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

Abstract

To provide a method of producing a phosphate-coated SmFeN-based anisotropic magnetic powder having a more excellent coercive force.SOLUTION: A method of producing a phosphate-coated SmFeN-based anisotropic magnetic powder includes a process of phosphoric acid treatment to obtain a SmFeN-based anisotropic magnetic powder coated on a surface with phosphate by adding inorganic acid to slurry including a SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound and adjusting pH of the slurry to 1 or greater and 4.5 or smaller.SELECTED DRAWING: None

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 the coercivity can be improved by forming a phosphate coating on the surface of an SmFeN-based anisotropic magnetic powder. For example, Patent Document 1 discloses a method of forming a phosphate coating on the surface of an SmFeN-based anisotropic magnetic powder by adding a phosphate treatment solution containing pH-adjusted orthophosphoric acid to a slurry containing an SmFeN-based anisotropic magnetic powder and water as a solvent.

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

[0004] Patent Document 3 discloses that the coercive force of an SmFeN-based anisotropic magnetic powder coated with a phosphate is increased by subjecting the 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 Application Publication No. 2017-210662 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-160794 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder having superior coercive force, and to provide such phosphate-coated SmFeN-based anisotropic magnetic powder. [Means for solving the problem]

[0007] A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to one embodiment of the present invention is characterized by including a phosphate treatment step in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate 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 whose surface is coated with phosphate.

[0008] Furthermore, a phosphate-coated SmFeN-based anisotropic magnetic powder according to one embodiment of the present invention is characterized in that it has a heat generation onset temperature of 170°C or higher in DSC, a phosphate content of more than 0.5 mass%, and 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-described embodiment, it is possible to provide a method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder having a superior coercive force, and the phosphate-coated SmFeN-based anisotropic magnetic powder. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are examples for embodying the technical concept of the present invention, and the present invention is not limited to the following. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0011] <Method for manufacturing phosphate-coated SmFeN-based anisotropic magnetic powder> The method for producing phosphate-coated SmFeN-based anisotropic magnetic powder of this embodiment is characterized by including a phosphate treatment step in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate 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 whose surface is coated with phosphate.

[0012] [Phosphating process] In the phosphate treatment step, an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound to adjust the pH of the slurry to between 1 and 4.5, thereby obtaining SmFeN-based anisotropic magnetic powder whose surface is coated with phosphate.

[0013] The phosphate-coated SmFeN-based anisotropic magnetic powder is formed by the reaction of a metal component (e.g., iron or samarium) contained in the SmFeN-based anisotropic magnetic powder with a phosphoric acid component contained in a phosphoric acid compound, resulting in the precipitation of a phosphate (e.g., iron phosphate or samarium phosphate) on the surface of the SmFeN-based anisotropic magnetic powder. Furthermore, by adding a rare earth compound to the slurry, the rare earth compound bonds to the surface of the SmFeN-based anisotropic magnetic powder, and a salt of the rare earth element and phosphoric acid precipitates. Furthermore, by using water as the solvent in this embodiment, phosphate with a smaller particle size is precipitated compared to when an organic solvent is used as the solvent, resulting in a phosphate-coated SmFeN-based anisotropic magnetic powder with a dense coating.

[0014] The content of the SmFeN-based anisotropic magnetic powder in the slurry is, for example, 1% by mass to 50% by mass, and preferably 5% by mass to 20% by mass from the viewpoint of productivity. The content of the phosphoric acid component (PO4) in the slurry is, for example, 0.01% by mass to 10% by mass, calculated as PO4, and preferably 0.05% by mass to 5% by mass from the viewpoint of reactivity of the phosphoric acid component and productivity.

[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 using water as a solvent, such as rare earth hydroxides, rare earth chlorides, rare earth sulfates, rare earth nitrates, and rare earth acetates, are preferred.

[0016] Examples of rare earth elements contained in the rare earth compound include Ce, Sm, Nd, Dy, Y, La, and Pr, with Ce, Sm, Nd, and Dy being preferred.

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

[0018] The rare earth hydroxide may be a hydroxide of 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.) More preferred are rare earth hydroxides represented by the formula (I), with Ce(OH)3, Nd(OH)3, Sm(OH)3, and Dy(OH)3 being particularly preferred. 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 produced from a rare earth chloride at a pH of 4 to 10, for example.

[0019] The rare earth chloride may be a compound represented by 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.) More preferred are rare earth chlorides represented by the formula: and CeCl3, NdCl3, SmCl3, and DyCl3 are particularly preferred. 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 by the phosphate 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. A content of 0.25% by mass or less tends to further improve the coercivity of the magnetic powder, while a content of 0.2% by mass or less can sometimes result in a powder with improved hot water resistance. There is no particular lower limit for the rare earth element content, but it can generally be 0.01% by mass or more, preferably 0.03% by mass or more. The content of rare earth elements in the magnetic powder is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0021] In the phosphate treatment step, most of the rare earth elements derived from the rare earth compound contained in the slurry adhere to the SmFeN-based anisotropic magnetic powder. Therefore, when the content of the 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 the rare earth elements contained in the rare earth compound is 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, relative to the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphate treatment step. A content of the rare earth elements contained in the rare earth compound of 0.25% by mass or less tends to further improve the coercivity of the magnetic powder, while a content of 0.2% by mass or less can sometimes result in improved hot water resistance. The lower limit of the content of the rare earth elements in the rare earth compound is not particularly limited, but it can generally be 0.01% by mass or more, preferably 0.03% by mass or more. The rare earth element precipitates on the surface of the SmFeN-based anisotropic magnetic powder as a salt with phosphoric acid.

