, metals containing iron group metal elements such as Fe, Co, and Ni have many magnetic materials and can be used as raw materials for magnetic members. For example, as an alloy containing Fe and a metal element other than Fe, an alloy containing Fe and one or more elements selected from the group consisting of Co, Ni, Zn, Cu, Mn, and Cr (containing Fe) The amount is 20% by mass or more). In particular, metal nanopowder made of Fe—Ni alloy, Fe—Co alloy, Ni—Co alloy, and Fe—Ni—Co alloy can be suitably used as a raw material for magnetic members.

  Hereinafter, specific examples of the present invention will be described with reference to test examples. In each of the test examples described later, a powder was manufactured through the steps of solution preparation → drying → separation → reduction, and the material, average particle diameter, and magnetic properties of the obtained powder were examined. However, in each test example to be described later, powder was produced under different conditions. Details will be described below.

[Test Example 1]
In this test, the temperature of the mixed liquid of the raw material metal powder, the carboxylic acid and the free carbonic acid source was changed.

  As raw metal powders, reduced iron powder (pure iron powder) having an average particle diameter of 50 μm and nickel powder (pure nickel powder) having an average particle diameter of 50 μm were prepared. The average particle size of each raw metal powder was measured by a wet method using a commercially available laser diffraction particle size distribution measuring device. The measurement of this average particle diameter is the same in the test examples described later.

  Weighed citric acid and distilled water were mixed to prepare a citric acid aqueous solution as a carboxylic acid solution. A mixed aqueous solution of this aqueous citric acid solution and the prepared reduced iron powder and nickel powder was prepared. The compounding ratio of the reduced iron powder and nickel powder was Fe: Ni = 3.9: 13.6 in molar ratio. Sodium hydrogen carbonate was prepared as a free carbonic acid generation source and added to this mixed aqueous solution to prepare a mixed solution. In this test, a test solution was prepared by holding the mixed solution at 25 ° C., 40 ° C., 63 ° C., 100 ° C., and 120 ° C. The ratio of the number of moles of citric acid in the mixture to the number of moles of the raw metal powder (here, the total number of moles of reduced iron powder and nickel powder, the same shall apply hereinafter) is citric acid: metal = 4: 1, sodium bicarbonate The ratio of the number of moles to the number of moles of the raw metal powder was sodium bicarbonate: metal = 3: 1. The pH of the mixed solution was 2. The test solution was prepared under an inert gas flow atmosphere in which Ar gas was circulated at a flow rate of 6 liter / min (L / min) and the oxygen content in the atmosphere was 60 ppm by volume.

  As a result, when the temperature of the mixed solution is set to 40 ° C. or more and 100 ° C. or less, the raw metal powder is sufficiently dissolved and the binding reaction with free carbonic acid occurs, and a uniform metal carbonate complex solution (precursor solution, sol) is obtained. Obtained. The time required for producing this metal carbonate complex solution (the time from mixing to completion of the reaction) is about 0.5 day / 1 kg. On the other hand, when the temperature is lower than 40 ° C., although the raw metal powder is dissolved, the reactivity is not good, and the reaction time may be lengthened. On the other hand, when the temperature exceeded 100 ° C., the raw metal powder was not sufficiently dissolved and the binding reaction with free carbonic acid was not sufficiently performed. The reason for this is thought to be that distilled water as a solvent boiled and a film was formed on the surface of the raw metal particles constituting the raw metal powder to inhibit the dissolution reaction.

  The obtained test solution was kept in a heated state (atmosphere) at 160 ° C. for 2 hours, dried, and then pulverized with a Comil pulverizer. The pulverized powder was heat-treated (separated) at 450 ° C. × 2 h (120 min) in the air, and then subjected to reduction treatment in a hydrogen atmosphere at 420 ° C. × 1 h (60 min). As a result, powder was obtained for all the samples.

