Method for producing rare earth transition metal alloy powder

Abstract

Provided is a method for producing a rare earth transition metal alloy powder having a low oxygen content and high quality. A method for producing a rare earth transition metal alloy powder, including: a reduction step of performing a heat treatment on a mixture containing at least an alloy raw material and a reducing agent in a non-oxidizing environment, the alloy raw material containing a rare earth metal, a transition metal, and oxygen, to obtain a reaction product containing a rare earth transition metal alloy and a byproduct from the reducing agent; and a wet treatment step of performing a washing treatment on the reaction product to obtain a rare earth transition metal alloy powder, in which, in the washing treatment, the reaction product is put into a washing liquid to obtain an alloy powder slurry, an acid washing treatment is performed on the obtained alloy powder slurry, and a chelation treatment of adding a chelating agent is performed on the alloy powder slurry after the acid washing treatment.

Description

Technical Field

[0001] This invention relates to a method for manufacturing rare earth transition metal alloy powders. Background Technology

[0002] Rare earth transition metal alloy powders are alloy powders mainly composed of rare earth metals and transition metals. Rare earth transition metal alloy powders, especially intermetallic compound powders, are widely used in various applications such as permanent magnet materials, hydrogen retention materials, optical and magnetic recording materials, and magnetic refrigeration materials. For example, Sm2Fe... 17 Sm2Fe is formed by nitriding alloy powder. 17 N3 series alloy powder, Nd2Fe 14 B-series alloy powder, SmCo5-series alloy powder, Sm2Co 17 PrCo5-based alloy powders exhibit significant magnetization and uniaxial magnetic anisotropy, making them useful as materials for permanent magnets. Furthermore, LaNi5-based alloy powders possess the characteristic of absorbing and retaining large amounts of hydrogen, making them suitable as hydrogen-absorbing materials. Using (Tb, Gd)-(Fe, Ni, Co)-based alloy powders to form thin films enables the formation of recording layers in optical and magnetic recording media. Further, La(Fe, Si)... 13 La(Fe,Si) is produced by hydrogenating alloy powder. 13 H x Rare earth transition metal alloy powders exhibit excellent magnetocaloric effects and hold promise as magnetic refrigeration materials. They are primarily used in the form of sintered bodies produced by powder metallurgy sintering or composites made by mixing them with resin binders.

[0003] Previously known methods for manufacturing rare earth transition metal alloy powders include the casting method and the reduction-diffusion method. Among them, the casting method uses rare earth metals and transition metals as raw materials, mixes these raw materials, dissolves them in an inactive gas environment, heat-treats the resulting alloy ingot to homogenize it, and then pulverizes it.

[0004] On the other hand, the reduction-diffusion method involves, for example, using rare earth oxides and transition metals as raw materials, mixing these raw materials with a reducing agent such as metallic calcium, and then heating them in a non-oxidizing gas environment to obtain a rare earth transition metal alloy. During the heating treatment, the rare earth oxides are reduced to rare earth metals, which diffuse into the transition metals to form an alloy (intermetallic compound). In the bulk reaction product obtained by the heating treatment, byproducts from the reducing agent remain along with the target alloy. Therefore, the reaction product is added to water to remove the byproducts from the reducing agent, and the reaction product is broken down and pulverized. The alloy powder obtained from further pulverization is subjected to acid washing and water washing to remove the remaining byproducts and unreacted substances, and then dried to obtain the target alloy powder.

[0005] The reduction-diffusion method has the advantages of using inexpensive rare-earth oxides as raw materials, having a simple process, and being able to manufacture alloy powders at a lower cost compared to the casting method. Further nitriding the alloy powder obtained by the reduction-diffusion method yields rare-earth transition metal alloy powders as nitrides.

[0006] Patent Document 1 discloses a method for manufacturing rare earth transition metal alloy powder using a reduction diffusion method. Specifically, it discloses a method for manufacturing alloy powder containing rare earth metals, wherein a mixture of rare earth oxide powder, powders of other metals, and at least one selected from alkali metals, alkaline earth metals, and their hydrides is heated in an inactive gas environment or under vacuum conditions, and the resulting mixture is then subjected to wet treatment to remove by-product CaO and residual Ca, thereby obtaining the alloy powder containing rare earth metals.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 61-295308.

[0010] In the reduction-diffusion method, the pulverized alloy powder is acid-washed to remove residual components. Dilute acetic acid and dilute hydrochloric acid are used in the acid washing process to lower the pH of the slurry containing the alloy powder, thereby effectively removing residual byproducts (calcium compounds, etc.) from the reducing agent and dissolving and removing rare-earth-rich secondary phases other than the target alloy (intermetallic compound). For example, in the manufacture of permanent magnet material Sm2Fe... 17 The master alloy of N3 is Sm2Fe 17 In the case of alloy powder, the bulk reaction product after reduction diffusion treatment contains Sm2Fe as the target intermetallic compound. 17In addition to the primary phase, it also contains Sm-rich secondary phases such as SmFe3 and SmFe2. These secondary phases degrade the magnet's properties, and are therefore removed through acid washing.

[0011] However, during the acid washing process, 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 in the slurry. Some of these ions remain after acid washing. These residual ions are oxidized and oxidized during subsequent treatments (water washing, drying, etc.) to become rare earth metal and transition metal hydroxides. The generated rare earth metal and transition metal hydroxides are present in the main phase alloy (Sm2Fe). 17 Oxygen concentration is increased due to surface precipitation of particles such as Sm2Fe. However, increasing the oxygen concentration degrades the properties of the alloy powder, making it undesirable. For example, in the case of Sm2Fe... 17 Sm2Fe is manufactured by nitriding alloy powder. 17 In the case of N3 alloy powder, even for Sm2Fe with high oxygen concentration... 17 When alloy powder undergoes nitriding treatment, nitrogen diffusion is uneven, making it difficult to obtain high-quality Sm2Fe. 17 N3. Therefore, it is desirable to suppress the formation of hydroxides caused by dissolved rare earth ions and transition metal ions. Summary of the Invention

[0012] The inventors conducted repeated and dedicated research to solve this problem. As a result, they realized that by chelating the rare earth ions and transition metal ions dissolved during acid washing, the formation of hydroxides can be suppressed, thereby obtaining rare earth transition metal alloy powder with low oxygen content and high quality.

[0013] This invention is based on the understanding that the subject of the invention is to provide a method for manufacturing rare earth transition metal alloy powder with low oxygen content and high quality.

[0014] This invention includes the solutions described in (1) to (10) below. It should be noted that the expression “~” in this specification includes the values ​​at both ends. That is, “X~Y” has the same meaning as “X and above and Y and below”.

[0015] (1) A method for manufacturing rare earth transition metal alloy powder, comprising the following steps:

[0016] The reduction process involves heating a mixture comprising at least an alloying raw material and a reducing agent under a non-oxidizing environment to obtain a reaction product containing a rare-earth transition metal alloy and byproducts from the reducing agent. The alloying raw material comprises rare-earth metals, transition metals, and oxygen.

[0017] A wet processing step involves washing the reaction products to obtain rare earth transition metal alloy powder.

[0018] During the washing process, the reaction product is added to the washing liquid to obtain an alloy powder slurry. The obtained alloy powder slurry is then subjected to acid washing treatment, and the acid-washed alloy powder slurry is then subjected to chelation treatment with the addition of a chelating agent.

[0019] (2) The method as described in (1) above, wherein the reduction step is a step of mixing at least rare earth oxide powder, transition metal powder and reducing agent to obtain a mixture and heating the mixture in a non-oxidizing environment to reduce the rare earth oxide powder and alloy it by diffusion in the transition metal powder, thereby obtaining a reaction product containing rare earth transition metal alloy components and byproducts from the reducing agent.

[0020] (3) The method as described in (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.

[0021] (4) The method as described in any one of (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 the rare earth ions and transition metal ions contained in the alloy powder slurry.

[0022] (5) The method as described in any one of (1) to (4) above, further comprising a hydrogen treatment step, wherein the hydrogen treatment step involves exposing the reaction product to a hydrogen environment prior to the washing treatment, thereby absorbing hydrogen and pulverizing it.

[0023] (6) The method as described in any one of (1) to (5) above, wherein the alloy powder slurry that has undergone the chelation treatment is subjected to water washing treatment.

[0024] (7) The method as described in any one of (1) to (6) above, wherein the oxygen content of the rare earth transition metal alloy powder is less than 0.16% by mass.

[0025] (8) The method as described in any one of (1) to (7) above, wherein the rare earth transition metal alloy powder is Sm2Fe 17 It is an alloy powder or Sm2Fe 17 N3 series alloy powder.

[0026] (9) The method as described in any one of (1) to (8) above, wherein,

[0027] The process includes, in sequence, the reduction process, the hydrogen treatment process, the nitriding process, and the wet treatment process.

[0028] In the hydrogen treatment process, the reaction products obtained in the reduction process are exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized.

[0029] In the nitriding process, the reaction product pulverized in the hydrogen treatment process is heated while a nitrogen-containing mixed gas flow is passed through the reaction product, thereby nitriding the rare earth transition metal alloy components in the reaction product.

[0030] In the wet treatment process, the reaction product after nitriding in the nitriding process is subjected to washing treatment.

[0031] (10) The method as described in any one of (1) to (8) above, wherein,

[0032] The process includes, in sequence, the reduction process, the hydrogen treatment process, the wet treatment process, and the nitriding process.

