JP2010196170A - Magnetic powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth-iron-nitrogen-based magnetic powder which has superior coercive force, has a superior squareness ratio, and can retain magnetic properties even in the atmosphere of 350°C or higher without firing, and to provide a production method therefor. <P>SOLUTION: The magnetic powder has a composition expressed by general formula of R<SB>x</SB>T<SB>100-x-y-z</SB>N<SB>y</SB>M<SB>z</SB>, wherein the M component is distributed eccentrically in the surface side of the powder, and wherein R represents at least one of rare earth elements including Y; T represents at least one metal of Fe and transition metals; M represents at least one element or an oxide thereof, which has standard Gibbs energy in the range of -80 kcal to -300 kcal at a temperature between 300 and 1,200°C; 3<x<30, 5<y<15 and 0.001<z<5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic powder, and more particularly to a rare earth-iron-nitrogen based magnetic powder excellent in heat resistance and a method for producing the same.

  Anisotropic rare earth-iron-nitrogen based magnetic powder has excellent magnetic properties and has attracted attention as a magnetic powder for rare earth bonded magnets replacing NdFeB based magnetic powder, and many technical reports have been proposed. . For example, a bonded magnet having a desired shape can be easily formed by melting and solidifying a compound obtained by mixing rare earth-iron-nitrogen based magnetic powder and thermoplastic resin with an injection molding machine. it can. In this way, injection molded products using rare earth-iron-nitrogen based magnetic materials are rich in shape freedom and can be integrally molded with other members. ing. As a method for producing a rare earth-iron-nitrogen based magnetic powder, a method is known in which a raw material powder having a size of several μm containing a rare earth oxide is used as a raw material, metal calcium is added as a reducing agent, reduction diffusion is performed, and subsequent nitriding is performed. It has been. As a result, a magnetic powder having a single magnetic domain powder size can be obtained without obtaining a mechanical pulverization step, so that a highly pure rare earth-iron-nitrogen based magnetic powder having excellent oxidation resistance can be obtained.

  However, the reductive diffusion reaction proceeds between the molten metallic calcium and the solid raw material, so that the solid raw materials easily aggregate. For this reason, it is difficult to obtain only the magnetic powder in a monodispersed state, and the coarse magnetic powder in an aggregated shape having an irregular shape is contained. When a large amount of such coarse magnetic powder is contained, the coercive force and residual magnetization are reduced. Therefore, attempts have been made to improve the magnetic properties by pulverizing rare earth-iron-nitrogen based magnetic powders, etching with acids, etc., and providing coatings. However, it was difficult to improve the initial degree of magnetization reduction by the demagnetization curve. As a result, it was difficult to improve both the coercive force and the squareness ratio. Further, the pulverization method causes damage to the crystal, and there is a problem that characteristics such as heat resistance are lowered. In addition, the etching method and the method of providing a coating have a problem with a decrease in residual magnetization per weight.

  On the other hand, for the purpose of improving the magnetic properties without adding special processing, M components such as Mg and Ti are added to the rare earth-iron-nitrogen alloy, and these are pulverized and then annealed, or A rare earth-iron-M-nitrogen based magnetic material having a two-phase separation type microstructure formed by adding the M component during sintering is disclosed. The two-phase-separated microstructure is composed of a phase having a large M content at the powder boundary portion of the microstructure and a phase having a small amount of M or no M at the center of the powder. The M component plays the role of providing a separation layer between the main phases of the rare earth-iron-nitrogen alloy according to the heat treatment, or further reacts with the main phase to form a low magnetic property region. Thereby, the interaction inside the particle, that is, the interaction between the magnetic regions can be weakened, thereby conversely improving the magnetic characteristics (see Patent Document 1).

  In addition, there is also a disclosure that the crystal structure is stabilized and the magnetic characteristics are improved by arranging the M component uniformly inside the powder (see Patent Document 2).

