Method for producing rare earth transition metal alloy powder

Abstract

To provide a manufacturing method for rare earth transition metal alloy powder with low oxygen content and high quality.SOLUTION: A manufacturing method for rare earth transition metal alloy powder includes: a reduction step of obtaining a reaction product containing a rare earth transition metal alloy and a byproduct derived from the reducing agent by applying a heat treatment under a non-oxidizing atmosphere to a mixture containing at least an alloying material containing a rare earth metal, transition metal components and oxygen, and a reducing agent; and a wet treatment step of obtaining a rare earth transition metal alloy powder by applying a washing process to the reaction product, where during the washing process, the reaction products are fed into the cleaning solution to obtain an alloy powder slurry, the resulting alloy powder slurry is subjected to an acid cleaning process, and the alloy powder slurry after acid cleaning is subjected to a chelation process by adding a chelating agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing rare earth transition metal alloy powder. [Background technology]

[0002] Rare earth transition metal alloy powder is an alloy powder mainly containing rare earth metals and transition metals. Rare earth transition metal alloy powder, especially intermetallic compound powder, is widely used in various applications such as permanent magnet materials, hydrogen storage materials, magneto-optical recording materials, and magnetic refrigeration materials. For example, SmFe 17 Nitrided Sm2Fe alloy powder 17 N3 alloy powder, Nd2Fe 14 B alloy powder, SmCo5 alloy powder, Sm2Co 17 The PrCo5-based alloy powder and the PrCo5-based alloy powder have large magnetization and uniaxial magnetic anisotropy, making them useful as permanent magnet materials. The LaNi5-based alloy powder is characterized by its ability to absorb and retain large amounts of hydrogen, and is used as a hydrogen storage material. The (Tb, Gd)-(Fe, Ni, Co)-based alloy powder can be used to form a thin film to form the recording layer of a magneto-optical recording medium. Furthermore, the La(Fe, Si) 13 La(Fe,Si) based alloy powder and its hydrogenated form 13 H x Rare earth-transition metal alloy powders exhibit excellent magnetocaloric effects and are considered promising magnetic refrigeration materials. Rare earth-transition metal alloy powders are primarily used in the form of sintered compacts produced by powder metallurgy sintering, or composites produced by kneading them with a resin binder.

[0003] Known methods for producing rare earth-transition metal alloy powder include melting and casting, reduction and diffusion, etc. Among these, the melting and casting method uses rare earth metals and transition metals as raw materials, blends these raw materials, melts them in an inert gas atmosphere, and heat-treats the resulting alloy ingot to make it homogenous, and then pulverizes it.

[0004] On the other hand, the reduction-diffusion method is a technique for obtaining a rare earth-transition metal alloy by mixing, for example, rare earth oxides and transition metals as raw materials with a reducing agent such as metallic calcium and then heat-treating them in a non-oxidizing gas atmosphere. During the heat treatment, the rare earth oxides are reduced to rare earth metals, which then diffuse into the transition metals to form an alloy (intermetallic compound). The bulk reaction product obtained by the heat treatment contains by-products derived from the reducing agent as well as the desired alloy. Therefore, the reaction product is placed in water to remove the by-products derived from the reducing agent and to disintegrate the reaction product into powder. The powdered alloy powder is then subjected to acid washing and water washing to remove excess by-products and unreacted materials, and then dried to obtain the desired alloy powder.

[0005] The reduction-diffusion method has the advantage that inexpensive rare earth oxides and the like can be used as raw materials, and the process is simple, making it possible to produce alloy powder at lower cost than the melt-casting method. Furthermore, by nitriding the alloy powder obtained by the reduction-diffusion method, it is possible to obtain rare earth transition metal alloy powder as a nitride.

[0006] Patent Document 1 discloses a method for producing rare earth transition metal alloy powder by a reduction diffusion method. Specifically, the method involves heating a mixture of rare earth oxide powder, powder of another metal, and at least one selected from alkali metals, alkaline earth metals, and hydrides thereof in an inert gas atmosphere or under vacuum, and then subjecting the reaction mixture to a wet treatment to remove by-produced CaO and residual Ca (claim 1 of Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 61-295308 Summary of the Invention [Problem to be solved by the invention]

[0008] In the reduction diffusion method, the alloy powder obtained by pulverization is subjected to acid washing to remove excess components. Dilute acetic acid or dilute hydrochloric acid is used in the acid washing, and by lowering the pH of the slurry containing the alloy powder, by-products (calcium compounds, etc.) derived from the remaining reducing agent are sufficiently removed, and rare earth-rich subphases other than the target alloy (intermetallic compound) are dissolved and removed. For example, in the case of Sm2Fe, a permanent magnet material, 17 Sm2Fe, the master alloy of N3 17 In the case of alloy powder production, the bulk reaction product after reduction and diffusion treatment contains the desired intermetallic compound, Sm2Fe. 17 In addition to the SmFe3 phase, the alloy contains Sm-rich subphases such as SmFe2 and SmFe3 phases. These subphases degrade the magnetic properties, so they are removed by acid washing.

[0009] During acid pickling, some of the rare earth metals and transition metals contained in the alloy powder become rare earth ions (Sm ions) and transition metal ions (Fe ions) and dissolve into the slurry, some of which remain after acid pickling. These remaining ions are oxidized and hydroxylated during subsequent treatments (water washing, drying, etc.) to become hydroxides of the rare earth metals and transition metals. The hydroxides of the rare earth metals and transition metals thus produced are then dissolved in the main phase alloy (SmFe 17 etc.) precipitate on the surface of the particles, increasing the oxygen concentration. This is undesirable because it deteriorates the properties of the alloy powder. For example, Sm2Fe 17 The alloy powder was nitrided to form Sm2Fe 17 When producing N3 alloy powder, Sm2Fe with a high oxygen concentration is used. 17 Even if the alloy powder is nitrided, the nitrogen diffusion is uneven, and it is difficult to obtain high-quality Sm2Fe 17 It becomes difficult to obtain N3. Therefore, it is desirable to suppress the formation of hydroxides due to the eluted rare earth ions and transition metal ions.

[0010] The present inventors have conducted extensive research to solve these problems, and as a result have discovered that chelating rare earth ions and transition metal ions eluted during acid washing can suppress the formation of hydroxides, thereby making it possible to obtain high-quality rare earth-transition metal alloy powder with a low oxygen content.

[0011] The present invention was completed based on these findings, and an object of the present invention is to provide a method for producing high-quality rare earth transition metal alloy powder with a low oxygen content. [Means for solving the problem]

[0012] The present invention encompasses the following aspects (1) to (10). In this specification, the expression "to" includes the numerical values on both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0013] (1) A method for producing a rare earth transition metal alloy powder, comprising the steps of: a reduction step of subjecting a mixture containing at least a rare earth metal, a transition metal, and oxygen as an alloy raw material, and a reducing agent to a heat treatment in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and a by-product derived from the reducing agent; a wet treatment step of subjecting the reaction product to a washing treatment to obtain a rare earth-transition metal alloy powder, During the washing treatment, the reaction product is introduced into a washing liquid to obtain an alloy powder slurry, the obtained alloy powder slurry is subjected to an acid washing treatment, and further a chelation treatment is performed by adding a chelating agent to the alloy powder slurry after the acid washing.

[0014] (2) The method according to (1) above, wherein the reduction step comprises mixing at least a rare earth oxide powder, a transition metal powder, and a reducing agent to obtain a mixture, and subjecting the mixture to a heat treatment in a non-oxidizing atmosphere to reduce the rare earth oxide powder and diffuse it into the transition metal powder to form an alloy, thereby obtaining a reaction product containing a rare earth-transition metal alloy component and a by-product derived from the reducing agent.

[0015] (3) The method according to (1) or (2) above, wherein the chelating agent is at least one selected from the group consisting of citric acid, gluconic acid, alkali metal salts of citric acid and / or gluconic acid, and alkaline earth metal salts of citric acid and / or gluconic acid.

[0016] (4) Any of the methods (1) to (3) above, wherein the content of the chelating agent in the alloy powder slurry is 1.0 to 5.0 times the amount (equivalent) required to chelate all of the rare earth ions and transition metal ions contained in the alloy powder slurry.

[0017] (5) Any of the methods (1) to (4) above, further comprising a hydrogen treatment step of exposing the reaction product to a hydrogen atmosphere before the washing treatment, thereby absorbing hydrogen and disintegrating the reaction product.

[0018] (6) The method according to any one of (1) to (5) above, wherein the alloy powder slurry that has been subjected to the chelation treatment is subjected to a water washing treatment.

[0019] (7) The method according to any one of (1) to (6) above, wherein the oxygen content of the rare earth transition metal alloy powder is 0.16 mass % or less.

[0020] (8) The rare earth transition metal alloy powder is SmFe 17 Sm2Fe alloy powder or Sm2Fe 17 The method according to any one of (1) to (7) above, wherein the powder is an N3-based alloy powder.

[0021] (9) The method includes the reduction step, the hydrogen treatment step, the nitriding step, and the wet treatment step in this order, In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product; In the nitriding step, a mixed gas flow containing nitrogen is passed through the reaction product while heating the reaction product disintegrated in the hydrogen treatment step, thereby nitriding the rare earth-transition metal alloy component in the reaction product; In any one of the above methods (1) to (8), in the wet treatment step, the reaction product nitrided in the nitriding step is subjected to a washing treatment.