[0033] In the hydrogen treatment process, the reaction products obtained in the reduction process are exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized.

[0034] In the wet processing step, the reaction products pulverized in the hydrogen treatment step are subjected to washing treatment.

[0035] In the nitriding process, the reaction product that has undergone washing in the wet treatment process is heated while a nitrogen-containing mixed gas flow is passed through the reaction product, thereby nitriding the rare earth transition metal alloy components in the reaction product.

[0036] The effects of the invention

[0037] According to the present invention, a method for manufacturing rare earth transition metal alloy powder with low oxygen content and high quality is provided. Attached Figure Description

[0038] Figure 1 This refers to Sm2Fe in Example 1. 17 Results of XPS depth direction analysis of N3 alloy powder.

[0039] Figure 2 This refers to Sm2Fe in Comparative Example 1. 17 Results of XPS depth direction analysis of N3 alloy powder. Detailed Implementation

[0040] Specific embodiments of the present invention (hereinafter referred to as "this embodiment") will be described below. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without changing the spirit of the present invention.

[0041] <<Preparation Method of Rare Earth Transition Metal Alloy Powder>>

[0042] The method for manufacturing rare earth transition metal alloy powder (hereinafter, sometimes simply referred to as "alloy powder") according to this embodiment includes the following steps: a reduction step, in which a mixture comprising at least an alloy raw material and a reducing agent is heated under a non-oxidizing environment to obtain a reaction product comprising a rare earth transition metal alloy and a byproduct from the reducing agent, wherein the alloy raw material contains rare earth metals, transition metals, and oxygen; and a wet treatment step, in which the obtained reaction product is washed to obtain rare earth transition metal alloy powder. Furthermore, during the washing treatment, the reaction product is added to a washing liquid to obtain an alloy powder slurry, the obtained alloy powder slurry is subjected to acid washing, and then the acid-washed alloy powder slurry is subjected to chelation treatment by adding a chelating agent. Each step will be described in detail below.

[0043] <Rare Earth Transition Metal Alloy Powder>

[0044] The rare-earth transition metal alloy powder of this embodiment is a powder composed of an alloy containing rare-earth metals (R) and transition metals (TM). Here, rare-earth metals (R) are 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 metals (TM) are a general term for metals (elements) between Group 3 and Group 11 of the periodic table. Furthermore, the concept of an alloy includes not only solid solutions but also eutectics and intermetallic compounds. Examples of intermetallic compounds include CaCu5 type and Th2Zn. 17 Type, Th2Ni 17 Type, TbCu7 type, ThMn 12 Type, NaZn 13 Type, Nd2Fe 14 Compounds with crystal structures such as type B and MgCu2.

[0045] There is no particular limitation on rare earth metals (R), but preferably 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). Furthermore, the rare earth transition metal alloy powder may contain only rare earth metals and transition metals, or it may contain other components for the purpose of stabilizing the crystal structure and improving properties. For example, it may also include 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). Further, components caused by alkali metals, alkaline earth metals, or their hydrides used as reducing agents, such as calcium (Ca) and magnesium (Mg), may sometimes remain in the alloy powder. These residues are permissible as long as the desired characteristics can be obtained.

[0046] Rare earth transition metal alloy powders, as long as they are alloys mainly composed of rare earth metals and transition metals, have no specific composition limitations. For example, Sm2Fe... 17 Sm2Fe after nitriding 17 N3, Nd2Fe 14 B, SmCo5, Sm2Co 17 Materials used in permanent magnets, such as PrCo5. Also suitable as hydrogen-retaining materials and optical / magnetic recording materials such as LaNi5, (Tb, Gd)-(Fe, Ni, Co). Also suitable as La(Fe, Si). 13 The hydrogenated La(Fe,Si) 13 H x Isomagnetic refrigeration materials. Rare earth transition metal alloy powder is preferably Sm2Fe. 17 It is an alloy powder or Sm2Fe 17 Nitrogen-based alloy powder. Here, Sm2Fe... 17 It is an alloy powder or Sm2Fe 17 N3 series alloy powder not only contains Sm2Fe 17 Sm2Fe 17 N3, and also includes powders formed by replacing some of the metals in these compounds with other metals such as manganese (Mn) and cobalt (Co). These alloy powders are useful as high-performance permanent magnet materials and their master alloy materials. It should be noted that there is no limitation on the content of rare earth metals in rare earth transition metal alloy powders, typically between 10% by mass and 60% by mass. In addition, there is no limitation on the average particle size of rare earth transition metal alloy powders, typically between 1.0 μm and 100 μm.

[0047] <Reduction Process>

[0048] In the reduction process, a mixture comprising at least an alloying raw material and a reducing agent is heated under a non-oxidizing environment. The alloying raw material contains rare earth metals, transition metals, and oxygen. The alloying raw material only needs to contain at least rare earth metals, transition metals, and oxygen as constituent elements. During the heat treatment, oxygen is removed from the alloying raw material under the action of the reducing agent, while simultaneously, the rare earth metals diffuse into the transition metals and alloy. Furthermore, this yields reaction products containing rare earth transition metal alloys and byproducts from the reducing agent.

[0049] The alloy raw material is preferably a mixture of rare earth oxide powder and transition metal powder. That is, the reduction process is a process of mixing at least rare earth oxide powder, transition metal powder and reducing agent to obtain a mixture (raw material mixing process) and a process of heating the mixture in a non-oxidizing environment to reduce the rare earth oxide powder and allow it to diffuse into the transition metal powder to alloy, thereby obtaining a reaction product containing rare earth transition metal alloy components and byproducts from the reducing agent (reduction diffusion process).

[0050] The following describes in detail the manufacturing steps when the alloy raw material is a mixture of rare earth oxide powder and transition metal powder.

[0051] (Rare earth oxide powder)

[0052] Rare earth oxide powder is a raw material for rare earth elements constituting the target alloy powder. There is no limitation, but 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 a rare earth oxide powder, a single powder can be used, or two or more powders can be mixed.

[0053] Rare earth oxide powders can be selected based on the composition of the target alloy powder. For example, in the manufacture of samarium iron nitride (Sm2Fe) powder... 17 N3-based alloy powders, samarium cobalt (SmCo5, Sm2Co) 17 In the case of NdFeB alloy powders, samarium oxide (Sm2O3) can be used. Additionally, in the preparation of NdFeB (Nd2Fe) alloys... 14 In the case of B) alloy powder, neodymium oxide (Nd2O3) can be selected.

[0054] The particle size of the rare earth oxide powder can be determined based on the composition of the obtained alloy powder and its intended use. However, it is preferable to determine the particle size of the rare earth oxide powder to ensure uniform distribution in the vicinity of 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. Powder with particles of 0.1 to 10 μm in diameter accounting for 80% or more of the total is particularly preferred. This improves the inmisivability of the raw materials and the operability of the raw material powder and reaction products. In addition, it allows for sufficient diffusion of rare earth metals in subsequent reduction diffusion processes. Rare earth oxide powder sometimes contains moisture and organic matter as impurities. These impurities sometimes increase the oxygen content of the final alloy powder. Therefore, the less impurities contained in the rare earth oxide powder, the better. For example, the loss on heating after heating to 1000°C is preferably 2% by mass or less, more preferably 1% by mass or less.

[0055] The amount of rare earth oxide powder is preferably 1.0 to 1.5 times the amount (equivalent) required to form the alloy powder with the target composition, more preferably 1.05 to 1.2 times. For example, when manufacturing samarium iron (Sm2Fe) 17 ) series alloy powder, samarium iron nitrogen (Sm2Fe) 17 When using N3-based alloy powders, the preferred amount of samarium oxide (Sm2O3) is a stoichiometric composition (Sm2Fe). 17 The amount of rare earth oxides (N3) is 1.0 to 1.5 times the required amount. By setting the amount of rare earth oxides to 1.0 times or more of the equivalent, the diffusion of rare earth metals (rare earth elements) in the transition metal powder becomes sufficient, and the desired properties of the final alloy powder can be adequately imparted. On the other hand, by setting it to 1.5 times or less of the equivalent, the formation of rare earth-rich heterogeneous phases can be suppressed.

[0056] (Transition metal powder)

[0057] The transition metal powder is a raw material for the transition metal constituting the target alloy powder. There is no limitation, but it is preferably 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). As the transition metal powder, a single powder may be used, or two or more powders may be mixed.

[0058] The transition metal powder can be selected simply based on the composition of the target alloy powder. For example, in the manufacture of samarium iron nitride (Sm2Fe) powder... 17 N3-based alloy powder, NdFeB (Nd2Fe) 14In the case of B) series alloy powders, only iron (Fe) powder needs to be selected. As the iron powder, reduced iron powder, gas-atomized powder, water-atomized powder, and / or electrolytic iron powder can be used. Additionally, in the manufacture of samarium cobalt (SmCo5, Sm2Co)... 17 In the case of alloy powders, only cobalt (Co) powder needs to be selected. When the transition metal powder is iron (Fe), cobalt (Co), nickel, or (Ni) powder, for example, reducing powder, gas atomizing powder, water atomizing powder, electrolytic powder, carbonyl powder, etc. can be used.

[0059] The particle size of the transition metal powder can be determined based on the composition and intended use of the resulting alloy powder. However, if the particle size of the transition metal powder is too large, the diffusion of rare earth metals into the interior will not be sufficient during the subsequent reduction diffusion process, sometimes leaving unalloyed phases. 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, it is preferable that particles with a particle size of 1 to 100 μm account for 70% or more of the total. This improves the operability of the raw material powder and the reaction products. In addition, it allows for sufficient diffusion of rare earth metals in the subsequent reduction diffusion process. Furthermore, the less impurities contained in the transition metal powder, the more preferable. For example, the loss on heating after heating to 1000°C is preferably 2% or less by mass, more preferably 1% or less by mass.

