TWI895751B - Alloy powder, pressed powder or sheet containing the above alloy powder, and magnetic device having the above pressed powder or sheet - Google Patents

Abstract

The present invention provides a method for producing an iron-nickel alloy powder having excellent powder properties and magnetic properties. The method is a method for producing an iron (Fe)-nickel (Ni) alloy powder containing at least iron (Fe) and nickel (Ni) as magnetic metals. The method further comprises the following steps: a preparation step of preparing a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjuster as starting materials; a crystallization step of preparing a reaction solution containing the starting materials and water, and crystallizing a crystallized powder containing the magnetic metal in the reaction solution through a reduction reaction; and a recovery step of recovering the crystallized powder from the reaction solution. The magnetic metal source comprises a water-soluble iron salt and a water-soluble nickel salt. The nucleating agent is a water-soluble salt of a metal that is more noble 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 ), and the pH adjuster is an alkali metal hydroxide.

Description

Alloy powder, pressed powder or sheet containing the above alloy powder, and magnetic device having the above pressed powder or sheet

The present invention relates to a method for producing iron (Fe)-nickel (Ni) alloy powder, iron (Fe)-nickel (Ni) alloy powder, a pressed powder or sheet containing the alloy powder, and an inductor, reactor, choke, noise filter, transformer, rotor, generator, or radio wave absorber incorporating the pressed powder or sheet.

Iron-nickel alloys, also known as permalloy, are soft magnetic materials with relatively high magnetic permeability, used in the cores of magnetic components such as chokes and inductors. In particular, iron-nickel alloy powders are used as the material for powdered cores (powdered magnetic cores), which are obtained by compression molding iron-nickel alloy powders.

There are various known types of mu-alloys, such as Mu-78 (Mu-alloy A) and Mu-45, each used based on its magnetic properties and intended use. Mu-78 is an iron-nickel alloy with a nickel content of approximately 78.5% by mass and exhibits high magnetic permeability. Mu-45 is an iron-nickel alloy with a nickel content of 45% by mass. Although its magnetic permeability is slightly lower, it exhibits a higher saturated magnetic flux density.

In recent years, the miniaturization and performance of mobile devices such as laptops and smartphones have been rapidly advancing. Consequently, magnetic components such as inductors are being required not only to improve magnetic properties but also to cope with higher frequencies. Consequently, materials for powder cores are being required to not only have higher magnetic flux density but also lower losses. Losses are primarily hysteresis and eddy current. To suppress hysteresis, it is effective to reduce the coercive force of the alloy powder. To suppress eddy current, it is effective to apply a thin insulating coating to the alloy powder surface to reduce eddy currents between particles, or to refine the alloy powder and reduce its particle size distribution. The reason is that if coarse particles are present, eddy currents can easily flow through them, causing losses due to Joule heat.

Traditionally, methods for producing fine alloy powders include atomization, vapor phase reduction, and dry reduction. The atomization method involves blowing water or gas into a molten metal to rapidly cool and solidify it. The vapor phase reduction method involves hydrogen reduction of a gaseous metal halide. The dry reduction method 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, chokes, inductors, and the like, produced by a vapor-phase reduction method (Patent Document 1, [0001] and [0014]). Patent Document 1 also describes heating a mixture of _NiCl₂ and _FeCl₃ to obtain vaporized chloride, which is then exposed to hydrogen to induce a reduction reaction, thereby producing a fine Ni-Fe alloy powder (Patent Document 1, [0016]). Furthermore, Patent Document 2 describes that Fe-Ni alloy powder used as a material for electronic components such as chokes and inductors is produced by reducing Fe and Ni oxides in a reducing gas (claim 1 of Patent Document 2).

On the other hand, the industry has proposed using wet methods to produce finer alloy powders. For example, Patent Document 3 discloses a method for producing nickel-iron alloy nanoparticles. The method is characterized by adding a reducing agent such as hydrazine to an aqueous solution containing nickel salt and iron salt, thereby simultaneously reducing the nickel ions and iron ions contained in the aqueous solution to produce nickel-iron alloy nanoparticles (claims 1-6 of Patent Document 3). Furthermore, it is believed that this production method can efficiently produce nickel-iron alloy nanoparticles on an industrial scale and at low production costs. These nickel-iron alloy nanoparticles are suitable as fillers for imparting magnetic properties, and the average primary particle size is less than 200 nm (Patent Document 3, [0015]).

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-193160

[Patent Document 2] Japanese Patent Application Laid-Open No. 2012-197474

[Patent Document 3] Japanese Patent Application Publication No. 2008-024961

Although it has been proposed to produce fine alloy powder by dry or wet methods, there is still room for improvement in the conventional technology in terms of obtaining alloy powder with excellent powder properties. For example, the average particle size of the alloy powder produced by the atomization method is relatively large, more than several μm, which does not fully meet the requirements of miniaturization. In addition, if the vapor phase reduction method proposed in Patent Document 1 is used, the particle size distribution of the obtained alloy powder is relatively wide. Therefore, the alloy powder contains coarse particles, which is not enough to reduce eddy loss. In addition, there is also the problem of unstable composition or particle size of the alloy powder. The dry reduction method proposed in Patent Document 2 requires high-temperature heating, so there is a problem that the obtained alloy powder is easily sintered to form coarse agglomerated particles.

The wet method proposed in Patent Document 3 differs from the dry method in that it conducts the reduction reaction at a low temperature, offering the advantage of being less likely to form coarse, agglomerated particles. Furthermore, even if agglomerated particles do form, the bonds between the particles are weak, making them easily disintegrated. However, the method proposed in Patent Document 3 requires the use of a large amount of hydrazine as a reducing agent. This significantly increases the cost of the reducing agent, making it impractical. Furthermore, the particle size distribution of the resulting alloy powder is rarely sufficiently small.

In light of this prior art, the inventors conducted intensive research. As a result, they discovered that, when producing iron-nickel alloy powders using a wet process, by using specific nucleating agents and complexing agents, alloy powders with excellent powder and magnetic properties can be obtained. Furthermore, they discovered that, when the iron content is relatively high, the addition of cobalt at a specified content ratio can accelerate the reduction reaction and spheroidization of the cobalt, resulting in spherical alloy powders with minimal agglomeration, a smooth surface, and a high saturated magnetic flux density, even with a very small amount of reducing agent.

The present invention was completed based on this insight, and its purpose is to provide a method for producing iron-nickel alloy powder with excellent powder properties and magnetic properties.

The present invention includes the following aspects (1) to (40). Furthermore, in this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

(1) A method for producing an iron (Fe)-nickel (Ni) alloy powder, wherein the iron (Fe)-nickel (Ni) alloy powder comprises at least iron (Fe) and nickel (Ni) as magnetic metals, the method comprising the following steps: a preparation step, wherein a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjusting agent are prepared as starting materials; a crystallization step, wherein a reaction solution comprising the starting materials and water is prepared; A method for preparing a crystalline powder containing the magnetic metal is provided. The method comprises: crystallizing a crystal powder containing the magnetic metal in a reaction solution by a reduction reaction; and recovering the crystal powder from the reaction solution. The magnetic metal source comprises a water-soluble iron salt and a water-soluble nickel salt; the nucleating agent is a water-soluble salt of a metal that is more noble 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 ); _and the pH adjusting agent is an alkali metal 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 (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), and ferrous nitrate (Fe(NO ₃ ) 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 (NiCl ₂ ), nickel sulfate (NiSO ₄ ), and nickel nitrate (Ni(NO ₃ ) ₂ ).

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

(5) The method according to any one 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)(CH ₂ COOH) ₂ COOH).

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

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

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

(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 (CoCl ₂ ), cobalt sulfate (CoSO ₄ ), and cobalt nitrate (Co(NO ₃ ) ₂ ).

(10) The method according to any one of (1) to (9) above, wherein the starting material further comprises an amine compound having two or more primary amine groups (-NH ₂ ), one primary amine group (-NH ₂ ) and one or more secondary amine groups (-NH-), or two or more secondary amine groups (-NH-) in the molecule.

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

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

(13) The method according to any one of (10) to (12) above, wherein the amine compound is at least one alkylene amine selected from the group consisting of ethylenediamine (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylenetetramine (H ₂ N(C ₂ H ₄ NH) ₂ C ₂ H ₄ NH ₂ ), tetraethylenepentamine (H ₂ N(C ₂ H ₄ NH) ₃ C ₂ H ₄ NH ₂ ), pentaethylenehexamine (H ₂ N(C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ), and propylenediamine (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ), and/or tris(2-aminoethyl)amine (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanolamine (H ₂ NC ₂ H ₄ NHC ₂ H ₄ OH), N-(2-aminoethyl)propanolamine (H ₂ NC ₂ H ₄ NHC ₃ H ₆ OH), 2,3-diaminopropionic acid (H ₂ NCH ₂ CH(NH)COOH), ethylenediamine-N,N'-diacetic acid (HOOCCH ₂ NHC ₂ H ₄ NHCH ₂ COOH), and 1,2-cyclohexanediamine (H ₂ NC ₆ H ₁₀ NH ₂ ).

(14) The method according to any one of (10) to (13) above, wherein the amount of the amine compound incorporated is not less than 0.01 mol% and not more than 5.00 mol% relative to the total amount of the magnetic metal.

(15) The method according to any one of (1) to (14) above, wherein, when preparing the reaction solution in the crystallization step, a metal salt raw material solution prepared by dissolving the magnetic metal source, the nucleating agent, and the complexing agent in water, a reducing agent solution prepared by dissolving the reducing agent in water, and a pH adjusting solution prepared by dissolving the pH adjusting agent in water are prepared respectively; the metal salt raw material solution and the pH adjusting solution are mixed to prepare a mixed solution; and the mixed solution is 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 set to be greater than 1 second and less than 180 seconds.

(18) The method according to any one of (1) to (14) above, wherein, when preparing the reaction solution in the crystallization step, a metal salt raw material solution prepared by dissolving the magnetic metal source, the nucleating agent, and the complexing agent in water, and a reducing agent solution prepared by dissolving the reducing agent and the pH adjusting agent in water are prepared separately, 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 vice versa, 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 set to be greater than 1 second and less than 180 seconds.

(21) The method according to any one of (1) to (20) above, wherein, in the crystallization step, before the reduction reaction is completed, an additional raw material solution prepared by dissolving at least one of the water-soluble nickel salt and the water-soluble cobalt salt in water is further added to the reaction solution and mixed.

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

(23) The method according to any one of (1) to (22) above, wherein the temperature of the reaction solution at the start of crystallization of the crystallization powder (reaction starting temperature) is 40°C to 90°C, and the temperature of the reaction solution maintained during crystallization after the start of crystallization (reaction holding temperature) is 60°C to 99°C.

(24) The method according to any one of (1) to (23) above further comprises a disintegration step, wherein the disintegration step is to perform a disintegration treatment using collision energy on the crystallized powder after the recovery step or during the recovery step, thereby disintegrating the agglomerated particles contained in the crystallized powder.

(25) As in the method of (24) above, the crystallized powder after the recovery step is crushed by dry crushing or wet crushing, or the crystallized powder during the recovery step is crushed 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 collision crushing.

(28) The method according to any one of (1) to (27) above further comprises a high temperature heat treatment step, wherein the crystallized powder after the recovery step or the crystallized powder during the recovery step is subjected to a heat treatment at a temperature exceeding 150°C and below 400°C in an inert environment, a reducing environment, or a vacuum environment, thereby improving the composition uniformity within the particles of the iron (Fe)-nickel (Ni) alloy powder.

(29) The method according to any one of (1) to (28) above further comprises an insulating coating step, wherein the insulating coating step is to perform an insulating coating treatment on the crystallization powder obtained through the recovery step, thereby forming an insulating coating layer composed of a metal oxide on the particle surface of the crystallization powder, thereby improving the insulation between the particles.

(30) The method of (29) above, wherein, during the insulating coating step, the crystallization powder is dispersed in a mixed solvent comprising water and an organic solvent, and a metal alkoxide is added and mixed into the mixed solvent to prepare a slurry. The metal alkoxide is hydrolyzed and dehydrated and condensed in the slurry to form an insulating coating composed of metal oxide on the surface of the crystallization powder particles. The crystallization powder with the insulating coating is then recovered from the slurry.

(31) The method of (30) above, wherein the metal alkoxide contains silane oxide (alkyl silicate) as a main component, and the metal oxide contains silicon dioxide (SiO ₂ ) as a main component.

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

(33) An iron (Fe)-nickel (Ni) alloy powder produced by any one of the methods (1) to (32) above.

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

CV value (%) = standard deviation of particle size/average particle size × 100‧‧‧(1)

(35) The alloy powder as described in (34) above, further comprising cobalt (Co) as a magnetic metal.

(36) The alloy powder as described in (34) or (35) above, wherein the amount of iron (Fe) is 10 mol% to 95 mol%, the amount of nickel (Ni) is 5 mol% to 90 mol%, and the amount of cobalt (Co) is 0 mol% to 40 mol%.

(37) The alloy powder as described in (34) or (35) above, wherein the crystallite diameter is less than 30 nm.

(38) The alloy powder as described in (34) or (35) above has a saturated magnetic flux density of 1 T (Tesla) or more and a coercive force of 2000 A/m or less.

(39) A pressed powder or tablet comprising the alloy powder of any one of (33) to (38) above.

(40) An inductor, a reactor, a choke, a noise filter, a transformer, a rotor, a generator, or a radio wave absorber, which comprises the pressed powder and/or sheet of (39) above.

According to the present invention, a method for producing iron-nickel alloy powder with excellent powder properties and magnetic properties is provided.

10: Inductor

12, 22, 32, 42, 52: Pressed powder core

14,24: Coil

16a, 16b: Input and output terminals

20: Chip Inductor

30: Reactor

34: 1st coil

36: Second coil

38: Connection

40: Stator

44,54: Winding

50: Rotor

56:Output shaft

[Figure 1] is a process diagram used to illustrate the method for manufacturing the alloy powder of this embodiment.

Figure 2 is a process diagram illustrating the preparation of the reaction solution and the production of alloy powder in the first embodiment.

Figure 3 is a process diagram illustrating the preparation of the reaction solution and the production of alloy powder in the first embodiment.

Figure 4 is a process diagram illustrating the preparation of the reaction solution and the production of alloy powder in the second embodiment.

Figure 5 is a process diagram illustrating the preparation of the reaction solution and the production of alloy powder in the second embodiment.

Figure 6 is a process diagram illustrating the preparation of the reaction solution and the production of alloy powder in the third embodiment.

[Figure 7] shows an example of using a powder compact containing alloy powder in an inductor (toroidal coil).

[Figure 8] shows an example of using a powder compact containing alloy powder in a chip inductor.

[Figure 9] shows an example of using a powder compact containing alloy powder in a reactor.

[Figure 10] shows an example of using a powder compact containing alloy powder in a stator of a rotating machine (motor) or a generator.

[Figure 11] shows an example of using a powder compact containing alloy powder in a rotor of a rotary machine (motor) or a generator.

Figure 12 shows the liquid temperature change in the reaction tank during the crystallization step of Example 1.

Figure 13 is a SEM image of the alloy powder obtained in Example 1.

Figure 14 is a SEM image of the alloy powder obtained in Example 2.

Figure 15 shows SEM images of the alloy powder obtained in Example 6 (before and after spiral jet disintegration treatment).

Figure 16 shows the STEM images and EDS line analysis results of the alloy powder obtained in Example 8 (before and after high-temperature heat treatment).

Figure 17 shows a STEM image of a particle cross-section of the alloy powder obtained in Example 9, along with EDS line analysis results.

Figure 18 is a SEM image of the alloy powder obtained in Example 10.

Figure 19 shows the SEM images of the alloy powder obtained in Example 12 (before and after insulation coating treatment).

Figure 20 is a SEM image of the alloy powder obtained in Example 13.

Figure 21 is a SEM image of the alloy powder obtained in Example 14.

Figure 22 is a SEM image of the alloy powder obtained in Comparative Example 1.

Figure 23 shows the SEM image of the alloy powder obtained in Comparative Example 2.

Figure 24 is a SEM image of the alloy powder obtained in Comparative Example 3.

The specific embodiments of the present invention (hereinafter referred to as "this embodiment") are described below. The present invention is not limited to the following embodiments and various modifications are possible without changing the gist of the present invention.

<<1. Method for producing iron-nickel alloy powder>>

The method for producing an iron (Fe)-nickel (Ni) alloy powder according to this embodiment includes the following steps: a preparation step of preparing starting materials comprising a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjuster; a crystallization step of preparing a reaction solution comprising the starting materials and water, wherein a crystallization powder comprising the magnetic metal is crystallized in the reaction solution through a reduction reaction; and a recovery step of recovering the crystallized powder from the reaction solution. Here, the iron (Fe)-nickel (Ni) alloy powder comprises at least iron (Fe) and nickel (Ni) as magnetic metals. Furthermore, the magnetic metal source comprises a water-soluble iron salt and a water-soluble nickel salt. The nucleating agent is a water-soluble salt of a metal that is more noble 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 (N ₂ H ₄ ).

The iron (Fe)-nickel (Ni) alloy powder (hereinafter sometimes referred to as "alloy powder") of this embodiment contains at least iron (Fe) and nickel (Ni). Furthermore, the alloy powder may also contain cobalt (Co) as needed. Specifically, 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 magnetic metals that exhibit ferromagnetism. Therefore, iron-nickel alloy powder or iron-nickel-cobalt alloy powder has a high saturated magnetic flux density and excellent magnetic properties. Furthermore, in this specification, "magnetic metal" is a general term for iron, nickel, and cobalt. That is, when the alloy does not contain cobalt, magnetic metal is a general term for iron and nickel; when the alloy contains cobalt, it is a general term for iron, nickel, and cobalt.

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

The alloy powder of this embodiment does not exclude the inclusion of other additives besides magnetic metals (Fe, Ni and Co). Examples of such additives include copper (Cu) and/or boron (B). However, in terms of maximizing the effects based on magnetic metals, the less the content of additives besides magnetic metals, the better. The content of other ingredients besides magnetic metals may be less than 10% by mass, less than 5% by mass, less than 1% by mass, or even 0% by mass. In addition, the alloy powder may contain impurities (inevitable impurities) that are inevitably mixed in during the manufacturing process. Examples of such inevitable impurities include oxygen (O), carbon (C), chlorine (Cl), and alkaline components (Na, K, etc.). Inevitable impurities may cause the properties of the alloy powder to deteriorate, so it is better to suppress their amount as much as possible. Regarding the amount of unavoidable impurities, oxygen (O), which is contained in the oxide film that inevitably forms on the surface of the alloy powder, is preferably 5% by mass or less, more preferably 3% by mass or less. On the other hand, the amount of carbon (C), chlorine (Cl), and alkaline components (such as Na and K) is 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, with the balance consisting of unavoidable impurities.

