Method for producing anisotropic magnetic powder

Abstract

To provide a method for producing anisotropic magnetic powder having excellent magnetic properties.SOLUTION: Iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, A method for producing an anisotropic magnetic powder includes a step of obtaining a slurry having a conductivity of 100 μS / cm or more, a step of removing water from the slurry to obtain a mixture of the iron oxide particles and the oxide particles of R, a step of obtaining a partial oxide by heat-treating the mixture under a reducing gas atmosphere, a step of obtaining alloy particles by reducing the partial oxide, and a step of obtaining anisotropic magnetic powder by nitriding the alloy particles.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a method for producing anisotropic magnetic powder by dropping an acidic aqueous solution of rare earth elements and iron into an alkaline solution to obtain a coprecipitate, oxidizing the coprecipitate, and then reducing and nitriding the coprecipitate.

[0003] Patent Document 2 discloses a method for producing anisotropic magnetic powder by reducing a mixture of iron oxide particles and oxide particles of a rare earth element by hydrogen heat treatment, further reducing the mixture to obtain an alloy, and then nitriding the alloy.

[0004] Patent Document 3 discloses a method for producing anisotropic magnetic powder by mixing iron oxide particles and rare earth element oxide particles in a slurry, washing the mixture until the electrical conductivity of the wastewater decreases, and then reducing and nitriding the mixture. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-080653 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-270379 [Patent Document 3] Patent Publication No. 2021-055188 Summary of the Invention [Problem to be solved by the invention]

[0006] It has been found that when producing an anisotropic magnetic powder by mixing iron oxide particles and rare earth oxide particles in a slurry, if the iron oxide particles and rare earth oxide particles are not sufficiently agglomerated, the magnetic properties of the resulting anisotropic magnetic powder tend to deteriorate.The present disclosure aims to provide a method for producing an anisotropic magnetic powder with excellent magnetic properties. [Means for solving the problem]

[0007] A method for producing an anisotropic magnetic powder according to an embodiment of the present disclosure includes: obtaining a slurry containing iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, the slurry having a conductivity of 100 μS / cm or more; removing water from the slurry to obtain a mixture of the iron oxide particles and the oxide particles of R; heat-treating the mixture in a reducing gas atmosphere to obtain a partial oxide; reducing the partial oxide to obtain alloy particles; and The method includes a step of obtaining an anisotropic magnetic powder by nitriding the alloy particles. [Effects of the Invention]

[0008] It is possible to provide a method for producing anisotropic magnetic powder with excellent magnetic properties. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows the appearance of the slurry obtained in the slurry preparation step of Comparative Example 1. [Figure 2] 1 shows the appearance of the slurry obtained in the slurry preparation step of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present disclosure are described in detail below. However, the embodiments described below are examples for embodying the technical concept of the present disclosure and are not intended to limit the present disclosure. In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Furthermore, when multiple substances corresponding to each component are present in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified.

[0011] The method for producing anisotropic magnetic powder in this embodiment is as follows: a step of obtaining a slurry containing iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, the slurry having a conductivity of 100 μS / cm or more (slurry preparation step); a step of removing water from the slurry to obtain a mixture of the iron oxide particles and the oxide particles of R (dehydration step); a step of heat-treating the mixture in a reducing gas atmosphere to obtain a partial oxide (pretreatment step); a step of obtaining alloy particles by reducing the partial oxide (reduction step); and a step of nitriding the alloy particles to obtain anisotropic magnetic powder (nitriding step); According to this embodiment, by mixing iron oxide particles having the above-mentioned average particle size with oxide particles of R (R is at least one selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having the above-mentioned average particle size, it is possible to reduce uneven distribution of the iron oxide particles and oxide particles of R in the mixture, and it is believed that magnetic properties are improved.

[0012] <Slurry preparation process> The slurry preparation process is a process for obtaining a slurry containing iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, and having a conductivity of 100 μS / cm or more.

