CN115376773A

CN115376773A - Rare earth iron-nitrogen-based magnetic powder, composite for bonded magnet, and method for producing rare earth iron-nitrogen-based magnetic powder

Info

Publication number: CN115376773A
Application number: CN202210517893.1A
Authority: CN
Inventors: 杉本谕; 松浦昌志; 石川尚; 米山幸伸
Original assignee: Tohoku University NUC; Sumitomo Metal Mining Co Ltd
Current assignee: Tohoku University NUC; Sumitomo Metal Mining Co Ltd
Priority date: 2021-05-18
Filing date: 2022-05-12
Publication date: 2022-11-22
Also published as: JP2022177699A

Abstract

A magnetic powder containing a rare earth element (R), iron (Fe) and nitrogen (N) as main constituent components, having an average particle diameter of 1.0 to 10.0 [ mu ] m, containing the rare earth element (R) in an amount of 22.0 to 30.0 mass%, and containing the nitrogen (N) in an amount of 2.5 to 4.0 mass%, the magnetic powder comprising: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion of any one of the crystal structures of type crystal; to be provided withAnd a shell layer having a thickness of 1nm or more and 30nm or less, provided on the surface of the core portion, the shell layer containing a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 or more and 5.0 or less, and further containing nitrogen (N) in an amount of more than 0 atomic% and 10 atomic% or less.

Description

Rare earth iron-nitrogen-based magnetic powder, composite for bonded magnet, and method for producing rare earth iron-nitrogen-based magnetic powder

Technical Field

The present invention relates to a rare earth iron-nitrogen-based magnetic powder, a composite for bonded magnets, a bonded magnet, and a method for producing the rare earth iron-nitrogen-based magnetic powder.

Background

Rare earth iron nitrogen series having Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type TbCu ₇ R of a crystal structure of the form ₂ Fe ₁₇ N _x The (R is a rare earth element) nitride compound has many coercivity generation mechanisms of a nucleation (nucleation) type, and is widely known as a magnetic material having excellent magnetic properties. Wherein the rare earth element (R) is samarium (Sm) and x =3 Sm ₂ Fe ₁₇ N ₃ The magnetic powder as the main phase compound is a high-performance magnetic powder for permanent magnets. Bonded magnets containing the magnetic powder and further containing a thermoplastic resin such as polyamide 12 or ethylene ethyl acrylate as a binder, or a thermosetting resin such as an epoxy resin or an unsaturated polyester resin are used in many applications.

As a compound of Sm ₂ Fe ₁₇ N ₃ As a method for producing a typical rare earth iron-nitrogen-based magnetic powder, a dissolution method and a reduction diffusion method are known. In the dissolution method, a rare earth metal is used as a raw material, and is dissolved and reacted together with a metal such as iron to prepare a magnetic powder. In contrast, in the reduction diffusion method, a rare earth oxide is used as a raw material, and the raw material is reduced and reacted with a metal such as iron to obtain a magnetic powder. Since inexpensive rare earth oxides can be used, the reduction diffusion method is considered to be a preferred method.

In addition, the rare earth iron-nitrogen-based magnetic powder has a disadvantage of poor heat resistance (oxidation resistance). If the powder has poor heat resistance, the magnetic properties are degraded by heating in the kneading/molding step in the production of the bonded magnet. In addition, the bonded magnet may be exposed to a high temperature of 100 ℃ or higher during use, and the magnetic properties may be degraded during such use. In order to solve these problems, it has been proposed to improve the heat resistance of a rare earth iron-nitrogen-based magnetic powder by replacing a part of iron (Fe) with another element, reducing the proportion of fine powder, or forming an oxidation-resistant coating on the surface of the powder.

For example, patent document 1, non-patent document 1, and non-patent document 2 propose to improve heat resistance and oxidation resistance by replacing a part of iron (Fe) with manganese (Mn) in a rare earth iron-nitrogen-based magnetic powder produced by a dissolution method or a reduction diffusion method. That is, patent document 1 discloses a magnetic material represented by the general formula R _α Fe _{(100-α-β-γ)} Mn _β N _γ (wherein 3. Ltoreq. Alpha. Ltoreq.20,0.5. Ltoreq. Beta. Ltoreq.25, 17. Ltoreq. Gamma. Ltoreq.25) and has an average particle size of 10 μm or more, and describes that Sm, fe and Mn are dissolved and mixed in a high-frequency melting furnace to prepare an alloy, and the alloy is subjected to a heat treatment in an ammonia mixed gas stream to prepare Sm-Fe-Mn-N-based powder having excellent oxidation resistance and temperature characteristics (claim 1 of patent document 1, item [0048 ]]～[0050]Section and [0070 ]]Segment). Further, non-patent document 1 or non-patent document 2 describes that Sm in which Mn is substituted for a part of Fe is used for a magnet powder produced by a reduction diffusion method ₂ (Fe，Mn) ₁₇ N _x (x > 4) magnet powder, with Sm ₂ Fe ₁₇ N ₃ The magnet powder exhibits excellent heat resistance compared to the magnet powder (page 881 of non-patent document 1).

Patent document 2 discloses a method for producing a rare earth-transition metal-nitrogen-based magnet alloy powder, including: a step (a) of pulverizing a master alloy containing a rare earth metal (R) and a Transition Metal (TM); a step (b) of mixing a rare earth oxide powder and a reducing agent with the crushed master alloy powder and performing a heat treatment in an inert gas; a step (c) of embrittling/pulverizing the obtained reaction product; a step (d) of nitriding the obtained reaction product powder to obtain a magnet alloy powder; and (e) a step (e) of washing the obtained magnet alloy powder with water, and it is described that the magnet alloy powder is easy to handle in the air because the magnet alloy powder has very few fine particles smaller than 1 μm, and becomes a magnet material excellent in heat resistance and weather resistance (claim 1 and paragraph [0025] of patent document 2).

Patent document 3 discloses a method for producing a rare earth-iron-nitrogen-based magnet powder for a bonded magnet, which includes a step of pulverizing a coarse rare earth-iron-nitrogen-based magnet powder in an organic solvent containing phosphoric acid, and describes that the magnet powder is added to phosphoric acid and treated to form a phosphate coating on the surface thereof in order to improve the weather resistance of the magnet (claim 1 and paragraph [0002] of patent document 3). Patent document 4 discloses a rare earth bonded magnet comprising an anisotropic rare earth alloy magnetic powder having a surface-coated metal layer and a resin, wherein Sm — Fe — N alloy magnetic powder produced by a reduction diffusion method is treated with Zn vapor to obtain a magnetic powder having a Zn coating layer of 0.05 μm on the surface, and further discloses a bonded magnet which can suppress demagnetization for a long time under high temperature conditions of about 180 ℃ or higher and can obtain high performance and heat resistance which have not been achieved in the past (claim 1, paragraph [0068], and paragraph [0071] of patent document 4).

Patent document 5 describes that a rare earth-transition metal alloy powder is produced by a reduction diffusion reaction method, and the reduction product after the heat treatment is subjected to hydrogen treatment, and the reduction product after the hydrogen treatment is naturally disintegrated only by exposure to the atmosphere, so that the time for the water washing separation step can be shortened, and further pulverization can be omitted (claim 1 and [0011] of patent document 5). Patent document 6 describes that a rare earth-transition metal alloy powder is produced by a reduction diffusion method, a reduction diffusion reaction product is charged into a closed container and subjected to a hydrogen treatment, a pressure higher than atmospheric pressure is set to self-heat the alloy, and then the pressure is continued so as to be higher than atmospheric pressure until the alloy substantially does not heat (claims 1 and 3 of patent document 6).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. H08-055712;

patent document 2: japanese patent laid-open publication No. 2005-272986;

patent document 3: japanese patent No. 5071160;

patent document 4: japanese patent laid-open No. 2003-168602;

patent document 5: japanese patent laid-open publication No. 11-124605;

patent document 6: japanese patent laid-open publication No. 2005-008950.

Non-patent document

Non-patent document 1: journal of electrical society, journal a,124 (2004) 881;

non-patent document 2: proc.12th int.Workshop on RE magnetics and the hair Applications, canberra, (1992) 218.

Disclosure of Invention

In a wide range of fields including general household appliances, communication/audio equipment, medical equipment, general industrial equipment, and the like, there is an increasing demand for a rare earth element-containing iron-based bonded magnet in which a magnet powder is mixed with a resin binder and molded. In addition, storage and transportation of the material for the bonded magnet, and conditions for using the product have become severe. Therefore, there is a need for a magnetic powder for bonded magnets that has more excellent heat resistance and high characteristics such as coercivity.

However, the techniques proposed in the past are not sufficient. For example, in the methods of patent document 1, non-patent document 1, and non-patent document 2 in which manganese (Mn) is used in place of part of iron (Fe), although the heat resistance of the magnetic powder is improved, there is a problem that the magnetization is reduced. Actually, patent document 1 shows that the saturation magnetization of the magnetic material (example 1) having an Mn content of 3.5 atomic% is 84emu/g, whereas the saturation magnetization of the magnetic material (example 4) having an Mn content increased to 10.3 atomic% is reduced to 72emu/g (patent document 1 [0069 ]]Segment table 1). Further, non-patent document 1 describes Sm ₂ (Fe，Mn) ₁₇ In the N compound, the Curie temperature T is increased with an increase in the amount of Mn _c And maximum magnetization σ _m Monotone decrease (the first of non-patent document 1)Page 885). In addition, although the methods of reducing the proportion of fine powder and the methods of forming an oxidation-resistant coating on the surface of the powder disclosed in patent documents 2 to 4 have some effects, there is still room for improvement in heat resistance.

The present inventors have made an attempt to solve the problem of rare earth iron-nitrogen (R) having a nucleation-type mechanism for generating coercivity ₂ Fe ₁₇ N ₃ ) The above-mentioned problems in the magnetic powder have been studied with great attention. The results gave the following insights: by forming a compound having R ₂ Fe ₁₇ N ₃ The compound phase acts as the main volume part (core part) of the interior and also has a ratio R ₂ Fe ₁₇ N ₃ The phase rich in the rare earth (R) serves as a core-shell structure of the surface layer (shell layer) of the particles, and thus magnetic powder having both high heat resistance and magnetic properties can be obtained.

The present invention has been made based on such findings, and an object thereof is to provide a rare earth iron-nitrogen-based magnetic powder having excellent heat resistance and magnetic properties, and a method for producing the same. Another object of the present invention is to provide a composite for bonded magnets containing a rare earth iron-nitrogen-based magnetic powder, and a bonded magnet.

Means for solving the problems

The present invention includes the following aspects (1) to (14). In this specification, the expressions "to" include numerical values at both ends thereof. For example, "a to b" has the same meaning as "a or more and b or less".

(1) A magnetic powder comprising a rare earth element (R), iron (Fe) and nitrogen (N) as main components, wherein,

the magnetic powder has an average particle diameter of 1.0 to 10.0 [ mu ] m, contains a rare earth element (R) in an amount of 22.0 to 30.0 mass%, contains nitrogen (N) in an amount of 2.5 to 4.0 mass%,

the magnetic powder is provided with: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion having any one of crystal structures of the type crystal structures; and a thickness of 1nm or more provided on the surface of the core portionAnd a shell layer of 30nm or less,

the shell layer contains a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen (N) in an amount of more than 0 to 10 atomic%,

the magnetic powder comprises compound particles composed of rare earth element (R) and phosphorus (P), and has residual magnetization σ _r Is 90Am ² More than/kg.

(2) The magnetic powder according to the above (1), wherein the shell layer is formed of a two-layer structure consisting of an outer layer and an inner layer,

the outer layer contains oxygen (O) and calcium (Ca) in addition to rare earth elements (R), iron (Fe) and nitrogen (N),

the inner layer contains oxygen (O) in addition to rare earth elements (R), iron (Fe), and nitrogen (N), but does not contain calcium (Ca).

(3) The magnetic powder according to (2) above, wherein the shell layer is formed of a two-layer structure consisting of an outer layer and an inner layer,

the R/Fe atomic ratio (A) of the outer layer and the R/Fe atomic ratio (B) of the inner layer satisfy B < A.

(4) The magnetic powder according to any one of the above (1) to (3), which contains samarium (Sm) as the rare earth element (R).

(5) The magnetic powder according to any one of (1) to (4) above, further comprising a phosphoric acid-based compound coating film on an outermost surface of the magnetic powder.

(6) The magnetic powder according to any one of the above (1) to (5), wherein the coercivity (H) after heating is obtained by heating at 300 ℃ for 1 hour in an argon (Ar) atmosphere _c，300 ) Coercive force (H) before heating _c ) Retention ratio of (H) _c，300 /H _c ) Is more than 70%.

(7) A composite for a bonded magnet, comprising the magnetic powder according to any one of the above (1) to (6) and a resin binder.

(8) A bonded magnet comprising the magnetic powder according to any one of the above (1) to (6) and a resin binder.

(9) A method for producing the rare earth iron-nitrogen-based magnetic powder according to any one of the above (1) to (6), comprising the steps of:

a preparation step of preparing a composition having Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type TbCu ₇ A rare earth iron alloy powder and a rare earth oxide powder having any of the crystal structures;

a mixing step of mixing 1 to 20 parts by mass of the rare earth oxide powder with 100 parts by mass of the rare earth iron alloy powder to prepare a raw material mixture containing a rare earth iron alloy powder having a particle size of 15.0 μm or less and a rare earth oxide powder having a particle size of 2.0 μm or less;

a reduction diffusion treatment step of adding a reducing agent to the raw material mixture in an amount of 1.1 to 10.0 times an equivalent amount required for reducing an oxygen component contained in the raw material mixture, mixing the mixture, and further heating the raw material mixture to which the reducing agent is added in a non-oxidizing atmosphere at a temperature in a range of 730 to 1050 ℃ to prepare a reduction diffusion reaction product;

a disintegration treatment step of subjecting the reduction-diffusion reaction product to a disintegration treatment by exposing the reduction-diffusion reaction product to a hydrogen atmosphere at a temperature of not more than 300 ℃ to allow the reduction-diffusion reaction product to absorb hydrogen; and

a nitriding heat treatment step of subjecting the reduction-diffusion reaction product subjected to the disintegration treatment to a nitriding heat treatment in a gas flow containing nitrogen and/or ammonia at a temperature in the range of 300 to 500 ℃ to produce a nitriding reaction product,

in any one or both of the preparation step and the mixing step, a phosphate compound coating is formed in the rare earth iron alloy powder.

