Smfen-based anisotropic magnetic powder, bonded maget, method for producing said smfen-based anisotropic magnetic powder, and method for producing said bonded maget

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

SmFeN-based anisotropic magnetic powder and bonded magnet, and their manufacturing method

[0001] The present disclosure relates to SmFeN-based anisotropic magnetic powder and bonded magnets, as well as methods for producing the same.

[0002] Patent Document 1 discloses a manufacturing method for pulverizing an SmFeN-based anisotropic magnetic powder using ceramic media in a solvent. However, the use of hard ceramic media is thought to result in the generation of fine particles due to chipping, which increases the oxygen content of the SmFeN-based anisotropic magnetic powder obtained after pulverization and reduces its magnetic properties.

[0003] Japanese Patent Application Laid-Open No. 2015-195326

[0004] The purpose of one embodiment of the present disclosure is to provide an SmFeN-based anisotropic magnetic powder and a method for producing the same that has excellent magnetic properties and a low oxygen content.The purpose of one embodiment of the present disclosure is to provide a bonded magnet and a method for producing the same that uses such an SmFeN-based anisotropic magnetic powder.

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

[0006] A method for producing a bonded magnet according to one embodiment of the present disclosure includes the steps of obtaining an SmFeN-based anisotropic magnetic powder by the above-described production 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 mass % or less.

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

[0009] According to an embodiment of the present disclosure, an SmFeN-based anisotropic magnetic powder and a manufacturing method thereof can be provided that has excellent magnetic properties and a low oxygen content.Furthermore, according to an embodiment of the present disclosure, a bonded magnet and a manufacturing method thereof can be provided that uses such an SmFeN-based anisotropic magnetic powder.

[0010] 1 is an SEM image of the magnetic powder produced in Example 1. FIG. 2 is an SEM image of the magnetic powder produced in Example 2. FIG. 3 is an SEM image of the magnetic powder produced in Comparative Example 1. FIG. 4 is an SEM image of the magnetic powder produced in Comparative Example 2.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments described below are examples for embodying the technical ideas of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

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

[0013] [Dispersion Process] In the dispersion process, SmFeN-based anisotropic magnetic powder containing Sm, Fe, and N is dispersed using resin-coated metal or resin-coated ceramic media. Dispersion here refers to the process in which agglomerated particles formed by sintering or agglomerated particles formed by magnetic agglomeration contained in the SmFeN-based anisotropic magnetic powder are separated 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 than when a non-resin-coated metal or non-resin-coated ceramic media collides with the SmFeN-based anisotropic magnetic powder, so dispersion is more likely to occur than pulverization. When SmFeN-based anisotropic magnetic powder is pulverized as in the past, the average particle size becomes significantly smaller, and microparticles are generated due to chipping, which tends to reduce the magnetic properties. Furthermore, the microparticles and the areas from which they were generated create highly active new surfaces, which make them prone to oxidation and increase the oxygen content. On the other hand, when dispersion is performed as in this embodiment, the resulting single particles are easily oriented in a magnetic field, which improves the magnetic properties. Furthermore, the generation of new surfaces associated with the generation of microparticles can be suppressed compared to pulverization, which is thought to make it less likely for the oxygen content to increase.

[0014] The dispersion device used in the dispersion step is, for example, a vibrating mill. The media used in a dispersion device such as a vibrating mill may be a resin-coated metal, and examples of such metal materials include iron, chrome steel, stainless steel, and steel. Furthermore, the media used in a dispersion device such as a vibrating mill may be a resin-coated ceramic, and examples of such ceramic materials include inorganic compounds such as metal or non-metal oxides, carbides, nitrides, and borides. More specifically, examples include alumina, silica, zirconia, silicon carbide, silicon nitride, barium titanate, and glass. Among these, iron and chrome steel are preferred because of their high specific gravity, low wear, 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 chrome steel media in a dispersion device.

[0015] Examples of resins used for coating include thermoplastic resins such as nylon 6, nylon 66, nylon 12, polypropylene, polyphenylene sulfide, and polyethylene, thermosetting resins such as epoxy resin and silicone resin, and combinations thereof. Thermoplastic resins can be formed by injection molding and have higher fluidity than thermosetting resins, allowing for thinner film thicknesses than when coated with thermosetting resins. This allows for a higher specific gravity of the media and a smaller size than when coated with thermosetting resins. Nylon, such as nylon 6, nylon 66, and nylon 12, is preferred as the thermoplastic resin. Nylon is relatively soft and inexpensive among thermoplastic resins. For example, nylon-coated iron media may be used in the dispersing 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 step is preferably 4 or more, more preferably 5 or more. If it is less than 4, the collision energy during dispersion becomes too small, making dispersion difficult. The upper limit is not particularly limited, but 8 or less is preferable, and 7.5 or less is more preferable. The specific gravity of the media used in the dispersion step may be 6 or more and 7.5 or less. Resin-coated metal or resin-coated ceramic media can be said to have a metal or ceramic 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. This can suppress an increase in the diameter of the media, making it suitable for dispersing SmFeN-based anisotropic magnetic powder and improving the σr of the resulting SmFeN-based anisotropic magnetic powder.

[0017] The dispersion step can be carried out in the presence of a solvent, but is preferably carried out in the absence of a solvent in order to prevent oxidation of the SmFeN-based anisotropic magnetic powder due to components contained in the solvent (such as water).

[0018] The dispersion step is preferably carried out in an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere in order to suppress oxidation of the SmFeN-based anisotropic magnetic powder. The nitrogen concentration in the nitrogen gas atmosphere may be 90% by volume or more, preferably 95% by volume or more. The argon concentration 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 inert gases such as nitrogen gas and argon gas are mixed. The inert gas concentration in the inert gas atmosphere may be 90% by volume or more, preferably 95% by volume or more.

