SmFeN-based anisotropic magnetic powder and bonded magnets, and methods for manufacturing the same.

Abstract

The present invention provides: an SmFeN-based anisotropic magnetic powder which exhibits excellent magnetic characteristics, while having a low oxygen content; and a method for producing this SmFeN-based anisotropic magnetic powder. The present invention provides a method for producing an SmFeN-based anisotropic magnetic powder, the method comprising: a step for preparing an SmFeN-based anisotropic magnetic powder before dispersion, the powder containing Sm, Fe and N; and a step for dispersing the SmFeN-based anisotropic magnetic powder before dispersion with use of metal media that are covered with a resin or ceramic media that are covered with a resin. The present invention also provides an SmFeN-based anisotropic magnetic powder which contains Sm, Fe and N, while having an average particle diameter of 2.5 μm to 5 μm, a remanent magnetization σr of 150 emu / g or more, and an oxygen content of 0.4% by mass or less.

Description

[Technical Field]

[0001] This disclosure relates to SmFeN-based anisotropic magnetic powders and bonded magnets, as well as methods for manufacturing them. [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, using a hard ceramic media may generate fine particles due to chipping, which could increase the oxygen content of the SmFeN-based anisotropic magnetic powder obtained after grinding and degrade its magnetic properties. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-195326 [Overview of the project] [Problems that the invention aims to solve]

[0004] One embodiment of the present disclosure aims to provide a SmFeN-based anisotropic magnetic powder and a method for producing the same, which has excellent magnetic properties and low oxygen content. Another embodiment of the present disclosure aims to provide a bonded magnet and a method for producing the same, which uses such a SmFeN-based anisotropic magnetic powder. [Means for solving the problem]

[0005] A method for producing SmFeN-based anisotropic magnetic powder according to one embodiment of the present disclosure includes the steps of: preparing a SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N before dispersion; and dispersing the SmFeN-based anisotropic magnetic powder before dispersion using a resin-coated metal medium or a resin-coated ceramic medium.

[0006] A method for manufacturing a bonded magnet according to one embodiment of the present disclosure includes the steps of obtaining SmFeN-based anisotropic magnetic powder by the above-described manufacturing method and mixing the SmFeN-based anisotropic magnetic powder with a resin.

[0007] The SmFeN-based anisotropic magnetic powder according to one embodiment of the present disclosure contains Sm, Fe, and N, has an average particle size of 2.5 μm or more and 5 μm or less, a remanent magnetization σr of 150 emu / g or more, and an oxygen content of 0.4% by mass or less.

[0008] A bonded magnet according to one embodiment of the present disclosure comprises the above-mentioned SmFeN-based anisotropic magnetic powder and a resin. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, a SmFeN-based anisotropic magnetic powder and a method for producing the same can be provided, which have excellent magnetic properties and low oxygen content. Furthermore, according to one embodiment of the present disclosure, a bonded magnet and a method for producing the same can be provided, which uses such a SmFeN-based anisotropic magnetic powder. [Brief explanation of the drawing]

[0010] [Figure 1] This is an SEM image of the magnetic powder prepared in Example 1. [Figure 2] This is an SEM image of the magnetic powder prepared in Example 2. [Figure 3] This is an SEM image of the magnetic powder prepared in Comparative Example 1. [Figure 4] This is an SEM image of the magnetic powder prepared in Comparative Example 2. [Modes for carrying out the invention]

[0011] 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.

[0012] The method for producing SmFeN-based anisotropic magnetic powder according to this embodiment includes a step of dispersing SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N using a resin-coated metal medium or a resin-coated ceramic medium. The method for producing SmFeN-based anisotropic magnetic powder according to this embodiment includes a step of preparing SmFeN-based anisotropic magnetic powder before dispersion containing Sm, Fe, and N, and in the dispersion step, dispersing this SmFeN-based anisotropic magnetic powder before dispersion using the medium.

[0013] [Dispersion process] In the dispersion process, SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N is dispersed using a resin-coated metal or resin-coated ceramic media. Dispersion here means that aggregated particles produced by sintering or magnetic aggregation contained in the SmFeN-based anisotropic magnetic powder separate into single particles or particles composed of a small number of particles (hereinafter also referred to as "single particles"). According to this embodiment, when a resin-coated metal or resin-coated ceramic media collides with the SmFeN-based anisotropic magnetic powder, the collision energy is smaller compared to when an uncoated metal or uncoated ceramic media collides with the SmFeN-based anisotropic magnetic powder, so dispersion is more likely to occur than pulverization. Conventionally, when SmFeN-based anisotropic magnetic powder is pulverized, the average particle size becomes significantly smaller, and fine particles are also generated due to chipping, which easily leads to a decrease in magnetic properties. Furthermore, highly active new surfaces are created in the fine particles and the original parts that generated the fine particles, making oxidation more likely and increasing the oxygen content. On the other hand, as in this embodiment, when dispersion is performed, the resulting single particles tend to orient themselves in a magnetic field, thus improving their magnetic properties. Furthermore, the generation of new surfaces associated with the formation of fine particles can be suppressed compared to pulverization, which is thought to make it less likely for the oxygen content to increase.