(10) The method according to (9) above, wherein, in the mixing step, a rare earth iron alloy powder and a rare earth oxide powder are mixed and pulverized in a pulverization solvent containing a phosphoric acid-based surface treatment agent, and a phosphoric acid-based compound film is formed in the rare earth iron alloy powder.

(11) The method according to (9) or (10) above, further comprising: and a step of performing a wet treatment for reducing the content of the reducing agent in the product by putting the reduction diffusion reaction product and/or the nitridation reaction product into a washing liquid containing water and/or glycol and disintegrating the product.

(12) The method according to any one of the above (9) to (11), further comprising: and forming a phosphoric acid compound coating film on the surface of the product after the nitriding heat treatment.

(13) The method according to any one of the above (9) to (12), wherein a heating loss of the raw material mixture is less than 1% by mass.

(14) The method according to any one of the above (9) to (13), wherein the heating treatment for producing the diffusion reaction product is performed for 0 to 10 hours.

Effects of the invention

The present invention provides a rare earth iron-nitrogen-based magnetic powder having excellent heat resistance and magnetic properties, and a method for producing the same. Further, the present invention provides a composite for bonded magnet containing a rare earth iron-nitrogen-based magnetic powder, and a bonded magnet.

Drawings

Fig. 1 shows an example of a schematic cross-sectional view of a magnetic powder.

Fig. 2 shows an SEM secondary electron image of the magnetic powder.

Fig. 3 shows a HAADF-TEM image of the magnetic powder.

Fig. 4 is a line extraction graph showing the EDS surface analysis results of the magnetic powder.

Fig. 5 shows the XRD spectrum of the magnetic powder.

Fig. 6 shows SEM reflection electron images of the magnetic powder.

Detailed Description

A specific embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.

Magnetic powder of rare earth element Fe-N system

The rare earth iron nitrogen-based magnetic powder of the present embodiment (hereinafter, collectively referred to as "magnetic powder" in some cases) contains a rare earth element (R), iron (Fe), and nitrogen (N) as main constituent components. The magnetic powder has an average particle diameter of 1.0-10.0 [ mu ] m, contains a rare earth element (R) in an amount of 22.0-30.0 mass%, and contains nitrogen (N) in an amount of 2.5-4.0 mass%. The magnetic powder is provided with: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion of any one of the crystal structures of type crystal; and a shell layer which is provided on the surface of the core portion and has a thickness of 1nm to 30 nm. The shell layer contains a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen (N) in an amount of more than 0 to 10 at%, and the magnetic powder further contains compound particles composed of the rare earth element (R) and phosphorus (P). Further, the residual magnetization σ of the magnetic powder _r Is 90Am ² More than/kg.

The rare earth element (R) is not particularly limited, and preferably contains at least one element selected from the group consisting of lanthanum (La), cerium (Ce), samarium (Sm), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), and terbium (Tb). Alternatively, it is preferable to further contain at least one element selected from the group consisting of dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). Among them, samarium (Sm) and/or neodymium (Nd) are particularly preferable because the effects of the present embodiment are remarkably exhibited. In the case of application to a bonded magnet, samarium (Sm) is preferably contained in an amount of 50 atomic% or more, and neodymium (Nd) is preferably contained in an amount of 50 atomic% or more in the case of application to a high-frequency magnetic material.

The magnetic powder may contain other components than the rare earth element (R), iron (Fe), and nitrogen (N). For example, cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr) may be contained. However, nickel (Ni), manganese (Mn), and chromium (Cr) are preferably contained in as small an amount as possible, because they risk lowering the magnetization. When the other components excluding the rare earth element (R), iron (Fe), and nitrogen (N) are contained, the content thereof is preferably 10 at% or less, more preferably 5 at% or less, and still more preferably 1 at% or less. However, the cobalt (Co) may be 20 atomic% or less. The magnetic powder may also contain rare earth elements (R), iron (Fe), and nitrogen (N), with the balance being unavoidable impurities.

The average particle diameter of the magnetic powder of the present embodiment is 1.0 μm or more and 10.0 μm or less. When the average particle diameter is less than 1.0. Mu.m, handling of the magnetic powder becomes difficult. In addition, the volume ratio of the core portion to the entire particle becomes small. Since the magnetic properties of the core portion are high, when the volume ratio thereof is reduced, the magnetic properties of the magnetic powder become difficult to improve. The average particle diameter may be 2.0 μm or more, or 3.0 μm or more. On the other hand, when the average particle diameter is larger than 10 μm, it is difficult to obtain a sufficiently high coercive force (H) as a magnetic material _c ). The average particle diameter may be 9.0 μm or less, or 8.0 μm or less.

The magnetic powder of the present embodiment contains the rare earth element (R) in an amount of 22.0 mass% or more and 30.0 mass% or less. When the rare earth element (R) in the composition of the entire magnetic powder is less than 22 mass%, the coercive force is lowered. On the other hand, if the amount is more than 30% by mass, the shell layer having low magnetization becomes thick, and the compound particles (RP compound particles) composed of the rare earth element (R) and the phosphorus (P) and the RFe become thick ₃ The nitride phase increases. Thus, the remanent magnetization (. Sigma.) _r ) And decreases. The amount of the rare earth element (R) is preferably 24.0 mass% or more and 29.0 mass% or less, and more preferably 25.0 mass% or more and 28.0 mass% or less.

In addition, the magnetic powder of the present embodiment contains nitrogen (N) in an amount of 2.5 mass% or more and 4.0 mass% or less, and when the amount of nitrogen (N) is less than 2.5 mass%, insufficiently nitrided particles are formed. Since the saturation magnetization and magnetic anisotropy of such particles are small, the residual magnetization and coercive force of the magnetic powder are reduced. On the other hand, when the amount of nitrogen (N) is more than 4.0 mass%, excessively nitrided particles increase, and the residual magnetization and coercive force decrease. The amount of nitrogen (N) is preferably 2.8 mass% or more and 3.6 mass% or less, and more preferably 2.9 mass% or more and 3.4 mass% or less.

Further, this embodiment modeThe magnetic powder of (1) comprises: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion of any of the crystal structures of the type crystal structures. By providing the core portion having such a crystal structure, a magnetic powder having excellent magnetic properties can be obtained. The crystal structure of the core part can be determined from the peak position obtained by ordinary powder X-ray diffraction. In this case, the shell layer is included and measured, but the thickness of the shell layer is sufficiently thinner than that of the core portion. Therefore, the influence of the shell layer is hardly seen in the X-ray diffraction pattern.

The magnetic powder of the present embodiment has a shell layer provided on the surface of the core portion. The shell layer has a thickness of 1nm to 30nm, contains a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen (N) in an amount of more than 0 atomic% and 10 atomic% or less. By providing such shell layers on the surface portions of particles (core portions) having an average particle diameter of 1 to 10 μm, both heat resistance and magnetic properties can be achieved. Here, it is presumed that the shell layer formed has become R than ₂ Fe ₁₇ N ₃ R phase and RFe phase rich in rare earth elements ₂ Phase, RFe ₃ Equal or a nitride of these. When R/Fe is less than 0.3, the composition of the shell layer approaches that of the core portion, and improvement of heat resistance cannot be expected. On the other hand, when R/Fe is larger than 5.0, residual magnetization may be lowered. R/Fe is preferably 0.5 to 3.0. When the thickness of the shell layer is less than 1nm, the effect of improving heat resistance is small, and when the thickness is more than 30nm, the residual magnetization intensity is reduced. The thickness is preferably 3nm or more and 20nm or less. If the shell layer does not contain nitrogen, the residual magnetization, coercive force, and heat resistance of the magnetic powder may decrease. On the other hand, even if the nitrogen content of the shell layer is more than 10 atomic%, the residual magnetization, coercive force, and heat resistance of the magnetic powder are reduced.

The magnetic powder of the present embodiment includes compound particles (RP compound particles) composed of a rare earth element (R) and phosphorus (P). Here, the RP compound particles contain a phosphated rare earth phase such as samarium phosphide (SmP). RP compound having an RFe inhibiting effect on deterioration of coercive force and heat resistance ₂ Phase, RFe ₃ The formation of phasesThe application is as follows. Therefore, by including the RP compound particles in the magnetic powder, deterioration in coercivity and heat resistance can be suppressed. The amount of the RP compound particles is not particularly limited. However, from the viewpoint of suppressing deterioration, the amount of the RP compound particles in the magnetic powder may be 0.01 mass% or more, 0.1 mass% or more, or 1.0 mass% or more. On the other hand, when the RP compound particles are too large, the residual magnetization may decrease. The amount of the RP compound particles may be 15.0 mass% or less, 10.0 mass% or less, or 5.0 mass% or less. The size of the particles of the RP compound is not limited, but is, for example, about 100nm to 5 μm.

Residual magnetization σ of the magnetic powder of the present embodiment _r Is 90Am ² More than/kg. In other words, the amount of α -Fe as a hetero-phase in the magnetic powder is small. When a large amount of α -Fe is contained in the magnetic powder, the magnetic characteristics of the magnetic powder are deteriorated. That is, since α -Fe is soft magnetic, when it is contained in a large amount, the squareness of the magnetization curve of the magnetic powder is deteriorated. When squareness is deteriorated, not only the remanent magnetization is decreased but also the retention rate of coercive force, that is, heat resistance is decreased. In addition, α — Fe functions as a diamagnetic field generating nucleus, and thus the coercive force of the particle is lowered. Since the magnetic powder of the present embodiment has a small amount of α -Fe, the remanent magnetization σ is used _r The magnetic properties are excellent. Sigma _r May be 95Am ² /kg or more, and may be 100Am ² /kg or more, and may be 105Am ² 110Am or more per kg ² More than/kg. Note that the remanent magnetization σ _r The measurement was performed in a state where the magnetic powder was oriented. Specifically, the measurement was carried out by the method carried out in the examples described later.

The magnetic powder preferably has a shell layer having a two-layer structure consisting of an outer layer and an inner layer. More preferably, the outer layer contains oxygen (O) and calcium (Ca) in addition to the rare earth element (R), iron (Fe), and nitrogen (N), and the inner layer contains oxygen (O) in addition to the rare earth element (R), iron (Fe), and nitrogen (N), but does not contain calcium (Ca). The structure of such a magnetic powder will be described with reference to fig. 1. FIG. 1 shows the magnetism in phantomAn example of a schematic cross-sectional view of a powder. The magnetic powder (1) is composed of a core (2), a shell inner layer (3) provided on the surface of the core (2), and a shell outer layer (4) provided on the surface of the shell inner layer (3). The core part (2) has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ Crystal structure of any of forms. The outer shell layer (4) contains calcium (Ca), whereas the inner shell layer (3) does not contain calcium (Ca). As described above, the effect of suppressing oxygen diffusion is expected by providing a two-layer structure of the outer layer containing Ca and the inner layer containing no Ca. In the present specification, the term "free of calcium (Ca) (Ca-free) means that the amount of Ca is less than 1.0 atomic%.

For the magnetic powder, it is preferable that the R/Fe atomic ratio (A) of the outer layer and the R/Fe atomic ratio (B) of the inner layer satisfy B < A. As described above, by making the composition of the outer layer richer in rare earth elements (R) than that of the inner layer, the effect of suppressing oxygen diffusion similar to that of Ca is expected.

Preferably, the magnetic powder contains samarium (Sm) as the rare earth element (R). Thereby, the magnetic powder can be suitably used as a bonded magnet.

The magnetic powder preferably further has a phosphoric acid-based compound coating on the outermost surface thereof. When a known phosphate compound coating is provided on the outer side of the shell layer of the magnetic powder, the stability in a humid environment can be improved. The thickness of the phosphate compound coating is preferably smaller than the thickness of the shell layer. For example, the thickness is 30nm or less, preferably 5nm or more and 20nm or less. When the thickness of the phosphate compound coating film is more than 30nm, the magnetic properties may be degraded.

For magnetic powders, the coercive force (H) _c ) May be 600kA/m or more, 800kA/m or more, 1000kA/m or more, 1200kA/m or more, or 1400kA/m or more. Further, the retention ratio (H) of the coercive force for the magnetic powder _c，300 /H _c ) May be 70% or more, may be 75% or more, may be 80% or more, may be 85% or more, or may be 90% or more. Here, the retention ratio of coercive force (H) _c，300 /H _c ) The magnetic powder was heated at 300 ℃ for 1.5 hours (90 minutes) in an argon (Ar) atmosphere, and then the resultant was heatedCoercive force (H) of (2) _c，300 ) Relative to coercive force (H) before heating _c ) The ratio of (a) to (b).

The magnetic powder of the present embodiment is characterized by having excellent magnetic properties, particularly magnetization and coercive force, in addition to excellent heat resistance and weather resistance. Namely, the magnetic powder is mixed with Sm ₂ Fe ₁₇ N ₃ Typical conventional magnetic powders have higher heat resistance than conventional magnetic powders. In addition, high heat resistance R obtained by substituting a part of iron (Fe) with other elements (Mn, cr) ₂ (Fe，M) ₁₇ N _x The magnetic powder (M = Cr, mn) has magnetic properties equal to or higher than those of the magnetic powder.

The magnetic powder of the present embodiment, which is excellent in heat resistance and magnetic properties, is preferably used when it is mixed with a resin binder to produce a bonded magnet. That is, when a bonded magnet is produced using a magnetic powder, the magnetic powder is sometimes exposed to high temperatures. For example, when a bonded magnet is produced using a highly heat-resistant thermoplastic resin such as a polyphenylene sulfide resin or an aromatic polyamide resin as a binder, the exposure temperature of the material may be higher than 300 ℃ in the mixing and kneading step or the injection molding step of the magnetic powder and the resin binder. The magnetic powder of the present embodiment suppresses deterioration of magnetic properties even after exposure to such a high temperature.

Method for producing rare earth iron-nitrogen-based magnetic powder

The method for producing the rare earth iron-nitrogen-based magnetic powder is not limited as long as the obtained magnetic powder satisfies the above requirements. However, it is preferably produced by a reduction diffusion method, and particularly preferably produced by the method described below.

