Method for producing anisotropic magnetic powder and anisotropic magnetic powder

Abstract

To provide magnetic powder having a narrow particle size distribution and having high residual magnetization, and a method for producing the same.SOLUTION: A method for producing anisotropic magnetic powder comprises: a pretreatment step in which an oxide comprising Sm and Fe is heat-treated in a reducing gas-containing atmosphere to obtain a partial oxide; a step in which the partial oxide is heat-treated in the presence of a reducer to obtain alloy particles; and a step in which the alloy particles are heat-treated at a first temperature of 400°C or more to 470°C or less in a nitrogen or ammonia-containing atmosphere and is thereafter heat-treated at a second temperature of 480°C or more to 610°C or less to obtain a nitride.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing anisotropic magnetic powder and anisotropic magnetic powder. [Background technology]

[0002] Patent Document 1 discloses an SmFeN-based sintered magnet, and discloses a magnetic powder with a small average particle size and low oxygen content for use in sintering. However, the magnetic powder is produced by pulverizing magnetic powder with an average particle size of 20 μm or more using a jet mill, which only allows for the production of powder with a wide particle size distribution.

[0003] Patent Document 2 discloses methods for producing SmFeN-based anisotropic magnetic powder, SmFeLaN-based anisotropic magnetic powder, and SmFeLaCoN-based anisotropic magnetic powder, and Patent Document 3 discloses methods for producing SmFeN-based anisotropic magnetic powder, SmFeLaN-based anisotropic magnetic powder, and SmFeWN-based anisotropic magnetic powder. Although the magnetic powders obtained in these patent documents have excellent magnetic properties, magnetic powders with even higher remanent magnetization are desired. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-55072 A [Patent Document 2] Japanese Patent Application Publication No. 2019-112716 [Patent Document 3] Japanese Patent Publication No. 2020-102606 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a magnetic powder having a narrow particle size distribution and high remanence, and a method for producing the same. [Means for solving the problem]

[0006] A method for producing an anisotropic magnetic powder according to one aspect of the present invention includes the steps of: a pretreatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide; heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles; and A step of heat-treating the alloy particles at a first temperature of 400°C or more and 470°C or less in a nitrogen or ammonia-containing atmosphere, and then heat-treating the alloy particles at a second temperature of 480°C or more and 610°C or less to obtain nitrides. Includes. [Effects of the Invention]

[0007] The method for producing anisotropic magnetic powder of the present invention involves nitriding at two temperatures, making it possible to produce anisotropic magnetic powder with a narrow particle size distribution and high remanence. This is particularly effective for magnetic powders containing La and having a large average particle size. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are examples for embodying the technical concept of the present invention, and the present invention 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.

[0009] The method for producing anisotropic magnetic powder of this embodiment includes the steps of: a pretreatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide; heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles; and A step of heat-treating the alloy particles at a first temperature of 400°C or more and 470°C or less in a nitrogen or ammonia-containing atmosphere, and then heat-treating the alloy particles at a second temperature of 480°C or more and 610°C or less to obtain nitrides. In particular, with oxides having large particle sizes, such as oxides containing La, nitriding may not progress sufficiently to the interior of the oxide particles, but by nitriding at two temperatures, the interior of the oxide particles is also sufficiently nitrided, and a magnetic powder with a narrow particle size distribution and high remanence can be obtained.

[0010] [Pretreatment process] The oxide containing Sm and Fe used in the pretreatment step may be prepared, for example, by mixing Sm oxide and Fe oxide. However, it is preferable to produce the oxide 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).

[0011] [Precipitation process] In the precipitation process, Sm and Fe raw materials are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. 17 When N3 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-mentioned solution. La is preferably contained in terms of remanence. W is preferably contained in terms of coercivity and squareness. Co and Ti are preferably contained in terms of temperature characteristics.

[0012] 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 can be used as the Sm raw material, and FeSO4 can be used as the Fe raw material. The concentration of the solution containing Sm and Fe can be adjusted appropriately within a range in which the Sm raw material and the Fe raw material are substantially soluble in the acidic solution. In terms of solubility, sulfuric acid can be used as the acidic solution.

