JP6024453B2 - Method for producing metal oxide powder - Google Patents

Description

  The present invention relates to an ultrafine metal oxide powder called nano-powder and a method for producing the same. In particular, the present invention relates to a method for producing a metal oxide 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 and iron oxide nano powder such as Fe ₃ O ₄ . Nano iron powders and nano powders of iron oxides such as Fe ₃ O ₄ are used, for example, as raw materials for magnetic members such as magnetic recording media using their magnetic properties.

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 or iron oxide nano 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. After drying, Fe ₃ O ₄ is formed by oxidation in air at room temperature.

  Other methods for producing 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

  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. . 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. There is also a possibility that oxides having different oxygen concentrations relative to the target oxide (oxides having an unfavorable oxygen concentration) are produced. 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 oxide powder which can manufacture metal oxide powder with sufficient productivity. Another object of the present invention is to provide a metal oxide powder excellent in productivity.

  The present inventors dissolved a metal powder such as iron powder in a carboxylic acid solution to prepare a precursor solution (sol) containing a metal complex, and dried the precursor solution to form a gel-like solid. We have obtained knowledge that nano-order metal oxide powders can be obtained by producing particles of metal oxides such as iron oxide and ferrite from gel-like solids. 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 manufacturing time of the precursor solution can be shortened, and consequently the manufacturing time of the nanopowder can be shortened. Moreover, it is expected that the amount of carboxylic acid used can be reduced by increasing the reactivity. In this way, (1) metal powders that can be manufactured relatively easily and carboxylic acids, carbonates that can generate free carbonic acid, carbon dioxide gas, etc. that are easy to handle are used as raw materials. Since the amount can be reduced and (3) the production time can be shortened, it can be said that the production method using the metal powder, the carboxylic acid solution, and the free carbonic acid can improve the productivity of the nanopowder. The present invention is based on these findings.

The method for producing a metal oxide powder of the present invention comprises the following solution preparation step, drying step, and separation step.
Solution preparation step A step of mixing a metal powder, a carboxylic acid solution, and a free carbonic acid source, and dissolving the 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.

  In the method for producing a metal oxide powder of the present invention, metal oxide particles are generated from a dried product (gel solid) obtained by drying a precursor solution (sol) by a method similar to a so-called sol-gel method. In particular, in the method for producing a metal oxide powder of the present invention, the reaction between a metal and an acid can proceed relatively gently by utilizing a carboxylic acid having properties of a weak acid and a chelating action in producing a sol. Therefore, each particle constituting the metal powder (hereinafter referred to as raw material 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 material 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 particle size of nano-order from particles having an oxide film formed by oxidizing only the surface layer. 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.

  In addition, in the method for producing a metal oxide powder of the present invention, in the production of the sol, the presence of free carbonic acid in the carboxylic acid solution can enhance the dissolution reactivity of the metal by the carboxylic acid and the binding reactivity with the carbonic acid. As compared with the case where free carbonic acid is not used, the production time of the (carbonic acid) metal complex can be shortened. Here, the present inventors have made various studies in order to increase the reactivity between the metal and the carboxylic acid in the production of the nanopowder using the 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, it was found that nano-powder of uniform size can be produced, preferably mass-produced.

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

  As described above, the manufacturing method of the metal oxide powder of the present invention is (1) the manufacturing process is complicated, toxic, easily deteriorated over time, difficult to handle, and more expensive. No need to use raw materials, (2) No need to use special equipment that handles microwaves, plasma, supercritical water, (3) Reduces production time, (4) Uniform size Therefore, nano powder can be stably produced with high productivity. Further, in the method for producing metal oxide 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 long-term storage in the atmosphere is possible. Therefore, if this precursor solution is prepared, a desired amount of nanopowder can be produced at any time. Also from this point, the manufacturing method of the metal oxide powder of the present invention has high industrial significance.

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

  In the above-mentioned form, by preparing one or more kinds of metal powder having a desired composition as a raw material, nano powder made of an oxide of a single metal element, or an oxide containing a plurality of kinds of metal elements (composite) Nano-powder containing oxides). In particular, when manufacturing nano powders of oxides containing multiple types of metal elements, it is not necessary to prepare raw materials such as alloys or compounds containing multiple types of metal elements. Excellent in properties.

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

  In the above-mentioned form, the metal powder is easy to handle, and since the reaction with the carboxylic acid proceeds sufficiently from the surface of the raw metal particles to the inside, the metal powder can be dissolved well. A metal complex can be formed stably. As a result, the above-described embodiment can produce a metal oxide powder finer than the metal powder used as a raw material with high productivity and stability.

  As one form of the manufacturing method of the metal oxide powder of this invention, the said free carbonic acid generation | occurrence | production source is from the group which consists of carbonated water, sodium carbonate, sodium hydrogencarbonate, ammonium carbonate, ammonium hydrogencarbonate, potassium carbonate, and potassium hydrogencarbonate. The form which is 1 type chosen 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 excellent in productivity of metal oxide nanopowder.

  As a form using the carbonated water or carbonate, the ratio of the number of moles of the free carbonic acid generation source and the number of moles of the metal powder (hereinafter referred to as carbonic acid molar ratio) is a free carbonic acid generation source: metal = 2: 1 to The form of 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 the nanopowder of a metal oxide by extension.

