Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/16—Metallic particles coated with a non-metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/059—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and Va elements, e.g. Sm2Fe17N2
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
  • H01F1/08—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets

Definitions

• the present invention relates to Sm-Fe-N sintered magnets and methods for producing them.
• Sm-Fe-N magnets are representative of rare earth-transition metal-nitrogen magnets, and have a high anisotropy magnetic field and saturation magnetization. Furthermore, because their Curie temperature is relatively higher than other rare earth-transition metal-nitrogen magnets, they have excellent heat resistance. For this reason, Sm-Fe-N magnets are used as one of the superior magnetic materials.
• Sm-Fe-N magnetic powder is used as the raw material for Sm-Fe-N magnets.
• An alloy of Sm and Fe is produced, for example, by a reduction-diffusion method using Ca (calcium). This method produces by-products such as CaO and unreacted metallic Ca, which must be removed by rinsing with water. However, rinsing with water increases the oxygen content of the alloy, which can degrade the magnetic properties of the resulting magnetic powder.
• Patent Document 1 describes a method in which an alloy of Sm and Fe is nitrided and then washed with water to convert unreacted metallic Ca into calcium nitride and quickly remove it.
• Patent Document 2 describes bubbling nitrogen gas into cleaning water to reduce the amount of dissolved oxygen in the cleaning water.
• Non-Patent Document 1 It is known that the magnetic properties (typically coercive force) of Sm-Fe-N magnetic powders tend to decrease during the sintering process. In recent years, it has been discovered that this decrease in coercive force during the sintering process is due to the decomposition of the main phase by a film containing oxides and/or hydroxides on the surface of the magnetic powder, resulting in the formation of ⁇ -Fe (see Non-Patent Document 1).
• the object of the present invention is to provide an Sm-Fe-N sintered magnet with high coercive force and a method for producing the same.
• the present invention provides a Sm-Fe-N sintered magnet with high coercive force and a method for producing the same.
• the Sm-Fe-N sintered magnet according to this embodiment includes a sintered body of a material containing Sm-Fe-N magnetic powder (hereinafter, sometimes referred to as "magnetic material").
• the Sm-Fe-N magnetic powder has an average particle size of 0.1 ⁇ m or more and 10 ⁇ m or less, and an oxygen content of 0.8 mass % or less.
• the oxygen content of Sm-Fe-N magnetic powder (hereinafter sometimes simply referred to as “magnetic powder”) is 0.8% by mass or less, which means that the formation of a film containing oxides and/or hydroxides (hereinafter sometimes simply referred to as “oxide film”) on the surface of the magnetic powder is suppressed.
• oxide film a film containing oxides and/or hydroxides
• the average particle size of the magnetic powder is 0.1 ⁇ m or more and 10 ⁇ m or less.
• the average particle size of the magnetic powder may be 7.5 ⁇ m or less, or 5.0 ⁇ m or less, in order to further increase the coercive force.
• the average particle size of the magnetic powder may be 0.5 ⁇ m or more, in order to suppress superparamagnetism.
• the "average particle size" of a powder refers to the particle size (D50) at the point where the cumulative value reaches 50% on a cumulative curve obtained by calculating the particle size distribution on a volume basis, with the total volume set to 100%.
• This average particle size can be measured using a laser diffraction/scattering particle size/particle size distribution measuring device (e.g., HELOS & RODOS Lens R1, manufactured by Nippon Laser Co., Ltd.) or an electron scanning microscope (e.g., SU8230, manufactured by Hitachi High-Technologies Corporation).
• the oxygen content of the magnetic powder is 0.80% by mass or less. It may be 0.60% by mass or less, or 0.40% by mass or less.
• the oxygen content of the magnetic powder is measured within seven days of washing with low-dissolved-oxygen water, as described below.
• the oxygen content of the magnetic powder can be measured using inert gas fusion-non-dispersive infrared (NDIR) or other methods.
• the oxygen content of the magnetic powder can be measured, for example, using an EMGA-830 (oxygen, nitrogen, and hydrogen analyzer, manufactured by Horiba, Ltd.).
• the oxygen content is measured on the magnetic powder sealed in a metal capsule, without exposure to the atmosphere, in a glove box where the oxygen concentration is controlled to 2 ppm or less.
• the amount of moisture contained in the magnetic powder may be 0.05% by mass or more. If the moisture amount is 0.05% by mass or more, it can be said that a washing process using water (water washing) was carried out when producing the magnetic powder. According to this embodiment, even when washing with water, the oxygen content of the resulting sintered magnet is suppressed to 0.8% by mass or less.
• the amount of moisture contained in the magnetic powder may be 0.07% by mass or more, and may be 0.09% by mass or more.
