Coated soft magnetic material and method of producing the same

Abstract

To provide a coated soft magnetic material with a coating exhibiting superior heat resistance and a method of producing the same.SOLUTION: A method of producing a coated soft magnetic material includes: a coating step of mixing an aqueous solution containing a phosphate compound and a metal oxoacid compound with a soft magnetic material to form a coating containing a metal phosphorus compound on the surface of the soft magnetic material.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to coated soft 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 soft 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 soft 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 metal oxoacid compound with a soft magnetic material, and forming a coating containing a metal phosphorus compound on the surface of the soft magnetic material.

[0006] A coated soft magnetic material according to one embodiment of the present disclosure includes a soft magnetic material and a coating provided on a surface of the soft magnetic material, the coating being an M-component-based material mainly containing an M component. phase and the M component phase and the soft magnetic material, and an M composition gradient phase located between the M component main phase and the soft magnetic material, in which the content of the M component decreases in a direction toward the soft magnetic material, wherein the thickness of the M composition gradient phase in a direction from the M component main phase toward the soft magnetic material is 20 nm or more, and the M component is Cr, W, Mn, Mo, Nb, or V. Effect of the Invention

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

[0008] [Figure 1A] 16 shows the results of line analysis of the coated soft magnetic material produced in Example 15. [Figure 1B] 1 shows a STEM (scanning transmission electron microscope) image of the coated soft magnetic material produced in Example 15. [Diagram 2] 1 shows a STEM image and an EDX (energy dispersive X-ray analysis) mapping image of a cross section of a compact of the coated soft magnetic material produced in Example 7. [Diagram 3] 13 shows the results of line analysis of the coated soft magnetic material produced in Example 7. [Figure 4] 13 shows the results of line analysis of the coated soft magnetic material produced in Example 7. [Figure 5A] FIG. 11 is a distribution diagram of Mn by STEM-EDX analysis of the coated soft magnetic material produced in Example 16. [Figure 5B] 13 is a histogram showing the distribution of the Mn content of the coated soft magnetic material produced in Example 16. 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 soft magnetic materials>> The method for producing a coated soft magnetic material of this embodiment is characterized by including a coating step of mixing an aqueous solution containing a phosphate compound and a metal oxo acid compound with a soft magnetic material, and forming a coating containing a metal phosphorus compound on the surface of the soft magnetic material. The metal component (e.g., iron) contained in the soft magnetic material reacts with the phosphate component contained in the phosphate compound to precipitate a phosphorus compound (e.g., iron phosphate) on the surface of the soft magnetic material. Furthermore, by allowing the metal oxo acid compound to coexist in the aqueous solution, a metal element derived from the metal oxo acid compound is bonded to the surface of the soft magnetic material, and a compound of the metal element and phosphorus is precipitated. The metal phosphorus compound may be a metal phosphate. The coating containing the metal phosphorus compound may be a coating containing a metal phosphate.

[0011] <Soft magnetic material> 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] The soft magnetic material is preferably in the form of a powder, since 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%.

[0018] Prior to the coating step, it is preferable to carry out a washing step in which the soft magnetic material is washed with an acidic aqueous solution in order to remove impurities and oxide films on the surface of the soft 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.

[0019] <Coating process> In the coating process, an aqueous solution containing a phosphoric acid compound and a metal oxo acid compound is mixed with the soft magnetic material. As a result, the metal component contained in the soft magnetic material reacts with the phosphoric acid component contained in the phosphoric acid compound, and a coating containing a phosphorus compound is formed on the surface of the soft magnetic material. Furthermore, the metal contained in the metal oxo acid compound bonds to the surface of the soft magnetic material, and a compound of the metal and phosphoric acid precipitates. The coating obtained in the coating process may be a coating containing a metal phosphorus compound, or a coating containing a metal phosphate. Depending on the combination of elements contained in the coating and the atmosphere during heating after the coating is formed, a coating containing a phosphorus compound other than a phosphate may be obtained by heating after the formation of the coating containing the metal phosphate.

[0020] In the coating step, the content of the soft magnetic material in the mixture of the aqueous solution containing the phosphoric acid compound and the metal oxo acid compound and the soft 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 coating film tends to become thicker and have improved heat resistance.

