JP6759855B2 - Method for manufacturing rare earth-iron-nitrogen alloy powder - Google Patents

Description

The present invention relates to a method for producing a rare earth-iron-nitrogen magnet powder, and more specifically, generation of coarse particles and generation of protrusions and crystal strains of fracture surface which can be the core of an inverse magnetic domain that deteriorates magnetic properties in a magnet crystal. The present invention relates to a method for producing a rare earth-iron-nitrogen magnet powder, in which a magnet powder having excellent magnetic properties can be obtained at low cost by using a reduction diffusion method.

Rare earth-iron-nitrogen magnets represented by Sm-Fe-N magnets are known as high-performance and inexpensive magnets. It is said that the Sm-Fe-N magnet powder exhibits maximum saturation magnetization when it is composed of Sm ₂ Fe ₁₇ Nx and has a composition of x = 3 (see Non-Patent Document 1).

The rare earth - iron - nitrogen based magnet, conventionally, a high-frequency furnace with Fe and Sm metals, rare earth is produced by arc furnace melting method using, for example - an iron alloy, or a Fe or Fe ₂ O _3, It is produced by nitriding a rare earth-iron alloy obtained by a reduction diffusion method in which a raw material such as Sm ₂ O ₃ and Ca are mixed and heat-treated.
The powdered rare earth-iron-nitrogen magnet thus obtained is finely pulverized until the average particle size becomes about several μm to 5 μm after nitriding because the coercive force generation mechanism is a new creation type. Will be done.

In the production of rare earth-iron alloy by the above melting method, heat treatment for melting, crushing, and homogenizing the composition of the raw material powder at 1500 ° C. or higher is required (see Patent Document 3), the steps are extremely complicated, and each step is extremely complicated. Since it is once exposed to the atmosphere, impurities are generated by oxidation, and nitriding is performed after wet treatment, but nitriding cannot proceed uniformly because the surface is oxidized during wet treatment, and saturation magnetization among the magnetic properties, The coercive force and squareness are reduced, and as a result, the maximum energy product is lowered. In addition, there is a problem that the rare earth metal required as a raw material is expensive.

On the other hand, if the reduction diffusion method is adopted for the production of the rare earth-iron alloy, an inexpensive rare earth oxide powder can be used as a raw material, which is advantageous in terms of cost as compared with the dissolution method. The applicant has proposed to improve the oxidation resistance by nitriding an alloy obtained by reducing and diffusing the raw material powder and coating the surface while finely pulverizing the obtained crude powder of RFeN (Patent Document 4). reference).

In the reduction diffusion method, a rare earth-iron alloy is usually produced by using iron powder of several tens of μm as a starting material, mixing a rare earth metal or a rare earth oxide with an alkaline earth metal, and then performing a reduction heat treatment. In the method, after the final nitriding treatment, the magnet alloy powder needs to be mechanically ground to several μm. However, there has been a problem that the crystal of the RFeN magnet alloy powder is subjected to protrusions and crystal strains of fracture surface which can be the core of the reverse magnetic domain due to this mechanical pulverization, and the magnetic characteristics are deteriorated.

On the other hand, by reducing the particle size of the powder used as a starting material, the particle size of the rare earth-iron alloy obtained by the reduction diffusion method can be suppressed to a small size, and magnet powder can be obtained without pulverization (Patent Documents 1 to 3). See) has been proposed.

In Patent Document 1, a rare earth oxide having an average particle size of less than 5 μm and a transition metal oxide having an average particle size of less than 5 μm are used, dry-mixed, and reduced in two steps to obtain an average particle size. A production method for obtaining a rare earth transition metal alloy powder having a particle size of less than 5 μm is disclosed.

In Patent Document 2, iron oxide particle powder having an average particle diameter of 0.1 to 10 μm and samarium oxide particle powder having an average particle diameter of 0.5 to 5.0 μm are wet-mixed or wet-ground and mixed to create a hydrogen gas atmosphere. The reduction reaction was carried out underneath to obtain a mixture of iron particles and samarium oxide particles, and the above mixture of iron particles and samarium oxide particles was stabilized in an oxygen-containing atmosphere to form an oxide film on the particle surface of the iron particles. Later, a method of mixing calcium to carry out a reduction and diffusion reaction has been proposed, and by forming an oxide film on the surface of the iron particles, the subsequent nitrided reaction can proceed uniformly and the sintering between particles can be suppressed. It is disclosed.

Further, in Patent Document 3, if rare earth elements and transition metals are dissolved with an acid or the like, ionized, completely mixed in a solution state, and precipitated by a precipitation reaction, the distribution of constituent elements in the precipitate particles is uniform. The average particle size is 0.05 to 20 μm, the particle shape is uniform, and a precipitate with a sharp particle size distribution can be obtained. Therefore, this precipitate is calcined to microscopically reduce rare earth elements and transition metal elements in the particles. It is disclosed that a homogeneous alloy powder having a well-organized particle shape can be obtained by using a reduction diffusion method after producing a mixed metal oxide.

However, in either case, it is not possible to suppress the occurrence of extremely large heat generation locally and local grain growth during the reduction diffusion heat treatment with alkaline earth metal, so that the deterioration of magnetic properties due to the generated coarse particles cannot be suppressed. Was not reached.

Further, the dry mixing method disclosed in Patent Document 1 has a problem that mixing non-uniformity is likely to occur due to specific gravity separation of raw materials, adhesion in an apparatus, aggregation, etc., and iron particles and samarium oxide disclosed in Patent Document 2. In the method of stabilizing the mixture with the particles in an oxygen-containing atmosphere, an oxide film is formed on the surface of the iron particles and then a reduction diffusion reaction is performed. However, referring to the examples, the average particle size is 3 μm or more. Some of them are large, exceeding 4 μm, and there is a problem that the magnetic properties are not sufficient because there are particles that are insufficiently nitrided. In addition, in the co-precipitation method by crystallization disclosed in Patent Document 3, rare earth compounds are used. Further problems have been pointed out, such as the formation of iron rare earth composite oxides remarkably during the reduction heat treatment with hydrogen due to the fine dispersion in the mixture.

From the above, the conventional method for producing a rare earth-transition metal alloy cannot eliminate the local grain growth, and the core of the reverse magnetic domain whose magnetic properties are deteriorated by the crystals of the magnet alloy powder during the pulverization treatment. There is a strong desire to establish a method for producing rare earth-iron-nitrogen magnet powder that does not cause the occurrence of possible fracture surface protrusions or crystal strain, and does not cause local grain growth of the magnet alloy powder. It was rare.

Japanese Unexamined Patent Publication No. 11-310807 JP-A-2003-297660 Japanese Patent No. 3698538 Japanese Patent No. 4135447

T. Iriyama IEEE TRANSATIONS ON MAGNETICS, VOL. 28, No. 5 (1992)

In view of such a situation of the prior art, the present invention suppresses the generation of coarse particles and the generation of protrusions and crystal strains on the fracture surface, which can be the core of the reverse magnetic domain that deteriorates the magnetic properties of the magnet crystal, and is excellent in magnetism. It is an object of the present invention to provide a method for producing a rare earth-iron-nitrogen magnet powder in which a magnet powder having characteristics can be obtained at low cost by using a reduction diffusion method.