  The powder of each sample obtained after the reduction was subjected to crystal phase analysis by X-ray diffraction. The results and production conditions are shown in Table 1. Moreover, the particle size of the powder of each obtained sample was measured with a commercially available particle size distribution measuring device (Microtrack BlueRaytrac manufactured by Nikkiso Co., Ltd.). The results are shown in Table 1. Further, the magnetic properties of each obtained sample were examined. The results are shown in Table 1. Here, saturation magnetization (G) was measured with a vibrating sample magnetometer (VSM-5SC-5HF type, manufactured by Toei Kogyo Co., Ltd.). Note that G = kA / m.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. From this, it was confirmed that a metal powder could be generated by using a mixed solution of the raw material metal powder, the carboxylic acid solution, and the free carbonic acid generation source. In particular, in Sample Nos. 1-2 to 1-4 where the temperature of the mixture was 40 ° C, 63 ° C, and 100 ° C, the presence of the binary alloy Fe-78.5Ni could be confirmed (mass ratio, below The same). In samples No. 1-2 to No. 1-4, the presence of phases other than Fe-78.5Ni could not be substantially confirmed. Further, Fe-78.5Ni confirmed in Samples Nos. 1-2 to 1-4 is a nanopowder having an average particle size of 65 nm or less as shown in Table 1, and these nanopowders. Had a uniform particle size distribution with little variation in particle size. Such nano-powder composed of Fe-78.5Ni has high saturation magnetization (here, 760 (G) or more) as shown in Table 1, and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, Fe, Ni and Fe-78.5Ni existed in Sample No. 1-1 in which the temperature of the mixed solution was 25 ° C. and Sample No. 1-5 in which the temperature of the mixed solution was 120 ° C. In addition, although these samples also have particles of 200 nm or less, they have large variation in particle size and large average particle size (here, the average particle size was measured in a state where all the generated particles were mixed. The same applies hereinafter). It is not a size generally called nano-powder (typically an average particle size of 200 nm or less). The reason for this is considered to be that when the temperature is too low, the metal carbonate complex cannot be formed satisfactorily because it is inferior in dissolution reactivity as described above, and it becomes difficult to form an alloy or coarse particles are easily generated. It is done. If the temperature is too high, the dissolution reaction is hindered by the coating as described above, which makes it difficult to alloy and coarse particles are easily generated. Samples No. 1-1 and No. 1-5 are inferior in magnetic properties to samples No. 1-2 to No. 1-4, which are only Fe-78.5Ni (here, all generated The magnetic properties were measured in a state where the particles were mixed. From this, it is possible to satisfactorily produce the precursor solution by setting the mixed solution of the raw metal powder, the carboxylic acid solution, and the free carbonic acid source to 40 ° C. or more and 100 ° C. or less. It can be said that the powder can be mass-produced with good and stable quality.

[Test Example 2]
In this test, the size of the raw metal powder was changed.

  As the raw metal powder, reduced iron powder (pure iron powder) with an average particle size of 0.3 μm, 1 μm, 50 μm, 100 μm, 250 μm and nickel powder with an average particle size of 0.3 μm, 1 μm, 50 μm, 100 μm, 250 μm (pure nickel powder) (All of the compounding ratios were Fe: Ni = 3.9: 13.4). A test solution was prepared under an inert gas flow atmosphere under the same conditions as in Test Example 1 except that the size of the raw metal powder was changed and the temperature of the mixed solution was 63 ° C. As a result, when a metal powder having an average particle size of 1 μm or more and 100 μm or less is used as a raw material, two types of raw material metal powder can be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol )was gotten. On the other hand, when a metal powder having an average particle size of less than 1 μm is used as a raw material, the raw material powder is bulky and difficult to handle, and a film tends to be formed on the surface of the raw metal powder, resulting in poor dissolution reactivity. On the other hand, when a metal powder having an average particle size of more than 100 μm was used as a raw material, the time until complete dissolution was longer compared to other samples.

  The obtained test solution was dried, ground, separated and reduced under the same conditions as in Test Example 1. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 2.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, in Sample Nos. 2-2 to 2-4 in which the average particle size of the raw metal powder was 1 μm or more and 100 μm or less, the presence of a binary alloy called Fe-78.5Ni could be confirmed. Existence of phases other than 78.5Ni could not be substantially confirmed. In addition, Fe-78.5Ni confirmed in samples No. 2-2 to No. 2-4 are all nano-powder having an average particle size of 70 nm or less as shown in Table 2, and variation in particle size. And a uniform particle size distribution. Such nano-powder made of Fe-78.5Ni has high saturation magnetization as shown in Table 2 (here, 710 (G) or more), and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, Fe, Ni and Fe-78.5Ni existed in Sample No. 2-1 in which the average particle size of the raw metal powder was less than 1 μm and Sample No. 2-5 in which the average particle size was more than 100 μm. In addition, these samples have particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is considered to be that when a coarse raw material is used, it takes a long time to dissolve and the dissolution becomes insufficient, which makes it difficult to form an alloy or easily produces coarse particles. When a fine raw material is used, it is considered that dissolution is hindered by the presence of the above-described coating, which makes it difficult to alloy and coarse particles are easily generated. From this, by setting the average particle size of the raw metal powder to 1 μm or more and 100 μm or less, the precursor solution can be manufactured satisfactorily. As a result, the metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably. It can be said.

