JP2017218623A - Production method of rare earth-iron-nitrogen system alloy powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a rare earth-iron-nitrogen system alloy powder having excellent magnetic characteristics by preparing single crystal particles having small crystal distortion, less fine powder and uniform particle sizes.SOLUTION: A production method of a rare earth-iron-nitrogen system alloy powder includes: a step 1 of preparing a mixture of a rare earth oxide powder and an iron powder as a starting raw material; a step 2 for performing a reduction diffusion treatment in an inert gas with a predetermined amount of calcium metal added; a step 3 of supplying a mixed gas of ammonia and hydrogen to perform a nitrogen treatment of reduction diffusion treated product in the air flow at a predetermined temperature; and a step 4 of charging a nitride treatment product block in water to treat in wet to break, the obtained magnet crude powder is cracked to obtain a cracked powder having a specific half-value width of a (113) plane and a specific rate of fine powder of less than 1 μm.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a rare earth-iron-nitrogen magnet powder, and more particularly, to produce a rare earth-iron-nitrogen magnet powder having excellent magnetic properties with a small crystal distortion and a small particle size. Regarding the method.

In recent years, rare earth-iron-nitrogen based magnets represented by Sm—Fe—N magnets are known as high performance and inexpensive magnets. The Sm—Fe—N magnet powder used as the magnet raw material powder is said to exhibit the maximum saturation magnetization by being composed of a composition of x = 3 in the case of Sm ₂ Fe ₁₇ Nx (non-patent document). 1).

This rare earth-iron-nitrogen based magnet has been conventionally used in a melting method in which a rare earth-iron alloy is produced using a high frequency furnace, an arc furnace or the like using Fe and Sm metal, Fe, Fe ₂ O ₃ , Sm ₂ O _3, etc. It is obtained by nitriding a mother alloy obtained by a reduction diffusion method in which rare earth-iron-nitrogen is produced by mixing heat treatment of Ca. The powdered rare earth-iron-nitrogen magnet thus obtained is pulverized until the average particle size is about several μm to about 5 μm because the coercive force generation mechanism is a nucleation type magnet. Used as a powder.

The melting method requires heat treatment for melting, pulverizing, and homogenizing the composition of the raw material powder at a high temperature of 1500 ° C. or higher (see Patent Document 3), and the process is extremely complicated. Impurities are generated by oxidation because of exposure to the material, and nitriding is performed after wet processing. However, since the surface is oxidized during wet processing, nitriding cannot proceed uniformly, and among the magnetic properties, saturation magnetization, coercive force, squareness There is a problem that the maximum energy product is lowered as a result. In addition, because the rare earth metal required as a raw material is expensive, the method for producing a rare earth-iron-nitrogen based magnet is more expensive than the reduction diffusion method in which an inexpensive rare earth oxide powder can be used as a raw material. It is.

  In the reduction diffusion method, iron powder of several tens of μm is usually used as a starting material, and after mixing a rare earth metal or rare earth oxide and an alkaline earth metal, a reduction heat treatment is performed to produce a master alloy. In the case of the method, after the final nitriding treatment, the mechanical pulverization is performed so that the particle size becomes several tens to several μm, so that the protrusion of the fracture surface and the crystal distortion that can become the core of the reverse axis occur and the magnetic properties are deteriorated. In addition, since a large amount of fine powder is generated, fluidity cannot be ensured when the obtained pulverized powder and resin are kneaded, and there is a risk that a molded product may be defective.

In order to solve such problems, methods have been proposed (see Patent Documents 1, 2, and 3) in which magnet powder is obtained without pulverization by reducing the particle diameter of the powder used as a starting material in advance. . None of these methods require a pulverization step, but since the sintering that occurs during the reduction-diffusion reaction cannot be completely prevented, the presence of polycrystalline particles reduces anisotropy. End up. Since the powders obtained by these methods are not single crystal particles, the sintered particles are fragile and fine powders are likely to be generated. Therefore, it cannot be said that the above problem has been solved.

Japanese Patent Laid-Open No. 11-310807 JP 2003-297660 A Japanese Patent Laid-Open No. 11-189811

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

  In view of such circumstances, an object of the present invention is a rare earth-iron-nitrogen magnet having excellent magnetic properties by producing single crystal particles with small crystal distortion, small amount of fine powder, and uniform particle size. An object of the present invention is to provide a method for producing a rare earth-iron-nitrogen alloy powder capable of obtaining a powder.

As a result of intensive research to solve the above-mentioned problems, the present inventors have made a reduction using a particle having a small particle size as a starting material in advance in order to improve the performance of rare earth-iron-nitrogen based magnet powder. When the rare earth-iron-nitrogen based magnet powder obtained by the diffusion method is used for wet crushing using a medium, a single crystal particle having a small amount of fine powder and a powder having a small particle size or a powder close to it is obtained with a small crystal distortion. By adjusting to the conditions, it was found that the magnetic properties of the obtained molded body were extremely high, and the present invention was completed.