[0013] The average particle size of the iron oxide particles is 0.1 μm or more and 0.4 μm or less, preferably 0.13 μm or more and 0.35 μm or less, and more preferably 0.15 μm or more and 0.25 μm or less. If the average particle size exceeds 0.4 μm, the magnetic properties tend to deteriorate due to poor miscibility with the R oxide particles. If the average particle size is less than 0.1 μm, the iron oxide particles contain a large amount of impurities, which act as a flux during the heat treatment described below, generating coarse particles, which tends to deteriorate the magnetic properties. Here, the average particle size in this embodiment is the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0014] The R oxide particles are at least one oxide selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu, with Sm oxide Sm2O3 being preferred from the standpoint of magnetic properties. The R oxide particles have an average particle size of 0.35 μm to 0.8 μm, preferably 0.45 μm to 0.75 μm, and more preferably 0.50 μm to 0.70 μm. If the average particle size is less than 0.35 μm, hydration reactions are likely to occur, which rapidly generate heat and make handling difficult. If the average particle size exceeds 0.8 μm, miscibility with iron oxide particles is reduced, which makes abnormal growth of iron oxide particles more likely in the pretreatment process described below, and therefore tends to degrade magnetic properties.

[0015] The average particle size of the R oxide particles is preferably 4 times or less the average particle size of the iron oxide particles. If it exceeds 4 times, the mixing property of the iron oxide particles and the R oxide particles tends to deteriorate.

[0016] The amount of R oxide particles blended is preferably 32.2 to 36.8 parts by weight, more preferably 33.2 to 35.3 parts by weight, per 100 parts by weight of iron oxide particles. If it exceeds 36.8 parts by weight, the proportion of R-rich nonmagnetic phase increases, and magnetic properties tend to deteriorate. If it is less than 32.2 parts by weight, α-Fe is generated, and magnetic properties, particularly coercivity, tend to deteriorate.

[0017] Examples of iron oxide particles include magnetite (Fe3O4) and hematite (Fe2O3). Among these, magnetite is preferred because it is easily magnetically agglomerated and allows solid-liquid separation even when it is fine.

[0018] Commercially available iron oxide particles within the above particle size range may be used as the iron oxide particles. For example, magnetite iron oxide particles can be synthesized by adding an alkaline agent to an aqueous iron solution to produce a slurry containing a precipitate of iron hydroxide (Fe(OH)2), followed by blowing an oxygen-containing gas such as air into the slurry at a temperature of 70 to 90°C and a pH of 7.0 to 9.5 (wet oxidation method). Iron raw materials for producing the iron hydroxide precipitate include iron sulfate, which is readily available. Examples of alkaline agents include alkali metal hydroxides and ammonia. However, alkali metal hydroxides are preferred, and sodium hydroxide is particularly preferred due to its low production costs and environmental impact. Furthermore, when magnetite iron oxide particles are synthesized from the precipitate of iron hydroxide particles, recrystallization occurs, making it easy to reduce the residual alkali metal concentration (described below).

[0019] The alkali metal concentration in the iron oxide particles is preferably 200 ppm or less, and more preferably 100 ppm or less. If the alkali metal concentration in the iron oxide particles exceeds 200 ppm, they act as a flux during the reduction step described below, generating coarse particles, which tends to deteriorate the magnetic properties. In addition, in the above-mentioned wet oxidation method, the alkali metal concentration can be reduced by through-washing the slurry of synthesized magnetite iron oxide particles with pure water. Through-washing here refers to the operation of washing the dehydrated cake in the filter without opening the filter.

[0020] A slurry containing iron oxide particles, R oxide particles, and water is obtained by mixing a slurry containing iron oxide particles with a slurry containing R oxide particles. Mixing may be performed by stirring, but precision mixing is preferred because it can reduce uneven distribution of the iron oxide particles and R oxide particles in the mixture to a small area (4 μm). Precision mixing methods include mixing using a bead mill or mixing using a beadless line mixer. When using a bead mill, the bead diameter is preferably 0.05 mm or more and 0.5 mm or less.

[0021] The amount of water in the slurry obtained in this step is preferably 50% by weight or more and 95% by weight or less, and more preferably 80% by weight or more and 90% by weight or less. The slurry obtained in this step may contain, in addition to water, organic solvents such as ethyl alcohol, isopropyl alcohol, n-butyl alcohol, dimethyl ether, ethyl methyl ether, diethyl ether, ethyl methyl ketone, and diethyl ketone. However, the amount of these organic solvents is preferably 10 parts by weight or less, and more preferably 3 parts by weight or less, per 100 parts by weight of water. The slurry need not contain an organic solvent.

[0022] After mixing the slurry containing iron oxide particles with the slurry containing R oxide particles, it is preferable to wash the mixture. By washing, alkali metal ions, sulfate ions, etc. contained in the mixture can be removed. Washing is preferably performed with pure water, and the conductivity of the effluent after washing is preferably less than 100 μS / cm, more preferably 30 μS / cm or less.

