Coated magnetic material and method of producing the same

Abstract

To provide a method of producing a magnetic material with a coating exhibiting superior heat resistance.SOLUTION: A method of producing a coated magnetic material includes: a coating step of mixing an aqueous solution containing a phosphate compound and a compound of a metallic element or a semimetallic element with a magnetic material, which is a soft magnetic material, to form a coating containing phosphate and the metallic element or the semimetallic element on the surface of the magnetic material; and a pH adjustment step of mixing an aqueous solution containing a phosphate compound and a compound of a metallic element or a semimetallic element with the magnetic material on which the coating is formed, and adjusting the pH of the mixture of the aqueous solution and the magnetic material on which the coating is formed to form a coating containing phosphate and the metallic element or the semimetallic element on the surface of the magnetic material.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to coated magnetic materials and methods for making the same. [Background technology]

[0002] Powder cores made by compacting soft magnetic powders are used as magnetic core materials for electric devices such as motors and transformers. If soft magnetic powder is compacted as is, eddy currents are generated throughout the component due to conduction between particles, resulting in large iron loss. In order to reduce the iron loss of powder cores, Patent Document 1 discloses a method of forming a coating containing hydroxyapatite on the surface of soft magnetic powder. Patent Document 2 discloses a method of forming a glassy insulating layer containing Cr or P as an essential element on the surface of soft magnetic powder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-127201 A [Patent Document 2] Japanese Patent Application Publication No. 6-132109 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a coated magnetic material having a coating with excellent heat resistance and a method for producing the same. [Means for solving the problem]

[0005] A method for producing a coated magnetic material according to one embodiment of the present disclosure includes a coating step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with a magnetic material that is a soft magnetic material, and forming a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material, and a pH adjustment step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with the magnetic material on which the coating has been formed, adjusting the pH of the mixed liquid in which the aqueous solution and the magnetic material on which the coating has been formed are mixed, and forming a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material.

[0006] A coated magnetic material according to one embodiment of the present disclosure comprises a magnetic material that is a soft magnetic material, and a coating provided on a surface of the magnetic material, the coating including, from the magnetic material side, a first region containing a first M component and phosphorus, and a second region containing a second M component and phosphorus, the average content of the first M component in the first region being smaller than the average content of the second M component in the second region, and the first M component and the second M component being one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a coated magnetic material having a coating with excellent heat resistance and a method for producing the same. [Brief description of the drawings]

[0008] [Figure 1] 13 shows the results of line analysis of the coated magnetic material produced in Example 27. [Diagram 2] 13 shows the results of line analysis of the coated magnetic material produced in Example 27. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present disclosure will be described in detail. However, the embodiments shown below are examples for embodying the technical ideas of the present disclosure, and the present disclosure 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 "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively.

[0010] <<Method of manufacturing coated magnetic materials>> The manufacturing method of the coated magnetic material of this embodiment is characterized by including a coating step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with a magnetic material that is a soft magnetic material, and forming a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material, and a pH adjustment step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with the magnetic material on which the coating has been formed, adjusting the pH of the mixed liquid in which the aqueous solution and the magnetic material on which the coating has been formed are mixed, and forming a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material.

[0011] <Magnetic materials> In this embodiment, a soft magnetic material is used as the magnetic material. The soft magnetic material is a material having a small coercive force and a high saturation magnetic flux density. Examples of the soft magnetic material include oxide-based soft magnetic materials and metal-based soft magnetic materials.

[0012] Examples of oxide-based soft magnetic materials include materials containing iron oxide and transition metals such as Ni, Zn, Cu, Mn, and Co. Specific examples include Mn-Zn-based soft ferrite, Ni-Zn-based soft ferrite, and Cu-Zn-based soft ferrite. Examples of metal-based soft magnetic materials include pure iron, Fe-X alloys (X: Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), silicon steel (Fe-Si), sendust (Fe-Si-Al), permendur (Fe-Co), permalloy (Fe-Ni), electromagnetic stainless steel (Fe-Cr), and ultra-quenched ribbon powder (Fe-Si-B, Fe-Si-BP-Cu). Examples of pure iron include atomized iron, reduced iron, electrolytic iron, and carbonyl iron.

[0013] The Fe-X alloy includes a first phase containing Fe and X, and a second phase containing X, in which the content of X when the sum of Fe and X contained in the first phase is taken as 100 atomic % is greater than the content of X when the sum of Fe and X contained in the first phase is taken as 100 atomic %. By using the Fe-X alloy as a soft magnetic material, the heat resistance can be further improved. X is one or more of Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si, and two or more may be selected from these. The first phase of the Fe-X alloy can have a crystal with a bcc structure containing Fe and X. Except when X contains Co, it is preferable that both the first phase and the second phase of the Fe-X alloy have a crystal with a bcc structure containing Fe and X. This can improve magnetization. The crystallite size of the bcc phase in the first phase and / or the second phase of the Fe-X alloy is preferably 1 nm or more and less than 100 nm. X may contain Ni and / or Co, as well as other additional components. In this case, the content of the additional components in the second phase is preferably greater than the content of the additional components in the first phase. The contents of the additional components in the first and second phases are the contents (atomic %) of the additional components when the sum of the X component including the additional components and Fe in the first and second phases is 100 atomic %. This makes it possible to achieve both low coercivity and improved magnetization.

