JP2000034503A - Alloy powder for Sm-Fe-N bonded magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve oxidation resistance by covering the surface of alloy powder particles with a specific protective layer that is thermally stable and has few defects such as vacancies, and furthermore, agglomeration of fine powders. The present invention provides an alloy powder for Sm-Fe-N-based bonded magnets, which realizes high magnetic properties when formed into a magnet by suppressing the above. SOLUTION: An Sm-Fe-N bond characterized in that the particle surface is coated with a protective layer composed of any one of a fluorine compound film, a polysilazane cured film, a silicon oxide film, and a silicon nitride film. Alloy powder for magnets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Sm-Fe-N based alloy powder for bonded magnets, and more particularly, to an oxide powder having a particle surface coated with a protective layer, having improved oxidation resistance and high magnetic properties. The present invention relates to an Sm—Fe—N based alloy powder for a bonded magnet that is realized.

[0002]

2. Description of the Related Art Bonded magnets obtained by molding a powder of a hard magnetic material using a binder are used as various permanent magnet materials for motors, speakers, microphones, small generators, and the like. In response to recent miniaturization and high output of equipment, rare earth alloy magnet materials having high magnetic properties have been used as hard magnetic materials to be used.

Sm-F, one of the rare earth alloy magnet materials
The alloy powder for e-N-based bonded magnets is obtained by nitriding an Sm-Fe-based alloy obtained by a manufacturing method such as a casting method, a quenching method, a reduction diffusion method, etc. to obtain an Sm-Fe-N-based alloy, and finely pulverized. is there. The pulverization is based on the nucleation type of the coercive force expression mechanism of the Sm-Fe-N magnet.
This is because, in order to increase the coercive force, it is necessary to pulverize to a single magnetic domain particle size.

[0004]

Generally, a rare earth alloy magnet material is apt to be oxidized because of containing a rare earth element as a component, and the oxidation deteriorates magnetic properties. The alloy powder for the Sm—Fe—N based bonded magnet, which is a rare earth alloy magnet material, is particularly remarkable because it is a fine powder. For this reason, the magnetic properties are greatly degraded due to oxidation in the heating step or handling in the production of the bonded magnet, and the excellent magnetic properties of the Sm-Fe-N-based alloy have not been fully utilized.

Another rare earth alloy magnet material, Sm-C
Various proposals have been made to improve the corrosion resistance of o-based and Nd-Fe-B-based alloy powders for rare earth bonded magnets. For example, the surface of the powder is subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment (for example, see JP-A-1-14902).
JP, JP-A-64-15301), forming a polymer film (for example, JP-A-4-257202), and performing metal plating (for example, JP-A-Heisei 4-257202). No. 7,142,246).

[0006] However, any of the above methods is applied to Sm-Fe
Even when applied to an alloy powder for a -N-based bonded magnet, the oxidation resistance is improved, but the properties of the powder surface are rough and the magnetic properties are deteriorated. Further, in order to obtain a sufficient oxidation resistance effect as a film, it is necessary to have a film thickness of about several tens of μm, so that the volume fraction of the material exhibiting magnetic characteristics decreases, and the magnetic characteristics deteriorate. I will.

[0007] Further, in any of the above methods, when the coating is formed, agglomeration of the fine powders also occurs, so that the directions of the magnetic anisotropy become uneven, and the deterioration of the magnetic properties is inevitable.

Accordingly, the present invention solves the above-mentioned problems and improves the oxidation resistance by coating the surface of the particles of the alloy powder with a specific protective layer that is thermally stable and has few defects such as voids. It is an object of the present invention to provide an alloy powder for Sm-Fe-N-based bonded magnets that realizes high magnetic properties when formed into a magnet by suppressing aggregation of fine powders.

[0009]

Means for Solving the Problems The alloy powder for an Sm-Fe-N-based bonded magnet of the present invention which solves the above-mentioned problems has a fluorine compound film, a polysilazane cured film,
It is characterized by being covered with a protective layer composed of either a silicon oxide film or a silicon nitride film. An underlayer may be formed below the protective layer.

[0010] The Sm-Fe-N alloy used in the present invention can be obtained by subjecting an Sm-Fe alloy having a hexagonal main phase to a nitriding treatment. The alloy composition was Sm 2
0 to 30% by weight, nitrogen is 1 to 5% by weight, and the rest is F
e occupies. For the purpose of improving the temperature characteristics without impairing the magnetic characteristics, a part of Fe may be replaced by Co.

