JP2005223263A - Method for manufacturing rare earth permanent magnet and resulting rare earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method in which a rare earth permanent magnet can be produced industrially easily by preliminarily compressing rare earth-iron-nitrogen magnet powder and then compacting the preform. <P>SOLUTION: After an oxide film previously containing 0.2 to 1.6 wt.% oxygen for the total amount is formed on the surface of the rare earth-iron-nitrogen magnet powder, the magnet powder having the oxide film is preliminarily compressed in a specified shape in a non-oxidizing atmosphere to form a preform of ≥40% in relative density, and then a magnet compact of ≥85% in relative density is obtained by compacting the preform at a temperature of 350 to 500°C in a non-oxidizing atmosphere. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a rare earth permanent magnet and the obtained rare earth permanent magnet. More specifically, after the rare earth-iron-nitrogen-based magnet powder is pre-compressed and molded, the preform is compacted to obtain an industrial product. The present invention relates to a method for producing a rare earth permanent magnet that can be easily produced, and a rare earth permanent magnet obtained thereby and having excellent magnetic properties.

  Permanent magnets are used in various applications including motors. The material of the permanent magnet is classified into R—Co (R is a rare earth element), R—Fe—B, R—Fe—N, and other rare earth magnets, ferrite magnets, alnico magnets, and the like. Magnets are classified into sintered magnets, bonded magnets, cast magnets and the like according to the manufacturing method.

  In order to increase the maximum energy product (BH) max of a magnet, it is necessary to consolidate the apparent density of the magnet body to the true density of the magnet material. As a method for manufacturing a magnet that increases the apparent density of a magnet body to near the true density of the magnet material, a sintering method applied to the manufacture of the above-described sintered magnet is generally used.

  However, with rare earth-iron-nitrogen based magnet powders represented by Sm-Fe-N magnets, the sintering method cannot be applied because the compound decomposes when heated to about 600 ° C. or higher. Nitriding method (see patent document 1), plasma sintering method (see patent document 2), hot isostatic pressing method (see patent document 3), impact compression method (see patent documents 4 and 5), energizing powder rolling The law (see Patent Document 6) has been studied.

  However, according to the method of nitriding after sintering of the master alloy as disclosed in Patent Document 1, it is expected that a bulk permanent magnet having a high saturation magnetization and a high Curie temperature will be obtained. Depending on the conditions, the sintered body may break due to the volume expansion of the rare earth iron-based alloy compound due to nitriding.

  Further, in Patent Document 2, rare earth-iron-nitrogen based magnet powder is sintered in high-pressure nitrogen gas or plasma-sintered in a vacuum atmosphere to suppress thermal decomposition at high temperature that occurs during sintering. However, there is a problem that it is difficult to stably obtain a magnet having a high coercive force only under the disclosed conditions.

  In Patent Document 3, a rare earth-iron-nitrogen based magnet powder compact pressed in a magnetic field is placed in an alumina container, and hot isostatic pressing (HIP) is performed at 1100 ° C. using nitrogen gas as a pressure medium. In this method, magnet powder is previously nitrided to remove an oxide film and an oxide layer, and thus the powder having improved moldability is hot isostatically pressed. However, as a result of investigations by the present inventors, it has been found that when a high temperature exceeding 1000 ° C. is applied to the magnet powder, the rare earth-iron-nitrogen based magnet powder is decomposed even if the nitrogen gas pressure is increased. In addition, since an alumina container is used, there is a problem that pressure is not applied to the molded body having open pores and the magnetic powder cannot be consolidated.

  In addition, in the shock compression methods of Patent Documents 4 and 5 and the like, decomposition and denitrification can be prevented, and a compact magnet having a high magnetic property with a relative density exceeding 85% can be obtained. Since it is used, there are safety restrictions as industrial production means.

  Further, Patent Document 6 discloses a high relative density compacted magnet obtained by an electric powder rolling method, but the coercive force of the magnets described in the examples is as low as 0.42 MA / m or less. Is. In addition, this method has a problem that it is impossible to manufacture an anisotropic magnet having the easy axis of magnet powder.

Under such circumstances, there has been a strong demand for a method that can easily and safely industrially produce a permanent magnet having a high coercive force and a maximum energy product and having excellent magnetic properties.
JP-A-5-121223 JP-A-5-135978 JP-A-5-217728 Japanese Patent Laid-Open No. 6-077027 JP 2002-319503 A JP 2000-294415 A

  Therefore, in view of the above-mentioned problems of the prior art, the object of the present invention is to easily produce industrially by pre-compacting rare earth-iron-nitrogen-based magnet powder and then compacting the preform. An object of the present invention is to provide a method for producing a rare earth permanent magnet, and a rare earth permanent magnet obtained thereby and having excellent magnetic properties.

  As a result of intensive studies to achieve the above object, the present inventors have optimized the composition of the rare earth-iron-nitrogen-based magnet powder, such as the amount of oxygen, and have performed hot isostatic pressing (HIP). Before compacting, by pre-compressing the raw material magnet powder to a specific relative density, a compacted rare earth permanent magnet having a high residual magnetic flux density and a high coercive force can be obtained. The headline and the present invention were completed.

  That is, according to the first aspect of the present invention, an oxide film containing 0.2 to 1.6% by weight of oxygen is formed in advance on the surface of the rare earth-iron-nitrogen based magnet powder. Thereafter, the magnet powder having the oxide film is pre-compressed into a predetermined shape in a non-oxidizing atmosphere to obtain a preform having a relative density of 40% or more, and the preform is then placed in a non-oxidizing atmosphere in a 350 There is provided a method for producing a rare earth permanent magnet, which is compacted at a temperature of ˜500 ° C. to obtain a magnet compact having a relative density of 85% or more.