JP-A-3-153852

JP-A-9-143636

JP-A-6-124812

  The application field of rare earth magnets, which has been applied to the OA field and the home appliance field, is expanding to use for automobiles as the automobiles become electric vehicles and drive-by-wire. The required heat-resistant temperature was 120 ° C. at most and 100 ° C. at most, but automobiles are required to have heat resistance of 150 ° C. or higher, and more than 200 ° C. In addition, as heat-resistant resins other than polyamide-based resins, such as PPS, PEEK, or LCP, are used as adaptation to the automotive field is examined in the future, the process temperature when using these resins is 350 ° C. or higher. The risk of ignition of raw material particles under such circumstances must also be taken into account. In order to prevent ignition, there is a method of sealing the whole process with an inert gas, but this is unrealistic industrially.

  However, the conventional rare earth-iron-nitrogen based alloy to which the M component is added by the above method cannot prevent ignition at 350 ° C. or higher in the atmosphere. Specifically, in the case of a two-phase separation type magnetic material, since there is no M component on the powder surface, ignition occurs in the atmosphere at a high temperature exceeding 350 ° C. Further, in the method of uniformly mixing the M component throughout the powder, as disclosed in the present invention, although the effect of stabilizing the crystal structure can be expected, since the M component is not unevenly distributed on the powder surface, The fire cannot be prevented. Theoretically, a technique for coating the M component using a sol-gel method or the like can also be studied, but in reality, it is impossible to coat the entire surface of a powder of several μm, and the surface is coated. There is always a risk of dropping off the M component. In order to prevent ignition, there is a method of sealing the whole process with an inert gas, but this is unrealistic industrially.

  The present invention has been made in view of the above circumstances, that is, it has a large remanent magnetization, is particularly excellent in coercive force and squareness ratio, and can retain magnetic properties without being ignited even at 350 ° C. or higher in the atmosphere. An object of the present invention is to provide a rare earth-iron-nitrogen based magnetic powder and a method for producing the same.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have found that the generation of a coarse powder that causes the deterioration of the magnetic properties is a raw material powder with a specific M component blended with the properties at the synthesis stage. It has been discovered that the generation of coarse particles can be suppressed by arranging the inner surface side in an unprecedented method and form. In addition, the magnetic powder obtained as a result has been found to be able to suppress the ignitability at 350 ° C. or higher in the atmosphere to the minimum, and further to have excellent magnetic heat resistance, and has achieved the present invention. .

Magnetic powder of the present invention is a magnetic powder represented by the general formula _{R x T 100-x-y} -z N y M z, wherein M component, that is unevenly distributed on the surface side of the powder body portion Wherein R is at least one of rare earth elements including Y, T is at least one of Fe and transition metals, and M is a standard Gibbs energy of −80 kcal to −300 kcal at 300 ° C. to 1200 ° C. A range of at least one element or oxide thereof, 3 <x <30, 5 <y <15, 0.001 <z <5). Thus, a magnetic powder in which a specific M component is unevenly distributed on the surface side inside the magnetic powder with a specific composition has both excellent dispersibility and oxidation resistance function, and is subjected to severe temperature conditions. Even underneath, reliability can be maintained for a long time. The M component is preferably unevenly distributed on the surface side inside the powder. Furthermore, it is more preferable to distribute gently from the surface toward the inside. Specifically, when the particle cross-sectional dimension is normalized with the surface being 0 and the center point being 1, the M component content value in the range of 0 to 0.3 is 50 atomic percent to 100 atomic percent of all M components. , In the range of 0.3 to 0.6, preferably in the range of 10 atomic percent or more and less than 30 atomic percent, in the range of dimension 0.6 to 1.0 in the range of 0 atomic percent or more and less than 30 atomic percent, Dropping off of the M component and reduction in oxidation resistance due to poor adhesion when the M component is applied on the powder surface can be suppressed.

  Further, on the demagnetization curve of a sample in which magnetic powder is completely oriented while applying a magnetic field in molten wax, the ratio of magnetic field Hk to true coercive force iHc when residual magnetization is reduced by 10% = square ratio It is preferable that Hk / iHc is 0.35 ≦ Hk ≦ 0.8, so that the magnetic powder has excellent orientation in a relatively low magnetic field of about 1 kOe (0.8 kA / M). In addition, when a molded magnet such as a bond magnet is used, the property that there is little demagnetization at high temperatures can be exhibited even if the permeance is low.

