JP7137830B2 - Method for producing alloy particles and alloy particles - Google Patents

Description

The present invention relates to a method for producing alloy particles of a rare earth element and a transition metal, and alloy particles of a rare earth element and a transition metal.

Samarium (Sm)-iron (Fe)-nitrogen (N)-based compounds and neodymium (Nd)-Fe-N-based compounds having a TbCu ₇ -type crystal phase (hereinafter collectively referred to as "specific rare earth-iron-based nitrides ”) has high magnetic properties and is attracting attention as a next-generation permanent magnet material. For example, (Sm _0.75 Zr _0.25 )(Fe _0.7 Co _0.3 ) 10N _x magnets are known to exhibit high saturation magnetization (Non-Patent Document 1).

Such "specific rare earth-iron nitride" particles are Sm-Fe alloy particles or Nd-Fe alloy particles having a TbCu ₇ type crystal phase (hereinafter collectively referred to as "specific rare earth-iron alloy particles ”) in an atmosphere containing nitrogen or ammonia.

Japanese Patent Application Laid-Open No. 2004-193207

S. Sakurada, A.; Tsutai, T.; Hirai, Y.; Yanagida, M.; Sahashi, S.; Abe, T. Kaneko, J.; Appl. Phys. 79 (1996) 4611 S. Sakurada, A.; Tsutai, T.; Arai, J.; JPN. Soc. Powder Powder Metallurgy 50 (2003) 626 K. Takagi, M.; Jinno, K.; Ozaki, J.; Magn. Magn. Mater. 454 (2018) 170 Kurima Kobayashi, Akiko Saito, Mika Nakamura, Electronics Theory A, 124 (2004) 863

When producing particles of a specific rare earth-iron alloy, which is a raw material for producing the above-mentioned specific rare earth-iron nitride particles, a superquenching method such as a melt spun method is often used. This is because in the specific rare earth-iron alloy, the TbCu ₇ type crystal phase is a non-equilibrium phase, and in general cooling treatment, the equilibrium phase Th ₂ Zn ₁₇ type crystal phase is generated, and the TbCu ₇ type crystal phase is generated. This is because no crystalline phase is generated.

By the way, in order to achieve high magnetization in a permanent magnet, it is necessary to strongly magnetize it only in a specific direction, that is, to make it an anisotropic magnet. In addition, in order to manufacture such an anisotropic magnet, the raw material alloy particles must be either single crystal particles or polycrystalline particles oriented in a specific direction.

However, in the above-mentioned ultra-quenching method, the crystal orientation of the obtained alloy particles is random and isotropic polycrystalline particles, and it is difficult to use it as a raw material for manufacturing a specific rare earth-iron nitride anisotropic magnet ( For example, Patent Document 1 and Non-Patent Document 2).

Another known method for producing particles of a specific rare earth-iron alloy is the HDDR (Hydrogenation-Decomposition-Desorption-Recombination) method. According to this method, it is reported that a TbCu ₇ -type Sm--Fe alloy can be produced by HDDR-treating Th ₂ Zn ₁₇ -type Sm--Fe alloy particles at about 650° C. or lower (Non-Patent Document 3).

However, even in the HDDR method, the crystal orientation within the resulting grains is random and isotropic polycrystalline grains.

Further, as a method for producing single-crystal alloy particles, there is a reduction diffusion method. In this reduction diffusion method, rare earth oxide particles and transition metal particles are heated in an inert gas atmosphere in the coexistence of calcium or calcium hydride as a reducing agent. The heating reduces the rare earth oxide particles to the metallic state and further diffuses the reduced rare earth element into the transition metal particles. As a result, the rare earth element and the transition metal are alloyed to produce specific rare earth-iron alloy particles.

In this reduction-diffusion method, calcium, which is a reducing agent, needs to come into contact with the rare earth oxide particles. However, when calcium is in a solid state, the contact area between calcium and rare earth oxide particles is small, and it is difficult to cause a reduction-diffusion reaction in a sufficient area and an allowable reaction time. On the other hand, if one attempts to use molten calcium to increase the reaction zone, then the processing temperature may need to be increased to about 850° C. or higher, which is the melting point of calcium. In this case, the Th ₂ Zn ₁₇ equilibrium phase is generated as described above.

As described above, the conventional method for producing specific rare earth-iron alloy particles has a problem that it is difficult to produce particles having a TbCu ₇ -type crystal phase in a single crystal state.

The present invention has been made in view of such a background, and in the present invention, a method for producing alloy particles of a rare earth element and a transition metal, which are substantially single crystals and have a TbCu ₇ type crystal phase intended to provide Another object of the present invention is to provide alloy particles of a rare earth element and a transition metal having such characteristics.

In the present invention, a method for producing alloy particles of a rare earth element and a transition metal, comprising:
(1) a step of preparing fine particles containing iron (Fe);
(2) a step of reducing and diffusing the rare earth compound in the molten salt in the presence of the reducing agent and the fine particles, whereby the rare earth element contained in the rare earth compound and the fine particles are alloyed; process and
has
the reducing agent is metallic calcium (Ca) and/or calcium hydride (CaH ₂ );
The rare earth compound has at least one selected from samarium (Sm) and neodymium (Nd) as a rare earth element,
A production method is provided, wherein the molten salt contains a halide of an alkali metal and/or an alkaline earth metal.

Further, in the present invention, alloy particles of a rare earth element and a transition metal,
The rare earth element has at least one selected from samarium (Sm) and neodymium (Nd),
the transition metal has at least iron (Fe),
The alloy particles have a TbCu ₇ -type crystal phase, and the ratio of the TbCu ₇ -type crystal phase to the total crystal phase is 50% by volume or more,
The alloy particles are substantially single crystal,
Alloy particles are provided having an average particle diameter in the range of 100 nm to 3000 nm.