As one form of the method for manufacturing the metal oxide powder of the present invention is a kind of gas, or two-component mixture gas of the free carbon dioxide source is selected Ri by carbonic gas及 beauty carbon monoxide gas, the In the solution preparation step, a form of mixing by bubbling the one kind of gas or the mixed gas may be mentioned.

  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 the nanopowder of a metal oxide by extension.

  As one form of the method for producing the metal oxide powder of the present invention, the carboxylic acid is 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 of 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. In addition, each of the acids listed is easy to handle and is commercially available and can be easily obtained. Thus, the above form is excellent in productivity of the metal oxide nanopowder.

  As one form of the method for producing the metal oxide powder of the present invention, the ratio of the number of moles of the carboxylic acid to the number of moles of the metal powder (hereinafter referred to as carboxylic acid mole ratio) is carboxylic acid: metal = 2: 1. The form which is set to -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 the metal oxide nanopowder.

  As one form of the manufacturing method of the metal oxide powder of the present invention, the solution preparation step has a flow atmosphere of inert gas, and the flow rate of the inert gas is 3 liter / min or more and 10 liter / min or less. Can be mentioned.

In a state before the starting 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 precipitation of a coarse metal oxide and metal carbonate resulting from these gases occurs.

  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 and nitrogen gas can suppress the formation of coarse metal oxides and metal carbonate precipitates, so that a solution of a metal carbonate complex can be produced satisfactorily and stably. Excellent productivity of nano powder.

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

  As one form of the manufacturing method of the metal oxide 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 oxide powder of the present invention, the reactivity can be enhanced by using free carbonic acid in addition to carboxylic acid. Therefore, it is not necessary to use a high temperature in preparation of the precursor solution. The temperature of the mixture of the carboxylic acid solution and the free carbonic acid source can be room temperature (about 25 ° C.). However, by raising the temperature of the mixed solution, it is possible to promote dissolution of metal powder and 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 the metal oxide nanopowder.

  As one form of the manufacturing method of the metal oxide 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-mentioned form, the pH of the mixed solution of the metal powder, the carboxylic acid solution, and the free carbonic acid source satisfies the above range, thereby suppressing recombination with hydrogen in the free carbonic acid and stabilizing the metal carbonate complex solution. It can be manufactured, and as a result, it is excellent in productivity of the metal oxide nano powder.

  As one form of the method for producing the metal oxide powder of the present invention, the heat treatment may be carried out such that the heating temperature is 300 ° C. or more and 630 ° C. or less and the holding time is 15 minutes or more and 4 hours or less.

  According to the above-described embodiment in which the heat treatment conditions are in the above range, the organic component can be removed satisfactorily, and the growth of metal oxide particles can be suppressed to produce a fine metal oxide powder.

  Examples of the metal oxide powder of the present invention obtained by the method for producing a metal oxide powder of the present invention include those having an average particle size of 8 nm or more and 200 nm or less.

  In the method for producing a metal oxide powder of the present invention, a metal oxide 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 oxide can be either one containing one metal element or two or more metal elements.

As one form of the metal oxide powder of the present invention, when the metal oxide is M and one or more elements selected from the group consisting of Co, Ni, Zn, Cu, Mn, and Cr, MFe ₂ O ₄ The form which is is mentioned.

The MFe ₂ O ₄ is generally called spinel ferrite, and the above form can be suitably used as a raw material for a magnetic member.

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

Hereinafter, the present invention will be described in more detail.
[Production method of metal oxide powder]
(Solution preparation process)
In the present invention, in producing an ultrafine metal oxide powder, first, a metal carbonate complex solution 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 metal powder is appropriately selected according to the material of the metal oxide to be manufactured. A metal oxide containing a single metal element can be obtained by using one kind of metal powder, and a metal oxide containing a plurality of metal elements can be obtained by using two or more kinds of metal powders. It is done. In other words, when producing a metal oxide containing a plurality of metal elements such as a composite oxide, it is better to prepare a plurality of metal powders according to the number of metal elements in the metal oxide, It is not necessary to use it as a raw material. Examples of the metal powder include one metal powder selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn, and Cr, or two or more metal powders. Each 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 metal oxide with a compounding ratio satisfying 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 productivity.

  When the metal powder used for the raw material 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 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 size of the metal powder (each metal powder when a plurality of metal powders are used) is preferably 100 μm or less. If it is this magnitude | size, metal powder can fully be melt | dissolved and a metal oxide powder finer than the metal powder of the raw material called nano order can be favorably manufactured using a raw material of micro order. The average particle size of the metal powder is more preferably 50 μm or less because the smaller the average particle size, the easier the dissolution proceeds and the shorter the dissolution time, and the easier the formation of fine metal oxide particles. However, if it is too small, (1) an oxide film is formed on the surface of the metal particles of the raw material, and the presence of this oxide film reduces the dissolution reactivity, (2) it is bulky and difficult to handle, and the workability decreases. As a result, the productivity of the metal oxide nanopowder is reduced. Accordingly, the average particle size of the metal powder is preferably 1 μm or more, and more preferably 10 μm or more. When using a plurality of metal powders, the average particle diameter of each metal powder may be the same or different.