[0060] Up to 20% by mass of the transition metal powder can be replaced with oxide powder of the transition metal. This allows for adjustment of the exothermic reaction in the subsequent reduction-diffusion reaction. Alternatively, the transition metal powder can also be an alloy powder.

[0061] Furthermore, in addition to transition metal powders, additives aimed at stabilizing the crystal structure and improving properties can also be added. These additives can be added individually or in the form of compounds such as oxides. Alternatively, they can be added as powders pre-alloyed with transition metals such as iron (Fe), cobalt (Co), and nickel (Ni). When using individual metal powders or oxide powders, it is preferable to use powders with particles of 20 μm or less comprising 80% or more of the total mass, and more preferably powders with particles of 10 μm or less comprising 80% or more of the total mass. When using oxide powders, it is preferable to select powders that do not decompose during the subsequent reduction-diffusion heat treatment. This is because if decomposition occurs during heating, the reducing agent is deactivated, making the reduction-diffusion reaction difficult. When using powders pre-alloyed with transition metals, it is preferable to use powders with particles of 0.1 to 10 μm comprising 80% or more of the total mass. Alternatively, mixed oxide powders of rare earth metals and transition metals, with additives mixed as needed, can also be used. The coprecipitate product, which is a starting material of salt, is calcined in the atmosphere and then mechanically pulverized. The resulting powder is then reduced with hydrogen or carbon to produce the mixed oxide powder.

[0062] (reducing agent)

[0063] The reducing agent is added to reduce oxide components such as rare earth oxide powder in subsequent reduction diffusion processes to promote alloy formation. As a reducing agent, at least one selected from alkali metals, alkaline earth metals, and their hydrides is used. Specifically, one or more 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 are preferred. From the viewpoint of operational safety and cost, lithium (Li) and / or calcium (Ca) are more preferred, and calcium (Ca) is particularly preferred. Most preferably, granular metallic calcium (Ca) is sieved to a sieve aperture diameter of 4.00 mm or less.

[0064] The reducing agent can also be used in combination with other raw material powders. Alternatively, it can be separated beforehand in a manner that allows the vapor of the reducing agent (such as Ca) to contact with the other raw material powders. By using the reducing agent in combination 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 the amount (equivalent) required to reduce the oxides in the mixture, more preferably 1.1 to 1.5 times. As long as the amount of reducing agent is within this range, the amount of unreacted substances and byproducts in the resulting reaction product can be minimized, and the reduction reaction can be carried out sufficiently.

[0065] (Other ingredients)

[0066] Depending on the requirements, other components besides rare earth oxide powders, transition metal powders, and reducing agents may be added. For example, rare earth metal powders and / or transition metal oxide powders may be added. Additionally, alloy powders of rare earth metals and transition metals, or their oxide powders, may be added. Furthermore, when manufacturing alloy powders containing components other than rare earth metals and transition metals, other raw materials may be added. For example, boron sources such as boron (B) and boron oxide (B₂O₃) may be added to manufacture Nd₂Fe as a permanent magnet material. 14 B alloy powder. Silicon sources such as silicon (Si) and silicon oxide (SiO2) can also be added to manufacture La(Fe,Si) as a magnetic refrigeration material. 13 H x alloy powder.

[0067] Furthermore, auxiliary additives for easily manufacturing alloy powders can also be added. Examples of auxiliary additives include disintegration accelerators that promote the disintegration of the reaction products in subsequent wet processing steps. Alkaline earth metal salts and oxides such as calcium chloride (CaCl2) and calcium oxide (CaO) can be used as disintegration accelerators. Preferably, the disintegration accelerator is uniformly mixed with other raw material powders simultaneously. This allows components from the disintegration accelerator (calcium compounds, etc.) to be uniformly present at the grain boundaries of the alloy crystals in the reaction products. Therefore, during slurry formation in subsequent wet processing steps, components from the disintegration accelerator dissolve in the aqueous solution, thereby effectively promoting disintegration. The amount of disintegration accelerator added is preferably 3 to 30% by mass, more preferably 7 to 20% by mass, relative to the total amount of oxides in the mixture. By setting the amount of disintegration accelerator within this range, unreacted substances and byproducts in the reaction products can be minimized, and the disintegration of the reaction products can be fully achieved.

[0068] (mix)

[0069] The mixing of raw materials involves uniformly mixing rare earth oxide powders, transition metal powders, reducing agents, and other components added as needed. Any known mixer, such as a ribbon mixer, rotary drum mixer, S-type mixer, V-type mixer, Notta mixer, Henschel mixer, super mixer, high-speed mixer, ball mill, vibratory mill, vertical ball mill (attritor), or jet mill, can be used.

[0070] The mixing process is preferably carried out in a vacuum or inert gas environment in a manner that prevents the reducing agent from contacting atmospheric oxygen or water vapor. Examples of inert gases include nitrogen (N2), argon (Ar), and helium (He). The resulting mixture is then placed in a heat treatment furnace, where the inert gas is supplied and the air inside the furnace is replaced. Argon (Ar) and helium (He) are examples of inert gases, with argon being the most commonly used. Furthermore, repeated vacuuming and inert gas replacement reduce residual oxygen levels, which is preferable.

[0071] Next, the mixture is subjected to a reduction-diffusion treatment. In the reduction-diffusion step, the mixture is heated in a non-oxidizing environment to obtain the reaction product. Here, a non-oxidizing environment refers to an environment that is substantially free of oxygen. As the ambient gas, an inert gas, such as argon (Ar) and / or helium (He), is preferred. In addition, the oxygen content in the environment is preferably 5% or less, more preferably 1% or less.

[0072] If the mixture is heated in a non-oxidizing environment, the rare earth oxide powder is reduced by a reducing agent to generate rare earth metals. The generated rare earth metals diffuse into the transition metal powder and alloy to form rare earth transition metal alloys. Furthermore, if the mixture contains oxides of other components besides rare earth oxide powder, these oxides are also reduced and diffused, incorporating into the alloy. On the other hand, the reducing agent is oxidized and becomes an oxide.

[0073] For example, samarium oxide (Sm2O3) as a rare earth oxide powder, iron (Fe) powder as a transition metal powder, and metallic calcium (Ca) as a reducing agent are used to manufacture samarium iron nitrogen (Sm2Fe). 17 N3)-based alloy powder or samarium iron (Sm2Fe) as its parent alloy powder 17 In the case of iron (Fe) powder, samarium oxide (Sm₂O₃) is reduced by a reducing agent (Ca) to form samarium (Sm). Then, the reduced samarium (Sm) diffuses into iron (Fe) powder to form Th₂Zn. 17 Samarium iron alloy (Sm2Fe) with a crystalline structure 17 On the other hand, metallic calcium (Ca), acting as a reducing agent, is oxidized to form calcium oxide (CaO). In the case of a concentration of more than an equivalence of metallic calcium, residual calcium (Ca) remains. This calcium oxide (CaO) and the residual calcium (Ca) constitute byproducts. Furthermore, depending on the circumstances, heterogeneous phases such as samarium iron compounds (SmFe3, etc.) may also be generated. Therefore, the reaction products after heat treatment contain rare earth transition metal alloy components (Sm2Fe). 17The product of this heat treatment includes byproducts from the reducing agent (CaO, Ca, etc.), and, depending on the circumstances, heterogeneous phases (SmFe3, etc.). Typically, the product of this heat treatment is a porous ingot.

[0074] The heat treatment is performed at a temperature above the melting point of the reducing agent and at a temperature at which the obtained rare-earth transition metal alloy components do not melt. Specifically, the heat treatment temperature is preferably 850–1200°C. If the temperature is above 850°C, the rare-earth metals diffuse uniformly in the transition metal powder, which improves the properties of the final alloy powder. Conversely, if the temperature is below 1200°C, the alloy components in the reaction products are prevented from solidifying, resulting in easier disintegration and pulverization in subsequent wet processing steps. Furthermore, the heat treatment is preferably performed considering the particle size of the raw materials and until the reduction and diffusion reactions are fully completed. Typically, the heating time is 1–10 hours, preferably 2–8 hours.

[0075] The above mainly describes the case where the alloy raw material is a mixture of rare earth oxide powder and transition metal powder. However, it is not limited to the above mixture, as long as the alloy raw material forms a rare earth transition metal alloy under the action of a reducing agent. For example, the alloy raw material can also be an oxide and / or partially reduced oxide (partial oxide) containing rare earth metals and transition metals, an alloy containing rare earth metals, transition metals and oxygen (e.g., an oxygen-containing SmFe alloy), or a mixture containing alloys of rare earth metals and transition metals and rare earth oxides (e.g., a mixture of SmFe alloy and Sm oxide). By using partially reduced oxides as the alloy raw material, the amount of reducing agent added in subsequent processes can be suppressed. The following describes an example of the preparation steps of a partially reduced oxide containing rare earth metals and transition metals.

[0076] First, a composite oxide containing rare earth metals (Re) and transition metals (TM) is prepared. Here, the composite oxide is a compound containing rare earth metals and transition metals as constituent elements. Therefore, it is different from a simple mixture of rare earth metal oxides and transition metal oxides.