The present invention can provide a method for producing alloy particles of a rare earth element and a transition metal, which are single crystals and have a TbCu7 _- type crystal phase. In addition, the present invention can provide alloy particles of a rare earth element and a transition metal having such characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow diagram schematically showing an example of a method for producing alloy particles of a rare earth element and a transition metal according to one embodiment of the present invention; FIG. 4 is a diagram schematically showing a correlation line used in calculating the proportion of a TbCu ₇ -type crystal phase contained in alloy particles of a rare earth element and a transition metal according to an embodiment of the present invention. 1 is a diagram collectively showing XRD patterns of Sm—Fe alloy particles produced by each method. FIG. 1 is a diagram showing an example of a cross-sectional FE-SEM (field emission scanning electron microscope) image (backscattered electron image) of a green compact formed from alloy particles according to one embodiment of the present invention. FIG. FIG. 2 is a diagram showing an example of a cross-sectional EBSD (electron backscatter diffraction) image of a green compact formed from alloy particles according to one embodiment of the present invention; 1 is a diagram collectively showing XRD patterns of Nd—Fe alloy particles produced by each method. FIG.

An embodiment of the present invention will be described below with reference to the drawings. In this specification, when a numerical range is expressed using "-", the numerical values at both ends thereof are included unless otherwise specified.

(Method for producing alloy particles according to one embodiment of the present invention)
A method for producing alloy particles of a rare earth element and a transition metal according to one embodiment of the present invention will be described with reference to FIG.

FIG. 1 schematically shows the flow of a method for producing alloy particles of a rare earth element and a transition metal according to one embodiment of the present invention (hereinafter referred to as "first production method").

As shown in FIG. 1, the first manufacturing method includes:
(1) a step of preparing fine particles containing iron (Fe) (step S110);
(2) A step of reducing and diffusing the rare earth compound in the molten salt in the presence of the reducing agent and the fine particles, whereby the rare earth element contained in the rare earth compound and the fine particles are alloyed to form an alloy. a step (step S120), in which particles are formed;
have

Each step will be described in detail below.

(Step S110)
First, fine particles containing iron (hereinafter referred to as "iron-containing fine particles") are prepared.

The iron-containing fine particles may contain another transition metal in addition to iron. Another transition metal may be, for example, cobalt (Co) and/or zirconium (Zr). In addition, when the iron-containing fine particles contain another transition metal, the total iron content is 50 atomic % or more.

A method for preparing the iron-containing fine particles is not particularly limited.

For example, iron-containing microparticles can be produced by reducing oxide microparticles containing iron. In this case, the iron-containing oxide fine particles may be produced by a hydrothermal synthesis method or a spray pyrolysis method. A hydrogen reduction method may also be used to reduce the oxide fine particles.

In the hydrogen reduction method, iron oxide fine particles are heat-treated in a hydrogen-containing atmosphere. The iron oxide fine particles are reduced during the heat treatment, and iron fine particles can be produced.

In the hydrogen reduction method, if the heat treatment temperature is too low, it takes a long time to reduce the oxide particles. On the other hand, if the heat treatment temperature is too high, grain growth of the particles will occur during the heat treatment, making it difficult to control the particle size of the fine particles.

Therefore, in the hydrogen reduction method, the heat treatment temperature is preferably in the range of 450°C to 700°C, more preferably in the range of 500°C to 600°C.

The iron-containing fine particles to be prepared have an average particle diameter in the range of, for example, 50 nm to 2500 nm. The average particle diameter of the iron-containing fine particles is preferably in the range of 60 nm to 2000 nm, more preferably in the range of 70 nm to 1000 nm.

The iron-containing fine particles having such dimensions can be used in the next step in substantially the same state without performing a subsequent pulverization step or the like. The iron-containing fine particles produced through the pulverization process may have crystal distortion due to the pulverization.

In the present application, the average diameter of the particles, that is, the average particle diameter, is obtained from 100 or more randomly selected particles from observation images of a field emission scanning electron microscope (FE-SEM). can be calculated by averaging

The size of the iron-containing microparticles can be controlled, for example, in spray pyrolysis by adjusting the concentration of iron ions contained in the iron ion solution used. Specifically, when the iron ion concentration contained in the iron ion solution is decreased, finer particles can be obtained, and when the iron ion concentration is increased, larger particles can be obtained.

(Step S120)
Next, the rare earth compound is reduced and diffused in the molten salt in the presence of the iron-containing fine particles prepared in step S110 and a reducing agent.

In this way, particles of an alloy of a rare earth element and a transition metal containing iron (hereinafter referred to as "RE-M alloy"), that is, RE-M alloy particles can be produced. Here M represents iron and, if present, other transition metals.

Here, as described above, in the conventional reduction-diffusion method, the region where the reduction reaction occurs in the rare earth oxide is limited to the portion where the solid calcium serving as the reducing agent contacts the rare earth oxide particles. Therefore, the conventional reduction diffusion method has the problem that it is difficult to form an alloy having a TbCu ₇ -type crystal phase in a sufficient range and reaction rate.

Also, to address this issue, if one attempts to use solid calcium in the molten state and raises the processing temperature above 850° C., this time the Th ₂ Zn ₁₇ equilibrium phase is produced instead of the TbCu ₇ type. There is a problem.

On the other hand, in the first production method, the reduction diffusion treatment of the rare earth compound is carried out in a medium of molten salt, and therefore the reducing agent exists in a molten state in the molten salt. Therefore, in the first production method, the rare earth compound can be reduced relatively quickly without heating the medium to a temperature range where the Th ₂ Zn ₁₇ equilibrium phase is generated. Moreover, the rare earth element produced by the reduction then diffuses into the iron-containing fine particles and is alloyed. This makes it possible to produce RE-M alloy particles having a TbCu ₇ -type phase.

Furthermore, as will be described later, in the first production method, the RE-M alloy particles produced are substantially in a single crystal state. Therefore, the RE-M alloy particles produced by the first production method can be significantly used as raw material alloy particles for anisotropic permanent magnets.

Here, each material used in step S120 will be described in detail.

(Iron-containing microparticles)
The amount of the iron-containing fine particles added is preferably not more than the amount calculated from the stoichiometric ratio with the rare earth element for forming the TbCu ₇ -type phase. This is to reduce the amount of unreacted iron-containing fine particles remaining after step S120.