  The average particle diameter of the 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 a metal oxide 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 Ri by carbonic gas及 beauty carbon monoxide gas, or two-component mixture gas thereof. It said one gas or upper Symbol mixed-gas, by mixing by bubbling in a mixture of a carboxylic acid solution to be described later with the metal powder, the free carbon dioxide can be easily generated in the mixture. 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 further improve the productivity of metal oxide 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 metal powder (total number of moles when using multiple types of materials) is 1, the number of moles of free carbonic acid generation source (total number of moles when using multiple types of materials) ) 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 metal powder, free carbonic acid is sufficiently present, and the bonding reaction between the metal and the free carbonic acid can be performed satisfactorily 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. Therefore, the number of moles of the free carbonic acid generating source is preferably 9 times or less the number of moles of the 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 above-mentioned carbonic acid molar ratio is more preferably free carbonic acid source: metal = 3: 1 to 7: 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, mixing the metal powder with the carboxylic acid solution can react gently with each raw metal particle constituting the metal powder and has a chelating action. The reaction can proceed and the metal powder can be dissolved. That is, unlike the case of using a strong acid, in the present invention using a carboxylic acid, the 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. Further, ultrafine metal oxide particles having a particle size of nano-order can be produced from the metal carbonate complex in the precursor solution.

  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 carboxylic acid in the carboxylic acid solution is preferably adjusted according to the amount of metal powder added. For example, when the number of moles of 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 twice or more. 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 metal powder, carboxylic acid is sufficiently present, so that the metal powder can be dissolved well without excess and deficiency, and the metal carbonate complex can be stabilized stably. 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 metal powder and the binding reaction with free carbonic acid are reduced. 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 the number of moles of 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 the metal oxide powder can be shortened to about 1/2 to 1/3 as compared with the case where no free carbonic acid generation 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 oxide nanopowder. The carboxylic acid molar ratio is more preferably carboxylic acid: metal = 3: 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, even if the mixed solution of the metal powder, the carboxylic acid solution, and the free carbonic acid generation source is at room temperature (for example, about 25 ° C.), the metal powder can be dissolved to form a metal carbonate complex. However, when the temperature of the mixed solution is increased, the progress of dissolution of the 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 above-mentioned dissolution and bonding can be promoted, and the production time can be further shortened by setting the temperature to 50 ° C. or higher, and further to 60 ° C. or higher. It 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 metal powder, the carboxylic acid solution, and the free carbonic acid generation source has a hydrogen ion index (pH) of more than 1 and less than 5 (1 × 10 ⁻¹ mol / liter more than 1 × 10 ^-5 mol / liter or less). In this range, recombination with hydrogen in free carbonic acid can be suppressed, and the metal powder can be dissolved and the binding reaction with free carbonic acid can be satisfactorily performed, so that the metal carbonate complex solution can be stably produced. If the pH is too high, the 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 reacts with the raw metal powder or the dissolved metal. 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 the 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 metal powder is a magnetic body, and the metal oxide to manufacture is also a magnetic body, a magnetic field can be applied. By applying a magnetic field, the metal components can be elongated in the direction in which the magnetic field is applied, resulting in metal oxide particles having a large aspect ratio, that is, elongated particles. Metal oxide particles having a large aspect ratio have excellent magnetic properties due to shape anisotropy. Therefore, the metal oxide powder 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, for example, in the atmosphere, and the drying step and the separation step described later can be performed when 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 300 ° C. to 630 ° C. and a holding time of 15 minutes to 4 hours. 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. Therefore, as described above, the heating temperature is preferably 630 ° C. or less, and the holding time is preferably 4 hours or less. The heat treatment conditions are more preferably a heating temperature of 350 ° C. to 630 ° C. and a holding time of 20 minutes to 4 hours. 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, by using a free carbonic acid source in addition to the carboxylic acid, the metal powder is uniformly dissolved and combined with the free carbonic acid as compared with the case where no free carbonic acid source is used. easy. Therefore, according to the method for producing a metal oxide powder of the present invention, a metal oxide powder having a uniform particle size distribution can be produced.

[Metal oxide powder]
As for the metal oxide powder of this invention, the particle diameter of each metal oxide particle which comprises is a nano order as mentioned above, and the average particle diameter is typically 200 nm or less. By adjusting the size of the metal powder used for the raw material, 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, the average particle diameter is 180 nm or less Furthermore, finer metal oxide powders of 150 nm or less, 100 nm or less, 80 nm or less, or 50 nm or less can be obtained. In addition, when the average particle size is 8 nm or more, further 10 nm or more, 15 nm or more, it is expected that preparation of raw materials and adjustment / control of manufacturing conditions can be easily performed and the productivity is excellent.

The metal oxide constituting the metal oxide powder of the present invention includes both an oxide containing only one kind of metal element and an oxide containing two or more kinds of metal elements. Specific metal elements include one or more selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn, and Cr. Among these, metal oxides containing iron group metal elements such as Fe, Co, and Ni have many magnetic substances and can be used as raw materials for magnetic members. A metal oxide containing Fe and a metal element other than Fe, specifically, when M is one or more elements selected from the group consisting of Co, Ni, Zn, Cu, Mn and Cr, MFe ₂ O What is represented by ₄ is a magnetic material called spinel ferrite, which can be 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 to be described later, a powder was produced through steps of solution preparation → drying → heat treatment, 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 metal powder, the carboxylic acid, and the free carbonic acid source was changed.