[Test Example 3]
In this test, the ratio (carboxylic acid molar ratio) between the number of moles of carboxylic acid and the number of moles of the raw metal powder was changed.

  Prepare raw metal powders of the same size and material as in Test Example 1 (reduced iron powder and nickel powder with an average particle size of 50 μm), and the same citric acid aqueous solution and sodium bicarbonate as in Test Example 1. In the same manner as in Test Example 1, a mixed solution was prepared. Except for changing the ratio between the number of moles of citric acid and the number of moles of the raw metal powder in the mixed solution, the temperature of the mixed solution was set to 63 ° C, the same conditions as in Test Example 1, A test solution was prepared under a flow atmosphere. In this test, citric acid and raw metal powder were prepared so that the molar ratio of carboxylic acid would satisfy citric acid: metal = 1: 1, 2: 1, 4: 1, 8: 1, 14: 1. In this test, the dissolution of the raw metal powder occurred in all the samples.

  The obtained test solution was dried, ground, separated and reduced under the same conditions as in Test Example 1. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 3.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, in Sample Nos. 3-2 to 3-4 with a carboxylic acid molar ratio of 2: 1 to 8: 1, the presence of a binary alloy called Fe-78.5Ni can be confirmed. Existence of phases other than 78.5Ni could not be substantially confirmed. In addition, Fe-78.5Ni confirmed in samples No. 3-2 to No. 3-4 are all nano-powder having an average particle size of 75 nm or less as shown in Table 3, and variation in particle size. And a uniform particle size distribution. The reason for this is considered to be that the raw metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. Such nano-powder made of Fe-78.5Ni has high saturation magnetization as shown in Table 3 (here, 700 (G) or more) and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, in Sample No. 3-1 in which the carboxylic acid molar ratio was 1: 1 and in Sample No. 3-5 in which the carboxylic acid molar ratio was 14: 1, Fe, Ni and Fe-78.5Ni were present. In addition, these samples have particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is that if the number of moles of carboxylic acid relative to the raw material metal powder is too small, the oxidation reaction with water and the precipitation of metal carbonates such as iron carbonate become dominant, resulting in dissolution of the raw material metal powder and free carbonic acid. This is thought to be because the binding reaction was lowered and it became difficult to alloy, or coarse particles were easily generated. If the number of moles of the carboxylic acid is too large, the reaction between the free carbonic acid and the carboxylic acid becomes remarkable. As a result, the dissolution of the raw metal powder and the binding reaction with the free carbonic acid are reduced, making it difficult to alloy and coarse particles. This is probably because it was easily generated. From this, the number of moles of carboxylic acid in the mixed solution should be 10 times or less of the number of moles of the raw metal powder, preferably carboxylic acid: metal = 2: 1 to 8: 1, As a result of good production, it can be said that metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably.

[Test Example 4]
In this test, the pH of the mixed solution of the raw metal powder, the carboxylic acid, and the free carbonic acid source was changed.

  Prepare raw metal powders of the same size and material as in Test Example 1 (reduced iron powder and nickel powder with an average particle size of 50 μm), and the same citric acid aqueous solution and sodium bicarbonate as in Test Example 1. In the same manner as in Test Example 1, a mixed solution was prepared. A test solution was prepared under an inert gas flow atmosphere under the same conditions as in Test Example 1 except that the pH of the mixture was changed and the temperature of the mixture was 63 ° C. In this test, sodium hydroxide was added to the mixed solution, and the added amount was adjusted to adjust the pH of the mixed solution, and the pH was set to 1,2,5,10. In this test, dissolution of the raw metal powder occurred in all the samples. In particular, when the pH was set to 2 or more and 5 or less, the raw metal powder could be dissolved uniformly and satisfactorily, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. On the other hand, if the pH is too low, recombination of free carbonic acid and hydrogen occurs, which inhibits the dissolution of the raw metal powder and the formation of the metal carbonate complex. If the pH is too high, the dissolution of the raw metal powder and the metal carbonate complex Is inhibited.