(reducing agent)
The reducing agent used in step S120 includes at least one of metallic calcium (Ca) and calcium hydride (CaH ₂ ).

In addition, as described above, the metallic calcium is in a molten state in the molten salt. On the other hand, calcium hydride is easily decomposed at high temperature to become metallic calcium. Therefore, it performs substantially the same role as metallic calcium during reduction diffusion treatment.

The amount of the reducing agent added is not particularly limited. For example, the molar ratio of reducing agent to added rare earth compound may range from 3:2 to 20:1.

(rare earth compound)
The rare earth compound used has at least one of samarium (Sm) and neodymium (Nd) as a rare earth element.

The rare earth compounds may be in the form of oxides or halides, for example. Halides include chlorides, bromides, iodides, fluorides, and the like. Among them, rare earth chlorides are preferred.

As the halide of the rare earth element, not only the anhydride but also the hydrate can be used. When using a hydrate, the hydrate may be used after being dehydrated in advance at a temperature of, for example, 100° C. or higher and not higher than the melting point or decomposition temperature of the hydrate.

Note that CaF ₂ is formed as a by-product when rare earth fluorides are used. This by-product is sparingly soluble and requires additional processing upon removal.

The rare earth compound may further contain iron. Alternatively, the rare earth compound may further comprise transition metals other than iron, such as Co and/or Zr. For example, when the rare earth compound is an oxide, the rare earth compound may include composite oxides such as SmFeO ₃ , SmCoO ₃ or NdCoO ₃ .

Although the amount of the rare earth compound added is not particularly limited, for example, the molar ratio of the iron-containing fine particles to the rare earth compound is in the range of 8:1 to 1:1.

The rare earth compound containing iron may be prepared at the same time as the iron-containing particles by hydrogen-reducing a rare earth-transition metal oxide obtained by a coprecipitation method or a spray pyrolysis method at a temperature of about 600°C. . As a result, SmFeO ₃ particles and fine iron particles can be obtained at the same time.

(Molten salt)
The molten salts used include halides of alkali metals or alkaline earth metals.

Alkali metals include lithium (Li), sodium (Na), and/or potassium (K). Alkaline earth metals include Mg (magnesium) and/or calcium (Ca).

In addition, it is not necessary to use these alone, and for example, a binary or ternary mixed salt may be used. Mixed salts of alkali metals and alkaline earth metals may also be used. Preferably, the mixed salt is a eutectic salt.

The halide may be chloride, bromide, or iodide.

The melting temperature of the molten salt is preferably less than 700°C, more preferably 650°C or less, and even more preferably 610°C or less.

(other additives)
In addition to the above compounds, a compound of a transition metal other than iron (hereinafter referred to as a "nonferrous transition metal compound") may be added to the molten salt.

The non-ferrous transition metal compound may, for example, contain, for example, cobalt and/or zirconium as transition metals.

Non-ferrous transition metal compounds may be in the form of oxides, halides, and the like. The non-ferrous transition metal compounds may be in the form of chlorides, for example _CoCl3 and _ZrCl4 .

When such non-ferrous transition metal compounds are added to the molten salt, RE-M alloy particles can finally be produced containing iron and another transition metal as transition metals. For example, when a nonferrous transition metal compound containing Co is added, rare earth element-Fe-Co alloy particles can be produced.

(Conditions for reduction diffusion treatment)
Reduction diffusion treatment is performed in an inert gas atmosphere. As the inert gas, for example, gas such as argon gas and/or helium gas is used.

The treatment temperature (that is, the temperature of the molten salt) varies depending on the rare earth compound. For example, when the rare earth compound contains samarium halide, the treatment temperature is in the range of 350°C or higher and lower than 800°C, preferably in the range of 550°C to 650°C.

On the other hand, when the rare earth compound contains a neodymium halide, the treatment temperature is in the range of 350°C or higher and lower than 650°C, preferably in the range of 500°C to 550°C.

The treatment time varies depending on the treatment temperature, but is, for example, 2 hours or longer, preferably 3 hours or longer.

Note that the reduction diffusion treatment may be started after preparing a mixed powder by mixing all the necessary materials such as the salt for the molten salt, the iron-containing fine particles, the reducing agent, and the rare earth compound. That is, the mixed powder may be put into a non-reactive crucible such as an iron crucible, and then the crucible may be heated to a predetermined temperature in an inert gas atmosphere to carry out reduction diffusion treatment.

Alternatively, the reduction diffusion treatment may be performed by adding iron-containing fine particles, a reducing agent, a rare earth compound, and the like to a molten salt that has been melted in advance at a high temperature in an inert gas atmosphere.

Substantially single-crystal RE-M alloy particles having a TbCu ₇ -type crystal phase can be produced by the above steps.

The resulting RE-M alloy particles have an average particle diameter ranging from 100 nm to 3000 nm. By nitriding this, a TbCu ₇ type RE-MN system anisotropic magnet powder can be produced.

Further, the obtained RE-M alloy particles preferably contain 50% by volume or more of the TbCu ₇ -type crystal phase with respect to the total crystal phase. As a result, it is expected that high magnetization characteristic of the TbCu ₇ type RE-MN system will be developed.

The product may contain a phase of unreacted transition metals (for example, iron, cobalt, etc.). The volume fractions of the TbCu ₇ -type crystalline phases are calculated excluding these phases. A specific method for calculating the volume ratio of the TbCu ₇ -type crystal phase will be described later.

(Alloy particles according to one embodiment of the present invention)
Next, alloy particles of a rare earth element and a transition metal according to one embodiment of the present invention will be described.

Alloy particles of a rare earth element and a transition metal (hereinafter referred to as "first alloy particles") according to one embodiment of the present invention contain at least one selected from samarium (Sm) and neodymium (Nd) as a rare earth element. and at least iron (Fe) as a transition metal.

However, the first alloy particles may further contain rare earth elements other than samarium and neodymium. Also, the first alloy particles may further contain a transition metal other than iron, such as cobalt and/or zirconium.

In the first alloy particles, the ratio of transition metal to rare earth element ranges from 86 atomic % to 94 atomic %.

