JP7831009B2 - (Fe)-nickel (Ni) alloy powder, compacted powder or sheet containing the alloy powder, and inductors, reactors, choke coils, noise filters, transformers, rotating machines, generators, or radio wave absorbers equipped with the compacted powder or sheet. - Google Patents

Description

This invention relates to (Fe)-nickel (Ni) alloy powder, compacted powder or sheet containing the alloy powder, and inductors, reactors, choke coils, noise filters, transformers, rotating machines, generators, or radio wave absorbers equipped with the compacted powder or sheet.

Permalloy, an iron-nickel alloy, is a soft magnetic material with high magnetic permeability and is used as the magnetic core of magnetic components such as choke coils and inductors. In particular, iron-nickel alloy powder is used as a material for compacted cores (compressed magnetic cores) obtained by compression molding.

Various types of permalloy are known, such as 78 permalloy (Permalloy A) and 45 permalloy, and they are used differently depending on their magnetic properties and applications. 78 permalloy is an iron-nickel alloy with a nickel content of approximately 78.5% by mass and is characterized by its high magnetic permeability. 45 permalloy is an iron-nickel alloy with a nickel content of 45% by mass and, while having slightly lower magnetic permeability, is characterized by its high saturation magnetic flux density.

In recent years, mobile devices such as laptops and smartphones have become increasingly miniaturized and high-performance. Consequently, magnetic components such as inductors require not only improved magnetic properties but also the ability to handle higher frequencies. To achieve this, the material used for compacted powder cores needs to have both high magnetic flux density and reduced losses. These losses primarily consist of hysteresis loss and eddy current loss. To suppress hysteresis loss, lowering the coercivity of the alloy powder is effective. On the other hand, to suppress eddy current loss, applying a thin insulating coating to the particle surface of the alloy powder to reduce interparticle eddy currents, and making the alloy powder finer while also reducing the particle size distribution are effective. This is because the presence of coarse particles facilitates eddy current flow, leading to losses due to Joule heating.

Conventional methods for producing fine alloy powders include atomization, gas-phase reduction, and dry reduction. Atomization involves rapidly cooling and solidifying molten metal by blowing water or gas onto it. Gas-phase reduction involves hydrogen reduction of metal halides in a gaseous state. Dry reduction involves reducing metal oxides using a reducing agent.

For example, Patent Document 1 describes a Ni-Fe alloy powder used as a material for noise filters, choke coils, inductors, etc., which is manufactured by a vapor-phase reduction method (Patent Document 1, [0001] and [0014]). Patent Document 1 also discloses a method for producing fine Ni-Fe alloy powder by heating a mixture of _NiCl2 and _FeCl3 , and bringing the vaporized chloride into contact with hydrogen gas to cause a reduction reaction (Patent Document 1, [0016]). Patent Document 2 also describes a method for producing Fe-Ni alloy powder used as a material for electronic components such as choke coils and inductors, which is manufactured by reducing Fe and Ni oxides in a reducing gas (Patent Document 2, Claim 1).

On the other hand, methods for producing finer alloy powders using wet processes have been proposed. For example, Patent Document 3 discloses a method for producing nickel-iron alloy nanoparticles, characterized by adding a reducing agent such as hydrazine to an aqueous solution containing a nickel salt and an iron salt, thereby simultaneously reducing the nickel and iron ions contained in the aqueous solution to produce nickel-iron alloy nanoparticles (Claim 1-6 of Patent Document 3). Furthermore, this manufacturing method allows for the efficient production of nickel-iron alloy nanoparticles with an average primary particle size of 200 nm or less, suitable as fillers for imparting magnetic properties, on an industrial scale at low manufacturing cost ([0015] of Patent Document 3).

Japanese Patent Publication No. 2003-193160 Japanese Patent Publication No. 2012-197474 Japanese Patent Publication No. 2008-024961

Although methods for producing fine alloy powders using dry and wet processes have been proposed, conventional techniques still have room for improvement in obtaining alloy powders with superior powder properties. For example, alloy powders produced by atomization have a large average particle size of several micrometers or more, which does not adequately meet the requirements for finer powders. Furthermore, the gas-phase reduction method proposed in Patent Document 1 results in a wide particle size distribution of the resulting alloy powder. Therefore, the alloy powder contains coarse particles, which is insufficient for reducing eddy current losses. There is also the problem of unstable composition and particle size of the alloy powder. The dry reduction method proposed in Patent Document 2 requires high-temperature heating, which leads to the problem that the resulting alloy powder is prone to sintering and forming coarse aggregated particles.

The wet method proposed in Patent Document 3 differs from the dry method in that the reduction reaction proceeds at low temperatures, which has the advantage of making it less likely for coarse aggregated particles to form. Furthermore, even if aggregated particles are formed, the bonds between the particles are not strong, making it easy to break them down. However, the method proposed in Patent Document 3 requires the use of a large amount of hydrazine as a reducing agent. Therefore, the cost of the reducing agent increases significantly, making it impractical. Also, the particle size distribution of the resulting alloy powder was not sufficiently small.

The inventors conducted thorough research in light of these conventional problems. As a result, they discovered that by using specific nucleating agents and complexing agents in the production of iron-nickel alloy powders by a wet process, alloy powders with excellent powder properties and magnetic properties can be obtained. Furthermore, they found that when the iron content is high, adding a predetermined proportion of cobalt allows for the production of spherical alloy powders with low aggregation, smooth surfaces, and high saturation magnetic flux density, using a very small amount of reducing agent, due to the cobalt's reduction reaction-promoting and spheroidization-promoting effects.

This invention was completed based on such findings and aims to provide an iron-nickel alloy powder with excellent powder properties and magnetic properties, a compacted powder or sheet containing the alloy powder, and an inductor, reactor, choke coil, noise filter, transformer, rotating machine, generator, or radio wave absorber equipped with the compacted powder or sheet.

This invention encompasses the following embodiments (1) to (40). In this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" is synonymous with "X or greater and Y or less."

(1) A method for producing iron (Fe)-nickel (Ni) alloy powder containing at least iron (Fe) and nickel (Ni) as magnetic metals, wherein the method comprises the following steps:
Preparation process: Prepare a magnetic metal source, nucleating agent, complexing agent, reducing agent, and pH adjuster as starting materials.
The process comprises: preparing a reaction solution containing the starting materials and water; a crystallization step in which the crystallization powder containing the magnetic metal is crystallized by a reduction reaction in the reaction solution; and a recovery step in which the crystallization powder is recovered from the reaction solution.
The magnetic metal source includes a water-soluble iron salt and a water-soluble nickel salt.
The nucleating agent is a water-soluble salt of a metal nobler than nickel,
The complexing agent is at least one selected from the group consisting of hydroxycarboxylic acids, salts of hydroxycarboxylic acids, and derivatives of hydroxycarboxylic acids.
The reducing agent is hydrazine ( _{N₂H₄ )} ,
The method wherein the pH adjusting agent is alkali hydroxide.

(2) The method of (1) above, wherein the water-soluble iron salt is at least one selected from the group consisting of ferrous chloride ( _FeCl₂ ), ferrous sulfate ( _FeSO₄ ), and ferrous nitrate (Fe( _NO₃ ) _₂ ).

(3) The method of (1) or (2) above, wherein the water-soluble nickel salt is at least one selected from the group consisting of nickel chloride ( _NiCl₂ ), nickel sulfate ( _NiSO₄ ), and nickel nitrate (Ni( _NO₃ ) _₂ ).

(4) The nucleating agent is at least one selected from the group consisting of copper salts, palladium salts, and platinum salts, according to any of the methods (1) to (3) above.

(5) The method according to _{any of (1) to (4) above, wherein the complexing agent is at least one hydroxycarboxylic acid selected from tartaric acid ((CH(OH)COOH)2 ) and} citric acid (C(OH)(CH2COOH)2COOH).

(6) The pH adjusting agent is at least one selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH), according to any of the methods (1) to (5) above.

(7) The magnetic metal further contains cobalt (Co),
The method according to any one of (1) to (6) above, wherein the magnetic metal source further comprises a water-soluble cobalt salt.

(8) The magnetic metal wherein the iron (Fe) content is 60 mol% or more and 85 mol% or less, and the cobalt (Co) content is 10 mol% or more and 30 mol% or less,
The method of (7) above, wherein the magnetic metal source contains 60 mol% or more and 85 mol% or less of water-soluble iron salt, and contains 10 mol% or more and 30 mol% or less of water-soluble cobalt salt.

(9) The method of (7) or (8) above, wherein the water-soluble cobalt salt is at least one selected from the group consisting of cobalt chloride ( _CoCl₂ ), cobalt sulfate ( _CoSO₄ ), and cobalt nitrate (Co( _NO₃ ) _₂ ).

(10) The method according to any of (1) to (9) above, wherein the starting material further comprises an amine compound containing two or more primary amino groups ( _-NH2 ), one primary amino group ( _-NH2 ) and one or more secondary amino groups (-NH-), or two or more secondary amino groups (-NH-) in its molecule.

(11) The method of (10) above, wherein the amine compound is at least one alkyleneamine and an alkyleneamine derivative.

(12) The method of (11), wherein the alkyleneamine and/or alkyleneamine derivative has at least the structure represented by (A) below, in which the nitrogen atom of the amino group in the molecule is bonded via a carbon chain having 2 carbon atoms.

(13) The amine compound is at least one alkyleneamine _selected from the group _consisting of _{ethylenediamine} ( _{H₂NC₂H₄NH₂} ), diethylenetriamine ( _{H₂NC₂H₄NHC₂H₄NH₂} ) _{, triethylenetetramine (H₂N(C₂H₄NH)₂C₂H₄NH₂), tetraethylenepentamine (H₂N(C₂H₄NH)₃C₂H₄NH₂ ) , pentaethylenehexamine ( H₂N ( C₂H₄NH ) ₄C₂H₄NH₂ ) , and propylenediamine ( CH₃CH ( NH₂ ) CH₂NH₂ ) ,} and/or _{tris ( 2 - aminoethyl} )amine _{( N ( C₂ The method according to} any one of ₍ 10) to ( _{12) above, wherein the alkyleneamine derivative is selected from the group consisting of H₄NH₂)₃ ) , N- ( 2 -} aminoethyl)ethanolamine ( _{H₂NC₂H₄NHC₂H₄OH} ), N-(2- _aminoethyl )propanolamine _{( H₂NC₂H₄NHC₃H₆OH} ), 2,3-diaminopropionic acid ( _H₂NCH₂CH (NH ₎ COOH), ethylenediamine-N, _{N' -} diacetic acid ( _{HOOCCH₂NHC₂H₄NHCH₂COOH} ), and 1,2-cyclohexanediamine ₍ H₂NC₆H₁₀NH₂).

(14) Any of the methods (10) to (13) above, wherein the amount of the amine compound relative to the total amount of the magnetic metal is 0.01 mol% or more and 5.00 mol% or less.

(15) When preparing the reaction solution in the crystallization step, one of the methods (1) to (14) above is used, wherein a metal salt raw material solution is prepared by dissolving the magnetic metal source, the nucleating agent, and the complexing agent in water, a reducing agent solution is prepared by dissolving the reducing agent in water, and a pH adjusting solution is prepared by dissolving the pH adjusting agent in water; the metal salt raw material solution and the pH adjusting solution are mixed to form a mixed solution; and the mixed solution is then mixed with the reducing agent solution.

(16) The method of (15) above, wherein when preparing the reaction solution, the pH adjusting solution and the reducing agent solution are sequentially added to the metal salt raw material solution and mixed.

(17) The method of (15) or (16) above, wherein the time required for mixing the mixed solution and the reducing agent solution is 1 second or more and 180 seconds or less.

(18) Any of the methods (1) to (14) above, wherein when preparing the reaction solution in the crystallization step, a metal salt raw material solution is prepared by dissolving the magnetic metal source, the nucleating agent, and the complexing agent in water, and a reducing agent solution is prepared by dissolving the reducing agent and the pH adjusting agent in water, and the metal salt raw material solution and the reducing agent solution are mixed.

(19) The method of (18) above, wherein when preparing the reaction solution, the reducing agent solution is added to the metal salt raw material solution, or conversely, the metal salt raw material solution is added to the reducing agent solution and mixed.

(20) The method of (18) or (19) above, wherein the time required for mixing the metal salt raw material solution and the reducing agent solution is 1 second or more and 180 seconds or less.

(21) Any of the methods (1) to (20) above, wherein, in the crystallization step, before the reduction reaction is completed, an additional raw material solution, in which at least one of the water-soluble nickel salt and the water-soluble cobalt salt is dissolved in water, is further added to the reaction solution and mixed.

(22) Any method (15) to (21) above, wherein an amine compound is incorporated into at least one of the metal salt raw material solution, the reducing agent solution, the pH adjusting solution, and the reaction solution.

(23) Any of the methods described in (1) to (22) above, wherein the temperature of the reaction solution at the start of crystallization of the crystallizing powder (reaction start temperature) is 40°C or higher and 90°C or lower, and the temperature of the reaction solution maintained during crystallization after the start of crystallization (reaction maintenance temperature) is 60°C or higher and 99°C or lower.

(24) Any method (1) to (23) above, further comprising a crushing step in which the crystallized powder after the recovery step or the crystallized powder during the recovery step is subjected to a crushing treatment using impact energy to crush the aggregated particles contained in the crystallized powder.

(25) The method of (24) above, wherein the crushing of the crystallized powder after the recovery process is performed by dry crushing or wet crushing, or the crushing of the crystallized powder during the recovery process is performed by wet crushing.

(26) The method of (25) above, wherein the dry crushing is spiral jet crushing.

(27) The method of (25) above, wherein the wet crushing is high-pressure fluid impingement crushing.

(28) Any method (1) to (27) above, further comprising a high-temperature heat treatment step in which the crystallized powder after the recovery step or the crystallized powder during the recovery step is subjected to a heat treatment at a temperature greater than 150°C and less than or equal to 400°C in an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere, thereby improving the compositional uniformity within the particles of the iron (Fe)-nickel (Ni) alloy powder.

(29) Any method (1) to (28) above, further comprising an insulating coating step, in which the crystallized powder obtained through the recovery step is subjected to an insulating coating treatment to form an insulating coating layer made of a metal oxide on the particle surface of the crystallized powder, thereby improving the insulating properties between particles.

(30) The method of (29) above, wherein, during the insulating coating step, crystallized powder is dispersed in a mixed solvent containing water and an organic solvent, a metal alkoxide is further added to the mixed solvent and mixed to prepare a slurry, the metal alkoxide is hydrolyzed and dehydrated condensation polymerized in the slurry to form an insulating coating layer made of a metal oxide on the particle surface of the crystallized powder, and then the crystallized powder with the insulating coating layer formed is recovered from the slurry.

(31) The method of (30) above, wherein the metal alkoxide mainly consists of silicon alkoxide (alkyl silicate) and the metal oxide mainly consists of silicon dioxide ( _SiO₂ ).

(32) The method of (30) or (31) above, wherein the hydrolysis of the metal alkoxide is carried out in the presence of a base catalyst (alkaline catalyst).

(33) Iron (Fe)-nickel (Ni) alloy powder manufactured by any of the methods described in (1) to (32) above.

(34) An iron (Fe)-nickel (Ni) alloy powder containing at least iron (Fe) and nickel (Ni) as magnetic metals, wherein the average particle size is 0.10 μm or more and 0.60 μm or less, and the coefficient of variation (CV value) obtained from the average particle size and standard deviation in the number particle size distribution according to the following formula (1) is 25% or less.

(35) The alloy powder of (34) further comprising cobalt (Co) as a magnetic metal.

(36) The alloy powder according to (34) or (35) above, wherein the iron (Fe) content is 10 mol% or more and 95 mol% or less, the nickel (Ni) content is 5 mol% or more and 90 mol% or less, and the cobalt (Co) content is 0 mol% or more and 40 mol% or less.

(37) The alloy powder of (34) or (35) above, having a crystallite size of 30 nm or less.

(38) The alloy powder according to (34) or (35) above, having a saturation magnetic flux density of 1 T (Tesla) or more and a coercivity of 2000 A/m or less.

(39) A compacted powder or sheet containing any of the alloy powders described in (33) to (38) above.

(40) An inductor, reactor, choke coil, noise filter, transformer, rotating machine, generator, or radio wave absorber comprising the compacted powder and/or sheet described in (39) above.

According to the present invention, an iron-nickel alloy powder exhibiting excellent powder properties and magnetic properties, a compacted powder or sheet containing the alloy powder, and an inductor, reactor, choke coil, noise filter, transformer, rotating machine, generator, or radio wave absorber equipped with the compacted powder or sheet are provided.

This is a process diagram illustrating the method for manufacturing the alloy powder according to this embodiment. This is a process diagram illustrating the preparation of the reaction solution and the production of the alloy powder in the first embodiment. This is a process diagram illustrating the preparation of the reaction solution and the production of the alloy powder in the first embodiment. This is a process diagram illustrating the preparation of the reaction solution and the production of the alloy powder in the second embodiment. This is a process diagram illustrating the preparation of the reaction solution and the production of the alloy powder in the second embodiment. This is a process diagram illustrating the preparation of the reaction solution and the production of the alloy powder in the third embodiment. This shows an example of applying a compacted powder containing alloy powder to an inductor (toroidal coil). This shows an example of applying a compacted powder containing alloy powder to a chip inductor. This shows an example of applying a compacted powder containing alloy powder to a reactor. This example shows the application of compacted powder containing alloy powder to the stators of rotating machinery (motors) and generators. This example shows the application of compacted powder containing alloy powder to the rotors of rotating machinery (motors) and generators. This figure shows the change in liquid temperature inside the reaction vessel during the crystallization process in Example 1. This is an SEM image of the alloy powder obtained in Example 1. This is an SEM image of the alloy powder obtained in Example 2. This is an SEM image of the alloy powder obtained in Example 6 (before and after spiral jet crushing treatment). These are STEM images and EDS line analysis results of the alloy powder obtained in Example 8 (before and after high-temperature heat treatment). These are the zSTEM image of the particle cross-section of the alloy powder obtained in Example 9, and the results of EDS line analysis. This is an SEM image of the alloy powder obtained in Example 10. This is an SEM image of the alloy powder obtained in Example 12 (before and after insulating coating treatment). This is an SEM image of the alloy powder obtained in Example 13. This is an SEM image of the alloy powder obtained in Example 14. This is an SEM image of the alloy powder obtained in Comparative Example 1. This is an SEM image of the alloy powder obtained in Comparative Example 2. This is an SEM image of the alloy powder obtained in Comparative Example 3.

Specific embodiments of the present invention (hereinafter referred to as "these embodiments") will be described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention.