  Furthermore, the heat resistance α is preferably 85% or more (provided that the α indicates a coercivity maintenance rate when the magnetic powder is heated in the atmosphere at 150 ° C. for 1 hour and allowed to cool to room temperature. ), Which makes it possible to maintain excellent reliability even in a severe environment.

  The M component is preferably at least one of the group consisting of Zr, Al, Ti, Si, B, V, Ta, Mn, Cr, Na, Zn, K, P, Mg, Li, or an oxide thereof. When the above-mentioned predetermined distribution of the M component is obtained in the magnetic particles, the effect of not only having excellent oxidation resistance but also extremely good dispersion of the magnetic particles is obtained. Is obtained. Further, the M component may be an oxide or a pure metal, but is preferably present in the form of an oxide.

A method of manufacturing a magnetic powder of the present invention is a general formula _{R x T 100-x-y} -z N y M manufacturing method of magnetic powder that you express in _z, 1) to R ions and T ions The first step of adding a precipitant capable of forming an insoluble salt to the solution having, followed by the addition of the M component, 2) calcining the resulting precipitate, and the combined oxidation of R and T A second step of obtaining a product powder, and 3) a third step of performing a reduction diffusion reaction with metallic calcium having a particle size of 10 mm or less (provided that R is a rare earth element including Y) At least one, T is at least one of Fe and transition metals, M is at least one element or oxide thereof having a standard Gibbs energy in the range of −80 kcal to −300 kcal at 300 ° C. to 1200 ° C. 3 <X <30, 5 <y <15, 0.001 <z <5.) Thereby, the magnetic powder which is excellent in dispersibility and in which M component is unevenly distributed on the surface side inside the powder is obtained.

  In addition, after the second step, the thickness of the composite oxide powder is adjusted to 20 mm or less in advance, and a hydrogen reduction reaction is performed in a furnace in which the dew point is adjusted to -10 ° C. or less. It is preferable to perform the three steps, whereby a magnetic powder having further excellent magnetic properties can be obtained.

  Since the rare earth-iron-nitrogen based magnetic powder of the present invention shares excellent heat resistance and oxidation resistance, it can be applied to various fields. For example, when used in bonded magnets, there is little deterioration in magnetic properties due to heating during molding, and the coercive force and squareness ratio are excellent, so a thin and small bonded magnet with high energy magnetic flux density can be realized. .

  In addition, the method for producing a rare earth-iron-nitrogen based magnetic powder according to the present invention starts with the co-precipitation reaction of R ions and T ions in the coprecipitation step, and then the M component (M is a standard Gibbs energy at 300 to 1200 ° C. Is at least one element in the range of −80 kcal to −300 kcal or an oxide thereof, and 3 <x <30, 5 <y <15, 0.001 <z <5). The mass transfer between the powders generated during the reduction diffusion process can be suppressed, and the rare earth-iron-nitrogen based magnetic powder of the present invention can be obtained efficiently.

Hereinafter, although an embodiment concerning the present invention is explained in full detail, it is an example for materializing the technical thought of the present invention, and is not limited to this.
Embodiment 1 FIG.
(Magnetic powder)
Magnetic powder of the present invention is a magnetic powder represented by the general formula _{R x T 100-x-y} -z N y M z, wherein M component particularly if unevenly distributed on the surface side of the powder body portion Not limited (provided that R is at least one of rare earth elements including Y, T is at least one of Fe and a transition metal, M is in the range of −80 kcal to −300 kcal of standard Gibbs energy at 300 ° C. to 1200 ° C.) And at least one element or oxide thereof, 3 <x <30, 5 <y <15, 0.001 <z <5).

  Here, the standard Gibbs energy in the present specification is the standard Gibbs energy when an element reacts with 1 mol of oxygen molecules to form an oxide.

