JPH05166615A - Production of magnet and mother alloy for it - Google Patents

Abstract

PURPOSE:To manufacture magnetic grains in a short time and provide a magnetic which has excellent magnetic characteristics by eliminating a process of melting mother alloy in the production of magnet composed of a rare earth element which contains Sm as an essential element, N and Fe or Fe and Co. CONSTITUTION:Mother alloy which contains a R2T17 phase and alpha-Fe phase of prescribed quantity is roughly crushed to be nitrided and then finely crushed to produce magnetic grains, or the mother alloy is roughly crushed and then finely crushed and nitrided to produce the magnetic grains. At that time, since melting process is eliminated, the alpha-Fe phase is provided as a rough grain separated from the magnetic grains after the process of fine crushing, the phase can be easily separated from the magnetic grains by classification. Thus, the magnetic grains are manufactured in a short time. Since the composition of the mother alloy does not change, the characteristics are provided as designed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Sm-Fe-N magnet and a master alloy used in the method.

[0002]

2. Description of the Related Art Sm-Co is a high-performance rare earth magnet.
System magnets and Nd-Fe-B system magnets are known, but in recent years, new rare earth magnets have been actively developed.

For example, with a composition near Sm ₂ Fe ₁₇ N _2.3 which is a compound of Sm ₂ Fe ₁₇ and N, 4πIs = 15.
4kG, Tc = 470 ° C., H _A = 14T basic physical properties are obtained, (BH) max of 10.5 MGOe is obtained as a metal bonded magnet with Zn as a binder, and
It has been reported that the introduction of N into the Sm ₂ Fe ₁₇ intermetallic compound significantly improved the Curie temperature and improved the thermal stability (PaperNo.S1.3 at the Sixth Internatio).
nal Symposium on Magnetic Anisotropy and Coercivity
in Rare Earth-Transition Metal Alloys, Pittsburgh,
PA, October 25, 1990. (Proceedings Book: Carnegie Mell
on University, Mellon Institute, Pittsburgh, PA 1521
3, USA)).

In this report, when Sm ₂ Fe ₁₇ N _2.3 powder was mixed with Zn powder and cold pressed, μ ₀ H
c = 0.2T (iHc = 2kG), but when further magnetically pressed and heat-treated at a temperature near the melting point of Zn to form a metal-bonded magnet, μ ₀ Hc = 0.6T (iHc =
6kG) has been obtained.

The magnet particles used in the metal-bonded magnets reported above have a particle size of about single crystal particles, and the coercive force generating mechanism is of the creation type. Therefore, the magnetic properties are easily affected by the surface state of the particles. That is, defects such as minute protrusions are generated on the surface of the magnet particles due to mechanical impact during crushing, oxidation of particles, etc., and when a magnetic field is applied on the side opposite to the magnetization direction, the defects become nuclei for generation of reverse magnetic domains. A domain wall is generated in the grain, but in a nucleation type magnet, there is no pinning site of the domain wall in the crystal grain, so domain wall movement easily occurs,
Coercive force is low. In the above report, when a metal bonded magnet is used, the magnet particles are brought into contact with a molten high-temperature binder, thereby reducing the surface roughness of the magnet particles and suppressing the generation of domain walls, and obtaining a high coercive force. it is conceivable that.

However, the metal bonded magnet is inferior in moldability to the resin bonded magnet using the resin binder and has a large specific gravity, so that the application field is limited.

[0007] Also, for a bonded magnet predicted from the theoretical value of (BH) max of Sm ₂ Fe ₁₇ magnet of about 59 MGOe.
The (BH) max of the metal-bonded magnet shown in the above report is lower than the (BH) max of about 40 MGOe, and the coercive force is particularly low.

Under these circumstances, the present inventors first
R (provided that R is at least one element selected from rare earth elements and contains Sm as an essential element), N and T (provided that T is Fe or Fe and Co). Proposes a magnet powder composed of magnet particles having a metal coating layer formed on the surface thereof, and a resin-bonded magnet in which the magnet powder is dispersed in a resin binder (Japanese Patent Application No. 3-139640). It is disclosed that a resin-bonded magnet having a high coercive force as well as a bonded magnet and better moldability than a metal bonded magnet can be obtained. Further, it is disclosed that when at least a part of the coating layer around the magnet particles is formed with a mixed portion containing the magnet particle constituent elements, extremely high coercive force can be obtained because defects on the magnet particle surface are favorably repaired. ing.

The present inventors have also proposed a metal bonded magnet having a mixed portion similar to the above proposal (Japanese Patent Application Nos. 3-139641 and 3-139642).

The magnet particles used for manufacturing various Sm-Fe-N magnets are obtained by subjecting a mother alloy ingot to solution treatment, coarse pulverization, nitriding treatment, and fine pulverization. Manufactured. The Sm-Fe-N magnet, Sm ₂ Fe ₁₇ N _x phase indicates hard magnetic, the other phase is responsible for reducing the magnetic properties as an impurity phase. However, when manufacturing the master alloy ingot, especially in the solidification process, SmF
Heterogeneous phases such as e ₃ , SmFe ₂ , and α-Fe inevitably occur. For this reason, EP 0 369 097 A1 proposes to subject these mother alloy ingots to solution treatment to eliminate these different phases.

[0011]

However, during the solution heat treatment, since the temperature is kept at a high temperature of about 1000 ° C. or higher,
Part of Sm may evaporate from the master alloy, resulting in a change in composition. Further, since the solution treatment time usually requires 10 hours or more, high productivity cannot be obtained. But,
If the solution treatment is not performed, a different phase occurs as described above, and high magnetic characteristics cannot be obtained.

The present invention has been made under these circumstances, and an object thereof is to shorten the manufacturing time and obtain a magnet having good magnetic characteristics when manufacturing a magnet containing Sm, Fe and N. And

[0013]

[Means for Solving the Problems]

Such an object is achieved by the present invention described in (1) to (7) below.