<<1. Method for manufacturing iron-nickel alloy powder>>
The method for producing iron (Fe)-nickel (Ni) alloy powder according to this embodiment comprises the following steps: a preparation step of preparing starting materials including a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjusting agent; a crystallization step of preparing a reaction solution containing these starting materials and water, and crystallizing the crystallized powder containing the magnetic metal in this reaction solution by a reduction reaction; and a recovery step of recovering the crystallized powder from the obtained reaction solution. Here, the iron (Fe)-nickel (Ni) alloy powder contains at least iron (Fe) and nickel (Ni) as magnetic metals. The magnetic metal source includes a water-soluble iron salt and a water-soluble nickel salt. The nucleating agent is a water-soluble salt of a metal nobler than nickel. The complexing agent is at least one selected from the group consisting of hydroxycarboxylic acids, salts of hydroxycarboxylic acids, and derivatives of hydroxycarboxylic acids. The reducing agent is _hydrazine ( _N₂H₄ ).

The iron (Fe)-nickel (Ni) alloy powder of this embodiment (hereinafter sometimes simply referred to as "alloy powder") contains at least iron (Fe) and nickel (Ni). The alloy powder may also contain cobalt (Co) as needed. That is, the alloy powder may be an iron-nickel alloy powder containing only iron and nickel, or an iron-nickel-cobalt alloy powder containing iron, nickel, and cobalt. Iron, nickel, and cobalt are all ferromagnetic magnetic metals. Therefore, iron-nickel alloy powders and iron-nickel-cobalt alloy powders have high saturation magnetic flux densities and excellent magnetic properties. In this specification, "magnetic metal" is a general term for iron, nickel, and cobalt. That is, if the alloy does not contain cobalt, "magnetic metal" is a general term for iron and nickel; if the alloy contains cobalt, it is a general term for iron, nickel, and cobalt.

The proportions of iron (Fe), nickel (Ni), and cobalt (Co) contained in the alloy powder of this embodiment are not particularly limited. The amount of iron may be 10 mol% to 95 mol%, 25 mol% to 90 mol%, or 40 mol% to 80 mol%. The amount of nickel may be 5 mol% to 90 mol%, 10 mol% to 75 mol%, or 20 mol% to 60 mol%. The amount of cobalt may be 0 mol% to 40 mol%, or 5 mol% to 20 mol%. However, the total amount of iron, nickel, and cobalt is 100 mol% or less.

The alloy powder of this embodiment does not exclude the inclusion of additive components other than magnetic metals (Fe, Ni, and Co). Examples of such additive components include copper (Cu) and/or boron (B). However, in order to maximize the effects based on magnetic metals, it is preferable that the content of additive components other than magnetic metals be as low as possible. The content of other components other than magnetic metals may be 10% by mass or less, 5% by mass or less, 1% by mass or less, or even 0% by mass. Furthermore, the alloy powder may contain impurities that are inevitably mixed in during the manufacturing process (unavoidable impurities). Examples of such unavoidable impurities include oxygen (O), carbon (C), chlorine (Cl), and alkaline components (Na, K, etc.). Since unavoidable impurities may cause deterioration of the properties of the alloy powder, it is preferable to minimize their amount as much as possible. For oxygen (O) contained in the oxide film that is always formed on the surface of the alloy powder, the amount of unavoidable impurities is preferably 5% by mass or less, and more preferably 3% by mass or less. On the other hand, the amounts of carbon (C), chlorine (Cl), and alkali components (Na, K, etc.) are preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The alloy powder may have a composition that includes a magnetic metal and the remainder consists of unavoidable impurities.

The alloy powder manufacturing method of this embodiment comprises at least a preparation step, a crystallization step, and a recovery step. Furthermore, a crushing step, a high-temperature heat treatment step, or an insulating coating step may be added after or during the recovery step, as needed. Figure 1 schematically shows an example of the process in the manufacturing method of this embodiment. While Figure 1 shows the crushing, high-temperature heat treatment, and insulating coating processes, these processes are optional and not mandatory. Also, when performing the crushing, high-temperature heat treatment, and/or insulating coating processes, there are no particular restrictions on the order in which these processes are carried out. If anything, it is preferable to perform the crushing process after the high-temperature heat treatment, because this reduces or eliminates the bonding (connection) between alloy particles strengthened by the high-temperature heat treatment. It is also preferable to perform the crushing process before the insulating coating, because this allows for a uniform insulating coating across the entire surface of each alloy particle whose bonding has been reduced or eliminated. In contrast, if the alloy particles are still bonded, an insulating coating layer will not be formed on the bonded areas. Therefore, it is preferable to reduce or eliminate the bonding as much as possible before the insulating coating process. Details of each step are described below.

<Preparation process>
In the preparation process, a magnetic metal source, nucleating agent, complexing agent, reducing agent, and pH adjuster are prepared as starting materials. The magnetic metal source consists of iron and nickel, but cobalt may be included as needed. Amine compounds may also be included in the starting materials. Each of the starting materials is described below.

(a) Magnetic metal source The magnetic metal source is a raw material for magnetic metals and includes at least a water-soluble iron salt and a water-soluble nickel salt. The iron salt is a raw material (iron source) for the iron component contained in the alloy powder and is not particularly limited as long as it is a readily water-soluble iron salt. Examples of iron salts include ferric chloride, ferric sulfate, ferric nitrate, or mixtures thereof, containing divalent and/or trivalent iron ions. The water-soluble iron salt is preferably at least one selected from the group consisting of ferrous chloride ( _FeCl₂ ), ferrous sulfate ( _FeSO₄ ), and ferrous nitrate (Fe( _NO₃ ) _₂ ). The nickel salt is a raw material (nickel source) for the nickel component contained in the alloy powder and is not particularly limited as long as it is a readily water-soluble nickel salt. The water-soluble nickel salt is preferably at least one selected from the group consisting of nickel chloride ( _NiCl₂ ), nickel sulfate ( _NiSO₄ ), and nickel nitrate (Ni( _NO₃ ) _₂ ), and particularly preferably at least one selected from the group consisting of nickel chloride ( _NiCl₂ ) and nickel sulfate ( _NiSO₄ ).

If necessary, the magnetic metal may further contain cobalt (Co), and the magnetic metal source may further contain a water-soluble cobalt salt. This makes it possible to manufacture iron-nickel-cobalt alloy powder. Iron-nickel-cobalt alloy powder, in which some of the iron and nickel are replaced with cobalt, is particularly characterized by a high saturation magnetic flux density.

Water-soluble cobalt salts have a reduction-promoting effect during the crystallization of alloy powders, and this effect becomes particularly pronounced when the iron (Fe) content in the magnetic metal is high, at 60 mol% or more. Furthermore, water-soluble cobalt salts also have a spheroidizing effect, transforming the alloy powder into smooth, spherical particles. Therefore, by setting the content of water-soluble iron salts to 60 mol% to 85 mol% and the content of water-soluble cobalt salts to 10 mol% to 30 mol% in the magnetic metal source, it is possible to obtain an iron-nickel-cobalt alloy powder with an extremely high saturation magnetic flux density (e.g., 2 T (Tesla) or more) and smooth, spherical surfaces, even with a very small amount of hydrazine used as a reducing agent. This alloy powder, for example, has an iron content of 60 mol% to 85 mol% and a cobalt content of 10 mol% to 30 mol%.

The water-soluble cobalt salt is not particularly limited as long as it is a readily water-soluble cobalt salt. Preferably, the water-soluble cobalt salt is at least one selected from the group consisting of cobalt chloride ( _CoCl₂ ), cobalt sulfate ( _CoSO₄ ), and cobalt nitrate (Co( _NO₃ ) _₂ ), and particularly preferably at least one selected from the group consisting of cobalt chloride ( _CoCl₂ ) and cobalt sulfate ( _CoSO₄ ).

(b) Nucleating agent The nucleating agent is a water-soluble salt of a metal nobler than nickel. This nucleating agent (water-soluble salt of a metal nobler than nickel) is preferentially reduced in the reaction solution during the subsequent crystallization step to generate initial nuclei, which promote the precipitation of crystallized powder. Here, a metal nobler than nickel is a metal whose potential in the standard potential series is higher than that of nickel in aqueous solution. A metal nobler than nickel can also be said to be a metal with a lower ionization tendency than nickel. Examples of such metals include tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), copper (Cu), silver (Ag), palladium (Pd), iridium (Ir), platinum (Pt), and gold (Au).

By using a water-soluble salt of a metal nobler than nickel as a nucleating agent, the formation of crystallized powder in the reaction solution during the subsequent crystallization process can be controlled. For example, increasing the amount of nucleating agent added can produce finer crystallized powder. In other words, during the crystallization process, ions and complex ions of magnetic metals contained in the reaction solution are reduced and precipitated, forming crystallized powder. Among magnetic metals, nickel has a nobler property than iron and cobalt, and its ionization tendency is low. Therefore, if a water-soluble salt of a metal nobler than nickel (nucleating agent) is included in the reaction solution, the metal nobler than nickel will be reduced and precipitated before all other magnetic metals. The precipitated metal nobler than nickel acts as an initial nucleus, and these initial nuclei grow to form crystallized powder composed of magnetic metals. Therefore, the particle size of the crystallized powder can be controlled by the amount of nucleating agent added, which determines the number of initial nuclei.

The nucleating agent is not particularly limited, as long as it is a water-soluble salt of a metal nobler than nickel. However, the nucleating agent is preferably at least one selected from the group consisting of copper salts, palladium salts, and platinum salts. Copper (Cu), palladium (Pd), and platinum (Pt) have particularly strong noble properties and low ionization tendencies. Therefore, they are particularly effective as nucleating agents. Examples of water-soluble copper salts, though not limited, include copper sulfate. Examples of water-soluble palladium salts, though not limited, include sodium palladium(II) chloride, ammonium palladium(II) chloride, palladium(II) nitrate, and palladium(II) sulfate. The nucleating agent is particularly preferably a palladium salt. Using a palladium salt makes it possible to control the particle size of the crystallized powder (alloy powder) to an even finer degree.

The amount of nucleating agent should be adjusted so that the particle size of the final alloy powder reaches the desired value. For example, the amount of nucleating agent relative to the total amount of magnetic metal may be between 0.001 mol ppm and 5.0 mol ppm, or between 0.005 mol ppm and 2.0 mol ppm. By setting the amount of nucleating agent within this range, alloy powder with an average particle size of 0.2 μm to 0.6 μm can be obtained. However, the amount of nucleating agent is not limited to the above range. For example, when producing fine alloy powder with an average particle size of less than 0.2 μm, the amount of nucleating agent should be set to more than 5.0 mol ppm.

(c) Complexing agent The complexing agent is at least one selected from the group consisting of hydroxycarboxylic acids, salts of hydroxycarboxylic acids, and derivatives of hydroxycarboxylic acids. This complexing agent (hydroxycarboxylic acid, etc.) has the effect of homogenizing the reaction in the subsequent crystallization step. That is, the magnetic metal component is dissolved in the reaction solution as magnetic metal ions ( ^Fe²⁺ , ^Ni²⁺ , etc.), but because the reaction solution becomes strongly alkaline due to the pH adjusting agent (NaOH, etc.), the amount of magnetic metal ions dissolved in the reaction solution is extremely small. However, in the presence of a complexing agent, the magnetic metal component can dissolve in larger quantities as complex ions (Fe complex ions, Ni complex ions, etc.). The presence of such complex ions increases the reduction reaction rate and suppresses the localized uneven distribution of magnetic metal components, making it possible to homogenize the reaction system. The complexing agent also has the effect of changing the balance of complex stability of multiple magnetic metal ions in the reaction solution. Therefore, in the presence of a complexing agent, the reduction reaction of the magnetic metal changes, and the balance between the nucleation rate and the grain growth rate changes. By using the complexing agent (such as a hydroxycarboxylic acid) specified in this embodiment, the above-mentioned effects work together in combination, and the reaction proceeds in a favorable direction, resulting in improved powder properties (particle size, particle size distribution, sphericity, and particle surface properties) of the resulting alloy powder. Furthermore, alloy powder with improved powder properties has excellent packing properties and is suitable as a raw material for compacted cores. In this respect, the complexing agent (such as a hydroxycarboxylic acid) of this embodiment can be said to have the functions of a reduction reaction accelerator, a sphericization accelerator, and a surface smoothing agent. A suitable complexing agent includes at least one hydroxycarboxylic acid selected from tartaric acid ((CH(OH)COOH) _₂ ) and citric acid (C(OH)( _CH₂COOH ) _₂COOH ).

The amount of complexing agent relative to the total amount of magnetic metal is preferably 5 mol% to 100 mol%, more preferably 10 mol% to 75 mol%, and even more preferably 15 mol% to 50 mol%. When the amount is 5 mol% or more, the functions of the complexing agent as a reduction reaction accelerator, spheroidization accelerator, and surface smoothing agent are fully exhibited, resulting in even better powder properties of the alloy powder (particle size, particle size distribution, spheroidity, and particle surface properties). Furthermore, when the amount is 100 mol% or less, the amount of complexing agent used can be reduced without significantly affecting the degree of complexing agent function, leading to reduced manufacturing costs.

(d) Reducing agent The reducing agent is hydrazine ( _N₂H₄ , molecular weight: 32.05). This reducing agent (hydrazine) has the effect of reducing _magnetic metal ions and complex ions in the reaction solution during the subsequent crystallization step. Hydrazine has the advantage of having strong reducing power and not generating by-products in the reaction solution as a result of the reduction reaction. In addition, it is easy to obtain high-purity hydrazine with few impurities.

In addition to anhydrous hydrazine, hydrated hydrazine ( _N₂H₄ · _H₂O , molecular weight: 50.06) _, which is hydrazine hydrate, is also known. Either can be used. As hydrated hydrazine, for example, commercially available industrial grade 60% by mass hydrated hydrazine can be used.

The amount of reducing agent required depends largely on the composition of the iron (Fe)-nickel (Ni) alloy powder; the higher the proportion of iron, which is difficult to reduce, the more reducing agent is needed. In addition to the composition of the alloy powder, the amount of reducing agent is also affected by the temperature of the reaction solution, as well as the amount of complexing agents and pH adjusters added. For example, if the iron content of the iron-nickel alloy powder is 60 mol% or less, the amount of reducing agent relative to the total amount of magnetic metal is preferably 1.8 to 7.0 in molar ratio, more preferably 2.0 to 6.0, and even more preferably 2.5 to 5.0. If the iron content of the iron-nickel alloy powder exceeds 60 mol% but is 75 mol% or less, the amount of reducing agent relative to the total amount of magnetic metal is preferably 2.5 to 9.0 in molar ratio, and more preferably 3.5 to 8.0. If the iron content of the iron-nickel alloy powder exceeds 75 mol% but is 95 mol% or less, the amount of reducing agent relative to the total amount of magnetic metal is preferably 3.5 to 10.0 in molar ratio, and more preferably 4.5 to 9.0. On the other hand, when manufacturing iron-nickel-cobalt alloy powder, the amount of reducing agent can be significantly reduced compared to iron-nickel alloy powder due to the action of the water-soluble cobalt salt mentioned above. The effect of the water-soluble cobalt salt is particularly pronounced when manufacturing alloy powders with a high iron content. For example, when manufacturing alloy powder with an iron content of 60 mol% to 85 mol% and a cobalt (Co) content of 10 mol% to 30 mol%, the amount of reducing agent relative to the total amount of magnetic metal is preferably 1.0 to 4.0 in molar ratio, and more preferably 1.2 to 2.0.

In either case, if the blending amount is above the lower limit mentioned above, the reduction of magnetic metal ions and complex ions proceeds sufficiently, and a crystallized powder (alloy powder) free from unreduced substances such as iron hydroxide can be obtained. Furthermore, if the blending amount is below the upper limit mentioned above, the amount of reducing agent (hydrazine) used can be reduced, leading to a reduction in manufacturing costs.

(e) pH adjuster The pH adjuster is alkali hydroxide. This pH adjuster (alkali hydroxide) has the effect of strengthening the reduction reaction of hydrazine, which is a reducing agent. That is, the higher the pH of the reaction solution, the stronger the reducing power of hydrazine. Therefore, by using alkali hydroxide as a pH adjuster, the reduction reaction of magnetic metal ions and complex ions in the reaction solution, and the precipitation of crystallized powder that accompanies it are promoted. The type of alkali hydroxide is not particularly limited. However, in terms of availability and cost, it is preferable that the pH adjuster contains at least one selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH).

The amount of pH adjuster (alkali hydroxide) should be adjusted so that the reducing power of the reducing agent (hydrazine) is sufficiently high. Specifically, the pH of the reaction solution at the reaction temperature is preferably 9.5 or higher, more preferably 10 or higher, and even more preferably 10.5 or higher. Therefore, the amount of alkali hydroxide should be adjusted so that the pH falls within this range.

(f) Amine compound If necessary, the starting material may further contain an amine compound. This amine compound contains two or more primary amino groups ( _-NH₂ ), one primary amino group ( _-NH₂ ) and one or more secondary amino groups (-NH-), or two or more secondary amino groups (-NH-) in its molecule.

Amine compounds have the effect of promoting the reduction reaction in the subsequent crystallization step. In other words, amine compounds function as complexing agents, complexing magnetic metal ions ( ^Fe²⁺ , ^Ni²⁺ , etc.) in the reaction solution to form complex ions (Fe complex ions, Ni complex ions, etc.). As a result of the presence of complex ions in the reaction solution, the reduction reaction is thought to proceed even further.

Furthermore, amine compounds have the effect of suppressing the self-decomposition of hydrazine, which is a reducing agent. That is, when crystallized powder made of magnetic metal precipitates in the reaction solution, the nickel (Ni) in this magnetic metal acts as a catalyst, which can cause hydrazine to decompose. This is called the self-decomposition of hydrazine. As shown in equation (1) below, this decomposition reaction is in which hydrazine ( _N₂H₄ ) decomposes into nitrogen ( _N₂ ) and ammonia ( _NH₃ ). Such self-decomposition _is undesirable because it impairs the function of hydrazine as a reducing agent.

Adding an amine compound to the reaction solution can suppress the autodecomposition of hydrazine. Although the detailed mechanism is unknown, it is speculated that this is because excessive contact between the hydrazine in the reaction solution and the crystallizing powder is prevented. Specifically, among the amino groups contained in the amine compound molecule, primary amino groups ( _-NH₂ ) and secondary amino groups (-NH-) are strongly adsorbed to the surface of the crystallizing powder in the reaction solution. It is thought that the amine compound molecule covers and protects the crystallizing powder, preventing excessive contact between the hydrazine molecule and the crystallizing powder, thereby suppressing the autodecomposition of hydrazine. Since the autodecomposition of hydrazine becomes more pronounced when the nickel content in the magnetic metal is high, the amine compound is particularly effective in such cases.