[0014] For example, a vibratory mill can be used as a dispersion device in the dispersion process. The media used in dispersion devices such as vibratory mills may be metal coated with resin, and examples of the material of the metal include iron, chromium steel, stainless steel, and steel. Alternatively, the media used in dispersion devices such as vibratory mills may be ceramics coated with resin, and examples of the material of the ceramics include inorganic compounds such as metal or nonmetal oxides, carbides, nitrides, and borides, 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 resin-coated iron or chromium steel media in the dispersion device.

[0015] 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. As the thermoplastic resin, it is preferable to use nylon such as nylon 6, nylon 66, and nylon 12. 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.

[0016] The specific gravity of the media 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 media used in the dispersion process may be 6 or more and 7.5 or less. The media coated with resin can be said to have, in other words, a core of metal or ceramics 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 media 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.

[0017] The dispersion process can 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 etc.) contained in the solvent.

[0018] 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 vol% or more, preferably 95 vol% or more. The concentration of argon in the argon gas atmosphere may be 90 vol% or more, preferably 95 vol% 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 vol% or more, preferably 95 vol% or more.

[0019] The diameter of the media 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 media is large, the contact with the powder decreases, and dispersion tends to be difficult to occur.

[0020] 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 media, and the amount of SmFeN-based anisotropic magnetic powder can be set to 3% to 20% of the volume, with 5% to 20% of the volume being preferred.

[0021] [Preparation process] The process includes a step of preparing the SmFeN-based anisotropic magnetic powder before dispersion. The step of preparing the SmFeN-based anisotropic magnetic powder before dispersion is, for example, a step of manufacturing the SmFeN-based anisotropic magnetic powder. The SmFeN-based anisotropic magnetic powder before dispersion used in the dispersion process can be manufactured by referring to, for example, the methods disclosed in Japanese Patent Publication No. 2017-117937 and Japanese Patent Publication No. 2021-055188, but an example of a method for manufacturing the SmFeN-based anisotropic magnetic powder before dispersion is described below. Note that the SmFeN-based anisotropic magnetic powder before dispersion is the magnetic powder before the dispersion process using the aforementioned resin-coated metal media or resin-coated ceramic media, and may undergo other pre-dispersion steps.

[0022] The SmFeN-based anisotropic magnetic powder used in the dispersion process can be produced by a manufacturing method that includes a pretreatment step of obtaining a partial oxide by heat-treating an oxide containing Sm and Fe in a reducing gas-containing atmosphere, a step of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent, a step of nitriding the alloy particles to obtain nitrides, and a step of washing the nitrides to obtain the SmFeN-based anisotropic magnetic powder before dispersion.

[0023] The oxide containing Sm and Fe used in the pretreatment step may be prepared by mixing Sm oxide and Fe oxide, or it can be prepared by mixing a solution containing Sm and Fe with a precipitating agent to obtain a precipitate containing Sm and Fe (precipitation step), and then calcining the precipitate to obtain an oxide containing Sm and Fe (oxidation step).

[0024] [Precipitation process] In the precipitation process, the Sm and Fe raw materials are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. (Sm2Fe) 17 When obtaining 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. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, and Lu may be added to the above solution. In terms of residual magnetic flux density, it is preferable to include La. In terms of coercivity and angular ratio, it is preferable to include W. In terms of temperature characteristics, it is preferable to include Co and Ti.

[0025] The Sm and Fe raw materials are not limited as long as they can dissolve in a strongly acidic solution. For example, in terms of availability, samarium oxide can be used as the Sm raw material and FeSO4 as the Fe raw material. The concentration of the solution containing Sm and Fe can be adjusted as appropriate within the range in which the Sm and Fe raw materials are substantially soluble in the acidic solution. In terms of solubility, sulfuric acid can be used as an acidic solution.

[0026] An insoluble precipitate containing Sm and Fe is obtained by reacting a solution containing Sm and Fe with a precipitating agent. Here, the solution containing Sm and Fe only needs to be a solution containing Sm and Fe when reacted with the precipitating agent. For example, the raw materials containing Sm and Fe may be prepared as separate solutions, and each solution may be added dropwise to react with the precipitating agent. Even when preparing separate solutions, the solutions should be adjusted appropriately so that each raw material is substantially soluble in the acidic solution. The precipitating agent is not limited to any alkaline solution that reacts with a solution containing Sm and Fe to produce a precipitate, and examples include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0027] The precipitation reaction is preferably carried out by dropwise adding a solution containing Sm and Fe and a precipitant to a solvent such as water, as this allows for easy adjustment of the particle properties of the precipitate. By appropriately controlling the supply rate of the solution containing Sm and Fe 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 uniform powder shape can be obtained. Using such a precipitate improves the magnetic properties of the final product, SmFeN-based anisotropic magnetic powder. 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.