That is, according to the first aspect of the present invention, there is provided a method for producing a rare earth-iron-nitrogen based magnet powder,
A method for producing a rare earth-iron-nitrogen alloy powder including the following steps 1 to 4 is provided.
Step 1. A step of preparing, as a starting material, a mixture of rare earth oxide powder and iron powder, or a mixture further containing at least one selected from rare earth iron composite oxide and iron oxide.
Step 2. A step of adding a predetermined amount of calcium metal to the mixture obtained in the step 1 and subjecting the mixture to a reduction diffusion treatment in an inert gas.
Step 3. Following the step 2, a step of supplying a mixed gas of ammonia and hydrogen and nitriding the reduced diffusion treatment product at a predetermined temperature in this air stream.
Step 4. The nitrided product obtained in Step 3 is put into water, wet-treated and disintegrated, and recovered as a magnet coarse powder. The obtained magnet coarse powder is crushed and subjected to powder X-ray diffraction after the pulverization treatment. (113) The half width of the surface is 0.1 deg. And a pulverized powder having a cumulative volume percentage of fine powder of less than 1 μm by laser diffraction type particle size distribution measurement of less than 10%.

According to a second invention of the present invention, in the first invention, the average particle size of the iron powder, rare earth iron composite oxide, and iron oxide in step 1 is 3 μm or less. A method for producing a base alloy powder is provided.

According to the third invention of the present invention, in the first invention, the metal calcium in step 2 has an average particle size of 4 mesh or less, and the amount of metal calcium required to reduce all oxides is 1 Provided is a method for producing a rare earth-iron-nitrogen based magnet powder characterized in that the equivalent weight is 1.5 equivalents or more and 3.0 equivalents or less.

According to a fourth invention of the present invention, in the first invention, the crushing process of step 4 is a wet crushing process using a ball for grinding as a medium. A method for producing magnet powder is provided.

According to a fifth aspect of the present invention, there is provided a method for producing a rare earth-iron-nitrogen based alloy powder characterized in that, in the first aspect, the alloy powder is Sm-Fe-N.

By the reduction diffusion treatment using a powder raw material having a small particle size by the production method of the present invention, when the obtained reduction diffusion treatment product is made uniform by wet crushing treatment using a medium, the crystal distortion is small, Further, by obtaining single crystal particles having a small amount of fine powder or powder close thereto as a pulverized powder, it is possible to obtain a rare earth-iron-nitrogen alloy powder having high-performance magnetic properties. A molded body obtained by molding this rare earth-iron-nitrogen based magnet powder can also achieve extremely high performance magnetic properties.

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

The method for producing a rare earth-iron-nitrogen alloy powder according to the present invention comprises a mixture of a rare earth oxide powder and an iron powder, or a mixture further containing at least one selected from a rare earth iron composite oxide and iron oxide in the mixture. Step 1 prepared as follows, Step 2 in which a predetermined amount of metallic calcium is added and reduction diffusion treatment in an inert gas, Following the reduction diffusion treatment, a mixed gas of ammonia and hydrogen is supplied. Step 3 of nitriding at a predetermined temperature, the finally obtained nitriding product is put into water and wet-treated to disintegrate, and the obtained magnet coarse powder is crushed to give a half of a specific (113) surface. It is a manufacturing method including step 4 of obtaining a pulverized powder having a value range and a specific fine powder ratio of less than 1 μm.

・ Rare earth-iron-nitrogen alloy powder >>
First, a rare earth-iron-nitrogen alloy to which the production method of the present invention is applied will be described.

In the rare earth-iron-nitrogen alloy according to the present invention, the rare earth element is selected from at least one element selected from Sm, Gd, Tb, and Ce, or from Pr, Nd, Dy, Ho, Er, Tm, and Yb. Examples include alloys that are at least one element, and examples include Sm—Fe—N alloys and Sm—Fe—Ti—N alloys in which the rare earth element is samarium (Sm), and Sm—Fe—N alloys. In particular, the present invention can be preferably applied to a composition of Sm ₂ Fe ₁₇ N ₃ containing 23.2% by mass or more and 23.6% by mass or less of the Sm amount with respect to the whole magnet powder.

・ Manufacturing method of rare earth-iron-nitrogen alloy powder >>
The production method of the present invention will be described in the order of steps.

1. Step 1: Raw material powder mixing treatment step (1) Raw material powder First, as a rare earth-iron-nitrogen magnet raw material, a mixture of rare earth oxide powder and iron powder, or a mixture of rare earth iron composite oxide and iron oxide. A mixture further containing at least one selected is prepared as a starting material.

One iron powder of the raw material powder has a mean particle size of preferably 3 μm or less, more preferably 1.5 μm or less, in order to reduce the size of the rare earth-iron master alloy to be produced later. This is because when the average particle size exceeds 3 μm, the coarse particles of the rare earth-iron mother alloy produced later grow to an average particle size of 20 μm or more, so the coercive force is greatly reduced and the nitriding process This is because of insufficient nitridation in the grains. Further, the iron oxide containing iron in addition to the iron powder for the same reason as above (other _Fe 2 _{O 3,} etc. FeO and _Fe 3 _{O 4),} for further samarium iron composite oxide containing samarium (such SmFeO ₃₎ However, the average particle size is preferably 3 μm or less, and more preferably 1.5 μm or less.

The rare earth oxide of the other raw material powder is at least one element selected from Sm, Gd, Tb, Ce, or at least one element selected from Pr, Nd, Dy, Ho, Er, Tm, Yb. Can be mentioned. Among them, those containing Sm are particularly preferable because the effects of the present invention can be remarkably exhibited. When Sm is contained, in order to obtain a high coercive force, Sm is preferably 60% by mass or more, preferably 90% by mass or more of the entire rare earth element, in order to obtain a high coercive force.