The amine compound is preferably at least one alkyleneamine and/or alkyleneamine derivative. Furthermore, the alkyleneamine and/or alkyleneamine derivative is preferably one having at least the structure represented by (A) below, in which the nitrogen atom of the amino group within the molecule is bonded via a carbon chain with two carbon atoms.

By using alkyleneamines or alkyleneamine derivatives as amine compounds, the effect of suppressing the self-decomposition of hydrazine (a reducing agent) can be made even more effective. This is thought to be because the short carbon chains contained in these alkyleneamines and alkyleneamine derivatives effectively suppress contact between the hydrazine molecule and the crystallization powder. In contrast, when the nitrogen atom of the amino group is bonded via an excessively long carbon chain, even if this amino group is adsorbed onto the crystallization powder, the carbon chain has a greater degree of freedom of movement. Therefore, it is speculated that contact between the crystallization powder and the hydrazine molecule is not effectively hindered.

Specific examples of alkyleneamines having the structure shown in ( _A ) above _are ethylenediamine (abbreviated as _EDA ) ( _{H₂NC₂H₄NH₂} ), diethylenetriamine (abbreviated as _DETA ) ( _{H₂NC₂H₄NHC₂H₄NH₂} ), triethylenetetramine (abbreviated as TETA) _{( H₂N ( C₂H₄NH ) ₂C₂H₄NH₂} ), tetraethylenepentamine (abbreviated as _TEPA ) _{( H₂N ( C₂H₄NH} ) _{₃C₂H₄NH₂} ), _{and pentaethylenehexamine} ( _{abbreviated as PEHA} ) _{( H₂N ( C₂H₄NH ) ₄C₂H₄NH₂ ) .} It is one or more selected from the group consisting of ), propylenediamine (also known as 1,2-diaminopropane, 1,2-propanediamine) (abbreviation: PDA) ( _CH3CH ( _NH2 ) _{CH2NH2 )} . Furthermore, specific examples _{of alkyleneamine derivatives having the structure represented in (A) above include tris(2-aminoethyl)amine (abbreviation: TAEA) (N(C2H4NH2)3 ) , N-} (2-aminoethyl)ethanolamine (also known as 2-(2-aminoethylamino)ethanol (abbreviation: _AEEA ) _{( H2NC2H4NHC2H4OH} ), N-( ₂ - _aminoethyl )propanolamine (also known as 2-( ₂ -aminoethylamino)propanol (abbreviation: AEPA) ( _{H2NC2H4NHC3H6OH} ), L(or _D , _DL ) _-2,3 -diaminopropionic acid (also known as 3-amino-L(or D,DL)-alanine) (abbreviation: DAPA) ( _{H2NCH2 )} It is one or more selected from CH(NH)COOH), ethylenediamine-N,N'-diacetic acid (also known as ethylene- _N , _N' -diglycine) (abbreviated as EDDA) ( _{HOOCCH₂NHC₂H₄NHCH₂COOH} ), and 1,2- _{cyclohexanediamine} (also known as _1,2 - _{diaminocyclohexane} ) (abbreviated as CHDA) ( _{H₂NC₆H₁₀NH₂ )} . These alkyleneamines and alkyleneamine derivatives are water-soluble, and among them, ethylenediamine and diethylenetriamine are preferred because they have a relatively strong inhibitory effect on the self-decomposition of hydrazine, and are readily available and inexpensive.

The structural formulas of ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), propylenediamine (PDA), tris(2-aminoethyl)amine (TAEA), N-(2-aminoethyl)ethanolamine (AEEA), N-(2-aminoethyl)propanolamine (AEPA), and L (or D,DL)-2,3-diaminopropionic acid (DAPA) are shown below in (B) to (M).

The amount of amine compound relative to the total amount of magnetic metal is preferably 0.00 mol% to 5.00 mol%, more preferably 0.01 mol% to 5.00 mol%, and even more preferably 0.03 mol% to 5.00 mol%. The amount of amine compound can be 0.00 mol%, i.e., no amine compound is required. However, by increasing the amount to 0.01 mol% or more, the effects of inhibiting hydrazine self-decomposition and promoting the reduction reaction based on the amine compound can be fully exhibited. Furthermore, by limiting the amount to 5.00 mol% or less, the function as a complexing agent can be appropriately expressed. Therefore, it is possible to improve the powder properties of the alloy powder (particle size, particle size distribution, sphericity, particle surface properties). If the amount of amine compound exceeds 5.00 mol%, the complexing agent effect becomes too strong. This may lead to abnormal particle growth and deterioration of the powder properties of the alloy powder.

<Crystallization process>
In the crystallization process, a reaction solution is prepared containing the prepared starting materials and water, and the crystallization powder containing the magnetic metal is crystallized in this reaction solution by a reduction reaction. The preparation of the reaction solution and the crystallization of the crystallization powder are described below. In actual manufacturing, the crystallization reaction usually begins simultaneously with the preparation of the reaction solution, although there is a possibility that the crystallization reaction may begin to some extent during the preparation of the reaction solution. The crystallization reaction referred to here is the reaction that occurs during the crystallization process. That is, it mainly consists of the reduction reaction by hydrazine (such as equation (6) described later), but also includes other reactions such as the autodecomposition reaction of hydrazine (equation (1) mentioned above). Therefore, the term crystallization reaction is used in a broader sense than reduction reaction.

In the crystallization process, at least one of several solutions, such as a metal salt raw material solution and a reducing agent solution, is heated and then mixed to prepare a reaction solution. The reaction solution is then heated and stirred in a reaction vessel to maintain a predetermined temperature, and the crystallization reaction proceeds under these conditions. General heating methods can be applied; for example, the reaction vessel may be placed in a water bath, or a steam-jacketed or heater-equipped reaction vessel may be used. The reaction vessel and the stirring blades for stirring the reaction solution must be made of an inert material that minimizes nucleation on their surfaces when in contact with the reaction solution, in order to avoid interfering with the action of the nucleating agent. Furthermore, they must possess excellent strength and thermal conductivity. To satisfy these requirements, metal containers coated with fluororesin (PTFE, PFA, etc.) (e.g., Teflon®-coated stainless steel containers) and stirring blades (e.g., Teflon®-coated stainless steel stirring blades) are suitable.

(a) Preparation of reaction solution First, the starting materials, a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, a pH adjusting agent, and, if necessary, an amine compound, can be dissolved in water and mixed to prepare the reaction solution. When preparing this reaction solution, it is preferable to use highly pure water in order to reduce the amount of impurities in the final alloy powder. As highly pure water, it is possible to use pure water with an electrical conductivity of 1 μS/cm or less, or ultrapure water with an electrical conductivity of 0.06 μS/cm or less, and among these, it is preferable to use pure water, which is inexpensive and readily available.

When the starting materials are solids, such as iron salts, nickel salts, cobalt salts, and alkali hydroxides, it is preferable to pre-mix and dissolve them in water to form an aqueous solution. Mixing the starting materials with water can be done by known methods such as stirring. The procedure for mixing the starting materials and aqueous solutions is not particularly limited, as long as the uniformity of the reaction solution is not impaired. However, from the viewpoint of ensuring the uniformity of the reaction solution, it is preferable to prepare aqueous solutions containing each starting material separately beforehand and then mix the prepared aqueous solutions. It is particularly preferable to prepare the reaction solution according to the first or second embodiment described below.

In the first embodiment, when preparing the reaction solution in the crystallization step, a metal salt raw material solution is prepared by dissolving a magnetic metal source, a nucleating agent, and a complexing agent in water; a reducing agent solution is prepared by dissolving a reducing agent in water; and a pH adjusting solution is prepared by dissolving a pH adjusting agent in water. The metal salt raw material solution and the pH adjusting solution are mixed to form a mixed solution, and the resulting mixed solution is then mixed with the reducing agent solution. Figures 2 and 3 show process diagrams illustrating an example of reaction solution preparation and alloy powder production in the first embodiment.

In the first embodiment, three solutions—a metal salt raw material solution, a reducing agent solution, and a pH adjusting solution—are prepared separately. The metal salt raw material solution is prepared by dissolving a magnetic metal source (water-soluble iron salt, water-soluble nickel salt, etc.), a nucleating agent (water-soluble salt of a metal nobler than nickel), and a complexing agent (hydroxycarboxylic acid, etc.) in water. The reducing agent solution is prepared by dissolving a reducing agent (hydrazine) in water. The pH adjusting solution is prepared by dissolving a pH adjusting agent (alkali hydroxide) in water. Next, the metal salt raw material solution and the pH adjusting solution are mixed to prepare a mixed solution. At this time, the magnetic metal salt (water-soluble iron salt, water-soluble nickel salt, etc.) contained in the metal salt raw material solution reacts with the alkali hydroxide contained in the pH adjusting agent to form a magnetic metal hydroxide. These hydroxides include iron hydroxide (Fe(OH) _₂ ), nickel hydroxide (Ni(OH) _₂ ), cobalt hydroxide (Co(OH) _₂ ), iron-nickel hydroxide ((Fe,Ni)(OH) _₂ ), and iron-nickel-cobalt hydroxide ((Fe,Ni,Co)(OH) _₂ ). Subsequently, the resulting mixed solution is mixed with a reducing agent solution to form a reaction solution.

In the first embodiment, the specific procedure for preparing the reaction solution is to sequentially add and mix the pH adjusting solution and the reducing agent solution to the metal salt raw material solution. In the first embodiment, which uses three types of solutions—metal salt raw material solution, reducing agent solution, and pH adjusting solution—the metal salt raw material solution has the largest volume. Therefore, sequentially adding and mixing the other solutions to the larger volume metal salt raw material solution achieves a more uniform mixing state than adding the metal salt raw material solution to the other solutions, allowing the reduction reaction to proceed uniformly in the reaction solution.

When incorporating an amine compound, it is sufficient to add the amine compound to at least one of the metal salt raw material solution, reducing agent solution, and pH adjusting agent solution. Alternatively, the amine compound may be added after all of these solutions have been mixed. Figure 2 shows an example of adding an amine compound to at least one of the metal salt raw material solution, reducing agent solution, and pH adjusting solution. Figure 3 shows an example of adding an amine compound to a reaction solution obtained by mixing all of the metal salt raw material solution, reducing agent solution, and pH adjusting solution.

In the first embodiment, a reaction solution is prepared by mixing a reducing agent solution with a mixed solution of a metal salt raw material solution and a pH adjuster, and the reduction reaction proceeds from the moment the reducing agent solution is added. When the reducing agent solution is mixed, the concentration of the reducing agent (hydrazine) rises sharply locally in the minute region where the reducing agent is added. The mixed solution also contains a pH adjuster (alkali hydroxide), and in the initial stage of mixing the reducing agent solution into this mixed solution, the pH of the mixed solution (reaction solution) is still high. As mentioned above, the higher the pH, the stronger the reducing agent (hydrazine) exhibits. Therefore, in the initial stage of mixing the reducing agent solution, the local reducing agent concentration and pH become high, and a reduction reaction that causes nucleation and crystallization powder generation due to the nucleating agent occurs rapidly. On the other hand, as the reducing agent solution is added, the pH of the mixed solution (reaction solution) gradually decreases. Therefore, in the final stage of mixing the reducing agent solution, the reducing power of the reducing agent is not as strong as in the initial stage, and the nucleation and reduction reaction proceeds slowly. Therefore, a difference in the reducing power of the reducing agent will occur between the initial and final stages of mixing the reducing solution.

If the difference in reducing power between the initial and final stages is large, the uniformity of the nucleation and reduction reactions will decrease, potentially leading to greater variation in the powder properties (particle size, surface smoothness, etc.) of the resulting crystallized powder. Therefore, it is desirable to minimize the difference in reducing power as much as possible. To achieve this, it is preferable to mix the reducing agent solution as quickly as possible. The time required to mix the reducing agent solution with the mixed solution of the metal salt raw material solution and pH adjuster (mixing time) is preferably 180 seconds or less, more preferably 120 seconds or less, and even more preferably 60 seconds or less. On the other hand, due to limitations of the manufacturing equipment, it may be difficult to shorten the mixing time excessively. The mixing time may be 1 second or more, 3 seconds or more, or 5 seconds or more.

Furthermore, when mixing the pH adjusting agent solution with the metal salt raw material solution, prolonged mixing time can lead to variations in the properties of the formed magnetic metal hydroxide, potentially causing variations in the powder properties of the crystallized powder. While this effect is not as significant as when mixing the reducing agent solution, shorter mixing times are preferable. The time required to mix the pH adjusting agent (mixing time) is preferably 180 seconds or less, more preferably 120 seconds or less, and even more preferably 80 seconds or less. The mixing time may also be 1 second or more, 3 seconds or more, or 5 seconds or more.

To suppress variations in the powder properties of crystallized powder, it is effective to mix the reducing agent solution and pH adjusting agent solution while stirring. Stirring prevents a rapid increase in the concentration of components in the solution, thus reducing variations in the properties of the crystallized powder. Stirring can be performed using a stirring device such as a stirring blade.

In the second embodiment, when preparing the reaction solution in the crystallization step, a metal salt raw material solution is prepared by dissolving a magnetic metal source, a nucleating agent, and a complexing agent in water, and a reducing agent solution is prepared by dissolving a reducing agent and a pH adjusting agent in water. The metal salt raw material solution and the reducing agent solution are then mixed. Figures 4 and 5 show process diagrams illustrating an example of reaction solution preparation and alloy powder production in the second embodiment.

In the second embodiment, two solutions—a metal salt raw material solution and a reducing agent solution—are prepared separately. The metal salt raw material solution is prepared by dissolving a magnetic metal source (water-soluble iron salt, water-soluble nickel salt, etc.), a nucleating agent (water-soluble salt of a metal nobler than nickel), and a complexing agent (hydroxycarboxylic acid, etc.) in water. The reducing agent solution is prepared by dissolving a reducing agent (hydrazine) and a pH adjusting agent (alkali hydroxide) in water. Then, the metal source raw material solution and the reducing agent solution are mixed to form a reaction solution. The second embodiment differs from the first embodiment in that the reducing agent solution contains a pH adjusting agent.

In the second embodiment, there are two possible methods for preparing the reaction solution: either adding the reducing agent solution to the metal salt raw material solution and mixing, or conversely, adding the metal salt raw material solution to the reducing agent solution and mixing. Unlike the first embodiment, the volume of the reducing agent solution, which contains both the reducing agent and the pH adjuster (alkali hydroxide), is equivalent to the volume of the metal salt raw material solution. Therefore, by adding one to the other and mixing, a homogeneous mixture can be achieved, allowing a uniform reduction reaction to proceed in the reaction solution.

However, under crystallization conditions where the proportion of reducing agents and pH adjusters (alkali hydroxides) relative to the metal salt raw materials is high, it is preferable to add and mix the metal salt raw material solution to the reducing agent solution. This is because, from the viewpoint of ensuring productivity in the crystallization process, it is desirable to maintain the concentration of the metal salt raw material in the reaction solution at or above a predetermined level (30-40 g/L of metal components). In other words, under the crystallization conditions described above, the volume of the reducing agent solution is considerably larger than the volume of the metal salt raw material solution. Therefore, adding and mixing the metal salt raw material solution, which has a smaller volume, to the reducing agent solution, which has a larger volume, allows for a more uniform mixing state and enables the reduction reaction to proceed uniformly in the reaction solution.

In the second embodiment, for the same reasons as in the first embodiment, the time required to mix the reducing agent solution with the metal salt solution (mixing time) is preferably 180 seconds or less, more preferably 120 seconds or less, and even more preferably 60 seconds or less. The mixing time may also be 1 second or more, 3 seconds or more, or 5 seconds or more. Stirring during the mixing of the reducing agent solution is also effective.

In the third embodiment, in the crystallization step of the first and second embodiments, an additional raw material solution is added and mixed into the reaction solution before the reduction reaction is completed. This enriches the surface of the crystallized powder with nickel and cobalt components. Here, the additional raw material solution is obtained by dissolving at least one of the aforementioned water-soluble nickel salt and water-soluble cobalt salt in water. A process diagram showing an example of alloy powder production in the third embodiment is shown in Figure 6.

In the third embodiment, an additional raw material solution is prepared in addition to the solution used to prepare the reaction solution in the first and second embodiments. This additional raw material solution is prepared by dissolving at least one of a water-soluble nickel salt and a water-soluble cobalt salt in water. The additional raw material solution can be added to the reaction solution by methods such as a single addition, partial addition, and/or dropwise addition. Although not necessary, it is preferable to add the solution before the reduction reaction is complete. Once the reduction reaction is completely finished, the crystallized particles begin to form aggregates. Adding the additional raw material solution at this timing to promote the precipitation of metal components by the reduction reaction may strengthen the bonds between particles contained in the aggregates.

Furthermore, the third embodiment has the advantage of reducing the amount of reducing agent used compared to the first and second embodiments. Iron ions (or iron hydroxide) are less easily reduced than nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide). Adding an additional starting material solution containing nickel or cobalt components to the reaction solution can accelerate the reduction reaction of the less easily reduced iron ions (or iron hydroxide) towards the end of crystallization.

The amount of magnetic metals (Ni, Co) in the additional raw material solution should be set according to the degree to which the crystallized powder surface is enriched with nickel and cobalt components. However, considering the overall compositional uniformity of the particles, it is preferable that the amount is between 5 mol% and 50 mol% relative to the total amount of magnetic metals (Ni, Co) excluding iron in the alloy powder. When the particle surface is enriched with nickel and cobalt components, the amount of iron components, which easily form a porous oxide film, decreases. Therefore, a dense oxide film is formed, suppressing oxidation of the particle surface, resulting in not only greater stability in the atmosphere but also improved magnetic properties such as saturation magnetic flux density.

(b) Crystallization of crystallized powder When the reaction solution is prepared, a reduction reaction occurs in this solution. That is, in the presence of a pH adjusting agent (alkali hydroxide) and a nucleating agent (salt of a metal nobler than nickel), ions and complex ions of the magnetic metal source are reduced by a reducing agent (hydrazine), thereby forming crystallized powder containing magnetic metal.

The reduction reactions in the crystallization process will be explained using reaction equations. The reduction reactions of iron (Fe), nickel (Ni), and cobalt (Co) are two-electron reactions, as shown in equations (2) to ( ₄ ) below. On the other hand, the reaction of hydrazine ( _N₂H₄ ) as a reducing agent is a four-electron reaction, as shown in equation (5) below.