(1) R (where R is one or more elements selected from rare earth elements and contains Sm as an essential element) is 5 to 15 atomic% and N is 0.5 to 25 atomic%. A method for producing a magnet containing, the balance being T (wherein T is Fe, or Fe and Co), wherein R is R
And a magnetizing step including a step of casting a master alloy containing T, a coarse pulverizing step, a nitriding step, and a fine pulverizing step, the R ₂ T ₁₇ phase as a main phase, and the α-Fe phase. To 0.0
Contains 2 to 15 vol%, and method for producing a magnet, which comprises using less master alloy than the content of the content of the R-rich R-T phases the alpha-Fe phase than R ₂ T ₁₇ ..

(2) The above-mentioned (1), wherein the mother alloy contains 0.05% by volume or less of the R-T phase, which is richer in R than R ₂ T _17, and 1/2 or less of the α-Fe phase. Magnet manufacturing method.

(3) The method for producing a magnet as described in (1) or (2) above, which comprises a step of removing, by classifying, the different phase particles having an α-Fe phase after the finely pulverizing step.

(4) The method for producing a magnet according to any one of the above (1) to (3), which has a step of forming a metal coating layer on at least a part of the surface of the magnet particles.

(5) The method for producing a magnet according to any one of the above (1) to (4), which comprises a step of producing the bonded magnet by dispersing the magnet particles in a resin or metal binder.

(6) The R ₂ T ₁₇ phase is the main phase, the α-Fe phase is contained in an amount of 0.02 to 15% by volume, and R is more preferable than R ₂ T _17.
A master alloy for magnet production, wherein the content of the rich RT phase is smaller than the content of the α-Fe phase.

(7) The mother alloy for magnet production according to the above (6), which contains the R-T phase richer in R than R ₂ T _{17 in an} amount of 0.05% by volume or less and 1/2 or less of the α-Fe phase. ..

[0022]

In the present invention, the R ₂ T ₁₇ phase and a predetermined amount of α-F are used.
The mother alloy containing the e phase is coarsely pulverized and nitrided, and then finely pulverized to produce magnet particles. Alternatively, the mother alloy is coarsely pulverized and finely pulverized, and then nitrided to produce magnet particles. In the present invention, since it is not necessary to subject the mother alloy to solution treatment, it is possible to manufacture magnet particles in an extremely short time, and
The characteristics as designed can be obtained without changing the composition of the mother alloy.

When the solution treatment is not performed, RT ₃ , R
Heterogeneous phases such as T ₂ and α-Fe remain, but RT ₃ and RT ₂
Since the R-rich RT phase such as the above does not easily coexist with the α-Fe phase, it is hardly contained in the master alloy used in the present invention. Further, since the α-Fe phase has high spreadability, it is difficult to be pulverized,
Since they exist as coarse particles independent of the magnet particles after the pulverization step, they can be easily separated from the magnet particles by classification.

Therefore, according to the present invention, a magnet having high magnetic characteristics can be manufactured in an extremely short time.

The magnet particles produced according to the present invention are Sm
₂ (Fe, Co) ₁₇ series alloy particles containing nitrogen (N). Since this magnet particle contains N, it has a high Curie temperature and is excellent in thermal stability. Further, by containing N, high saturation magnetization is obtained, anisotropic energy is also improved, and high coercive force is obtained. The improvement of magnetic characteristics is
It is considered that N forms an interstitial solid solution at a specific position of the crystal lattice, thereby optimizing the distance between Fe atoms and the distance between Fe atoms and rare earth metal atoms.

[0026]

Specific Structure The specific structure of the present invention will be described in detail below.

<Magnet Composition> The magnet produced according to the present invention contains R, N and T.

R is Sm alone or one or more of Sm and other rare earth elements. Examples of rare earth elements other than Sm include Y, La, Ce, Pr, Nd, and E.
u, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
Etc. If the amount of rare earth elements other than Sm is too large, the crystal magnetic anisotropy decreases, so the content of rare earth elements other than Sm is preferably 70% or less of R. The content rate of R is
It is 5 to 15 atom%, preferably 7 to 14 atom%. R
If the content is less than the above range, the coercive force iHc will decrease, and if it exceeds the above range, the residual magnetic flux density Br will decrease.

The N content is 0.5 to 25 atom%, preferably 5 to 20 atom%. In the present invention, a part of N may be replaced with C and / or Si. In this case, the N content is 0.5 atomic% or more,
The total content of N, C and Si is 25 atomic% or less. If the N content is less than the above range, the Curie temperature is not raised and the saturation magnetization is insufficiently improved. If the total content of N, C and Si exceeds the above range, Br is lowered. C and / or Si contained in place of part of N
Shows an effect of improving saturation magnetization, coercive force and Curie temperature. The lower limit of the total content of C and Si is not particularly limited, but if the total content is 0.25 atom% or more, the above-mentioned effects are sufficiently exhibited.

The Curie temperature of the magnet is about 430 to 650 ° C. although it depends on the composition.

T is Fe, or Fe and Co,
The content of Fe in T is 20 atomic% or more, especially 30 atomic%.
The above is preferable. If the content of Fe in T is less than the above range, Br will decrease. There is no particular upper limit to the Fe content in T, but if it exceeds 80 atomic%, Br tends to decrease.

Elements other than the above, such as Mn, Ni and Zn, may be contained in the magnet. The content of these elements is preferably 3% by weight or less. Also, B,
Elements such as O, P, and S may be contained, but the content of these elements is preferably 2% by weight or less.

The magnet mainly has a Th ₂ Zn ₁₇ type rhombohedral crystal structure.

<Production Method> The production method of the present invention has a magnet particle production step including a step of casting a master alloy containing R and T, a coarse pulverization step, a nitriding step, and a fine pulverization step. In the present invention, usually, a coarse crushing step, a nitriding step,
The pulverization process is performed in this order. In this case, in the coarse crushing step, the mother alloy is coarsely crushed to obtain alloy particles, in the nitriding step, the alloy particles are subjected to a nitriding treatment to obtain nitride particles, and in the fine crushing step, the nitride particles are finely crushed to magnet particles. And Hereinafter, this case will be described.

Manufacturing Method of Master Alloy A master alloy ingot is manufactured by mixing each raw material metal and alloy and then melting and casting the mixture.