[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] The metal oxoacid compound contained in the aqueous solution is an acid compound containing a metal atom and an oxygen atom. By carrying out the coating process in an aqueous solution of a metal oxoacid compound, the amount of the coating film attached to the surface of the soft magnetic material can be increased, and the heat resistance can be improved. The metal oxoacid compound includes an oxoacid compound of a metal element M, i.e., Cr, W, Mn, Mo, Nb, or V, such as CrO4 2- Chromic acid, WO4 2- Tungstic acid, MnO4 2- Manganic acids such as MoO4 2- Molybdic acid, NbO3 - Niobate, VO4 3-Vanadate such as vanadate and polyoxoacids thereof (collectively referred to as M oxyacids) are preferred. These oxoacid compounds may be salts of oxoacid compounds with alkali metal elements such as Na, K, Li, alkaline earth metal elements such as Ca, Ba, phosphoric acid, silicic acid, etc., as long as they can form oxoacids in an aqueous solution. These metal oxoacid compounds are also referred to as M oxoacid compounds. The M component in the oxoacid may act on the surface together with the iron component in the magnetic powder that has been dissolved by the acidic component in the aqueous solution to form a passive film. For example, M may stabilize the inner layer of the passive film, produce a coating with fewer defects, or the M oxyacid may be adsorbed to defective parts of the coating to improve the coverage rate and provide excellent oxidation resistance and heat resistance. For example, the coating has a continuous phase with a gradient of M composition from the iron oxide-based phase on the surface of the soft magnetic material such as the iron-based magnetic powder to the phosphoric acid compound-based phase (M component-based phase) where the M composition is relatively constant. Such a continuous phase can function as a base for the phosphate compound-based phase of the coating, which is mainly composed of phosphate compounds. Here, "the M composition is relatively constant" means that the content of the M component is within a range of 50 atomic % to 150 atomic % of the median M content in the phosphate compound-based phase. The phosphate compound-based phase may have a relatively constant Fe composition, and the continuous phase may have a gradient in the Fe composition.

[0024] The presence of this gradient phase, i.e., the gradient phase, makes it difficult for cracks or separations to occur between the coating and the soft magnetic material due to thermal or mechanical stress. This makes it possible to suppress the deterioration of the soft magnetic material that occurs when heated to a strain relief temperature. The gradient phase of M composition is thought to be generated by the action of M oxyacid. It is preferable for the soft magnetic material to contain M components and Ni, etc., since this further stabilizes the coating. For example, Fe-X (X=Mn), Fe-X (X=Ni), Fe-X (X=Mn, Ni), Fe-X (X=M), Fe-X alloy, Fe-Si, etc. are suitable soft magnetic materials.

[0025] The content of the metal oxo acid compound in the aqueous solution is preferably from 0.001 to 10% by mass, more preferably from 0.01 to 5% by mass, in which case the metal oxo acid compound tends to have high solubility in water and high storage stability.

[0026] The aqueous solution used in the coating step may further contain a compound of a metal element or a metalloid element other than the above-mentioned metal oxoacid compound.

[0027] Examples of the metal elements include transition metal elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Pd, Pt, Cu, 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 metalloid elements include B, Si, and Ge. Among these, metal elements are preferable.

[0028] In order to obtain a coated soft magnetic material with excellent heat resistance, the metal element is preferably one that has a small Gibbs energy change (ΔG) in the oxidation reaction in the temperature range (e.g., 400°C to 700°C) when the coated soft magnetic material is heated. The metal element is preferably an element with an oxidation reaction rate of -300 kJ / mol O2 or less. The metal element is preferably a rare earth metal element, and more preferably Sm, Nd, La, or Dy. Table 1 shows the Gibbs free energies of metal element oxides at 600°C. [Table 1]

[0029] Examples of compounds of metal elements or metalloid elements include oxides, chlorides, hydroxides, sulfates, nitrates, acetates, etc. of metal elements or metalloid elements, and chlorides are preferred because they tend to generate ions in an aqueous solution and tend to form complex compounds with Fe ions present in the aqueous solution. The above compounds of metal elements or metalloid elements may be used alone or in combination with two or more kinds in addition to the metal oxo acid compound.

[0030] 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.