When magnetic metal chlorides ( _FeCl₂ , _NiCl₂ , _CoCl₂ ) are used as a magnetic metal source and sodium hydroxide (NaOH) is used as a pH adjuster, as shown in equation (6) below, the magnetic metal chloride and sodium hydroxide first undergo a neutralization reaction to produce hydroxides ((Fe, Ni, Co)(OH) _₂, etc.). Then, these hydroxides ((Fe, Ni, Co)(OH) _₂, etc.) are reduced by the action of a reducing agent (hydrazine) to form a crystallized powder. To reduce 1 mole of magnetic metal (Fe, Ni, Co), 0.5 moles of reducing agent (hydrazine) are required. Also, as can be seen from equation (5) above, the higher the alkalinity (pH), the higher the reducing power of hydrazine. Therefore, sodium hydroxide used as a pH adjuster also has the effect of promoting the reduction reaction by hydrazine.

In the reduction reaction of equation (6) above, the reduction of ions (or hydroxides) of each element of the magnetic metal (Fe, Ni, Co) proceeds to some extent simultaneously through co-reduction. Here, co-reduction refers to the phenomenon in which another reduction reaction occurs incidentally when a reduction reaction of one element takes place. However, as mentioned above, iron ions (or iron hydroxide) are less easily reduced than nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide). Therefore, towards the end of the crystallization reaction, nickel ions (or nickel hydroxide) and cobalt ions (or cobalt hydroxide) tend to be consumed and disappear in the reduction reaction in the reaction solution, leaving behind iron ions (or iron hydroxide). This tendency is particularly pronounced when the iron content is high (for example, when the iron content of the alloy powder exceeds 60 mol%). When such a phenomenon occurs, not only does it take a long time to complete the crystallization reaction (reduction reaction), but a non-uniform gradient structure is likely to be formed within the particles. When a gradient structure is formed, the center of the resulting alloy powder particles becomes rich in nickel and cobalt, while the composition becomes iron-rich closer to the particle surface.

In contrast, in the third embodiment described above, additional raw material solution is added to the reaction solution during the crystallization reaction to accelerate the reduction reaction of iron ions (or iron hydroxide), which are difficult to reduce, towards the end of the crystallization process. Therefore, it becomes possible to extend the crystallization reaction (reduction reaction) time, especially when the iron content is high, and to improve the non-uniformity of the composition within the resulting alloy powder particles.

The reaction solution temperature at the start of crystallization of the crystallized powder (reaction start temperature) is preferably 40°C to 90°C, more preferably 50°C to 80°C, and even more preferably 60°C to 70°C. Here, the reaction solution at the start of crystallization refers to the reaction solution containing the starting materials and water immediately after preparation. Furthermore, the temperature of the reaction solution maintained during crystallization after the start of crystallization (reaction holding temperature) is preferably 60°C to 99°C, more preferably 70°C to 95°C, and even more preferably 80°C to 90°C. To adjust the reaction start temperature within a suitable range, it is desirable to preheat at least one of the multiple solutions used in preparing the reaction solution, such as the metal salt raw material solution and the reducing agent solution. To adjust the reaction holding temperature within a suitable range, it is desirable to continue heating the reaction solution after its preparation.

From the viewpoint of obtaining crystallized powder with a sharp particle size distribution by achieving more uniform nucleation, it is preferable, if possible, to preheat one of several solutions (e.g., metal salt raw material solution and reducing agent solution) to 70°C, while keeping the other solution unheated (e.g., at 25°C), and then add and mix them to prepare a reaction solution at a predetermined temperature (e.g., 55°C). In contrast, preheating both solutions (e.g., metal salt raw material solution and reducing agent solution) to 70°C tends to result in non-uniform nucleation. That is, when two solutions are added and mixed, heat generation occurs. Therefore, the added and mixed solution (reaction solution) becomes locally hot (e.g., around 78°C) at the start of mixing, causing instantaneous nucleation. This results in a state where nucleation occurs while the two solutions are being added and mixed, which easily leads to non-uniform nucleation.

While methods such as drastically shortening the addition time between the two solutions or vigorous stirring can be considered to improve nucleation homogenization, such methods are not necessarily preferable. In the method described above, where only one solution is preheated (e.g., to 70°C) before adding and mixing to prepare the reaction mixture, the mixed solution (reaction mixture) is maintained at a low temperature (e.g., 55°C) and does not experience localized high temperatures. Because the timing of nucleation is delayed, nucleation proceeds only after the two solutions are thoroughly mixed. Therefore, nucleation is more likely to occur uniformly. The above describes a more preferable example and does not exclude cases where all of the multiple solutions, such as the metal salt raw material solution and the reducing agent solution, are preheated. The heating of the solutions and their temperatures should be set so that the reaction start temperature and reaction holding temperature fall within the range described above.

If the reaction initiation temperature is excessively low, nucleation becomes more uniform, but the reduction reaction proceeds slowly, and the heating time required to raise the temperature to the reaction holding temperature at which reduction can be accelerated becomes longer. Similarly, if the reaction holding temperature is excessively low, the reduction reaction proceeds slowly, and the heating time required for crystallization becomes longer. In either case, the cycle time required for the crystallization process becomes longer, and productivity decreases. In addition, because hydrazine self-decomposition progresses, a large amount of hydrazine is required, resulting in increased manufacturing costs. If the reaction initiation temperature and reaction holding temperature are high, the reduction reaction is accelerated, the cycle time required for the crystallization process is shortened, and the resulting crystallized powder tends to be highly crystalline. However, at the same time, the rate of hydrazine self-decomposition increases. Therefore, if the reaction initiation temperature and reaction holding temperature are excessively high, not only will nucleation become non-uniform, but excessive high crystallization may worsen the smoothness of the particle surface, potentially leading to increased surface irregularities. Also, if crystallization is not terminated at the appropriate time, hydrazine may be preferentially consumed through self-decomposition by the reduction reaction. Therefore, there are concerns that a large amount of hydrazine will be required, leading to increased manufacturing costs. By setting the reaction initiation temperature and reaction holding temperature within the aforementioned optimal range, it becomes possible to manufacture high-performance alloy powders at a low cost while maintaining high productivity.

<Recovery Process>
In the recovery process, the crystallized powder is recovered from the reaction solution obtained in the crystallization process. The recovery of the crystallized powder can be carried out by known methods. For example, a method of solid-liquid separation of the crystallized powder from the reaction solution can be used using separation equipment such as a Denver filter, filter press, centrifuge, or decanter. The crystallized powder may also be washed during or after solid-liquid separation. Washing can be carried out using a washing solution. High-purity pure water with a conductivity of 1 μS/cm or less can be used as the washing solution. The crystallized powder after washing may be subjected to a drying treatment. The drying treatment can be carried out using a general-purpose drying device such as an air dryer, hot air dryer, inert gas atmosphere dryer, reducing gas atmosphere dryer, or vacuum dryer at a temperature of 40°C to 150°C, preferably 50°C to 120°C. However, from the standpoint of preventing deterioration of magnetic properties due to excessive oxidation of the crystallized powder during the drying process, it is preferable to use an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer rather than an air dryer or a hot air dryer using air.

Furthermore, crystallized powder dried in a sealed container of an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer has a particle surface that is not significantly oxidized. Therefore, if the powder is immediately removed from the dryer and exposed to the atmosphere after drying, the particle surface will oxidize rapidly, and the heat generated by this oxidation reaction may cause the crystallized powder to burn. This phenomenon is particularly likely to occur with fine crystallized powder (for example, particle size of 0.1 μm or less). Therefore, it is desirable to perform a slow oxidation treatment to stabilize the particle surface of crystallized powder that has not been significantly oxidized after drying by forming a thin oxide film in advance. A specific procedure for slow oxidation treatment is to lower the temperature of the crystallized powder, which has been heated and dried in a sealed container of an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer, to room temperature to about 40°C, and then supply a gas with a low oxygen concentration (for example, nitrogen gas or argon gas containing 0.1 to 2 volume percent oxygen) into the sealed container, slowly oxidizing the particle surface of the crystallized powder little by little to form a thin oxide film. Crystallized powder that has undergone slow oxidation treatment is less susceptible to oxidation and is therefore stable, and does not pose a risk of generating heat or combustion even when left exposed to the atmosphere.

<High-temperature heat treatment process>
A high-temperature heat treatment step may be included after or during the recovery process, in which the crystallized powder is subjected to high-temperature heat treatment. If high-temperature heat treatment is performed after the recovery process, it may be performed after the drying process. If high-temperature heat treatment is performed during the recovery process, it may be performed instead of the drying process. The high-temperature heat treatment may be performed in an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere at a temperature of more than 150°C and 400°C or less, preferably 200°C to 350°C or less. High-temperature heat treatment promotes the diffusion of dissimilar elements such as Fe and Ni within the iron (Fe)-nickel (Ni) alloy particles, thereby improving the compositional uniformity within the particles, or adjusting magnetic properties such as magnetic force. If necessary, the aforementioned deoxidation treatment may be performed after the high-temperature heat treatment.

<Crushing process>
If necessary, a crushing step may be included in which the crystallized powder recovered in the recovery step, or the crystallized powder before drying during the recovery process, is subjected to crushing treatment. When alloy particles constituting the crystallized powder precipitate during the crystallization step, the alloy particles may come into contact with each other and fuse together, forming agglomerated particles. Therefore, the crystallized powder obtained through the crystallization step may contain coarse agglomerated particles. As mentioned above, coarse agglomerated particles can cause eddy currents to flow through them, increasing losses due to Joule heating, or hindering the packing properties of the powder. Agglomerated particles can be crushed by including a crushing step after or during the recovery step. Crushing can be performed using dry crushing methods such as spiral jet crushing or counterjet mill crushing, wet crushing methods such as high-pressure fluid impact crushing, or other general-purpose crushing methods. Dry crushing can be directly applied to the dry crystallized powder recovered in the recovery step. Also, if the dry crystallized powder after the recovery step is made into a slurry, wet crushing can be applied to it. Furthermore, if the slurry-like crystallized powder obtained during the recovery process is not yet dried, wet crushing can be applied directly. These crushing methods utilize the collision energy of particles to break down aggregated particles. Since surface smoothing also progresses due to collisions during the crushing process, this effect also contributes to improving the packing properties of the powder.

<Insulation coating process>
If necessary, an insulating coating process may be added after the recovery process. In the insulating coating process, the crystallized powder obtained through the recovery process is subjected to an insulating coating treatment to form an insulating coating layer made of a high-resistance metal oxide on the particle surface of the crystallized powder, thereby improving the insulation between particles. Similar to the increased loss due to eddy currents in coarse aggregated particles, in compacted powder cores obtained by compression molding of iron-nickel alloy powder, there is a risk that eddy currents flowing between particles will increase due to contact between alloy particles. By forming an insulating coating layer, it is possible to suppress the generation of eddy currents due to contact between alloy particles.

In the insulating coating process, crystallized powder is dispersed in a mixed solvent containing water and an organic solvent. A metal alkoxide is then added to the mixed solvent and mixed to prepare a slurry. In the resulting slurry, the metal alkoxide is hydrolyzed and dehydrated, undergoing polymerization to form an insulating coating layer on the particle surface of the crystallized powder. Subsequently, the cake-like crystallized powder with the insulating coating layer is separated from the slurry using a solid-liquid method. The separated crystallized powder is dried to recover the crystallized powder with a highly resistant insulating coating layer made of metal oxide. Heat treatment may be applied to the separated and dried crystallized powder as needed. Since the hydrolysis reaction of metal alkoxide in a mixed solvent containing water and an organic solvent proceeds very slowly, a small amount of hydrolysis catalyst, such as an acid or base (alkali), is generally added to accelerate the reaction. In this embodiment, the addition of a base catalyst (alkaline catalyst) is also preferable.

As high-resistance metal oxides, those _primarily composed of at least one selected from the group consisting of silicon dioxide ( _SiO₂ ), aluminum oxide ( _Al₂O₃ ), zirconium oxide ( _ZrO₂ ), and titanium dioxide ( _TiO₂ ) are preferred. Those primarily composed of silicon dioxide ( _SiO₂ ) are particularly preferred because they are inexpensive and have excellent insulating properties.

To obtain such metal oxides, the metal alkoxide used in the slurry for the insulating coating process is selected to be one that can ultimately form a metal oxide through hydrolysis and dehydration condensation polymerization. Specifically, a slurry mainly composed of at least one selected from the group consisting of silicon alkoxide (alkyl silicate), aluminum alkoxide (alkyl aluminate), zirconium alkoxide (alkyl zirconate), and titanium alkoxide (alkyl titanate) is preferred, with silicon alkoxide (alkyl silicate) being particularly preferred as the main component. If necessary, a small amount of a component that is incorporated into the insulating coating layer through hydrolysis (e.g., boron alkoxide) may be added to the above-mentioned metal alkoxide when the metal alkoxide undergoes hydrolysis and dehydration condensation polymerization to form the insulating coating layer.

The surface of the insulating coated alloy powder is coated with a highly resistive inorganic metal oxide. Organic functional groups may be introduced to the surface of this inorganic material as needed. Specifically, one method involves adding small amounts of silicon-based, titanium-based, zirconium-based, or aluminum-based coupling agents to the metal alkoxide used in the insulating coating process, thereby incorporating the organic functional groups into the metal oxide during the hydrolysis and dehydration condensation polymerization of the metal alkoxide. Another method involves surface-treating the insulating coated alloy powder with the aforementioned coupling agents to modify the metal oxide surface with organic functional groups. In either method, the introduction of organic functional groups increases the affinity with resins, thus improving the strength of the molded product when the insulating coated alloy powder is combined with a resin binder and molded.

Specific examples of silicon alkoxides (alkyl silicates) include, for example, tetramethoxysilane (also known as tetramethyl orthosilicate, silicon tetramethoxide) (abbreviation: TMOS) (Si( _OCH3 ) ₄ ), tetraethoxysilane (also known as tetraethyl orthosilicate, silicon tetraethoxide) (abbreviation: TEOS) (Si( _OC2H5 ) ₄ ), tetrapropoxysilane (also known as tetrapropyl orthosilicate, silicon tetrapropoxide) (Si( _OC3H7 ) _{4) ,} and tetrabutoxysilane (also known as tetrabutyl orthosilicate, and silicon tetrabutoxide) (Si( _{OC4H9 )} ) _. One or more selected from ₄ , etc. are also acceptable. Alternatively, these alkoxides may be obtained by substituting the alkoxyl group of one of these alkoxides with another alkoxyl group, or commercially available alkyl silicates as silicate oligomers that have already undergone polymerization to 4-5mers (for example, Elsilicate 40 (trade name), Elsilicate 48 (trade name), Methylsilicate 51 (trade name) manufactured by Colcoat, etc.). Among these, tetraethoxysilane (TEOS) is preferred because it is less harmful, readily available, and inexpensive.

Specific examples of aluminum alkoxides (alkylaluminates) include one or more selected from aluminum trimethoxide (Al( _OCH3 ) ₃ ), aluminum triethoxide (Al( _OC2H5 ) ₃ ), aluminum triisopropoxide ₍ Al( _O -iso- _C3H7 ) _{3 )} , aluminum tri-n-butoxide (Al(O- _n - _C4H9 ) ₃ ), aluminum tri-sec-butoxide (Al(O-s- _C4H9 ) ₃ ), and aluminum tri-tert-butoxide (Al(O-t- _C4H9 ) _{3 )} .

Specific examples of zirconium alkoxides (alkyl zirconates) include, for example, one _{or more} selected from zirconium tetraethoxide (Zr( _OC2H5 ) ₄ ), zirconium tetra-n-propoxide (Zr(O-n _{- C3H7} ) ₄ ), zirconium tetraisopropoxide (Zr(O-iso- _C3H7 ) ₄ ), zirconium tetra-n-butoxide (Zr(O-n _{- C4H9} ) ₄ ), zirconium tetra-tert-butoxide (Zr(O-t- _C4H9 ) ₄ ), zirconium tetraisobutoxide (Zr(O-iso- _C4H9 ) _{4 )} , _and others.

Specific examples of titanium alkoxides (alkyl titanates) include one or more selected from, for example, titanium tetramethoxide (Ti( _OCH3 ) ₄ ), titanium tetraethoxide (Ti( _OC2H5 ) ₄ ), titanium tetraisopropoxide (Ti(O-iso _{- C3H7} ) _{4 )} , titanium tetraisobutoxide ( _Ti (O- _iso - _C4H9 ) ₄ ), titanium tetra-n-butoxide (Ti(O-n- _C4H9 ) ₄ ), titanium tetra-tert-butoxide (Ti(O-t- _C4H9 ) ₄ ), and titanium tetra-sec-butoxide (Ti(O-s- _C4H9 ) _{4 ) .}

Other metal alkoxides include one _or more boron alkoxides (alkyl boronates), such as boron trimethoxide (B( _OCH3 ) ₃ ), boron triethoxide (B( _OC2H5 ) ₃ ), and boron tri-tert-butoxide (B(O-t- _C4H9 ) _{3 )} .

The organic solvent used in the slurry for insulating coating treatment should preferably form a mixed solvent with water and dry reasonably well. That is, it should have high compatibility with water and a relatively low boiling point (around 60°C to 90°C). In addition, it should be safe, easy to handle, readily available, and inexpensive. Considering these factors, denatured alcohol with ethyl alcohol as the main component is preferred.

The hydrolysis and dehydration condensation polymerization reactions of metal alkoxides in insulating coating treatment will be explained using reaction equations, specifically for the case where silicon alkoxide (Si(OR) ₄ , R: alkyl group) is used as the metal alkoxide.

In the hydrolysis reaction, in the presence of a base catalyst (alkaline catalyst) such as ammonia ( _NH₃ ), as shown in equation (7) below, the silicon atom (Si) is directly attacked by the nucleophilic hydroxyl ion ( ^OH⁻ ), and one of the alkoxy groups (-OR) is hydrolyzed first. This reduces the charge on the silicon atom, making it even more susceptible to attack by the nucleophilic hydroxyl ion ( ^OH⁻ ). As a result, as shown in equation (8) below, all four alkoxy groups (-OR) are hydrolyzed and converted into silanol groups (Si-OH). Thus, when a base catalyst (alkaline catalyst) is used, all alkoxy groups (-OR) in the hydrolyzed silicon alkoxide molecule are hydrolyzed, resulting in a state in the slurry where completely hydrolyzed molecules (Si(OH) _₄ ) and molecules that are not hydrolyzed at all (Si(OR) _₄ ) coexist.

On the other hand, in the presence of an acid catalyst such as nitric acid ( _HNO₃ ), as shown in equation (9) below, the silicon atom (Si) becomes more susceptible to attack by water ( _H₂O ) due to the protonation of the alkoxy group (-OR) by protons ( ^H⁺ ). Therefore, one of the alkoxy groups (-OR) is hydrolyzed first and converted into a silanol group (Si-OH). Although the details are omitted, when this happens, the charge on the silicon atom and the charge on the oxygen atom (O) decreases, making it less susceptible to attack by protons ( ^H⁺ ). Therefore, the next hydrolysis does not occur immediately, and the alkoxy groups (-OR) of other unhydrolyzed silicon alkoxide molecules become more susceptible to hydrolysis. In this way, when an acid catalyst is used, the hydrolysis of the alkoxy group (-OR) proceeds uniformly in all silicon alkoxide molecules, as shown in equation (10) below. Therefore, there are no molecules that are completely hydrolyzed or not hydrolyzed at all, and a state is created in the slurry where uniformly hydrolyzed molecules (Si(OH) _₂X₂ (OR) _₄-X₄ ; 0 < x < 4) exist.