[0014] When the first phase and the second phase have a bcc crystal structure containing Fe and an X component, the second phase / first phase X component ratio, which is the ratio of the content of the X component in the second phase to the content of the X component in the first phase, can be 1 or more, and can be 1.1 or more and 10 5 The content of the X component in the first phase and the second phase is the content (atomic %) of the X component when the sum of Fe and X in the first phase and the second phase is 100 atomic %. With the second phase / first phase X component ratio being such a value, it is possible to achieve both low coercive force and high magnetization, and it is suitable as a soft magnetic material with excellent high frequency characteristics.

[0015] When Ti or Mn is contained as the X component, the ratio of the Ti or Mn content in the second phase to the content in the first phase, that is, the second phase / first phase component ratio, is 2 times or more and 10 5 When the X component contains one of Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si, the second phase / first phase component ratio is preferably 1.5 times or more and 10 times or less. 5 When Ni or Co is contained as the X component, the second phase / first phase component ratio is preferably more than 1, and more preferably 1.1 times or more and 10 times or less. 5 It is more preferable that the ratio is less than 10 times. With these second phase / first phase X component ratios, it is possible to achieve both low coercivity and high magnetization, and for example, a soft magnetic material having a coercivity of 10 Oe or less and a magnetization of 0.3 T or more can be obtained. By using such a soft magnetic material, it is possible to realize lower losses in high frequency applications. The Fe-X alloy can have a structure in which nano-order X composition fluctuations exist due to a disproportionation reaction during reduction, and the nano-scale first phase and second phase are connected by ferromagnetic coupling. It is believed that such a structure brings about low coercivity and high magnetization. The Fe-X alloy can be obtained, for example, by the methods described in WO2017 / 164376 and WO2018 / 155608.

[0016] The soft magnetic materials listed above may be used alone or in combination of two or more. Metal-based soft magnetic materials are preferred as soft magnetic materials. This is because metal-based soft magnetic materials can easily reduce the electrical resistance of the magnetic material compact by coating, which will be described later, and can easily reduce losses, making it easier to improve magnetization. Among metal-based soft magnetic materials, pure iron or Fe-X alloys are preferred. Among them, Fe-X alloys in which X is Mn (this alloy is referred to as "Fe-X(X=Mn)"), Fe-X alloys in which X is Ni (this alloy is referred to as "Fe-X(X=Ni)"), or Fe-X alloys in which X is Mn and Ni (this alloy is referred to as "Fe-X(X=Mn,Ni)") are more preferred. These components listed as X may be X's main component. In the case of X=Mn, Ni, components in which the content is smaller than these may be included in addition to these. It is more preferred that X is substantially composed of these components. Fe-X (X=Mn) tends to have higher electrical resistance and heat resistance than Fe powder (pure iron). This is thought to be due to the inclusion of an X-rich phase. As predicted by the Slater-Pauling curve, Fe-X (X=Ni) has high magnetization when the Ni content is higher than 0 and less than 12 atomic %. Fe-X (X=Mn, Ni) can combine the advantages of both Fe-X (X=Mn) and Fe-X (X=Ni). In other words, it is possible to reduce electrical resistance, thereby reducing eddy current loss, improve heat resistance, and improve magnetization.

[0017] When the magnetic material is a powder of an Fe-X alloy, the Fe-X alloy can be produced, for example, by reducing ferrite powder containing an X component, which is difficult to reduce mainly with hydrogen, in a reducing gas containing hydrogen gas, and generating a first phase and a second phase by a disproportionation reaction. The Fe-X alloy powder obtained in this way has a relatively large specific surface area and has compositional fluctuations in the X component. The large specific surface area increases the bonding strength with the coating, and the nanoscale fluctuations of the X component can strengthen the bonding between the M component and the X component when the M component contained in the coating described later is a component that has affinity for the X component. It is believed that one or both of these factors make it easier to form an M component-containing coating with good adhesion on the surface of the magnetic material. For example, compared to using pure iron as the magnetic material, using an Fe-X alloy as the magnetic material can reduce not only hysteresis loss but also eddy current loss, and improve iron loss. Therefore, the magnetic material for forming the coating containing the M component of this embodiment is preferably an Fe-X alloy.

[0018] The magnetic material is preferably a powder because it is easy to mold a powder magnetic core of any shape. The particle diameter D50 of the magnetic powder can be, for example, 1 μm or more and 5 mm or less, preferably 5 μm or more and 1 mm or less, and more preferably 10 μm or more and 500 μm or less. In this range, the coercive force can be suppressed, and distortion during annealing can be suppressed. Here, the particle diameter D50 is the particle diameter at which the integrated value of the particle size distribution based on the volume of the magnetic powder corresponds to 50%.

[0019] Prior to the coating step, it is preferable to carry out a washing step in which the magnetic material is washed with an acidic aqueous solution in order to remove impurities and oxide films on the surface of the magnetic material. Examples of acid compounds used for washing include inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid, and examples of organic acids include acetic acid, formic acid, oxalic acid, and tartaric acid. The pH during washing is preferably less than pH 7, and more preferably less than pH 3. The washing time is preferably 1 minute or more and 10 hours or less. It is preferable to stir the aqueous solution during washing.