According to a second aspect of the present invention, in the first aspect, the rare earth-iron-nitrogen based magnet powder is a magnet powder having a Th ₂ Zn ₁₇ type crystal structure. A method for producing the rare earth permanent magnet described in 1) is provided.

  According to the third aspect of the present invention, in the first aspect, the rare earth-iron-nitrogen based magnet powder is 23.5-25 wt% R (rare earth element), 2.8-5.1. There is provided a method for producing a rare earth permanent magnet characterized in that N (nitrogen) in weight percent and the balance is T (transition metal element and inevitable impurities essential for Fe).

  According to the fourth invention of the present invention, in the third invention, the rare earth-iron-nitrogen based magnet powder contains 50% by weight or more of Sm as R (rare earth element), and further contains Mn as a transition metal element. 7% by weight or less is provided, and a method for producing a rare earth permanent magnet is provided.

  According to a fifth aspect of the present invention, in the first aspect, before the pre-compression molding, 10% by weight or less of Zn powder is added to the magnet powder having an oxide film. A method of manufacturing a rare earth permanent magnet is provided.

  According to a sixth invention of the present invention, in the first invention, when pre-compression molding, the anisotropic magnet powder is molded while applying a magnetic field of 400 kA / m or more. A method of manufacturing a rare earth permanent magnet is provided.

  Furthermore, according to the seventh aspect of the present invention, there is provided a method for producing a rare earth permanent magnet according to the first aspect, wherein the preform is consolidated by hot isostatic pressing (HIP). The

On the other hand, according to an eighth invention of the present invention, a rare earth characterized by being obtained by the production method of any one of the first to seventh inventions and having a maximum energy product (BH) max of 30 kJ / m ³ or more. A permanent magnet is provided.

  According to the present invention, since the rare earth-iron-nitrogen based magnet powder having an oxide film formed on the surface of the magnet powder is pre-compressed under specific conditions and then consolidated in a non-oxidizing atmosphere, the relative density is 85%. As described above, a rare earth-iron-nitrogen compacted magnet having excellent magnetic properties can be manufactured industrially easily and stably.

  Hereinafter, the method for producing a rare earth permanent magnet of the present invention and the rare earth permanent magnet obtained thereby will be described in detail.

  The method for producing a rare earth permanent magnet of the present invention is a method in which the following magnet powder is pre-compressed under specific conditions and then compacted to a desired relative density.

1. Magnet powder The magnet powder used in the present invention is not particularly limited as long as it is a rare earth-iron-nitrogen based magnet powder, and is a known Th ₂ Zn ₁₇ type (for example, Japanese Patent No. 2703281 and Japanese Patent Application Laid-Open No. 08-055712). Or an R—Fe—N system having a TbCu ₇ type (for example, Japanese Patent No. 3332405) crystal structure and an R—Fe—MN system having a ThMn ₁₂ type (for example, Japanese Patent No. 3073807) crystal structure (R is Rare earth elements, M is Mn, V, Ti, Cr, Mo, etc.) magnet powder. Although not only anisotropic magnet powder but also isotropic magnet gold powder is targeted, magnet powder having an anisotropic magnetic field (HA) of 4.0 MA / m or more is preferable.

Among the above-mentioned magnet powders, it has a Th ₂ Zn ₁₇ type crystal structure, 23.5 to 25% by weight of R (rare earth element, including 50% by weight or more of Sm), 2.8 to 5.1% by weight. R-Fe-N alloy powders in which N (nitrogen) and the balance are T (transition metal elements and inevitable impurities essential for Fe) are preferable because they have high saturation magnetization and magnetic anisotropy. .

  Here, when the rare earth element R is less than 23.5% by weight, the coercive force of the magnet is lowered, and when it exceeds 25% by weight, the residual magnetic flux density is lowered, so that the maximum energy product is lowered. Further, when the nitrogen N is less than 2.8% by weight, the coercive force of the magnet is lowered, and when it exceeds 5.1% by weight, the residual magnetic flux density is lowered, so that the maximum energy product is lowered. Further, if the Sm content is less than 50% by weight of the rare earth element R, the coercive force of the magnet is lowered.

  In addition, if M is contained in an amount of 7% by weight or less in addition to Fe as T, the coercive force generation mechanism of the magnet powder becomes a pinning type, and in this case, the coercive force is good because it has good heat resistance. Rare earth permanent magnets can be obtained.

  When the element for expressing the coercive force exceeds 7% by weight, the magnetization of the magnet powder decreases. A preferable amount of Mn or the like is 2 to 6% by weight, and a more preferable amount is 3 to 5% by weight.

  There are no particular limitations on the method for producing the mother alloy for the rare earth-iron-nitrogen magnet, and a melting casting method for producing an alloy ingot by melting the raw material, or mixing a reducing agent with the raw metal oxide. A reduction diffusion method in which a mother alloy is produced by reducing and diffusing rare earth elements in iron can be employed. In the present invention, the preferred method is the reduction diffusion method.

  For example, as described in JP-A-61-295308, this reduction diffusion method uses rare earth oxide powder and other metal powder (in the present invention, iron, cobalt, manganese, etc. as required). And a reducing agent component (residual impurities) such as CaO and residual Ca produced as a by-product after the reaction product mixture is wet-treated after heating a mixture of the reducing agent such as Ca in an inert gas atmosphere or the like. This is a method of directly obtaining an alloy powder by removing.