Dehydration condensation polymerization is a reaction in which siloxane bonds (Si-O-Si) are formed by the dehydration condensation polymerization of silanol groups (Si-OH) between hydrolyzed silicon alkoxide molecules, as shown in equation (11) below. When this dehydration condensation polymerization reaction proceeds and is completed, silicon dioxide ( _SiO₂ ) is produced as shown in equation (12) below.

In summary, when the hydrolysis and dehydration condensation polymerization of silicon alkoxide are completed, silicon dioxide ( _SiO₂ ) and alcohol are produced as shown in equation ₍ 13) below. For example, when tetraethoxysilane (TEOS: Si(OR) _₄ , R: _C₂H₅ ) is used _{, silicon dioxide (SiO₂) and ethyl alcohol (C₂H₅OH ) are} produced.

The above equation (13) is valid regardless of whether a base catalyst (alkaline catalyst) or acid catalyst is used, as long as the silicon alkoxide undergoes hydrolysis. However, the form of silicon dioxide ( _SiO₂ ) produced during the dehydration condensation polymerization is greatly influenced by the state of hydrolysis by the hydrolysis catalyst mentioned above.

In silicon alkoxide molecules (Si(OH) _₂X₄ (OR) _₄-X ; 0 < x < 4) uniformly hydrolyzed by an acid catalyst, unhydrolyzed alkoxy groups (-OR) exist within the molecule. Therefore, when dehydration condensation polymerization of the silanol groups (Si-OH) proceeds between molecules, hydrolyzed polymers are formed in a linear or branched linear structure. When this occurs in the slurry during insulating coating treatment, hydrolyzed polymers of silicon alkoxide are formed on the particle surface made of iron oxide (FeO) or nickel oxide (NiO) of the crystallized powder. However, because these polymers are formed in a linear or branched linear structure, they do not densify easily in the solvent of the slurry, and therefore, the formation of a dense insulating coating layer is not easy.

On the other hand, when a base catalyst (alkaline catalyst) is used, completely hydrolyzed molecules (Si(OH) _₄ ) are present. Therefore, as intermolecular dehydration condensation polymerization of silanol groups (Si-OH) proceeds, dense hydrolyzed polymers are formed in a massive polymer. Consequently, even in the solvent of the slurry during the insulating coating process, dense hydrolyzed polymers of silicon alkoxide are formed on the particle surface of the crystallized powder, which consists of iron oxide (FeO) and nickel oxide (NiO), resulting in the formation of a dense insulating coating layer. However, when a base catalyst (alkaline catalyst) is used, there is a possibility that molecules that have not been hydrolyzed at all (Si(OR) _₄ ) may be present. However, as will be described later, molecules that have not been hydrolyzed at all and particulate silicon alkoxide hydrolyzed polymers (silica sols) with very small molecular weights that remain in the slurry without being consumed by the insulating coating of the crystallized powder are removed from the system along with the filtrate during the filtration and washing process of the insulating coating step. Therefore, they do not affect the insulating coating process.

For the reasons stated above, hydrolysis of metal alkoxides in insulating coating treatment is preferable to using a base catalyst (alkaline catalyst) rather than an acid catalyst. However, the preferred catalyst differs depending on whether the coating is applied to a substrate using a solvent. Specifically, when used as a binder in a coating solution applied to a substrate and then dried, rather than for coating particle surfaces in a solvent, a polymerized metal alkoxide in a linear or branched linear shape using the aforementioned acid catalyst is preferable.

Regarding the timing of hydrolysis of metal alkoxides in insulating coating treatment, previous descriptions have described a method in which hydrolysis is performed by a hydrolysis catalyst after the crystallization powder and metal alkoxide are uniformly mixed in a slurry. However, this embodiment is not limited to this timing of hydrolysis. For example, it is also possible to prepare a metal oxide sol (silica sol in the case of silicon alkoxide) obtained by pre-hydrolyzing the metal alkoxide with a hydrolysis catalyst, and then mix this metal oxide sol with the crystallization powder to form a slurry. If the average molecular weight of the metal oxide sol is small, around 500 to 5000, the effect of the timing of metal alkoxide hydrolysis is almost negligible. This is because the bonding between iron oxide (FeO) or nickel oxide (NiO) on the surface of the crystallization powder and the hydrolysis groups of the metal oxide sol (silanol groups (Si-OH) in the case of silicon alkoxide) covers the surface of the crystallization powder particles with small metal oxide sol particles, and then polymerization of the sol particles proceeds.

In insulating coating treatment, from the viewpoint of uniformly forming the insulating coating layer, it is preferable to subject the slurry containing crystallization powder, water, organic solvent, metal alkoxide, and hydrolysis catalyst to treatment such as stirring with a stirring blade using a stirrer or stirring by rotating the container using a dedicated roller. The treatment time and temperature for insulating coating treatment vary depending on the type of metal alkoxide applied and the required thickness of the insulating coating layer. For example, generally, metal methoxides have a higher hydrolysis rate than metal ethoxides. Therefore, the treatment time and temperature should be set appropriately and are not particularly limited. For example, the treatment time can be several hours to about one week, and the treatment temperature can be room temperature to 60°C. If the treatment temperature is high, around 40°C to 60°C, the treatment speed can be increased to several times that of room temperature.

The thickness of the insulating coating layer is not generally limited, as it depends on the required degree of insulation. Generally speaking, 1 nm to 30 nm is preferred, 2 nm to 25 nm is more preferred, and 3 nm to 20 nm is even more preferred. Excessive thickness will only lead to saturation of the insulating properties while decreasing the content of soft magnetic components, thus degrading magnetic properties such as saturation magnetic flux density. Within the above thickness range, it is possible to achieve insulating function of the insulating coating layer without significantly degrading magnetic properties.

The crystallized powder, in which an insulating coating layer has been formed by the hydrolysis and dehydration condensation polymerization of metal alkoxides, is separated from the slurry as a cake-like crystallized powder using known separation devices such as a Denver filter, filter press, centrifuge, or decanter. If necessary, the crystallized powder may be washed during solid-liquid separation. For washing, water, organic solvents such as relatively low-boiling alcohols, or mixtures thereof can be used as the washing solution. As mentioned above, if metal alkoxides or their hydrolyzed polymers (unhydrolyzed molecules or metal oxide sols with small molecular weights) remain in the slurry without being consumed by the insulating coating, these are removed from the system along with the filtrate and washing wastewater during solid-liquid separation and washing.

The solid-liquid separated cake-like crystallized powder is dried and, if necessary, heat-treated to recover the crystallized powder with an insulating coating layer made of a high-resistance metal oxide. Drying is not particularly restricted as long as excessive oxidation during drying is suppressed. However, it is preferable to use drying equipment such as an inert gas atmosphere dryer, a reducing gas atmosphere dryer, or a vacuum dryer, and the drying should be performed at a temperature between 40°C and 150°C. The higher the drying temperature, the more the dehydration and condensation polymerization of the metal alkoxide hydrolysate polymer constituting the insulating coating layer progresses, resulting in a harder, denser, and more insulating metal oxide. For further improvement, heat treatment between 150°C and 450°C may be performed in an inert gas atmosphere, a reducing gas atmosphere, or a vacuum. Since the insulating coating layer has already been formed, deoxidation treatment is generally not necessary after drying.

The insulating properties of crystallized powder (alloy powder) are significantly improved by insulating coating treatment. For example, while the resistivity of compacted iron-nickel alloy powder (applied pressure: 64 MPa) is usually 0.1 Ω·cm or less, applying insulating coating treatment to this iron-nickel alloy powder, which involves forming an insulating coating layer of silicon dioxide ( _SiO₂ ) with a thickness of about 0.015 μm (15 nm), improves the resistivity of compacted powder to ^10⁶ Ω·cm or more.

In this way, the iron (Fe)-nickel (Ni) alloy powder of this embodiment can be manufactured. The manufacturing method of this embodiment is characterized by the use of a specific nucleating agent (a water-soluble salt of a metal nobler than nickel) that has the effect of refining the alloy powder, and a specific complexing agent (such as a hydroxycarboxylic acid) that has the effects of promoting reduction reactions, promoting spheroidization, and smoothing the surface. This makes it possible to improve the powder properties while maintaining the magnetic properties of the alloy powder after manufacturing. Specifically, the average particle size of the alloy powder after manufacturing can be freely controlled, making it possible to obtain fine alloy powder. Furthermore, the resulting alloy powder has a narrow particle size distribution and uniform particle size. Moreover, this alloy powder is spherical and has a smooth surface. Therefore, it has excellent packing properties. While not limited to this, by using an amine compound that functions as a hydrazine self-decomposition inhibitor and a reduction reaction accelerator, the amount of hydrazine used can be reduced. Therefore, it is possible to reduce manufacturing costs and improve the powder properties of the alloy powder.

<<2. Iron-nickel alloy powder>>
The iron (Fe)-nickel (Ni) alloy powder of this embodiment contains at least iron (Fe) and nickel (Ni) as magnetic metals. Furthermore, this alloy powder has an average particle size of 0.10 μm or more and 0.60 μm or less, and the coefficient of variation (CV value) obtained from the average particle size and standard deviation in the number particle size distribution according to the following formula (14) is 25% or less.

The iron (Fe)-nickel (Ni) alloy powder of this embodiment has a small particle size distribution. Furthermore, the average particle size of this alloy powder can be freely controlled. Therefore, it is easy to refine and reduce the particle size distribution. Moreover, it is spherical, has high surface smoothness, and exhibits excellent packing properties. Having these advantages, the alloy powder of this embodiment can be used in various electronic components such as noise filters, choke coils, inductors, and radio wave absorbers, and is particularly suitable as a material for compacted cores for choke coils and inductors.

The average particle size of the alloy powder is preferably 0.10 μm to 0.60 μm, and more preferably 0.10 μm to 0.50 μm. By moderately increasing the average particle size, deterioration of magnetic properties and reduction in packing capacity due to surface oxidation can be suppressed. Conversely, by moderately decreasing the average particle size, eddy current losses can be reduced.

The alloy powder preferably has a coefficient of variation (CV) of 25% or less in its particle size distribution, more preferably 20% or less, and even more preferably 15% or less. Here, the coefficient of variation is an indicator of particle size variation; a smaller coefficient of variation indicates a narrower particle size distribution. By keeping the coefficient of variation low, the number of coarse particles and excessively fine particles with high surface oxidation is reduced, thus preventing an increase in eddy current loss while maintaining excellent magnetic properties. The coefficient of variation (CV) is calculated by determining the average particle size and standard deviation in the particle size distribution of the alloy powder, and using these values according to equation (14) below.

The alloy powder may contain cobalt (Co) as needed. That is, the alloy powder may be an iron-nickel alloy powder containing only iron and nickel, or an iron-nickel-cobalt alloy powder containing iron, nickel, and cobalt. Iron, nickel, and cobalt are all ferromagnetic metals. Therefore, iron-nickel alloy powders and iron-nickel-cobalt alloy powders have high saturation magnetic flux densities and excellent magnetic properties.

The proportions of iron (Fe), nickel (Ni), and cobalt (Co) contained in the alloy powder are not particularly limited. For example, the amount of iron (Fe) in the alloy powder may be 10 mol% to 95 mol%, the amount of nickel (Ni) may be 5 mol% to 90 mol%, and the amount of cobalt (Co) may be 0 mol% to 40 mol%. The amount of iron may be 25 mol% to 90 mol%, or 40 mol% to 80 mol%. The amount of nickel may be 10 mol% to 75 mol%, or 20 mol% to 60 mol%. The amount of cobalt may be 5 mol% to 20 mol%. However, the total amount of iron, nickel, and cobalt must be 100 mol% or less.

The compact density of alloy powders depends on the composition and particle size of the alloy powder. When the iron content is high, the specific gravity of the alloy decreases, causing the compact density to decrease. Similarly, when the particle size is small, it becomes more difficult for the particles to pack together, also causing the compact density to decrease. Therefore, for iron-nickel alloy powders with an average particle size of 0.3 μm to 0.5 μm and a specific gravity of 8.2 to 8.3, and an iron content of 45 mol% to 60 mol% iron (Fe), the compact density (applied pressure: 100 MPa) is preferably 3.60 g/ ^cm³ or higher, and more preferably 3.70 g/ ^cm³ or higher. Furthermore, in the case of an iron-nickel alloy powder with an average particle size of 0.3 μm to 0.5 μm and a specific gravity of 7.9 to 8.0, where the iron content is 10 mol% to 20 mol% iron (Fe), the compaction density (applied pressure: 100 MPa) is preferably 3.45 g/ ^cm³ or higher, and more preferably 3.55 g/ ^cm³ or higher. Regarding the particle size of the alloy powder, when the average particle size is refined from 0.3 μm to 0.5 μm to about 0.2 μm to ^0.25 μm, the compaction density (applied pressure: 100 MPa) tends to decrease by about 0.1 g/cm³. By increasing the compaction density, it becomes possible to produce compaction cores with excellent magnetic properties (magnetic flux density).

The crystallite size of the alloy powder is preferably 30 nm or less, and more preferably 10 nm or less. Keeping the crystallite size moderately small has the effect of making it easier to obtain low coercivity, similar to amorphous soft magnetic materials.

Preferably, the saturation magnetic flux density of the alloy powder is 1 T (Tesla) or higher, and the coercivity is 2000 A/m or lower. Increasing the saturation magnetic flux density of the alloy powder can improve the magnetic properties (magnetic flux density) of the compacted core. Furthermore, suppressing the coercivity of the alloy powder can prevent an increase in hysteresis loss. A saturation magnetic flux density of 1.2 T or higher is more preferable, and 1.5 T (Tesla) or higher is even more preferable. A coercivity of 1600 A/m or lower is more preferable, and 1200 A/m or lower is even more preferable.

The manufacturing method of the alloy powder in this embodiment is not limited, as long as it satisfies the requirements described above. However, it is preferable that it be manufactured by the method described above.

As mentioned above, iron ions (or iron hydroxide) are less easily reduced than nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide). Therefore, in iron (Fe)-nickel (Ni) alloy powders with a high iron content (for example, alloy powders with an iron content exceeding 60 mol%), a gradient structure (or core-shell structure) is likely to form within the particle, where the center of the particle is rich in nickel and cobalt, and the composition becomes iron-rich closer to the particle surface. This makes the composition within the particle prone to non-uniformity.

Regarding how such non-uniform composition within particles affects the properties of alloy powder, it does not significantly impact magnetic properties (saturation magnetic flux density, coercivity, etc.). This is because, for example, saturation magnetic flux density shows a positive correlation with the iron content (the higher the iron content, the higher the saturation magnetic flux density). Therefore, even if the composition becomes non-uniform within the particles, creating regions with higher and lower iron content than the average, regions with higher and lower saturation magnetic flux density will also emerge. On average, this results in a value that is almost the same as when the composition is non-uniform across the entire alloy powder. Furthermore, regarding coercivity, since its composition dependence in iron-nickel (-cobalt) systems is not very large to begin with, it does not change significantly with the degree of compositional non-uniformity that occurs within particles.

On the other hand, the heterogeneous composition within the particles may affect chemical and physical properties such as oxidation resistance and thermal expansion coefficient. For example, regarding oxidation resistance, if the particle surface has a more iron-rich composition due to the gradient structure, oxidation may progress more easily, potentially worsening oxidation resistance. However, if the particle surface can be modified to a nickel-rich composition using the third embodiment described above, it may be possible to improve oxidation resistance. Next, regarding thermal expansion coefficient, unlike the case of saturation magnetic flux density, the thermal expansion coefficient of iron-nickel alloys does not show a positive or negative correlation with the iron content, and is characterized by being extremely small only when the iron content is around 65 mol% (64 mass%). Low thermal expansion alloys with this composition are called Invar alloys (main components are 65 mol% iron and 35 mol% nickel). In this composition, if the composition is non-uniform within the particles, the coefficient of thermal expansion will not decrease in either the region with an iron content greater than or less than 65 mol%. Therefore, when using iron (Fe)-nickel (Ni) alloy powder as Invar alloy powder, it is necessary to homogenize the composition through methods such as the high-temperature heat treatment mentioned above.

To the best of our knowledge, there is no known method for producing iron-nickel alloy powder with such excellent properties simply and inexpensively. For example, Patent Document 3 discloses a method for producing nickel-iron alloy nanoparticles by a wet process, but this method does not use a nucleating agent consisting of a water-soluble salt of a metal nobler than nickel, nor a complexing agent consisting of hydroxycarboxylic acid, etc. Therefore, it is presumed that the alloy powder produced by this method has inferior powder properties (particle size, particle size distribution, sphericity, particle surface properties). In fact, Patent Document 3 shows a transmission electron microscope image of a fine powder sample (Figure 1 of Patent Document 3), and judging from this image, the coefficient of variation (CV value) in the particle size distribution of the fine powder is large, approximately 35%.

Furthermore, the method described in Patent Document 3, which does not use nucleating agents or complexing agents, requires the use of a large amount of reducing agent (hydrazine) to obtain fine alloy powder. In fact, in the example described in Patent Document 3, alloy nanoparticles are produced using 16.6 g of nickel chloride hexahydrate, 4.0 g of ferrous chloride tetrahydrate, and 135 g of hydrazine positional hydrate as raw materials. Based on these proportions, this means that approximately 30 times the molar ratio of hydrazine is used relative to the total amount of iron and nickel. Such a method requiring a large amount of hydrazine significantly increases the cost of the reducing agent, making it impractical.

The alloy powder of this embodiment is not limited in its usage as long as it satisfies the requirements described above. The alloy powder may be used alone or mixed with other inorganic and/or organic materials. For example, a compact containing only the alloy powder may be prepared. Alternatively, the alloy powder and ferrite powder may be mixed to form a metal-ferrite composite material. In this case, the high saturation magnetic flux density of the alloy powder and the high electrical resistance of the ferrite can be utilized complementaryly. Furthermore, the alloy powder and organic resin may be mixed and kneaded to produce a metal-organic resin composite material. Using this composite material allows for the creation of a composite material with excellent magnetic properties, high degree of shape freedom, and high dimensional accuracy.

