Method for producing rare earth transition metal alloy powder

Abstract

A method for producing rare earth transition metal alloy powder is provided that allows for efficient acid cleaning while minimizing the environmental impact problems that arise in industrial production. [Solution] A method for producing rare earth transition metal alloy powder, comprising the following steps: a reduction-diffusion step of heating a raw material mixture containing at least a rare earth metal, a transition metal, and oxygen, and a reducing agent, in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent; and a wet treatment step of washing the reaction product to obtain rare earth transition metal alloy powder, wherein the wet treatment step comprises a sub-step of adding and disintegrating the reaction product in water to produce an alloy powder slurry; a sub-step of washing the alloy powder slurry with water; and a sub-step of adding a buffer and hydrochloric acid to the alloy powder slurry that has undergone the water washing treatment to acid wash the alloy powder slurry, wherein the buffer is a carboxylic acid, and the buffer ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups contained in the carboxylic acid to the sum of the amount of carboxyl groups contained in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is 5 mol% or more and 90 mol% or less.

Description

Technical Field

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

Background Art

[0002] Rare earth transition metal alloy powder is an alloy powder mainly containing rare earth metals and transition metals. Rare earth transition metal alloy powder, particularly intermetallic compound powder, is widely used in various applications such as permanent magnet materials, hydrogen storage materials, magneto-optical recording materials, and magnetic refrigeration materials. For example, Sm2Fe 17 N3 alloy powder obtained by nitriding the alloy powder of the system, or Nd2Fe 17 B-based alloy powder, SmCo5-based alloy powder, Sm2Co 14 -based alloy powder, and PrCo5-based alloy powder have large magnetization and uniaxial magnetic anisotropy and are useful as materials for permanent magnets. In addition, LaNi5-based alloy powder has the characteristic of absorbing and retaining a large amount of hydrogen and is used as a hydrogen storage material. (Tb, Gd)-(Fe, Ni, Co)-based alloy powder can form a recording layer of a magneto-optical recording medium by forming a thin film using this. Furthermore, La(Fe, Si) 17 -based alloy powder and La(Fe, Si) 13 -based alloy powder hydrogenated with this 13 H x -based alloy powder exhibits an excellent magnetocaloric effect and is regarded as promising as a magnetic refrigeration material. Rare earth transition metal alloy powder is mostly used mainly in the form of a sintered body produced by sintering this by powder metallurgy or a composite produced by kneading with a resin binder.

[0003] As methods for producing rare earth transition metal alloy powder, methods such as a melting casting method and a reduction diffusion method have been conventionally known. Among these, the melting casting method is a method in which rare earth metals and transition metals are used as raw materials, these raw materials are formulated, then melted in an inert gas atmosphere, and the obtained alloy ingot is heat-treated for homogenization and then pulverized.

[0004] On the one hand, the reduction-diffusion method is a technique that uses, for example, rare-earth oxides and transition metals as raw materials. These raw materials are mixed with a reducing agent such as metallic calcium and then heat-treated in a non-oxidizing gas atmosphere to obtain a rare-earth transition metal alloy. During the heat treatment, the rare-earth oxide is reduced to a rare-earth metal, and this rare-earth metal diffuses into the transition metal to form an alloy (intermetallic compound). In the massive reaction product obtained by the heat treatment, by-products derived from the reducing agent remain together with the target alloy. Therefore, the reaction product is put into water to remove the by-products derived from the reducing agent and to disintegrate and pulverize the reaction product. Further, the alloy powder obtained by pulverization is subjected to pickling and water washing to remove surplus by-products and unreacted substances, and then dried to obtain the target alloy powder.

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

[0006] Patent Document 1 discloses a method for producing a rare-earth transition metal alloy powder by the reduction-diffusion method. Specifically, a mixture of a rare-earth oxide powder, a powder of another metal, and at least one selected from alkali metals, alkaline earth metals, and hydrides thereof is heated in an inert gas atmosphere or under vacuum, and then the reaction product mixture is wet-treated to remove by-produced CaO and residual Ca, and a method for producing an alloy powder containing a rare-earth metal is disclosed (Claim 1 of Patent Document 1). Further, Patent Document 1 describes that washing with dilute acid is effective for removing微量残留したCa(OH)2 and oxide films, and it is carried out using acetic acid or hydrochloric acid (upper right column, page 5 of Patent Document 1).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] Although the production of rare-earth transition alloy powders by reduction-diffusion is known, there was room for improvement in the conventional method. Specifically, in conventional manufacturing methods, the reaction products are acid-washed to remove residues such as Ca(OH)2. Acetic acids and other carboxylic acids are frequently used as the acid. However, using carboxylic acids has the problem of increasing wastewater treatment costs.

[0009] To explain this point, in response to the growing environmental awareness in recent years, there is a demand to reduce the biochemical oxygen demand (BOD) of wastewater discharged from industrial production. BOD is an indicator of organic matter pollution in wastewater, and wastewater with high BOD levels poses a significant environmental burden. Discharging wastewater with high BOD levels outside of factories leads to water pollution in rivers, lakes, and seas, so the Water Pollution Control Law requires that the BOD of wastewater be kept below a specified value. In this regard, since carboxylic acids are organic acids, using them alone results in a high BOD in the wastewater obtained after treatment, increasing treatment costs.

[0010] A method using hydrochloric acid for acid washing during alloy powder production has also been proposed. Since hydrochloric acid is an inorganic acid, it is expected that using it will reduce wastewater treatment costs. However, the inventors have found that when hydrochloric acid is used for treatment, the acid washing proceeds unevenly, resulting in a decrease in the yield and properties of the alloy powder. Hydrochloric acid is a strong acid with a high degree of ionization. Therefore, even if the slurry in the washing tank is thoroughly stirred, the reaction between the slurry products (alloy components, by-products) and hydrochloric acid proceeds locally and rapidly at the point where the hydrochloric acid is added, resulting in an uneven reaction. In other words, although the reaction proceeds at the point where the hydrochloric acid is added, the hydrochloric acid is consumed at that point, and the reaction and acid washing at other points become insufficient. As a result, the acid washing process becomes uneven throughout the slurry.

[0011] While increasing the amount of hydrochloric acid added could be considered to advance the acid cleaning process, this would lead to excessive reaction at the hydrochloric acid injection site, resulting in over-dissolution of the alloy powder. Therefore, it has been difficult to obtain alloy powder with excellent properties in high yield using acid cleaning with hydrochloric acid alone.

[0012] In light of these problems, the inventors conducted thorough research. As a result, they found that when producing rare earth transition metal alloy powder by reduction-diffusion method, by using a predetermined buffer solution and hydrochloric acid in combination when acid-washing the reaction product, and by limiting the buffer solution ratio to a predetermined range, it is possible to efficiently acid-wash the product while suppressing the environmental burden that occurs in industrial production. Consequently, it is possible to obtain alloy powder with excellent properties in high yield.

[0013] This invention was completed based on such knowledge, and aims to provide a method for producing rare earth transition metal alloy powder that can efficiently perform acid washing while suppressing the environmental burden problems that arise in industrial production. [Means for solving the problem]

[0014] The present invention encompasses the following embodiments (1) to (7). In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0015] (1) A method for producing rare earth transition metal alloy powder, comprising the following steps; A reduction-diffusion step involves heating a mixture of alloying raw materials containing rare earth metals, transition metals, and oxygen, as well as a reducing agent, under a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent. The process includes a wet treatment step of washing the reaction product to obtain rare earth transition metal alloy powder, The wet processing step includes a sub-step of preparing an alloy powder slurry by adding and disintegrating the reaction product in water, a sub-step of subjecting the alloy powder slurry to a water washing treatment, and a sub-step of subjecting the alloy powder slurry to an acid washing treatment by adding a buffer and hydrochloric acid to the water-washed alloy powder slurry. The buffer solution is a carboxylic acid, A method in which the buffer solution ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups contained in the carboxylic acid (N1) to the sum of the amount of carboxyl groups contained in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is 5 mol% or more and 90 mol% or less.

[0016] (2) The method of (1) above, wherein the buffer solution ratio [N1 / (N1+N2)] is 5 mol% or more and 50 mol% or less.

[0017] (3) The method of (1) or (2) above, wherein the carboxylic acid is at least one selected from the group consisting of formic acid, acetic acid, citric acid, gluconic acid, oxalic acid, and glycolic acid.

[0018] (4) Any of the methods (1) to (3) above, wherein during the acid washing, a buffer solution is first added to the alloy powder slurry, and then hydrochloric acid is added.

[0019] (5) The reduction-diffusion step, the nitriding step, and the wet treatment step are included in this order, In the nitriding step, while heating the reaction product obtained in the reduction-diffusion step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The wet treatment step involves any of the methods (1) to (4) described above, in which the reaction product nitrided in the nitriding step is subjected to a washing treatment.

[0020] (6) The reduction-diffusion step, the hydrogen treatment step, the nitriding step, and the wet treatment step are included in this order, In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the nitriding step, while heating the reaction product that was crushed in the hydrogen treatment step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The wet treatment step involves any of the methods (1) to (4) described above, in which the reaction product nitrided in the nitriding step is subjected to a washing treatment.