The first alloy particles are substantially single crystal and have an average particle diameter in the range of 100 nm to 3000 nm. The average particle diameter is preferably in the range from 200 nm to 2000 nm.

The first alloy particles have a TbCu ₇ -type crystal phase. The ratio of the TbCu ₇ -type crystalline phase to the total crystalline phase is 50% by volume or more, preferably 60% by volume or more, and more preferably 70% by volume or more.

The volume fraction of the TbCu ₇ -type crystal phase contained in the alloy particles can be obtained as follows from the X-ray diffraction (XRD) measurement results using CoKα rays for the alloy particles.

In the case of Sm—Fe alloy particles, the diffraction peak near the angle 2θ=43.6° in the XRD measurement results corresponds to the Th ₂ Z ₁₇ type crystal phase. On the other hand, the peak near the angle 2θ=42° corresponds to both the Th ₂ Z ₁₇ -type and TbCu ₇ -type crystal phases.

Therefore, in the present application, the ratio I _43.6 /I ₄₂ is used as an index of the content of the TbCu ₇ type crystal phase. Here, I43.6 represents the intensity of the diffraction peak near the angle 2θ= _43.6 °, and I42 represents the intensity of the diffraction peak near the angle 2θ= ₄₂ °.

The closer the ratio I _43.6 /I ₄₂ is to 0, the higher the ratio of the TbCu ₇ type crystal phase contained in the target sample. In particular, the ratio I _43.6 /I ₄₂ =0 means that 100% of the TbCu ₇ type crystalline phase is included.

Here, a sample containing only the Th ₂ Z ₁₇ crystal phase is prepared as a standard sample. The ratio I _43.6 /I ₄₂ is determined from the XRD measurement results obtained for the standard sample. This value (assumed to be Pr) corresponds to the case where the volume fraction of the _{TbCu 7} -type crystal phase is 0%. On the other hand, as described above, the ratio I _43.6 /I ₄₂ =0 corresponds to the case where the volume fraction of the TbCu ₇ type crystal phase is 100%.
Therefore, from these relationships, a correlation straight line between the ratio I _43.6 /I ₄₂ and the volume fraction of the TbCu ₇ -type crystal phase can be obtained. For example, as shown in FIG. 2, when the horizontal axis is the ratio I _43.6 /I ₄₂ and the vertical axis is the volume fraction (%) of the TbCu ₇ type crystal phase, the point (P _r , 0) and the point A correlation straight line L passing through (0,100) is obtained.

From the ratio I _43.6 /I ₄₂ obtained for the target alloy particles, the volume fraction of the TbCu ₇ type crystal phase can be calculated using the correlation straight line L.

In the above description, Sm—Fe alloy particles are assumed, but in the case of Nd—Fe alloy particles, the volume fraction of the TbCu ₇ -type crystal phase contained in the alloy particles can be calculated in the same manner. can.

The first alloy particles having such characteristics can be significantly used, for example, as raw material particles of a specific rare earth-iron nitride that constitutes a permanent magnet having high magnetic properties.

Such alloy particles can be produced, for example, using the first production method described above.

The present embodiment will be specifically described below. In the following description, Examples 1 to 16 are examples, and Examples 21 to 25 are comparative examples.

(Example 1)
Alloy particles were produced by the following method.

(Preparation of fine iron particles)
First, iron oxide particles were synthesized using a hydrothermal decomposition method.

After 245 g of iron nitrate nonahydrate and 33 g of calcium nitrate were dissolved in 1200 ml of water, 1110 ml of 2 mol/L potassium hydroxide aqueous solution was added dropwise while stirring. After the resulting solution was stirred at room temperature for an additional hour, it was poured into a heat-resistant airtight container, covered, and allowed to stand at 110° C. for 12 hours.

Next, a precipitate in the solution was recovered by centrifugal separation, washed with water, and vacuum-dried. Cube-shaped hematite particles with a particle size of about 90 nm were thus obtained. Calcium nitrate was used to prevent sintering of the fine iron particles during the hydrogen reduction treatment in the next step.

Next, using the obtained particles, hydrogen reduction treatment was performed at 500° C. for 6 hours in a hydrogen atmosphere. As a result, fine iron particles having an average particle diameter of about 100 nm were obtained.

(Reduction diffusion treatment)
First, lithium chloride powder and samarium chloride hexahydrate powder were dehydrated and dried in a vacuum atmosphere at 250° C. for 12 hours to obtain anhydrous lithium chloride and anhydrous samarium chloride powders.

Next, 0.2 g of the aforementioned iron fine particles, 0.6 g of lithium chloride powder, 0.4 g of samarium chloride powder, and 0.2 g of metallic calcium particles were mixed to prepare a mixture.

The resulting mixture was placed in an iron crucible and subjected to heat treatment (reduction diffusion treatment) in a high-frequency furnace. The furnace was filled with an argon gas atmosphere, and the heat treatment was performed at 750° C. for 2 hours.

The heat treatment temperature was controlled using a control thermocouple placed in the iron crucible. During the heat treatment, there was a fluctuation of about ±10° C. around the set temperature depending on whether the high frequency was turned on or off.

After heat treatment, the reaction product was removed from the iron crucible. In addition, washing treatment was carried out in order to remove lithium chloride and calcium components contained in the reaction product.

However, when the reaction product comes into contact with water, there is a possibility that calcium contained in the reaction product may cause a rapid reaction. Therefore, first, the reaction product was immersed in ethanol, and water was gradually added thereto for washing treatment.

After washing, the reaction product was vacuum dried. As a result, samarium (Sm)-iron (Fe) alloy particles (hereinafter referred to as "sample 1") were obtained.

(Examples 2 to 5)
Alloy particles were produced in the same manner as in Example 1, except that the heat treatment temperature in the reduction diffusion treatment was changed to the temperature shown in Table 1 below. The Sm—Fe alloy particles obtained in Examples 2 to 5 are hereinafter referred to as “Sample 2” to “Sample 5”, respectively.

