Method for producing magnetic particles, magnetic particles, and permanent magnet using same

Abstract

A method for producing magnetic particles according to the present invention comprises: a step for mixing manganese particles, an aluminum source, an activator containing a halide, and an anti-sintering agent to obtain mixed powder, wherein the maximum particle diameter of the manganese particles is not more than 50 μm and the maximum particle diameter of the anti-sintering agent is 0.0002 to 3 times the maximum particle diameter of the manganese particles; a step for subjecting the manganese particles to calorizing treatment to obtain a treated mixture which contains particles containing a manganese-aluminum alloy, wherein the proportion (Al / Mn) of aluminum to manganese in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 in terms of mass ratio; and a step for recovering the particles containing the manganese-aluminum alloy from the treated mixture.

Description

Method for producing magnetic particles, magnetic particles, and permanent magnet using the same

[0001] The present invention relates to a method for producing magnetic particles and to magnetic particles.

[0002] It has been known that magnetic particles of manganese-aluminum alloys containing the τ phase can be used as magnetic materials.

[0003] Japanese Patent Application Laid-Open No. 2019-44265

[0004] In general, magnetic particles of manganese-aluminum alloy can be produced through the following steps: (1) forming a powder by a melt atomization method or the like (gas atomization process), and (2) heat treating the powder.

[0005] The process (1) produces powder mainly composed of the ε phase, which is not a ferromagnetic phase, and therefore requires the heat treatment (aging treatment) (2) to convert the ε phase into the τ phase, which is a ferromagnetic phase.

[0006] However, such a manufacturing process is complicated, and there is a demand for a simpler method for manufacturing magnetic particles of a manganese-aluminum alloy containing the τ phase.

[0007] The present invention has been made in view of the above background, and an object of the present invention is to provide a method for more easily producing magnetic particles containing a manganese-aluminum alloy, and to provide magnetic particles containing a manganese-aluminum alloy obtained by such a distinctive process.

[0008] The present invention provides a method for producing magnetic particles containing a manganese-aluminum alloy, the method comprising the steps of: (i) mixing manganese particles, an aluminum source, an activator containing a halide, and a sintering inhibitor to obtain a mixed powder, wherein the maximum particle size of the manganese particles is 50 μm or less, and the maximum particle size of the sintering inhibitor is 0.0002 to 3 times the maximum particle size of the manganese particles; (ii) heating the mixed powder to a temperature in the range of 1000°C to 1235°C to calorify the manganese particles to obtain a treated mixture having particles containing a manganese-aluminum alloy, wherein the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 by mass; and (iii) recovering particles containing the manganese-aluminum alloy from the treated mixture.

[0009] The present invention also provides magnetic particles comprising a manganese-aluminum alloy and alumina, wherein the abundance of the alumina contained in the magnetic particles is in the range of 0.1% by mass to 30% by mass, the abundance of the manganese-aluminum alloy contained in the magnetic particles is in the range of 70% by mass to 99% by mass, the manganese-aluminum alloy has a τ phase, and the abundance of the τ phase relative to the manganese-aluminum alloy is in the range of 10% by mass to 99% by mass, and the magnetic particles have a maximum particle size of 50 μm or less and a coercive force of 1000 Oe or more.

[0010] The present invention provides a method for more easily producing magnetic particles containing a manganese-aluminum alloy, and also provides magnetic particles containing a manganese-aluminum alloy obtained by such a unique process.

[0011] It is a diagram showing a schematic example of a flow of a method for manufacturing magnetic particles according to one embodiment of the present invention. It is a photograph showing the morphology of magnetic particles according to one embodiment of the present invention. It is a photograph showing the morphology of magnetic particles according to another embodiment of the present invention. It is a photograph showing the morphology of magnetic particles according to a comparative example. It is a graph showing the particle size distribution measured for magnetic particles according to one embodiment of the present invention and magnetic particles according to a comparative example.

[0012] An embodiment of the present invention will be described below.

[0013] As described above, conventional methods for producing magnetic particles of manganese-aluminum alloys require gas atomization and subsequent aging treatment, and there is a demand for a simpler method for producing magnetic particles of manganese-aluminum alloys containing the τ phase.

[0014] Under these circumstances, the present inventors have realized that by employing a calorification treatment, it may be possible to produce magnetic particles of a manganese-aluminum alloy in a single treatment.

[0015] Calorizing is a technique for diffusing and penetrating aluminum from the surface to the interior of a workpiece at high temperatures. When manganese particles are used as the workpiece, aluminum penetrates into the manganese particles during the calorizing process, forming a manganese-aluminum alloy. Therefore, by setting the ratio of manganese to aluminum and the temperature in the reaction system within a predetermined range, it is possible to form a manganese-aluminum alloy containing the τ phase after the calorizing process.

[0016] It is believed that such a calorifying treatment can produce magnetic particles containing a manganese-aluminum alloy by a process simpler than conventional processes.

