Manufacturing method for SmFeN-based rare earth magnets

Abstract

To provide a method for manufacturing an SmFeN-based rare earth magnet having high magnetic characteristics.SOLUTION: A method for manufacturing an SmFeN-based rare earth magnet includes the steps of: dispersing SmFeN-based anisotropic magnetic powder containing Sm, Fe, La, W, R (R is at least one selected from the group consisting of Ti, Ba and Sr) and N using a medium of metal or ceramic coated with a resin, and obtaining the dispersed SmFeN-based anisotropic magnetic powder; mixing the dispersed SmFeN-based anisotropic magnetic powder and modified material powder, and obtaining mixed powder; compression molding the mixed powder in a magnetic filed, and obtaining a magnetic field molding; pressure sintering the magnetic molding, and obtaining a sintered body; and heat treating the sintered body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing SmFeN-based rare earth magnets. [Background technology]

[0002] Patent Document 1 discloses a manufacturing method for grinding SmFeN-based anisotropic magnetic powder using a ceramic media in a solvent. However, it was thought that using a hard ceramic media would generate fine particles due to chipping, increasing the oxygen content of the SmFeN-based anisotropic magnetic powder obtained after grinding, and thus degrading its magnetic properties.

[0003] Patent Document 2 discloses a method for manufacturing SmFeN-based rare earth magnets, which involves pre-compressing SmFeN-based anisotropic magnetic powder in a magnetic field of 6 kOe or higher, followed by warm compaction molding at a temperature of 600°C or lower and a molding surface pressure of 1 to 5 GPa. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-195326 [Patent Document 2] International Publication No. 2015 / 199096 [Overview of the project] [Problems that the invention aims to solve]

[0005] This disclosure aims to provide a method for manufacturing SmFeN-based rare-earth magnets with high magnetic properties. [Means for solving the problem]

[0006] A method for manufacturing an SmFeN-based rare earth magnet according to one aspect of this disclosure is: The process includes: dispersing an SmFeN-based anisotropic magnetic powder containing Sm, Fe, La, W, R (where R is at least one selected from the group consisting of Ti, Ba, and Sr), and N using a resin-coated metal or ceramic medium to obtain dispersed SmFeN-based anisotropic magnetic powder; mixing the dispersed SmFeN-based anisotropic magnetic powder with a modifier powder to obtain a mixed powder; compressing the mixed powder in a magnetic field to obtain a magnetic field molded body; pressurizing and sintering the magnetic field molded body to obtain a sintered body; and heat-treating the sintered body. [Effects of the Invention]

[0007] This disclosure provides a method for manufacturing SmFeN-based rare-earth magnets with high magnetic properties. [Brief explanation of the drawing]

[0008] [Figure 1] This is an SEM image of the SmFeN-based anisotropic magnetic powder in Example 1. [Figure 2] This is an SEM image of the SmFeN-based anisotropic magnetic powder in Example 2. [Figure 3] This is an SEM image of the SmFeN-based anisotropic magnetic powder in Example 3. [Figure 4] This is an SEM image of the SmFeN-based anisotropic magnetic powder in Comparative Example 1. [Figure 5] This is an SEM image of the SmFeN-based anisotropic magnetic powder in Comparative Example 2. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described in detail below. However, the embodiments shown below are merely examples for realizing the technical concept of this disclosure, and this disclosure is not limited to these. In this specification, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. Furthermore, numerical ranges indicated using "~" indicate a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively.

[0010] The method for manufacturing an SmFeN-based rare earth magnet according to this embodiment is characterized by comprising the steps of: dispersing an SmFeN-based anisotropic magnetic powder containing Sm, Fe, La, W, R (where R is at least one selected from the group consisting of Ti, Ba, and Sr), and N using a resin-coated metal or ceramic medium to obtain dispersed SmFeN-based anisotropic magnetic powder; mixing the dispersed SmFeN-based anisotropic magnetic powder with a modifier powder to obtain a mixed powder; compressing the mixed powder in a magnetic field to obtain a magnetic field molded body; pressurizing and sintering the magnetic field molded body to obtain a sintered body; and heat-treating the sintered body.

[0011] Disperse SmFeN-based anisotropic magnetic powder containing Sm, Fe, La, W, R (R is at least one selected from the group consisting of Ti, Ba, and Sr), and N using a resin-coated metal or ceramic medium. Here, the term "dispersion" means separating and dispersing the agglomerated particles formed by sintering or magnetic agglomeration contained in the SmFeN-based anisotropic magnetic powder into single particles or particles composed of a small number of particles (hereinafter referred to as "single particles"). Further, when the resin-coated metal or ceramic medium collides with the SmFeN-based anisotropic magnetic powder, the collision energy is smaller than when the uncoated metal or ceramic medium collides with the SmFeN-based anisotropic magnetic powder, so dispersion is more likely to occur than pulverization. Conventionally, when the SmFeN-based anisotropic magnetic powder is pulverized, the average particle size is significantly reduced, and fine particles due to chipping are also generated, so the magnetic properties are likely to deteriorate. Also, in the fine particles and the original part where the fine particles are generated, a highly active new surface is formed, so oxidation is likely to occur and the oxygen content is likely to increase. On the other hand, when dispersion is performed as in the present embodiment, the generated single particles are likely to be oriented in a magnetic field, so the magnetic properties are high. Also, since the generation of new surfaces accompanying the generation of fine particles can be suppressed compared to pulverization, it is considered that the oxygen content is unlikely to increase.

[0012] For dispersion in the dispersion process, a vibratory mill is used as a dispersion device. The media used in dispersion devices such as vibratory mills can have a metal core and a resin coating thereon. Examples of metal materials include iron, chromium steel, stainless steel, and steel. The media used in dispersion devices such as vibratory mills can also have a ceramic core and a resin coating thereon. Examples of ceramic materials include inorganic compounds such as metal or nonmetal oxides, carbides, nitrides, and borides, and more specifically, alumina, silica, zirconia, silicon carbide, silicon nitride, barium titanate, and glass. Among these, iron and chromium steel are preferred because they have high dispersion capacity due to their high specific gravity, low wear due to their high hardness, and the iron-containing wear particles generated by wear have little effect on the SmFeN-based anisotropic magnetic powder. In other words, it is preferable to use iron or chromium steel media coated with resin in the dispersion device. Examples of coating resins include thermoplastic resins such as nylon 6, nylon 66, nylon 12, polypropylene, polyphenylene sulfide, and polyethylene, as well as thermosetting resins such as epoxy resins and silicone resins, and combinations thereof. Thermoplastic resins can be formed by injection molding and have higher fluidity compared to thermosetting resins, allowing for thinner film thicknesses than when coated with thermosetting resins. Therefore, the specific gravity of the media can be increased and the size reduced compared to when coated with thermosetting resins. It is preferable to use nylon such as nylon 6, nylon 66, and nylon 12 as the thermoplastic resin. This is because nylon is relatively soft and inexpensive among thermoplastic resins. For example, iron media coated with nylon may be used in a dispersion device. This allows for the dispersion of SmFeN-based anisotropic magnetic powder while further suppressing the generation of fine powder.