• the amount of moisture contained in the magnetic powder may be 0.10% by mass or less.
• the moisture content of magnetic powder can be measured using the Karl Fischer method.
• the moisture content can be measured using an AQ-2250 (trace moisture analyzer, manufactured by HIRANUMA Co., Ltd.).
• the peak intensity ratio (P1/P2) between the peak intensity P1 of the metal oxide containing Fe and Sm with a binding energy of 528.0 eV to 529.5 eV and the peak intensity P2 of the metal hydroxide containing Fe and Sm with a binding energy of 529.6 eV to 532.0 eV can be 0.5 or less.
• a peak intensity ratio (P1/P2) of 0.5 or less means that the oxide film on the surface of the magnetic powder contains a smaller proportion of metal oxides containing Fe and Sm than metal hydroxides containing Fe and Sm. Although the reason for this is unclear, in this case the coercive force of the sintered magnet is increased.
• the peak intensity ratio (P1/P2) may be 0.05 or greater, 0.1 or greater, or 0.2 or greater.
• the peak intensity ratio (P1/P2) may be 0.48 or less, 0.45 or less, 0.40 or less, or 0.30 or less.
• Peak intensities P1 and P2 can be obtained using X-ray photoelectron spectroscopy (XPS).
• XPS is a surface analysis method used to analyze solid surfaces and is also known as ESCA (Electron Spectroscopy for Chemical Analysis).
• Peak intensity P1 is the intensity of the highest peak in the binding energy range of 528.0 eV to 529.5 eV in the XPS spectrum.
• Peak intensity P2 is the intensity of the highest peak in the binding energy range of 529.6 eV to 532.0 eV in the XPS spectrum.
• Peak intensities P1 and P2 can be measured, for example, using a Quantes (scanning dual X-ray photoelectron spectrometer, ULVAC-PHI, Inc.). Measurement conditions may be: X-ray source: Al, accelerating voltage: 15 kV, X-ray beam intensity: 25 W, X-ray spot size: 100 ⁇ m.
• the coercive force H cjp of the magnetic powder may be 700 kA/m or more, and may be 720 kA/m or more.
• the coercive force H cjp of the magnetic powder may be measured using, for example, a VSM-5HSC10 vibrating sample magnetometer manufactured by Toei Kogyo Co., Ltd.
• Sm—Fe—N sintered magnets are obtained by sintering (firing) a magnetic material containing the Sm—Fe—N magnetic powder at high temperatures. Because the Sm—Fe—N magnetic powder according to the present disclosure has a low oxygen content, oxide films are less likely to form, and the resulting magnets have high coercivity even after undergoing the sintering process.
• the coercive force H cjs of the sintered magnet is, for example, 780 kA/m or more, and may be 785 kA/m or more.
• the magnetic material used in this embodiment may consist essentially of Sm-Fe-N magnetic powder, but may also contain one or more other materials, such as magnetic powders consisting of a rare earth element other than Sm, Fe, and N, or magnetic powders consisting of a rare earth element including Sm, a transition metal element other than Fe, and N.
• rare earth elements other than Sm include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb).
• transition metal elements other than Fe include cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium (Ti), Zr (zirconia), niobium (Nb), and tungsten (W).
• the Sm-Fe-N sintered magnet of this embodiment may contain trace elements that are unavoidably mixed in, such as carbon (C), silicon (Si), and aluminum (Al).
• All of the above steps are carried out, for example, in a glove box purged with an inert gas (one or a mixture of two or more gases, such as nitrogen, argon, and helium), preferably in a glove box connected to a gas circulation type oxygen and moisture purifier.
• an inert gas one or a mixture of two or more gases, such as nitrogen, argon, and helium
• Figure 1 is a flowchart showing the method for manufacturing a sintered magnet in embodiment 1.
• the amount of Sm relative to the total amount of Sm and Fe may be, for example, 9 atm% or more and 14 atm% or less.
• the average particle size of the alloy powder may be, for example, 1 ⁇ m or more and 50 ⁇ m or less.
• precursor powders for Sm-Fe alloys include mixed powders of Sm compound powder, iron powder, and iron oxide powder, Sm-Fe oxide powder, and Sm-Fe hydroxide powder.
• the precursor powder is prepared, for example, by coprecipitation.
• the precursor powder may be pre-reduced in a reducing atmosphere. Pre-reduction is carried out, for example, by heating the precursor powder to 400°C or higher in a hydrogen atmosphere.
• the reduction-diffusion method is carried out, for example, by mixing a precursor powder of Sm—Fe alloy with calcium (Ca) or calcium hydride (CaH 2 ) and heating the mixture in an inert gas atmosphere at a temperature equal to or higher than the melting point of Ca (approximately 842°C).