[0020] <Coating process> In the coating process, an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element is mixed with a magnetic material, which is a soft magnetic material. As a result, the metal component, the phosphate component, and the metal element or the metalloid element contained in the magnetic material react with each other, and a coating containing the phosphate and the metal element or the metalloid element is formed on the surface of the magnetic material. In this embodiment, the metal element or the metalloid element of the compound contained in the aqueous solution is also referred to as the M component.

[0021] Examples of the phosphoric acid compound contained in the aqueous solution 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-based compounds, hypophosphites-based compounds, pyrophosphoric acid-based compounds, and polyphosphoric acid-based compounds, and organic phosphoric acids. These compounds may be used alone or in combination of two or more kinds.

[0022] The content of the phosphoric acid compound in the aqueous solution is preferably 0.0001% by mass or more and 50% by mass or less, and more preferably 0.001% by mass or more and 10% by mass or less, calculated as PO. Within these ranges, the solubility of the phosphoric acid compound in water tends to be high, and the storage stability tends to be high.

[0023] Examples of the metal element of the M component include transition metal elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Pd, Pt, Ag, and Au, rare earth metal elements such as Ce, Sm, La, Dy, Nd, Y, and Pr, alkali metal elements such as Li, Na, K, Rb, and Cs, alkaline earth metal elements such as Ca, Sr, and Ba, and typical metal elements other than metalloids such as Zn, Cd, and Al. Examples of the metalloid element of the M component include B, Si, and Ge.

[0024] In order to obtain a coated magnetic material having excellent heat resistance, the element used as the M component is preferably a metal element having a relatively small Gibbs free energy change (ΔG) of the oxidation reaction in the temperature range (e.g., 400°C to 700°C) when the coated magnetic material is heated. It is preferable to use an element having a Gibbs free energy change of -300 kJ / mol O2 or less in the oxidation reaction at 600°C as the M component. The M component is preferably one or more of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, Ta, Nb, Al, Ce, La, Nd, Sm, and Dy, and more preferably one or more of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta. Table 1 shows the Gibbs free energy change of the oxidation reaction of metal element oxides at 600°C. [Table 1]

[0025] Elements with a Gibbs free energy change (ΔG) of oxidation reaction at 600°C greater than -300 kJ / mol O2 are easily reduced by Fe, and therefore tend to become metallic in the refining / coating / fixing process described below and the heating process in the manufacturing method of compacts. This increases eddy current loss and tends to reduce efficiency. Magnetic powders with a coating containing a metal element with a relatively small Gibbs free energy change (ΔG) of oxidation reaction can suppress the increase in eddy current loss due to such heat treatment. For this reason, it is possible to perform distortion relief annealing at a relatively high temperature, for example, 400°C to 700°C, which reduces hysteresis loss and reduces overall iron loss.

[0026] Examples of the compounds of metal elements or metalloid elements include oxides, oxo acids, chlorides, hydroxides, sulfates, nitrates, acetates, phosphates, carbonates, and other oxo acid compounds of metal elements or metalloid elements, and oxo acid compounds are preferred. Among these, metal oxo acid compounds are preferred, and transition metal oxo acid compounds are more preferred. The above compounds of metal elements or metalloid elements may be used alone or in combination of two or more.

[0027] The content of the compound of a metal element or a metalloid element in the aqueous solution is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass, in which case the solubility in water and storage stability tend to be high.

[0028] The time for the film-forming reaction in the coating step is preferably from 1 minute to 10 hours, and more preferably from 5 minutes to 2 hours.

[0029] The main component of the reaction solvent in the coating step is water, and it may be a mixed solvent of water and a hydrophilic organic solvent. When these solvents are used, phosphates having smaller particle sizes are precipitated compared to when a hydrophobic organic solvent is used, and a dense coating is formed. When a mixed solvent of water and a hydrophilic organic solvent is used, examples of the hydrophilic organic solvent include ethanol, methanol, 2-propanol, acetone, and 2-butanone. The content of the hydrophilic organic solvent in the mixed solvent is preferably 0.1% by mass or more and 80% by mass or less, more preferably 1% by mass or more and 50% by mass or less.

[0030] In the coating step, the content of the magnetic material in the mixture of the aqueous solution containing the phosphate compound and the compound of a metal element or a metalloid element and the magnetic material is preferably 0.0001% by mass to 70% by mass, more preferably 0.01% by mass to 10% by mass. Within these ranges, the thickness of the coating tends to be stable.

[0031] In the coating process, as long as an aqueous solution containing a phosphate compound and a rare earth compound can be finally mixed with a magnetic material that is a soft magnetic material, the mixing order of each component does not matter. In the coating process, first, it is preferable to mix an aqueous solution containing a rare earth compound with the magnetic material, and then mix the phosphate compound. By mixing the aqueous solution containing the rare earth compound with the magnetic material in advance, the rare earth compound is likely to adhere or bind to the surface of the magnetic material, and the amount of the film containing the phosphorus compound can be increased. When mixing the aqueous solution containing the rare earth compound with the magnetic material in advance, after mixing these, preferably under the conditions of pH 2 or more and 12 or less, more preferably pH 4 or more and 10 or less, still more preferably pH 5 or more and 8 or less, preferably for 1 minute or more, more preferably for 5 minutes or more, and then an aqueous solution containing a phosphate compound can be added.