[0022] The phosphoric acid aqueous solution can be obtained by mixing a phosphoric acid compound with water. Examples of phosphoric acid compounds include phosphate-based compounds such as orthophosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, zinc phosphate, and calcium phosphate; inorganic phosphoric acids such as hypophosphorous acid, hypophosphite, pyrophosphate, and polyphosphoric acid; and organic phosphoric acids. These compounds may be used alone or in combination of two or more. Furthermore, for the purpose of improving the water resistance and corrosion resistance of the coating and the magnetic properties of the magnetic powder, oxoacid salts such as molybdate, tungstate, vanadate, and chromate, oxidizers such as sodium nitrate and sodium nitrite, and chelating agents such as EDTA may also be added.

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

[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. The components can be mixed in any order. However, it is preferable to first mix the SmFeN-based anisotropic magnetic powder, water, and rare earth compound, and then add an aqueous phosphoric acid solution containing the phosphate compound. Mixing the SmFeN-based anisotropic magnetic powder, water, and rare earth compound first facilitates bonding of the rare earth compound 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 the SmFeN-based anisotropic magnetic powder, water, and rare earth compound first, the mixture is stirred, preferably for at least 5 minutes, more preferably at least 10 minutes, before adding the aqueous phosphoric acid solution containing the phosphate compound. In this case, the pH during mixing and stirring can be between 4 and 10, preferably between 5 and 8.

[0025] In the phosphate treatment process, the pH of the slurry is adjusted to 1 to 4.5 by adding an inorganic acid, preferably 1.6 to 3.9, and more preferably 2 to 3. If the pH is less than 1, the phosphate-coated SmFeN-based anisotropic magnetic powder tends to aggregate from locally large amounts of precipitated phosphate, resulting in a decrease in coercivity. If the pH is greater than 4.5, the amount of precipitated phosphate decreases, resulting in insufficient coating and a decrease in coercivity. Examples of inorganic acids that can be added include hydrochloric acid, nitric acid, sulfuric acid, boric acid, and hydrofluoric acid. During the phosphate treatment process, inorganic acids are added as needed to maintain the pH within the above range. While inorganic acids are used from the perspective of wastewater treatment, organic acids can be used in combination depending on the purpose. Examples of organic acids include acetic acid, formic acid, and tartaric acid. A mixture of inorganic and organic acids may also be used.

[0026] The lower limit of the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder obtained by 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. If the phosphate content is 0.5% by mass or less, the effect of the phosphate coating tends to be reduced, and if it exceeds 4.5% by mass, the phosphate-coated SmFeN-based anisotropic magnetic powder tends to aggregate together, resulting in a decrease in 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 inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0027] The pH of a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound can be adjusted to a range of 1 to 4.5 for 10 minutes or more, preferably 30 minutes or more to reduce areas where the coating is thin. In the early stages of pH maintenance, the pH rises quickly, so the intervals between additions of inorganic acid for pH control are short, but as coating progresses, the pH fluctuations gradually slow down and the intervals between additions of inorganic acid become longer, allowing the reaction endpoint to be determined.

[0028] [Oxidation process after phosphate treatment] In the oxidation step after the phosphate treatment, the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphate treatment step is subjected to an oxidation treatment by heat treating it in an oxygen-containing atmosphere at a temperature of 150°C to 330°C. By heat treating the phosphate-coated SmFeN-based anisotropic magnetic powder in an oxygen-containing atmosphere at a high temperature of 150°C to 330°C, the surface of the phosphate-coated SmFeN-based anisotropic magnetic powder base material is oxidized to form 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 the phosphoric acid treatment is carried out by heat treating 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%, more preferably 3.5% to 10%. During the oxidation reaction, the gas is preferably exchanged 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 the phosphoric acid treatment is preferably 150°C or higher and 330°C or lower, more preferably 200°C or higher and 330°C or lower, even more preferably 200°C or higher and 250°C or lower, and particularly preferably 210°C or higher and 230°C or lower. If the temperature is lower than 150°C, the iron oxide layer is not sufficiently formed, and hot water resistance tends to be reduced. If the temperature exceeds 330°C, the iron oxide layer is excessively formed, and coercive force tends to be reduced. The heat treatment time is preferably 3 hours or higher and 10 hours or lower.

[0031] The oxidation step after the phosphoric acid treatment is preferably carried out so that the phosphate coating portion present on the surface of the SmFeN-based anisotropic magnetic powder has a first region, the Sm atomic concentration of the first region is higher than the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder, and the Sm atomic concentration of the first region is 0.5 to 4 times the Fe atomic concentration of the first region. The Sm atomic concentration of the first region can be 1.02 times or more, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more, of the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder. The Sm atomic concentration of the first region can be 3 times or less of the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder. The Sm atomic concentration of the first region is preferably 0.6 to 3.5 times, more preferably 0.7 to 3 times, of the Fe atomic concentration in the first region. 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 in STEM-EDX line analysis.