• the heating time may be, for example, 1 hour to 10 hours.
• the Sm—Fe alloy Prior to nitriding and washing, the Sm—Fe alloy may be crushed or pulverized, and then classified as necessary. Fine powder is removed from the crushed powder by classification. Crushing, pulverization, and classification are performed under conditions such that the average particle size of the resulting Sm—Fe—N magnetic powder is 0.1 ⁇ m or more and 10 ⁇ m or less.
• Crushing or grinding can be carried out using, but is not limited to, an agate mortar, a jet mill (airflow grinding type, etc.), a ball mill, etc.
• airflow grinding jet mills include, but are not limited to, the MC44 manufactured by Micromachinacade.
• Classification can be carried out using, but is not limited to, an airflow classifier, etc.
• Nitriding treatment (S12) The nitriding treatment is typically carried out by heat treatment in a nitrogen atmosphere, an ammonia atmosphere, a mixed atmosphere of ammonia and hydrogen, or a mixed atmosphere of nitrogen and hydrogen, whereby nitrogen is incorporated into the crystals of the alloy powder, thereby obtaining a Sm—Fe—N precursor powder.
• the partial pressure of the nitrogen may be 10 kPa or more and 100 kPa or less, and the heating time may be 5 hours or more and 30 hours or less.
• the partial pressure of the ammonia when the total pressure of the mixed gas is 100 kPa, the partial pressure of the ammonia may be 20 kPa or more and 40 kPa or less, and the heating time may be 10 minutes or more and 50 minutes or less.
• the heating temperature is preferably 350°C or higher and 550°C or lower, and more preferably 400°C or higher and 550°C or lower. Using this heating temperature prevents decomposition into SmN and Fe, which can occur when the nitriding reaction is carried out at a higher temperature, and allows the reaction to proceed more sufficiently than when the nitriding reaction is carried out at a lower temperature.
• the above-mentioned nitriding treatment is typically carried out under atmospheric pressure, preferably at a pressure of 90 kPa or more and 1.10 kPa or less, and more preferably at a pressure of 95 kPa or more and 105 kPa or less.
• the Sm—Fe—N precursor powder is washed with low-dissolved oxygen water having a dissolved oxygen content of 0.50 mg/L or less.
• the Sm—Fe—N precursor powder contains CaO and unreacted Ca as by-products. Therefore, washing with water is usually performed.
• By-products can be physically removed by washing.
• By-products can also be removed by chemical reaction with the low-dissolved oxygen water.
• Ca reacts with the low-dissolved oxygen water to form calcium hydroxide, which dissolves in the low-dissolved oxygen water.
• the dissolved oxygen content of the liquid can be measured, for example, using a D210-PD (dissolved oxygen meter, manufactured by Horiba, Ltd.).
• Washing with water normally promotes the formation of oxides and/or hydroxides (particularly hydroxide formation) of the contained metals on the surface of Sm-Fe-N precursor powder. Washing with low-dissolved oxygen water suppresses the formation of these oxides and/or hydroxides, making it difficult for an oxide film to form on the surface of the magnetic powder, and as a result, the oxygen content of the magnetic powder is reduced to 0.8 mass% or less. By using this magnetic powder, decomposition of the main phase by the oxide film during the sintering process is suppressed, resulting in a sintered magnet with high coercivity.
• washing is performed using low-dissolved oxygen water with a liquid temperature of greater than 10°C and less than 30°C, and a pH of greater than 4.0 and less than 9.0. This results in magnetic powder with an oxygen content of 0.80% by mass or less.
• Low-dissolved oxygen water can be obtained, for example, by degassing equipment equipped with reduced pressure, ultrasonic vibration, helium purging, a gas-permeable membrane, or a combination of these.
• Washing is performed, for example, by adding the Sm-Fe-N precursor powder to low-dissolved-oxygen water and then stirring. The stirring is then stopped, and the resulting precipitate is removed and dried to obtain the Sm-Fe-N magnetic powder.
• Washing may be performed multiple times. For example, the Sm-Fe-N precursor powder is added to low-dissolved oxygen water, stirred, allowed to stand, the supernatant liquid is removed, and new low-dissolved oxygen water is added. The above procedure may then be repeated the desired number of times.
• the stirring time may be from 1 minute to 30 minutes. The number of repetitions may be from 2 to 10 times.
• the magnetic powder may be washed with acetic acid or hydrochloric acid, etc. This will further remove any remaining Ca.
• Drying can be performed by vacuuming.
• the degree of vacuum can be, for example, -95 kPa or less.
• the treatment time can be, for example, 1 hour or more and 10 hours or less.
• the inside of the vacuum device is maintained in a low-oxygen atmosphere, and can be a vacuum of, for example, 5 Pa or less, or can be filled with an inert gas atmosphere, or inert gas can be flowed in under reduced pressure.