The master alloy ingot contains the R ₂ T ₁₇ phase and α
-Fe phase is contained, and the content of α-Fe phase is 0.02 to
It is 15% by volume, preferably 0.5 to 10% by volume. α
When the content of the —Fe phase is less than the above range, RT ₃ and R
The content of R-rich RT phase such as T ₂ increases. Since the solution treatment is not performed in the present invention, it is necessary to suppress the content of the R-rich RT phase. Further, when the content of the α-Fe phase is small, the α-Fe phase becomes fine and is dispersed in the alloy, and it becomes impossible to separate and remove only the α-Fe phase during fine pulverization described later. On the other hand, when the content of the α-Fe phase exceeds the above range, the energy efficiency of fine pulverization decreases.

It should be noted that R-T which is richer in R than R ₂ T ₁₇
Phases such as RT ₃ phase, RT ₂ phase and RT phase inevitably occur in the casting process, but in order to obtain high magnetic properties, R
It is necessary to make the content of the rich RT phase smaller than the content of the α-Fe phase. By appropriately selecting the casting conditions, the content of the R-rich RT phase can be made 0.05 vol% or less and 1/2 or less of the α-Fe phase, and high magnetic characteristics can be obtained.

The contents of α-Fe phase and RT phase in the mother alloy ingot can be quantified by analysis of peak height in X-ray diffraction chart or EPMA.

The master alloy ingot has the R ₂ T ₁₇ phase as the main phase. The crystal grain size of the mother alloy ingot is not particularly limited,
The size is preferably such that single crystal particles can be obtained by fine pulverization described later.

Method for Producing Alloy Particles In the present invention, the above-mentioned mother alloy ingot is roughly crushed without solution treatment to obtain alloy particles. By coarse crushing, α-
Part of the Fe phase separates from the main phase.

The average particle size of the alloy particles is not particularly limited, but in order to obtain sufficient oxidation resistance, the average particle size of the alloy particles is preferably 2 μm or more, more preferably 10 μm.
As described above, the thickness is more preferably 15 μm or more, preferably about 1000 μm or less, and more preferably 200 μm or less.

The crushing means is not particularly limited, and various ordinary crushers may be used.

In the present invention, the average particle size means the weight average particle size D ₅₀ obtained by sieving. The weight average particle diameter D ₅₀ is a particle diameter when the weight is added from the particles having a smaller diameter and the total weight becomes 50% of the total weight of all the particles.

Method for producing nitrided particles Next, the alloy particles are subjected to a nitriding treatment to form a solid solution of N to obtain nitrided particles. In this nitriding treatment, the alloy particles are heat-treated in a nitrogen atmosphere, whereby the alloy particles absorb nitrogen. In order to form a solid solution of N as described above, it is preferable to perform the nitriding treatment under the following conditions.
The holding temperature is preferably 400 to 700 ° C, particularly preferably 450 to 650 ° C. Temperature holding time is 0.5-2
It is preferably set to 00 hours, particularly 2 to 100 hours.

If the mother alloy ingot is occluded with hydrogen and crushed, and if the alloy particles are subjected to the nitriding process without exposing to the atmosphere, generation of an oxide film on the particle surface can be suppressed. In this case, high reactivity is obtained.

Further, by occluding hydrogen in the alloy, a fine gas passage is formed in the alloy, and during the subsequent nitriding treatment, nitrogen penetrates to the deep portion of the alloy, so that N is absorbed. It becomes possible to easily form a solid solution.
Therefore, alloy particles having a large size can be nitrided, and the oxidation resistance of the alloy particles and the nitride particles can be improved. For example, the distance to the surface is 0.25
Even alloy particles having a region of mm or more, further 5 mm or more can be nitrided. However, for uniform nitriding, the distance from the surface is 15 mm.
It is preferable to use an alloy particle having a size and shape such that there is no portion exceeding the above.

The hydrogen storage treatment is a process of storing hydrogen in the alloy by heat treatment in a hydrogen gas atmosphere.
The heat treatment temperature at this time is 350 ° C. or lower, particularly 100 to 3
It is preferable to set the temperature to 00 ° C, and the temperature holding time is 0.5 to
It is preferably 24 hours, particularly 1 to 10 hours. The pressure of the hydrogen gas is 0.1 to 10 atm, especially 0.5.
It is preferable to set the pressure to 2 atm.

The atmosphere for storing hydrogen is not limited to hydrogen gas, but may be a mixed atmosphere of hydrogen gas and inert gas. In this case, the inert gas is preferably He or Ar, or a mixed gas thereof.

When the hydrogen storage treatment is performed before the nitriding treatment, the holding temperature during the nitriding treatment can be lowered, and
Nitriding is possible at 50 to 650 ° C, especially at 400 to 550 ° C. However, the temperature at this time is preferably higher than the temperature of the hydrogen storage treatment.

In order to improve the productivity, it is preferable to carry out a nitriding treatment without releasing hydrogen from the alloy after the hydrogen storage treatment. In this case, since hydrogen in the alloy is released from the alloy by heating during the nitriding treatment, hydrogen is not substantially contained in the nitride particles, and the hydrogen content can be kept within the above range.

However, it is also possible to release hydrogen from the alloy after the hydrogen occlusion treatment and then perform the nitriding treatment. in this case,
By subjecting the alloy storing hydrogen to a heat treatment in a reduced pressure atmosphere, hydrogen can be released from the alloy.
In this case, the heat treatment temperature is preferably 200 to 400 ° C., and the temperature holding time is preferably 0.5 to 2 hours. The pressure is 1 × 10 ^-2 Torr or less, especially 1 ×
It is preferably 10 ⁻³ Torr or less, and heat treatment is preferably performed in an Ar gas atmosphere.

In order to make the distribution of nitrogen atoms in the nitride particles uniform, it is preferable to subject the nitride particles to a heat treatment in a non-oxidizing atmosphere such as an Ar atmosphere. The temperature during this heat treatment is
The temperature is preferably higher than the temperature at which the alloy particles are nitrided. Specifically, the temperature is 20% higher than the temperature during the nitriding treatment.
Higher than ℃, 700 ℃ to prevent decomposition reaction
It is preferably not more than about this level. Further, in order to make the distribution of nitrogen atoms more uniform, it is preferable to use nitride particles in which there is no region where the distance from the surface exceeds 30 μm. By performing the heat treatment under such conditions, it is possible to obtain the nitride particles in which the ratio of the surface nitrogen atom concentration to the central nitrogen atom concentration is about 0.80 or more. The distribution of nitrogen atoms in the nitride particles can be confirmed by EPMA or the like.

