Method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, and phosphate-coated SmFeN-based anisotropic magnetic powder

Abstract

This invention provides a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder with superior coercivity. [Solution] The present invention relates to a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, which includes a phosphoric acid treatment step, in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphoric acid compound, and a rare earth compound to adjust the pH of the slurry to 1 or more and 4.5 or less, thereby obtaining SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface.

Description

[Technical Field]

[0001] The present invention relates to a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, and to phosphate-coated SmFeN-based anisotropic magnetic powder. [Background technology]

[0002] It is known that forming a phosphate coating on the surface of SmFeN-based anisotropic magnetic powder improves its coercivity. For example, Patent Document 1 discloses a method for forming a phosphate coating on the surface of SmFeN-based anisotropic magnetic powder by adding a pH-adjusted phosphoric acid treatment solution containing orthophosphoric acid to a slurry containing SmFeN-based anisotropic magnetic powder with water as the solvent.

[0003] Patent Document 2 discloses a method in which a pH-adjusted phosphoric acid treatment solution is added to a slurry containing large-particle SmFeN-based anisotropic magnetic powder in an organic solvent, and then the SmFeN-based anisotropic magnetic powder is pulverized to reduce its particle size, while also forming a phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder.

[0004] Patent Document 3 discloses that the coercivity of a magnetic powder can be increased by subjecting a phosphate-coated SmFeN-based anisotropic magnetic powder to a slow oxidation treatment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-056101 [Patent Document 2] Japanese Patent Publication No. 2017-210662 [Patent Document 3] Japanese Patent Publication No. 2014-160794 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder having superior coercivity, and to provide phosphate-coated SmFeN-based anisotropic magnetic powder. [Means for solving the problem]

[0007] A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to one aspect of the present invention is characterized by including a phosphoric acid treatment step, in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphoric acid compound, and a rare earth compound to adjust the pH of the slurry to 1 or more and 4.5 or less, thereby obtaining SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface.

[0008] Furthermore, a phosphate-coated SmFeN-based anisotropic magnetic powder according to one aspect of the present invention is characterized in that the exothermic onset temperature in DSC is 170°C or higher, the phosphate content is greater than 0.5% by mass, and it contains at least one rare earth element selected from the group consisting of Ce, Nd, and Dy. [Effects of the Invention]

[0009] According to the above embodiment, a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder having superior coercivity, and a phosphate-coated SmFeN-based anisotropic magnetic powder can be provided. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described in detail below. However, the embodiments shown below are merely examples for realizing the technical concept of the present invention, and the present invention is not limited to these. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. Furthermore, numerical ranges indicated using "~" represent a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively.

[0011] <Method for producing phosphate-coated SmFeN-based anisotropic magnetic powder> The method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to this embodiment is characterized by including a phosphoric acid treatment step, in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphoric acid compound, and a rare earth compound to adjust the pH of the slurry to 1 or more and 4.5 or less, thereby obtaining SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface.

[0012] [Phosphoric Acid Treatment Process] In the phosphoric acid treatment process, an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphoric acid compound, and a rare earth compound to adjust the pH of the slurry to between 1 and 4.5. This yields an SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface.

[0013] Phosphate-coated SmFeN-based anisotropic magnetic powder is formed when metal components (e.g., iron or samarium) contained in the SmFeN-based anisotropic magnetic powder react with phosphate components contained in phosphate compounds, causing phosphates (e.g., iron phosphate, samarium phosphate) to precipitate on the surface of the SmFeN-based anisotropic magnetic powder. Furthermore, by coexisting with rare earth compounds in the slurry, the rare earth compounds bond to the surface of the SmFeN-based anisotropic magnetic powder, and salts of the rare earth element and phosphoric acid precipitate. Furthermore, according to this embodiment, by using water as the solvent, phosphates with smaller particle sizes precipitate compared to when an organic solvent is used, thus obtaining a phosphate-coated SmFeN-based anisotropic magnetic powder with a dense coating.

[0014] The content of SmFeN-based anisotropic magnetic powder in the slurry is, for example, 1% by mass or more and 50% by mass or less, and is preferably 5% by mass or more and 20% by mass or less from the viewpoint of productivity. The content of the phosphate component (PO4) in the slurry is, in terms of the amount in terms of PO4, for example, 0.01% by mass or more and 10% by mass or less, and preferably 0.05% by mass or more and 5% by mass or less from the viewpoints of the reactivity and productivity of the phosphate component.

[0015] The rare earth compound is not particularly limited as long as it contains a rare earth element, but compounds that generate rare earth ions in a slurry having water as a solvent, such as rare earth hydroxides, rare earth chlorides, rare earth sulfates, rare earth nitrates, and rare earth acetates, are preferable.

[0016] Examples of the rare earth element contained in the rare earth compound include Ce, Sm, Nd, Dy, Y, La, Pr, etc., and Ce, Sm, Nd, Dy are preferable.

[0017] Among these rare earth compounds, rare earth hydroxides and rare earth chlorides are preferable.

[0018] As the rare earth hydroxide, the following formula (1): R-(OH) X (1) (In formula (1), R is Ce, Nd, Sm, or Dy, and x is 1, 2, 3, or 4) The rare earth hydroxide represented by is more preferable, and Ce(OH)3, Nd(OH)3, Sm(OH)3, Dy(OH)3 are particularly preferable. These rare earth hydroxides may be dissolved in the slurry and exist in the form of rare earth ions. The rare earth hydroxide may be, for example, produced from a rare earth chloride at a pH of 4 or more and 10 or less.

[0019] As the rare earth chloride, the following formula (2): R-(Cl) X (2) (In formula (2), R is Ce, Nd, Sm, or Dy, and x is 1, 2, 3, or 4) The rare earth chloride represented by is more preferable, and CeCl3, NdCl3, SmCl3, DyCl3 are particularly preferable. These rare earth chlorides may be dissolved in the slurry and exist in the form of rare earth ions.

[0020] The content of rare earth elements in the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphoric acid treatment step can be, for example, 0.25% by mass or less, preferably 0.2% by mass or less, more preferably 0.18% by mass or less, and even more preferably 0.15% by mass or less. When the concentration is 0.25% by mass or less, the coercivity of the magnetic powder tends to improve, and when it is 0.2% by mass or less, a product with improved resistance to hot water may be obtained. The lower limit of the rare earth element content is not particularly limited, but it can generally be 0.01% by mass or more, and 0.03% by mass or more is preferred. The content of rare earth elements in magnetic powder is measured using ICP emission spectroscopy (ICP-AES).