[0032] After the coating process and before the pH adjustment process, the magnetic material with the film formed may be purified. The purification of the magnetic material with the film formed can be performed, for example, by heating at 100°C or more and 500°C or less, or by filter filtration.

[0033] <pH Adjustment Process> In the pH adjustment process, an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element is mixed with the magnetic material on which the film is formed in the coating process, and the pH of the mixed solution in which the aqueous solution and the magnetic material on which the film is formed are mixed is adjusted. If the pH adjustment is not performed, the pH of the aqueous solution may increase as phosphoric acid derived from the phosphate compound adheres to the magnetic material, which may inhibit the formation of the film. However, the formation of the film can be promoted by adjusting the pH.

[0034] As the aqueous solution containing a phosphate compound, a compound of a metal element or a metalloid element, and a solvent used in the pH adjustment process, the types described for the coating process can be used. Also, the same type as the coating process may be used, or a different type may be used.

[0035] In particular, when a compound of a metal element or metalloid element used in the pH adjustment process is a different type from the compound of a metal element or metalloid element used in the coating process, the metal element or metalloid element in the coating process tends to accumulate in the thickness direction of the coating that is ultimately formed near the magnetic material base material, and the metal element or metalloid element in the pH adjustment process tends to accumulate near the surface of the coating.

[0036] The aqueous solution in the pH adjustment step may be obtained by adding a phosphoric acid compound and / or a compound of a metal element or a metalloid element to the aqueous solution in the coating step. In this case, the pH adjustment step can be carried out after the coating step without purifying the magnetic material on which the coating is formed.

[0037] The content of the phosphoric acid compound in the aqueous solution in the pH adjustment step is preferably 0.0001% by mass or more and 50% by mass or less, and more preferably 0.001% by mass or more and 10% by mass or less, calculated as PO4. Within these ranges, the solubility of the phosphoric acid compound in water tends to be high, and the storage stability tends to be high.

[0038] The content of the compound of a metal element or a metalloid element in the aqueous solution in the pH adjustment step is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass. Within these ranges, the compound tends to have high solubility in water and high storage stability.

[0039] In the mixture of the aqueous solution containing the phosphoric acid compound and the compound of the metal element or metalloid element in the pH adjustment step and the magnetic material, the content of the magnetic material is preferably 0.0001% by mass to 90% by mass, more preferably 0.01% by mass to 10% by mass. Within these ranges, the thickness of the coating tends to be stable.

[0040] The pH adjustment range is preferably lower than the pH of the mixed solution in which the aqueous solution and the magnetic material are mixed in the coating process, more preferably 0.01 or more lower, even more preferably 0.1 or more lower, and even more preferably 1 or more lower. In addition, the specific pH adjustment range is preferably adjusted to 0 or more and less than 7, more preferably 1 or more and less than 4.5, even more preferably 1.6 or more and less than 3.9, and even more preferably 2 or more and less than 3. If the pH is less than 0, etching of the magnetic material becomes dominant, and the coating may not be formed sufficiently. By setting the pH to 1 or more, the precipitation rate of the phosphate can be reduced compared to the case of a pH below 1, and the thickness of the coating formed can be easily controlled. If the pH is 7 or more, the amount of phosphate precipitation decreases, which tends to result in insufficient coating and increased loss, so a pH of less than 7 is preferable. By setting the pH to 4.5 or less, the precipitation rate of the phosphate can be kept not too slow.

[0041] The acid added to adjust the pH may be an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid. Examples of organic acids include acetic acid, formic acid, oxalic acid, and tartaric acid. From the viewpoint of waste liquid treatment, it is preferable to use an inorganic acid, but an organic acid may be used in combination depending on the purpose. A mixture of an inorganic acid and an organic acid may be used.

[0042] The time for the film formation reaction in the pH adjustment step is preferably 1 minute to 20 hours, more preferably 5 minutes to 10 hours. During the pH adjustment step, inorganic acid may be added as needed to keep the pH within the above range. In the initial stage of the coating step, the pH rises quickly, so it is preferable to shorten the interval at which inorganic acid is added for pH adjustment.

[0043] <Purification / film fixation process> After the pH adjustment step, the coated magnetic material may be purified by, for example, heating at 100° C. to 800° C., filtering, or the like to remove liquid components.

[0044] Also, after the pH adjustment step, a coating fixation step may be performed. In the coating fixation step, the purified coated magnetic material is treated at high temperature to bake phosphorus onto the magnetic material. The temperature condition of the high temperature treatment is preferably 50°C or higher and 500°C or lower, more preferably 100°C or higher and 300°C or lower. The time of the high temperature treatment is preferably 1 minute or higher and 100 hours or lower, more preferably 10 minutes or higher and 10 hours or lower.

[0045] <Coated magnetic materials> The coated magnetic material of this embodiment has a magnetic material that is a soft magnetic material and a coating provided on the surface of the magnetic material. The particle diameter D50 of the coated magnetic material produced in this embodiment is preferably 1 μm to 5 mm, more preferably 5 μm to 1 mm, and even more preferably 10 μm to 500 μm. In this range, the coercive force can be suppressed and distortion during annealing can be prevented. Here, the particle diameter D50 is the particle diameter at which the integrated value of the particle size distribution based on the volume of the coated magnetic material corresponds to 50%.