The method for producing alloy powder according to this embodiment includes at least a preparation step, a crystallization step, and a recovery step. Furthermore, a crushing step or a high-temperature heat treatment step may be included after or during the recovery step, as needed. Alternatively, an insulating coating step may be provided after the recovery step. FIG1 schematically illustrates an example of a manufacturing process according to this embodiment. FIG1 illustrates crushing treatment, high-temperature heat treatment, and insulating coating treatment, but these treatments can be provided as needed and are not required. Furthermore, when crushing treatment, high-temperature heat treatment, and/or insulating coating treatment are performed, there is no particular limitation on the order in which these treatments are performed. If absolutely necessary, it's best to perform a disintegration treatment after high-temperature heat treatment. This reduces or eliminates the bonds between alloy particles that were strengthened by the high-temperature heat treatment. Furthermore, it's best to perform a disintegration treatment before the insulating coating. This allows the insulating coating to be applied uniformly across the entire surface of each alloy particle where bonds have been reduced or eliminated. In contrast, if alloy particles are already bonded, an insulating coating cannot form on the bonded areas. Therefore, it's best to minimize or eliminate bonds before the insulating coating. The following describes each step in detail.

<Preparation Steps>

In the preparation step, a magnetic metal source, a nucleating agent, a complexing agent, a reducing agent, and a pH adjuster are prepared as starting materials. The magnetic metal source is composed of iron and nickel raw materials, and may also include a cobalt raw material as needed. Furthermore, the starting materials may include an amine compound. Each raw material is described below.

(a) Magnetic metal source

The magnetic metal source is a raw material for magnetic metal 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 the iron salt include ferric chloride, ferric sulfate, ferric nitrate, or mixtures thereof containing divalent and/or trivalent iron ions. As for the water-soluble iron salt, it is preferably at least one selected from the group consisting of ferrous chloride (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), and ferrous nitrate (Fe(NO ₃ ) 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 (NiCl ₂ ), nickel sulfate (NiSO ₄ ), and nickel nitrate (Ni(NO ₃ ) ₂ ). In particular, it is preferably at least one selected from the group consisting of nickel chloride (NiCl ₂ ) and nickel sulfate (NiSO ₄ ).

Alternatively, the magnetic metal may further include cobalt (Co), and the magnetic metal source may further include a water-soluble cobalt salt. This allows the production of iron-nickel-cobalt alloy powder. Iron-nickel-cobalt alloy powders in which cobalt replaces a portion of the iron or nickel have a particularly high saturated magnetic flux density.

Water-soluble cobalt salts accelerate the reduction reaction during crystallization of alloy powder (reduction-promoting effect). This reduction-promoting effect becomes more pronounced when the iron (Fe) content in the magnetic metal is above 60 mol%. Furthermore, water-soluble cobalt salts also help alloy powder form spherical particles with smooth surfaces (spheroidization-promoting effect). Therefore, if the content of the water-soluble iron salt in the magnetic metal source is set to 60 mol% to 85 mol% and the content of the water-soluble cobalt salt is set to 10 mol% to 30 mol%, even with a very small amount of hydrazine used as a reducing agent, spherical iron-nickel-cobalt alloy powder with an extremely high saturated magnetic flux density (e.g., 2 Teslas or more) and a smooth surface can be obtained. For example, the iron content of this alloy powder is 60 mol% to 85 mol%, and the cobalt content is 10 mol% to 30 mol%.

The water-soluble cobalt salt is not particularly limited as long as it is readily water-soluble. The water-soluble cobalt salt is preferably at least one selected from the group consisting of cobalt chloride (CoCl ₂ ), cobalt sulfate (CoSO ₄ ), and cobalt nitrate (Co(NO ₃ ) ₂ ), and particularly preferably at least one selected from the group consisting of cobalt chloride (CoCl ₂ ) and cobalt sulfate (CoSO ₄ ).

(b) Nucleating agent

The nucleating agent is a water-soluble salt of a metal that is more noble than nickel. This nucleating agent (water-soluble salt of a metal that is more noble than nickel) has the following function: it is preferentially reduced in the reaction solution during the subsequent crystallization step, forming initial nuclei that promote the precipitation of crystallized powder. Here, a metal that is more noble than nickel refers to a metal that has a higher potential than nickel in the standard electric potential series in aqueous solution. Furthermore, a metal that is more noble than nickel can also be referred to as 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 that is more noble than nickel as a nucleating agent, the formation of crystallized powder in the reaction solution can be controlled during the subsequent crystallization step. For example, increasing the amount of nucleating agent added results in finer crystallized powder. Specifically, during the crystallization step, the ions or error ions of the magnetic metal contained in the reaction solution are reduced and precipitated, forming the crystallized powder. Among magnetic metals, nickel has a more noble metal-oriented nature than iron or cobalt, and its ionization tendency is lower. Therefore, if a water-soluble salt of a metal that is more noble than nickel (a nucleating agent) is included in the reaction solution, the metal that is more noble than nickel will be reduced and precipitated before all magnetic metals. The precipitated metal that is more noble than nickel acts as initial nuclei, which then undergo grain growth to form a crystallized powder composed of magnetic metal. Therefore, the particle size of the crystallized powder can be controlled by adjusting the amount of nucleating agent added to determine the number of initial nuclei.

The nucleating agent is not particularly limited, as long as it is a water-soluble salt of a metal that is more noble metal-oriented 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 properties that are more noble metal-oriented and have a low ionization tendency. Therefore, they are highly effective as nucleating agents. The water-soluble copper salt is not particularly limited, and copper sulfate is an example. Water-soluble palladium salts are not particularly limited, and examples include sodium palladium(II) chloride, ammonium palladium(II) chloride, palladium(II) nitrate, and palladium(II) sulfate. Palladium salts are particularly suitable as nucleating agents. Using palladium salts allows for finer particle size control of the crystallized powder (alloy powder).

The nucleating agent content should be adjusted to achieve the desired particle size of the resulting alloy powder. For example, the nucleating agent content relative to the total weight of the magnetic metal can 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 nucleating agent content within this range, alloy powders with an average particle size of between 0.2 μm and 0.6 μm can be obtained. However, the nucleating agent content is not limited to this range. For example, when producing fine alloy powders with an average particle size of less than 0.2 μm, a nucleating agent content exceeding 5.0 mol ppm is sufficient.

(c) Complexing agents

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 complexing agent (hydroxycarboxylic acid, etc.) has the following function, namely, to achieve uniform reaction in the subsequent crystallization step. That is, the magnetic metal component dissolves in the reaction solution in the form of magnetic metal ions (Fe2 ⁺ , Ni2 ⁺ , etc.), but the pH adjuster (NaOH, etc.) makes the reaction solution highly alkaline, so the amount of magnetic metal ions dissolved in the reaction solution is extremely small. However, if the complexing agent is present, the magnetic metal component can be dissolved in large quantities in the form of complex ions (Fe complex ions, Ni complex ions, etc.). The presence of such complexing ions increases the reduction reaction rate and suppresses the local segregation of magnetic metal components, thereby achieving homogenization of the reaction system. In addition, the complexing agent has the following effect, namely, changing the complex stability balance of multiple magnetic metal ions in the reaction solution. Therefore, if a complexing agent is present, the reduction reaction of the magnetic metal changes, and the balance between the nucleation rate and the grain growth rate changes. By using the specific complexing agent (hydroxycarboxylic acid, etc.) in this embodiment, not only the above-mentioned effect is additionally exerted, but the reaction is also developed in a better direction. As a result, the powder properties of the obtained alloy powder (particle size, particle size distribution, sphericity, and surface properties of the particles) are improved. Furthermore, the alloy powder with improved powder properties has excellent filling properties and is suitable for use as a raw material for powder cores. Based on this aspect, the complexing agent (hydroxycarboxylic acid, etc.) of this embodiment can be said to function as a reduction reaction promoter, a spheroidization promoter, and a surface smoothing agent. Suitable complexing agents include at least one hydroxycarboxylic acid selected from tartaric acid ((CH(OH)COOH) ₂ ) and citric acid (C(OH)(CH ₂ COOH) ₂ COOH).

The complexing agent content relative to the total weight of the 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%. A content of 5 mol% or greater fully demonstrates its functions as a reduction reaction accelerator, spheroidization promoter, and surface smoothing agent, resulting in improved alloy powder properties (particle size, particle size distribution, sphericity, and particle surface properties). Furthermore, a content of 100 mol% or less minimizes significant variation in the complexing agent's performance, reducing the amount of complexing agent used and ultimately reducing manufacturing costs.

(d) Reducing agent

The reducing agent is hydrazine (N ₂ H ₄ , molecular weight: 32.05). This reducing agent (hydrazine) has the following function: it reduces the magnetic metal ions and error ions in the reaction solution during the subsequent crystallization step. Hydrazine not only has a strong reducing power but also has the advantage of not forming byproducts associated with the reduction reaction in the reaction solution. Furthermore, high-purity hydrazine with few impurities can be easily obtained.

Regarding hydrazine, in addition to anhydrous hydrazine, hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) is also known as a hydrazine hydrate. Either can be used. As hydrazine hydrate, for example, commercially available industrial-grade 60% by mass hydrazine hydrate can be used.

The amount of reducing agent incorporated is largely dependent on the composition of the iron (Fe)-nickel (Ni) alloy powder. The greater the proportion of non-reducible iron, the greater the amount required. Furthermore, in addition to the alloy powder composition, factors such as the reaction solution temperature and the amount of complexing agent or pH adjuster incorporated are also influential. For example, when the iron content of the iron-nickel alloy powder is 60 mol% or less, the amount of reducing agent incorporated, measured in molar ratio, relative to the total amount of magnetic metal, is preferably 1.8 to 7.0, 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% and is less than 75 mol%, the amount of the reducing agent blended in a molar ratio relative to the total weight of the magnetic metal is preferably 2.5 to 9.0, and more preferably 3.5 to 8.0. If the iron content of the iron-nickel alloy powder exceeds 75 mol% and is less than 95 mol%, the amount of the reducing agent blended in a molar ratio relative to the total weight of the magnetic metal is preferably 3.5 to 10.0, and more preferably 4.5 to 9.0. On the other hand, when producing iron-nickel-cobalt alloy powder, the aforementioned effect of the water-soluble cobalt salt allows the amount of reducing agent incorporated into the powder to be significantly reduced compared to iron-nickel alloy powder. The effect of the water-soluble cobalt salt is particularly significant when producing alloy powders with a high iron content. For example, when producing alloy powders 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 incorporated, measured in molar ratios relative to the total amount of magnetic metal, is preferably 1.0 to 4.0, and more preferably 1.2 to 2.0.

In either case, if the blending amount is above the lower limit, the magnetic metal ions and error ions will be fully reduced, resulting in a crystallized powder (alloy powder) free of unreduced materials such as iron hydroxide. Furthermore, if the blending amount is below the upper limit, the amount of reducing agent (hydrazine) used can be reduced, thereby reducing manufacturing costs.

(e) pH adjuster

The pH adjuster is an alkali metal hydroxide. This pH adjuster (alkali metal hydroxide) has the effect of enhancing the reduction reaction of hydrazine, which serves as a reducing agent. Specifically, the higher the pH of the reaction solution, the stronger the reducing power of hydrazine. Therefore, using an alkali metal hydroxide as a pH adjuster promotes the reduction reaction of magnetic metal ions and complex ions in the reaction solution, and the resulting precipitation of crystallized powder. The type of alkali metal hydroxide is not particularly limited. However, considering availability and cost, the pH adjuster preferably includes at least one selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Regarding the amount of the pH adjuster (alkali metal hydroxide) incorporated, it is sufficient to prepare the reducing agent (hydrazine) so that its reducing power 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 the alkali metal hydroxide incorporated can be adjusted so that the pH falls within this range.

(f) Amine compounds

The starting material may further include an amine compound as needed. The amine compound contains two or more primary amine groups (-NH ₂ ), one primary amine group (-NH ₂ ) and one or more secondary amine groups (-NH-), or two or more secondary amine groups (-NH-) in the molecule.

Amine compounds promote the reduction reaction in the subsequent crystallization step. Specifically, they act as complexing agents, causing magnetic metal ions (such as Fe₂ ⁺ and Ni₂ ⁺ ) in the reaction solution to undergo complexation reactions, forming complex ions (such as Fe and Ni complexes). Furthermore, the presence of complex ions in the reaction solution is believed to further promote the reduction reaction.

Furthermore, amine compounds have the effect of inhibiting the autodecomposition of hydrazine, which acts as a reducing agent. That is, when crystallized powder composed of a magnetic metal precipitates in the reaction solution, the nickel (Ni) in the magnetic metal acts as a catalyst, potentially causing the hydrazine to _decompose . This is called autodecomposition of hydrazine. As shown in the following formula (1), the decomposition reaction is a reaction in which hydrazine ( _N2H4 ) decomposes into nitrogen ( _N2 ) and ammonia ( _NH3 ). If this autodecomposition occurs, the function of hydrazine as a reducing agent will be impaired, which is undesirable.

3N ₂ H ₄ →N ₂ ↑+4NH ₃ ‧‧‧(1)

By adding an amine compound to the mixing solution in advance, the self-decomposition of hydrazine can be suppressed. Although the detailed mechanism is not clear, it is speculated that the reason is that it prevents the hydrazine in the reaction solution from excessive contact with the crystallization powder. That is, the amine groups contained in the amine compound molecules, especially the primary amine groups ( _-NH2 ) or the secondary amine groups (-NH-), will be firmly adsorbed on the surface of the crystallization powder in the reaction solution. It is believed that the amine compound molecules cover the crystallization powder and protect it, thereby preventing the hydrazine molecules from excessive contact with the crystallization powder, thereby suppressing the self-decomposition of hydrazine. If the nickel content in the magnetic metal is high, the self-decomposition of hydrazine becomes significant, so the amine compound will play an effective role in this case.

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

By using such alkylene amines or alkylene amine derivatives as the amine compound, the autodecomposition inhibition effect of hydrazine (reducing agent) can be more effectively exerted. This is believed to be because the carbon chains contained in such alkylene amines or alkylene amine derivatives are relatively short, effectively inhibiting the contact between hydrazine molecules and the crystallization powder. In contrast, when the nitrogen atom of the amine group is bonded via an excessively long carbon chain, even if the amine group is adsorbed to the crystallization powder, the carbon chain has greater freedom of movement. Therefore, it is speculated that the contact between the crystallization powder and the hydrazine molecules cannot be effectively blocked.

Specific examples of the alkylene amine having the structure represented by (A) above are selected from ethylenediamine (abbreviated as EDA) (H ₂ NC ₂ H ₄ NH ₂ ), diethylenetriamine (abbreviated as DETA) (H ₂ NC ₂ H ₄ NHC ₂ H ₄ NH ₂ ), triethylenetetramine (abbreviated as TETA) (H ₂ N(C ₂ H ₄ NH) ₂ C ₂ H ₄ NH ₂ ), tetraethylenepentamine (abbreviated as TEPA) (H ₂ N(C ₂ H ₄ NH) ₃ C ₂ H ₄ NH ₂ ), pentaethylenehexamine (abbreviated as PEHA) (H ₂ N(C ₂ H ₄ NH) ₄ C ₂ H ₄ NH ₂ ), propylenediamine (also known as 1,2-diaminopropane, 1,2-propylenediamine) (abbreviated as PDA) (CH ₃ CH(NH ₂ )CH ₂ NH ₂ ) or more. Specific examples of the alkyleneamine derivative having the structure represented by (A) above are selected from tris(2-aminoethyl)amine (abbreviated as TAEA) (N(C ₂ H ₄ NH ₂ ) ₃ ), N-(2-aminoethyl)ethanolamine (also known as 2-(2-aminoethylamino)ethanol) (abbreviated as AEEA) (H ₂ NC ₂ H ₄ NHC ₂ H ₄ OH), N-(2-aminoethyl)propanolamine (also known as 2-(2-aminoethylamino)propanol) (abbreviated as AEPA) (H ₂ NC ₂ H ₄ NHC ₃ H ₆ OH), L (or D, DL)-2,3-diaminopropionic acid (also known as 3-amino-L (or D, DL)-alanine) (abbreviated as DAPA) (H ₂ NCH ₂ At _least one of: ethylenediamine-N,N'-diacetic acid (also known as N,N'-ethylenediglycine) (abbreviated as EDDA) _{( HOOCCH2NHC2H4NHCH2COOH} ), and 1,2-cyclohexanediamine (also known as _1,2 -diaminocyclohexane) (abbreviated as CHDA) _{( H2NC6H10NH2} ). These alkylene amines or _alkylene amine derivatives _are water-soluble. Among them, ethylenediamine and diethylenetriamine are preferred because they have a relatively strong inhibitory effect on the autolysis of hydrazine, are readily available, and are 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. (B) to (M)

The amount of the amine compound incorporated relative to the total amount of the 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 the amine compound incorporated may be 0.00 mol%, i.e., no amine compound is incorporated. However, by setting the incorporation amount to 0.01 mol% or more, the amine compound's effect of inhibiting hydrazine's autodecomposition and promoting the reduction reaction can be fully exerted. Furthermore, by setting the incorporation amount to 5.00 mol% or less, the complexing agent function can be appropriately exhibited. Consequently, the powder properties of the alloy powder (particle size, particle size distribution, sphericity, and particle surface properties) can be further improved. If the amine compound content exceeds 5.00 mol%, its complexing effect may become too strong. This can lead to abnormal particle growth and deterioration of the alloy powder's properties.

<Crystallization Steps>

In the crystallization step, a reaction solution containing the prepared starting materials and water is prepared, and the crystallization powder containing the above-mentioned magnetic metal is crystallized in the reaction solution by a reduction reaction. The preparation of the reaction solution and the crystallization of the crystallization powder are described below. In actual production, although the crystallization reaction usually starts at the same time as the reaction solution is prepared, it is also possible that the crystallization reaction starts during the preparation of the reaction solution, although the possibility is extremely small. In addition, the crystallization reaction described here refers to the reaction occurring during the crystallization process. That is, although the reduction reaction (such as the following formula (6)) initiated by hydrazine is the main reaction, it also includes the self-decomposition reaction of hydrazine (such as the above formula (1)). Therefore, the term crystallization reaction is used in a broader sense than the reduction reaction.

In the crystallization step, at least one of a plurality of solutions such as a metal salt raw material solution or a reducing agent solution is heated and mixed to prepare a reaction liquid. The reaction liquid is heated and stirred in a reaction tank while being maintained at a predetermined temperature, and the crystallization reaction is performed in this state. Heating can be performed by a general method, for example, a method of installing a reaction tank (reaction vessel) in a water bath, or a method of using a reaction tank with a steam jacket or a reaction tank with a heater. The reaction tank (reaction vessel) or the stirring blades used to stir the reaction liquid are required to be inactive materials that make nucleation on their surfaces as difficult as possible when in contact with the reaction liquid, in order not to hinder the function of the nucleating agent, and are required to have excellent strength or thermal conductivity. To meet these requirements, for example, it is appropriate to coat metal containers (Teflon (registered trademark) coated stainless steel containers, etc.) or stirring blades (Teflon (registered trademark) coated stainless steel stirring blades, etc.) with fluororesins (PTFE, PFA, etc.).