Preferably, the alloy powder is applied to a compact or sheet. This compact or sheet contains the alloy powder described above. The compact is produced by press molding or other pressure molding of the alloy powder, or a mixture of alloy powder and other components. Other components include inorganic or organic materials other than alloy powder, or additives such as lubricants. The compact may also be heat-treated after pressure molding to remove the strain applied during molding. A sheet can be produced by adding a solvent and, if necessary, additives such as a binder to the alloy powder to form a paste, and then forming or coating the resulting paste onto a substrate.

The alloy powder of this embodiment is suitable for magnetic devices due to its excellent magnetic properties. Examples of such magnetic devices include inductors, reactors, choke coils, noise filters, transformers, rotating machines, generators, and radio wave absorbers. Inductors, reactors, choke coils, noise filters, transformers, rotating machines, generators, and radio wave absorbers comprise the aforementioned compacted powder and/or sheets. Furthermore, the magnetic device may also be a chip component such as a chip inductor.

Figure 7 shows an example of applying a compacted powder containing alloy powder to an inductor (toroidal coil). The inductor (10) consists of a toroidal compacted powder core (12) and a coil (14) arranged to circumfer the compacted powder core (12). Input and output terminals (16a, 16b) are provided at both ends of the coil (14). The compacted powder core (12) can be manufactured by press-molding alloy powder and, if necessary, additives such as lubricants. The coil (14) can be manufactured by winding a wire around the compacted powder core (12). To prevent electrical conductivity between the compacted powder core (12) and the coil (14), it is desirable to manufacture the coil (14) using insulated wire or to interpose an insulating sheet between the compacted powder core (12) and the coil (14).

Figure 8 shows an example of applying compacted powder to a chip inductor. The chip inductor (20) consists of a compacted powder core (22) and a coil (24) embedded in the compacted powder core (22). The chip inductor (20) can be manufactured by pre-fabricating the coil (24) and then pressure-molding it together with alloy powder.

Figure 9 shows an example of applying compacted powder to a reactor. The reactor (30) comprises a compacted powder core (32), a first coil (34) arranged to circumfer one end of the compacted powder core (32), a second coil (36) arranged to circumfer the other end of the compacted powder core (32), and a connecting portion (38) that electrically connects the first coil (32) and the second coil (34).

Figure 10 shows an example of applying compacted powder to the stator of a rotating machine (motor) or generator. The direction of magnetic flux during operation is indicated by arrows in the figure. The stator (40) has a compacted powder core (42) and windings (44). The windings (44) are provided inside the compacted powder core (42) and are arranged to circumfer each of the multiple protrusions on the core (42).

Figure 11 shows an example of applying compacted powder to the rotor of a rotating machine (motor) or generator. The rotor (50) has a compacted powder core (52), windings (54), and an output shaft (56). The windings (54) are arranged to circle each of the multiple protrusions on the outside of the compacted powder core (52). The output shaft (56) is fixed to the center of the compacted powder core (52).

The present invention will be described in further detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

(1) Preparation of iron-nickel alloy powder [Example 1]
In Example 1, an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni) was prepared according to the procedure shown in Figure 5. In Example 1, when preparing the reaction solution, a reducing solution at room temperature was added to a metal salt raw material solution heated using a water bath and mixed.

<Preparation process>
As a water-soluble iron salt, ferrous chloride tetrahydrate ( _FeCl₂・_4H₂O , molecular weight: 198.81, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared, and as a water-soluble nickel salt, nickel chloride hexahydrate ( _NiCl₂・_6H₂O , molecular weight: 237.69, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared. In addition, ammonium palladium(II) chloride (also known as ammonium tetrachloropalladium(II)ate) (( _NH₄ ) _₂PdCl₄ , molecular weight: _284.31 , reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared as a nucleating agent, trisodium citrate dihydrate ( _Na₃ ( _C₃H₅O (COO) _₃ )・_2H₂O , molecular weight: _294.1 , reagent manufactured by Wako Pure Chemical Industries, Ltd.) as a complexing agent, commercially available industrial-grade 60% by mass hydrated hydrazine (manufactured by MGC Otsuka Chemical Co., Ltd.) as _a reducing agent, and sodium hydroxide (NaOH, molecular weight: 40.0, reagent manufactured by Wako Pure Chemical Industries, Ltd.) as a pH adjuster were prepared. The 60% by mass hydrated hydrazine was prepared by diluting hydrated hydrazine ( _N₂H₄・_H₂O , molecular weight: 50.06) 1.67 times with pure water. Furthermore _, ethylenediamine (EDA; _{H₂NC₂H₄NH₂} , _molecular weight: 60.1, reagent manufactured by Wako Pure Chemical Industries _, Ltd.) was prepared as an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) relative to the total amount of magnetic metals (Fe and Ni) was 0.037 mass ppm (0.02 mol ppm). The amount of trisodium citrate relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that the molar ratio was 0.362 (36.2 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 173.60 g of ferrous chloride tetrahydrate, 207.55 g of nickel chloride hexahydrate, 9.93 μg of palladium(II) ammonium chloride, and 185.9 g of trisodium citrate dihydrate in 1200 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was 4.85 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that it was 4.96 in molar ratio. Specifically, 346 g of sodium hydroxide was dissolved in 850 mL of pure water to prepare a sodium hydroxide solution, and 707 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that the amount of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.05 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallized powder The prepared metal salt raw material solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 70°C. Then, a reducing agent solution at a liquid temperature of 25°C was added to the metal salt raw material solution being heated in the water bath and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 55°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 32.3 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 55°C). As shown in Figure 12, the temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 70°C from 10 minutes after the start of the reaction (reaction holding temperature 70°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution changed color to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. The reaction solution was black at this time, but the supernatant became clear within 20 minutes of the start of the reaction. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.41 μm.

[Example 2]
In Example 2, an iron-nickel alloy powder (iron-nickel-cobalt alloy powder) containing 50 mol% iron (Fe), 40 mol% nickel (Ni), and 10 mol% cobalt (Co) was prepared according to the procedure shown in Figure 3. In Example 2, when preparing the reaction solution, a pH adjustment solution (alkali hydroxide solution) at room temperature was first added to a metal salt raw material solution heated using a water bath, followed by a reducing agent solution at room temperature, and then mixed.

<Preparation process>
The same raw materials as in Example 1 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a complexing agent, a reducing agent, a pH adjuster, and an amine compound. In addition, cobalt chloride hexahydrate ( _CoCl₂・_6H₂O , molecular weight: 237.93, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared as a water-soluble cobalt salt.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), cobalt chloride hexahydrate (water-soluble cobalt salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.037 mass ppm (0.02 mol ppm) relative to the total amount of magnetic metals (Fe, Ni, and Co). In addition, the amount of trisodium citrate relative to the total amount of magnetic metals (Fe, Ni, and Co) was weighed so that the molar ratio was 0.362 (36.2 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 173.60 g of ferrous chloride tetrahydrate, 166.04 g of nickel chloride hexahydrate, 41.55 g of cobalt chloride hexahydrate, 9.93 μg of palladium(II) ammonium chloride, and 185.9 g of trisodium citrate dihydrate in 1200 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing hydrazine (reducing agent) and water was prepared. At this time, the amount of hydrazine was set so that the molar ratio to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was 4.85. Specifically, 707 g of 60% by mass hydrated hydrazine was weighed to prepare the reducing agent solution.

(c) Preparation of pH adjustment solution (alkali hydroxide solution) A pH adjustment solution (alkali hydroxide solution) containing sodium hydroxide (pH adjuster) and water was prepared. At this time, the amount of sodium hydroxide was weighed so that the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was 4.96 in molar ratio. Specifically, 346 g of sodium hydroxide was dissolved in 850 mL of pure water to prepare the pH adjustment solution.

(d) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that the amount of ethylenediamine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.05 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared metal salt raw material solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 70°C. Then, a pH adjustment solution (alkali hydroxide solution) at a liquid temperature of 25°C was added to the metal salt raw material solution being heated in the water bath and mixed for a mixing time of 10 seconds. Subsequently, a reducing agent solution at a liquid temperature of 25°C was added and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 55°C. The concentration of magnetic metals (Fe, Ni, and Co) in the reaction solution was 32.3 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 55°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 70°C from 10 minutes after the start of the reaction (reaction holding temperature 70°C). The reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ), nickel hydroxide (Ni(OH) _₂ ), and cobalt hydroxide (Co(OH) _₂ ) in the reaction solution. The change to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution changed color to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel-cobalt crystallized powder to precipitate in the reaction solution. The reaction solution was black at this time, but the supernatant became clear within 20 minutes of the start of the reaction. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron, nickel, and cobalt components in the reaction solution were reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after completion was a slurry containing iron-nickel-cobalt crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel-cobalt crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel-cobalt alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.33 μm.

[Example 3]
In Example 3, an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni) was prepared according to the procedure shown in Figure 5. In Example 3, when preparing the reaction solution, a reducing solution at room temperature was added to a metal salt raw material solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 1 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, and an amine compound. In addition, tartaric acid ((CH(OH)COOH) ₂ , molecular weight: 150.09, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared as a complexing agent instead of trisodium citrate dihydrate.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), tartaric acid (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.037 mass ppm (0.02 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). The amount of tartaric acid relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that the molar ratio was 0.200 (20.0 mol%). Specifically, 173.60 g of ferrous chloride tetrahydrate, 207.55 g of nickel chloride hexahydrate, 9.93 μg of palladium(II) ammonium chloride, and 52.4 g of tartaric acid were dissolved in 1200 mL of pure water to prepare the metal salt raw material solution.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was 4.85 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that it was 4.96 in molar ratio. Specifically, 346 g of sodium hydroxide was dissolved in 850 mL of pure water to prepare a sodium hydroxide solution, and 707 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution was prepared in the same manner as in Example 1.

(d) Preparation of reaction solution and precipitation of crystallized powder Using the above metal salt raw material solution, reducing agent solution, and amine compound solution, the reaction solution was prepared and crystallized powder was precipitated in the same manner as in Example 1. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 33.0 g/L.

<Recovery Process>
From the slurry-like reaction solution obtained in the crystallization process, an iron-nickel alloy powder (iron-nickel alloy powder) was prepared in the same manner as in Example 1. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.40 μm.

[Example 4]
In Example 4, an iron-nickel alloy powder containing 56 mol% iron (Fe) and 44 mol% nickel (Ni) was prepared according to the procedure shown in Figure 5. In Example 4, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 1 were prepared as a nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound. In addition, as a water-soluble iron salt, ferrous sulfate heptahydrate ( _FeSO₄・_7H₂O , molecular weight: 278.05, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared instead of ferrous chloride tetrahydrate, and as a water-soluble nickel salt, nickel sulfate hexahydrate ( _NiSO₄・_6H₂O , molecular weight: 262.85, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared instead of nickel chloride hexahydrate.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.37 mass ppm (0.2 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). The amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that the molar ratio was 0.318 (31.8 mol%). Specifically, 272.0 g of ferrous sulfate heptahydrate, 202.0 g of nickel sulfate hexahydrate, 99.3 μg of palladium(II) ammonium chloride, and 163.5 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare the metal salt raw material solution.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was 6.41 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that it was 4.67 in molar ratio. Specifically, 326 g of sodium hydroxide was dissolved in 800 mL of pure water to prepare a sodium hydroxide solution, and 934 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution was prepared in the same manner as in Example 1.

(d) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 70°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 59°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 32.6 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 59°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the reaction started, and was maintained at 70°C after 10 minutes from the start of the reaction (reaction holding temperature 70°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. At this point, the reaction solution was black, but within 30 minutes of the start of the reaction, the supernatant became clear. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after completion was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.38 μm.

[Example 5]
In Example 5, an iron-nickel alloy powder containing 51 mol% iron (Fe) and 49 mol% nickel (Ni) with a nickel-rich surface composition was prepared according to the procedure shown in Figure 6. At this time, an additional raw material solution was added and mixed towards the end of the crystallization process. Specifically, first, the crystallization of an iron-nickel alloy powder containing 56 mol% iron (Fe) and 44 mol% nickel (Ni) was carried out in the same manner as in Example 4, except that the amount of hydrazine as a reducing agent was different. During this crystallization, a water-soluble nickel salt aqueous solution was added to the reaction solution as an additional raw material solution and mixed.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.37 mass ppm (0.2 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.318 (31.8 mol%). Specifically, 272.0 g of ferrous sulfate heptahydrate, 202.0 g of nickel sulfate hexahydrate, 99.3 μg of palladium(II) ammonium chloride, and 163.5 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare the metal salt raw material solution.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that, in the reaction solution to be prepared in the subsequent crystallization step, the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 4.85 in molar ratio (4.41 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). The amount of sodium hydroxide was also weighed so that the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 4.67 in molar ratio (4.24 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). Specifically, 326 g of sodium hydroxide was dissolved in 800 mL of pure water to prepare a sodium hydroxide solution, and 707 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that, in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.16 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material solution An additional raw material solution containing nickel sulfate hexahydrate (water-soluble nickel salt) and water was prepared. At this time, the amount of magnetic metal (Ni) in the obtained additional raw material solution was 0.175 moles, which was weighed to be 0.10 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution of 1.747 moles. Specifically, 46.0 g of nickel sulfate hexahydrate was dissolved in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 70°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 57°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 35.2 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 57°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at 70°C after 10 minutes from the start of the reaction (reaction holding temperature 70°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. From 11 minutes after the start of the reaction to 16 minutes after the start of the reaction, additional starting material solution was added dropwise and mixed to promote the reduction of iron ions (or iron hydroxide), which are difficult to reduce, and to advance the reduction reaction so that the surface of the precipitated iron-nickel crystallized powder would become more nickel-rich. After the addition of the additional starting material solution, the concentration of magnetic metals (Fe and Ni) in the reaction solution was 32.8 g/L. The reaction solution was black at this time, but the supernatant became clear within 30 minutes of the start of the reaction. It is considered that the reduction reaction was completely finished, and all the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.40 μm.

[Example 6]
In Example 6, the crystallized powder obtained in Example 1 was subjected to a spiral jet crushing treatment, a dry crushing method, using a miniature jet crusher (JKE-30, Nippon Pneumatic Co., Ltd.) at a crushing gas pressure of 0.5 MPa to produce an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The resulting alloy powder had a sharp particle size distribution, similar to Example 1, with an average particle size of 0.41 μm. Furthermore, the spiral jet crushing treatment reduced aggregated particles, improving packing efficiency (increasing compact density), and reduced surface irregularities, resulting in a composition of very smooth spherical particles.

[Example 7]
In Example 7, following the crystallization process, the slurry-like crystallized powder before drying was subjected to a high-pressure fluid impingement treatment, which is a wet crushing process, to produce an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni).

<Recovery process (including crushing process)>
A slurry-like reaction solution containing iron-nickel crystallized powder obtained by the same crystallization process as in Example 1 was filtered and washed, and then a washed crystallized powder slurry with a concentration of 20% by mass of iron-nickel crystallized powder was prepared using pure water with an conductivity of 1 μS/cm. The above filtration and washing was carried out using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The washed crystallized powder slurry was subjected to crushing treatment by passing it through a high-pressure fluid impingement crushing apparatus (manufactured by Sugino Machine; pressure: 200 MPa) for two passes, and then subjected to solid-liquid separation treatment to recover cake-like iron-nickel crystallized powder. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. Then, the dried crystallized powder was cooled to 35°C in a vacuum, and then subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen to obtain iron-nickel alloy powder. The resulting alloy powder had a sharp particle size distribution, similar to Example 1, with an average particle size of 0.41 μm. Furthermore, the high-pressure fluid impact crushing treatment reduced aggregated particles, improving packing efficiency (increasing compacted particle density), and reduced surface irregularities, resulting in a composition of very smooth spherical particles.

[Example 8]
In Example 8, the crystallized powder obtained according to the procedure shown in Figure 6 was subjected to high-temperature heat treatment to produce an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni). In Example 8, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 2.81 mass ppm (1.50 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.724 (72.4 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 318.1 g of ferrous sulfate heptahydrate, 161.9 g of nickel sulfate heptahydrate, 750.5 μg of palladium(II) ammonium chloride, and 374.7 g of trisodium citrate dihydrate in 950 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 8.98 in molar ratio, and the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was weighed so that the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 7.07 in molar ratio. Specifically, 497.5 g of sodium hydroxide was dissolved in 1218 mL of pure water to prepare a sodium hydroxide solution, and 1318 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metal (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.06 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 80°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 71°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 25.0 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 71°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 80°C from 10 minutes after the start of the reaction (reaction holding temperature 80°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise to the reaction solution and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. At this point, the reaction solution was black, but within 40 minutes of the start of the reaction, the supernatant became clear. It is considered that the reduction reaction was completely finished, and all the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallization powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallization powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallization powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen.

<High-temperature heat treatment process>
The crystallized powder obtained in this manner was subjected to a high-temperature heat treatment by heating at 350°C for 60 minutes in a nitrogen atmosphere to produce an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni). The resulting alloy powder had a sharp particle size distribution, similar to Example 1, with an average particle size of 0.27 μm. Furthermore, the high-temperature heat treatment promoted the diffusion of Fe and Ni within the iron (Fe)-nickel (Ni) alloy particles, improving the compositional uniformity within the particles and reducing variations in properties within the particles.

[Example 9]
In Example 9, an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni) with a nickel-rich surface composition was prepared according to the procedure shown in Figure 6. During this process, an additional raw material solution was added and mixed in the middle of the crystallization process. Specifically, a metal salt raw material solution at room temperature was added and mixed to a reducing solution heated using a water bath to prepare a reaction solution, and the crystallization of the iron-nickel alloy powder containing 67.4 mol% iron (Fe) and 32.6 mol% nickel (Ni) was first carried out. During this crystallization process, a water-soluble nickel salt aqueous solution was added and mixed into the reaction solution as an additional raw material solution.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.97 mass ppm (0.52 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.750 (75.0 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 318.1 g of ferrous sulfate heptahydrate, 145.7 g of nickel sulfate hexahydrate, 250.0 μg of palladium(II) ammonium chloride, and 374.7 g of trisodium citrate dihydrate in 500 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that, in the reaction solution to be prepared in the subsequent crystallization step, the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 7.62 in molar ratio (7.36 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). Also, the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was weighed so that the amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 7.33 in molar ratio (7.07 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). Specifically, 497.5 g of sodium hydroxide was dissolved in 1218 mL of pure water to prepare a sodium hydroxide solution, and 1080 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metal (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.06 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material solution An additional raw material solution containing nickel sulfate hexahydrate (water-soluble nickel salt) and water was prepared. At this time, the amount of magnetic metal (Ni) in the obtained additional raw material solution was 0.0616 moles, which was weighed to be 0.035 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution of 1.760 moles. Specifically, 16.2 g of nickel sulfate hexahydrate was dissolved in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 80°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 75°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 29.1 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 75°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the reaction started, and was maintained at 80°C after 10 minutes from the start of the reaction (reaction holding temperature 80°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution turned dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. From 25 minutes to 35 minutes after the start of the reaction, additional starting material solution was added dropwise and mixed to promote the reduction of iron ions (or iron hydroxide), which are difficult to reduce, and to advance the reduction reaction so that the surface of the precipitated iron-nickel crystallized powder became more nickel-rich. After adding the additional starting material solution, the concentration of magnetic metals (Fe and Ni) in the reaction solution was 28.4 g/L. The reaction solution was black at this time, but the supernatant became clear within 40 minutes from the start of the reaction. It is considered that the reduction reaction was completely finished, and all the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.39 μm.