The Sm—Fe alloy is manufactured by a casting method, a quenching method, a reduction diffusion method, or the like. For the purpose of growing the hexagonal main phase in the alloy, a heat treatment may be performed before the nitriding step. For efficient nitriding, it is desirable to make the alloy into a powder. In this case, the particle size of the powder also affects the fine pulverization step after the nitriding treatment, and the particle size range is desirably 20 to 63 μm. The type of crusher used for crushing the alloy is not limited, but to prevent oxidation of the alloy powder,
It is desirable to have a structure that can be crushed in an inert atmosphere.

In the nitridation process of the Sm-Fe alloy, accompanying removal of adsorbed gas from the surface of the alloy particles, pulverization by hydrogen gas treatment, and heat treatment for uniformly diffusing nitrogen into the alloy powder are performed. Is also good.

It is desirable that the powder after nitriding is finely pulverized to an average particle size of several μm before being formed as a bonded magnet. In order to finely pulverize the Sm-Fe-N-based alloy, wet pulverization using an organic solvent or dry pulverization in a trace oxygen atmosphere can be performed. Various known crushers can be used, and the crushing method is not particularly limited.

When the protective layer is a fluorine compound film, the preferred average thickness is 0.1 to 0.2 μm. As the fluorine compound, known compounds can be used, but it is desirable that the composition can be cured at a low temperature of 150 ° C. or lower. This is because, when a film is formed at a high temperature exceeding 150 ° C., the structure of the Sm—Fe—N alloy changes, and the magnetic properties deteriorate. Further, it is desirable that the solvent be soluble. This is because a film can be formed from a solution, and a film can be uniformly formed on the powder surface.

In order to form a protective layer composed of a fluorine compound film on the particle surface of the alloy powder for Sm-Fe-N-based bonded magnet, for example, a fluorine compound is dissolved while stirring the alloy powder at room temperature with a stirrer. The solvent can be sprayed. At this time, it is preferable to make the inside of the stirrer an oxygen gas atmosphere of 0.1 to 1 vol%. If the amount of oxygen is outside the above range, it becomes difficult to form an efficient film, or Sm-
This is because it causes oxidation and structural change of the Fe—N-based alloy, thereby deteriorating magnetic properties.

After the spraying, the stirrer is operated, for example, at a heating rate of 1 to 3 ° C.
/ Min to 100-150 ° C. In order to achieve both uniform and dense film formation and suppression of magnetic property deterioration, the conditions are set at an appropriate heating rate and firing temperature.

When the protective layer is a cured polysilazane film, known polysilazane can be used.
It is desirable to be able to cure at a low temperature of 0 ° C. or lower. Fifteen
When a film is formed at a high temperature exceeding 0 ° C., Sm—Fe—N
This is because the structure of the system alloy changes and magnetic properties deteriorate. Further, it is desirable that the solvent be soluble. This is because a film can be formed from a solution, and a film can be uniformly formed on the powder surface.

In order to form a cured polysilazane film on the particle surface of the alloy powder for Sm-Fe-N-based bonded magnet, for example, the polysilazane is dissolved while stirring the Sm-Fe-N-based alloy fine powder in a stirrer at room temperature. This is performed by spraying the solvent. The stirrer used is desirably a stirrer having two or more stirring blades rotating at a high speed of 6 m / s or more in peripheral speed and capable of giving a large shear force to the alloy powder. This is because if the shearing power is weak, the fine powders agglomerate during the formation of the film, and as a result, the magnetic properties are reduced.

When stirring, the inside of the stirrer is 0.1 to 1 vol.
% Oxygen gas atmosphere is preferable. If the oxygen content is outside the above range, it becomes difficult to form an efficient film,
This is because oxidation or structural change of the m-Fe-N-based alloy is caused, and magnetic properties are deteriorated.

After spraying, the stirrer is turned on, for example, at a heating rate of 1 to 3 ° C.
/ Min to 100-150 ° C. In order to achieve both uniform and dense film formation and suppression of magnetic property deterioration, the conditions are set at an appropriate heating rate and firing temperature.