[0019] The diameter of the media is preferably 2 mm to 100 mm, more preferably 3 mm to 15 mm, and even more preferably 3 mm to 10 mm. If the diameter is less than 2 mm, it is difficult to coat with resin, and if the diameter exceeds 100 mm, the media is too large and there is little contact with the powder, making dispersion difficult.

[0020] When a vibration mill is used in the dispersion process, the amount of media can be, for example, 60% by volume or more and 70% by volume or less, and the amount of SmFeN-based anisotropic magnetic powder can be 3% by volume or more and 20% by volume or less, and preferably 5% by volume or more and 20% by volume or less, relative to the volume of the container containing the SmFeN-based anisotropic magnetic powder and media.

[0021] [Preparation Step] The dispersion step is preceded by a step of preparing pre-dispersed SmFeN-based anisotropic magnetic powder. The step of preparing pre-dispersed SmFeN-based anisotropic magnetic powder is, for example, a step of producing and obtaining SmFeN-based anisotropic magnetic powder. The pre-dispersed SmFeN-based anisotropic magnetic powder used in the dispersion step can be produced, for example, by referring to the methods disclosed in JP 2017-117937 A or JP 2021-055188 A. An example of a method for producing pre-dispersed SmFeN-based anisotropic magnetic powder is described below. Note that the pre-dispersed SmFeN-based anisotropic magnetic powder is a magnetic powder before the dispersion step using the resin-coated metal media or resin-coated ceramic media described above, and may have undergone other pre-dispersion steps.

[0022] The pre-dispersion SmFeN-based anisotropic magnetic powder used in the dispersion step can be produced by a manufacturing method including the following steps: a pretreatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide; a step of heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles; a step of nitriding the alloy particles to obtain nitrides; and a step of washing the nitrides to obtain the pre-dispersion SmFeN-based anisotropic magnetic powder.

[0023] The oxide containing Sm and Fe used in the pretreatment step may be prepared by mixing Sm oxide and Fe oxide, but it can also be produced by a step of mixing a solution containing Sm and Fe with a precipitant to obtain a precipitate containing Sm and Fe (precipitation step), and a step of calcining the precipitate to obtain an oxide containing Sm and Fe (oxidation step).

[0024] [Precipitation Step] In the precipitation step, a Sm raw material and an Fe raw material are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. ２ Fe１７ N ３ When the above is obtained 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 contain La. In terms of coercive force and squareness ratio, it is preferable to contain W. In terms of temperature characteristics, it is preferable to contain Co and Ti.

[0025] The Sm raw material and the Fe raw material are not limited as long as they can be dissolved in a strongly acidic solution. For example, in terms of ease of availability, samarium oxide is used as the Sm raw material, and FeSO is used as the Fe raw material. ４ The concentration of the solution containing Sm and Fe can be appropriately adjusted within a range in which the Sm raw material and the Fe raw material are substantially dissolved in the acidic solution. In terms of solubility, sulfuric acid or the like can be used as the acidic solution.

[0026] An insoluble precipitate containing Sm and Fe is obtained by reacting a solution containing Sm and Fe with a precipitant. The solution containing Sm and Fe may be a solution containing Sm and Fe upon reaction with the precipitant. For example, a raw material containing Sm and a raw material containing Fe may be prepared as separate solutions, and each solution may be added dropwise to react with the precipitant. Even when prepared as separate solutions, the concentrations of each raw material are appropriately adjusted so that they are substantially soluble in the acidic solution. The precipitant may be any alkaline solution that can react with the solution containing Sm and Fe to produce a precipitate, including aqueous ammonia, caustic soda, etc., with caustic soda being preferred.

[0027] The precipitation reaction is preferably carried out by dropping a solution containing Sm and Fe and a precipitant into 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 Sm and Fe solution and the precipitant, the reaction temperature, the concentration of the reaction solution, the pH during the reaction, and other factors, a precipitate with a uniform distribution of constituent elements, a narrow particle size distribution, and a regular powder shape can be obtained. Using such a precipitate improves the magnetic properties of the final SmFeN-based anisotropic magnetic powder. The reaction temperature is preferably 0°C to 50°C, more preferably 35°C to 45°C. The reaction solution concentration, in terms of total metal ion concentration, is preferably 0.65 mol / L to 0.85 mol / L, more preferably 0.7 mol / L to 0.85 mol / L. The reaction pH is preferably 5 to 9, more preferably 6.5 to 8.

[0028] The solution containing Sm and Fe preferably further contains 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 contain La in terms of residual magnetic flux density, it is preferable to contain W in terms of coercive force and squareness ratio, and it is preferable to contain 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, and for example, La is preferable in terms of availability. ２ O ３ , LaCl ３ The acidic solution is appropriately adjusted so that the Sm raw material, the Fe raw material, the La raw material, the W raw material, the Co raw material, and the Ti raw material are substantially dissolved in the acidic solution, and sulfuric acid is used as the acidic solution in terms of solubility. The W raw material may be ammonium tungstate, the Co raw material may be cobalt sulfate, and the Ti raw material may be titania sulfate.

[0029] When the 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 containing Sm, Fe, and one or more metals selected from the group consisting of La, W, Co, and Ti is obtained. Here, the solution only needs to contain one or more metals selected from the group consisting of La, W, Co, and Ti when reacted with the precipitant. For example, each raw material may be prepared as a separate solution, and each solution may be added dropwise to react with the precipitant, or the solution may be prepared together with the solution containing Sm and Fe.

[0030] The powder obtained in the precipitation step largely determines the particle size, shape, and particle size distribution of the SmFeN-based anisotropic magnetic powder that is finally obtained. When the particle sizes of the obtained powder are measured using a laser diffraction wet particle size distribution analyzer, it is preferable that the size and distribution of the entire powder is such that it is substantially in 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 remove the solvent from the separated material in order to prevent the precipitate from redissolving in the remaining solvent during the heat treatment in the subsequent oxidation step, which may result in aggregation of the precipitate when the solvent evaporates, or changes in particle size distribution, powder particle diameter, etc. Specific examples of the method for removing the solvent include, when water is used as the solvent, drying in an oven at 70°C or higher and 200°C or lower for 5 hours to 12 hours.