Since the magnet particles are manufactured by pulverizing the nitride particles, by homogenizing the distribution of nitrogen atoms in the nitride particles, magnet particles having a uniform nitrogen content, that is, magnet particles having a uniform coercive force can be obtained. As a result, a magnet having a high squareness ratio is realized.

Manufacturing Method of Magnet Particles Next, the polycrystalline nitride particles are finely pulverized to obtain almost single crystal magnet particles.

The average particle size of the magnet particles is not particularly limited,
It may be appropriately determined according to the application so that a desired coercive force can be obtained. For example, when it is applied to a resin-bonded magnet, the particle diameter of a single magnetic domain, for example, 0.5 to 1
Grind to about 0 μm. In addition, in the case of applying a metal coating layer described later on the surface of the magnet particles to apply to a resin bonded magnet, or to apply to a metal bonded magnet,
The necessary coercive force can be obtained without crushing the particles to a particle size of a single magnetic domain. In these cases, for example, 3 to 50 μm
The average particle size may be about the same.

The α-Fe phase in the nitride particles is separated from the main phase by fine pulverization. To obtain a magnet with high magnetic characteristics, α
It is preferable to remove the heterophase particles having the —Fe phase from the finely pulverized powder. The α-Fe phase is hard to be pulverized, and α
Since most of the -Fe phase has a larger volume than the magnet particles having the above particle diameter, the α-Fe phase separated from the main phase becomes coarse particles and exists in the finely pulverized powder. Therefore, it is preferable to remove the heterogeneous particles by classification. The particle diameter of the heterogeneous particles is about 5 to 200 μm.

The crushing means is not particularly limited, and various ordinary crushers may be used.

In the present invention, in addition to such a method,
The particles after coarse pulverization and fine pulverization may be nitrided. Also in this case, since the coarse particles of the α-Fe phase are separated from the main phase during fine pulverization, classification can be performed in the same manner as above.

<Bonded Magnet> The magnet particles produced as described above are usually applied to various bonded magnets. Bonded magnets are magnets having a structure in which magnet particles are dispersed in a binder, and resin-bonded magnets that use a resin as a binder and metal-bonded magnets that use a metal as a binder are generally used. It is suitable for any of these.

When the magnet particles are applied to a bonded magnet, it is preferable that the magnet particles have a particle size of about single crystal particles. However, since the coercive force generating mechanism of the magnet particles is a nucleation type, the magnetic characteristics are easily influenced by the surface state of the particles. That is, defects such as minute protrusions are generated on the surface of the magnet particles due to mechanical impact during crushing, oxidation of particles, etc., and when a magnetic field is applied on the side opposite to the magnetization direction, the defects become nuclei for generation of reverse magnetic domains. A domain wall is generated in the grain, but in a nucleation type magnet, the domain wall is easily moved because there is no pinning site of the domain wall in the crystal grain, so that a high coercive force cannot be obtained.

In a metal-bonded magnet, since the surface of the magnet particle comes into contact with a molten high temperature binder at the time of manufacture, surface defects such as protrusions existing on the surface of the magnet particle are smoothed and the surface roughness is reduced, so that a reverse magnetic domain is generated. Nuclei are reduced and a high coercive force is obtained.

Further, even when a metal coating layer is formed on the surface of the magnet particles, the surface defects of the magnet particles can be repaired. Therefore, the magnet particles having such a coating layer can be dispersed in a resin binder. Thus, it is possible to obtain a high coercive force even in the resin bonded magnet.

When a mixed portion containing an element forming the magnet particles is formed in the binder around the magnet particles or the coating layer around the magnet particles, an extremely high coercive force can be obtained.

The mixed portion is formed by mutually diffusing the element constituting the binder or the coating layer and the element constituting the magnet particle, and has a magnetic property different from that of the magnet particle. Surface defects such as protrusions that cause the surface roughness of the magnet particles become part of the mixed portion due to the above-mentioned mutual diffusion and are magnetically isolated from the magnet particles.
The substantial surface roughness of the magnet particle surface becomes extremely small,
It is considered that extremely high coercive force can be obtained because the nuclei of reverse domain generation are significantly reduced.

Hereinafter, these bonded magnets will be described in detail.

<Resin Bonded Magnet>

Coating Layer When applied to a resin-bonded magnet, it is preferable to form a coating layer as described above.

The metal constituting the coating layer is not particularly limited as long as it can coat the surface of the magnet particles and can repair defects on the surface of the magnet particles. However, it is preferable to select a metal that can form a mixed portion described below between the coating layer and the magnet particles.

Such a metal has a melting point of 150 to
A simple metal, an alloy, and an intermetallic compound at about 500 ° C. are preferable, and for example, Zn, Sn, Pb, Mg—Ba, Ba.
-Pb, Bi, In, Bi-Li, Ni-Ce, Ce-
Ga, Ce-Zn, etc. are mentioned. Of these, Zn or Sn is particularly preferable.

The coating layer does not have to be a continuous film coating the entire surface of the magnet particles. That is, since the magnet particles having the above-mentioned composition have a large magnetocrystalline anisotropy energy, a sufficient coercive force improving effect is obtained if the coating layer covers at least a part of the surface of the magnet particles, preferably 70% or more of the surface. To be realized.

The thickness of the coating layer is preferably 0.1 μm or more, more preferably 0.5 μm or more in order to improve the coercive force. In addition, although there is no particular upper limit on the thickness of the coating layer, in order to increase the filling rate of the magnet particles in the resin-bonded magnet and obtain good moldability during the production of the resin-bonded magnet, it is usually 25 μm or less. It is preferable that

The ratio of the coating layer to the total of the magnet particles and the coating layer is preferably 0.5 to 15% by volume. When the ratio of the coating layer is less than the above range, it is difficult to set the thickness of the coating layer to the above range, and when the ratio exceeds the above range, the magnet particle filling rate may be increased when applied to the resin bonded magnet. It becomes difficult, and the moldability also decreases.