[0017] However, simply applying calorizing treatment to manganese alloys may result in the reduction of oxides in the reaction system and the oxidation of aluminum, which may cause a solid-state contact reaction (thermit reaction) that generates a large amount of heat. If such a thermite reaction occurs, the treatment environment may become extremely hot, and there is a risk that the particles in the treated mixture (hereinafter referred to as the "treated mixture") may become strongly adhered to each other.

[0018] To address this problem, it is conceivable to use a sintering inhibitor during the calorification treatment, and utilize the gaps formed between the sintering inhibitors to carry out the calorification treatment of the manganese particles within the gaps.

[0019] In this case, the gaps serve to provide "small compartments" for reaction that are separated from each other, thereby reducing the possibility of manganese particles adhering to sintering inhibitors, etc., even if a thermite reaction occurs within the reaction system.

[0020] However, if the gap size is too large, this method has the problem that the particle size of the magnetic particles of the resulting manganese-aluminum alloy becomes too large, and magnetic particles with a large particle size may not provide good magnetic properties.

[0021] The present inventors have been diligently conducting research and development to address these newly arising problems, and have discovered that the above problems can be resolved by appropriately controlling the particle sizes of both the sintering inhibitor and the manganese particles, which led to the present invention.

[0022] That is, one embodiment of the present invention provides a method for producing magnetic particles containing a manganese-aluminum alloy, the method comprising the steps of: (i) mixing manganese particles, an aluminum source, an activator containing a halide, and a sintering inhibitor to obtain a mixed powder, wherein the maximum particle size of the manganese particles is 50 μm or less, and the maximum particle size of the sintering inhibitor is 0.0002 to 3 times the maximum particle size of the manganese particles; (ii) heating the mixed powder to a temperature in the range of 1000°C to 1235°C to calorify the manganese particles to obtain a treated mixture having particles containing a manganese-aluminum alloy, wherein the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 by mass; and (iii) recovering particles containing the manganese-aluminum alloy from the treated mixture.

[0023] In one embodiment of the present invention, the aforementioned calorification process is utilized to produce magnetic particles of manganese-aluminum alloy containing tau phase.

[0024] In one embodiment of the present invention, unlike conventional gas atomization methods, magnetic particles of manganese-aluminum alloy containing τ phase can be produced directly after treatment, making it possible to produce magnetic particles of manganese-aluminum alloy through a relatively simple process.

[0025] In one embodiment of the present invention, the manganese particles have a maximum particle diameter (hereinafter referred to as D （１）ｍａｘ ") is used as a sintering inhibitor. （２）ｍａｘ ") is 0.0002 x D （１）ｍａｘ That's it, 3xD （１）ｍａｘ The following particles are used:

[0026] The maximum particle diameter D of the sintering inhibitor （２）ｍａｘ is the maximum particle diameter D of manganese particles （１）ｍａｘ It is 3 times or less, preferably 1 time or less, and more preferably 0.225 times or less.

[0027] When the particle sizes of the materials are selected in this way, the gaps formed between the sintering inhibitor particles during the calorification process can be utilized to carry out the calorification process within the gaps, significantly reducing the possibility of the manganese particles adhering to the sintering inhibitor, etc., even if a thermite reaction occurs in the reaction system.

[0028] Furthermore, when the particle diameter relationship described above is selected, the gap size becomes relatively small, and it is possible to obtain magnetic particles of manganese-aluminum alloy with a relatively small particle diameter, which in turn makes it possible to obtain magnetic particles of manganese-aluminum alloy with relatively good magnetic properties, such as high coercive force.

[0029] For example, in one embodiment of the present invention, magnetic particles of manganese-aluminum alloy having a maximum particle size of 50 μm or less can be obtained immediately after collection.

[0030] (Method for Producing Magnetic Particles According to an Embodiment of the Present Invention) Next, with reference to FIG. 1, a method for producing magnetic particles according to an embodiment of the present invention will be described in more detail.

[0031] FIG. 1 is a schematic diagram showing an example of the flow of a method for producing magnetic particles according to an embodiment of the present invention.

[0032] As shown in FIG. 1 , a method for producing magnetic particles according to one embodiment of the present invention (hereinafter referred to as the “first production method”) includes: (1) a step of mixing manganese particles, an aluminum source, an activator containing a halide, and a sintering inhibitor to obtain a mixed powder (step S110); (2) a step of heating the mixed powder to a temperature in the range of 1000° C. to 1235° C. to calorify the manganese particles and obtain a treated mixture having particles containing a manganese-aluminum alloy (step S120); and (3) a step of recovering particles containing the manganese-aluminum alloy from the treated mixture (step S130).

[0033] Each step will be described in more detail below.

[0034] (Step S110) First, a mixed powder is prepared.

[0035] The mixed powder contains manganese particles, a sintering inhibitor, an aluminum source, and an activator. Each component will be described below.

[0036] (Manganese particles) Maximum particle diameter D of manganese particles （１）ｍａｘ is selected to be 50 μm or less. （１）ｍａｘ is, for example, in the range of 0.01 μm to 50 μm, preferably in the range of 0.01 μm to 25 μm, and more preferably in the range of 0.01 μm to 10 μm.