[0021] (7) The reduction-diffusion step, the hydrogen treatment step, the wet treatment step, and the nitriding step are included in this order, In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the wet treatment step, the reaction product crushed in the hydrogen treatment step is subjected to a washing treatment to obtain a rare earth transition metal alloy powder. In the nitriding step, a nitrogen-containing stream is passed over the rare earth transition metal alloy powder obtained by the cleaning step in the wet treatment step while heating the powder, thereby obtaining nitrided rare earth transition metal alloy powder, according to any of the methods (1) to (4) above. [Effects of the Invention]

[0022] The present invention provides a method for producing rare earth transition metal alloy powder that can efficiently perform acid cleaning while suppressing the environmental burden problems that arise in industrial production. [Modes for carrying out the invention]

[0023] Specific embodiments of the present invention (hereinafter referred to as "these embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without altering the gist of the invention. Furthermore, in this specification, any combination of preferred embodiments can be adopted as long as technical consistency can be maintained. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

[0024] <<1. Method for producing rare earth transition metal alloy powder>> This embodiment relates to a method for producing rare earth transition metal alloy powder (hereinafter sometimes simply referred to as "alloy powder"). This production method includes the following steps: a reduction-diffusion step in which a raw material mixture containing an alloy raw material containing a rare earth metal, a transition metal, and oxygen, and at least a reducing agent, is subjected to heat treatment in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent; and a wet treatment step in which the reaction product is subjected to a washing treatment to obtain rare earth transition metal alloy powder. The wet treatment step also includes a sub-step in which the reaction product is added to water and disintegrated to produce an alloy powder slurry; a sub-step in which the alloy powder slurry is subjected to a water washing treatment; and a sub-step in which a buffer solution and hydrochloric acid are added to the alloy powder slurry that has been subjected to the water washing treatment to perform an acid washing of the alloy powder slurry. Furthermore, the buffer solution is a carboxylic acid, and the buffer solution ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups in the carboxylic acid (N1) to the sum of the amount of carboxyl groups in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is between 5 mol% and 90 mol%. Details of each step are described below.

[0025] <Reduction-diffusion process> In the reduction-diffusion process, a raw material mixture is prepared that contains alloying raw materials including rare earth metals (R), transition metals (TM), and oxygen (O), as well as a reducing agent. The alloying raw materials only need to contain at least rare earth metals, transition metals, and oxygen as constituent elements. During the reduction-diffusion treatment, the oxygen in the alloying raw materials is removed by the action of the reducing agent, and consequently, the rare earth metal diffuses into the transition metal to form an alloy. As a result, a reduction-diffusion treated product (reaction product) is obtained that contains a rare earth-transition metal alloy and by-products derived from the reducing agent.

[0026] [In the case of alloy raw materials - powder mixtures] The alloy raw material may be a powder mixture, that is, a mixture of rare earth oxide powder and transition metal powder. The rare earth oxide powder is the raw material of the rare earth metal that constitutes the target alloy powder. The type of rare earth metal may be selected according to the composition of the target alloy powder. Although not limited, examples of rare earth metals include one or more selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), and ytterbium (Yb). As the rare earth oxide powder, one type of powder may be used alone, or two or more types of powders may be mixed and used.

[0027] The rare earth metal preferably contains samarium (Sm). By selecting Sm, it becomes possible to produce samarium iron nitride (Sm2Fe 17 N3)-based magnetic powder, which is an alloy powder. The Sm2Fe 17 N3-based magnetic powder has excellent magnetic properties and is useful as a bonded magnet material. In this case, Sm may be used in combination with other rare earth metals other than Sm, such as La and / or Ce. For example, 70 atomic% or more of the rare earth metal may be Sm, and 30 atomic% or less may be composed of other elements (La, Ce, etc.).

[0028] The particle size of the rare earth oxide powder may be determined according to the composition and use of the obtained alloy powder. However, it is desirable to determine the particle size of the rare earth oxide powder so that it is uniformly distributed in the vicinity of the transition metal particles in the obtained mixture. The average particle size D 50 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. Particularly preferred is a powder in which particles with a particle size of 0.1 to 10 μm account for 80 mass% or more of the whole. This improves the raw material mixing property and the handling property of the raw material powder and the reaction product. In addition, it becomes possible to sufficiently advance the diffusion of the rare earth metal in the subsequent reduction diffusion process. In this specification, the average particle size D 50This represents the cumulative 50% diameter in the volume-based particle size distribution. The volume-based particle size distribution can be determined using an airflow-dispersive laser diffraction particle size distribution analyzer.

[0029] Rare earth oxide powders may contain moisture and organic matter as impurities. These impurities can increase the oxygen content of the final alloy powder. Therefore, it is preferable to have a low amount of impurities in the rare earth oxide powder. For example, the weight loss after heating to 1000°C is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0030] Transition metal powder is a raw material for the transition metal that constitutes the target alloy powder. The type of transition metal should be selected according to the composition of the target alloy powder. While not limited to these, examples include 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). A single type of transition metal powder may be used alone, or two or more types of powder may be mixed and used.

[0031] The transition metal preferably contains iron (Fe). By selecting Fe, the alloy powder samarium iron nitrogen (Sm2Fe) is formed. 17 This enables the production of N3-based magnetic powders. In this case, Fe may be used in combination with one or more other transition metals selected from the group consisting of Cr, Mn, Co, and Ni. For example, 90 atomic percent or more of the transition metal may be Fe, and 10 atomic percent or less may be other elements (Cr, Mn, Co, Ni, etc.). When the transition metal powder is iron (Fe), cobalt (Co), nickel, or (Ni) powder, for example, reducing powder, gas atomized powder, water atomized powder, electrolytic powder, carbonyl powder, etc., can be used.

[0032] As the transition metal powder, only metal powder may be used, or a portion of it may be replaced with metal oxide powder. Furthermore, not only transition metals but also other metals, such as rare earth metals, may be used. For example, as the transition metal powder, metal powder (Fe, etc.), metal oxide powder (Fe2O3, Fe3O4, FeO, etc.), and rare earth transition metal alloy powder (R2Fe) may be used. 17 Examples of suitable materials include rare earth transition metal composite oxide powders (such as RFeO3). However, using oxide powders may result in a thermite reaction during reduction-diffusion treatment. To suppress the rapid exothermic reaction caused by this reaction, it is preferable to limit the proportion of oxide powder in the total transition metal powder to 50% by mass or less.

[0033] When the transition metal powder is a metal powder, the average particle size D of the transition metal powder is considered when taking into account the diffusion length of the rare earth metal at the reduction-diffusion treatment temperature. 50 The particle size is preferably 100 μm or less, and more preferably 50 μm or less. On the other hand, if the transition metal powder is an oxide powder, the D of the transition metal powder 50 The particle size is preferably 10 μm or less, and more preferably 5 μm or less.

[0034] [For alloy raw materials other than powder mixtures] The alloying raw material may be an oxide and / or partially reduced oxide (partial oxide) containing a rare earth metal and a transition metal, an alloy containing a rare earth metal, a transition metal and oxygen (e.g., an oxygen-containing SmFe alloy), or a mixture of an alloy containing a rare earth metal and a transition metal and a rare earth oxide (e.g., a mixture of SmFe alloy and Sm oxide). By using a partially reduced oxide as the alloying raw material, it is possible to reduce the amount of reducing agent added in subsequent processes. An example of the procedure for producing a partially reduced oxide containing a rare earth metal and a transition metal is described below.

[0035] First, a composite oxide containing a rare earth metal (Re) and a transition metal (TM) is prepared. The method of obtaining the composite oxide is not limited. For example, the composite oxide can be synthesized by a wet process. To synthesize a composite oxide by a wet process, a hydroxide can be produced by a neutralization reaction from an acid solution containing the rare earth metal and the transition metal, and the resulting hydroxide can be heat-treated. Then, the prepared composite oxide can be heated under a reducing atmosphere to obtain a partially reduced oxide containing the rare earth metal and the transition metal.

[0036] [Reducing agent] A reducing agent is added during the subsequent reduction-diffusion treatment to reduce oxide components such as rare earth oxide powder and promote alloy formation. At least one reducing agent 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 safety during handling and cost, Li and / or Ca are more preferred, and Ca is particularly preferred.

[0037] The reducing agent is preferably in granular form. Increasing the coarseness of the reducing agent promotes the penetration and diffusion of the reducing agent, which is heated and melted during the reduction-diffusion treatment, within the raw material mixture. The particle size of the reducing agent is preferably 100 mesh or larger (coarser than 100 mesh sieve), and more preferably 32 mesh or larger. On the other hand, if the reducing agent is finer, it is possible to further improve its dispersibility within the raw material mixture. The particle size of the reducing agent is preferably 4 mesh or smaller (finer than 4 mesh sieve), and more preferably 9 mesh or smaller.