  Component M in the present invention is at least one element or oxide thereof having a standard Gibbs energy in the range of −80 kcal to −300 kcal at 300 ° C. to 1200 ° C., preferably −100 to −260, more preferably −150. It is preferably a kind of element having a standard Gibbs energy of ˜−260 kcal or an oxide thereof. Thereby, when a predetermined distribution of the M component is obtained in the magnetic particles, not only has excellent oxidation resistance, but also an effect that the dispersion of the magnetic particles becomes extremely good is obtained. Specifically, at least one of the group of Zr, Al, Ti, Si, B, V, Ta, Mn, Cr, Na, Zn, K, P, Mg, Li, and Ce or an oxide thereof is preferably used. it can.

In the magnetic powders represented by the general formula _{R x T 100-x-y} -z N y M z, M component is unevenly distributed on the surface side of the inner powder. As described above, the M component is not formed on the surface of the magnetic powder as a film, but is distributed unevenly in the inside of the powder, particularly on the surface side as a composition of the magnetic powder, so that the magnetization of the powder alone is greatly reduced. Even better oxidation resistance can be obtained without incurring, and at the same time, the dispersibility of the entire powder is greatly improved, so that the squareness ratio is improved. As a result, the magnetic characteristics are improved. In addition, even if the powder is exposed to an environment of 350 ° C. in the atmosphere, it does not ignite.

(Method for producing magnetic powder)
The magnetic powder of the present invention has a specific component M on the inner surface side of the powder. In order to obtain such a magnetic powder, it is important that the M component is uniformly arranged around the mother alloy, instead of being mixed with the mother alloy and the M component during the synthesis of the mother alloy. Therefore, the method for producing magnetic powder of the present invention includes the following steps in order to make the M component unevenly distributed on the surface side inside the powder in the reduction diffusion method.

(First step)
The first step of the present invention is characterized in that, in the step of synthesizing a raw material from a solution containing R ions and T ions, the M component is precipitated after these main components are precipitated. For example, a Sm-Fe precipitate is deposited by adding a precipitating agent capable of co-precipitating them into a reaction tank solution obtained by ionizing Sm and Fe to reduce ion solubility. Next, the M component is added while stirring the Sm-Fe precipitate in the reaction tank. Thereby, a high concentration raw material powder is obtained on the surface side inside the particles.

  In the production method of the present invention, the constituent cation is uniformly mixed in a solvent. Therefore, it is necessary to prepare a solution in which rare earth elements and transition metals, which are constituent components of these alloys, are dissolved. An acid aqueous solution can be used as a solvent that can ionize and dissolve these metal elements in common. Preferred acids include mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and can dissolve the above metal ions at a high concentration. Further, as another method for preparing the metal element solution, it is also possible to dissolve chlorides, sulfates and nitrates of these constituent metals in water. The solution is not limited to an aqueous solution, but may be a solution in which an organic metal such as a metal alkoxide is dissolved in an organic solvent such as alcohol, acetone, cyclohexane, tetrahydrofuran, or the like.

  Anions (nonmetal ions) such as hydroxide ions, carbonate ions, and oxalate ions can be preferably used as substances that generate salts insoluble with these ions from a solution in which the metal ions are dissolved. That is, a solution of a substance that can supply these ions can be used. For example, oxalic acid can be used as a substance for supplying oxalate ions such as ammonium bicarbonate and sodium bicarbonate as a substance for supplying carbonate ions as a substance for supplying hydroxide ions such as ammonia and caustic soda. In the case of a solution in which a metal alkoxide is dissolved in an organic solvent, a precipitate can be deposited in the form of a metal hydroxide by adding water. In addition, any substance that reacts with a metal ion to produce an insoluble salt can be applied to the present invention. As a method for producing an insoluble salt of hydroxide, a sol-gel method can be preferably used.