[0023] The coefficient of variation (CV) of the mixture distribution, which indicates the uneven distribution of iron oxide particles and R oxide particles in the slurry, is preferably 23% or less, more preferably 22% or less, and particularly preferably 21% or less. If the coefficient of variation exceeds 23%, the magnetic properties of the anisotropic magnetic powder tend to deteriorate. The coefficient of variation of the mixture distribution can be determined by taking a backscattered electron image of the mixture at 5000x magnification, dividing the image into squares with corners equivalent to 4 μm, calculating the area ratio of iron oxide to R oxide particles for each square, and calculating the variation in the area ratio.

[0024] The conductivity of the slurry obtained in this step is 100 μS / cm or more. There is no particular upper limit to the conductivity, but it is generally 500 μS / cm or less. The conductivity of the slurry is the conductivity measured for water, which is the dispersion medium, and specifically, for example, is the value measured for the washing wastewater or the supernatant of the slurry, excluding the influence of iron oxide particles and R oxide particles.

[0025] Iron oxide particles are magnetic and tend to aggregate and precipitate. Furthermore, the R contained in the R oxide particles has the property of bonding with hydroxide ions in the slurry to form a light-weight hydroxide of R. Therefore, the iron oxide particles and the R oxide particles may separate without forming a complex. In this embodiment, the conductivity of the slurry is set to 100 μS / cm or higher, which adjusts the surface charge of the iron oxide particles and the R oxide particles and promotes the aggregation and formation of a complex. This can prevent the slurry from separating into a layer of iron oxide particles and a layer of R hydroxide particles.

[0026] After mixing a slurry containing iron oxide particles with a slurry containing R oxide particles, if the conductivity of the resulting slurry is less than 100 μS / cm, it is preferable to add an alkaline agent to adjust the conductivity to 100 μS / cm or more. Furthermore, after the aforementioned cleaning with pure water has been performed, it is preferable to add an alkaline agent to adjust the conductivity to 100 μS / cm or more. The alkaline agent is not particularly limited as long as it can increase the conductivity. However, preferred alkaline agents are ammonia, ammonium salts such as ammonium bicarbonate and ammonium tungstate, and calcium salts such as calcium hydroxide, which do not remain as impurities in subsequent processes, and ammonia is more preferred because it is vaporized in subsequent processes.

[0027] When a gas such as ammonia is used as the alkaline agent, it is preferable to prepare an aqueous solution containing the alkaline agent and add the aqueous solution to a slurry containing iron oxide particles, R oxide particles, and water. The amount of aqueous solution containing the alkaline agent is determined so that the conductivity of the slurry becomes the desired value. When ammonia is used as the alkaline agent, the concentration of the aqueous ammonia solution is preferably 1 wt / w% or more and 35 wt / w% or less, and more preferably 5 wt / w% or more and 30 wt / w% or less.

[0028] When using a solid such as an ammonium salt or calcium salt as the alkaline agent, the average particle size should be large enough to prepare an aqueous solution or slurry containing the alkaline agent. When using a solid that is not easily soluble in water, such as calcium hydroxide, as the alkaline agent, a slurry containing the alkaline agent can be prepared and added to a slurry containing iron oxide particles, R oxide particles, and water.

[0029] The average particle size of the solid alkaline agent is preferably 4 times or less the average particle size of the iron oxide particles. If it exceeds 4 times, the mixing ability of the iron oxide particles and the oxide particles of R tends to deteriorate.

[0030] When a solid alkaline agent is added, the amount added is preferably 8 to 48 parts by weight, and more preferably 18 to 32 parts by weight, per 100 parts by weight of iron oxide particles. If the amount exceeds 48 parts by weight, the particle size of the magnetic powder tends to become smaller, and magnetic properties, particularly remanence, tend to decrease, while if the amount is less than 8 parts by weight, the effect of suppressing sintering of the iron oxide particles tends to decrease.

[0031] The solid alkaline agent may be mixed with the iron oxide particles before the pretreatment step, and the mixing method is not particularly limited, but it is preferable to mix a slurry of the solid alkaline agent with a slurry containing iron oxide particles, R oxide particles, and water. Mixing may be performed by stirring, but precision mixing is preferred because it can reduce uneven distribution of the iron oxide particles, R oxide particles, and alkaline agent in the mixture.