The particle size of the rare earth oxide powder is preferably 5 μm or less in average particle size and smaller than the particle size of iron powder in that it is easy to diffuse in the solid phase and non-uniform diffusion does not occur.

(2) Mixing method As a method for obtaining a mixed powder, each powder is wet-mixed with a ball mill, a bead mill, or an attritor using water or alcohol as a solvent, or a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, or a nauter. In addition to dry mixing such as mixers, Henschel mixers, high-speed mixers, vibration mills, etc., hydroxides or oxyhydroxides that have already been mixed by the coprecipitation method by reaction crystallization are manufactured and oxides are obtained by heat treatment, etc. As the mixing method, various known methods can be used.

In addition to the method of directly obtaining a mixed powder as described above, in order to obtain a desired substance ratio, heat treatment at a high temperature is once performed, samarium iron composite oxide is manufactured, or iron powder is produced by hydrogen reduction. It is also possible to carry out a method of including the process in the process.

2. Step 2: Reduction diffusion treatment step (1) Reduction diffusion treatment Next, the mixed raw material powder obtained in the above step 1 is further mixed with metallic calcium, heat-treated at a predetermined temperature in an inert gas atmosphere, and reduced diffusion. To obtain a rare earth-iron master alloy having a Th ₂ Zn ₁₇ type crystal structure.

In general, as described above, the reduction diffusion method is performed by filling a reaction vessel with a mixture of metallic calcium as a reducing agent, and evacuating the atmosphere, and then introducing an inert gas to replace the inert gas atmosphere. For example, the alloy powder is obtained by heating at 950 ° C. or more and 1200 ° C. or less in an argon gas atmosphere.

In the present invention, the metallic calcium used as the reducing agent is preferably granular metallic calcium classified to 4 mesh or less in terms of handling safety, reactivity, and cost. The amount of metallic calcium added when the amount of metallic calcium required to reduce all the raw material oxide is 1 equivalent is preferably 1.5 equivalents or more and 3.0 equivalents or less, and more preferably 1.5 equivalents or more and 2 equivalents or less. Less than 0.0 equivalent is more preferable. This is because if it is less than 1.5 equivalents, it will be insufficient due to evaporation of evaporated water and metallic calcium during heat treatment, and if it is more than 3.0 equivalents, excessive metal calcium will be a factor that hinders grain growth. There is a problem that even if the temperature of the main calcination is raised, it becomes difficult to increase, and gas absorption at the time of nitriding after reductive diffusion is hindered by excess metallic calcium, so that nitriding tends to be uneven. The reducing agent is mixed with the raw material powder or separated so that the metal vapor can come into contact with the raw material powder. However, if the reducing agent is mixed and reduced and diffused, the reaction product becomes porous, and the subsequent nitriding is performed. Processing can be performed efficiently.

It is also effective to mix an additive that promotes the decay of the reaction product in the wet treatment step after the nitriding treatment, together with the raw material powder and the reducing agent. As the disintegration accelerator, an alkaline earth metal salt or oxide such as calcium chloride can be used, and can be uniformly mixed simultaneously with the raw material powder. Here, the inert gas is at least one selected from argon and helium.

In the present invention, since the starting material prepared by adjusting the particle size of the raw material powder to a specific particle size is used, it is preferable that the heat treatment temperature of the reduction diffusion treatment is in the range of 850 ° C. or higher and 1180 ° C. or lower. Below 850 ° C, the diffusion of rare earth elements in the iron powder becomes non-uniform, the coercive force and squareness of the resulting rare earth-iron-nitrogen alloy powder are reduced, and the time required for diffusion becomes very long, Productivity deteriorates. When the temperature exceeds 1180 ° C., the generated rare earth-iron mother alloy undergoes grain growth, so that uniform nitriding becomes difficult, and the saturation magnetization, squareness, and coercive force of the magnet powder may decrease. Further, the amount of evaporation of Sm increases, and there is a possibility that a coarse magnet powder having a desired composition cannot be obtained, and an excessive amount is required, resulting in high cost. Therefore, by setting the temperature within the range of 850 ° C. or higher and 1180 ° C. or lower, such a phenomenon does not occur, and the primary particles are small and become a sintered secondary particle body. There is an effect that crystal distortion hardly occurs at the time of subsequent crushing.

Here, the product obtained by the reduction diffusion treatment, for example, when metallic calcium is used as the reducing agent, rare earth-iron mother alloy having a Th ₂ Zn ₁₇ type crystal structure and calcium oxide, unreacted surplus It is a massive mixture composed of metallic calcium and the like. Further, when the granular metal calcium is mixed with the raw material powder and subjected to the reduction diffusion treatment, a porous massive mixture is obtained.

In contrast, the melting method disclosed in Patent Document 3 uses a rare earth metal as the rare earth material, which is more expensive than the rare earth oxide material used in the reduction diffusion method. In particular, the difference in the case of Sm where the rare earth element provides excellent magnetic properties is significant. Moreover, the unnecessary powder generated by the particle size adjustment reduces the product yield and further increases the powder cost. In addition, the melting method requires a homogenization heat treatment step for eliminating the α-Fe phase in the obtained alloy, and further includes a step of coarsely pulverizing the alloy subjected to the homogenization heat treatment before introducing nitrogen, and a coarse pulverization step. This is not preferable because it requires a step of adjusting the particle size of the powder.