  The obtained test solution was dried, ground, separated and reduced under the same conditions as in Test Example 1. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 4.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, the presence of a binary alloy called Fe-78.5Ni was confirmed in Samples No. 4-2 and No. 4-3 where the pH of the mixed solution was 2, 5, and other than Fe-78.5Ni The presence of the phase could not be substantially confirmed. In addition, Fe-78.5Ni confirmed in Samples No. 4-2 and No. 4-3 are both nanopowder having an average particle size of 80 nm or less as shown in Table 4, and variation in particle size. And a uniform particle size distribution. Such nano-powder made of Fe-78.5Ni has high saturation magnetization (here, 720 (G) or more) as shown in Table 4, and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, in sample No. 4-1 in which the pH of the mixed solution was 1, and in sample No. 4-4 in which the pH was 10, Fe, Ni and Fe-78.5Ni were present. In addition, although these samples have particles of 200 nm or less, the variation in the particle diameter is large and the average particle diameter is also large. The reason for this is considered to be that, if the pH is too low or too high, the dissolution of the metal is hindered as described above, making it difficult to alloy and making it easy to produce coarse particles. From this, it can be said that by setting the pH of the mixed solution to more than 1 and 5 or less, the precursor solution can be manufactured satisfactorily, and as a result, metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably.

[Test Example 5]
In this test, the ratio between the number of moles of free carbonic acid generation source and the number of moles of raw metal powder (carbonic acid mole ratio) was changed.

  Prepare raw metal powders of the same size and material as in Test Example 1 (reduced iron powder and nickel powder with an average particle size of 50 μm), and the same citric acid aqueous solution and sodium bicarbonate as in Test Example 1. In the same manner as in Test Example 1, a mixed solution was prepared. Inert gas, under the same conditions as in Test Example 1, except that the ratio of the number of moles of sodium hydrogen carbonate and the number of moles of raw metal powder in the mixed liquid was changed, and the temperature of the mixed liquid was 63 ° C. A test solution was prepared under a flow atmosphere of In this test, sodium hydrogen carbonate and raw metal powder were prepared so that the carbonic acid molar ratio satisfied carbonic acid: metal = 1: 1,2: 1,3: 1,9: 1,13: 1. In this test, the dissolution of the raw metal powder occurred in all the samples. When the number of moles of free carbonic acid source relative to the number of moles of raw metal powder is less than 2 times (here, the molar ratio of carbonic acid is 1: 1), precipitation of metal carbonates such as iron carbonate and water and raw materials in aqueous solution Oxidation reaction with metal powder is dominant, and the metal dissolution reactivity is inferior, and in the case of more than 9 times (in this case, the carbonic acid molar ratio is 13: 1), the reaction between carboxylic acid and free carbonic acid is remarkable. Thus, the dissolution reactivity of the metal is inferior.

  The obtained test solution was dried, ground, separated and reduced under the same conditions as in Test Example 1. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 5.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, in Sample Nos. 5-2 to 5-4 with a carbonic acid molar ratio of 2: 1 to 9: 1, the presence of a binary alloy called Fe-78.5Ni could be confirmed. Existence of phases other than Ni could not be substantially confirmed. In addition, Fe-78.5Ni confirmed in samples No. 5-2 to No. 5-4 are all nano-powder having an average particle size of 105 nm or less as shown in Table 5, and variation in particle size. And a uniform particle size distribution. The reason for this is considered to be that the raw metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. Such nano-powder made of Fe-78.5Ni has a high saturation magnetization (here, 700 (G) or more) as shown in Table 5, and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, in Sample No. 5-1 in which the carbonic acid molar ratio was 1: 1 and in Sample No. 5-5 in which the ratio was 13: 1, Fe, Ni and Fe-78.5Ni were present. In addition, these samples have particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is that if the number of moles of the free carbonic acid generating source relative to the raw metal powder is too small or too large, the dissolution reactivity of the metal is lowered, making it difficult to alloy and making it easy to produce coarse particles. It is thought that it was because. From this, the number of moles of the free carbonic acid generation source in the mixed solution should be 2 to 9 times the number of moles of the raw metal powder, that is, the carbonic acid molar ratio should be carbonic acid: metal = 2: 1 to 9: 1. By doing so, it can be said that the metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably as a result of the good production of the precursor solution.