  In order to produce rare earth-iron-based master alloy powder by this method, (1) a reducing agent is mixed with the raw material powder of oxide and iron powder containing rare earth elements, and (2) the mixture is heated to a specific temperature. Then, the rare earth element is reduced and diffused into the iron-based alloy, (3) the obtained reaction product is disintegrated by hydrogen treatment, and (4) the disintegrated powder is produced by wet treatment.

(1) Preparation of raw material powder As described above, an oxide powder containing a rare earth element and an iron powder are mixed and used as the raw material powder. The oxide containing a rare earth element used in the present invention is not particularly limited, but is at least one element selected from Sm, Gd, Tb, and Ce, or Pr, Nd, Dy, Ho, Er, Tm. And an oxide containing at least one element selected from Yb. Among these, oxides containing Sm are particularly preferable because the effects of the present invention can be remarkably exhibited. In the case of an oxide containing Sm, in order to obtain a high coercive force, Sm needs to be 50% by weight or more, preferably 90% by weight or more of the whole rare earth.

  In addition, the above raw material powder includes Mn, Cr, Nb, Mo, Sb, Ge, Zr, V, Si, Al, Ta, Cu, etc., in order to improve coercive force, improve productivity, and reduce costs. One or more may be added, but the amount added is preferably 7% by weight or less in total. Moreover, as an unavoidable impurity, C, B, etc. may contain 5 weight% or less.

(2) Reduction diffusion Next, the raw material powder and the reducing agent are put into a reaction vessel and heat-treated under specific conditions to reduce the rare earth oxide and other oxide raw materials and diffuse them into the iron powder. Thus, a rare earth-iron master alloy is produced.

  The reducing agent is selected from alkali metals, alkaline earth metals, and hydrides thereof, and metallic calcium is preferable in terms of handling safety and cost. The reducing agent can be mixed with the raw material powder or separated so that calcium vapor can come into contact with the raw material powder. When separated, uniform nitriding is promoted, and the squareness of the obtained magnet powder can be improved.

  It is also effective to mix with the raw material powder an additive that promotes the decay of the reaction product in the subsequent wet processing step. As the disintegration accelerator, alkaline earth metal salts such as calcium chloride, calcium oxide and the like can be used, and they are uniformly mixed simultaneously with the raw material powder.

  It is important that the raw material powders are mixed uniformly so as not to separate due to differences in powder characteristics. As a mixing method, for example, a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, a Nauter mixer, a Henschel mixer, a super mixer, a high speed mixer, a ball mill, a vibration mill, an attritor, a jet mill and the like can be used.

  The reduction temperature is desirably in the range of 1090 to 1250 ° C, particularly 1100 to 1230 ° C. When the temperature is lower than 1090 ° C., the diffusion of rare earth elements and the like is not uniform with respect to the iron powder, and the coercive force and squareness of the rare earth-iron-nitrogen based magnet powder produced using the iron powder are reduced. When the temperature exceeds 1250 ° C., the generated rare earth-iron mother alloy undergoes grain growth and sinters with each other. Therefore, uniform nitriding becomes difficult, and the squareness of the magnet powder decreases.

(3) Hydrogen treatment When a reduction diffusion reaction is performed using calcium as a reducing agent, the obtained rare earth-iron-based master alloy becomes a massive mixture composed of calcium oxide, unreacted excess metallic calcium, and the like. Therefore, hydrogen treatment is performed on this reaction product.

  The hydrogen treatment is performed at a temperature of 500 ° C. or less, but it is necessary to set the reaction temperature and time so that the particle size of the taken-out collapsed product is 10 mm or less, preferably 1 mm or less. In the state where the collapsed material exceeds 10 mm, uniform nitriding becomes difficult in the nitriding treatment step performed subsequent to the wet treatment, and the squareness of the magnet powder is lowered.

(4) Wet treatment The reaction product collapsed by the hydrogen treatment is brought into the wet treatment process as soon as possible, and a by-product (residual impurities from the rare earth-iron mother alloy due to a reducing agent component such as calcium oxide). ) Is removed.

  The reaction product is brought into the wet treatment process as quickly as possible. When the collapsed reaction product is left in the atmosphere for a long time, the generated rare earth-iron master alloy is oxidized and at the same time a reducing agent such as calcium carbonate. This is because the component carbonate is generated and difficult to remove, and as a result, nitriding does not proceed uniformly, and the magnetism, coercive force, and squareness of the finally obtained magnet powder are lowered. Accordingly, the collapsed reaction product may be wet-treated within 3 days, preferably within 1 day in the atmosphere, or within 2 weeks when stored in an inert gas atmosphere as a work-in-process.

In the wet treatment, first, the disintegrated product is put into water, and decantation-water injection-decantation is repeated to remove much of Ca (OH) ₂ . A properly hydrotreated reaction product reacts with water more vigorously than a conventional hydrotreated product.

Next, in order to remove residual Ca (OH) ₂ , acid washing is performed using acetic acid and / or hydrochloric acid. At this time, the hydrogen ion concentration (pH) of the aqueous solution is preferably in the range of 4-6.

  After completion of such treatment, for example, it is washed with water, dehydrated with an organic solvent such as alcohol or acetone, and dried in an inert gas atmosphere or in vacuum, whereby a rare earth-iron-based mother alloy powder can be obtained.