[0031] For the purpose of improving the water resistance and corrosion resistance of the coating and the magnetic properties of the magnetic powder, an oxidizing agent such as sodium nitrate or sodium nitrite, or a chelating agent such as EDTA may be further added. When the aqueous solution contains an oxidizing agent, the concentration is preferably 0.0001% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 1% by mass or less. When the aqueous solution contains a chelating agent, the concentration is preferably 0.0001% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 1% by mass or less.

[0032] Examples of the reaction solvent in the coating step include water and a mixed solvent of water and a hydrophilic organic solvent. When these solvents are used, a phosphoric acid compound having a smaller particle size is precipitated compared to when a hydrophobic organic solvent is used, and a dense coating is formed. Among these, water is preferred. 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.

[0033] The reaction time for forming a coating on the surface of the magnetic material is preferably from 1 minute to 10 hours, and more preferably from 5 minutes to 2 hours.

[0034] In the coating process, as long as the aqueous solution containing the phosphoric acid compound and the metal oxo acid compound can be mixed with the soft magnetic material, the order of mixing the components is not particularly limited. However, it is preferable to first mix the aqueous solution containing the metal oxo acid compound with the soft magnetic material, and then add the phosphoric acid compound or the aqueous solution containing the phosphoric acid compound. By mixing the aqueous solution containing the metal oxo acid compound with the soft magnetic material in advance, the metal element derived from the metal oxo acid compound is easily bonded to the surface of the soft magnetic material, and the amount of the coating can be increased. When the aqueous solution containing the metal oxo acid compound is mixed with the soft magnetic material in advance, the phosphoric acid compound or the aqueous solution containing the phosphoric acid compound can be added after mixing and stirring for preferably 5 minutes or more, more preferably 10 minutes or more.

[0035] In the coating process, the pH of the aqueous solution may increase as phosphoric acid derived from the phosphoric acid compound adheres to the soft magnetic material. In this case, the pH of the aqueous solution may be adjusted by adding an inorganic acid or an organic acid. When adjusting the pH, the pH range can be set to more than 0 and less than 7, preferably 1 to 4.5, more preferably 1.6 to 3.9, and even more preferably 2 to 3. By setting the pH to 1 or more, the deposition rate of the phosphoric acid compound can be reduced compared to when the pH is less than that, and the thickness of the coating film to be formed can be easily controlled. When the pH is 7 or more, the deposition amount of the phosphoric acid compound 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 deposition rate of the phosphoric acid compound can be set to a level that is not too slow. The acid to be added 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 inorganic acid and organic acid may be used. When adjusting the pH, inorganic acid or organic acid may be added as needed during the coating process so that the pH is within the above range. Since the pH rises quickly in the initial stage of the coating process, it is preferable to shorten the interval of adding inorganic acid or organic acid for pH control.

[0036] The pH can be adjusted to a range of 1 to 4.5 by adding an inorganic or organic acid to the aqueous solution for 1 minute or more, preferably for 10 minutes or more, and more preferably for 30 minutes or more in order to reduce the areas where the coating is thin. In the initial stage of pH maintenance, the pH rises quickly, so it is preferable to add inorganic or organic acid for pH control at short intervals. As the coating progresses, the pH changes gradually slower, and the intervals between additions of inorganic or organic acid become longer, so that the end point of the reaction can be determined.

[0037] After the coating step, the soft magnetic material on which the coating is formed may be purified by, for example, heating at 100° C. or higher and 500° C. or lower, filtering, or the like.

[0038] In the method for producing the coated soft magnetic material of this embodiment, the coating step may be performed only once, or may be performed two or more times. By performing the coating step two or more times, a thick coating containing a metal phosphorus compound can be formed on the surface of the soft magnetic material. The upper limit of the number of times the coating step is performed is not particularly limited, but can be, for example, 10 or less.

[0039] When the coating step is performed two or more times, the soft magnetic material may be purified between the coating steps. The magnetic material on which the coating is formed can be purified by, for example, heating at 100°C or higher and 500°C or lower, filtering, or the like.