(Example 6)
Alloy particles were produced in the same manner as in Example 1. However, in Example 6, the amount of calcium added was changed to 0.5 g in the reduction diffusion treatment. Also, the reduction diffusion treatment conditions were changed to 650° C. for 12 hours. Furthermore, an external heater heating type tubular furnace was used as the processing apparatus.

A thermocouple was inserted inside the tubular furnace to monitor the temperature change during the reduction diffusion treatment. As a result, the temperature was stable within ±1° C. of the set temperature.

As a result, alloy particles (hereinafter referred to as "Sample 6") were obtained.

(Example 7)
Alloy particles were produced in the same manner as in Example 6. However, in Example 7, a mixed salt of lithium chloride and potassium chloride was used as the molten salt. The molar ratio (LiCl:KCl) of the mixed salt was 0.6:0.4 (eutectic composition). Also, the reduction diffusion treatment was performed at 600°C.

As a result, alloy particles (hereinafter referred to as "Sample 7") were obtained.

(Example 8)
Alloy particles were produced in the same manner as in Example 6. However, in Example 8, a mixed salt of lithium chloride and lithium bromide was used as the molten salt. The molar ratio (LiCl:LiBr) of the mixed salt was 0.4:0.6 (eutectic composition). Also, the reduction diffusion treatment was performed at 600°C.

As a result, alloy particles (hereinafter referred to as "Sample 8") were obtained.

(Example 9)
Alloy particles were produced by the following method.

(Preparation of mixed powder of fine iron particles and SmFeO ₃ particles)
After 65 g of iron nitrate nonahydrate and 13 g of samarium nitrate were dissolved in 800 ml of water, 120 ml of a 2 mol/L potassium hydroxide aqueous solution was added dropwise while stirring. The resulting solution was further stirred overnight at room temperature to give a suspension.

The suspension was collected by filtration, washed, and then dried in air at 120° C. overnight in a hot air drying oven to obtain a sample.

The resulting sample was coarsely pulverized using a blade mill. Further, this was wet ground in ethanol with a stainless ball mill using a tumbling mill.

Next, the pulverized powder was separated by a centrifugal method, dried in a vacuum, and then reduced at 700° C. for 6 hours under a hydrogen stream.

From the XRD measurement results, it was confirmed that the obtained powder was a mixed powder of α-Fe fine particles and SmFeO ₃ particles.

As a result of FE-SEM observation and EDX analysis, it was found that the average particle diameter of the α-Fe particles was about 700 nm, and the average particle diameter of the SmFeO ₃ particles was about 150 nm.

(Reduction diffusion treatment)
Calcium chloride and potassium chloride were weighed so that the molar ratio was 0.25:0.75, and heated to 700° C. in an argon atmosphere to prepare a calcium chloride-potassium chloride eutectic salt. note that. Calcium chloride and potassium chloride were kept at 250° C. for 12 hours in a vacuum atmosphere and dried before use.

Next, 0.3 g of the mixed powder described above, 0.5 g of calcium chloride-potassium chloride eutectic salt, and 0.2 g of calcium were mixed.

The resulting mixture was placed in an iron crucible and heat-treated in an externally heated tubular furnace. The furnace was filled with an argon gas atmosphere, and heat treatment was performed at 700° C. for 12 hours.

After the heat treatment, the reaction product was taken out from the iron crucible and washed as in Example 1.

As a result, alloy particles (hereinafter referred to as "Sample 9") were obtained.

(Example 10)
Alloy particles were produced in the same manner as in Example 6.

However, in Example 10, the iron fine particles were produced as follows.

(Preparation of fine iron particles)
Iron oxide particles were prepared by dissolving 60 g of iron nitrate nonahydrate in a nitric acid aqueous solution containing 50 ml of nitric acid and 500 ml of water and subjecting the solution to spray pyrolysis.

The spray pyrolysis treatment was carried out using nitrogen gas (flow rate of 3 L/min) as a carrier gas by a 4-zone heating method (each zone set at 400°C, 600°C, 800°C and 900°C). Using the obtained iron oxide particles, hydrogen reduction was performed at 500° C. for 6 hours in a hydrogen atmosphere. As a result, fine iron particles having an average particle size of about 1200 nm were obtained.

After that, the same reduction diffusion treatment as in Example 6 was performed to obtain alloy particles (hereinafter referred to as "Sample 11").

(Example 11)
Alloy particles were produced in the same manner as in Example 10.

However, in this Example 11, 300 g of iron nitrate nonahydrate was used in preparing the fine iron powder. The reaction time for the reduction diffusion treatment was 24 hours.

As a result, alloy particles (hereinafter referred to as "Sample 11") were obtained.

(Example 12)
Alloy particles were produced by the following method.

(Preparation of iron-cobalt alloy fine particles)
After dissolving 171 g of iron nitrate nonahydrate, 53 g of cobalt nitrate hexahydrate, and 33 g of calcium nitrate in 1200 ml of water, 1110 ml of a 2 mol/L potassium hydroxide aqueous solution was added dropwise with stirring. did. After the resulting solution was stirred at room temperature for an additional hour, it was poured into a heat-resistant airtight container, covered, and allowed to stand at 110° C. for 12 hours.

Next, a precipitate in the solution was recovered by centrifugal separation, washed with water, and vacuum-dried.

Using the obtained particles, hydrogen reduction was performed at 500° C. for 6 hours in a hydrogen atmosphere. As a result, iron-cobalt fine particles having an average particle diameter of about 100 nm were obtained.

Elemental analysis of the iron-cobalt fine particles was performed by FE-SEM-EDX analysis. The elemental ratio of iron and cobalt was 69:31 (Fe:Co) as a result of averaging the measurement results at 10 locations.

(Reduction diffusion treatment)
Next, in the same manner as in Example 6, the iron-cobalt fine particles were subjected to reduction diffusion treatment.

As a result, alloy particles (hereinafter referred to as "Sample 12") were obtained.

As a result of EDX measurement of sample 12, the elemental ratio of Fe:Co was 67:33.

(Example 13)
Alloy particles were produced in the same manner as in Example 6.