As a result of intensive research on the production of rare earth-iron-nitrogen magnet powder using the reduction diffusion method in order to solve the conventional problems, the present inventors have conducted excessive research on the rare earth raw material powder at the raw material mixing stage. In the case of fine particles or rare earth compounds dispersed in a very fine state, a large amount of iron rare earth composite oxide RFeO ₃ (R is a rare earth element) is generated during the reduction heat treatment with hydrogen, and the next step It was found that a large thermit heat generation was generated during the reduction and diffusion treatment with the alkaline earth metal of the above, causing the local grain growth of the magnet alloy.
In order to improve the performance of the rare earth-iron-nitrogen magnet powder, it is possible to prevent the rare earth compound from being dispersed in a fine state at the stage of wet mixing the iron compound powder and the rare earth compound powder, and to use the raw material. As the powder, a mixed powder having a total chlorine ion concentration of 0.1% by weight or less was used, and in the hydrogen reduction heat treatment step of the next step, the rare earth iron composite oxide RFeO ₃ (R) was added to the obtained reduction mixture powder. If the formation of rare earth elements) is suppressed, the increase in local heat generation is suppressed in the reduction and diffusion step, the generation of coarse particles due to the grain growth of the rare earth-iron alloy is suppressed, and the number of coarse particles is very small. We have found that a rare earth-iron-based mother alloy can be obtained, and if the rare earth-iron-based mother alloy is nitrided, a rare earth-iron-nitrogen-based magnet powder having excellent magnetic properties can be obtained. It came to be completed.

That is, according to the first invention of the present invention, there is a method for producing a rare earth-iron-nitrogen magnet powder, which comprises a step of nitriding the rare earth-iron mother alloy powder obtained by the reduction diffusion method.
An iron compound powder and rare earth compound powder of the magnet raw material, wet mixed treated with water or an organic solvent and then filtered to remove the magnet material from processing liquid and dried, a first step of obtaining a mixed powder,
The pre-Symbol mixed powder was heat-treated in a hydrogen stream, a second step of obtaining a reduced mixture powder,
Was added before Symbol reduced mixture powder alkaline earth to the metal, and mixed in an inert gas atmosphere, after heat treatment at a temperature of from 900 to 1180 ° C., cooling the reaction product obtained in the same atmosphere The third step of obtaining a rare earth-iron base alloy by
Before SL earth - the reaction product comprising an iron-based matrix alloy, supplying a mixed gas containing at least ammonia and hydrogen were produced by nitriding treatment by heat treatment in the mixed gas flow rare earth - iron - nitrogen A fourth step of obtaining a nitriding product mass containing a system magnet coarse powder, and
Next, the obtained nitriding product mass containing the rare earth-iron-nitrogen magnet coarse powder was put into water and wet-treated to disintegrate, and the obtained rare earth-iron-nitrogen magnet crude powder was crushed. And the fifth step to obtain rare earth-iron-nitrogen magnet powder,
Have a,
The total concentration of chloride ions eluted in the mixed powder when dispersed in water is 0.1% by weight or less with respect to the mixture powder.
The reduced mixture powder (the _R a rare earth element) rare earth iron composite oxide RFeO 3 or less the existence ratio is 6% by weight of rare earth - iron - method for producing nitrogen-based magnetic powder is provided.

Further, according to the second invention of the present invention, in the first invention of the present invention, the rare earth-iron-nitrogen magnet coarse powder obtained by the method for producing a rare earth-iron-nitrogen magnet powder is primary. It is a mixed powder consisting of secondary particles obtained by gathering a plurality of particles and sintering them into a grape shape and primary particles.
Provided by a method for producing a rare earth-iron-nitrogen magnet powder, characterized in that the cumulative number percentage of primary particles having a major axis particle diameter of 4 μm or more is less than 5%.

Further, according to the third invention of the present invention, in the first invention of the present invention, the rare earth-iron-nitrogen magnet powder is Sm-Fe-N. Provided by a method of producing a powder.

Further, according to the fourth invention of the present invention, in the first invention of the present invention, the amount of Sm is 23.2 to 23.6% by weight based on the total amount of the magnet powder. It is provided by a method for producing an iron-nitrogen magnet powder.

Further, according to the fifth invention of the present invention, in the first invention of the present invention, the iron compound in the first step is one or more selected from iron oxide, iron oxyhydroxide, and iron hydroxide. , The rare earth compound is provided by a method for producing a rare earth-iron-nitrogen magnet powder, which is characterized in that the rare earth compound is at least one selected from a rare earth oxide and a rare earth hydroxide.

Further, according to the sixth invention of the present invention, in the first invention of the present invention, a test in which either the iron compound powder or the rare earth compound powder is dispersed in water in advance by the wet mixing treatment of the first step. When the aqueous solution shows acidity, an organic solvent is used as the solvent, while when the aqueous solution shows alkalinity, water or an organic solvent is used as the solvent. -Provided by a method for producing nitrogen-based magnet powder.

Further, according to the seventh invention of the present invention, in the first invention of the present invention, the temperature range of the heat treatment in the second step is 500 to 800 ° C., which is a rare earth-iron-nitrogen magnet powder. Provided by the manufacturing method of.

Further, according to the eighth invention of the present invention, in the first invention of the present invention, the amount of the alkaline earth metal in the third step is defined as one equivalent of the amount sufficient to reduce the amount of unreduced oxygen. The present invention is provided by a method for producing a rare earth-iron-nitrogen magnet powder, which is characterized by having 1.1 to 3.0 equivalents.

Further, according to the ninth invention of the present invention, in the first invention of the present invention, in the fifth step, the grape-like secondary particles are crushed with a crushing strength to crush the grape-like secondary particles, and the primary particle mass is not crushed. The present invention is provided by a method for producing a rare earth-iron-nitrogen magnet powder.

According to the method for producing a rare earth-iron-nitrogen magnet powder of the present invention, the rare earth iron composite produced during hydrogen reduction is regulated so that the chlorine that can be contained in the raw material powder is equal to or less than a specific chlorine ion concentration. Since it is possible to significantly reduce the abundance of oxide RFeO ₃ (R is a rare earth element) and suppress the grain growth after the reduction and diffusion treatment, it is not necessary to increase the crushing strength of coarse particles. It is possible to suppress the generation of nuclei and crystal strain, and it is possible to produce high-performance rare earth-iron-nitrogen magnet powder, and the production cost is low, so its industrial value is extremely high. large.

SEM image of rare earth-iron-nitrogen magnet powder produced by the production method of the present invention (Example 1) after crushing with a ball mill (left side: particle surface observation, right side: particle cross section by reflected electron image) It is a photograph showing observation).

SEM image of rare earth-iron-nitrogen magnet powder produced by the conventional (Comparative Example 1) magnet powder after crushing with a ball mill (left side: particle surface observation, right side: particle cross-sectional observation by reflected electron image) ) Is a photograph showing.

SEM image of rare earth-iron-nitrogen magnet powder produced by the conventional (Comparative Example 4) magnet powder after crushing with a ball mill (left side: particle surface observation, right side: particle cross-sectional observation by reflected electron image) ) Is a photograph showing.

Hereinafter, the method for producing the rare earth-iron-nitrogen magnet powder of the present invention will be described in detail.

The present invention is a method for producing a rare earth-iron-nitrogen magnet powder that nitrides a rare earth-iron mother alloy powder obtained by a reduction diffusion method.
A mixed powder in which the iron compound powder and the rare earth compound powder are wet-mixed in water or an organic solvent, filtered and dried so that the total concentration of chloride ions contained in the mixed powder is 0.1% by weight or less. The first step to get
The obtained mixed powder is heat-treated in a hydrogen stream so that the amount of rare earth iron composite oxide RFeO ₃ (R is a rare earth element) produced in the obtained reduction mixture powder is 6% by weight or less. The second step and
An alkaline earth metal is added to the obtained reduction mixture powder, mixed, and heat-treated at a temperature of 900 to 1180 ° C. in an inert gas atmosphere, and then the obtained reaction product is cooled in the same atmosphere. The third step of obtaining a rare earth-iron-based mother alloy by
Next, a mixed gas containing at least ammonia and hydrogen was supplied to the obtained reaction product containing the rare earth-iron base alloy, and heat treatment was performed in the mixed gas stream to generate nitriding treatment. The fourth step of obtaining a nitriding product mass containing a rare earth-iron-nitrogen magnet coarse powder, and
Next, the obtained nitriding product mass containing the rare earth-iron-nitrogen magnet coarse powder was put into water and wet-treated to disintegrate, and the obtained rare earth-iron-nitrogen magnet crude powder was crushed. It is provided with a fifth step of obtaining a rare earth-iron-nitrogen magnet powder.