[0022] (10) The method includes the reduction step, the hydrogen treatment step, the wet treatment step, and the nitriding step in this order, In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product; In the wet treatment step, the reaction product disintegrated in the hydrotreatment step is subjected to a washing treatment, The method according to any one of (1) to (8), wherein in the nitriding step, a mixed gas flow containing nitrogen is passed through the reaction product while heating the reaction product that has been subjected to the cleaning treatment in the wet treatment step, thereby nitriding the rare earth-transition metal alloy component in the reaction product. [Effects of the Invention]

[0023] According to the present invention, a method for producing a rare earth transition metal alloy powder having a low oxygen content and high quality is provided. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows the results of XPS depth profile analysis of the Sm2Fe17N3 alloy powder of Example 1. [Figure 2] 1 shows the results of XPS depth profile analysis of the Sm2Fe17N3 alloy powder of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0026] <<Manufacturing method for rare earth transition metal alloy powder>> The method for producing a rare earth-transition metal alloy powder (hereinafter sometimes simply referred to as "alloy powder") of this embodiment includes the following steps: a reduction step in which a mixture containing an alloy raw material containing a rare earth metal, a transition metal, and oxygen, and a reducing agent is heat-treated in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth-transition metal alloy and by-products derived from the reducing agent; and a wet treatment step in which the resulting reaction product is washed to obtain a rare earth-transition metal alloy powder. During the washing step, the reaction product is poured into a washing solution to obtain an alloy powder slurry, which is then subjected to an acid washing step. Finally, a chelating step is performed in which a chelating agent is added to the washed alloy powder slurry. Each step is described in detail below.

[0027] <Rare earth transition metal alloy powder> The rare earth transition metal alloy powder of this embodiment is a powder composed of an alloy containing a rare earth metal (R) and a transition metal (TM). Here, rare earth metal (R) is a general term for metals (elements) that constitute the group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71 in the periodic table. Transition metal (TM) is a general term for metals (elements) that are located between Group 3 and Group 11 in the periodic table. Furthermore, the concept of alloys includes not only solid solutions but also eutectics and intermetallic compounds. Examples of intermetallic compounds include CaCu5-type, Th2Zn 17 type, Th2Ni 17 type, TbCu7 type, ThMn 12 Type, NaZn 13 Type, Nd2Fe 14 Examples include compounds having crystal structures such as B-type and MgCu2-type.

[0028] The rare earth metal (R) is not particularly limited, but preferably includes at least one selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), and ytterbium (Yb). The rare earth-transition metal alloy powder may contain only rare earth metals and transition metals, or may contain other components for stabilizing the crystal structure or improving properties. For example, it may contain manganese (Mn), chromium (Cr), copper (Cu), titanium (Ti), vanadium (V), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), boron (B), carbon (C), nitrogen (N), and / or hydrogen (H). Furthermore, components resulting from the alkali metals, alkaline earth metals, or their hydrides used as reducing agents, such as calcium (Ca) and magnesium (Mg), may remain in the alloy powder. These residues are acceptable as long as the desired properties are obtained.

[0029] The rare earth transition metal alloy powder is not limited in composition as long as it is an alloy mainly containing rare earth metals and transition metals. For example, SmFe 17 and its nitrided form, Sm2Fe 17 N3, Nd2Fe 14 B, SmCo5, Sm2Co 17 and PrCo5. Hydrogen storage materials and magneto-optical recording materials such as LaNi5 and (Tb, Gd)-(Fe, Ni, Co) are also suitable. La(Fe, Si) 13 and its hydrogenated form, La(Fe,Si) 13 H x Preferably, the rare earth transition metal alloy powder is SmFe 17 Sm2Fe alloy powder or Sm2Fe 17 N3-based alloy powder. Here, Sm2Fe 17 Sm2Fe alloy powder or Sm2Fe 17 N3-based alloy powder is Sm2Fe 17 and SmFe 17This includes not only N3 but also powders in which some of the metals in these compounds have been replaced with other metals such as manganese (Mn) or cobalt (Co). These alloy powders are useful as high-performance permanent magnet materials and their master alloy materials. The rare earth metal content in the rare earth transition metal alloy powder is not limited, but is typically 10% by mass to 60% by mass. The average particle size of the rare earth transition metal alloy powder is not limited, but is typically 1.0 μm to 100 μm.

[0030] <Reduction process> In the reduction step, a mixture containing at least a rare earth metal, a transition metal, and oxygen, and a reducing agent is subjected to a heat treatment in a non-oxidizing atmosphere. The alloy raw material may contain at least a rare earth metal, a transition metal, and oxygen as constituent elements. During the heat treatment, oxygen in the alloy raw material is removed by the action of the reducing agent, and the rare earth metal diffuses into the transition metal and is alloyed. This results in a reaction product containing a rare earth-transition metal alloy and by-products derived from the reducing agent.

[0031] Preferably, the alloy raw material is a mixture of rare earth oxide powder and transition metal powder. That is, the reduction step includes a step of mixing at least rare earth oxide powder, transition metal powder, and a reducing agent to obtain a mixture (raw material mixing step), and a step of subjecting the mixture to heat treatment in a non-oxidizing atmosphere to reduce the rare earth oxide powder and diffuse it into the transition metal powder to form an alloy, thereby obtaining a reaction product containing rare earth-transition metal alloy components and by-products derived from the reducing agent (reduction-diffusion step).

[0032] The manufacturing procedure when the alloy raw material is a mixture of rare earth oxide powder and transition metal powder will be described in detail below.

[0033] (Rare earth oxide powder) The rare earth oxide powder is a source of rare earth elements that constitute the target alloy powder. While not limited to, it is preferably an oxide powder of at least one rare earth metal selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), and ytterbium (Yb). As the rare earth oxide powder, one type of powder may be used alone, or two or more types of powders may be mixed and used.

[0034] The rare earth oxide powder may be selected depending on the composition of the desired alloy powder. For example, samarium iron nitrogen (SmFe 17 N3) alloy powder and samarium cobalt (SmCo5, Sm2Co 17 When producing )-based alloy powder, samarium oxide (Sm2O3) should be selected. Also, neodymium iron boron (Nd2Fe 14 When producing B)-based alloy powder, neodymium oxide (Nd2O3) should be selected.

[0035] The particle size of the rare earth oxide powder can be determined depending on the composition and application of the resulting alloy powder. However, it is desirable to determine the particle size of the rare earth oxide powder so that it is uniformly distributed near the transition metal particles in the resulting mixture. The average particle size of the rare earth oxide powder is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. In particular, a powder in which particles with a particle size of 0.1 to 10 μm account for 80 mass% or more of the total is preferred. This improves the raw material mixability and improves the handleability of the raw material powder and reaction products. It also enables sufficient diffusion of the rare earth metal in the subsequent reduction-diffusion process. Rare earth oxide powder may contain moisture and organic matter as impurities. These impurities may increase the oxygen content of the final alloy powder. Therefore, it is preferable to have a small amount of impurities in the rare earth oxide powder. For example, the heat loss after heating to 1000°C is preferably 2 mass% or less, more preferably 1 mass% or less.

[0036] The amount of rare earth oxide powder to be blended is preferably 1.0 to 1.5 times, more preferably 1.05 to 1.2 times, the amount (equivalent) required to form an alloy powder of the target composition. For example, samarium iron (SmFe 17 )-based alloy powder and samarium iron nitrogen (SmFe 17 When manufacturing N3-based alloy powder, the amount of samarium oxide (Sm2O3) added is determined based on the stoichiometric composition (Sm2Fe 17 The amount of rare earth oxide blended is preferably 1.0 to 1.5 times the amount required in N3). By making the amount of rare earth oxide blended 1.0 times or more the equivalent amount, the rare earth metal (rare earth element) can be sufficiently diffused into the transition metal powder, making it possible to fully impart the desired properties to the final alloy powder. On the other hand, by making the amount 1.5 times or less the equivalent amount, the formation of a rare earth-rich heterophase can be suppressed.

[0037] (transition metal powder) The transition metal powder is a raw material for the transition metal that constitutes the desired alloy powder. While not limited to, one or more selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), chromium (Cr), manganese (Mn), zinc (Zn), molybdenum (Mo), and tungsten (W) are preferred. As the transition metal powder, one type of powder may be used alone, or two or more types of powder may be mixed and used.

[0038] The transition metal powder may be selected depending on the composition of the desired alloy powder. For example, samarium iron nitrogen (SmFe 17 N3) alloy powder and neodymium iron boron (Nd2Fe 14 When producing B)-based alloy powder, iron (Fe) powder can be selected. As the iron powder, reduced iron powder, gas atomized powder, water atomized powder, and / or electrolytic iron powder can be used. In addition, samarium cobalt (SmCo5, Sm2Co 17When producing a transition metal powder, cobalt (Co) powder can be selected. When the transition metal powder is iron (Fe), cobalt (Co), nickel, or Ni powder, for example, reduced powder, gas atomized powder, water atomized powder, electrolytic powder, carbonyl powder, etc. can be used.

[0039] The particle size of the transition metal powder can be determined depending on the composition and application of the resulting alloy powder. However, if the particle size of the transition metal powder is excessively large, the rare earth metal may not diffuse sufficiently deep into the powder during the subsequent reduction-diffusion step, resulting in the remaining unalloyed phase. The average particle size of the transition metal powder is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less, and particularly preferably 50 μm or less. Furthermore, a powder in which particles with a particle size of 1 to 100 μm account for 70 mass% or more of the total is preferred. This improves the handleability of the raw material powder and reaction products. Furthermore, it allows the rare earth metal to diffuse sufficiently during the subsequent reduction-diffusion step. Furthermore, the amount of impurities contained in the transition metal powder is preferably low. For example, the weight loss after heating to 1000°C is preferably 2 mass% or less, more preferably 1 mass% or less.