[0028] The solution containing Sm and Fe is preferably further containing one or more metals selected from the group consisting of La, W, Co, and Ti, in terms of magnetic properties. For example, it is preferable to include La in terms of residual magnetic flux density, W in terms of coercivity and angular ratio, and Co and Ti in terms of temperature properties. The La raw material is not limited as long as it can be dissolved in a strongly acidic solution, for example, La2O3 and LaCl3 can be used in terms of availability. The solution is appropriately adjusted so that the La, W, Co and Ti raw materials, along with the Sm and Fe raw materials, are substantially soluble in an acidic solution, and sulfuric acid is a good example of an acidic solution in terms of solubility. Ammonium tungstate can be used as a W raw material, cobalt sulfate as a Co raw material, and titania sulfate as a Ti raw material.

[0029] If a solution containing Sm and Fe further contains one or more metals selected from the group consisting of La, W, Co, and Ti, an insoluble precipitate is obtained containing Sm, Fe, and one or more metals selected from the group consisting of La, W, Co, and Ti. Here, the solution only needs to contain one or more metals selected from the group consisting of La, W, Co, and Ti when reacting with the precipitating agent. For example, each raw material may be prepared as a separate solution, and each solution may be added dropwise to react with the precipitating agent, or it may be prepared together with the solution containing Sm and Fe.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] [Oxidation process] The oxidation process involves calcining the precipitate formed in the precipitation process to obtain an oxide containing Sm and Fe. For example, the precipitate can be converted into an oxide 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.

[0034] 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.

[0035] 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.

[0036] [Pre-treatment process] The pretreatment step is a process in which the oxide containing Sm and Fe, as described above, is heat-treated in a reducing gas-containing atmosphere to obtain a partial oxide in which a portion of the oxide has been reduced.

[0037] 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).

[0038] 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 and Fe 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 adjust the dew point in the reaction furnace to -10°C or lower.

[0039] [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. From the viewpoint of magnetic properties, the heat treatment temperature is preferably 920°C to 1200°C, more preferably 950°C to 1150°C, and even more preferably 980°C to 1100°C.

[0040] As a heat treatment separate from the heat treatment described above in the reduction process, the material may be heat-treated at a first temperature of 1000°C to 1090°C, followed by a second temperature lower than the first temperature, between 980°C and 1070°C. The first temperature is preferably between 1010°C and 1080°C, and the second temperature is preferably between 990°C and 1060°C. The temperature difference between the first and second temperatures is preferably such that the second temperature is 15°C to 60°C lower than the first temperature, and more preferably between 15°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.

[0041] 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.

[0042] 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.

[0043] [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 in a nitrogen atmosphere and nitriding without the need for grinding, thus enabling uniform nitriding.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] [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.

[0051] [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.

[0052] 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.

[0053] 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.

[0054] [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 this disclosure, 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.

[0055] 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.

[0056] 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 is less likely to re-oxidize 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.

[0057] 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.

[0058] [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.

[0059] 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.

[0060] 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.

[0061] [Surface treatment process] Surface treatment may be performed on the SmFeN-based anisotropic magnetic powder obtained in the post-processing step. For example, a phosphoric acid solution may be added as a surface treatment agent to the magnetic particle solids obtained in the nitriding step at a rate of 0.10 to 10% by mass as PO4. The surface-treated SmFeN-based anisotropic magnetic powder can be obtained by separating it from the solution and drying it as appropriate.

[0062] A SmFeN-based anisotropic magnetic powder according to one aspect of this disclosure is characterized by containing Sm, Fe, and N, having an average particle size of 2.5 μm or more and 5 μm or less, a remanent magnetization σr of 150 emu / g or more, and an oxygen content of 0.4% by mass or less.