[0013] The specific gravity of the medium used in the dispersion process is preferably 4 or more, more preferably 5 or more. If it is less than 4, the collision energy during dispersion becomes too small, and thus dispersion tends to be difficult to occur. The upper limit is not particularly limited, but preferably 8 or less, more preferably 7.5 or less. The specific gravity of the medium used in the dispersion process may be 6 or more and 7.5 or less. The medium of metal coated with resin or the medium of ceramics coated with resin can have a metal or ceramics core and a resin film coating the core. The thickness of the resin film can be, for example, 0.1 μm or more and 5 mm or less. Thereby, an increase in the diameter of the medium can be suppressed, so it is suitable for the dispersion of SmFeN-based anisotropic magnetic powder, and σr of the obtained SmFeN-based anisotropic magnetic powder can be improved.

[0014] The dispersion process can also be carried out in the presence of a solvent, but it is preferably carried out in the absence of a solvent from the viewpoint of suppressing the oxidation of SmFeN-based anisotropic magnetic powder by components (such as moisture) contained in the solvent.

[0015] The dispersion process is preferably carried out in an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere from the viewpoint of suppressing the oxidation of SmFeN-based anisotropic magnetic powder. The concentration of nitrogen in the nitrogen gas atmosphere may be 90% by volume or more, preferably 95% by volume or more. The concentration of argon in the argon gas atmosphere may be 90% by volume or more, preferably 95% by volume or more. The inert gas atmosphere may be an atmosphere in which two or more kinds of inert gases such as nitrogen gas and argon gas are mixed. The concentration of the inert gas in the inert gas atmosphere may be 90% by volume or more, preferably 95% by volume or more.

[0016] The diameter of the medium of metal or ceramics coated with resin is preferably 2 mm or more and 100 mm or less, more preferably 3 mm or more and 15 mm or less, and even more preferably 3 mm or more and 10 mm or less. If it is less than 2 mm, it is difficult to coat with resin, and if it exceeds 100 mm, since the medium is large, the contact with the powder becomes less, and dispersion tends to be difficult to occur.

[0017] When using a vibratory mill in the dispersion process, the amount of media can be set to, for example, 60% to 70% of the volume of the container holding the SmFeN-based anisotropic magnetic powder and the media, and the amount of SmFeN-based anisotropic magnetic powder can be set to 3% to 25% of the volume, with 4% to 20% of the volume being preferable.

[0018] The SmFeN-based anisotropic magnetic powder used in the dispersion process can be prepared by referring to methods disclosed, for example, in Japanese Patent Publication No. 2017-117937 and Japanese Patent Publication No. 2021-055188. An example of a method for producing SmFeN-based anisotropic magnetic powder is described below.

[0019] The SmFeN-based anisotropic magnetic powder used in the dispersion process is obtained by a pretreatment step in which an oxide containing Sm, Fe, La, W, and R (where R is at least one selected from the group consisting of Ti, Ba, and Sr) is heat-treated in a reducing gas-containing atmosphere to obtain a partial oxide. A step of obtaining alloy particles by heat-treating the aforementioned partial oxide in the presence of a reducing agent. A step of nitriding the alloy particles to obtain a nitride, and This can be produced by a manufacturing method that includes the step of washing the nitride to obtain SmFeN-based anisotropic magnetic powder.

[0020] The oxide containing Sm, Fe, La, W, and R (where R is at least one selected from the group consisting of Ti, Ba, and Sr) used in the pretreatment step may be prepared by mixing Sm oxide, Fe oxide, La oxide, W oxide, and R oxide, or it can be prepared by mixing a solution containing Sm, Fe, La, W, and R with a precipitating agent to obtain a precipitate containing Sm, Fe, La, W, and R (precipitation step), and then calcining the precipitate to obtain an oxide containing Sm, Fe, La, W, and R (oxidation step).

[0021] [Precipitation process] In the precipitation step, the Sm, Fe, La, W, and R raw materials are dissolved to prepare a solution containing Sm, Fe, La, W, and R. (Sm2Fe) 17 When obtaining the material with N3 as the main phase, the molar ratio of Sm to Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, and more preferably 2.0:17 to 2.5:17. A magnetic material with a high residual magnetic flux density can be obtained because it contains La, W, and R. In addition to La, W, and R, raw materials such as Co, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, and Lu may be added to the above solution.

[0022] The Sm, Fe, La, W, and R raw materials are not limited as long as they are soluble. For example, in terms of availability, samarium oxide can be used as the Sm raw material, FeSO4 as the Fe raw material, La2O3 or LaCl3 as the La raw material, ammonium tungstate as the W raw material, and oxides of R (titanium oxide, strontium oxide, barium oxide), carbonates (strontium carbonate, barium carbonate), chlorides (strontium chloride, barium chloride), and sulfates (titanium sulfate) can be used as the R raw material. The concentration of the solution containing Sm, Fe, La, W, and R can be adjusted as appropriate within the range in which the Sm, Fe, La, W, and R raw materials are substantially soluble in the solution.

[0023] An insoluble precipitate containing Sm, Fe, La, W, and R is obtained by reacting a solution containing Sm, Fe, La, W, and R with a precipitating agent. Here, the solution containing Sm, Fe, La, W, and R only needs to be a solution containing Sm, Fe, La, W, and R when reacted with the precipitating agent. For example, a solution containing Sm, a solution containing Fe, a solution containing La, a solution containing W, and a solution containing R may be prepared separately, and each solution may be added dropwise to react with the precipitating agent. Alternatively, a solution containing Sm, Fe, La, W, and R may be prepared separately as a solution containing Sm and Fe, and a solution containing La, W, and R may be added dropwise to react with the precipitating agent. Even when preparing separate solutions, the amounts should be adjusted appropriately so that each raw material is substantially soluble in the solution. The precipitating agent is not limited to alkaline solutions that react with a solution containing Sm, Fe, La, W, and R to produce a precipitate, and examples include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0024] The precipitation reaction is preferably carried out by dropwise adding a solution containing Sm, Fe, La, W, and R, and a precipitant, to a solvent such as water, since the properties of the precipitate particles can be easily adjusted. By appropriately controlling the supply rate of the solution containing Sm, Fe, La, W, and R and the precipitant, the reaction temperature, the concentration of the reaction solution, and the pH during the reaction, a precipitate with a homogeneous distribution of constituent elements, a narrow particle size distribution, and a well-formed powder shape can be obtained. By using such a precipitate, the magnetic properties of the final product, SmFeN-based anisotropic magnetic powder, are improved. The reaction temperature is preferably 0°C to 50°C, and more preferably 35°C to 45°C. The reaction solution concentration is preferably 0.65 mol / L to 0.85 mol / L, and more preferably 0.7 mol / L to 0.85 mol / L, as the total concentration of metal ions. The reaction pH is preferably 5 to 9, and more preferably 6.5 to 8.