At least a part of the mixed portion coating layer is preferably formed with a mixed portion containing a magnet particle constituent element. The mixed portion is formed by mutual diffusion of the magnet particle constituent element and the coating layer constituent element, and exists around the magnet particle. Due to the presence of this mixed portion, the deterioration of the coercive force is remarkably improved.

In the mixed portion, at least T and / or R, particularly Fe and /
Alternatively, Sm is contained. It is preferable that the magnet particle constituent element and the coating layer constituent element exist as an intermetallic compound, and it is particularly preferable that the intermetallic compound of T of the magnet particle and the coating layer constituent element is included in the mixed portion. For example, when the coating layer is made of Zn, Zn ₇ Fe
It is preferable that intermetallic compounds such as ₃ , Zn ₉ Fe ₁ and Sm ₂ Zn ₁₇ are contained, and particularly Zn ₇ Fe ₃ and Zn ₉
Fe ₁ is preferably contained.

The thickness of the mixed portion is preferably 0.05 μm or more, particularly 0.5 μm or more in order to obtain a high coercive force. There is no particular upper limit on the thickness of the mixed portion, and the entire coating layer may be the mixed portion, but it is preferably 10 μm or less in order to obtain high saturation magnetization.

When a plurality of magnet particles are in contact with each other in the coating layer and are present as secondary particles, the mixed portion is present around the secondary particles.

The composition and thickness of the mixed portion can be measured by X-ray diffraction or electron probe microanalyzer (EPMA). In addition, in this specification, the thickness of the mixed portion means that the content ratio of the magnet particle constituent elements is 10 to 90.
The thickness of the region is atomic%.

Method for forming coating layer and mixed portion The method for forming the coating layer on the surface of the magnet particles is not particularly limited and may be appropriately selected depending on the material of the coating layer and the like.

For example, the coating layer is thermal CVD, plasma C
It can be formed by various vapor phase growth methods such as a CVD method such as VD and a PVD method such as vapor deposition, sputtering and ion plating.

Of these, the CVD method is preferable because it has a high step coverage and can form a coating layer having a substantially uniform thickness on the entire surface of the magnet particles. In particular, thermal CVD
When using, since the coating layer is formed while heating the magnet particles, by appropriately selecting the conditions at the time of forming the coating layer, the coating layer constituent element and the magnet particle constituent element are mutually diffused, and the above-mentioned mixed The part can be easily formed. Further, for example, when magnet particles are placed on a heated dish and thermal CVD is performed while vibrating or rotating the dish, a substantially uniform and uniform thickness is obtained on the surface of the magnet particles. A coating layer can be formed.

In the case of forming the coating layer by thermal CVD, various organic metals may be used as the source gas, for example, various alkoxides such as zinc alkoxide and metal soap such as zinc stearate can be used.

The coating layer can also be formed by mechanical energy. For example, the coating layer raw material particles containing the coating layer constituent elements are mixed with the magnet particles, and mechanical energy is applied to these particles to fuse them. At this time, mechanical energy is applied so that at least the magnetic characteristics of the magnet particles are not destroyed.

As a method of applying mechanical energy as described above, it is easy to control the coating conditions and work, form a continuous film having a uniform and uniform thickness, and easily control the film thickness. Fusion is preferred.

In the present specification, the mechanofusion is a technique in which mechanical energy, particularly mechanical strain force is applied between a plurality of different material particles to cause a mechanochemical reaction. As a device for applying such mechanical strain force, there is, for example, a powder or granular material processing device as described in JP-A-63-42728.
Specifically, a mechanofusion system manufactured by Hosokawa Micron Co., Ltd. or a hybridization system manufactured by Nara Machinery Co., Ltd. is suitable.

FIG. 1 shows an example of the mechanofusion coating device.
Shown in. In FIG. 1, the mechanofusion coating device 7
Rotates the casing 8 containing the powder at a high speed to form the powder layer 6 on the inner peripheral surface 81 thereof, and at the same time, causes the friction piece 91 and the scraping piece 95 to rotate relative to the casing 8 to form the inner periphery of the casing 8. On the surface 81, the friction layer 91 compresses and rubs the powder layer 6, and at the same time, the scraping piece 95 scrapes, disperses, and agitates.

Various conditions for the mechanofusion may be appropriately set according to the composition of the raw material particles of the coating layer and the intended composition of the coating layer. For example, the mixing time is 20 to 40 minutes in the above apparatus. The rotation speed of the casing 8 is 800
˜2000 rpm, temperature: 15˜70 ° C., other conditions may be normal. The average particle diameter of the coating layer raw material particles is preferably about 0.5 to 10 μm.

By properly selecting various conditions in such a mechanofusion, it is possible to form the mixed portion together with the formation of the coating layer.

The coating layer can also be formed by liquid phase plating. As the liquid phase plating, various kinds of electroplating or electroless plating may be used.

When the coating layer is formed by each of the above-mentioned methods, the magnet particles may agglomerate. However, when the coating layer is applied to the resin bonded magnet, it may be crushed if necessary. Multiple magnet particles may be present.

In addition to the method of directly forming the coating layer on the magnet particles as described above, the method of crushing the metal-bonded magnet in which the magnet particles are dispersed in the metal binder is also used. Can be produced. In this case, the binder serves as the coating layer.

There is no particular limitation on the method for producing the crushed metal bonded magnet. For example, when a magnet powder composed of magnet particles and a binder powder composed of binder particles are mixed and molded and then heat treated, the magnet particles can be bonded by the binder, and a metal bonded magnet is obtained.

When this method is used, a binder capable of binding magnet particles at 550 ° C. or lower, preferably 500 ° C. or lower is used. Further, the average particle diameter of the binder powder is not particularly limited, but in order to mix it uniformly with the magnet powder,
It is preferably about 0.5 to 30 μm. The mixing means is also not particularly limited, and, for example, a Raikai machine or the like may be used.