• an orientation process, a magnetization process, and a molding process may be performed prior to pressure sintering. This aligns the easy magnetization axis of the Sm—Fe—N magnetic powder, resulting in higher magnetic properties.
• the applied magnetic field may be, for example, a static magnetic field of 1 T or more, or a pulsed magnetic field.
• the resulting material containing the Sm—Fe—N magnetic powder is filled into a mold.
• the process is carried out in an atmosphere with a low oxygen concentration, where the volumetric oxygen concentration is 2 ppm or less.
• the mold used may have any shape, and for example, a cylindrical mold can be used, but is not limited thereto.
• Pressure sintering may be performed, for example, by hot pressing or electric sintering.
• Hot pressing is a common sintering method in which heating is performed while applying pressure in an inert atmosphere such as Ar.
• Electric sintering is a method in which a certain pressure is applied to a mold and an electric current is applied while maintaining this pressure.
• the inside of the pulse electric sintering machine is maintained at a vacuum of, for example, 5 Pa or less.
• the applied pressure may be higher than atmospheric pressure and may be a pressure capable of forming a sintered magnet, for example, in the range of 100 MPa to 2000 MPa.
• Electric sintering is performed, for example, at a temperature of 400°C to 600°C for a time of 30 seconds to 10 minutes.
• Embodiment 2 This embodiment differs from Embodiment 1 in the method for preparing the Sm—Fe alloy powder used to manufacture the Sm—Fe—N sintered magnet. This difference will be explained below.
• the other steps in the method for manufacturing the Sm—Fe—N sintered magnet are the same as in Embodiment 1, so their explanation will be omitted.
• the configuration of the sintered magnet is the same as in Embodiment 1, so their explanation will be omitted.
• the Sm-Fe alloy powder is prepared by melt spinning.
• Melt spinning is a method in which molten Sm-Fe alloy is injected into a rapidly rotating metal roll and rapidly cooled.
• the Sm-Fe alloy solidifies into a thin ribbon, which is then crushed and heat-treated in an inert atmosphere to obtain the Sm-Fe alloy powder.
• the alloy powder prepared by the melt spinning method is (2) crushed, pulverized, and classified, and (3) nitrided. It is then (4) washed with low-dissolved-oxygen water, (5) oriented and magnetized, (6) packed, and (7) pressurized sintered in a low-oxygen atmosphere.
• Embodiment 3 This embodiment differs from Embodiment 1 in the temperature of the low-dissolved-oxygen water used for cleaning. This difference is explained below.
• the other configurations of the method for producing a Sm—Fe—N sintered magnet and the configuration of the sintered magnet are the same as those in Embodiment 1, so explanations thereof will be omitted.
• Figure 2 is a flowchart showing a method for manufacturing a sintered magnet in embodiment 3.
• Example 1 (i) Preparation of alloy powder by reduction diffusion method: 2.87 g of a mixed powder of samarium oxide powder and iron powder and 0.36 g of metallic calcium with an average particle size of 2 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas was introduced. The temperature was raised to 950°C and maintained for 5 hours to prepare a Sm—Fe alloy.
• Example 1 the processes from (ii) crushing to (v) filling were all carried out in a glove box (nitrogen substituted) connected to a gas circulation type oxygen and moisture purifier.
• the oxygen concentration in the glove box was kept below 1 ppm.
• the samples were moved between each device to avoid exposure to the atmosphere.
• Pressurized firing was carried out in an Ar atmosphere.
• oxygen content The oxygen content of the Sm--Fe--N magnetic powder was measured by inert gas fusion-non-dispersive infrared absorption method (NDIR method) under the conditions described above.
• VSM vibrating sample magnetometer
• moisture content The moisture content of the Sm—Fe—N magnetic powder was measured by the Karl Fischer method. The moisture content of the Sm—Fe—N precursor powder before washing was 0.040 mass % in both the Examples and Comparative Examples.
• Example 2 and Comparative Example 2 Except for preparing the Sm—Fe alloy powder by melt spinning, Sm—Fe—N sintered magnets were obtained and evaluated in the same manner as in Example 1 and Comparative Example 1. The results are shown in Table 2.
• ⁇ 5> The Sm—Fe—N sintered magnet of any one of ⁇ 1> to ⁇ 4>, wherein the Sm—Fe—N magnetic powder has an average particle size of 0.5 ⁇ m or more and 5 ⁇ m or less.
• ⁇ 6> ⁇ 5> The Sm—Fe—N sintered magnet of any one of ⁇ 1> to ⁇ 5>, wherein the oxygen content of the Sm—Fe—N magnetic powder is 0.4 mass % or less.

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