[0021] During the phosphoric acid treatment process, many of the rare earth elements derived from the rare earth compounds contained in the slurry adhere to the SmFeN-based anisotropic magnetic powder. Therefore, when the content of rare earth elements is within the above range, the amount of rare earth compound added to the slurry can be such that the content of rare earth elements in the rare earth compound is 0.25% by mass or less relative to the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphoric acid treatment step, preferably 0.2% by mass or less, more preferably 0.18% by mass or less, and even more preferably 0.15% by mass or less. When the rare earth element content in the rare earth compound is 0.25% by mass or less, the coercivity of the magnetic powder tends to improve, and when it is 0.2% by mass or less, a product with improved resistance to hot water may be obtained. Furthermore, while there is no particular lower limit to the content of rare earth elements in the rare earth compound, it can generally be 0.01% by mass or more, and 0.03% by mass or more is preferred. Rare earth elements precipitate on the surface of SmFeN-based anisotropic magnetic powder as salts with phosphoric acid.

[0022] A phosphoric acid solution is obtained by mixing a phosphoric acid compound with water. Examples of phosphate compounds include phosphates such as orthophosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, zinc phosphate, and calcium phosphate, as well as inorganic phosphates such as hypophosphorous acid, hypophosphite, pyrophosphate, and polyphosphate, and organic phosphates. These may be used individually or in combination of two or more types. Furthermore, to improve water resistance, corrosion resistance, and the magnetic properties of the magnetic powder through coating, oxo salts such as molybdate, tungstate, vanadate, and chromate, oxidizing agents such as sodium nitrate and sodium nitrite, and chelating agents such as EDTA may be added.

[0023] The concentration of phosphoric acid in the aqueous phosphoric acid solution (in terms of PO4 equivalent) is, for example, 5% by mass or more and 50% by mass or less, and is preferably 10% by mass or more and 30% by mass or less from the viewpoint of solubility of the phosphoric acid compound, storage stability, and ease of chemical treatment. The pH of the phosphoric acid aqueous solution is, for example, between 1 and 4.5, and is preferably between 1.5 and 4 in order to easily control the precipitation rate of phosphate. pH can be adjusted using dilute hydrochloric acid, dilute sulfuric acid, etc.

[0024] The method for preparing a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound is not particularly limited, and the components may be mixed in any order. However, it is preferable to mix the SmFeN-based anisotropic magnetic powder, water, and the rare earth compound beforehand, and then add an aqueous phosphate solution containing the phosphate compound. By pre-mixing SmFeN-based anisotropic magnetic powder, water, and rare earth compounds, the rare earth compounds can more easily bond to the surface of the SmFeN-based anisotropic magnetic powder, thereby increasing the amount of phosphate contained in the final SmFeN-based anisotropic magnetic powder. When mixing SmFeN-based anisotropic magnetic powder, water, and rare earth compounds in advance, after mixing, the mixture is preferably stirred for 5 minutes or more, more preferably for 10 minutes or more, before adding an aqueous phosphoric acid solution containing a phosphoric acid compound. In this case, the pH during mixing and stirring can be between 4 and 10, and is preferably between 5 and 8.

[0025] In the phosphoric acid treatment step, the pH of the slurry is adjusted to 1 to 4.5 by adding an inorganic acid, but it is preferable to adjust it to 1.6 to 3.9, and more preferably to 2 to 3. When the pH is less than 1, the phosphate-coated SmFeN-based anisotropic magnetic powders tend to aggregate, starting from locally precipitated phosphates, which reduces their coercivity. When the pH exceeds 4.5, the amount of phosphate precipitate decreases, resulting in insufficient coating and a tendency for the coercivity to decrease. Examples of inorganic acids that can be added include hydrochloric acid, nitric acid, sulfuric acid, boric acid, and hydrofluoric acid. During the phosphoric acid treatment process, inorganic acids are added as needed to maintain the pH within the above range. Inorganic acids are used for wastewater treatment, but organic acids can be used in combination depending on the purpose. Examples of organic acids include acetic acid, formic acid, and tartaric acid. Inorganic acids and organic acids may be used in combination.

[0026] The lower limit of the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphate treatment step is preferably greater than 0.5% by mass, more preferably 0.55% by mass or more, and even more preferably 0.75% by mass or more. The upper limit of the phosphate content is preferably 4.5% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less. When the phosphate content is 0.5% by mass or less, the effect of coating with phosphate tends to be reduced, and when it exceeds 4.5% by mass, the phosphate-coated SmFeN-based anisotropic magnetic powders tend to aggregate, reducing their coercivity. The phosphate content in the magnetic powder is expressed as the amount of PO4 molecules (i.e., the content in terms of phosphate ions) measured using ICP emission spectrometry (ICP-AES).

[0027] The adjustment of a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound to a pH range of 1 to 4.5 can be carried out for 10 minutes or more, and is preferably carried out for 30 minutes or more in order to reduce the area where the coating is thin. In the initial stages of pH maintenance, the pH rises rapidly, so the interval between adding inorganic acids for pH control is short. However, as coating progresses, the pH fluctuations gradually slow down, and the interval between adding inorganic acids lengthens, allowing the reaction endpoint to be determined.

[0028] [Oxidation process after phosphoric acid treatment] In the oxidation process after phosphoric acid treatment, the SmFeN-based anisotropic magnetic powder coated with the phosphate obtained in the phosphoric acid treatment process is subjected to oxidation treatment by heat treatment at 150°C to 330°C in an oxygen-containing atmosphere. When phosphate-coated SmFeN-based anisotropic magnetic powder is heat-treated at a high temperature of 150°C to 330°C in an oxygen-containing atmosphere, the surface of the phosphate-coated SmFeN-based anisotropic magnetic powder is oxidized, forming a thick iron oxide layer, which tends to improve the hot water resistance of the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0029] The oxidation step after phosphoric acid treatment is carried out by heat treatment of the phosphate-coated SmFeN-based anisotropic magnetic powder in an oxygen-containing atmosphere. The reaction atmosphere preferably contains oxygen in an inert gas such as nitrogen or argon. The oxygen concentration is preferably 3% to 21%, and more preferably 3.5% to 10%. During the oxidation reaction, it is preferable to exchange the gas at a flow rate of 2 L / min to 10 L / min per 1 kg of magnetic powder.

[0030] The heat treatment temperature in the oxidation step after phosphoric acid treatment is preferably 150°C to 330°C, more preferably 200°C to 330°C, even more preferably 200°C to 250°C, and particularly preferably 210°C to 230°C. Below 150°C, the iron oxide layer is not sufficiently formed, and the resistance to hot water tends to decrease. When the temperature exceeds 330°C, an excessive iron oxide layer tends to form, leading to a decrease in coercivity. The heat treatment time is preferably between 3 hours and 10 hours.

[0031] The oxidation step after phosphoric acid treatment is preferably carried out such that the phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder has a first region, the Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, and the Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region. The Sm atom concentration in the first region can be 1.02 times or more the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more. The Sm atom concentration in the first region can be three times or less the Sm atom concentration in the SmFeN-based anisotropic magnetic powder. The Sm atom concentration in the first region is preferably 0.6 times or more and 3.5 times or less than the Fe atom concentration in the first region, and more preferably 0.7 times or more and 3 times or less. The atomic concentrations (atm%) of the SmFeN-based anisotropic magnetic powder and the first region are determined by averaging the atomic concentrations (atm%) in each region obtained from STEM-EDX line analysis.