[0038] [Other ingredients] If necessary, other components besides alloy raw materials and reducing agents may be added. For example, rare earth metal powder and / or transition metal oxide powder may be added. Alternatively, alloy powders of rare earth metals and transition metals, or their oxide powders, may be added. Furthermore, when producing alloy powders containing components other than rare earth metals and transition metals, raw materials of other components may be added. Examples of such components include zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and / or bismuth (Bi). For example, Nd2Fe, a permanent magnet material. 14 To produce B alloy powder, a boron source such as boron (B) or boron oxide (B2O3) may be added. La(Fe,Si) is a magnetic refrigeration material. 13 H x To produce alloy powder, a silicon source such as silicon (Si) or silicon oxide (SiO2) may be added.

[0039] Furthermore, auxiliary additives may be added to facilitate the production of alloy powders. Examples of auxiliary additives include disintegration accelerators that promote the disintegration of the reaction product in a subsequent wet processing step. Alkaline earth metal salts or alkaline earth metal oxides such as calcium chloride (CaCl2) and calcium oxide (CaO) can be used as disintegration accelerators. It is desirable to uniformly mix the disintegration accelerator at the same time as the other raw material powders. This allows components derived from the disintegration accelerator (such as calcium compounds) to be uniformly present at the grain boundaries of the alloy crystal particles in the reaction product. Therefore, when the mixture is slurryed in the subsequent wet processing step, the components derived from the disintegration accelerator dissolve into the aqueous solution, effectively promoting disintegration. The amount of disintegration accelerator added is preferably 3 to 30% by mass, and more preferably 7 to 20% by mass, relative to the total amount of oxides in the mixture. By keeping the amount of disintegration accelerator within this range, it is possible to sufficiently promote the disintegration of the reaction product while minimizing the amount of unreacted materials and by-products in the reaction product.

[0040] [mixture] Raw material mixing may be carried out by known methods, either wet or dry. For dry mixing, dry mixers such as ribbon blenders, tumblers, S-shaped blenders, V-shaped blenders, Nauter mixers, Henschel mixers, Mirallo, Novilta, Mechanofusion, high-speed mixers, and / or vibrating mills may be used. For wet mixing, water or organic solvents may be used as the mixing medium, and the raw materials may be mixed in a wet mixer such as a ball mill and / or bead mill, and then dried. However, in the case of wet mixing, it is preferable to wet mix the raw materials other than the reducing agent (metallic calcium, etc.) and then add the reducing agent.

[0041] The amount of reducing agent contained in the raw material mixture is preferably 1.05 equivalents or more and 3.0 equivalents or less, and more preferably 1.1 equivalents or more and 2.0 equivalents or less. Here, equivalents are an indicator of the amount necessary to reduce the oxides contained in the raw material mixture. The minimum amount necessary to reduce all oxides is 1 equivalent. By setting the amount of reducing agent to 1.05 equivalents or more, the reduction of oxides can be sufficiently advanced. On the other hand, if the amount of reducing agent is excessive, there is a risk that excess components of the reducing agent will remain. If excess components of the reducing agent remain, this can cause problems. For example, if a nitriding process is included, nitriding may be inhibited.

[0042] Next, the raw material mixture is subjected to a reduction-diffusion treatment. In the reduction-diffusion process, the prepared raw material mixture is heated under a reduced pressure gas or inert gas atmosphere to produce a reduction-diffusion treated product. During the reduction-diffusion treatment, rare earth oxides are reduced by the action of a reducing agent (such as metallic Ca), and rare earth metals are produced. The produced rare earth metals diffuse into the transition metal to form a rare earth transition metal alloy. Therefore, the reduction-diffusion treated product contains a rare earth transition metal alloy as the main phase, by-products derived from the reducing agent (such as CaO), and, in some cases, other different phases.

[0043] During heating, the raw material mixture is filled into an iron reaction vessel, heated to the heating temperature, held for a predetermined time, and then cooled. The heating temperature is preferably between 800°C and 1200°C. A heating temperature of 800°C or higher allows the reduction reaction of oxides by the reducing agent to proceed sufficiently. A heating temperature of 1200°C or lower prevents excessive sintering of alloy particles in the reaction product (reduction-diffusion treated product) generated by the reduction-diffusion reaction. The temperature and holding time should be determined so that the rare earth metal diffuses to the center of the iron particles in the raw material mixture, and no transition metal-rich phase remains. Furthermore, to reduce residual gases such as oxygen and moisture in the reaction vessel, the vessel may be evacuated and replaced with an inert gas before or during heating. It is also preferable to maintain an inert gas atmosphere during the cooling process to prevent oxidation of the reaction product and maintain its activity.

[0044] <Hydrogen Decomposition Process> If necessary, a hydrogen decomposition step may be added after the reduction-diffusion step. In the hydrogen decomposition step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere to decompose, thereby producing decomposed material (decomposed reaction product). The reaction product obtained by the reduction-diffusion treatment may contain rare-earth-rich phases containing an excess of rare earth elements. For example, if the rare-earth metal is Sm and the transition metal is Fe, it may contain Sm-rich phases such as SmFe5 phase, SmFe3 phase and / or SmFe2 phase. When the reaction product is exposed to a hydrogen atmosphere, these rare-earth-rich phases absorb hydrogen and expand in volume. As a result, cracks form in the reaction product, which can then be decomposed. The size of the decomposed material is not limited, but for example, it is 10 mm or less. If the decomposed material is large, it may be decomposed mechanically.

[0045] <Nitriding Process> If necessary, a nitriding step may be added after the reduction-diffusion step. In the nitriding step, the reaction product obtained in the reduction-diffusion step or the hydrogen decomposition step is heat-treated in a nitrogen-containing gas stream to produce nitrides (nitrided reaction products). Through the nitriding treatment, the rare-earth transition metal alloy components contained in the reaction product are nitrided to produce rare-earth transition metal nitrogen-based compounds (nitrided alloy components).

[0046] During the nitriding treatment, it is preferable to first perform a pretreatment process at least once, in which the surrounding atmosphere of the crushed material is reduced to a pressure of 50 kPa or less, and then repressurized using a hydrogen-free pretreatment gas. Next, after the pretreatment is complete, a nitriding gas (nitrogen-containing gas) that may contain hydrogen is supplied to the surrounding atmosphere, and the reaction product is heated under the supplied nitriding gas atmosphere to transform it into a nitride. It is preferable to use a nitrogen-containing gas such as nitrogen and / or ammonia as the nitriding gas. In addition, in order to control the nitriding reaction rate, other gases such as hydrogen, argon, and helium may be included in the nitrogen-containing gas (nitriding gas). For example, a mixed gas containing ammonia and hydrogen can sufficiently nitride even the interior of large alloy particles with a particle size exceeding 10 μm. The heating temperature of the reaction product (nitriding temperature) is preferably 350°C to 500°C, and more preferably 400°C to 480°C. In addition, it is preferable to heat treat the nitride after the nitriding treatment with hydrogen gas, an inert gas, or a reduced pressure gas.

[0047] The nitriding process may be performed after the wet treatment process described later. In that case, the rare earth transition metal alloy powder obtained by the cleaning process in the wet treatment process can be heated while a nitrogen-containing airflow is passed through the rare earth transition metal alloy powder to produce nitrided rare earth transition metal alloy powder.

[0048] <Wet processing process> In the wet processing step, the reaction products are washed to obtain rare earth transition metal alloy powder. If the hydrogen decomposition step and nitriding step are not included, the reaction products obtained in the reduction-diffusion step are washed directly. On the other hand, if the hydrogen decomposition step and nitriding step are included, the decomposed product (decomposed reaction products) obtained in the hydrogen decomposition step and the nitrided product (nitrided reaction products) obtained in the nitriding step are washed. The wet processing step also includes a sub-step (slurry preparation step) in which the reaction products are added to water and disintegrated to produce an alloy powder slurry, a sub-step (water washing step) in which the alloy powder slurry is washed with water, and a sub-step (acid pickling step) in which a buffer solution and hydrochloric acid are added to the water-washed alloy powder slurry to perform an acid washing treatment on the alloy powder slurry. In other words, the washing treatment in the wet processing step is a process of preparing an alloy powder slurry and then washing the obtained slurry with water and acid.

[0049] [Slurry preparation] First, the reaction products are added to water and allowed to disintegrate to produce an alloy powder slurry. The reaction products contain not only the desired alloy components but also by-products derived from the reducing agent (such as CaO) and other phases (rare earth-rich phases). When the reaction products are added to water, the by-products derived from the reducing agent (such as CaO) contained in the reaction products are converted into hydroxides (such as Ca(OH)2). Consequently, the bonds between the alloy particles loosen, the reaction products disintegrate, and a suspension (slurry) is obtained in which components that do not dissolve in the washing solution (alloy components, Ca(OH)2, etc.) are dispersed.

[0050] [Water washing] Next, the prepared alloy powder slurry is subjected to a water washing treatment. This treatment removes some or all of the by-products (such as Ca(OH)2) derived from the reducing agent. The method of water washing is not limited. For example, a series of operations including stirring, standing, and decantation can be performed on the slurry containing the alloy components. Water may be added to the slurry as needed. The by-products (such as Ca(OH)2) derived from the reducing agent contained in the slurry have a significantly different specific gravity from the alloy components. Therefore, by performing decantation, the by-products derived from the reducing agent can be largely removed along with the supernatant water of the slurry. From the viewpoint of obtaining a high-purity alloy powder, it is preferable to repeat the series of operations.