[0037] In addition, the average particle diameter of manganese particles (hereinafter referred to as "D （１）ａｖｅ ") may be in the range of, for example, 0.01 μm to 50 μm.

[0038] In the present application, the "maximum particle diameter" is understood to be the maximum length of a line passing through the center of gravity of a particle. Therefore, when the particle is spherical, the "maximum particle diameter" corresponds to the diameter.

[0039] In the present application, the "average particle size" is measured by the method specified in JIS Z 8801.

[0040] That is, several sieves with different mesh sizes are stacked on top of each other in order of size, starting with the smallest, and the particles to be measured are vibrated for a certain period of time at a certain amplitude to sieve them. Next, the mass of the particles remaining on each sieve is measured, and the particle size distribution of the particle mass is graphed. The particle size corresponding to 50% of the cumulative value of the obtained particle size distribution is defined as the "average particle size."

[0041] (Sintering inhibitor) Maximum particle diameter D of sintering inhibitor （２）ｍａｘ is the maximum particle diameter D of manganese particles （１）ｍａｘ The value is selected to be 0.0002 times or more and 3 times or less.

[0042] Maximum particle diameter D of sintering inhibitor （２）ｍａｘ For example, 2×D （１）ｍａｘ or less, or 1 x D （１）ｍａｘ It may be the following:

[0043] Maximum particle diameter D of sintering inhibitor （２）ｍａｘ is the maximum particle diameter D of manganese particles （１）ｍａｘIt is preferably 1 time or less, and more preferably 0.225 times or less.

[0044] Alternatively, the maximum particle diameter D of the sintering inhibitor （２）ｍａｘ is the maximum particle diameter D of the manganese particles （１）ｍａｘ It may be 0.2 times or more and 2 times or less.

[0045] Specifically, the maximum particle diameter D of the sintering inhibitor （２）ｍａｘ may be 150 μm or less.

[0046] The sintering inhibitor may include at least one of alumina, kaolin, calcia, zirconia, magnesia, and silicon oxide.

[0047] The sintering inhibitor may have at least one shape selected from the group consisting of, for example, a sphere, a triangular pyramid, a triangular prism, a tetrahedron, a cone, and a cylinder. When the particles of the sintering inhibitor have a shape other than a sphere, the particle size of the sintering inhibitor is the maximum dimension of the particle.

[0048] The average particle diameter of the sintering inhibitor (hereinafter referred to as "D （２）ａｖｅ ") may be in the range of 0.01 μm to 150 μm, for example.

[0049] Furthermore, when the particle size distribution of the sintering inhibitor is measured, it may have two or more particle size distribution peaks. For example, the sintering inhibitor may have three types of particles: large particles having a large particle size, medium particles having a medium particle size, and small particles having a small particle size. In this case, three particle size distribution peaks appear in the particle size distribution.

[0050] When the sintering inhibitor has multiple particle size distribution peaks, it becomes possible to control the size of the gap more precisely.

[0051] (Aluminum Source) The aluminum source may be aluminum metal particles or aluminum alloy particles.

[0052] The average particle diameter of the aluminum source (hereinafter referred to as D （３）ａｖｅ The average particle diameter D of the aluminum source is, for example, in the range of 0.1 μm to 300 μm. （３）ａｖｅWhen the particle size is 0.1 μm or less, the aluminum source easily penetrates into the gaps between the sintering inhibitors, and the heat treatment time can be shortened.

[0053] Average particle diameter D of aluminum source （３）ａｖｅ is preferably in the range of 0.01 μm to 75 μm, and more preferably in the range of 0.01 μm to 10 μm.

[0054] (Activator) The activator has the role of forming metal halide vapor during the calorification treatment of manganese particles and accelerating the calorification treatment.

[0055] The activator may include, for example, at least one of ammonium chloride, aluminum chloride, and aluminum fluoride, and is added in an amount ranging from 0.1% by mass to 10% by mass relative to the total mass of the manganese particles and the aluminum source.

[0056] (Mixed Powder) The above components are mixed to prepare a mixed powder.

[0057] The amount of manganese particles contained in the entire mixed powder is, for example, in the range of 3% by mass to 45% by mass. The amount of aluminum source contained in the entire mixed powder is, for example, in the range of 1% by mass to 15% by mass. The amount of sintering inhibitor contained in the entire mixed powder can be appropriately adjusted based on the amount of manganese particles and the amount of aluminum source, but is, for example, in the range of 40% by mass to 96% by mass.

[0058] In the mixed powder, the aluminum source is added so that the mass ratio of aluminum to manganese (Al / Mn) contained in the manganese-aluminum alloy particles to be produced falls within the range of 25 / 75 to 35 / 65.

[0059] For example, the mass ratio P represented by the following formula may be in the range of 65 to 75: Ratio P (%) = {X / (X+Y)} × 100, where X is the mass of the manganese particles contained in the mixed powder, and Y is the mass of aluminum contained in the aluminum source contained in the mixed powder.