[0032] After the precipitation step, a step of separating and washing the resulting precipitate may be included. The washing step is carried out until the conductivity of the supernatant solution reaches 5 mS / m ２ The process is continued as appropriate until the following is achieved: In the step of separating the precipitate, for example, a solvent (preferably water) is added to the obtained precipitate and mixed, followed by filtration, decantation, or the like.

[0033] [Oxidation Step] The oxidation step is a step of obtaining an oxide containing Sm and Fe by firing the precipitate formed in the precipitation step. For example, the precipitate can be converted into an oxide by heat treatment. When the precipitate is heat treated, it must be performed in the presence of oxygen, for example, in an air atmosphere. Furthermore, since it must be performed in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms.

[0034] The heat treatment temperature in the oxidation step (hereinafter referred to as the oxidation temperature) is not particularly limited, but is preferably 700°C or higher and 1300°C or lower, and more preferably 900°C or higher and 1200°C or lower. If the temperature is lower than 700°C, oxidation will be insufficient, and if the temperature exceeds 1300°C, the desired shape, average particle size, and particle size distribution of the SmFeN-based anisotropic magnetic powder will tend not to be obtained. The heat treatment time is also not particularly limited, but is preferably 1 hour or higher and 3 hours or lower.

[0035] The oxide particles obtained are oxide particles in which Sm and Fe are thoroughly mixed microscopically within the oxide particles, and which reflect the shape, particle size distribution, etc. of the precipitates.

[0036] [Pretreatment Step] The pretreatment step is a step in which the oxide containing Sm and Fe is heat-treated in an atmosphere containing a reducing gas to obtain a partial oxide in which part of the oxide is reduced.

[0037] Here, the term "partial oxide" refers to an oxide in which a portion of an oxide has been reduced. The oxygen concentration of the partial oxide is not particularly limited, but is preferably 10% by mass or less, and more preferably 8% by mass or less. If the oxygen concentration exceeds 10% by mass, the heat generated by reduction with Ca in the reduction step increases, and the firing temperature increases, which tends to result in particles that have undergone abnormal particle growth. Here, the oxygen concentration of the partial oxide can be measured by non-dispersive infrared absorption (ND-IR).

[0038] The reducing gas is hydrogen (H ２ ), carbon monoxide (CO), methane (CH ４The reducing gas is appropriately selected from hydrocarbon gases such as ammonium hydroxide, ammonium nitrate ...

[0039] [Reduction Step] The reduction step is a step of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent, for example, by bringing the partial oxide into contact with calcium melt or calcium vapor. From the viewpoint of magnetic properties, the heat treatment temperature is preferably 920°C or higher and 1200°C or lower, more preferably 950°C or higher and 1150°C or lower, and even more preferably 980°C or higher and 1100°C or lower.

[0040] As a heat treatment separate from the heat treatment described above in the reduction step, a heat treatment may be performed at a first temperature of 1000°C to 1090°C, followed by a heat treatment at a second temperature of 980°C to 1070°C, which is lower than the first temperature. The first temperature is preferably 1010°C to 1080°C, and the second temperature is preferably 990°C to 1060°C. The temperature difference between the first and second temperatures is preferably such that the second temperature is lower than the first temperature by 15°C to 60°C, more preferably by 15°C to 30°C. 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 viewpoint of productivity, continuous performance is preferred. The duration of each heat treatment is preferably less than 120 minutes, more preferably less than 90 minutes, from the viewpoint of conducting the reduction reaction more uniformly. The lower limit of the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more.

[0041] The reducing agent, metallic calcium, is used in granular or powder form, with an average particle size of preferably 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, metallic calcium is preferably added in an amount 1.1 to 3.0 times, and more preferably 1.5 to 2.5 times, the reaction equivalent (the stoichiometric amount required to reduce the rare earth oxide, including the amount required to reduce the Fe component when it is in the form of an oxide).

[0042] In the reduction step, a disintegration accelerator can be used as needed together with metallic calcium as a reducing agent. This disintegration accelerator is used as appropriate to promote disintegration and granulation of the product in the post-treatment step described below, and examples thereof 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% by mass or more and 30% by mass or less, preferably 5% by mass or more and 30% by mass or less, based on the samarium oxide.

[0043] [Nitriding Process] The nitriding process is a process for obtaining anisotropic magnetic particles by nitriding the alloy particles obtained in the reducing process. Since the particulate precipitate obtained in the precipitation process is used, porous aggregate alloy particles are obtained in the reducing process. This allows for immediate nitriding by heat treatment in a nitrogen atmosphere without pulverization, thereby enabling uniform nitriding.

[0044] The heat treatment temperature in the nitriding treatment of the alloy particles (hereinafter referred to as the nitriding temperature) is preferably 300 to 610°C, particularly preferably 400 to 550°C, and is performed by replacing the atmosphere with a nitrogen atmosphere within this temperature range. The heat treatment time may be set to a time sufficient to ensure that the alloy particles are sufficiently and uniformly nitrided.

[0045] The heat treatment temperature in the nitriding treatment of the alloy particles can be a first temperature of 400°C or higher and 470°C or lower, followed by a second temperature of 480°C or higher and 610°C or lower. If the nitriding is not performed at the first temperature but at a high second temperature, the nitriding will proceed rapidly, causing abnormal heat generation, which may decompose the SmFeN-based anisotropic magnetic powder and significantly reduce the magnetic properties. In addition, the atmosphere in the nitriding step is preferably a substantially nitrogen-containing atmosphere, as this can slow down the nitriding process.