The content of the binder powder in the mixture of the magnet powder and the binder powder is not particularly limited,
If the content of the binder powder is too low, it becomes difficult to obtain a uniform coating layer when crushed due to poor moldability, and if the content is too high, the coating layer becomes too thick, so normally, It is preferably 2 to 25% by volume.
The molding means is not particularly limited, but usually compression molding is performed. The pressure during molding is not particularly limited, but is usually about 0.2 to 16 t / cm ² .

In such a case, since the metal bonded magnet is crushed and used, it is not necessary to impart anisotropy to the metal bonded magnet, but crushed powder containing a plurality of magnet particles in the coating layer can be obtained. In this case, it is preferable that the directions of easy magnetization axes of the plurality of magnet particles be oriented. For such orientation, the above-mentioned molding may be performed in a magnetic field.

The heat treatment temperature for binding the magnet particles with the binder is 550 ° C. or lower, preferably 500 ° C. or lower. When the heat treatment temperature exceeds 550 ° C., the magnet powder is decomposed and N is released, resulting in extremely low magnetic properties. The heat treatment temperature is not particularly limited as long as it is 550 ° C. or lower, and may be appropriately selected depending on the melting point of the binder so that the required viscosity can be obtained. Sufficient thermal stability cannot be obtained. Further, the temperature holding time during the heat treatment is preferably about 10 minutes to 5 hours. The heat treatment means is not particularly limited, but means for heating while applying pressure is preferable, and for example, hot pressing, plasma activated sintering (PAS), etc. are preferable.

When a pressurizing and heating means such as a hot press is used for binding the magnet particles with the binder, even if the heat treatment temperature is lower than the melting point of the binder, that is, the binder is not in a molten state, It is possible to form metal bonded magnets.

After the heat treatment, it is cooled. By cooling in a magnetic field, it is possible to favorably maintain the anisotropy due to the above-mentioned magnetic field molding.

In this method, the mixed portion is formed during the heat treatment and the cooling when the magnet particles are bound with the binder. In order to obtain a high coercive force by controlling the composition and thickness of the mixed portion, the temperature during heat treatment and cooling and its temporal change may be appropriately controlled.

When manufacturing a metal bonded magnet, molding may be performed by a casting method. When the casting method is used, a fluid in which magnet powder is dispersed in a molten binder is formed by casting. The method for producing the fluid is not particularly limited. For example, a method may be used in which the binder is melted to form a molten metal, and the magnet powder is put into this and stirred and mixed, or alternatively, the binder powder and the magnet powder are mixed and then heated to melt the binder. The method of doing may be used.

When the method of introducing the magnet powder into the molten metal binder is used, there is no particular limitation on the means for stirring and mixing the magnet powder and the binder. For example, the impeller made of a material (stainless steel etc.) that does not react with the binder is used for stirring. A method etc. can be used.

The content of the binder in the fluid is not particularly limited, but if the content of the binder is too low, the moldability deteriorates and it becomes difficult to obtain a uniform coating layer when pulverized, and the content is too high. Since the coating layer becomes too thick when pulverized, it is usually preferable to set the binder content to 10 to 40% by volume.

Further, after producing the above fluid, a part of the binder may be removed if necessary. A certain amount or more of binder is required to uniformly disperse the magnet powder in the binder, but when manufacturing a metal-bonded magnet with a relatively simple shape such as a plate, high fluidity is required during molding. Therefore, the binder amount may be small. When used in the manufacture of resin-bonded magnets, the shape of metal-bonded magnets may be simple lumps or plates,
After dispersing with a sufficient amount of binder, molding can be performed even if a part of the binder is removed, whereby the thickness of the coating layer can be reduced. If the thickness of the coating layer can be reduced, the filling rate of the magnet particles can be increased when forming the resin bonded magnet, and the moldability does not decrease. As a method of removing a part of the binder, for example, filtration or centrifugation is preferable, and a method of heating under reduced pressure to evaporate the binder may be used.

The fluid composed of the molten binder and the magnet powder is cooled and solidified in the mold, but when the solidification temperature of the binder is lower than the Curie temperature of the magnet powder, the particles are solidified in the magnetic field. Since the easy axis of magnetization can be oriented and an anisotropic metal bonded magnet can be obtained, it is possible to improve the magnetic characteristics when a plurality of magnet particles are contained in the coating layer as described above. ..

The temperature of the fluid during dispersion and casting is
The temperature is 550 ° C. or lower, preferably 500 ° C. or lower. When the temperature of the fluid exceeds 550 ° C., the magnet powder is decomposed and N is released, resulting in extremely low magnetic characteristics. The temperature of the fluid is not particularly limited as long as it is 550 ° C. or lower, and may be appropriately selected according to the melting point of the binder so that the viscosity required for casting can be obtained, but a binder that melts below 150 ° C. is used. If so, practically sufficient thermal stability cannot be obtained.

The mixed portion due to mutual diffusion of the magnet particle constituent elements and the binder constituent elements can be formed by appropriately selecting the conditions for dispersing the magnet powder in the molten binder, casting, and cooling. is there.

There is no particular limitation on the method of crushing the metal bonded magnet produced by these methods.
It may be crushed with a disc mill or an attritor.
By pulverizing, magnet particles having a metallic binder as a coating layer are obtained. It is preferable that the coating layer be pulverized so that one magnet particle is contained therein, but a plurality of magnet particles may be contained as described above.

When a preferable mixed portion cannot be obtained by the various coating layer forming methods described above, the mixed particles are formed and the composition and thickness of the mixed portion are controlled by subjecting the magnet particles having the coating layer to heat treatment. It is possible. Further, in the method using the metal bonded magnet, such heat treatment may be applied to the metal bonded magnet before crushing.

There is no particular limitation on the holding temperature and the temperature holding time during such heat treatment, and the conditions for forming the mixed portion effective for improving the magnetic properties may be appropriately selected.
Usually, it is about 10 minutes to 5 hours at 250 to 470 ° C.