The method for producing a rare earth iron-nitrogen-based magnetic powder according to the present embodiment includes the steps of: a preparation step of preparing a composition having Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type TbCu ₇ A rare earth iron alloy powder and a rare earth oxide powder having any of the crystal structures; a mixing step of mixing 1 to 20 parts by mass of a rare earth oxide powder with 100 parts by mass of the rare earth iron alloy powder to obtain a mixture containing a rare earth iron alloy powder having a particle size of 15.0 μm or less and a rare earth iron alloy powder having a particle size of 2.0 μm or lessA raw material mixture of earth oxide powders; a reduction diffusion treatment step of adding a reducing agent to the raw material mixture in an amount of 1.1 to 10.0 times the equivalent weight required for reducing the oxygen component contained in the raw material mixture, mixing the mixture, and further heating the raw material mixture to which the reducing agent is added in a non-oxidizing atmosphere at a temperature in the range of 730 to 1050 ℃ to produce a reduction diffusion reaction product; a disintegration treatment step of exposing the reduction-diffusion reaction product to a hydrogen gas atmosphere at a temperature of not more than 300 ℃ to allow the reduction-diffusion reaction product to absorb hydrogen, thereby subjecting the reduction-diffusion reaction product to disintegration treatment; and a nitriding heat treatment step of subjecting the reduction-diffusion reaction product subjected to the disintegration treatment to a nitriding heat treatment in a gas flow containing nitrogen and/or ammonia at a temperature in the range of 300 to 500 ℃ to produce a nitriding reaction product. In addition, in either or both of the preparation step and the mixing step, a phosphate compound coating is formed in the rare earth iron alloy powder. The details of each step will be described below.

< preparation Process >

In the preparation step, a rare earth iron alloy powder and a rare earth oxide powder are prepared. Here, the rare earth ferroalloy powder is a material mainly used for forming the core part and has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type TbCu ₇ A powder of any one of the crystal structures of the forms, e.g. R ₂ Fe ₁₇ The composition of the powder. The rare earth iron alloy powder may be selected so as to have a particle size of 15.0 μm or less in the subsequent mixing step. That is, a powder having a particle diameter of 15.0 μm or less may be used, or a powder having a particle diameter of more than 15.0 μm may be used. When the powder having a particle size of more than 15 μm is used, it may be pulverized in the mixing step so that the particle size is 15.0 μm or less. Note that, in this specification, the concept of an alloy includes not only a solid solution of a plurality of metals but also an intermetallic compound and a mixed crystal. The material may be crystalline or amorphous.

Rare earth iron alloy powder (R) ₂ Fe ₁₇ Powder, etc.) can be produced by a known method, for example, a reduction diffusion method, a melt-casting method, a liquid quenching method, or the like. In the case of using the reduction-diffusion method, the alloy powder having a desired particle diameter can be directly produced by adjusting conditions such as the size of iron particles as a raw material and the temperature during the reduction-diffusion reaction. Alternatively, the starting material composed of alloy powder or alloy nuggets having a larger particle size may be pulverized to a desired particle size.

In addition, the rare earth iron alloy powder produced by the reduction diffusion method contains hydrogen in the intermetallic compound to become a hydrogen-containing compound (R) depending on the production conditions ₂ Fe ₁₇ H _x Powder, etc.) of a rare earth iron alloy containing hydrogen. The hydrogen-containing compound may be mixed with a rare earth iron alloy (R) ₂ Fe ₁₇ ) Does not change compared to the crystal structure of (a), but the lattice constant increases. In addition, even in the case of production by the melt casting method or the liquid quenching method, the alloy powder which is crushed while storing hydrogen may be a hydrogen-containing compound having a large lattice constant. The alloy powder does not interfere even in such a hydrogen-containing state. However, the water content (loss on heating) of the rare earth iron alloy powder is preferably less than 1% by mass.

The rare earth oxide powder is a raw material mainly used for forming a shell layer. The rare earth element (R) constituting the rare earth oxide powder may be the same as or different from the rare earth element constituting the rare earth iron alloy powder. However, both are preferably the same. The rare earth oxide powder may be selected so as to have a particle size of 2.0 μm or less in the subsequent mixing step. That is, a powder having a particle size of 2.0 μm or less may be used, or a powder having a particle size of more than 2.0 μm may be used. When the powder having a particle size of more than 2.0 μm is used, it may be pulverized to a particle size of 2.0 μm or less in the mixing step.

< mixing Process >

In the mixing step, 1 to 20 parts by mass of a rare earth oxide powder is mixed with 100 parts by mass of the prepared rare earth iron alloy powder to obtain a raw material mixture. When the amount of the rare earth oxide powder is less than 1 part by massIn this case, the rare earth metal alloy powder (R) is subjected to a reduction diffusion treatment described later ₂ Fe ₁₇ Powder, etc.) generates α -Fe on the surface, and the coercivity of the finally obtained magnetic powder is lowered. On the other hand, when the amount of the rare earth oxide powder is more than 20 parts by mass, RFe rich in rare earth (R) is generated in a large amount compared with the rare earth iron alloy ₃ And/or RFe ₂ The yield of the compound, the magnetic powder finally obtained, is reduced.

In the production method of the present embodiment, a phosphate compound coating is formed in the rare-earth iron alloy powder in either or both of the preparation step and the mixing step. Therefore, the rare earth iron alloy powder in the mixture obtained in the mixing step has a phosphoric acid compound coating. For example, when the particle size of the prepared rare earth iron alloy powder is 15.0 μm or less, a phosphoric acid compound coating may be formed in advance in the alloy powder. Alternatively, in the present mixing step, a phosphoric acid-based compound coating may be formed on the rare earth iron alloy powder. In any case, the rare earth iron alloy powder in the mixture obtained in the mixing step may have a phosphoric acid compound coating. By providing the phosphoric acid-based compound coating film in this manner, the coercivity and heat resistance of the magnetic powder to be produced can be improved. That is, in the subsequent reduction diffusion reaction step, phosphorus (P) contained in the phosphoric acid-based compound coating film reacts with the remaining rare earth element (R), thereby precipitating compound particles (RP compound particles) composed of the rare earth element (R) and phosphorus (P). The RP compound particles inhibit coarse RFe which causes deterioration of coercive force and heat resistance of the magnetic powder ₂ Phase, RFe ₃ And (5) generating a phase. On the other hand, when a rare earth iron alloy powder not coated with a phosphoric acid compound is used, coarse RFe is generated separately from the shell layer ₂ Phase, RFe ₃ The phase may deteriorate the coercivity and heat resistance of the magnetic powder.

In order to form the phosphoric acid-based compound coating, the rare earth iron alloy powder may be subjected to a surface treatment using a phosphoric acid-based surface treatment agent. As the phosphoric acid-based surface treatment agent, a known compound disclosed in patent document 3 can be used. Specific examples thereof include phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, linear polyphosphoric acids, cyclic metaphosphoric acid, ammonium phosphate, magnesium ammonium phosphate, zinc phosphate series, zinc calcium phosphate series, manganese phosphate series, iron phosphate series, and the like. Phosphoric acid may be mixed with a chelating agent or a neutralizing agent as a treating agent.

The surface treatment may be performed by a known method. For example, when a film is formed in the preparation step, the rare earth iron alloy powder may be immersed in a solution containing a phosphoric acid-based surface treatment agent to form a film, and then solid-liquid separation may be performed to recover the rare earth iron alloy powder on which the film is formed. In the case where the coating film is formed in the mixing step, a pre-mixture of the rare earth iron alloy powder and the rare earth oxide powder may be immersed in a solvent containing a phosphoric acid-based surface treatment agent to form the coating film. In the case of forming the coating film, the rare earth iron alloy powder and/or the rare earth oxide powder may be pulverized in the solvent using a pulverizer such as a medium-stirring pulverizer. The kind of the solvent is not particularly limited. For example, organic solvents such as alcohols such as isopropyl alcohol, ethanol, and methanol, lower hydrocarbons such as pentane and hexane, aromatic hydrocarbons such as benzene, toluene, and xylene, ketones, and mixtures thereof can be used.

The formation of the phosphate compound coating may be performed by either or both of the preparation step and the mixing step. However, it is preferably carried out by a mixing process. In this case, it is preferable that the rare earth iron alloy powder and the rare earth oxide powder are mixed and pulverized in a pulverization solvent containing a phosphoric acid-based surface treatment agent to form a phosphoric acid-based compound coating film in the rare earth iron alloy powder. That is, when the rare earth iron alloy powder is pulverized, a new surface appears. If a coating is formed in the mixing step, a coating can be provided also on a new surface appearing in the mixing step. In addition, the mixing, pulverization, and coating formation of the raw material powders (rare earth iron alloy powder, rare earth oxide powder) can be performed collectively at one time, contributing to reduction in production cost.

The optimum coating amount of the phosphoric acid-based compound coating film depends on the particle size and surface area of the rare earth iron alloy powder, and therefore cannot be determined in a short time. However, when the coating is formed using a solvent containing a phosphoric acid-based surface treatment agent, the amount of phosphoric acid can be set to 0.1 to 0.5mol/kg with respect to the entire rare earth iron alloy powder.

The raw material mixture obtained in the mixing step contains a rare earth iron alloy powder having a phosphate compound coating and a particle size of 15.0 μm or less and a rare earth oxide powder having a particle size of 2.0 μm or less. That is, the maximum particle diameters of the rare earth iron alloy powder and the rare earth oxide powder contained in the raw material mixture are 15.0 μm or less and 2.0 μm or less, respectively. The rare earth iron alloy powder is a raw material to be a core of the magnetic powder. The grain size of the alloy powder is only about the grain size (1.0 μm or more and 10.0 μm or less) of the magnetic powder at the maximum, considering the amount of grain growth, aggregation and sintering, and shell formation by the subsequent reduction diffusion heat treatment. Therefore, the particle size of the alloy powder in the raw material mixed powder is set to 15.0 μm or less. In addition, the rare earth oxide powder is preferably a fine powder in order to form a shell layer uniformly with a desired thickness. Therefore, the particle diameter of the oxide powder in the raw material mixed powder is 2.0 μm or less. The particle diameter of the oxide powder is preferably 1.5 μm or less, more preferably 1.0 μm or less. The particle size can be easily confirmed using a Scanning Electron Microscope (SEM).

In the mixing step, the mixing operation of the rare earth iron alloy powder and the rare earth oxide powder is important. In order to provide a uniform shell layer, it is preferable to uniformly disperse the rare earth oxide powder while making the particle size as small as possible. The mixing may be performed by either a dry method or a wet method. Dry mixing using a henschel Mixer, a flow Mixer (CONPIX, 1246712531125001246312494), a mechanical Mixer (michano Hybrid, 125131245912594125125125125125941251249542, 124124125521241259412542, a mechanical fusion machine (mecano fusion, 1251312459124941251250112512512512512512512512512512512540729, 125125125125125125125125125125125125125125125125019), a precision Mixer (nobelta, 1249499125992312412512579; \\ 1245295, (1250212480\\ 1245276125409 (12519\\12471124731248612512), MIRALO (125111252112512525125; \1247112579\\ 1246712509125091254054) or dry mixers (Spartan Mixer, 1247312497\\12523124125791251251251251251251251251251251251). Wet mixing is carried out using a bead mill, ball mill, nano homogenizer (NanoMizer, 1249412494, 12470125400, 124124124781247840), wet cyclone, homogenizer, vertical disperser (DISSOLVER, 1248712451781249612540), high speed mixer (FILMIX, 125011245112523125231241252312463.

When the rare earth iron alloy powder and the rare earth oxide powder are mixed, these can be simultaneously finely pulverized to a desired particle size. In this case, the phosphate compound coating film can be formed during the fine grinding. By adding rare earth oxide powder and finely pulverizing at the same time, a uniform mixture can be obtained. As the fine grinding, a dry grinder such as a jet mill, a wet fine grinder such as a vibration grinder, a rotary ball mill, or a medium agitation grinder can be used. For wet micro-pulverization, organic solvents such as lower hydrocarbons such as ketones and hexane, aromatic hydrocarbons such as toluene, alcohols such as ethanol and isopropanol, fluorine-based inactive liquids, or mixtures thereof can be used as the pulverization medium. Alternatively, the formation of a phosphate compound coating film can be performed during the micro-pulverization by using, as a pulverization medium, an organic solvent to which a phosphate surface treatment agent such as orthophosphoric acid is added. This method is preferable because a phosphoric acid compound coating is formed on the pulverized rare-earth iron alloy powder, and the rare-earth oxide powder is finely pulverized and uniformly dispersed. In the wet method, the organic solvent may be dried and removed from the slurry after the fine pulverization to obtain a raw material mixture.

The heating loss of the raw material mixture is preferably less than 1 mass%. The heating loss is an amount of impurities contained in the dried mixed powder, and is mainly water. In addition, carbon may be contained depending on the kind of the organic solvent, the dispersion aid, or the treatment process used in the mixing. When the heating loss is more than 1 mass%, a large amount of water vapor or carbonic acid gas may be generated in the subsequent reduction-diffusion treatment. When water vapor or carbonic acid gas is generated in a large amount, they oxidize the reducing agent (Ca particles, etc.) and suppress the reduction diffusion reaction. As a result, α -Fe, which is undesirable in obtaining excellent magnetic characteristics, is generated in the finally obtained magnetic powder. Therefore, the raw material mixture is preferably sufficiently dried under reduced pressure. This removes not only the moisture contained therein but also the carbon sufficiently. The heating loss was determined by measuring the loss α when a 50g sample was heated at 400 ℃ for 5 hours in vacuum.

< reduction diffusion treatment Process >

In the reduction diffusion treatment step, a reducing agent is added to and mixed with the obtained raw material mixture, and the raw material mixture to which the reducing agent is added is further subjected to a heating treatment to obtain a reduction diffusion reaction product. Here, the amount of the reducing agent added is an amount of 1.1 to 10.0 times the equivalent amount necessary for reducing the oxygen component contained in the raw material mixture. The heat treatment is performed in a non-oxidizing atmosphere at a temperature in the range of 730 to 1050 ℃.

As the reducing agent, at least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and hydrides thereof can be used. Among them, calcium (Ca) is particularly useful. The reducing agent is often supplied in the form of particles. Reducing agents having a particle size of 0.5 to 3.0mm are preferably used.

The amount of the reducing agent (Ca particles, etc.) added is 1.1 to 10.0 times the equivalent weight. Here, the equivalent weight means an amount necessary for reducing oxygen components in the raw material mixture, that is, oxygen and the rare earth oxide powder contained in the rare earth iron alloy powder. When the amount of addition is less than 1.1 times, the reduction of the oxide becomes insufficient, and therefore, diffusion of the rare earth element (R) generated by the reduction becomes difficult. On the other hand, when the amount of addition is more than 10 times, the reducing agent remains excessively, which is not preferable. The large amount of residual reducing agent may inhibit diffusion of the rare earth element (R). In addition, the amount of residue generated by the reducing agent increases, and it takes time to remove the residue.