[0040] When the coating step is performed two or more times, it is preferable that the aqueous solution in the k-th coating step is obtained by adding a metal oxo acid compound to the aqueous solution in the k-1-th coating step. In this case, the k-th coating step can be performed without purifying the soft magnetic material after the k-1-th coating step. k is an integer of 2 or more, but when the coating step is performed n times, k is preferably any integer of 2 to n. When k is any integer of 2 to n, an aqueous solution obtained by adding a metal oxo acid compound to the aqueous solution in the coating step is used in all coating steps from the second step onwards.

[0041] The concentration of the metal oxoacid compound added to the aqueous solution in the k-1th coating step may be appropriately determined depending on the reaction time of the kth coating step and the type of metal oxoacid compound, but is preferably 0.01 to 50 times, and more preferably 0.1 to 10 times, the content of the rare earth compound in the aqueous solution in the kth coating step. Within these ranges, unevenness in the thickness of the coating can be reduced.

[0042] When the coating step is performed two or more times, the metal oxo acid compound in the m-th coating step may be different from the metal oxo acid compound in the m-1-th coating step, where m is an integer of 2 or more. When the metal oxo acid compound in the m-th coating step is different from the metal oxo acid compound in the m-1-th coating step, the metal elements derived from the metal oxo acid compound in the m-1-th coating step and the metal elements derived from the metal oxo acid compound in the m-th coating step tend to accumulate in this order in the surface direction of the coating that is finally formed from the soft magnetic material base material.

[0043] When the coating step is performed two or more times, the pH of the mixture of the aqueous solution and the soft magnetic material in the p-th coating step is preferably lower than the pH of the mixture of the aqueous solution and the soft magnetic material in the p-1-th coating step, and the difference is preferably 0.1 or more, more preferably 1 or more. In addition, as the phosphoric acid compound reacts with the soft magnetic material, the amount of free phosphoric acid in the aqueous solution decreases, and the pH of the mixture of the aqueous solution and the soft magnetic material may increase. When the pH varies during the reaction, the pH of the mixture of the aqueous solution and the soft magnetic material in the p-1-th coating step refers to the pH at the end of the p-1-th coating step. When the pH of the mixture of the aqueous solution and the soft magnetic material in the p-th coating step is lower than the p-1-th coating step, the efficiency of forming a coating containing a metal phosphorus compound on the soft magnetic material can be improved.

[0044] Although p is an integer of 2 or more, when the covering step is performed n times, p is preferably any integer of 2 or more and n or less. When p is any integer of 2 or more and n or less, in the second and all subsequent covering steps, an aqueous solution having a lower pH than the mixed solution of the aqueous solution and the soft magnetic material in the previous covering step is used.

[0045] In the p-th coating step, it is preferable to add an inorganic acid or an organic acid to the aqueous solution to adjust the pH to 0 or more and less than 7. The pH range is more preferably 1.6 to 3.9, and even more preferably 2 to 3. If the pH is less than 0, the deposition rate of the phosphorus compound tends to be too fast, making it difficult to control the film thickness. If the pH is 7 or more, the deposition amount of the phosphorus compound decreases, so that the coating becomes insufficient and iron loss tends to increase. If the pH exceeds 7, the deposition rate of the phosphorus compound tends to slow down. Examples of the acid to be added include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid, and organic acids such as 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 can be used in combination depending on the purpose. A mixture of an inorganic acid and an organic acid may be used. The adjustment of the pH to the range of 0 to less than 7 can be performed for 1 minute or more, and it is preferable to perform the adjustment for 30 minutes or more in order to reduce the area where the thickness of the coating part is thin.

[0046] After the coating step, the coated soft magnetic material may be purified by, for example, heating at 100° C. or higher and 500° C. or lower, filtering, or the like to remove liquid components.

[0047] Also, after the coating step, a coating fixing step may be performed. In the coating fixing step, the refined coated soft magnetic material is subjected to high-temperature treatment 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 for 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.

[0048] <<Method of manufacturing molded products>> The method for producing a molded body according to the present embodiment is characterized by including a step of obtaining a coated soft magnetic material and a step of heating the coated soft magnetic material. In the step of obtaining the coated soft magnetic material, the method described above for the method for producing the coated soft magnetic material can be carried out.

[0049] In the heating step, the coated soft 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 soft 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 soft 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. This makes it possible to suppress the progress of oxidation of the coated soft magnetic material, and thus to suppress deterioration of the characteristics.