[0032] [Silica treatment process] The phosphoric acid-treated SmFeN-based anisotropic magnetic powder may be silica-treated if necessary. Forming a silica thin film on the magnetic powder can improve oxidation resistance. The silica thin film can be formed, for example, by mixing alkyl silicate, phosphate-coated SmFeN-based anisotropic magnetic powder, and an alkaline solution.

[0033] [Silane coupling treatment process] The magnetic powder after silica treatment may be further treated with a silane coupling agent. By subjecting the magnetic powder with a thin silica film formed thereon to silane coupling treatment, a coupling agent film is formed on the thin silica film, improving the magnetic properties of the magnetic powder, as well as improving wettability with resin and the strength of the magnet.The silane coupling agent may be selected according to the type of resin and is not particularly limited. Examples of suitable silane coupling agents 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 Mercaptopropyltrimethoxysilane, 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-isocyanatopropyltriethoxysilane Examples of silane coupling agents include silane, polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis(trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)tetrasulfane, γ-isocyanatepropyltrimethoxysilane, 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 alone or in combination of two or more. The amount of silane coupling agent added is preferably 0.2 to 0.8 parts by weight, more preferably 0.25 to 0.6 parts by weight, per 100 parts by weight of magnetic powder. If the amount is less than 0.2 parts by weight, the effect of the silane coupling agent is small, but if the amount is more than 0.8 parts by weight, the magnetic powder tends to aggregate, reducing the magnetic properties of the magnetic powder and magnet.

[0034] After the phosphoric acid treatment step, oxidation step, silica treatment, or silane coupling treatment, the SmFeN-based anisotropic magnetic powder 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 a heat generation onset temperature of 170°C or higher in DSC, a phosphate content of more than 0.5 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. A content of 0.25% by mass or less tends to further improve the coercivity of the magnetic powder, while a content of 0.2% by mass or less can sometimes result in a powder with improved hot water resistance. There is no particular lower limit for the rare earth element content, but it can generally be 0.01% by mass or more, preferably 0.03% by mass or more. The content of rare earth elements in the magnetic powder is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0037] Phosphate-coated SmFeN-based anisotropic magnetic powders have a heat generation onset temperature in DSC of 170°C or higher, preferably 200°C or higher, and more preferably 260°C or higher. The heat generation onset temperature in DSC is a comprehensive evaluation of the density, thickness, oxidation resistance, etc. of the phosphate coating, and a high coercive force is obtained when the temperature is 170°C or higher. The heat generation onset temperature in DSC can be measured under the conditions described in the Examples.

[0038] In the XRD diffraction pattern of the phosphate-coated SmFeN-based anisotropic magnetic powder, the ratio (I) / (II) 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 is 2.0 × 10 -2 Preferably, it is 1.0 x 10 or less. -2 The diffraction peak intensity (I) of the (110) plane of αFe represents the amount of αFe present as an impurity, and the ratio (I) / (II) is preferably 2.0×10 or less. -2 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 calculated as SmFe 17 The αFe peak height ratio can be calculated by dividing this by the diffraction peak intensity of the (300) plane of N3 and multiplying it by 10,000. A low αFe peak height ratio means a low content of the impurity αFe.

[0039] The carbon content of the phosphate-coated SmFeN-based anisotropic magnetic powder is preferably 1000 ppm or less, and more preferably 800 ppm or less. The carbon content indicates the amount of organic impurities in the phosphate. If the carbon content exceeds 1000 ppm, the phosphate-coated SmFeN-based anisotropic magnetic powder is exposed to high temperatures during the process of producing a bonded magnet, causing the organic impurities to decompose and defects in the coating, which tends to reduce the coercive force. 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. 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. If the phosphate content is 0.5% by mass or less, the effect of the phosphate coating tends to be reduced. If the phosphate content exceeds 4.5% by mass, the phosphate-coated SmFeN-based anisotropic magnetic powder tends to aggregate, resulting in a decrease in coercivity. The phosphate content in the magnetic powder is expressed in terms of the PO4 molecule amount measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0041] The thickness of the phosphate coating portion of the phosphate-coated SmFeN-based anisotropic magnetic powder is preferably 10 nm or more and 200 nm or less in terms of the coercive force of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the phosphate coating portion can be measured by performing composition analysis on a cross section of the phosphate-coated SmFeN-based anisotropic magnetic powder using EDX line analysis.

[0042] After the oxidation step after the above-mentioned phosphoric acid treatment, the phosphate coating portion present on the surface of the SmFeN-based anisotropic magnetic powder has a first region, and it is preferable that the Sm atomic concentration in the first region is higher than the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder, and that the Sm atomic concentration in the first region is 0.5 to 4 times the Fe atomic concentration in the first region.