Hereinafter, each step will be described in detail.

1. 1. Method for Producing Rare Earth-Iron Mother Alloy (1-a) First Step: Mixing Raw Material Powder First, the iron compound powder and rare earth compound powder, which are the raw materials for magnets, are wet-mixed in water or an organic solvent, and after filtration. dry.

In the present invention, the oxide powder is dispersed in water, centrifuged, and the supernatant is used to analyze the eluted chlorine concentration to obtain a mixed powder having a total chlorine ion concentration of 0.1% by weight or less. Try to use. The method for measuring the chlorine ion concentration is not particularly limited, but anion chromatography can be used.

The iron compound powder includes iron oxide; Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , iron oxyhydroxide; FeOOH, iron (II) hydroxide; Fe (OH) ₂ , iron (III) hydroxide; Fe ( OH) ₃ can be preferably used. Further, an oxide starting from chloride can be used as a compound, but since it contains chlorine, it is roasted in an oxygen-containing atmosphere, for example, at a temperature of 800 ° C. or higher in the atmosphere after mixing and drying. Is desirable.

In order to reduce the particle size of the rare earth-iron mother alloy produced later, the particle size of the iron compound powder is preferably 3 μm or less, and more preferably 1 μm or less in terms of average particle size. This is because when the average particle size exceeds 3 μm, the particle size of the rare earth-iron mother alloy produced later becomes larger than the particle size of the iron compound powder, so that large particles are likely to be formed and the coercive force is lowered, and the nitriding process is performed. This is because it causes insufficient nitriding in the particles.

The rare earth compound powder is not particularly limited, but at least one element selected from Sm, Gd, Tb, and Ce, or at least one element selected from Pr, Nd, Dy, Ho, Er, Tm, and Yb. It is preferably one or more selected from rare earth oxides and rare earth hydroxides containing elements. Among them, a rare earth compound containing Sm is particularly preferable because it enables the effect of the present invention to be remarkably exhibited.
When Sm is contained, it is preferable that Sm is 60% by weight or more, preferably 90% by weight or more of the total rare earth elements in order to obtain a high coercive force. As the form of the compound, oxides and hydroxides are preferable, and the particle size is preferably smaller than the particle size of the iron compound so that diffusion in the solid phase is easy and non-uniform diffusion does not occur. However, when a fine powder of less than 0.1 μm is used, it is not preferable because it causes a large amount of iron rare earth composite oxide to be produced.

There are two types of mixing methods: dry mixing and wet mixing. Since dry mixing handles fine powder, the powders may agglomerate or adhere to the inner wall of the mixing device due to the effects of static electricity and moisture in the atmosphere. Wet mixing is preferable because uniform mixing is difficult. As another method, there is also a method of producing a coprecipitated powder of iron and rare earths by crystallization as described above, but since the rare earth salts are finely dispersed in a very fine state, during the reduction heat treatment with hydrogen. This is not preferable because it causes a problem of producing a large amount of iron rare earth composite oxide.

In wet mixing, when the particle size of the rare earth compound powder is larger than the particle size of the iron compound powder, a mixing method in which the particle size of the rare earth compound powder is made smaller than that of the iron compound powder by using a medium such as ball mill mixing or bead mill mixing. It is preferable to use. When the rare earth compound powder is smaller than the particle size of the iron compound powder, it is mixed by a method such as stirring and mixing using a stirring blade, or ball mill mixing using a ball having a size that is difficult to be crushed or a ball having a light specific gravity. Is preferable.

At this time, it is desirable to disperse either the iron compound or the rare earth compound used for mixing in water in advance and check the pH of the aqueous solution. When the aqueous solution is acidic, it is preferable to use an organic solvent as the solvent. As the organic solvent, alcohols such as ethyl alcohol, isopropyl alcohol and n-butanol, or dimethyl ether, ethyl methyl ether, diethyl ether, ethyl methyl ketone and diethyl ketone are preferable, but ethanol or isopropyl alcohol is more preferable and the organic solvent is used. It is more preferable that the solvent does not contain water.

On the other hand, when an aqueous solution in which either an iron compound or a rare earth compound is dispersed in water exhibits alkalinity, water or an organic solvent can be used as the solvent.

When the dispersion solution shows acidity when the raw material compound is dispersed in water, the organic solvent is used when the solvent is water, for example, when a rare earth oxide is used as the rare earth compound, a part of the rare earth oxide is used. Dissolves in water and then reprecipitates to form fine rare earth hydroxides, and the presence of these rare earth hydroxides causes the iron rare earth composite oxide RFeO ₃ (R) during hydrogen reduction in the next step. This is because rare earth elements) are formed. Furthermore, the presence of this iron rare earth composite oxide RFeO ₃ (R is a rare earth element) causes a large amount of heat to be generated in the reduction heat treatment step with the alkaline earth metal, and finally the coercive force is lowered. Alternatively, the generated rare earth-iron mother alloy particles may cause grain growth locally, resulting in insufficient nitriding inside the particles during the nitriding treatment.

The wet-mixed slurry is then filtered and dried, and the drying method may be any method such as stationary drying, fluid drying, air flow drying, stirring drying, vacuum drying, and vibration drying.

In the obtained mixed powder composed of an iron compound and a rare earth compound, it is necessary to confirm that the total chloride ion concentration is 0.1% by weight or less when dispersed in water before use. This is because when a mixed powder having a total chlorine ion concentration of more than 0.1% by weight is used, the acidic water vapor dissolved as hydrogen chloride in the water vapor generated during the next reduction heat treatment with hydrogen attacks the rare earth compound and dissolves it. This is because the rare earth compound is finely dispersed in the iron compound or the iron powder that has already been reduced by decomposition by heating, and rapidly proceeds in the direction of promoting the formation of the iron rare earth composite oxide RFeO ₃ (R is a rare earth element).

Since the total chlorine ion concentration of the mixed powder must be 0.1% by weight or less, chloride is not used as the iron compound or rare earth compound of the raw material powder, and even when oxides or the like are used, chloride is used as the raw material. It is preferable not to use the starting material. When an oxide starting from chloride is used as a compound, as described above, after mixing and drying, the mixed powder is roasted in an oxygen-containing atmosphere, for example, at a temperature of 800 ° C. or higher in the air. It is preferable to reduce the chlorine ion concentration of.

(1-b) Second Step: Hydrogen Reduction In the second step, the mixed powder obtained in the first step is heat-treated in a hydrogen stream to obtain a rare earth iron composite oxidation in the reduced mixture powder. This is a step of reducing the amount of product RFeO ₃ (R is a rare earth element) to 6% by weight or less.

Hydrogen reduction is performed by heat-treating the mixed powder prepared in (1-a) in a hydrogen stream. The heat treatment temperature range is preferably 500 to 800 ° C.
This is because when the temperature drops below 500 ° C, the reduction is insufficient and iron oxide tends to remain, and the crystals after reduction are unstable, so they oxidize immediately when they come into contact with the atmosphere and return to iron oxide again. is there. If the heat treatment temperature exceeds 800 ° C, the particles are reduced but the high temperature causes the particles of the starting material to grow and increase the particle size, and the coercive force decreases when the rare earth-iron matrix alloy is obtained in the next process. This is because the particle size becomes large enough to make it. The heat treatment temperature range is more preferably 550 to 700 ° C. The heat treatment time is not particularly limited, but can be, for example, 1 to 5 hours. The hydrogen flow rate is also not particularly limited, but can be, for example, 1 to 100 ml / (min · g).

Hydrogen reduction devices include stationary muffle furnaces, elevating furnaces, rotary kilns, pusher furnaces capable of continuous production, roller harsher kilns, etc., but devices with good gas reaction efficiency such as rotary kilns are available. , It is preferable because the reduction is completed in a short time. Hydrogen reduction is possible even in a stationary muffle furnace or an elevating furnace if it takes time, but more preferably, the mixed powder in the sack is used so that the discharge of steam from the mixed powder and the permeation of hydrogen gas can be performed without delay. It is desirable to increase the reaction efficiency by various methods such as thinning the layer thickness, increasing the amount of introduced gas, and making the container a mesh type.