[0046] The term "substantially" used here is used in consideration of the fact that elements other than nitrogen are inevitably included 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 step is preferably 400°C or higher and 470°C or lower, and more preferably 410°C or higher and 450°C or lower. If the temperature is lower than 400°C, the nitriding proceeds very slowly, and if the temperature exceeds 470°C, excessive nitriding 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 or higher and 40 hours or lower, and more preferably 20 hours or lower. If the temperature is lower than 1 hour, the nitriding may not proceed sufficiently, and if the temperature exceeds 40 hours, productivity will be reduced.

[0048] The second temperature is preferably 480°C or higher and 610°C or lower, and more preferably 500°C or higher and 550°C or lower. If the temperature is lower than 480°C, nitriding may not proceed sufficiently if the particles are large, and if the temperature exceeds 610°C, excessive nitriding or decomposition is likely to occur. The heat treatment time at the second temperature is preferably 15 minutes or higher and 5 hours or lower, and more preferably 30 minutes or higher and 2 hours or lower. If the temperature is lower than 15 minutes, nitriding may not proceed sufficiently, and if the temperature exceeds 5 hours, productivity will be reduced.

[0049] The heat treatment at the first temperature and the heat treatment at the second temperature may be carried out continuously, and a 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 carry out the heat treatments continuously.

[0050] [Post-treatment process] The product obtained after the nitriding process contains, in addition to the magnetic particles, by-produced CaO, unreacted metallic calcium, etc., and these may be in the form of a composite sintered mass. The product obtained after the nitriding process is put into cooling water to convert the CaO and metallic calcium into calcium hydroxide (Ca(OH) ２ ) can be separated from the SmFeN-based anisotropic magnetic powder as a suspension. Furthermore, residual calcium hydroxide may be thoroughly removed by washing the SmFeN-based anisotropic magnetic powder with acetic acid or the like. When the product is put into water, the oxidation of metallic calcium by water and the hydration reaction of by-product CaO cause the composite sintered mass reaction product to disintegrate, i.e., to become finer.

[0051] [Alkaline Treatment Step] The product obtained after the nitriding step may be introduced into an alkaline solution. Examples of alkaline solutions used in the alkaline treatment step include an aqueous calcium hydroxide solution, an aqueous sodium hydroxide solution, and an aqueous ammonia solution. Among these, an aqueous calcium hydroxide solution and an 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 step, a Sm-rich layer containing a certain amount of oxygen remains and functions as a protective layer, thereby suppressing an increase in oxygen concentration due to the alkaline treatment.

[0052] The pH of the alkaline solution used in the alkaline treatment step is not particularly limited, but is preferably equal to or greater than 9, and more preferably equal to or greater than 10. If the pH is less than 9, the reaction rate when calcium hydroxide is formed is high and heat generation is large, so that the oxygen concentration in the finally obtained SmFeN-based anisotropic magnetic powder tends to be high.

[0053] In the alkali treatment step, the moisture content of the SmFeN-based anisotropic magnetic powder obtained after treatment with the alkaline solution can be reduced by a method such as decantation, if necessary.

[0054] [Acid Treatment Step] After the alkali treatment step, an acid treatment step may be further performed. In the acid treatment step, at least a portion of the Sm-rich layer is removed to reduce the oxygen concentration in the entire magnetic powder. In addition, in the manufacturing method according to the embodiment of the present disclosure, since no pulverization 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 the powder does not contain fine powder generated by pulverization or the like, making it possible to suppress an increase in the oxygen concentration.

[0055] The acid used in the acid treatment step is not particularly limited, and examples thereof include hydrogen chloride, nitric acid, sulfuric acid, acetic acid, etc. Among these, hydrogen chloride and nitric acid are preferred in that no impurities remain.

[0056] The amount of acid used in the acid treatment step is preferably 3.5 parts by mass or more and 13.5 parts by mass or less, more preferably 4 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the 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 of acid exceeds 13.5 parts by mass, reoxidation is likely to occur when exposed to the atmosphere, and the SmFeN-based anisotropic magnetic powder is dissolved, which tends to increase costs. By using an amount of acid of 3.5 parts by mass or more and 13.5 parts by mass or less, per 100 parts by mass of the SmFeN-based anisotropic magnetic powder, an Sm-rich layer oxidized to a degree that makes reoxidation less likely to occur when exposed to the atmosphere after the acid treatment can cover the surface of the SmFeN-based anisotropic magnetic powder, resulting in a SmFeN-based anisotropic magnetic powder with a low oxygen concentration, a small average particle size, and a narrow particle size distribution.

[0057] In the acid treatment step, the moisture content of the SmFeN-based anisotropic magnetic powder obtained after the acid treatment can be reduced by a method such as decantation, if necessary.

[0058] [Dehydration Step] It is preferable to include a dehydration step after the acid treatment step. The dehydration step reduces the moisture content in the solid content before vacuum drying, and can suppress the progression of oxidation during drying that occurs when the solid content before vacuum drying contains more moisture. Here, the dehydration step refers to a process in which pressure or centrifugal force is applied to reduce the moisture content of the solid content after treatment compared to the solid content before treatment, and does not include simple decantation, filtration, or drying. The dehydration method is not particularly limited, but examples include squeezing, centrifugation, etc.

[0059] The amount of water contained in the SmFeN-based anisotropic magnetic powder after dehydration is not particularly limited, but is preferably 13% by mass or less, more preferably 10% by mass or less, in order to suppress the progression of oxidation.

[0060] The SmFeN-based anisotropic magnetic powder obtained by acid treatment, or the SmFeN-based anisotropic magnetic powder obtained by acid treatment followed by dehydration, 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 longer, and more preferably 3 hours or longer.