[0060] After the mixed powder is prepared, the mixed powder may be subjected to a pressing process, if necessary.

[0061] By carrying out the pressing process, the mixed powder is pulverized, and the sintering inhibitor and manganese particles in the mixed powder are made finer, so that finer manganese-aluminum alloy particles can be obtained after the subsequent step S130.

[0062] The pressing process may be performed using, for example, a press, and a pressure of between 10 MPa and 1000 MPa may be applied to the mixed powder.

[0063] In addition to or separately from the pressing process, the mixed powder may be subjected to a vibration process, which allows the mixed particles to be packed more densely and to form smaller gaps.

[0064] (Step S120) Next, the mixed powder prepared in step S110 is heat-treated. For this purpose, the mixed powder may be filled into a reaction vessel.

[0065] The reaction vessel is heated to calorify the manganese particles, i.e., aluminum produced from the aluminum source diffuses into the manganese particles, forming magnetic particles containing a manganese-aluminum alloy.

[0066] When the reaction vessel is heated, a large amount of heat is generated by the thermite reaction between the mixed powders as the aluminum reacts with the trace amounts of oxygen contained in the manganese particles.

[0067] However, in the first manufacturing method, as described above, the gaps formed between the sintering inhibitors are utilized to perform the calorification treatment of the manganese particles within the gaps, and therefore the first manufacturing method can significantly suppress the problem of the manganese particles adhering to the sintering inhibitor, etc.

[0068] In the first manufacturing method, the maximum particle diameter D of the manganese particles （１）ｍａｘ and the maximum particle diameter D of the sintering inhibitor （２）ｍａｘ is selected as described above, thereby optimizing the size of the gap and forming magnetic particles of manganese-aluminum alloy with a small particle size.

[0069] Here, the volume ratio of the sintering inhibitor to the volume of the reaction vessel is preferably in the range of 10% to 74%, and the volume ratio of the mixed powder to the volume of the reaction vessel is preferably in the range of 50% to 99%.

[0070] The treatment atmosphere during the calorifying treatment may be any atmosphere that does not contain oxygen, such as an argon gas atmosphere.

[0071] The treatment temperature is in the range of 1000° C. to 1235° C., preferably in the range of 1150° C. to 1230° C., and more preferably in the range of 1190° C. to 1225° C. If the treatment temperature is low, the amount of τ phase produced is small, and if the treatment temperature is too high, the phase will aggregate into clumps.

[0072] The holding time at the maximum temperature is, for example, 0.5 hours or more, preferably 5 hours or more, and more preferably 10 hours or more.

[0073] The cooling after the treatment may be performed by furnace cooling or by controlling the cooling rate, for example, between 0.01°C / min and 100°C / min. However, the material may be held at a predetermined temperature during the cooling process.

[0074] The cooling temperature may be controlled in steps.

[0075] The pressure inside the reaction vessel is, for example, in the range of 1 to 30 atmospheres. The pressure is preferably 1.5 atmospheres or more, more preferably 2 atmospheres or more, and even more preferably 3 atmospheres or more.

[0076] The pressure is preferably 30 atmospheres or less, more preferably 20 atmospheres or less, and even more preferably 10 atmospheres or less.

[0077] The process pressure may be increased by sealing the reaction vessel used in the reaction. In this case, for example, the pressure in the reaction vessel may be increased by gasifying an activator. Such an activator may include at least one of ammonium chloride, aluminum chloride, and aluminum fluoride.

[0078] Alternatively, the pressure in the reaction vessel may be increased by filling the reaction vessel with an additional gas, which may be selected from an inert gas, hydrogen, or chlorine.

[0079] The temperature and pressure may be controlled independently.

[0080] According to step S120, a treated mixture is formed.

[0081] (Step S130) Next, magnetic particles of manganese-aluminum alloy are separated and recovered from the treated mixture formed in step S120.

[0082] The recovery method is not particularly limited, but for example, a magnetic separation method may be employed.

[0083] The magnetic separation method is a method for selectively recovering particles having a magnetic phase by using the magnetic force of a magnet or the like.

[0084] In the magnetic separation method, non-magnetic materials such as sintering inhibitors are removed from the treated mixture by the magnetic force exerted only by the magnetic material, and magnetic particles of manganese-aluminum alloy can be separated and recovered.

[0085] In the first manufacturing method, even if the gap size is controlled as described above, some of the magnetic particles of the manganese-aluminum alloy may stick together.

[0086] In this case, magnetic particles of manganese-aluminum alloy may be separated and recovered from the treated mixture by crushing using a ball mill or a jaw crusher.

[0087] In the first manufacturing method, magnetic particles containing a manganese-aluminum alloy can be manufactured by the steps described above.

[0088] The first manufacturing method is characterized in that the magnetic particles obtained contain a small amount of alumina.

[0089] This is believed to be because part of the aluminum constituting the manganese-aluminum alloy is oxidized during the calorifying treatment.

[0090] The amount of alumina contained in the produced magnetic particles is in the range of 0.1% by mass to 30% by mass, and may be in the range of 1% by mass to 10% by mass, based on the weight of the magnetic particles.