[0050] It is preferable to include a step of pressing the coated soft magnetic material to obtain a pressure-molded product 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.

[0051] The pressure conditions are preferably 0.01 GPa or more and 10 GPa or less, and 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 soft 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 with the coated soft 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.

[0052] When pressurizing, the coated soft magnetic material may be pressed alone. When pressurizing, the coated soft magnetic material may be mixed with a binder, a 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 soft magnetic material. When the amount of binder used is within the above range, a molded body having excellent mechanical strength such as impact resistance and small eddy current loss among iron losses can be obtained. Depending on the application, whether or not to use a resin, and the type of resin if used, are selected.

[0053] 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 parts by weight to 10 parts by weight, more preferably 0.01 parts by weight to 5 parts by weight, per 100 parts by weight of the coated soft 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.

[0054] 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 soft 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 soft 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 soft magnetic material to the volume of the compact.

[0055] Since the molded body obtained in this embodiment is an aggregate of coated soft 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 soft magnetic material may partially react and fuse with the coating of the adjacent coated soft magnetic material, and the soft magnetic materials may be integrated while maintaining the insulating state between them. The soft magnetic material of this embodiment can obtain a molded body 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 desirable 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.

[0056] <<Coated soft magnetic material>> The coated soft magnetic material of this embodiment is characterized by having a soft magnetic material and a coating containing a metal phosphorus compound provided on the surface of the soft magnetic material. The method for producing the coated soft magnetic material of this embodiment is not particularly limited, but it can be obtained, for example, by the above-mentioned method for producing a coated soft magnetic material. The material and particle size of the soft magnetic material are as described above with respect to the method for producing a coated soft magnetic material.

[0057] The coating of this embodiment includes an M component. The M component is preferably Cr, W, Mn, Mo, Nb, or V. The coating can have, in the direction from the surface of the coating toward the soft magnetic material, a phase mainly containing the M component with a relatively constant composition (M component-based phase), and an M composition gradient phase located between the M component-based phase and the soft magnetic material and in which the content of the M component decreases. This makes it possible to obtain a coated soft magnetic material with excellent heat resistance. The minimum M component content of the M composition gradient phase is preferably 0.2 to 0.8 times the content of the M component in the M component-based phase. This makes it possible to obtain a coating stably. The thickness of the M composition gradient phase is preferably 1 nm to 1 μm. This makes it possible to obtain a film that is less susceptible to cracking or separation due to stress. Such a content and thickness further improve the heat resistance of the coated soft magnetic material. The thickness of the M composition gradient phase is more preferably 20 nm to 200 nm.

[0058] The coating of the present embodiment contains a metal phosphorus compound. Metal components constituting the metal phosphorus compound include transition metal elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Pd, Pt, Cu, Ag, and Au, as well as 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 elements other than metalloids such as Zn, Cd, and Al. Metalloid elements include B, Si, and Ge. Among these metals, those with a small Gibbs energy change (ΔG) in the oxidation reaction at 400° C. or more and 700° C. or less are preferable in terms of improving the heat resistance of the coating. An element having a Gibbs energy change (ΔG) of an oxidation reaction at 600°C of -300 kJ / mol O2 or less is preferred, a rare earth metal element is more preferred, and Sm, Nd, La, and Dy are even more preferred. The metal phosphorus compound may contain only one of these metals or may contain two or more of them, and preferably contains, for example, a rare earth metal element and a non-rare earth metal element. Examples of the non-rare earth metal element include metals other than rare earth metal elements among the metal components constituting the metal phosphorus compound described above. In addition, these metals may be metals derived from the soft magnetic material, which is the base material, during the production of the coated soft magnetic material, or may be metals contained in the aqueous solution used in the coating process.

[0059] The thickness of the coating containing the metal phosphorus compound is preferably 2 nm to 10 μm, more preferably 5 nm to 500 nm, from the viewpoint of the insulation property and heat resistance of the coated soft magnetic material. The thickness of the coating can be measured by performing a composition analysis by line analysis using EDX on a cross section of the coated soft magnetic material.