[0025] The powder obtained in the precipitation process roughly determines the particle size, shape, and particle size distribution of the final SmFeN-based anisotropic magnetic powder. When the particle size of the obtained powder is measured using a laser diffraction wet particle size analyzer, it is preferable that the size and distribution of the total powder fall within the range of 0.05 μm to 20 μm, preferably 0.1 μm to 10 μm.

[0026] After separating the precipitate, it is preferable to desolvent the separated material to prevent the precipitate from redissolving in the remaining solvent during the subsequent oxidation heat treatment, which can lead to aggregation of the precipitate, changes in particle size distribution, powder particle size, etc., as the solvent evaporates. Specifically, a method for desolvation is to dry the material in an oven at 70°C to 200°C for 5 to 12 hours, for example, when water is used as the solvent.

[0027] The process may include a step of separating and washing the precipitate after the precipitation step. The washing step is performed when the conductivity of the supernatant solution is 5 mS / m 2 Continue as needed until the following is achieved. For example, to separate the precipitate, a solvent (preferably water) can be added to the obtained precipitate and mixed, after which filtration, decantation, or the like can be used.

[0028] [Oxidation process] The oxidation process involves calcining the precipitate formed in the precipitation process to obtain oxides containing Sm, Fe, La, W, and R. For example, the precipitate can be converted into oxides by heat treatment. When heat treating the precipitate, it must be done in the presence of oxygen, for example, in an atmospheric environment. Furthermore, because it must be done in the presence of oxygen, it is preferable that the nonmetallic portion of the precipitate contains oxygen atoms.

[0029] The heat treatment temperature in the oxidation process (hereinafter referred to as the oxidation temperature) is not particularly limited, but is preferably 700°C to 1300°C, and more preferably 900°C to 1200°C. Below 700°C, oxidation is insufficient, and above 1300°C, the desired shape, average particle size, and particle size distribution of the SmFeN-based anisotropic magnetic powder tend not to be obtained. The heat treatment time is also not particularly limited, but is preferably 1 hour to 3 hours.

[0030] The resulting oxides exhibit sufficient microscopic mixing of Sm and Fe within the oxide particles, and the shape and particle size distribution of the precipitate are reflected in the oxide particles.

[0031] [Pre-treatment process] The pretreatment step is a process in which an oxide containing the aforementioned Sm, Fe, La, W, and R is heat-treated in a reducing gas-containing atmosphere to obtain a partial oxide in which a portion of the oxide has been reduced.

[0032] Here, a partial oxide refers to an oxide in which a portion of the oxide has been reduced. The oxygen concentration of the partial oxide is not particularly limited, but it is preferably 10% by mass or less, and more preferably 8% by mass or less. If it exceeds 10% by mass, the exothermic reaction with Ca during the reduction process increases, and the firing temperature rises, which tends to result in particles with abnormal particle growth. The oxygen concentration of the partial oxide can be measured by non-dispersive infrared absorption spectroscopy (ND-IR).

[0033] The reducing gas can be appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), methane (CH4), and combinations thereof, but hydrogen gas is preferred in terms of cost, and the gas flow rate is appropriately adjusted within a range where oxides do not scatter. The heat treatment temperature in the pretreatment step (hereinafter referred to as the pretreatment temperature) is preferably 300°C to 950°C, with a lower limit of 400°C or higher, more preferably 750°C or higher, and an upper limit of less than 900°C. When the pretreatment temperature is 300°C or higher, the reduction of oxides containing Sm, Fe, La, W, and R proceeds efficiently. When the temperature is 950°C or lower, particle growth and segregation of oxide particles are suppressed, and the desired particle size can be maintained. The heat treatment time is not particularly limited, but can be 1 hour to 50 hours. Furthermore, when hydrogen is used as the reducing gas, it is preferable to adjust the thickness of the oxide layer used to 20 mm or less, and to further adjust the dew point in the reaction furnace to -10°C or lower.

[0034] [Reduction Process] The reduction process is a process of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent. For example, reduction is carried out by contacting the partial oxide with a calcium melt or calcium vapor. The heat treatment temperature is preferably 920°C to 1200°C, more preferably 950°C to 1150°C, and even more preferably 1000°C to 1100°C, from the viewpoint of magnetic properties.

[0035] As a heat treatment separate from the heat treatment described above in the reduction process, heat treatment may be performed at a first temperature of 950°C to 1150°C, followed by heat treatment at a second temperature lower than the first temperature, between 930°C and 1130°C. The first temperature is preferably between 1000°C and 1100°C, and the second temperature is preferably between 980°C and 1080°C. The temperature difference between the first and second temperatures is preferably such that the second temperature is 10°C to 60°C lower than the first temperature, and more preferably between 10°C and 30°C lower. The heat treatment at the first temperature and the heat treatment at the second temperature may be performed consecutively, and heat treatment at a temperature lower than the second temperature may be included between these heat treatments, but from the viewpoint of productivity, it is preferable to perform them consecutively. From the viewpoint of performing the reduction reaction more uniformly, the time for each heat treatment is preferably less than 120 minutes, more preferably less than 90 minutes, and the lower limit of the heat treatment time is preferably 10 minutes or more, and more preferably 30 minutes or more.

[0036] The reducing agent, metallic calcium, is used in granular or powder form, but its average particle size is preferably 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, it is preferable to add metallic calcium in an amount of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce the rare earth oxide, and including the amount required to reduce the Fe component if it is in oxide form), with 1.5 to 2.5 times being more preferable.

[0037] In the reduction process, a disintegration accelerator can be used along with the reducing agent, metallic calcium, as needed. This disintegration accelerator is used as appropriate to promote the disintegration and granulation of the product during the post-treatment process described later, and examples include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used in a proportion of 1% to 30% by mass, preferably 5% to 30% by mass, per samarium oxide.

[0038] [Nitriding process] The nitriding process is a process in which anisotropic magnetic particles are obtained by nitriding the alloy particles obtained in the reduction process. Since particulate precipitate obtained in the aforementioned precipitation process is used, porous, solid alloy particles are obtained in the reduction process. This allows for immediate heat treatment under a nitrogen atmosphere and nitriding without the need for grinding, thus enabling uniform nitriding.

[0039] The heat treatment temperature (hereinafter referred to as the nitriding temperature) for nitriding alloy particles is preferably 300 to 610°C, and particularly preferably 400 to 550°C, and the treatment is carried out by replacing the atmosphere with a nitrogen atmosphere within this temperature range. The heat treatment time should be set to ensure that the nitriding of the alloy particles is sufficiently uniform.

[0040] In the nitriding treatment of alloy particles, the heat treatment temperature can be adjusted by first heat treatment at a temperature of 400°C to 470°C, followed by a second heat treatment at a temperature of 480°C to 610°C. If heat treatment is performed at the high temperature of the second temperature without nitriding at the first temperature, abnormal heat generation may occur due to the rapid progression of nitriding, which can cause the SmFeN-based anisotropic magnetic powder to decompose and significantly reduce its magnetic properties. Furthermore, the atmosphere during the nitriding process is preferably substantially nitrogen-containing, as this can slow down the progression of nitriding.