[0061] [Surface Treatment Step] The SmFeN-based anisotropic magnetic powder obtained in the post-treatment step may be subjected to a surface treatment. For example, a phosphoric acid solution is added as a surface treatment agent to the magnetic particle solid content obtained in the nitriding step. ４ The powder is added in an amount of 0.10 to 10 mass % as a surface-treated SmFeN-based anisotropic magnetic powder by separating it from the solution and drying it as needed.

[0062] The SmFeN-based anisotropic magnetic powder according to one embodiment of the present disclosure contains Sm, Fe, and N, and is characterized by 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.

[0063] The average particle size of the SmFeN-based anisotropic magnetic powder is 2.5 μm or more and 5 μm or less, and preferably 2.6 μm or more and 4.5 μm or less. If it is less than 2.5 μm, the surface area is large and oxidation is likely to occur, and if it exceeds 5 μm, the SmFeN-based anisotropic magnetic powder will have a multi-domain structure, which tends to deteriorate the magnetic properties. Here, the average particle size means the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0064] The particle size D10 of the SmFeN 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 it is less than 0.5 μm, the filling amount of the SmFeN anisotropic magnetic powder in the bonded magnet will be small, resulting in a decrease in magnetization, while if it exceeds 3 μm, the coercivity of the bonded magnet will tend to decrease. Here, D10 is the particle size at which the integrated value of the particle size distribution on a volume basis of the SmFeN anisotropic magnetic powder corresponds to 10%.

[0065] The particle size D50 of the SmFeN anisotropic magnetic powder is preferably 2 μm or more and 5 μm or less, and 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 anisotropic magnetic powder in the bonded magnet will be small, resulting in a decrease in magnetization, and if it exceeds 5 μm, the coercivity of the bonded magnet will tend to decrease. Here, D50 is the particle size at which the integrated value of the particle size distribution on a volume basis of the SmFeN anisotropic magnetic powder corresponds to 50%.

[0066] The particle size D90 of the SmFeN anisotropic magnetic powder is preferably 3 μm or more and 7 μm or less, and 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 anisotropic magnetic powder in the bonded magnet will be small, resulting in a decrease in magnetization, and if it exceeds 7 μm, the coercivity of the bonded magnet will tend to decrease. Here, D90 is the particle size at which the integrated value of the particle size distribution based on volume of the SmFeN anisotropic magnetic powder corresponds to 90%.

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

[0068] The oxygen content of the SmFeN-based anisotropic magnetic powder is 0.4% by mass or less, preferably 0.38% by mass or less, more preferably 0.3% by mass or less, and particularly preferably 0.25% by mass or less. If the oxygen content exceeds 0.4% by mass, there will be a lot of oxygen on the particle surface, which will cause the formation of α-Fe. Note that the oxygen content analysis is performed after the SmFeN-based anisotropic magnetic powder obtained after all steps have been completed has been left in the air for 30 minutes or more.

[0069] The SmFeN-based anisotropic magnetic powder in this embodiment is typically represented by the following general formula: Sm ｖ Fe(100-v-w-x-y-zu-u)N ｗ La ｘ W ｙ Co ｚ Ti ｕ (wherein 3≦v≦30, 5≦w≦15, 0≦x≦0.3, 0≦y≦2.5, 0≦z≦2.5, and 0≦u≦2.5).

[0070] In the general formula, v is specified to be 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 coercive force of the SmFeN anisotropic magnetic powder and making it impossible to produce a practical magnet, and if it exceeds 30, Sm elements precipitate, making the SmFeN anisotropic magnetic powder unstable in the air and reducing the remanence. Furthermore, w is specified to be 5 or more and 15 or less because, if it is less than 5, almost no coercive force is exhibited, and if it exceeds 15, nitrides of Sm and iron itself are formed.

[0071] When La is contained, the La content is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.15 mass % or more and 1 mass % or less, from the viewpoint of residual magnetic flux density.

[0072] When W is contained, the content of W 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 coercive force and squareness ratio.

[0073] When Co is contained, the Co content is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.15 mass % or more and 1 mass % or less, from the viewpoint of temperature characteristics.

[0074] When Ti is contained, the content of Ti is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.15 mass % or more and 1 mass % or less, from the viewpoint of temperature characteristics.

[0075] The content of N is preferably 3.3 mass % or more and 3.5 mass % or less. If it exceeds 3.5 mass %, excessive nitriding occurs, and if it is less than 3.3 mass %, nitriding becomes insufficient, and both tend to deteriorate the magnetic properties.

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

[0077] The span of the SmFeN-based anisotropic magnetic powder, defined by the following formula: Span = (D90 - D10) / D50 (where D10, D50, and D90 are particle sizes corresponding to 10%, 50%, and 90% of the integrated value of the particle size distribution on a volume basis, respectively), 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 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. If the circularity is below 0.50, the flowability will be poor, resulting in stress between particles during magnetic field compaction, resulting in reduced magnetic properties. A scanning electron microscope (SEM) is used to measure the circularity, with Sumitomo Metal Technology's Particle Analysis Ver. 3 used as 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 determined by measuring approximately 1000 to 10000 particles. Generally, the smaller the particle diameter, the higher the circularity, so the circularity was measured for particles of 1 μm or more. The circularity was measured using the following formula: 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] The bonded magnet is 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. A method for manufacturing a bonded magnet includes the steps of obtaining an 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 a bonded magnet may further include the steps of aligning easy magnetization domains in an orienting 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 magnetizing magnetic field.

[0081] The resin contained in the composite material may be a thermosetting resin or a thermoplastic resin, but is preferably a thermoplastic resin, such as polyphenylene sulfide resin (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), polypropylene (PP), and polyethylene (PE).