[0032] [Silica Treatment Process] The SmFeN-based anisotropic magnetic powder after phosphoric acid treatment may be subjected to silica treatment as needed. By forming a thin silica film on magnetic powder, oxidation resistance can be improved. A silica thin film can be formed, for example, by mixing an alkyl silicate, a phosphate-coated SmFeN-based anisotropic magnetic powder, and an alkaline solution.

[0033] [Silane Coupling Process] The magnetic powder after silica treatment may be further treated with a silane coupling agent. By subjecting magnetic powder with a silica thin film to silane coupling treatment, a coupling agent film is formed on the silica thin film, improving the magnetic properties of the magnetic powder, as well as the wettability with resin and the strength of the magnet. Silane coupling agents are not particularly limited and should be selected according to the type of resin, but examples include 3-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, and γ-methyl Captopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethylenedisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyl Trichlorosilane, vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, oleidopropyltriethoxysilane, γ-isocyanatetopropyltriethoxy Silane coupling agents include silane, polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis(trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)tetrasulfan, γ-isocyanatetopropyltrimethoxysilane, vinylmethyldimethoxysilane, 1,3,5-N-tris(3-trimethoxysilylpropyl)isocyanurate, t-butylcarbamatetrialkoxysilane, and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine. These silane coupling agents may be used individually or in combination of two or more. The amount of silane coupling agent added is preferably 0.2 parts by weight or more and 0.8 parts by weight or less, and more preferably 0.25 parts by weight or more and 0.6 parts by weight or less, per 100 parts by weight of magnetic powder. Below 0.2 parts by weight, the effect of the silane coupling agent is small, and above 0.8 parts by weight, it tends to reduce the magnetic properties of the magnetic powder and magnets due to aggregation of the magnetic powder.

[0034] SmFeN-based anisotropic magnetic powders that have undergone phosphoric acid treatment, oxidation, silica treatment, or silane coupling treatment can be filtered, dehydrated, and dried by conventional methods.

[0035] <Phosphate-Coated SmFeN-Based Anisotropic Magnetic Powder> The phosphate-coated SmFeN-based anisotropic magnetic powder of this embodiment is characterized by having an exothermic onset temperature of 170°C or higher in DSC, a phosphate content greater than 0.5% by mass, and containing at least one rare earth element selected from the group consisting of Ce, Nd, and Dy. This phosphate-coated SmFeN-based anisotropic magnetic powder is obtained by the method described above.

[0036] The content of at least one rare earth element selected from the group consisting of Ce, Nd, and Dy in the phosphate-coated SmFeN-based anisotropic magnetic powder can be, for example, 0.25% by mass or less, preferably 0.2% by mass or less, more preferably 0.18% by mass or less, and even more preferably 0.15% by mass or less. When the concentration is 0.25% by mass or less, the coercivity of the magnetic powder tends to improve, and when it is 0.2% by mass or less, a product with improved resistance to hot water may be obtained. The lower limit of the rare earth element content is not particularly limited, but it can generally be 0.01% by mass or more, and 0.03% by mass or more is preferred. The content of rare earth elements in magnetic powder is measured using ICP emission spectroscopy (ICP-AES).

[0037] The phosphate-coated SmFeN-based anisotropic magnetic powder has an exothermic onset temperature of 170°C or higher in DSC, but is preferably 200°C or higher, and more preferably 260°C or higher. The exothermic onset temperature in DSC is determined by a comprehensive evaluation of the density, thickness, and oxidation resistance of the phosphate coating, and high coercivity is obtained when the temperature is 170°C or higher. The exothermic start temperature in DSC can be measured under the conditions described in the examples.

[0038] In the XRD diffraction pattern, the phosphate-coated SmFeN-based anisotropic magnetic powder exhibits a ratio (I) / (II) of 2.0 × 10⁻¹⁰ of the diffraction peak intensity (I) of the (110) plane of αFe to the diffraction peak intensity (II) of the (300) plane of the SmFeN-based anisotropic magnetic powder. -2 Preferably, it is 1.0 × 10 -2 The following is more preferable: The diffraction peak intensity (I) of the (110) plane of αFe represents the abundance of the impurity αFe, and the aforementioned ratio (I) / (II) is 2.0 × 10⁻⁶. -2 High coercivity can be obtained when the following conditions are met. Furthermore, the diffraction peak intensity in the XRD diffraction pattern was measured using a powder X-ray crystal diffractometer (manufactured by Rigaku, X-ray wavelength: CuKa1), and the diffraction peak intensity of the (110) plane of αFe was measured as Sm2Fe. 17 The αFe peak height ratio can be obtained by dividing the value by the diffraction peak intensity of the (300) plane of N3 and then multiplying by 10,000. A low αFe peak height ratio indicates a low content of αFe, which is an impurity.

[0039] The phosphate-coated SmFeN-based anisotropic magnetic powder preferably has a carbon content of 1000 ppm or less, and more preferably 800 ppm or less. The carbon content indicates the amount of organic impurities in the phosphate. When the carbon content exceeds 1000 ppm, the phosphate-coated SmFeN-based anisotropic magnetic powder is exposed to high temperatures during the manufacturing process of bonded magnets, causing the organic impurities to decompose and defects to form in the coating, which tends to reduce the coercivity. Here, the carbon content can be measured by the TOC method.

[0040] The phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder is preferably greater than 0.5% by mass, more preferably 0.55% by mass or more, and even more preferably 0.75% by mass or more. Furthermore, the upper limit of the phosphate content is preferably 4.5% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less. When the phosphate content is 0.5% by mass or less, the effect of coating with phosphate tends to be reduced, and when it exceeds 4.5% by mass, the phosphate-coated SmFeN-based anisotropic magnetic powders tend to aggregate, reducing their coercivity. The phosphate content in the magnetic powder is expressed as the amount of PO4 molecules, measured using ICP emission spectroscopy (ICP-AES).

[0041] In phosphate-coated SmFeN-based anisotropic magnetic powder, the thickness of the phosphate coating is preferably 10 nm to 200 nm, from the viewpoint of the coercivity of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the phosphate coating can be measured by performing compositional analysis using EDX line analysis on a cross-section of the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0042] After the oxidation process following the phosphoric acid treatment described above, the phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder has a first region, and it is preferable that the Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, and that the Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region.

[0043] The Sm atom concentration in the first region can be 1.02 times or more the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more. The Sm atom concentration in the first region can be three times or less the Sm atom concentration in the SmFeN-based anisotropic magnetic powder. The Sm atom concentration in the first region is preferably 0.6 times or more and 3.5 times or less than the Fe atom concentration in the first region, and more preferably 0.7 times or more and 3 times or less. Because the relationship between the Sm atom concentration and Fe atom concentration in the first region is within the range described above, the Fe atom concentration near the surface of the SmFeN-based anisotropic magnetic powder decreases, and the content of samarium phosphate, which has low solubility in water, increases, which tends to further improve water resistance.