  By controlling the reaction between metal ions and nonmetal ions, it is possible to obtain an ideal alloy powder raw material with a uniform distribution of constituent elements in the precipitate powder, a sharp particle size distribution, and a well-shaped powder shape. it can. The use of such raw materials improves the magnetic properties of the final product alloy powder (magnetic material). This precipitation reaction can be controlled by appropriately setting the supply rate of metal ions and non-metal ions, the reaction temperature, the reaction solution concentration, the stirring state of the reaction solution, the pH during the reaction, and the like. To set these conditions, first select the best yield for the precipitate, observe the independence of the precipitate powder (powder shape), sharpness of the particle size distribution of the precipitate powder, etc. While determining each condition. Needless to say, the form of the precipitate varies greatly depending on what kind of chemical species is selected as a raw material and what kind of precipitation reaction is applied. By this precipitation step, the powder diameter, powder shape, and particle size distribution of the alloy powder as the final magnetic material are approximately determined. As described above, the control of the precipitation reaction is very important in that the powder performance is closely reflected in the magnetic material. It is preferable that the powder size of the precipitate powder is 0.05 to 20 μm, and preferably has a size and distribution such that almost all the powder falls in the range of 0.1 to 10 μm. Moreover, it is preferable that an average powder diameter exists in the range of 0.1-10 micrometers. In the thus obtained precipitate powder, the rare earth element and the transition metal element are present in a sufficiently mixed state.

  In the first step, the method for adding the M component is not particularly limited, but it is most preferable to add it in an ionic state. In addition, it is possible to add the M component in a colloidal or solid powder form. Moreover, a process can be accelerated | stimulated by adding a precipitant after adding M component.

(Second step)
In the present invention, the precipitate obtained from the precipitation reaction is calcined to produce a composite oxide of R and T. Usually, the deposit is calcined by removing the solvent before calcination. This is because if the solvent is sufficiently removed in this step, firing is easy. In addition, when the precipitate has a high solubility in a solvent at a high temperature, it is particularly necessary to remove the solvent sufficiently. This is because the precipitate powder dissolves and the powder aggregates, adversely affecting the particle size distribution and the powder diameter.

  At the time of firing the precipitate, an insoluble salt composed of metal ions and non-metal ions is heated, so that the non-metal ions are decomposed to generate a metal oxide. Therefore, this firing is preferably performed under oxygen-rich conditions. In addition, it is preferable to select one containing oxygen as a constituent element of the nonmetallic ion. Such include hydroxide ions, bicarbonate ions, oxalate ions, citrate ions and the like. Conversely, sulfide ions and the like are ions that cause precipitation in common with these metals, but are not suitable because they do not easily decompose into oxides because they do not contain oxygen. Phosphate ions, borate ions, silicate ions, etc. are also substances that form insoluble salts with rare earth ions, transition metal ions, but phosphates, borates, and silicates are easily oxidized by subsequent firing. It does not generate a product and is difficult to apply to the present invention. Therefore, the non-metal ions that can be preferably applied to the precipitation reaction constituting the present invention include inorganic salts that can easily generate oxides when heated, such as hydroxide ions, carbonate ions, oxalate ions, and the like. It is an insoluble organic salt that burns easily. In addition, when an insoluble organic salt is hydrolyzed with water like an alkoxide to form a hydroxide, it is preferable to heat it once as a hydroxide.

  Since the main point of this baking is to decompose the non-metallic ions to obtain a metal oxide, the baking temperature is also set at a temperature equal to or higher than the temperature at which such decomposition reaction occurs. Therefore, although the firing temperature varies depending on the type of metal ion and the type of nonmetal ion, it is appropriate to fire at a temperature of 800 to 1300 ° C. for several hours, more preferably in the range of 900 to 1100 ° C. To do. In this case, it is preferable that the atmosphere of the furnace is sufficiently blown with air using a blower or the like, or oxygen is introduced into the furnace and fired.

  By this firing, a metal oxide powder in which the rare earth element and the transition metal element are microscopically mixed in the powder and the M component is unevenly distributed on the surface side inside the powder is obtained. This oxide powder is an oxide that inherits the shape distribution of the precipitate powder as it is.