[0041] In this context, "substantially" is used considering that elements other than nitrogen are inevitably present due to the inclusion of impurities, etc. For example, the proportion of nitrogen in the atmosphere is 95% or more, preferably 97% or more, and more preferably 99% or more.

[0042] The first temperature in the nitriding process is preferably 400°C to 470°C, and more preferably 410°C to 450°C. Below 400°C, nitriding proceeds very slowly, and above 470°C, hypernitriding or decomposition tends to occur due to heat generation. The heat treatment time at the first temperature is not particularly limited, but is preferably 1 hour to 40 hours, and more preferably 20 hours or less. Below 1 hour, nitriding may not proceed sufficiently, and above 40 hours, productivity will be poor.

[0043] The second temperature is preferably between 480°C and 610°C, and more preferably between 500°C and 550°C. Below 480°C, nitriding may not proceed sufficiently if the particles are large, and above 610°C, hypernitriding or decomposition is likely to occur. The heat treatment time at the second temperature is preferably between 15 minutes and 5 hours, and more preferably between 30 minutes and 2 hours. Below 15 minutes, nitriding may not proceed sufficiently, and above 5 hours, productivity will be poor.

[0044] The heat treatment at the first temperature and the heat treatment at the second temperature may be performed consecutively, and a heat treatment at a temperature lower than the second temperature may be included between these heat treatments; however, from the standpoint of productivity, it is preferable to perform them consecutively.

[0045] [Post-processing steps] The product obtained after the nitriding process contains not only magnetic particles but also by-products such as CaO and unreacted metallic calcium, which may form a composite sintered lump. The product obtained after the nitriding process can be immersed in cooling water to separate the CaO and metallic calcium from the SmFeN-based anisotropic magnetic powder as calcium hydroxide (Ca(OH)2) suspensions. Any remaining calcium hydroxide may be thoroughly removed by washing the SmFeN-based anisotropic magnetic powder with acetic acid or the like. When the product is immersed in water, the oxidation of metallic calcium by water and the hydration reaction of by-product CaO cause the composite sintered lump reaction product to disintegrate, i.e., become finer, leading to pulverization.

[0046] [Alkali treatment process] The product obtained after the nitriding process may be added to an alkaline solution. Examples of alkaline solutions used in the alkaline treatment process include aqueous calcium hydroxide solution, aqueous sodium hydroxide solution, and aqueous ammonia solution. Among these, aqueous calcium hydroxide solution and aqueous sodium hydroxide solution are preferred in terms of wastewater treatment and high pH. In the alkaline treatment of the product obtained after the nitriding process, an Sm-rich layer containing a certain amount of oxygen remains and functions as a protective layer, thus suppressing the increase in oxygen concentration due to the alkaline treatment.

[0047] The pH of the alkaline solution used in the alkaline treatment process is not particularly limited, but it is preferably 9 or higher, and more preferably 10 or higher. If the pH is less than 9, the reaction rate when calcium hydroxide is formed is fast and the heat generation is large, so the oxygen concentration of the final SmFeN-based anisotropic magnetic powder tends to be high.

[0048] In the alkaline treatment process, the SmFeN-based anisotropic magnetic powder obtained after treatment with an alkaline solution can have its moisture content reduced by methods such as decantation, if necessary.

[0049] [Acid treatment process] The process may include an acid treatment step after the alkali treatment step. In the acid treatment step, at least a portion of the aforementioned Sm-rich layer is removed to reduce the oxygen concentration in the entire magnetic powder. Furthermore, in the manufacturing method described in the embodiment of the present invention, since no grinding or the like is performed, the average particle size of the SmFeN-based anisotropic magnetic powder is small, the particle size distribution is narrow, and it does not contain fine powder generated by grinding or the like, thus making it possible to suppress the increase in oxygen concentration.

[0050] The acid used in the acid treatment process is not particularly limited, and examples include hydrogen chloride, nitric acid, sulfuric acid, and acetic acid. Among these, hydrogen chloride and nitric acid are preferred because they do not leave any impurities behind.

[0051] The amount of acid used in the acid treatment process is preferably 3.5 parts by mass to 13.5 parts by mass, and more preferably 4 parts by mass to 10 parts by mass, per 100 parts by mass of SmFeN-based anisotropic magnetic powder. If the amount is less than 3.5 parts by mass, oxides remain on the surface of the SmFeN-based anisotropic magnetic powder, resulting in a high oxygen concentration. If the amount exceeds 13.5 parts by mass, re-oxidation is likely to occur when exposed to air, and the cost tends to increase as the SmFeN-based anisotropic magnetic powder is dissolved. By setting the amount of acid to 3.5 parts by mass to 13.5 parts by mass per 100 parts by mass of SmFeN-based anisotropic magnetic powder, an Sm-rich layer oxidized to a degree that makes re-oxidation less likely when exposed to air after acid treatment can cover the surface of the SmFeN-based anisotropic magnetic powder, resulting in SmFeN-based anisotropic magnetic powder with a low oxygen concentration, small average particle size, and narrow particle size distribution.

[0052] In the acid treatment process, the SmFeN-based anisotropic magnetic powder obtained after acid treatment can have its moisture content reduced by methods such as decantation, if necessary.

[0053] [Dehydration process] It is preferable to include a dehydration step after the acid treatment step. Dehydration reduces the moisture content in the solid before vacuum drying, thereby suppressing the progression of oxidation during drying that occurs when the solid before vacuum drying contains more moisture. Here, dehydration refers to a process that reduces the moisture content of the solid after treatment relative to the solid before treatment by applying pressure or centrifugal force, and does not include simple decantation, filtration, or drying. The dehydration method is not particularly limited, but examples include pressing and centrifugal separation.

[0054] The amount of moisture contained in the SmFeN-based anisotropic magnetic powder after dehydration is not particularly limited, but it is preferably 13% by mass or less, and more preferably 10% by mass or less, from the standpoint of suppressing the progression of oxidation.

[0055] SmFeN-based anisotropic magnetic powder obtained by acid treatment, or SmFeN-based anisotropic magnetic powder obtained by dehydration treatment after acid treatment, is preferably vacuum dried. The drying temperature is not particularly limited, but is preferably 70°C or higher, and more preferably 75°C or higher. The drying time is also not particularly limited, but is preferably 1 hour or more, and more preferably 3 hours or more.

[0056] The obtained SmFeN-based anisotropic magnetic powder preferably contains Sm, Fe, La, W, R (where R is at least one selected from the group consisting of Ti, Ba, and Sr), has an average particle size of 2.0 μm or more and 4.0 μm or less, a remanent magnetization σr of 152 emu / g or more, and an oxygen content of 0.5% by mass or less.