[0043] The Sm atomic concentration of the first region can be 1.02 times or more, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more, of the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder. The Sm atomic concentration of the first region can be 3 times or less of the Sm atomic concentration in the SmFeN-based anisotropic magnetic powder. The Sm atomic concentration of the first region is preferably 0.6 to 3.5 times, more preferably 0.7 to 3 times, of the Fe atomic concentration in the first region. When the relationship between the Sm atomic concentration and the Fe atomic concentration in the first region is within the above-mentioned range, the Fe atomic 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 a region including a layer showing the maximum P (phosphorus) peak in STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the first region can be 1 nm or more and 200 nm or less, and preferably 3 nm or more and 100 nm or less. The atomic concentration (atm%) of each element in the first region, the second region described below, and the Mo-rich layer is determined by averaging the atomic concentration (atm%) in each region in STEM-EDX line analysis.

[0045] The phosphate coating portion further has a second region on the first region, and the Sm atomic concentration in the second region is preferably 1 / 3 or less of the Fe atomic concentration in the second region. The Sm atomic concentration in the second region is more preferably 1 / 5 or less, and even more preferably 1 / 10 or less, of the Fe atomic concentration in the second region. The Sm atomic concentration in the second region can be 0 or more times the Fe atomic concentration in the second region. Here, the second region is a region including a layer that shows the maximum peak of Fe (iron) in the phosphate coating portion in a STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the second region can be 1 nm or more to 200 nm or less, and preferably 5 nm or more to 100 nm or less. When the second region is provided on the first region as described above, even if there are areas where the phosphate coating portion has a relatively thin film thickness, the area is reinforced by the iron-containing region, which tends to further improve water resistance.

[0046] The Fe atomic concentration in the second region is preferably at least twice, and more preferably at least three times, the Fe atomic concentration in the first region. The Fe atomic concentration in the second region is preferably no more than 10 times the Fe atomic concentration in the first region. The Fe atomic concentration in the second region is preferably 0.25 to 1 times, and more preferably 0.5 to 0.8 times, the Fe atomic concentration in the SmFeN-based anisotropic magnetic powder base material. The P (phosphorus) atomic concentration in the second region is preferably lower than the P atomic concentration in the first region. The P atomic concentration in the second region is preferably no more than 1 / 5 times, and more preferably no more than 1 / 10 times, the P atomic concentration in the first region. By setting the P atomic concentration in the second region as described above, water resistance tends to be further improved.

[0047] When molybdate is blended into the reaction slurry in the phosphate treatment step, the phosphate coating portion may have a high-Mo concentration layer in the first region and the second region. It is preferable that there are three high-Mo concentration layers in the phosphate coating portion, that is, it is preferable that there are three peaks of Mo (molybdenum) in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. Also, the high-Mo concentration layer can be confirmed by mapping analysis of STEM-EDX. The high-Mo concentration layer is a region including the layer showing the peak of Mo (molybdenum) in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the high-Mo concentration layer is preferably 1 nm or more and 40 nm or less. When having three high-Mo concentration layers as described above, by forming a phosphate coating portion having more layer structures, the water resistance tends to be improved.

[0048] The Mo atomic concentration of the high-Mo 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 high-Mo concentration layer. Also, the Mo atomic concentration of the high-Mo 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 high-Mo concentration layer. The Sm atomic concentration, Fe atomic concentration, and Mo atomic concentration can be measured by performing composition analysis by line analysis using EDX on the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0049] <Method for producing SmFeN-based anisotropic magnetic powder> In the method for producing the phosphate-coated SmFeN-based anisotropic magnetic powder described above, the SmFeN-based anisotropic magnetic powder used in the phosphate 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 process of nitriding the alloy particles obtained in the reduction process (nitriding process) The polymerizable composition produced by the method comprising the steps of:

[0050] [Precipitation process] In the precipitation process, Sm and Fe raw materials are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. 17 When N3 is obtained as the main phase, the molar ratio of Sm to Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, and more preferably 2.0:17 to 2.5:17. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, and Lu may be added to the above-mentioned solution.

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

[0052] An insoluble precipitate containing Sm and Fe is obtained by reacting a solution containing Sm and Fe with a precipitant. The solution containing Sm and Fe is sufficient as long as it becomes a solution containing Sm and Fe upon reaction with the precipitant. For example, raw materials containing Sm and Fe may be prepared as separate solutions, and each solution may be added dropwise to react with the precipitant. Even when prepared as separate solutions, the concentrations of each raw material are appropriately adjusted so that they are substantially soluble in the acidic solution. The precipitant is not limited as long as it is an alkaline solution that reacts with the solution containing Sm and Fe to produce a precipitate. Examples include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0053] The precipitation reaction is preferably carried out by dropping a solution containing Sm and Fe and a precipitant into a solvent such as water, as this allows for easy adjustment of the particle properties of the precipitate. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the concentration of the reaction solution, the pH during the reaction, and other factors, a precipitate with a uniform distribution of constituent elements, a sharp particle size distribution, and a regular powder shape can be obtained. Using such a precipitate improves the magnetic properties of the final product, the magnetic powder. The reaction temperature can be set to 0 to 50°C, preferably 35 to 45°C. The concentration of the reaction solution is preferably 0.65 mol / L to 0.85 mol / L, more preferably 0.7 mol / L to 0.84 mol / L, in terms of the total concentration of metal ions. The pH during the reaction is preferably 5 to 9, more preferably 6.5 to 8.