(Preprocessing)
In the present invention, as a pretreatment in the third step, a part of the composite oxide powder can be reduced in advance. In this pretreatment reduction step, the composite oxide powder is heated in a reducing atmosphere with a normal reducing gas, such as reduction with a reducing gas with a hydrocarbon gas such as H2, CO, CH4, etc. Oxygen combined with the metal can be gradually removed in the form of H2O or CO. The heating temperature in this case is set in the range of 300 to 900 ° C. At lower temperatures than this range, reduction of transition metal oxides is unlikely to occur, and at temperatures higher than this range, reduction occurs, but the oxide powder undergoes powder growth and segregation at higher temperatures and deviates from the desired powder diameter. It is. Therefore, the heating temperature is more preferably in the range of 400 to 800 ° C. Moreover, when using hydrogen, it is necessary to adjust the thickness of the raw material powder to be supplied to 20 mm or less and further to adjust the dew point in the reaction furnace to -10 ° C. or less. Thereby, the aggregation preventing effect by the M component can be maintained.

(Third process)
In the reduction diffusion step of the present invention, the R and T composite oxide powder containing the component M at a specific site is mixed with metallic calcium and heated in an inert gas atmosphere or in a vacuum, thereby producing a rare earth oxide. Is reduced and diffused by contacting with calcium melt or its vapor.

  Metallic calcium is used in the form of particles or powder, but preferably has a particle size of 10 mm or less, which can further prevent aggregation during the reduction-diffusion reaction. In addition, the calcium metal is the reaction equivalent (the stoichiometric amount necessary for reducing the rare earth oxide, and includes the amount necessary for reducing the transition metal when used in the form of an oxide. ) Of 1.1 to 3.0 times, preferably 1.5 to 2.0 times the amount.

  In the present invention, a disintegration accelerator can be used together with the reducing agent as necessary. This disintegration accelerator is appropriately used for promoting the disintegration and granulation of the product in the wet treatment described later, such as calcium chloride disclosed in JP-A-63-105909. Examples include alkaline earth metal salts and calcium oxide. These decay accelerators are used in a proportion of 1 to 30% by weight, in particular 5 to 30% by weight, based on the rare earth oxide used as the rare earth source.

  In the present invention, the raw material powder described above, a reducing agent, and a disintegration promoter used as necessary are mixed, and the mixture is reduced by heating in an inert atmosphere other than nitrogen, for example, argon gas. . The heat treatment temperature for the reduction is preferably 700 to 1200 ° C., particularly 800 to 1100 ° C., and the heat treatment time is not particularly limited, but in order to perform the reduction reaction uniformly, It can be performed in a time range of 10 minutes to 10 hours, and more preferably in a range of 10 minutes to 2 hours.

  Hereinafter, although an example concerning the present invention is given and explained, it is not limited to this example.

Example 1.
(Raw material adjustment process)
First, an Fe—Sm sulfuric acid solution is formed. Mix and dissolve 3.3 kg of pure water and 8.37 kg of FeSO ₄ .7H ₂ O, add 0.812 kg of Sm ₂ O ₃ and 1.24 kg of 70% sulfuric acid, and stir well to dissolve completely. Next, pure water is added to the above solution and finally adjusted so that Fe is 0.726 mol / l and Sm is 0.112 mol / l. This is designated as a Fe-Sm sulfuric acid solution.

  Next, the Fe—Sm sulfuric acid solution is added dropwise to 3 kg of pure water maintained at a temperature of 35 ° C. while stirring, and at the same time, an ammonia solution is added dropwise to adjust the pH to 7.5. Thereby, the slurry which has Fe-Sm hydroxide precipitation which is a hardly soluble salt is obtained.

Next, a pure aqueous solution containing 73.0 g of Al ₂ (SO ₄ ) _{3 is} added to the slurry while stirring. Thereafter, by further dropwise addition with an ammonia solution, an Fe—Sm—Al hydroxide precipitate is obtained.

  The Fe—Sm—Al hydroxide precipitate is washed and separated, then dried and fired at about 1000 ° C. in the atmosphere to obtain Fe—Sm—Al oxide.

(Hydrogen reduction process)
3 kg of the obtained oxide is put into a steel container so as to have a bulk thickness of 15 mm. The container is placed in a furnace, and a hydrogen gas atmosphere is formed by maintaining the inside of the furnace at a constant dew point of −25 ° C. Thereafter, the temperature is raised to 700 ° C. and held for 20 hours. As a result, a black Fe—Sm—Al oxide is obtained in which 95% of the oxygen bonded to the Fe component is reduced.