[0057] The average particle size of SmFeN-based anisotropic magnetic powder can be, for example, 2.0 μm to 4.0 μm from the viewpoint of magnetic properties, and preferably 2.3 μm to 3.5 μm. Here, the average particle size refers to the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0058] The particle size D10 of the SmFeN-based anisotropic magnetic powder is preferably 0.5 μm or larger, and more preferably 1.0 μm or larger. Below 0.5 μm, the magnetization of the SmFeN-based anisotropic magnetic powder tends to decrease significantly. Here, D10 is the particle size corresponding to 10% of the cumulative volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0059] The particle size D50 of the SmFeN-based anisotropic magnetic powder is preferably 2.0 μm or more and 3.5 μm or less, and more preferably 2.5 μm or more and 3.2 μm or less. If the particle size is less than 2.0 μm, the amount of SmFeN-based anisotropic magnetic powder filling the sintered magnet becomes small, resulting in a decrease in magnetization. If it exceeds 3.5 μm, the magnetic powder tends to aggregate, reducing the magnetic properties. Here, D50 is the particle size that corresponds to 50% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0060] The particle size D90 of the SmFeN-based anisotropic magnetic powder is preferably 3.5 μm or more and 5.5 μm or less, and more preferably 4.0 μm or more and 5.0 μm or less. If the particle size is less than 3.5 μm, the amount of SmFeN-based anisotropic magnetic powder filling the sintered magnet becomes small, resulting in a decrease in magnetization, and if it exceeds 5.5 μm, the coercivity of the sintered magnet tends to decrease. Here, D90 refers to the particle size corresponding to 90% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0061] The remanent magnetization σr is 152 emu / g or higher, but 153 emu / g or higher is preferable.

[0062] The oxygen content in the SmFeN-based anisotropic magnetic powder is 0.5% by mass or less, preferably 0.4% by mass or less, and more preferably 0.35% by mass or less. If it exceeds 0.5% by mass, a large amount of oxygen will be present on the particle surface, causing the formation of α-Fe. The oxygen content analysis shall be performed after the SmFeN-based anisotropic magnetic powder obtained after all processes have been completed has been left in the air for 30 minutes or more.

[0063] The resulting SmFeN-based anisotropic magnetic powder is typically expressed by the following general formula: Sm v Fe (100-v―w-x-y-z) N w La x W y R z (In the equation, 3≦v≦30, 5≦w≦15, 0.05≦x≦0.3, 0.05≦y≦2.5, and 0.0001≦z≦0.3.) It is represented as follows.

[0064] In the general formula, v is defined as 3 or more and 30 or less because if it is less than 3, the unreacted portion of the iron component (α-Fe phase) separates, reducing the coercivity of the SmFeN-based anisotropic magnetic powder and rendering it unsuitable as a practical magnet. If it exceeds 30, the Sm element precipitates, making the SmFeN-based anisotropic magnetic powder unstable in the atmosphere and reducing the residual magnetic flux density. Furthermore, w is defined as 5 or more and 15 or less because if it is less than 5, almost no coercivity is produced, and if it exceeds 15, Sm and nitrides of iron itself are formed. x is defined as 0.05 or more and 0.3 or less because if it is less than 0.05, the effect of the addition is insufficient, and if it exceeds 0.3, Sm and nitrides of iron itself are formed, significantly reducing the magnetization. y is defined as 0.05 or more and 2.5 or less because if it is less than 0.05, the effect of the addition is insufficient, and if it exceeds 2.5, Sm and nitrides of iron itself are formed, significantly reducing the magnetization. The reason why z is defined as being between 0.0001 and 0.3 is that below 0.0001 the effect of the additive is insufficient, and above 0.3, Sm or nitrides of iron itself are formed, causing a significant decrease in magnetization.

[0065] From the viewpoint of residual magnetic flux density, the La content is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.15% by mass or more and 1% by mass or less.

[0066] From the viewpoint of coercivity, the W content is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.15% by mass or more and 1% by mass or less.

[0067] From the viewpoint of temperature characteristics, the R content is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less.

[0068] The nitrogen content is preferably between 3.3% by mass and 3.5% by mass. If it exceeds 3.5% by mass, it becomes hypernitrided, and if it is less than 3.3% by mass, it becomes insufficiently nitrided, and in both cases, the magnetic properties tend to deteriorate.

[0069] The following formula for SmFeN-based anisotropic magnetic powder Span = (D90 - D10) / D50 (Here, D10, D50, and D90 are the particle diameters corresponding to the integrated values of the particle size distribution based on volume being 10%, 50%, and 90% respectively.) The span defined by is 2 or less, preferably 1.8 or less, more preferably 1.6 or less, and particularly preferably 1.3 or less. When it exceeds 2, large particles are present, and the magnetic properties tend to deteriorate.)

[0070] The average value of the roundness of the SmFeN-based anisotropic magnetic powder is preferably 0.50 or more, more preferably 0.70 or more, and particularly preferably 0.75 or more. When the roundness is less than 0.50, the fluidity deteriorates, and stress is applied between particles during magnetic field forming, resulting in a decrease in magnetic properties. For the measurement of roundness, a scanning electron microscope (SEM) is used, and Sumitomo Metal Technology's Particle Analysis Ver. 3 is used as the image analysis software. The SEM image taken at 3000 times magnification is binarized by image processing, and the roundness is determined for each particle. The roundness defined in the present invention means the average value of the roundness obtained by measuring about 1000 to 10000 particles. Generally, as the number of particles with a small particle diameter increases, the roundness increases, so the roundness of particles of 1 μm or more was measured. In the measurement of roundness, the definition formula: roundness = (4πS / L 2 ) is used. However, S is the two-dimensional projected area of the particle, and L is the two-dimensional projected perimeter.)

[0071] [Mixing step with the modifier powder] In the mixing step, the dispersed SmFeN-based anisotropic magnetic powder and the modifier powder are mixed to obtain a mixed powder. Examples of the modifier powder include zinc, zinc alloy, or a combination thereof. The blending amount of the modifier powder is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less, based on the SmFeN-based anisotropic magnetic powder from the viewpoint of residual magnetization. The lower limit can be, for example, 1% by mass or more.)

[0072] If the zinc alloy is represented by Zn-M 2 then M 2The element can be selected from elements that, when alloyed with Zn (zinc), lower the melting point of the zinc alloy below the melting point of Zn, as well as unavoidable impurity elements. This improves sinterability in the pressure sintering process described later. 2 For example, Zn and M 2 Examples include elements that form eutectic alloys with such M 2 Typical examples include Sn, Mg, and Al, as well as combinations thereof. Sn is tin, Mg is magnesium, and Al is aluminum. Elements that do not cause melting point depression or impair the properties of the resulting product are also considered. 2 It can be selected as such. In addition, unavoidable impurity elements refer to impurities contained in the raw materials of the modifier powder, etc., whose inclusion cannot be avoided, or whose avoidance would lead to a significant increase in manufacturing costs.