[0091] The amount of manganese-aluminum alloy contained in the magnetic particles is in the range of 70% by mass to 99% by mass, and may be in the range of 86% by mass to 98% by mass.

[0092] The magnetic particles may also contain compounds other than those mentioned above, such as compounds combining at least some of Mn, Al, O, and C, or compounds derived from impurities.

[0093] Furthermore, in the manganese-aluminum alloy contained in the magnetic particles, the τ phase may be in the range of 10% by mass to 99% by mass relative to the manganese-aluminum alloy, and the τ phase is preferably, for example, 30% by mass or more, and more preferably 50% by mass or more, relative to the manganese-aluminum alloy.

[0094] The manganese-aluminum alloy contained in the magnetic particles may contain at least one of the ε phase, β phase, and γ phase in addition to the τ phase.

[0095] In this application, the τ phase means a tetragonal structure of MnAl, the ε phase means a hexagonal structure of MnAl, and the β phase means a hexagonal structure of MnAl. ３ Al ２ means a Cubic structure, and the γ phase means Mn ５ Al ８ means a rhombohedral structure.

[0096] However, the ε phase is preferably present in an amount of 10 mass % or less based on the total mass of the manganese-aluminum alloy.

[0097] (Magnetic Particles According to an Embodiment of the Invention) Next, magnetic particles according to an embodiment of the invention will be described.

[0098] In one embodiment of the present invention, there is provided magnetic particles comprising: a manganese-aluminum alloy; and alumina; wherein an abundance ratio of the alumina contained in the magnetic particles is in the range of 0.1% by mass to 30% by mass; an abundance ratio of the manganese-aluminum alloy contained in the magnetic particles is in the range of 70% by mass to 99% by mass; the manganese-aluminum alloy has a τ phase; and an abundance ratio of the τ phase relative to the manganese-aluminum alloy is in the range of 10% by mass to 99% by mass; and wherein the magnetic particles have a maximum particle size of 50 μm or less and a coercive force of 1000 Oe (Oersted) or more.

[0099] In one embodiment of the present invention, the magnetic particles have a maximum particle diameter of 50 μm or less (hereinafter referred to as D （ｓ）ｍａｘ The maximum particle diameter D （ｓ）ｍａｘ may be 40 μm or less.

[0100] The magnetic particles according to one embodiment of the present invention are manufactured by a calorification process, such as the first manufacturing method described above, in which a small amount of alumina is formed during the infiltration and alloying of the manganese particles with aluminum.

[0101] Therefore, the magnetic particles according to one embodiment of the present invention are characterized by having alumina in addition to the manganese-aluminum alloy.

[0102] In one embodiment of the present invention, the content of alumina in the magnetic particles is preferably low. The lower limit is 0.1% by mass or more, and may be 1% by mass or more, 2% by mass or more, or 2.5% by mass or more. The upper limit is preferably 15% by mass or less, and more preferably 10% by mass or less. When the content of alumina is low, the content of the nonmagnetic phase decreases, and the content of the ferromagnetic τ phase can be increased.

[0103] Generally, alumina tends to be concentrated on the outermost surface of the magnetic particles, but alumina may also be present inside the magnetic particles.

[0104] The content of the manganese-aluminum alloy contained in the magnetic particles according to one embodiment of the present invention is in the range of 70% by mass to 99% by mass, and preferably in the range of 80% by mass to 99% by mass.

[0105] In one embodiment of the present invention, the abundance ratio of the τ phase is in the range of 10 mass % to 99 mass %, for example, 30 mass % or more, and preferably 40 mass % or more.

[0106] The magnetic particles according to one embodiment of the present invention have a coercive force of 1000 Oe or more, for example, 1100 Oe or more, and may be 1150 Oe or more.

[0107] Furthermore, in the magnetic particles according to one embodiment of the present invention, the abundance of the τ phase in the manganese-aluminum alloy is in the range of 10% by mass to 99% by mass, preferably 30% by mass or more, and more preferably 40% by mass or more.

[0108] In the magnetic particles according to one embodiment of the present invention, the manganese-aluminum alloy may contain at least one of an ε phase, a β phase, and a γ phase in addition to the τ phase, but the ε phase contained in the manganese-aluminum alloy is preferably 10 mass % or less.

[0109] Furthermore, the manganese-aluminum alloy contained in the magnetic particles according to one embodiment of the present invention may contain 65 to 75 mass % manganese and 25 to 35 mass % aluminum.

[0110] The magnetic particles according to one embodiment of the present invention have a high coercive force of 1000 Oe or more, and therefore can be used in permanent magnets.

[0111] For example, a MnAl-based permanent magnet can be manufactured by molding and sintering a powder containing magnetic particles according to an embodiment of the present invention. The MnAl-based permanent magnet may have any shape. For example, the MnAl-based permanent magnet may have a rectangular parallelepiped, arch shape, or C shape.