However, in Example 13, 0.09 g of CoCl ₂ was added to the iron crucible during the reduction diffusion treatment.

As a result, alloy particles (hereinafter referred to as "Sample 13") were obtained.

As a result of EDX measurement of sample 13, the elemental ratio of Fe:Co was 84:16.

(Example 14)
Alloy particles were produced in the same manner as in Example 1.

However, in Example 14, the rare earth source used in the reduction diffusion treatment was changed from samarium chloride hexahydrate to neodymium chloride hexahydrate. Also, the heat treatment (reduction diffusion treatment) temperature was set to 600°C.

As a result, alloy particles (hereinafter referred to as "Sample 14") were obtained.

(Example 15)
Alloy particles were produced in the same manner as in Example 14.

However, in Example 15, the lithium chloride-potassium chloride eutectic salt used in Example 7 was used as the molten salt for the reduction diffusion treatment. Also, the reduction diffusion treatment temperature was set to 550°C.

As a result, alloy particles (hereinafter referred to as "Sample 15") were obtained.

(Example 16)
Alloy particles were produced in the same manner as in Example 15.

However, in Example 16, the reduction diffusion treatment temperature was set to 500°C.

As a result, alloy particles (hereinafter referred to as "Sample 16") were obtained.

(Example 21)
Alloy particles were produced in the same manner as in Example 1.

However, in Example 21, the heat treatment temperature in the reduction diffusion treatment was changed to 800°C.

As a result, alloy particles (hereinafter referred to as "Sample 21") were obtained.

(Example 22)
An attempt was made to produce alloy particles by the same method as in Example 1.

However, in Example 22, lithium chloride was not added in the reduction diffusion treatment. That is, reduction diffusion treatment was performed without using molten salt. Moreover, the reduction diffusion treatment was performed at 700°C.

This gave a product (hereinafter referred to as "Sample 22").

(Example 23)
Alloy particles were produced in the same manner as in Example 9.

However, in Example 23, the reduction diffusion treatment was performed without using molten salt. The conditions for the reduction diffusion treatment were 870° C. and 2 hours.

As a result, alloy particles (hereinafter referred to as "Sample 23") were obtained.

(Example 24)
Alloy particles were produced in the same manner as in Example 14. However, in Example 24, the temperature of the reduction diffusion treatment was changed to 700°C.

As a result, alloy particles (hereinafter referred to as "Sample 24") were obtained.

(Example 25)
Alloy particles were produced in the same manner as in Example 14. However, in Example 25, the temperature of the reduction diffusion treatment was changed to 650°C.

As a result, alloy particles (hereinafter referred to as "Sample 25") were obtained.

Table 1 below summarizes the raw materials used in the production of each sample, the conditions of the reduction diffusion treatment, and the like.

（評価）
製作した各サンプルを用いて、以下の評価を行った。

(evaluation)
The following evaluation was performed using each manufactured sample.

(Evaluation of crystal structure and phase ratio)
The crystal structure of the sample was identified by X-ray diffraction (XRD) measurement using CoKα radiation.

Also, from the obtained XRD pattern, the content rate (volume ratio) of the TbCu ₇ -type crystal phase contained in the sample was calculated by the method described above. The product may contain a phase of unreacted transition metal (for example, iron, cobalt, etc.). Such content calculations do not take into account the amount of unreacted iron contained in the sample (ie, the effect of unreacted iron content is eliminated).

As will be described later, Samples 21 and 23 contain only the Th ₂ Z ₁₇ -type crystal phase and do not contain the TbCu ₇ -type crystal phase. Therefore, these samples were used as the aforementioned reference samples. As a result of the measurement, both the ratio I _43.6 /I ₄₂ (that is, P _r ) of samples 21 and 23 were about 0.4. Therefore, the volume fraction of the TbCu ₇ -type crystal phase at the ratio I _43.6 /I ₄₂ =0.4 = 0%, and the volume fraction of the TbCu ₇ -type crystal phase at the ratio I _43.6 /I ₄₂ = 0 = A correlation straight line L was created as 100%.

(Evaluation of average particle diameter)
The average particle diameter of each sample was calculated as follows. First, in the elemental mapping image of the sample, alloy particles and unreacted iron-containing fine particles were discriminated. Next, 100 or more alloy particles were selected at random, and the particle diameters of these particles were measured by field emission scanning electron microscope (FE-SEM) images. The obtained results were averaged to obtain the average particle diameter of the alloy particles.

The elemental mapping image of the sample was taken using an EDX (energy dispersive X-ray analysis) device attached to the FE-SEM.

(Single crystal evaluation)
A green compact obtained by pressurizing the sample at a pressure of 200 MPa was used to determine whether each fine particle contained in the sample was a single crystal. A focused ion beam (FIB) device was used to expose a cross-section of the green compact, and this cross-section was evaluated using an electron backscatter diffraction (EBSD) analyzer attached to the FE-SEM device.

EBSD analyzers can image designated crystal planes in each grain. That is, in the image obtained by the EBSD analyzer (hereinafter referred to as "EBSD image"), if a single crystal face is observed in each particle, such particles are presumed to be single crystals. If multiple crystal faces are found within each grain, such grains can be determined to be polycrystalline.

In the EBSD analyzer, when referring to the TbCu ₇ type Sm—Fe phase, use the PDF card # 04-014-3296, and when referring to the TbCu ₇ type Nd—Fe phase, use the PDF card # Crystal structure parameters of 00-040-0876 were used.

Furthermore, an EBSD analyzer was used to measure the average crystal grain size of the alloy particles.

(result)
Table 2 below summarizes the evaluation results obtained for each sample.