(Reduction diffusion process)
Next, a metallic Ca powder having a particle size corresponding to twice the equivalent of 10 mm or less with respect to the oxygen content of the black Fe—Sm—Al oxide is added. After performing evacuation, Ar gas is introduced, the temperature is raised to 1050 ° C., and held for 1 to 2 hours to obtain Fe—Sm—Al powder. Here, “the particle size is 10 mm or less” in the present specification means that the wire mesh is passed through a wire mesh screen using a wire mesh made of stainless steel with a wire diameter of 1.5 mm, an opening of 10 mm, and a weave of twill weave. Point to.

(Nitriding process)
Next, after cooling to 100 ° C., evacuation is performed, and the temperature is increased to 450 ° C. while nitrogen gas is continuously introduced, and the temperature is maintained for 20 hours.

(Washing)
The obtained processed product (lump) is put into pure water and stirred. After standing still, drain the supernatant. Repeat the above decantation 8 times.

(Acid treatment)
Next, a 99.9% aqueous acetic acid solution is added and stirred. After standing still, drain the supernatant. The obtained slurry is solid-liquid separated and dried by vacuum drying. Magnetic powder thus obtained _is represented by _{Sm 9.20 Fe 77.29 N 12.39 Al 1.12} .

Example 2.
In Al material preparation, instead of Al ₂ (SO _{4) 3} 73.0g containing pure water solution, except using TiOSO ₄ 36.1 g containing pure aqueous solution, in the same manner as in Example 1 _Sm 9.30 _{Fe 77.72} N _12.46 Ti _0.52 magnetic powder is formed.

Example 3.
In Al material preparation, instead of Al ₂ (SO _{4) 3} 73.0g containing pure water solution, except using MnSO ₄ 31.7 g containing pure aqueous solution, in the same manner as in Example 1 _Sm 9.28 _{Fe 77.72} N1 _2.46 Mn _0.54 magnetic powder is formed.

Example 4
In raw material adjustment, 33.3 g of Al (OH) ₃ (as anhydrous) colloidal solution is used as an Al component to be added to a slurry having a pure aqueous solution Fe—Sm hydroxide precipitate containing 73.0 g of Al ₂ (SO ₄ ) _3. Otherwise, the Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1.

Embodiment 5 FIG.
In raw material adjustment, 21.8 g of Al ₂ O ₃ powder is used as the Al component added to the slurry having Fe—Sm hydroxide precipitate, and mixed with a high-speed decoction stirrer to obtain Fe—Sm—Al oxide. Otherwise, the Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1.

Example 6
In the hydrogen reduction step, Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1 and Example 1 except that the dew point in the furnace is maintained at −50 ° C.

Example 7
In the reducing diffusion step, Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1 except that the metal Ca powder having a particle size of 5 mm or less is added.

Comparative Example 1
In the raw material adjustment step, a pure aqueous solution containing 73.0 g of Al ₂ (SO ₄ ) _{3 is} added to the Fe—Sm sulfuric acid solution while stirring, and at the same time, an ammonia solution is dropped to form Fe—Sm—Al water which is a hardly soluble salt. Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1 except that an oxide precipitate is formed.

Comparative Example 2
In a high-frequency melting furnace, 350 g of metal samarium having a purity of 99.9%, 1000 g of metal iron having a purity of 99.99%, and 7 g of metal aluminum having a purity of 99.99% are melted at 1800 ° C. Next, the molten metal is poured into a water-cooled copper crucible to form an ingot. Next, annealing is performed at 1300 ° C. for 20 hours in an argon stream for the purpose of homogenization. Subsequently, the ingot is pulverized with a jaw crusher and further pulverized with a ball mill to an average particle size of 2.5 μm. The fine particles were nitrided at 450 ° C. for 10 hours in a nitrogen stream. The composition formula of the obtained alloy is Sm _9.50 Fe _77.01 N _11.90 Al _1.59 , and an alloy powder having almost the same composition as in Example 1 is obtained.