[0044] Here, the first region is the region that encompasses the layer showing the maximum peak of P (phosphorus) in the STEM-EDX line analysis of phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the first region can be between 1 nm and 200 nm, and preferably between 3 nm and 100 nm. The atomic concentrations of each element in the first region, the second region (described later), and the Mo high-concentration layer are as follows: (atm%) is obtained by averaging the atomic concentrations (atm%) in each region in the STEM-EDX line analysis.

[0045] The phosphate coating portion preferably has a second region on top of the first region, and the Sm atom concentration in the second region is preferably 1 / 3 or less of the Fe atom concentration in the second region. The Sm atom concentration in the second region is more preferably 1 / 5 or less of the Fe atom concentration in the second region, and even more preferably 1 / 10 or less. The Sm atom concentration in the second region can be 0 times or more the Fe atom concentration in the second region. Here, the second region is the area that encompasses the layer showing the maximum Fe (iron) peak in the phosphate coating in the STEM-EDX line analysis of phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the second region can be between 1 nm and 200 nm, and is preferably between 5 nm and 100 nm. As described above, when the second region is located above the first region, even if there are areas where the phosphate coating is relatively thin, the iron-containing region reinforces it, and the water resistance tends to improve further.

[0046] The Fe atom concentration in the second region is preferably at least twice, and more preferably at least three times, the Fe atom concentration in the first region. The Fe atom concentration in the second region is preferably 10 times or less than the Fe atom concentration in the first region. Furthermore, the Fe atom concentration in the second region is preferably 0.25 times or more and 1 time or less than the Fe atom concentration in the SmFeN-based anisotropic magnetic powder that is the base material, and more preferably 0.5 times or more and 0.8 times or less. Furthermore, P in the second region It is preferable that the (phosphorus) atom concentration is lower than the P atom concentration in the first region. The P atom concentration in the second region is preferably 1 / 5 or less of the P atom concentration in the first region, and more preferably 1 / 10 or less. By setting the P atom concentration in the second region as described above, water resistance tends to improve further.

[0047] If molybdate is added to the reaction slurry during the phosphoric acid treatment process, the phosphate coating portion may have a high-concentration Mo layer within the first and second regions. It is preferable that there are three high-concentration Mo layers in the phosphate coating, that is, it is preferable that there are three Mo (molybdenum) peaks in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. Furthermore, the high-concentration Mo layer can also be confirmed by STEM-EDX mapping analysis. The high-Mo concentration layer is a region that includes the layer showing a Mo (molybdenum) peak in the STEM-EDX line analysis of phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the high-concentration Mo layer is preferably between 1 nm and 40 nm. When having three Mo high-concentration layers as described above, it tends to become a phosphate coating part having more layer structures, and thus the water resistance tends to be improved.

[0048] The Mo atomic concentration of the Mo high-concentration layer is preferably 1.1 times or more and 40 times or less, more preferably 2 times or more and 20 times or less, the Mo atomic concentration of the first region other than the Mo high-concentration layer. Also, the Mo atomic concentration of the Mo high-concentration layer is preferably 1.1 times or more and 20 times or less, more preferably 2 times or more and 10 times or less, the Mo atomic concentration of the second region other than the Mo high-concentration layer. The Sm atomic concentration, Fe atomic concentration, and Mo atomic concentration can be measured by performing a composition analysis by line analysis using EDX on the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0049] <Manufacturing method of SmFeN-based anisotropic magnetic powder>In the manufacturing method of the phosphate-coated SmFeN-based anisotropic magnetic powder described above, the SmFeN-based anisotropic magnetic powder used in the phosphoric acid treatment step is not particularly limited. For example, a step of mixing a solution containing Sm and Fe with a precipitating agent to obtain a precipitate containing Sm and Fe (precipitation step), a step of firing the precipitate to obtain an oxide containing Sm and Fe (oxidation step), a step of heat-treating the oxide in an atmosphere containing a reducing gas to obtain a partial oxide (pretreatment step), a step of reducing the partial oxide (reduction step), and a nitride treatment step of nitriding the alloy particles obtained in the reduction step (nitriding step). Those manufactured by a method including can be preferably used.

[0050] [Precipitation step]In the precipitation step, a Sm raw material and an Fe raw material are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. Sm2Fe 17 When obtaining Sm2FeN3 as the main phase, the molar ratio of Sm and Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, more preferably 2.0:17 to 2.5:17. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, Lu may be added to the above-described solution.

[0051] The Sm and Fe raw materials are not limited as long as they can be dissolved in a strongly acidic solution. For example, in terms of availability, samarium oxide can be used as a raw material for Sm, and FeSO4 can be used as a raw material for Fe. The concentration of the solution containing Sm and Fe can be adjusted as appropriate within the range in which the Sm and Fe raw materials are substantially soluble in the acidic solution. In terms of solubility, sulfuric acid is a good example of an acidic solution.

[0052] By reacting a solution containing Sm and Fe with a precipitating agent, an insoluble precipitate containing Sm and Fe is obtained. Here, the solution containing Sm and Fe only needs to be a solution containing Sm and Fe when it reacts with the precipitating agent. For example, the raw materials containing Sm and Fe can be prepared as separate solutions, and each solution can be added dropwise to react with the precipitating agent. Even when preparing them as separate solutions, each ingredient should be adjusted appropriately so that it is substantially soluble in the acidic solution. The precipitating agent is not limited to any alkaline solution that reacts with a solution containing Sm and Fe to produce a precipitate, and examples include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0053] The precipitation reaction is preferably carried out by adding a solution containing Sm and Fe, and a precipitating agent, dropwise to a solvent such as water, because the properties of the precipitate particles can be easily adjusted. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the concentration of the reaction solution, and the pH during the reaction, a precipitate with a homogeneous distribution of constituent elements, a sharp particle size distribution, and a well-formed powder shape can be obtained. By using such precipitates, the magnetic properties of the final magnetic powder product are improved. The reaction temperature can be 0 to 50°C, and is preferably 35 to 45°C. The reaction solution concentration is preferably 0.65 mol / L to 0.85 mol / L as the total concentration of metal ions, and more preferably 0.7 mol / L to 0.84 mol / L. The pH during the reaction is preferably between 5 and 9, and more preferably between 6.5 and 8.

[0054] The precipitate obtained in the precipitation process roughly determines the particle size, powder shape, and particle size distribution of the final magnetic powder. When the particle size of the obtained particles is measured using a laser diffraction wet particle size analyzer, it is preferable that the size and distribution of the total powder fall approximately within the range of 0.05 to 20 μm, preferably 0.1 to 10 μm. Furthermore, the average particle size of the precipitate is measured as the particle size corresponding to 50% of the volume accumulation from the small particle size side in the particle size distribution, and is preferably within the range of 0.1 to 10 μm.