In the mixing step, it is preferable to uniformly mix the raw material mixture and the reducing agent (Ca particles and the like). As mixers, a V blender, S blender, ribbon mixer, ball mill, henschel mixer, mechanical fusion machine (Mechanofusion, 12513\\\124941250112517125409; \\ 12494991252379), a Hybridization system (hybridizate system, 1245212502124801241245276125711259, 125112412512412571861251251251251251251251251251251251251251251253. It is preferable to mix them uniformly, and particularly, to mix them with the rare earth iron alloy powder as the raw material so that the rare earth oxide powder does not segregate. This is because segregation of the rare earth oxide powder causes variation in the thickness of the shell layer.

Next, the raw material mixture to which the reducing agent is added is subjected to a heating treatment to obtain a reduction-diffusion reaction product. For example, the heat treatment may be performed as follows. That is, the obtained mixture was charged into an iron crucible, and the crucible was placed in a reaction vessel and set in an electric furnace. From the mixing to the installation in the electric furnace, contact with the atmosphere or water vapor is preferably avoided as much as possible. In order to remove the air or water vapor remaining in the mixture, it is preferable to evacuate the reaction vessel and replace it with an inert gas such as helium (He) or argon (Ar).

Next, the inside of the reaction vessel is evacuated again, and the mixture is subjected to a reduction diffusion treatment in a non-oxidizing atmosphere while introducing an inert gas such as helium (He) or argon (Ar) into the vessel. It is important that the heat treatment is performed under a temperature condition in the range of 730 to 1050 ℃. When the temperature is less than 730 ℃, the rare earth oxide is reduced by a reducing agent (Ca particles or the like) which turns into vapor, but it is difficult to perform reduction on the rare earth iron alloy powder (R) ₂ Fe ₁₇ Powder, etc.) forms a shell layer by a diffusion reaction. Therefore, it is not desirable to improve the heat resistance of the finally obtained magnetic powder. On the other hand, when it exceeds 1050 ℃, grain growth or aggregation and sintering of the magnetic powder progress, and the residual magnetization or coercive force decreases. The heat treatment temperature is preferably 750 to 1000 ℃.

The heating holding time and the heating temperature may be set together in order to suppress grain growth, aggregation, and sintering of the finally obtained magnetic powder. For example, the temperature is maintained for 0 to 10 hours under the set temperature condition. When it exceeds 8 hours, grain growth or aggregation and sintering sometimes become remarkable, and it becomes difficult to obtain a magnetic powder having a target average particle diameter of 1 μm or more and 10 μm or less. The holding time may be 0 to 8 hours, 0 to 5 hours, or 0 to 3 hours. The retention time "0 hour" means that the sample is cooled immediately after the set temperature is reached.

By such heat treatment, the alloy is formed to have Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core part of a rare earth iron alloy having any of crystal structures of the type crystal structures, and a shell layer formed by a diffusion reaction of a reduced rare earth element (R). The shell layer contains a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen (N) in an amount of more than 0 atomic% and 10 atomic% or less. In addition, since the rare earth iron alloy powder is provided with the phosphoric acid-based compound coating, phosphorus (P) contained in the coating reacts with the remaining rare earth element (R) in the diffusion reaction by heating. As a result, compound particles (RP compound particles) composed of the rare earth element (R) and the phosphorus (P) are precipitated in the magnetic powder.

The rare earth iron-nitrogen-based magnetic powder has a nucleation-type coercivity generation mechanism. When a soft magnetic phase such as α -Fe or the like, or a crystal defect that reduces the magnetic anisotropy of crystal, or the like, is present on the particle surface, this becomes a nucleation (nucleation) for the diamagnetic region, thereby reducing the particle coercive force. The conventional magnetic powder has poor heat resistance due to decomposition of R by heating ₂ Fe ₁₇ N ₃ The compound phase generates a soft magnetic phase such as α -Fe or Fe nitride, which becomes a nuclei for generating a diamagnetic zone. In contrast, in the present embodiment, the heat resistance (oxidation resistance) of the magnetic powder is improved by forming a shell layer having an R/Fe atomic ratio of 0.3 or more and 5.0 or less on the surface. The reason for this is presumably because of the shell layer and R ₂ Fe ₁₇ N ₃ The compound is less likely to decompose by heating, as compared with the compound. In addition, for example, this effect can be advantageously obtained when the heat treatment conditions are set to two stages.

That is, in the step of the reduction diffusion treatment, the heating treatment conditions are set to two stages, and the temperature is maintained at 730 to 810 ℃ for 0.5 to 4 hours in the former stage and further increased to 800 to 1000 ℃ for 3 hours in the latter stageThe method can be used. Under these conditions, the rare earth oxide powder is sufficiently reduced to a rare earth metal, R ₂ Fe ₁₇ The rare earth iron alloy serves as a core portion, and the diffusion reaction of the rare earth element (R) is promoted on the surface thereof to form a shell layer.

The reaction product after the heat treatment is composed of rare earth iron alloy particles (R) having a shell layer on the surface ₂ Fe ₁₇ Powder, etc.), R metal, RFe ₃ And/or RFe ₂ A compound, RP compound particles, and a component derived from a reducing agent. Here, the component derived from the reducing agent is composed of by-produced reducing agent oxide particles (CaO and the like) and unreacted residual reducing agent (Ca and the like).

< Process of disintegration treatment >

In the disintegration treatment step, the product after the reduction diffusion treatment (reduction diffusion reaction product) is exposed to a hydrogen gas atmosphere at a temperature of not more than 300 ℃, and the reduction diffusion reaction product is caused to absorb hydrogen, thereby subjecting the reduction diffusion reaction product to disintegration treatment. In this manner, by exposing the product to a hydrogen atmosphere under a predetermined condition, the R metal and RFe contained in the product ₃ And/or RFe ₂ The compound absorbs hydrogen. At this time, the volume expands, and therefore, the product is disintegrated by the expansion. Inert gases such as argon, helium, and nitrogen may be mixed in hydrogen gas to perform the fragmentation treatment. However, it is preferred to work in a hydrogen only environment. In this case, in order to prevent oxygen from remaining, it is preferable to replace the atmosphere in the heating furnace with an inert gas such as argon before introducing hydrogen. In this case, it is preferable to once exhaust the furnace after the inert gas replacement and then introduce hydrogen gas.

The hydrogen absorption treatment (decomposition treatment) is started by heating the reduction-diffusion reaction product to a predetermined temperature, for example, 50 to 200 ℃ in a hydrogen atmosphere. The reaction product absorbs hydrogen with self-heating, which results in faster absorption. As a result of the absorption causing self-heating, the temperature of the reaction product is higher than the heating temperature. However, in this case, it is important to keep the temperature of the reaction product at 300 ℃ or lower. When the temperature of the reaction product is more than 300 ℃, heterogeneous α -Fe may remain in the magnetic powder as the final product. When α -Fe remains, the squareness of the magnetization curve deteriorates, and the residual magnetization of the magnetic powder decreases.

In order to keep the reaction product at a low temperature of 300 ℃ or lower, the partial pressure of hydrogen to the reaction product may be reduced to gradually absorb hydrogen. Examples of the method for reducing the hydrogen partial pressure include a method of reducing the amount of hydrogen to be supplied and a method of using a mixed gas of a hydrogen gas and an inert gas. Preferably, the hydrogen absorption treatment (the disintegration treatment) is performed under a negative pressure condition lower than atmospheric pressure by suppressing the amount of hydrogen supplied. Thereby easily maintaining the reaction product at a low temperature. In this regard, in the manufacturing methods disclosed in patent documents 5 and 6, the hydrogen absorption treatment is performed under atmospheric pressure conditions or under pressurized conditions. However, if the hydrogen absorption treatment is performed in an environment at atmospheric pressure or higher, the hydrogen absorption may be performed too quickly. Therefore, the temperature of the reaction product becomes high, which is higher than 300 ℃, and as a result, α -Fe sometimes remains in the magnetic powder. Actually, the present inventors have conducted investigations, and as a result, when the temperature of the reaction product is higher than 300 ℃, the residual magnetization of the finally obtained magnetic powder is low. α -Fe was observed in the XRD profile of the magnetic powder, and therefore, it was considered that the decrease in remanent magnetization was caused by the generated α -Fe.

< Heat treatment Process of nitriding >

In the nitriding heat treatment step, the product after the reduction diffusion treatment or the disintegration treatment (reduction diffusion reaction product) is subjected to nitriding heat treatment in a gas flow of a nitrogen and/or ammonia-containing gas to produce a nitriding reaction product. The nitriding heat treatment may be performed by a known method, and may be performed, for example, with nitrogen (N) ₂ ) Gas environment, nitrogen (N) ₂ ) Gas and hydrogen (H) ₂ ) Mixed environment of gas, ammonia (NH) ₃ ) Gas environment, ammonia (NH) ₃ ) Gas and hydrogen (H) ₂ ) Mixed environment of gas, ammonia (NH) ₃ ) Qi and nitrogen (N) ₂ ) Mixed gas environment of gas, ammonia (NH) ₃ ) Gas and nitrogen (N) ₂ ) Gas and hydrogen (H) ₂ ) The gas is carried out in a mixed gas environment.

The nitriding heat treatment is carried out at a temperature in the range of 300 to 500 ℃. When the heating temperature is less than 300 ℃, nitriding is not performed, and therefore, it is not preferable. If the temperature is more than 500 ℃, the alloy is decomposed into a nitride of a rare earth element and iron, which is not preferable. The heating temperature may be 350 ℃ or higher, or 400 ℃ or higher. The heating temperature may be 480 ℃ or lower, or 450 ℃ or lower.

The treatment time of the nitriding heat treatment may be determined by the type of gas, the flow rate of the gas, and the heating temperature. The smaller the gas flow rate and heating temperature (low), the longer the treatment time. Set to ammonia (NH) ₃ ) Gas and hydrogen (H) ₂ ) In the case of a gas mixture atmosphere, for example, the time is preferably 1 to 6 hours, more preferably 2 to 4 hours. In addition, nitrogen (N) is set ₂ ) In the case of a gaseous atmosphere, for example, it is preferably 10 to 40 hours, and the reaction is performed under a condition of being mixed with hydrogen (H) ₂ ) In the case of a gas-mixed atmosphere, it is preferably 5 to 25 hours. Recovering the cooled nitriding reaction product after the nitriding heat treatment. Further, the magnet powder may be heated in vacuum or in an inert gas atmosphere such as argon after the nitriding heat treatment, if necessary. This discharges nitrogen and hydrogen excessively introduced into the magnetic powder, thereby making the nitrogen distribution in the magnetic powder core portion more uniform. As a result, the squareness of the magnetic powder is improved.

< Wet processing step >

If necessary, a step (wet treatment step) of subjecting the product (reduction diffusion reaction product and/or nitriding reaction product) obtained in the reduction diffusion treatment step and/or nitriding heat treatment step to wet treatment may be provided. In the wet treatment, the reduction diffusion reaction product and/or the nitridation reaction product are put into a washing liquid containing water and/or glycol and disintegrated. This reduces the components derived from the reducing agent (by-product oxide particles of the reducing agent and unreacted residual reducing agent) in the product. The product is put into a washing liquid (water and/or glycol) and left for 0.1 to 24 hours, and then is finely disintegrated to be slurry. The pH of the slurry is about 10 to 12. The addition of the washing solution, stirring, and removal of the supernatant (decantation) were repeated until the pH became 10 or less. Then, acetic acid or the like is added as necessaryWeak acid until the pH of the slurry is 6-7 to dissolve and remove the reducing agent component (Ca (OH) of the hydroxide in the slurry ₂ Etc.). Including metal from R, RFe in the slurry ₃ And/or RFe ₂ In the case of the remaining nitrides of the compounds, the washing was continued with stirring while adding an acid in order to maintain the pH at 6 to 7, and these remaining nitrides were dissolved and removed. Then, the residual acid component is removed by washing with water and/or glycol, and further, after substitution with an alcohol such as methanol or ethanol, solid-liquid separation is performed and drying is performed. Drying by heating to 100-300 deg.C, preferably 150-250 deg.C in vacuum or inert gas atmosphere.

As the glycol, one or more alkylene glycols selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol can be used. Preference is given to using these diols and mixtures thereof directly. When the viscosity is high and it is difficult to separate and remove the reaction product and the reducing agent component after slurrying, a glycol diluted with water can be used. However, the water content in the washing liquid is preferably 50 mass% or less. Here, the water content is expressed as a percentage of the mass ratio of water/(glycol + water). When the water content is more than 50 mass%, the oxidation of the particles may become remarkable. The water content is more preferably 30% by mass or less, still more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The amount of the diol to be used is not particularly limited, and 2 to 10 times the equivalent amount of the diol to be reacted with the reducing agent component in the reaction product can be used. It is preferable to use a diol in an amount of 3 to 8 times the mass of the reaction product.

< Process for micronization >

If necessary, a step (fine-pulverization treatment step) of subjecting the product obtained in the nitriding heat treatment step and/or the wet treatment step to a pulverization/fine-pulverization treatment may be provided. Depending on the conditions of the reduction-diffusion treatment, the obtained powder sometimes sinters and causes necking. When the finally obtained magnetic powder is applied to an anisotropic magnet material, degradation of the orientation in the magnetic field of the magnetic powder due to necking can be prevented by disintegrating the powder. The pulverization can be carried out using a dry pulverizer such as a jet mill or a wet pulverizer such as a medium-stirring pulverizer. In any of the above-described crushers, it is preferable to operate under a weak crushing condition to such an extent that the necked portion is released so as to hold the shell layer while avoiding a crushing condition due to strong shearing or collision.

< Process for Forming coating film >

If necessary, a step (coating film forming step) of forming a phosphate compound coating film on the surface of the obtained product (powder) may be provided. In particular, when the magnetic powder is used in applications where the powder is used in a high-humidity environment, stability of powder characteristics can be improved by providing a phosphoric acid compound coating film. As disclosed in patent document 3, the kind of phosphate compound coating and the method for forming the same are known. In the present embodiment, the phosphate compound coating can be thinly provided in consideration of the shell layer. Since the magnetization may decrease when the thickness is larger than 20nm, a film having a thickness of about 5 to 20nm is preferable.

The magnetic powder of the present embodiment can be manufactured in this manner. The magnetic powder contains a rare earth element (R), iron (Fe), and nitrogen (N) as main constituent components, has an average particle diameter of 1.0 to 10.0 [ mu ] m, contains the rare earth element (R) in an amount of 22.0 to 30.0 mass%, and contains the nitrogen (N) in an amount of 2.5 to 4.0 mass%. Further, the magnetic powder includes: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion of any one of crystal structures of types; and a shell layer having a thickness of 1nm to 30nm provided on the surface of the core portion. The shell layer contains a rare earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen (N) in an amount of more than 0 atomic% and not more than 10 atomic%. The magnetic powder further contains compound particles (RP compound particles) composed of a rare earth element (R) and phosphorus (P). The magnetic powder has the effect of having not only excellent heat resistance and weather resistance but also excellent magnetic properties.