[0063] The average particle size of SmFeN-based anisotropic magnetic powder is between 2.5 μm and 5 μm, but preferably between 2.6 μm and 4.5 μm. Below 2.5 μm, oxidation is likely to occur due to the large surface area, and above 5 μm, the SmFeN-based anisotropic magnetic powder tends to develop a multi-domain structure, resulting in a decrease in magnetic properties. Here, the average particle size refers to the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0064] The particle size D10 of the SmFeN-based anisotropic magnetic powder is preferably 0.5 μm or more and 3 μm or less, and more preferably 1 μm or more and 2 μm or less. If the particle size is less than 0.5 μm, the amount of SmFeN-based anisotropic magnetic powder filling the bonded magnet becomes small, resulting in a decrease in magnetization. On the other hand, if the particle size exceeds 3 μm, the coercivity of the bonded magnet tends to decrease. Here, D10 is the particle size that corresponds to 10% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0065] The D50 of the SmFeN-based anisotropic magnetic powder is preferably 2 μm or more and 5 μm or less, more preferably 2.5 μm or more and 4.5 μm or less. If it is less than 2 μm, the filling amount of the SmFeN-based anisotropic magnetic powder in the bonded magnet becomes small, resulting in a decrease in magnetization. If it exceeds 5 μm, the coercive force of the bonded magnet tends to decrease. Here, D50 is the particle size corresponding to 50% of the integrated value of the particle size distribution based on the volume of the SmFeN-based anisotropic magnetic powder.

[0066] The D90 of the SmFeN-based anisotropic magnetic powder is preferably 3 μm or more and 7 μm or less, more preferably 4.5 μm or more and 6.5 μm or less. If it is less than 3 μm, the filling amount of the SmFeN-based anisotropic magnetic powder in the bonded magnet becomes small, resulting in a decrease in magnetization. If it exceeds 7 μm, the coercive force of the bonded magnet tends to decrease. Here, D90 is the particle size corresponding to 90% of the integrated value of the particle size distribution based on the volume of the SmFeN-based anisotropic magnetic powder.

[0067] The residual magnetization σr is 150 emu / g or more, preferably 151 emu / g or more.

[0068] The oxygen content contained in the SmFeN-based anisotropic magnetic powder is 0.4 mass% or less, preferably 0.38 mass% or less, more preferably 0.3 mass% or less, and particularly preferably 0.25 mass% or less. If it exceeds 0.4 mass%, there is a lot of oxygen on the particle surface, which causes the formation of α-Fe. The analysis of the oxygen content shall be carried out after leaving the SmFeN-based anisotropic magnetic powder obtained after all processes in the atmosphere for 30 minutes or more.

[0069] The SmFeN-based anisotropic magnetic powder in this embodiment typically has the following general formula Sm v Fe (100-v―w-x-y-z-u) N w La x W y Co z Ti u (In the formula, 3 ≤ v ≤ 30, 5 ≤ w ≤ 15, 0 ≤ x ≤ 0.3, 0 ≤ y ≤ 2.5, 0 ≤ z ≤ 2.5, 0 ≤ u ≤ 2.5.)

[0070] In the general formula, v is defined as being between 3 and 30 because, if it is less than 3, the unreacted portion of the iron component (α-Fe phase) separates, reducing the coercivity of the SmFeN anisotropic magnetic powder and rendering it unsuitable as a practical magnet. If it exceeds 30, Sm elements precipitate, making the SmFeN anisotropic magnetic powder unstable in the atmosphere and reducing the residual magnetic flux density. Similarly, w is defined as being between 5 and 15 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.

[0071] If La is included, 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, from the viewpoint of residual magnetic flux density.

[0072] When W is included, 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, from the viewpoint of coercivity and angular ratio.

[0073] When Co is included, from the viewpoint of temperature characteristics, the Co 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.

[0074] If Ti is included, the Ti 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, from the viewpoint of temperature characteristics.

[0075] 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.

[0076] Among these, SmFeN, SmFeLaN, SmFeLaWN, and SmFeLaCoN are preferred.

[0077] The following formula for SmFeN-based anisotropic magnetic powder Span = (D90 - D10) / D50 (Here, D10, D50, and D90 represent particle sizes corresponding to 10%, 50%, and 90% of the cumulative particle size distribution based on volume, respectively.) The span defined by is preferably 1.6 or less, and more preferably 1.3 or less. If it exceeds 1.6, large particles are present, and the magnetic properties tend to deteriorate.

[0078] The average circularity of SmFeN-based anisotropic magnetic powder is preferably 0.50 or higher, more preferably 0.70 or higher, and particularly preferably 0.75 or higher. If the circularity falls below 0.50, the fluidity deteriorates, causing stress between particles during magnetic field shaping, which reduces the magnetic properties. For measuring circularity, a scanning electron microscope (SEM) is used, and Sumitomo Metal Technology's Particle Analysis Ver.3 is used as the image analysis software. SEM images taken at 3000x magnification are binarized by image processing, and the circularity is determined for each particle. The circularity defined in this disclosure refers to the average circularity obtained by measuring approximately 1000 to 10000 particles. Generally, the circularity increases as there are more particles with smaller diameters, so the circularity was measured for particles of 1 μm or larger. The definition formula for measuring circularity is: Circularity = (4πS / L 2 ) is used, where S is the two-dimensional projected area of ​​the particle and L is the two-dimensional projected perimeter.

[0079] The SmFeN-based anisotropic magnetic powder of this embodiment has high remanent magnetization and can therefore be used, for example, as a sintered magnet or a bonded magnet.