  In the present invention, the rare earth-iron-nitrogen based magnet powder is obtained by subjecting the rare earth-iron based mother alloy powder to a nitriding heat treatment at 400 to 500 ° C., preferably 410 to 460 ° C., in a mixed gas stream of ammonia and hydrogen. . However, when a part of Fe as T is contained by 7% by weight or less as M, Cr, V, etc., the ammonia partial pressure ratio is set to 0.4 to 0.8, preferably 0.4 to 0.6. .

Here, if the ratio of the ammonia partial pressure to the total air flow pressure is less than 0.4, nitriding does not proceed over a long period of time, and the amount of nitrogen cannot be increased to 0.35% by weight or more. When the ratio exceeds 0.8, the nitrogen composition is not uniform near the surface and near the center of each magnet powder, and in particular, the amorphous phase increases near the surface, and the Sm ₂ Fe ₁₇ N ₃ compound crystal phase 10 Since the crystal orientation of the ˜30 nm cell is disturbed, the magnetization and squareness of the magnet powder are reduced.

  When the heating temperature is less than 400 ° C., nitriding is difficult to proceed. On the other hand, when the heating temperature exceeds 500 ° C., the alloy may be decomposed into rare earth nitride and iron, which is not preferable. If the heating temperature is too low or the heating time is too short, an unnitrided phase will remain inside the powder. Conversely, if the temperature is too high or the heating time is too long, it will be overnitrided, and the magnet powder's magnetization, coercive force, squareness will be Therefore, the processing conditions are optimized as appropriate. As the heating device, a stationary heating furnace, a fluidized bed heating furnace, a rotary heating furnace, etc. can be used. In order to make the contact between the alloy fine powder and the gas uniform, the powder is stirred. However, nitriding may be performed.

  The average particle size of the magnet powder thus obtained is preferably 1 to 30 μm, particularly 2 to 25 μm. If the average particle size is less than 1 μm, it is difficult to handle the magnet powder industrially, and if it exceeds 30 μm, it becomes difficult to achieve a relative density of 85% or more by compaction.

The magnet powder has an oxide film formed on the surface thereof, and the oxygen content is 0.2 to 1.6% by weight, particularly 0.5 to 1.0% by weight, based on the total amount of the magnet powder. is required.
The oxide film formed on the surface of the magnet powder is a method that gradually oxidizes the magnet powder itself in an oxygen controlled atmosphere to form a gradual oxide film, or using a coating agent, sputtering, CVD (chemical vapor deposition) For example, it can be formed by a method of coating an oxide such as alumina or silica on magnet powder. In the present invention, the oxide film is preferably a slow oxide film.

  When the amount of oxygen is less than 0.2% by weight, the magnet powder is active, so that handling in the pre-compression molding process is industrially difficult. On the other hand, if it exceeds 1.6% by weight, the magnet powder itself is oxidized in the magnet powder compacting step performed subsequent to the pre-compression molding, and a sufficient coercive force cannot be obtained. As long as 0.2 to 1.6% by weight of oxygen is present as an oxide film such as a gradual oxide film, the coercive force reduction is at an acceptable level.

  Such magnet powder having oxygen as a gradual oxide film can be easily obtained by processing in an atmosphere in which the amount of oxygen is controlled. For example, when a rare earth-iron-based alloy is obtained and then magnet powder is produced by pulverization, if the dry pulverization using a jet mill or the like, the magnet powder is pulverized in an inert gas containing a predetermined amount of oxygen, or In the case of wet pulverization using a ball mill or the like, known means such as drying in an inert gas containing a predetermined amount of oxygen after pulverizing the magnet powder can be used.

  On the other hand, when producing a compacted magnet by the method described in detail below using magnet powder that does not form an oxide film as in the prior art, decomposition or denitrification of Sm-Fe-N compounds or magnet powder The coercive force of the obtained compacted magnet is low because the magnetic interaction between particles due to metal bonding between particles is strengthened, and it is not sufficient as a practical material. On the other hand, when the magnetic powder according to the present invention is used, decomposition and denitrification of the compound can be prevented when compacted, and a decrease in coercive force can be prevented.

  The rare earth-iron-based magnet powder thus obtained may be mixed with magnet powder such as ferrite and alnico unless the object of the present invention is impaired.

2. Pre-compression molding The magnet powder is pre-compression molded into a predetermined shape while applying a magnetic field as necessary in a non-oxidizing atmosphere before consolidation. A high relative density cannot be obtained even if only compaction described later is performed without pre-compression molding.

  At the time of pre-compression, the atmosphere needs to be non-oxidizing (for example, an atmosphere of argon gas, helium gas, nitrogen gas, or vacuum).

  When Zn powder is added to rare earth-iron-nitrogen based magnet powder and the magnet powder is used as a mixed powder with Zn powder, the soft magnetic phase and defects on the surface of the magnet powder are reduced when pre-compression molding is performed. Therefore, it is particularly suitable. In this case, since the magnetization decreases when the amount of Zn powder added is large, the amount added must be 10% by weight or less, for example, preferably 3 to 10% by weight.