(a) Preparation of reaction solution

First, the starting materials (magnetic metal source, nucleating agent, complexing agent, reducing agent, pH adjuster, and, if necessary, amine compound) are dissolved in water and mixed to prepare a reaction solution. To reduce impurities in the resulting alloy powder, the water used in preparing this reaction solution is preferably high-purity. Pure water with a conductivity of 1 μS/cm or less, or ultrapure water with a conductivity of 0.06 μS/cm or less, can be used. Purified water is preferred, as it is inexpensive and readily available.

When the starting materials are solid, such as iron salts, nickel salts, cobalt salts, and alkaline metal hydroxides, it is preferable to pre-mix them with water and dissolve them to prepare an aqueous solution. The starting materials and water can be mixed by known methods such as stirring. The order of mixing the starting materials or aqueous solutions is not particularly limited, as long as it does not compromise the homogeneity of the reaction solution. However, from the perspective of ensuring the homogeneity of the reaction solution, it is preferable to pre-prepare aqueous solutions containing each starting material and then mix the prepared aqueous solutions. Preparing the reaction solution according to the first or second aspect described below is particularly preferred.

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 are prepared separately: a metal salt raw material solution, a reducing agent solution, and a pH adjusting solution. 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 (a water-soluble salt of a metal more noble 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 metal hydroxide) in water. The metal salt raw material solution and the pH adjusting solution are then mixed to form a mixed solution. At this point, the magnetic metal salts (water-soluble iron salts, water-soluble nickel salts, etc.) contained in the metal salt raw material solution react with the alkaline metal hydroxides contained in the pH adjuster to form magnetic metal hydroxides. 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 ). The resulting mixed solution is then mixed with a reducing agent solution to form a reaction solution.

The preferred preparation sequence for the reaction solutions in the first embodiment is to sequentially add the pH adjusting solution and the reducing agent solution to the metal salt raw material solution and mix them. In the first embodiment, which uses three solutions: the metal salt raw material solution, the reducing agent solution, and the pH adjusting solution, the metal salt raw material solution has the largest volume. This is because, compared to adding the metal salt raw material solution to other solutions, sequentially adding the other solutions to the larger volume of the metal salt raw material solution and mixing them allows for more uniform mixing, allowing the reduction reaction to proceed uniformly throughout the reaction solution.

When adding an amine compound, simply add the amine compound to at least one of the metal salt raw material solution, reducing agent solution, and pH adjusting agent solution. Alternatively, all of these solutions can be mixed before adding the amine compound. Figure 2 shows the addition of the amine compound to at least one of the metal salt raw material solution, reducing agent solution, and pH adjusting solution. Figure 3 shows the addition of the amine compound to the reaction solution obtained by mixing the metal salt raw material solution, reducing agent solution, and pH adjusting solution.

In the first embodiment, a reducing agent solution is mixed with a mixed solution of a metal salt raw material solution and a pH adjuster to prepare a reaction solution. The reduction reaction proceeds from the time the reducing agent solution is added. During the mixing of the reducing agent solution, the reducing agent (hydrazine) concentration locally and rapidly increases in the microregion where the reducing agent is added. Furthermore, the mixed solution contains a pH adjuster (alkali metal hydroxide), and the pH of the mixed solution (reaction solution) remains relatively high during the initial stages of adding the reducing agent solution. As mentioned above, the higher the pH, the stronger the reducing agent (hydrazine) can exert its reducing power. Therefore, in the initial stage of the mixed reducing agent solution, the reducing agent concentration and pH are locally high, causing the nucleation of the nucleating agent and the reduction reaction to form crystallized powder to occur rapidly. Meanwhile, as the reducing agent solution is added, the pH of the mixed solution (reaction solution) gradually decreases. Consequently, in the final stage of the mixed reducing agent solution, the reducing agent's reducing power is not as strong as in the initial stage, causing nucleation and reduction reactions to proceed more slowly. Consequently, there is a difference in the reducing agent's reducing power between the initial and final stages of the mixed reducing agent solution.

A large difference in reducing power between the initial and final stages can reduce the uniformity of the nucleation and reduction reactions, potentially leading to greater variability in the resulting crystallized powder's properties (particle size, surface smoothness, etc.). Therefore, it is ideal to minimize the difference in reducing power. Therefore, it is ideal 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 the pH adjuster (mixing time) is preferably 180 seconds or less, more preferably 120 seconds or less, and even more preferably 60 seconds or less. However, due to limitations in the production equipment, it may be difficult to shorten the mixing time. The mixing time can be 1 second or longer, 3 seconds or longer, or even 5 seconds or longer.

Furthermore, when mixing the pH adjuster solution with the metal salt raw material solution, prolonged mixing can similarly lead to uneven properties in the resulting magnetic metal hydroxide, potentially causing uneven properties in the crystallized powder. While this effect is not as significant as when mixing with the reducing agent solution, a shorter mixing time is preferred. The time required for mixing the pH adjuster (mixing time) is preferably 180 seconds or less, more preferably 120 seconds or less, and even more preferably 80 seconds or less. Alternatively, the mixing time can be 1 second or more, 3 seconds or more, or 5 seconds or more.

Stirring the reducing agent solution or pH adjuster solution while mixing is also effective in suppressing variations in the properties of the crystallized powder. This stirring prevents a rapid increase in the concentration of the components in the solution, thereby suppressing 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, obtained by dissolving a magnetic metal source, a nucleating agent, and a complexing agent in water, and a reducing agent solution, obtained by dissolving a reducing agent and a pH adjuster in water, are prepared separately. The metal salt raw material solution and the reducing agent solution are then mixed. Figures 4 and 5 show a process flow diagram illustrating an example of the reaction solution preparation and alloy powder production in the second embodiment.

In the second aspect, two solutions, a metal salt source solution and a reducing agent solution, are prepared separately. The metal salt source solution is prepared by dissolving a magnetic metal source (water-soluble iron salt, water-soluble nickel salt, etc.), a nucleating agent (a water-soluble salt of a metal more noble 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 adjuster (alkali metal hydroxide) in water. The metal source source solution and the reducing agent solution are then mixed to form a reaction solution. The second aspect differs from the first aspect in that the reducing agent solution contains a pH adjuster.

The specific preparation sequence for the reaction solution in the second embodiment can be either: adding the reducing agent solution to the metal salt raw material solution and mixing; or vice versa, adding the metal salt raw material solution to the reducing agent solution and mixing. Unlike the first embodiment, the reducing agent solution, which contains both the reducing agent and the pH adjuster (alkaline metal hydroxide), has the same volume as the metal salt raw material solution. Therefore, by adding one to the other and mixing, a uniform mixing state is achieved, allowing the reduction reaction to proceed uniformly throughout the reaction solution.

However, under crystallization conditions where the ratio of the reducing agent or pH adjuster (alkali metal hydroxide) to the metal salt raw material is high, it is preferable to add the metal salt raw material solution to the reducing agent solution and mix them. This is because, to ensure productivity in the crystallization step, it is ideal to maintain the metal salt raw material concentration in the reaction solution above the specified level (30-40 g/L as metal component). That is, under these crystallization conditions, the volume of the reducing agent solution is significantly greater than the volume of the metal salt raw material solution. Therefore, adding a smaller amount of metal salt raw material solution to a larger amount of reducing agent solution and mixing them together can achieve a uniform mixing state, allowing the reduction reaction to proceed uniformly in the reaction solution.

In the second aspect, for the same reasons as in the first aspect, 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. Furthermore, the mixing time may be 1 second or more, 3 seconds or more, or 5 seconds or more. Stirring the reducing agent solution during mixing is also effective.

In the third aspect, during the crystallization step of the first or second aspect, an additional raw material liquid is added to the reaction solution and mixed before the reduction reaction is complete. This enriches the surface of the crystallized powder with nickel or cobalt. Here, the additional raw material liquid is prepared by dissolving at least one of the aforementioned water-soluble nickel salt and water-soluble cobalt salt in water. A process diagram illustrating an example of alloy powder production in the third aspect is shown in Figure 6.

In the third aspect, in addition to the solution used to prepare the reaction solution in the first or second aspect, an additional raw material solution is prepared. 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 all at once, in batches, and/or dropwise. It is preferably added before the reduction reaction is complete, but this is not essential. When the reduction reaction is complete, the crystallized particles begin to form aggregates. Adding the additional raw material solution at this time allows the metal components to precipitate through the reduction reaction, potentially strengthening the bonds between the particles within the aggregates.

Furthermore, the third aspect has the advantage of reducing the amount of reducing agent used compared to the first or second aspects. This is because iron ions (or iron hydroxide) are less susceptible to reduction than nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide). Adding an additional raw material solution containing nickel or cobalt to the reaction solution can promote the reduction reaction of the less susceptible iron ions (or iron hydroxide) during the final crystallization stage.

The amount of magnetic metal (Ni, Co) added to the raw material solution can be adjusted based on the degree to which the crystallized powder surface is enriched with nickel or cobalt. However, considering the overall uniformity of the particle composition, a range of 5 mol% to 50 mol% relative to the total amount of magnetic metal (Ni, Co) other than iron in the alloy powder is preferred. Enriching the particle surface with nickel or cobalt reduces the amount of iron that tends to form a porous oxide film. This creates a dense oxide film, suppressing oxidation on the particle surface. This not only improves stability in atmospheric conditions but also enhances magnetic properties such as saturated magnetic flux density.

(b) Crystallization of crystallized powder

When preparing the reaction solution, a reduction reaction occurs within it. Specifically, in the presence of a pH adjuster (alkaline metal hydroxide) and a nucleating agent (a salt of a metal more noble than nickel), a reducing agent (hydrazine) reduces the ions or error ions of the magnetic metal source, thereby forming a crystallized powder containing the magnetic metal.

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

Fe ²⁺ +2e ^- →Fe↓(two-electron reaction)‧‧‧(2)

Ni ²⁺ +2e ^- →Ni↓(two-electron reaction)‧‧‧(3)

Co ²⁺ +2e ^- →Co↓(two-electron reaction)‧‧‧(4)

N ₂ H ₄ →N ₂ ↑+4H ⁺ +4e ^- (four-electron reaction)‧‧‧(5)

When using a magnetic metal chloride ( _FeCl2 , _NiCl2 , _CoCl2 ) as the magnetic metal source and sodium hydroxide (NaOH) as the pH adjuster, as shown in the following formula (6), the magnetic metal chloride and sodium hydroxide first undergo a neutralization reaction to produce hydroxides ((Fe, Ni, Co)(OH) ₂ , etc.). Then, the hydroxides ((Fe, Ni, Co)(OH) ₂ , etc.) are reduced by the action of a reducing agent (hydrazine) to form crystallized powder. To reduce 1 mol of the magnetic metal (Fe, Ni, Co), 0.5 mol of reducing agent (hydrazine) is required. Furthermore, observing the above formula (5), it can be seen that 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 initiated by hydrazine.

(Fe,Ni,Co)Cl ₂ +1/2N ₂ H ₄ +2NaOH→(Fe,Ni,Co)(OH) ₂ ↓+1/2N ₂ H ₄ +2NaCl→(Fe,Ni,Co)↓+1/2N ₂ ↑+2NaCl+2H ₂ O ‧‧‧(6)

In the reduction reaction of formula (6) above, the reduction of the elemental ions (or hydroxides) of the magnetic metals (Fe, Ni, and Co) proceeds simultaneously to a certain extent through co-reduction. Here, co-reduction refers to the phenomenon in which the reduction reaction of a certain element also causes other reduction reactions to occur. However, as mentioned above, iron ions (or iron hydroxide) are less susceptible to reduction than nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide). Therefore, in the final stage of the crystallization reaction, nickel ions (or nickel hydroxide) or cobalt ions (or cobalt hydroxide) in the reaction solution are consumed by the reduction reaction and disappear, leaving only residual iron ions (or iron hydroxide). This trend is particularly pronounced when the iron content is high (for example, when the iron content of the alloy powder exceeds 60 mol%). If this phenomenon occurs, not only does it take a long time for the crystallization reaction (reduction reaction) to complete, but it also tends to form a gradient structure with uneven composition within the particles. If this gradient structure forms, the resulting alloy powder will have a nickel- or cobalt-rich composition at the center of the particle, while the composition becomes increasingly iron-rich towards the particle surface.

In contrast, in the third aspect described above, additional raw material liquid is added to the reaction solution during the crystallization reaction, accelerating the reduction reaction of the less reducible iron ions (or iron hydroxide) in the final stage of crystallization. This can alleviate the prolonged crystallization (reduction) reaction and the resulting compositional inhomogeneity within the alloy powder particles, particularly when the iron content is high.

The temperature of the reaction solution at the start of crystallization of the crystallized powder (reaction starting 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 raw 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 starting temperature within an appropriate range, it is desirable to preheat at least one of the multiple solutions used to prepare the reaction solution, such as the metal salt raw material solution or the reducing agent solution. In order to maintain the reaction temperature within an appropriate range, it is ideal to continue heating the reaction solution after preparing it.

From the perspective of achieving more uniform nucleation and a crystallized powder with a steep particle size distribution, it is preferable, if possible, to preheat one of the multiple solutions, such as the metal salt source solution or the reducing agent solution, (e.g., to 70°C), while leaving the other solution unheated (e.g., maintained at 25°C), and then adding and mixing them to prepare a reaction solution at a predetermined temperature (e.g., 55°C). In contrast, preheating both solutions (e.g., the metal salt source solution and the reducing agent solution) (e.g., to 70°C) can easily lead to uneven nucleation. Specifically, when the two solutions are added and mixed, mixing heat occurs. Consequently, the solution (reaction solution) resulting from the addition and mixing will locally reach a high temperature (e.g., around 78°C) at the start of mixing, causing nucleation to occur instantaneously. The two solutions are added and mixed simultaneously with nucleation, which can easily lead to uneven nucleation.

Although it is possible to improve the uniformity of nucleation by extremely shortening the time it takes to add the two solutions or by vigorously stirring them, this method is hardly the best approach. If the method described above is used, where only one solution is preheated (for example, to 70°C) before adding and mixing to prepare the reaction solution, the solution (reaction solution) that is added and mixed is maintained at a low temperature (for example, 55°C) and does not locally reach a high temperature. The timing of nucleation is delayed, so nucleation occurs after the two solutions are fully mixed. This makes it easier for nucleation to occur uniformly. The above describes a more optimal example, but does not exclude the possibility of preheating all of the multiple solutions, such as the metal salt raw material solution or the reducing agent solution. Simply set the solution heating and temperature so that the reaction starting temperature and reaction holding temperature fall within the above ranges.

If the reaction starting temperature is too low, nucleation becomes more uniform, but the reduction reaction slows down, and the heating time required to reach the reaction holding temperature that promotes the reduction reaction increases. Similarly, if the reaction holding temperature is too low, the reduction reaction slows down, and the heating time required for crystallization increases. In either case, the crystallization cycle time is prolonged, reducing productivity. Furthermore, since hydrazine undergoes autolysis, a large amount of hydrazine is required, resulting in increased production costs. If the reaction starting temperature or the reaction holding temperature is higher, the reduction reaction is promoted, the crystallization cycle time is shortened, and the resulting crystallized powder exhibits a highly crystalline tendency. However, the rate of hydrazine autolysis increases. Therefore, if the reaction starting temperature or the reaction holding temperature is too high, not only will uneven nucleation occur, but excessively high crystallization can also degrade the smoothness of the particle surface, potentially increasing surface irregularities. Furthermore, if crystallization is not terminated at an appropriate time, hydrazine may be consumed preferentially due to self-decomposition during the reduction reaction. Consequently, a large amount of hydrazine is required, potentially increasing manufacturing costs. By setting the reaction starting temperature or the reaction holding temperature within the appropriate range described above, high-performance alloy powder can be produced cost-effectively while maintaining high productivity.

<Recycling Steps>

In the recovery step, crystallized powder is recovered from the reaction solution obtained in the crystallization step. The crystallized powder can be recovered by any known method. For example, a separation device such as a Denver filter, filter press, centrifuge, or decanter can be used to separate the crystallized powder from the reaction solution into solid and liquid. Alternatively, the crystallized powder can be washed during or after the solid-liquid separation. This washing can be performed using a washing liquid. High-purity water with a conductivity of 1 μS/cm or less can be used as the washing liquid. The washed crystallized powder can be dried. Drying can be performed 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 between 40°C and 150°C, preferably between 50°C and 120°C. However, to prevent deterioration of magnetic properties due to excessive oxidation of the crystallized powder during drying, using an inert gas atmosphere dryer, reducing gas atmosphere dryer, or vacuum dryer is preferred over using an air dryer or a hot air dryer using atmospheric air.

Furthermore, crystallization powder dried in a sealed container in an inert gas dryer, a reducing gas dryer, or a vacuum dryer does not undergo excessive surface oxidation. Therefore, when the crystallization powder is immediately removed from the dryer and released into the atmosphere, the particle surface rapidly oxidizes, and the heat generated by the oxidation reaction may cause the crystallization powder to burn. This phenomenon is particularly prone to occur with fine crystallization powder (e.g., particle size 0.1 μm or less). Therefore, it is ideal to perform a slow oxidation treatment, which pre-forms a thin oxide film on the surface of the crystallization powder particles, which remain largely unoxidized after drying, to stabilize them. As a specific example of a slow oxidation treatment procedure, consider the following method: After heat-drying the crystallized powder in a sealed container in an inert gas dryer, a reducing gas dryer, or a vacuum dryer, the temperature is lowered to approximately room temperature to 40°C. A gas with a low oxygen concentration (e.g., nitrogen or argon containing 0.1-2% oxygen by volume) is then introduced into the sealed container to slowly oxidize the surface of the crystallized powder particles, forming a thin oxide film. Crystallized powder subjected to the slow oxidation treatment is resistant to oxidation and stable, so even when exposed to the atmosphere, it does not generate heat or ignite.

<High temperature heat treatment step>

A high-temperature heat treatment step may be performed on the crystallized powder after or during the recovery step. When the high-temperature heat treatment is performed after the recovery step, it can be performed after the drying step. Alternatively, when the high-temperature heat treatment is performed during the recovery step, it can be performed instead of the drying step. The high-temperature heat treatment can be performed in an inert atmosphere, a reducing atmosphere, or a vacuum environment at a temperature exceeding 150°C and below 400°C, preferably between 200°C and 350°C. High-temperature heat treatment can promote the diffusion of foreign elements such as Fe and Ni within the iron (Fe)-nickel (Ni) alloy particles, thereby improving the compositional uniformity within the particles and enhancing magnetic properties such as magnetism. Furthermore, the aforementioned slow oxidation treatment can be performed after the high-temperature heat treatment, if necessary.