[0013] 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 is sufficient as long as it becomes a solution containing Sm and Fe upon reaction with the precipitant. For example, raw materials containing Sm and 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 is not limited as long as it is an alkaline solution that reacts with the solution containing Sm and Fe to produce a precipitate. Examples of the precipitant include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0014] 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 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 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 product, the magnetic powder. The reaction temperature can be set to 0°C or higher and 50°C or lower, preferably 35°C or higher and 45°C or lower. The concentration of the reaction solution is preferably 0.65 mol / L or higher and 0.85 mol / L or lower, and more preferably 0.7 mol / L or higher and 0.85 mol / L or lower, in terms of the total concentration of metal ions. The reaction pH is preferably 5 to 9, more preferably 6.5 to 8.

[0015] From the viewpoint of magnetic properties, the solution containing Sm and Fe preferably further contains one or more metals selected from the group consisting of La, W, Co, and Ti. For example, from the viewpoint of remanence, it is preferable to contain La; from the viewpoint of coercivity, it is preferable to contain W; and from the viewpoint of temperature characteristics, it is preferable to contain Co and Ti. The La raw material is not limited as long as it can be dissolved in a strongly acidic solution, and examples thereof include La2O3 and LaCl3 in terms of ease of availability. The La raw material, W raw material, Co raw material, and Ti raw material are appropriately adjusted so that they are substantially soluble in the acidic solution along with the Sm raw material and the Fe raw material. The acidic solution may be sulfuric acid in terms of solubility. An example of a W raw material is ammonium tungstate, an example of a Co raw material is cobalt sulfate, and an example of a titanium raw material is titania sulfate.

[0016] 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.

[0017] The powder obtained in the precipitation step largely determines the particle size, shape, and particle size distribution of the final magnetic powder. 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 substantially within the range of 0.05 μm to 20 μm, preferably 0.1 μm to 10 μm.

[0018] 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 size, 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.

[0019] After the precipitation step, the resulting precipitate may be separated and washed. 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.

[0020] [Oxidation process] The oxidation step is a step of obtaining an oxide containing Sm and Fe by calcining 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 the air atmosphere. Furthermore, since it must be performed in the presence of oxygen, it is preferable that the non-metallic part of the precipitate contains oxygen atoms.

[0021] 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 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.

[0022] The resulting oxide particles are oxide particles in which Sm and iron are thoroughly mixed microscopically within the oxide particles, and the shape, particle size distribution, etc. of the precipitates are reflected.

[0023] [Pretreatment process] 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.

[0024] 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 increases during the reduction process, 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) spectroscopy.

[0025] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H), carbon monoxide (CO), and methane (CH). Hydrogen gas is preferred from a cost perspective, and the gas flow rate is appropriately adjusted within a range that does not cause oxides to scatter. The heat treatment temperature in the pretreatment step (hereinafter referred to as the pretreatment temperature) is preferably 300°C or higher and 950°C or lower, with the lower limit being more preferably 400°C or higher and even more preferably 750°C or higher. The upper limit is more preferably less than 900°C. A pretreatment temperature of 300°C or higher allows efficient reduction of oxides containing Sm and Fe. Furthermore, a pretreatment temperature of 950°C or lower suppresses particle growth and segregation of oxide particles, allowing the desired particle diameter to be maintained. The heat treatment time is not particularly limited, but can be 1 hour or higher and 50 hours or lower. When hydrogen is used as the reducing gas, it is preferable to adjust the thickness of the oxide layer to 20 mm or less, and further to adjust the dew point inside the reactor to -10°C or less.

[0026] [Reduction process] 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 contacting the partial oxide 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.

[0027] 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 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 heat treatment is preferable. 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.

[0028] The reducing agent, metallic calcium, is used in granular or powder form, with a 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).

[0029] 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 during the water washing step described below, 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% by mass to 30% by mass, preferably 5% by mass to 30% by mass, based on the samarium oxide.

[0030] [Nitriding process] The nitriding process involves heat-treating the alloy particles obtained in the reduction process in a nitrogen- or ammonia-containing atmosphere at a first temperature of 400°C to 470°C, followed by a second temperature of 480°C to 610°C to obtain anisotropic magnetic particles. Because the particulate precipitate obtained in the precipitation process is used, porous, agglomerated alloy particles are obtained in the reduction process. This allows for immediate nitriding in a nitrogen atmosphere without pulverization, ensuring uniform nitriding. If nitriding is not performed at the first temperature but at a high second temperature, the rapid nitriding process can cause abnormal heat generation, leading to decomposition of SmFeN and a significant decrease in magnetic properties. Furthermore, the atmosphere used in the nitriding process is preferably a substantially nitrogen-containing atmosphere, as this slows the nitriding process. The term "substantially" is used here to take into account the inevitable inclusion of elements other than nitrogen due to impurities, etc. For example, the nitrogen content in the atmosphere is 95% or more, preferably 97% or more, and more preferably 99% or more.