When the individual particles of the rare earth-iron-nitrogen based magnet powder are isotropic powders, the magnet powder is pre-compressed in a non-oxidizing atmosphere before consolidation. In this case, the relative density of the preform must be 40% or more. If the relative density of the preform is less than 40%, even if it is consolidated, the relative density of 85% or more cannot be obtained.
Since the isotropic magnet does not need to consider disorder of orientation, the upper limit of the relative density is not particularly limited. Usually, the relative density can be pre-compressed to about 70% by increasing the pressure.
It does not specifically limit about a pressure, What is necessary is just the pressure conditions from which a preform with a relative density of 40% or more is obtained. As for the temperature, it is desirable that the oxidation of the magnet powder does not proceed during the precompression molding, and it is usually preferable to carry out at normal temperature.

  The method for pre-compression is not particularly limited, and a conventionally used press method or the like can be used. In order to obtain a good magnet powder orientation in the pre-compression step, it can be performed by a cold isostatic press (CIP) or a press using a rubber mold as disclosed in JP-A-05-271705. In some cases, it is effective to press using an aluminum capsule.

On the other hand, when the individual particles of the rare earth-iron-nitrogen based magnet powder are anisotropic powders, the magnet powder is easily compressed while preliminarily compressing it while applying a magnetic field, so that the easy axis of magnet magnet is aligned in the magnetic field direction, The magnet obtained by subsequent compaction can be an anisotropic rare earth permanent magnet having a higher residual magnetic flux density.
The magnetic field applied during the pre-compression is 400 kA / m or more, preferably 1000 kA / m or more, more preferably 1500 kA / m or more, and the pre-compression is performed so that the relative density of the preform is 40 to 55% while applying the magnetic field. To do. If the orientation magnetic field is less than 400 kA / m, the magnet powder cannot be sufficiently oriented.

  Even in this anisotropic magnet powder, as in the case of isotropic magnet powder, if the relative density of the preform is less than 40%, the relative density of 85% or more cannot be obtained even if the preform is consolidated. However, when the relative density exceeds 55%, the orientation of the magnet powder of the preform formed by the magnetic field is disturbed, so that the residual magnetic flux density of the anisotropic rare earth permanent magnet obtained by consolidation in the next step is reduced. The maximum energy product is reduced. Therefore, in the case of anisotropic magnet powder, it is preferable that the relative density of the preform is 40 to 55%.

3. Consolidation of preformed body Consolidation is a step of compressing a preformed body obtained by precompression molding into a magnet molded body having a magnet powder density increased to 85% or more.

  As a means for consolidation, a hot isostatic pressing method, a plasma sintering method, and an impact compression method can be applied. However, since the impact compression method has safety restrictions, either the hot isostatic pressing method or the plasma sintering method is suitable.

  At the time of consolidation, the atmosphere needs to be a non-oxidizing gas (for example, argon gas, helium gas, nitrogen gas) atmosphere or a vacuum. The sample temperature during consolidation is 500 ° C. or lower, preferably 490 ° C. or lower. Consolidation at a temperature exceeding 500 ° C. is not preferable because the rare earth-iron-nitrogen based magnet powder is decomposed.

  Furthermore, when manufacturing an anisotropic magnet in which the easy axis of magnet powder is oriented, the hot isostatic pressing method in which the orientation disorder of the easy axis of magnet powder hardly occurs in the consolidation process is more preferable. .

  In this case, it is desirable to perform hot isostatic pressing after enclosing the preform in an aluminum capsule having the same inner shape as the preform and sealing the capsule. The aluminum capsules are plastically deformed when hot isostatically pressed to consolidate the preformed body therein. In an alumina container as described in Patent Document 3 (Japanese Patent Laid-Open No. 5-217728), the container cannot be compacted because it does not deform.

  If there is a gap between the aluminum capsule and the preform, consolidation is achieved by filling the gap with a nitride powder such as boron nitride powder, silicon nitride powder, aluminum nitride powder, or calcium nitride powder. Can do. Other than nitride powder, for example, oxide powder is not preferable because it reacts with powder filled with rare earth-iron-nitrogen based magnet powder and magnetic properties are deteriorated. The atmosphere in the sealed capsule is preferably a vacuum or a non-oxidizing atmosphere such as argon gas, helium gas, nitrogen gas or the like.

  Moreover, as a pressure medium of an isostatic press, argon gas, helium gas, and nitrogen gas with a purity of 99.99% or more are desirable. In the case of consolidation by hot isostatic pressing, the temperature is 350 to 500 ° C, preferably 400 to 490 ° C. This is because if the temperature is lower than 350 ° C., consolidation does not proceed, and if it is higher than 500 ° C., the magnet powder is decomposed to produce α-Fe and the coercive force is reduced.

  The pressure is preferably 100 to 200 MPa, particularly 150 to 200 MPa. This is because if the pressure is lower than 100 MPa, consolidation does not proceed and a hot isostatic press exceeding 200 MPa has a safety problem.

4). Rare earth permanent magnet The rare earth permanent magnet of the present invention is a permanent magnet produced by the above method and having a relative density of 85% or more, preferably 90% or more. Examples of the permanent magnet include Sm—Fe—N, Sm—Fe—Mn—N, and mixed permanent magnets of these and Zn powder, all of which are excellent in high coercive force and maximum energy product. Has magnetic properties.

For example, in the Sm-Fe-N permanent magnet, the coercive force HcJ is 0.60 MA / m or more and (BH) max is 80 kJ / m ³ or more. In the Sm-Fe-Mn-N permanent magnet, It has excellent magnetic properties such as a coercive force HcJ of 0.50 MA / m or more and (BH) max of 30 kJ / m ³ or more.
On the other hand, in an Sm-Fe-N permanent magnet manufactured by adding a predetermined amount of Zn powder to magnet powder during ball milling, the coercive force HcJ is 0.50 MA / m or more, and (BH) max is 160 kJ / m. ^It has excellent magnetic properties of ³ or more.