<Disintegration steps>

A disintegration step can be added as needed to the crystallized powder recovered in the recovery step, or to the crystallized powder before drying during the recovery process. During the crystallization step, the alloy particles that precipitate the crystallized powder can come into contact and fuse to form agglomerated particles. Consequently, the crystallized powder obtained from 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 heat or hindering the powder's packing properties. By adding a disintegration step after or during the recovery process, agglomerated particles can be disintegrated. Disintegration can be performed using dry methods such as spiral jet disintegration or back-jet mill disintegration, wet methods such as high-pressure fluid collision disintegration, or other common disintegration methods. Dry disintegration can be applied directly to the crystallized powder recovered as a dry powder in the recovery step. Alternatively, if the crystallized powder after the recovery step is in a slurry form, wet disintegration can be applied. Furthermore, if the crystallized powder is in a slurry form before drying, it can be directly subjected to wet disintegration. These disintegration methods utilize the energy of particle collisions to break up agglomerated particles. Collisions during the disintegration process also promote surface smoothing, which contributes to improved powder filling properties.

<Insulation coating steps>

An insulating coating step can be performed after the recovery step, if necessary. In this step, the crystallized powder obtained from the recovery step is treated with an insulating coating. This forms an insulating coating layer composed of a high-resistance metal oxide on the surface of the crystallized powder particles, thereby improving the insulation between the particles. Similar to the increased losses caused by eddy currents in coarse, agglomerated particles, the powder cores obtained by compression molding of iron-nickel alloy powders may increase eddy currents flowing between the particles due to contact between the alloy particles. By forming an insulating coating, eddy currents generated by contact between alloy particles can be suppressed.

In the insulating coating process, the crystallized powder is dispersed in a mixed solvent containing water and an organic solvent. A metal alkoxide is then added and mixed into the mixed solvent to prepare a slurry. The metal alkoxide undergoes hydrolysis, dehydration, and condensation in the resulting slurry, forming an insulating coating on the surface of the crystallized powder particles. The crystallized powder, which has formed the insulating coating, is then separated from the slurry by solid-liquid separation. The separated crystallized powder is then dried to recover the crystallized powder with the insulating coating formed thereon, which is composed of a high-resistance metal oxide. The separated and dried crystallized powder may be subjected to a heat treatment, if necessary. The hydrolysis reaction of metal alkoxides in a mixed solvent containing water and an organic solvent proceeds very slowly if left as is. Therefore, a trace amount of a hydrolysis catalyst such as an acid or alkali is generally added to accelerate the reaction. In this embodiment, the addition of an alkali catalyst is also preferred.

High-resistance metal oxides preferably contain at least one selected from the group consisting of silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), and titanium dioxide (TiO ₂ ) as their main component. Silicon dioxide (SiO ₂ ) is particularly preferred due to its low cost and excellent insulating properties.

To obtain such metal oxides, the metal alkoxide used in the slurry for insulating coating treatments is preferably an alkoxide that can ultimately form a metal oxide through hydrolysis and dehydration condensation. Specifically, it is preferred that the alkoxide be primarily composed of at least one selected from the group consisting of silane oxides (alkyl silicates), aluminum oxides (alkyl aluminums), zirconium oxides (alkyl zirconiums), and titanium oxides (alkyl titaniums). Among these, alkoxides primarily composed of silane oxides (alkyl silicates) are particularly preferred. Furthermore, if necessary, a small amount of a component (such as boroalkoxide, etc.) that is absorbed into the insulating coating by hydrolysis and dehydration condensation of the metal alkoxide to form the insulating coating can be added to the metal alkoxide.

The surface of the alloy powder treated with the insulating coating is coated with a high-resistance metal oxide, which is an inorganic substance. Organic functional groups can also be introduced into the surface of the inorganic substance as needed. Specifically, for example, a method involves doping the metal alkoxide used in the insulating coating with a small amount of a silicon-, titanium-, zirconium-, or aluminum-based coupling agent. During the hydrolysis, dehydration, and condensation of the metal alkoxide, the organic functional groups are absorbed into the metal oxide. Alternatively, the insulating coating-treated alloy powder is surface-treated with the aforementioned coupling agent to modify the metal oxide surface with organic functional groups. Regardless of the method, the introduction of organic functional groups improves compatibility with the resin. Therefore, when the insulating coated alloy powder is mixed with a resin binder and molded, the strength of the resulting molded product can be expected to be improved.

Specific examples of silane oxides (alkyl silicates) include, for example, one or more selected from tetramethoxysilane (also known as tetramethyl orthosilicate, tetramethoxysilane) (abbreviated as TMOS) (Si(OCH ₃ ) ₄ ), tetraethoxysilane (also known as tetraethyl orthosilicate, tetraethoxysilane) (abbreviated as TEOS) (Si(OC ₂ H ₅ ) ₄ ), tetrapropoxysilane (also known as tetrapropyl orthosilicate, tetrapropoxysilane) (Si(OC ₃ H ₇ ) ₄ ), and tetrabutoxysilane (also known as tetrabutyl orthosilicate and tetrabutoxysilane) (Si(OC ₄ H ₉ ) ₄ ). Alternatively, the alkoxy group of such alkoxides may be substituted with another alkoxy group, or a commercially available alkyl silicate oligomer that has been polymerized to a tetramer or pentamer (e.g., Ethyl Silicate 40 (trade name), Ethyl Silicate 48 (trade name), Methyl Silicate 51 (trade name), etc., manufactured by COLCOAT Corporation) may be used. Of these, tetraethoxysilane (TEOS) is preferred due to its low toxicity, ease of availability, and low price.

Specific examples of aluminum alkoxides (alkyl aluminates) include, for example, one or more selected from aluminum trimethoxide (Al(OCH ₃ ) ₃ ), aluminum triethoxide (Al(OC ₂ H ₅ ) ₃ ), aluminum triisopropoxide (Al(O-iso-C ₃ H ₇ ) ₃ ), aluminum tri-n-butoxide (Al(OnC ₄ H ₉ ) ₃ ), aluminum tri-sec-butoxide (Al(OsC ₄ H ₉ ) ₃ ), and aluminum tri-tert-butoxide (Al(OtC ₄ H ₉ ) ₃ ).

Specific examples of zirconium alkoxides (alkyl zirconates) include at least one selected from zirconium _{tetraethoxide} (Zr( _OC2H5 ) ₄ ), zirconium tetra-n-propoxide (Zr( _OnC3H7 ) ₄ ), zirconium tetraisopropoxide ₍ Zr(O-iso _{-C3H7 ) 4} ), zirconium tetra-n-butoxide ( _Zr ( _OnC4H9 ) ₄ ), zirconium tetra-t-butoxide (Zr _{( OtC4H9} ) ₄ ), and zirconium tetraisobutoxide (Zr(O-iso- _C4H9 ) ₄ ) _.

Specific examples of titanium alkoxides (alkyl titanium esters) include at least one selected from titanium tetramethoxide (Ti(OCH ₃ ) ₄ ), titanium tetraethoxide (Ti(OC ₂ H ₅ ) ₄ ), titanium tetraisopropoxide (Ti(O-iso-C ₃ H ₇ ) ₄ ), titanium tetraisobutoxide (Ti(O-iso-C ₄ H ₉ ) ₄ ), titanium tetra-n-butoxide (Ti(OnC ₄ H ₉ ) ₄ ), titanium tetra-tert-butoxide (Ti(OtC ₄ H ₉ ) ₄ ), and titanium tetra-sec-butoxide (Ti(OsC ₄ H ₉ ) ₄ ).

Examples of other metal alkoxides include one or more selected from boroalkoxides (alkyl borate), such as boron trimethoxide (B(OCH ₃ ) ₃ ), boron triethoxide (B(OC ₂ H ₅ ) ₃ ), and boron tri-tert-butoxide (B(OtC ₄ H ₉ ) ₃ .

Organic solvents used in the slurry for insulating coating treatments are preferably those that form a mixed solvent with water and are easily dried. Specifically, they are highly compatible with water and have a relatively low boiling point (around 60°C to 90°C). Furthermore, they are preferably safe, easy to handle, readily available, and inexpensive. Taking all these factors into consideration, modified alcohols with ethanol as the main component are preferred.

When silane oxide (Si(OR) ₄ , R: alkyl) is used as the metal alkoxide, the hydrolysis reaction and dehydration-polycondensation reaction of the metal alkoxide in the insulation coating treatment are explained using reaction formulas.

In the hydrolysis reaction, in the presence of an alkali catalyst such as ammonia (NH ₃ ), as shown in formula (7) below, the silicon atom (Si) is directly attacked by a nucleophilic hydroxyl ion (OH ^- ), causing one alkoxy group (-OR) to hydrolyze first. As a result, the charge on the silicon atom decreases, making it increasingly susceptible to attack by the nucleophilic hydroxyl ion (OH ^- ). As a result, as shown in formula (8) below, the four alkoxy groups (-OR) are completely hydrolyzed to form silanol groups (Si-OH). Thus, if an alkali catalyst is used, all alkoxy groups (-OR) of the hydrolyzed silane oxide molecules are hydrolyzed, thereby producing a state in which completely hydrolyzed molecules (Si(OH) ₄ ) and completely unhydrolyzed molecules (Si(OR) ₄ ) coexist in the slurry.

Si(OR) ₄ +H ₂ O[+OH ^- ]→Si(OH)(OR) ₃ +ROH[+OH ^- ]‧‧‧(7)

Si(OR) ₄ +4H ₂ O[+OH ^- ]→Si(OH) ₄ +4ROH[+OH ^- ]‧‧‧(8)

On the other hand, in the presence of an acid catalyst such as nitric acid (HNO ₃ ), as shown in the following formula (9), the protonation of the alkoxy group (-OR) based on the proton (H ⁺ ) makes the silicon atom (Si) easily attacked by water (H ₂ O). Therefore, first, one alkoxy group (-OR) undergoes hydrolysis to become a silanol group (Si-OH). In this way, the charge on the silicon atom and the charge on the oxygen atom (O) decrease, and therefore it is not easily attacked by the proton (H ⁺ ), and detailed description is omitted. Therefore, the next hydrolysis does not occur immediately, and the alkoxy group (-OR) of other unhydrolyzed silane oxide molecules is easily hydrolyzed. In this way, if an acid catalyst is used, as shown in the following formula (10), the alkoxy group (-OR) in all silane oxide molecules is hydrolyzed evenly. Therefore, a state is produced in the slurry in which neither completely hydrolyzed molecules nor completely unhydrolyzed molecules exist, but uniformly hydrolyzed molecules (Si(OH) _x (OR) _4-x ; 0<x<4) exist.

Si(OR) ₄ +H ₂ O[+H ⁺ ]→Si(OH)(OR) ₃ +ROH[+H ⁺ ]‧‧‧(9)

Si(OR) ₄ +xH ₂ O[+H ⁺ ]→Si(OH) _X (OR) _4-X +xROH[+H ⁺ ]‧‧‧(10)(0<x<4)

As shown in the following formula (11), the dehydration condensation reaction is a reaction in which silanol groups (Si-OH) of hydrolyzed silane oxide molecules undergo dehydration condensation to form siloxane bonds (Si-O-Si). When the dehydration condensation reaction proceeds and ends, silicon dioxide (SiO2) is generated as shown in the following formula ( ₁₂ ).

Si(OH) ₄ +Si(OH) ₄ →(OH) ₃ Si-O-Si(OH) ₃ +H ₂ O‧‧‧(11)

Si(OH) ₄ →SiO ₂ +2H ₂ O‧‧‧(12)

To summarize the above, when the hydrolysis and dehydration condensation of silane oxide are completed, silicon dioxide (SiO ₂ ) and alcohol are generated as shown in the following formula (13). For example, when tetraethoxysilane (TEOS: Si(OR) ₄ , R: C ₂ H ₅ ) is used, silicon dioxide (SiO ₂ ) and ethanol (C ₂ H ₅ OH) are generated.

Si(OR) ₄ +2H ₂ O→SiO ₂ +4ROH‧‧‧(13)

As long as the silane oxide is hydrolyzed, regardless of whether an alkali catalyst or an acid catalyst is used, the above formula (13) is valid. The morphology of silicon dioxide (SiO ₂ ) produced during the dehydration and polycondensation is greatly affected by the hydrolysis state produced by the above hydrolysis catalyst.

Silane oxide molecules (Si(OH) _x (OR) _{4- x} ; 0<x<4) uniformly hydrolyzed using an acid catalyst contain unhydrolyzed alkoxy groups (-OR) within the molecule. Therefore, when the silane oxide groups (Si-OH) undergo dehydration and condensation between molecules, they form hydrolyzed polymers with linear or branched molecular weights. If these hydrolyzed polymers are generated in the slurry used in insulating coatings, they form on the surfaces of particles composed of iron oxide (FeO) or nickel oxide (NiO) in the crystallized powder. However, due to their linear or branched molecular weights, they are difficult to densify in the slurry solvent, making it difficult to form a dense insulating coating.

On the other hand, when using an alkali catalyst, completely hydrolyzed molecules (Si(OH) ₄ ) exist. Therefore, if the silanol groups (Si-OH) undergo dehydration and condensation between molecules, a dense hydrolyzed polymer with a high molecular weight is formed. Therefore, even in the solvent of the slurry used in the insulation coating process, a dense hydrolyzed polymer of silane oxide is formed on the surface of particles composed of iron oxide (FeO) or nickel oxide (NiO) in the crystallization powder, resulting in a dense insulation coating. Furthermore, when using an alkali catalyst, completely unhydrolyzed molecules (Si(OR) ₄ ) may exist. However, as described below, any completely unhydrolyzed molecules or very small molecular weight particulate hydrolyzed polymers of silane oxide (silica sol) that remain in the slurry during the insulation coating process and are not consumed by the crystallized powder insulation coating will be removed from the system along with the filter liquid during the filtration and washing process of the insulation coating step. Therefore, they will not affect the insulation coating process.

For these reasons, an alkali catalyst is preferred over an acid catalyst for the hydrolysis of metal alkoxides in insulating coatings. In this regard, the preferred catalyst differs from that used when coating a substrate with a solvent. Specifically, when using the catalyst as a binder for a coating solution that is applied to the substrate and then dried, rather than coating the particle surface in a solvent, it is preferable to use the acid catalyst in a linear or branched polymer.

Regarding the hydrolysis timing of metal alkoxides in insulating coating treatments, the following method has been described: hydrolysis is performed using a hydrolysis catalyst while the crystallization powder and metal alkoxide are uniformly mixed in a slurry. However, this embodiment is not limited to performing the hydrolysis at this time. For example, a metal oxide sol (or, in the case of a silane oxide, a silane sol) obtained by pre-hydrolyzing the metal alkoxide using a hydrolysis catalyst can be prepared and mixed with the crystallization powder to form a slurry. The smaller the average molecular weight of the metal oxide sol, approximately 500 to 5000, the less likely it is to affect the hydrolysis timing of the metal alkoxide. The reason for this is that the iron oxide (FeO) or nickel oxide (NiO) on the surface of the crystallization powder bonds with the hydrolyzed groups of the metal oxide sol (silanol groups (Si-OH) in the case of silane oxides), causing the surface of the crystallization powder particles to be covered by smaller metal oxide sol particles, which then aggregate with each other.

To achieve uniform formation of the insulating coating during the insulating coating treatment, the slurry containing crystallization powder, water, organic solvent, metal alkoxide, and hydrolysis catalyst is preferably stirred using a stirrer with impellers or a dedicated roller with container rotation. The treatment time and temperature for the insulating coating treatment vary depending on the type of metal alkoxide used and the desired insulating coating thickness. For example, the hydrolysis rate of metal methoxide is generally greater than that of metal ethoxide. Therefore, the treatment time and temperature can be appropriately set without particular limitation. For example, you can set the processing time to a few hours to a week and the processing temperature to between room temperature and 60°C. If the processing temperature is raised to around 40°C to 60°C, the processing speed can be increased several times compared to room temperature.

The thickness of the insulating coating also depends on the desired degree of insulation, so there's no one-size-fits-all approach. However, a typical thickness is 1nm to 30nm, more preferably 2nm to 25nm, and even more preferably 3nm to 20nm. Even if the thickness is too thick, the insulation becomes saturated, while the soft magnetic component content decreases, degrading magnetic properties like saturated flux density. Within this range, the insulating coating can fully perform its insulating function without significantly degrading magnetic properties.

Crystallized powder with an insulating coating, formed by hydrolysis and dehydration-condensation of metal alkoxides, is separated from the slurry into agglomerated crystallized powder using a known separation device such as a Denver filter, filter press, centrifuge, or decanter. The crystallized powder can be washed during the solid-liquid separation process, if necessary. The washing solution can be water, an organic solvent such as an alcohol with a relatively low boiling point, or a mixture of these solvents. As mentioned above, if there are metal alkoxides or their hydrolyzed polymers (unhydrolyzed molecules or metal oxide sols with smaller molecular weight) that are not consumed by the insulation coating and remain in the slurry, they are removed from the system along with the filter liquid or cleaning wastewater during solid-liquid separation or cleaning.

The solid-liquid separated bulk crystallization powder is dried and, if necessary, heat-treated to recover the crystallization powder having an insulating coating composed of a high-resistance metal oxide. There are no particular restrictions on the drying process, as long as excessive oxidation during drying can be suppressed. However, it is suitable to use a drying device such as an inert gas environment dryer, a reducing gas environment dryer, or a vacuum dryer, and to perform the drying process at a temperature of 40°C to 150°C. The higher the drying temperature, the more likely the metal alkoxide hydrolyzed polymer constituting the insulating coating will undergo dehydration and condensation, resulting in a harder, denser, and more insulating metal oxide. If further improvement is desired, heat treatment above 150°C and below 450°C can be performed in an inert gas environment, a reducing gas environment, or a vacuum. Furthermore, since an insulating coating has already been formed, a slow oxidation treatment after drying is essentially unnecessary.

Insulating coating treatment significantly improves the insulation properties of crystallized powder (alloy powder). For example, the pressed powder resistivity (applied pressure: 64 MPa) of untreated iron-nickel alloy powder is typically below 0.1 Ω·cm. In contrast, if the iron-nickel alloy powder is subjected to insulating coating treatment to form an insulating coating layer composed of silicon dioxide (SiO ₂ ) with a thickness of approximately 0.015 μm (15 nm), the pressed powder resistivity is improved to over 10 ⁶ Ω·cm.