(2) Cooling of reaction product In the present invention, the reaction product after the reduction-diffusion reaction is continuously maintained at 300 ° C or lower, preferably 50 ° C or higher and 280 ° C without changing the atmospheric gas as an inert gas. Hereinafter, it is more preferably cooled to 100 ° C. or more and 250 ° C. or less. If the temperature after cooling exceeds 300 ° C, the nitridation reaction with the reaction product proceeds rapidly during nitriding, which may increase the α-Fe phase. It is desirable to cool to a lower temperature. This is because, at temperatures exceeding 300 ° C., the reaction product is active, so the alloy is rapidly nitrided, and the intermetallic compound having a Th ₂ Zn ₁₇ type crystal structure is decomposed into an Fe-rich phase and SmN. Because it is presumed.

After cooling, the wet reaction is not performed on the reaction product, which is a porous massive mixture, and the atmosphere gas is changed from an inert gas to a mixed gas containing at least ammonia and hydrogen, and the process proceeds to the next nitriding step. If the reaction product is exposed to the atmosphere at this time, the active rare earth-iron mother alloy powder in the reaction product is oxidized and the reactivity is deactivated. It is important to bring it into the nitriding process so that it is not exposed to (oxygen).

3. Process 3: Nitriding process (1) Nitriding process In the nitriding process, after the inert gas of the atmospheric gas is discharged, the temperature is raised to a mixed gas containing at least ammonia and hydrogen, and the reaction product is heated to a specific temperature. Heat to.

The nitriding gas needs to contain at least ammonia and hydrogen, and argon, nitrogen, helium, etc. can be mixed to control the reaction. The amount of the nitriding gas is preferably an amount sufficient for the amount of nitrogen in the magnet powder to be 3.3% by mass or more and 3.7% by mass or less.

  The ratio of ammonia to the total airflow pressure (ammonia partial pressure) is 0.2 or more and 0.6 or less, preferably 0.3 or more and 0.5 or less. If the ammonia partial pressure is less than 0.2, nitriding of the mother alloy does not proceed over a long period of time, and the amount of nitrogen cannot be made 3.3 mass% or more and 3.7 mass% or less. Saturation magnetization and coercivity are reduced. Exceeding 0.6 is not preferable because nitriding proceeds excessively.

It is important that a mixed gas stream containing ammonia and hydrogen is supplied at a nitriding temperature of 350 ° C. or higher and 500 ° C. or lower, preferably 400 ° C. or higher and 480 ° C. or lower, and the mother alloy is subjected to a nitriding heat treatment. When the temperature is lower than 350 ° C., it takes a long time to introduce 3.3 mass% or more and 3.7 mass% or less of nitrogen into the rare earth-iron master alloy in the reaction product. Disappear. On the other hand, when the temperature exceeds 500 ° C., the Sm ₂ Fe ₁₇ phase, which is the main phase, is decomposed to produce α-Fe, and thus the squareness of the demagnetization curve of the finally obtained rare earth-iron-nitrogen based magnet powder. Is unfavorable because it decreases. From the cooling temperature to the nitriding temperature, it is desirable to raise the temperature relatively rapidly at a rate of 4 ° C. or more and 10 ° C. or less per minute in order to increase production efficiency. Further, the holding time at the cooling temperature is not particularly required. This is because no effect on nitriding is observed even if the temperature is kept at the cooling temperature.

  The retention time of the nitriding treatment is 100 minutes to 300 minutes, preferably 140 minutes to 250 minutes, although it depends on the nitriding temperature. If it is less than 100 minutes, nitriding becomes insufficient, while if it exceeds 300 minutes, nitriding proceeds excessively, which is not preferable.

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

  Thereby, the nitrogen distribution in the individual crystal cells constituting the magnet powder can be made more uniform, and the squareness can be improved. The holding time for the heat treatment is 30 minutes to 200 minutes, preferably 60 minutes to 250 minutes.

4). Step 4: Crushing treatment step (1) Wet treatment In the present invention, the treated product after nitriding is wet treated, and a by-product (such as calcium oxide or calcium nitride) of a reducing agent component contained therein is removed. Separate and remove from rare earth-iron-nitrogen magnet powder.

As described above, the wet treatment is performed on the magnet powder after the nitridation. When the reaction product is wet-treated before nitriding, the surface of the mother alloy is oxidized during this wet treatment process, thereby varying the degree of nitridation. Because it can be used.

  In addition, if the treatment product is left in the atmosphere for a long time after nitriding, an oxide of a reducing agent component such as calcium is generated and difficult to remove, or the surface of the magnet powder is oxidized, resulting in non-uniform nitriding. The squareness decreases due to the decrease in the ratio of nuclei and the formation of nuclei of new creation. Therefore, the nitriding product left in the atmosphere is preferably wet-treated within two weeks after being taken out from the reactor.