[0080] Bonded magnets are made from the SmFeN-based anisotropic magnetic powder of this embodiment and a resin. By including this SmFeN-based anisotropic magnetic powder, a composite material with high magnetic properties can be constructed. The method for manufacturing bonded magnets includes the steps of obtaining SmFeN-based anisotropic magnetic powder by the method of this embodiment and mixing the SmFeN-based anisotropic magnetic powder with a resin. The method for manufacturing bonded magnets may further include the steps of aligning the easily magnetized magnetic domains in an orientation magnetic field while heat-treating the composite material obtained by mixing the SmFeN-based anisotropic magnetic powder and the resin, and then pulse-magnetizing the composite material in a magnetization magnetic field.

[0081] The resin included in the composite material may be a thermosetting resin or a thermoplastic resin, but a thermoplastic resin is preferred. Specific examples of thermoplastic resins include polyphenylene sulfide resin (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), polypropylene (PP), polyethylene (PE), and the like.

[0082] The mass ratio of SmFeN-based anisotropic magnetic powder to resin (resin / SmFeN-based anisotropic magnetic powder) when obtaining the composite material is preferably 0.05 to 0.20, more preferably 0.10 to 0.15, and even more preferably 0.11 to 0.14. Furthermore, the packing density of SmFeN-based anisotropic magnetic powder in the composite material is preferably 50 to 75 volume%, more preferably 60 to 70 volume%, and even more preferably 65 to 70 volume%.

[0083] The composite material can be obtained, for example, by mixing SmFeN-based anisotropic magnetic powder and a resin using a kneader at a temperature preferably between 200 and 350°C, more preferably between 280 and 330°C.

[0084] Bonded magnets can be manufactured using composite materials. Specifically, for example, a bonded magnet can be obtained by first heat-treating the composite material and aligning the easily magnetized magnetic domains with an orientation magnetic field (orientation step), and then by pulse magnetizing it with a magnetizing magnetic field (magnetization step).

[0085] The heat treatment temperature in the orientation process is preferably 90 to 200°C, and more preferably 100 to 150°C. The magnitude of the orientation magnetic field in the orientation process can be, for example, 720 kA / m. The magnitude of the magnetization magnetic field in the magnetization process can be, for example, 1500 to 2500 kA / m.

[0086] The manufacturing method for bonded magnets may include a step of injection molding a composite material (compound for bonded magnets). The molding temperature in injection molding is not particularly limited and can be set appropriately according to the processing temperature of the thermoplastic resin used.

[0087] By fabricating a bonded magnet using the SmFeN-based anisotropic magnetic powder of this embodiment, a bonded magnet with high magnetic properties can be obtained. The bonded magnet comprises the SmFeN-based anisotropic magnetic powder of this embodiment and a resin. For example, by fabricating a bonded magnet using the SmFeN-based anisotropic magnetic powder of this embodiment, the square aspect ratio Hk of the resulting bonded magnet can be improved. The dispersed SmFeN-based anisotropic magnetic powder may contain fine particles, and the more fine particles it contains, the greater the coercivity iHc tends to increase, and as the coercivity iHc increases, the square aspect ratio Hk also tends to increase. However, since fine particles are easily degraded by heating, the higher the proportion of fine particles, the more likely the coercivity iHC will decrease when a magnet is fabricated from the magnetic powder, and the more likely the square aspect ratio Hk will decrease. For example, as shown in Example 3 and Comparative Example 4 described later, the coercivity iHc and square aspect ratio Hk can be improved by using the SmFeN-based anisotropic magnetic powder of this embodiment to produce bonded magnets compared to those without it, which is thought to be because the magnetic powder content of the SmFeN-based anisotropic magnetic powder of this embodiment is relatively small.

[0088] Bonded magnets may contain PPS as the resin. By using PPS, bonded magnets with excellent water resistance can be obtained. The molding temperature for manufacturing bonded magnets using PPS is, for example, 300-340°C. Since the molding temperature for nylon 12 is, for example, 250°C, the molding temperature of PPS is relatively high. SmFeN-based anisotropic magnetic powder tends to have lower heat resistance as the proportion of fine particles increases. SmFeN-based anisotropic magnetic powder obtained by dispersion using a resin-coated metal or resin-coated ceramic media is less likely to generate fine particles. For this reason, it is suitable for manufacturing bonded magnets using PPS. When PPS is used as the resin, the proportion of fine particles in the SmFeN-based anisotropic magnetic powder used, that is, the proportion of fine particles to the total number of particles in the SmFeN-based anisotropic magnetic powder, may be 10% or less, or 5% or less. SmFeN-based anisotropic magnetic powder does not have to contain fine particles. Here, "fine particles" refers to particles with a diameter of 0.3 μm or less.