By performing hydrogen reduction by the above method, the amount of the rare earth iron composite oxide RFeO ₃ (R is a rare earth element) is reduced in the obtained reduction mixed powder.

However, when the rare earth compound is a fine powder of less than 0.1 μm, or when the rare earth compound is dissolved in the solvent when the raw material compound is mixed to become a fine rare earth compound, which exists on the surface of the iron compound, when hydrogen is reduced. , Iron rare earth compound oxide RFeO ₃ (R is a rare earth element) is promoted, and in addition to iron powder and rare earth oxide, iron rare earth compound oxide RFeO ₃ (R is a rare earth element) may be contained in a large amount. However, the abundance ratio of this iron rare earth composite oxide RFeO ₃ (R is a rare earth element) must be 6% by weight or less. This is because if the abundance ratio of the rare earth iron composite oxide RFeO ₃ (R is a rare earth element) exceeds 6% by weight, local grain growth will occur in the next reduction / diffusion step. More preferably, the abundance ratio of the iron rare earth composite oxide RFeO ₃ (R is a rare earth element) is 5.5% by weight or less.

(1-c) Third step: Reduction diffusion and cooling of reaction product Next, in the third step, an alkaline earth metal was added to the reduction mixture powder obtained in the second step. The mixture is mixed and heat-treated at a temperature of 900 to 1180 ° C. in an inert gas atmosphere, and then the obtained reaction product is cooled in the same atmosphere to obtain a rare earth-iron system having a Th ₂ Zn _17- type crystal structure. Obtain a mother alloy. The amount of alkaline earth metal is preferably 1.1 to 3.0 equivalents, where 1 equivalent is an amount that only reduces the amount of unreduced oxygen.

In the reduction diffusion method, as described above, a mixture of a rare earth oxide powder and an iron powder, a reducing agent for an alkaline earth metal such as Ca is heated in an inert gas atmosphere, for example, at 900 to 1180 ° C., and then a reaction product is produced. Is a method for directly obtaining a rare earth-iron-based mother alloy powder by wet-treating the mixture to remove the reducing agent components such as CaO and residual Ca produced as a by-product.

In the present invention, iron powder and rare earth oxide powder, and further, a reduction mixture powder in which a rare earth iron composite oxide is present and a reducing agent are mixed, put into a reaction vessel, and heat-treated at a temperature of 900 to 1180 ° C. The rare earth oxide and other remaining oxide raw materials are reduced, and the reduced rare earth element is diffused into the iron powder to form a rare earth-iron mother alloy having a Th ₂ Zn _17- type crystal structure.

Here, each raw material compound powder in the reduction mixture obtained in the previous step needs to be uniformly mixed together with the reducing agent so as not to be separated according to the respective powder characteristics. As the mixing method, for example, a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, a Nauter mixer, a Henschel mixer, a high-speed mixer, a vibration mill and the like can be used.

As the reducing agent, an alkaline earth metal can be used, and from the viewpoint of handling safety and cost, granular metallic calcium or metallic magnesium classified into a mesh size of 4.00 mm or less is preferable. The reducing agent is mixed with the reducing mixture powder or separated so that the metal vapor can come into contact with the reducing mixture powder. It is preferable to mix the reducing agent and the powder in the reduction mixture and perform reduction diffusion because the reaction product becomes porous and the subsequent nitriding treatment can be efficiently performed.

It is also effective to mix the reducing mixture powder and the reducing agent with an additive that promotes the disintegration of the reaction product in the subsequent wet treatment step. As the disintegration accelerator, salts or oxides of alkaline earth metals such as calcium chloride can be used, and they are uniformly mixed at the same time as the reduction mixture powder. Here, as the inert gas, one or more kinds selected from argon and helium are used.

The heat treatment temperature at the time of reduction diffusion needs to be in the range of 900 to 1180 ° C. Below 900 ° C, the time required for diffusion becomes very long, productivity is lacking, and the diffusion of rare earth elements becomes non-uniform with respect to iron powder, and the rare earth-iron-nitrogen magnet obtained in the next step of nitriding treatment. It is not preferable because the coercive force and squareness of the powder are reduced. Further, when the temperature exceeds 1180 ° C., the rare earth-iron mother alloy produced undergoes grain growth, which makes it difficult to uniformly nitrid in the nitriding process in the next step, and the saturation magnetization, squareness, and coercive force of the magnet powder decrease. This is not preferable. In addition, the amount of evaporation of rare earth elements becomes very large, and an excessive amount of rare earth elements is required to compensate for this, resulting in high cost. Such a phenomenon does not occur when the heat treatment temperature is 900 to 1180 ° C. In addition, a plurality of primary particles are gathered to form a mixed powder of secondary particles sintered into a grape shape and primary particles, but the particles are baked together. The formation is weak, and there is an advantage that crystal strain is unlikely to occur during crushing after the nitriding treatment.

Here, the reaction product obtained by the reduction diffusion reaction is, for example, when metallic calcium is used as the reducing agent, a rare earth-iron mother alloy having a Th ₂ Zn _17- type crystal structure and calcium oxide, and an unreacted surplus. It is a massive mixture consisting of metallic calcium and the like. Further, when granular metallic calcium is mixed with the raw material powder and subjected to a reduction diffusion reaction, it becomes a porous massive mixture.

On the other hand, the rare earth element and the transition metal used in Patent Document 3 are dissolved with an acid or the like to be ionized, completely mixed in a solution state, precipitated by a precipitation reaction, and the particle size distribution is sharp. A substance is obtained, and this precipitate is calcined to form a metal oxide in which a rare earth element and a transition metal element are microscopically mixed in the particles, and then the particle shape is adjusted by using a reduction diffusion method. In the method of obtaining a homogeneous alloy powder, a rare earth metal is used as a rare earth raw material, so that the method is more expensive than the rare earth oxide raw material used in the reduction diffusion method. In particular, the cost difference depending on the case where the rare earth element is Sm which brings about excellent magnetic properties is remarkable. In addition, unnecessary powder generated by particle size adjustment lowers the product yield and further raises the powder cost. Further, in the method of firing and reducing and diffusing from the precipitate, a homogenization heat treatment step is required to eliminate the α-Fe phase and the like existing in the obtained alloy, and the alloy is homogenized and heat-treated before introducing nitrogen. It is not preferable because the powder cost is further increased, for example, a step of coarsely pulverizing and adjusting the particle size is required.

In the third step, the reaction product after the reduction / diffusion reaction is continuously cooled without changing the atmospheric gas as an inert gas. The cooling is preferably 300 ° C. or lower, and is cooled to 50 to 280 ° C., more preferably 100 to 250 ° C. If the temperature after cooling exceeds 300 ° C, the nitriding reaction with the reaction product will proceed rapidly during nitriding in the next step, which may increase the α-Fe phase. It is desirable to cool to a temperature below ° C. This is because at temperatures above 300 ° C, the alloy is rapidly nitrided due to the activity of the reaction product, and some of the intermetallic compounds having a Th ₂ Zn _17- type crystal structure are in the Fe-rich phase and SmN. This is because it is presumed that it decomposes into.

After cooling, the reaction product, which is a porous massive mixture, is not wet-treated, but the atmosphere gas is changed from an inert gas to a mixed gas containing at least ammonia and hydrogen, and the process proceeds to the next nitriding step. At this time, when the reaction product is exposed to the atmosphere, the active rare earth-iron mother alloy powder in the reaction product is oxidized and the reactivity is deactivated, and as a result, the degree of nitriding can be varied. It is necessary to bring it into the nitriding process so that it is not exposed to (oxygen).

2. 2. Method for producing rare earth-iron-nitrogen magnet powder (2-a) Fourth step: Nitriding treatment In the fourth step, the reaction product containing the rare earth-iron mother alloy obtained in the third step is used. , A mixed gas containing at least ammonia and hydrogen is supplied, and heat treatment is performed in the mixed gas stream to obtain a nitriding product mass containing a rare earth-iron-nitrogen magnet coarse powder produced by nitriding.