[0051] [Pickling process] Next, the alloy powder slurry that has been washed with water is subjected to acid washing. Specifically, acid is added to the alloy powder slurry. Even if by-products from the reducing agent (such as Ca(OH)2) or other phases (such as rare earth-rich phases) remain in the slurry, they can be removed by acid washing.

[0052] The manufacturing method of this embodiment is characterized by the use of both a buffer solution (carboxylic acid) and hydrochloric acid as the acid added to the alloy powder slurry. Furthermore, it is characterized by limiting the proportion of the buffer solution added to the alloy powder slurry to a predetermined range (5 mol% to 90 mol%). This makes it possible to obtain alloy powder with excellent properties in high yield while minimizing environmental impact.

[0053] The buffer solution (carboxylic acid) has the effect of suppressing large local fluctuations in slurry pH in a washing tank into which hydrochloric acid, a strong acid, is added. However, the carboxylic acid used as a buffer solution is an organic acid. If the proportion of carboxylic acid added is excessively high, the BOD of the wastewater will increase, and treatment costs will increase. From the viewpoint of suppressing the increase in treatment costs, the buffer solution proportion should be kept below 90 mol%. On the other hand, if the proportion of hydrochloric acid added is excessively high, efficient acid washing becomes difficult. That is, problems arise such as uneven acid washing or excessive dissolution of the alloy powder. From the viewpoint of suppressing these problems and obtaining alloy powder with excellent properties in high yield, the buffer solution proportion should be 5 mol% or more. The buffer solution proportion is preferably 5 mol% to 50 mol%, and more preferably 10 mol% to 35 mol%.

[0054] The buffer solution ratio is the ratio of the amount of carboxyl groups (N1) in the carboxylic acid to the total amount of hydrochloric acid (N2) added to the alloy powder slurry. For example, in the case of a monocarboxylic acid containing one carboxyl group, the amount of substance (N) is equal to the amount of substance of the carboxylic acid. When using a dicarboxylic acid containing two carboxyl groups, the amount of substance of the carboxyl groups (N1) is twice the amount of substance of the carboxylic acid. When using a tricarboxylic acid containing three carboxyl groups, the amount of substance of the carboxyl groups (N1) is three times the amount of substance of the carboxylic acid.

[0055] The buffer solution is not particularly limited as long as it is a carboxylic acid. However, it is desirable that the acid dissociation constant pKα is in the range of 2.0 to 7.0, preferably 3.0 to 6.0, and more preferably 3.0 to 5.0. Examples of such buffer solutions (carboxylic acids) include at least one selected from the group consisting of formic acid, acetic acid, citric acid, gluconic acid, oxalic acid, and glycolic acid. A single carboxylic acid may be used as the buffer solution, or a combination of multiple carboxylic acids may be used.

[0056] The order in which the buffer solution (carboxylic acid) and hydrochloric acid are added is not limited. The buffer solution and hydrochloric acid may be mixed beforehand and the resulting mixture added to the slurry in the washing tank, or they may be added separately. However, it is particularly preferable to add the buffer solution to the alloy powder slurry first, and then add the hydrochloric acid. This is because adding the hydrochloric acid after the buffer solution has spread throughout the slurry can more effectively mitigate the rapid reaction at the points where the hydrochloric acid is added. The total amount of acid (buffer solution and hydrochloric acid) added should be adjusted so that the desired composition is obtained in the final alloy powder. The temperature of the slurry in the pickling process is not particularly limited.

[0057] If necessary, the alloy powder slurry that has undergone acid cleaning may be subjected to water cleaning again. Alternatively, a surface treatment may be performed by adding an aqueous phosphoric acid solution to the alloy powder slurry to form a phosphorus-containing protective film on the surface of the alloy particles.

[0058] <Drying process> If necessary, a drying step may be provided to dry the wet-processed material (alloy powder) obtained by the wet-processing. The drying method is not limited. For example, a deliquidation treatment may be performed on the slurry containing the wet-processed material to obtain a cake containing alloy powder, and the obtained cake may be dried. Deliquidation may be performed using known solid-liquid separation devices such as a Nutsch, filter press, and / or centrifuge. Drying may be performed by vacuum drying or heat drying. To improve the efficiency of drying, the cake may be stirred during drying. Furthermore, to improve the efficiency of drying even more, the solvent in the slurry before deliquidation may be replaced. For example, the water contained in the slurry may be replaced with an alcohol such as methanol, ethanol, and / or propanol.

[0059] <Grinding process> If necessary, a step (grinding step) may be provided to grind the wet-treated material (alloy powder) after wet treatment or drying. The grinding method is not limited and may be wet or dry. When wet grinding is performed, it is preferable to grind in an organic solvent. When dry grinding is performed, it is preferable to grind in an inert atmosphere. Furthermore, a surface treatment to impart weather resistance to the treated material may be applied simultaneously with or after grinding.

[0060] In one preferred embodiment, the manufacturing method of this embodiment includes a reduction-diffusion step, a nitriding step, and a wet treatment step in this order. In the nitriding step, while heating the reaction product obtained in the reduction-diffusion step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare-earth transition metal alloy components in the reaction product. In the wet treatment step, the reaction product nitrided in the nitriding step is subjected to a washing treatment.

[0061] In another preferred embodiment, the manufacturing method of this embodiment includes, in this order, a reduction-diffusion 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-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and breaking it down. In the nitriding step, while heating the reaction product broken down in the hydrogen treatment step, a stream of nitrogen-containing gas is passed over the reaction product, thereby nitriding the rare earth transition metal alloy components in the reaction product. In the wet treatment step, the reaction product nitrided in the nitriding step is subjected to a washing treatment.

[0062] In another, more preferred embodiment, the manufacturing method of this embodiment includes, in this order, a reduction-diffusion 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-diffusion step is exposed to a hydrogen atmosphere to absorb hydrogen and disintegrate. In the wet treatment step, the reaction product disintegrated in the hydrogen treatment step is subjected to a washing treatment to obtain a rare earth transition metal alloy powder. In the nitriding step, while heating the rare earth transition metal alloy powder obtained by the washing treatment in the wet treatment step, a stream of nitrogen-containing gas is flowed over the rare earth transition metal alloy powder to obtain a nitrided rare earth transition metal alloy powder.

[0063] In this way, the rare earth transition metal alloy powder of this embodiment can be produced. In the production method of this embodiment, when acid washing the reaction product, a predetermined buffer solution and hydrochloric acid are used in combination, and the buffer solution ratio is limited to a predetermined range. Therefore, acid washing can be performed efficiently while suppressing the environmental burden problems that occur in industrial production. As a result, it is possible to obtain alloy powder with excellent properties in high yield.

[0064] The rare earth transition metal alloy powder obtained by the manufacturing method of this embodiment has an average particle size D 50 However, the particle size is usually between 1 μm and 50 μm, preferably between 1 μm and 30 μm, and more preferably between 1 μm and 10 μm. This alloy powder can be applied to known uses such as permanent magnet materials, hydrogen storage materials, magneto-optical recording materials, and magnetic refrigeration materials, and is particularly suitable for use as a permanent magnet material. [Examples]

[0065] The present invention will be described in more detail using the following examples. However, the present invention is not limited to the following examples.

[0066] (1) Evaluation of alloy powder As will be explained later, Sm2Fe 17 N3 alloy powder (e.g., A1-A8 and C1-C3), Sm2Fe 17 Alloy powders (e.g., B1-B4 and D1-D3), Nd2Fe 14 B alloy powders (e.g., E1-E3), SmCo5 alloy powders (e.g., F1-F3), and LaNi5 alloy powders (e.g., G1-G3) were prepared. The properties of the obtained alloy powders were then evaluated as follows.

[0067] <xrd> The crystalline structure of the alloy powder was evaluated using powder X-ray diffraction (XRD). X-ray diffraction measurements were performed using a Cu target under conditions of an acceleration voltage of 45 kV and a current of 40 mA, scanning 2θ at a speed of 2 minutes / deg. The resulting XRD patterns were then analyzed to identify the crystalline structure.

[0068] <Composition analysis> The amounts of rare earth metals (R), boron (B), and calcium (Ca) in the alloy powder were analyzed by ICP emission spectrometry. The amount of nitrogen (N) was analyzed by thermal conductivity, and the amount of oxygen (O) was analyzed by infrared absorption spectroscopy. For water-soluble chlorine (Cl) in the alloy powder, the powder was immersed in pure water, extracted at 100°C, and the filtered filtrate was analyzed by ion chromatography.

[0069] <Environmental load> After the acid washing treatment was completed and stirring was stopped to allow the alloy powder to settle, the tap water was sampled, and its biochemical oxygen consumption (BOD) was determined in accordance with JIS K0102. The BOD of the tap water when acid washing was performed with buffer (carboxylic acid) only was defined as A, and the BOD of the tap water when acid washing was performed with both buffer (carboxylic acid) and hydrochloric acid was defined as B. The environmental burden was defined as B / A. A smaller B / A indicates a greater effect in mitigating the environmental burden.