[Test Example 6]
In this test, the flow rate of the atmospheric gas during preparation of the test solution was changed.

Prepare raw metal powders of the same size and material as in Test Example 1 (reduced iron powder and nickel powder with an average particle size of 50 μm), and the same citric acid aqueous solution and sodium bicarbonate as in Test Example 1. In the same manner as in Test Example 1, a mixed solution was prepared. In forming the inert gas flow atmosphere, except that the flow rate of the inert gas (Ar gas in this case) was changed and the temperature of the mixed solution was 63 ° C, the conditions were the same as in Test Example 1, and A test solution was prepared under an active gas flow atmosphere. In this test, the flow rate of Ar gas was 1 liter / min, 4 liter / min, 6 liter / min, 10 liter / min, and 12 liter / min. In any sample, the amount of oxygen in the atmosphere is 60 ppm by volume. In this test, dissolution of the raw metal powder occurred in all the samples. When the Ar gas flow rate was 3 liters / min or more and 10 liters / min or less, the raw metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. If the flow rate of Ar gas is less than 3 liters / min, it is difficult to efficiently remove CO ₂ gas generated by the reaction and released from the solution and oxygen in the atmosphere to the outside. A coarse metal oxide is easily formed. If it exceeds 10 liters / min, the unreacted free carbonic acid cannot be sufficiently removed out of the solution and further out of the atmosphere, and the excess free carbonic acid remaining in the solution reacts with the metal carbonate complex to react again. The formation of carbonate precipitates or the formation of coarse metal carbonates ultimately promotes the formation of coarse metal particles.

  The obtained test solution was dried, ground, separated and reduced under the same conditions as in Test Example 1. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 6.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, sample No. 6-2 to No. 6-4 where the atmosphere for preparing the test solution was an inert gas flow atmosphere and the gas flow rate was 3 liter / min to 10 liter / min. The presence of the binary alloy Fe-78.5Ni was confirmed, and the presence of phases other than Fe-78.5Ni could not be substantially confirmed. In addition, Fe-78.5Ni confirmed in samples No. 6-2 to No. 6-4 are all nanopowder having an average particle size of 140 nm or less as shown in Table 6, and variation in particle size. And a uniform particle size distribution. Such nano-powder made of Fe-78.5Ni has a high saturation magnetization (here, 700 (G) or more) as shown in Table 6, and can be said to be suitable for use as a raw material for magnetic members.

  On the other hand, Fe, Ni and Fe-78.5Ni existed in Sample No. 6-1 in which the gas flow rate was reduced and Sample No. 6-5 in which the gas flow rate was increased. In addition, these samples have particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is considered to be that it becomes difficult to alloy due to the presence of an unfavorable gas such as in the atmosphere as described above, or coarse particles are easily generated. From this, in the preparation of the precursor solution, when the atmosphere gas flow atmosphere, the flow rate of the gas is 3 liter / min or more (preferably 4 liter / min or more) 10 liter / min or less, the precursor As a result of good production of the solution, it can be said that metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably.

[Test Example 7]
In this test, the conditions of the separation process or the reduction process were changed.

  Prepare raw metal powders of the same size and material as in Test Example 1 (reduced iron powder and nickel powder with an average particle size of 50 μm), and the same citric acid aqueous solution and sodium bicarbonate as in Test Example 1. In the same manner as in Test Example 1, a mixed solution was prepared. A test solution was prepared under a flow atmosphere of an inert gas under the same conditions as in Test Example 1 except that the temperature of the mixed solution was 63 ° C. (pH of the mixed solution = 2). All samples were able to dissolve the raw metal powder satisfactorily and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained.

  The obtained test solution (precursor solution) was dried and ground in order under the same conditions as in Test Example 1, and then subjected to heat treatment (separation) and reduction treatment under the conditions shown in Tables 7 and 8. Sample Nos. 7-1 to 7-23 shown in Table 7 changed the separation conditions, and Samples No. 8-1 to No. 8-26 shown in Table 8 changed the reducing conditions. The separation conditions for samples No.7-1 to No.7-23 are as follows: atmosphere is air, heating temperature is 250 ° C, 350 ° C, 450 ° C, 500 ° C, 800 ° C, and holding time is 10 min, 20 min , 2h (120min), 4h (240min), 6h (360min), and the reduction conditions were the same as in Test Example 1 (420 ° C x 1h (60min), hydrogen atmosphere). The separation conditions for Sample Nos. 8-1 to 8-26 were the same as in Test Example 1 (450 ° C x 2h (120min), in the air), and the reduction conditions were an atmosphere of hydrogen and a heating temperature of 250 ° C. , 300 ° C, 420 ° C, 550 ° C, 650 ° C, and holding time was 5 min, 10 min, 30 min, 1 h (60 min), 3 h (180 min), 5 h (300 min). As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Tables 7 and 8.