As the nitriding gas, a mixed gas containing at least ammonia and hydrogen is required, and argon, nitrogen, helium and the like can be mixed in order to control the reaction. The amount of nitriding gas is preferably an amount sufficient for the amount of nitrogen in the magnet powder to be 3.3 to 3.7% by weight.

The ratio of ammonia to the total mixed gas pressure (ammonia partial pressure) is preferably 0.2 to 0.6, and more preferably 0.3 to 0.5. If the partial pressure of ammonia is less than 0.2, the nitriding of the mother alloy does not proceed even over a long period of time, the amount of nitrogen cannot be 3.3 to 3.7% by weight, and the resulting magnet powder is saturated. Magnetization and coercive force are reduced.

A mixed gas containing at least ammonia and hydrogen is supplied at a nitriding temperature of 350 to 500 ° C., preferably 400 to 480 ° C., to heat-treat the rare earth-iron base alloy in the reaction product. If the temperature is less than 350 ° C, it takes a long time to introduce 3.3 to 3.7% by weight of nitrogen into the rare earth-iron base alloy in the reaction product, and the industrial advantage is lost. On the other hand, when the temperature exceeds 500 ° C, the main phase Sm ₂ Fe ₁₇ phase is decomposed to generate α-Fe, so that the demagnetization curve of the finally obtained rare earth-iron-nitrogen magnet powder Squareness may decrease. From the cooling temperature at which the reaction product was cooled in the previous step to the nitriding temperature, it is desirable to raise the temperature relatively rapidly at a rate of 4 to 10 ° C. per minute in order to improve the production efficiency. Further, the holding time at the cooling temperature is not particularly required. This is because holding it has no effect on nitriding.

The holding time of the nitriding treatment depends on the nitriding temperature, but is preferably 100 to 300 minutes, more preferably 140 to 250 minutes. If it is less than 100 minutes, nitriding becomes insufficient, while if it exceeds 300 minutes, nitriding may proceed too much.

In the present invention, it is desirable to further heat-treat the alloy powder in hydrogen gas or an inert gas such as nitrogen gas, argon gas or helium gas following the nitriding treatment. Particularly preferred is heat treatment with hydrogen gas followed by heat treatment with nitrogen gas and / or argon gas.

As a result, the nitrogen distribution in the individual crystal cells constituting the rare earth-iron-nitrogen magnet powder can be further made uniform, and the squareness can be improved. The holding time of the heat treatment is preferably 30 to 200 minutes, more preferably 60 to 250 minutes.

(2-b) Fifth Step: Wet Treatment, Fine Grinding, Drying Next, the nitriding product mass containing the rare earth-iron-nitrogen magnet coarse powder obtained in the fourth step is put into water. The rare earth-iron-nitrogen magnet powder is crushed to obtain a rare earth-iron-nitrogen magnet powder.

As described above, the nitriding product mass containing the rare earth-iron-nitrogen magnet coarse powder after nitriding is put into water and wet-treated to disintegrate the nitriding product mass, and the nitriding product mass is destroyed. By-products (calcium oxide, calcium nitride, etc.) of the reducing agent component contained in the above can be separated and removed from the rare earth-iron-nitrogen magnet powder.

The wet treatment of the magnet powder after the completion of nitriding is that if the reaction product containing the rare earth-iron base alloy is wet treated before the nitriding, the surface of the rare earth-iron mother alloy is oxidized in this wet treatment process. This is because the degree of nitriding of the rare earth-iron base alloy after that can be varied.

In addition, if the nitriding product mass is left in the air for a long period of time after nitriding, oxides of reducing agent components such as calcium are generated and difficult to remove, or the surface of rare earth-iron-nitrogen magnet powder is oxidized. Nitriding becomes non-uniform, and the ratio of the main phase decreases and the formation of nuclei nuclei reduces the squareness. Therefore, it is preferable that the nitriding product mass left in the air is wet-treated within 2 weeks after being taken out from the reaction vessel.

In the wet treatment, first, the nitriding product mass is put into water to disintegrate the mass, and decantation-water injection-decantation is repeated to remove most of the generated Ca (OH) ₂ . Further, if necessary, in order to remove the residual Ca (OH) ₂ , acid cleaning is performed with one or more selected from acetic acid and hydrochloric acid. The hydrogen ion concentration of the aqueous solution at this time may be in the range of pH 4 to 7. If an excessive amount of rare earth element is added when the raw materials are mixed, the rare earth element has an effect of the excess rare earth element during the reduction and diffusion treatment, and the rare earth element has a Th ₂ Zn _17- type crystal structure as the main phase. A non-magnetic phase that is large in quantity and lowers saturation magnetization may be generated and exists, and pickling is performed so that the amount of rare earth elements in the main phase is 23.2 to 23.6% by weight, which is a preferable range. , It is preferable to remove the non-magnetic phase having a large amount of rare earth elements.

After the completion of the acid cleaning treatment, a rare earth-iron-nitrogen magnet coarse powder can be obtained by washing with water, dehydrating with an organic solvent such as alcohol or acetone, and drying in an inert gas atmosphere or in a vacuum. it can.

The rare earth-iron-nitrogen magnet coarse powder obtained above is a mixed powder composed of secondary particles obtained by gathering a plurality of primary particles and sintered into a grape shape and primary particles, and has a length of the primary particles. When the axial particle size is confirmed and measured by SEM, the cumulative number percentage of the primary particles having the major particle size of 4 μm or more is less than 5%. The cumulative number percentage of the primary particles having a semimajor particle diameter of 4 μm or more is preferably less than 2%. This is a primary particle, and when the number of particles with a major axis particle diameter of 4 μm or more is increasing, nitriding has not progressed to the center of the particle when the particle cross section is confirmed, and there are particles with insufficient nitriding. In addition to the fact that rare earth-iron-nitrogen magnets have a new creation type coercive force generation mechanism, they also cause a decrease in saturation magnetization, squareness, and coercive force due to the large particles. Is.

As described above, the rare earth-iron-nitrogen magnet coarse powder is a mixed powder composed of secondary particles obtained by gathering a plurality of primary particles and sintering them into a grape shape and primary particles, and such a coarse magnet powder. Is put into a crusher together with a solvent, and the primary particle mass is not crushed, but is crushed weakly to the extent that the sintered portion of the rare earth-iron-nitrogen magnet powder composed of secondary particles comes off, and then filtered and dried. It is preferable to do so.

The crusher used for crushing is widely used in various chemical industries dealing with solids, and is not particularly limited as long as it is a crushing device for crushing various materials. Among them, the wet pulverization method using a medium stirring mill or a bead mill is preferable in that the composition of the powder and the particle size can be easily made uniform. As the crushing conditions, as described above, it is preferable that the rare earth-iron-nitrogen magnet powder composed of secondary particles is crushed weakly to the extent that the sintered portion is disengaged, and the crushing is not strong enough to break the primary particles. Conditions may be set as appropriate.

As the solvent used for pulverization, isopropyl alcohol, ethanol, toluene, methanol, hexane and the like can be used, but isopropyl alcohol is particularly preferable. After pulverization, it may be filtered using a filter having a predetermined opening and dried to obtain a rare earth-iron-nitrogen magnet powder.

3. 3. Rare earth-iron-nitrogen magnet powder The rare earth-iron-nitrogen magnet powder obtained by the above production method is a rare earth element-iron-nitrogen magnet powder having a Th ₂ Zn ₁₇ type or Th ₂ Ni ₁₇ type crystal structure. is there. The rare earth-iron-nitrogen magnet powder is an intermetallic compound having a rhombohedral, hexagonal, tetragonal or monoclinic crystal structure, and is a Th ₂ Zn _17- type magnet alloy powder. For example, Sm ₂ Fe ₁₇ N ₃ alloy, Nd ₂ Fe ₁₇ N _{3 and the} like can be mentioned, and examples of the Th ₂ Ni ₁₇ type magnet alloy powder include Gd ₂ Fe ₁₇ N _{3 and the} like.