[0031] The first temperature in the nitriding step is 400°C or higher and 470°C or lower, but 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 is likely 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 time is shorter than 1 hour, the nitriding may not proceed sufficiently, and if the time exceeds 40 hours, productivity will be reduced.

[0032] The second temperature is 480°C or higher and 610°C or lower, but 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, over-nitriding or decomposition is likely to occur. The heat treatment time at the second temperature is preferably 15 minutes to 5 hours, and more preferably 30 minutes to 2 hours. If the temperature is lower than 15 minutes, nitriding may not proceed sufficiently, and if the temperature exceeds 5 hours, productivity will decrease.

[0033] 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.

[0034] [Post-processing process] The product obtained after the nitriding process contains magnetic particles as well as by-product CaO, unreacted metallic calcium, and other compounds, which may form a composite sintered mass. The product obtained after the nitriding process can be poured into cooling water, where the CaO and metallic calcium are separated from the magnetic powder as a calcium hydroxide (Ca(OH)2) suspension. Any remaining calcium hydroxide can be thoroughly removed by washing the magnetic powder with acetic acid or the like. When the product is poured into water, the oxidation of the metallic calcium by water and the hydration reaction of the by-product CaO cause the composite sintered mass reaction product to disintegrate, i.e., become finer.

[0035] [Alkali treatment process] The product obtained after the nitriding step may be placed in an alkaline solution. Examples of alkaline solutions used in the alkaline treatment step include calcium hydroxide aqueous solution, sodium hydroxide aqueous solution, and ammonia aqueous solution. Among these, calcium hydroxide aqueous solution and sodium hydroxide aqueous solution are preferred in terms of wastewater treatment and high pH. The alkaline treatment of the product leaves an Sm-rich layer containing a certain amount of oxygen, which functions as a protective layer, thereby suppressing an increase in oxygen concentration due to the alkaline treatment.

[0036] The pH of the alkaline solution used in the alkaline treatment step is not particularly limited, but is preferably at least 9, and more preferably at least 10. If the pH is less than 9, the reaction rate when calcium hydroxide is formed is high and heat is generated, which tends to increase the oxygen concentration in the anisotropic magnetic powder obtained as a result.

[0037] In the alkaline treatment step, the moisture content of the magnetic powder obtained after treatment with the alkaline solution can be reduced by a method such as decantation, if necessary.

[0038] [Acid treatment process] The alkaline treatment step may be followed by an acid treatment step in which the magnetic powder is treated with an acid. In the acid treatment step, at least a portion of the Sm-rich layer is removed to reduce the oxygen concentration in the magnetic powder as a whole. Furthermore, in the manufacturing method according to an embodiment of the present invention, since no pulverization or other processes are performed, the anisotropic magnetic powder has a small average particle size, a narrow particle size distribution, and does not contain fine powder generated by pulverization or other processes, making it possible to suppress an increase in the oxygen concentration.

[0039] 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.

[0040] The amount of acid used in the acid treatment step is preferably 3.5 to 13.5 parts by weight, more preferably 4 to 10 parts by weight, per 100 parts by weight of magnetic powder. If the amount is less than 3.5 parts by weight, oxides remain on the surface of the magnetic powder, resulting in a high oxygen concentration. If the amount is more than 13.5 parts by weight, reoxidation is likely to occur when exposed to the atmosphere, and the magnetic powder dissolves, which tends to increase costs. By using an amount of acid of 3.5 to 13.5 parts by weight per 100 parts by weight of magnetic powder, a Sm-rich layer oxidized to a degree that makes reoxidation less likely when exposed to the atmosphere after acid treatment can cover the magnetic powder surface, resulting in an anisotropic magnetic powder with a low oxygen concentration, a small average particle size, and a narrow particle size distribution.

[0041] In the acid treatment step, the moisture content of the magnetic powder obtained after the acid treatment can be reduced by a method such as decantation, if necessary.

[0042] [Dehydration process] 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, dehydration refers to a process in which the moisture content of the solid content after treatment is reduced compared to the solid content 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 squeezing, centrifugation, etc.