[0032] The slurry containing iron oxide particles, R oxide particles, and water may further contain compounds of metals such as La, W, Ti, Ba, and Sr. These metals may be used alone or in combination of two or more. Examples of compounds of these metals include oxides, chlorides, ammonium salts, sulfates, and carbonates. The average particle size of the compounds of these metals is preferably 0.1 μm or more and 1 μm or less.

[0033] The amount of the compound of these metals is preferably 0 to 20 parts by weight, more preferably 5 to 10 parts by weight, per 100 parts by weight of the total amount of the iron oxide particles and the oxide particles of R. If the amount exceeds 20 parts by weight, σr tends to decrease.

[0034] The slurry preparation process may involve mixing iron oxide particles with an average particle size of 0.1 μm to 0.4 μm, R oxide particles with an average particle size of 0.5 μm to 0.8 μm, and water to obtain a slurry, and then determining whether or not an alkaline agent needs to be added by checking the state of the slurry. The state of the slurry may be checked by measuring the conductivity of the supernatant liquid of the slurry or the washing wastewater, or by observing the slurry. For example, the need for the addition of an alkaline agent may be determined when the measured conductivity is less than 100 μS / cm. Furthermore, the need for the addition of an alkaline agent may be determined when a slurry containing iron oxide particles and a slurry containing R oxide particles are mixed, left for a predetermined period of time, and visually observed to confirm turbidity. One cause of turbidity is the hydroxide of R. The oxide particles of R do not aggregate with the iron oxide particles to form a complex, but rather R binds to hydroxide ions in the slurry. The more hydroxide of R is formed, the more turbid the slurry becomes. If it is determined that the addition of an alkaline agent is necessary, the alkaline agent is added to the slurry to obtain a slurry with a conductivity of 100 μS / cm or more. Note that the pH also changes when an alkaline agent is added, but since the pH can be affected by ions that are not related to the aggregation of iron oxide particles and R oxide particles, it is more appropriate to use the conductivity as a criterion.

[0035] <Dehydration process> The dehydration step is a step of removing water from the slurry obtained in the slurry preparation step to obtain a mixture of iron oxide particles and oxide particles of R. The water is preferably removed by spray drying the slurry at a temperature of about 200°C or higher and 250°C or lower.

[0036] <Pretreatment process> The pretreatment step is a step in which the mixture of iron oxide particles obtained in the dehydration step and oxide particles of R is heat-treated in a reducing gas atmosphere to obtain a partial oxide in which most of the iron oxide contained therein is reduced.

[0037] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H), carbon monoxide (CO), and methane (CH), but hydrogen gas is preferred from a cost perspective. 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, more preferably 400°C or higher, even more preferably 750°C or higher, and preferably lower than 900°C. A pretreatment temperature of 300°C or higher allows the reduction of iron oxide to proceed efficiently. Furthermore, a pretreatment temperature of 950°C or lower suppresses particle growth and segregation of iron particles generated by reduction, allowing the desired particle size to be maintained. Furthermore, when hydrogen is used as the reducing gas, it is preferable to adjust the thickness of the oxide layer used to 20 mm or less and further adjust the dew point in the reactor to -10°C or less.

[0038] <Reduction process> The reduction step is a step of reducing the obtained partial oxide to obtain alloy particles. Specifically, for example, the partial oxide is mixed with metallic calcium, and the mixture is heat-treated in an inert gas atmosphere other than nitrogen, such as argon, or in vacuum to obtain alloy particles containing iron and R.

[0039] The oxide is reduced by contacting it with calcium melt or calcium vapor. The heat treatment temperature in the reduction step (hereinafter referred to as reduction temperature) is preferably 700°C or higher and 1200°C or lower, and more preferably 800°C or higher and 1100°C or lower. From the viewpoint of carrying out the reduction reaction more uniformly, the heat treatment time can be in the range of 10 minutes to 10 hours, and is preferably in the range of more than 10 minutes to 2 hours.

[0040] Metallic calcium is used in granular or powder form, with the particle size preferably being 10 mm or less. This allows for more effective suppression of particle necking during the reduction reaction. Metallic calcium can be added in an amount ranging from 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce rare earth oxides, including the amount required to reduce iron oxides), and preferably from 1.5 to 2.5 times.