[0082] When obtaining the composite material, the mass ratio of the SmFeN anisotropic magnetic powder to the resin (resin / SmFeN anisotropic magnetic powder) is preferably 0.05 to 0.20, more preferably 0.10 to 0.15, and even more preferably 0.11 to 0.14. The filling rate of the SmFeN 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 the SmFeN-based anisotropic magnetic powder and the resin using a kneader, preferably at 200 to 350°C, more preferably at 280 to 330°C.

[0084] The composite material can be used to produce a bonded magnet. Specifically, the composite material is heat-treated while aligning the easy magnetization domains in an orienting magnetic field (orientation step), and then pulse-magnetized in a magnetizing magnetic field (magnetization step), to produce a bonded magnet.

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

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

[0087] By producing a bonded magnet using the SmFeN-based anisotropic magnetic powder of this embodiment, it is possible to obtain a bonded magnet with high magnetic properties. The bonded magnet includes the SmFeN-based anisotropic magnetic powder of this embodiment and a resin. For example, by producing a bonded magnet using the SmFeN-based anisotropic magnetic powder of this embodiment, it is possible to improve the squareness ratio Hk of the resulting bonded magnet. The dispersed SmFeN-based anisotropic magnetic powder may contain fine particles. The more fine particles contained, the higher the coercivity iHc tends to increase, and as the coercivity iHc increases, the squareness ratio Hk also tends to increase. However, because fine particles are easily degraded by heating, the higher the proportion of fine particles contained, the more likely it is that the coercivity iHC and squareness ratio Hk will decrease when a magnet is produced from the magnetic powder. For example, as in Example 3 and Comparative Example 4 described below, by producing a bonded magnet using the SmFeN-based anisotropic magnetic powder of this embodiment, the coercive force iHc and squareness ratio Hk can be improved compared to those not using the powder, 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 a resin. By using PPS, bonded magnets with excellent water resistance can be obtained. The molding temperature for producing bonded magnets using PPS is, for example, 300 to 340°C. The molding temperature for nylon 12 is, for example, 250°C, so the molding temperature for PPS can be considered relatively high. The higher the proportion of fine powder in SmFeN-based anisotropic magnetic powder, the lower its heat resistance tends to be. SmFeN-based anisotropic magnetic powder obtained by dispersing using resin-coated metal or resin-coated ceramic media is less likely to produce fine powder. Therefore, it is suitable for producing bonded magnets using PPS. When PPS is used as a resin, the proportion of fine powder in the SmFeN-based anisotropic magnetic powder used, i.e., the ratio of fine powder particles to the total number of particles in the SmFeN-based anisotropic magnetic powder, may be 10% or less, or even 5% or less. The SmFeN-based anisotropic magnetic powder does not need to contain fine powder particles. Here, fine particles (fine powder) refer to particles having a particle size of 0.3 μm or less.

[0089] The residual magnetic flux density Br of the bonded magnet of this embodiment can be 0.80 T or more and 1.35 T or less, or may be 0.90 T or more and 1 T or less. The coercive force iHc can be 7,500 Oe or more and 20,000 Oe or less, or may be 12,200 Oe or more and 13,000 Oe or less. The squareness ratio Hk can be 5,100 Oe or more and 20,000 Oe or less, or may be 7,000 Oe or more and 9,000 Oe or less. The maximum energy product BHmax can be 16 MGOe or more and 25 MGOe or less, or may be 18 MGOe or more and 22 MGOe or less. Hk / iHc can be 0.55 or more and 0.90 or less, or may be 0.70 or more and 0.80 or less.

[0090] A sintered magnet is produced by molding and sintering the SmFeN anisotropic magnetic powder of this embodiment. The SmFeN 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] As disclosed in JP 2017-055072 A, for example, a sintered magnet is produced by sintering an SmFeN-based anisotropic magnetic powder in an atmosphere with an oxygen concentration of 0.5 volume ppm or less at a temperature of more than 300°C and less than 600°C under a pressure of 1000 MPa or more and 1500 MPa or less.

[0092] As disclosed in International Publication No. 2015 / 199096, for example, sintered magnets are produced by pre-compressing SmFeN-based anisotropic magnetic powder in a magnetic field of 6 kOe or more, followed by warm compaction molding at a temperature of 600°C or less and a molding surface pressure of 1 to 5 GPa.

[0093] As disclosed in JP 2016-082175 A, for example, a sintered magnet is produced by cold compacting a mixture containing an SmFeN-based anisotropic magnetic powder and a metal binder at a molding surface pressure of 1 to 5 GPa, and then heating the mixture at a temperature of 350 to 600°C for 1 to 120 minutes.

[0094] Examples will be described below. Unless otherwise specified, "%" is by mass.

[0095] [Evaluation] The metal content, average particle size, particle size distribution, nitrogen content, oxygen content, remanence σr, coercive force iHc, and squareness ratio Hk of the SmFeN-based anisotropic magnetic powder were evaluated using the following methods. The remanence Br, coercive force iHc, squareness 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 the SmFeN-based anisotropic magnetic powder was measured by dissolving it in hydrochloric acid and then using an ICP-AES method (device name: Optima 8300).

[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 measuring device (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 a 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 into a sample container together with paraffin wax, the paraffin wax was melted using a dryer, and then the easy magnetization domains were aligned in an aligning magnetic field of 16 kA / m. This magnetically oriented sample was pulse-magnetized in a magnetizing magnetic field of 32 kA / m, and the remanent 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 magnet> The residual magnetic flux density Br, coercive force iHc, squareness ratio Hk and maximum energy product BHmax of the bonded magnet were measured using a BH curve tracer (manufactured by Riken Denshi Co., Ltd.).

[0101] Production Example 1 [Precipitation step] FeSO was added to 2.0 kg of pure water. ４ ・7H ２ 5.0 kg of Sm was mixed and dissolved. ２ O ３ 0.49 kg, La ２ O ３ 0.035 kg of iron and 0.74 kg of 70% sulfuric acid were added and thoroughly stirred to completely dissolve the iron. 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, thereby preparing a SmFeLa sulfuric acid solution.