[Example 10]
In Example 10, an iron-nickel alloy powder containing 80 mol% iron (Fe) and 20 mol% nickel (Ni), with a high iron content, was prepared according to the procedure shown in Figure 6. During this process, an additional raw material solution was added and mixed in the middle of the crystallization process. Specifically, a metal salt raw material solution at room temperature was added and mixed to a reducing solution heated using a water bath to prepare a reaction solution, and the crystallization of the iron-nickel alloy powder containing 83.3 mol% iron (Fe) and 16.7 mol% nickel (Ni) was first carried out. During this crystallization process, a water-soluble nickel salt aqueous solution was added and mixed into the reaction solution as an additional raw material solution.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.79 mass ppm (0.42 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.754 (75.4 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 394.3 g of ferrous sulfate heptahydrate, 74.6 g of nickel sulfate hexahydrate, 201.6 μg of palladium(II) ammonium chloride, and 377.5 g of trisodium citrate dihydrate in 836 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that, in the reaction solution to be prepared in the subsequent crystallization step, the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 9.40 in molar ratio (9.02 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). The amount of sodium hydroxide was also weighed so that, relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 7.37 in molar ratio (7.07 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). Specifically, 501.3 g of sodium hydroxide was dissolved in 1228 mL of pure water to prepare a sodium hydroxide solution, and 1334 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that, in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metal (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.07 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material solution An additional raw material solution containing nickel sulfate hexahydrate (water-soluble nickel salt) and water was prepared. At this time, the amount of magnetic metal (Ni) in the obtained additional raw material solution was 0.0709 moles, which was weighed to be 0.04 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution of 1.773 moles. Specifically, 18.64 g of nickel sulfate hexahydrate was dissolved in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 80°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 71°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 24.5 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 71°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 80°C from 10 minutes after the start of the reaction (reaction holding temperature 80°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. From 8 minutes after the start of the reaction to 18 minutes after the start of the reaction, additional starting material solution was added dropwise and mixed to promote the reduction of iron ions (or iron hydroxide), which are difficult to reduce, and to advance the reduction reaction so that the surface of the precipitated iron-nickel crystallized powder would become more nickel-rich. After adding the additional starting material solution, the concentration of magnetic metals (Fe and Ni) in the reaction solution was 24.2 g/L. The reaction solution was black at this time, but the supernatant became clear within 60 minutes of the start of the reaction. It is considered that the reduction reaction was completely finished, and all the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the crystallized powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.48 μm.

[Example 11]
In Example 11, an iron-nickel alloy powder containing 90 mol% iron (Fe) and 10 mol% nickel (Ni), with a high iron content, was prepared according to the procedure shown in Figure 6. During this process, an additional raw material solution was added and mixed in the middle of the crystallization process. Specifically, a metal salt raw material solution at room temperature was added and mixed to a reducing solution heated using a water bath to prepare a reaction solution, and the crystallization of the iron-nickel alloy powder containing 91.8 mol% iron (Fe) and 8.2 mol% nickel (Ni) was first carried out. During this crystallization process, a water-soluble nickel salt aqueous solution was added and mixed into the reaction solution as an additional raw material solution.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.77 mass ppm (0.41 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.369 (36.9 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 446.0 g of ferrous sulfate heptahydrate, 37.5 g of nickel sulfate heptahydrate, 202.6 μg of palladium(II) ammonium chloride, and 189.7 g of trisodium citrate dihydrate in 720 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that, in the reaction solution to be prepared in the subsequent crystallization step, the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 9.15 in molar ratio (8.97 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). The amount of sodium hydroxide was also weighed so that, relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction was 8.29 in molar ratio (8.13 in molar ratio relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution was added). Specifically, 579 g of sodium hydroxide was dissolved in 1418 mL of pure water to prepare a sodium hydroxide solution, and 1334 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that, in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metal (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.07 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material solution An additional raw material solution containing nickel sulfate hexahydrate (water-soluble nickel salt) and water was prepared. At this time, the amount of magnetic metal (Ni) in the obtained additional raw material solution was 0.0356 moles, which was weighed to be 0.02 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution of 1.747 moles. Specifically, 9.37 g of nickel sulfate hexahydrate was dissolved in 100 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 85°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 78°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 25.0 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 78°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at 85°C after 10 minutes from the start of the reaction (reaction holding temperature 85°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution turned dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. From 8 minutes after the start of the reaction to 18 minutes after the start of the reaction, additional starting material solution was added dropwise and mixed to promote the reduction of iron ions (or iron hydroxide), which are difficult to reduce, and to advance the reduction reaction so that the surface of the precipitated iron-nickel crystallized powder would become more nickel-rich. After adding the additional starting material solution, the concentration of magnetic metals (Fe and Ni) in the reaction solution was 24.8 g/L. The reaction solution was black at this time, but the supernatant became clear within 50 minutes from the start of the reaction. It is considered that the reduction reaction was completely finished, and all the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after the completion of the reaction was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, an iron-nickel alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.38 μm.

[Example 12]
In Example 12, the crystallized powder obtained according to the procedure shown in Figure 5 was subjected to an insulating coating treatment to produce an iron-nickel alloy powder containing 55 mol% iron (Fe) and 45 mol% nickel (Ni) coated with silicon dioxide ( _SiO₂ ), an insulating metal oxide. In Example 12, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.56 mass ppm (0.3 mol ppm) relative to the total amount of magnetic metals (Fe and Ni). In addition, the amount of trisodium citrate dihydrate relative to the total amount of magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.543 (54.3 mol%). Specifically, a metal salt raw material solution was prepared by dissolving 267.7 g of ferrous sulfate heptahydrate, 207.1 g of nickel sulfate heptahydrate, 149.3 μg of palladium(II) ammonium chloride, and 279.6 g of trisodium citrate dihydrate in 950 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was 4.85 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) was also weighed so that it was 4.95 in molar ratio. Specifically, 346 g of sodium hydroxide was dissolved in 848 mL of pure water to prepare a sodium hydroxide solution, and 709 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(c) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that in the reaction solution for the subsequent crystallization step, the amount of ethylenediamine relative to the total amount of magnetic metal (Fe and Ni) after the addition of additional raw material solution was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.05 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallized powder The prepared reducing agent solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 70°C. Then, the metal salt raw material solution, which was heated in the water bath, was added to the reducing agent solution at a liquid temperature of 25°C and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 59°C. The concentration of magnetic metals (Fe and Ni) in the reaction solution was 33.9 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 59°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the reaction started, and was maintained at 70°C after 10 minutes from the start of the reaction (reaction holding temperature 70°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ) and nickel hydroxide (Ni(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate in the reaction solution. At this point, the reaction solution was black, but within 30 minutes of the start of the reaction, the supernatant became clear. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron and nickel components in the reaction solution were reduced to metallic iron and metallic nickel. The reaction solution after completion was a slurry containing iron-nickel crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel crystallization powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallization powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallization powder to 35°C in a vacuum, the crystallization powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, dry crystallization powder (iron-nickel alloy powder) was obtained. The obtained crystallization powder (alloy powder) consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.39 μm.

<Insulation coating process>
50.0 g of the crystallized powder (alloy powder) obtained in the above recovery process was placed in a sealed polypropylene container, and 7.0 g of pure water and 50.0 g of ethyl alcohol ( _C₂H₅OH , molecular weight: 46.07, reagent manufactured by Wako Pure Chemical Industries _, Ltd.) were added to disperse the crystallized powder (alloy powder) in the mixed solvent of water and ethyl alcohol. Then, 9.8 g of tetraethoxysilane (also known as tetraethyl orthosilicate, tetraethyl silicate) (abbreviation: TEOS) (Si( _OC₂H₅ ) _{₄ ,} molecular weight: 208.33, reagent manufactured by Wako Pure Chemical Industries, Ltd.) as a silicon alkoxide was added and thoroughly mixed. Finally, 2.4 g of 1% by mass aqueous ammonia as a base catalyst (alkaline catalyst) for the hydrolysis of the silicon alkoxide was added while stirring to obtain a homogeneous slurry. The 1% by mass aqueous ammonia mentioned above was prepared by diluting the reagent's 28-30% by mass aqueous ammonia ( _NH3 , molecular weight: 17.03, reagent manufactured by Wako Pure Chemical Industries, Ltd.) with pure water. The crystallization powder (alloy powder), water, ethyl alcohol, tetraethoxysilane, and 1% by mass aqueous ammonia were all used at room temperature, and all additions and mixing were also carried out at room temperature.

The slurry containing crystallizing powder (alloy powder), water, ethyl alcohol, tetraethoxysilane, and ammonia was kept at 40°C for two days in a rotating polypropylene sealed container. While stirring the slurry, hydrolysis and dehydration condensation polymerization of tetraethoxysilane proceeded, forming an insulating coating layer on the particle surface of the crystallizing powder (alloy powder) mainly composed of hydrolyzed polymers of tetraethoxysilane (with a small amount of silanol groups (Si-OH) but a composition almost entirely of silicon dioxide ( _SiO₂ )). After this, the slurry was subjected to filtration washing and solid-liquid separation treatment to recover the cake-like crystallizing powder (alloy powder). Filtration washing was performed first with ethanol containing 50% by mass of pure water, and then with ethanol. Furthermore, the hydrolyzed polymer of tetraethoxysilane that remains in the slurry without being consumed as an insulating coating on the surface of the crystallized powder (alloy powder) particles is a particle with a very small molecular weight (silica sol) and is removed as filtrate during filtration and washing, so it does not remain in the recovered cake-like crystallized powder (alloy powder).

The recovered cake-like crystallized powder (alloy powder) was dried in a vacuum dryer at 50°C, and then subsequently subjected to heat treatment at 150°C for 2 hours in a vacuum. This heat treatment caused further dehydration and condensation polymerization of the hydrolyzed polymer of tetraethoxysilane constituting the insulating coating layer, resulting in harder and denser silicon dioxide ( _SiO₂ ), further improving the insulating properties of the insulating coating layer. This insulating coating treatment yielded iron-nickel alloy powder with an insulating coating layer made of high-resistance silicon dioxide ( _SiO₂ ) formed on the particle surface. The obtained alloy powder consisted of spherical particles with a smooth surface. The particle size distribution was sharp, with an average particle size of 0.42 μm, and the thickness of the insulating coating layer was estimated to be approximately 0.015 μm (approximately 15 nm). Furthermore, the resistivity of the compacted powder (applied pressure: 64 MPa) increased significantly after the insulating coating treatment, from 0.04 Ω·cm before the insulating coating treatment to over the measurement range (> ^10⁷ Ω·cm).

[Example 13]
In Example 13, an iron-nickel alloy powder (iron-nickel-cobalt alloy powder) containing 80 mol% iron (Fe), 10 mol% nickel (Ni), and 10 mol% cobalt (Co) was prepared according to the procedure shown in Figure 5. In Example 13, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 4 were prepared as a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a complexing agent, a reducing agent, a pH adjuster, and an amine compound. In addition, cobalt sulfate heptahydrate ( _CoSO₄・_7H₂O , molecular weight: 281.103, reagent manufactured by Wako Pure Chemical Industries, Ltd.) was prepared as a water-soluble cobalt salt.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), cobalt sulfate heptahydrate (water-soluble cobalt salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.38 mass ppm (0.2 mol ppm) relative to the total amount of magnetic metals (Fe, Ni, and Co). In addition, the amount of trisodium citrate was weighed so that the molar ratio was 0.362 (36.2 mol%) relative to the total amount of magnetic metals (Fe, Ni, and Co). Specifically, a metal salt raw material solution was prepared by dissolving 394.1 g of ferrous sulfate heptahydrate, 46.6 g of nickel sulfate heptahydrate, 49.8 g of cobalt sulfate heptahydrate, 100.8 μg of palladium(II) ammonium chloride, and 188.7 g of trisodium citrate dihydrate in 1000 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was 3.65 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe, Ni, and Co) was also weighed so that it was 7.07 in molar ratio. Specifically, 501 g of sodium hydroxide was dissolved in 1227 mL of pure water to prepare a sodium hydroxide solution, and 540 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(d) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that the amount of ethylenediamine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.07 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared metal salt raw material solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 85°C. Then, the metal salt raw material solution at a liquid temperature of 25°C was added to the reducing agent solution heated in the water bath and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 70°C. The concentration of magnetic metals (Fe, Ni, and Co) in the reaction solution was 31.2 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 70°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the reaction started, and was maintained at 85°C after 10 minutes from the start of the reaction (reaction holding temperature 85°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ), nickel hydroxide (Ni(OH) _₂ ), and cobalt hydroxide (Co(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel-cobalt crystallized powder to precipitate in the reaction solution. The reaction solution was black at this time, but the supernatant became clear within 40 minutes of the start of the reaction. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron, nickel, and cobalt components in the reaction solution were reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after completion was a slurry containing iron-nickel-cobalt crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel-cobalt crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, nitrogen gas containing 1.0 volume% oxygen was supplied to deoxidize the crystallized powder. In this way, an iron-nickel-cobalt alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.42 μm.

[Example 14]
In Example 14, an iron-nickel alloy powder (iron-nickel-cobalt alloy powder) containing 70 mol% iron (Fe), 10 mol% nickel (Ni), and 20 mol% cobalt (Co) was prepared according to the procedure shown in Figure 5. In Example 14, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 13 were prepared as a water-soluble iron salt, water-soluble nickel salt, water-soluble cobalt salt, nucleating agent, complexing agent, reducing agent, pH adjuster, and amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), cobalt sulfate heptahydrate (water-soluble cobalt salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.38 mass ppm (0.2 mol ppm) relative to the total amount of magnetic metals (Fe, Ni, and Co). In addition, the amount of trisodium citrate was weighed so that the molar ratio was 0.362 (36.2 mol%) relative to the total amount of magnetic metals (Fe, Ni, and Co). Specifically, a metal salt raw material solution was prepared by dissolving 343.0 g of ferrous sulfate heptahydrate, 46.3 g of nickel sulfate heptahydrate, 99.1 g of cobalt sulfate heptahydrate, 100.2 μg of palladium(II) ammonium chloride, and 187.6 g of trisodium citrate dihydrate in 1100 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was 1.46 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe, Ni, and Co) was also weighed so that it was 7.07 in molar ratio. Specifically, 499 g of sodium hydroxide was dissolved in 1221 mL of pure water to prepare a sodium hydroxide solution, and 215 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(d) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that the amount of ethylenediamine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.06 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared metal salt raw material solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 85°C. Then, the metal salt raw material solution at a liquid temperature of 25°C was added to the reducing agent solution heated in the water bath and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 67°C. The concentration of magnetic metals (Fe, Ni, and Co) in the reaction solution was 33.7 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 67°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 85°C from 10 minutes after the start of the reaction (reaction holding temperature 85°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ), nickel hydroxide (Ni(OH) _₂ ), and cobalt hydroxide (Co(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution's color changed to dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel-cobalt crystallized powder to precipitate in the reaction solution. The reaction solution was black at this time, but the supernatant became clear within 40 minutes of the start of the reaction. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron, nickel, and cobalt components in the reaction solution were reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after completion was a slurry containing iron-nickel-cobalt crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel-cobalt crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, the powder was subjected to deoxidation treatment by supplying nitrogen gas containing 1.0 volume% oxygen. In this way, iron-nickel-cobalt alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.40 μm.

[Example 15]
In Example 15, an iron-nickel alloy powder (iron-nickel-cobalt alloy powder) containing 65 mol% iron (Fe), 10 mol% nickel (Ni), and 25 mol% cobalt (Co) was prepared according to the procedure shown in Figure 5. In Example 15, when preparing the reaction solution, a metal salt raw material solution at room temperature was added to a reducing solution heated using a water bath and mixed.

<Preparation process>
The same raw materials as in Example 13 were prepared as a water-soluble iron salt, water-soluble nickel salt, water-soluble cobalt salt, nucleating agent, complexing agent, reducing agent, pH adjuster, and amine compound.

<Crystallization process>
(a) Preparation of metal salt raw material solution A metal salt raw material solution was prepared containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), cobalt sulfate heptahydrate (water-soluble cobalt salt), palladium(II) ammonium chloride (nucleating agent), trisodium citrate dihydrate (complexing agent), and water. At this time, the metal salt raw material solution was weighed so that the amount of palladium (Pd) was 0.37 mass ppm (0.2 mol ppm) relative to the total amount of magnetic metals (Fe, Ni, and Co). The amount of trisodium citrate was also weighed so that the molar ratio was 0.362 (36.2 mol%) relative to the total amount of magnetic metals (Fe, Ni, and Co). Specifically, a metal salt raw material solution was prepared by dissolving 317.6 g of ferrous sulfate heptahydrate, 46.2 g of nickel sulfate heptahydrate, 123.5 g of cobalt sulfate heptahydrate, 100.0 μg of palladium(II) ammonium chloride, and 187.1 g of trisodium citrate dihydrate in 1100 mL of pure water.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the amount of hydrazine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was 1.47 in molar ratio. The amount of sodium hydroxide relative to the total amount of magnetic metals (Fe, Ni, and Co) was also weighed so that it was 7.07 in molar ratio. Specifically, 497 g of sodium hydroxide was dissolved in 1216 mL of pure water to prepare a sodium hydroxide solution, and 215 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution.