[0041] 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 water washing 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 to 30% by mass, preferably 5% by mass to 30% by mass, based on the rare earth oxide used as the rare earth source.

[0042] <Nitriding process> The nitriding process is a process in which the alloy particles obtained in the reduction process are nitrided to obtain anisotropic magnetic particles. Because the reduction process produces a porous sintered mass, the particles can be immediately heat-treated in a nitrogen atmosphere to be nitrided without being pulverized, allowing for uniform nitriding.

[0043] The heat treatment temperature in the nitriding treatment of the alloy particles (hereinafter referred to as the nitriding temperature) is preferably 300°C or higher and 600°C or lower, and more preferably 400°C or higher and 550°C or lower. The alloy particles can be nitrided by replacing the atmosphere with a nitrogen atmosphere within these temperature ranges. The heat treatment time may be set to a time sufficient to ensure that the alloy particles are nitrided sufficiently and uniformly, for example, about 2 hours or higher and 30 hours or lower.

[0044] <Water washing process> A water washing process may be performed following the nitriding process. In this process, the sintered body obtained in the nitriding process is immersed in cold water to disintegrate the sintered body and separate the anisotropic magnetic particles from impurities. The product obtained after the nitriding process may contain, in addition to magnetic particles, by-product CaO, unreacted metallic calcium, and other compounds, forming a composite sintered mass. In this case, the product can be immersed in cooling water to separate the CaO and metallic calcium from the magnetic particles as a calcium hydroxide (Ca(OH)2) suspension. The remaining calcium hydroxide can be further removed by washing the magnetic particles with acetic acid or other suitable agents. When the product is immersed in water, the oxidation of the metallic calcium by water and the hydration of the by-product CaO cause the composite sintered mass reaction product to disintegrate, i.e., become finer. If a surface treatment is performed, a phosphoric acid solution may be added as a surface treatment agent in a range of 0.10% to 10% by mass (as PO4) of the solid content of the magnetic particles obtained in the nitriding process. The anisotropic magnetic powder is obtained by separating the product from the solution and drying it appropriately.

[0045] The anisotropic magnetic powder obtained as described above is typically represented by the following general formula: R x Fe (100-x-y) N y (In the formula, R represents at least one selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu, x is 3 or more and 30 or less, and y is 5 or more and 15 or less.) From the viewpoint of magnetic properties, R is preferably Sm.

[0046] In the general formula, x is specified to be 3 to 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 nitride and making the magnet unusable, while if it exceeds 30, at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu precipitates, making the magnetic powder unstable in air and reducing the remanence. Furthermore, y is specified to be 5 to 15 because, if it is less than 5, almost no coercive force is exhibited, and if it exceeds 15, nitrides of at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu and iron itself are formed.

[0047] <Composite materials> A composite material can be produced by mixing the anisotropic magnetic powder of this embodiment with a resin. By including the anisotropic magnetic powder of this embodiment, a composite material with high magnetic properties can be formed.

[0048] 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).

[0049] When obtaining a composite material, the mixing weight ratio of the anisotropic magnetic powder to the resin (resin / magnetic powder) is preferably 0.10 or more and 0.15 or less, and more preferably 0.11 or more and 0.14 or less.

[0050] The composite material can be obtained, for example, by mixing anisotropic magnetic powder and resin at a temperature of 280° C. or higher and 330° C. or lower using a kneader.

[0051] <Bonded magnet> The composite material described above can be used to produce a bonded magnet. Specifically, the composite material can be heat-treated while aligning the axis of easy magnetization in an orienting magnetic field (orientation step), and then pulse-magnetized in a magnetizing magnetic field (magnetization step), to produce a bonded magnet.

[0052] The heat treatment temperature in the orientation step is preferably 90°C or higher and 200°C or lower, and more preferably 100°C or higher and 150°C or lower. 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 kA / m or higher and 2500 kA / m or lower.

[0053] This embodiment may include, for example, the following aspects. <1> obtaining a slurry containing iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, the slurry having a conductivity of 100 μS / cm or more; removing water from the slurry to obtain a mixture of the iron oxide particles and the oxide particles of R; heat-treating the mixture in a reducing gas atmosphere to obtain a partial oxide; reducing the partial oxide to obtain alloy particles; and A step of obtaining an anisotropic magnetic powder by nitriding the alloy particles. A method for producing an anisotropic magnetic powder comprising:

[0054] <2> Item 2. The method for producing an anisotropic magnetic powder according to Item 1, wherein the slurry further contains at least one selected from the group consisting of La, W, Ti, Ba, and Sr.