[0102] The entire amount of the prepared SmFeLa sulfuric acid solution was added dropwise to 20 kg of pure water maintained at a temperature of 40°C over a period of 70 minutes from the start of the reaction while stirring, and 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 subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0103] [Oxidation Step] The hydroxide obtained in the precipitation step was calcined in air at 1000° C. for 1 hour. After cooling, a red SmFeLa oxide was obtained as a raw material powder.

[0104] [Pretreatment Step] 100 g of the SmFeLa oxide obtained in Production Example 1 was placed in a steel container to a bulk thickness of 10 mm. The container was placed in a furnace, and after reducing the pressure to 100 Pa, the container was heated to the pretreatment temperature of 850°C while introducing hydrogen gas, and maintained at that temperature for 15 hours. The oxygen concentration was measured using non-dispersive infrared spectroscopy (ND-IR) (EMGA-820, manufactured by Horiba, Ltd.) and found to be 5% by mass. This revealed that the oxygen bonded to Sm was not reduced, and that a black partial oxide was obtained in which 95% of the oxygen bonded to Fe was reduced.

[0105] [Reduction step] 60 g of the partial oxide obtained in the pretreatment step and 19.2 g of metallic calcium having an average particle size of approximately 6 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The mixture was heated to a first temperature of 1,045°C and maintained for 45 minutes, and then cooled to a second temperature of 1,000°C and maintained for 30 minutes to obtain SmFeLa alloy particles.

[0106] [Nitriding step] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated to a vacuum, and while introducing nitrogen gas, the temperature was increased to a first temperature of 430°C and held for 3 hours, and then increased to a second temperature of 500°C and held for 1 hour, and then cooled to obtain an aggregated product containing magnetic particles.

[0107] [Post-treatment process] The aggregated 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 product was vacuum dried at 80°C for 3 hours to obtain SmFeN-based anisotropic magnetic powder.

[0108] Production Example 2 [Precipitation step] FeSO was added to 2.0 kg of pure water. ４ ・7H ２ 5.0 kg of Sm was mixed and dissolved. ２ O ３ 0.49 kg, La ２ O ３0.035 kg of iron and 0.74 kg of 70% sulfuric acid were added and thoroughly stirred to completely dissolve the iron. 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, thereby preparing a SmFeLa sulfuric acid solution.

[0109] The entire amount of the prepared SmFeLa sulfuric acid solution and 0.14 kg of 18% ammonium tungstate were added dropwise to 20 kg of pure water maintained at a temperature of 40°C over a period of 70 minutes from the start of the reaction while stirring. At the same time, 15% ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. The resulting slurry was washed with pure water by decantation, and the hydroxide was subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

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

[0111] The pre-treatment process to the post-treatment process were the same as in Production Example 1 to obtain an SmFeN-based anisotropic magnetic powder.

[0112] The SmFeN anisotropic magnetic powder and media (iron-core nylon media, diameter 10 mm, Vickers constant of nylon coating 7, specific gravity 7.48, nylon layer thickness approximately 1 to 3 mm) were placed in a container so that the SmFeN anisotropic magnetic powder obtained in Production Example 1 accounted for 5 volume % and the media accounted for 60 volume % relative to the volume of the container used for the vibration mill. Dispersion was carried out in a nitrogen atmosphere for 30 minutes using the vibration mill to obtain an SmFeN anisotropic magnetic powder.

[0113] The SmFeN anisotropic magnetic powder and media (iron-core nylon media, diameter 10 mm, Vickers constant of nylon coating 7, specific gravity 7.48, nylon layer thickness approximately 1 to 3 mm) were placed in a container so that the SmFeN anisotropic magnetic powder obtained in Production Example 2 accounted for 5 volume % and the media accounted for 60 volume % relative to the volume of the container used for the vibration mill. Dispersion was carried out in a nitrogen atmosphere for 30 minutes using the vibration mill to obtain an SmFeN anisotropic magnetic powder.

[0114] Comparative Example 1 The SmFeN anisotropic magnetic powder obtained in Production Example 1 and media (chrome steel balls; SUJ2, diameter 2.3 mm, Vickers constant 760, specific gravity 7.77) were placed in a container so that the SmFeN anisotropic magnetic powder and media accounted for 5 volume % and 60 volume % of the volume of the container used for the vibration mill. Dispersion was carried out in a nitrogen atmosphere for 60 minutes using the vibration mill to obtain an SmFeN anisotropic magnetic powder.

[0115] The SmFeN-based anisotropic magnetic powder obtained in Production Example 2 and media (chrome steel balls; SUJ2, diameter 2.3 mm, Vickers constant 760, specific gravity 7.77) were placed in a container used for a vibration mill so that the SmFeN-based anisotropic magnetic powder and media accounted for 5 volume % and 60 volume %, respectively, relative to the volume of the container. Dispersion was carried out in a vibration mill for 60 minutes under a nitrogen atmosphere to obtain an SmFeN-based anisotropic magnetic powder.

[0116] Comparative Example 3 The SmFeN anisotropic magnetic powder obtained in Production Example 2 and media (made of nylon, diameter 10 mm, Vickers constant 7, specific gravity 1.13) were placed in a container used for a vibration mill so that the SmFeN anisotropic magnetic powder and media accounted for 5 volume % and 60 volume %, respectively, relative to the volume of the container. Dispersion was carried out in a vibration mill for 60 minutes under a nitrogen atmosphere to obtain an SmFeN anisotropic magnetic powder.