（Ｓｍ－Ｆｅ系合金粒子の製造結果：サンプル１～サンプル１３、およびサンプル２１～サンプル２３）
ＸＲＤ測定結果から、サンプル１～サンプル１３は、いずれもＳｍ－Ｆｅ系合金粒子を含むことがわかった。また、サンプル１～サンプル１３は、いずれもＴｂＣｕ_７型の結晶相を含むことがわかった。なお、サンプル１２およびサンプル１３では、ＴｂＣｕ_７型の結晶相は、Ｓｍ－Ｆｅ－Ｃｏ系合金粒子に対応し、サンプル１－サンプル１１では、ＴｂＣｕ_７型の結晶相は、いずれもＳｍ－Ｆｅ合金粒子に対応する。

(Production results of Sm—Fe alloy particles: Samples 1 to 13 and Samples 21 to 23)
From the XRD measurement results, it was found that Samples 1 to 13 all contained Sm--Fe alloy particles. It was also found that all of Samples 1 to 13 contained a TbCu ₇ -type crystal phase. In Samples 12 and 13, the TbCu ₇ -type crystal phase corresponds to Sm—Fe—Co-based alloy particles, and in Samples 1 to 11, the TbCu ₇ -type crystal phases are all Sm—Fe alloys. Corresponds to particles.

On the other hand, although samples 21 and 23 contain Sm—Fe alloy particles, their crystal phase was found to be Th ₂ Zn ₁₇ type. In sample 22, the reaction hardly progressed, and a significant amount of Sm--Fe alloy particles could not be formed.

From the calculation result of the ratio I _43.6 /I ₄₂ , it was found that the TbCu ₇ type crystal phase was contained at a content of at least 50% by volume in samples 1 to 13. Also, in some samples, the content of the TbCu ₇ type crystalline phase was found to be almost 100%.

FIG. 3 collectively shows the XRD patterns of the particles according to Samples 1 to 5 and Sample 21. FIG. All of these samples used lithium chloride as a molten salt and were obtained after performing reduction diffusion treatment for 2 hours, but the temperature of the reduction diffusion treatment was different in each case.

From FIG. 3, only the diffraction pattern corresponding to the Th ₂ Zn ₁₇ -type crystal phase was observed in sample 21 subjected to the reduction diffusion treatment at 800°C. On the other hand, samples 2 to 5, which were subjected to the reduction diffusion treatment at 550° C. to 700° C., showed diffraction patterns of the TbCu ₇ -type crystal phase.

In addition, in Example 1 in which the reduction diffusion treatment was performed at 750° C., the diffraction pattern was intermediate between the two, and the Sm—Fe alloy particles had a Th ₂ Zn ₁₇ -type crystal phase and a TbCu ₇ -type crystal phase. It can be seen that it is a mixture of

Thus, when lithium chloride is used as the molten salt, in the Sm—Fe alloy, the Th ₂ Zn ₁₇ -type crystal phase begins to form from a temperature range of 750° C. or higher, and at a temperature of 800° C. or higher, the generated phase becomes large. It can be said that part or all becomes a crystalline phase of Th ₂ Zn ₁₇ type.

Here, in sample 5, the temperature of the reduction diffusion treatment is 550° C., which is lower than the melting point (605° C.) of lithium chloride. That is, in sample 5, Sm--Fe alloy particles having a TbCu ₇ -type crystal phase were produced although the reduction diffusion treatment was performed at a temperature lower than the melting point of lithium chloride. This is probably because lithium chloride and samarium chloride formed a eutectic salt and the melting temperature decreased.

Referring to Table 2 again, Samples 6 to 13 all had a long reduction diffusion treatment time of 12 hours. In these cases, it can be seen that the average grain diameter of the obtained Sm--Fe alloys increases due to the progress of grain growth as compared with the samples under the same conditions other than the reduction diffusion treatment temperature.

FIG. 4 shows an example of an FE-SEM image of sample 6. As shown in FIG. 5 shows an example of an EBSD image of sample 6. In FIG.

From these figures, it was confirmed that the inside of each particle had a single crystal orientation and was a single crystal.

Similarly, it was found that single-crystal alloy particles were produced in Samples 1 to 5 and Samples 7 to 13 as well.

The aforementioned Table 2 collectively shows the average particle diameter and the average crystal grain size of each alloy particle calculated from FIGS. 4 and 5 .

In addition, in the FE-SEM image of FIG. 4, ultrafine particles of about 10 nm are observed. Since this is considered to be crushed powder generated during the compacting process, it is excluded from the measurement of the average particle diameter.

In samples 1 to 13, the average crystal grain size estimated from the EBSD image and the average particle diameter estimated from the FE-SEM image were almost equal. This also confirms the formation of single-crystal grains in these samples.

In each of Samples 1 to 13, the average crystal grain size estimated from the EBSD image is slightly smaller than the average particle diameter estimated from the FE-SEM image. This is because in the EBSD method, if an oxide layer or the like exists on the surface of the TbCu ₇ -type crystal phase particles, such a layer is excluded as a substance different from the Sm-Fe alloy in the analyzer. It is considered to be

From sample 9, it can be seen that even when SmFeO ₃ is used as the rare earth compound, Sm—Fe alloy particles having a TbCu ₇ type crystal phase can be produced, as in the case of using SmCl ₃ .

In addition, in sample 9, a large amount of unreacted iron component remained. This is attributed to the use of _SmFeO3 oxide as the samarium source. That is, SmCl ₃ can form eutectic salts with salts such as lithium chloride, so that Sm ions can easily diffuse in the molten salt. On the other hand, SmFeO ₃ is difficult to dissolve in the molten salt, and diffusion of Sm ions did not proceed sufficiently, so that unreacted iron remained. However, even in sample 9, it is possible to produce Sm--Fe alloy particles having a TbCu ₇ -type crystal phase.

From the results of Samples 10 and 11, when the average particle diameter of the iron fine particles used was 1200 nm (Sample 10) and 2300 nm (Sample 11), TbCu ₇ -type It has been found that alloy powders containing crystalline phases can be produced.

Also, from sample 12, it was found that Sm--Fe--Co alloy particles having a TbCu ₇ -type crystal phase can be produced even when iron-cobalt fine particles are used instead of iron fine particles. Similarly, from sample 13, it was found that Sm--Fe--Co alloy particles having a TbCu ₇ -type crystal phase can be produced even when cobalt chloride is added in addition to the rare earth chloride.

(Production results of Nd—Fe alloy particles: Samples 14 to 16 and Samples 24 to 25)
Samples 14 to 16 and samples 24 to 25 were also evaluated in the same manner as the Sm--Fe alloy particles.