  As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, the separation conditions were as follows: Sample Nos. 7-6 to No.7-8, Nos. In No.7-13, No.7-16 to No.7-18, the existence of binary alloy called Fe-78.5Ni could be confirmed, and the existence of phases other than Fe-78.5Ni could not be substantially confirmed. . Samples No.8-7 to No.8-10, No.8-13 to No.8-, in which the heating conditions are 300 ° C to 550 ° C and the holding time is 10 minutes to 3 hours. 16, No. 8-19 to No. 8-21, the presence of Fe-78.5Ni could be confirmed, and the presence of phases other than Fe-78.5Ni could not be substantially confirmed. The Fe-78.5Ni confirmed in these samples is a nano-powder having an average particle size of 180 nm or less as shown in Tables 7 and 8, and the variation in particle size is small and uniform. It had a particle size distribution. Such nano-powder made of Fe-78.5Ni has a high saturation magnetization (here, 700 (G) or more) as shown in Tables 7 and 8, and can be said to be suitable for use as a raw material for magnetic members.

On the other hand, the separation conditions were as follows: Sample No. 7-1 to No. 7-4, No. 7-20 to No. 7-23 with heating temperature less than 320 ° C. or more than 500 ° C., retention time less than 20 minutes or In samples No.7-5, No.7-9, No.7-10, No.7-14, No.7-15, and No.7-19 over 4 hours, Fe-78.5Ni was present. In some cases, Fe-78.5Ni was present, but phases other than Fe-78.5Ni were also present. On the other hand, the reduction conditions were as follows: Sample No.8-1 to No.8-5, No.8-23 to No.8-26 with heating temperature less than 300 ° C. or more than 550 ° C., holding time less than 10 minutes or Fe-78.5Ni is present in samples No.8-6, No.8-11, No.8-12, No.8-17, No.8-18, and No.8-22 over 3 hours. In some cases, Fe-78.5Ni was present, but phases other than Fe-78.5Ni were also present. To describe the specific production phase, the sample in which the heating temperature in the separation process or the reduction process is too low or the holding time is too short includes oxides such as Fe ₂ O ₃ and NiO and simple metals such as Ni and Fe. However, in addition to the above, iron carbonate, nickel carbonate, iron hydroxide, and nickel hydroxide were also present in samples that were too low in the heating temperature of the separation process and samples that were low in heating temperature and too short in holding time. This sample also failed to confirm Fe-78.5Ni. Fe, Ni, and Fe-78.5Ni existed in samples in which the heating temperature in the separation process or the reduction process was too high or the holding time was too long. These samples include samples having particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is that if the heating temperature in the separation step is too low or if the holding time is too short, the organic components and moisture could not be removed sufficiently, and the above carbonates and oxides are likely to remain, It is thought that due to these residuals, the reduction treatment was insufficient and the particles were likely to become coarse particles. If the heating temperature in the reduction step is too low or if the holding time is too short, oxygen or the like cannot be sufficiently removed, and it is considered that coarse particles are easily formed. This is probably because when the heating temperature in the separation process or the reduction process is too high or the holding time is too long, the organic components, oxygen, and the like can be removed, but they easily grow to become coarse particles. From this, when performing separation and reduction on the precursor solution in order, the separation conditions are as follows: the heating temperature is 320 ° C. to 500 ° C. (preferably 350 ° C. or more), the holding time is 20 minutes to 4 hours, and the reduction conditions are By setting the heating temperature to 300 ° C. or more and 550 ° C. or less and the holding time to 10 minutes or more and 3 hours or less, it can be said that metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably.

[Test Example 8]
In this test, compared to Test Example 1, a sample with a different carboxylic acid type, a sample with a different type of free carbonic acid generation source, a sample with a different material for the raw metal powder, and a different atmospheric gas were used. A sample was prepared.