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

[0055] After separating the precipitate, it is preferable to remove the solvent from the separated precipitate in order to prevent the precipitate from redissolving in the remaining solvent during the heat treatment in the subsequent oxidation step, which may result in aggregation of the precipitate when the solvent evaporates, or changes in particle size distribution, powder particle size, etc. Specific examples of the method for removing the solvent include drying in an oven at 70 to 200°C for 5 to 12 hours when water is used as the solvent.

[0056] The precipitation step may be followed by a step of separating and washing the resulting precipitate. The washing step is appropriately carried out until the conductivity of the supernatant solution becomes 5 mS / m or less. The step of separating the precipitate may involve, for example, adding a solvent (preferably water) to the resulting precipitate and mixing, followed by filtration, decantation, or the like.

[0057] [Oxidation process] The oxidation step is a step of obtaining an oxide containing Sm and Fe by calcining the precipitate formed in the precipitation step. For example, the precipitate can be converted into an oxide by heat treatment. When the precipitate is heat treated, it must be performed in the presence of oxygen, for example, in the air. Furthermore, since it must be performed in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms.

[0058] The heat treatment temperature in the oxidation step (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. If the temperature is less than 700°C, oxidation will be insufficient, and if the temperature exceeds 1300°C, the desired shape, average particle size, and particle size distribution of the magnetic powder will tend not to be obtained. The heat treatment time is also not particularly limited, but is preferably 1 to 3 hours.

[0059] The oxide particles obtained are oxide particles in which Sm and Fe are thoroughly mixed microscopically within the oxide particles, and the shape, particle size distribution, etc. of the precipitates are reflected.

[0060] [Pretreatment process] The pretreatment step is a step in which an oxide containing Sm and Fe is heat-treated in an atmosphere containing a reducing gas, thereby obtaining a partial oxide in which part of the oxide is reduced.

[0061] Here, the term "partial oxide" refers to an oxide in which a portion of an 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. If the oxygen concentration exceeds 10% by mass, the heat generated by reduction with Ca, the reducing agent, increases during the reduction process, and the calcination temperature increases, tending to result in particles that have undergone abnormal particle growth. The oxygen concentration of the partial oxide can be measured by non-dispersive infrared absorption (ND-IR).

[0062] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H), carbon monoxide (CO), and methane (CH), but hydrogen gas is preferred from a cost perspective, and the gas flow rate is appropriately adjusted within a range that does not cause oxides to scatter. The heat treatment temperature in the pretreatment step (hereinafter referred to as the pretreatment temperature) is 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, when the pretreatment temperature is 950°C or lower, particle growth and segregation of oxide particles are suppressed, and the desired particle size can be maintained.

[0063] [Reduction process] The reduction step is a step of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent at 920°C to 1200°C. For example, reduction is carried out by contacting the partial oxide with calcium melt or calcium vapor. From the viewpoint of magnetic properties, the heat treatment temperature is preferably 950°C to 1150°C, more preferably 980°C to 1100°C. From the viewpoint of carrying out the reduction reaction more uniformly, 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, with a particle size of preferably 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, metallic calcium can be added in an amount of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce Sm oxide, including the amount required to reduce Fe when it is in the form of oxide), with 1.5 to 2.0 times being preferred.

[0065] In the reduction step, a disintegration accelerator can be used as needed together with metallic calcium as a reducing agent. This disintegration accelerator is used as appropriate to promote disintegration and granulation of the product during the water washing step described below, and examples thereof include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used in a proportion of 1 to 30% by mass, preferably 5 to 28% by mass, based on the Sm oxide used as the Sm source.

[0066] [Nitriding process] The nitriding process is a process for obtaining anisotropic magnetic particles by nitriding the alloy particles obtained in the reduction process. Since the particulate precipitate obtained in the precipitation process is used, porous agglomerated alloy particles are obtained in the reduction process. This allows for immediate nitriding by heat treatment in a nitrogen atmosphere without pulverization, ensuring uniform nitriding.

[0067] The heat treatment temperature in the nitriding treatment of the alloy particles (hereinafter referred to as the nitriding temperature) is preferably 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 a time sufficient to ensure that the nitriding of the alloy particles is sufficiently uniform.

[0068] The product obtained after the nitriding step may contain, in addition to the magnetic particles, by-product CaO, unreacted metallic calcium, etc., which may form a composite sintered mass. In such cases, the product may be poured into cooling water to separate the CaO and metallic calcium from the magnetic particles as a calcium hydroxide (Ca(OH)2) suspension. Furthermore, the remaining calcium hydroxide may be thoroughly removed by washing the magnetic particles with acetic acid or the like.

[0069] SmFeN anisotropic magnetic powder is Th2Zn 17 It has a crystal structure of the type Sm x Fe 100-x-y N y It is a nitride composed of samarium (Sm), which is a rare earth metal, iron (Fe), and nitrogen (N), represented by the formula: where x is preferably 8.1 atomic % or more and 10 atomic % or less, y is 13.5 atomic % or more and 13.9 atomic % or less, and the remainder is preferably Fe.