[0073] Zn-M 2 In a zinc alloy represented by Zn and M 2 The proportion (molar ratio) of M relative to the entire zinc alloy should be determined appropriately so that the sintering temperature is suitable. 2 The ratio (molar ratio) may be, for example, 0.05 or more, 0.10 or more, or 0.20 or more, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0074] The particle size D50 (median diameter) of the modifier powder is not particularly limited, but may be 0.1 μm or more, 0.5 μm or more, 1 μm or more, or 2 μm or more, and may be 12 μm or less, 11 μm or less, 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, or 4 μm or less. The particle size D50 (median diameter) is measured, for example, by dry laser diffraction and scattering.

[0075] A low oxygen content in the modifier powder is preferable because it allows for greater absorption of oxygen from the SmFeN powder. From this viewpoint, the oxygen content of the modifier powder is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less, relative to the total amount of modifier powder. On the other hand, drastically reducing the oxygen content of the modifier powder leads to increased manufacturing costs. For this reason, the oxygen content of the modifier powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, relative to the total amount of modifier powder.

[0076] The method of mixing with the modifier powder is not particularly limited and includes mortars, muller wheel mixers, agitator mixers, mechanofusion, V-type mixers, and ball mills. These methods can also be combined. A V-type mixer is a device that has a container made of two cylindrical containers connected in a V shape, and by rotating the container, the powder inside the container is mixed by repeated aggregation and separation due to gravity and centrifugal force.

[0077] [Magnetic field forming process] In the magnetic field molding process, a magnetic field molded body is obtained by compressing and molding a mixed powder in a magnetic field. Magnetic field orientation can impart orientation to the magnetic field molded body, thereby imparting anisotropy to SmFeN-based rare earth magnets and improving their residual magnetization. The magnetic field molding method can be any well-known method, such as compressing and molding a mixed powder using a mold with a magnetic field generator installed around it. The molding pressure may be 10 MPa or more, 20 MPa or more, 30 MPa or more, 50 MPa or more, 100 MPa or more, or 150 MPa or more, and may be 1500 MPa or less, 1000 MPa or less, or 500 MPa or less. The magnitude of the applied magnetic field may be 500 kA / m or more, 1000 kA / m or more, 1500 kA / m or more, or 1600 kA / m or more, and may be 20000 kA / m or less, 15000 kA / m or less, 10000 kA / m or less, 5000 kA / m or less, 3000 kA / m or less, or 2000 kA / m or less. Methods for applying the magnetic field include applying a static magnetic field using an electromagnet and applying a pulsed magnetic field using alternating current.

[0078] [Pressure sintering process] In the pressure sintering process, the magnetic field molded body is pressure-sintered to obtain a sintered body. The method of pressure sintering is not particularly limited, and examples include preparing a die having a cavity and a punch that can slide inside the cavity, inserting the magnetic field molded body into the cavity, and sintering the magnetic field molded body while applying pressure to it with the punch. The pressure sintering conditions can be appropriately selected so that the magnetic field molded body can be sintered (hereinafter sometimes referred to as "pressure sintering") while applying pressure to it. If the sintering temperature is 300°C or higher, the Fe on the particle surface of the SmFeN-based anisotropic magnetic powder and the modifier powder (for example, metallic zinc) slightly interdiffuse within the magnetic field molded body, contributing to sintering. The sintering temperature may be, for example, 310°C or higher, 320°C or higher, 340°C or higher, or 350°C or higher. On the other hand, if the sintering temperature is 400°C or lower, the Fe on the particle surface of the SmFeN-based anisotropic magnetic powder and the modifier powder will not excessively interdiffuse, which will not interfere with the heat treatment process described later or adversely affect the magnetic properties of the resulting sintered body. From these viewpoints, the sintering temperature may be 400°C or lower, 390°C or lower, 380°C or lower, or 370°C or lower.

[0079] Regarding the sintering pressure, a sintering pressure that can increase the density of the sintered body can be appropriately selected. Typically, the sintering pressure may be 100 MPa or more, 200 MPa or more, 400 MPa or more, 600 MPa or more, 800 MPa or more, or 1000 MPa or more, and may be 2000 MPa or less, 1800 MPa or less, 1600 MPa or less, 1500 MPa or less, 1300 MPa or less, or 1200 MPa or less.

[0080] The sintering time can be appropriately determined so that the Fe on the particle surface of the SmFeN-based anisotropic magnetic powder and the metallic zinc of the modifier powder slightly interdiffuse. Note that the heating time to reach the heat treatment temperature is not included in the sintering time. The sintering time may be, for example, 1 minute or more, 2 minutes or more, or 3 minutes or more, and may be 30 minutes or less, 20 minutes or less, 10 minutes or less, or 5 minutes or less.

[0081] After the sintering time has elapsed, the sintered body is cooled to complete the sintering process. A faster cooling rate helps to suppress oxidation of the sintered body. The cooling rate may be, for example, 0.5°C / second or more and 200°C / second or less. For the sintering atmosphere, an inert gas atmosphere is preferred in order to suppress oxidation of the magnetically molded body and the sintered body. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0082] [Heat treatment process] In the heat treatment process, the sintered body is heat-treated. The heat treatment causes a film-like Fe-Zn alloy phase to form on the surface of the SmFeN-based anisotropic magnetic powder particles, further strengthening the bond between the SmFeN-based anisotropic magnetic powder particles and the modifier powder particles (hereinafter sometimes referred to as "solidification"), while simultaneously promoting modification. If the heat treatment temperature is 350°C or higher, the Fe-Zn alloy phase is appropriately formed on almost the entire surface of the particles, enabling solidification and modification. The heat treatment temperature may also be 360°C or higher, 370°C or higher, or 380°C or higher.

[0083] The magnetic phase in SmFeN-based anisotropic magnetic powder is Th2Zn 17 Type and / or Th2Ni 17 The sintered body has a specific crystalline structure, and the formation of the Fe-Zn alloy phase saturates after a heat treatment time of 40 hours. From the viewpoint of economic efficiency (shorter treatment time), the heat treatment time is preferably 40 hours or less, 35 hours or less, 30 hours or less, 25 hours or less, or 24 hours or less. To suppress oxidation of the sintered body, it is preferable to heat treat the sintered body in a vacuum or in an inert gas atmosphere. Here, the inert gas atmosphere includes a nitrogen gas atmosphere. The heat treatment of the sintered body may be carried out in the mold used for pressure sintering, but no pressure is applied to the sintered body during the heat treatment. As a result, if the above heat treatment conditions are satisfied, a normal magnetic phase and an Fe-Zn alloy phase are appropriately formed, and there is no excessive interdiffusion between Fe and Zn. [Examples]

[0084] Examples are described below. Unless otherwise specified, "%" refers to mass.

[0085] [evaluation] The content of each metal, average particle size, particle size distribution, nitrogen content, oxygen content, and remanent magnetization σr of SmFeN-based anisotropic magnetic powder were evaluated using the following methods.

[0086] <Content of each metal> The content of each metal (Sm, Fe, W, etc.) in SmFeN-based anisotropic magnetic powder was measured by dissolving it in hydrochloric acid and using the ICP-AES method (instrument name: Optima8300).