[0077] There are no limitations on the method for obtaining the composite oxide. Commercially available composite oxides containing rare earth metals and transition metals can also be used. Alternatively, it can be a byproduct or recycled product generated during the manufacture of materials such as magnetic materials containing rare earth metals and transition metals. However, it is preferred to synthesize the composite oxide via a wet process. Specifically, the composite oxide is obtained by heating after wet treatment of the rare earth oxide and transition metal compound. By performing wet synthesis, a composite oxide in which rare earth metals and transition metals are uniformly dispersed at the atomic level can be produced.

[0078] To synthesize composite oxides via a wet process, a hydroxide is generated from an acid solution containing rare earth metals and transition metals through a neutralization reaction, followed by heat treatment of the resulting hydroxide. 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. There are no limitations on the form of the rare earth metal raw material and the transition metal raw material dissolved in the acid solution. For example, rare earth oxides such as samarium oxide (Sm₂O₃) can be used. Additionally, transition metal sulfates and nitrates, such as ferrous sulfate (FeSO₄), can be used as transition metal raw materials. The type of acid solution is determined based on the raw materials; for example, aqueous solutions of sulfuric acid and nitric acid can be used. It is preferable to adjust the pH of the acid solution to ensure complete dissolution of the rare earth metal raw material and the transition metal raw material.

[0079] Next, an alkaline solution is added to the obtained raw material solution. This causes a neutralization reaction, yielding a slurry containing rare earth metal and transition metal hydroxides, such as Sm-Fe hydroxide, as precipitates. Examples of alkaline solutions include ammonia solution, aqueous solutions containing ammonium bicarbonate, ammonium hydroxide, sodium hydroxide, potassium hydroxide, and / or urea. Adding the alkaline solution dropwise is preferred to obtain a uniform and fine hydroxide. The precipitates in the obtained slurry are then recovered by methods such as filtration. Alternatively, the precipitates can be washed with a washing solution such as ion-exchanged water. This washing process helps to reduce the amount of impurities in the final magnet powder.

[0080] Next, the recovered precipitate is dried and then subjected to heat treatment. This yields a composite oxide containing rare earth metals and transition metals, such as Sm-Fe oxide. Drying can be performed at a temperature that efficiently removes moisture, for example, 80°C or higher and 400°C or lower. Drying can also be performed under reduced pressure, or by circulating a drying gas during drying. The heating environment is not limited as long as a composite oxide is obtained. For example, an oxygen-containing environment such as a mixture of air, oxygen, and inert gases, or a mixture of air and inert gases, can be used. The heating temperature is preferably 500°C or higher and 1400°C or lower, more preferably 700°C or higher and 1200°C or lower. If the heating temperature is too low, the oxidation of the precipitate may be insufficient. On the other hand, if the heating temperature is too high, the resulting oxide may undergo particle growth.

[0081] As needed, other components besides rare earth metals and transition metals, such as additives, may be added to the composite oxide. There are no limitations on such components; examples include one or more components selected from the group consisting of silicon (Si), aluminum (Al), titanium (Ti), zirconium (Zr), zinc (Zn), and copper (Cu). Other components may also be added by dissolving them together with the rare earth metal and transition metal raw materials in an acid solution.

[0082] Next, the prepared composite oxide is heated in a reducing environment to obtain a partially reduced oxide containing rare earth metals and transition metals. Through pre-reduction, a portion of the composite oxide, particularly the transition metal component, is reduced. By incorporating the pre-reduction process, the amount of reducing agent required in subsequent processes can be reduced. Furthermore, it promotes uniform reduction of the reduction-diffusion treated material.

[0083] The heating environment in the pre-reduction process is not particularly limited, as long as it allows for the partial reduction of the composite oxide. Examples include environments containing hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and / or methane (CH4). The heating temperature in the pre-reduction process is preferably 400°C or higher and 900°C or lower. Furthermore, the heating time is preferably 0.5 hours or higher and 10 hours or lower.

[0084] As described above, partially reduced oxides containing rare earth metals and transition metals can be obtained. If the obtained partially reduced oxides are used as alloying raw materials, and a mixture containing the oxides and a reducing agent is heated under a non-oxidizing environment, the oxides of the rare earth metals and transition metals contained in the mixture are reduced under the action of the reducing agent, thereby generating rare earth metals and transition metals. The generated rare earth metals diffuse into the transition metals, thereby alloying to form a rare earth transition metal alloy. On the other hand, the reducing agent is oxidized and becomes a byproduct (oxide, etc.) from the reducing agent. Therefore, a reaction mixture containing a rare earth transition metal alloy and byproducts from the reducing agent is obtained. The heating treatment can be performed under the same conditions as in the case where the alloying raw material is a mixture of rare earth oxide powder and transition metal powder.

[0085] <Hydrogen Treatment Process>

[0086] If necessary, a hydrogen treatment step can be added after the reduction step (reduction-diffusion step). In the hydrogen treatment step, the reaction products obtained in the reduction step are exposed to a hydrogen environment and pulverized to obtain pulverized reaction products (pulverized material).

[0087] Rare earth transition metal alloys (intermetallic compounds) mostly absorb hydrogen and expand in volume. For example, SmFe3 expands in volume by 19% due to hydrogen absorption. Similarly, Sm2Fe... 17 Volume expansion of 3.4%, Nd2Fe 14Boron 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 or its surface properties. However, all hydrogen absorption reactions are exothermic. Therefore, in rare-earth transition metal alloys containing multiple intermetallic compounds, chain reactions sometimes occur. That is, the absorption begins with a compound that absorbs hydrogen at low temperatures, which releases heat, causing the alloy temperature to rise, and then subsequent compounds absorb hydrogen.

[0088] Hydrogen treatment is carried out in a hydrogen environment using a hydrogen-containing gas. The hydrogen-containing gas can be hydrogen (H2) alone, or a mixture of hydrogen (H2) and a non-reactive gas such as argon (Ar) or helium (He). However, using hydrogen alone is preferred. In this case, it is preferable to purge the furnace environment with a non-reactive gas such as argon before introducing hydrogen to prevent residual oxygen (O2). Furthermore, in this situation, it is preferable to temporarily vent the furnace after purging with a non-reactive gas before introducing hydrogen. After hydrogen treatment, the process is switched back to a non-reactive gas such as argon, and the reaction products (crushed material) are recovered. It should be noted that the hydrogen treatment step is not necessarily a mandatory step.

[0089] <Wet Processing Procedure>

[0090] In the wet processing step, the resulting reaction product is washed to obtain rare earth transition metal alloy powder. Without a hydrogen treatment step, the reaction product obtained in the reduction step (reduction-diffusion step) is washed. With a hydrogen treatment step, the reaction product (pulverized material) after hydrogen treatment is washed. Furthermore, if the nitriding treatment step (described later) is performed after the reduction step, the reaction product (nitride) after nitriding is washed.

[0091] In wet processing, the reaction products are first added to a washing solution to obtain an alloy powder slurry. Specifically, the reaction products are added to the washing solution and stirred. The products added to the washing solution disintegrate into a slurry. At this point, byproducts from the reducing agent react with water to form components from the solid byproducts, consisting of hydroxides. Therefore, the components from the solid byproducts include hydroxides of alkali metals and / or alkaline earth metals. For example, when using metallic calcium (Ca) as a reducing agent, the product after the reduction process contains rare earth transition metal alloy components and byproducts (CaO, Ca). During water washing, these byproducts (CaO, Ca) react with water to form calcium hydroxide (Ca(OH)2). Calcium hydroxide has low solubility in water, so most of it becomes a suspension suspended in the water. The slurry obtained by water washing is a suspension of rare earth transition metal alloy components and components from the solid byproducts (Ca(OH)2). By separating components from solid byproducts in the slurry from rare earth transition metal alloy components, high-purity, high-performance alloy powders can be obtained.

[0092] Water, ethylene glycol, or a mixture of water and ethylene glycol can be used as the washing solution. Ion-exchanged water is preferred as the water. One or more ethylene glycols selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol are preferred as the ethylene glycol.

[0093] The separation of components from solid byproducts can be performed by decantation. Decantation can be performed once or multiple times. For example, it can be repeated: the reaction product is added to a washing solution, stirred, allowed to stand, and the supernatant is removed; the washing solution is then added to the resulting residue, stirred, allowed to stand, and the supernatant is removed again. Rare earth transition metal alloy components have a relatively high specific gravity, while components from solid byproducts have a relatively low specific gravity. Therefore, the components from solid byproducts with lower specific gravity can be separated and removed together with the supernatant by decantation. Alternatively, gravity separators such as liquid cyclones or centrifuges can be used instead of decantation, or in conjunction with decantation, to separate and remove components from solid byproducts.

[0094] Then, the obtained alloy powder slurry is subjected to acid washing. Acid washing can more effectively remove components and heterogeneous phases from solid byproducts. For example, components from solid byproducts (such as Ca(OH)2) that were not completely removed by using the washing solution, along with heterogeneous phases (such as SmFe3) in the product, can be removed together. For example, acid washing is performed by adding acid to the alloy powder slurry while stirring. Inorganic or organic acids such as hydrochloric acid, acetic acid, nitric acid, and sulfuric acid can be used as the type of acid.