When the protective layer is a silicon oxide film or a silicon nitride film, the preferable average film thickness is 0.01 to 0.1 μm.
m. The film can be formed by, for example, a sputtering method. The sputtering device is not particularly limited as long as an insulator can be used as a target.

In the case of forming a silicon oxide film, a SiO ₂ target is used as a target material, and 0.1 to 10 vol%
Oxygen - argon mixed gas atmosphere, In the case of forming a silicon nitride coating using a SiN ₄ Target 0.1
Reactive sputtering is performed in a 10 vol% nitrogen-argon mixed gas atmosphere. This is because if the concentration of oxygen or nitrogen in the atmosphere is less than 0.1 vol%, the formed film tends to have defects, and if the concentration exceeds 10 vol%, the film forming speed is reduced, and the film cannot be formed efficiently.

[0023]

Example 1 An Sm-Fe-based (25% by weight Sm) alloy produced by high frequency melting by a casting method was subjected to a heat treatment at 1100 ° C. for 24 hours in an argon gas atmosphere. This heat-treated alloy is pulverized to 20 to 63 μm
Alloy coarse powder. This alloy coarse powder was heat-treated at 250 ° C. for 2 hours in a hydrogen gas atmosphere. Subsequently, the inside of the furnace was replaced with a nitrogen gas atmosphere, and heat treatment was performed at 480 ° C. for 72 hours. Further, the inside of the furnace was replaced with an argon gas atmosphere,
Heat treatment was performed at 480 ° C. for 24 hours. The Sm-Fe-N-based alloy coarse powder obtained by the heat treatment was pulverized by a vibration ball mill using dehydrated ethanol as a solvent to obtain a fine powder having an average particle size of about 4 µm.

While stirring the fine powder in a stirrer in a nitrogen-oxygen mixed gas atmosphere of 0.1 vol% oxygen,
The fluorine compound solution was added dropwise so that the amount of the fluorine compound was 1% by weight based on the amount of the fine powder. As the fluorine compound, an amorphous fluorine resin solution (manufactured by Asahi Glass Co., Ltd., trade name: Cytop) is used, and as the stirrer, a high-speed stirrer (Fukae Kogyo Co., Ltd.)
(Trade name: High Speed Mixer FS-1).

After the dropwise addition, the temperature was raised to 150 ° C. at a rate of 1 ° C./min, kept at that temperature for 2 hours, and then cooled to form a fluorine compound film.

With respect to the fine powder on which the coating was formed,
It was kept in a constant temperature and high humidity bath at 90% RH for 1000 hours, and the magnetic characteristics before and after the holding were compared to examine the thermal characteristics. The magnetic properties were measured using a vibrating sample magnetometer (VSM) by mixing fine powder with paraffin and molding the mixture in a magnetic field of 20 kOe. Note that no demagnetizing field correction was performed in this measurement. Table 1 shows the results.

Example 2 A fluorine compound solution was
A fluorine compound film was formed in the same manner as in Example 1 except that the amount of the fluorine compound was dropped to 2% by weight based on the amount of the fine powder used in Example 1, and the same evaluation as in Example 1 was performed. . Table 1 shows the results.

Comparative Example 1 The fine powder obtained in Example 1 before forming the fluorine compound film was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 3 35 V was added to an Sm-Fe (25% by weight Sm) alloy powder produced by the reduction diffusion method.
ol% ammonia gas-hydrogen gas atmosphere at 480 ° C.
Heat treatment was performed for 6 hours. Then, the inside of the furnace was replaced with an argon gas atmosphere, and heat treatment was performed at 480 ° C. for 2 hours. The Sm-Fe-N-based alloy powder obtained by the heat treatment was finely pulverized by a jet mill using nitrogen gas as a carrier to obtain a fine powder having an average particle diameter of 3 µm.

While stirring the fine powder in a stirrer in a nitrogen-oxygen mixed gas atmosphere of 0.1 vol% oxygen,
The fluorine compound solution was added dropwise so that the amount of the fluorine compound was 1% by weight based on the amount of the fine powder. The same fluorine compound and stirrer as in Example 1 were used. After dropping, 1 ° C / mi
The temperature was raised to 150 ° C. with n, and the temperature was maintained for 2 hours, followed by cooling to form a fluorine compound film.

Example 1 of the fine powder having a film formed thereon
The same evaluation was made. Table 1 shows the results.