[0055] <3> Item 3. The method for producing an anisotropic magnetic powder according to Item 1 or 2, wherein in the step of obtaining the slurry, an alkaline agent is added to adjust the electrical conductivity to 100 μS / cm or more.

[0056] <4> Item 4. The method for producing an anisotropic magnetic powder according to any one of items 1 to 3, wherein the coefficient of variation of the mixture distribution of the mixture is 23% or less.

[0057] <5> Item 5. The method for producing an anisotropic magnetic powder according to any one of items 1 to 4, wherein the iron oxide particles are Fe3O4 particles.

[0058] <6> Item 6. The method for producing an anisotropic magnetic powder according to any one of items 1 to 5, wherein the alkali metal concentration in the iron oxide particles is 200 ppm or less.

[0059] <7> Item 7. The method for producing an anisotropic magnetic powder according to any one of Items 1 to 6, wherein R is Sm. [Example]

[0060] Examples will be described below. Unless otherwise specified, "%" is by mass.

[0061] (1) Comparative Example 1 (Slurry preparation process) 15.02 kg of ferrous sulfate (FeSO4·7H2O) with an iron concentration of 8% was added to 50 kg of pure water, and while stirring, 25% caustic soda was added until the pH reached 10.5 to create an iron hydroxide slurry. After heating this iron hydroxide slurry to 70-85°C, aeration was performed while controlling the pH at 8.0-9.0, creating a slurry containing 4.17 kg of magnetite (Fe3O4) with an average particle size of 0.20 μm as iron oxide particles.

[0062] While stirring 3 kg of pure water, 1.42 kg of samarium oxide (Sm2O3) was dissolved little by little to avoid aggregation, to prepare a samarium oxide slurry. The samarium oxide particles in this slurry were then pulverized until their average particle size was 0.50 μm.

[0063] The samarium oxide slurry was added to the magnetite slurry and stirred, followed by precision mixing using a bead mill (bead diameter 0.3 mm) to create an oxide slurry in which iron and samarium were mixed uniformly at the microscopic level. This oxide slurry was stirred at 80°C for 2 hours and then washed with pure water until the effluent conductivity was 30 μS / cm or less. At this point, turbidity was observed in the oxide slurry (Figure 1). It is believed that the turbidity of the oxide slurry is due to the fact that the iron oxide particles and samarium oxide particles did not form a complex, and the samarium combined with the hydroxide ions in the slurry, resulting in the precipitation of samarium hydroxide.

[0064] (Dehydration process) The washed oxide slurry was dehydrated to a solid content of 30-50% to increase the concentration of the slurry. The increased concentration of the oxide slurry was pumped and spray-dried at approximately 250°C to obtain 4.44 kg of black Fe and Sm mixed oxide.

[0065] (Pretreatment process) 4.44 kg of the oxide powder obtained above was reduced in a hydrogen reduction furnace at approximately 800°C to reduce the oxygen concentration in the powder to 5.8 mass% or less, and 3.42 kg of hydrogen-reduced powder was recovered.

[0066] (Reduction process) Metallic calcium (particle diameter approximately 6 mm) was prepared in an amount 2.25 times equivalent to the amount of oxygen contained in the powder obtained in the pretreatment process, and mixed with the hydrogen-reduced powder. Specifically, 103.8 g of hydrogen-reduced powder and 29.8 g of metallic calcium were mixed, press-molded, and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1010°C and held there for 1 hour to obtain Fe-Sm alloy particles.

[0067] (nitriding process) After the reduction step, the mixture was cooled to 100°C, evacuated, and then nitrogen gas was introduced while the temperature was increased to 360°C and maintained at that temperature for 22 hours. Thereafter, the temperature was increased to 460°C and maintained at that temperature for 7 hours, yielding a reaction product containing anisotropic magnetic powder.

[0068] (Water washing process) The lumpy reaction 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, 240 g of 6% hydrochloric acid was poured and stirred until the pH reached 4.5. After that, 4.0 g of 99.9% acetic acid was poured and stirred for 1 minute. The obtained slurry was subjected to solid-liquid separation, and then vacuum dried at 80°C for 3 hours to obtain an anisotropic magnetic powder. The obtained anisotropic magnetic powder was SmFe 17 Represented by N3.