[0070] The average particle size of the SmFeN-based anisotropic magnetic powder is 2 μm or more and 5 μm or less, and preferably 2.5 μm or more and 4.8 μm or less. If it is less than 2 μm, the filling amount of the magnetic powder in the bonded magnet will be small, resulting in a decrease in magnetization, and if it exceeds 5 μm, the coercive force of the bonded magnet will tend 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 anisotropic magnetic powder is 1 μm or more and 3 μm or less, and preferably 1.5 μm or more and 2.5 μm or less. If it is less than 1 μm, the filling amount of the magnetic powder in the bonded magnet will be small, resulting in reduced magnetization, while if it exceeds 3 μm, the coercive force of the bonded magnet will tend to decrease. Here, D10 is the particle size at which the integrated value of the particle size distribution based on volume of the SmFeN anisotropic magnetic powder corresponds to 10%.

[0072] The particle size D50 of the SmFeN anisotropic magnetic powder is 2.5 μm or more and 5 μm or less, and preferably 2.7 μm or more and 4.8 μm or less. If it is less than 2.5 μm, the filling amount of the magnetic powder in the bonded magnet will be small, resulting in reduced magnetization, while if it exceeds 5 μm, the coercive force of the bonded magnet will tend to decrease. Here, D50 is the particle size at which the integrated value of the particle size distribution based on volume of the SmFeN anisotropic magnetic powder corresponds to 50%.

[0073] The particle size D90 of the SmFeN anisotropic magnetic powder is 3 μm or more and 7 μm or less, and preferably 4 μm or more and 6 μm or less. If it is less than 3 μm, the filling amount of the magnetic powder in the bonded magnet will be small, resulting in a decrease in magnetization, and if it exceeds 7 μm, the coercive force of the bonded magnet will tend to decrease. Here, D90 is the particle size at which the integrated value of the particle size distribution based on volume of the SmFeN anisotropic magnetic powder corresponds to 90%.

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

[0075] The circularity of the SmFeN-based anisotropic magnetic powder is not particularly limited, but is preferably 0.5 or more, and more preferably 0.6 or more. If it is less than 0.5, the flowability will be poor, and stress will be applied between particles during molding, resulting in a deterioration of magnetic properties. Here, to measure the circularity, an SEM image taken at 3000x magnification is binarized by image processing, and the circularity is determined for each particle. The circularity defined in the present invention means the average value of the circularity determined by measuring approximately 1000 to 10000 particles. Generally, the circularity increases as the number of particles with smaller particle diameters increases, so the circularity is measured for particles of 1 μm or more. The definition formula for measuring the circularity is: circularity = (4πS / L 2 ) is used, where S is the two-dimensional projected area of ​​the particle, and L is the two-dimensional projected perimeter.

[0076] <Manufacturing method for bonded magnet compounds> The manufacturing method for a bonded magnet compound of this embodiment is characterized by including the steps of obtaining the phosphate-coated SmFeN-based anisotropic magnetic powder of the above-described embodiment and kneading the magnetic powder with a resin, thereby further improving coercivity. Furthermore, when polypropylene is used as the resin, hot water resistance is further improved. Of these, the phosphate-coated SmFeN-based anisotropic magnetic powder is obtained by the above-described method.

[0077] [Mixing process] In the process of kneading the phosphate-coated SmFeN-based anisotropic magnetic powder with the resin, the mixture of phosphate-coated SmFeN-based anisotropic magnetic powder and resin is kneaded at 180 to 300°C using a kneader such as a single-screw kneader or twin-screw kneader. For example, after mixing the magnetic powder and resin powder in a mixer, strands are extruded using a twin-screw extruder, air-cooled, and then cut into pieces several millimeters in size using a pelletizer to obtain a bonded magnet compound in the form of pellets.

[0078] When the resin used is polypropylene, the weight-average molecular weight of the polypropylene is preferably 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, while if it is greater than 200,000, the viscosity of the bonded magnet compound tends to increase. Furthermore, to improve the bondability with the coupling-treated magnetic powder, the polypropylene is preferably acid-modified; for example, polypropylene acid-modified with maleic anhydride is preferably used. The acid modification ratio of the polypropylene is preferably 0.1% by weight to 10% by weight. If it is less than 0.1% by weight, the adhesion with the magnetic powder will be insufficient, and the mechanical strength and water resistance of the bonded magnet will decrease. If it exceeds 10% by weight, the water absorption rate of the resin will increase, reducing the water resistance of the bonded magnet.

[0079] The content of the phosphate-coated SmFeN-based anisotropic magnetic powder in the bonded magnet compound is preferably 80% to 95% by mass, more preferably 90% to 95% by mass to obtain high magnetic properties, while the content of the resin in the bonded magnet compound is preferably 3% to 20% by mass, more preferably 5% to 15% by mass to ensure flowability.

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

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

[0082] For the purpose of improving hot water resistance, a mixture or polymer alloy of the above-mentioned crystalline resin mixed with an amorphous resin 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), can be used. In the present invention, for example, a polymer alloy of modified polyphenylene ether (m-PPE) and polypropylene can be suitably used.