  As the raw metal powder, materials shown in Table 9 and those having an average particle diameter were prepared. Then, the production conditions of each sample were set as shown in Table 9, and powders were produced in the same procedure as in Test Example 1 (preparation of test solution → drying → separation → reduction). The main differences from Test Example 1 were that sample No. 9-1 used malic acid as the carboxylic acid (mixture temperature 63 ° C), and sample No. 10-1 contained carbonic acid as a free carbonic acid source. Point using ammonium hydrogen (mixture temperature 76 ° C), sample No. 11-1 uses carbon dioxide gas as a free carbonic acid source, mixed liquid of raw metal powder and citric acid aqueous solution (mixture temperature 70 Sample solution No. 12-1 was prepared by reducing iron powder (Fe) and cobalt powder (pure) as in Test Example 1 in that the test solution was prepared while bubbling carbon dioxide gas at (° C.). (Cobalt powder, average particle size of 40 μm) (mixing ratio is Fe: Co = 13: 7 in molar ratio), sample No. 100 uses oleic acid, sample No. 200 uses test solution The atmosphere at the time of preparation is a flow atmosphere (flow rate: 6 liter / min) of a mixed gas of argon and oxygen (the amount of oxygen is 130 ppm by volume). The carboxylic acid molar ratio is from carboxylic acid: metal (here, the total molar ratio of a plurality of metals) = 3: 1 to 5: 1, and the carbonic acid molar ratio is the free carbonic acid source: metal = 2: 1 to 4: 1. Selected from each.

  In addition, the temperature of the mixed solution of Samples No. 12-1, No. 100, No. 200 was 63 ° C. The flow rate of the atmospheric gas during the preparation of the test solution was 6 liters / min for all samples. The oxygen content was 60 ppm in mass ratio for all samples except for sample No. 12-1 and No. 200, 55 ppm for sample No. 12-1, and 130 ppm for sample No. 200. As for pH, except for sample No. 100, all samples were set to pH = 2, and sample No. 100 was set to pH = 4.

  The obtained test solution of each sample was dried under the following conditions, then pulverized in the same manner as in Test Example 1, and further heat treated under the conditions shown in Table 9 (separation conditions selected from 400 ° C to 490 ° C). The sample was subjected to reduction treatment under the conditions of 420 ° C. × 1 h (60 min) and hydrogen atmosphere. As a result, powder was obtained for all the samples. The obtained powder was subjected to crystal phase analysis, average particle size measurement, and magnetic property measurement in the same manner as in Test Example 1. The results and production conditions are shown in Table 9. Drying was performed at the following temperature, all samples were performed in the air, and the holding time was 2 hours. 175 ° C for sample No.9-1, 189 ° C for sample No.10-1, 150 ° C for sample No.11-1, 170 ° C for sample No.12-1, 160 for sample No.100 and No.200 ° C.

As a result of the crystal phase analysis, the presence of metal was confirmed in all the samples. In particular, in this test, citric acid and malic acid were used, and samples No. 9-1 to No. 12-1 in which the atmosphere during the preparation of the precursor solution was an Ar flow atmosphere, Fe-78.5Ni and Fe _0.65 The presence of an alloy such as Co _0.35 (here, binary alloys) could be confirmed, and the presence of phases other than the alloy could not be substantially confirmed. In addition, the alloys confirmed in samples No. 9-1 to No. 12-1 are both nanopowder having an average particle size of 65 nm or less as shown in Table 9, and the variation in particle size is small, It had a uniform particle size distribution. The reason for this is considered to be that the raw metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. In particular, nanopowder made of alloys such as Fe-78.5Ni and Fe _0.65 Co _0.35 has a high saturation magnetization (here, 715 (G) or more) as shown in Table 9, and is suitable for use as a raw material for magnetic members. I can say that.