This method enables the production of iron (Fe)-nickel (Ni) alloy powder according to this embodiment. The production method of this embodiment is characterized by the use of a specific nucleating agent (a water-soluble salt of a metal more noble than nickel) that refines the alloy powder, and a specific complexing agent (such as a hydroxycarboxylic acid) that promotes reduction, spheroidization, and surface smoothing. This method maintains the magnetic properties of the resulting alloy powder while improving the powder properties. Specifically, the average particle size of the resulting alloy powder can be freely controlled, resulting in a fine alloy powder. Furthermore, the resulting alloy powder has a narrow and uniform particle size distribution. Furthermore, the alloy powder is spherical and has a smooth surface, resulting in excellent filling properties. Furthermore, by using an amine compound that functions as a hydrazine autolysis inhibitor and reduction reaction promoter, the amount of hydrazine used can be reduced, but not limited. This can 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, the average particle size of the alloy powder is 0.10 μm or more and 0.60 μm or less, and the coefficient of variation (CV value) calculated according to the following formula (14) based on the average particle size and standard deviation in the number particle size distribution is 25% or less.

CV value (%) = standard deviation of particle size/average particle size × 100‧‧‧(14)

The iron (Fe)-nickel (Ni) alloy powder of this embodiment has a small particle size distribution. Furthermore, the average particle size of the alloy powder can be freely controlled. Therefore, miniaturization can be easily performed while simultaneously reducing the particle size distribution. Furthermore, the alloy powder is spherical and has a smooth surface, providing excellent filling properties. With these advantages, the alloy powder of this embodiment can be used in various electronic components such as noise filters, chokes, inductors, and radio wave absorbers. It is particularly suitable as a material for powder cores for chokes and inductors.

The average particle size of the alloy powder is preferably 0.10 μm to 0.60 μm, more preferably 0.10 μm to 0.50 μm. By appropriately increasing the average particle size, deterioration of magnetic properties and reduced filling capacity due to surface oxidation can be suppressed. Furthermore, by appropriately reducing the average particle size, eddy current loss can be suppressed.

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. The coefficient of variation is an indicator of particle size unevenness; a smaller coefficient of variation indicates a narrower particle size distribution. By suppressing the coefficient of variation, the number of coarse particles or excessively fine particles with significant surface oxidation is reduced, thereby maintaining excellent magnetic properties and preventing an increase in eddy current loss. Furthermore, the coefficient of variation (CV) is calculated by determining the average particle size and standard deviation in the number particle size distribution of the alloy powder using the following formula (14).

CV value (%) = standard deviation of particle size/average particle size × 100‧‧‧(14)

The alloy powder may also contain cobalt (Co) if desired. Specifically, the alloy powder can 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 magnetic metals that exhibit ferromagnetism. Therefore, iron-nickel alloy powder or iron-nickel-cobalt alloy powder has a higher saturated magnetic flux density and excellent magnetic properties.

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

The pressed powder density of alloy powder depends on its composition and particle size. A higher iron content reduces the specific gravity of the alloy, resulting in a lower pressed powder density. Similarly, smaller particle sizes make it difficult for particles to pack together, leading to a decreasing pressed powder density. Therefore, for an iron-nickel alloy powder with an average particle size of 0.3-0.5 μm, a specific gravity of 8.2-8.3, an iron content of 45-60 mol% iron (Fe), the pressed powder density (applied pressure: 100 MPa) is preferably 3.60 g/ ^cm³ or higher, and more preferably 3.70 g/ ^cm³ or higher. Furthermore, for an iron-nickel alloy powder with an average particle size of 0.3μm to 0.5μm, a specific gravity of 7.9 to 8.0, and an iron content of 10 mol% to 20 mol% iron (Fe), the powder density (applied pressure: 100 MPa) is preferably 3.45 g/ ^cm³ or higher, and more preferably 3.55 g/ ^cm³ or higher. Regarding the alloy powder particle size, if the average particle size is reduced from 0.3μm to 0.5μm to approximately 0.2μm to 0.25μm, the powder density (applied pressure: 100 MPa) tends to decrease to approximately 0.1 g/ ^cm³ . By increasing the powder density, powder cores with excellent magnetic properties (magnetic flux density) can be produced.

The alloy powder's crystallite diameter is preferably 30 nm or less, more preferably 10 nm or less. By appropriately reducing the crystallite diameter, a smaller coercive force, similar to that of amorphous soft magnetic materials, can be easily achieved.

The alloy powder preferably has a saturated magnetic flux density of 1 T (Tesla) or higher and a coercive force of 2000 A/m or lower. Increasing the saturated magnetic flux density of the alloy powder improves the magnetic properties (magnetic flux density) of the powder core. Furthermore, suppressing the coercive force of the alloy powder prevents an increase in hysteresis loss. The saturated magnetic flux density is more preferably 1.2 T (Tesla) or higher, and more preferably 1.5 T (Tesla) or higher. The coercive force is more preferably 1600 A/m or lower, and more preferably 1200 A/m or lower.

The alloy powder of this embodiment can be produced by any method as long as it meets the above requirements. However, it is preferably produced by the above method.

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, iron (Fe)-nickel (Ni) alloy powders with a high iron content (for example, an alloy powder with an iron content exceeding 60 mol%) tend to develop a gradient structure (or core-shell structure) within the particles. Specifically, the particle center is rich in nickel or cobalt, while the composition becomes increasingly rich in iron toward the particle surface. This results in a non-uniform composition within the particle.

As for how this intra-particle compositional heterogeneity affects the properties of the alloy powder, it does not significantly affect the magnetic properties (saturated magnetic flux density, coercive force, etc.). This is because, for example, the saturated magnetic flux density is positively correlated with the iron content (the higher the iron content, the higher the saturated magnetic flux density). Therefore, even if the compositional heterogeneity within the particles creates regions with iron contents above and below the average, the saturated magnetic flux density will also have regions above and below the average. However, the average value of the alloy powder as a whole will remain virtually unchanged compared to a case with heterogeneous composition. Furthermore, regarding retention, the compositional dependence of the iron-nickel (-cobalt) system is not that significant, and the degree of compositional heterogeneity within the particles does not significantly change.

On the other hand, the aforementioned uneven composition within the particles may affect chemical and physical properties such as oxidation resistance and thermal expansion. For example, regarding oxidation resistance, if the particle surface composition becomes more iron-rich due to the gradient structure, oxidation may progress more readily, potentially degrading oxidation resistance. However, if the particle surface composition is modified to a nickel-rich composition using the third aspect, oxidation resistance may actually be improved. Secondly, regarding thermal expansion, the thermal expansion coefficient of iron-nickel alloys differs from that of saturated magnetic flux density in that it shows neither a positive nor a negative correlation with the iron content. Instead, the thermal expansion coefficient becomes extremely low only around 65 mol% (64 mass%) iron. This low thermal expansion alloy is known as an invar alloy (65 mol% iron and 35 mol% nickel as the main components). In this case, if the composition is not uniform within the particles, the thermal expansion coefficient will not decrease, regardless of whether the iron content is greater than 65 mol% or less than 65 mol%. Therefore, when using iron (Fe)-nickel (Ni) alloy powder as a constant temperature alloy powder, it is necessary to achieve a uniform composition through the high-temperature heat treatment mentioned above.

To the best of the inventors' knowledge, there is currently no method for simply and inexpensively producing iron-nickel alloy powders with such excellent properties. For example, although Patent Document 3 proposes a wet process for producing nickel-iron alloy nanoparticles, this method does not utilize a nucleating agent composed of a water-soluble salt of a metal that is more noble than nickel, or a complexing agent composed of a hydroxycarboxylic acid or the like. Therefore, the powder properties (particle size, particle size distribution, sphericity, and particle surface properties) of the alloy powder produced by this method are expected to be suboptimal. In fact, Patent Document 3 shows a transmission electron microscope photograph of a fine powder sample used as an example (Figure 1 of Patent Document 3). Based on this photograph, it is estimated that the coefficient of variation (CV value) in the particle size distribution of the fine powder is relatively large, at approximately 35%.

Furthermore, the method of Patent 3, which does not use a nucleating agent or complexing agent, requires a large amount of reducing agent (hydrazine) to obtain fine alloy powder. In fact, in Example 3, 16.6 g of nickel chloride hexahydrate, 4.0 g of ferrous chloride tetrahydrate, and 135 g of hydrazine monohydrate were used as raw materials to produce alloy nanoparticles. Based on these doping amounts, approximately 30 times the molar ratio of hydrazine was incorporated relative to the combined amount of iron and nickel. A method requiring such a large amount of hydrazine would significantly increase the cost of the reducing agent, making it impractical.

The alloy powder of this embodiment can be used in any manner as long as it meets the aforementioned requirements. The alloy powder can be used alone or mixed with other inorganic and/or organic materials. For example, a powder compact containing only the alloy powder can be produced. Alternatively, the alloy powder can be mixed with ferrite powder to produce a metal-ferrite composite. In this case, the alloy powder's high saturated magnetic flux density and the ferrite's high electrical resistivity can be utilized complementarily. Furthermore, the alloy powder can be mixed and kneaded with an organic resin to produce a metal-organic resin composite. Using this composite, a composite with excellent magnetic properties, high dimensional accuracy, and high degree of shape freedom can be achieved.

The alloy powder is preferably used to form a powder compact or sheet. The powder compact or sheet comprises the alloy powder described above. A powder compact is produced by subjecting the alloy powder, or a mixture of the alloy powder and other components, to a press-forming process such as compression molding. Other components include inorganic or organic materials other than the alloy powder, or additives such as lubricants. Furthermore, the powder compact may be heat-treated after press-forming to remove strain induced during molding. Sheets can be produced by adding a solvent and, if necessary, a binder or other additive to the alloy powder to form a paste. The resulting paste is then formed into a sheet or coated onto a substrate to form a sheet.

The alloy powder of this embodiment has excellent magnetic properties and is therefore suitable for use in magnetic devices. Examples of such magnetic devices include inductors, reactors, chokes, noise filters, transformers, rotors, generators, and radio wave absorbers. These inductors, reactors, chokes, noise filters, transformers, rotors, generators, and radio wave absorbers incorporate the aforementioned pressed powder and/or sheet. Furthermore, the magnetic device may be a chip component such as a chip inductor.

FIG7 shows an example of applying a powder compact containing alloy powder to an inductor (ring coil). The inductor (10) is composed of a ring-shaped powder compact core (12) and a coil (14) arranged to surround the powder compact core (12). Input and output terminals (16a, 16b) are provided at both ends of the coil (14). The powder compact core (12) can be manufactured by compacting alloy powder and, if necessary, additives such as lubricants. The coil (14) can be wound around the powder compact core (12) using a wire. In order to prevent conduction between the powder core (12) and the coil (14), it is ideal to use a covered wire to make the coil (14) or to place an insulating sheet between the powder core (12) and the coil (14).

FIG8 shows an example of applying powdered metal to a chip inductor. The chip inductor (20) is composed of a powdered metal core (22) and a coil (24) embedded in the powdered metal core (22). The chip inductor (20) can be manufactured by pre-manufacturing the coil (24) and then pressurizing the coil (24) and the alloy powder together to form a single piece.

FIG9 shows an example of applying powder pressing to a reactor. The reactor (30) includes: a powder pressing core (32), a first coil (34) arranged in the form of a sheet surrounding one side of the powder pressing core (32), a second coil (36) arranged in the form of a sheet surrounding the other side of the powder pressing core (32), and a connecting portion (38) for electrically connecting the first coil (34) and the second coil (36).

FIG10 shows an example of applying powder compacts to the stator of a rotating machine (motor) or a generator. Furthermore, the arrows in the figure indicate the direction of magnetic flux during operation. The stator (40) has a powder compact core (42) and a winding (44). The winding (44) is arranged so as to surround each of a plurality of protrusions on the core (42), and the plurality of protrusions are arranged on the inner side of the powder compact core (42).

FIG11 shows an example of applying powder compaction to a rotor of a rotary machine (motor) or a generator. The rotor (50) has a powder compaction core (52), a winding (54), and an output shaft (56). The winding (54) is arranged so as to surround each of a plurality of protrusions of the core (52), and the plurality of protrusions are arranged on the outer side of the powder compaction core (52). The output shaft (56) is fixed to the center of the powder compaction core (52).

[Example]

The present invention is described in more 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 (Fe-Ni alloy powder) containing 50 mol% iron (Fe) and 50 mol% nickel (Ni) was prepared according to the sequence shown in Figure 5. In Example 1, when preparing the reaction solution, a room-temperature reducing solution was added to a metal salt raw material solution heated in a water bath and mixed.

<Preparation Steps>

Ferrous chloride tetrahydrate (FeCl ₂ ‧4H ₂ O, molecular weight: 198.81, Wako Jun Chemical Industries Co., Ltd.) and nickel chloride hexahydrate (NiCl ₂ ‧6H ₂ O, molecular weight: 237.69, Wako Jun Chemical Industries Co., Ltd.) were prepared as water-soluble iron salts and nickel salts. In addition, ammonium palladium(II) chloride (also known as ammonium tetrachloropalladate(II)) (( _NH4 ) _2PdCl4 , molecular weight: _284.31 , Wako Pure Chemical Industries, Ltd., reagent) was prepared as a nucleating agent, trisodium citrate dihydrate ( _Na3 ( _C3H5O (COO) ₃ )· _2H2O , _molecular weight: 294.1, Wako Pure Chemical Industries, Ltd., reagent) was prepared as a complexing agent, commercially available industrial grade 60 mass% hydrazine hydrate (manufactured by MGC Otsuka Chemical Co., Ltd.) was prepared as a reducing agent, and sodium hydroxide (NaOH, molecular weight: 40.0, Wako Pure Chemical Industries, Ltd., reagent) was prepared as a pH adjuster. 60% by mass hydrazine hydrate was prepared by diluting hydrazine hydrate (N ₂ H ₄ ·H ₂ O, molecular weight: 50.06) to 1.67 times with pure water. Furthermore, ethylenediamine (EDA; H ₂ NC ₂ H ₄ NH ₂ , molecular weight: 60.1, Wako Pure Chemical Industries, Ltd.) was prepared as the amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. The metal salt stock solution was weighed so that the amount of palladium (Pd) relative to the total amount of the magnetic metals (Fe and Ni) was 0.037 mass ppm (0.02 mol ppm). Furthermore, the amount of trisodium citrate relative to the total amount of the magnetic metals (Fe and Ni) was weighed so that the molar ratio was 0.362 (36.2 mol%). Specifically, 173.60 g of ferrous chloride tetrahydrate, 207.55 g of nickel chloride hexahydrate, 9.93 μg of ammonium palladium(II) chloride, and 185.9 g of trisodium citrate dihydrate were dissolved in 1200 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe and Ni) is 4.85. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe and Ni) is 4.96. Specifically, 346 g of sodium hydroxide is dissolved in 850 mL of pure water to prepare a sodium hydroxide solution. 707 g of 60% by mass hydrazine hydrate is added to this sodium hydroxide solution and mixed to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) in the reaction solution prepared in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.05 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallization powder

The prepared metal salt stock solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 70°C. The reducing agent solution at 25°C was then added to the heated metal salt stock solution in the water bath and mixed for 10 seconds to obtain a reaction solution at 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 starting temperature 55°C). As shown in Figure 12, the temperature of the reaction solution continued to rise after the reaction started by heating the water bath and was maintained at 70°C (reaction holding temperature 70°C) 10 minutes after the start of the reaction. Regarding the color of the reaction solution, it was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. In addition, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started, when the color of the reaction solution turned dark gray, to 13 minutes after the reaction started, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 20 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron and nickel components in the reaction solution have all been reduced to metallic iron and metallic nickel. The reaction solution after the reaction is a slurry containing the iron-nickel crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.41μm.

[Example 2]

In Example 2, an iron-nickel alloy powder (Fe-Ni-Co alloy powder) containing 50 mol% iron (Fe), 40 mol% nickel (Ni), and 10 mol% cobalt (Co) was prepared according to the sequence shown in Figure 3. In Example 2, to prepare the reaction solution, a room-temperature pH-adjusting solution (alkaline metal hydroxide solution) was first added to a metal salt raw material solution heated in a water bath. A room-temperature reducing agent solution was then added and mixed.

<Preparation Steps>

The same raw materials as in Example 1 were prepared: 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 (CoCl ₂ ·6H ₂ O, molecular weight: 237.93, Wako Pure Chemical Industries, Ltd.) was also prepared as a water-soluble cobalt salt.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

A metal salt stock solution containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), cobalt chloride hexahydrate (water-soluble cobalt salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water was prepared. The metal salt stock solution was weighed so that the amount of palladium (Pd) relative to the total amount of the magnetic metals (Fe, Ni, and Co) was 0.037 mass ppm (0.02 molar ppm). Furthermore, the amount of trisodium citrate relative to the total amount of the magnetic metals (Fe, Ni, and Co) was weighed to a molar ratio of 0.362 (36.2 mol%). Specifically, 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 ammonium palladium(II) chloride, and 185.9 g of trisodium citrate dihydrate were dissolved in 1200 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing hydrazine (reducing agent) and water. The hydrazine doping amount is set so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is 4.85. Specifically, weigh 707 g of 60% by mass hydrazine hydrate to prepare the reducing agent solution.

(c) Preparation of pH adjustment solution (alkaline metal hydroxide solution)

Prepare a pH-adjusting solution (alkaline metal hydroxide solution) containing sodium hydroxide (pH adjuster) and water. Weigh the solution so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is 4.96. Specifically, dissolve 346 g of sodium hydroxide in 850 mL of pure water to prepare the pH-adjusting solution.

(d) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the mixture so that the molar ratio of ethylenediamine to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.05 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared metal salt stock solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 70°C. A pH adjustment solution (alkaline metal hydroxide solution) at 25°C was then added and mixed for 10 seconds to the heated metal salt stock solution in the water bath. The reducing agent solution at 25°C was then added and mixed for another 10 seconds, resulting in a reaction solution at 55°C. The concentration of the magnetic metals (Fe, Ni, and Co) in the reaction solution was 32.3 g/L. This initiated the reduction reaction (crystallization reaction) (reaction starting temperature 55°C). The temperature of the reaction solution continued to rise after the reaction began by heating in a water bath and was maintained at 70°C (reaction holding temperature 70°C) 10 minutes after the reaction began. The color of the reaction solution was dark green immediately after the reaction began (preparation of the reaction solution), but changed to dark gray after a few minutes. The reason for the dark green color immediately after the reaction began is believed to be that the reaction according to formula (6) above proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ), nickel hydroxide (Ni(OH) ₂ ), and cobalt hydroxide (Co(OH) ₂ ) in the reaction solution. Furthermore, the color changed to dark gray a few minutes after the reaction began, which is believed to be due to the nucleation of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started and 13 minutes after the reaction started, when the color of the reaction solution turned dark gray, the amine compound solution was added dropwise to the reaction solution and mixed to advance the reduction reaction. This caused iron-nickel-cobalt crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 20 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron component, nickel component, and cobalt component in the reaction solution have all been reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after the reaction is a slurry containing iron-nickel-cobalt crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel-cobalt crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel-cobalt alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.33μm.