(d) Preparation of amine compound solution An amine compound solution containing ethylenediamine (amine compound) and water was prepared. At this time, the amount of ethylenediamine was weighed so that the amount of ethylenediamine relative to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution to be prepared in the subsequent crystallization step was a trace amount of 0.01 (1.0 mol%) in molar ratio. Specifically, 1.06 g of ethylenediamine was dissolved in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallized powder The prepared metal salt raw material solution was placed in a Teflon® coated stainless steel container (reaction vessel) with stirring blades, which was set up in a water bath, and heated while stirring until the liquid temperature reached 85°C. Then, the metal salt raw material solution at a liquid temperature of 25°C was added to the reducing agent solution heated in the water bath and mixed for a mixing time of 10 seconds to obtain a reaction solution at a liquid temperature of 67°C. The concentration of magnetic metals (Fe, Ni, and Co) in the reaction solution was 33.7 g/L. This initiated the reduction reaction (crystallization reaction) (reaction start temperature 67°C). The temperature of the reaction solution continued to rise due to heating in the water bath after the start of the reaction, and was maintained at a liquid temperature of 85°C from 10 minutes after the start of the reaction (reaction holding temperature 85°C). The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but changed to dark gray after a few minutes. The dark green color immediately after the start of the reaction is thought to be due to the reaction proceeding according to equation (6) above, which formed a coprecipitate of iron hydroxide (Fe(OH) _₂ ), nickel hydroxide (Ni(OH) _₂ ), and cobalt hydroxide (Co(OH) _₂ ) in the reaction solution. The change in color to dark gray a few minutes after the start of the reaction is thought to be due to nucleation caused by the action of the nucleating agent (palladium salt).

From 3 minutes after the start of the reaction, when the reaction solution turned dark gray, to 13 minutes after the start of the reaction, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel-cobalt crystallized powder to precipitate in the reaction solution. The reaction solution was black at this time, but the supernatant became clear within 30 minutes of the start of the reaction. It is considered that the reduction reaction of equation (6) above was completed, and all of the iron, nickel, and cobalt components in the reaction solution were reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after completion was a slurry containing iron-nickel-cobalt crystallized powder.

<Recovery Process>
The slurry-like reaction solution obtained in the crystallization process was subjected to filtration washing and solid-liquid separation to recover a cake-like iron-nickel-cobalt crystallized powder. Filtration washing was performed using pure water with an conductivity of 1 μS/cm until the conductivity of the filtrate filtered from the slurry was 10 μS/cm or less. The recovered cake-like crystallized powder was dried in a vacuum dryer set to 50°C. After cooling the dried crystallized powder to 35°C in a vacuum, nitrogen gas containing 1.0 volume% oxygen was supplied to deoxidize the crystallized powder. In this way, an iron-nickel-cobalt alloy powder was obtained. The obtained alloy powder consisted of spherical particles with smooth surfaces. The particle size distribution was sharp, and the average particle size was 0.42 μm.

[Comparative Example 1]
In Comparative Example 1, palladium(II) ammonium chloride (nucleating agent) was not added when preparing the metal salt raw material solution. Otherwise, the reaction solution was prepared and crystallized powder was precipitated in the same manner as in Example 1 to produce an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The concentration of magnetic metals (Fe and Ni) in the reaction solution was 32.3 g/L. The obtained alloy powder consisted of spherical particles, and the surface of these particles was uneven. The particle size distribution was sharp, and the average particle size was 0.65 μm.

[Comparative Example 2]
In Comparative Example 2, trisodium citrate dihydrate (complexing agent) was not added when preparing the metal salt raw material solution. Otherwise, the reaction solution was prepared and crystallized powder was precipitated in the same manner as in Example 1 to produce an iron-nickel alloy powder containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The concentration of magnetic metals (Fe and Ni) in the reaction solution was 33.3 g/L. The obtained alloy powder consisted of irregularly shaped particles, and the surface of these particles was uneven. The particle size distribution was broad, and the average particle size was 0.26 μm.

[Comparative Example 3]
In Comparative Example 3, when preparing the metal salt raw material solution, palladium(II) ammonium chloride (nucleating agent) and trisodium citrate dihydrate (complexing agent) were not added. Also, when preparing the reducing agent solution, a large amount of hydrazine (reducing agent) was added. Otherwise, the iron-nickel alloy powder (iron-nickel alloy powder) was prepared in the same manner as in Example 1. The preparation of the metal salt raw material solution and the reducing agent solution was carried out as shown below.

(a) Preparation of metal salt raw material solution A metal salt raw material solution containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), and water was prepared. Specifically, 173.60 g of ferrous chloride tetrahydrate and 207.55 g of nickel chloride hexahydrate were dissolved in 1200 mL of pure water to prepare the metal salt raw material solution.

(b) Preparation of reducing agent solution A reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water was prepared. At this time, the amount of hydrazine was weighed so that the molar ratio of the amount of magnetic metal (Fe and Ni) to the total amount of magnetic metal (Fe and Ni) in the reaction solution to be prepared in the subsequent crystallization step was 19.4. The amount of sodium hydroxide was also weighed so that the molar ratio of the amount of magnetic metal (Fe and Ni) was 4.96. Specifically, 346 g of sodium hydroxide was dissolved in 850 mL of pure water to prepare a sodium hydroxide solution, and 2828 g of 60% by mass of hydrated hydrazine was added to this sodium hydroxide solution and mixed to prepare the reducing agent solution. The reducing agent solution was heated to a liquid temperature of 37°C before use so that the reaction start temperature would be 55°C when the reducing agent solution was added and mixed with the metal salt raw material solution.

The resulting alloy powder consisted of relatively smooth, spherical particles. The particle size distribution was broad, with an average particle size of 0.22 μm.

The manufacturing conditions for the alloy powders in Examples 1-15 and Comparative Examples 1-3 are summarized in Table 1.

(2) Evaluation of iron-nickel alloy powders The iron-nickel alloy powders obtained in Examples 1 to 15 and Comparative Examples 1 to 3 were evaluated for various properties as follows.

<Composition analysis>
X-ray diffraction (XRD) measurements were performed using an X-ray diffractometer, and the presence or absence of alloy powder formation was confirmed from the obtained XRD data.

<Analysis of Metal Impurities>
The impurity content was analyzed. Oxygen content was measured using an oxygen analyzer (LECO Corporation, TC436) via the inert gas melting method, while carbon and sulfur content were measured using a carbon-sulfur analyzer (LECO Corporation, CS600) via the combustion method. Chlorine content was measured using an X-ray fluorescence analyzer (Spectris, Inc., Magix), and silicon and sodium content were measured using an ICP emission spectrometer (Agilent Technologies, Inc., 5100).

<Particle size (average particle size, coefficient of variation)>
The alloy powder was observed using a scanning electron microscope (SEM; JEOL Ltd., JSM-7100F) (magnification: 5,000 to 80,000 times). The observed images (SEM images) were analyzed, and the average particle size and the standard deviation of particle diameter, obtained by number mean, were calculated from the results. Furthermore, the coefficient of variation (CV value) was calculated according to equation (14) below to determine the particle size (average particle size, coefficient of variation) of the alloy powder.

<Intraparticle composition analysis>
A thin film of approximately 100 nm in thickness was created by embedding alloy powder in resin using a focused ion beam (FIB) system. The cross-section of the alloy particles in the processed sample was observed using a scanning transmission electron microscope (STEM; Hitachi High-Technologies Corporation, HD-2300A). The observation was performed under magnification conditions of 100,000 to 200,000x. The compositional distribution within the alloy particles was then determined by line analysis using an energy-dispersive x-ray spectroscopy (EDS) system. In this case, the composition was calculated from the detection count of characteristic X-rays (K-lines) of the measured element.

<Crystallite size>
The alloy powder was analyzed by X-ray diffraction (XRD), and the crystallite size was evaluated based on Scherrer's formula from the full width at half maximum of the X-ray diffraction peak of the (111) plane. The XRD measurement conditions were the same as those for the compositional analysis. The crystallite size represents the degree of crystallinity; a larger crystallite size indicates higher crystallinity.

<Density of compacted powder>
The compaction density of alloy powder was evaluated. Specifically, approximately 0.3 g of alloy powder was filled into a cylindrical hole (inner diameter 5 mm) of a mold. Then, using a press machine, it was molded into pellets with a diameter of 5 mm and a height of 3-4 mm at a pressure of 100 MPa. The mass and height of the obtained pellets were measured at room temperature, and the compaction density was calculated.

<Resistivity of compacted powder>
The resistivity of compacted alloy powder was measured using a powder resistance measurement system (Mitsubishi Chemical Analytec, MCP-PD51) to evaluate its conductivity (insulation). Specifically, approximately 4 g of alloy powder was filled into the cylindrical sample chamber of the device, and a pressure of 64 MPa was applied using the press attached to the device to determine the resistivity of the compacted powder (unit: Ω・cm).

<Magnetic properties (saturation magnetic flux density, coercivity)>
The magnetic properties (saturation magnetic flux density (T: Tesla), coercivity (A/m)) of the alloy powder were evaluated using a vibrating sample magnetometer (VSM). The values of saturation magnetic flux density and coercivity were calculated from the B-H curve (magnetic hysteresis curve) obtained from the measurements. In Comparative Example 2, the alloy powder was not subjected to magnetic property measurements because its shape was irregular and unsuitable for use in devices such as inductors.

(3) Evaluation Results The evaluation results obtained for Examples 1 to 15 and Comparative Examples 1 to 3 are summarized in Table 2. SEM images of the alloy powders obtained in Examples 1, 2, 10, 13, and 14 are shown in Figures 13, 14, 18, 20, and 21, and the SEM image of the alloy powder obtained in Example 6 is shown in Figures 15(a) and (b). Here, Figure 15(a) is the SEM image of the alloy powder before spiral jet crushing treatment, and Figure 15(b) is the SEM image of the alloy powder after spiral jet crushing treatment. Furthermore, STEM images of the particle cross-sections and EDS line analysis results of the alloy powders obtained in Examples 8 and 9 are shown in Figures 16(a), (b), and 17, respectively. Here, Figure 16(a) is the STEM image of the particle cross-section and EDS line analysis results of the alloy powder before high-temperature heat treatment, and Figure 16(b) is the STEM image of the particle cross-section and EDS line analysis results of the alloy powder after high-temperature heat treatment. SEM images of the alloy powder obtained in Example 12 are shown in Figures 19(a) and (b). Here, Figure 19(a) is an SEM image of the alloy powder before insulating coating treatment, and Figure 19(b) is an SEM image of the alloy powder after insulating coating treatment. Furthermore, SEM images of the respective alloy powders obtained in Comparative Examples 1 to 3 are shown in Figures 22 to 24.

Examples 1, 3, and Comparative Examples 1-3 all describe the production of iron-nickel alloy powder using a reaction initiation temperature of 55°C and a reaction holding temperature of 70°C during the crystallization process. In Examples 1 and 3, which used trace amounts of specific nucleating agents and complexing agents, the resulting alloy powders were fine, with an average particle size of 0.40-0.41 μm, a low CV value, and a sharp particle size distribution, despite the low amount of hydrazine used as a reducing agent. Furthermore, these alloy powders were spherical and had smooth surfaces.

On the other hand, in Comparative Example 1, which did not use a nucleating agent, the resulting alloy powder had a large average particle size of 0.65 μm compared to Examples 1 and 3, making refinement difficult. Furthermore, although spherical, it had significant surface irregularities. In Comparative Example 2, which did not use a complexing agent, the resulting alloy powder had a fine average particle size of 0.26 μm, but it had a high CV value and a wide particle size distribution. Moreover, the alloy powder had significant surface irregularities and an irregular shape. In Comparative Example 3, which did not use a nucleating agent or complexing agent and contained a large amount of reducing agent (hydrazine), the resulting alloy powder was a relatively smooth, spherical powder. This is thought to be due to a strong reduction reaction caused by the large amount of hydrazine. The resulting alloy powder also had a fine average particle size of 0.22 μm. However, it had a high CV value and a wide particle size distribution.

Example 2 describes the production of an iron-nickel-cobalt alloy powder using a specific nucleating agent and complexing agent, with a reaction initiation temperature of 55°C and a reaction holding temperature of 70°C during the crystallization process. Despite the low amount of hydrazine used as a reducing agent, the resulting alloy powder was fine, with an average particle size of approximately 0.3 μm, and exhibited a sharp particle size distribution. Furthermore, the alloy powder had a smooth, spherical surface. The saturation magnetization of the alloy powder was also high.

Example 5 describes the production of an iron-nickel alloy powder containing 51 mol% iron (Fe) and 49 mol% nickel (Ni) with a nickel-rich surface composition, by adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization. A dense oxide film is formed due to the nickel-rich surface composition, suppressing oxidation of the particle surface. Therefore, this alloy powder is not only more stable in the atmosphere but also exhibits excellent magnetic properties, such as saturation magnetic flux density.

Example 6 describes the production of spherical, very smooth-surfaced iron-nickel alloy powder by subjecting the dry crystallized powder obtained through the crystallization and recovery processes to spiral jet crushing. Example 7 describes the production of spherical, very smooth-surfaced iron-nickel alloy powder by subjecting the slurry-like crystallized powder (a portion of the powder obtained during the recovery process after the crystallization) to high-pressure fluid impact crushing. These alloy powders exhibit not only smooth surfaces but also reduced aggregated particles. Therefore, packing performance is improved (compacted particle density increases). Furthermore, the reduction in aggregated particles is expected to improve eddy current loss between particles.

Example 8 describes the production of an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni) by subjecting the crystallized powder, obtained in a crystallization process with a reaction initiation temperature of 71°C and a reaction holding temperature of 80°C, to high-temperature heat treatment to improve the uniformity of the composition within the particles. As is clear from Figure 16(b), this alloy powder achieves a uniform composition within the particles (65 mol% iron and 35 mol% nickel), and is expected to be used not only as a soft magnetic material but also as a low thermal expansion material (Invar alloy).

Example 9 describes the production of an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni) with a nickel-rich surface composition by adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization. As is clear from Figure 17, a nickel-rich layer approximately 10-15 nm thick is formed on the particle surface. This nickel-rich surface composition results in the formation of a dense oxide film, suppressing oxidation of the particle surface. Therefore, this alloy powder is not only more stable in the atmosphere but also exhibits excellent magnetic properties, such as saturation magnetic flux density.

Examples 10 and 11 describe the production of iron-nickel alloy powders containing 80 mol% iron (Fe) and 20 mol% nickel (Ni), and iron-nickel alloy powders containing 90 mol% iron (Fe) and 10 mol% nickel (Ni), respectively. These were achieved by adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization, thereby promoting the reduction of iron ions (or iron hydroxide) that are difficult to reduce, and resulting in a nickel-rich composition on the particle surface. Despite having a high iron content of 80 mol% to 90 mol%, close to pure iron, the alloy powders obtained were fine with an average particle size of approximately 0.4 to 0.5 μm, a sharp particle size distribution, a smooth surface, and spherical shape, without reduction failure even with a relatively small amount of hydrazine used as a reducing agent. Furthermore, the saturation magnetization of the alloy powders was as high as that of pure iron powder (1.95 T to 2.0 T).

Compared to Examples 1-7, Examples 8-11 show a lower compaction density of the iron-nickel alloy powder obtained. However, while the true specific gravity of the iron-nickel alloy powders in Examples 1-7 (iron-nickel alloy powder containing 56-50 mol% Fe and 44-50 mol% Ni, and iron-nickel-cobalt alloy powder containing 50 mol% Fe, 40 mol% Ni, and 10 mol% Co) is 8.2-8.25, the true specific gravity of the iron-nickel alloy powders in Examples 8 and 9 (iron-nickel alloy powder containing 65 mol% Fe and 35 mol% Ni) is 8.1. The true specific gravity of the iron-nickel alloy powder of Example 0 (containing 80 mol% Fe and 20 mol% Ni) is 8.0, and the true specific gravity of the iron-nickel alloy powder of Example 11 (containing 90 mol% Fe and 10 mol% Ni) is 7.9. Considering that the true specific gravity of iron-nickel alloy powder decreases as the iron content increases, it can be seen that the compacted powder density in each example is good.

Example 12 describes a method for producing an iron-nickel alloy powder in which the particle surface is coated with high-resistance silicon dioxide ( _SiO₂ ) by applying an insulating coating to the crystallized powder obtained as a dry powder through the crystallization and recovery processes. Because the insulation between particles of this alloy powder is greatly improved (the resistivity of the compacted powder increases significantly), improvement in eddy current loss between particles can be expected.

Examples 13 to 15 describe the production of iron-nickel alloy powders with a cobalt content of 10 mol% to 25 mol% and a high iron content of 65 mol% to 80 mol% by adding a water-soluble cobalt salt to a magnetic metal source in addition to water-soluble iron salt and water-soluble nickel salt, thereby promoting the reduction of iron ions (or iron hydroxide) that are difficult to reduce. Specifically, these are examples of producing iron-nickel-cobalt alloy powders containing 80 mol% Fe, 10 mol% Ni, and 10 mol% Co; iron-nickel-cobalt alloy powders containing 70 mol% Fe, 10 mol% Ni, and 20 mol% Co; and iron-nickel-cobalt alloy powders containing 65 mol% Fe, 10 mol% Ni, and 25 mol% Co. Despite a high iron content of 65 mol% to 80 mol%, spherical alloy powder was obtained without reduction failure even with a very small amount of hydrazine used as a reducing agent, thanks to the reduction reaction-promoting effect of cobalt addition. This alloy powder had a fine average particle size of approximately 0.4 μm, a sharp particle size distribution, and a smooth surface. Furthermore, the saturation magnetization of the alloy powder was as high as or even higher than that of pure iron powder (1.95 T to 2.0 T).

Furthermore, the true specific gravity of the iron-nickel alloy powders (iron-nickel-cobalt alloy powders) obtained in Examples 13-15 is estimated to be around 8.0-8.1, but the compacted powder density was high and excellent in all cases. This is thought to be because the reduction reaction was completed before particle aggregation progressed due to the reduction reaction-promoting effect of cobalt addition, and as a result, particle aggregation during crystallization was suppressed. It is also thought that the improved particle packing ability due to the spheroidization-promoting effect of cobalt addition, another effect of cobalt addition, played a role.

Claims (7)

An iron (Fe)-nickel (Ni) alloy powder containing at least iron (Fe) and nickel (Ni) as magnetic metals, wherein the average particle size is 0.10 μm or more and 0.60 μm or less, and the coefficient of variation (CV value) obtained from the average particle size and standard deviation in the number particle size distribution according to the following formula (1) is 25% or less.
The alloy powder according to claim 1, further comprising cobalt (Co) as a magnetic metal. The alloy powder according to claim 1 or 2, wherein the iron (Fe) content is 10 mol% or more and 95 mol% or less, the nickel (Ni) content is 5 mol% or more and 90 mol% or less, and the cobalt (Co) content is 0 mol% or more and 40 mol% or less. The alloy powder according to claim 1 or 2, wherein the crystallite size is 30 nm or less. The alloy powder according to claim 1 or 2, wherein the saturation magnetic flux density is 1 T (Tesla) or more, and the coercivity is 2000 A/m or less. A compacted powder or sheet containing the alloy powder described in any one of claims 1 to 5. An inductor, reactor, choke coil, noise filter, transformer, rotating machine, generator, or radio wave absorber comprising the compacted powder and/or sheet described in claim 6.