[0060] The coating provided on the surface of the soft magnetic material preferably contains oxygen and phosphorus in addition to the metal phosphorus compound. The oxygen content is preferably greater than the phosphorus content. There may be a region in the thickness direction of the coating where the oxygen content is greater than the phosphorus content, but the region in the thickness direction of the coating where the oxygen content is greater than the phosphorus content is preferably 10% or more, more preferably 50% or more, and even more preferably the entire region. The oxygen content is preferably 1 time or more, more preferably 3 times or more, that of phosphorus. The upper limit of the oxygen content can be, for example, 10 times or less that of phosphorus.

[0061] The content of the M component as a non-rare earth metal element may decrease after reaching a maximum value in the direction from the surface of the coating toward the soft magnetic material, and then start to increase. When the coating step is performed two or more times during the formation of the coating, and the pH of the mixture of the aqueous solution and the soft magnetic material in the p-th coating step (p is an integer of 2 or more) is lower than the pH of the mixture of the aqueous solution and the soft magnetic material in the p-1th coating step, the content of the non-rare earth metal element shows this distribution, and the heat resistance of the coating tends to improve. The minimum value before the content of the non-rare earth metal element decreases after reaching a maximum value and starts to increase is preferably 0.9 times or less of the maximum value, and more preferably 0.5 times or less. The lower limit of the minimum value is not limited, but can be 0.001 times or more of the maximum value.

[0062] In the coating, each of the metals 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 soft magnetic material using EDX line analysis. If the coating contains a phosphate compound or a composite oxide in a microcrystalline state, the mechanical strength is increased and the heat resistance is improved.

[0063] The content of the rare earth metal element in the coated soft magnetic material is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. When it is 0.0001% by mass or more, it tends to withstand heat treatment at high temperatures, when it is 0.01% by mass or more, it tends to withstand heat treatment at higher temperatures, and when it is 0.1% by mass or more, it tends to obtain a material with improved insulation. The upper limit of the content of the rare earth metal element can be 50% by mass or less, and preferably 10% by mass or less. When the content of the rare earth metal element contained in the coated soft magnetic material exceeds 50% by mass, the magnetic permeability of the coated soft magnetic material decreases, and the characteristics may be deteriorated. The content of the rare earth metal element in the coated soft magnetic material is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0064] The phosphorus content in the coated soft magnetic material is preferably 0.0001% by mass or more and 15% by mass or less, and more preferably 0.001% by mass or more and 5% by mass or less. Within the above range, the heat resistance tends to be improved. The phosphorus content in the coated soft magnetic material is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0065] The iron loss W of the coated soft magnetic material is preferably 210 W / kg or less, more preferably 100 W / kg or less, and even more preferably 80 W / kg or less. The lower limit of the iron loss W can be, for example, 4 W / kg or more. The hysteresis loss W of the coated soft magnetic material h is preferably 80 W / kg or less, more preferably 60 W / kg or less, and even more preferably 50 W / kg or less. h The lower limit of the eddy current loss W of the coated soft magnetic material can be set to 3.9 W / kg or more. e is preferably 130 W / kg or less, more preferably 40 W / kg or less, and even more preferably 35 W / kg or less. eThe lower limit of can be 0.1 W / kg or more. These losses are values ​​measured at a maximum magnetic flux density (Bmax) of 1 T and a frequency of 400 Hz by the method described in the Examples. In this embodiment, such numerical ranges can be set for a molded body that has undergone a heating process. The heating temperature in the heating process can be, for example, 600°C. A molded body in which losses such as iron loss W are within these numerical ranges may not contain resin and glass. When a coated magnetic material, rather than a molded body, has undergone a heating process, the iron loss W and hysteresis loss W measured for the coated magnetic material are h , eddy current loss W e may be in the ranges mentioned above.

[0066] <<Molded body>> The molded body of the present embodiment is characterized in that it contains the coated soft magnetic material. The molded body can be obtained by the above-mentioned manufacturing method for the molded body. The molded body can be used for various applications as a dust core with suppressed iron loss. The molded body can be applied to, for example, a transformer, a coil, a head, an inductor, a reactor, a core (magnetic core), a yoke, various actuators, and the like. The molded body can be used as a soft magnetic part incorporated in various motors such as a motor for a rotating machine and a linear motor. Examples of the motor for a rotating machine include a voice coil motor, an induction motor, and a reactance motor.