As far as the present inventors know, the magnetic powder of the present embodiment and the method for producing the same have not been known. For example, patent document 2 discloses a method for producing a rare earth-transition metal-nitrogen-based magnet alloy powder, which includes: a step (a) of pulverizing a master alloy containing a rare earth metal (R) and a Transition Metal (TM); and a step (b) of mixing the pulverized master alloy powder with a rare earth oxide powder and a reducing agent, and heating the mixture in an inert gas. However, unlike the production method of the present embodiment, patent document 2 does not use fine rare earth oxide powder having a particle size of 2.0 μm or less. Only the master alloy was pulverized, and then the rare earth oxide powder was mixed. Therefore, the method of patent document 2 cannot form a core-shell structure.

Patent document 3 discloses that a phosphate coating is formed by pulverizing a coarse rare earth-iron-nitrogen magnet powder in an organic solvent containing phosphoric acid. However, the target for forming the phosphate coating is the magnet powder after the nitriding treatment, not the rare earth iron alloy powder as the raw material. Therefore, it is significantly different from the manufacturing method of the present embodiment. In addition, patent document 3 does not use fine rare earth oxide powder having a particle size of 2.0 μm or less. Therefore, the method of patent document 3 cannot form a core-shell structure.

Patent document 4 discloses a rare earth bonded magnet comprising an anisotropic rare earth alloy-based magnetic powder having a surface-coated metal layer and a resin, wherein the metal of the surface-coated metal layer is a single metal or an alloy comprising at least one of Zn, sn, in, al, si, and rare earth elements (claims 1 and 2 of patent document 4). However, patent document 4 does not disclose or suggest that the surface-coated metal layer is a material completely different from the shell layer of the present embodiment and contains a rare earth element (R), iron (Fe), and nitrogen (N) so that the R/Fe atomic ratio is 0.3 or more and 5.0 or less.

< Compound for bonded magnet >

The composite for bonded magnets of the present embodiment includes the rare earth iron-nitrogen-based magnetic powder and a resin binder. The composite is prepared by mixing magnetic powder and a resin binder. The mixing may be carried out by using a Banbury mixer, a KNEADER, a roll, a kneading extruder (KNEADER-RUDER, \\12491, 12540125\\ 1248012540125, and a mixing machine such as a single-screw extruder or a twin-screw extruder, and the magnetic powder and the resin binder are melted and mixed to obtain the magnetic powder and the resin binder.

The resin binder may be any one of a thermoplastic resin and a thermosetting resin. The type of the thermoplastic resin-based adhesive is not particularly limited. Examples of the resin include polyamide resins such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 612, aromatic nylons and modified nylons obtained by partially modifying or copolymerizing these molecules, straight-chain polyphenylene sulfide resins, crosslinked polyphenylene sulfide resins, semi-crosslinked polyphenylene sulfide resins, low-density polyethylene, linear low-density polyethylene resins, high-density polyethylene resins, ultrahigh-molecular-weight polyethylene resins, polypropylene resins, ethylene-vinyl acetate copolymer resins, ethylene-ethyl acrylate copolymer resins, ionomer resins, polymethylpentene resins, polystyrene resins, acrylonitrile-butadiene-styrene copolymer resins, acrylonitrile-styrene copolymer resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl acetate resins, polyvinyl alcohol resins, polyvinyl butyral resins, polyvinyl formal resins, methacrylic resins, polyvinylidene fluoride resins, polychlorotrifluoroethylene resins, tetrafluoroethylene-hexafluoropropylene copolymer resins, ethylene-tetrafluoroethylene copolymer resins, tetrafluoroethylene-vinyl ether copolymer resins, polytetrafluoroethylene resins, polycarbonate resins, polyacetal resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polyphenylene oxide resins, polyphenylene ether terephthalate resins, polyphenylene ether sulfone resins, polyether ether ketone resins, polyether sulfone resins, and the like. Further, homopolymers of these, random copolymers with other monomers, block copolymers, graft copolymers, and resins obtained by modifying the terminal groups with other monomers may be mentioned. Examples of the thermosetting resin include unsaturated polyester resins and epoxy resins.

Among them, nylon 12 and modified nylon thereof, nylon-based elastomer, and polyphenylene sulfide resin are preferable from the viewpoint of various properties of the obtained molded article and easiness of the production method thereof. It is of course also possible to use mixtures of two or more of these thermoplastic resins.

In the present embodiment, sm is used as the conventional raw material powder ₂ Fe ₁₇ N ₃ The magnetic powder has high heat resistance compared with the magnetic powder, and has high heat resistance R ₂ (Fe，M) ₁₇ N _x The magnetic powder (M = Cr, mn) has magnetic properties equal to or higher than those of the magnetic powder. Since the magnetic powder has high heat resistance, it can be molded at high temperature using a thermoplastic resin such as polyphenylene sulfide resin or aromatic polyamide resin, which has high heat resistance of the resin itself, as a binder, and is therefore effective for producing a high-performance and high-heat-resistant bonded magnet.

The amount of the resin binder to be blended is not particularly limited, and is preferably 1 to 50 parts by mass per 100 parts by mass of the composite. When the amount is less than 1 part by mass, not only is the kneading torque significantly increased and the fluidity reduced, thereby making molding difficult, but also the magnetic properties may become insufficient. On the other hand, when the amount is more than 50 parts by mass, desired magnetic properties may not be obtained. The amount of the resin binder may be 3 to 50 parts by mass, 5 to 30 parts by mass, or 7 to 20 parts by mass.

Additives such as a reactive diluent, a non-reactive diluent, a thickener, a lubricant, a mold release agent, an ultraviolet absorber, a flame retardant, and various stabilizers, and a filler may be blended in the composite within a range not to impair the object of the present embodiment. In addition, other magnetic powder than the magnetic powder of the present embodiment may be blended according to the required magnetic characteristics. As the other magnet powder, magnet powder used in a general bonded magnet can be used, and examples thereof include rare earth magnet powder, ferrite magnet powder, alnico magnet powder, and the like. Not only anisotropic magnet powder but also isotropic magnet powder can be mixed, but preferably magnet powder having an anisotropic magnetic field HA of 4.0MA/m (50 kOe) or more is used.

< bonded magnet >

The bonded magnet of the present embodiment includes the rare earth iron-nitrogen-based magnetic powder and a resin binder. The bonded magnet is produced by subjecting the above-mentioned compound for bonded magnet to injection molding, extrusion molding or compression molding. A particularly preferred molding method is injection molding. The components and the content ratio thereof in the bonded magnet are the same as those in the bonded magnet composite.

When the composite for a bonded magnet is injection molded, the molding is preferably performed under conditions in which the maximum history temperature is 330 ℃ or lower, preferably 310 ℃ or lower, and more preferably 300 ℃ or lower. When the maximum history temperature is higher than 330 ℃, the magnetic properties may be degraded. However, the bonded magnet of the present embodiment has higher magnetic properties than the case of using conventional magnetic powder having no shell layer.

When the composite for bonded magnets contains anisotropic magnetic powder, an anisotropic bonded magnet can be produced by assembling the magnetic circuit into a mold of a molding machine and applying an orientation magnetic field to a molding space (mold cavity) of the composite. In this case, a bonded magnet having high magnetic properties can be obtained by setting the orientation magnetic field to 400kA/m or more, preferably 800kA/m or more. When the composite for a bonded magnet contains isotropic magnetic powder, the orientation may be performed without applying an orientation magnetic field to the molding space (mold cavity) of the composite.

The bonded magnet of the present embodiment is useful in a wide range of fields such as automobiles, general household appliances, communication/audio equipment, medical equipment, and general industrial equipment. In addition, according to the present embodiment, since the magnetic powder has high heat resistance and high magnetic characteristics, the magnetic powder can be subjected to powder compaction and sintering to manufacture a magnet. Therefore, a high-performance magnet without a binder can be obtained with reduced deterioration in coercive force.

Examples

The present invention is further illustrated in detail using the following examples. However, the present invention is not limited to the following examples.

(1) Evaluation of

In the production of the rare earth iron nitrogen-based magnetic powder, various properties were evaluated as follows.

< particle size of powder >

The powder was observed with a Scanning Electron Microscope (SEM) to evaluate the particle diameter. In the observation, in the SEM reflected electron image having a magnification of about 1000 times, each component particle was discriminated from a difference in contrast, and the major axis diameter was obtained as the particle diameter. In addition, a laser diffraction particle size distribution meter (HELOS, japan laser, ltd.) was used&RODOS) was calculated to find the 50% particle diameter (D) in the volume distribution of the powder ₅₀ ) This is referred to as the average particle diameter.

< heating decrement >

50g of the powder was heated at 400 ℃ for 5 hours in a vacuum, and the weight loss (. Alpha.) by heating was determined by comparing the mass before and after heating. Specifically, (mass before heating-mass after heating)/mass before heating is defined as heating loss (α).

< magnetic Property >

Measurement of magnetic characteristics (remanent magnetization σ) of powder Using vibrating sample magnetometer _r And coercive force H _c ). The measurement was carried out according to the bonded magnet test method guide BMG-2005 (Japan bonded magnetic materials Association). First, about 20mg of a powder sample was loaded into a case made of transparent acryl having an inner diameter of 2mm × a length of 7mm together with paraffin. The measurement sample was prepared by heating the case with a dryer while applying a magnetic field of 1.6MA/m in the longitudinal direction to melt the paraffin, orienting the powder, and then cooling and solidifying the paraffin. The magnetization field of the sample was 3.2MA/m.

< Heat resistance >

By comparing the coercive force (H) of the powder before and after heating _c ) The heat resistance of the powder was evaluated. The heating was performed under an argon (Ar) atmosphere at atmospheric pressure under conditions of 300 ℃x90 minutes. Measurement of coercive force (H) before heating _c ) And coercive force (H) after heating _c，300 ) The retention ratio (H) of coercive force was calculated _c，300 /H _c )。

< crystal structure of powder >

The crystal structure of the powder was evaluated by a powder X-ray diffraction (XRD) method. X-ray diffraction measurement was performed by scanning a Cu target at an acceleration voltage of 45kV and a current of 40mA at a speed of 2 θ of 2 min/deg. Subsequently, the obtained X-ray diffraction (XRD) spectrum was analyzed to identify the crystal structure.

< compositional analysis of the Shell layer, thickness >

The compositional analysis and the average thickness of the shell layer were evaluated using a transmission electron microscope (TEM; japanese Electron Co., ltd.; JEM-ARM200F; acceleration voltage 200 kV) and an EDS detector (Saimer Feishell science, NSS). In this case, a 100nm thick section chip prepared by embedding a powder in a thermosetting resin and processing the resin by a focused ion beam apparatus was used as an observation sample.

< composition of magnetic powder >

The rare earth (R) composition (amount) and the nitrogen (N) composition (amount) of the magnetic powder were analyzed by ICP emission spectroscopy and thermal conductivity method, respectively.

(2) Preparation of rare earth iron-nitrogen magnetic powder

Rare earth iron-nitrogen-based magnetic powders were prepared and evaluated for the properties of examples 1 to 9 and comparative examples 1 to 11. The production conditions and properties of the magnetic powder are shown in tables 1 and 2.

[ example 1]

< preparation Process >

Preparing Sm ₂ Fe ₁₇ Alloy powder samarium oxide (Sm) was prepared as a rare earth iron alloy powder ₂ O ₃ ) The powder was made into a rare earth oxide powder. Sm ₂ Fe ₁₇ The alloy powder (rare earth iron alloy powder) was prepared as follows.

Preparing the average particle diameter (D) ₅₀ ) Samarium oxide (Sm) of 2.3 μm ₂ O ₃ ) Powder, average particle diameter (D) ₅₀ ) 40 μm iron (Fe) powder and granular metallic calcium (Ca). Then, 0.44kg of samarium oxide powder, 1.0kg of iron powder, and 0.23kg of granular calcium metal were mixed by a mixer. The resultant mixture was placed in an iron crucible, and heat-treated under an argon (Ar) gas atmosphere at 1150 ℃ for 8 hours, thereby obtaining a reaction product.

The reaction product taken out after cooling was poured into 2L of water and left for 12 hours in an argon atmosphereAnd slurrying. After discarding the supernatant of the slurry, 2L of water was newly added and stirred, and the supernatant in which calcium hydroxide was suspended was discarded after the SmFe alloy powder settled. The operations of water addition, stirring and supernatant removal were repeated until the pH became 11 or less. Then, while stirring the alloy powder and 2L of water, acetic acid was added to a pH of 6, and after stirring was continued for 30 minutes in this state, the supernatant liquid was discarded. The operation of adding 2L of water and stirring was performed five times again and the supernatant was discarded, and finally, after replacing the water with alcohol, the alloy powder was recovered by using a suction filter. The recovered alloy powder was charged into a mixer, and stirred and dried under reduced pressure at 100 ℃ for 10 hours to obtain 1.3kg of Sm ₂ Fe ₁₇ Alloy powder (rare earth iron alloy powder). Obtained Sm ₂ Fe ₁₇ The average particle size of the alloy powder was 30 μm.

The obtained rare earth iron alloy powder had a composition of 24.5 mass% of samarium (Sm), 0.15 mass% of oxygen (O), 0.54 mass% of hydrogen (H), less than 0.01 mass% of calcium (Ca) and the balance of iron (Fe), and Th was ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ As the main phase.

< mixing Process >

100g of samarium oxide powder (rare earth oxide powder) was premixed in Sm obtained in preparation step by means of a tumbling mixer ₂ Fe ₁₇ 1kg of alloy powder (rare earth iron alloy powder). Average particle diameter (D) of samarium oxide powder used ₅₀ ) The thickness was 2.3. Mu.m. In addition, with respect to Sm ₂ Fe ₁₇ The amount of samarium oxide added was 10 parts by mass per 100 parts by mass of the alloy powder. A slurry was obtained by pulverizing the obtained premix with a media-stirring pulverizer using a mixed solution of 2.2kg of isopropyl alcohol and 23.1g of 85% phosphoric acid as a solvent.

The obtained slurry was charged into a mixer, heated while reducing the pressure to evaporate the solvent, and cooled to room temperature. Then, while continuing stirring by using a mixer, nitrogen gas having an oxygen concentration of 4 vol% was passed through the mixture, and while paying attention to prevent the oxidation heat generation of the mixed powder from exceeding 40 ℃, the oxygen concentration was gradually increased to 10 vol%, and after confirming the end of the heat generation, the pulverized mixture was recovered. The recovered pulverized mixture was charged into an electric furnace, and when it was heated to 210 ℃ under vacuum at elevated temperature, deterioration of the vacuum degree due to gas emission was confirmed. After the gas generation was completed and the vacuum degree was restored, the pulverized mixture (raw material mixture) was cooled and taken out.