In the wet treatment, first, the disintegrated product is put into water, and decantation-water injection-decantation is repeated to remove most of the produced Ca hydroxide. Further, if necessary, acid cleaning is performed using acetic acid or hydrochloric acid in order to remove residual Ca hydroxide. The hydrogen ion concentration of the aqueous solution at this time is preferably in the range of pH 4 to 7. There may be a non-magnetic phase around the main phase that lowers the saturation magnetization of the magnetic properties due to the influence of Sm added excessively during reduction diffusion, and the Sm content is 23.2% by mass or more and 23.6% by mass. It is preferable to perform pickling so as to be as follows.

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

(2) Crushing and drying The obtained rare earth-iron-nitrogen based magnet coarse powder is formed from two types of primary particles in addition to secondary particles obtained by sintering a large number of particles having a small particle size. Yes. Such a magnet coarse powder is put into a pulverizer together with a solvent and crushed so weakly that the sintered portion of the rare earth-iron-nitrogen based magnet powder composed of secondary particles is removed, and then using a filter with a predetermined opening. Filtration and drying give a rare earth-iron-nitrogen magnet fine powder.

The pulverization of rare earth-iron-nitrogen based alloy powder in the present invention is widely used in various chemical industries that handle solids, and among the pulverizers for pulverizing various materials to a desired degree, powder particles A wet pulverization method such as a ball mill, a bead mill, or a medium agitation mill excellent in diameter control is suitable, but it is particularly important that the pulverization level is set to a level that does not cause strong pulverization to break the primary particles.

  As a solvent used for pulverization, isopropyl alcohol, ethanol, toluene, methanol, hexane, or the like can be used, and isopropyl alcohol is particularly preferable. The medium may be any material such as silicon nitride, zirconia, alumina, glass, SUJ2, and stainless steel, but silicon nitride is particularly desirable. This is because, since the specific gravity of the medium is small, the force applied to the powder can be reduced even when the medium is filled, and the wear is very small.

The rare earth-iron-nitrogen based alloy powder of the present invention, after pulverization, has a half width of 0.1 deg. It is important that fine particles of less than 1 μm are less than 10% in cumulative volume percentage by laser diffraction type particle size distribution measurement. At this time, the half width of the (113) plane by powder X-ray diffraction was 0.1 deg. If the powder is pulverized until it becomes the above powder, the crystal distortion increases and the coercive force decreases. In addition, if the amount of particles less than 1 μm by laser diffraction particle size distribution measurement is 10% or more in cumulative volume percentage, too much fine powder is present, so that the coercive force decreases sharply because of weakness to heating when manufacturing a molded product. Moreover, there is a possibility that the molding itself cannot be performed due to poor fluidity during kneading with the resin.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all. In the present invention, the obtained magnet powder was measured and evaluated by the following method.

≪Evaluation≫
(1) Magnetic properties (coercivity (iHc, unit kA / m))
The magnetic properties of the alloy powder are rare earth-iron-nitrogen based in stearic acid by applying an orientation magnetic field of 1600 A / m according to Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005. A sample was prepared by orienting magnet powder, and measurement was performed by magnetizing with a magnetic field of 4000 kA / m. The specific gravity of the magnetic alloy powder was 7.67 g / cm ^3, and the coercive force (iHc, unit kA / m) was measured using a vibrating sample magnetometer with a maximum magnetic field of 1200 kA / m without correcting the demagnetizing field.

(2) Half width of (113) plane by powder X-ray diffraction The crystallinity of the pulverized rare earth-iron-nitrogen alloy powder was measured with a powder X-ray diffractometer (XRD: Mac Science M03XHF), and the measurement results From (113) plane, the half width (deg.) Was calculated.

(3) Laser diffraction type particle size distribution Laser diffraction type particle size distribution measuring apparatus manufactured by Sympatec: Measured with Heros Rhodes, and the cumulative volume percentage of particles less than 1 μm was calculated.

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

(5) Fluidity (Melt index MI method)
The obtained magnet alloy powder sample and nylon 12 were kneaded for 30 minutes in a 200 ° C. lab plast mill, and the composition for a bonded magnet was pulverized by a plastic pulverizer to form a pellet for molding. This was measured using a melt indexer, measuring temperature: 250 ° C., load: 21.6 kg, die swell: diameter 2.1 mm × thickness 8 mm, and the flowability (cm ³ / second). The larger this value, the higher the fluidity and the better the injection moldability.

(6) Injection moldability The obtained pellets were subjected to a cylinder temperature of 230 ° C. and a mold temperature of 80 ° C. by applying an orientation magnetic field of 560 kA / m in the 7 mm direction with an injection molding machine with a clamping pressure of 50 tons, and a diameter of 10 mm × A cylindrical rare earth magnet having a thickness of 7 mm was manufactured. At this time, it was determined whether the molded product had defects such as insufficient filling, flow mark, jetting, and the like. The case where there was no defect was considered good.

Example 1
As a starting material powder, 100.0 g of iron oxide Fe ₂ O ₃ powder (purity 99%) having an average particle size of 0.7 μm, produced by a reaction crystallization method, and samarium oxide Sm having an average particle size of 2.8 μm 31.8 g of ₂ O ₃ powder (purity 99.5%) was weighed, then iron oxide weighed in a 500 ml plastic container was dispersed in 130 g of pure water to form a slurry, and further samarium oxide was added to this. Ball mill mixing was carried out for 20 hours by adding a 5/32 inch diameter metal ball made by SUJ2. Thereafter, the slurry was discharged from the plastic container, separated from the metal balls, and then dried at 40 ° C. for 20 hours in a stationary vacuum freeze dryer.