[0043] The amount of water contained in the magnetic powder after dehydration is not particularly limited, but is preferably 13% by mass or less, and more preferably 10% by mass or less, in order to suppress the progression of oxidation.

[0044] The magnetic powder obtained by acid treatment, or the 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.

[0045] [Surface treatment process] The 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 in an amount of 0.10 to 10 wt% (as PO4) based on the solid content of the magnetic particles obtained in the nitriding step. The surface-treated magnetic powder is obtained by separating it from the solution and drying it as appropriate.

[0046] The anisotropic magnetic powder according to one embodiment of the present invention comprises: The average particle size measured under dry conditions using a laser diffraction particle size distribution analyzer is 2 μm or more and 6 μm or less, and is calculated using the following formula: Span = (D90-D10) / D50 (Here, 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.) The span defined by is 1.6 or less, Contains Sm, Fe, La, and N The N content is 3.3 mass% or more and 3.5 mass% or less, The residual magnetization σr is 145 emu / g or more.

[0047] The anisotropic magnetic powder in this embodiment can be produced, for example, by the manufacturing method described above, but because the magnetic powder is not mechanically crushed by grinding or the like, the anisotropic magnetic powder has a low oxygen concentration, a small average particle diameter, a narrow particle size distribution (small span), and a high residual magnetic flux density.

[0048] The anisotropic magnetic powder in this embodiment is typically represented by the following general formula: Sm v Fe (100-v―w-x-y-z-u) N w La x W y Co z Ti u (Wherein, 3≦v≦30, 5≦w≦15, 0.1≦x≦0.3, 0≦y≦2.5, 0≦z≦2.5, and 0≦u≦2.5.) It is expressed as:

[0049] In the general formula, v is specified to be between 3 and 30 because, if it is less than 3, the unreacted portion of the iron component (α-Fe phase) separates, reducing the coercive force of the magnetic powder and making it unsuitable for practical use, while if it exceeds 30, Sm elements precipitate, making the magnetic powder unstable in the air and reducing the remanence. Furthermore, w is specified to be between 5 and 15 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] When Ti is contained, the Ti 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.

[0054] 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 magnetic properties tend to deteriorate.

[0055] The average particle size of the anisotropic magnetic powder is 2 μm to 6 μm, preferably 3 μm to 6 μm, and more preferably 4 μm to 6 μm. If the particle size is less than 2 μm, the surface area is large and oxidation is likely to occur. If the particle size exceeds 6 μm, the magnetic powder will have a multi-domain structure, which tends to deteriorate the magnetic properties. Here, the average particle size refers to the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0056] The anisotropic magnetic powder has the following formula: Span = (D90-D10) / D50 (Here, 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.) The span defined by is 1.6 or less, preferably 1.3 or less. If it exceeds 1.6, large particles are present, and the magnetic properties tend to deteriorate.

[0057] The average circularity of the 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, which will result 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 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 invention 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.

[0058] The magnetic powder preferably has a residual magnetization σr of 145 emu / g or more, more preferably 147 emu / g or more. The saturation magnetization σm is preferably 148 emu / g or more, more preferably 150 emu / g or more. Furthermore, the σr / σm ratio is preferably 0.96 or more, more preferably 0.98 or more.

[0059] The 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.

[0060] The bonded magnet is made from the anisotropic magnetic powder of this embodiment and a resin. By including this anisotropic magnetic powder, a composite material with high magnetic properties can be formed.

[0061] The resin contained in the composite material may be either 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), or polyethylene (PE).

[0062] When obtaining a composite material, the weight ratio of the anisotropic magnetic powder to the resin (resin / magnetic powder) is preferably 0.10 to 0.15, and more preferably 0.11 to 0.14.

[0063] The composite material can be obtained, for example, by mixing anisotropic magnetic powder and resin at 280 to 330°C using a kneader.

[0064] 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 process), and then pulse-magnetized in a magnetizing magnetic field (magnetization process), to produce a bonded magnet.

[0065] 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 orienting 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.

[0066] A sintered magnet is produced by molding and sintering the anisotropic magnetic powder of this embodiment. The 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.

[0067] As disclosed in JP 2017-055072 A, for example, sintered magnets are produced by sintering magnetic powder in an atmosphere with an oxygen concentration of 0.5 ppm by volume 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.