In the present invention, after forming the coating layer, a part of the coating layer may be removed if necessary. For example, when the coating layer is made of Zn, the mixed portion contains Zn ₇ Fe ₃ ,
Zn and Zn ₇ Fe ₃ are non-magnetic. Then, as described above, since the coating layer may have an action of repairing the surface defects of the magnet particles, if the coating layer in the region exceeding the thickness required for repairing the surface defects of the magnet particles is removed, It is possible to further improve the magnetic characteristics while maintaining the coercive force improving effect. In particular, when the method of pulverizing the metal bonded magnet among the above-mentioned coating layer forming methods is used, this method is effective because the coating layer tends to be thick.

The method of removing a part of the coating layer is not particularly limited, but a method of washing the magnet particles having the coating layer with an alkaline solution or an acidic solution is preferable. For example, when the coating layer is made of Zn, Zn is an amphoteric compound, so that it easily dissolves in both an alkaline solution and an acidic solution.
On the other hand, Zn ₇ Fe ₃ which is a constituent of the mixed portion is difficult to dissolve in these solutions. Therefore, only the coating layer other than the mixed portion can be selectively removed. Various conditions such as pH and temperature of the solution used for partially removing the coating layer, cleaning time and cleaning method are not particularly limited, and suitable conditions may be experimentally determined. For example, 0.1 to 0 A 2 mol / l Na ₂ CO ₃ solution is heated to about 50 to 70 ° C., and magnet particles having a coating layer are put into this solution for 10 minutes to 4 minutes.
By stirring for about an hour, most of the coating layer can be removed leaving the mixed portion.

Even when the mixed portion is not formed, it is possible to remove a part of the coating layer by controlling the dissolution time.

Method for producing resin- bonded magnet The magnet particles having the coating layer produced as described above are dispersed in a resin binder to obtain a resin-bonded magnet.

The resin-bonded magnet may be manufactured by an ordinary method. That is, first, the magnet particles having the coating layer and the resin binder are mixed, shaped, and heat-treated as necessary.

There is no particular limitation on the molding method, and either a compression bonded magnet using compression molding or an injection bonded magnet using injection molding may be used.

The binder to be used is not particularly limited, and various resins used for known resin-bonded magnets may be used. For example, in the case of compression bonded magnets, various thermosetting resins such as epoxy resins using various curing agents may be used, and in the case of injection bonded magnets, various thermoplastic resins such as polyamide resins may be used. The state of the binder at the time of mixing is not particularly limited.

There is no particular limitation on the method of mixing the magnet particles and the binder, and a horizontal rotary cylindrical mixer, a cubic cube mixer,
Any of a vertical double cone type mixer, a V type mixer, a plow plate mixer, a spiral mixer, a ribbon mixer, an impact rotary mixer and the like may be used. The conditions for compression molding or injection molding are not particularly limited, and may be appropriately selected from known conditions.

The resin-bonded magnet may contain a lubricant, a coupling agent, a plasticizer, an antioxidant, etc., if necessary, in addition to the above-mentioned magnet particles and binder.

<Metal Bonded Magnet> When the above-mentioned magnet particles are applied to a metal bonded magnet, a metal bonded magnet may be produced by the same method as in forming the coating layer.

[0119]

EXAMPLES Specific examples of the present invention will be given below.

[Example 1] <Production of mother alloy ingot> First, a mother alloy ingot was produced by high frequency induction heating. Mother alloy ingot is T
The crystal grains had a rhombohedral crystal structure of h ₂ Zn ₁₇ type, and the average grain size was about 8 μm. The crystal structure was confirmed by the X-ray diffraction method. The composition of the mother alloy ingot and the contents of the Sm ₂ Fe ₁₇ phase, the Sm-Fe phase richer than Sm ₂ Fe ₁₇ phase and the α-Fe phase in the ingot are shown in Table 1 below. In Table 1, the Sm-rich Sm-Fe phase is simply referred to as the Sm-Fe phase. Note that some mother alloys were subjected to solution treatment at 1150 ° C. for 20 hours. The content of each phase after the solution treatment is also shown. The quantification of each phase is
It was performed by X-ray diffraction and EPMA.

<Production of Alloy Particles> Each mother alloy ingot was crushed to an average particle diameter of 100 μm or less to obtain alloy particles.

<Production of Nitride Particles> Next, the alloy particles were subjected to a nitriding treatment to produce nitride particles. The nitriding treatment was performed by heat treatment at 450 ° C. for 10 hours in an N ₂ gas atmosphere.

<Production of Magnet Particles> Nitride particles were finely ground to 2 μm with an attritor. Magnet particles using a mother alloy that has not been subjected to solution heat treatment are 6 kgf / cm after fine pulverization.
Classified with a cyclone classifier using nitrogen gas of ² ,
Coarse particles (particle size of about 10 μm or more) containing α-Fe phase as a main component were removed. In addition, magnet particles No. 1 shown in Table 1
In Nos. 3 and 3, since the area of the α-Fe phase in the mother alloy was small, the removal rate of the α-Fe phase by classification was lower than in Nos. 5 and 6.

Table 1 shows the coercive forces iHc and Hk and the saturation magnetization 4πIs of these magnet particles. Hk is
It is the external magnetic field strength when the magnetic flux density in the second quadrant of the magnetic hysteresis loop becomes 90% of the residual magnetic flux density. If Hk is low, a high energy product cannot be obtained. The magnetic properties were measured by VSM with the magnet powder oriented.

[0125]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, magnet particles Nos. 5 and 6 produced using a mother alloy ingot having an α-Fe phase content within the range of the present invention and containing no Sm-rich Sm-Fe phase.
Has a higher coercive force than Nos. 1 and 3 using a mother alloy containing an Sm-rich Sm-Fe phase exceeding the α-Fe phase, and has a high removal rate of α-Fe phase particles, resulting in saturation magnetization Particles with a high alloy solution-treated mother alloy
Magnetic properties equivalent to those of Nos. 2 and 4 are obtained. As described above, according to the present invention, it is possible to omit the solution treatment that requires a long time.

On the other hand, the Sm-rich Sm-Fe phase was converted to α-Fe.
Magnet particles No. 1 and 3 which contained more than one phase and had a low removal rate of α-Fe phase particles by classification, had low saturation magnetization,
Further, Hk is low because particles having a low iHc are mixed.

Example 2 <Manufacture of Resin Bonded Magnet> Using the magnet particles manufactured in Example 1, a resin bonded magnet was manufactured.