100.0 g of the dried mixed powder was flowed at 25 ml / min · g in a box-type atmosphere furnace, heated to 700 ° C. at a heating rate of 5 ° C./min and held for 4 hours, then cooled to room temperature, The hydrogen reduction product was recovered by replacing with air.

3.6 g of metal calcium particles (purity 99%) having a particle size of 4 mesh (Tyler mesh) or less were mixed with 16 g of this hydrogen reduction product with a conditioning mixer (MX-201: manufactured by Sinky) for 30 seconds. This was inserted into a stainless steel reaction vessel, and the inside of the vessel was evacuated with a rotary pump to replace Ar gas. Then, while flowing Ar gas, the temperature was raised to 850 ° C., held for 10 hours, and further raised to 1050 ° C. After holding for a time and carrying out a reduction heat treatment, it was cooled to 250 ° C. while circulating Ar gas in the furnace.

Next, the Ar gas is switched to an ammonia-hydrogen mixed gas having an ammonia partial pressure of 0.33, the temperature is raised, held at 420 ° C. for 200 minutes, then switched to hydrogen gas at the same temperature and held for 30 minutes, It switched to nitrogen gas, hold | maintained for 30 minutes, and cooled.

  The taken porous mass reaction product was immediately poured into pure water, and collapsed to obtain a slurry. From this slurry, the Ca hydroxide suspension was separated by decantation, the operation of stirring pure water for 1 minute after pouring and then decanting was repeated 5 times to obtain an Sm—Fe—N alloy powder slurry.

  While stirring the obtained alloy powder slurry, dilute acetic acid was added dropwise, and the pH was maintained at pH 5.0 for 7 minutes. After washing with water 6 times with pure water and further solvent substitution with isopropyl alcohol, the alloy powder is filtered and vacuum-dried at 150 ° C., whereby primary particles and secondary particles obtained by sintering the primary particles are sintered. Sm—Fe—N coarse powder having an average particle size of 5.5 μm was obtained.

  Using a rotary ball mill as a crushing treatment device, crushing in a 300 cc container containing 10 g of powder, 100 g of isopropyl alcohol and 1 kg of SUJ2 balls (4 mm), crushing at a rotational frequency of 30 Hz for 45 minutes, surface treatment with phosphoric acid, and vacuum at room temperature It dried and the Sm-Fe-N fine powder was obtained.

As magnetic properties of the obtained magnet powder, the holding power of the alloy powder was applied with an orientation magnetic field of 1600 A / m according to the Japan Bond Magnet Industry Association, Bond Magnet Test Method Guidebook, BM-2002, BM-2005. A sample was prepared by orienting rare earth-iron-nitrogen magnet powder in stearic acid, and magnetized with a magnetic field of 4000 kA / m. The specific gravity of the magnetic alloy powder was 7.67 g / cm ^3, and the coercive force (iHc, unit kA / m) was measured using a vibrating sample magnetometer with a maximum magnetic field of 1200 kA / m without correcting the demagnetizing field.

The X-ray density of the powder calculated from the analytical composition and the lattice constant of the Th ₂ Zn ₁₇ type crystal structure was 7.67 g / cm ³ , and the saturation magnetic flux density 4πIm was converted with this value. As a result, the coercive force (iHc) was as high as 1061 kA / m.

Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.082 deg. Further, the cumulative volume percentage of particles less than 1 μm by laser diffraction type particle size distribution measurement was 8.4%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.68 cm. ^The injection moldability was good at ³ / sec.

(Example 2)
In the crushing process of Step 4, all the processes were performed in the same manner as in Example 1 except that the medium of the rotary ball mill was changed from SUJ2 to silicon nitride to obtain Sm—Fe—N fine powder.

  As a result of evaluating magnetic characteristics of the obtained fine powder, coercive force (iHc) was as high as 1093 kA / m.

Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.071 deg. Further, the cumulative volume percentage of particles less than 1 μm by laser diffraction type particle size distribution measurement was 6.8%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.88 cm. ^The injection moldability was good at ³ / sec.

(Example 3)
In the crushing process of Step 4, the crushing processing device was changed from a rotary ball mill to a bead mill, and crushing for 20 minutes at a rotational frequency of 30 Hz in a container containing 1 kg of powder, 2 kg of isopropyl alcohol, and 220 g of silicon nitride balls (3 mm). Except for the change, the same treatment as in Example 2 was performed to obtain Sm—Fe—N fine powder.

  As a result of obtaining the magnetic characteristics, the coercive force (iHc) was as high as 1093 kA / m.

Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.068 deg. Furthermore, the ratio of less than 1 μm by the particle size distribution measurement was 5.7%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.92 cm. ^The injection moldability was good at ³ / sec.

Example 4
Except that the medium was changed from silicon nitride to stabilized zirconia in the crushing process of step 4, the same process as in Example 3 was performed to obtain Sm—Fe—N fine powder.

As a result of evaluating the magnetic characteristics, the coercive force (iHc) was as high as 1109 kA / m.