[0095] Next, the acid-washed alloy powder slurry undergoes a chelation treatment with the addition of a chelating agent. This chelation treatment yields alloy powder with low oxygen content. Specifically, during acid washing, rare earth ions and transition metal ions dissolve from the alloy powder into the washing solution. These ions, either as monomers or in complexes, become hydroxides and adhere to the surface of the alloy powder, increasing its oxygen content. While water washing after acid washing can remove rare earth and transition metal ions to some extent, it is insufficient to completely prevent the formation and adhesion of hydroxides. In contrast, chelation treatment chelates the rare earth and transition metal ions, forming stable complexes. Therefore, the formation and adhesion of hydroxides can be prevented. Furthermore, the result is alloy powder with low oxygen content.

[0096] 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, o-phenanthroline, and bipyridine. The chelating agent is preferably 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.

[0097] Alternatively, during chelation treatment, alkaline solutions such as sodium hydroxide or potassium hydroxide can be added to the alloy powder slurry. In this case, the chelating agent and the alkaline solution can be added separately, or a mixed aqueous solution of the chelating agent and the alkaline solution can be added. By adding the alkaline solution, the amount of chelating agent required for the chelation treatment can be reduced. Furthermore, since the slurry can be made closer to neutral (pH ~ 7), damage to the alloy powder in the slurry can be reduced. When using a mixed aqueous solution of the chelating agent and the alkaline solution, the pH of the mixed aqueous solution is preferably 5.0 or higher and 7.5 or lower.

[0098] The method of chelation treatment is not limited as long as the alloy powder can be chelated. For example, a method can be described by adding a chelating agent to the alloy powder slurry while stirring it. Preferably, the amount of chelating agent added is sufficient to chelate all the rare earth ions and transition metal ions in the slurry. Specifically, the content of chelating agent in the slurry is preferably 1.0 to 5.0 times the amount (equivalent) required to chelate all the rare earth ions and transition metal ions contained in the slurry.

[0099] Acid washing and / or chelation treatment can each be performed once, or multiple times. Alternatively, a water washing step can be added before or after the acid washing and chelation treatments. Further water washing of the alloy powder slurry after chelation treatment is particularly preferred. This effectively removes chelated rare earth ions and transition metal ions. Water washing only requires one or more steps of discarding the supernatant of the alloy powder slurry and adding water with stirring.

[0100] The alloy powder, after washing, is recovered and dried to obtain rare earth transition metal alloy powder. The recovery of the alloy powder can be achieved through solid-liquid separation processes such as filtration or centrifugation of the slurry or cake containing the alloy powder. Furthermore, if the water contained in the slurry or cake is replaced with an alcohol such as methanol, ethanol, or isopropanol, the processing time in the subsequent drying process is shortened. Drying is preferably carried out at 30–250°C, more preferably 40–100°C. However, sometimes the alloy powder absorbs hydrogen due to the washing process. In this case, from the viewpoint of reducing residual hydrogen, vacuum drying at a temperature below 200°C is preferred.

[0101] <Nitriding process>

[0102] In the manufacturing method of this embodiment, a step of nitriding the product (nitriding treatment step) may be provided as needed. By providing this step, samarium iron nitride (Sm2Fe) can be obtained. 17 Nitride-based alloy powders such as N3. Nitriding can be performed at any time, as long as it occurs after the reduction process (reduction-diffusion process). The reaction products obtained in the reduction process can be nitrided, the pulverized material obtained in the hydrogen treatment process can be nitrided, or the alloy powder obtained in the wet treatment process can be nitrided.

[0103] In nitriding, the products (reaction products, pulverized materials, alloy powder) are heated to a preferred temperature of 350–500°C, more preferably 400–480°C, while a nitrogen-containing mixed gas stream is circulated. This nitrides the rare-earth transition metal alloy composition. Setting the heating temperature to 350°C or higher allows for a shorter nitriding reaction time, increasing efficiency. However, excessively high heating temperatures can sometimes cause decomposition of the main phase. For example, when samarium iron (Sm2Fe) is subjected to excessive heating... 17 Samarium iron nitride (Sm2Fe) is produced by nitriding rare earth transition metal alloys. 17 When processing N3-based alloy powders, if the nitriding temperature is too high, samarium iron (Sm2Fe) may sometimes become the main phase. 17The main phase decomposes to form αFe. Since αFe reduces the squareness of the demagnetization curve of the magnetic powder, its formation is undesirable. This decomposition of the main phase can be suppressed by setting the nitriding temperature below 500°C.

[0104] The nitriding gas flowing during the nitriding process only needs to contain at least nitrogen atoms; nitrogen and ammonia are preferred. Alternatively, hydrogen, argon, etc., can be included to control the reaction. When using a mixed gas stream of ammonia and hydrogen, the mixing ratio (gas flow ratio) is preferably ammonia:hydrogen = 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.

[0105] <Heat Treatment Process>

[0106] If necessary, the product obtained in the nitriding treatment (nitride-based alloy powder) can be further subjected to heat treatment in an inert gas environment. Inert gases include, for example, hydrogen, nitrogen, argon, and helium. By performing this heat treatment, the nitrogen distribution within each crystal unit constituting the obtained alloy powder becomes more uniform, further improving the properties of the alloy powder. The heat treatment temperature is preferably 350–500°C, more preferably 400–480°C. The holding time is preferably 20–200 minutes, more preferably 30–150 minutes.

[0107] <Micro-pulverization process>

[0108] As needed, the products (alloy powders) obtained from wet treatment, nitriding, or heat treatment processes can also be micronized. In the micronization process, the powder and a grinding medium are placed together in a pulverizer and pulverized until the average particle size reaches 1–3 μm. Isopropanol, ethanol, toluene, methanol, hexane, etc., can be used as the grinding medium. Furthermore, by adding a surface treatment agent to the pulverizing solvent, surface treatment of the alloy powder can be performed simultaneously with pulverization. Examples of surface treatment agents include phosphoric acid compounds such as orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate, and aluminum phosphate.

[0109] According to a preferred embodiment, the manufacturing method of this embodiment sequentially includes a reduction step, a hydrogen treatment step, a nitriding step, and a wet treatment step. In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized. In the nitriding step, while heating the pulverized reaction product from the hydrogen treatment step, a nitrogen-containing mixed gas stream is passed through the reaction product stream, thereby nitriding the rare earth transition metal alloy components in the reaction product. In the wet treatment step, the nitrided reaction product from the nitriding step is washed.

[0110] In another preferred embodiment, the manufacturing method of this embodiment sequentially includes a reduction step, a hydrogen treatment step, a wet treatment step, and a nitriding step. In the hydrogen treatment step, the reaction product obtained in the reduction step is exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized. In the wet treatment step, the pulverized reaction product from the hydrogen treatment step is washed. In the nitriding step, while heating the reaction product (alloy powder) that has undergone washing in the wet treatment step, a nitrogen-containing mixed gas flow is passed through the reaction product (alloy powder), thereby nitriding the rare earth transition metal alloy component in the reaction product.

[0111] As described above, the rare earth transition metal alloy powder of this embodiment can be manufactured. According to the manufacturing method of this embodiment, by chelating the rare earth ions and transition metal ions dissolved in the slurry during acid washing, the formation of hydroxides and the adhesion of alloy powder can be prevented. Furthermore, as a result, rare earth transition metal alloy powder with low oxygen content and high quality can be obtained. For example, it is not limited to reducing the oxygen content of the rare earth transition metal alloy powder 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.

[0112] The rare earth transition metal alloy powder obtained by the manufacturing method of this embodiment can be applied to known uses such as permanent magnet materials, hydrogen retention materials, optical and magnetic recording materials, and magnetic refrigeration materials, and is particularly suitable for use as a permanent magnet material.

[0113] Example

[0114] The invention is further illustrated in detail using the following embodiments. However, the invention is not limited to the following embodiments.

[0115] (1) Preparation and evaluation of alloy powder

[0116] Preparation of Sm2Fe 17 N3 alloy powder, Sm2Fe 17 Alloy powder, Nd2Fe 14 B alloy powder, SmCo5 alloy powder, and LaNi5 alloy powder. Furthermore, the various properties of the obtained alloy powders are evaluated below.

[0117] <XRD>

[0118] The crystal structure of the alloy powder was evaluated using powder X-ray diffraction (XRD). XRD measurements were performed using a Cu target at an accelerating voltage of 45 kV and a current of 40 mA, with a scanning rate of 2θ = 2 minutes / deg. The obtained XRD patterns were then analyzed to identify the crystal structure.

[0119] <Composition Analysis>

[0120] The amounts of rare earth metals (R), boron (B), calcium (Ca), and oxygen (O) in the alloy powder were analyzed by ICP-N (Inductively Coupled Phosphorus) spectroscopy and infrared absorption spectrometry, respectively.

[0121] <XPS>

[0122] The thickness of the oxide layer on the surface of the alloy powder was evaluated using X-ray photoelectron spectroscopy (XPS). Specifically, the thickness of the oxide layer on the surface of Fe 2p was evaluated using an X-ray photoelectron spectroscopy apparatus. 3 / 2 Depth-direction spectral analysis was performed. Argon (Ar) ion etching was performed along the depth direction, and measurements were repeatedly taken to determine the etching time required for the main peak to change from the Fe oxide peak (around 710 eV) to the metal peak (around 706 eV). The oxide layer thickness, converted to SiO2, was then calculated using the obtained etching time.