Examples of the present invention and comparative examples are shown below, but the present invention is not limited to these examples.
The relative density was measured by coating the sample with paraffin and using an automatic hydrometer DH manufactured by Toyo Seiki Seisakusho. The magnetic properties were measured by using a DC self-recording magnetometer TRF-5 manufactured by Toei Kogyo Co., Ltd. after processing the consolidated sample into a cylindrical shape. At this time, the sample was previously magnetized with a pulse magnetic field having a peak magnetic field of 3200 kA / m.

(Example 1)
Purity 99.9 wt%, particle size: sieve opening 104 μm (150 mesh, Tyler standard, the same applies hereinafter) Electrolytic Fe powder: 7.5 kg and purity 99 wt% average particle size sieve opening 43 μm (325 Mesh) oxidized Sm powder: 3.4 kg, granular metal Ca having a purity of 99% by weight: 1.5 kg, and anhydrous Ca chloride powder: 0.17 kg were mixed using a V blender. The obtained mixture was put in a stainless steel container and heated at 1150 ° C. for 8 hours in an argon atmosphere to cause a reduction diffusion reaction.
Next, the reaction product was cooled and then poured into water to be disintegrated. The obtained slurry was repeatedly washed with water and acid with acetic acid to remove unreacted Ca and by-produced CaO. The obtained slurry was filtered, replaced with ethanol, and then vacuum-dried to obtain 25 wt% Sm-bal. About 10 kg of Fe alloy powder was obtained. Here, bal. Indicates the remaining part.
Next, this powder was loaded into a tube furnace, heated in an ammonia-hydrogen mixed gas atmosphere having an ammonia partial pressure of 0.35 at 465 ° C. for 6 hours (nitriding treatment), and then heated in argon gas at 465 ° C. for 2 hours ( (Annealing treatment) to obtain an Sm—Fe—N alloy powder. X-ray analysis of this powder showed a diffraction line (Sm ₂ Fe ₁₇ N ₃ intermetallic compound) having a rhombohedral Th ₂ Zn ₁₇ type crystal structure.
Next, this Sm—Fe—N alloy powder was ball milled using dehydrated hexane as a solvent and subjected to gradual oxidation using a mixer in a nitrogen gas atmosphere having an oxygen concentration of 0.3 vol%. The obtained Sm—Fe—N magnet powder has a Fisher average particle size of 1.4 μm, an Sm composition of 24.0% by weight, an N composition of 3.6% by weight, an oxygen content of 0.2% by weight, bal . Fe. The oxygen content of the magnet powder was measured by EGMA (manufactured by Horiba).
The obtained Sm—Fe—N magnet powder was filled in a rubber mold in a nitrogen gas atmosphere, oriented by applying a pulse magnetic field of 2000 kA / m, and then hydrostatically pressed at 180 MPa, and approximately 11 mm in diameter × high A cylindrical preform with a thickness of 25 mm was obtained. The relative density of the obtained preform was 46%. Here, the relative density is calculated with the true density of the Sm—Fe—N magnet powder as the X-ray density (7.67 g / cc).
The preform was housed in an aluminum capsule having an outer diameter of 14 mm and an inner diameter of 11 mm, and sealed up and down. The sealed interior was evacuated. The capsule was placed in a hot isostatic press having a graphite heater, and compacted at 450 ° C. and 200 MPa for 30 minutes using argon gas as a pressure medium. The relative density of the compacted magnet taken out from the capsule was measured, and the magnetic properties were evaluated with a self-recording magnetometer. The relative density was 90%, the coercive force HcJ was 0.82 MA / m, and (BH) max was 155 kJ / m ³ . there were.

(Example 2)
Slow oxidation was performed with an oxygen concentration of 2% by volume, Sm 23.7% by weight, N 3.3% by weight, oxygen amount 1% by weight, bal. A compacted magnet was produced in the same manner as in Example 1 except that the Sm—Fe—N magnet powder magnet powder made of Fe was preformed at 200 MPa. The relative density of the preform was 54%. The relative density of the obtained compacted magnet was 89%, the coercive force HcJ was 0.64 MA / m, and (BH) max was 124 kJ / m ³ .

(Example 3)
Slow oxidation was performed with an oxygen concentration of 1.7% by volume, and the composition of the Sm—Fe—N magnet powder magnet powder was Sm 23.8 wt%, N 3.4 wt%, oxygen content 0.8 wt%, bal. A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform compacted at 190 MPa was 50%. The relative density of the obtained compacted magnet was 91%, the coercive force HcJ was 0.75 MA / m, and (BH) max was 113 kJ / m ³ .

Example 4
An Sm- (Fe, Mn) alloy was obtained in the same manner as in Example 1 except that the reduction diffusion was performed with the amount of oxidized Sm powder being 3.7 kg, Fe powder 7.1 kg, and Mn dioxide 0.7 kg. This powder was loaded into a tubular furnace, heated in an ammonia-hydrogen mixed gas atmosphere with an ammonia partial pressure of 0.5 at 465 ° C. for 10 hours (nitriding treatment), and then heated in argon gas at 465 ° C. for 2 hours (annealing treatment). Sm— (Fe, Mn) —N magnet powder having a Fisher average particle diameter of 18 μm was obtained. X-ray analysis of this powder showed a diffraction line (Sm ₂ (Fe, Mn) ₁₇ N ₃ intermetallic compound) having a rhombohedral Th ₂ Zn ₁₇ type crystal structure. The magnet powder composition was Sm 24.7% by weight, Mn 3.4% by weight, N 5.0% by weight, oxygen content 0.5% by weight, bal. Fe.
Using this magnet powder, a compacted magnet was produced in the same manner as in Example 1. The relative density of the preform that was pre-compressed at 190 MPa was 44%. The relative density of the obtained compacted magnet was 87%, the coercive force HcJ was 0.78 MA / m, and (BH) max was 40 kJ / m ³ . The relative density is calculated as 7.66 g / cc obtained from the X-ray diffraction of the true density of the Sm— (Fe, Mn) —N magnet powder.