Further, the half width of the (113) plane by XRD measured for the strain of the crushed magnet powder was 0.074 deg. Furthermore, the cumulative volume percentage of particles less than 1 μm by laser diffraction particle size distribution measurement was 7.5%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.80 cm. ^The injection moldability was good at ³ / sec.

(Example 5)
In the pulverization process of Step 4, the pulverization apparatus is changed from a ball mill to a medium agitation mill, and pulverized in a container containing 1 kg of powder, 2 kg of isopropyl alcohol and 10 kg of SUJ2 balls (4 mm) for 35 minutes at a peripheral speed of 100 rpm. Except for the change, the treatment was performed in the same manner as in Example 1 to obtain Sm-Fe-N fine powder.

  As a result of evaluating the magnetic characteristics, the coercive force (iHc) was as high as 1045 kA / m.

Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.093 deg. Further, the cumulative volume percentage of particles less than 1 μm by laser diffraction particle size distribution measurement was 9.6%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.53 cm. ^The injection moldability was good at ³ / sec.

(Comparative Example 1)
In the crushing treatment step of Step 4, all the treatments were performed in the same manner as in Example 1 except that the ball diameter of the medium was changed from 4 mm of Example 1 to 6 mm and the crushing treatment time was changed from 45 minutes to 40 minutes. -Fe-N fine powder was obtained.

  As a result of evaluating the magnetic characteristics, the coercive force (iHc) was 901 kA / m, which was significantly lower than that of Example 1. Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.120 deg. In comparison with Example 1, the particle volume distribution was broader, and the cumulative volume percentage of particles less than 1 μm by laser diffraction particle size distribution measurement was greatly increased to 16.5%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.21 cm. ^It decreased to ³ / second and the injection moldability was poor.

(Comparative Example 2)
Except that the crushing time of the crushing treatment conditions in Step 4 was extended from 20 minutes to 45 minutes in Example 3 and the rotation frequency was changed from 30 Hz to 25 Hz, all the treatments were carried out in the same manner as in Example 3, and Sm- Fe-N fine powder was obtained.

  As a result of evaluating the magnetic properties, the coercive force (iHc) was 925 kA / m, which was significantly lower than that of Example 3. Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.118 deg. In comparison with Example 3, the particle volume distribution was broader, and the cumulative volume percentage of particles less than 1 μm by laser diffraction particle size distribution measurement was significantly increased to 9.5%.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.57 cm. ^Although it decreased to ³ / sec, the injection moldability was good.

(Comparative Example 3)
Except that the silicon nitride ball diameter of the medium in the crushing treatment condition of step 4 was changed from 3 mm of Example 3 to 2 mm, and the crushing treatment time was changed from 20 minutes to 30 minutes, all the same as in Example 3. The treatment was performed to obtain Sm—Fe—N fine powder.

  As a result of evaluating the magnetic characteristics, the coercive force (iHc) was 1117 kA / m, which was as high as that of Example 3. Further, the half width of the (113) plane by XRD measured for the strain of the crushed magnet powder was 0.092 deg. However, the cumulative volume percentage of particles less than 1 μm by laser diffraction type particle size distribution measurement was 18.7%, and the number of fine particles increased significantly.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.13 cm. ³ / sec, which was significantly worse than Example 3, and the injection moldability was also poor.

(Comparative Example 4)
All the same as Example 5 except that the diameter of the SUJ2 ball of the medium agitating mill in Step 4 was changed from 4 mm to 6 mm in Example 5 and the crushing time was changed from 30 minutes to 25 minutes. The treatment was carried out to obtain Sm—Fe—N fine powder.

  As a result of evaluating the magnetic characteristics, the coercive force (iHc) was 853 kA / m, which was significantly lower than that of Example 5. Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.135 deg. In comparison with Example 5, the cumulative volume percentage of particles less than 1 μm by laser diffraction type particle size distribution measurement was 20.1%, and the number of fine particles increased significantly.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.09 cm. ³ / sec, which was significantly worse than Example 5, and the injection moldability was also poor.

(Comparative Example 5)
As a starting material powder, 10.97 g of iron powder having an average particle diameter of 40 μm and 5.03 g of samarium oxide Sm ₂ O ₃ powder (purity 99.5%) having an average particle diameter of 2.8 μm are weighed and dried. After mixing, 3.6 g of metal calcium particles (purity 99%) having a particle size of 4 mesh (Tyler mesh) or less were mixed for 30 seconds with a conditioning mixer (MX-201: manufactured by Sinky).

  This was inserted into a stainless steel reaction vessel, and the inside of the vessel was evacuated with a rotary pump to replace Ar gas. Then, while flowing Ar gas, the temperature was raised to 850 ° C., held for 10 hours, and further raised to 1050 ° C. After holding for a time and carrying out a reduction heat treatment, it was cooled to 250 ° C. while circulating Ar gas in the furnace. Next, the Ar gas is switched to an ammonia-hydrogen mixed gas having an ammonia partial pressure of 0.50 and the temperature is raised, held at 420 ° C. for 140 minutes, then switched to hydrogen gas at the same temperature and held for 30 minutes, It switched to nitrogen gas, hold | maintained for 30 minutes, and cooled.