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

[0084] [Manufacturing method of bonded magnets] Bonded magnets can be manufactured using a bonded magnet compound and an appropriate molding machine. Specifically, for example, the bonded magnet compound is molten in the barrel of the molding machine, and then injection-molded into a mold to which a magnetic field is applied, aligning the axis of easy magnetization (orientation process), and after cooling and solidifying, magnetizing with an air-core coil or magnetizing yoke (magnetization process) to obtain a bonded magnet.

[0085] The barrel temperature is selected depending on the type of resin used and can be 160°C to 320°C, and the mold temperature can be, for example, 30°C to 150°C. The orienting magnetic field in the orienting step is generated using an electromagnet or permanent magnet, and the strength of the magnetic field is preferably 4 kOe or more, more preferably 6 kOe or more. The strength of the magnetizing magnetic field in the magnetizing step is preferably 20 kOe or more, more preferably 30 kOe or more.

[0086] [Bonded magnet] The bonded magnet of this embodiment is characterized by containing the phosphate-coated SmFeN-based anisotropic magnetic powder of the above-described embodiment and a resin. Such bonded magnets may maintain a total flux of 95% or more after 1,000 hours of immersion in hot water at 120°C. A bonded magnet's total flux after a 1,000-hour hot water resistance test in which it is immersed in hot water at 120°C is 95% or more of its pre-test total flux, indicating high hot water resistance. A value of 96% or more is preferable, and 97% or more is even more preferable. The total flux value can be obtained, for example, by measuring the change in magnetic flux within a search coil when a bonded magnet molded product placed inside the search coil is pulled out of the search coil using a flux meter (manufactured by Nippon Denji Sokki; model: NFX-1000). The bonded magnet can also be obtained by the above-described method.

[0087] The bonded magnet of this embodiment is resistant to hot water, and therefore can be suitably used as a driving source for fuel pumps and water pumps in automobiles, motorcycles, and the like. [Example]

[0088] Example 1 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. 0.49 kg of Sm2O3 and 0.74 kg of 70% sulfuric acid were then added and stirred thoroughly to completely dissolve the solution. Next, pure water was added to the resulting solution, and the final Fe concentration was adjusted to 0.726 mol / L and the Sm concentration to 0.112 mol / L, creating a 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 40°C over 70 minutes from the start of the reaction while stirring. 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 resulting slurry was washed with pure water by decantation, and the hydroxide was subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

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

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

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

[0093] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated to a vacuum. While introducing nitrogen gas, the temperature was raised to 450°C and maintained at that temperature for 23 hours to obtain a bulk product containing magnetic particles.

[0094] [Water washing process] The aggregated product obtained in the nitriding step was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice, followed by dehydration and drying, followed by mechanical crushing to obtain SmFeN-based anisotropic magnetic powder (average particle size 3 μm).

[0095] [Phosphating process] The phosphate treatment solution was prepared by mixing 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1, with the pH adjusted to 2 and the PO concentration adjusted to 20% by mass with pure water and dilute hydrochloric acid. The resulting SmFeN-based anisotropic magnetic powder was mixed in multiple batches to obtain a slurry containing 1,000 g of the powder. Hydrogen chloride and 70 g of dilute hydrochloric acid were added to the slurry and stirred for 1 minute to remove surface oxide films and contaminants. The slurry was then repeatedly drained and refilled with water until the conductivity of the supernatant liquid reached 100 μS / cm or less, yielding a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the resulting slurry, 3.7 g of cerium chloride (CeCl3) was added to the treatment tank. The pH was adjusted to a range of 5–8 using sodium hydroxide and maintained for 30 minutes, resulting in the precipitation of a cerium compound containing cerium hydroxide (Ce(OH)3) on the magnetic powder surface. Next, 100 g of the prepared phosphate treatment solution was added to the treatment tank. The pH of the phosphate treatment reaction slurry was controlled at 2.5 ± 0.1 by adding 6 wt% hydrochloric acid from time to time and maintained for 30 minutes. The resulting mixture was then suction filtered, dehydrated, and vacuum dried to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder containing cerium. The cerium content of the magnetic powder at the stage where the cerium compound containing cerium hydroxide was precipitated on the magnetic powder surface was 0.05% by mass, and the cerium content of the magnetic powder after the phosphate treatment was also 0.05% by mass. This indicates that most of the cerium contained in the cerium compound previously precipitated on the magnetic powder surface remained present after the phosphate treatment.

[0096] [Oxidation process after phosphate treatment] 1000 g of phosphate-coated SmFeN-based anisotropic magnetic powder containing cerium was gradually heated from room temperature in an atmosphere of a mixed gas of nitrogen and air (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 same procedure as in Example 1 was carried out except that the amount of cerium chloride was changed to 7.4 g, and an oxidation-treated, rare earth element-containing, phosphate-coated SmFeN-based anisotropic magnetic powder was obtained.

[0098] Example 3 The same procedure as in Example 1 was carried out except that the amount of cerium chloride was changed to 15.2 g, and an oxidation-treated, rare earth element-containing, phosphate-coated SmFeN-based anisotropic magnetic powder was obtained.

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

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

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

[0102] Example 7 The same procedure as in Example 1 was carried out except that 8.8 g of neodymium chloride was used instead of cerium chloride, and an oxidation-treated, rare earth element-containing, phosphate-coated SmFeN-based anisotropic magnetic powder was obtained.