The pulverized mixture was observed by SEM reflection electron image, and Sm was a result ₂ Fe ₁₇ Alloy particles (Sm) ₂ Fe ₁₇ Fine powder) of 10 μm in the maximum particle diameter, samarium oxide particles (Sm) ₂ O ₃ Fine powder) has a maximum particle diameter of 1.0 μm. With respect to the composition of the pulverized mixture, samarium (Sm) was 28.8 mass%, phosphorus (P) was 0.54 mass%, oxygen (O) was 3.7 mass%, hydrogen (H) was 0.41 mass%, and the remainder was iron (Fe). Average particle diameter (D) of the mixture as a whole ₅₀ ) And was 1.2 μm. TEM observation was performed after FIB cross-section processing, and the results were Sm ₂ Fe ₁₇ A phosphate compound film containing Sm, fe, P and O is formed on the surface of the alloy particles. The thickness of the coating is 5 to 10nm. The weight loss (α) of the pulverized mixture by heating was 0.4 mass%.

< reduction diffusion treatment Process >

The obtained pulverized mixture was subjected to reduction diffusion treatment. First, 46.6g of a reducing agent was added to 200g of the pulverized mixture, followed by mixing. As the reducing agent, granular calcium metal (Ca) was used which was on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent to be mixed was 2.5 times the amount (equivalent) of the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 930 ℃ for 2 hours, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

< crushing treatment Process >

The recovered reaction product was placed in a tube furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, the pressure in the furnace was temporarily reduced to-100 kPa, and hydrogen (H) was introduced ₂ ) Hydrogen (H) gas to atmospheric pressure at a flow rate of 1L/min ₂ ) The temperature in the gas stream was raised to 150 ℃ and held for 30 minutes for cooling. The reaction product begins to absorb hydrogen after the temperature rises to be higher than 80 ℃, and the internal pressure of the tubular furnace is reduced to the maximum60kPa and a temperature rise was started. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the valve on the exhaust side of the tube furnace was closed to continue the supply of hydrogen gas at a maximum flow rate of 1L/min. The maximum temperature of the reaction product due to heat generation was 170 ℃. After cooling, the reaction product is obtained after a disintegration treatment.

< Heat treatment Process of nitriding >

The reaction product after the cleavage treatment was introduced into nitrogen (N) at a flow rate of 200 cc/min ₂ ) The temperature was raised in the gas stream, maintained at 450 ℃ for 24 hours and then cooled. Thereby, a nitriding reaction product was obtained.

< Wet processing step >

The recovered nitriding reaction product is subjected to wet treatment. First, 20g of the nitriding reaction product was charged into 200cc of ion-exchanged water. Subsequently, the mixture was left to stand in an argon (Ar) gas atmosphere for 1 hour for slurrying, and the supernatant of the slurry was discarded. 200cc of ion-exchanged water was newly added and stirred for 1 minute, and left to stand until the nitrided alloy powder settled, and the supernatant liquid in which the calcium component was suspended was discarded. The operations of adding ion-exchanged water and removing the supernatant were repeated 15 times. Then, 100cc of isopropyl alcohol was added thereto, stirred, and filtered using a suction filter. The obtained filter cake was put into a static drier and dried in vacuum at 150 ℃ for 1 hour. Thereby, a rare earth iron-nitrogen-based magnetic powder was obtained.

The rare earth iron-nitrogen-based magnetic powder obtained was analyzed by XRD, and it was confirmed that it had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ In addition to the peaks, a peak of the SmP phase was also seen. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) And 3.6 μm. As a result of SEM secondary electron image observation, aggregation of spherical particles having a size of 100nm to 5 μm was confirmed as shown in FIG. 2.

As shown in table 2, the composition of the magnetic powder was 27.1 mass% of Sm, 3.0 mass% of N, and 0.26 mass% of P. In addition, as for the magnetic characteristics, the remanent magnetization (σ) _r ) Is 101Am ² Kg, coercive force (H) _c ) Is 1006kA/m. This is achievedIn addition, as for heat resistance, coercive force (H) after heating _c，300 ) 922kA/m, retention ratio (H) _c，300 /H _c ) The content was 92%.

The particle surfaces of the obtained magnetic powder were subjected to TEM observation. In this case, a sample of a cross-sectional sheet obtained by embedding a thermosetting resin with magnetic powder and then processing the embedded resin was used as an observation sample. Fig. 3 shows an HAADF (high angle annular dark field) image of the surface, and fig. 4 shows a line extraction diagram of the EDS (energy dispersive X-ray analysis) plane analysis result in the thickness direction. Fig. 4 is a graph obtained by line extraction of a composition obtained by performing EDS analysis from point X to point Y in fig. 3, where the left end of the horizontal axis corresponds to point X in fig. 3 and the right end corresponds to point Y. In addition, it is normalized that the total amount of Sm, fe, N, ca, O and P amounts to 100 atomic%.

As shown in fig. 3, a shell layer having a thickness of about 10nm is formed on the surface of the magnetic powder particle. When attention is paid to the contrast of the HAADF image, it is known that the bright outer layer and the dark inner layer constitute the shell layer. The outer layer of these thicknesses is about 4nm and the inner layer is about 6 nm. As shown in FIG. 4, the Sm/Fe ratio (A) of the outer layer was at most 2.5. Due to the main phase Sm as a nucleus ₂ Fe ₁₇ N ₃ About 0.12, and therefore, the outer layer was confirmed to be rich in Sm. The outer layer contains at most 7 atomic% of N, and also contains O and Ca. On the other hand, it is found that the Sm/Fe ratio (B) of the inner layer on the side of the main phase is about 0.2, and Sm is enriched in the inner layer compared with the main phase. The inner layer contains at most about 5 atomic% of N, and contains O but no Ca. The Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 2]

The reduction diffusion treatment, the disintegration treatment, the nitriding heat treatment, and the wet treatment were performed as follows. Except for this, rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< reduction diffusion treatment Process >

To 200g of the pulverized mixture (raw material mixture) prepared in example 1 was added 46.6g of a reducing agent, followed by mixing. As the reducing agent, granular calcium metal (Ca) was used which was on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent to be mixed was 2.5 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere, held at 900 ℃ for 2 hours, and then cooled. Thereby, a product of the reduction-diffusion reaction is obtained.

< crushing treatment Process >

The recovered reaction product was placed in a tubular furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, the pressure in the furnace was temporarily reduced to-100 kPa, and hydrogen (H) was introduced ₂ ) Gas up to atmospheric pressure at a flow rate of 1L/min of hydrogen (H) ₂ ) The temperature in the gas stream was raised to 300 ℃ and held for 30 minutes for cooling. The reaction product starts to absorb hydrogen after the temperature rises above 110 ℃, and the temperature starts to rise while the internal pressure of the tube furnace is reduced to a maximum of-70 kPa. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the valve on the exhaust side of the tube furnace was closed to continue the supply of hydrogen gas at a maximum flow rate of 1L/min. The maximum temperature of the reaction product was 300 ℃. After cooling, the reaction product is obtained after a disintegration treatment.

< nitriding Heat treatment Process >

The reaction product after the cleavage was introduced into nitrogen (N) at a flow rate of 200 cc/min ₂ ) The temperature was raised in the gas stream, kept at 450 ℃ for 24 hours and then cooled. Thereby, a nitriding reaction product was obtained.

< Wet processing step >

10g of the recovered nitriding reaction product was charged into 100cc of ion-exchanged water. Next, the mixture was left to stand in an argon (Ar) gas atmosphere for 2 hours to form a slurry, and the supernatant of the slurry was discarded. 100cc of ion-exchanged water was added again, stirred for 1 minute, left until the nitrided alloy powder settled, and the supernatant liquid in which the calcium component was suspended was discarded. The operations of adding ion-exchanged water and removing the supernatant were repeated 15 times. Then, 50cc of isopropyl alcohol was added thereto and stirred, and filtered using a suction filter. The obtained filter cake was put into a static dryer and dried under vacuum at 150 ℃ for 1 hour. Thereby, a rare earth iron-nitrogen-based magnetic powder was obtained.

The rare earth iron-nitrogen-based magnetic powder obtained was analyzed by XRD, and it was confirmed that it had Th as shown in fig. 5 ₂ Zn ₁₇ A crystalline structure. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) The thickness was 3.3. Mu.m. As a result of observation of the electron image by SEM reflection, aggregation of spherical particles having a size of several 100nm to 4 μm was confirmed as shown in FIG. 6.

As shown in FIG. 5, except that Th was seen in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is the peak of the SmP phase. The content of the SmP phase was 3.3% by mass according to the analysis by tewald (Rietveld). In addition, particles with a size number of 100nm to 2 μm, expressed in the bright contrast of fig. 6, are the SmP phase.

As shown in table 2, the composition of the magnetic powder was 27.5 mass% of Sm, 3.1 mass% of N, and 0.27 mass% of P. In addition, as for the magnetic characteristics, the remanent magnetization is 102Am ² Per kg, and the coercive force is 1123kA/m. Further, as for heat resistance, coercive force (H) after heating _c，300 ) Was 851kA/m. Retention ratio (H) _c，300 /H _c ) It was 76%. The surface of the particle was observed by TEM in the same manner as in example 1, and a shell layer having a thickness of 2nm was formed. The shell layer has an Sm/Fe ratio of at most 0.5 and an N content of at most 3 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but does not contain Ca, the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 3]

The wet treatment was performed as follows. Except for this, a rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< Wet processing step >

20g of the nitridation reaction product prepared in example 1 was put into ethylene glycol 1L having a water content of 20 mass% as defined by water/(ethylene glycol + water). Then, slurrying was performed with stirring for 3 hours in an argon (Ar) gas atmosphere, and a supernatant of the slurry was discarded. 1L of ethylene glycol having a water content of 20 mass% was added again and stirred for 5 minutes, and the mixture was allowed to stand until the nitrided alloy powder settled, and the supernatant in which the calcium component was suspended was discarded. The operations of adding ethylene glycol and removing the supernatant were repeated 3 times in an argon (Ar) gas atmosphere. Then, dehydrated ethanol 500cc was added and stirred, and left until the nitrided alloy powder settled, and the supernatant was discarded. The operations of adding dehydrated ethanol and removing the supernatant were repeated 3 times in an argon (Ar) gas atmosphere. Finally, the mixture was filtered using a suction filter, and the obtained filter cake was put into a mixer and dried under vacuum at 150 ℃ for 1 hour with stirring. Thereby, a rare earth iron-nitrogen-based magnetic powder was obtained.

The rare earth iron nitrogen-based magnetic powder obtained was analyzed by XRD, and as a result, it was confirmed that it had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is the peak of the SmP phase. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) And 4.4 μm. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 5 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 10nm thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 2.1 and an N content of at most 5 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but no Ca, and the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 4]

The wet treatment was performed as follows. Except for this, rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< Wet processing procedure >

The nitriding reaction product prepared in example 1 was put into ethylene glycol 1L, and stirred for 3 hours in an argon (Ar) gas atmosphere to form a slurry. The supernatant of the slurry was discarded, 1L of ethylene glycol was added again and stirred for 10 minutes, and left to stand until the powder of the nitrided alloy settled, and the supernatant in which the calcium component was suspended was discarded. The operations of adding ethylene glycol and removing the supernatant were repeated 10 times under an argon atmosphere. Then, dehydrated ethanol 500cc was added and stirred, and left to stand until the nitrided alloy powder settled and the supernatant was discarded. The operations of adding dehydrated ethanol and removing the supernatant were repeated 5 times under an argon atmosphere. Finally, the filtrate was filtered using a suction filter under an argon (Ar) gas atmosphere, and the resulting filter cake was put into a mixer and dried under stirring under vacuum at 150 ℃ for 1 hour. Thereby, a rare earth iron-nitrogen-based magnetic powder was obtained.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is the peak of the SmP phase. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) It was 4.8 μm. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 5 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 22 nm-thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 3.7 and an N content of at most 9 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but does not contain Ca, the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 5]

Mixing and reductive diffusion treatment were performed as follows. Except for this, a rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< mixing Process >

The pulverizing time of the media-agitation pulverizer was adjusted when preparing the pulverized mixture. Except for this, mixing was performed in the same manner as in example 1. In the pulverized mixture, sm ₂ Fe ₁₇ The maximum particle diameter of the alloy particles was 7 μm, and the maximum particle diameter of the samarium oxide particles was 0.6 μm. The composition of the pulverized mixture was 28.6 mass% of Sm, 0.57 mass% of P, 4.7 mass% of O, 0.48 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) Is 1.1 μm. At Sm ₂ Fe ₁₇ The surface of the alloy particles is coated with a phosphoric acid compound having a thickness of 5 to 10nm. The weight loss (α) by heating of the pulverized mixture was 0.8 mass%.

< reduction diffusion treatment Process >

To 200g of the obtained pulverized mixture was added 70.6g of a reducing agent and mixed. As the reducing agent, granular calcium metal (Ca) was used which was on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent was 3.0 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 730 ℃ for 10 hours, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

The obtained reaction product was subjected to nitriding heat treatment and wet treatment in the same manner as in example 1 to prepare a magnetic powder.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is a peak of the SmP phase. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) The thickness was 2.8. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of from 10nm to 3 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 6 nm-thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 1.8 and an N content of at most 6 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but does not contain Ca, the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 6]

Mixing, reduction diffusion treatment, disintegration treatment, and nitriding heat treatment were performed as follows. Except for this, rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< mixing Process >

The pulverizing time of the media-agitation pulverizer was adjusted when preparing the pulverized mixture. Except for this, mixing was performed in the same manner as in example 1. FlourIn the crushed mixture, sm ₂ Fe ₁₇ The maximum particle diameter of the alloy particles was 15 μm, and the maximum particle diameter of the samarium oxide particles was 1.8 μm. The composition of the pulverized mixture was 29.1 mass% of Sm, 0.52 mass% of P, 2.5 mass% of O, 0.28 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) It was 2.7 μm. At Sm ₂ Fe ₁₇ The surface of the alloy particles is coated with a phosphoric acid compound having a thickness of 5 to 10nm. The weight loss (α) of the pulverized mixture by heating was 0.2 mass%.