Comparative Example 2 The fine powder obtained in Example 3 before forming the fluorine compound film was evaluated in the same manner as in Example 1. Table 1 shows the results.

[0033]

[Table 1]

Example 4 An amount of 1% by weight polysilazane with respect to the amount of the fine powder was stirred while the fine powder used in Example 1 was stirred in a stirrer in a nitrogen-oxygen mixed gas atmosphere of 0.1 vol% oxygen. The polysilazane solution was dropped so that As the polysilazane, perhydropolysilazane (trade name: Hervic low temperature type, manufactured by NE Chemcat) was used. The same stirrer as in Example 1 was used.

After dropping, the temperature was raised to 150 ° C. at a rate of 3 ° C./min, kept at that temperature for 2 hours, and then cooled to form a cured polysilazane film.

The fine powder on which the film was formed was heated at 200 ° C.
Was heat-treated in an atmospheric furnace for 1 hour, and the magnetic characteristics before and after the heat treatment were compared to examine the thermal characteristics. Magnetic properties were measured in the same manner as in Example 1. Table 2 shows the results.

Example 5 A polysilazane cured film was formed in the same manner as in Example 4, except that the polysilazane solution was dropped so that the amount of polysilazane was 2% by weight. The thermal characteristics of the fine powder having the film formed thereon were examined in the same manner as in Example 4. Table 2 shows the results.

Example 6 ... The fine powder used in Example 1 was sputtered for 10 minutes in a 0.2 vol% oxygen mixed gas atmosphere of an argon-oxygen gas by an ion gun type sputtering apparatus using a SiO ₂ target. did. During the sputtering, the fine powder was kept stirring. The thermal characteristics of the fine powder on which the silicon oxide film was formed were examined in the same manner as in Example 4. Table 2 shows the results.

Example 7 A fine powder on which a silicon oxide film was formed was obtained in the same manner as in Example 6, except that the sputtering time was 30 minutes. The thermal characteristics of the obtained fine powder were examined in the same manner as in Example 4. Table 2 shows the results.

Example 8: The fine powder used in Example 1 was sputtered for 30 minutes in a 0.2 vol% nitrogen-argon-nitrogen mixed gas atmosphere by an ion gun type sputtering apparatus using a SiN ₄ target. did. During the sputtering, the fine powder was kept stirring. The thermal characteristics of the fine powder on which the silicon nitride film was formed were examined in the same manner as in Example 4. Table 2 shows the results.

Example 9: The fine powder used in Example 3 was sputtered in an argon-oxygen mixed gas atmosphere of 0.2 vol% oxygen by an ion gun type sputtering apparatus using an SiO ₂ target for 30 minutes. did. During the sputtering, the fine powder was kept stirring. The thermal characteristics of the fine powder on which the silicon oxide film was formed were examined in the same manner as in Example 4. Table 2 shows the results.

Comparative Example 3 The fine powder obtained in Example 4 before forming the cured polysilazane film was evaluated in the same manner as in Example 4. Table 2 shows the results.

[0043]

[Table 2]

From the above results, according to the present invention, Sm-
It can be seen that the oxidation resistance of the alloy powder for the Fe—N based bonded magnet is improved and high magnetic properties are realized.

[0045]

According to the present invention, the particle surface of the alloy powder is
The coating is coated with a specific protective layer that is thermally stable and has few defects such as vacancies, improves oxidation resistance, and suppresses agglomeration of fine powders to achieve high magnetic properties when used as a magnet. An alloy powder for Sm-Fe-N-based bonded magnets was provided.

Claims (5)

[Claims] 1. An alloy powder for an Sm—Fe—N bonded magnet, wherein the particle surface of the Sm—Fe—N alloy is coated with a protective layer. 2. The alloy powder for an Sm—Fe—N-based bonded magnet according to claim 1, wherein the protective layer is formed of a fluorine compound film. 3. The alloy powder for an Sm—Fe—N-based bonded magnet according to claim 1, wherein the protective layer is formed of a cured polysilazane film. 4. The alloy powder for an Sm—Fe—N-based bonded magnet according to claim 1, wherein the protective layer is formed of a silicon oxide film. 5. The alloy powder for an Sm—Fe—N-based bonded magnet according to claim 1, wherein the protective layer comprises a silicon nitride film.