Examples of the rare earth element (R) include Sm, Nd, Pr, Y, La, Ce, and Gd, which may be used alone or in combination of two, but among these, Sm and Nd are effective. In particular, those containing 80% by mass or more of Sm are preferable. Fe is an essential component of the transition metal element (T), and a part of the transition metal element (T) may be replaced with Co.

The rare earth-iron-nitrogen magnet powder includes C, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, It can contain Ta, W, Re, Os, Ir, Pt, or Au. Although elements other than transition metals are included in these, all of them shall be treated according to the transition metal element (T). If these components are added in an amount of 3% by mass or less, preferably 0.05 to 0.5% by mass, the weather resistance and heat resistance of the magnet can be further enhanced.

Of these, if one or more selected from Al, Si, Ca, V, Cr, Mn, Cu, Mo, Zr, Nb, Ta, etc. is added, the coercive force is improved, the productivity is improved, and the cost is reduced. Can be planned. In this case, the amount added is preferably 3% by weight or less based on the total weight of the transition metal (T).

Examples of the rare earth-iron-nitrogen magnet powder that are particularly preferable as the magnet alloy powder of the present invention include Sm-Fe-N. In particular, it is more preferable that the amount of Sm is 23.2 to 23.6% by weight based on the entire magnet powder.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples. The characteristic values of the obtained rare earth-iron-nitrogen magnet powder were measured by the following method.

(1) Magnetic characteristics The magnetic characteristics of the rare earth-iron-nitrogen magnet alloy powder are based on the Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005, and an orientation magnetic field of 1600 kA / m. A sample in which rare earth-iron-nitrogen magnet powder was oriented in stearic acid was prepared, and magnetized with a magnetic field of 4000 kA / m for measurement.
Using a vibrating sample magnetometer with a maximum magnetic field of 1200 kA / m without demagnetizing field correction, the specific gravity of the magnet alloy powder is 7.67 g / cm ³ , saturation magnetization: 4πIm (T), coercive force: iHc (kA). / M), Squareness: Hk (kA / m) was measured. Hk represents the angularity of the demagnetization curve, and is the magnitude of the demagnetizing field when the magnetization 4πI takes 90% of the residual magnetization 4πIr in the second quadrant.

(2) Particle shape The particle surface shape and cross section of the rare earth-iron-nitrogen magnet powder before crushing were observed with a scanning electron microscope (SEM: Carl Zeiss, ULTRA55).

(3) Particle size distribution The average particle size was measured by a laser diffraction type particle size distribution measuring device manufactured by Symbolec: Heros Rhodes.
The particle major axis particle size corresponds to the measured particle size by magnifying the photograph taken by 1000 times the particle size of the primary particles from the SEM image and measuring the major axis particle size with a ruler with a minimum scale of 1 mm. The cumulative number of primary particles having a major axis particle diameter of 4 μm or more was determined from the total number of particles and the number of particles having a particle size of 4 μm or more.

(4) Calculation of product ratio of hydrogen-reduced product In the second step, data obtained by X-ray diffraction measurement of the reduced mixture powder obtained by hydrogen-reducing the dry mixed powder using a powder X-ray diffractometer is obtained. Based on this, the produced compounds were identified, and the ratio of each compound was determined by calculating a semi-quantitative value using a Rietbelt analysis for the abundance ratio of those compounds.

(5) Chloride ion concentration The chloride ion concentration was measured by using anion chromatography. After the oxide powder was dispersed in water, it was centrifuged, and the elution chlorine concentration was measured using the supernatant.

(Example 1)
[First step]
As the raw material powder for magnets, 100.0 g of iron oxide Fe ₂ O ₃ powder (Fe purity 99%) produced from nitrate and having an average particle size of 0.7 μm and powder having a particle size of 0.1 to 10 μm are 96 of the whole. 31.8 g of samarium oxide Sm ₂ O ₃ powder (Sm ₂ O ₃ purity 99.5%) accounting for% was weighed. Next, iron oxide weighed in a 500 cc plastic container was dispersed in 130 g of isopropyl alcohol to form a slurry, and then samarium oxide was further added, and a metal ball having a diameter of 5/32 inch made of SUJ2 was added thereto. Ball mill mixing was performed for 24 hours.
Then, the slurry was discharged from the plastic container, separated from the metal balls, and then dried in a stationary vacuum dryer at 40 ° C. for 20 hours. As shown in Table 1, the mixed powder had a total chlorine ion concentration of less than 0.01% by weight.

[Second step]
100.0 g of the dried mixed powder was charged into a box-type atmosphere furnace, hydrogen was flowed at 25 ml / (min · g), heated to 600 ° C. at a heating rate of 5 ° C./min, held for 4 hours, and then kept at room temperature. The hydrogen reduction product was recovered by gradually replacing the inside with air.
A part of the hydrogen-reduced product at this time was identified by XRD, and its abundance ratio was calculated as a semi-quantitative value by Rietveld analysis. The abundance ratio at this time was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 68.6: 30.8: 0.6 (% by weight).

[Third step]
To 16 g of this hydrogen-reduced product, 3.6 g of metallic calcium particles (Ca purity 99%) having a particle size of 4 mesh (Tyler mesh) or less was added and mixed with a conditioning mixer (MX-201: manufactured by Shinky) for 30 seconds.
This is inserted into a stainless steel reaction vessel, the inside of the vessel is evacuated with a rotary pump to replace Ar gas, the temperature is raised to 950 ° C while flowing Ar gas, and after holding for 8 hours, Ar gas is kept in the furnace to 250 ° C. Was cooled while circulating.

[Fourth step]
Next, the Ar gas was switched to an ammonia-hydrogen mixed gas having an ammonia partial pressure of 0.33 to raise the temperature, held at 450 ° C. for 200 minutes, then switched to hydrogen gas at the same temperature and held for 30 minutes, and further. It was switched to nitrogen gas and held for 30 minutes to cool.

[Fifth step]
When the removed porous mass reaction product mass was immediately put into pure water, it collapsed to obtain a slurry. From this slurry, a Ca (OH) ₂ suspension was separated by decantation, pure water was poured, and the mixture was stirred for 1 minute, and then decantation was repeated 5 times to obtain an alloy powder slurry.
Dilute acetic acid was added dropwise to the obtained alloy powder slurry with stirring, and the mixture was kept at pH 5.0 for 7 minutes. After filtering the alloy powder, it is washed with water several times with ethanol and vacuum dried at 35 ° C., and then Sm-Fe-N consisting of primary particles and grape-like secondary particles obtained by sintering the primary particles. A magnet alloy powder was obtained.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.2% by weight, N3.33% by weight, O0.17% by weight, and the balance Fe.
This Sm-Fe-N magnet alloy powder was crushed in ethanol using a vibrating ball mill at 5/32 inches of SUJ2 balls at a frequency of 30 Hz for 30 minutes and vacuum dried at room temperature.

<Magnetic characteristics>
The magnetic characteristics of the obtained Sm-Fe-N magnet alloy powder were subjected to saturation magnetization: 4πIm (T) according to the above measurement method using a vibration sample type magnetic field meter with a maximum magnetic field of 1200 kA / m without demagnetizing field correction. , Cohesive force: iHc (kA / m), Squareness: Hk (kA / m) were measured.
The X-ray density of the powder calculated from the analytical composition and the lattice constant of the Th ₂ Zn _17- type crystal structure was 7.67 g / cm ³ , and the saturation magnetic flux density of 4πIm was converted by this value. iHc is a coercive force. Hk represents the angularity of the demagnetization curve, and is the magnitude of the demagnetizing field when the magnetization 4πI takes a value of 90% of 4πIr in the second quadrant.
The results are shown in Table 2, and 4πIm = 1.42T, iHc = 889kA / m, and Hk = 413kA / m, and high characteristics were obtained.