[0040] Up to 20% by mass of the transition metal powder may be replaced with a transition metal oxide powder, which can adjust the heat generation amount of the subsequent reduction-diffusion reaction. The transition metal powder may also be an alloy powder.

[0041] In addition to the transition metal powder, additive components may be added to stabilize the crystal structure or improve properties. The additive components may be added alone or in the form of compounds such as oxides. Alternatively, they may be added as powders pre-alloyed with transition metals such as iron (Fe), cobalt (Co), and nickel (Ni). When using a single metal powder or oxide powder, it is preferable to use powders in which particles with a particle size of 20 μm or less account for 80 mass% or more of the total, and more preferably powders in which particles with a particle size of 10 μm or less account for 80 mass% or more of the total. When using oxide powder, it is preferable to select powders that do not decompose during the temperature rise process in the subsequent reduction-diffusion heat treatment. This is because decomposition during the temperature rise deactivates the reducing agent, making it difficult for the reduction-diffusion reaction to occur. When using powders pre-alloyed with transition metals, it is preferable to use powders in which particles with a particle size of 0.1 to 10 μm account for 80% or more of the total. Mixed oxide powders of rare earth metals, transition metals, and optional additive components may also be used. This mixed oxide powder can be produced by air-calcining a co-precipitation product using salt as a starting material, mechanically pulverizing the product, and reducing the resulting powder with hydrogen or carbon.

[0042] (reducing agent) The reducing agent is added to reduce oxide components such as rare earth oxide powder in the subsequent reduction-diffusion step to promote alloy formation. The reducing agent is at least one selected from alkali metals, alkaline earth metals, and their hydrides. Specifically, at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and their hydrides is preferred. From the viewpoints of safety during handling and cost, lithium (Li) and / or calcium (Ca) are more preferred, with calcium (Ca) being particularly preferred. Among these, granular metallic calcium (Ca) sieved to a mesh size of 4.00 mm or less is most preferred.

[0043] The reducing agent may be mixed with other raw material powders before use. Alternatively, the reducing agent (e.g., Ca) may be separated so that its vapor can come into contact with the other raw material powders. If the reducing agent is mixed with other raw material powders, a porous reaction product can be obtained after the reduction-diffusion reaction. The amount of reducing agent added is preferably 1.05 to 2.0 times, and more preferably 1.1 to 1.5 times, the amount (equivalent) required to reduce the oxides in the mixture. If the amount of reducing agent is within this range, the reduction reaction can proceed sufficiently while minimizing the amount of unreacted materials and by-products in the resulting reaction product.

[0044] (Other ingredients) If necessary, other components may be added in addition to the rare earth oxide powder, transition metal powder, and reducing agent. For example, rare earth metal powder and / or transition metal oxide powder may be added. Also, alloy powder of rare earth metal and transition metal or its oxide powder may be added. Furthermore, when producing an alloy powder containing components other than rare earth metal and transition metal, raw materials of other components may be added. For example, NdFe, which is a permanent magnet material, may be added. 14 To produce B alloy powder, a boron source such as boron (B) or boron oxide (BO) may be added. 13 H x To produce alloy powders, a silicon source such as silicon (Si) or silicon oxide (SiO2) may be added.

[0045] Further, auxiliary additives may be added to facilitate the production of the alloy powder. Examples of auxiliary additives include disintegration accelerators that accelerate the disintegration of the reaction product in the subsequent wet processing step. Examples of disintegration accelerators include alkaline earth metal salts and alkaline earth metal oxides, such as calcium chloride (CaCl) and calcium oxide (CaO). It is desirable to uniformly mix the disintegration accelerator with the other raw material powders at the same time. This allows components derived from the disintegration accelerator (e.g., calcium compounds) to be uniformly present at the grain boundaries of the alloy crystals in the reaction product. Therefore, when the mixture is slurried in the subsequent wet processing step, the components derived from the disintegration accelerator are dissolved into the aqueous solution, effectively accelerating disintegration. The amount of the disintegration accelerator added is preferably 3 to 30 mass% and more preferably 7 to 20 mass% of the total amount of oxides in the mixture. By setting the amount of the disintegration accelerator within this range, it is possible to minimize the amount of unreacted materials and by-products in the reaction product while sufficiently promoting the disintegration of the reaction product.

[0046] (mixture) The raw materials are mixed uniformly, including the rare earth oxide powder, transition metal powder, reducing agent, and other components that may be added as needed, using a known mixer such as a ribbon blender, tumbler, S-blender, V-blender, Nauta mixer, Henschel mixer, super mixer, high-speed mixer, ball mill, vibration mill, attritor, or jet mill.

[0047] The mixing is preferably carried out in a vacuum or in an inert gas atmosphere to prevent the reducing agent from coming into contact with oxygen or water vapor in the atmosphere. Examples of inert gases include nitrogen (N2), argon (Ar), and helium (He). The mixture obtained by mixing is placed in a heat treatment furnace, and an inert gas is supplied to replace the air inside the furnace. Examples of inert gases include argon (Ar) and helium (He), but argon is usually used. Repeated evacuation and inert gas replacement are also preferred because they reduce residual oxygen.

[0048] The mixture is then subjected to a reduction-diffusion treatment. In the reduction-diffusion step, the mixture is heat-treated in a non-oxidizing atmosphere to obtain a reaction product. Here, the non-oxidizing atmosphere is an atmosphere that is substantially free of oxygen. The atmospheric gas is preferably an inert gas, such as argon (Ar) gas and / or helium (He) gas. The amount of oxygen in the atmosphere is preferably 5% or less, more preferably 1% or less.

[0049] When the mixture is heated in a non-oxidizing atmosphere, the rare earth oxide powder is reduced by the action of the reducing agent to produce rare earth metals. The produced rare earth metals diffuse into the transition metal powder and are alloyed to form a rare earth-transition metal alloy. If the mixture contains oxides of components other than the rare earth oxide powder, the oxides of the other components are also reduced and diffused and incorporated into the alloy. Meanwhile, the reducing agent is oxidized and converted into an oxide.

[0050] For example, samarium iron nitrogen (SmFe) can be produced by using samarium oxide (SmO) as the rare earth oxide powder, iron (Fe) powder as the transition metal powder, and metallic calcium (Ca) as the reducing agent. 17 N3)-based alloy powder and its master alloy powder, samarium iron (Sm2Fe 17 When producing samarium oxide (Sm2O3) based alloy powder, the reducing agent (Ca) reduces it to samarium (Sm). The reduced samarium (Sm) then diffuses into iron (Fe) powder to form Th2Zn 17 Samarium-iron alloy (SmFe) with the morphological crystal structure 17 ) is produced. Meanwhile, metallic calcium (Ca), which is a reducing agent, is oxidized to calcium oxide (CaO). When metallic calcium is blended in an amount greater than the equivalent amount, excess calcium (Ca) remains. This calcium oxide (CaO) and excess calcium (Ca) constitute by-products. Furthermore, in some cases, heterogeneous phases such as samarium iron compounds (SmFe3, etc.) may also be produced. Therefore, the reaction product after heat treatment is a rare earth transition metal alloy component (Sm2Fe 17The product after this heat treatment is usually a porous ingot.

[0051] The heat treatment is carried out at a temperature above the melting point of the reducing agent but not below the melting point of the resulting rare earth-transition metal alloy components. Specifically, the heat treatment temperature is preferably 850 to 1200°C. A temperature of 850°C or higher ensures uniform diffusion of the rare earth metal into the transition metal powder, thereby improving the properties of the final alloy powder. A temperature of 1200°C or lower prevents the alloy components in the reaction product from sintering too strongly, thereby facilitating disintegration and pulverization in the subsequent wet processing step. Furthermore, the heat treatment is preferably carried out until the reduction and diffusion reactions have progressed sufficiently, taking into account the particle size of the raw materials. The heating time is typically 1 to 10 hours, preferably 2 to 8 hours.

[0052] The above description has mainly focused on the case where the alloy raw material is a mixture of rare earth oxide powder and transition metal powder. However, the alloy raw material is not limited to the above-mentioned mixture, as long as it becomes a rare earth-transition metal alloy under the action of a reducing agent. For example, the alloy raw material may be an oxide and / or a partially reduced oxide (partial oxide) containing a rare earth metal and a transition metal, an alloy containing a rare earth metal, a transition metal, and oxygen (e.g., an oxygen-containing SmFe alloy), or a mixture of an alloy containing a rare earth metal and a transition metal and a rare earth oxide (e.g., a mixture of an SmFe alloy and an Sm oxide). Using a partially reduced oxide as the alloy raw material makes it possible to reduce the amount of reducing agent added in the subsequent process. An example of a procedure for preparing a partially reduced oxide containing a rare earth metal and a transition metal is described below.

[0053] First, a composite oxide containing a rare earth metal (Re) and a transition metal (TM) is prepared. Here, the composite oxide is a compound (double oxide) containing a rare earth metal and a transition metal as constituent elements. Therefore, it is distinguished from a simple mixture of a rare earth metal oxide and a transition metal oxide.