[0069] (Vibration mill process) The anisotropic magnetic powder obtained above was placed in a 500 ml metal pot containing 900 g of 2.5 mm diameter beads (SUJ2) and dry-pulverized using a vibration mill. After that, the anisotropic magnetic powder was sieved to recover only the powder.

[0070] (2) Examples 1 and 2 (Slurry preparation process) 15.02 kg of ferrous sulfate (FeSO4·7H2O) with an iron concentration of 8% was added to 50 kg of pure water, and while stirring, 25% caustic soda was added until the pH reached 10.5 to create an iron hydroxide slurry. After heating this iron hydroxide slurry to 70-85°C, aeration was performed while controlling the pH at 8.0-9.0, creating a slurry containing 4.17 kg of magnetite (Fe3O4) with an average particle size of 0.20 μm as iron oxide particles.

[0071] While stirring 3 kg of pure water, 1.42 kg of samarium oxide (Sm2O3) was dissolved little by little to avoid aggregation, to prepare a samarium oxide slurry. The samarium oxide particles in this slurry were then pulverized until their average particle size was 0.50 μm.

[0072] The samarium oxide slurry was added to the magnetite slurry and stirred. Precision mixing was performed using a bead mill (bead diameter 0.3 mm) to produce an oxide slurry in which iron and samarium were uniformly mixed at the microscopic level. This oxide slurry was stirred at 80°C for 2 hours. The slurry was washed with pure water until the effluent conductivity was 30 μS / cm or less. A 28 wt% aqueous ammonia solution was then added until the conductivity of the liquid component of the oxide slurry reached 107 μS / cm (Example 1) or 120 μS / cm (Example 2). No turbidity was observed in the oxide slurry of Example 2 (Figure 2).

[0073] After the slurry preparation step, the dehydration step, pretreatment step, reduction step, nitriding step, water washing step, and vibration mill step were carried out under the same conditions as in Comparative Example 1, and the anisotropic magnetic powder was recovered.

[0074] (3) Evaluation of magnetic properties The anisotropic magnetic powders obtained in the above examples and comparative examples were filled into a sample container together with paraffin wax. The paraffin wax was melted using a dryer, and then the easy magnetic domains were aligned in an orienting magnetic field of 16 kA / m. This magnetically oriented sample was pulse-magnetized in a magnetizing magnetic field of 32 kA / m, and the remanence (σr), coercivity (iHc), and squareness (Hk) were measured using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m. The measurement results are shown in Table 1.

[0075] [Table 1]

[0076] As shown in Table 1, the magnetic powders of Examples 1 and 2, which had high electrical conductivity in the liquid component of the oxide slurry, had improved remanence (σr) compared to the magnetic powder of Comparative Example 1.

Claims

1. obtaining a slurry containing iron oxide particles having an average particle size of 0.1 μm or more and 0.4 μm or less, oxide particles of R (R is at least one element selected from the group consisting of Sc, Y, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) having an average particle size of 0.5 μm or more and 0.8 μm or less, and water, the slurry having a conductivity of 100 μS / cm or more; removing water from the slurry to obtain a mixture of the iron oxide particles and the oxide particles of R; heat-treating the mixture in a reducing gas atmosphere to obtain a partial oxide; reducing the partial oxide to obtain alloy particles; and A step of obtaining an anisotropic magnetic powder by nitriding the alloy particles. A method for producing an anisotropic magnetic powder comprising:

2. 2. The method for producing an anisotropic magnetic powder according to claim 1, wherein the slurry further contains at least one element selected from the group consisting of La, W, Ti, Ba, and Sr.

3. 3. The method for producing an anisotropic magnetic powder according to claim 1, wherein in the step of obtaining the slurry, an alkaline agent is added to adjust the electrical conductivity to 100 [mu]S / cm or more.

4. The method for producing an anisotropic magnetic powder according to claim 1 or 2, wherein the coefficient of variation of the mixture distribution of the mixture is 23% or less.

5. The iron oxide particles are Fe ３ O ４ The method for producing anisotropic magnetic powder according to claim 1 or 2, wherein the anisotropic magnetic powder is in the form of particles.

6. 3. The method for producing an anisotropic magnetic powder according to claim 1, wherein the concentration of alkali metal in the iron oxide particles is 200 ppm or less.

7. The method for producing an anisotropic magnetic powder according to claim 1 or 2, wherein R is Sm.

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