[Example 3]

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

<Preparation Steps>

Prepare the same raw materials as in Example 1: a water-soluble iron salt, a water-soluble nickel salt, a nucleating agent, a reducing agent, a pH adjuster, and an amine compound. Also, prepare tartaric acid ((CH(OH)COOH) ₂ , molecular weight: 150.09, Wako Pure Chemical Industries, Ltd.) as a complexing agent instead of trisodium citrate dihydrate.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous chloride tetrahydrate (water-soluble iron salt), nickel chloride hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), tartaric acid (chelating agent), and water. The metal salt stock solution is weighed so that the amount of palladium (Pd) is 0.037 mass ppm (0.02 molar ppm) relative to the total amount of the magnetic metals (Fe and Ni). Furthermore, the tartaric acid is weighed so that the molar ratio relative to the total amount of the magnetic metals (Fe and Ni) is 0.200 (20.0 mol%). Specifically, 173.60 g of ferrous chloride tetrahydrate, 207.55 g of nickel chloride hexahydrate, 9.93 μg of ammonium palladium(II) chloride, and 52.4 g of tartaric acid were dissolved in 1200 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe and Ni) is 4.85. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe and Ni) is 4.96. Specifically, 346 g of sodium hydroxide is dissolved in 850 mL of pure water to prepare a sodium hydroxide solution. 707 g of 60% by mass hydrazine hydrate is added to this sodium hydroxide solution and mixed to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution in the same manner as in Example 1.

(d) Preparation of reaction solution and precipitation of crystallization powder

Using the aforementioned 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.

<Recycling Steps>

Iron-nickel alloy powder (Fe-Ni alloy powder) was prepared from the slurry obtained in the crystallization step using the same method as in Example 1. The resulting alloy powder consisted of smooth, spherical particles with a steep particle size distribution and an average particle size of 0.40 μm.

[Example 4]

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

<Preparation Steps>

The same raw materials as in Example 1 were prepared as a nucleating agent, a reducing agent, a pH adjuster, a complexing agent, and an amine compound. Furthermore, ferrous sulfate heptahydrate ( _FeSO₄ · _7H₂O , molecular weight: 278.05, Wako Jun Chemical Industries, Ltd., a reagent) was prepared in place of ferrous chloride tetrahydrate as the water-soluble iron salt, and nickel sulfate hexahydrate (NiSO₄ _{· 6H₂O} , molecular weight: 262.85, Wako Jun Chemical Industries, Ltd., a reagent) was prepared in place of nickel chloride hexahydrate as the water-soluble nickel salt.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium (II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the amount of palladium (Pd) relative to the total amount of the magnetic metals (Fe and Ni) is 0.37 mass ppm (0.2 molar ppm). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total amount of the magnetic metals (Fe and Ni) is 0.318 (31.8 mol%). Specifically, 272.0 g of ferrous sulfate heptahydrate, 202.0 g of nickel sulfate hexahydrate, 99.3 μg of ammonium palladium(II) chloride, and 163.5 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe and Ni) is 6.41. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe and Ni) is 4.67. Specifically, 326 g of sodium hydroxide is dissolved in 800 mL of pure water to prepare a sodium hydroxide solution. 934 g of 60% by mass hydrazine hydrate is added to this sodium hydroxide solution and mixed to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution in the same manner as in Example 1.

(d) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 70°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 59°C). The temperature of the reaction solution continued to rise after the reaction started by heating it in a water bath and was maintained at 70°C (reaction holding temperature 70°C) 10 minutes after the start of the reaction. Regarding the color of the reaction solution, it was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. Furthermore, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started, when the color of the reaction solution turned dark gray, to 13 minutes after the reaction started, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 30 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron and nickel components in the reaction solution have all been reduced to metallic iron and metallic nickel. The reaction solution after the reaction is a slurry containing the iron-nickel crystallization powder.

<Recycling Steps>

The slurry obtained from the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover agglomerated iron-nickel crystallized powder. Filtering and cleaning are performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from the slurry is below 10 μS/cm. The recovered agglomerated crystallized powder is dried in a vacuum dryer set at 50°C. The dried crystallized powder is then cooled to 35°C in a vacuum oven and slowly oxidized by the addition of nitrogen containing 1.0 volume percent oxygen. This results in iron-nickel alloy powder consisting of smooth, spherical particles. The particle size distribution is steep, with an average particle size of 0.38μm.

[Example 5]

In Example 5, an iron-nickel alloy powder (Fe-Ni alloy powder) having a nickel-rich surface composition and comprising 51 mol% iron (Fe) and 49 mol% nickel (Ni) was produced according to the sequence shown in Figure 6. An additional raw material solution was added and mixed at the final stage of the crystallization step. Specifically, crystallization of the iron-nickel alloy powder (Fe-Ni alloy powder) comprising 56 mol% iron (Fe) and 44 mol% nickel (Ni) was performed in the same manner as in Example 4, except for the difference in the amount of hydrazine incorporated as a reducing agent. During the crystallization, an aqueous solution of a water-soluble nickel salt was added to the reaction solution and mixed.

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content is 0.37 mass ppm (0.2 molar ppm) relative to the total weight of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total weight of the magnetic metals (Fe and Ni) is 0.318 (31.8 mol%). Specifically, 272.0 g of ferrous sulfate heptahydrate, 202.0 g of nickel sulfate hexahydrate, 99.3 μg of ammonium palladium(II) chloride, and 163.5 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. Weigh the solution so that the molar ratio of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (total amount of magnetic metals (Fe and Ni) upon addition of the additional raw material solution) is 4.85 (4.41 relative to the total amount of magnetic metals (Fe and Ni) upon addition of the additional raw material solution). Also, weigh the solution so that the molar ratio of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (total amount of magnetic metals (Fe and Ni) upon addition of the additional raw material solution) is 4.67 (4.24 relative to the total amount of magnetic metals (Fe and Ni) upon addition of the additional raw material solution). Specifically, 326 g of sodium hydroxide was dissolved in 800 mL of pure water to prepare a sodium hydroxide solution. 707 g of 60% by mass hydrazine hydrate was added and mixed into the sodium hydroxide solution to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.16 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material liquid

Prepare an additional raw material solution containing nickel sulfate hexahydrate (a water-soluble nickel salt) and water. Weigh the solution so that the amount of magnetic metal (Ni) in the additional raw material solution is 0.175 mol, which is 0.10 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution (1.747 mol). Specifically, dissolve 46.0 g of nickel sulfate hexahydrate in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the solution reached 70°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 57°C). The temperature of the reaction solution continued to rise after the reaction started by heating it in a water bath and was maintained at 70°C (reaction holding temperature 70°C) 10 minutes after the start of the reaction. Regarding the color of the reaction solution, it was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. Furthermore, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

For 10 minutes, from 3 minutes after the reaction started, when the reaction solution turned dark gray, to 13 minutes after, the amine compound solution was added dropwise and mixed to promote the reduction reaction. This caused iron-nickel crystallized powder to precipitate into the reaction solution. From 11 minutes to 16 minutes after the reaction started, additional raw material solution was added dropwise while mixing. This promoted the reduction of the less reducible iron ions (or iron hydroxide) and simultaneously promoted the reduction reaction, resulting in a nickel-rich surface composition of the precipitated iron-nickel crystallized powder. The concentration of magnetic metals (Fe and Ni) in the reaction solution after the addition of the additional raw material solution was 32.8 g/L. The reaction solution was black at this point, but within 30 minutes of the reaction starting, the supernatant became transparent. This indicates that the reduction reaction was complete, with all the iron and nickel components in the reaction solution reduced to metallic iron and metallic nickel. The reaction solution after the reaction was a slurry containing iron-nickel crystallization powder.

<Recycling Steps>

The slurry obtained from the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover agglomerated iron-nickel crystallized powder. Filtering and cleaning are performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from the slurry is below 10 μS/cm. The recovered agglomerated crystallized powder is dried in a vacuum dryer set at 50°C. The dried crystallized powder is then cooled to 35°C in a vacuum oven and slowly oxidized by the addition of nitrogen containing 1.0 volume percent oxygen. This results in an iron-nickel alloy powder consisting of smooth, spherical particles. The particle size distribution is steep, with an average particle size of 0.40μm.

[Example 6]

In Example 6, the crystallized powder obtained in Example 1 was subjected to a spiral jet pulverization process, a dry pulverization method, using an ultra-compact jet mill (Nippon Pneumatic Co., Ltd., JKE-30) at a pulverization gas pressure of 0.5 MPa. This produced an iron-nickel alloy powder (Fe-Ni alloy powder) containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The resulting alloy powder exhibited a steep particle size distribution similar to that of Example 1, with an average particle size of 0.41 μm. Furthermore, the spiral jet pulverization process reduced agglomerated particles, improving packing properties (increasing the density of the pressed powder) and reducing surface irregularities, resulting in very smooth spherical particles.

[Example 7]

In Example 7, as described below, following the crystallization step, the slurry-like crystallized powder before drying was subjected to wet crushing using high-pressure fluid collision crushing during the recovery step to produce an iron-nickel alloy powder (iron-nickel alloy powder) containing 50 mol% iron (Fe) and 50 mol% nickel (Ni).

<Recycling Steps (including Disintegration Step)>

The slurry-like reaction solution containing the iron-nickel crystallization powder obtained in the same crystallization step as in Example 1 was filtered and washed, and then a washed crystallization slurry containing 20% by mass of the iron-nickel crystallization powder was prepared using pure water with a conductivity of 1 μS/cm. The filtration and washing was performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from the slurry reached 10 μS/cm or less. The washed crystallization slurry was then disintegrated by passing it through a high-pressure fluid collision disintegration device (manufactured by SUGINO MACHINE; pressure: 200 MPa) in two paths, and then subjected to solid-liquid separation to recover the agglomerated iron-nickel crystallization powder. The recovered agglomerated crystallized powder was dried in a vacuum dryer set at 50°C. The dried crystallized powder was then cooled to 35°C in a vacuum oven and then slowly oxidized by the addition of nitrogen containing 1.0 volume percent oxygen to produce an iron-nickel alloy powder. The resulting alloy powder exhibited a steep particle size distribution similar to that of Example 1, with an average particle size of 0.41 μm. Furthermore, the high-pressure fluid impact disintegration treatment reduced agglomerated particles, improving packing properties (increasing the density of the pressed powder) and reducing surface irregularities, resulting in very smooth spherical particles.

[Example 8]

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

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content is 2.81 mass ppm (1.50 molar ppm) relative to the total amount of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total amount of the magnetic metals (Fe and Ni) is 0.724 (72.4 mol%). Specifically, 318.1 g of ferrous sulfate heptahydrate, 161.9 g of nickel sulfate hexahydrate, 750.5 μg of ammonium palladium(II) chloride, and 374.7 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. Weigh the reaction solution prepared in the subsequent crystallization step so that the molar ratio of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction is 8.98. Furthermore, weigh the sodium hydroxide so that the molar ratio relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction is 7.07. Specifically, prepare a sodium hydroxide solution by dissolving 497.5 g of sodium hydroxide in 1218 mL of pure water. Prepare a reducing agent solution by adding and mixing 1318 g of 60% by mass hydrazine hydrate to this sodium hydroxide solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.06 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the solution reached 80°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds to obtain a reaction solution at 71°C. The concentration of the magnetic metals (Fe and Ni) in the reaction solution was 25.0 g/L. This initiated the reduction reaction (crystallization reaction) (reaction starting temperature 71°C). The temperature of the reaction solution continued to rise after the reaction started by heating in a water bath and was maintained at 80°C (reaction holding temperature 80°C) for 10 minutes after the start of the reaction. The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. In addition, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

From 3 minutes after the reaction started, when the color of the reaction solution turned dark gray, to 13 minutes after the reaction started, the amine compound solution was added dropwise and mixed to advance the reduction reaction. This caused iron-nickel crystallized powder to precipitate into the reaction solution. The reaction solution was black at this point, but within 40 minutes of the reaction starting, the supernatant became transparent. The reduction reaction was considered complete, and the iron and nickel components in the reaction solution were all reduced to metallic iron and metallic nickel. The reaction solution after the reaction was a slurry containing the iron-nickel crystallized powder.

<Recycling Steps>

The slurry obtained from the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover agglomerated iron-nickel crystallized powder. Filtering and cleaning are performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from the slurry is below 10 μS/cm. The recovered agglomerated crystallized powder is dried in a vacuum dryer set at 50°C. The dried crystallized powder is then cooled to 35°C in a vacuum atmosphere and slowly oxidized by the addition of nitrogen containing 1.0 volume percent oxygen.

<High temperature heat treatment step>

The resulting crystallized powder was subjected to a high-temperature heat treatment at 350°C for 60 minutes in a nitrogen atmosphere to produce an iron-nickel alloy powder (Fe-Ni alloy powder) containing 65 mol% iron (Fe) and 35 mol% nickel (Ni). The resulting alloy powder exhibited a steep particle size distribution similar to that of 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 intra-particle property variations.

[Example 9]

In Example 9, an iron-nickel alloy powder (Fe-Ni alloy powder) having a nickel-rich surface composition and comprising 65 mol% iron (Fe) and 35 mol% nickel (Ni) was produced according to the sequence shown in Figure 6. During the crystallization step, an additional raw material solution was added and mixed. Specifically, a room-temperature metal salt raw material solution was added and mixed to a reducing solution heated in a water bath to prepare a reaction solution. Crystallization of the iron-nickel alloy powder (Fe-Ni alloy powder) containing 67.4 mol% iron (Fe) and 32.6 mol% nickel (Ni) was first performed. Also, during the crystallization, a water-soluble nickel salt aqueous solution was added and mixed to the reaction solution as the additional raw material solution.

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content in the resulting metal salt stock solution is 0.97 mass ppm (0.52 molar ppm) relative to the total weight of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total weight of the magnetic metals (Fe and Ni) is 0.750 (75.0 mol%). Specifically, 318.1 g of ferrous sulfate heptahydrate, 145.7 g of nickel sulfate hexahydrate, 250.0 μg of ammonium palladium(II) chloride, and 374.7 g of trisodium citrate dihydrate were dissolved in 500 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. Weigh the solution so that the molar ratio of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (7.62 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) in the reaction solution prepared in the subsequent crystallization step is 7.36. Furthermore, weigh the solution so that the molar ratio of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (7.07 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) is 7.33. Specifically, 497.5 g of sodium hydroxide was dissolved in 1218 mL of pure water to prepare a sodium hydroxide solution. 1080 g of 60% by mass hydrazine hydrate was added and mixed into the sodium hydroxide solution to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.06 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material liquid

Prepare an additional raw material solution containing nickel sulfate hexahydrate (a water-soluble nickel salt) and water. Weigh the solution so that the amount of magnetic metal (Ni) in the additional raw material solution is 0.0616 mol, which is 0.035 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution (1.760 mol). Specifically, dissolve 16.2 g of nickel sulfate hexahydrate in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the solution reached 80°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds to obtain a reaction solution at 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 starting temperature 75°C). The temperature of the reaction solution continued to rise after the reaction started by heating in a water bath and was maintained at 80°C (reaction holding temperature 80°C) for 10 minutes after the start of the reaction. The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. In addition, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

For 10 minutes, from 3 minutes after the reaction started, when the reaction solution turned dark gray, to 13 minutes after, the amine compound solution was added dropwise and mixed to promote the reduction reaction. This caused iron-nickel crystallized powder to precipitate into the reaction solution. From 25 minutes to 35 minutes after the reaction started, additional raw material solution was added dropwise while mixing. This promoted the reduction of the less reducible iron ions (or iron hydroxide) and simultaneously promoted the reduction reaction, resulting in a nickel-rich surface composition of the precipitated iron-nickel crystallized powder. The concentration of magnetic metals (Fe and Ni) in the reaction solution after the addition of the additional raw material solution was 28.4 g/L. The reaction solution was black at this point, but within 40 minutes of the reaction starting, the supernatant became transparent. This indicates that the reduction reaction was complete, with all the iron and nickel components in the reaction solution reduced to metallic iron and metallic nickel. The reaction solution after the reaction was a slurry containing iron-nickel crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.39μm.

[Example 10]

In Example 10, an iron-nickel alloy powder (Fe-Ni alloy powder) with a composition containing 80 mol% iron (Fe) and 20 mol% nickel (Ni) with a high iron content was produced according to the sequence shown in Figure 6. During the crystallization step, an additional raw material solution was added and mixed. Specifically, a room-temperature metal salt raw material solution was added and mixed to a reducing solution heated in a water bath to prepare a reaction solution. Crystallization of the iron-nickel alloy powder (Fe-Ni alloy powder) containing 83.3 mol% iron (Fe) and 16.7 mol% nickel (Ni) was first performed. Furthermore, during this crystallization, a water-soluble nickel salt aqueous solution was added and mixed to the reaction solution as the additional raw material solution.

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content is 0.79 mass ppm (0.42 molar ppm) relative to the total amount of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total amount of the magnetic metals (Fe and Ni) is 0.754 (75.4 mol%). Specifically, 394.3 g of ferrous sulfate heptahydrate, 74.6 g of nickel sulfate hexahydrate, 201.6 μg of ammonium palladium(II) chloride, and 377.5 g of trisodium citrate dihydrate were dissolved in 836 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. Weigh the solution so that the molar ratio of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (9.40 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) in the reaction solution prepared in the subsequent crystallization step is 9.02. Furthermore, weigh the solution so that the molar ratio of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (7.37 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) is 7.07. Specifically, 501.3 g of sodium hydroxide was dissolved in 1228 mL of pure water to prepare a sodium hydroxide solution. 1334 g of 60% by mass hydrazine hydrate was added and mixed into the sodium hydroxide solution to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.07 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material liquid

Prepare an additional raw material solution containing nickel sulfate hexahydrate (a water-soluble nickel salt) and water. Weigh the solution so that the amount of magnetic metal (Ni) in the additional raw material solution is 0.0709 mol, which is 0.04 times the total amount of magnetic metal (Fe and Ni) in the metal salt raw material solution (1.773 mol). Specifically, dissolve 18.64 g of nickel sulfate hexahydrate in 200 mL of pure water to prepare the additional raw material solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the solution reached 80°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds to obtain a reaction solution at 71°C. The concentration of the magnetic metals (Fe and Ni) in the reaction solution was 24.5 g/L. This initiated the reduction reaction (crystallization reaction) (reaction starting temperature 71°C). The temperature of the reaction solution continued to rise after the reaction started by heating in a water bath and was maintained at 80°C (reaction holding temperature 80°C) for 10 minutes after the start of the reaction. The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. In addition, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

From 3 minutes after the reaction started, when the color of the reaction solution turned dark gray, to 13 minutes after the reaction started, the amine compound solution was added dropwise and mixed to promote the reduction reaction. This caused iron-nickel crystallized powder to precipitate into the reaction solution. From 8 minutes after the reaction started, to 18 minutes after the reaction started, additional raw material solution was added dropwise while mixing. This promoted the reduction of the less reducible iron ions (or iron hydroxide) and simultaneously promoted the reduction reaction, resulting in a nickel-rich surface composition of the precipitated iron-nickel crystallized powder. The concentration of magnetic metals (Fe and Ni) in the reaction solution after the addition of the additional raw material solution was 24.2 g/L. The reaction solution was black at this point, but within 60 minutes of the reaction starting, the supernatant became transparent. This indicates that the reduction reaction was complete, with all the iron and nickel components in the reaction solution reduced to metallic iron and metallic nickel. The reaction solution after the reaction was a slurry containing iron-nickel crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.48μm.