[0054] The method for obtaining the composite oxide is not limited. A commercially available composite oxide containing a rare earth metal and a transition metal may be used. Alternatively, a by-product or recycled product produced during the production of a material containing a rare earth metal and a transition metal, such as a magnetic material, may be used. However, the composite oxide is preferably synthesized by a wet method. Specifically, the composite oxide is obtained by subjecting a rare earth oxide and a transition metal compound to a wet treatment and then heating the compound. Wet synthesis makes it possible to produce a composite oxide in which the rare earth metal and the transition metal are uniformly dispersed at the atomic level.

[0055] To synthesize a composite oxide using a wet method, hydroxides are generated from an acid solution containing rare earth metals and transition metals by a neutralization reaction, and the resulting hydroxides are then heat-treated. Specifically, a raw material solution is first prepared by dissolving the rare earth metal raw material and the transition metal raw material in an acid solution. The rare earth metal raw material and the transition metal raw material are not limited as long as they dissolve in the acid solution. Examples of the rare earth metal raw material and the transition metal raw material include rare earth oxides such as samarium oxide (Sm2O3). Examples of the transition metal raw material include sulfates and nitrates of transition metals, such as ferrous sulfate (FeSO4). The type of acid solution can be determined depending on the raw materials, and examples include aqueous sulfuric acid and aqueous nitric acid solutions. In this case, it is preferable to adjust the pH of the acid solution so that the rare earth metal raw material and the transition metal raw material are completely dissolved.

[0056] Next, an alkaline solution is added to the resulting raw material solution. This causes a neutralization reaction, resulting in a slurry containing hydroxides containing rare earth metals and transition metals, such as Sm-Fe hydroxide, as a precipitate. Examples of alkaline solutions include aqueous ammonia, ammonium bicarbonate, ammonium hydroxide, sodium hydroxide, potassium hydroxide, and / or urea. To obtain uniform, fine hydroxides, it is preferable to add the alkaline solution dropwise. The precipitate in the resulting slurry is then recovered by filtration or other methods. The precipitate may be washed using a washing solution such as ion-exchanged water. This washing process reduces the amount of impurities in the final magnet powder.

[0057] The recovered precipitate is then dried and further subjected to a heat treatment. This allows for the production of a composite oxide containing a rare earth metal and a transition metal, such as Sm-Fe oxide. Drying can be performed at a temperature capable of efficiently removing moisture, for example, 80°C to 400°C. Drying can be performed under reduced pressure, or a drying gas can be circulated during drying. The heat treatment atmosphere is not limited as long as a composite oxide is obtained. Examples include oxygen-containing atmospheres such as air, a mixed gas of oxygen and an inert gas, or a mixed gas of air and an inert gas. The heat treatment temperature is preferably 500°C to 1400°C, more preferably 700°C to 1200°C. An excessively low heat treatment temperature may result in insufficient oxidation of the precipitate. On the other hand, an excessively high heat treatment temperature may result in grain growth of the resulting oxide.

[0058] If necessary, other components besides rare earth metals and transition metals, such as additive components, may be added to the composite oxide. Such components include, but are not limited to, components containing one or more selected from the group consisting of silicon (Si), aluminum (Al), titanium (Ti), zirconium (Zr), zinc (Zn), and copper (Cu). The other components may be added by dissolving them in an acid solution together with the rare earth metal and transition metal raw materials.

[0059] The prepared composite oxide is then heated in a reducing atmosphere to obtain a partially reduced oxide containing rare earth metals and transition metals. This pre-reduction reduces a portion of the composite oxide, particularly the transition metal components. The pre-reduction step reduces the amount of reducing agent required in the subsequent steps. It also promotes uniform reduction of the reduced-diffusion product.

[0060] The heating atmosphere in the pre-reduction step is not particularly limited as long as it partially reduces the composite oxide. Examples include an atmosphere containing a hydrocarbon gas such as hydrogen (H), carbon monoxide (CO), and / or methane (CH). The heating temperature in the pre-reduction step is preferably 400°C or higher and 900°C or lower. The heating time is preferably 0.5 hours or higher and 10 hours or lower.

[0061] In this way, a partially reduced oxide containing a rare earth metal and a transition metal is obtained. When the resulting partially reduced oxide is used as an alloy raw material and a mixture containing this and a reducing agent is subjected to a heat treatment in a non-oxidizing atmosphere, the action of the reducing agent reduces the rare earth metal and transition metal oxides contained in the mixture, producing rare earth metals and transition metals. The produced rare earth metals diffuse into the transition metals and are alloyed to form a rare earth-transition metal alloy. Meanwhile, the reducing agent is oxidized and converted into by-products (oxides, etc.) derived from the reducing agent. Therefore, a reaction mixture containing a rare earth-transition metal alloy and by-products derived from the reducing agent is obtained. The heat treatment can be performed under the same conditions as when the alloy raw material is a mixture of rare earth oxide powder and transition metal powder.

[0062] <Hydrogen treatment process> If necessary, a hydrogen treatment step may be performed after the reduction step (reduction-diffusion step). In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere and crushed, thereby obtaining a crushed reaction product (crushed material).

[0063] Many rare earth transition metal alloys (intermetallic compounds) expand in volume when they absorb hydrogen. For example, SmFe3 expands in volume by 19% when it absorbs hydrogen. Similarly, Sm2Fe 17 is 3.4%, Nd2Fe 14 B expands in volume by 5.4%, LaNi5 by 27%, and SmCo5 by 7.4%. The temperature at which intermetallic compounds absorb hydrogen varies depending on the type of compound and its surface properties. However, all hydrogen absorption reactions are exothermic. Therefore, when a rare earth transition metal alloy contains multiple intermetallic compounds, a chain reaction can occur. That is, absorption begins with the compound that absorbs hydrogen at a low temperature, which generates heat, which raises the temperature of the alloy, causing the next compound to absorb hydrogen.

[0064] The hydrogen treatment is carried out in a hydrogen atmosphere using a hydrogen-containing gas. The hydrogen-containing gas may be hydrogen (H2) gas alone, or a mixture of hydrogen (H2) gas and an inert gas such as argon (Ar) or helium (He) may be used. However, it is preferable to use hydrogen gas alone. In this case, to prevent oxygen (O2) from remaining, it is preferable to replace the atmosphere in the furnace with an inert gas such as argon before introducing hydrogen gas. In this case, it is also preferable to evacuate the furnace after replacing the atmosphere with the inert gas and then introduce hydrogen gas. After the hydrogen treatment is completed, the gas is switched to an inert gas such as argon, and the reaction product (crushed material) is recovered. The hydrogen treatment process is not necessarily an essential process.

[0065] <Wet processing process> In the wet treatment step, the resulting reaction product is washed to obtain rare earth transition metal alloy powder. If the hydrogen treatment step is not performed, the reaction product obtained in the reduction step (reduction diffusion step) is washed. If the hydrogen treatment step is performed, the reaction product (crushed material) crushed by the hydrogen treatment is washed. Furthermore, if the nitriding treatment step described below is performed after the reduction step, the nitrided reaction product (nitride) is washed.

[0066] In the wet treatment process, the reaction product is first introduced into a cleaning solution to obtain an alloy powder slurry. Specifically, the reaction product is introduced into the cleaning solution and stirred. The product disintegrates into a slurry. During this process, the by-products derived from the reducing agent react with water and convert to solid by-product-derived components consisting of hydroxides. Therefore, the solid by-product-derived components contain alkali metal and / or alkaline earth metal hydroxides. For example, if calcium (Ca) metal is used as the reducing agent, the product after the reduction process contains rare earth-transition metal alloy components and by-products (CaO, Ca). During water washing, these by-products (CaO, Ca) react with water and convert to calcium hydroxide (Ca(OH)2). Because calcium hydroxide has low solubility in water, most of it becomes a suspension and floats in the water. The slurry obtained by water washing is a suspension of rare earth-transition metal alloy components and solid by-product-derived components (Ca(OH)2). By separating the solid by-product-derived components in the slurry from the rare earth-transition metal alloy components, a high-purity, high-performance alloy powder can be obtained.

[0067] The cleaning solution may be water, glycol, or a mixture of water and glycol. Ion-exchanged water is preferred as the water. One or more glycols selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol are preferred.

[0068] The solid by-product-derived components can be separated by decantation. Decantation may be performed once or multiple times. For example, the reaction product may be placed in a washing solution, stirred, and allowed to stand, followed by removal of the supernatant. The resulting residue may be further mixed with washing solution, stirred, allowed to stand, and then the supernatant may be removed. While the rare earth-transition metal alloy components have a relatively high specific gravity, the solid by-product-derived components have a low specific gravity. Therefore, decantation can be used to separate and remove the solid by-product-derived components, which have a low specific gravity, together with the supernatant. Alternatively, instead of or in addition to decantation, the solid by-product-derived components may be separated and removed using a gravity separator such as a liquid cyclone or a centrifuge.

[0069] Next, the obtained alloy powder slurry is subjected to an acid washing treatment. By acid washing, solid by-product-derived components and heterogeneous phases can be more effectively removed. For example, solid by-product-derived components (Ca(OH)2, etc.) that were not completely removed by the treatment with the washing solution can be removed along with heterogeneous phases (SmFe3, etc.) in the product. The acid washing treatment is carried out, for example, by adding an acid to the alloy powder slurry while stirring it. The type of acid that can be used includes inorganic acids such as hydrochloric acid, acetic acid, nitric acid, and sulfuric acid, as well as organic acids.