As a result, it was found that Samples 14 to 16 all contained Nd--Fe alloy particles. It was also found that all of Samples 14 to 16 contained a TbCu ₇ -type crystal phase.

In contrast, samples 24 and 25 contained Nd—Fe alloy particles, but the crystal phase was found to be Th ₂ Zn ₁₇ type.

The content of the TbCu ₇ -type crystal phase contained in each sample was calculated in the same manner as in the case of the Sm—Fe alloy particles described above.

As shown in Table 2 above, from the calculation results of the ratio I _43.6 /I ₄₂ , it was found that the TbCu ₇ type crystal phase was contained at a content of at least 53% by volume in samples 14 to 16. rice field. Also, in some samples, the content of the TbCu ₇ type crystalline phase was found to be almost 100%.

FIG. 6 collectively shows the XRD patterns of alloy particles according to Samples 14 to 16 and Samples 24 to 25. As shown in FIG. All of these samples used lithium chloride as a molten salt and were obtained after performing reduction diffusion treatment for 2 hours, but the temperature of the reduction diffusion treatment was different in each case.

From FIG. 6, only the diffraction pattern corresponding to the Th ₂ Zn ₁₇ -type crystal phase was observed in Samples 24 and 25 subjected to reduction diffusion treatment at 650° C. or higher. On the other hand, in Samples 14 to 16, which were subjected to the reduction diffusion treatment at 500° C. to 600° C., the positions of the diffraction peaks were shifted to the high angle side, and the peak near the angle 2θ=43.4° Since disappearance can be confirmed, it is found that Nd--Fe alloy particles having a TbCu ₇ -type crystal phase are formed.

Note that, in Example 14 in which the reduction diffusion treatment was performed at 600° C., the diffraction pattern was intermediate between that of Sample 25 and Sample 15, and the Nd—Fe alloy particles had a Th ₂ Zn ₁₇ -type crystal phase and a TbCu ₇ -type crystal phase. It can be seen that it is a mixture with the crystal phase of

Therefore, when lithium chloride is used as the molten salt, in the Nd—Fe alloy, the Th ₂ Zn ₁₇ type crystal phase begins to form from a temperature range of 600° C. or higher, and at 650° C. or higher, most of the generated phase or It can be said that all become a Th ₂ Zn ₁₇ -type crystal phase.

In samples 14 to 16 as well, the evaluation of the EBSD images of each sample confirmed that the inside of each particle had a single crystal orientation and was a single crystal.

From Table 2 described above, also in samples 14 to 16, the average grain size estimated from the EBSD image and the average grain size estimated from the FE-SEM image were almost equal. Also from this, it was confirmed that single-crystal particles were formed in these samples.

High performance TbCu _{7 -} type Sm-Fe- Production of N anisotropic magnet powder and Nd--Fe--N anisotropic magnet powder is expected.

Claims (16)

A method for producing alloy particles of a rare earth element and a transition metal, comprising:
(1) a step of preparing fine particles containing iron (Fe);
(2) a step of reducing and diffusing the rare earth compound in the molten salt in the presence of the reducing agent and the fine particles, whereby the rare earth element contained in the rare earth compound and the fine particles are alloyed; process and
has
the reducing agent is metallic calcium (Ca) and/or calcium hydride (CaH ₂ );
The rare earth compound has at least one selected from samarium (Sm) and neodymium (Nd) as a rare earth element,
The molten salt contains an alkali metal and/or alkaline earth metal halide ,
When the rare earth compound has Sm as a rare earth element, the step (2) is performed at a temperature of 350° C. or more and less than 800° C.,
The production method , wherein the step (2) is carried out at a temperature of 350°C or higher and lower than 650°C when the rare earth compound contains Nd as the rare earth element . The step (2) includes mixing the reducing agent, the fine particles, the rare earth compound, and the molten salt compound, and heating the resulting mixture to a predetermined temperature in an inert gas atmosphere. 2. The manufacturing method of claim 1, wherein the method is performed by: 3. The manufacturing method according to claim 2, wherein the mixture further includes a transition metal compound other than iron. 4. The manufacturing method according to claim 3, wherein the compound of a transition metal other than iron includes a halide of cobalt (Co). In the step (2), the compound for the molten salt is heated to a predetermined temperature in an inert gas atmosphere to form the molten salt, and the reducing agent and the fine particles are contained in the molten salt. , the production method according to claim 1, which is carried out by adding said rare earth compound. 6. The production method according to claim 5, wherein a transition metal compound other than iron is further added to the molten salt. 7. The manufacturing method according to claim 6, wherein said compound of a transition metal other than iron includes a halide of cobalt (Co). The manufacturing method according to any one of claims 1 to 7, wherein the fine particles further contain cobalt (Co). 9. The manufacturing method according to any one of claims 1 to 8, wherein the rare earth compound comprises a rare earth element oxide or halide. 9. The manufacturing method according to any one of claims 1 to 8, wherein said rare earth compound comprises a composite oxide of a rare earth element and a transition metal. The manufacturing method according to any one of claims 1 to 10, wherein the molten salt contains lithium chloride. The production method according to any one of claims 1 to 11 , wherein the fine particles have an average particle diameter in the range of 50 nm to 2500 nm. Alloy particles of a rare earth element and a transition metal,
The rare earth element has at least one selected from samarium (Sm) and neodymium (Nd),
the transition metal has at least iron (Fe),
The alloy particles have a TbCu ₇ -type crystal phase, and the ratio of the TbCu ₇ -type crystal phase to the total crystal phase is 50% by volume or more,
The alloy particles are single crystals,
Alloy particles having an average particle diameter in the range of 100 nm to 3000 nm. 14. The alloy particles of claim 13 , wherein the ratio of said transition metal to said rare earth element ranges from 86 atomic % to 94 atomic %. 15. Alloy particles according to claim 13 or 14 , wherein the transition metal further comprises cobalt (Co). 16. The alloy particles according to any one of claims 13 to 15 , wherein the transition metal is 50 atomic % or more iron.

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