[Example 11]

In Example 11, an iron-nickel alloy powder (Fe-Ni alloy powder) with a composition containing 90 mol% iron (Fe) and 10 mol% nickel (Ni) with a high iron content was produced according to the sequence shown in Figure 6. During the crystallization step, an additional raw material solution was added and mixed. Specifically, a room-temperature metal salt raw material solution was added and mixed to a reducing solution heated in a water bath to prepare a reaction solution. Crystallization of the iron-nickel alloy powder (Fe-Ni alloy powder) containing 91.8 mol% iron (Fe) and 8.2 mol% nickel (Ni) was first performed. Furthermore, during the crystallization, a water-soluble nickel salt aqueous solution was added and mixed to the reaction solution as the additional raw material solution.

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content is 0.77 mass ppm (0.41 molar ppm) relative to the total amount of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total amount of the magnetic metals (Fe and Ni) is 0.369 (36.9 mol%). Specifically, 446.0 g of ferrous sulfate heptahydrate, 37.5 g of nickel sulfate hexahydrate, 202.6 μg of ammonium palladium(II) chloride, and 189.7 g of trisodium citrate dihydrate were dissolved in 720 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. Weigh the solution so that the molar ratio of hydrazine relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (8.97 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) in the reaction solution prepared in the subsequent crystallization step is 9.15. Furthermore, weigh the solution so that the molar ratio of sodium hydroxide relative to the total amount of magnetic metals (Fe and Ni) at the start of the reaction (8.13 relative to the total amount of magnetic metals (Fe and Ni) when the additional raw material solution is added) is 8.29. Specifically, 579 g of sodium hydroxide was dissolved in 1418 mL of pure water to prepare a sodium hydroxide solution. 1334 g of 60% by mass hydrazine hydrate was added and mixed into the sodium hydroxide solution to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.07 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of additional raw material liquid

Prepare an additional stock solution containing nickel sulfate hexahydrate (a water-soluble nickel salt) and water. Weigh the solution so that the amount of magnetic metal (Ni) in the additional stock solution is 0.0356 mol, which is 0.02 times the total amount of magnetic metal (Fe and Ni) in the metal salt stock solution (1.747 mol). Specifically, dissolve 9.37 g of nickel sulfate hexahydrate in 100 mL of pure water to prepare the additional stock solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the liquid temperature reached 85°C. The metal salt raw material solution at a liquid temperature of 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds to obtain a reaction solution at a liquid temperature of 78°C. The concentration of the magnetic metals (Fe and Ni) in the reaction solution was 25.0 g/L. This initiated the reduction reaction (crystallization reaction) (reaction starting temperature 78°C). The temperature of the reaction solution continued to rise after the reaction started by heating in a water bath and was maintained at 85°C (reaction holding temperature 85°C) for 10 minutes after the start of the reaction. The color of the reaction solution was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. The reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

For 10 minutes, from 3 minutes after the reaction started, when the reaction solution turned dark gray, to 13 minutes after the reaction started, an amine compound solution was added dropwise and mixed to promote the reduction reaction. This caused iron-nickel crystallized powder to precipitate into the reaction solution. From 8 minutes to 18 minutes after the reaction started, additional raw material solution was added dropwise and mixed to promote the reduction of the less reducible iron ions (or iron hydroxide). This also promoted the reduction reaction, resulting in a nickel-rich surface composition of the precipitated iron-nickel crystallized powder. The concentration of magnetic metals (Fe and Ni) in the reaction solution after the addition of the additional raw material solution was 24.8 g/L. The reaction solution was black at this point, but within 50 minutes of the reaction starting, the supernatant became transparent. This indicates that the reduction reaction was complete, with all the iron and nickel components in the reaction solution reduced to metallic iron and metallic nickel. The reaction solution after the reaction was a slurry containing iron-nickel crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.38μm.

[Example 12]

In Example 12, the crystallized powder obtained according to the sequence shown in Figure 5 was subjected to an insulating coating treatment to produce an iron-nickel alloy powder (Fe-Ni alloy powder) coated with an insulating metal oxide, namely silicon dioxide (SiO ₂ ). The resulting powder contained 55 mol% iron (Fe) and 45 mol% nickel (Ni). In Example 12, to prepare the reaction solution, a room-temperature metal salt raw material solution was added to a reducing solution heated in a water bath and mixed.

<Preparation Steps>

Prepare the same raw materials as in Example 4 as water-soluble iron salt, water-soluble nickel salt, nucleating agent, reducing agent, pH adjuster, complexing agent, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water. Weigh the solution so that the palladium (Pd) content is 0.56 mass ppm (0.3 molar ppm) relative to the total amount of the magnetic metals (Fe and Ni). Furthermore, weigh the solution so that the molar ratio of trisodium citrate dihydrate relative to the total amount of the magnetic metals (Fe and Ni) is 0.543 (54.3 mol%). Specifically, 267.7 g of ferrous sulfate heptahydrate, 207.1 g of nickel sulfate hexahydrate, 149.3 μg of ammonium palladium(II) chloride, and 279.6 g of trisodium citrate dihydrate were dissolved in 950 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe and Ni) is 4.85. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe and Ni) is 4.95. Specifically, 346 g of sodium hydroxide is dissolved in 848 mL of pure water to prepare a sodium hydroxide solution. 709 g of 60% by mass hydrazine hydrate is added to this sodium hydroxide solution and mixed to prepare a reducing agent solution.

(c) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution so that the molar ratio of ethylenediamine relative to the total amount of magnetic metals (Fe and Ni) after the addition of the additional raw material solution in the reaction solution in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.05 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(d) Preparation of reaction solution and precipitation of crystallization powder

The prepared reducing agent solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring blade in a water bath and heated while stirring until the solution reached 70°C. The metal salt raw material solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 59°C). The temperature of the reaction solution continued to rise after the reaction started by heating it in a water bath and was maintained at 70°C (reaction holding temperature 70°C) 10 minutes after the start of the reaction. Regarding the color of the reaction solution, it was dark green immediately after the start of the reaction (preparation of the reaction solution), but turned dark gray after a few minutes. The reason for the dark green color immediately after the start of the reaction is believed to be that the reaction according to the above formula (6) proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ) and nickel hydroxide (Ni(OH) ₂ ) in the reaction solution. Furthermore, the reason for the dark gray color a few minutes after the start of the reaction is believed to be that nucleation occurred due to the action of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started, when the color of the reaction solution turned dark gray, to 13 minutes after the reaction started, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 30 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron and nickel components in the reaction solution have all been reduced to metallic iron and metallic nickel. The reaction solution after the reaction is a slurry containing the iron-nickel crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover agglomerated iron-nickel crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from filtering the slurry reaches 10 μS/cm or less. The recovered agglomerated crystallization powder is dried in a vacuum dryer set at 50°C. The dried crystallization powder is then cooled to 35°C in a vacuum and slowly oxidized by supplying nitrogen containing 1.0 volume % oxygen. This results in a dry crystallization powder (iron-nickel alloy powder). The resulting crystallized powder (alloy powder) consists of smooth, spherical particles. The particle size distribution is steep, with an average particle size of 0.39 μm.

<Insulation coating steps>

50.0 g of the crystallized powder (alloy powder) obtained in the above recovery step was placed in a sealed polypropylene container, and then 7.0 g of pure water and 50.0 g of ethanol (C ₂ H ₅ OH, molecular weight: 46.07, Wako Pure Chemical Industries, Ltd.) were added to disperse the crystallized powder (alloy powder) in the mixed solvent of water and ethanol. Then, 9.8 g of tetraethoxysilane (also known as tetraethyl orthosilicate, tetraethyl silicate) (abbreviated as TEOS) (Si(OC ₂ H ₅ ) ₄ , molecular weight: 208.33, Wako Pure Chemical Industries, Ltd.) as a silane oxide was added and mixed thoroughly. Then, an alkali catalyst (alkali) was added to hydrolyze the silane oxide. 2.4 g of 1% ammonia water (catalyst) was added to the mixture while stirring to form a uniform slurry. The 1% ammonia water was prepared by diluting the 28-30% ammonia water (NH ₃ , molecular weight: 17.03, manufactured by Wako Pure Chemical Industries, Ltd.) in the reagent with pure water. The crystallization powder (alloy powder), water, ethanol, tetraethoxysilane, and 1% ammonia water were all used at room temperature, and all addition and mixing were also performed at room temperature.

The slurry, consisting of crystallization powder (alloy powder), water, ethanol, tetraethoxysilane, and ammonia, is stored in a rotating, sealed polypropylene container at 40°C for two days. While the slurry is stirred, the tetraethoxysilane undergoes hydrolysis and dehydration-condensation, forming an insulating coating primarily composed of a hydrolyzed polymer of tetraethoxysilane (primarily composed of silicon dioxide ( _SiO2 ), although containing a small amount of silanol groups (Si-OH)). The slurry is then filtered, cleaned, and subjected to solid-liquid separation to recover the crystallization powder (alloy powder) in agglomerates. Filter cleaning is performed first with ethanol containing 50% pure water by mass, followed by ethanol. Furthermore, the hydrolyzed polymer of tetraethoxysilane that remains in the slurry after being consumed by the insulating coating on the surface of the crystallization powder (alloy powder) particles is a very small molecular weight particle (silica sol) and is removed as a filter liquid during filtration and cleaning, so it does not remain in the recovered bulk crystallization powder (alloy powder).

The recovered agglomerated crystallized powder (alloy powder) is dried in a vacuum dryer at 50°C and then heated in a vacuum at 150°C for 2 hours. This heating further dehydrates and condenses the hydrolyzed polymer of tetraethoxysilane that makes up the insulating coating, transforming it into harder and denser silicon dioxide (SiO ₂ ), further enhancing the insulating properties of the insulating coating. This insulating coating treatment yields an iron-nickel alloy powder with an insulating coating composed of high-resistance silicon dioxide (SiO ₂ ) formed on the particle surface. The resulting alloy powder consists of smooth, spherical particles. The particle size distribution is steep, with an average particle size of 0.42 μm. The thickness of the insulating coating is estimated to be approximately 0.015 μm (approximately 15 nm). Furthermore, the insulating coating treatment significantly increases the powder resistivity (applied pressure: 64 MPa) from 0.04 Ω·cm before the insulating coating treatment to well beyond the measurable range (>10 ⁷ Ω·cm).

[Example 13]

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

<Preparation Steps>

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 (CoSO ₄ ·7H ₂ O, molecular weight: 281.103, Wako Pure Chemical Industries, Ltd.) was also prepared as a water-soluble cobalt salt.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

A metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), cobalt sulfate heptahydrate (water-soluble cobalt salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water was prepared. The metal salt stock solution was weighed so that the amount of palladium (Pd) relative to the total amount of the magnetic metals (Fe, Ni, and Co) was 0.38 mass ppm (0.2 mol ppm). Furthermore, the amount of trisodium citrate relative to the total amount of the magnetic metals (Fe, Ni, and Co) was weighed so that the molar ratio was 0.362 (36.2 mol%). Specifically, 394.1 g of ferrous sulfate heptahydrate, 46.6 g of nickel sulfate hexahydrate, 49.8 g of cobalt sulfate heptahydrate, 100.8 μg of ammonium palladium(II) chloride, and 188.7 g of trisodium citrate dihydrate were dissolved in 1000 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe, Ni, and Co) is 3.65. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe, Ni, and Co) is 7.07. Specifically, 501 g of sodium hydroxide is dissolved in 1227 mL of pure water to prepare a sodium hydroxide solution. 540 g of 60% by mass hydrazine hydrate is added to this sodium hydroxide solution and mixed to prepare a reducing agent solution.

(d) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the mixture so that the molar ratio of ethylenediamine to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.07 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared metal salt stock solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 85°C. The metal salt stock solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 70°C). The temperature of the reaction solution continued to rise after the reaction began by heating in a water bath and was maintained at 85°C (reaction holding temperature 85°C) for 10 minutes after the reaction began. The color of the reaction solution was dark green immediately after the reaction began (preparation of the reaction solution), but changed to dark gray after a few minutes. The reason for the dark green color immediately after the reaction began is believed to be that the reaction according to formula (6) above proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ), nickel hydroxide (Ni(OH) ₂ ), and cobalt hydroxide (Co(OH) ₂ ) in the reaction solution. Furthermore, the color changed to dark gray a few minutes after the reaction began, which is believed to be due to the nucleation of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started and 13 minutes after the reaction started, when the color of the reaction solution turned dark gray, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel-cobalt crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 40 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron component, nickel component, and cobalt component in the reaction solution have all been reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after the reaction is a slurry containing the iron-nickel-cobalt crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel-cobalt crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel-cobalt alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.42μm.

[Example 14]

In Example 14, an iron-nickel alloy powder (Fe-Ni-Co alloy powder) containing 70 mol% iron (Fe), 10 mol% nickel (Ni), and 20 mol% cobalt (Co) was prepared according to the sequence shown in Figure 5. In Example 14, to prepare the reaction solution, a room-temperature solution of the metal salt raw materials was added to a reducing solution heated in a water bath and mixed.

<Preparation Steps>

Prepare the same raw materials as in Example 13 as water-soluble iron salt, water-soluble nickel salt, water-soluble cobalt salt, nucleating agent, complexing agent, reducing agent, pH adjuster, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

A metal salt stock solution containing ferrous sulfate heptahydrate (water-soluble iron salt), nickel sulfate hexahydrate (water-soluble nickel salt), cobalt sulfate heptahydrate (water-soluble cobalt salt), ammonium palladium(II) chloride (nucleating agent), trisodium citrate dihydrate (chelating agent), and water was prepared. The metal salt stock solution was weighed so that the amount of palladium (Pd) relative to the total amount of the magnetic metals (Fe, Ni, and Co) was 0.38 mass ppm (0.2 molar ppm). Furthermore, the amount of trisodium citrate relative to the total amount of the magnetic metals (Fe, Ni, and Co) was weighed to a molar ratio of 0.362 (36.2 mol%). Specifically, 343.0 g of ferrous sulfate heptahydrate, 46.3 g of nickel sulfate hexahydrate, 99.1 g of cobalt sulfate heptahydrate, 100.2 μg of ammonium palladium(II) chloride, and 187.6 g of trisodium citrate dihydrate were dissolved in 1100 mL of pure water to prepare a metal salt raw material solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe, Ni, and Co) is 1.46. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe, Ni, and Co) is 7.07. Specifically, 499 g of sodium hydroxide is dissolved in 1221 mL of pure water to prepare a sodium hydroxide solution. To this sodium hydroxide solution, 215 g of 60% by mass hydrazine hydrate is added and mixed to prepare the reducing agent solution.

(d) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the solution as follows: The molar ratio of ethylenediamine to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.06 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared metal salt stock solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 85°C. The metal salt stock solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 67°C). The temperature of the reaction solution continued to rise after the reaction began by heating in a water bath and was maintained at 85°C (reaction holding temperature 85°C) for 10 minutes after the reaction began. The color of the reaction solution was dark green immediately after the reaction began (preparation of the reaction solution), but changed to dark gray after a few minutes. The reason for the dark green color immediately after the reaction began is believed to be that the reaction according to formula (6) above proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ), nickel hydroxide (Ni(OH) ₂ ), and cobalt hydroxide (Co(OH) ₂ ) in the reaction solution. Furthermore, the color changed to dark gray a few minutes after the reaction began, which is believed to be due to the nucleation of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started and 13 minutes after the reaction started, when the color of the reaction solution turned dark gray, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel-cobalt crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 40 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron component, nickel component, and cobalt component in the reaction solution have all been reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after the reaction is a slurry containing the iron-nickel-cobalt crystallization powder.

<Recycling Steps>

The slurry obtained from the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover agglomerated iron-nickel-cobalt crystallized powder. Filtering and cleaning are performed using pure water with a conductivity of 1 μS/cm until the conductivity of the filtrate obtained from the slurry drops to below 10 μS/cm. The recovered agglomerated crystallized powder is dried in a vacuum dryer set at 50°C. The dried crystallized powder is then cooled to 35°C in a vacuum and slowly oxidized by the addition of nitrogen containing 1.0 volume percent oxygen. This results in an iron-nickel-cobalt alloy powder consisting of smooth, spherical particles. The particle size distribution is steep, with an average particle size of 0.40μm.

[Example 15]

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

<Preparation Steps>

Prepare the same raw materials as in Example 13 as water-soluble iron salt, water-soluble nickel salt, water-soluble cobalt salt, nucleating agent, complexing agent, reducing agent, pH adjuster, and amine compound.

<Crystallization Steps>

(a) Preparation of metal salt raw material solution

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

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. The reaction solution prepared in the subsequent crystallization step is weighed so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe, Ni, and Co) is 1.47. Furthermore, the sodium hydroxide is weighed so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe, Ni, and Co) is 7.07. Specifically, 497 g of sodium hydroxide is dissolved in 1216 mL of pure water to prepare a sodium hydroxide solution. To this sodium hydroxide solution, 215 g of 60% by mass hydrazine hydrate is added and mixed to prepare the reducing agent solution.

(d) Preparation of amine compound solution

Prepare an amine compound solution containing ethylenediamine (amine compound) and water. Weigh the mixture so that the molar ratio of ethylenediamine to the total amount of magnetic metals (Fe, Ni, and Co) in the reaction solution prepared in the subsequent crystallization step is a trace amount of 0.01 (1.0 mol%). Specifically, dissolve 1.06 g of ethylenediamine in 18 mL of pure water to prepare the amine compound solution.

(e) Preparation of reaction solution and precipitation of crystallization powder

The prepared metal salt stock solution was placed in a Teflon (registered trademark)-coated stainless steel container (reaction tank) equipped with a stirring paddle in a water bath and heated while stirring until the solution reached 85°C. The metal salt stock solution at 25°C was then added to the heated reducing agent solution in the water bath and mixed for 10 seconds, resulting in a reaction solution at 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 starting temperature 67°C). The temperature of the reaction solution continued to rise after the reaction began by heating in a water bath and was maintained at 85°C (reaction holding temperature 85°C) for 10 minutes after the reaction began. The color of the reaction solution was dark green immediately after the reaction began (preparation of the reaction solution), but changed to dark gray after a few minutes. The reason for the dark green color immediately after the reaction began is believed to be that the reaction according to formula (6) above proceeded, forming a co-precipitate of iron hydroxide (Fe(OH) ₂ ), nickel hydroxide (Ni(OH) ₂ ), and cobalt hydroxide (Co(OH) ₂ ) in the reaction solution. Furthermore, the color changed to dark gray a few minutes after the reaction began, which is believed to be due to the nucleation of the nucleating agent (palladium salt).