[0123] <Magnetic properties>

[0124] Stearic acid was added to the alloy powder, and dehydrated ethanol was used as a solvent. The powder was then pulverized using a vibratory ball mill until the average particle size reached 2.3 μm. Next, the magnetic properties of the pulverized powder were measured according to the Guidelines for Test Methods of Bonded Magnets (BMG-2005) of the Japan Association for Bonded Magnetic Materials, using a vibrating sample magnetometer (VSM). Based on the measurement results, the remanent magnetization σr, coercivity Hc, and squareness Hk were determined. It should be noted that squareness Hk is the intensity of the demagnetizing field equivalent to 90% of the remanent magnetization σr on the magnetization curve (demagnetization curve) in the second quadrant.

[0125] [Example 1]

[0126] In Example 1, Sm2Fe was used. 17 Preparation and evaluation of N3 alloy powder. The alloy powder was prepared according to the following steps.

[0127] <Mixed Process>

[0128] The average particle size (D) is mixed by the mixer. 50 625g of samarium oxide (Sm2O3) powder with a particle size of 3.2μm and an average particle size (D) 50The mixture is obtained by mixing 1550g of 37μm iron (Fe) powder and 250g of granular metallic calcium (Ca) with a particle size of less than 2.0mm.

[0129] <Reduction and Diffusion Process>

[0130] The resulting mixture was placed in an iron crucible and heated at 1060°C for 8 hours under an argon (Ar) atmosphere, then cooled to room temperature. The reaction product was thus obtained.

[0131] <Hydrogen Treatment>

[0132] The cooled reaction product was placed in a sealed container and then placed in hydrogen gas to absorb hydrogen. This process pulverizes the reaction product into fine particles smaller than 10 mm.

[0133] <Nitriding Treatment>

[0134] The pulverized reaction product (pulverized material) was placed in a tubular furnace and subjected to heat treatment at 430°C for 9 hours in a mixed gas of ammonia and hydrogen (ammonia partial pressure 0.75). Then, the gas was switched to nitrogen, and the product was heat-treated for another hour before cooling. This yielded the nitride.

[0135] <Wet treatment>

[0136] 1250g of the nitrided reaction product (nitride) was added to 4L of water for slurry preparation. The slurry was repeatedly decanted 7 times using 4L of water to separate the Ca(OH)2 suspension.

[0137] Then, add 4L of water to the processed material (crushed material) after Ca(OH)2 separation, and add 294g of 45% acetic acid dropwise while stirring. Then, discard the supernatant (acid washing treatment).

[0138] 4 L of water was added again to the treated material (pulverized material) after acid washing and stirring, and the supernatant was discarded (first water washing treatment). Next, 4 L of water was added to the treated material after the first water washing treatment and stirring was performed. The concentrations of samarium (Sm) and iron (Fe) ions in the supernatant of the treatment solution were analyzed. They were 100 mg / L (0.7 mmol / L) and 200 mg / L (4 mmol / L), respectively. Therefore, 32 g of 25% citric acid aqueous solution was added to the stirred treatment solution (second water washing treatment (chelation treatment)). The amount of citric acid ions in the treatment solution was 42 mmol, which is equivalent to 3.4 times the amount (equivalent) required to completely chelate Sm and Fe ions. Then, the supernatant of the treatment solution was discarded, and the operation of adding only 4 L of water to the treated material, stirring, and then discarding the supernatant was repeated twice more (third and fourth water washing treatments).

[0139] After the fourth water washing treatment, the supernatant of the treatment solution was discarded and replaced with ethanol as a solvent, followed by filtration to obtain an alloy powder cake. The obtained alloy powder cake was dried at 60°C under reduced pressure using a mixer to obtain alloy powder.

[0140] The obtained powder has Th2Zn 17 Sm2Fe with a crystalline structure 17 N3 alloy powder. Additionally, it has a composition of Sm: 23.2 wt%, N: 3.4 wt%, Ca: less than 0.01 wt%, and O: 0.11 wt%. (Example) Figure 1 As shown, XPS analysis confirmed that the oxide layer thickness was 20 nm.

[0141] [Example 2]

[0142] 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 aqueous solution. This mixed aqueous solution was prepared in advance by mixing 82.0 g of citric acid aqueous solution (0.1 mol / L; 1.9%) and 118 g of sodium citrate aqueous solution (0.1 mol / L; 2.5%). Furthermore, the amount of citrate ions in the treatment solution was 20 mmol, which is equivalent to 1.6 times the amount (equivalent) required to completely chelate samarium (Sm) and iron (Fe) ions. Otherwise, the alloy powder was prepared in the same manner as in Example 1. The resulting powder had Th₂Zn 17 Sm2Fe with a crystalline structure 17 N3 alloy powder. It also has a composition of Sm: 23.3% by mass, Ca: less than 0.01% by mass, and O: 0.09% by mass.

[0143] [Example 3]

[0144] 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 aqueous solution. This mixed aqueous solution was prepared in advance by mixing 48 g of citric acid aqueous solution (0.1 mol / L; 1.9%) and 203 g of sodium citrate aqueous solution (0.1 mol / L; 2.5%). Furthermore, the amount of citrate ions in the treatment solution was 73 mmol, which is equivalent to 2.0 times the amount (equivalent) required to completely chelate Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 1. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 N3 alloy powder. It also has a composition of Sm: 23.3% by mass, Ca: less than 0.01% by mass, and O: 0.10% by mass.

[0145] [Example 4]

[0146] 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 aqueous solution. This mixed aqueous solution was prepared beforehand by mixing 0.2 mol / L sodium hydroxide aqueous solution with 498 g of citric acid aqueous solution (0.1 mol / L; 1.9%) to achieve a pH of 5.6. Furthermore, the amount of citric acid ions in the treatment solution was 49 mmol, which is equivalent to 4.0 times the amount (equivalent) required to chelate all the total moles of Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 1. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 N3 alloy powder. It also has a composition of Sm: 23.2% by mass, Ca: less than 0.01% by mass, and O: 0.15% by mass.

[0147] [Comparative Example 1]

[0148] During the second water washing treatment (chelation treatment), no citric acid aqueous solution was added. Otherwise, the alloy powder was prepared in the same manner as in Example 1. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 N3 alloy powder. Additionally, it has a composition of Sm: 23.3% by mass, Ca: less than 0.01% by mass, and O: 0.22% by mass. (Example) Figure 2 As shown, XPS analysis confirmed that the oxide layer thickness was 40 nm. This thickness is twice that of the oxide layer in Example 1.

[0149] [Example 5]

[0150] In Example 5, Sm2Fe was processed. 17 Preparation and evaluation of alloy powders. The alloy powders were prepared according to the following steps.

[0151] <Mixed Process>

[0152] The average particle size (D) is mixed by the mixer. 50 565g of samarium oxide (Sm2O3) powder with a particle size of 3.2μm and an average particle size (D) 50 The mixture is obtained by mixing 1200g of 40μm iron (Fe) powder and 230g of granular metallic calcium (Ca) with a particle size of less than 2.0mm.

[0153] <Reduction and Diffusion Process>

[0154] The resulting mixture was placed in an iron crucible and heated under an argon (Ar) atmosphere at 1070°C for 4 hours, then cooled to room temperature. The reaction product was thus obtained.

[0155] <Hydrogen Treatment>

[0156] The reaction product, after cooling, was subjected to the same hydrogen treatment as in Example 1 to obtain a pulverized product.

[0157] <Wet treatment>

[0158] 1250g of the pulverized reaction product (pulverized material) was added to 4L of water for slurry preparation. The slurry was repeatedly decanted 7 times using 4L of water to separate the Ca(OH)2 suspension.

[0159] Then, add 4L of water to the processed material (crushed material) after Ca(OH)2 separation, and add 55g of 50% acetic acid dropwise while stirring. Then, discard the supernatant (acid washing treatment).

[0160] After acid washing, 4L of water was added again to the pulverized material and stirred. The supernatant was discarded (first water wash). Next, 4L of water was added to the material after the first water wash, and 28g of a 40% citric acid aqueous solution was added while stirring (second water wash (chelation treatment)). The citrate ion concentration in the treatment solution was 62mmol, which is equivalent to 4.8 times the amount (equivalent) required to completely chelate Sm and Fe ions. The supernatant of the treatment solution was discarded, and this process of adding only 4L of water, stirring, and then discarding the supernatant was repeated twice more (third and fourth water washes).

[0161] After the fourth water washing treatment, the supernatant of the treatment solution was discarded, and the solution was replaced with ethanol as a solvent, followed by filtration to obtain an alloy powder cake. The obtained alloy powder cake was then dried at 80°C under reduced pressure using a mixer to obtain alloy powder.

[0162] The obtained powder has Th2Zn 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.1% by mass, Ca: 0.01% by mass, and O: 0.12% by mass.

[0163] [Example 6]

[0164] 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 the 40% citric acid aqueous solution. This mixed aqueous solution was prepared in advance by mixing 84.0 g of 0.1 mol / L citric acid aqueous solution and 66.0 g of 0.1 mol / L sodium citrate aqueous solution. The amount of citrate ions in the treatment solution was 15 mmol, which is equivalent to 1.2 times the amount (equivalent) required to completely chelate Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.3% by mass, Ca: 0.02% by mass, and O: 0.11% by mass.

[0165] [Example 7]

[0166] 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 aqueous 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 aqueous solution. The amount of citrate ions in the treatment solution was 32 mmol, which is equivalent to 2.6 times the amount (equivalent) required to completely chelate Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.4% by mass, Ca: 0.05% by mass, and O: 0.15% by mass.