[0070] Next, a chelation treatment is performed by adding a chelating agent to the alloy powder slurry after acid washing. The chelation treatment makes it possible to obtain alloy powder with a low oxygen content. Specifically, during the acid washing treatment, rare earth ions and transition metal ions are eluted from the alloy powder into the washing solution. These ions, either singly or in complex form, become hydroxides, which adhere to the surface of the alloy powder and increase the oxygen content of the alloy powder. While a water washing treatment after acid washing can remove rare earth ions and transition metal ions to some extent, it is difficult to completely prevent the formation and adhesion of hydroxides using water washing alone. In contrast, a chelation treatment chelates the rare earth ions and transition metal ions to form stable complexes. This prevents the formation and adhesion of hydroxides. As a result, it is possible to obtain alloy powder with a low oxygen content.

[0071] The chelating agent is not limited as long as it can chelate rare earth ions and / or transition metal ions. Examples include citric acid, gluconic acid, alkali metal salts of citric acid and / or gluconic acid, alkaline earth metal salts of citric acid and / or gluconic acid, ethylenediamine, ethylenediaminetetraacetic acid, phenanthroline, and bipyridine. Preferably, the chelating agent is at least one selected from the group consisting of citric acid, gluconic acid, alkali metal salts of citric acid and / or gluconic acid, and alkaline earth metal salts of citric acid and / or gluconic acid.

[0072] Furthermore, during the chelation treatment, an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide may be added to the alloy powder slurry. In this case, the chelating agent and the alkaline aqueous solution may be added separately, or a mixed aqueous solution of the chelating agent and the alkaline aqueous solution may be added. By adding the alkaline aqueous solution, the amount of chelating agent required for the chelation treatment can be reduced. Furthermore, the slurry can be brought closer to neutrality (pH ~ 7), thereby reducing damage to the alloy powder in the slurry. When using a mixed aqueous solution of the chelating agent and the alkaline aqueous solution, the pH of the mixed aqueous solution is preferably 5.0 or more and 7.5 or less.

[0073] The chelation treatment method is not limited as long as it can chelate the alloy powder. For example, a method of adding a chelating agent to an alloy powder slurry while stirring the slurry can be used. The amount of chelating agent added is preferably an amount sufficient to chelate all of the rare earth ions and transition metal ions in the slurry. Specifically, the content of the chelating agent in the slurry is preferably 1.0 to 5.0 times the amount (equivalent) required to chelate all of the rare earth ions and transition metal ions contained in the slurry.

[0074] The acid washing and / or chelation treatment may be performed once or multiple times. A step of washing the alloy powder with water may be added before or after the acid washing or chelation treatment. It is particularly preferable to further wash the alloy powder slurry that has been subjected to the chelation treatment with water. This makes it possible to thoroughly remove chelated rare earth ions and transition metal ions. The water washing may be performed by discarding the supernatant of the alloy powder slurry, adding water, and stirring the mixture once or multiple times.

[0075] The alloy powder after the washing treatment can be recovered and dried to obtain a rare earth transition metal alloy powder. The alloy powder can be recovered by subjecting the slurry or cake containing the alloy powder to solid-liquid separation treatment such as filtration or centrifugation. Furthermore, if the water contained in the slurry or cake is replaced with an alcohol such as methanol, ethanol, or isopropanol, the processing time for the subsequent drying step can be shortened. Drying is preferably carried out at 30 to 250°C, more preferably 40 to 100°C. However, the washing treatment may cause the alloy powder to absorb hydrogen. In this case, vacuum drying at a temperature of 200°C or less is preferable to reduce the amount of residual hydrogen.

[0076] <Nitriding process> In the manufacturing method of this embodiment, a step of nitriding the product (nitriding treatment step) may be further provided as necessary. By providing this step, samarium iron nitride (SmFe 17 Nitride-based alloy powders such as N3 can be obtained. The nitriding treatment can be carried out at any time after the reduction step (reduction-diffusion step). The reaction product obtained in the reduction step may be nitrided, the crushed material obtained in the hydrogen treatment step may be nitrided, or the alloy powder obtained in the wet treatment step may be nitrided.

[0077] In the nitriding treatment, the product (reaction product, crushed material, alloy powder) is heated to preferably 350 to 500°C, more preferably 400 to 480°C, while a nitrogen-containing mixed gas flow is passed through it. This causes the rare earth transition metal alloy components to be nitrided. If the heating temperature is 350°C or higher, the nitriding reaction takes place in a short time, improving efficiency. On the other hand, if the heating temperature is too high, the main phase may decompose. For example, samarium iron (SmFe 17 ) is nitrided to form samarium iron nitrogen (SmFe 17 When producing samarium iron (SmFe)-based alloy powder, if the nitriding temperature is too high, the main phase 17 ) may decompose to form αFe. αFe is undesirable because it reduces the squareness of the demagnetization curve of the magnet powder. By setting the nitriding temperature to 500°C or less, it is possible to suppress this decomposition of the main phase.

[0078] The nitriding gas flowing during the nitriding treatment needs only to contain at least nitrogen atoms, and nitrogen gas or ammonia gas is suitable. Furthermore, to control the reaction, hydrogen, argon, or the like may also be contained. When a mixed gas flow of ammonia and hydrogen is used, the mixture ratio (gas flow ratio) of ammonia:hydrogen is preferably 10-95:5-90, more preferably 30-90:10-70. Within this range, the flow rate of ammonia becomes sufficient, further improving the nitriding efficiency.

[0079] <Heat treatment process> If necessary, the product (nitride alloy powder) obtained by the nitriding treatment may be further subjected to heat treatment in an inert gas atmosphere. Examples of inert gas include hydrogen gas, nitrogen gas, argon gas, and helium gas. By performing such heat treatment, the nitrogen distribution within the individual crystal cells constituting the obtained alloy powder becomes uniform, making it possible to further improve the properties of the alloy powder. The heat treatment temperature is preferably 350 to 500°C, more preferably 400 to 480°C. The holding time is preferably 20 to 200 minutes, more preferably 30 to 150 minutes.

[0080] <Fine grinding process> If necessary, the product (alloy powder) obtained in the wet treatment, nitriding, or heat treatment process may be finely pulverized. In the fine pulverization process, the pulverized material is placed in a pulverizer together with media and pulverized until the average particle size is 1 to 3 μm. Isopropyl alcohol, ethanol, toluene, methanol, hexane, etc. can be used as the media. Furthermore, adding a surface treatment agent to the pulverization solvent makes it possible to perform surface treatment of the alloy powder simultaneously with pulverization. Examples of surface treatment agents include phosphate compounds such as orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate, and aluminum phosphate.

[0081] According to a preferred aspect, the manufacturing method of this embodiment includes a reduction step, a hydrogen treatment step, a nitriding step, and a wet treatment step, in this order. In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product. In the nitriding step, the reaction product disintegrated in the hydrogen treatment step is heated while a mixed gas flow containing nitrogen is passed through the reaction product, thereby nitriding the rare earth-transition metal alloy component in the reaction product. In the wet treatment step, the reaction product nitrided in the nitriding step is subjected to a cleaning treatment.

[0082] According to another preferred aspect, the manufacturing method of this embodiment includes a reduction step, a hydrogen treatment step, a wet treatment step, and a nitriding step, in this order. In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product. In the wet treatment step, the reaction product disintegrated in the hydrogen treatment step is washed. In the nitriding step, the reaction product (alloy powder) washed in the wet treatment step is heated while a mixed gas flow containing nitrogen is passed through the reaction product (alloy powder), thereby nitriding the rare earth-transition metal alloy component in the reaction product.

[0083] In this manner, the rare earth-transition metal alloy powder of this embodiment can be produced. According to the production method of this embodiment, the rare earth ions and transition metal ions dissolved in the slurry during acid washing are chelated, thereby preventing the formation of hydroxides and the adhesion of the alloy powder. As a result, a high-quality rare earth-transition metal alloy powder with a low oxygen content can be obtained. For example, but not limited to, the oxygen content of the rare earth-transition metal alloy powder can be reduced to 0.16% by mass or less, 0.14% by mass or less, 0.12% by mass or less, 0.10% by mass or less, 0.08% by mass or less, or 0.06% by mass or less.

[0084] The rare earth transition metal alloy powder obtained by the manufacturing method of this embodiment can be used in known applications such as permanent magnet materials, hydrogen storage materials, magneto-optical recording materials, and magnetic refrigeration materials, and is particularly suitable for use as permanent magnet materials. [Example]

[0085] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0086] (1) Preparation and evaluation of alloy powder SmFe 17 N3 alloy powder, Sm2Fe 17 Alloy powder, Nd2Fe 14 B alloy powder, SmCo5 alloy powder, and LaNi5 alloy powder were prepared. The alloy powders obtained were evaluated for various properties as follows.

[0087] <xrd> The crystal structure of the alloy powder was evaluated by powder X-ray diffraction (XRD). X-ray diffraction measurements were performed using a Cu target under conditions of an accelerating voltage of 45 kV and a current of 40 mA, scanning 2θ at a rate of 2 min / deg. The obtained XRD pattern was then analyzed to identify the crystal structure.

[0088] <Composition analysis> The amounts of rare earth metals (R), boron (B), calcium (Ca) and oxygen (O) in the alloy powder were analyzed by ICP emission spectroscopy and infrared absorption spectroscopy, respectively.