<Particle surface texture, aggregated state, coarse particles>
Moreover, when the particle surface texture was confirmed by SEM as shown in FIG. 1 (left), a smooth surface state was observed, and agglomerates and coarse particles were hardly observed.

<Particle cross-section observation>
When the particle cross section was observed by SEM as shown in FIG. 1 (right), there was no residual iron and the inside of the particle was uniformly nitrided. Here, in the reflected electron image, the contrast is black when there is residual iron, and the contrast is slightly white when nitriding is insufficient, so that it can be clearly judged.

<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 1.6% as shown in Table 1.

(Example 2)
Under the conditions of Example 1, Fe ₂ O ₃ having an average particle size of 0.9 μm starting from chloride was used as an iron compound as a powder, mixed and dried by a ball mill, and then roasted at 800 ° C. in the air. After that, it was changed to perform reduction heat treatment with hydrogen. Except for this, when the same procedure as in Example 1 was carried out, as shown in Table 1, the total chloride ion concentration of the mixed powder before hydrogen reduction was 0.09% by weight, and it was present after hydrogen reduction. The ratio was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 67.2: 27.5: 5.3 (% by weight).
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles and grape-like secondary particles in which the primary particles were sintered were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.4% by weight, N3.35% by weight, O0.16% by weight, and the balance Fe.

<Magnetic characteristics>
After crushing in the same manner as in Example 1, sampling was performed to determine the magnetic characteristics.
The results are shown in Table 2, and 4πIm = 1.40T, iHc = 865kA / m, and Hk = 409kA / m, and high characteristics were obtained.
<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 4.2% as shown in Table 1.

(Example 3)
As a magnet raw material powder, and iron oxide _Fe 2 _{O 3} powder 100.0g of an average particle diameter of chloride departure 0.9 .mu.m, samarium oxide Sm ₂ having a particle size accounts for 96% of the total 0.1~10μm powder O ₃ powder 31.8g was weighed and then slurried by dispersing the iron oxide was weighed C. in plastic container 500cc of pure water 130 g. At this time, since the pH is 2.3, calcium oxide (Kanto Chemical Co., Inc.) is added as a powder to adjust the pH to 8.1, and then samarium oxide is further added to this, and the diameter is 5/32 inch made by SUJ2. The metal balls of the above were added, and the ball mill was mixed and dried for 24 hours.
The obtained mixed powder initially had a chlorine ion concentration of 0.18% by weight, but by roasting this mixed powder under the conditions of Example 2 (roasting at 800 ° C. in the air), Table 1 shows. As shown, after reducing the chlorine ion concentration to 0.07% by weight, further hydrogen reduction was performed. The abundance ratio of the mixed powder after hydrogen reduction was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 67.6: 28.3: 4.1 (% by weight).
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles and grape-like secondary particles obtained by sintering the primary particles were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.3% by weight, N3.33% by weight, O0.15% by weight, and the balance Fe. The magnetic characteristics were measured by sampling after crushing in the same manner as in Example 1. The results are shown in Table 2, and 4πIm = 1.41T, iHc = 880kA / m, and Hk = 410kA / m, and high characteristics were obtained.

<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 3.5% as shown in Table 1.

(Comparative Example 1)
In the production conditions of Example 2, iron oxide Fe ₂ O ₃ powder having an average particle size starting from chloride of 0.9 μm is used, except that the mixed powder before hydrogen reduction is reduced without roasting. This was done in the same manner as in Example 2. As shown in Table 1, the mixed powder before hydrogen reduction has a high total chloride ion concentration of 0.21% by weight, and the abundance ratio of SmFeO ₃ is α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 63. The ratio was 0.0: 16.8: 20.2 (% by weight), and the amount of SmFeO ₃ produced was larger than that in the examples.
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles, grape-like secondary particles obtained by sintering the primary particles with each other, and other coarse primary particles were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.3% by weight, N3.31% by weight, O0.16% by weight, and the balance Fe.

<Magnetic characteristics>
After crushing in the same manner as in Example 1, sampling was performed to determine the magnetic characteristics. The results are shown in Table 2, and the results were 4πIm = 1.35T, iHc = 706kA / m, and Hk = 322kA / m.
<Particle surface texture, aggregated state, coarse particles>
Further, as shown in FIG. 2 (left), in Comparative Example 1, when the particle surface texture was confirmed by SEM, the surface condition was smooth due to weak pulverization, but agglomerates and coarse particles were slightly observed. ..
<Particle cross-section observation>
As shown in FIG. 2 (right), when the particle cross section was observed by SEM, residual iron and coarse particles were also found. Here, in the reflected electron image, if there is residual iron, the contrast appears black, so it can be clearly judged.
<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 12.5% as shown in Table 1.

(Comparative Example 2)
Under the production conditions of Example 2, the roasting temperature before hydrogen reduction was lowered to 400 ° C. to reduce the chlorine concentration of the mixed powder before hydrogen reduction, and the total chlorine ion concentration was 0.13. The procedure was carried out in the same manner as in Example 2 except that the weight was set to%. The abundance ratio after hydrogen reduction was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 66.8: 26.3: 6.9 (% by weight).
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles, grape-like secondary particles obtained by sintering the primary particles with each other, and other coarse primary particles were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.5% by weight, N3.34% by weight, O0.17% by weight, and the balance Fe.

<Magnetic characteristics>
The magnetic properties were determined by sampling after crushing in the same manner as in Example 1. The results are shown in Table 2, and the results were 4πIm = 1.38T, iHc = 790kA / m, and Hk = 390kA / m.
<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 5.8% as shown in Table 1.

(Comparative Example 3)
Under the production conditions of Example 3, the mixed powder was mixed and dried with a ball mill, and the mixed powder before hydrogen reduction was reduced to hydrogen without roasting. The mixed powder is the same as in Example 3 except that the total chlorine ion concentration is 0.18% by weight. The abundance ratio of the mixed powder after hydrogen reduction was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 64.7: 21.0: 14.3 (% by weight).
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles, grape-like secondary particles obtained by sintering the primary particles with each other, and other coarse primary particles were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.4% by weight, N3.32% by weight, O0.17% by weight, and the balance Fe.

<Magnetic characteristics>
The magnetic properties were determined by sampling after crushing in the same manner as in Example 1. The results are shown in Table 2, and the results were 4πIm = 1.37T, iHc = 726kA / m, and Hk = 367kA / m.
<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 9.0% as shown in Table 1.

(Comparative Example 4)
In the production conditions of Example 2, Fe ₂ O ₃ and Sm ₂ O ₃ were used as raw material compounds, and at the time of initial powder mixing, wet mixing was not performed, but dry mixing was performed using a Julia mixer (manufactured by Tokuju Kosakusho). Other than that, when hydrogen reduction was performed using the conditions of Example 2, the chlorine concentration in the mixed powder before hydrogen reduction was 0.25% by weight in total of the chlorine ion concentration, and the abundance ratio after hydrogen reduction. Was α-Fe: Sm ₂ O ₃ : SmFeO ₃ = 61.3: 12.5: 26.2 (% by weight).
Then, under the same conditions as in Example 1, reduction diffusion, nitriding treatment, and wet treatment were performed to obtain a sm-Fe-N magnet alloy crude powder. In the obtained powder, primary particles, grape-like secondary particles obtained by sintering the primary particles with each other, and other coarse primary particles were observed.
The composition of this Sm-Fe-N magnet alloy powder was Sm23.4% by weight, N3.33% by weight, O0.16% by weight, and the balance Fe.