[0112] A method for producing an MnAl-based permanent magnet using magnetic particles according to one embodiment of the present invention will be described below, but the method for producing an MnAl-based permanent magnet is not limited to this, and other known methods may also be used. For example, the MnAl-based permanent magnet according to this embodiment may be produced by hot working.

[0113] In the compacting step, a powder containing magnetic particles according to one embodiment of the present invention is compacted into a desired shape. The compacting may be performed by any method. In one embodiment, the magnetic particles are filled into a mold and pressurized. The resulting compact is sintered in a vacuum or inert gas atmosphere to obtain a sintered body.

[0114] Although dry molding, in which magnetic particles are molded as they are, is shown here, wet molding, in which a slurry of magnetic particles dispersed in a solvent such as oil is molded, can also be applied. Furthermore, the shape of the compact obtained by molding the magnetic particles can be any shape.

[0115] The MnAl-based permanent magnet obtained by the above method can be magnetized to become a MnAl-based permanent magnet product. The MnAl-based permanent magnet according to one embodiment of the present invention is suitable for use in motors, generators, and the like.

[0116] The method for manufacturing the permanent magnet is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known manufacturing methods can be used.

[0117] Examples of the present invention will be described below. In the following description, Examples 1 to 7 are examples, and Examples 11 and 12 are comparative examples.

[0118] Example 1 A powder was prepared in the following manner.

[0119] First, 68 g of manganese particles (maximum particle size 50 μm, average particle size 25 μm) and 32 g of aluminum particles (average particle size 75 μm) as an aluminum source were thoroughly mixed with 300 ml of ethanol by ball milling (10 mmφ monomalon balls) to obtain a first powder.

[0120] Next, ammonium chloride particles (0.4% by mass) as an activator and alumina particles (75.0% by mass) (maximum particle size: 100 μm, average particle size: 75 μm) as a sintering inhibitor were added to this first powder (24.6% by mass), and then these were thoroughly mixed to prepare a mixed powder.

[0121] In the mixed powder, the ratio of aluminum particles to the manganese particle content X and the aluminum particle content Y (Y / (X+Y)) is 32 mass %. The ratio D （２）ｍａｘ / D （１）ｍａｘ was 2.00.

[0122] The mixed powder was then packed into a heat-resistant container with a lid. The calculated packing ratio of the alumina particles was 74 volume %. The manganese particles, aluminum particles, and ammonium chloride particles were packed so as to occupy 80% of the remaining voids (26%).

[0123] Next, the pressure inside the heat-resistant container was reduced, and the atmosphere was replaced with argon, and then the heat-resistant container was heated to 1215° C. After being held at 1215° C. for 10 hours, the heat-resistant container was cooled in the furnace.

[0124] Thereafter, the treated mixture was removed from the heat-resistant container, and the magnetic particles were separated and collected by magnetic separation, thereby obtaining a powder containing the magnetic particles.

[0125] Examples 2 to 7 Powders were prepared in the same manner as in Example 1. However, in Examples 2 to 7, the size of each particle contained in the mixed powder was changed from that in Example 1.

[0126] In Example 7, the mixed powder was subjected to a pressing treatment before the calorifying treatment. The pressing treatment was carried out by filling the mixed powder into a mold and applying a pressure of 200 MPa using a hydraulic press.

[0127] Example 11 A powder was prepared in the following manner.

[0128] First, 350 g of manganese particles (maximum particle size 75 μm) and 157.5 g of aluminum particles (200 mesh) were thoroughly mixed to prepare a mixed powder.

[0129] In the mixed powder, the ratio of aluminum particles to the manganese particle content X and the aluminum particle content Y (Y / (X+Y)) was 31% by mass.

[0130] Next, this mixed powder was placed in a crucible, which was then set in a gas atomizer and heated to 1550° C. by a heating coil, so that the mixed powder was in a fully molten state.

[0131] The molten metal was then dropped downward from a molten metal outlet with an orifice diameter of 2 mm installed at the bottom of the crucible. Argon gas was sprayed onto the falling molten metal at an atomization pressure of 5 MPa. The molten metal became fine droplets and was rapidly cooled and solidified while falling down the tower in the gas atomization device.

[0132] This produced a powder containing spherical particles.

[0133] Example 12 Powder was prepared in the same manner as in Example 1. However, in Example 12, the size of each particle contained in the mixed powder was changed from that in Example 1.

[0134] Table 1 below shows the specifications of the mixed powders used to produce the powders in each example.

[0135] Table 2 below also summarizes the process conditions used to produce each powder.

[0136] 2 to 4 show examples of the morphology of particles contained in the powder produced in Example 2, the powder 3 produced in Example 3, and the powder produced in Example 11, respectively.

[0137] (Evaluation) The following evaluations were carried out using each of the powders described above.

[0138] (X-ray Diffraction Analysis) X-ray diffraction analysis of each powder was performed using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation). From the obtained diffraction patterns, the mass fraction of each phase in the particles contained in the powder was determined by Rietveld analysis.

[0139] Rietveld refinement was performed using the program RIETAN-FP.