[0046] In the coating, oxygen is preferably more than phosphorus. In this case, there is at least a part of the region in the thickness direction of the coating where oxygen is more than phosphorus. The region in which oxygen is more than phosphorus is preferably 10% or more of the thickness direction of the coating, more preferably 50% or more, and even more preferably the entire region. The oxygen content is preferably more than 1 time that of phosphorus, and can be 2 times or more, or may be 3 times or more. The upper limit of the oxygen content can be, for example, 10 times or less of phosphorus.

[0047] The coating contains phosphorus and an M component (metal element or semi-metal element). The phosphorus may constitute phosphoric acid. From the viewpoint of the insulating property and heat resistance of the coated magnetic material, the thickness of the coating is preferably 1 nm or more and 10 μm or less, and more preferably 5 nm or more and 500 nm or less. The thickness of the coating can be measured by performing a composition analysis by line analysis using energy dispersive X-ray analysis (EDX) on a cross section of the coated magnetic material.

[0048] The content of the metal element or metalloid element in the coated magnetic material that is attached in the coating process and the pH adjustment process is preferably 0.01% by mass to 0.25% by mass, more preferably 0.03% by mass to 0.2% by mass, and even more preferably 0.04% by mass to 0.18% by mass. Within the above range, the insulation properties of the coated magnetic material are easily improved and iron loss is easily suppressed. The content of the metal element or metalloid element in the coated magnetic material is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0049] The coating of this embodiment can include, in order from the magnetic material side, a first region containing the first M component and phosphorus, and a second region containing the second M component and phosphorus. The average content of the first M component in the first region is smaller than the average content of the second M component in the second region. The first M component and the second M component are each one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta. By having such a coating, a coated magnetic material with excellent heat resistance can be obtained. The first M component and the second M component may be the same or different. The first M component and the second M component are, for example, the same element.

[0050] The coating of this embodiment may have a layer or region (referred to as an H layer) mainly containing the M component with a relatively constant content in the direction from the surface toward the magnetic material, and a layer or region (referred to as an L layer) in which the content of the M component decreases and the M component becomes relatively constant again. In the direction from the L layer toward the magnetic material, the content of the M component further decreases and reaches the surface of the magnetic material. The content of the M component in the H layer being relatively constant means that it is within a range of ±50% of the average value of the H layer. The content of the M component in the L layer being relatively constant means that it is within a range of ±100% of the average value of the L layer. The ratio of the average value of the M component content in the L layer to the content of the M component in the H layer is preferably 0.1 to 0.9 times. More preferably, it is 0.15 to 0.7 times, and even more preferably, it is 0.2 to 0.5 times.

[0051] It is presumed that the H layer is formed in the pH adjustment step, and the L layer is formed in the coating step. By adding the M component in the coating step, a base layer called the L layer can be formed. And, by adding the M component in the pH adjustment step, a compound of the M component can be formed in the presence of the L layer, so that the content of the M component in the obtained H layer can be increased, and the heat resistance can be improved. In addition, the presence of the base layer called the L layer can suppress a sudden change in the composition of the M component, so that the resistance of the coating to heat and mechanical stress can be improved. Between the H layer and the L layer, there may be an I layer whose content of the M component is between the H layer and the L layer. The I layer is easily formed by repeating the coating step and the pH adjustment step multiple times.

[0052] In the coating, each metal may be present in either a crystalline or amorphous form. The concentration (atomic %) of each metal in the coating can be measured by performing a composition analysis on the coated magnetic material by line analysis using EDX. The coating can contain a phosphate compound and / or a complex oxide in a microcrystalline state. The inclusion of a phosphate compound or a complex oxide in a microcrystalline state in the coating can increase the mechanical strength and improve the heat resistance.

[0053] The content of phosphorus in the coated magnetic material that is attached in the coating process and the pH adjustment process is preferably 0.0001% by mass to 50% by mass, more preferably 0.001% by mass to 5% by mass. Within the above range, heat resistance tends to improve. The phosphorus content in the coated magnetic material is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0054] The iron loss W of the coated magnetic material is preferably 700 W / kg or less, more preferably 420 W / kg or less. The lower limit of the iron loss W may be, for example, 10 W / kg or more. These losses are values ​​measured at a maximum magnetic flux density (Bmax) of 1 T and a frequency of 1000 Hz by the method described in the examples. In this embodiment, the compact that has undergone the heating process may be in such a numerical range. The heating temperature in the heating process may be, for example, 600° C. The compact in which losses such as the iron loss W are within these numerical ranges may not contain resin and glass. When the coated magnetic material, not the compact, has undergone the heating process, the iron loss W measured for the coated magnetic material may be in the above-mentioned range.

[0055] <<Method of manufacturing molded products>> The method for producing a molded body of this embodiment is characterized by including a step of obtaining a coated magnetic material and a heating step of heating the coated magnetic material. In the step of obtaining the coated magnetic material, the method described above for the method for producing the coated magnetic material can be carried out.