[0070] <Magnetic properties> Bonded magnets were fabricated from alloy powder, and their magnetic properties were evaluated. First, 0.9 kg of alloy powder was wet-milled in a ball mill using 1.8 kg of 2-propanol as a solvent until the 50% diameter was 1.8 μm. During the grinding process, 19 g of 85% phosphoric acid was added. The supernatant was removed from the ground slurry, and magnetic powder was obtained by mixer drying in a reduced-pressure atmosphere at 130°C and in a nitrogen gas atmosphere with an oxygen concentration of 3%. Polyamide 12 resin was added to this magnetic powder so that it comprised 90.8% by mass, and the mixture was heated and kneaded at 200°C. The resulting mixture was injection-molded in an oriented magnetic field of 15 kOe to produce molded products (bonded magnets) with a diameter of 20 mm and a height of 13 mm.

[0071] Next, the magnetic properties (magnetic flux density Br, coercivity HcJ) of the obtained bonded magnets (molded products) were measured using a DC recording magnetometer (Toei Kogyo Co., Ltd., TRF-5BH). Furthermore, a humidity resistance test was conducted by leaving the bonded magnets in an 85°C, 85%RH atmosphere for 1000 hours, and the magnetic properties of the bonded magnets after the test were measured. Finally, the degradation rate of the coercivity HcJ of the bonded magnets after the humidity resistance test relative to the initial value was evaluated.

[0072] (2) Preparation of alloy powder [Experimental Example A] In Experimental Example A, acetic acid was used as the buffer (carboxylic acid), and Sm2Fe 17 N3 alloy powders were prepared and evaluated (Examples A1 to A8).

[0073] [Example A1 (Example)] <Mixing process> Average particle size (D 50 625g of samarium oxide (Sm2O3) powder with a particle size of 3.2μm, average particle size (D 50 A mixture was obtained by mixing 1550g of iron (Fe) powder with a particle size of 37 μm and 250g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less in a mixer.

[0074] <Reduction-diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 1100°C for 6 hours, followed by cooling. This yielded the reaction product.

[0075] <Hydrogen treatment> The reaction products, after cooling, were placed in a sealed container and left in a hydrogen gas atmosphere to absorb hydrogen. This pulverized the reaction products, yielding a pulverized material with a particle size of 10 mm or less.

[0076] <Nitriding treatment> The crushed reaction product (crushed material) was charged into a tubular furnace, the pressure inside the furnace was reduced to 10 kPa, then returned to atmospheric pressure with nitrogen gas, and then switched to a mixed gas of ammonia and hydrogen (ammonia partial pressure 0.8 atm). This mixed gas was flowed through the furnace while heat treatment was performed at 440°C for 10 hours. After that, the gas was switched back to nitrogen gas and heat treatment was performed for another hour before cooling. This yielded nitride.

[0077] <Wet processing> 1250g of the reaction product (nitride) after nitriding was added to 4L of water to form a slurry (slurry preparation). The supernatant of this slurry was discarded, and 4L of fresh water was added. This decantation operation, involving stirring, standing, and discarding the supernatant, was repeated 7 times to separate and remove the Ca(OH)2 suspension (water washing treatment).

[0078] Next, 4 L of water was added to the treated material (slurry) after Ca(OH)2 separation to bring the slurry temperature to 20°C. Then, while stirring the slurry with water added, 31.8 g of 90% acetic acid was added dropwise over 10 minutes, followed by 180.7 g of 35% hydrochloric acid over 50 minutes. The amount of acetic acid added corresponded to 21.5 mol% of the total moles of acetic acid and hydrochloric acid added. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid, and the pH slowly changed within the range of 5 to 6 as the acid washing time progressed. Stirring was continued after the addition of hydrochloric acid, and when the pH reached 7, stirring was stopped and the supernatant was discarded (acid washing treatment).

[0079] After the acid washing treatment, 4 L of water was added to the treated material (slurry), stirred, allowed to stand, and the supernatant was discarded. This decantation process was repeated four times (water washing treatment). After the fourth water washing treatment, the supernatant of the treatment solution was discarded and replaced with ethanol, and the solution was further filtered 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.

[0080] The resulting powder is Th2Zn 17 Sm2Fe with a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.2% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.10% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0081] [Example A2 (Example)] In the acid washing treatment, a solution was prepared by pre-mixing 31.8 g of 90% acetic acid and 144.6 g of 35% hydrochloric acid. This mixture was then added dropwise to the material (slurry) over 60 minutes while stirring. The amount of acetic acid added corresponded to 21.5 mol% of the total moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. The pH of the slurry during the dropwise addition of the mixture fluctuated in small increments of approximately 0.5.

[0082] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.3% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.11% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0083] [Example A3 (Example)] In the acid washing treatment, 14.8 g of 90% acetic acid was added dropwise over 5 minutes while stirring the material (slurry), and then 207.3 g of 35% hydrochloric acid was added dropwise over 55 minutes. The amount of acetic acid added corresponded to 10.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid, and the pH slowly changed within the range of 5 to 6 as the acid washing time progressed.

[0084] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.2% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.10% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0085] [Example A4 (Example)] In the acid washing treatment, 7.4 g of 90% acetic acid was added dropwise over 3 minutes while stirring the material (slurry), and then 218.8 g of 35% hydrochloric acid was added dropwise over 57 minutes. The amount of acetic acid added corresponded to 5.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. The small fluctuations in the slurry pH during the addition of hydrochloric acid were small, within a range of about 0.3, and the pH slowly changed within the range of 5 to 6 as the acid washing time progressed.

[0086] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.3% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.10% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0087] [Example A5 (Example)] In the acid washing treatment, 132.8 g of 90% acetic acid was added dropwise over 54 minutes while stirring the material (slurry), and then 23.0 g of 35% hydrochloric acid was added dropwise over 6 minutes. The amount of acetic acid added corresponded to 90.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. The minute fluctuations in the slurry pH during the addition of hydrochloric acid were extremely small, with a range of less than 0.1, and the pH slowly changed within the range of 5 to 6 as the acid washing time progressed.

[0088] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.3% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.10% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0089] [Example A6 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 147.5 g of 90% acetic acid was added dropwise over 60 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example A1. Although there was a slow change in slurry pH due to the addition of acetic acid, no rapid fluctuations in slurry pH were observed.

[0090] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. Its composition was Sm: 23.2% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, and O: 0.10% by mass. Hydrochloric acid was not used, and no water-soluble chlorine (Cl) was detected.

[0091] [Example A7 (comparative example)] In the acid washing treatment, 3.0 g of 90% acetic acid was added dropwise over 1 minute while stirring the material (slurry), and then 225.7 g of 35% hydrochloric acid was added dropwise over 59 minutes. The amount of acetic acid added corresponded to 2.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.0.

[0092] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. Its composition was Sm: 23.4% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.15% by mass, and water-soluble chlorine Cl: 2 ppm by mass.

[0093] [Example A8 (Comparative Example)] In the acid washing treatment, acetic acid was not used; instead, 230.3 g of 35% hydrochloric acid was added dropwise over 60 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example A1. When only hydrochloric acid was used, despite stirring the slurry, the hydrochloric acid reacted rapidly at the local point of addition, causing the slurry pH to fluctuate significantly more than in Comparative Example 1, at approximately 1.5 in small increments.

[0094] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.5% by mass, N: 3.5% by mass, Ca: less than 0.01% by mass, O: 0.17% by mass, and water-soluble chlorine Cl: 9 ppm by mass.

[0095] [Experimental Example B] In Experimental Example B, acetic acid was used as the buffer (carboxylic acid), and Sm2Fe 17 We prepared and evaluated alloy powders (Examples B1 to B4).

[0096] [Example B1 (Example)] <Mixing process> Average particle size (D 50 ) 125g of samarium oxide (Sm2O3) powder with a particle size of 2.9μm, average particle size (D 50 A mixture was obtained by mixing 310 g of iron (Fe) powder with a particle size of 32 μm and 50 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less in a mixer.

[0097] <Reduction-diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 1070°C for 6 hours, followed by cooling. This yielded the reaction product.

[0098] <Hydrogen treatment> The reaction products, after cooling, were placed in a sealed container and left in a hydrogen gas atmosphere to absorb hydrogen. This pulverized the reaction products, yielding a pulverized material with a particle size of 10 mm or less.

[0099] <Wet processing> 144g of the reaction product after hydrogen treatment was added to 0.5L of water to form a slurry (slurry preparation). The supernatant of this slurry was discarded, and 0.5L of fresh water was added, stirred, allowed to stand, and the supernatant was discarded. This decantation operation was repeated 7 times to separate and remove the Ca(OH)2 suspension (water washing treatment).