(Example 5)
The nitriding time was 9 hours, Sm 24.3% by weight, Mn 3.6% by weight, N 4.8% by weight, oxygen content 0.2% by weight, bal. Fe, Sm— (Fe, Mn) —N magnet powder having an average particle size of 15 μm was obtained. Using this magnet powder, a compacted magnet was produced in the same manner as in Example 4 except that the hot isostatic pressing temperature was 490 ° C.
The relative density of the preform was 41%. The relative density of the obtained compacted magnet was 88%, the coercive force HcJ was 0.58 MA / m, and (BH) max was 35 kJ / m ³ .

(Example 6)
The preformed body obtained in Example 5 was placed on a graphite die, and compacted by performing discharge plasma sintering at 465 ° C. for 10 minutes while applying a pressure of 100 MPa in an argon gas atmosphere. The relative density of the obtained compacted magnet was 90%, the coercive force HcJ was 0.84 MA / m, and (BH) max was 85 kJ / m ³ .

(Example 7)
Sm 22.8 wt%, N 3.4 wt%, Zn 4.7 wt% in the same manner as in Example 1 except that 5 wt% Zn powder added to the Sm—Fe—N alloy powder was ball milled. %, Oxygen content is 0.6% by weight, bal. A mixed powder of Fe Sm—Fe—N magnet powder and Zn (average particle size 3.4 μm) was produced. This powder was subjected to a transverse magnetic field press at 200 MPa while applying a magnetic field of 1500 kA / m in an argon gas atmosphere to obtain a preform. The relative density of the preform was 42%. The relative density of the mixed powder is calculated with a theoretical density of 7.64 g / cc. The preform was compacted in the same manner as in Example 1. The relative density of the obtained compacted magnet was 87%, the coercive force HcJ was 0.56 MA / m, and (BH) max was 168 kJ / m ³ .

(Example 8)
Sm 21.6 wt%, N 3.1 wt%, Zn 9.5 wt%, oxygen content 0.4 wt%, except that the amount of Zn powder added was 10 wt% , Bal. A mixed powder of Fe Sm—Fe—N magnet powder and Zn (average particle size 3.6 μm) was produced. This powder was pre-compressed in the same manner as in Example 7 and then consolidated. The density of the preform was 45%. The relative density of the obtained compacted magnet was 93%, the coercive force HcJ was 0.91 MA / m, and (BH) max was 162 kJ / m ³ .

(Comparative Example 1)
Slow oxidation was performed with an oxygen concentration of 0.1% by volume, Sm 24.1% by weight, N 3.6% by weight, oxygen content 0.1% by weight, bal. An Sm—Fe—N magnet powder of Fe was obtained. An attempt was made to produce a compacted magnet in the same manner as in Example 1, but the magnet powder burned during the pre-compression molding operation.

(Comparative Example 2)
Slow oxidation was performed with an oxygen concentration of 4% by volume, and the composition of the Sm—Fe—N magnet powder was changed to Sm 23.5 wt%, N 3.0 wt%, oxygen content 1.7 wt%, A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform was 45%. The relative density of the obtained compacted magnet was 90%, the coercive force HcJ was 0.45 MA / m, and (BH) max was 60 kJ / m ³ .

(Comparative Example 3)
A compacted magnet was produced in the same manner as in Example 2 except that the pre-compression was performed at 150 MPa. The relative density of the preform was 38%. The relative density of the obtained compacted magnet was 84%, the coercive force HcJ was 0.65 MA / m, and (BH) max was 98 kJ / m ³ .

(Comparative Example 4)
A consolidated magnet was produced in the same manner as in Example 2 except that the pre-compression was performed at 220 MPa. The relative density of the preform was 57%. The relative density of the obtained compacted magnet was 92%, the coercive force HcJ was 0.62 MA / m, and (BH) max was 100 kJ / m ³ .

(Comparative Example 5)
A consolidated magnet was produced in the same manner as in Example 2 except that the temperature at the time of consolidation was 510 ° C. The relative density of the preform was 54%. The relative density of the obtained compacted magnet was 90%, the coercive force HcJ was 0.33 MA / m, and (BH) max was 28 kJ / m ³ .

(Comparative Example 6)
A consolidated magnet was produced in the same manner as in Example 6 except that discharge plasma sintering was performed in the air using a die made of super steel. The relative density of the obtained compacted magnet was 52%, the coercive force HcJ was 0.11 MA / m, and (BH) max was 12 kJ / m ³ .

(Comparative Example 7)
A compacted magnet was manufactured in the same manner as in Example 1 except that a phosphate film was formed on the magnet powder instead of the gradual oxide film, followed by pre-compression. The film thickness of the phosphate formed by pulverizing the magnet powder in the phosphoric acid solution was 20 nm, and the oxygen content was 1.9% by weight. The relative density of the obtained compacted magnet was 86%, the coercive force HcJ was 0.26 MA / m, and (BH) max was 27 kJ / m ³ .