< reduction diffusion treatment Process >

To 200g of the obtained pulverized mixture was added 122.7g of a reducing agent and mixed. As the reducing agent, granular calcium metal (Ca) was used which was on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent was 9.8 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible, heated under an argon (Ar) gas atmosphere, held at 860 ℃ for 4 hours, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

< crushing treatment >

The recovered reaction product was placed in a tubular furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, the pressure in the furnace was temporarily reduced to-100 kPa, and hydrogen (H) was introduced ₂ ) Gas up to atmospheric pressure at a flow rate of 1L/min of hydrogen (H) ₂ ) The temperature in the gas stream was raised to 150 ℃ and held for 30 minutes for cooling. The reaction product starts to absorb hydrogen after the temperature rises to more than 90 ℃, and the temperature starts to rise while the internal pressure of the tube furnace is reduced to maximum-60 kPa. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the supply of hydrogen gas was continued at a maximum flow rate of 1L/min by closing the valve on the exhaust side of the tubular furnace. The maximum temperature of the reaction product due to heat generation was 200 ℃. After cooling, a reaction product was obtained after pulverization.

< Heat treatment Process of nitriding >

Ammonia (NH) was added to the reaction product after pulverization at a flow rate of 50 cc/min ₃ ) Gas and hydrogen (H) flow rate of 100 cc/min ₂ ) Heating in the gas stream of the gas mixture toHeld at 420 ℃ for 2 hours and then cooled. Thereby, a nitriding reaction product was obtained.

The obtained nitriding reaction product was subjected to wet treatment in the same manner as in example 1 to prepare a magnetic powder.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is the peak of the SmP phase. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) The thickness was 9.1. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 4 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 8 nm-thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 2.9 and an N content of at most 7 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but does not contain Ca, the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 7]

Mixing, reduction diffusion treatment, and nitriding heat treatment were performed as follows. Except for this, rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< mixing Process >

The pulverizing time of the media-agitation pulverizer was adjusted when preparing the pulverized mixture. Except for this, mixing was performed in the same manner as in example 1. In the comminuted mixture, sm ₂ Fe ₁₇ The maximum particle diameter of the alloy particles was 3 μm, and the maximum particle diameter of the samarium oxide particles was 0.2 μm. The composition of the pulverized mixture was 27.5 mass% of Sm, 0.61 mass% of P, 6.2 mass% of O, 0.51 mass% of H, and the balance of Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) Is 1.1 μm. At Sm ₂ Fe ₁₇ The surface of the alloy particles is coated with a phosphoric acid compound having a thickness of 5 to 10nm. The weight loss (α) of the pulverized mixture by heating was 0.9 mass%.

< reduction diffusion treatment Process >

To 200g of the obtained pulverized mixture was added 217.4g of a reducing agent and mixed. As the reducing agent, granular calcium metal (Ca) was used on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent was 7.0 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere, held at 1050 ℃ for 0.5 hour, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

< crushing treatment Process >

The recovered reaction product was placed in a tubular furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, the pressure in the furnace was temporarily reduced to-100 kPa, and hydrogen (H) was introduced ₂ ) Gas up to atmospheric pressure, hydrogen (H) at a flow rate of 1L/min ₂ ) The temperature in the gas stream was raised to 150 ℃ and held for 30 minutes for cooling. The reaction product starts to absorb hydrogen after the temperature rises above 100 ℃, and the temperature starts to rise while the internal pressure of the tube furnace is reduced to a maximum of-55 kPa. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the supply of hydrogen gas was continued at a maximum flow rate of 1L/min by closing the valve on the exhaust side of the tubular furnace. The maximum temperature of the reaction product due to heat generation was 160 ℃. After cooling, the reaction product is obtained after a disintegration treatment.

< nitriding Heat treatment Process >

Ammonia (NH) was added to the reaction product after the decomposition treatment at a flow rate of 50 cc/min ₃ ) Gas and hydrogen (H) at a flow rate of 100 cc/min ₂ ) The temperature of the mixed gas flow of the gases is increased, and the mixed gas flow is kept at 430 ℃ for 2 hours and then cooled. Thereby, a nitriding reaction product was obtained.

The rare earth iron nitrogen-based magnetic powder obtained was analyzed by XRD, and as a result, it was confirmed that it had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was seen in the XRD profile except that ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is a peak of the SmP phase. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) It was 4.2 μm. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 5 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 14nm thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 4.5 and an N content of at most 8 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but no Ca, and the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 8]

Mixing, reduction diffusion treatment, disintegration treatment, and nitriding heat treatment were performed as follows. Except for this, a rare earth iron-nitrogen-based magnetic powder was prepared in the same manner as in example 1.

< mixing Process >

The amount of samarium oxide mixed was set to 200g in the preparation of a pulverized mixture, and the pulverizing time of a media-stirring pulverizer was adjusted. Relative to Sm ₂ Fe ₁₇ 100 parts by mass of the alloy powder, and the amount of samarium oxide mixed is equivalent to 20 parts by mass. Except for this, mixing was performed in the same manner as in example 1. In the pulverized mixture, sm ₂ Fe ₁₇ The maximum particle diameter of the alloy particles is 12 μm, and the maximum particle diameter of the samarium oxide particles is 1.1 μm. The composition of the pulverized mixture was 33.8 mass% of Sm, 0.52 mass% of P, 3.5 mass% of O, 0.38 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) It was 1.7 μm. At Sm ₂ Fe ₁₇ The surface of the alloy particles is coated with a phosphoric acid compound having a thickness of 5 to 10nm. The weight loss (α) by heating of the pulverized mixture was 0.5 mass%.

< reduction diffusion treatment Process >

To 200g of the obtained pulverized mixture was added 31.6g of a reducing agent and mixed. As the reducing agent, granular calcium metal (Ca) was used on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent to be mixed was 1.8 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere, held at 820 ℃ for 3 hours, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

< crushing Process >

The recovered reaction product was placed in a tubular furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, the pressure in the furnace was temporarily reduced to-100 kPa, and hydrogen (H) was introduced ₂ ) Gas up to atmospheric pressure at a flow rate of 1L/min of hydrogen (H) ₂ ) The temperature in the gas stream was raised to 150 ℃ for 30 minutes and cooled. When the temperature of the reaction product is increased to more than 80 ℃, the reaction product starts to absorb hydrogen, and the temperature starts to rise while the internal pressure of the tube furnace is reduced to the maximum value of-87 kPa. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the supply of hydrogen gas was continued at a maximum flow rate of 1L/min by closing the valve on the exhaust side of the tubular furnace. The maximum temperature of the reaction product due to heat generation was 250 ℃. After cooling, the reaction product is obtained after a disintegration treatment.

< nitriding Heat treatment Process >

The resultant nitriding reaction product was subjected to wet treatment in the same manner as in example 1 to prepare a magnetic powder.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is a peak of the SmP phase. The average particle diameter (D50) measured by a laser diffraction particle size distribution meter was 5.2. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 5 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a 17nm thick shell layer having a two-layer structure. The shell layer has an Sm/Fe ratio of at most 4.9, an N content of at most 10 atomsAnd (5) percent of children. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but no Ca, and the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

[ example 9]

< mixing Process >

In the preparation of the pulverized mixture, the amount of samarium oxide was set to 10g, and the pulverizing time of the media-agitation pulverizer was adjusted. Relative to Sm ₂ Fe ₁₇ The amount of samarium oxide added was 1 part by mass per 100 parts by mass of the alloy powder. Except for this, mixing was performed in the same manner as in example 1. In the pulverized mixture, sm ₂ Fe ₁₇ The maximum particle size of the alloy particles was 4 μm, and the maximum particle size of the samarium oxide particles was 0.3 μm. The composition of the pulverized mixture was 23.8 mass% of Sm, 0.43 mass% of P, 5.8 mass% of O, 0.29 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) Is 1.3 μm. At Sm ₂ Fe ₁₇ The surface of the alloy particles is coated with a phosphoric acid compound having a thickness of 5 to 10nm. The weight loss (α) by heating of the pulverized mixture was 0.3 mass%.

< reduction diffusion treatment Process >

To 200g of the obtained pulverized mixture was added 34.9g of a reducing agent and mixed. As the reducing agent, granular calcium metal (Ca) was used on a sieve having a mesh opening size of 1.0mm and under a sieve having a mesh opening size of 2.0 mm. The amount of the reducing agent to be mixed was 1.2 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture. Then, the mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere, held at 1000 ℃ for 1 hour, and then cooled. Thereby, a reaction product (reduction-diffusion reaction product) is obtained.

< crushing treatment Process >

The recovered reaction product was placed in a tubular furnace, and the gas in the furnace was replaced with argon (Ar) gas. Then, atHydrogen (H) at a flow rate of 1L/min ₂ ) The temperature in the gas stream was raised to 150 ℃ and held for 30 minutes for cooling. The reaction product starts to absorb hydrogen after the temperature rises above 130 ℃, and the temperature starts to rise while the internal pressure of the tube furnace is reduced to a maximum of-40 kPa. During the heat generation due to the hydrogen absorption, the pressure in the furnace was negative, and therefore, the supply of hydrogen gas was continued at a maximum flow rate of 1L/min by closing the valve on the exhaust side of the tubular furnace. The maximum temperature of the reaction product was 150 ℃. After cooling, the reaction product is obtained after a disintegration treatment.

< nitriding Heat treatment Process >

The reaction product after the cleavage treatment was introduced into nitrogen (N) at a flow rate of 200 cc/min ₂ ) The temperature was raised in the gas stream, kept at 470 ℃ for 20 hours and then cooled. Thereby, a nitriding reaction product was obtained.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. In addition, th was observed in the XRD profile ₂ Zn ₁₇ Sm of type crystal structure ₂ Fe ₁₇ N ₃ Also seen is the peak of the SmP phase. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) It was 3.7 μm. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 7 μm was confirmed in the same manner as in example 1. Further, TEM observation of the particle surface resulted in formation of a shell layer having a two-layer structure and a thickness of 5 nm. The shell layer has an Sm/Fe ratio of at most 1.3 and an N content of at most 6 atomic%. Further, the shell layer is composed of an outer layer and an inner layer, the outer layer contains Sm, fe, N, O and Ca, whereas the inner layer contains Sm, fe, N and O but does not contain Ca, the Sm/Fe ratio (A) of the outer layer and the Sm/Fe ratio (B) of the inner layer satisfy the relationship of A > B.

Comparative example 1

The reduction diffusion treatment was carried out at 710 ℃ for 2 hours. Except for this, magnetic powder was prepared in the same manner as in example 1.

Analysis of the obtained rare earth by XRDAs a result of using the iron-nitrogen-based magnetic powder, it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. However, in addition to this, diffraction lines of α -Fe are also observed. As a result of TEM observation of the particle surface, the shell layer was not confirmed.

Comparative example 2

The reduction diffusion treatment was performed at 1100 ℃ for 1 hour. In addition, ammonia (NH) was used at a flow rate of 50 cc/min for the nitriding heat treatment ₃ ) Gas and hydrogen (H) flow rate of 100 cc/min ₂ ) The nitriding time was set to 3 hours for the gas mixture. Except for this, magnetic powder was prepared in the same manner as in example 1.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. Further, SEM/EDS analysis revealed that coarse SmFe particles were observed between the particles ₃ And (4) phase(s). Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) And 10.4 μm. The surface of the particle was observed by TEM, and as a result, the shell layer could not be confirmed.

Comparative example 3

The mixing amount of samarium oxide was increased to 220g (relative to Sm) in preparing the pulverized mixture ₂ Fe ₁₇ 100 parts by mass of the alloy powder, corresponding to 22 parts by mass). In addition, in the reduction diffusion treatment, the amount of particulate metallic calcium (reducing agent) was set to 64.5g (3.3 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture). Further, ammonia (NH) was used at a flow rate of 50 cc/min for the nitriding heat treatment ₃ ) Gas and hydrogen (H) flow rate of 100 cc/min ₂ ) The nitriding time was set to 3 hours for the gas mixture. Except for this, magnetic powder was prepared in the same manner as in example 1.

Sm was found to be a substance obtained by observing the pulverized mixture through SEM reflected electron image ₂ Fe ₁₇ The maximum particle size of the alloy particles was 12 μm, and the maximum particle size of the samarium oxide particles was 1.4 μm. The composition of the pulverized mixture was 32.2 mass% of Sm, 0.52 mass% of P, 3.9 mass% of O, 0.02 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) Is composed of2.5 μm. The weight loss (α) of the pulverized mixture by heating was 0.7 mass%.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) The thickness was 3.3. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 8 μm was confirmed. In addition, in the SEM observation, a large amount of SmFe was observed in addition to SmP particles ₃ A nitride phase. TEM observation was performed on the particle surface, and as a result, a shell layer was observed. The shell layer has a thickness of 32nm, a Sm/Fe ratio of at most 5.3, and an N content of at most 16 atomic%.

Comparative example 4

The amount of samarium oxide mixed was reduced to 9g (relative to Sm) in the preparation of a pulverized mixture ₂ Fe ₁₇ Alloy powder 100 parts by mass, corresponding to 0.9 part by mass). In addition, in the reduction diffusion treatment, the amount of particulate metallic calcium (reducing agent) was set to 36.1g (3.0 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture). Except for this, magnetic powder was prepared in the same manner as in example 1.

The pulverized mixture was observed by SEM reflection electron image, and as a result, sm ₂ Fe ₁₇ The maximum particle size of the alloy particles was 9 μm, and the maximum particle size of the samarium oxide particles was 0.7 μm. The composition of the pulverized mixture was 24.4 mass% of Sm, 0.51 mass% of P, 2.4 mass% of O, 0.01 mass% of H, and the balance of Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) It was 2.1 μm. The weight loss (α) by heating of the pulverized mixture was 0.3 mass%.

The rare earth iron nitrogen-based magnetic powder obtained was analyzed by XRD, and as a result, it was confirmed that it had Th ₂ Zn ₁₇ A crystalline structure. However, in addition to this, strong diffraction lines for α -Fe are also observed. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) It was 4.6. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 7 μm was confirmed. As a result of TEM observation of the particle surface, the shell layer was not confirmed.

Comparative example 5

The nitriding heat treatment was carried out at 290 ℃ for 24 hours. Except for this, magnetic powder was prepared in the same manner as in example 1.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) It was 4.8 μm. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 7 μm was confirmed. When TEM observation was performed on the particle surface, the N content was the background level (background level) although a two-layer shell was formed.

Comparative example 6

The nitriding heat treatment was performed at 510 ℃ for 3 hours. In addition, ammonia (NH) was used at a flow rate of 50 cc/min for the nitriding heat treatment ₃ ) Gas and hydrogen (H) at a flow rate of 100 cc/min ₂ ) A mixture of gases. Except for this, magnetic powder was prepared in the same manner as in example 1.