[0100] Next, 0.5 L of water was added to the treated material (slurry) after Ca(OH)2 separation to bring the slurry temperature to 6°C. Then, while stirring the slurry with water added, 1.2 g of 90% acetic acid was added dropwise over 2 minutes, followed by 3.6 g of 35% hydrochloric acid, which was added dropwise over 10 minutes. The amount of acetic acid added corresponded to 35.0 mol% of the total moles of acetic acid and hydrochloric acid added. The slurry pH change during the addition of hydrochloric acid was gradual. Stirring continued after the addition of hydrochloric acid, and when the pH reached 7, stirring was stopped and the supernatant was discarded (acid washing treatment).

[0101] After the acid washing treatment, 0.5 L of water was added to the treated material (slurry), stirred, allowed to stand, and the supernatant was discarded. This decantation operation was repeated four times (water washing treatment). After the fourth water washing treatment, the supernatant of the treatment solution was discarded and replaced with ethanol, and the solution was further filtered 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.

[0102] The resulting powder is Th2Zn 17 Sm2Fe with a type crystal structure 17 It was an alloy powder. It also had the following composition: Sm: 24.4% by mass, Ca: less than 0.01% by mass, O: 0.18% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0103] [Example B2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 3.5 g of 90% acetic acid was added dropwise over 12 minutes while stirring the treated material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example B1. Although there was a slow change in slurry pH due to the addition of acetic acid, no rapid fluctuations in slurry pH were observed.

[0104] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. Its composition was Sm: 24.4% by mass, Ca: less than 0.01% by mass, and O: 0.17% by mass. Hydrochloric acid was not used, and no water-soluble chlorine (Cl) was detected.

[0105] [Example B3 (Comparative Example)] In the acid washing treatment, 0.1 g of 90% acetic acid was added dropwise over 0.5 minutes while stirring the material (slurry), and then 5.3 g of 35% hydrochloric acid was added dropwise over 9 minutes. The amount of acetic acid added corresponded to 3.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example B2. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 0.8.

[0106] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. It also had the following composition: Sm: 24.6% by mass, Ca: less than 0.01% by mass, O: 0.20% by mass, and water-soluble chlorine Cl: 3 ppm by mass.

[0107] [Example B4 (comparative example)] During the acid washing treatment, 5.5 g of 35% hydrochloric acid was added dropwise over 10 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example B2. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.4.

[0108] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. It also had the following composition: Sm: 25.0% by mass, Ca: less than 0.01% by mass, O: 0.23% by mass, and water-soluble chlorine Cl: 10 ppm by mass.

[0109] [Experimental Example C] In Experimental Example C, citric acid was used as the buffer (carboxylic acid), and Sm2Fe 17 N3 alloy powders were prepared and evaluated (Examples C1 to C3).

[0110] [Example C1] In the acid washing treatment, 86.3 g of 40% citric acid was added dropwise over 8 minutes while stirring the material (slurry), and then 318.0 g of 35% hydrochloric acid was added dropwise over 52 minutes. The amount of citric acid added corresponded to 15.0 mol% of the total number of moles of citric acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example A1. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid, and the pH slowly changed within the range of 4 to 6 as the acid washing time progressed.

[0111] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.2% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, O: 0.09% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0112] [Example C2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 575.0 g of 40% citric acid was added dropwise over 60 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example C1. Although there was a slow change in slurry pH due to the addition of citric acid, no rapid fluctuations in slurry pH were observed.

[0113] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. Its composition was Sm: 23.2% by mass, N: 3.4% by mass, Ca: less than 0.01% by mass, and O: 0.08% by mass. Hydrochloric acid was not used, and no water-soluble chlorine (Cl) was detected.

[0114] [Example C3 (Comparative Example)] In the acid washing treatment, 11.5 g of 40% citric acid was added dropwise over 3 minutes while stirring the material (slurry), and then 366.6 g of 35% hydrochloric acid was added dropwise over 57 minutes. The amount of citric acid added corresponded to 2.0 mol% of the total number of moles of citric acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example C1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.2.

[0115] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an N3 alloy powder. It also had the following composition: Sm: 23.4% by mass, N: 3.5% by mass, Ca: less than 0.01% by mass, O: 0.14% by mass, and water-soluble chlorine Cl: 2 ppm by mass.

[0116] [Experimental Example D] In Experiment Example D, citric acid was used as the buffer (carboxylic acid), and Sm2Fe 17 We prepared and evaluated alloy powders (Examples D1 to D3).

[0117] [Example D1 (Example)] In the acid washing treatment, 1.2 g of 25% citric acid was added dropwise over 1 minute while stirring the material (slurry), and then 7.7 g of 35% hydrochloric acid was added dropwise over 8 minutes. The amount of citric acid added corresponded to 6.0 mol% of the total number of moles of citric acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example B1. The small fluctuations in the slurry pH during the addition of hydrochloric acid were slow and remained around 0.2.

[0118] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. It also had the following composition: Sm: 24.3% by mass, Ca: less than 0.01% by mass, O: 0.16% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0119] [Example D2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 20.2 g of 25% citric acid was added dropwise over 9 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example B1. Although there was a slow change in slurry pH due to the addition of citric acid, no rapid fluctuations in slurry pH were observed.

[0120] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. Its composition was Sm: 24.3% by mass, Ca: less than 0.01% by mass, and O: 0.17% by mass. Hydrochloric acid was not used, and no water-soluble chlorine (Cl) was detected.

[0121] [Example D3 (Comparative Example)] In the acid washing treatment, 0.6 g of 25% citric acid was added dropwise over 1 minute while stirring the material (slurry), and then 8.0 g of 35% hydrochloric acid was added dropwise over 9 minutes. The amount of acetic acid added corresponded to 3.0 mol% of the total number of moles of acetic acid and hydrochloric acid added. Otherwise, the alloy powder was prepared in the same manner as in Example B1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.3.

[0122] The resulting powder is Th2Zn 17 Sm2Fe has a type crystal structure 17 It was an alloy powder. It also had the following composition: Sm: 24.5% by mass, Ca: less than 0.01% by mass, O: 0.18% by mass, and water-soluble chlorine Cl: 4 ppm by mass.

[0123] [Experimental Example E] In Experimental Example E, gluconic acid was used as the buffer (carboxylic acid), and Nd2Fe 14 We prepared and evaluated B alloy powders (Examples E1 to E3).

[0124] [Example E1 (Example)] <Mixing process> Average particle size (D 50 405g of neodymium oxide (Nd2O3) powder with a particle size of 3.7μm, average particle size (D 50 A mixture was obtained by mixing 608 g of iron (Fe) powder with a particle size of 40 μm, 67 g of ferroboron powder (B content 18.7% by mass) with a particle size of 200 mesh or less, 217 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less, and 20 g of anhydrous calcium chloride (CaCl2) in a mixer under an argon (Ar) atmosphere.

[0125] <Reduction-diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 1000°C for 2 hours, then cooled to room temperature. This yielded the reaction product.

[0126] <Hydrogen treatment> The reaction product, after cooling, was subjected to hydrogen treatment similar to that in Example A1 to obtain a cleaved product.

[0127] <Wet processing> 1000g of the crushed reaction product (crushed material) was added to 4L of water to form a slurry (slurry preparation). The supernatant water of this slurry was discarded, and decantation was repeated 10 times using 4L of fresh water to separate the Ca(OH)2 suspension (water washing treatment).

[0128] Next, 4 L of water was added to the treated material (slurry) after Ca(OH)2 separation to bring the slurry temperature to 8°C. Then, while stirring the slurry with water added, 42.0 g of 50% gluconic acid was added dropwise over 40 minutes, followed by the dropwise addition of 11.1 g of 35% hydrochloric acid over 10 minutes. The amount of gluconic acid added corresponded to 50 mol% of the total moles of gluconic acid and hydrochloric acid added. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid. Stirring continued after the addition of hydrochloric acid, and when the pH reached 7, stirring was stopped and the supernatant was discarded (acid washing treatment).

[0129] After the acid washing treatment, 4 L of water was added to the treated material (slurry), stirred, allowed to stand, and the supernatant was discarded. This decantation process was repeated five times (water washing treatment). After the fifth water washing treatment, the supernatant of the treatment solution was discarded and replaced with ethanol, and the solution was further filtered to obtain an alloy powder cake. The obtained alloy powder cake was dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0130] The resulting powder is tetragonal Nd2Fe. 14 It was an alloy powder with phase B as the main phase. It also had the following composition: Nd: 33.0 mass%, B: 1.3 mass%, Ca: 0.02 mass%, O: 0.19 mass%, and water-soluble chlorine Cl: less than 1 mass ppm.

[0131] [Example E2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 84.0 g of 50% gluconic acid was added dropwise over 50 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example E1. Although there was a slow change in slurry pH due to the addition of gluconic acid, no rapid fluctuations in slurry pH were observed.

[0132] The resulting powder is tetragonal Nd2Fe. 14 It was an alloy powder with phase B as the main phase. It also had the following composition: Nd: 33.1% by mass, B: 1.3% by mass, Ca: 0.03% by mass, O: 0.20% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0133] [Example E3 (Comparative Example)] During the acid washing treatment, 22.3 g of 35% hydrochloric acid was added dropwise over 50 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example E1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 2.1.