[0089] <xps> The thickness of the oxide layer on the surface of the alloy powder was evaluated by X-ray photoelectron spectroscopy (XPS). 3 / 2 The spectra were analyzed in the depth direction. Measurements were repeated while performing argon (Ar) ion etching in the depth direction, and the etching time required for the main peak to change from the Fe oxide peak (near 710 eV) to the metal peak (near 706 eV) was determined. The obtained etching time was used to calculate the oxide layer thickness in SiO2 equivalent.

[0090] <Magnetic properties> Stearic acid was added to the alloy powder, and the powder was pulverized in a vibrating ball mill using dehydrated ethanol as a solvent until the average particle size reached 2.3 μm. The magnetic properties of the pulverized powder were then measured using a vibrating sample magnetometer (VSM) in accordance with the Bonded Magnet Testing Method Guidebook BMG-2005 published by the Japan Bonded Magnetic Materials Association. Based on the measurement results, the remanence σr, coercivity Hc, and squareness Hk were calculated. The squareness Hk is the strength of the demagnetization field on the magnetization curve (demagnetization curve) in the second quadrant that corresponds to 90% of the remanence σr.

[0091] [Example 1] In Example 1, SmFe 17 The N3 alloy powder was prepared and evaluated by the following procedure.

[0092] <Mixing process> Average particle size (D 50 625g of samarium oxide (Sm2O3) powder with an average particle size (D) of 3.2μm 50 A mixture was obtained by mixing 1550 g of iron (Fe) powder having a particle size of 37 μm and 250 g of granular metallic calcium (Ca) having a particle size of 2.0 mm or less in a mixer.

[0093] <Reduction and diffusion process> The resulting mixture was placed in an iron crucible and heated in an argon (Ar) gas atmosphere at 1060°C for 8 hours, and then cooled to room temperature, thereby obtaining a reaction product.

[0094] <Hydrogen treatment> After cooling, the reaction product was taken out and placed in a sealed container, and left in hydrogen gas in the sealed container to absorb hydrogen. This crushed the reaction product, yielding crushed material with a particle size of 10 mm or less.

[0095] <Nitriding treatment> The crushed reaction product (crushed material) was placed in a tubular furnace and heat-treated at 430°C for 9 hours in a mixed gas of ammonia and hydrogen (ammonia partial pressure 0.75 atm). The gas was then switched to nitrogen gas and heat-treated for another hour, after which it was cooled. This yielded nitrides.

[0096] <Wet processing> 1250 g of the reaction product (nitride) after nitriding was added to 4 L of water to form a slurry. This slurry was decanted seven times using 4 L of water to separate the Ca(OH)2 suspension.

[0097] Next, 4 L of water was added to the treated material (crushed material) after separation of Ca(OH)2, and 294 g of 45% acetic acid was added dropwise while stirring, after which the supernatant was discarded (pickling treatment).

[0098] After the acid washing treatment, 4 L of water was added to the crushed material and stirred, and the supernatant was discarded (first water washing treatment). Subsequently, 4 L of water was added to the crushed material and stirred. The samarium (Sm) and iron (Fe) ion concentrations in the supernatant were analyzed and found to be 100 mg / L (0.7 mmol / L) and 200 mg / L (4 mmol / L), respectively. Therefore, 32 g of 25% citric acid solution was added to the stirred treatment solution (second water washing treatment (chelation treatment)). The amount of citrate ions in the treatment solution was 42 mmol, which was 3.4 times the amount (equivalent) required to chelate all of the Sm and Fe ions. The supernatant was then discarded, and 4 L of water alone was added to the treated material, stirred, and the supernatant was discarded. This procedure was repeated twice (third and fourth water washing treatments).

[0099] After the fourth water washing, the supernatant was discarded and the solvent was replaced with ethanol, followed by filtration to obtain an alloy powder cake, which was then dried at 60°C under reduced pressure in a mixer to obtain an alloy powder.

[0100] The resulting powder was Th2Zn 17 SmFe with a type crystal structure 17 The powder was an N3 alloy. It had a composition of 23.2 mass% Sm, 3.4 mass% N, less than 0.01 mass% Ca, and 0.11 mass% O. XPS analysis confirmed that the oxide layer had a thickness of 20 nm, as shown in Figure 1.

[0101] [Example 2] During the chelation treatment, a mixed solution of citric acid and sodium citrate was added to the treatment solution instead of 32 g of 25% citric acid. This mixed solution was prepared in advance by mixing 82.0 g of citric acid (0.1 mol / L; 1.9%) and 118 g of sodium citrate (0.1 mol / L; 2.5%). The amount of citrate ions in the treatment solution was 20 mmol, which was 1.6 times the amount (equivalent) required to chelate all of the samarium (Sm) and iron (Fe) ions. Except for this, the alloy powder was prepared in the same manner as in Example 1. The obtained powder was Th2Zn 17 Sm2Fe with a crystalline structure 17 The powder was an N3 alloy, and had a composition of 23.3 mass % Sm, less than 0.01 mass % Ca, and 0.09 mass % O.

[0102] [Example 3] During the chelation treatment, a mixed aqueous solution of citric acid and sodium citrate was added to the treatment solution instead of 32 g of 25% citric acid solution. This mixed aqueous solution was prepared in advance by mixing 48 g of citric acid solution (0.1 mol / L; 1.9%) and 203 g of sodium citrate solution (0.1 mol / L; 2.5%). The amount of citrate ions in the treatment solution was 73 mmol, which was 2.0 times the amount (equivalent) required to chelate all of the Sm and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 1. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The powder was an N3 alloy, and had a composition of 23.3 mass % Sm, less than 0.01 mass % Ca, and 0.10 mass % O.

[0103] [Example 4] During the chelation treatment, a mixed aqueous solution of citric acid and sodium hydroxide was added to the treatment solution instead of 32 g of 25% citric acid. This mixed aqueous solution was prepared in advance by mixing 498 g of citric acid (0.1 mol / L; 1.9%) with 0.2 mol / L sodium hydroxide to adjust the pH to 5.6. The amount of citrate ions in the treatment solution was 49 mmol, which was 4.0 times the amount (equivalent) required to chelate all of the total moles of Sm and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 1. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The powder was an N3 alloy, and had a composition of 23.2 mass % Sm, less than 0.01 mass % Ca, and 0.15 mass % O.

[0104] [Comparative Example 1] During the second water washing treatment (chelation treatment), no citric acid solution was added. Except for this, the alloy powder was prepared in the same manner as in Example 1. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The powder was an N3 alloy. It had a composition of 23.3 mass% Sm, less than 0.01 mass% Ca, and 0.22 mass% O. XPS analysis confirmed that the oxide layer had a thickness of 40 nm, as shown in Figure 2. This thickness was twice that of the oxide layer in Example 1.

[0105] [Example 5] In Example 5, SmFe 17 The alloy powder was prepared and evaluated by the following procedure.

[0106] <Mixing process> Average particle size (D 50 565g of samarium oxide (Sm2O3) powder with an average particle size (D) of 3.2μm 50 A mixture was obtained by mixing 1200 g of iron (Fe) powder having a particle size of 40 μm and 230 g of granular metallic calcium (Ca) having a particle size of 2.0 mm or less in a mixer.

[0107] <Reduction and diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 1070°C for 4 hours, and then cooled to room temperature, thereby obtaining a reaction product.

[0108] <Hydrogen treatment> After cooling, the reaction product was taken out and subjected to the same hydrogen treatment as in Example 1 to obtain a crushed product.

[0109] <Wet processing> 1250 g of the crushed reaction product (crushed material) was added to 4 L of water to form a slurry. This slurry was decanted seven times using 4 L of water to separate a Ca(OH)2 suspension.

[0110] Next, 4 L of water was added to the treated material (crushed material) after separation of Ca(OH)2, and 55 g of 50% acetic acid was added dropwise while stirring, after which the supernatant was discarded (pickling treatment).

[0111] After the acid washing treatment, 4 L of water was added to the treated material (crushed material) and stirred, and the supernatant was discarded (first water washing treatment). Subsequently, 4 L of water was added to the treated material after the first water washing treatment, and 28 g of 40% aqueous citric acid solution was added while stirring (second water washing treatment (chelation treatment)). The amount of citrate ions in the treatment solution was 62 mmol, which was 4.8 times the amount (equivalent) required to chelate all of the Sm and Fe ions. The supernatant of the treatment solution was discarded, and another 4 L of water alone was added, stirred, and the supernatant was discarded. This procedure was repeated twice (third and fourth water washing treatments).

[0112] After the fourth water washing, the supernatant was discarded and the solvent was replaced with ethanol, followed by filtration to obtain an alloy powder cake, which was then dried at 80°C under reduced pressure in a mixer to obtain an alloy powder.

[0113] The resulting powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of 24.1 mass % Sm, 0.01 mass % Ca, and 0.12 mass % O.

[0114] [Example 6] During the chelation treatment, a mixed aqueous solution of citric acid and sodium citrate was added to the treatment solution instead of 28 g of 40% citric acid solution. This mixed aqueous solution was prepared in advance by mixing 84.0 g of citric acid solution (0.1 mol / L) and 66.0 g of sodium citrate solution (0.1 mol / L). The amount of citrate ions in the treatment solution was 15 mmol, which was 1.2 times the amount (equivalent) required to chelate all of the Sm and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 5. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of Sm: 24.3 mass %, Ca: 0.02 mass %, and O: 0.11 mass %.