[0055] After separating the precipitate, it is preferable to desolvent the separated precipitate to prevent it from redissolving in the remaining solvent during the subsequent oxidation heat treatment, which can lead to aggregation of the precipitate, changes in particle size distribution, powder particle size, etc., as the solvent evaporates. Specific methods for solvent removal include, for example, drying in an oven at 70-200°C for 5-12 hours when water is used as the solvent.

[0056] The process may include a step of separating and washing the resulting precipitate after the precipitation step. The washing process should be carried out as needed until the conductivity of the supernatant solution is 5 mS / m or less. For the separation of the precipitate, for example, a solvent (preferably water) can be added to the obtained precipitate and mixed, after which filtration, decantation, or the like can be used.

[0057] [Oxidation Process] The oxidation process is a process in which an oxide containing Sm and Fe is obtained by calcining the precipitate formed in the precipitation process. For example, precipitates can be converted into oxides through heat treatment. When heat-treating a precipitate, it must be done in the presence of oxygen, for example, in an atmospheric environment. Furthermore, since the process must be carried out in the presence of oxygen, it is preferable that the nonmetallic portion of the precipitate contains oxygen atoms.

[0058] The heat treatment temperature in the oxidation process (hereinafter referred to as the oxidation temperature) is not particularly limited, but is preferably 700 to 1300°C, and more preferably 900 to 1200°C. Below 700°C, oxidation is insufficient, and above 1300°C, the desired shape, average particle size, and particle size distribution of the magnetic powder tend not to be obtained. The heat treatment time is not particularly limited, but 1 to 3 hours is preferred.

[0059] The resulting oxides exhibit sufficient microscopic mixing of Sm and Fe within the oxide particles, and the shape and particle size distribution of the precipitate are reflected in the oxide particles.

[0060] [Pretreatment process] The pretreatment process is a process in which an oxide containing Sm and Fe is heat-treated in a reducing gas-containing atmosphere to obtain a partial oxide in which a portion of the oxide has been reduced.

[0061] Here, a partially oxide refers to an oxide in which a portion of the oxide has been reduced. The oxygen concentration of the oxide is not particularly limited, but is preferably 10% by mass or less, and more preferably 8% by mass or less. When the amount exceeds 10% by mass, the heat generated by reduction with the reducing agent Ca during the reduction process increases, leading to a higher firing temperature and a tendency for abnormally grown particles to form. Here, the oxygen concentration of the partial oxide can be measured by non-dispersive infrared absorption spectroscopy (ND-IR).

[0062] The reducing gas can be appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4), but hydrogen gas is preferred in terms of cost, and the gas flow rate is appropriately adjusted within a range that does not cause oxide dispersion. The heat treatment temperature in the pretreatment step (hereinafter referred to as the pretreatment temperature) is in the range of 300°C to 950°C, preferably 400°C or higher, more preferably 750°C or higher, and preferably less than 900°C. When the pretreatment temperature is 300°C or higher, the reduction of oxides containing Sm and Fe proceeds efficiently. Furthermore, below 950°C, particle growth and segregation of oxide particles are suppressed, allowing the desired particle size to be maintained.

[0063] [Reduction Process] The reduction process is a process in which alloy particles are obtained by heat-treating the partial oxide at a temperature of 920°C to 1200°C in the presence of a reducing agent. For example, reduction is carried out by contacting the partial oxide with a calcium melt or calcium vapor. The heat treatment temperature is preferably 950°C to 1150°C, and more preferably 980°C to 1100°C, from the viewpoint of magnetic properties. From the viewpoint of ensuring a more uniform reduction reaction, the heat treatment time is preferably less than 120 minutes, more preferably less than 90 minutes, and the lower limit of the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more.

[0064] The reducing agent, metallic calcium, is used in granular or powder form, but its particle size is preferably 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, metallic calcium can be added in an amount of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce the Sm oxide, and if Fe is in oxide form, the amount required to reduce it), with 1.5 to 2.0 times being preferable.

[0065] In the reduction process, a reducing agent, such as metallic calcium, can be used, along with a disintegration accelerator as needed. This disintegration accelerator is used as appropriate during the washing process described later to promote the disintegration and granulation of the product, and examples include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used at a ratio of 1 to 30% by mass, preferably 5 to 28% by mass, per Sm oxide used as the Sm source.

[0066] [Nitriding step] The nitriding step is a step of obtaining anisotropic magnetic particles by subjecting the alloy particles obtained in the reduction step to nitriding treatment. Since the particulate precipitate obtained in the above precipitation step is used, porous massive alloy particles are obtained in the reduction step. As a result, heat treatment can be immediately performed in a nitrogen atmosphere for nitriding without performing a pulverization treatment, so that nitriding can be performed uniformly.

[0067] The heat treatment temperature (hereinafter, nitriding temperature) in the nitriding treatment of the alloy particles is preferably a temperature of 300 to 600 ° C, particularly preferably 400 to 550 ° C, and is performed by replacing the atmosphere with a nitrogen atmosphere within this temperature range. The heat treatment time may be set to such an extent that nitriding of the alloy particles is sufficiently uniform.

[0068] The product obtained after the nitriding step contains, in addition to the magnetic particles, by-produced CaO, unreacted metallic calcium, etc., and may be in a sintered massive state in which these are combined. Therefore, in that case, this product can be put into cooling water to separate CaO and metallic calcium from the magnetic particles as a calcium hydroxide (Ca(OH)2) suspension. Furthermore, the remaining calcium hydroxide may be sufficiently removed by washing the magnetic particles with acetic acid or the like.

[0069] The SmFeN-based anisotropic magnetic powder has a Th2Zn 17 type crystal structure, and is a nitride composed of samarium (Sm), iron (Fe), and nitrogen (N), which are rare earth metals represented by the general formula Sm x Fe 100-x-y N y . Here, x is preferably 8.1 atomic % or more and 10 atomic % or less, y is preferably 13.5 atomic % or more and 13.9 atomic % or less, and the balance is mainly Fe.

[0070] The average particle size of the SmFeN-based anisotropic magnetic powder is 2 μm or more and 5 μm or less, preferably 2.5 μm or more and 4.8 μm or less. Below 2 μm, the amount of magnetic powder packed into the bonded magnet decreases, resulting in reduced magnetization. Above 5 μm, the coercivity of the bonded magnet tends to decrease. Here, the average particle size is the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0071] The particle size D10 of the SmFeN-based anisotropic magnetic powder is 1 μm or more and 3 μm or less, preferably 1.5 μm or more and 2.5 μm or less. Below 1 μm, the amount of magnetic powder packed into the bonded magnet decreases, resulting in reduced magnetization. On the other hand, above 3 μm, the coercivity of the bonded magnet tends to decrease. Here, D10 refers to the particle size corresponding to 10% of the cumulative volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0072] The particle size D50 of the SmFeN-based anisotropic magnetic powder is 2.5 μm or more and 5 μm or less, preferably 2.7 μm or more and 4.8 μm or less. Below 2.5 μm, the amount of magnetic powder packed into the bonded magnet decreases, resulting in reduced magnetization. Above 5 μm, the coercivity of the bonded magnet tends to decrease. Here, D50 refers to the particle size that corresponds to 50% of the cumulative volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0073] The particle size D90 of the SmFeN-based anisotropic magnetic powder is 3 μm or more and 7 μm or less, preferably 4 μm or more and 6 μm or less. Below 3 μm, the amount of magnetic powder packed into the bonded magnet decreases, resulting in reduced magnetization. Above 7 μm, the coercivity of the bonded magnet tends to decrease. Here, D90 refers to the particle size that corresponds to 90% of the cumulative volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0074] The span of the SmFeN-based anisotropic magnetic powder, defined as follows: span = (D90 - D10) / D50, is 2 or less from the viewpoint of coercivity, and preferably 1.5 or less.