Comparative Example 3
In Example 1, after removing the Al component, the other steps are the same and the SmFeN magnetic powder is formed. Thereafter, an Al film is formed on the powder surface by sputtering while stirring the powder in a rotary vacuum vessel equipped with a rod-type aluminum cathode. The atmosphere gas is Ar, the pressure is 5 Pa, the discharge voltage is DC 2.0 kV, and the discharge current is 50 mA. The composition formula of the obtained powder is Sm _9.25 Fe _77.68 N _12.45 Al _0.62 . Here, the composition formula in this specification is based on chemical analysis.

Comparative Example 4
In the hydrogen reduction step, Sm—Fe—N—Al magnetic powder is formed in the same manner as in Example 1 except that the dew point in the furnace is maintained at −5 ° C.

The Al component distribution state and magnetic properties of the magnetic powders obtained in the above Examples and Comparative Examples were measured by the following method, and the obtained observations and measurement results are summarized in Table 1.

(M component distribution state)
10 g of magnetic powder is put into 1 liter of 1N hydrochloric acid aqueous solution. As a preliminary experiment, a part of the powder is picked up at regular intervals, and the particle size data is acquired, and at the same time, necessary elemental analysis is performed by ICP in addition to the M component. Based on this data, the same system is analyzed again. That is, the solution is analyzed when it is etched to a predetermined distance from the powder surface (in the case of the present invention, 30% and 60% from the surface). Thus, the distribution state of the M component in the particles is measured.

(Magnetic properties)
The obtained magnetic powder is packed in a sample container together with paraffin wax, and the paraffin wax is melted with a dryer, and then its easy magnetization domains are aligned with an orientation magnetic field of 16 kA / m. This magnetically oriented sample is pulse magnetized with a magnetizing magnetic field of 32 kA / m, and coercive force, squareness ratio, and residual magnetization are measured using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m.

(Heat-resistant)
A predetermined amount of the obtained magnetic powder is put in a container and heated in the atmosphere at 300 ° C. for 4 hours. After the law at room temperature, the coercive force is measured by the above method, and the ratio of the coercive force before and after heating is calculated as the heat resistance α. It means that it is excellent in heat resistance, so that this heat resistance (alpha) is large.

(Ignitability)
Furthermore, in order to investigate the ignitability, 5 g of the magnetic powder is placed in a 350 ° C. air atmosphere oven on a thin stainless steel tray. At that time, confirm whether to ignite.

  INDUSTRIAL APPLICABILITY The present invention can be used as a permanent magnetic material for motors used in high-temperature and high-humidity environments such as computer hard disks, laser printers, MRI (magnetic resonance diagnostic apparatus), and automobile-related parts.

Claims (3)

A magnetic powder represented by the general formula Sm _x Fe _100-xyz N _{y Mz} ,
A first step of adding a precipitating agent capable of generating an insoluble salt to a solution having Sm ions and Fe ions, followed by addition of an M component;
A second step of firing the obtained precipitate to obtain a composite oxide powder of Sm and Fe;
A third step of performing a reduction diffusion reaction with metallic calcium having a particle size of 10 mm or less,
Obtained by

When the M component is normalized with the surface being 0 and the center point being 1 in the cross-sectional dimension of the magnetic powder, the M component content value in the range of 0 to 0.3 is 50 atomic% or more of the total M component. Is in the range of 10 atomic% or more and less than 30 atomic% in the range of dimension 0.3 to 0.6, and in the range of 0 atomic% or more and less than 30 atomic% in the range of dimension 0.6 to 1.0. A magnetic powder characterized in that the abundance decreases from the surface side inside the powder toward the center.
(However, M is at least one element selected from the group consisting of Al, Ti, and Mn or an oxide thereof, and 3 <x <30, 5 <y <15, and 0.001 <z <5.)   2. The magnetic particle according to claim 1, wherein the squareness ratio Hk is 0.35 ≦ Hk ≦ 0.8. The magnetic particles according to claim 1, wherein the heat resistance α is 85% or more.
(However, α represents the maintenance ratio of coercive force when the magnetic particles are heated in air at 150 ° C. for 1 hour and allowed to cool to room temperature.)