  As the raw metal powder, reduced iron powder (pure iron powder, Fe) having an average particle diameter of 50 μm and nickel powder (pure nickel powder, Ni) having an average particle diameter of 50 μm were prepared. The average particle diameter of each metal powder was measured by a wet method using a commercially available laser diffraction particle size distribution measuring apparatus. 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 mixing ratio of the reduced iron powder and the nickel powder was Fe: Ni = 2: 1 in terms of 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 between the number of moles of citric acid and the number of moles of metal powder in the mixed solution (here, the total number of moles of reduced iron powder and nickel powder, the same shall apply hereinafter) is citric acid: metal = 4: 1, and sodium bicarbonate The ratio of the number of moles to the number of moles of 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 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. It was. 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., the metal powder is dissolved, but the reactivity is not good and the reaction time may be prolonged. On the other hand, when the temperature exceeded 100 ° C., the 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 metal particles constituting the 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 at 520 ° C. for 30 minutes in the air. As a result, powder was obtained for all the samples.

The powder of each sample obtained after the heat treatment 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 (emu / g) and coercive force (Oe) were measured with a vibrating sample magnetometer (VSM-5SC-5HF type, manufactured by Toei Kogyo Co., Ltd.). Note that emu / g = A · m ² / kg and Oe = (10 ³ / 4π) A / m.

As a result of the crystal phase analysis, the presence of metal oxide could be confirmed in any sample. From this, it was confirmed that a metal oxide powder could be generated by using a mixed solution of a metal powder, a carboxylic acid solution, and a free carbonic acid source. In particular, the presence of NiFe ₂ O ₄ that is spinel ferrite was confirmed in Samples Nos. 1-2 to 1-4 where the temperature of the mixed solution was 40 ° C, 63 ° C, and 100 ° C. In Samples Nos. 1-2 to 1-4, the presence of phases other than NiFe ₂ O ₄ could not be substantially confirmed. Further, NiFe ₂ O ₄ confirmed in samples No. 1-2 to No. 1-4 is a nanopowder having an average particle size of 90 nm or less as shown in Table 1, and these nanopowders. Had a uniform particle size distribution with little variation in particle size. As shown in Table 1, the nanopowders made of NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 25 (emu / g) or more, coercivity 35 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, 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 mixture was 120 ° C., particles of various materials such as Fe ₂ O ₃ , NiO, α-Fe, and Ni Although it was confirmed that NiFe ₂ O ₄ was present, NiFe ₂ O ₄ could not be confirmed. 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 that when the temperature is too low, the metal carbonate complex cannot be formed satisfactorily because of poor solubility reactivity as described above, and coarse particles are likely to be generated, or oxides other than the desired composition ( Here, it is considered that Fe ₂ O ₃ and NiO) are easily generated, and α-Fe components and Ni are easily left. If the temperature is too high, the dissolution reaction is hindered by the film as described above, and coarse particles are easily generated, or oxides other than the desired composition (here, Fe ₂ O ₃ and NiO) are generated. This is probably because the α-Fe component and Ni are likely to remain. These produced phases are inferior to NiFe ₂ O _{4 in} magnetic properties (here, the magnetic properties were measured in a state where all the produced particles were mixed; the same applies hereinafter). From this, by making the mixed solution of the metal powder, the carboxylic acid solution and the free carbonic acid source to be 40 ° C. or higher and 100 ° C. or lower, the precursor solution can be manufactured favorably. As a result, the metal oxide nano powder is improved. And it can be said that mass production can be performed stably.

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

  Reduced iron powder (pure iron powder, Fe) with an average particle size of 0.3μm, 1μm, 50μm, 100μm, 250μm and nickel powder with an average particle size of 0.3μm, 1μm, 50μm, 100μm, 250μm (Pure nickel powder, Ni) were prepared (all blending ratios were Fe: Ni = 2: 1). 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 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 metal powders can be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) can be obtained. Obtained. On the other hand, when the metal powder has an average particle size of less than 1 μm, the raw material powder is bulky and difficult to handle, and a film is easily formed on the surface of the raw metal powder, resulting in poor dissolution reactivity. On the other hand, when the metal powder had an average particle size of more than 100 μm, the time until complete dissolution was longer than that of other samples.

  The obtained test solution was dried, ground and heat-treated 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 oxide could be confirmed in any sample. In particular, in this test, the samples No.2-2~No.2-4 and the average particle diameter of the raw material of the metal powder is 1μm or 100μm or less, the presence of NiFe ₂ O ₄ can be confirmed, except NiFe ₂ O ₄ The presence of the phase of this was not substantially confirmed. In addition, NiFe ₂ O ₄ confirmed in samples No. 2-2 to No. 2-4 are all nano-powder having an average particle size of 80 nm or less as shown in Table 2, and variation in particle size. And a uniform particle size distribution. As shown in Table 2, the nanopowders composed of such NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 25 (emu / g) or more, coercivity 45 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, in sample No. 2-1 in which the average particle size of the raw metal powder is less than 1 μm and in sample No. 2-5 in which the average particle size is more than 100 μm, various kinds of materials such as Fe ₂ O ₃ , NiO, α-Fe, Ni Although there were particles of the material, NiFe ₂ O ₄ could not be confirmed. 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. This is because when coarse raw materials are used, it takes a long time to dissolve and the dissolution becomes insufficient, so that coarse particles are likely to be generated, or oxides other than the desired composition (here Fe ₂ O ₃ And NiO) are likely to be generated, and α-Fe components and Ni are likely to remain. When a fine raw material is used, dissolution is hindered by the presence of the above-mentioned film, so that coarse particles are easily generated, or oxides other than the desired composition (here, Fe ₂ O ₃ and NiO) are formed. This is thought to be because the α-Fe component and Ni are likely to remain. From this, it can be said that 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, and as a result, the metal oxide nanopowder can be mass-produced successfully and stably.