[0089] The residual magnetic flux density Br of the bonded magnet in this embodiment can be 0.80T or more and 1.35T or less, and may be 0.90T or more and 1T or less. The coercivity iHc can be 7500Oe or more and 20000Oe or less, and may be 12200Oe or more and 13000Oe or less. The square aspect ratio Hk can be 5100Oe or more and 20000Oe or less, and may be 7000Oe or more and 9000Oe or less. The maximum energy product BHmax can be 16MGOe or more and 25MGOe or less, and may be 18MGOe or more and 22MGOe or less. Hk / iHc can be 0.55 or more and 0.90 or less, and may be 0.70 or more and 0.80 or less.

[0090] Sintered magnets are manufactured by molding and sintering the SmFeN-based anisotropic magnetic powder of this embodiment. The SmFeN-based anisotropic magnetic powder of this embodiment is suitable for sintered magnets because it has a low oxygen concentration, a small average particle size, a narrow particle size distribution, and a high residual magnetic flux density.

[0091] Sintered magnets are manufactured, for example, by sintering SmFeN-based anisotropic magnetic powder in an atmosphere with an oxygen concentration of 0.5 ppm by volume or less, at a temperature higher than 300°C but lower than 600°C, and at a pressure of 1000 MPa to 1500 MPa.

[0092] Sintered magnets are manufactured by 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, as shown, for example, in International Publication No. 2015 / 199096.

[0093] Sintered magnets are produced, for example, by cold-consolidating a mixture containing SmFeN-based anisotropic magnetic powder and a metal binder at a molding surface pressure of 1 to 5 GPa, as shown in Japanese Patent Application Publication No. 2016-082175, and then heating it at a temperature of 350 to 600°C for 1 to 120 minutes. [Examples]

[0094] Examples are described below. Unless otherwise specified, "%" refers to mass.

[0095] [evaluation] The content of each metal, average particle size, particle size distribution, nitrogen content, oxygen content, remanent magnetization σr, coercivity iHc, and square aspect ratio Hk of the SmFeN-based anisotropic magnetic powder were evaluated using the following methods. The remanent magnetic flux density Br, coercivity iHc, square aspect ratio Hk, and maximum energy product BHmax of the bonded magnet were evaluated using the following methods.

[0096] <Content of each metal> The content of each metal (Sm, Fe, La, 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).

[0097] <Average particle size and particle size distribution> The average particle size and particle size distribution of the SmFeN-based anisotropic magnetic powder were measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS manufactured by Nippon Laser Co., Ltd.).

[0098] <Nitrogen content and oxygen content> The nitrogen content and oxygen content of the SmFeN-based anisotropic magnetic powder were measured by the thermal conductivity method (EMGA-820 manufactured by Horiba, Ltd.).

[0099] <Residual magnetization σr, coercive force iHc and squareness ratio Hk of SmFeN-based anisotropic magnetic powder> The obtained SmFeN-based anisotropic magnetic powder was packed in a sample container together with paraffin wax, and after melting the paraffin wax with a dryer, the easy magnetization directions were aligned in an orientation magnetic field of 16 kA / m. This magnetically oriented sample was pulse magnetized in a magnetization magnetic field of 32 kA / m, and the residual magnetization σr, coercive force iHc, and squareness ratio Hk were measured using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m.

[0100] <Residual magnetic flux density Br, coercive force iHc, squareness ratio Hk and maximum energy product BHmax of bonded magnets> For the bonded magnets, the residual magnetic flux density Br, coercive force iHc, squareness ratio Hk, and maximum energy product BHmax were measured using a BH curve tracer (manufactured by Riken Denshi Co., Ltd.).

[0101] Production Example 1 [Precipitation step] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Further, 0.49 kg of Sm2O3, 0.035 kg of La¬2O3, and 0.74 kg of 70% sulfuric acid were added and stirred well to be completely dissolved. Next, pure water was added to the obtained solution, and finally, the solution was adjusted so that the Fe concentration became 0.726 mol / L and the Sm concentration became 0.112 mol / L to obtain a SmFeLa sulfuric acid solution.

[0102] 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% ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. The obtained slurry was washed with pure water by decantation, and then the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0103] [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.

[0104] [Pre-treatment process] 100 g of SmFeLa oxide obtained in Production Example 1 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, and 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0105] [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.

[0106] [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.

[0107] [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.

[0108] 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, 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.

[0109] 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% ammonium tungstate were added dropwise over 70 minutes from the start of the reaction while stirring. Simultaneously, 15% ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. The obtained slurry was washed with pure water by decantation, and the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0110] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFeLaW oxide was obtained as the raw material powder.

[0111] SmFeN-based anisotropic magnetic powder was obtained by following the same procedure as in Manufacturing Example 1, from the pre-treatment step to the post-treatment step.