[0140] The profile function used was Toratani's extended split Pseude-Voigt function. Fitting was performed so that the reliability factor Rwp (R-weighted pattern), which is generally considered a guideline, was less than 10% for the entire analysis range.

[0141] The analysis range was 2θ=10° to 120°.

[0142] The results of the X-ray diffraction analysis showed that the powders produced in Examples 1 to 7 mainly contained manganese-aluminum alloy and alumina.

[0143] Table 3 below shows the calculated abundance ratios of each phase in the powders produced in Examples 1 and 4.

[0144] From Table 3, it was found that the powders produced in Examples 1 and 4 contained τ-phase and alumina. In particular, it was found that in these powders, the τ-phase was present in an amount of 40 mass% or more and the alumina was present in an amount of 5 mass% or more.

[0145] (Measurement of Particle Size Distribution) The particle size distribution of each of the powders produced in Examples 2, 3 and 11 was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.).

[0146] FIG. 5 summarizes the results obtained.

[0147] 5, it was found that the particle diameter of each of the powders produced in Examples 2 and 3 was finer than that of the powder of Example 11.

[0148] (Measurement of maximum particle diameter) The maximum particle diameter D of the powder produced in each example was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.). （ｓ）ｍａｘwas measured.

[0149] (Measurement of Coercive Force) The coercive force of the powder produced in each example was measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) (VSM-C7-10A).

[0150] Table 4 below shows the maximum particle diameter D measured for each powder. （ｓ）ｍａｘ and coercivity values ​​are shown together.

[0151] From Table 4, the maximum particle diameter D （ｓ）ｍａｘ It was found that the thickness was 50 μm or less.

[0152] It was also found that the powders produced in Examples 1 to 7 had a high coercive force of 1000 Oe or more.

[0153] (Aspects of the Invention) The present invention may have the following aspects.

[0154] (Aspect 1) A method for producing magnetic particles containing a manganese-aluminum alloy, the method comprising the steps of: (i) mixing manganese particles, an aluminum source, an activator containing a halide, and a sintering inhibitor to obtain a mixed powder, wherein the maximum particle size of the manganese particles is 50 μm or less, and the maximum particle size of the sintering inhibitor is 0.0002 to 3 times the maximum particle size of the manganese particles; (ii) heating the mixed powder to a temperature in the range of 1000°C to 1235°C to calorify the manganese particles to obtain a treated mixture having particles containing a manganese-aluminum alloy, wherein the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 by mass; and (iii) recovering particles containing the manganese-aluminum alloy from the treated mixture.

[0155] (Aspect 2) The method of aspect 1, wherein the recovering step is carried out using a magnetic separation method.

[0156] (Aspect 3) The method according to aspect 1 or 2, further comprising the step of pressing or vibrating the mixed powder before the step of calorifying the manganese particles.

[0157] (Aspect 4) The method according to any one of Aspects 1 to 3, wherein the average particle size of the sintering inhibitor is in the range of 0.01 μm to 150 μm.

[0158] (Aspect 5) The method according to any one of Aspects 1 to 4, wherein the sintering inhibitor has two or more particle size distribution peaks when the particle size distribution is measured.

[0159] (Aspect 6) The method according to any one of Aspects 1 to 5, wherein the sintering inhibitor has at least one shape selected from the group consisting of a sphere, a triangular pyramid, a triangular prism, a tetrahedron, a cone, and a cylinder.

[0160] (Aspect 7) The method according to any one of Aspects 1 to 6, wherein the mixed powder is filled into a reaction vessel, and a volume ratio of the sintering inhibitor to the volume of the reaction vessel is in the range of 10% to 74%.

[0161] (Aspect 8) The method according to any one of Aspects 1 to 7, wherein the mixed powder is filled into a reaction vessel, and a filling rate of the mixed powder with respect to the volume of the reaction vessel is in the range of 50% to 99%.

[0162] (Aspect 9) The method of any one of Aspects 1 to 8, wherein the activator comprises at least one selected from the group consisting of ammonium chloride, aluminum chloride, and aluminum fluoride.

[0163] (Aspect 10) The method according to any one of Aspects 1 to 9, wherein the active agent is contained in an amount ranging from 0.1% by mass to 10% by mass based on the total amount of the mixed powder.

[0164] (Aspect 11) The method according to any one of Aspects 1 to 10, wherein the manganese particles have an average particle size of 0.01 μm to 50 μm.

[0165] (Aspect 12) The method according to any one of Aspects 1 to 11, wherein the aluminum source has an average particle size of 0.1 μm to 300 μm.

[0166] (Aspect 13) The method according to any one of Aspects 1 to 12, wherein the calorification treatment is carried out in a pressurized environment.

[0167] (Aspect 14) The method according to aspect 13, wherein the pressurized environment is achieved by introducing an inert gas into a sealed reaction vessel.

[0168] (Aspect 15) The method according to Aspect 13 or 14, wherein the pressurized environment is achieved by gas generated from the mixed powder filled in a sealed reaction vessel.