[0056] <Heating process> In the heating step, the coated magnetic material is heated. The heating temperature can be, for example, 100°C or more and 1200°C or less. The heating step can be performed, for example, to remove distortion caused by pressure and / or to obtain an integrated molded body by partially reacting the coating of the coated magnetic material. In order to remove distortion caused by pressure, the heating temperature is preferably 300°C or more and 1000°C or less, and more preferably 400°C or more and 700°C or less. Since the coated magnetic material used in this embodiment has a coating with excellent heat resistance, loss of the coating is suppressed even after the heating step. The heating temperature may be 500°C or more. In this case, it is preferable that the molded body does not contain resin and glass. This is because deterioration of resin and glass is likely to become significant at high temperatures of 500°C or more. The heating step time is preferably 1 minute or more and 100 hours or less, and more preferably 10 minutes or more and 10 hours or less. The heating step may be performed in a nitrogen atmosphere or in air. The heating step is preferably performed in an inert atmosphere such as an argon atmosphere or a vacuum. When the magnetic material contains Fe, heating in a nitrogen atmosphere may cause the magnetic material to be nitrided, resulting in a deterioration in its properties. Therefore, it is preferable to carry out the heating step in an inert atmosphere other than a nitrogen atmosphere.

[0057] It is preferable to include a step of obtaining a pressure-molded product by pressing the covered magnetic material before the heating step. In this case, the heating step is a step of heating the pressure-molded product obtained in the step of obtaining a pressure-molded product.

[0058] The pressure conditions are preferably 0.01 GPa or more and 10 GPa or less, more preferably 0.5 GPa or more and 5 GPa or less. A pressure-molded product of a desired shape can be obtained by filling a mold with the coated magnetic material and then applying pressure. When a mold is used, a lubricant, which will be described later, may be applied to the inner wall of the mold cavity before filling the mold with the coated magnetic material. By applying a lubricant to the inner wall of the mold cavity, the releasability of the pressure-molded product from the mold can be improved.

[0059] When pressing, the coated magnetic material may be pressed alone, or may be mixed with a binder, lubricant, etc. and then pressed. Examples of binders include thermosetting resins such as epoxy resin, urethane resin, phenol resin, methacrylic resin, acrylic resin, and silicone resin, and thermoplastic resins such as polyamide resin. The amount of binder used is preferably 0.01 parts by weight to 1000 parts by weight, more preferably 1 part by weight to 50 parts by weight, per 100 parts by weight of the coated magnetic material. When the amount of binder used is within the above range, a molded body having excellent mechanical strength and low iron loss can be obtained.

[0060] As the lubricant, metal soaps such as zinc stearate, calcium stearate, and lithium stearate, amines or amides such as 1,2-bis(stearoylamino)ethane, long-chain hydrocarbons such as wax, silicone oil, etc. can be used. The amount of the lubricant used is preferably 0.00001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, per 100 parts by weight of the coated magnetic material. When the amount of the lubricant used is within the above range, the releasability of the pressure-molded product from the mold cavity can be improved.

[0061] The packing rate of the compact obtained in this embodiment can be 10% or more and 100% or less, and preferably 80% or more and 100% or less. The packing rate here refers to the ratio (percentage) of the density of the compact to the true density. The ratio (percentage) of the volume of the coated magnetic material to the volume of the compact obtained in this embodiment can be 40% or more and 100% or less, and preferably 80% or more and 100% or less. The ratio of the area of ​​the coated magnetic material to the area of ​​the compact in a cross section of a part of the compact may be regarded as the ratio of the volume of the coated magnetic material to the volume of the compact.

[0062] Since the molded body obtained in this embodiment is an aggregate of coated magnetic materials having a coating excellent in heat resistance, the coating is maintained even after the heating process, and losses such as iron loss are suppressed. After the heating process, the coating of each coated magnetic material may partially react and fuse with the coating of the adjacent coated magnetic material, and the magnetic materials may be integrated while maintaining the insulating state between them. The molded body of this embodiment can be obtained from the coated magnetic material without using a binding material (binder) such as resin or glass. Resin may cause eddy currents when carbonized by heat treatment. Glass may also deteriorate by heat treatment. For this reason, when a binder such as resin or glass is used, it is preferable to heat at a relatively low temperature even if a heat treatment is performed. By making the molded body free of resin and glass, it is possible to suppress an increase in loss even when heated at a relatively high temperature, such as 500°C or higher. In addition, by heating at a relatively high temperature, the distortion caused by pressure can be more effectively removed. In addition, by using the above-mentioned lubricant in combination, the density of the molded body can be increased, adjacent coated magnetic materials can be bonded by chemical reaction, and the mechanical strength can be improved.

[0063] The present disclosure includes the following aspects. (Section 1) a coating step of mixing an aqueous solution containing a phosphoric acid compound and a compound of a metal element or a metalloid element with a magnetic material that is a soft magnetic material, and forming a coating containing phosphoric acid and the metal element or the metalloid element on the surface of the magnetic material; a pH adjustment step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with the magnetic material on which the coating is formed, and adjusting the pH of the mixed liquid in which the aqueous solution and the magnetic material on which the coating is formed are mixed, to form a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material.

[0064] (Section 2) In the pH adjustment step, the pH is adjusted to be lower than the pH of a mixed solution obtained by mixing the aqueous solution and the magnetic material in the coating step. Item 1. A method for producing the covered magnetic material according to item 1.

[0065] (Section 3) The aqueous solution in the pH adjustment step is obtained by adding a compound of the metal element or metalloid element to the aqueous solution in the coating step. Item 3. A method for producing a covered magnetic material according to item 1 or 2.