[0134] The resulting powder is tetragonal Nd2Fe. 14 It was an alloy powder with phase B as the main phase. It also had the following composition: Nd: 33.9 mass%, B: 1.4 mass%, Ca: 0.03 mass%, O: 0.32 mass%, and water-soluble chlorine Cl: 13 mass ppm.

[0135] [Experimental Example F] In Experimental Example F, SmCo5 alloy powder was prepared and evaluated using formic acid as a buffer solution (carboxylic acid) (Examples F1 to F3).

[0136] [Example F1 (Example)] <Mixing process> Average particle size (D 50 A mixture was obtained by mixing 371 g of samarium oxide (Sm2O3) powder with a particle size of 2.3 μm, 669 g of electrolytic cobalt (Co) powder with a particle size of 325 mesh or less, 161 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less, and 37 g of anhydrous calcium chloride (CaCl2) in a mixer under an argon (Ar) atmosphere.

[0137] <Reduction-diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 1050°C for 2 hours, then cooled to room temperature. This yielded the reaction product.

[0138] <Hydrogen treatment> The reaction product, after cooling, was subjected to hydrogen treatment similar to that in Example A1 to obtain a cleaved product.

[0139] <Wet processing> 1000g of the resulting reaction product (disintegrated material) was added to 4L of water to form a slurry (slurry preparation). The supernatant water of this slurry was discarded, and decantation was repeated 10 times using 4L of fresh water to separate the Ca(OH)2 suspension (water washing treatment).

[0140] Next, 4 L of water was added to the treated material (slurry) after Ca(OH)2 separation to bring the slurry temperature to 25°C. Then, while stirring the slurry with water added, 3.2 g of 88% formic acid was added dropwise over 5 minutes, followed by 32.6 g of 35% hydrochloric acid, which was added dropwise over 35 minutes. The amount of formic acid added corresponded to 20 mol% of the total moles of formic acid and hydrochloric acid added. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid. Stirring continued after the addition of hydrochloric acid, and when the pH reached 7, stirring was stopped and the supernatant was discarded (acid washing treatment).

[0141] After the acid washing treatment, 4 L of water was added to the treated material (slurry), stirred, allowed to stand, and the supernatant was discarded. This decantation operation was repeated five times (water washing treatment). After the fifth water washing treatment, the supernatant of the treatment solution was discarded and replaced with 2-propanol, and the solution was further filtered to obtain an alloy powder cake. The obtained alloy powder cake was dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0142] The obtained powder was an SmCo5 alloy powder with a CaCu5-type crystal structure. It had a composition of Sm: 33.9% by mass, Ca: 0.01% by mass, O: 0.04% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0143] [Example F2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 16.2 g of 88% formic acid was added dropwise over 50 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example F1. Although there was a slow change in slurry pH due to the addition of formic acid, no rapid fluctuations in slurry pH were observed.

[0144] The obtained powder was an SmCo5 alloy powder with a CaCu5-type crystal structure. It had a composition of Sm: 34.0 mass%, Ca: 0.02 mass%, O: 0.05 mass%, and water-soluble chlorine Cl: less than 1 mass ppm.

[0145] [Example F3 (Comparative Example)] During the acid washing treatment, 40.8 g of 35% hydrochloric acid was added dropwise over 50 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example F1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.3.

[0146] The obtained powder was an SmCo5 alloy powder with a CaCu5-type crystal structure. It had a composition of Sm: 34.4% by mass, Ca: 0.01% by mass, O: 0.08% by mass, and water-soluble chlorine Cl: 7 ppm by mass.

[0147] [Experimental Example G] In Experimental Example G, LaNi5 alloy powder was prepared and evaluated using formic acid as a buffer solution (carboxylic acid) (Examples G1 to G3).

[0148] [Example G1 (Example)] <Mixing process> Average particle size (D 50 ) 112g of lanthanum oxide (La2O3) powder with a particle size of 5.7μm, average particle size (D 50 A mixture was obtained by mixing 204 g of carbonyl nickel (Ni) powder with a particle size of 10.3 μm, 49.7 g of granular metallic calcium (Ca) with a particle size of 2.0 mm or less, and 11.2 g of anhydrous calcium chloride (CaCl2) in a mixer under an argon (Ar) atmosphere.

[0149] <Reduction-diffusion process> The resulting mixture was placed in an iron crucible and heated under an argon (Ar) gas atmosphere at 970°C for 5 hours, then cooled to room temperature. This yielded the reaction product.

[0150] <Hydrogen treatment> The reaction product, after cooling, was subjected to hydrogen treatment similar to that in Example A1 to obtain a cleaved product.

[0151] <Wet processing> 300g of the resulting reaction product (disintegrated material) was added to 1L of water to form a slurry (slurry preparation). Decantation of this slurry with 1L of water was repeated 7 times to separate the Ca(OH)2 suspension (water washing treatment).

[0152] Next, 1 L of water was added to the treated material (slurry) after Ca(OH)2 separation to bring the slurry temperature to 28°C. Then, while stirring the slurry with water added, 1.0 g of 88% formic acid was added dropwise over 2 minutes, followed by 10.5 g of 35% hydrochloric acid added dropwise over 10 minutes. The amount of formic acid added corresponded to 20 mol% of the total moles of formic acid and hydrochloric acid added. There were almost no small fluctuations in the slurry pH during the addition of hydrochloric acid. Stirring continued after the addition of hydrochloric acid, and when the pH reached 7, stirring was stopped and the supernatant was discarded (acid washing treatment).

[0153] After the acid washing treatment, 1 liter of water was added to the treated material (slurry), stirred, allowed to stand, and the supernatant was discarded. This decantation procedure was repeated five times (water washing treatment). After the fifth water washing treatment, the supernatant of the treated solution was discarded, the solvent was replaced with 2-propanol, and the solution was filtered to obtain an alloy powder cake. The obtained alloy powder cake was dried at 50°C under reduced pressure using a mixer to obtain alloy powder.

[0154] The obtained powder was a LaNi5 alloy powder with a CaCu5-type crystal structure. It also had a composition of La: 33.0 mass%, Ca: 0.08 mass%, O: 0.05 mass%, and water-soluble chlorine Cl: less than 1 mass ppm.

[0155] [Example G2 (Conventional Example)] In the acid washing treatment, hydrochloric acid was not used. Instead, 5.2 g of 88% formic acid was added dropwise over 12 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example G1. Although there was a slow change in slurry pH due to the addition of formic acid, no rapid fluctuations in slurry pH were observed.

[0156] The obtained powder was a LaNi5 alloy powder with a CaCu5-type crystal structure. It also had a composition of La: 33.1% by mass, Ca: 0.09% by mass, O: 0.06% by mass, and water-soluble chlorine Cl: less than 1 ppm by mass.

[0157] [Example G3 (comparative example)] During the acid washing treatment, 13.2 g of 35% hydrochloric acid was added dropwise over 12 minutes while stirring the material (slurry). Otherwise, the alloy powder was prepared in the same manner as in Example G1. The pH of the slurry during the addition of hydrochloric acid fluctuated in small increments, showing a large range of approximately 1.0.

[0158] The obtained powder was a LaNi5 alloy powder with a CaCu5-type crystal structure. It also had the following composition: La: 33.4% by mass, Ca: 0.09% by mass, O: 0.10% by mass, and water-soluble chlorine Cl: 8 ppm by mass.

[0159] (3) Evaluation results The composition of the alloy powders obtained in Experimental Examples A to G and the results of the environmental impact assessment are shown in Tables 1 and 3 to 8 below. In addition, the magnetic properties (Br, HcJ, and HcJ degradation rate) of the bonded magnet molded product obtained in Experimental Example A are summarized in Table 2 below.

[0160] [Experimental Example A (Examples A1-A8)] Using acetic acid as a buffer, Sm2Fe 17 In Experimental Example A, which involved the production of N3 alloy powder, Examples A1-A4 (Examples), which used a combination of acetic acid and hydrochloric acid for acid washing, yielded alloy powders with a composition equivalent to that of Example A6 (Conventional Example), which used only acetic acid. Furthermore, in Examples A1-A4, the amount of water-soluble Cl, which is a concern for deterioration of moisture resistance, was all below the detection limit (1 ppm by mass). In addition, the environmental burden (0.05-0.22) was reduced to 1 / 20 to 1 / 5 of that of Example A6. The environmental burden of Example A5 (Example) (0.90) was only reduced by 10% compared to Example A6. Nevertheless, the properties of the bonded magnet molded product were good. On the other hand, in Example A7 (Comparative Example), which had a small buffer solution (acetic acid) ratio (2 mol%), and Example A8 (Comparative Example), which used only hydrochloric acid for acid washing, although the environmental burden (0.02, 0.00) was good, the acid washing was not performed uniformly. As a result, the Sm composition (23.4 or 23.5% by mass) was high. Furthermore, the amount of oxygen (0.15 or 0.17 mass%) in Examples A7 and A8 was higher than that of Examples A1 to A5 (0.10 to 0.11 mass%). This result suggests residual impurities due to heterogeneous acid washing. Moreover, the amount of water-soluble Cl (2 or 9 mass ppm) in Examples A7 and A8 was higher than that of Examples A1 to A5.