[0112] 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 30 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0113] 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%, 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%. The mixture was dispersed in a nitrogen atmosphere for 30 minutes using a vibratory mill to obtain SmFeN-based anisotropic magnetic powder.

[0114] Comparative Example 1 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 (chromium steel balls; SUJ2, diameter 2.3 mm, Vickers constant 760, specific gravity 7.77) 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.

[0115] Comparative Example 2 The SmFeN-based anisotropic magnetic powder obtained in Production Example 2 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 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] Comparative Example 3 The SmFeN-based anisotropic magnetic powder obtained in Production Example 2 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 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.

[0117] Table 1 shows the results of measuring the average particle size, particle size distribution, remanent magnetization σr, coercivity iHc, squareness ratio Hk, oxygen concentration, and nitrogen concentration of the SmFeN-based anisotropic magnetic powders obtained in Example 1, Example 2, and Comparative Examples 1 to 3 using the method described above. Table 2 shows the results of measuring the content of each metal. In addition, the magnetic powders obtained in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were imaged using a scanning electron microscope (SU3500, Hitachi High-Technologies, 5KV, 5000x magnification). The results are shown in Figures 1 to 4.

[0118] [Table 1]

[0119] [Table 2]

[0120] In Examples 1 and 2, where an iron core coated with nylon resin was used as the media for dispersion, it was confirmed that the residual magnetization 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, as shown in Figures 3 and 4, Comparative Examples 1 and 2 had a large amount of fine magnetic powder particles, while Examples 1 and 2 had relatively few.

[0121] Example 3 100 parts by mass of SmFeN-based anisotropic magnetic powder obtained in Example 1 were mixed with 6.6 parts by mass of nylon 12 in a mixer. The resulting mixed powder was kneaded at 210°C using a twin-screw kneader to obtain a compound for bonded magnets as a composite material. Bonded magnets were fabricated by injection molding of the compound for bonded magnets at a molding temperature of 250°C using an injection molding machine.

[0122] Example 4 A bonded magnet was fabricated in the same manner as in Example 3, except that the SmFeN-based anisotropic magnetic powder obtained in Example 2 was used as the SmFeN-based anisotropic magnetic powder.

[0123] Example 5 Bonded magnets were fabricated in the same manner as in Example 4, except that the molding temperature was set to 230°C.

[0124] Example 6 100 parts by mass of SmFeN-based anisotropic magnetic powder obtained in Example 2 were mixed with 11 parts by mass of polyphenylene sulfide resin in a mixer. The resulting mixed powder was kneaded at 310°C using a twin-screw kneader to obtain a compound for bonded magnets as a composite material. Bonded magnets were fabricated by injection molding of the compound for bonded magnets at a molding temperature of 310°C using an injection molding machine.

[0125] Comparative Example 4 100 parts by mass of SmFeN-based anisotropic magnetic powder obtained in Comparative Example 1 were mixed with 6.9 parts by mass of nylon 12 in a mixer. The resulting mixed powder was kneaded at 210°C using a twin-screw kneader to obtain a compound for bonded magnets as a composite material. Bonded magnets were fabricated by injection molding of the compound for bonded magnets at a molding temperature of 250°C using an injection molding machine.

[0126] Comparative Example 5 A bonded magnet was fabricated in the same manner as in Comparative Example 4, except that the SmFeN-based anisotropic magnetic powder obtained in Comparative Example 2 was used as the SmFeN-based anisotropic magnetic powder.

[0127] Comparative Example 6 100 parts by mass of SmFeN-based anisotropic magnetic powder obtained in Comparative Example 2 were mixed with 13.9 parts by mass of polyphenylene sulfide resin in a mixer. The resulting mixed powder was kneaded at 310°C using a twin-screw kneader to obtain a compound for bonded magnets as a composite material. Bonded magnets were fabricated by injection molding of the compound for bonded magnets using a mold at a molding temperature of 310°C.

[0128] Table 3 shows the results of measuring the residual magnetic flux density Br, coercivity iHc, aspect ratio Hk, and maximum energy product BHmax for the bonded magnets obtained in Examples 3 to 6 and Comparative Examples 4 to 6 using the method described above. Table 3 also shows the amount of magnetic powder filled, the injection pressure during molding, and Hk / iHc.

[0129] [Table 3]

[0130] In Examples 3 to 6, which are bonded magnets using the SmFeN-based anisotropic magnetic powder of Examples 1 and 2, it was confirmed that the residual magnetic flux density and maximum energy product were higher compared to Comparative Examples 4 to 6, which are bonded magnets using the SmFeN-based anisotropic magnetic powder of Comparative Examples 1 and 2. [Industrial applicability]

[0131] The SmFeN-based anisotropic magnetic powder obtained by the manufacturing method of this disclosure has a low oxygen concentration and excellent magnetic properties, making it suitable for use in bonded magnets and sintered magnets.