[0066] (Section 4) the compound of the metal element or metalloid element in the pH adjustment step is different from the compound of the metal element or metalloid element in the coating step; Item 4. A method for producing a covered magnetic material according to any one of items 1 to 3.

[0067] (Section 5) In the coating step, an aqueous solution containing a compound of the metal element or metalloid element is mixed with the magnetic material, and then the phosphate compound is mixed. Item 5. A method for producing a covered magnetic material according to any one of items 1 to 4.

[0068] (Section 6) In the pH adjustment step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less. Item 6. A method for producing a covered magnetic material according to any one of items 1 to 5.

[0069] (Section 7) Item 7. The method for producing a covered magnetic material according to any one of items 1 to 6, wherein the metal element or metalloid element in the covering step is one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta.

[0070] (Section 8) Item 8. The method for producing a covered magnetic material according to any one of Items 1 to 7, wherein the metal element or metalloid element in the pH adjustment step is one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta.

[0071] (Section 9) Obtaining a coated magnetic material by the method according to any one of items 1 to 8; and a heating step of heating the covered magnetic material.

[0072] (Section 10) A magnetic material that is a soft magnetic material and a coating provided on a surface of the magnetic material, the coating includes, in order from the magnetic material side, a first region containing a first M component and phosphorus, and a second region containing a second M component and phosphorus; an average content of the first M component in the first region is smaller than an average content of the second M component in the second region; The coated magnetic material, wherein the first M component and the second M component are one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta. EXAMPLES

[0073] Examples will be described below. Unless otherwise specified, "%" is by weight.

[0074] (1) Evaluation method (1-1) Iron loss The magnetic powder was placed in a die with an inner diameter of 10 mm and an outer diameter of 14 mm, compacted under a pressure of 1 GPa, and then heat-treated in an Ar atmosphere at 600°C for 1 hour to produce a toroidal compact. The resulting compact was wound with 50 turns of copper wire on the primary side and 50 turns on the secondary side to prepare an evaluation sample. Using these evaluation samples, the W10 / 1000 (iron loss at 1000 Hz and 1 T) value was evaluated using a BH analyzer (SY-8218, manufactured by Iwasaki Electric Co., Ltd.).

[0075] (1-2) Film thickness and atomic concentration The thickness and atomic concentration of the coating of the coated magnetic material were measured as follows. First, the obtained coated magnetic material was molded into a disk shape of φ10 mm, and heated in an Ar atmosphere at 600 ° C for 1 hour to obtain a molded body. The obtained molded body was embedded in Epocure resin, processed by ion milling, and a sample was taken out by a microsampling method and thinned by FIB (focused ion beam). The obtained sample was estimated by a scanning transmission electron microscope (STEM; JEOL; acceleration voltage 200 kV) and an energy dispersive X-ray analyzer (EDX; JEOL). The atomic concentration in the coating was obtained by line analysis from the outside to the inside of the coated magnetic material in steps of 0.24 nm, observing the continuous change in atomic concentration of each constituent element, and measuring the range in which the phosphorus (P) atomic concentration is 1 atomic % or more. At this time, since there was a risk that a large amount of carbon (C) in the resin used to prepare the cross-sectional sample might be detected depending on the measurement location, the atomic concentration was calculated as the total of elements excluding C.

[0076] (2) Examples 1 to 28 and Comparative Examples 1 to 3 (2-1) Manufacturing of coated magnetic materials (ii) Preparation of soft magnetic materials: Examples 1-2, Comparative Examples 1-2 As the soft magnetic materials (magnetic materials) of Examples 1 and 2 and Comparative Examples 1 and 2, commercially available water-atomized iron powder was prepared.

[0077] (i-ii) Preparation of soft magnetic materials: Examples 3 to 28, Comparative Example 3 As the soft magnetic materials (magnetic materials) of Examples 3 to 28 and Comparative Example 3, Fe-X alloys were prepared. The Fe-X alloys were produced by the following method. First, an aqueous solution was prepared using MnCl2·4H2O (manganese (II) chloride tetrahydrate), NiCl2·6H2O (nickel (II) chloride hexahydrate), and FeCl2·4H2O (iron (II) chloride tetrahydrate) as raw materials, and potassium hydroxide was used as a pH adjuster to produce Mn-Ni-ferrite. The obtained ferrite was heated to 950°C at a rate of 12°C / min, then heated to 1050°C at a rate of 2°C / min, and reduced in a hydrogen atmosphere at 1050°C for 1 hour. After this, the temperature was rapidly lowered to room temperature, and deoxidized in an argon atmosphere with an oxygen partial pressure of 3% by volume for 30 minutes, and Fe was obtained. 96 Ni 3.9 Mn 0.1 The soft magnetic material with the composition of Fe-Ni-Mn powder was obtained. 50 was 250 μm.

[0078] (ii) Cleaning of soft magnetic materials 10 g of the soft magnetic material shown in Table 2 was added to an aqueous solution adjusted to pH 1.1 or less with dilute hydrochloric acid, and stirred for 10 minutes to remove the surface oxide film and dirt components.