[0167] [Example 8]

[0168] During the chelation treatment, an aqueous solution prepared by adjusting 18g of citric acid aqueous solution to pH 6.0 with 1mol / L potassium hydroxide aqueous solution was added to the treatment solution instead of 28g of 40% citric acid aqueous solution. The amount of citric acid ions in the treatment solution was 37mmol, which is equivalent to 3.0 times the amount (equivalent) required to completely chelate Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.5% by mass, Ca: 0.03% by mass, and O: 0.18% by mass.

[0169] [Example 9]

[0170] During the chelation treatment, 47g of a 40% tripotassium citrate aqueous solution was added to the treatment solution instead of 28g of a 40% citric acid aqueous solution. The amount of citrate ions in the treatment solution was 61mmol, which is equivalent to 5.0 times the amount (equivalent) required to completely chelate Sm and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.6% by mass, Ca: 0.01% by mass, and O: 0.10% by mass.

[0171] [Comparative Example 2]

[0172] During the second water washing treatment (chelation treatment), no citric acid aqueous solution was added. Otherwise, the alloy powder was prepared in the same manner as in Example 5. The resulting powder had Th2Zn... 17 Sm2Fe with a crystalline structure 17 Alloy powder. It also has a composition of Sm: 24.5% by mass, Ca: 0.01% by mass, and O: 0.38% by mass.

[0173] [Examples 10-14 and Comparative Example 3]

[0174] In Experimental Examples 10-14 and Comparative Example 3, the Sm2Fe prepared in Examples 5-9 and Comparative Example 2 were used respectively. 17 Sm2Fe was prepared by nitriding alloy powder. 17 N3 alloy powder was used, and its magnetic properties were evaluated. The nitriding treatment was carried out according to the following steps.

[0175] <Nitriding Treatment>

[0176] The obtained Sm2Fe 17 40g of alloy powder was charged into a tubular furnace and heat-treated at 465°C for 3.5 hours in a mixed gas of ammonia and hydrogen (ammonia partial pressure 0.50 atm). Then, the gas was switched to hydrogen for 0.5 hours, followed by heat treatment with nitrogen for another 0.5 hours, and then cooling. The resulting treated product (nitride) exhibited Th₂Zn content. 17 Sm2Fe with a crystalline structure 17 N3 alloy powder.

[0177] [Example 15]

[0178] Nd2Fe was carried out in Example 15 14 Preparation and evaluation of alloy B powder. The alloy powder was prepared according to the following steps.

[0179] <Mixed Process>

[0180] In an argon (Ar) environment, the average particle size (D) is mixed using a mixer. 50 405g of neodymium oxide (Nd₂O₃) powder with a particle size of 3.7μm and an average particle size (D) 50 The mixture is obtained by mixing 608g of 40μm iron (Fe) powder, 67g of boron iron (B content 18.7% by mass) powder with a particle size of less than 200 mesh, 217g of granular metallic calcium (Ca) with a particle size of less than 2.0mm, and 20g of anhydrous calcium chloride (CaCl2).

[0181] <Reduction and Diffusion Process>

[0182] The resulting mixture was placed in an iron crucible and heated at 1000°C for 2 hours under an argon (Ar) atmosphere, then cooled to room temperature. The reaction product was thus obtained.

[0183] <Hydrogen Treatment>

[0184] The reaction product, after cooling, was subjected to the same hydrogen treatment as in Example 1 to obtain a pulverized product.

[0185] <Wet treatment>

[0186] 1000g of the pulverized reaction product (pulverized material) was added to 4L of water for slurry preparation. The slurry was repeatedly decanted 10 times using 4L of water to separate the Ca(OH)2 suspension.

[0187] Then, 4L of water was added to the processed material (crushed material) after Ca(OH)2 separation, and 50% acetic acid was added dropwise while stirring to maintain the pH of the slurry at 6.0 for 5 minutes. Then, the supernatant was discarded (acid washing treatment).

[0188] Add 4L of water to the pickled material (pulverized material) and stir for 2 minutes, then discard the supernatant (first water wash). Next, add 4L of water to the material after the first water wash, and while stirring, add 30g of 50% gluconic acid aqueous solution (second water wash (chelation treatment)). The gluconic acid ion content in the treatment solution is 76mmol, which is equivalent to 2.1 times the amount (equivalent) required to completely chelate Nd and Fe ions. Discard the supernatant of the treatment solution, and repeat the process of adding only 4L of water, stirring, and then discarding the supernatant twice more (third and fourth water washes).

[0189] After the fourth water washing treatment, the supernatant of the treatment solution was discarded, and the solution was replaced with ethanol as a solvent, followed by filtration to obtain an alloy powder cake. The obtained alloy powder cake was then dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0190] The obtained powder is tetragonal Nd2Fe 14 An alloy powder with B phase as the main phase. It also has a composition of Nd: 33.0 wt%, B: 1.30 wt%, Ca: 0.02 wt%, and O: 0.10 wt%.

[0191] [Example 16]

[0192] 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 aqueous solution. This mixed aqueous solution was prepared in advance by dissolving 3 g of sodium gluconate in 30 g of 50% gluconic acid aqueous solution. The amount of citrate ions in the treatment solution was 55 mmol, which is equivalent to 1.5 times the amount (equivalent) required to completely chelate Nd and Fe ions. Otherwise, the alloy powder was prepared in the same manner as in Example 15. The resulting powder was a tetragonal Nd₂Fe₂ alloy. 14 An alloy powder with B phase as the main phase. It also has a composition of Nd: 33.2 wt%, B: 1.32 wt%, Ca: 0.03 wt%, and O: 0.15 wt%.

[0193] [Example 17]

[0194] During the chelation treatment, 80g of a 50% potassium gluconate aqueous solution was added instead of 30g of a 50% gluconic acid aqueous solution. The amount of citrate ions in the treatment solution was 171 mmol, which is equivalent to 4.7 times the amount (equivalent) required to completely chelate Nd and Fe ions. Alloy powder was prepared in the same manner as in Example 15. The resulting powder was a tetragonal Nd₂Fe₂ alloy. 14 An alloy powder with B phase as the main phase. It also has a composition of Nd: 33.6 wt%, B: 1.35 wt%, Ca: 0.05 wt%, and O: 0.09 wt%.

[0195] [Comparative Example 4]

[0196] During the second water washing treatment (chelation treatment), no gluconic acid aqueous solution was added. Otherwise, the alloy powder was prepared in the same manner as in Example 15. The resulting powder was a tetragonal Nd₂Fe₂O₃. 14 An alloy powder with B phase as the main phase. It also has a composition of Nd: 33.1 wt%, B: 1.30 wt%, Ca: 0.02 wt%, and O: 0.33 wt%.

[0197] [Example 18]

[0198] In Example 18, the SmCo5 alloy powder was prepared and evaluated. The alloy powder was prepared according to the following steps.

[0199] <Mixed Process>

[0200] In an argon (Ar) environment, the average particle size (D) is mixed using a mixer. 50 A mixture was prepared by mixing 371g of samarium oxide (Sm2O3) powder with a particle size of 2.3μm, 669g of cobalt (Co) powder with a particle size of less than 325 mesh, 161g of granular metallic calcium (Ca) with a particle size of less than 2.0mm, and 37g of anhydrous calcium chloride (CaCl2).

[0201] <Reduction and Diffusion Process>

[0202] The resulting mixture was placed in an iron crucible and heated at 1050 °C for 2 hours under an argon (Ar) atmosphere, then cooled to room temperature. The reaction product was thus obtained.

[0203] <Hydrogen Treatment>

[0204] The reaction product, after cooling, was subjected to the same hydrogen treatment as in Example 1 to obtain a pulverized product.

[0205] <Wet treatment>

[0206] 1000g of the resulting reaction product (crushed material) was added to 4L of water for slurry preparation. The slurry was repeatedly decanted five times using 4L of water to separate the Ca(OH)2 suspension.

[0207] Then, 4L of water was added to the processed material (crushed material) after Ca(OH)2 separation, and 90% acetic acid was added dropwise while stirring to maintain the pH of the slurry at 6.0 for 20 minutes. Then, the supernatant was discarded (acid washing treatment).

[0208] Add 4L of water to the pickled material (pulverized material) and stir for 2 minutes, then discard the supernatant (first water wash). Next, add 4L of water to the material after the first water wash, and while stirring, add 14g of a 25% citric acid aqueous solution (second water wash (chelation treatment)). The amount of citric acid ions in the treatment solution is 18mmol, which is equivalent to 1.5 times the amount (equivalent) required to completely chelate Sm and Co ions. Discard the supernatant of the treatment solution, and repeat the process twice more, adding only 4L of water to the material, stirring, and then discarding the supernatant (third and fourth water washes).

[0209] After the fourth water washing treatment, the supernatant of the treatment solution was discarded, and the solvent was replaced with 2-propanol. After filtration, alloy powder cakes were obtained. The alloy powder cakes were dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0210] The obtained powder is an SmCo5 alloy powder with a CaCu5-type crystal structure. It also has a composition of Sm: 33.0% by mass, Ca: 0.08% by mass, and O: 0.05% by mass.

[0211] [Comparative Example 5]

[0212] During the second water washing treatment (chelation treatment), no citric acid aqueous solution was added. Otherwise, the alloy powder was prepared in the same manner as in Example 18. The resulting powder was an SmCo5 alloy powder with a CaCu5-type crystal structure. It also had a composition of Sm: 33.3% by mass, Ca: 0.09% by mass, and O: 0.18% by mass.

[0213] [Example 19]

[0214] In Example 19, the LaNi5 alloy powder was prepared and evaluated. The alloy powder was prepared according to the following steps.