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

  As the raw metal powder, 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 were prepared. Then, a liquid mixture was prepared in the same manner as in Test Example 1. Flow of inert gas under the same conditions as in Test Example 1 except that the ratio between the number of moles of citric acid and the number of moles of metal powder in the mixture was changed and the temperature of the mixture was 63 ° C. A test solution was prepared under an atmosphere. In this test, citric acid and 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, dissolution of metal powder occurred in any sample.

  The obtained test solution was dried, ground and heat-treated 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 oxide could be confirmed in any sample. In particular, in this test, the carboxylic acid molar ratio of 2: 1 to 8: In 1 sample Nanba3-2～nanba3-4, presence of NiFe ₂ O ₄ is confirmed, other than NiFe ₂ O ₄ The presence of the phase could not be substantially confirmed. In addition, NiFe ₂ O ₄ confirmed in samples No. 3-2 to No. 3-4 are all nano-powder having an average particle size of 80 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 metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. As shown in Table 3, the nanopowders composed of such NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 25 (emu / g) or more, coercivity 45 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, Sample No. 3-1 with a carboxylic acid molar ratio of 1: 1 and Sample No. 3-5 with a 14: 1 molar ratio of various materials such as Fe ₂ O ₃ , NiO, α-Fe, Ni Although there were particles, NiFe ₂ O ₄ could not be confirmed. 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 metal powder is too small, the oxidation reaction with water and the precipitation of metal carbonates such as iron carbonate will be dominant, resulting in the dissolution of metal powder and the binding reaction with free carbonic acid. Decrease, it becomes easy to generate coarse particles, oxides other than the desired composition (Fe ₂ O ₃ and NiO here) are easily generated, and α-Fe component and Ni are likely to remain. It is thought that it was because. 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 metal powder and the binding reaction with the free carbonic acid are reduced, and coarse particles are likely to be produced. This is probably because oxides (in this case, Fe ₂ O ₃ and NiO) other than the above composition are easily formed, and α-Fe components and Ni are likely to remain. From this, the number of moles of carboxylic acid in the mixed solution should be 10 times or less the number of moles of metal powder, preferably carboxylic acid: metal powder = 2: 1 to 8: 1. As a result of good production, it can be said that the metal oxide nanopowder can be mass-produced satisfactorily and stably.

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

  As the raw metal powder, 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 were prepared. Then, a liquid mixture was prepared in the same manner as in Test Example 1. 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 metal powder occurred in all samples. In particular, when the pH was 2 or more and 5 or less, the 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 will occur, inhibiting the dissolution of metal powder and the formation of metal carbonate complexes, and if the pH is too high, the dissolution of metal powder and the stability of metal carbonate complexes will be inhibited. Is inhibited.

  The obtained test solution was dried, ground and heat-treated 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 oxide could be confirmed in any sample. In particular, in this test, the presence of NiFe ₂ O ₄ was confirmed in Samples No. 4-2 and No. 4-3 in which the pH of the mixed solution was 2, 5, and the presence of phases other than NiFe ₂ O ₄ was confirmed. Virtually not confirmed. In addition, NiFe ₂ O ₄ confirmed in samples No. 4-2 and No. 4-3 are both nanopowder having an average particle size of 70 nm or less as shown in Table 4, and variation in particle size. And a uniform particle size distribution. As shown in Table 4, the nanopowders made of NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 30 (emu / g) or more, coercivity 50 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, Sample No. 4-1 in which the pH of the mixed solution is 1, and Sample No. 4-4 in which the pH is 10 include particles of various materials such as Fe ₂ O ₃ , NiO, α-Fe, and Ni. However, NiFe ₂ O ₄ could not be confirmed. 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 that if the pH is too low or too high, the dissolution of the metal is inhibited as described above, and coarse particles are likely to be generated, or an oxide other than the desired composition (here Fe ₂ O ₃ and NiO) are likely to be generated, and α-Fe component and Ni are likely to remain. From this fact, 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 produced satisfactorily, and as a result, the metal oxide 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 metal powder (carbonic acid mole ratio) was changed.

  As the raw metal powder, 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 were prepared. Then, a liquid mixture was prepared in the same manner as in Test Example 1. Except for changing the ratio between the number of moles of sodium hydrogen carbonate and the number of moles of metal powder in the mixed solution, the temperature of the mixed solution was set to 63 ° C., and under the same conditions as in Test Example 1, A test solution was prepared under a flow atmosphere. In this test, sodium hydrogen carbonate and 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, dissolution of metal powder occurred in any sample. If the number of moles of free carbonic acid source relative to the number of moles of metal powder is less than twice (in this case, the molar ratio of carbonic acid is 1: 1), precipitation of metal carbonates such as iron carbonate or water and metal powder in aqueous solution Oxidation reaction with is superior, the dissolution reactivity of the metal 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 becomes prominent Inferior to metal dissolution reactivity.