[0079] (iii) Covering process To the washed soft magnetic material, an aqueous solution containing a compound of a metal element or a nonmetal element shown in Table 2 in an amount of 10 mass% relative to the coated magnetic material was added, and the mixture was stirred for 15 minutes. Next, an aqueous phosphoric acid solution of pH 2 containing a phosphoric acid compound shown in Table 2 in an amount of 4 mass% relative to the coated magnetic material was added, and the mixture was stirred for 7 minutes. The final concentrations of each component were 1.6 mass% soft magnetic material, 0.16 mass% compound of a metal element or a nonmetal element, and 0.4 mass% phosphoric acid compound (PO4 equivalent). The pH of the treatment tank increased from 3 to 5.

[0080] (iv) pH adjustment process An aqueous solution containing a compound of a metal element or nonmetal element listed in Table 2 in an amount of 10% by mass relative to the coated magnetic material was added, and the reaction mixture was stirred for 30 minutes while controlling the pH of the mixture to within the range of 2.5±0.1 by adding 6% by mass hydrochloric acid from time to time.

[0081] (v) Drying and baking The coated magnetic material after the pH adjustment step was dried by heating at 100° C. for 4 hours in a vacuum state, and then heated at 200° C. for 4 hours to bake the coating.

[0082] (2-2) Production of Molded Products The obtained coated magnetic material was used to produce a molded body for iron loss evaluation by the method described above in the iron loss evaluation method. Also, the obtained coated magnetic material of Example 27 was used to produce a molded body for coating evaluation by the method described above in the coating thickness and atomic concentration evaluation method.

[0083] The iron loss of the resulting compact was measured by the above-mentioned method, and the results are shown in Table 2.

[0084] [Table 2]

[0085] In the columns for the coating step and pH adjustment step in Table 2, test examples in which these steps were performed are marked with ◯, and test examples in which these steps were not performed are marked with -. Compared to Comparative Example 1 in which the coating step and pH adjustment step were not performed, the iron loss was reduced in Examples 1 and 2 in which the same soft magnetic material was used. Similarly, compared to Comparative Example 3 in which the coating step and pH adjustment step were not performed, the iron loss was reduced in Examples 3 to 28 in which the same soft magnetic material was used. Compared to Comparative Example 2 in which only the coating step was performed, the iron loss was reduced in Example 2 in which the same soft magnetic material and metal element compound were used.

[0086] 1 and 2 show the results of line analysis of metal elements, P and O near the surface of a molded article for coating evaluation using the coated magnetic material of Example 27. Fig. 2 is an enlarged view of the 0 to 50 atomic % region of Fig. 1.

[0087] In Figures 1 and 2, the thickness of the coating on the magnetic material surface was approximately 30 nm. In Figure 2, O was more than P over the entire range of the coating. There were two regions with different Mo contents in the direction from the surface of the coating toward the magnetic material, and the average Mo content in the region closer to the magnetic material was smaller than the average Mo content in the region farther from the magnetic material. Mo is thought to originate from sodium molybdate salt added in the coating process and pH adjustment process.

Claims

1. a coating step of mixing an aqueous solution containing a phosphoric acid compound and a compound of a metal element or a metalloid element with a magnetic material that is a soft magnetic material, and forming a coating containing phosphoric acid and the metal element or the metalloid element on the surface of the magnetic material; a pH adjustment step of mixing an aqueous solution containing a phosphate compound and a compound of a metal element or a metalloid element with the magnetic material on which the coating is formed, adjusting the pH of the mixed liquid in which the aqueous solution and the magnetic material on which the coating is formed are mixed, and forming a coating containing phosphoric acid and the metal element or metalloid element on the surface of the magnetic material.

2. In the pH adjustment step, the pH is adjusted to be lower than the pH of a mixed solution obtained by mixing the aqueous solution and the magnetic material in the coating step. A method for producing the covered magnetic material according to claim 1.

3. The aqueous solution in the pH adjustment step is obtained by adding a compound of the metal element or metalloid element to the aqueous solution in the coating step. A method for producing the covered magnetic material according to claim 1 or 2.

4. the compound of the metal element or metalloid element in the pH adjustment step is different from the compound of the metal element or metalloid element in the coating step; A method for producing the covered magnetic material according to claim 1 or 2.

5. In the coating step, an aqueous solution containing a compound of the metal element or metalloid element is mixed with the magnetic material, and then the phosphate compound is mixed. A method for producing the covered magnetic material according to claim 1 or 2.

6. In the pH adjustment step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less. A method for producing the covered magnetic material according to claim 1 or 2.

7. 3. The method for producing a covered magnetic material according to claim 1 or 2, wherein the metal element or semi-metal element in the covering step is one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta.

8. 3. The method for producing a covered magnetic material according to claim 1 or 2, wherein the metal element or semi-metal element in the pH adjustment step is one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta.

9. Obtaining a coated magnetic material by the method according to claim 1 or 2; and a heating step of heating the covered magnetic material.

10. A magnetic material that is a soft magnetic material and a coating provided on a surface of the magnetic material, the coating includes, in order from the magnetic material side, a first region containing a first M component and phosphorus, and a second region containing a second M component and phosphorus; an average content of the first M component in the first region is smaller than an average content of the second M component in the second region; The coated magnetic material, wherein the first M component and the second M component are one or more selected from the group consisting of Mo, W, Zn, Fe, Hf, Ti, Zr, Ni, Ca, Ba, Na, Cr, V, K, Mn, Mg, Si, and Ta.

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