  On the other hand, in sample No. 100 using oleic acid, only Fe and Ni exist, that is, only a single metal exists, and in sample No. 200 in which the atmosphere at the time of preparing the test solution is an atmosphere with a large amount of oxygen, Fe, Ni and Fe-78.5Ni existed. In addition, these samples have particles of 200 nm or less, but have a large variation in particle size and a large average particle size, and are not generally called nanopowder. The reason for this is that by using oleic acid, it is difficult to cause a dissolution reaction that reaches the inside of the metal as in the case of using citric acid or malic acid, making it difficult to alloy or forming coarse particles easily. This is thought to be because It is thought that the atmosphere with a large amount of oxygen prevails in the oxidation reaction of metals and the like, and the dissolution reactivity of the metal is lowered, making it difficult to form an alloy or forming coarse particles easily. From this, carboxylic acid such as citric acid or malic acid is used instead of oleic acid, and the atmosphere at the time of preparing the precursor solution is an atmosphere with a small amount of oxygen, preferably the amount of oxygen is 100 ppm or less, more preferably 80 ppm by volume. By setting the following inert gas atmosphere, it can be said that the metal nanopowder (here, alloy nanopowder) can be mass-produced satisfactorily and stably as a result of the good production of the precursor solution.

  Moreover, from this test result and the above-mentioned test result, it turns out that the metal nanopowder of various materials, especially alloy powder can be manufactured by changing the material of raw material metal powder and adjusting manufacturing conditions suitably.

  In addition, this invention is not limited to embodiment mentioned above, It can change suitably, without deviating from the summary of this invention. For example, the type of carboxylic acid, the material / particle size of the raw metal powder, the material of the free carbonic acid source, the material of the atmospheric gas, etc. can be appropriately changed.

  When the metal powder of the present invention is, for example, a magnetic material, a so-called semi-hard magnetic material such as a magnetic recording medium, a magnetic member such as a magnet such as a bond magnet or a sintered magnet, a printing toner, a contrast medium, or heat generated by thermal treatment. It can be suitably used as a raw material for a medical member such as a body. In addition, the metal powder of the present invention can be suitably used, for example, for raw materials such as pigments and catalysts, and for conductive pastes and conductive inks when conductive. The method for producing a metal powder of the present invention can be suitably used for the production of the metal powder of the present invention.

Claims (3)

The original rates genus powder, a carboxylic acid solution, and mixing the free carbon dioxide source, and the solution preparation step of preparing a precursor solution by dissolving the raw material metal powder in the acid solution,
A drying step of drying the precursor solution and removing a carbonic acid component to obtain a dried body;
A separation step of heat-treating the dried body to remove organic components in the dried body to produce a metal oxide powder;
The metal oxide powder is subjected to a reduction treatment, and an average particle size is 200 nm or less, comprising a reduction step of producing an alloy powder composed of the metal element of the raw metal powder ,
In the solution preparation step,
The raw metal powder is Fe powder, Co powder or Ni powder, and the average particle size of each powder is 1 μm or more and 100 μm or less,
The carboxylic acid is citric acid or malic acid, and the ratio of the number of moles of the carboxylic acid and the number of moles of the raw metal powder is carboxylic acid: metal = 2: 1 to 8: 1,
The free carbonic acid source is sodium hydrogen carbonate or ammonium hydrogen carbonate or carbon dioxide gas,
When the sodium hydrogen carbonate or the ammonium hydrogen carbonate is used, the ratio of the number of moles of the free carbonic acid source and the number of moles of the raw metal powder is set to free carbonic acid source: metal = 2: 1 to 9: 1. In the case of the carbon dioxide gas, it is mixed by bubbling,
The atmosphere of the solution preparation step is an inert gas flow atmosphere, and the flow rate of the inert gas is 4 liters / min or more and 10 liters / min or less, and the oxygen amount in the atmosphere is 100 ppm or less by volume,
The temperature of the mixed solution is 40 ° C. or more and 100 ° C. or less, and the pH of the mixed solution is more than 1 and 5 or less,
The heat treatment in the separation step is an air atmosphere, an argon atmosphere, or a nitrogen atmosphere, a heating temperature is 350 ° C. or more and 500 ° C. or less, a holding time is 20 minutes or more and 4 hours or less,
The reduction treatment in the reduction step is a hydrogen atmosphere or a reducing atmosphere of 30% by volume or more of hydrogen and an inert gas, a heating temperature of 300 ° C. or more and 550 ° C. or less, and a holding time of 10 minutes or more 3 The manufacturing method of the metal powder made into time or less . 2. The method for producing metal powder according to claim 1 , wherein the inert gas is one gas selected from the group consisting of Ar, He, Ne, and nitrogen, or a mixed gas of two or more. 3. The method for producing metal powder according to claim 1, wherein the reduction treatment is performed in a hydrogen atmosphere.