[0068] As disclosed in International Publication No. 2015 / 199096, for example, sintered magnets are produced by pre-compressing magnetic powder in a magnetic field of 6 kOe or greater, followed by warm compaction at a temperature of 600°C or less and a molding surface pressure of 1 to 5 GPa.

[0069] As disclosed in JP 2016-082175 A, for example, a sintered magnet is produced by cold compacting a mixture containing 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. [Example]

[0070] Examples will be described below. Unless otherwise specified, "%" is by mass.

[0071] [evaluation] The content of each metal, nitrogen concentration, average particle size, particle size distribution, remanent magnetization σr, and saturation magnetization σm were evaluated by the following methods.

[0072] <Content of each metal> The content of each metal (Sm, Fe, La, Co, etc.) was measured by dissolving in hydrochloric acid and then using ICP-AES (instrument name: Optima8300). <Nitrogen concentration> The nitrogen concentration was measured by a thermal conductivity method (EMGA-820 manufactured by Horiba, Ltd.).

[0073] <Average particle size and particle size distribution> The average particle size and particle size distribution were measured using a laser diffraction particle size distribution measuring device (HELOS&RODOS, manufactured by Japan Laser Co., Ltd.).

[0074] <Residual magnetization σr, saturation magnetization σm> The magnetic powder obtained was packed into a sample container together with paraffin wax, and after the paraffin wax was melted in a dryer, the easy magnetic 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 and saturation magnetization σm were measured using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m.

[0075] Manufacturing Example 1 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. 0.49 kg of Sm2O3 and 0.74 kg of 70% sulfuric acid were then added and stirred thoroughly to completely dissolve the solution. Next, pure water was added to the resulting solution, and the final Fe concentration was adjusted to 0.726 mol / L and the Sm concentration to 0.112 mol / L, creating a SmFe sulfuric acid solution.

[0076] [Precipitation process] The entire amount of the prepared SmFe sulfate solution was added dropwise to 20 kg of pure water maintained at 40°C over 70 minutes while stirring. At the same time, 15% ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFe 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.

[0077] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFe oxide was obtained as raw powder.

[0078] Manufacturing Example 2 The same procedure as in Production Example 1 was carried out except that 0.035 kg of La2O3 was added, thereby obtaining a red SmFeLa oxide.

[0079] Manufacturing Example 3 A red SmFeLaCo oxide was obtained in the same manner as in Production Example 1, except that 0.071 kg of 31.8% LaCl3 and 0.015 kg of 20.8% cobalt sulfate were added.

[0080] Example 1 [Pretreatment process] 100 g of the SmFe 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 a non-dispersive infrared spectrometer (ND-IR) (EMGA-820, manufactured by Horiba, Ltd.) and found to be 5% by mass. This indicated 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.

[0081] [Reduction process] 60 g of the partial oxide obtained in the pretreatment step and 19.2 g of metallic calcium with an average particle diameter 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 1045°C and held there for 45 minutes, then cooled to a second temperature of 1000°C and held there for 30 minutes to obtain SmFe alloy particles.

[0082] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated and, while introducing nitrogen gas, the temperature was increased to a first temperature of 430°C and held there for 3 hours, then increased to a second temperature of 500°C and held there for 1 hour, and then cooled to obtain an aggregated product containing magnetic particles.

[0083] [Post-processing process] The aggregated product obtained in the nitriding step was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice.

[0084] [Surface treatment process] A phosphoric acid solution was added to the resulting slurry. The phosphoric acid solution was added in an amount of 1 wt% (as PO4) based on the magnetic particle solid content. After stirring for 5 minutes, solid-liquid separation was carried out, followed by vacuum drying at 80°C for 3 hours to obtain magnetic powder. The content and composition of the resulting magnetic powder are shown in Table 1. The composition was calculated from the content of each metal and nitrogen analysis.

[0085] Example 2 The same procedures as in Example 1 were carried out except that the second temperature in the nitriding step was changed to 520°C.

[0086] Comparative Example 1 The same procedure as in Example 1 was carried out except that in the nitriding step, the temperature was raised to a first temperature of 430°C, held for 3 hours, and then cooled to obtain a mass product containing magnetic particles.

[0087] The residual magnetization σr, nitrogen concentration, and particle size distribution were measured by the above-mentioned methods using the magnetic powders obtained in Examples 1 and 2 and Comparative Example 1. The evaluation results are shown in Table 2.