[0115] [Example 7] During the chelation treatment, 15 g of a mixed aqueous solution of citric acid and calcium citrate tetrahydrate was added to the treatment solution instead of 28 g of 40% citric acid solution. This mixed aqueous solution was prepared in advance by dissolving 0.5 g of calcium citrate tetrahydrate in 30 g of 40% citric acid solution. The amount of citrate ions in the treatment solution was 32 mmol, which was 2.6 times the amount (equivalent) required to chelate all of the Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of 24.4 mass % Sm, 0.05 mass % Ca, and 0.15 mass % O.

[0116] [Example 8] During the chelation treatment, instead of 28 g of 40% citric acid solution, an aqueous solution of 18 g of citric acid solution adjusted to pH 6.0 with 1 mol / L potassium hydroxide solution was added to the treatment solution. The amount of citrate ions in the treatment solution was 37 mmol, which was 3.0 times the amount (equivalent) required to chelate all of the Sm and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 5. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of Sm: 24.5 mass %, Ca: 0.03 mass %, and O: 0.18 mass %.

[0117] [Example 9] During the chelation treatment, 47 g of 40% tripotassium citrate aqueous solution was added to the treatment solution instead of 28 g of 40% citric acid aqueous solution. The amount of citrate ions in the treatment solution was 61 mmol, which was 5.0 times the amount (equivalent) required to chelate all of the Sm and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 5. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of Sm: 24.6 mass %, Ca: 0.01 mass %, and O: 0.10 mass %.

[0118] Comparative Example 2 During the second water washing treatment (chelation treatment), no citric acid solution was added. Except for this, the alloy powder was prepared in the same manner as in Example 5. The obtained powder was Th2Zn 17 SmFe with a type crystal structure 17 The alloy powder had a composition of Sm: 24.5 mass %, Ca: 0.01 mass %, and O: 0.38 mass %.

[0119] [Examples 10 to 14 and Comparative Example 3] In Experimental Examples 10 to 14 and Comparative Example 3, the SmFe alloys prepared in Examples 5 to 9 and Comparative Example 2 were used. 17 The alloy powder was nitrided to form Sm2Fe 17 The N3 alloy powder was prepared and its magnetic properties were evaluated. The nitriding treatment was carried out according to the following procedure.

[0120] <Nitriding treatment> The obtained SmFe 17 40 g of alloy powder was placed in a tubular furnace and heat-treated in a mixed gas of ammonia and hydrogen (ammonia partial pressure 0.50 atm) at 465°C for 3.5 hours. The gas was then switched to hydrogen gas for 0.5 hours, and then to nitrogen gas for another 0.5 hours, after which the alloy powder was cooled. The resulting treated product (nitride) was Th2Zn 17 SmFe with a type crystal structure 17 It was N3 alloy powder.

[0121] [Example 15] In Example 15, NdFe 14 The alloy powder B was prepared and evaluated by the following procedure.

[0122] <Mixing process> Average particle size (D 50 405g of neodymium oxide (Nd2O3) powder with an average particle size (D) of 3.7μm 50 A mixture was obtained by mixing 608 g of iron (Fe) powder with a particle size of 40 μm, 67 g of ferroboron powder (B content 18.7 mass%) with a particle size of 200 mesh or less, 217 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less, and 20 g of anhydrous calcium chloride (CaCl) in an argon (Ar) atmosphere using a mixer.

[0123] <Reduction and diffusion process> The resulting mixture was placed in an iron crucible and heated in an argon (Ar) gas atmosphere at 1000°C for 2 hours, and then cooled to room temperature, thereby obtaining a reaction product.

[0124] <Hydrogen treatment> After cooling, the reaction product was taken out and subjected to the same hydrogen treatment as in Example 1 to obtain a crushed product.

[0125] <Wet processing> 1000 g of the crushed reaction product (crushed material) was added to 4 L of water to form a slurry. This slurry was decanted 10 times using 4 L of water to separate a Ca(OH)2 suspension.

[0126] Next, 4 L of water was added to the treated material (crushed material) after separation of Ca(OH)2, and 50% acetic acid was added dropwise while stirring so that the slurry pH was maintained at 6.0 for 5 minutes, after which the supernatant was discarded (acid washing treatment).

[0127] After the acid washing treatment, 4 L of water was added to the treated material (crushed material) and stirred for 2 minutes, and the supernatant was discarded (first water washing treatment). Subsequently, 4 L of water was added to the treated material after the first water washing treatment, and 30 g of a 50% aqueous solution of gluconic acid was added while stirring (second water washing treatment (chelation treatment)). The amount of gluconate ions in the treatment solution was 76 mmol, which was 2.1 times the amount (equivalent) required to chelate all of the Nd and Fe ions. The supernatant of the treatment solution was discarded, and another 4 L of water alone was added, stirred, and the supernatant was discarded. This procedure was repeated twice (third and fourth water washing treatments).

[0128] After the fourth water washing, the supernatant was discarded and the solvent was replaced with ethanol, followed by filtration to obtain an alloy powder cake, which was then dried at 50°C under reduced pressure in a mixer to obtain an alloy powder.

[0129] The resulting powder is tetragonal Nd2Fe 14 The alloy powder had a B phase as the main phase and had a composition of Nd: 33.0 mass %, B: 1.30 mass %, Ca: 0.02 mass %, and O: 0.10 mass %.

[0130] [Example 16] During the chelation treatment, 20 g of a mixed aqueous solution of gluconic acid and sodium gluconate was added instead of 30 g of 50% gluconic acid. This mixed aqueous solution was prepared in advance by dissolving 3 g of sodium gluconate in 30 g of 50% gluconic acid. The amount of citrate ions in the treatment solution was 55 mmol, which was 1.5 times the amount (equivalent) required to chelate all of the Nd and Fe ions. Except for this, the alloy powder was prepared in the same manner as in Example 15. The obtained powder was tetragonal Nd2Fe 14 The alloy powder had a B phase as the main phase and had a composition of 33.2 mass% Nd, 1.32 mass% B, 0.03 mass% Ca, and 0.15 mass% O.

[0131] [Example 17] During the chelation treatment, 80 g of a 50% aqueous solution of potassium gluconate was added instead of 30 g of a 50% aqueous solution of gluconic acid. The amount of citrate ions in the treatment solution was 171 mmol, which was 4.7 times the amount (equivalent) required to chelate all of the Nd and Fe ions. Except for this, an alloy powder was prepared in the same manner as in Example 15. The obtained powder was tetragonal NdFe 14 The alloy powder had a B phase as the main phase and had a composition of Nd: 33.6 mass %, B: 1.35 mass %, Ca: 0.05 mass %, and O: 0.09 mass %.

[0132] Comparative Example 4 During the second water washing treatment (chelation treatment), no gluconic acid solution was added. Except for this, the alloy powder was prepared in the same manner as in Example 15. The obtained powder was tetragonal NdFe 14 The alloy powder had a B phase as the main phase and had a composition of 33.1 mass% Nd, 1.30 mass% B, 0.02 mass% Ca, and 0.33 mass% O.

[0133] [Example 18] In Example 18, SmCo5 alloy powder was produced and evaluated. The alloy powder was produced according to the following procedure. <Mixing process> Average particle size (D 50 A mixture was obtained by mixing 371 g of samarium oxide (Sm2O3) powder with a particle size of 2.3 μm, 669 g of electrolytic cobalt (Co) powder with a particle size of 325 mesh or less, 161 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less, and 37 g of anhydrous calcium chloride (CaCl2) in a mixer under an argon (Ar) atmosphere.

[0134] <Reduction and diffusion process> The resulting mixture was placed in an iron crucible and heated in an argon (Ar) gas atmosphere at 1050°C for 2 hours, and then cooled to room temperature, thereby obtaining a reaction product.

[0135] <Hydrogen treatment> After cooling, the reaction product was taken out and subjected to the same hydrogen treatment as in Example 1 to obtain a crushed product.

[0136] <Wet processing> 1000 g of the resulting reaction product (crushed material) was added to 4 L of water to form a slurry. This slurry was decanted five times using 4 L of water to separate a Ca(OH)2 suspension.

[0137] Next, 4 L of water was added to the treated material (crushed material) after separation of Ca(OH)2, and 90% acetic acid was added dropwise while stirring so that the slurry pH was maintained at 6.0 for 20 minutes, after which the supernatant was discarded (acid washing treatment).

[0138] After the acid washing treatment, 4 L of water was added to the treated material (crushed material), and the mixture was stirred for 2 minutes. The supernatant was then discarded (first water washing treatment). Subsequently, 4 L of water was added to the treated material after the first water washing treatment, and 14 g of 25% aqueous citric acid solution was added while stirring (second water washing treatment (chelation treatment)). The amount of citrate ions in the treatment solution was 18 mmol, which was 1.5 times the amount (equivalent) required to chelate all of the Sm and Co ions. The supernatant of the treatment solution was discarded, and 4 L of water alone was added to the treated material, stirred, and the supernatant was discarded. This procedure was repeated twice (third and fourth water washing treatments).

[0139] After the fourth water washing, the supernatant was discarded and the solvent was replaced with 2-propanol, followed by filtration to obtain an alloy powder cake, which was then dried at 50°C under reduced pressure in a mixer to obtain the alloy powder.

[0140] The obtained powder was a SmCo5 alloy powder having a CaCu5-type crystal structure and a composition of 33.0 mass % Sm, 0.08 mass % Ca, and 0.05 mass % O.

[0141] Comparative Example 5 During the second water washing treatment (chelation treatment), no citric acid solution was added. Otherwise, an alloy powder was prepared in the same manner as in Example 18. The obtained powder was a SmCo5 alloy powder with a CaCu5-type crystal structure. Its composition was 33.3 mass% Sm, 0.09 mass% Ca, and 0.18 mass% O.