[0075] The circularity of the SmFeN-based anisotropic magnetic powder is not particularly limited, but is preferably 0.5 or higher, and more preferably 0.6 or higher. Below 0.5, poor fluidity leads to stress between particles during molding, resulting in reduced magnetic properties. Here, to measure circularity, SEM images taken at 3000x magnification are binarized using image processing, and the circularity is calculated for each individual particle. In this invention, circularity refers to the average value of circularity obtained by measuring approximately 1,000 to 10,000 particles. Generally, the more small particles there are, the higher the circularity becomes; therefore, the circularity is measured for particles 1 μm or larger. In measuring circularity, the defining formula is: Circularity = (4πS / L 2 Use ). However, S is the two-dimensional projected area of ​​the particle, and L is the two-dimensional projected perimeter.

[0076] <Method for manufacturing a compound for bonded magnets> The method for manufacturing a compound for bonded magnets according to this embodiment is characterized by including the steps of obtaining the phosphate-coated SmFeN-based anisotropic magnetic powder of the embodiment described above, and kneading the magnetic powder with a resin, thereby further improving the coercivity. Furthermore, using polypropylene as the resin improves its resistance to hot water. Of these, the phosphate-coated SmFeN-based anisotropic magnetic powder is obtained by the method described above.

[0077] [Mixing Process] In the process of mixing phosphate-coated SmFeN-based anisotropic magnetic powder with resin, the mixture of phosphate-coated SmFeN-based anisotropic magnetic powder and resin is mixed at 180-300°C using a mixer such as a single-screw mixer or twin-screw mixer. For example, a compound for bonded magnets can be obtained in pellet form by mixing magnetic powder and resin powder in a mixer, extruding the strand with a twin-screw extruder, air-cooling it, and then cutting it into pieces of a few millimeters in size with a pelletizer.

[0078] When the resin used is polypropylene, it is preferable that the weight-average molecular weight of the polypropylene is in the range of 20,000 to 200,000. If the weight-average molecular weight is less than 20,000, the mechanical strength of the bonded magnet after molding decreases, and if it is greater than 200,000, the viscosity of the compound for bonded magnets tends to increase. Furthermore, in order to improve the bonding properties with the coupling-treated magnetic powder, it is preferable that the polypropylene is acid-modified. For example, polypropylene acid-modified with maleic anhydride is preferably used. The acid modification rate for polypropylene is preferably 0.1% by weight or more and 10% by weight or less. If the amount falls below 0.1% by weight, adhesion with the magnetic powder becomes insufficient, reducing the mechanical strength and water resistance of the bonded magnet. When the resin content exceeds 10% by weight, its water absorption rate increases, reducing the water resistance of the bonded magnet.

[0079] The content of phosphate-coated SmFeN-based anisotropic magnetic powder in the compound for bonded magnets is preferably 80% to 95% by mass, and more preferably 90% to 95% by mass from the viewpoint of obtaining high magnetic properties. On the other hand, the resin content in the compound for bonded magnets is preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less from the viewpoint of ensuring fluidity.

[0080] In addition to phosphate-coated SmFeN-based anisotropic magnetic powder and resin, thermoplastic elastomers and antioxidants such as phosphorus-based antioxidants can be kneaded together simultaneously. When a thermoplastic elastomer is included, the mass ratio of the resin to the thermoplastic elastomer is preferably in the range of 90:10 to 50:50, and more preferably in the range of 89:11 to 70:30 from the viewpoint of impact resistance. Furthermore, if a phosphorus-based antioxidant is included, the content of the phosphorus-based antioxidant in the compound for bonded magnets is preferably 0.1% by mass or more and 2% by mass or less.

[0081] In addition to the aforementioned polypropylene (PP), other crystalline resins with low water absorption rates, such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), and polyethylene (PE), can be used as resins in compounds for water-resistant bonded magnets.

[0082] To improve the resistance to hot water, mixtures or polymer alloys can be used that are obtained by mixing the aforementioned crystalline resin with amorphous resins having a glass transition temperature (Tg) of 100°C or higher, such as modified polyphenylene ether (m-PPE), cycloolefin polymer (COP), or cycloolefin copolymer (COC). In the present invention, for example, modified polyphenylene ether A polymer alloy of (m-PPE) and polypropylene can be suitably used.

[0083] <Compound for bonded magnets> The compound for bonded magnets of this embodiment is characterized by containing the phosphate-coated SmFeN-based anisotropic magnetic powder of the embodiment described above and a resin. By including the phosphate-coated SmFeN-based anisotropic magnetic powder of the above-described embodiment and a resin, the coercivity of bonded magnets made using this bonded magnet compound is improved. The compound for bonded magnets is obtained by the method described above.

[0084] [Method for manufacturing bonded magnets] Bonded magnets can be manufactured using a compound for bonded magnets and an appropriate molding machine. Specifically, for example, a bonded magnet can be obtained by injecting a compound for bonded magnets, which has been molten in a molding machine barrel, into a mold under a magnetic field, aligning the easy magnetization axis (orientation step), cooling and solidifying it, and then magnetizing it with an air-core coil or magnetizing yoke (magnetization step).

[0085] The barrel temperature is selected depending on the type of resin used, ranging from 160°C to 320°C, and similarly, the mold temperature can be, for example, 30°C to 150°C. The orientation magnetic field in the orientation process is generated using electromagnets or permanent magnets, and the magnitude of the magnetic field is preferably 4 kOe or more, and more preferably 6 kOe or more. Furthermore, the magnitude of the magnetization magnetic field in the magnetization process is preferably 20 kOe or more, and more preferably 30 kOe or more.

[0086] [Bonded Magnet] The bonded magnet of this embodiment is characterized by comprising the phosphate-coated SmFeN-based anisotropic magnetic powder of the above-described embodiment and a resin. Such bonded magnets can retain over 95% of their pre-test total flux after 1000 hours of immersion in hot water at 120°C. The total flux of a bonded magnet after a hot water resistance test, in which it is held for 1000 hours under immersion conditions at 120°C, being 95% or more of the total flux before the test indicates high resistance to hot water. 96% or more is preferable, and 97% or more is more preferable. The total flux value can be obtained, for example, by measuring the change in magnetic flux inside the search coil by pulling out a bonded magnet molded product placed inside the search coil to the outside of the search coil, using a flux meter (manufactured by Nippon Denji Sokki; model: NFX-1000). Furthermore, bonded magnets can be obtained by the method described above.