[0088] [Table 1]

[0089] [Table 2]

[0090] From the results in Table 2, in Examples 1 and 2, when nitriding was performed at 430°C and then at 500°C or 520°C, the nitrogen concentration increased compared to Comparative Example 1, and the remanent magnetization σr became higher.

[0091] Example 3 The same procedure as in Example 1 was carried out except that the SmFeLa oxide obtained in Production Example 2 was used. Table 3 shows the content and composition of the obtained magnetic powder.

[0092] Example 4 The same procedures as in Example 3 were carried out except that the second temperature in the nitriding step was changed to 520°C.

[0093] Example 5 The same procedures as in Example 3 were carried out except that the second temperature in the nitriding step was changed to 550°C.

[0094] Example 6 The same procedures as in Example 3 were carried out except that the second temperature in the nitriding step was changed to 600°C.

[0095] Comparative Example 2 The same procedure as in Example 3 was carried out except that in the nitriding step, the temperature was raised to a first temperature of 430°C, held for 3 hours, and then cooled to obtain a mass product containing magnetic particles.

[0096] The residual magnetization σr, nitrogen concentration, and particle size distribution were measured by the above-mentioned methods using the magnetic powders obtained in Examples 3 to 6 and Comparative Example 2. The evaluation results are shown in Table 4.

[0097] [Table 3]

[0098] [Table 4]

[0099] The results in Table 4 show that in Examples 3 to 6, even when the magnetic powders had larger average particle sizes than those in Examples 1 and 2, when nitrided at 430°C and then at 500 to 600°C, the nitrogen concentration increased compared to Comparative Example 2. The remanent magnetization σr was even higher than in Examples 1 and 2.

[0100] Example 7 The same procedure as in Example 1 was carried out except for using the SmFeLaCo oxide obtained in Production Example 3. Table 5 shows the content and composition of the obtained magnetic powder.

[0101] Example 8 The same procedures as in Example 7 were carried out except that the second temperature in the nitriding step in Example 7 was changed to 520°C.

[0102] Example 9 The same procedures as in Example 7 were carried out except that the second temperature in the nitriding step was changed to 550°C.

[0103] Example 10 The same procedures as in Example 7 were carried out except that the second temperature in the nitriding step was changed to 600°C.

[0104] Comparative Example 3 The same procedure as in Example 7 was carried out except that in the nitriding step, the temperature was raised to a first temperature of 430°C, held for 3 hours, and then cooled to obtain a mass product containing magnetic particles.

[0105] The residual magnetization σr, nitrogen concentration, and particle size distribution were measured by the above-mentioned methods using the magnetic powders obtained in Examples 7 to 10 and Comparative Example 3. The evaluation results are shown in Table 6.

[0106] [Table 5]

[0107] [Table 6]

[0108] The results in Table 6 show that in Examples 7 to 9, even when the magnetic powders had larger average particle sizes than those in Examples 1 and 2, when nitrided at 430°C and then at 500 to 600°C, the nitrogen concentration increased compared to Comparative Example 3. The remanent magnetization σr was even higher than in Examples 1 and 2. [Industrial Applicability]

[0109] The anisotropic magnetic powder obtained by the manufacturing method of the present invention has a small average particle size, a narrow particle size distribution, and a high remanence σr, making it particularly suitable for use in bonded magnets.

Claims

1. The average particle size measured under dry conditions using a laser diffraction particle size distribution analyzer is 2 μm or more and 6 μm or less, The following formula Span = (D90 - D10) / D50 (Here, 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.) The span defined by is 1.6 or less, Contains Sm, Fe, La, and N, The N content is 3.3 mass% or more and 3.5 mass% or less, An anisotropic magnetic powder having a remanent magnetization σr of 145 emu / g or more.

2. The following general formula Sm ｖ Fe （１００－ｖ－ｗ－ｘ－ｙ－ｚ－ｕ） N ｗ La ｘ W ｙ Co ｚ Ti ｕ (Wherein, 3≦v≦30, 5≦w≦15, 0.1≦x≦0.3, 0≦y≦2.5, 0≦z≦2.5, and 0≦u≦2.5.) 2. The anisotropic magnetic powder according to claim 1, wherein the anisotropic magnetic powder is represented by the formula:

3. 3. An anisotropic magnetic powder according to claim 1, wherein the remanent magnetization σr is 147 emu / g or more.

4. A sintered magnet or bonded magnet comprising the anisotropic magnetic powder according to claim 1 or 2.

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