  The taken porous mass reaction product was immediately poured into pure water, and collapsed to obtain a slurry. From this slurry, the Ca hydroxide suspension was separated by decantation, the operation of stirring pure water for 1 minute after pouring and then decanting was repeated 5 times to obtain an Sm—Fe—N alloy powder slurry.

  While stirring the obtained alloy powder slurry, dilute acetic acid was added dropwise, and the pH was maintained at pH 5.0 for 7 minutes. After washing with water 6 times with pure water and further solvent substitution with isopropyl alcohol, the alloy powder is filtered and vacuum-dried at 150 ° C., whereby primary particles and secondary particles obtained by sintering the primary particles are sintered. Sm—Fe—N coarse powder having an average particle diameter of 21 μm was obtained.

  Using a bead mill, in a container containing 1 kg of powder, 2 kg of isopropyl alcohol, and 220 g of silicon nitride balls (3 mm), the powder was crushed for 120 minutes at a rotational frequency of 30 Hz, surface-treated with phosphoric acid, and vacuum-dried at room temperature and then Sm-Fe- N fine powder was obtained.

As a result of evaluating the magnetic properties, the coercive force (iHc) was 877 kA / m, which was significantly lower than that of Example 3. Further, the half width of the (113) plane by XRD measured for strain of the crushed magnet powder was 0.124 deg. In comparison with Example 3, it was broader, and the cumulative volume percentage of particles of less than 1 μm by laser diffraction type particle size distribution measurement was 17.3%, and the fine particles were greatly increased.

Next, nylon 12 was added so that the magnetic powder volume ratio was 60%, kneaded with a lab plast mill, and then injection molded at 230 ° C. to produce a bonded magnet. The fluidity was 0.15 cm. ³ / sec, which was significantly worse than Example 3, and the injection moldability was also poor.

As described above, in Examples 1 to 5, by appropriately adjusting the crushing conditions in each of the ball mill, the bead mill, and the medium agitation mill, by suppressing the generation of fine powder and suppressing the crystal distortion, a high coercive force ( iHc) is obtained, and good flowability and injection moldability of a molded body using this powder are achieved.

In addition, in Comparative Examples 1-5 which deviated from the conditions of this invention, it turns out that fluidity | liquidity and injection moldability cannot be made compatible in the produced molded object.

In Comparative Examples 1 and 4, even if the same average particle diameter is aimed at by increasing the medium ball diameter to 6 mm, the crystal distortion is large, and the amount of fine powder increases due to the potential to shift from crushing to pulverization. The coercive force, fluidity, and injection moldability are all reduced.

In Comparative Example 2, since the impact was eased by lowering the peripheral speed and the powder was crushed over time, the crystal distortion finally increased, but the amount of fine powder could be suppressed. Therefore, the coercive force is low, but the fluidity and injection moldability are good.

In Comparative Example 3, since the media ball diameter was reduced to 2 mm and crushed, the applied force was weakened and the crystal distortion was reduced. However, the amount of fine powder increased in the direction of the media and increased in coercive force. Injection moldability is poor.

In Comparative Example 5, since the manufacturing process was changed greatly and started from a large particle size, the particle size of the Sm—Fe—N coarse powder was as large as 21 μm, and it was a powder composed of single particles instead of polycrystalline secondary particles, and was weak. Hard to break with force. Therefore, it takes a lot of time to grind under the same conditions, the crystal distortion is large and the amount of fine powder is increased, and the coercive force, fluidity and injection moldability are all lowered.

Claims (5)

A method for producing a rare earth-iron-nitrogen magnet powder,
A method for producing a rare earth-iron-nitrogen based alloy powder comprising the following steps 1 to 4.
Step 1. A step of preparing, as a starting material, a mixture of rare earth oxide powder and iron powder, or a mixture further containing at least one selected from rare earth iron composite oxide and iron oxide.
Step 2. A step of adding a predetermined amount of calcium metal to the mixture obtained in the step 1 and subjecting the mixture to a reduction diffusion treatment in an inert gas.
Step 3. Following the step 2, a step of supplying a mixed gas of ammonia and hydrogen and nitriding the reduced diffusion treatment product at a predetermined temperature in this air stream.
Step 4. The nitrided product obtained in Step 3 is put into water, wet-treated and disintegrated, and recovered as a magnet coarse powder. The obtained magnet coarse powder is crushed and subjected to powder X-ray diffraction after the pulverization treatment. (113) The half width of the surface is 0.1 deg. And a pulverized powder having a cumulative volume percentage of fine particles of less than 1 μm by laser diffraction type particle size distribution measurement of less than 10%. 2. The method for producing a rare earth-iron-nitrogen based magnet powder according to claim 1, wherein the average particle size of the iron powder, rare earth iron composite oxide, and iron oxide in Step 1 is 3 μm or less. The metal calcium in the step 2 has an average particle diameter of 4 mesh or less, and 1.5 equivalents or more and 3.0 equivalents or less when the amount of metal calcium required to reduce all oxides is 1 equivalent. The method for producing a rare earth-iron-nitrogen based magnet powder according to claim 1. The method for producing a rare earth-iron-nitrogen based magnet powder according to claim 1, wherein the crushing treatment in the step 4 is a wet crushing treatment using a grinding ball as a medium. The method for producing a rare earth-iron-nitrogen based alloy powder according to claim 1, wherein the alloy powder is Sm-Fe-N.