The rare earth iron nitrogen-based magnetic powder obtained was analyzed by XRD, and as a result, it was confirmed that it had Th ₂ Zn ₁₇ Crystal structure of form (iv). However, in addition to this, strong diffraction lines for α -Fe are also observed. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) The thickness was 3.1. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of 100nm to 6 μm was confirmed. When the surface of the particles in the powder was observed by TEM, a shell layer having a two-layer structure was formed, but the amount of N was 14 atomic% at most.

Comparative example 7

The pulverizing time of the media-agitation pulverizer was adjusted when preparing the pulverized mixture. In addition, in the reduction diffusion treatment, the amount of the particulate metallic calcium (reducing agent) was set to 38.8g (2.5 times as much as the amount required for reduction calculated from the oxygen amount of the pulverized mixture). Except for this, magnetic powder was prepared in the same manner as in example 1.

In the pulverized mixture, sm ₂ Fe ₁₇ The maximum particle diameter of the alloy particles is 18 mu m, and oxygenThe maximum particle diameter of samarium oxide particles was 2.8. Mu.m. The composition of the pulverized mixture was 29.0 mass% of Sm, 0.55 mass% of P, 3.1 mass% of O, 0.009 mass% of H, and the balance Fe. Average particle diameter (D) of the mixture as a whole ₅₀ ) It was 3.7 μm. The weight loss (α) by heating of the pulverized mixture was 0.05 mass%.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) It was 8.1 μm. As a result of SEM observation, aggregation of spherical particles having a size of 1 μm to 10 μm was confirmed. As a result of TEM observation of the particle surface, a portion having a shell layer formed and a portion having no shell layer formed were observed. Therefore, the formation of the shell layer is biased.

Comparative example 8

In the reduction-diffusion treatment, the amount of particulate calcium metal (reducing agent) to be mixed was set to 18.5g (1.0 time as much as the amount required for reduction calculated from the oxygen amount of the pulverized mixture). Except for this, magnetic powder was prepared in the same manner as in example 1.

The rare earth iron nitrogen-based magnetic powder obtained was analyzed by XRD, and as a result, it was confirmed that it had Th ₂ Zn ₁₇ A crystalline structure. However, in addition to this, strong diffraction lines for α -Fe are also observed. Average particle diameter (D) measured by laser diffraction particle size distribution analyzer ₅₀ ) It was 7.3 μm. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 8 μm was confirmed. Further, TEM observation of the particle surface resulted in failure to confirm the shell layer.

Comparative example 9

In the reduction diffusion treatment, the amount of particulate metallic calcium (reducing agent) to be mixed was set to 202.1g (10.9 times the amount required for reduction calculated from the oxygen amount of the pulverized mixture). Except for this, magnetic powder was prepared in the same manner as in example 1.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ A crystalline structure. However, in addition theretoStrong diffraction lines for alpha-Fe are also observed. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) It was 9.2 μm. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 10 μm was confirmed. As a result of TEM observation of the particle surface, the shell layer was not confirmed.

Comparative example 10

Preparing commercially available Sm ₂ Fe ₁₇ N ₃ The characteristics of the magnetic powder (SFN alloy fine powder B, manufactured by sumitomo metal mine gmbh) were evaluated. As a result of examining heat resistance, coercivity (H) before heating was observed _c ) 844kA/m, coercive force after heating (H) _c，300 ) 407kA/m, retention (H) _c ， ₃₀₀ /H _c ) The content was 48%.

Comparative example 11

The flow rate of hydrogen gas in the disintegration treatment step was set to 10L/min. Except for this, magnetic powder was prepared in the same manner as in example 2. In the decomposition treatment step, the reaction product starts to absorb hydrogen after the temperature is raised to more than 118 ℃, and the amount of hydrogen gas supplied increases, so that the negative pressure in the furnace does not occur. The reaction product generated heat drastically, and its maximum temperature was 370 ℃.

The obtained rare earth iron-nitrogen-based magnetic powder was analyzed by XRD, and it was confirmed that the powder had Th ₂ Zn ₁₇ Crystal structure of form (iv). However, in addition to this, a diffraction line of α -Fe is also observed. Average particle diameter (D) measured by a laser diffraction particle size distribution meter ₅₀ ) The thickness was 2.9. Mu.m. As a result of SEM observation, aggregation of spherical particles having a size of several 100nm to 5 μm was confirmed. As a result of TEM observation of the particle surface in the powder, a shell layer having a two-layer structure was formed, but fine precipitates considered to be α -Fe were separately observed on the core surface.

TABLE 1 production conditions of rare earth iron-nitrogen-based magnetic powder

Note 1) "W" means ion-exchanged water.

Note 2) "EG" means ethylene glycol.

(3) Evaluation results

The rare earth iron-nitrogen-based magnetic powders of examples 1 to 12 mainly contain samarium (Sm), iron (Fe), and nitrogen (N), and the amount of samarium (Sm) is 23.2 to 29.9 mass% and the amount of nitrogen (N) is 2.8 to 3.9 mass%. The magnetic powder has Th ₂ Zn ₁₇ A crystal structure of the form, the average particle diameter of which is 2.8 to 9.1 μm. Further, the magnetic powder has a shell layer having an Sm/Fe atomic ratio of 0.5 to 4.9, containing 3 to 10 atomic% nitrogen (N), and having a thickness of 2 to 22nm on the particle surface. The magnetic powder has 90Am ² Residual magnetization (. Sigma.)/kg or more _r ) And a coercive force (H) of 754kA/m or more _c ) Retention ratio of coercive force (H) _c，300 /H _c ) Is more than 71%. The magnetic powder exhibits high heat resistance.

In contrast, since the magnetic powder of comparative example 1 had a reduction diffusion temperature (710 ℃) lower than 730 ℃ during production, no shell layer was observed, and the retention ratio of coercive force (43%) according to the heat resistance test was less than 70%. In addition, since the magnetic powder of comparative example 2 had a reduction diffusion temperature (1100 ℃ C.) higher than 1050 ℃ at the time of production, the average particle diameter (10.4 μm) thereof was larger than 10 μm, the coercive force (420 kA/m) was low, and the retention rate (55%) of the coercive force was lower than 70%.

The amount of samarium oxide (relative to Sm) added to the magnetic powder of comparative example 3 during production ₂ Fe ₁₇ 22 parts by mass of the alloy powder 100 parts by mass) is more than 20 parts by mass. Therefore, the samarium amount (32.2 mass%) was more than 30 mass%, and the nitrogen amount (5.2 mass%) was more than 4.0 mass%. In addition, a large amount of SmFe was observed in the powder ₃ A phase nitride. As a result, the thickness (32 nm) of the shell layer was more than 30nm, the Sm/Fe atomic ratio (5.3) was more than 5.0, and the remanent magnetization (50 Am) ² /kg) is low. In addition, the amount of samarium oxide (relative to Sm) mixed in the production of the magnetic powder of comparative example 4 ₂ Fe ₁₇ 0.9 part by mass of the alloy powder 100 parts by mass) is less than 1 part by mass. Therefore, the amount of samarium (21.9 mass%) was less than 22 mass%. As a result, it was not observedShell layer, residual magnetization (43 Am) ² /kg) and low coercive force (283 kA/m).

The nitriding temperature (290 ℃ C.) for the production of the magnetic powder of comparative example 5 was less than 300 ℃. Therefore, the nitrogen amount (1.7 mass%) is less than 2.5 mass%. In addition, although the shell was observed, nitrogen in the shell was the background level of the TEM/EDS detector. As a result, the residual magnetization of the magnetic powder (39 Am) ² /kg) and low coercive force (109 kA/m). The magnetic powder of comparative example 6 was produced at a nitriding temperature (510 ℃ C.) of more than 500 ℃. The magnetic powder has a nitrogen content (5.3 mass%) of more than 4.0 mass% and a residual magnetization (48 Am) ² /kg) and a low coercive force (227 kA/m).

Sm in the starting Material for the magnetic powder of comparative example 7 ₂ Fe ₁₇ The maximum particle diameter (18 μm) of the alloy powder is larger than 15 μm, and the maximum particle diameter (2.8 μm) of the samarium oxide powder is larger than 2 μm. Therefore, there are particles in which the shell layer is observed and particles in which the shell layer is not observed, and there is variation in the formation of the shell layer. This is considered to be because each particle size of the raw material powder is coarse, and unevenness occurs when samarium reduced in the reduction diffusion step penetrates into the raw material. As a result, the remanent magnetization (77 Am) ² /kg) and low coercive force (491 kA/m). The retention rate of coercive force (47%) was less than 70%, and the heat resistance was poor.

The amount of calcium metal added (1.0 time the equivalent) was less than 1.1 times for the magnetic powder of comparative example 8. Therefore, the magnetic powder had a samarium amount (21.7 mass%) of less than 22 mass% and a nitrogen (N) amount (2.3 mass%) of less than 2.5 mass%. Remanent magnetization (53 Am) ² /kg) and low coercive force (173 kA/m). And no shell layer was observed. The retention rate of coercive force (36%) was significantly lower than 70%, and the heat resistance was poor. In the magnetic powder of comparative example 9, the amount of calcium metal added (10.9 times the equivalent weight) was more than 10 times. Therefore, the magnetic powder has a samarium amount (21.5 mass%) of less than 22 mass% and a nitrogen amount (1.9 mass%) of less than 2.5 mass%. It is considered that the amount of calcium is excessive and the diffusion of samarium is suppressed. Remanent magnetization (48 Am) ² /kg) and low coercive force (93 kA/m). And no shell layer was observed. The retention rate of coercive force (43%) was less than 70%, and the heat resistance was poor.

For use ofCommercially available Sm as a conventional example ₂ Fe ₁₇ N ₃ In comparative example 10 of the magnetic powder, the retention ratio of the coercive force (48%) was less than 70%.

The magnetic powder of comparative example 11 did not generate negative pressure in the furnace due to sufficient hydrogen supply in the disintegration treatment step, and the reaction product generated heat drastically due to rapid hydrogen absorption, and its temperature was far higher than 300 ℃ and reached 370 ℃. Although the total amount of samarium, nitrogen (N), and phosphorus (P) was the same as in example 2, the average particle size was reduced to 2.9. Mu.m, the squareness of the magnetization curve was reduced, and the residual magnetization (85 Am) was obtained ² The coercive force (1007 kA/m) was reduced as compared with example 2. This is considered to be caused by the precipitated α -Fe. Further, the retention ratio of coercive force (68%) was less than 70%, and the heat resistance was poor.

TABLE 2 Properties of rare earth iron-nitrogen-based magnetic powder

Note 1) "BG" refers to background level.

Claims

1. A magnetic powder of a rare earth iron-nitrogen system comprising R, fe and N as main constituent elements,

the magnetic powder has an average particle diameter of 1.0 to 10.0 [ mu ] m, contains a rare earth element R in an amount of 22.0 to 30.0 mass%, contains nitrogen N in an amount of 2.5 to 4.0 mass%,

the magnetic powder is provided with: has Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type and TbCu ₇ A core portion of any one of the crystal structures of type crystal; and a shell layer which is provided on the surface of the core portion and has a thickness of 1nm to 30nm,

the shell layer contains a rare earth element R and Fe such that the R/Fe atomic ratio is 0.3 to 5.0, and further contains nitrogen N in an amount of more than 0 atom% to 10 atom%,

the magnetic powder contains compound particles composed of rare earth element R and phosphorus P, and has remanent magnetization σ _r Is 90Am ² More than kg.

2. The magnetic powder according to claim 1,

the shell layer is composed of a two-layer structure consisting of an outer layer and an inner layer,

the outer layer contains oxygen O and calcium Ca in addition to rare earth elements R, iron Fe and nitrogen N,

the inner layer contains oxygen O, but does not contain calcium Ca, in addition to rare earth elements R, iron Fe, and nitrogen N.

3. The magnetic powder according to claim 2,

the R/Fe atomic ratio A of the outer layer and the R/Fe atomic ratio B of the inner layer satisfy B < A.

4. The magnetic powder according to any one of claims 1 to 3, wherein samarium Sm is contained as the rare earth element R.

5. The magnetic powder according to any one of claims 1 to 4, further comprising a phosphate compound coating film on the outermost surface of the magnetic powder.

6. The magnetic powder according to any one of claims 1 to 5, wherein the coercivity H after heating is obtained after heating at a temperature of 300 ℃ for 1 hour in an argon Ar atmosphere _c，300 Relative to coercive force H before heating _c Retention ratio of (2), namely H _c，300 /H _c Is more than 70 percent.

7. A composite for a bonded magnet, comprising the magnetic powder according to any one of claims 1 to 6 and a resin binder.

8. A bonded magnet comprising the magnetic powder according to any one of claims 1 to 6 and a resin binder.

9. A method for producing the rare earth iron-nitrogen-based magnetic powder according to any one of claims 1 to 6, comprising:

a preparation step of preparing a composition having Th ₂ Zn ₁₇ Type Th ₂ Ni ₁₇ Type TbCu ₇ Rare earth iron alloy powder and rare earth oxide powder having any one of crystal structures of type crystal structures;

a reduction diffusion treatment step of adding a reducing agent to the raw material mixture in an amount of 1.1 to 10.0 times the equivalent weight required for reducing the oxygen component contained in the raw material mixture, mixing the mixture, and further heating the raw material mixture to which the reducing agent has been added in a non-oxidizing atmosphere at a temperature in the range of 730 to 1050 ℃ to produce a reduction diffusion reaction product;

in either or both of the preparation step and the mixing step, a phosphoric acid-based compound coating is formed on the rare earth iron alloy powder.

10. The method according to claim 9, wherein in the mixing step, a rare-earth iron alloy powder and a rare-earth oxide powder are mixed and ground in a grinding solvent containing a phosphoric acid-based surface treatment agent, and a phosphoric acid-based compound film is formed in the rare-earth iron alloy powder.

11. The method of claim 9 or 10, further comprising: and a step of performing a wet treatment for reducing the content of the reducing agent in the product by putting the reduction diffusion reaction product and/or the nitridation reaction product into a washing liquid containing water and/or glycol and disintegrating the product.

12. The method of any of claims 9 to 11, further comprising: and forming a phosphoric acid compound coating film on the surface of the product after the nitriding heat treatment.

13. The method according to any one of claims 9 to 12, wherein the heating loss of the raw material mixture is less than 1 mass%.

14. The method according to any one of claims 9 to 13, wherein the heat treatment for producing the diffusion reaction product is performed for 0 to 10 hours.