  The obtained test solution was dried, ground and heat-treated 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 oxide could be confirmed in any sample. In particular, in this study, the carbonate molar ratio of 2: 1 to 9: In 1 sample Nanba5-2～nanba5-4, confirmed the presence of the NiFe ₂ O ₄ is, NiFe ₂ O ₄ other phases The presence of was not substantially confirmed. In addition, NiFe ₂ O ₄ confirmed in samples No. 5-2 to No. 5-4 is a nano-powder having an average particle size of 120 nm or less as shown in Table 5, and the variation in particle size And a uniform particle size distribution. The reason for this is considered to be that the metal powder could be dissolved well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained. As shown in Table 5, the nanopowders composed of such NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 25 (emu / g) or more, coercivity 45 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, Sample No. 5-1 with a carbonic acid molar ratio of 1: 1, and Sample No. 5-5 with a 13: 1 carbonic acid molar ratio, particles of various materials such as Fe ₂ O ₃ , NiO, α-Fe, Ni However, NiFe ₂ O ₄ could not be confirmed. 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 generation source relative to the metal powder is too small or too large, the metal dissolution reactivity is lowered, and coarse particles are easily generated, or oxidation other than the desired composition is performed. This is thought to be because products (here, Fe ₂ O ₃ and NiO) are easily generated, and α-Fe components and Ni are likely to remain. From this, the number of moles of free carbonic acid generation source in the mixed solution should be 2 to 9 times the number of moles of metal powder, that is, the carbonic acid molar ratio should be carbonic acid: metal = 2: 1 to 9: 1. As a result, it can be said that the metal oxide 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.

As the raw metal powder, 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 were prepared. Then, a liquid mixture was prepared in the same manner as in Test Example 1. 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 metal powder occurred in all samples. When the Ar gas flow rate was 3 liters / min or more and 10 liters / min or less, the 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 staying in the solution reacts with the metal carbonate complex again to react with the carbonic acid. A precipitate of metal carbonate such as iron is formed, or formation of coarse metal oxide is finally promoted by formation of coarse metal carbonate.

  The obtained test solution was dried, ground and heat-treated 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 oxide could be confirmed in any sample. 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 NiFe ₂ O ₄ could be confirmed, and the presence of phases other than NiFe ₂ O ₄ could not be substantially confirmed. In addition, NiFe ₂ O ₄ confirmed in samples No. 6-2 to No. 6-4 is a nano-powder having an average particle size of 180 nm or less as shown in Table 6, and the variation in particle size And a uniform particle size distribution. As shown in Table 6, the nanopowders made of NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 30 (emu / g) or more, coercivity 40 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, in sample No. 6-1 with a reduced gas flow rate and sample No. 6-5 with an increased gas flow, particles of various materials such as Fe ₂ O ₃ , NiO, α-Fe, and Ni exist, but NiFe ₂ O ₄ could not be confirmed. 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. This is because, as described above, due to the presence of an unfavorable gas such as in the atmosphere, coarse particles are easily generated, or oxides other than the desired composition (Fe ₂ O ₃ and NiO in this case) are generated. This is thought to be because the α-Fe component and Ni are likely to remain. 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 producing the solution well, it can be said that the metal oxide nanopowder can be mass-produced satisfactorily and stably.

[Test Example 7]
In this test, the heat treatment conditions were changed.

  As the raw metal powder, 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 were prepared. Then, a liquid mixture was prepared in the same manner as in Test Example 1. 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 metal powder well and uniformly, and a uniform metal carbonate complex solution (precursor solution, sol) was obtained.

  The obtained test solution (precursor solution) was dried and pulverized in order under the same conditions as in Test Example 1, and then subjected to heat treatment under the conditions shown in Table 7. In this test, the atmosphere is air, the heating temperature is 250 ° C, 350 ° C, 520 ° C, 630 ° C, 800 ° C, and the holding time is 10 min, 20 min, 30 min, 1 h (60 min), 4 h (240 min), It was either 5h (300min). 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 7.

As a result of the crystal phase analysis, the presence of metal oxide could be confirmed in any sample. In particular, in this test, sample Nos. 7-7 to No. 7-10 and Nos. 7-13, in which the heat treatment conditions were a heating temperature of 300 ° C. to 630 ° C. and a holding time of 15 minutes to 4 hours. Nanba7-16, the Nanba7-19～nanba7-21 presence of NiFe ₂ O ₄ to check the presence of NiFe ₂ O ₄ other phases could not be confirmed substantially. In addition, as shown in Table 7, the NiFe ₂ O ₄ confirmed in these samples is a nanopowder having an average particle size of 160 nm or less, and also has a small variation in particle size and a uniform particle size distribution. Had. As shown in Table 7, the nanopowders made of NiFe ₂ O ₄ have both high saturation magnetization and coercivity (here, saturation magnetization is 25 (emu / g) or more, coercivity 45 (Oe) or more). It can be said that it can be suitably used as a raw material for magnetic members.