[0087] Since the bonded magnet of this embodiment is resistant to hot water, it can be suitably used as a drive source for fuel pumps and water pumps in automobiles, motorcycles, and the like. [Examples]

[0088] (Example 1) 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Furthermore, Sm2O3 0.49 kg and 0.74 kg of 70% sulfuric acid were added and the mixture was stirred well until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus creating a Sm-Fe sulfuric acid solution.

[0089] [Precipitation process] The entire amount of the prepared Sm-Fe sulfuric acid solution was added dropwise to 20 kg of pure water maintained at a temperature of 40°C while stirring for 70 minutes from the start of the reaction, and at the same time, a 15% aqueous ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing Sm-Fe hydroxide. The obtained slurry was washed with pure water by decantation, and then the hydroxide was separated into solid and liquid components. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0090] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, a red Sm-Fe oxide was obtained as the raw material powder.

[0091] [Pretreatment step] 100g of Sm-Fe oxide was placed in a steel container to a thickness of 10mm. The container was placed inside the furnace, the pressure was reduced to 100 Pa, and then the temperature was raised to the pretreatment temperature of 850°C while introducing hydrogen gas, and maintained at that temperature for 15 hours. The oxygen concentration was measured using non-dispersive infrared absorption spectroscopy (ND-IR) (EMGA-820, Horiba, Ltd.) and found to be 5% by mass. This revealed that the oxygen bonded to Sm was not reduced, while 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0092] [Reduction Process] 60g of partial oxide obtained in the pretreatment process and 19.2g of metallic calcium with an average particle size of approximately 6mm were mixed and placed in the furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. Fe-Sm alloy particles were obtained by raising the furnace temperature to 1045°C and holding it for 45 minutes.

[0093] [Nitriding Process] Subsequently, the furnace temperature was cooled to 100°C, then the furnace was evacuated, and the temperature was raised to 450°C while introducing nitrogen gas. This temperature was maintained for 23 hours to obtain a massive product containing magnetic particles.

[0094] [Washing process] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding the solution to pure water, stirring, and decanting was repeated 10 times. Next, 2.5g of 99.9% acetic acid was added and the mixture was stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding the material to pure water, stirring, and decanting was repeated twice, followed by dehydration and drying, and then mechanical crushing to obtain SmFeN-based anisotropic magnetic powder (average particle size 3 μm).

[0095] [Phosphoric Acid Treatment Process] As a phosphoric acid treatment solution, a mixture of 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1 was prepared, and the pH was adjusted to 2 and the PO4 concentration to 20% by mass with pure water and dilute hydrochloric acid. Cerium chloride was also prepared. The washing process was carried out in multiple batches, and the resulting SmFeN-based anisotropic magnetic powder was mixed to obtain a slurry containing 1000g. To this slurry, dilute hydrochloric acid (70 g of hydrogen chloride) was added and stirred for 1 minute to remove surface oxide film and contaminants. Then, the process of draining and adding water was repeated until the conductivity of the supernatant liquid was 100 μS / cm or less, yielding a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the obtained slurry, 3.7 g of cerium chloride (CeCl3) was added entirely to the treatment tank, and the pH was adjusted to a range of 5-8 using sodium hydroxide and maintained for 30 minutes, causing cerium compounds containing cerium hydroxide (Ce(OH)3) to precipitate on the surface of the magnetic powder. Next, 100g of the prepared phosphoric acid treatment solution was added entirely to the treatment tank, and then 6% by weight hydrochloric acid was added as needed to control the pH of the phosphoric acid treatment reaction slurry within the range of 2.5 ± 0.1, and this was maintained for 30 minutes. Next, the powder was subjected to suction filtration, dehydration, and vacuum drying to obtain a cerium-containing phosphate-coated SmFeN-based anisotropic magnetic powder. At the stage when a cerium compound containing cerium hydroxide was deposited on the surface of the magnetic powder, the cerium content in the magnetic powder was 0.05% by mass, and the cerium content in the magnetic powder after phosphoric acid treatment was also 0.05% by mass. This indicates that most of the cerium contained in the cerium compound deposited on the magnetic powder surface beforehand remains present even after phosphoric acid treatment.

[0096] [Oxidation process after phosphoric acid treatment] 1000 g of cerium-containing phosphate-coated SmFeN-based anisotropic magnetic powder was gradually heated from room temperature in an atmosphere of nitrogen and air mixed gas (oxygen concentration 4%, 5 L / min), and heat-treated at a maximum temperature of 230°C for 8 hours to obtain oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0097] (Example 2) The procedure was carried out in the same manner as in Example 1, except that the amount of cerium chloride was 7.4 g, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0098] (Example 3) The procedure was carried out in the same manner as in Example 1, except that the amount of cerium chloride was 15.2 g, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0099] (Example 4) The procedure was carried out in the same manner as in Example 1, except that 2.2 g of samarium chloride (SmCl3) was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0100] (Example 5) The procedure was carried out in the same manner as in Example 1, except that 4.4 g of samarium chloride was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0101] (Example 6) The procedure was carried out in the same manner as in Example 1, except that 4.4 g of neodymium chloride (NdCl3) was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0102] (Example 7) The procedure was carried out in the same manner as in Example 1, except that 8.8 g of neodymium chloride was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0103] (Example 8) The procedure was carried out in the same manner as in Example 1, except that 4.5 g of dysprosium chloride (DyCl3) was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0104] (Example 9) The procedure was carried out in the same manner as in Example 1, except that 9.0 g of dysprosium chloride was used instead of cerium chloride, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder containing rare earth elements.

[0105] (Reference Example) Except for not adding cerium chloride and sodium hydroxide and not precipitating the cerium compound, the procedure was carried out in the same manner as in Example 1 to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0106] (Comparative Example 1) Magnetic powder was obtained by carrying out the water washing step in the same manner as in Example 1. As a phosphoric acid treatment solution, a mixture of 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1 was prepared, and the pH was adjusted to 2.5 and the PO4 concentration to 20% by mass using pure water and dilute hydrochloric acid. The slurry containing 1000 g of SmFeN-based anisotropic magnetic powder obtained in the water washing step was stirred for 1 minute in dilute hydrochloric acid (hydrogen chloride:70 g) to remove surface oxide film and contaminants. Then, the process of draining and adding water was repeated until the conductivity of the supernatant liquid was 100 μS / cm or less, to obtain a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the resulting slurry, 100g of the prepared phosphoric acid treatment solution was added entirely to the treatment tank. The pH of the phosphoric acid-treated reaction slurry increased from 2.5 to 6 over 5 minutes. After stirring for 15 minutes, the material was filtered by suction, dehydrated, and vacuum dried to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder.