<Magnetic characteristics>
The magnetic properties were determined by sampling after crushing in the same manner as in Example 1. The results are shown in Table 2, and the results were 4πIm = 1.32T, iHc = 693kA / m, and Hk = 310kA / m.
<Particle surface texture, aggregated state, coarse particles>
Further, as shown in FIG. 3 (left), in Comparative Example 4, when the particle surface texture was confirmed by SEM, the surface condition was smooth due to weak pulverization, but agglomerates and coarse particles were slightly observed. ..
<Particle cross-section observation>
As shown in FIG. 3 (right), when the particle cross section was observed by SEM, non-uniform diffusion of Sm into the Fe particles was confirmed due to the effect of dry mixing, and the inside of the Fe particles was uniformly nitrided. Coarse particles were also found. Here, in the reflected electron image, the contrast is black when there is residual iron, the contrast is slightly white when the nitriding is insufficient, and white when Sm is more than the main phase Sm ₂ Fe ₁₇ Nx. I was able to make a clear decision.
<Presence ratio of semimajor particle diameter of 4 μm or more>
Further, as a result of calculating the abundance ratio of the semimajor axis particle diameter of 4 μm or more from the crushed magnet powder by the cumulative number percentage, it was 14.1% as shown in Table 1.

"Evaluation"
From Table 1 and 2 shows the above results, in Example 1, as a starting material iron compound, using the iron oxide Fe ₂ O ₃ powder produced from nitrates, In Example 2, as a starting material iron compound, chloride Iron oxide Fe ₂ O ₃ powder produced from a product was used, but after mixing the raw material compounds, iron reduction was performed after reducing the chlorine ion concentration of the mixed powder by roasting in the air. The amount of iron rare earth composite oxide RFeO ₃ (R is a rare earth element) produced was suppressed to 0.1% by weight or less. As a result, the Sm-Fe-N magnet alloy powder obtained by the reduction / diffusion treatment was observed to have a smooth surface state, almost no agglomerates or coarse particles were observed, and the magnetic properties were saturated magnetization and coercive force. It can be seen that both, and squareness have high characteristics.

On the other hand, Comparative Examples 1 to 4 are examples in which iron oxide Fe ₂ O ₃ powder starting from chloride was used as the raw material iron compound, and Comparative Examples 1 and ₃ in which wet mixing was performed were roasted before hydrogen reduction. However, in Comparative Example 2, roasting was performed before hydrogen reduction, but the chlorine concentration before hydrogen reduction could not be reduced because the roasting temperature was as low as 400 ° C. Since the chlorine concentration before hydrogen reduction was high in all cases, a large amount of SmFeO ₃ was produced by hydrogen reduction, and the Sm-Fe-N magnet alloy powder obtained by the reduction diffusion treatment contained many coarse primary particles. It has also been confirmed that there are particles in which nitriding has not progressed to the inside of the particles, and as a result, deterioration of the overall magnetic properties has been confirmed.

As described above, these results show that when the chlorine concentration in the raw material mixture exceeds 0.1% by weight in total of the chlorine ion concentration, the chlorine combined with hydrogen during hydrogen reduction becomes hydrogen chloride and is generated at the same time. It dissolves in the steam to form hydrochloric acid gas, which dissolves the raw material compound Sm ₂ O _3, and the resulting Sm compound is then reprecipitated as fine crystals and reacts with Fe or Fe ₂ O ₃ to form an iron rare earth complex oxidation. It promotes the formation of SmFeO ₃ which is a compound, and when a large amount of iron rare earth composite oxide SmFeO ₃ is present in this reduction mixture powder, it is locally very large during the reduction and diffusion treatment using an alkaline earth metal in the next step. It is considered that the rare earth-iron alloy became coarser particles because heat was generated and local grain growth was caused.

Further, Comparative Example 4 is a case where the raw material compound is dry-mixed instead of wet-mixed, but the non-uniform mixing of Fe ₂ O ₃ and Sm ₂ O ₃ , which is a drawback of dry mixing, has an effect. In addition, since Fe ₂ O ₃ starting from chloride is used as the raw iron compound, the chlorine concentration in the raw material mixture before hydrogen reduction is high, and a large amount of SmFe O ₃ is produced by hydrogen reduction, and the next step It is probable that the heat generated in the iron led to the generation of coarse particles, resulting in the lowest magnetic properties.

The rare earth-iron-nitrogen magnet obtained by the manufacturing method of the present invention can be used as a compacted magnet as it is, or as an inexpensive bond magnet mixed with a binder resin, and is widely used for consumer or industrial parts. Will be done.

Claims (9)

A method for producing a rare earth-iron-nitrogen magnet powder, which comprises a step of nitriding a rare earth-iron mother alloy powder obtained by the reduction diffusion method.
An iron compound powder and rare earth compound powder of the magnet raw material, wet mixed treated with water or an organic solvent and then filtered to remove the magnet material from processing liquid and dried, a first step of obtaining a mixed powder,
The pre-Symbol mixed powder was heat-treated in a hydrogen stream, a second step of obtaining a reduced mixture powder,
Was added before Symbol reduced mixture powder alkaline earth to the metal, and mixed in an inert gas atmosphere, after heat treatment at a temperature of from 900 to 1,180 ° C., cooling the reaction product obtained in the same atmosphere The third step of obtaining a rare earth-iron base alloy by
Before SL earth - the reaction product comprising an iron-based matrix alloy, supplying a mixed gas containing at least ammonia and hydrogen were produced by nitriding treatment by heat treatment in the mixed gas flow rare earth - iron - nitrogen A fourth step of obtaining a nitriding product mass containing a system magnet coarse powder, and
Next, the obtained nitriding product mass containing the rare earth-iron-nitrogen magnet coarse powder was put into water and wet-treated to disintegrate, and the obtained rare earth-iron-nitrogen magnet crude powder was crushed. And the fifth step to obtain rare earth-iron-nitrogen magnet powder,
Have a,
The total concentration of chloride ions eluted in the mixed powder when dispersed in water is 0.1% by weight or less with respect to the mixture powder.
The abundance ratio of the rare earth iron composite oxide RFeO ₃ (R is a rare earth element) in the reduction mixture powder is 6% by weight or less.
A method for producing a rare earth-iron-nitrogen magnet powder. The rare earth-iron-nitrogen magnet coarse powder obtained by the production method of claim 1 is a mixed powder composed of secondary particles obtained by gathering a plurality of primary particles and sintering them into a grape shape, and primary particles. A method for producing a rare earth-iron-nitrogen magnet powder, characterized in that the cumulative number percentage of primary particles having a major axis particle diameter of 4 μm or more is less than 5%. The method for producing a rare earth-iron-nitrogen magnet powder according to claim 1 or 2, wherein the rare earth-iron-nitrogen magnet powder is Sm-Fe-N. The method for producing a rare earth-iron-nitrogen magnet powder according to any one of claims 1 to 3, wherein the amount of Sm is 23.2 to 23.6% by weight based on the total amount of the magnet powder. The iron compound in the first step is one or more selected from iron oxide, iron oxyhydroxide, and iron hydroxide, and the rare earth compound is one or more selected from rare earth oxides and rare earth hydroxides. The method for producing a rare earth-iron-nitrogen magnet powder according to any one of claims 1 to 4, wherein the rare earth-iron-nitrogen magnet powder is produced. In the wet mixing treatment of the first step, a test in which either the iron compound powder or the rare earth compound powder is dispersed in water is performed in advance, and when the aqueous solution shows acidity, an organic solvent is used as the solvent, while the aqueous solution is used. The method for producing a rare earth-iron-nitrogen magnet powder according to any one of claims 1 to 5, wherein when water is alkaline, water or an organic solvent is used as the solvent. The method for producing a rare earth-iron-nitrogen magnet powder according to any one of claims 1 to 6, wherein the temperature range of the heat treatment in the second step is 500 to 800 ° C. Claims 1 to 3.0 characterized in that the amount of alkaline earth metal in the third step is 1.1 to 3.0 equivalents, where 1 equivalent is an amount sufficient to reduce the amount of unreduced oxygen. The method for producing a rare earth-iron-nitrogen magnet powder according to any one of 7 . The rare earth according to any one of claims 1 to 8, wherein the crushing in the fifth step is performed with a crushing strength for crushing grape-like secondary particles and a crushing strength for which the primary particle mass is not crushed. A method for producing iron-nitrogen magnet powder.