On the other hand, the heat treatment conditions were as follows: Sample No.7-1 to No.7-5, No.7-23 to No.7-27 with heating temperature less than 300 ° C or more than 630 ° C, holding time less than 15 minutes or For samples No. 7-6, No. 7-11, No. 7-12, No. 7-17, No. 7-18, No. 7-22 over 4 hours, Fe ₂ O ₃ , NiO, Although particles of various materials such as α-Fe, Ni, iron carbonate, nickel carbonate, iron hydroxide and nickel hydroxide exist, NiFe ₂ O ₄ could not be confirmed. More specifically, when the heating temperature during the heat treatment is too low or when the holding time is too short, the above-described various materials exist. In particular, when the heating temperature during heat treatment is less than 300 ° C., or when the heating temperature is low and the holding time is too short, metal carbonates and hydroxides are likely to be present. When the heating temperature during the heat treatment is too high or the holding time is too long, only metal oxides such as Fe ₂ O ₃ and NiO tend to exist. In addition, although there are samples in which particles of 200 nm or less exist, these samples 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 when the heating temperature during the heat treatment is too low or the holding time is too short, the above-mentioned carbonates and hydroxides are likely to remain because organic components and moisture cannot be sufficiently removed. This is probably because oxides (in this case, Fe ₂ O ₃ and NiO) other than the desired composition are likely to be generated due to these residues, and coarse particles are easily formed. When the heating temperature at the time of heat treatment is too high or when the holding time is too long, although organic components and moisture can be removed, it is considered that the particles easily grew to become coarse particles. From this, when performing heat treatment on the precursor solution, the heat treatment conditions are as follows: heating temperature is 300 ° C. or more and 630 ° C. or less (preferably 350 ° C. or more), holding time is 15 minutes or more (preferably 20 minutes or more) 4 hours By setting it as follows, it can be said that the metal oxide nanopowder can be mass-produced satisfactorily and stably from the precursor solution.

[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 metal powder material, and a sample with a different atmospheric gas Was made.

  As the raw material metal powder, the materials shown in Table 8 and those having an average particle diameter were prepared. Then, the production conditions of each sample were set as shown in Table 8, and powders were produced in the same procedure as in Test Example 1 (preparation of test solution → drying → heat treatment). The main differences from Test Example 1 are that sample No. 8-1 used malic acid as the carboxylic acid (mixture temperature 63 ° C), and sample No. 9-1 contained carbonic acid as a free carbonic acid source. Point using ammonium hydrogen (mixture temperature 76 ° C), sample No. 10-1 uses carbon dioxide gas as a free carbonic acid source, mixed solution of metal powder and citric acid aqueous solution (mixture temperature 70 ° C ), The point where the test solution was prepared while bubbling carbon dioxide gas (flow rate was 5 liters / min), sample No. 100 was used with oleic acid, and sample No. 200 was the atmosphere during preparation of the test solution. 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).

  Samples No. 11-1 to No. 16-1 are samples in which the material of the metal powder is different from that of Test Example 1. Here, in addition to reduced iron powder (Fe) and nickel powder (Ni) similar to Test Example 1, cobalt powder (pure cobalt powder, Co, average particle size 40 μm), zinc powder (pure zinc powder, Zn, average A particle size of 60 μm) and copper powder (pure copper powder, Cu, average particle size of 30 μm) were prepared. Sample No. 11-1 uses reduced iron powder and cobalt powder (mixing ratio is Fe: Co = 2: 1 in molar ratio), and sample No. 12-1 uses reduced iron powder and zinc powder. (Mixing ratio is Fe: Zn = 2: 1 in molar ratio), Sample No. 13-1 uses reduced iron powder, cobalt powder and zinc powder (Mixing ratio is Fe: Molar ratio: (Co: Zn = 2: 0.5: 0.5), Sample No. 14-1 uses reduced iron powder, nickel powder, and cobalt powder (mixing ratio is Fe: Ni: Co = 2: 0.5: 0.5 in molar ratio) In sample No. 15-1, nickel powder was used, and in sample No. 16-1, copper powder was used. As shown in Table 8, the temperature of the mixed solution is selected from 57 ° C to 74 ° C depending on the material, the flow rate of the atmospheric gas during preparation of the test solution is 6 liters / min or 3 liters / min, and the amount of oxygen is The mass ratio was selected from 43 ppm to 60 ppm. In any sample, the carboxylic acid molar ratio is selected from carboxylic acid: metal (herein, the total molar ratio of a plurality of metals, the same applies hereinafter) = 2: 1 to 5: 1, and the carbonic acid molar ratio is a free carbonic acid source. : Metal = selected from 2: 1 to 6: 1, pH was selected from 2 to 4 respectively.

  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 8 (temperature selected from 380 ° C. to 620 ° C. × For 30 min in the air). 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 8. Drying was performed at the following temperature, all samples were performed in the air, and the holding time was 2 hours. Sample No.8-1 is 175 ° C, Sample No.9-1 is 189 ° C, Sample No.10-1 is 150 ° C, Sample No.11-1 is 170 ° C, Sample No.12-1 is 164 ° C, Sample No.13-1 is 167 ° C, Sample No.14-1 is 163 ° C, Sample No.15-1 is 150 ° C, Sample No.16-1 is 140 ° C, Sample No.100, No.200 is 160 ° C. Samples No. 15-1 and No. 16-1 were not measured for magnetic properties.