[0087] <Average particle size and particle size distribution> The average particle size and particle size distribution of SmFeN-based anisotropic magnetic powder were measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS from Nippon Laser Co., Ltd.).

[0088] <Circularity> The circularity coefficient was calculated by binarizing SEM images of SmFeN-based anisotropic magnetic powder, taken at 3000x magnification, using image processing software (Sumitomo Metal Technology Co., Ltd. Particle Analysis Ver3).

[0089] <Nitrogen content and oxygen content> The nitrogen and oxygen content of the SmFeN-based anisotropic magnetic powder was measured by the thermal conductivity method (EMGA-820, manufactured by Horiba, Ltd.).

[0090] <Remanent magnetization σr, coercivity iHc, and aspect ratio Hk> The obtained SmFeN-based anisotropic magnetic powder was packed into a sample container with paraffin wax, the paraffin wax was melted using a dryer, and then its easy magnetization domains were aligned using an orientation magnetic field of 16 kA / m. This magnetically oriented sample was pulse-magnetized with a magnetization magnetic field of 32 kA / m, and the remanent magnetization σr, coercivity iHc, and angularity ratio Hk were measured using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m.

[0091] Manufacturing Example 1 [Precipitation process] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O, 0.035 kg of La2O, 0.006 kg of titanium dioxide, and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final Fe concentration to 0.726 mol / L and the Sm concentration to 0.112 mol / L, thus obtaining the SmFeLaTi sulfuric acid solution.

[0092] To 20 kg of pure water maintained at 40°C, the entirety of the prepared SmFeLaTi sulfuric acid solution was added dropwise with stirring over 70 minutes from the start of the reaction, while simultaneously adding 0.190 kg of 15% by mass ammonia solution and 13% by mass ammonium tungstate solution dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLaWTi hydroxide. After washing with pure water by decantation, the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0093] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFeLaWTi oxide was obtained as the raw material powder.

[0094] [Pre-treatment process] 100 g of SmFeLaWTi oxide was placed in a steel container to a thickness of 10 mm. The container was placed in a furnace, the pressure was reduced to 100 Pa, and then the temperature was raised to the pretreatment temperature of 850°C while introducing hydrogen gas, and it was held at that temperature for 15 hours. The oxygen concentration was measured by non-dispersive infrared absorption spectroscopy (ND-IR) (EMGA-820, Horiba, Ltd.) and was found to be 5 mass%. This indicates that the oxygen bonded to Sm was not reduced, while 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0095] [Reduction Process] 60 g of partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle size of approximately 6 mm were mixed and placed in the furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1060°C and held for 45 minutes to obtain SmFeLaWTi alloy particles.

[0096] [Nitriding process] Next, the furnace temperature was cooled to 100°C, then the system was evacuated, and while introducing nitrogen gas, the temperature was raised to the first temperature of 430°C and held for 3 hours. Subsequently, the temperature was raised to the second temperature of 520°C and held for 1 hour, after which it was cooled to obtain a massive product containing magnetic particles.

[0097] [Post-processing steps] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated twice. After solid-liquid separation, the mixture was vacuum-dried at 80°C for 3 hours to obtain SmFeN-based anisotropic magnetic powder.

[0098] [Acid treatment process] To 100 parts by mass of the powder obtained in the post-processing step, a 6% hydrochloric acid aqueous solution was added to obtain 4.3 parts by mass of hydrogen chloride, and the mixture was stirred for 1 minute. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated twice. After solid-liquid separation, the mixture was vacuum-dried at 80°C for 3 hours to obtain SmFeN-based anisotropic magnetic powder.

[0099] Manufacturing Example 2 [Precipitation process] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O, 0.035 kg of La2O, 0.010 kg of strontium carbonate, and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus obtaining the SmFeLaSr sulfuric acid solution.

[0100] To 20 kg of pure water maintained at 40°C, the entirety of the prepared SmFeLaSr sulfuric acid solution was added dropwise with stirring over 70 minutes from the start of the reaction, while simultaneously adding 0.190 kg of 15% by mass ammonia solution and 13% by mass ammonium tungstate solution dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLaWSr hydroxide. After washing with pure water by decantation, the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0101] The oxidation process, pretreatment process, reduction process, nitriding process, posttreatment process, and acid treatment process were carried out in the same manner as in Production Example 1.

[0102] Manufacturing Example 3 [Precipitation process] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O, 0.035 kg of La2O, 0.014 kg of barium carbonate, and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus obtaining the SmFeLaBa sulfuric acid solution.

[0103] To 20 kg of pure water maintained at 40°C, the entirety of the prepared SmFeLaBa sulfuric acid solution was added dropwise with stirring over 70 minutes from the start of the reaction, while simultaneously adding 0.190 kg of 15% by mass ammonia solution and 13% by mass ammonium tungstate solution dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLaWBa hydroxide. After washing with pure water by decantation, the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0104] The oxidation process, pretreatment process, reduction process, nitriding process, posttreatment process, and acid treatment process were carried out in the same manner as in Production Example 1.

[0105] Manufacturing Example 4 [Precipitation process] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O, 0.035 kg of La2O, and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus obtaining the SmFeLa sulfuric acid solution.

[0106] The entirety of the prepared SmFeLa sulfuric acid solution was added dropwise to 20 kg of pure water maintained at 40°C, while stirring for 70 minutes from the start of the reaction. Simultaneously, 15% by mass ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. After washing with pure water by decantation, the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0107] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFeLa oxide was obtained as the raw material powder.

[0108] [Pre-treatment process] 100 g of SmFeLa oxide was placed in a steel container to a thickness of 10 mm. The container was placed in a furnace, the pressure was reduced to 100 Pa, and then the temperature was raised to the pretreatment temperature of 850°C while introducing hydrogen gas, and it was held at that temperature for 15 hours. The oxygen concentration was measured by non-dispersive infrared absorption spectroscopy (ND-IR) (EMGA-820, Horiba, Ltd.) and was found to be 5 mass%. This indicates that the oxygen bonded to Sm was not reduced, while 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0109] [Reduction Process] 60 g of partial oxide obtained in the pretreatment step and 19.2 g of metallic calcium with an average particle size of approximately 6 mm were mixed and placed in the furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The mixture was raised to a first temperature of 1045°C and held for 45 minutes, and then cooled to a second temperature of 1000°C and held for 30 minutes to obtain SmFeLa alloy particles.

[0110] [Nitriding process] Next, the furnace temperature was cooled to 100°C, then the system was evacuated and nitrogen gas was introduced while the temperature was raised to the first temperature of 430°C and held for 3 hours. Subsequently, the temperature was raised to the second temperature of 500°C and held for 1 hour, after which it was cooled to obtain a massive product containing magnetic particles.

[0111] [Post-processing steps] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated twice. After solid-liquid separation, the mixture was vacuum-dried at 80°C for 3 hours to obtain SmFeN-based anisotropic magnetic powder.

[0112] Manufacturing Example 5 [Precipitation process] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O, 0.035 kg of La2O, and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus obtaining the SmFeLa sulfuric acid solution.