(Reference Example 1)
Reduction diffusion was carried out with an input amount of oxidized Sm of 3.2 kg, and oxygen was gradually oxidized with an oxygen concentration of 2% by volume. , Oxygen content 0.9% by weight, bal. A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform was 46%. The relative density of the obtained compacted magnet was 89%, the coercive force HcJ was 0.28 MA / m, and (BH) max was 21 kJ / m ³ .

(Reference Example 2)
Reduced diffusion was performed with an input amount of oxidized Sm of 3.8 kg, and oxygen was gradually oxidized with an oxygen concentration of 2% by volume. , 1% by weight of oxygen, bal. A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform was 46%. The relative density of the obtained compacted magnet was 91%, the coercive force HcJ was 0.68 MA / m, and (BH) max was 34 kJ / m ³ .

(Reference Example 3)
The nitriding time was 4 hours, and the composition of the Sm—Fe—N magnet powder was Sm 24.1 wt%, N 2.7 wt%, oxygen content 1.1 wt%, bal. A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform was 47%. The relative density of the obtained compacted magnet was 88%, the coercive force HcJ was 0.32 MA / m, and (BH) max was 19 kJ / m ³ .

(Reference Example 4)
The nitriding time was 13 hours, and the composition of the Sm—Fe—N magnet powder was Sm 24 wt%, N 5.2 wt%, oxygen content 1.2 wt%, bal. A consolidated magnet was produced in the same manner as in Example 1 except that Fe was used. The relative density of the preform was 46%. The relative density of the obtained compacted magnet was 87%, the coercive force HcJ was 0.3 MA / m, and (BH) max was 25 kJ / m ³ .

(Reference Example 5)
A consolidated magnet was produced in the same manner as in Example 2 except that the pulse orientation magnetic field was changed to 300 kA / m. The relative density of the preform was 54%. The relative density of the obtained compacted magnet was 89%, the coercive force HcJ was 0.70 MA / m, and (BH) max was 74 kJ / m ³ .

"Evaluation"
From the above Comparative Examples 1 and 2, it can be seen that when the oxygen content of the magnet powder deviates from 0.2 to 1.6% by weight, a problem in handling and a significant reduction in coercive force occur. By comparing Comparative Examples 3 and 4 with Example 2, when the relative density of the preform is off 40 to 55%, the relative density after the consolidation process does not increase or the maximum energy product decreases. I understand that. In Comparative Example 5, the sample temperature at the time of consolidation was made to exceed 500 ° C., and it can be seen that the coercive force was lowered. In Comparative Example 6, it can be seen that the coercive force is reduced because the atmosphere during consolidation is not a non-oxidizing atmosphere. Further, in Comparative Example 7, since the oxygen amount exceeded 1.6% by weight, the coercive force was not sufficient.

  In addition, although the reference examples 1-5 are the compacted magnets manufactured on the conditions of this invention, since conditions remove | deviated from the preferable range, the magnetic characteristic deteriorated rather than the Example. For example, it can be seen from Reference Examples 1 and 2 that when the rare earth element R deviates from 23.5 to 25% by weight, the coercive force decreases and the maximum energy product decreases. From Reference Examples 3 and 4, it can be seen that when the nitrogen N deviates from 2.8 to 5.1% by weight, the coercive force decreases and the maximum energy product decreases. In Reference Example 5, it is understood that the orientation magnetic field in the preliminary compression molding step is less than 400 kA / m, and the maximum energy product is reduced.

Claims (8)

  An oxide film containing 0.2 to 1.6% by weight of oxygen is formed on the surface of the rare earth-iron-nitrogen magnet powder in advance, and the magnet powder having the oxide film is made non-oxidizing. Pre-compression molding into a predetermined shape in an atmosphere to obtain a preform with a relative density of 40% or more, and then compacting the preform in a non-oxidizing atmosphere at a temperature of 350 to 500 ° C. to give a relative density of 85. % Rare earth permanent magnet manufacturing method, characterized by obtaining a magnet molded body of at least%. The method for producing a rare earth permanent magnet according to claim 1, wherein the rare earth-iron-nitrogen based magnet powder is a magnet powder having a Th ₂ Zn ₁₇ type crystal structure.   Rare earth-iron-nitrogen based magnet powder is 23.5-25 wt% R (rare earth element), 2.8-5.1 wt% N (nitrogen) and the balance is T (Fe is an essential transition metal The method for producing a rare earth permanent magnet according to claim 1, wherein the element is an element and an unavoidable impurity.   The rare earth-iron-nitrogen based magnet powder contains Sm as a R (rare earth element) at 50% by weight or more, and further contains Mn as a transition metal element at 7% by weight or less. Magnet manufacturing method.   2. The method for producing a rare earth permanent magnet according to claim 1, wherein 10% by weight or less of Zn powder is added to the magnet powder having an oxide film before the pre-compression molding.   2. The method for producing a rare earth permanent magnet according to claim 1, wherein the pre-compression molding is performed while applying a magnetic field of 400 kA / m or more to the anisotropic magnet powder. 3.   The method for producing a rare earth permanent magnet according to claim 1, wherein the preform is compacted by hot isostatic pressing (HIP). A rare earth permanent magnet obtained by the production method according to claim 1 and having a maximum energy product (BH) max of 30 kJ / m ³ or more.