As a result of the crystal phase analysis, the presence of metal oxide could be confirmed in any sample. In particular, in this test, citric acid and malic acid were used, and samples No. 8-1 to No. 16-1 in which the atmosphere at the time of preparing the precursor solution was an Ar flow atmosphere, NiFe ₂ O ₄ , CoFe ₂ The presence of spinel ferrite such as O ₄ , ZnFe ₂ O ₄ , Zn _0.5 Co _0.5 Fe ₂ O ₄ , Ni _0.5 Co _0.5 Fe ₂ O ₄ , NiO, Cu ₂ O can be confirmed. Other than spinel ferrite, NiO, Cu ₂ O The presence of the phase of this was not substantially confirmed. In addition, as shown in Table 8, the metal oxides confirmed in Samples No. 8-1 to No. 16-1 are all nanopowder having an average particle size of 85 nm or less, and there are also variations in particle size. It had a small and uniform particle size distribution. The reason for this is considered to be that the 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 spinel ferrite such as samples No. 8-1 to No. 14-1 has high saturation magnetization and coercive force as shown in Table 8, for example, saturation magnetization is 40 (emu / g) And a sample having a coercive force of 250 (Oe) or more can be suitably used as a raw material for a magnetic member. In addition, NiO nanopowder is used for, for example, glass and ceramic colorants, and Cu ₂ O is a p-type semiconductor. Therefore, Cu ₂ O nanopowder can be used for rectifiers and solar cell materials. Is done.

On the other hand, in sample No. 100 using oleic acid and sample No. 200 in which the atmosphere at the time of preparation of the test solution was an atmosphere with a large amount of oxygen, various materials such as Fe ₂ O ₃ , NiO, α-Fe, Ni were used. Although there were particles, spinel ferrite could not be confirmed. 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 for a dissolution reaction to reach the inside of the metal as in the case of using citric acid or malic acid. This is probably because oxides other than those (here, Fe ₂ O ₃ and NiO) are easily generated, and α-Fe components and Ni are easily left. By making the atmosphere with a large amount of oxygen, the oxidation reaction of metals and the like becomes dominant, so that the dissolution reactivity of the metal is reduced, coarse particles are easily generated, and oxides other than the desired composition (here, Fe ₂ This is probably because O ₃ ) is easily generated, and α-Fe component and Ni are likely to remain. 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 an inert gas atmosphere with an oxygen amount of 100 ppm or less by volume As a result, it can be said that the metal oxide 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 oxide powder of various materials can be manufactured by changing the material of the metal powder of a raw material and adjusting manufacturing conditions suitably. For example, when the heating temperature at the time of heat treatment is increased or the holding time is increased, an oxide having a large amount of oxygen can be generated.

  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 metal powder, the material of the free carbonic acid source, the material of the atmospheric gas, and the like can be appropriately changed.

  When the metal oxide powder of the present invention is a magnetic material, for example, 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 a thermal treatment. It can be suitably used as a raw material for a medical member such as a heating element. Moreover, the metal oxide powder of this invention can be utilized suitably for raw materials, such as a pigment, a coloring agent, a semiconductor member, for example. The manufacturing method of the metal oxide powder of this invention can be utilized suitably for manufacture of the said metal oxide powder of this invention.

Claims (5)

A solution preparation step of mixing a metal powder, a carboxylic acid solution, and a free carbonic acid source, and dissolving the metal powder in the carboxylic acid solution to prepare a precursor solution;
A drying step of drying the precursor solution and removing a carbonic acid component to obtain a dried body;
A separation step of applying heat treatment to the dried body to remove organic components in the dried body to produce a metal oxide powder ;
In the solution preparation step,
The average particle diameter of the metal powder is 1 μm or more and 100 μm or less,
The ratio between the number of moles of the free carbonic acid source and the number of moles of the metal powder is free carbonic acid source: metal = 2: 1 to 9: 1,
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 metal powder is carboxylic acid: metal = 2: 1 to 8: 1,
With an inert gas flow atmosphere in which the oxygen amount in the atmosphere is 100 ppm or less by volume, the flow rate of the inert gas is 3 liters / min to 10 liters / min,
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 a method for producing a metal oxide powder in which the heating temperature is 300 ° C. or higher and 630 ° C. or lower, and the holding time is 15 minutes or longer and 4 hours or shorter .   2. The metal oxide according to claim 1, wherein the metal powder is one metal powder selected from the group consisting of Fe, Co, Ni, Zn, Cu, Mn, and Cr, or two or more metal powders. Powder manufacturing method. The free carbon dioxide generating source, carbonated water, sodium carbonate, sodium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, potassium carbonate, and one selected from the group consisting of potassium bicarbonate, or two or more kinds according to claim 1 or 3. A method for producing the metal oxide powder according to claim 2 . The free carbon dioxide source is a type of gas, or two-component mixture gas selected Ri by carbonic gas及 beauty carbon monoxide gas,
3. The method for producing a metal oxide powder according to claim 1, wherein in the solution preparation step, the one kind of gas or the mixed gas is mixed by bubbling. 5. The metal oxidation 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. A method for producing powder.