First, an epoxy resin powder was dissolved in an organic solvent, and then magnet particles were put into the organic solvent and stirred to obtain a slurry. The slurry was dried with a spray dryer and the magnet particles were coated with an epoxy resin. Specifically, discharging the slurry into nitrogen gas which is injected at a pressure of 8 kgf / cm ^2, dried with nitrogen gas at a flow rate of 50 m ³ / 10min to the slurry 1 kg.

Next, the magnet particles were compression-molded and further heat-cured to obtain a resin-bonded magnet.

When the coercive force of these resin-bonded magnets was measured, magnetic properties were obtained according to the magnet particles used.

<Formation of coating layer>

Mechanofusion method The coating layer raw material powder made of Zn particles having an average particle diameter of 1.2 μm and the magnet powder made of the above magnet particles were mixed, and the coating layer raw material particles and the magnet particles were fused by the mechanofusion method. A coating layer was formed on the surface of the magnet particles. The mechanofusion was performed by a mechanofusion system manufactured by Hosokawa Micron Co., Ltd. The conditions at that time were 1500 rpm of the casing rotation speed and 40 minutes of processing time.

Thermal CVD Method Zinc stearate was used as a source gas, and a coating layer was formed on the surface of the magnet particles by the thermal CVD method. At the time of CVD, the magnet powder was placed on the heated dish and the magnet powder was uniformly heated while vibrating the dish.
The temperature of the magnet powder was 200 ° C.

A crushed metal-bonded magnet, a mixture of the powder of the binder having an average particle diameter of 15 μm and the above-mentioned magnet particles was prepared with a cemented carbide liquor machine. Zn (melting point 419 ° C.) was used as the binder, and the content of the binder powder in the mixture was 12.5% by volume. The mixture was compression-molded, and the obtained molded body was subjected to pressure heat treatment by hot pressing. Press time for hot pressing is 1 hour, holding temperature is 450 ℃, pressurizing pressure is 8t / cm
² The hot pressing was performed in a nitrogen gas flow of 1 atm.

After hot pressing, it was cooled to obtain a metal bonded magnet. The metal bonded magnet was crushed by a disc mill to obtain magnet particles having a coating layer. It should be noted that some of the pulverized powder had a structure in which a coating layer surrounds around 10 or less agglomerated magnet particles.

After crushing the metal-bonded magnet, 70
Magnet particles were prepared by immersing in a 0.5 mol / l solution of Na ₂ CO _{3 at 0} ° C. to dissolve and remove a part of the coating layer.

After the coating layer was formed by each of the above methods, the magnet particles were heat-treated in a nitrogen gas atmosphere. Heat treatment is 450
It was carried out at ℃ for 1 hour.

After the heat treatment, the magnet particles having the coating layer were subjected to X-ray diffraction, and the kinds of compounds contained in the mixed portion were examined. As a result, SmN, Sm ₂ Zn ₁₇ , Fe ₂ N,
Fe ₃ Zn ₇ etc. were confirmed.

A resin-bonded magnet was produced in the same manner as above using the magnet particles having the coating layer formed thereon. When the coercive force of these resin bonded magnets was measured, the coercive force was improved with respect to each of the bonded magnets.

Further, when Sn was used as the material for forming the coating layer, magnet particles having the coating layer were prepared by the above-mentioned respective methods and measured by EPMA in the same manner as described above, the presence of the mixed portion was confirmed. Further, as a result of X-ray diffraction, the presence of FeSn ₂ was confirmed in the mixed portion.

In each of the above examples, the F of the magnet particles was
When a part of e is replaced by Co, increase in Tc, 4πIs
Was observed and a slight decrease in iHc was observed.

[0143]

According to the present invention, the solution treatment of the mother alloy is unnecessary, so that the magnet particles can be produced in an extremely short time, and the α-Fe phase which deteriorates the magnetic properties can be easily separated. A magnet with good magnetic properties can be obtained. Further, since the solution treatment at high temperature for a long time is not performed, the composition of the master alloy does not change and the characteristics as designed can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a coating device by mechanofusion used when forming a coating layer on the surface of magnet particles.

[Explanation of symbols]

 6 Powder layer 7 Mechanofusion coating device 8 Casing 91 Friction piece 95 Scraping piece

Claims (7)

[Claims] 1. Containing 5 to 15 atomic% of R (wherein R is one or more elements selected from rare earth elements and including Sm as an essential element) and 0.5 to 25 atomic% of N And the balance is T (where T is Fe, or Fe and C
It is o. ) Is a method for producing a magnet, the method comprising the steps of casting a master alloy containing R and T, a coarse pulverizing step, a nitriding step, and a fine pulverizing step, and ₂ T ₁₇ phase as a main phase, alpha-Fe phase containing 0.02 to 15 vol%, and the content of the content of the R-rich R-T phases the alpha-Fe phase than R ₂ T ₁₇ A method of manufacturing a magnet, characterized in that less master alloy is used. 2. The mother alloy contains 0.05% by volume or less of an R-T phase richer in R than R ₂ T ₁₇ and 1 /% of an α-Fe phase.
The method for producing a magnet according to claim 1, wherein the magnet contains 2 or less. 3. The method according to claim 1, further comprising a step of classifying different phase particles having an α-Fe phase after the finely pulverizing step.
Alternatively, the method for manufacturing the magnet according to the item 2. 4. The method according to claim 1, further comprising the step of forming a metal coating layer on at least a part of the surface of the magnet particles.
The method for producing a magnet according to any one of 1. 5. The method for producing a magnet according to claim 1, further comprising the step of dispersing the magnet particles in a resin or metal binder to produce a bonded magnet. 6. An R ₂ T ₁₇ phase as a main phase, an α-Fe phase in an amount of 0.02 to 15% by volume, and an R-T phase richer in R than R ₂ T ₁₇ is contained in the α-Fe phase. A master alloy for magnet production, characterized in that it is less than the content of the Fe phase. 7. The master alloy for magnet production according to claim 6, wherein the R-T phase richer in R than R ₂ T ₁₇ is contained in an amount of 0.05% by volume or less and 1/2 or less of the α-Fe phase.