Within 10 minutes, from 3 minutes after the reaction started and 13 minutes after the reaction started, when the color of the reaction solution turned dark gray, the amine compound solution was added dropwise to the reaction solution and mixed to promote the reduction reaction. This caused the iron-nickel-cobalt crystallization powder to precipitate into the reaction solution. The color of the reaction solution at this time was black, but within 30 minutes from the start of the reaction, the supernatant of the reaction solution became transparent. It is considered that the reduction reaction of the above formula (6) has ended, and the iron component, nickel component, and cobalt component in the reaction solution have all been reduced to metallic iron, metallic nickel, and metallic cobalt. The reaction solution after the reaction is a slurry containing the iron-nickel-cobalt crystallization powder.

<Recycling Steps>

The slurry-like reaction liquid obtained in the crystallization step is filtered, cleaned, and subjected to solid-liquid separation to recover the bulk iron-nickel-cobalt crystallization powder. Filtering and cleaning is performed using pure water with a conductivity of 1μS/cm until the conductivity of the filter liquid obtained from filtering the slurry becomes less than 10μS/cm. The recovered bulk crystallization powder is dried in a vacuum dryer set at 50°C. Then, the dried crystallization powder is cooled to 35°C in a vacuum, and nitrogen containing 1.0 volume % of oxygen is supplied to slowly oxidize the crystallization powder. In this way, iron-nickel-cobalt alloy powder is obtained. The obtained alloy powder is composed of spherical particles with smooth surfaces. The particle size distribution is steep, with an average particle size of 0.42μm.

[Comparative example 1]

In Comparative Example 1, no ammonium palladium(II) chloride (nucleating agent) was added during the preparation of the metal salt raw material solution. Otherwise, the reaction solution was prepared and crystallization powder was precipitated in the same manner as in Example 1 to produce an iron-nickel alloy powder (Fe-Ni alloy powder) containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The concentration of the magnetic metals (Fe and Ni) in the reaction solution was 32.3 g/L. The resulting alloy powder consisted of spherical particles with an uneven surface. The particle size distribution was steep, with an average particle size of 0.65 μm.

[Comparative example 2]

In Comparative Example 2, trisodium citrate dihydrate (a complexing agent) was not added during the preparation of 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 prepare an iron-nickel alloy powder (Fe-Ni alloy powder) containing 50 mol% iron (Fe) and 50 mol% nickel (Ni). The concentration of the magnetic metals (Fe and Ni) in the reaction solution was 33.3 g/L. The resulting alloy powder consisted of distorted particles with an uneven surface. The particle size distribution was broad, with an average particle size of 0.26 μm.

[Comparative example 3]

In Comparative Example 3, ammonium palladium(II) chloride (nucleating agent) and trisodium citrate dihydrate (chelating agent) were not added during the preparation of the metal salt raw material solution. Furthermore, a large amount of hydrazine (reducing agent) was added during the preparation of the reducing agent solution. Otherwise, iron-nickel alloy powder (iron-nickel alloy powder) was prepared in the same manner as in Example 1. The metal salt raw material solution and reducing agent solution were prepared as follows.

(a) Preparation of metal salt raw material solution

Prepare a metal salt stock solution containing ferrous chloride tetrahydrate (a water-soluble iron salt), nickel chloride hexahydrate (a water-soluble nickel salt), and water. Specifically, dissolve 173.60 g of ferrous chloride tetrahydrate and 207.55 g of nickel chloride hexahydrate in 1200 mL of pure water to prepare the metal salt stock solution.

(b) Preparation of reducing agent solution

Prepare a reducing agent solution containing sodium hydroxide (pH adjuster), hydrazine (reducing agent), and water. In this case, weigh the reaction solution prepared in the subsequent crystallization step so that the molar ratio of hydrazine to the total amount of magnetic metals (Fe and Ni) is 19.4. Furthermore, weigh the sodium hydroxide so that the molar ratio of sodium hydroxide to the total amount of magnetic metals (Fe and Ni) is 4.96. Specifically, prepare a sodium hydroxide solution by dissolving 346 g of sodium hydroxide in 850 mL of pure water. Then, add and mix 2828 g of 60% by mass hydrazine hydrate to the sodium hydroxide solution to prepare a reducing agent solution. Furthermore, when adding and mixing the reducing agent solution into the metal salt raw material solution, the reducing agent solution was heated to a liquid temperature of 37°C before use, so that the reaction starting temperature would be 55°C.

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

The production conditions for the alloy powders of Examples 1 to 15 and Comparative Examples 1 to 3 are summarized in Table 1.

(2) Evaluation of Iron-Nickel Alloy Powder

The iron-nickel alloy powders obtained in Examples 1-15 and Comparative Examples 1-3 were evaluated for various properties as shown below.

<Composition Analysis>

X-ray diffraction (XRD) analysis was performed using an X-ray diffraction device to confirm the presence of alloy powder from the obtained XRD data.

<Analysis of Metal Impurities>

Impurity content was analyzed. Oxygen content was measured using an oxygen analyzer (TC436, manufactured by LECO Corporation) by the inert gas fusion method, and carbon and sulfur content was measured using a carbon-sulfur analyzer (CS600, manufactured by LECO Corporation) by the combustion method. Chlorine content was measured using a fluorescent X-ray analyzer (Magix, manufactured by Spectris Corporation), and silicon and sodium content were measured using an ICP optical emission spectrometer (5100, manufactured by Agilent Technologies, Inc.).

<Particle size (average particle size, coefficient of variation)>

The alloy powder was observed using a scanning electron microscope (SEM; manufactured by JEOL Ltd., JSM-7100F) (magnification: 5000-80000 times). The observed images (SEM images) were analyzed, and the average particle size and standard deviation of the particle size were calculated based on the number average. Furthermore, the coefficient of variation (CV value) was calculated according to the following formula (14) to determine the particle size of the alloy powder (average particle size, coefficient of variation).

CV value (%) = standard deviation of particle size/average particle size × 100‧‧‧(14)

<Particle composition analysis>

Alloy powder embedded in resin was processed into thin films with a thickness of approximately 100 nm using a focused ion beam (FIB) device. The cross-section of the alloy particles was observed using a scanning transmission electron microscope (STEM; Hitachi High-Technologies Corporation, HD-2300A). Observation was performed at magnifications of 100,000 to 200,000x. The compositional distribution within the alloy particles was then determined using energy dispersive X-ray spectroscopy (EDS) analysis. The composition was calculated from the detection counts of characteristic X-rays (K-rays) of the elements being measured.

<Crystalline Diameter>

The alloy powder was analyzed by X-ray diffraction (XRD). The crystallite diameter was evaluated based on the Scherrer formula using the half-width of the X-ray diffraction peak from the (111) plane. XRD measurements were performed under the same conditions as the composition analysis. The crystallite diameter indicates the degree of crystallization; larger crystallite diameters indicate higher crystallinity.

<Powder density>

The pressed powder density of the alloy powder was evaluated. Specifically, approximately 0.3 g of alloy powder was filled into a cylindrical hole (5 mm inner diameter) of a mold. Subsequently, a press was used to form pellets with a diameter of 5 mm and a height of 3-4 mm using a pressure of 100 MPa. The mass and height of the resulting pellets were measured at room temperature to calculate the pressed powder density.

<Powder resistivity>

The pressed powder resistivity of the alloy powder was measured using a powder resistance measurement system (MCP-PD51, manufactured by Mitsubishi Chemical Analytech) to evaluate its conductivity (insulation). Specifically, approximately 4g of alloy powder was placed in the cylindrical specimen chamber of the device. A pressure of 64MPa was applied using the included press. The pressed powder resistivity (unit: Ω·cm) was then calculated.

<Magnetic properties (saturated magnetic flux density, coercive force)>

The alloy powder's magnetic properties (saturated magnetic flux density (T: Tesla) and coercive force (A/m)) were evaluated using a vibrating specimen magnetometer (VSM). The saturated magnetic flux density and coercive force values were calculated from the B-H curve (hysteresis curve) obtained during the measurements. The alloy powder obtained in Comparative Example 2 was not tested for magnetic properties due to its distorted shape, making it unsuitable for use in components such as inductors.

(3) Evaluation results

The evaluation results obtained for Examples 1-15 and Comparative Examples 1-3 are summarized in Table 2. Furthermore, 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, respectively. SEM images of the alloy powder obtained in Example 6 are shown in Figures 15(a) and 15(b). Figure 15(a) shows an SEM image of the alloy powder before spiral jet disintegration treatment, and Figure 15(b) shows an SEM image of the alloy powder after spiral jet disintegration treatment. Furthermore, STEM images of particle cross-sections and EDS line analysis results of the alloy powders obtained in Examples 8 and 9 are shown in Figures 16(a), 16(b), and 17, respectively. Figure 16(a) shows a STEM image and EDS line analysis results of a particle cross-section of the alloy powder before high-temperature heat treatment, while Figure 16(b) shows a STEM image and EDS line analysis results of a particle cross-section 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). Figure 19(a) shows a SEM image of the alloy powder before insulation coating treatment, while Figure 19(b) shows a SEM image of the alloy powder after insulation coating treatment. Furthermore, SEM images of the alloy powders obtained in Comparative Examples 1-3 are shown in Figures 22-24.

Examples 1, 3, and Comparative Examples 1-3 all produced iron-nickel alloy powders by setting the reaction starting temperature in the crystallization step to 55°C and the reaction holding temperature to 70°C. In Examples 1 and 3, which used extremely small amounts of specific nucleating and complexing agents, despite the relatively small amount of hydrazine used as a reducing agent, the resulting alloy powders exhibited a fine average particle size of 0.40-0.41 μm, a low CV value, and a steep particle size distribution. Furthermore, the alloy powders were spherical and had a smooth surface.

On the other hand, in Comparative Example 1, in which no nucleating agent was used, the average particle size of the alloy powder obtained was larger, at 0.65 μm, compared to Example 1 or Example 3, making it difficult to refine. Furthermore, although the alloy powder was spherical, the surface had significant unevenness. In Comparative Example 2, in which no complexing agent was used, although the average particle size of the alloy powder obtained was fine, at 0.26 μm, the CV value was larger, and the particle size distribution was wider. Furthermore, the surface of the alloy powder had significant unevenness and a distorted shape. In Comparative Example 3, in which no nucleating agent or complexing agent was used but a large amount of reducing agent (hydrazine) was added, the alloy powder obtained was a spherical powder with a relatively smooth surface. This is believed to be due to the strong reduction reaction caused by the high amount of hydrazine incorporated. Furthermore, the average particle size of the resulting alloy powder was very fine, at 0.22 μm. However, the CV value was large, and the particle size distribution was broad.

Example 2 uses specific nucleating agents and complexing agents, setting the reaction starting temperature in the crystallization step to 55°C and the reaction holding temperature to 70°C to produce iron-nickel-cobalt alloy powder. Despite the relatively small amount of hydrazine used as a reducing agent, the resulting alloy powder has a fine average particle size of approximately 0.3 μm and a steep particle size distribution. Furthermore, the alloy powder is spherical with a smooth surface. Furthermore, the alloy powder exhibits a high saturation magnetization.

Example 5 involves adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization to produce an iron-nickel alloy powder with a nickel-rich surface composition comprising 51 mol% iron (Fe) and 49 mol% nickel (Ni). This nickel-rich surface composition forms a dense oxide film, which suppresses oxidation on the particle surface. As a result, the alloy powder is not only more stable in atmospheric conditions but also exhibits excellent magnetic properties, such as saturated magnetic flux density.

Example 6 describes a method for producing spherical iron-nickel alloy powder with a very smooth surface by subjecting the crystallized powder obtained as a dry powder through the crystallization and recovery steps to spiral jet disintegration. Furthermore, Example 7 describes a method for producing spherical iron-nickel alloy powder with a very smooth surface by subjecting the slurry of crystallized powder obtained during the recovery step after the crystallization step to high-pressure fluid collision disintegration. These alloy powders not only exhibit a smoother surface but also contain fewer agglomerated particles. This improves packing properties (increases the density of the pressed powder). Furthermore, by reducing agglomerated particles, it is expected that eddy current loss between particles will be improved.

Example 8 involves high-temperature heat treatment of the crystallized powder obtained by setting the reaction starting temperature to 71°C and the reaction holding temperature to 80°C during the crystallization step. This results in an iron-nickel alloy powder containing 65 mol% iron (Fe) and 35 mol% nickel (Ni), with improved compositional uniformity within the particles. As shown in Figure 16(b), this alloy powder achieves a uniform composition within the particles (65 mol% iron and 35 mol% nickel). In addition to its potential use as a soft magnetic material, it is also expected to be used as a low thermal expansion material (e.g., a constant-temperature alloy).

Example 9 involves adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization, producing an iron-nickel alloy powder with a nickel-rich surface composition comprising 65 mol% iron (Fe) and 35 mol% nickel (Ni). As shown in Figure 17, a nickel-rich layer approximately 10-15 nm thick forms on the particle surface. This nickel-rich surface composition creates a dense oxide film, which suppresses surface oxidation. As a result, the alloy powder is not only more stable in atmospheric conditions but also exhibits excellent magnetic properties, such as saturated magnetic flux density.

Examples 10 and 11 respectively produce an iron-nickel alloy powder containing 80 mol% iron (Fe) and 20 mol% nickel (Ni) and an iron-nickel alloy powder containing 90 mol% iron (Fe) and 10 mol% nickel (Ni) with a higher iron content, by adding and mixing an additional raw material solution containing a water-soluble nickel salt to the reaction solution during crystallization. This promotes the reduction of iron ions (or iron hydroxide) that are difficult to reduce, while also increasing the nickel content on the particle surface. Even with a high iron content of 80 to 90 mol%, approaching pure iron, and a relatively small amount of hydrazine used as a reducing agent, poor reduction can be achieved, resulting in spherical alloy powders with a fine average particle size of approximately 0.4 to 0.5 μm, a steep particle size distribution, and a smooth surface. Furthermore, the saturated magnetization of the alloy powder is as high as that of pure iron powder (1.95 T to 2.0 T).

Compared to Examples 1 to 7, the pressed powder density of the iron-nickel alloy powder obtained in Examples 8 to 11 is smaller. However, the true specific gravity of the iron-nickel alloy powders of Examples 1 to 7 (iron-nickel alloy powders containing 56 to 50 mol% Fe and 44 to 50 mol% Ni, and iron-nickel-cobalt alloy powders containing 50 mol% Fe, 40 mol% Ni, and 10 mol% Co) is 8.2 to 8.25. In contrast, the true specific gravity of the iron-nickel alloy powders of Examples 8 and 9 (iron-nickel alloy powders containing 65 mol% Fe and 35 mol% Ni) is 8.2 to 8.25. The true specific gravity of Example 10 (Fe-Ni alloy powder containing 80 mol% Fe and 20 mol% Ni) is 8.0, and the true specific gravity of Example 11 (Fe-Ni alloy powder containing 90 mol% Fe and 10 mol% Ni) is 7.9. Considering that the true specific gravity of the Fe-Ni alloy powder decreases with increasing iron content, it can be seen that the pressed powder density of each example is good.

Example 12 is an example of an iron-nickel alloy powder produced by subjecting the crystallized powder, obtained as a dry powder after the crystallization and recovery steps, to an insulating coating treatment, resulting in particles coated with high-resistance silicon dioxide (SiO ₂ ). This alloy powder significantly enhances interparticle insulation (resistivity of the pressed powder increases significantly), thus potentially reducing eddy current losses between particles.

Examples 13-15 describe the use of a water-soluble cobalt salt in addition to a water-soluble iron salt and a water-soluble nickel salt in the magnetic metal source to promote the reduction of the less reducible iron ions (or iron hydroxide), thereby producing an iron-nickel alloy powder having a cobalt content of 10 mol% to 25 mol% and an iron content of 65 mol% to 80 mol%. Specifically, examples include the production of an iron-nickel-cobalt alloy powder containing 80 mol% Fe, 10 mol% Ni, and 10 mol% Co; an iron-nickel-cobalt alloy powder containing 70 mol% Fe, 10 mol% Ni, and 20 mol% Co; and an iron-nickel-cobalt alloy powder containing 65 mol% Fe, 10 mol% Ni, and 25 mol% Co. Even with compositions containing relatively high iron contents of 65 to 80 mol%, and thanks to the enhanced reduction reaction achieved by the addition of cobalt, the use of a very small amount of hydrazine as a reducing agent allows for the production of spherical alloy powders without reduction defects. The alloy powders have a fine average particle size of approximately 0.4 μm, a steep particle size distribution, and a smooth surface. Furthermore, the saturated magnetization of the alloy powder is equal to or higher than that of pure iron powder (1.95T~2.0T).

Furthermore, although the true specific gravity of the iron-nickel alloy powders (iron-nickel-cobalt alloy powders) obtained in Examples 13-15 is estimated to be approximately 8.0-8.1, the pressed powder densities were all relatively high and good. This is believed to be due to the reduction reaction acceleration effect achieved by the addition of cobalt, which terminates the reduction reaction before the particles aggregate, thereby suppressing aggregation of the particles during crystallization. This is also believed to be related to the fact that the addition of cobalt also promotes spheroidization, which improves the packing properties of the particles.

Claims (8)

An alloy powder is an iron (Fe)-nickel (Ni) alloy powder containing at least iron (Fe) and nickel (Ni) as magnetic metals, and has an average particle size of 0.27 μm or more and 0.60 μm or less, and a coefficient of variation (CV value) calculated according to the following formula (1) based on the average particle size and standard deviation in the number particle size distribution is 25% or less. CV value (%) = standard deviation of particle size/average particle size × 100 ………… (1). The alloy powder of claim 1 further comprises cobalt (Co) as a magnetic metal. The alloy powder of claim 1 or 2, wherein the amount of iron (Fe) is not less than 10 mol% and not more than 95 mol%, the amount of nickel (Ni) is not less than 5 mol% and not more than 90 mol%, and the amount of cobalt (Co) is not less than 0 mol% and not more than 40 mol%. For alloy powders as claimed in claim 1 or 2, the crystallite diameter is less than 30 nm. For the alloy powders described in claim 1 or 2, the saturated magnetic flux density shall be 1 T (Tesla) or greater and the coercive force shall be 2000 A/m or less. A powder compact comprising the alloy powder according to any one of claims 1 to 5. A sheet comprising the alloy powder according to any one of claims 1 to 5. A magnetic device is an inductor, a reactor, a choke, a noise filter, a transformer, a rotor, a generator, or a radio wave absorber, and comprises the powder compact of claim 6 and/or the sheet of claim 7.