[0067] The present disclosure includes the following aspects. (Section 1) A method for producing a coated soft magnetic material, comprising a coating step of mixing an aqueous solution containing a phosphoric acid compound and a metal oxoacid compound with a soft magnetic material, and forming a coating containing a metal phosphorus compound on the surface of the soft magnetic material.

[0068] (Section 2) Item 2. The method for producing a coated soft magnetic material according to item 1, wherein the metal oxoacid compound is an oxoacid compound of Cr, W, Mn, Mo, Nb, or V.

[0069] (Section 3) Item 3. The method for producing a coated soft magnetic material according to item 1 or 2, wherein an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less.

[0070] (Section 4) Item 4. The method for producing a coated soft magnetic material according to item 3, wherein the adjustment is carried out for 10 minutes or more.

[0071] (Section 5) In the coating step, an aqueous solution containing a metal oxoacid compound is mixed with a soft magnetic material, and then the phosphate compound is mixed therewith. Item 5. A method for producing a coated soft magnetic material according to any one of items 1 to 4.

[0072] (Section 6) Item 6. The method for producing a coated soft magnetic material according to any one of items 1 to 5, wherein the coating step is carried out two or more times.

[0073] (Section 7) The aqueous solution in the k-th (where k is an integer of 2 or more) coating step is The metal oxoacid compound is added to the aqueous solution in the (k-1)-th coating step. Item 7. A method for producing a coated soft magnetic material according to item 6.

[0074] (Section 8) The metal oxoacid compound in the m-th coating step (where m is an integer of 2 or more) is The metal oxo acid compound in the (m-1)th coating step is different from the metal oxo acid compound in the (m-1)th coating step. Item 7. A method for producing a coated soft magnetic material according to item 6.

[0075] (Section 9) Obtaining a coated soft magnetic material by the method according to any one of items 1 to 8; and a heating step of heating the coated soft magnetic material.

[0076] (Section 10) A soft magnetic material and a coating provided on a surface of the soft magnetic material, the coating has an M component main phase mainly containing an M component, and an M composition gradient phase located between the M component main phase and the soft magnetic material, in which the content of the M component decreases in a direction toward the soft magnetic material, the thickness of the M composition gradient phase in a direction from the M component main phase toward the soft magnetic material is 20 nm or more; The coated soft magnetic material, wherein the M component is Cr, W, Mn, Mo, Nb, or V. EXAMPLES

[0077] Examples will be described below. Unless otherwise specified, "%" is by weight.

[0078] (1) Evaluation method (1-1) Iron loss The soft magnetic material was placed in a die with an inner diameter of 10 mm and an outer diameter of 14 mm, and molded at a pressure of 1 GPa except for Example 16, and then heat-treated in an Ar atmosphere at 600 ° C for 1 hour to produce a toroidal compact. In Example 16, 0.2 mass% of a lubricant (1,2-bis(stearoylamino)ethane, zinc stearate) was added to the soft magnetic material, which was placed in the same die and molded at 200 ° C at a pressure of 1.5 GPa, and then heat-treated in an air atmosphere at 520 ° C, and then heat-treated in an Ar atmosphere at 600 ° C for 1 hour to produce a toroidal compact. These compacts were wound with 50 turns of copper wire on the primary side and 50 turns on the secondary side to prepare evaluation samples. Using these evaluation samples, the value of W10 / 400 (iron loss at 400 Hz and 1 T) was evaluated using a BH analyzer (SY-8218, Iwasaki Electric Co., Ltd.). At the same time, the iron loss value was measured at 10Hz to 1kHz at a magnetic flux density of 1T, and the hysteresis loss W at 400Hz and 1T was calculated by fitting with a quadratic polynomial. h 10 / 400 and eddy current loss W e I asked for 10 / 400.

[0079] (1-2) Film thickness and atomic concentration The thickness and atomic concentration of the coating of the coated soft magnetic material were measured as follows. First, the obtained coated soft magnetic material was molded into a disk shape of φ10 mm, heated at 600 ° C for 1 hour, and the obtained molded body was embedded in Epocure resin, then processed by ion milling, 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 soft magnetic material in steps of 0.791 nm or 0.957 nm, observing the continuous change in atomic concentration of each constituent element, and measuring the range where 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.