[0117] The SmFeN-based anisotropic magnetic powders obtained in Example 1, Example 2, and Comparative Examples 1 to 3 were measured for average particle size, particle size distribution, remanence σr, coercive force iHc, squareness ratio Hk, oxygen concentration, and nitrogen concentration using the methods described above, and the results are shown in Table 1, and the results of measuring the content of each metal are shown in Table 2. In addition, the magnetic powders obtained in Example 1, Example 2, and Comparative Examples 1 and 2 were photographed with a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation, 5 KV, 5000x magnification). The results are shown in Figures 1 to 4.

[0118]

[0119]

[0120] It was confirmed that Examples 1 and 2, in which dispersion was performed using iron cores coated with nylon resin as media, had higher remanent magnetization than Comparative Examples 1 and 2, in which dispersion was performed using chrome steel balls not coated with resin as media, and Comparative Example 3, in which dispersion was performed using nylon resin as media. Also, as shown in Figures 3 and 4, Comparative Examples 1 and 2 contained a large amount of fine magnetic powder particles, whereas Examples 1 and 2 contained relatively few.

[0121] Example 3: 100 parts by mass of the SmFeN-based anisotropic magnetic powder obtained in Example 1 was 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 bonded magnet compound as a composite material. Using an injection molding machine, the bonded magnet compound was injection molded at a molding temperature of 250°C to produce a bonded magnet.

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

[0123] Example 5 A bonded magnet was produced 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 the SmFeN-based anisotropic magnetic powder obtained in Example 2 was 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 bonded magnet compound as a composite material. Using an injection molding machine, the bonded magnet compound was injection molded at a molding temperature of 310°C to produce a bonded magnet.

[0125] Comparative Example 4 100 parts by mass of the SmFeN-based anisotropic magnetic powder obtained in Comparative Example 1 was 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 bonded magnet compound as a composite material. Using an injection molding machine, the bonded magnet compound was injection molded at a molding temperature of 250°C to produce a bonded magnet.

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

[0127] Comparative Example 6: 100 parts by mass of the SmFeN-based anisotropic magnetic powder obtained in Comparative Example 2 was 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 bonded magnet compound as a composite material. Using a mold, the bonded magnet compound was injection molded at a molding temperature of 310°C to produce a bonded magnet.

[0128] For the bonded magnets obtained in Examples 3 to 6 and Comparative Examples 4 to 6, the residual magnetic flux density Br, coercive force iHc, squareness ratio Hk, and maximum energy product BHmax were measured using the methods described above, and the results are shown in Table 3. Table 3 also shows the magnetic powder filling amount, injection pressure during molding, and Hk / iHc.

[0129]

[0130] It was confirmed that Examples 3 to 6, which are bonded magnets using the SmFeN-based anisotropic magnetic powders of Examples 1 and 2, have higher residual magnetic flux density and maximum energy product than Comparative Examples 4 to 6, which are bonded magnets using the SmFeN-based anisotropic magnetic powders of Comparative Example 1 and Comparative Example 2.

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

[0132] The present disclosure (1) is a method for producing an SmFeN-based anisotropic magnetic powder, comprising the steps of: preparing an 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] The present disclosure (2) is a method for producing an SmFeN-based anisotropic magnetic powder according to the present disclosure (1), in which the specific gravity of the media is 4 or more.

[0134] The present disclosure (3) is a method for producing the SmFeN-based anisotropic magnetic powder according to the present disclosure (1) or (2), which is dispersed in the absence of a solvent.

[0135] The present disclosure (4) is a method for producing an SmFeN-based anisotropic magnetic powder according to any one of the present disclosures (1) to (3), wherein the step of preparing the SmFeN-based anisotropic magnetic powder before dispersion includes a pretreatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide, a step of heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles, 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] The present disclosure (5) is a method for producing an SmFeN-based anisotropic magnetic powder according to any one of the present disclosures (1) to (4), wherein the SmFeN-based anisotropic magnetic powder further contains La.

[0137] The present disclosure (6) is a method for producing an SmFeN-based anisotropic magnetic powder according to the present disclosure (5), in which the SmFeN-based anisotropic magnetic powder further contains W.

[0138] The present disclosure (7) is a method for producing a bonded magnet, comprising the steps of obtaining an SmFeN-based anisotropic magnetic powder by the production method described in any one of the present disclosures (1) to (6), and mixing the SmFeN-based anisotropic magnetic powder with a resin.

[0139] The present disclosure (8) is a method for producing a bonded magnet according to the present disclosure (7), in which the resin is a polyphenylene sulfide resin.

[0140] The present disclosure (9) is an SmFeN-based anisotropic magnetic powder 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 mass% or less.

[0141] The present disclosure (10) is a bonded magnet containing the SmFeN-based anisotropic magnetic powder according to the present disclosure (9) and a resin.

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

Claims

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

2. 2. The method for producing an SmFeN based anisotropic magnetic powder according to claim 1, wherein the media has a specific gravity of 4 or more.

3. 2. The method for producing SmFeN based anisotropic magnetic powder according to claim 1, wherein the media is made of iron or chrome steel coated with a resin.

4. The method for producing the SmFeN system anisotropic magnetic powder according to claim 1, wherein the powder is dispersed in the absence of a solvent.

5. 2. The method for producing SmFeN-based anisotropic magnetic powder according to claim 1, wherein the step of preparing the pre-dispersed SmFeN-based anisotropic magnetic powder includes a pre-treatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide, a step of heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles, a step of nitriding the alloy particles to obtain nitrides, and a step of washing the nitrides to obtain the pre-dispersed SmFeN-based anisotropic magnetic powder.

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

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

8. A method for producing a bonded magnet, comprising the steps of obtaining an SmFeN anisotropic magnetic powder by the method according to any one of claims 1 to 7, and mixing the SmFeN anisotropic magnetic powder with a resin.

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

10. A SmFeN-based anisotropic magnetic powder containing Sm, Fe and N, having an average particle size of 2.5 μm or more and 5 μm or less, a residual 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 anisotropic magnetic powder according to claim 10 and a resin.

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