[0169] (Aspect 16) Magnetic particles comprising a manganese-aluminum alloy and alumina, wherein a content of the alumina contained in the magnetic particles is in the range of 0.1% by mass to 30% by mass, a content of the manganese-aluminum alloy contained in the magnetic particles is in the range of 70% by mass to 99% by mass, the manganese-aluminum alloy has a τ phase, and a content of the τ phase relative to the manganese-aluminum alloy is in the range of 10% by mass to 99% by mass, and the magnetic particles have a maximum particle size of 50 μm or less and a coercive force of 1000 Oe or more.

[0170] (Embodiment 17) The magnetic particles according to embodiment 16, wherein the manganese-aluminum alloy further includes at least one of an ε phase, a β phase, and a γ phase.

[0171] (Embodiment 18) The magnetic particles according to embodiment 17, wherein the manganese-aluminum alloy contains 10 mass % or less of the ε phase.

[0172] (Aspect 19) The magnetic particles according to any one of aspects 16 to 18, wherein the manganese-aluminum alloy contains 65% to 75% by mass of manganese and 25% to 35% by mass of aluminum.

[0173] (Aspect 20) A MnAl-based permanent magnet comprising the magnetic particles according to any one of aspects 16 to 19.

[0174] This application claims priority based on Japanese Patent Application No. 2023-193429, filed on November 14, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A method for producing magnetic particles containing a manganese-aluminum alloy, comprising the steps of: (i) mixing manganese particles, an aluminum source, an activator containing a halide, and a sintering inhibitor to obtain a mixed powder, wherein the manganese particles have a maximum particle size of 50 μm or less, and the maximum particle size of the sintering inhibitor is 0.0002 to 3 times the maximum particle size of the manganese particles; (ii) heating the mixed powder to a temperature in the range of 1000° C. to 1235° C. to calorify the manganese particles to obtain a treated mixture having particles containing a manganese-aluminum alloy, wherein the ratio of aluminum to manganese (Al / Mn) in the manganese-aluminum alloy is in the range of 25 / 75 to 35 / 65 by mass; and (iii) recovering particles containing the manganese-aluminum alloy from the treated mixture.

2. The method of claim 1, wherein the recovering step is performed using magnetic separation.

3. The method of claim 1, further comprising the step of pressing or vibrating the mixed powder before the step of calorifying the manganese particles.

4. The method of claim 1, wherein the average particle size of the sintering inhibitor ranges from 0.01 μm to 150 μm.

5. The method according to claim 1, wherein the sintering inhibitor has two or more particle size distribution peaks when the particle size distribution is measured.

6. The method of claim 1, wherein the sintering inhibitor has at least one shape selected from the group consisting of a sphere, a triangular pyramid, a triangular prism, a tetrahedron, a cone, and a cylinder.

7. The method according to claim 1, wherein the mixed powder is filled into a reaction vessel, and a volume ratio of the sintering inhibitor to the volume of the reaction vessel is in the range of 10% to 74%.

8. The method according to claim 1, wherein the mixed powder is filled into a reaction vessel, and a filling rate of the mixed powder with respect to a volume of the reaction vessel is in the range of 50% to 99%.

9. The method of claim 1, wherein the activator comprises at least one selected from the group consisting of ammonium chloride, aluminum chloride, and aluminum fluoride.

10. The method according to claim 1, wherein the active agent is contained in an amount ranging from 0.1% by mass to 10% by mass based on the total amount of the mixed powder.

11. The method of claim 1, wherein the manganese particles have an average particle size of 0.01 μm to 50 μm.

12. The method of claim 1, wherein the average particle size of the aluminum source is 0.1 μm to 300 μm.

13. The method of claim 1, wherein the calorification is carried out in a pressurized environment.

14. The method of claim 13, wherein the pressurized environment is achieved by introducing an inert gas into a sealed reaction vessel.

15. The method according to claim 13, wherein the pressurized environment is achieved by gas generated from the mixed powder filled in a sealed reaction vessel.

16. A magnetic particle comprising: a manganese-aluminum alloy; and alumina; wherein a content of the alumina contained in the magnetic particle is in the range of 0.1% by mass to 30% by mass; a content of the manganese-aluminum alloy contained in the magnetic particle is in the range of 70% by mass to 99% by mass; the manganese-aluminum alloy has a τ phase; and a content of the τ phase relative to the manganese-aluminum alloy is in the range of 10% by mass to 99% by mass; and the magnetic particle has a maximum particle size of 50 μm or less and a coercive force of 1000 Oe or more.

17. The magnetic particle according to claim 16, wherein the manganese-aluminum alloy further comprises at least one of an ε phase, a β phase, and a γ phase.

18. The magnetic particles according to claim 17, wherein the manganese-aluminum alloy contains 10 mass % or less of the ε phase.

19. Magnetic particles according to claim 16, wherein the manganese-aluminum alloy comprises, by weight, 65% to 75% manganese and 25% to 35% aluminum.

20. A MnAl-based permanent magnet comprising the magnetic particles according to claim 16.

Images