[0132] (1) This disclosure is a method for producing SmFeN-based anisotropic magnetic powder, comprising the steps of: preparing a SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N before dispersion; and dispersing the SmFeN-based anisotropic magnetic powder before dispersion using a resin-coated metal medium or a resin-coated ceramic medium.

[0133] Disclosure (2) is a method for producing the SmFeN-based anisotropic magnetic powder described in Disclosure (1), wherein the specific gravity of the media is 4 or more.

[0134] Disclosure (3) is a method for producing the SmFeN-based anisotropic magnetic powder described in Disclosure (1) or (2) in the absence of a solvent.

[0135] (4) of this disclosure is a method for producing SmFeN-based anisotropic magnetic powder according to any one of (1) to (3) of this disclosure, comprising the steps of preparing the SmFeN-based anisotropic magnetic powder before dispersion, a pretreatment step of obtaining a partial oxide by heat-treating an oxide containing Sm and Fe in a reducing gas-containing atmosphere, a step of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent, a step of nitriding the alloy particles to obtain a nitride, and a step of washing the nitride to obtain the SmFeN-based anisotropic magnetic powder before dispersion.

[0136] Disclosure (5) is a method for producing an SmFeN-based anisotropic magnetic powder according to any one of items (1) to (4) of this disclosure, wherein the SmFeN-based anisotropic magnetic powder further comprises La.

[0137] This disclosure (6) is a method for producing the SmFeN-based anisotropic magnetic powder described in this disclosure (5), wherein the SmFeN-based anisotropic magnetic powder further comprises W.

[0138] This disclosure (7) includes a step of obtaining SmFeN-based anisotropic magnetic powder by a manufacturing method described in any one of items (1) to (6) of this disclosure, A step of mixing the SmFeN-based anisotropic magnetic powder with a resin, This is a method for manufacturing bonded magnets, including [the specified component].

[0139] This disclosure (8) is a method for manufacturing a bonded magnet according to this disclosure (7), wherein the resin is a polyphenylene sulfide resin.

[0140] This disclosure (9) is an SmFeN-based anisotropic magnetic powder comprising Sm, Fe, and N, having an average particle size of 2.5 μm or more and 5 μm or less, a remanent magnetization σr of 150 emu / g or more, and an oxygen content of 0.4 mass% or less.

[0141] Disclosure (10) is a bonded magnet comprising the SmFeN-based anisotropic magnetic powder described in Disclosure (9) and a resin.

[0142] This disclosure (11) is a bonded magnet according to this disclosure (10), wherein the resin is a polyphenylene sulfide resin.

Claims

1. A method for producing SmFeN-based anisotropic magnetic powder, comprising the steps of: preparing a SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N before dispersion; and dispersing the SmFeN-based anisotropic magnetic powder before dispersion using a resin-coated metal medium or a resin-coated ceramic medium.

2. A method for producing SmFeN-based anisotropic magnetic powder according to claim 1, wherein the specific gravity of the media is 4 or more.

3. The method for producing SmFeN-based anisotropic magnetic powder according to claim 1, wherein the media is an iron or chromium steel media coated with resin.

4. A method for producing an SmFeN-based anisotropic magnetic powder according to claim 1, wherein the powder is dispersed in the absence of a solvent.

5. A method for producing SmFeN-based anisotropic magnetic powder according to claim 1, comprising the steps of: preparing the SmFeN-based anisotropic magnetic powder before dispersion, a pretreatment step of obtaining a partial oxide by heat-treating an oxide containing Sm and Fe in a reducing gas-containing atmosphere; obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent; nitriding the alloy particles to obtain a nitride; and washing the nitride to obtain the SmFeN-based anisotropic magnetic powder before dispersion.

6. The method for producing the SmFeN-based anisotropic magnetic powder according to claim 1, wherein the SmFeN-based anisotropic magnetic powder further contains La.

7. The method for producing SmFeN-based anisotropic magnetic powder according to claim 6, wherein the SmFeN-based anisotropic magnetic powder further comprises W.

8. A method for manufacturing a bonded magnet, comprising the steps of: obtaining SmFeN-based anisotropic magnetic powder by a manufacturing method described in any one of claims 1 to 7; and mixing the SmFeN-based anisotropic magnetic powder with a resin.

9. The method for manufacturing a bonded magnet according to claim 8, wherein the resin is a polyphenylene sulfide resin.

10. An SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N, with an average particle size of 2.5 μm or more and 5 μm or less, a remanent magnetization σr of 150 emu / g or more, and an oxygen content of 0.4 mass% or less.

11. A bonded magnet comprising the SmFeN-based anisotropic magnetic powder described in claim 10 and a resin.

12. The bonded magnet according to claim 11, wherein the resin is a polyphenylene sulfide resin.

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