[0142] [Example 19] In Example 19, LaNi5 alloy powder was produced and evaluated. The alloy powder was produced according to the following procedure.

[0143] <Mixing process> Average particle size (D 50 112 g of lanthanum oxide (La2O3) powder with an average particle size (D) of 5.7 μm 50 A mixture was obtained by mixing 204 g of carbonyl nickel (Ni) powder having a particle size of 10.3 μm, 49.7 g of granular metallic calcium (Ca) having a particle size of 2.0 mm or less, and 11.2 g of anhydrous calcium chloride (CaCl) in a mixer under an argon (Ar) atmosphere.

[0144] <Reduction and diffusion process> The resulting mixture was placed in an iron crucible and heated in an argon (Ar) gas atmosphere at 970°C for 5 hours, and then cooled to room temperature, yielding a reaction product.

[0145] <Hydrogen treatment> After cooling, the reaction product was taken out and subjected to the same hydrogen treatment as in Example 1 to obtain a crushed product.

[0146] <Wet processing> 300 g of the resulting reaction product (crushed material) was added to 1 L of water to form a slurry. This slurry was decanted seven times using 1 L of water to separate a Ca(OH)2 suspension.

[0147] Next, 1 L of water was added to the treated material (crushed material) after separation of Ca(OH)2, and 20% diluted hydrochloric acid was added dropwise while stirring so that the slurry pH was maintained at 5.0 for 20 minutes, after which the supernatant was discarded (acid washing treatment).

[0148] After the acid washing treatment, 1 L of water was added to the treated material (crushed material), which was then stirred for 2 minutes, and the supernatant was discarded (first water washing treatment). Subsequently, 1 L of water was added to the treated material after the first water washing treatment, and 17 g of 25% aqueous citric acid solution was added while stirring (second water washing treatment (chelation treatment)). The amount of citrate ions in the treatment solution was 22 mmol, which was 1.8 times the amount (equivalent) required to chelate all of the La and Ni ions. The supernatant of the treatment solution was discarded, and then 1 L of water alone was added to the treated material, which was stirred, and the supernatant was discarded. This procedure was repeated twice more (third and fourth water washing treatments).

[0149] After the fourth water washing, the supernatant was discarded and the solvent was replaced with 2-propanol, followed by filtration to obtain an alloy powder cake, which was then dried at 50°C under reduced pressure in a mixer to obtain the alloy powder.

[0150] The obtained powder was a LaNi5 alloy powder having a CaCu5-type crystal structure and a composition of La: 33.0 mass %, Ca: 0.08 mass %, and O: 0.05 mass %.

[0151] Comparative Example 6 During the second water washing treatment (chelation treatment), no citric acid solution was added. Otherwise, an alloy powder was prepared in the same manner as in Example 19. The obtained powder was a LaNi5 alloy powder with a CaCu5-type crystal structure. Its composition was 33.3 mass% La, 0.09 mass% Ca, and 0.18 mass% O.

[0152] (2) Evaluation results The compositions and component analysis results of the rare earth transition metal alloy powders obtained in Examples 1 to 9, Examples 15 to 19, Comparative Examples 1, 2, and Comparative Examples 4 to 6 are summarized in Tables 1 to 5.

[0153] SmFe 17 In the case of N3 alloy powder, the oxygen content of the chelation-treated samples (Examples 1 to 4) was 0.09 to 0.15 mass%, while the oxygen content of the sample without chelation treatment (Comparative Example 1) was 0.22 mass% (Table 1). 17 In the case of alloy powder, the oxygen content of the chelation-treated samples (Examples 5 to 9) was 0.10 to 0.18 mass%, while the oxygen content of the sample without chelation treatment (Comparative Example 2) was 0.38 mass% (Table 2). 14 In the case of alloy powders with B phase as the main phase, the oxygen content of the chelation-treated samples (Examples 15-17) was 0.09-0.15 mass%, while the oxygen content of the sample without chelation treatment (Comparative Example 4) was 0.33 mass% (Table 3). In the case of SmCo5 alloy powders, the oxygen content of the chelation-treated sample (Example 18) was 0.05 mass%, while the oxygen content of the sample without chelation treatment (Comparative Example 5) was 0.18 mass% (Table 4). In the case of LaNi5 alloy powders, the oxygen content of the chelation-treated sample (Example 19) was 0.05 mass%, while the oxygen content of the sample without chelation treatment (Comparative Example 6) was 0.18 mass% (Table 5). As such, it was found that the oxygen content in the alloy powders could be halved by performing chelation treatment, regardless of the composition.

[0154] Also SmFe 17 The N3 alloy powder was subjected to XPS depth profile analysis. The results are shown in Figures 1 and 2 and Table 1. The oxide layer thickness on the particle surface of the chelation-treated sample (Example 1) was 20 nm, while the oxide layer thickness of the sample without chelation treatment (Comparative Example 1) was 40 nm. The chelation treatment reduced the oxide layer thickness to about half, which is thought to have contributed to the reduction in the oxygen content.

[0155] SmFe obtained in Examples 10 to 14 and Comparative Example 3 17 The magnetic properties of the N3 alloy powder are shown in Table 6. These alloy powders were obtained in Examples 5 to 9 and Comparative Example 2 using the SmFe 17 It is obtained by nitriding and finely pulverizing alloy powder (mother alloy).

[0156] The samples (Examples 10 to 14) made from the master alloys with low oxygen content (Examples 5 to 9) had a coercive force H c and angularity H k was higher than that of the sample (Comparative Example 3) made from the master alloy with a high oxygen content (Comparative Example 2).

[0157] Furthermore, the SmFe obtained in Examples 10 to 14 and Comparative Example 3 17 The N3 alloy powder was embedded in resin and polished, and the SEM backscattered electron images of the particle cross sections were observed. Compared to Examples 10 to 14, the powder of Comparative Example 3 showed a greater number of particles with non-nitrided portions (unnitrided phases) inside the particles.

[0158] From the above results, it can be seen that the manufacturing method of this embodiment in which chelation treatment is performed makes it possible to obtain high-quality rare earth transition metal alloy powder with a low oxygen content.

[0159] [Table 1]

[0160] [Table 2]

[0161] [Table 3]

[0162] [Table 4]

[0163] [Table 5]

[0164] [Table 6] < / xps> < / xrd>

Claims

1. 1. A method for producing a rare earth transition metal alloy powder, comprising the steps of: a reduction step of subjecting a mixture containing at least an alloy raw material containing a rare earth metal, a transition metal, and oxygen, and a reducing agent to a heat treatment in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and a by-product derived from the reducing agent; a wet treatment step of subjecting the reaction product to a washing treatment to obtain a rare earth-transition metal alloy powder, During the washing treatment, the reaction product is introduced into a washing liquid to obtain an alloy powder slurry, the obtained alloy powder slurry is subjected to an acid washing treatment, and further a chelation treatment is performed by adding a chelating agent to the alloy powder slurry after the acid washing.

2. 2. The method according to claim 1, wherein the reduction step comprises: mixing at least a rare earth oxide powder, a transition metal powder, and a reducing agent to obtain a mixture; and subjecting the mixture to a heat treatment in a non-oxidizing atmosphere to reduce the rare earth oxide powder and diffuse it into the transition metal powder to form an alloy, thereby obtaining a reaction product containing a rare earth-transition metal alloy component and a by-product derived from the reducing agent.

3. 3. The method according to claim 1, wherein the chelating agent is at least one selected from the group consisting of citric acid, gluconic acid, alkali metal salts of citric acid and / or gluconic acid, and alkaline earth metal salts of citric acid and / or gluconic acid.

4. 3. The method according to claim 1, wherein the content of the chelating agent in the alloy powder slurry is 1.0 to 5.0 times the amount (equivalent) required to chelate all of the rare earth ions and transition metal ions contained in the alloy powder slurry.

5. 3. The method of claim 1, further comprising a hydrogen treatment step prior to said washing step, in which said reaction product is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it.

6. 3. The method according to claim 1, wherein the chelated alloy powder slurry is subjected to a water washing treatment.

7. 3. The method according to claim 1, wherein the rare earth-transition metal alloy powder has an oxygen content of 0.16% by mass or less.

8. The rare earth transition metal alloy powder is Sm ２ Fe １７ Sm-based alloy powder or Sm ２ Fe １７ N ３ 3. The method according to claim 1, wherein the alloy powder is a ZnO-based alloy powder.

9. The method includes the reduction step, the hydrogen treatment step, the nitriding step, and the wet treatment step in this order, In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product; In the nitriding step, a mixed gas flow containing nitrogen is passed through the reaction product while heating the reaction product disintegrated in the hydrogen treatment step, thereby nitriding the rare earth-transition metal alloy component in the reaction product; The method according to claim 1 or 2, wherein in the wet treatment step, the reaction product nitrided in the nitriding step is subjected to a washing treatment.

10. The method includes the reduction step, the hydrogen treatment step, the wet treatment step, and the nitriding step in this order, In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating the product; In the wet treatment step, the reaction product disintegrated in the hydrotreatment step is subjected to a washing treatment, 3. The method according to claim 1, wherein in the nitriding step, a mixed gas flow containing nitrogen is passed through the reaction product while heating the reaction product that has been subjected to the cleaning treatment in the wet treatment step, thereby nitriding the rare earth-transition metal alloy component in the reaction product.

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