[0107] (Comparative Example 2) [Reduction Process 2] A crucible filled with a mixed powder consisting of 52.5 g of iron powder with an average particle size (D50) of approximately 50 μm, 21.3 g of samarium oxide powder with an average particle size (D50) of 3 μm, and 10.5 g of metallic calcium was placed inside the furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. Fe-Sm alloy particles were obtained by raising the temperature to 1150°C and holding it for 5 hours.

[0108] [Nitriding Process 2] Next, the Fe-Sm alloy particles were heat-treated in an ammonia-hydrogen mixed gas at 420°C for 23 hours to obtain a massive product containing magnetic particles.

[0109] [Washing Process 2] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding the solution to pure water, stirring, and decanting was repeated 10 times. Next, 2.5g of 99.9% acetic acid was added and the mixture was stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding the mixture to pure water, stirring, and decanting was repeated twice. Next, dehydration and drying treatments were performed to obtain SmFeN-based anisotropic magnetic powder (average particle size 30 μm).

[0110] [Phosphoric Acid Treatment Step 2] 15 g of the obtained magnetic powder was sealed in a glass bottle with 0.44 g of 85% orthophosphoric acid aqueous solution, 100 ml of isopropanol (IPA), and 200 g of 10 mm diameter alumina beads, and ground in a vibrating ball mill for 120 minutes. Subsequently, the slurry was filtered and then vacuum-dried at 100°C to obtain Comparative Example 2, a phosphate-coated SmFeN-based anisotropic magnetic powder (average particle size 1.5 μm).

[0111] [Magnetic powder evaluation] (Intrinsic Coercivity iHc) For each magnetic powder obtained in Examples 1 to 9, Reference Examples, and Comparative Examples 1 and 2, the magnetic properties (intrinsic coercivity iHc) were measured using a VSM (Vibrating Sample Magnetometer, manufactured by RIKEN Electronics; Model: BHV-55). The intrinsic coercivity iHc was measured before oxidation treatment, after oxidation treatment, and after a water resistance test in which the magnetic powder was immersed in water at 100°C for 8 hours. The rate of decrease in intrinsic coercivity (iHc) due to the water resistance test was calculated from the iHc values ​​after oxidation treatment and after the water resistance test. Table 1 shows the measurement results of the magnetic powder before oxidation treatment. Table 2 shows the measurement results of the magnetic powder after oxidation treatment.

[0112] (PO4 deposition amount) The phosphorus concentration in each magnetic powder obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 was measured using ICP emission spectroscopy (ICP-AES) and converted to the concentration as phosphate ions (PO4). The results are shown in Table 1.

[0113] (Amount of rare earth elements attached) The concentrations of rare earth elements in each magnetic powder obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 were measured using ICP emission spectroscopy (ICP-AES) to determine the amount of rare earth elements attached. The results are shown in Tables 1 and 2. Furthermore, for Examples 4 and 5, which used Sm as the rare earth element, the results were confirmed as follows based on ICP emission spectroscopy. In the reference example, Examples 4 and 5, a correlation was confirmed between the amount of Sm added and the Sm-to-Fe content ratio confirmed by ICP emission spectroscopy, thereby considering the amount of samarium added during samarium chloride addition as the amount of rare earth elements attached.

[0114] (DSC exothermic onset temperature) 20 mg of each magnetic powder obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 was weighed out, and DSC analysis was performed using a high-temperature differential scanning thermal analyzer (DSC6300, Hitachi High-Tech Science Corporation) under the following measurement conditions: air atmosphere (200 mL / min), room temperature to 400°C (heating rate: 20°C / min), and reference: alumina (20 mg) to measure the exothermic onset temperature. The results of the DSC analysis are shown in Table 1. A high exothermic onset temperature indicates that heat generation due to oxidation is less likely, meaning that the phosphate coating is more densely formed.

[0115] (αFe peak height ratio) The XRD patterns of each magnetic powder obtained in Examples 1 to 9, Reference Examples, and Comparative Examples 1 and 2 were measured using a powder X-ray crystal diffractometer (manufactured by Rigaku, X-ray wavelength: CuKa1). The diffraction peak intensity of the (110) plane of αFe is measured in Sm2Fe 17 The αFe peak height ratio was determined by dividing the value by the diffraction peak intensity of the (300) plane of N3 and then multiplying by 10,000. The results are shown in Table 1. A low αFe peak height ratio indicates a low content of αFe, which is an impurity.

[0116] (Total Carbon Content) The total carbon (TC) content in each magnetic powder obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 was measured using a combustion catalyst oxidation type total organic carbon (TOC) meter (Shimadzu Corporation; Model: SSM-5000A). The results are shown in Table 1.

[0117] [Table 1]

[0118] [Table 2]

[0119] Table 1 confirms that magnetic powders with rare earth elements attached tend to exhibit increased coercivity. Furthermore, Table 2 shows that the magnetic powders obtained in Examples 1, 2, 4, 6, and 8, in which the amount of rare earth elements attached was 0.2% by mass or less, showed improved resistance to hot water after oxidation treatment compared to the reference example.

Claims

1. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, comprising a phosphoric acid treatment step, wherein an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphoric acid compound, and a rare earth compound to adjust the pH of the slurry to 1 or more and 4.5 or less, thereby obtaining SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface.

2. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1, wherein the content of rare earth elements in the rare earth compound is 0.25% by mass or less relative to the phosphate-coated SmFeN-based anisotropic magnetic powder.

3. The aforementioned rare earth compound is defined by the following formula (1): R-(OH) Ｘ (1) A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1 or 2, wherein the rare earth hydroxide is represented by formula (1) (wherein R is Ce, Nd, Sm, or Dy, and x is 1, 2, 3, or 4).

4. The aforementioned rare earth hydroxide is Ce(OH) ３ , Nd(OH) ３ , Sm(OH) ３ , and Dy (OH) ３ A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 3, wherein at least one of the group consisting of is selected from the group consisting of the following.

5. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 4, wherein the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder is greater than 0.5% by mass.

6. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 5, comprising performing the adjustment for 10 minutes or more in the phosphate treatment step.

7. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 6, wherein the pH is adjusted to 1.6 or more and 3.9 or less in the phosphate treatment step.

8. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 7, comprising an oxidation step of heat-treating the phosphate-coated SmFeN-based anisotropic magnetic powder in an oxygen-containing atmosphere at 150°C to 330°C after a phosphoric acid treatment step.

9. A phosphate-coated SmFeN-based anisotropic magnetic powder having an exothermic onset temperature of 170°C or higher in DSC, a phosphate content greater than 0.5% by mass, and containing at least one rare earth element selected from the group consisting of Ce, Nd, and Dy.

10. In the XRD diffraction pattern, the ratio (I) / (II) of the diffraction peak intensity of the (110) plane of αFe (I) to the diffraction peak intensity of the (300) plane of the SmFeN-based anisotropic magnetic powder (II) is 2.0 × 10⁻⁶. －２ The phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 9 is as follows:

11. A phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 9 or 10, wherein the carbon content is 1000 ppm or less.

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