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

[0104] Example 9 The same procedure as in Example 1 was carried out except that 9.0 g of dysprosium chloride was used instead of cerium chloride, and an oxidation-treated, rare earth element-containing, phosphate-coated SmFeN-based anisotropic magnetic powder was obtained.

[0105] (Reference example) An oxidation-treated, phosphate-coated SmFeN-based anisotropic magnetic powder was obtained in the same manner as in Example 1, except that cerium chloride and sodium hydroxide were not added and cerium compounds were not precipitated.

[0106] (Comparative Example 1) The same procedure as in Example 1 was followed up to the water washing step to obtain magnetic powder. A phosphate treatment solution was prepared by mixing 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1, and adjusting the pH to 2.5 and the PO concentration to 20% by mass with pure water and dilute hydrochloric acid. A slurry containing 1000 g of SmFeN-based anisotropic magnetic powder obtained in the water washing step was stirred in dilute hydrochloric acid containing 70 g of hydrogen chloride for 1 minute to remove surface oxide films and contaminants. After this, draining and adding water was repeated until the conductivity of the supernatant liquid reached 100 μS / cm or less, yielding a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the resulting slurry, 100 g of the prepared phosphate treatment solution was poured into the treatment tank. The pH of the phosphate treatment reaction slurry rose from 2.5 to 6 over 5 minutes. After stirring for 15 minutes, the mixture was filtered by suction, dehydrated, and dried in a vacuum to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder.

[0107] (Comparative Example 2) [Reduction step 2] A crucible filled with a mixture 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 calcium metal was placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1150°C and maintained for 5 hours to obtain Fe-Sm alloy particles.

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

[0109] [Water washing process 2] The aggregated product obtained in the nitriding step was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice. Subsequently, dehydration and drying were performed to obtain SmFeN-based anisotropic magnetic powder (average particle size 30 μm).

[0110] [Phosphating process 2] 15 g of the obtained magnetic powder was sealed in a glass bottle together with 0.44 g of 85% orthophosphoric acid aqueous solution, 100 ml of isopropanol (IPA), and 200 g of alumina beads with a diameter of 10 mm, and subjected to a pulverization treatment for 120 minutes in a vibration ball mill. After that, the slurry was filtered and vacuum dried at 100 °C to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder (average particle size 1.5 μm) of Comparative Example 2.

[0111] [Magnetic particle evaluation] (Magnetic powder specific coercive force iHc) The magnetic properties (intrinsic coercivity iHc) of each of the magnetic powders obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 were measured using a VSM (Vibrating Sample Magnetometer, manufactured by Riken Denshi Co., Ltd.; Model: BHV-55). The intrinsic coercivity iHc was measured before and after the 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 iHc due to the water resistance test was calculated from the intrinsic coercivity iHc after the oxidation treatment and after the water resistance test. Table 1 shows the measurement results for the magnetic powder before the oxidation treatment. Table 2 shows the measurement results for the magnetic powder after the oxidation treatment.

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

[0113] (Rare earth element deposition amount) The rare earth element concentrations in the magnetic powders obtained in Examples 1 to 9, Reference Example, and Comparative Examples 1 and 2 were measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the rare earth element adhesion weights. The results are shown in Tables 1 and 2. For Examples 4 and 5, which used Sm as the rare earth element, the results of ICP atomic emission spectroscopy were confirmed as follows. In the Reference Example, Examples 4, and 5, a correlation was confirmed between the amount of Sm added and the Sm / Fe content ratio confirmed by ICP atomic emission spectroscopy. Therefore, the amount of samarium added when samarium chloride was added was considered to be the rare earth element adhesion weight.

[0114] (DSC heat generation 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 subjected to DSC analysis using a high-temperature differential scanning calorimeter (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 alumina (20 mg) as the reference, to measure the heat generation onset temperature. The results of the DSC analysis are shown in Table 1. A high heat generation onset temperature means that heat generation due to oxidation is less likely to occur, and therefore the phosphate coating is more densely formed.

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

[0116] (total carbon content) The total carbon (TC) content in each of the magnetic powders obtained in Examples 1 to 9, the Reference Example, and Comparative Examples 1 and 2 was measured using a combustion catalytic oxidation 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 the magnetic powders to which rare earth elements are attached tend to have an increased coercive force. Table 2 also reveals that the magnetic powders obtained in Examples 1, 2, 4, 6, and 8, in which the amount of rare earth element attached is 0.2 mass% or less, have improved hot water resistance after oxidation treatment compared to the Reference Example.

Claims

1. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder, which includes a phosphate treatment step in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, a phosphate compound, and a rare earth compound, and the pH of the slurry is adjusted to 1 or more and 4.5 or less, thereby obtaining SmFeN-based anisotropic magnetic powder whose surface is coated with phosphate.

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

3. The rare earth compound is represented by 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. be) 3. The method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1, wherein the rare earth hydroxide is represented by the formula:

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

5. 5. The method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1, wherein the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder is greater than 0.5 mass %.

6. 6. The method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1, wherein the adjustment is carried out for 10 minutes or more in the phosphate treatment step.

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

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

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