[0161] Next, examining the magnetic properties of bonded magnet molded products made from alloy powder, the residual magnetic flux density Br (7.2-7.4 kG) of Examples A1-A6 (Examples or Conventional Examples) was relatively high, while the Br (7.1 kG) of Examples A7 and A8 (Comparative Examples), where residual impurities were a concern, was low. Furthermore, the coercivity HcJ (10.9-11.5 kOe) of Examples A1-A6 was relatively high, while the HcJ (10.7 kOe) of Examples A7 and A8 was low. In addition, examining the results of the humidity resistance test, the HcJ degradation rate (18.1% or 19.0%) of Examples A7 and A8, where water-soluble Cl residue was confirmed, was higher than the degradation rate (15.8-16.1%) of Examples A1-A5.

[0162] In the acid washing process, in Example A1, acetic acid was added dropwise first, followed by hydrochloric acid, whereas in Example A2, the same amounts of acetic acid and hydrochloric acid as in Example A1 were mixed before being added dropwise. In Example A1, the small fluctuations in the slurry pH during dropwise washing were smaller, suggesting that a more uniform acid washing was performed. This is also reflected in the fact that the Sm composition and O content of Example A1 were slightly lower than in Example A2, and the coercivity degradation rate of the bonded magnet molded product was also kept lower in Example A1.

[0163] [Table 1]

[0164] [Table 2]

[0165] [Experimental Example B (Examples B1-B4)] Using acetic acid as a buffer, Sm2Fe 17 In Experimental Example B, where alloy powders were produced, Example B1 (Example), which used a combination of acetic acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of Example B2 (Conventional Example), which used only acetic acid. Furthermore, Example B1 had a good environmental impact (0.35), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, in Example B3 (Comparative Example), which had a small buffer solution (acetic acid) ratio (3 mol%), and Example B4 (Comparative Example), which used only hydrochloric acid for acid washing, although the environmental impact (0.03, 0.00) was good, the acid washing was not performed uniformly. As a result, the Sm composition (24.6, 25.0% by mass) was high. In addition, the amount of O in Examples B3 and B4 (0.20, 0.23% by mass) was higher than that of Example B1 (0.18% by mass). This suggests the presence of impurities due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in Examples B3 and B4 (3, 10 ppm by mass) was higher than that in Example B1.

[0166] [Table 3]

[0167] [Experimental Example C (Examples C1-C3)] Using citric acid as a buffer, Sm2Fe 17 In Experimental Example C, which involved the production of N3 alloy powder, Example C1 (Example), which used a combination of citric acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of Example C2 (Conventional Example), which used only citric acid. Furthermore, Example C1 had a good environmental impact (0.15), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, in Example C3 (Comparative Example), which had a smaller buffer solution (citric acid) ratio (2 mol%), although the environmental impact (0.02) was good, the acid washing was not performed uniformly. As a result, the Sm composition (23.4% by mass) was high. In addition, the amount of O in Example C3 (0.14% by mass) was higher than that in Example C1 (0.09% by mass). This suggests the presence of impurities due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in Example C3 (2 ppm by mass) was higher than in Example C1.

[0168] [Table 4]

[0169] [Experimental Example D (Examples D1-D3)] Using citric acid as a buffer, Sm2Fe 17 In Experimental Example D, which involved the production of alloy powder, Example D1 (Example), which used a combination of citric acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of Example D2 (Conventional Example), which used only citric acid. Furthermore, Example D1 had a good environmental impact (0.06), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, in Example D3 (Comparative Example), which had a smaller buffer solution (citric acid) ratio (3 mol%), although the environmental impact (0.03) was good, the acid washing was not performed uniformly. As a result, the Sm composition (24.5% by mass) was high. In addition, the amount of O in Example D3 (0.18% by mass) was higher than that in Example D1 (0.16% by mass). This suggests the presence of impurities due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in Example D3 (4 ppm by mass) was higher than in Example D1.

[0170] [Table 5]

[0171] [Experimental Example E (Examples E1-E3)] Using gluconic acid as a buffer, Nd2Fe 14 In experimental example E, which involved producing alloy B powder, example E1 (example), which used gluconic acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of example E2 (conventional example), which used gluconic acid alone. Furthermore, example E1 had a good environmental impact (0.50), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, example E3, which used hydrochloric acid alone for acid washing, had a good environmental impact (0.00), but the acid washing was not performed uniformly. As a result, the Nd composition (33.9% by mass) was high. In addition, the amount of O in example E3 (0.32% by mass) was higher than that in example E1 (0.19% by mass). This suggests residual impurities due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in example E3 (13 ppm by mass) was higher than that in example E1.

[0172] [Table 6]

[0173] [Experimental Example F (Examples F1-F3)] In Experimental Example F, where SmCo5 alloy powder was produced using formic acid as a buffer solution, Example F1 (Example), which used both formic acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of Example F2 (Conventional Example), which used only formic acid. Furthermore, Example F1 had a good environmental impact (0.20), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, in Example F3 (Comparative Example), which used only hydrochloric acid for acid washing, although the environmental impact (0.00) was good, the acid washing was not performed uniformly. As a result, the Sm composition (34.4% by mass) was high. In addition, the amount of O in Example F3 (0.11% by mass) was higher than that of Example F1 (0.04% by mass). This suggests the presence of impurities due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in Example F3 (7 ppm by mass) was higher than that in Example F1.

[0174] [Table 7]

[0175] [Experimental Example G (Examples G1-G3)] In Experimental Example G, where LaNi5 alloy powder was produced using formic acid as a buffer solution, Example G1 (Example), which used both formic acid and hydrochloric acid for acid washing, yielded alloy powder with a composition equivalent to that of Example G2 (Conventional Example), which used only formic acid. Furthermore, Example G1 had a good environmental impact (0.20), and the amount of water-soluble Cl was below the detection limit (1 ppm by mass). On the other hand, in Example G3 (Comparative Example), which used only hydrochloric acid for acid washing, although the environmental impact (0.00) was good, the acid washing was not performed uniformly. As a result, the La composition (33.5% by mass) was high. In addition, the amount of O in Example G3 (0.10% by mass) was higher than that of Example G1 (0.05% by mass). This suggests that impurities remained due to non-uniform acid washing. Moreover, the amount of water-soluble Cl in Example G3 (8 ppm by mass) was higher than that in Example G1.

[0176] [Table 8]

[0177] From the results above, it is understood that this embodiment provides a method for producing rare earth transition metal alloy powder that can efficiently perform acid cleaning while suppressing the environmental burden problems that arise in industrial production.< / xrd>

Claims

1. A method for producing rare earth transition metal alloy powder, comprising the following steps: A reduction-diffusion step involves heating a mixture of alloying raw materials containing rare earth metals, transition metals, and oxygen, as well as a reducing agent, under a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent. The process includes a wet treatment step of washing the reaction product to obtain rare earth transition metal alloy powder, The wet processing step includes a sub-step of preparing an alloy powder slurry by adding and disintegrating the reaction product in water, a sub-step of subjecting the alloy powder slurry to a water washing treatment, and a sub-step of subjecting the alloy powder slurry to an acid washing treatment by adding a buffer and hydrochloric acid to the water-washed alloy powder slurry. The buffer solution is a carboxylic acid, A method in which the buffer solution ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups contained in the carboxylic acid (N1) to the sum of the amount of carboxyl groups contained in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is 5 mol% or more and 90 mol% or less.

2. The method according to claim 1, wherein the buffer solution ratio [N1 / (N1+N2)] is 5 mol% or more and 50 mol% or less.

3. The method according to claim 1 or 2, wherein the carboxylic acid is at least one selected from the group consisting of formic acid, acetic acid, citric acid, gluconic acid, oxalic acid, and glycolic acid.

4. The method according to claim 1 or 2, wherein, during the acid washing, a buffer solution is first added to the alloy powder slurry, and then hydrochloric acid is added.

5. The reduction-diffusion step, the nitriding step, and the wet treatment step are included in this order. In the nitriding step, while heating the reaction product obtained in the reduction-diffusion step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The method according to claim 1 or 2, wherein the wet treatment step involves washing the reaction product nitrided in the nitriding step.

6. The reduction-diffusion step, the hydrogen treatment step, the nitriding step, and the wet treatment step are included in this order. In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the nitriding step, while heating the reaction product that was crushed in the hydrogen treatment step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The method according to claim 1 or 2, wherein the wet treatment step involves washing the reaction product nitrided in the nitriding step.

7. The reduction-diffusion step, the hydrogen treatment step, the wet treatment step, and the nitriding step are included in this order. In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the wet treatment step, the reaction product crushed in the hydrogen treatment step is subjected to a washing treatment to obtain a rare earth transition metal alloy powder. The method according to claim 1 or 2, wherein in the nitriding step, a stream of nitrogen-containing air is passed over the rare earth transition metal alloy powder obtained by the cleaning step in the wet treatment step while heating the powder, thereby obtaining nitrided rare earth transition metal alloy powder.

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