[0113] To 20 kg of pure water maintained at 40°C, the entirety of the prepared SmFeLa sulfuric acid solution and 0.14 kg of 18% by mass ammonium tungstate solution were added dropwise over 70 minutes from the start of the reaction while stirring. Simultaneously, 15% by mass ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLaW hydroxide. After washing with pure water by decantation, the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0114] Except for the omission of the final acid treatment step, the oxidation, pretreatment, reduction, nitriding, and posttreatment steps were carried out in the same manner as in Production Example 1.

[0115] Example 1 [Dispersion process] The SmFeN-based anisotropic magnetic powder obtained in Production Example 1 was placed in a container used for a vibratory mill, with the SmFeN-based anisotropic magnetic powder and media (iron core nylon media, 10 mm in diameter, Vickers constant of nylon coating of 7, specific gravity of 7.48, nylon layer thickness of approximately 1-3 mm) making up 5 volume% of the container's volume. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0116] Example 2 [Dispersion process] In a container used for a vibratory mill, the SmFeN-based anisotropic magnetic powder obtained in Production Example 2 was placed in a volume of 5 vol%, and the media (iron core nylon media, 10 mm in diameter, Vickers constant of nylon coating of 7, specific gravity of 7.48, nylon layer thickness of approximately 1-3 mm) was placed in a volume of 60 vol%, respectively. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0117] Example 3 [Dispersion process] The SmFeN-based anisotropic magnetic powder obtained in Production Example 3 was placed in a container used for a vibratory mill, with the SmFeN-based anisotropic magnetic powder and media (iron core nylon media, 10 mm in diameter, Vickers constant of nylon coating of 7, specific gravity of 7.48, nylon layer thickness of approximately 1-3 mm) making up 5 volume% of the container's volume. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0118] Comparative Example 1 The SmFeN-based anisotropic magnetic powder obtained in Production Example 4 was placed in a container used for a vibratory mill, with the SmFeN-based anisotropic magnetic powder and media (chromium steel balls; SUJ2, diameter 2.3 mm, Vickers constant 760, specific gravity 7.77) making up 5% by volume of the container's volume. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0119] Comparative Example 2 The SmFeN-based anisotropic magnetic powder obtained in Production Example 5 was placed in a container used for a vibratory mill, with the SmFeN-based anisotropic magnetic powder and media (chromium steel balls; SUJ2, diameter 2.3 mm, Vickers constant 760, specific gravity 7.77) making up 5% by volume relative to the container's volume. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0120] Comparative Example 3 The SmFeN-based anisotropic magnetic powder obtained in Production Example 4 was placed in a container used for a vibratory mill, with the SmFeN-based anisotropic magnetic powder and media (made of nylon, 10 mm in diameter, Vickers constant 7, specific gravity 1.13) making up 5% by volume relative to the container's volume. The mixture was dispersed in a nitrogen atmosphere for 60 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0121] Table 1 shows the results of measuring the average particle size, particle size distribution, circularity, remanent magnetization σr, coercivity iHc, squareness ratio Hk, oxygen concentration, and nitrogen concentration of the SmFeN-based anisotropic magnetic powders obtained in Examples 1-3 and Comparative Examples 1-3 using the method described above. Table 2 shows the results of measuring the content of each metal, and Table 3 shows the compositional formula. In addition, the magnetic powders obtained in Examples 1-3 and Comparative Examples 1 and 2 were imaged using a scanning electron microscope (SU3500, Hitachi High-Technologies 5KV 5000x). The results are shown in Figures 1-5.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] In Examples 1-3, where an iron core coated with nylon resin was used as the media for dispersion, the residual magnetic flux density was higher compared to Comparative Examples 1 and 2, where chromium steel balls not coated with resin were used as the media, and Comparative Example 3, where nylon resin was used as the media for dispersion. Furthermore, while Comparative Examples 1 and 2 had a large number of fine magnetic powder particles, as shown in Figures 4 and 5, Examples 1-3 had relatively few, as shown in Figures 1 to 3.

[0126] (Fabrication of SmFeN-based rare earth magnets) SmFeN-based rare earth magnets were fabricated using the SmFeN-based anisotropic magnetic powders obtained in Examples 1-3 and Comparative Examples 1-3, following the procedure below.

[0127] [Mixing process with modifier powder] Metallic zinc powder was prepared as the modifier powder. 50 The particle size was 0.5 μm. Furthermore, the purity of the metallic zinc powder was 99.9% by mass.

[0128] The SmFeN-based anisotropic magnetic powders obtained in Examples 1-3 and Comparative Examples 1-3 were mixed with the modifier powder to obtain a mixed powder. The amount of metallic zinc mixed into the mixed powder was 5% by mass.

[0129] [Magnetic field forming process] A magnetic field molded body was obtained by compressing a mixed powder in a magnetic field. The compression pressure was 50 MPa. The applied magnetic field was 1600 kA / m.

[0130] [Pressure sintering process] A magnetic field molded body was pressure-sintered to obtain a sintered body. The pressure-sintering conditions were a sintering temperature of 400°C, a sintering pressure of 1500 MPa, and a sintering time of 5 minutes.

[0131] [Heat treatment process] SmFeN-based rare earth magnets were obtained by heat treatment of the sintered body. The heat treatment conditions were a vacuum atmosphere, a heat treatment temperature of 380°C, and a heat treatment time of 24 hours.

[0132] The magnetic properties of the obtained SmFeN-based rare-earth magnets were measured. The magnetic properties were measured at room temperature using a vibrating sample magnetometer (VSM). The results are shown in Table 4.

[0133] [Table 4]

[0134] Table 4 shows that in Examples 1-3, where an iron core coated with nylon resin was used as the media for dispersion, the residual magnetization and coercivity of the SmFeN-based rare earth magnet were higher compared to Comparative Examples 1 and 2, where an uncoated chromium steel ball was used as the media for dispersion, and Comparative Example 3, where nylon resin was used as the media for dispersion.

Claims

1. A step of obtaining dispersed SmFeN-based anisotropic magnetic powder by dispersing SmFeN-based anisotropic magnetic powder containing Sm, Fe, La, W, R (where R is at least one selected from the group consisting of Ti, Ba, and Sr), and N using a resin-coated metal or ceramic medium, The process involves mixing the dispersed SmFeN-based anisotropic magnetic powder with the modifier powder to obtain a mixed powder. The process involves compressing and molding the aforementioned mixed powder in a magnetic field to obtain a magnetic field molded body, A method for manufacturing an SmFeN-based rare earth magnet, comprising the steps of: pressurizing and sintering the magnetic field molded body to obtain a sintered body; and heat-treating the sintered body.

2. The method for producing an SmFeN-based rare earth magnet according to claim 1, wherein the dispersed SmFeN-based anisotropic magnetic powder has an average particle size of 2.0 μm or more and 4.0 μm or less, a remanent magnetization σr of 152 emu / g or more, and an oxygen content of 0.5% by mass or less.

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