[0215] <Mixed Process>

[0216] In an argon (Ar) environment, the average particle size (D) is mixed using a mixer. 50 112g of lanthanum oxide (La2O3) powder with a particle size of 5.7μm and an average particle size (D) 50 The mixture was prepared by mixing 204g of 10.3μm carbonyl nickel (Ni) powder, 49.7g of granular metallic calcium (Ca) with a particle size of less than 2.0mm, and 11.2g of anhydrous calcium chloride (CaCl2).

[0217] <Reduction and Diffusion Process>

[0218] The resulting mixture was placed in an iron crucible and heated at 970°C for 5 hours under an argon (Ar) atmosphere, then cooled to room temperature. The reaction product was thus obtained.

[0219] <Hydrogen Treatment>

[0220] The reaction product, after cooling, was subjected to the same hydrogen treatment as in Example 1 to obtain a pulverized product.

[0221] <Wet treatment>

[0222] 300g of the obtained reaction product (crushed material) was added to 1L of water for slurry preparation. The slurry was repeatedly decanted 7 times using 1L of water to separate the Ca(OH)2 suspension.

[0223] Then, add 1L of water to the processed material (crushed material) after Ca(OH)2 separation, and while stirring, add 20% dilute hydrochloric acid dropwise to maintain the pH of the slurry at 5.0 for 20 minutes. Then, discard the supernatant (acid washing treatment).

[0224] Add 1L of water to the pickled material (pulverized material) and stir for 2 minutes, then discard the supernatant (first water wash). Next, add 1L of water to the material after the first water wash, and while stirring, add 17g of a 25% citric acid aqueous solution (second water wash (chelation treatment)). The amount of citric acid ions in the treatment solution is 22mmol, which is equivalent to 1.8 times the amount (equivalent) required to completely chelate La and Ni ions. Discard the supernatant of the treatment solution, and repeat the process twice more, adding only 1L of water to the material, stirring, and then discarding the supernatant (third and fourth water washes).

[0225] After the fourth water washing treatment, the supernatant of the treatment solution was discarded, and the solvent was replaced with 2-propanol. After filtration, alloy powder cakes were obtained. The alloy powder cakes were dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0226] The obtained powder is a LaNi5 alloy powder with a CaCu5-type crystal structure. It also has a composition of La: 33.0% by mass, Ca: 0.08% by mass, and O: 0.05% by mass.

[0227] [Comparative Example 6]

[0228] During the second water washing treatment (chelation treatment), no citric acid aqueous solution was added. Otherwise, the alloy powder was prepared in the same manner as in Example 19. The resulting powder was a LaNi5 alloy powder with a CaCu5-type crystal structure. It also had a composition of La: 33.3% by mass, Ca: 0.09% by mass, and O: 0.18% by mass.

[0229] (2) Evaluation Results

[0230] The composition and component analysis results of the rare earth transition metal alloy powders obtained in Examples 1-9, Examples 15-19, Comparative Example 1, Comparative Example 2, and Comparative Examples 4-6 are summarized in Tables 1-5.

[0231] In Sm2Fe 17 In the case of N3 alloy powder, the oxygen content of the chelated samples (Examples 1-4) was 0.09-0.15% by mass, compared to 0.22% by mass of the unchelated sample (Comparative Example 1) (Table 1). In Sm2Fe 17 In the case of alloy powder, the oxygen content of the chelated samples (Examples 5-9) was 0.10-0.18% by mass, compared to 0.38% by mass of the unchelated sample (Comparative Example 2) (Table 2). In the case of Nd2Fe... 14In the case of alloy powders with B phase as the main phase, the oxygen content of the chelated samples (Examples 15-17) was 0.09-0.15% by mass, compared to 0.33% by mass of the unchelated sample (Comparative Example 4) (Table 3). In the case of SmCo5 alloy powder, the oxygen content of the chelated sample (Example 18) was 0.05% by mass, compared to 0.18% by mass of the unchelated sample (Comparative Example 5) (Table 4). In the case of LaNi5 alloy powder, the oxygen content of the chelated sample (Example 19) was 0.05% by mass, compared to 0.18% by mass of the unchelated sample (Comparative Example 6) (Table 5). As described above, it can be seen that regardless of the composition, chelation treatment can halve the oxygen content in the alloy powder.

[0232] In addition, for Sm2Fe 17 XPS depth-direction analysis was performed on N3 alloy powder. The results are shown below. Figure 1 , 2 And Table 1. The oxide layer thickness on the particle surface of the chelated sample (Example 1) was 20 nm, compared to 40 nm for the unchelated sample (Comparative Example 1). The chelation treatment reduced the oxide layer thickness to about half, which is believed to contribute to the reduction of oxygen content.

[0233] The Sm2Fe obtained in Examples 10-14 and Comparative Example 3 17 The magnetic properties of the N3 alloy powder are shown in Table 6. These alloy powders are Sm2Fe obtained in Examples 5-9 and Comparative Example 2. 17 It is obtained by nitriding and micronizing alloy powder (master alloy).

[0234] Compared to the sample prepared from the high-oxygen master alloy (Comparative Example 2) (Comparative Example 3), the samples prepared from the low-oxygen master alloy (Examples 5-9) (Examples 10-14) have a higher coercivity H. c and squareness H k higher.

[0235] In addition, the Sm2Fe obtained in Examples 10-14 and Comparative Example 3 17 The N3 alloy powder was embedded in resin and ground, and the SEM reflected electron images of the particle cross-section were observed. As a result, compared with Examples 10-14, more particles with unnitrided portions (unnitrided phases) inside the particles were observed in the powder of Comparative Example 3.

[0236] Based on the above results, it can be understood that the manufacturing method of this embodiment, which involves chelation treatment, yields rare earth transition metal alloy powder with low oxygen content and high quality.

[0237] Table 1. Composition and component analysis results of alloy powder

[0238]

[0239] Table 2. Composition and component analysis results of alloy powders

[0240]

[0241] Table 3. Composition and component analysis results of alloy powders

[0242]

[0243] Table 4. Composition and component analysis results of alloy powder

[0244]

[0245] Table 5. Composition and component analysis results of alloy powders

[0246]

[0247] Table 6 Sm2Fe 17 Magnetic properties of N3 alloy powder

[0248]

Claims

1. A method for manufacturing rare earth transition metal alloy powder, wherein, The process includes the following steps: The reduction process involves heating a mixture comprising at least an alloying raw material and a reducing agent under a non-oxidizing environment to obtain a reaction product containing a rare-earth transition metal alloy and byproducts from the reducing agent. The alloying raw material comprises rare-earth metals, transition metals, and oxygen. A wet processing step involves washing the reaction products to obtain rare earth transition metal alloy powder. During the washing process, the reaction products are added to the washing solution to obtain an alloy powder slurry. The obtained alloy powder slurry is then subjected to acid washing, followed by chelation treatment with the addition of a chelating agent. The chelating agent is at least one selected from the group consisting of alkali metal salts of citric acid, gluconic acid, citric acid and / or gluconic acid, and alkaline earth metal salts of citric acid and / or gluconic acid.

2. The method as described in claim 1, wherein, The reduction process includes at least mixing rare earth oxide powder, transition metal powder and reducing agent to obtain a mixture, and then heating the mixture in a non-oxidizing environment to reduce the rare earth oxide powder and allow it to diffuse and alloy in the transition metal powder, thereby obtaining a reaction product containing rare earth transition metal alloy components and byproducts from the reducing agent.

3. The method as described in claim 1 or 2, wherein, The chelating agent content in the alloy powder slurry is the amount required to chelate all the rare earth ions and transition metal ions contained in the alloy powder slurry, i.e., 1.0 to 5.0 times the equivalent amount.

4. The method as described in claim 1 or 2, wherein, It also includes a hydrogen treatment process, which involves exposing the reaction products to a hydrogen environment prior to the washing process, thereby absorbing hydrogen and pulverizing them.

5. The method as described in claim 1 or 2, wherein, The alloy powder slurry that has undergone the chelation treatment is subjected to water washing.

6. The method as described in claim 1 or 2, wherein, The oxygen content of the rare earth transition metal alloy powder is less than 0.16% by mass.

7. The method as described in claim 1 or 2, wherein, The rare earth transition metal alloy powder is Sm2Fe. 17 It is an alloy powder or Sm2Fe 17 N3 series alloy powder.

8. The method as claimed in claim 1 or 2, wherein, The process includes, in sequence, the reduction process, the hydrogen treatment process, the nitriding process, and the wet treatment process. In the hydrogen treatment process, the reaction products obtained in the reduction process are exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized. In the nitriding process, the reaction product pulverized in the hydrogen treatment process is heated while a nitrogen-containing mixed gas flow is passed through the reaction product, thereby nitriding the rare earth transition metal alloy components in the reaction product. In the wet treatment process, the reaction product after nitriding in the nitriding process is subjected to washing treatment.

9. The method as claimed in claim 1 or 2, wherein, The process includes, in sequence, the reduction process, the hydrogen treatment process, the wet treatment process, and the nitriding process. In the hydrogen treatment process, the reaction products obtained in the reduction process are exposed to a hydrogen environment, thereby absorbing hydrogen and being pulverized. In the wet processing step, the reaction products pulverized in the hydrogen treatment step are subjected to washing treatment. In the nitriding process, the reaction product that has undergone washing in the wet treatment process is heated while a nitrogen-containing mixed gas flow is passed through the reaction product, thereby nitriding the rare earth transition metal alloy components in the reaction product.

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