[0080] (2-1) Manufacturing of coated soft magnetic materials (ii) Preparation of Soft Magnetic Materials: Examples 1 to 15, Comparative Examples 1 to 6 As the soft magnetic materials of Examples 1 to 15 and Comparative Examples 1 to 6, Fe-X alloys were prepared. The Fe-X alloys were prepared 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 Mn-Ni-ferrite was prepared using potassium hydroxide as a pH adjuster. 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 to obtain soft magnetic materials. The D50 of the Fe-Ni-Mn powder was 250μm. The composition of the Fe-X alloys in Examples 7 to 10 and 15 and Comparative Examples 1 to 6 was Fe. 96 Ni 3.9 Mn 0.1 The composition of the Fe-X alloys in Examples 1 to 6 and 11 to 14 was Fe95.5 Ni 4.4 Mn 0.1 It was.

[0081] (i-ii) Preparation of soft magnetic material: Example 16 A soft magnetic material was produced in the same manner as in Example 1, except that the raw materials were MnSO4·5H2O (manganese (II) sulfate pentahydrate), NiSO4·6H2O (nickel (II) sulfate hexahydrate, and FeSO4·7H2O (iron (II) sulfate heptahydrate), and the pH adjuster was NaOH.

[0082] (i-iii) Preparation of soft magnetic materials: Examples 17 to 18, Comparative Example 7 As the soft magnetic materials of Examples 17-18, commercially available water-atomized iron powder was prepared.

[0083] (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.

[0084] (iii-i) Coating step: Examples 1 to 7, 16, and 17, and Comparative Examples 3 to 6 The chloride of the additive element and the metal oxo acid compound shown in Table 2 were added to the washed soft magnetic material as an aqueous solution containing 10% by mass of each of the additive element and the metal oxo acid compound shown in Table 2 relative to the soft magnetic material, and the mixture was stirred for 15 minutes. Next, the phosphoric acid compound shown in Table 2 was added as an aqueous phosphoric acid solution of pH 2 containing 40% by mass of the coated soft magnetic material, and the mixture was stirred for 7 minutes. The final concentrations of each component were 1.6% by mass of the soft magnetic material, 0.16% by mass of the chloride of the additive element and the metal oxo acid compound, and 0.4% by mass of the phosphoric acid compound (PO4 equivalent). The pH of the treatment tank rose from 3 to 5. Next, the metal oxo acid compound shown in Table 2 was added as an aqueous solution containing 10% by mass of each of the soft magnetic material, and the mixture was stirred for 30 minutes while controlling the pH of the reaction mixture to a range of 2.5±0.1 by adding 6% by mass of hydrochloric acid from time to time.

[0085] (iii-ii) Coating step: Examples 8 to 15, 18, and Comparative Example 2 The metal oxo acid compound shown in Table 2 was added to the washed soft magnetic material as an aqueous solution containing 10% by mass of the soft magnetic material, and the mixture was stirred for 15 minutes. Next, the phosphoric acid compound shown in Table 2 was added to the coated soft magnetic material as an aqueous solution of phosphoric acid with a pH of 2, containing 40% by mass of the coated soft magnetic material, and the mixture was stirred for 7 minutes. The final concentrations of each component were 1.6% by mass of the soft magnetic material, 0.16% by mass of the metal oxo acid compound, and 0.4% by mass of the phosphoric acid compound (PO4 equivalent). The pH of the treatment tank rose from 3 to 5.

[0086] (iii-iii) No coating process: Comparative Examples 1 and 7 In Comparative Examples 1 and 7, no coating step was carried out.

[0087] (iv-i) Drying and baking: Examples 1 to 18 and Comparative Examples 2 to 6 The soft magnetic material after the coating process 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.

[0088] (iv-ii) No drying or baking: Comparative Examples 1 and 7 Comparative Examples 1 and 7 were not subjected to drying and baking.

[0089] (2-2) Production of Molded Products The obtained coated soft magnetic materials were used to manufacture compacts for iron loss evaluation by the method described above in the iron loss evaluation method. Also, the obtained coated magnetic materials of Examples 7, 15, and 16 were used to manufacture compacts for coating evaluation by the method described above in the coating thickness and atomic concentration evaluation method.

[0090] The iron loss (hysteresis loss and eddy current loss) of the obtained compact for iron loss evaluation was measured by the above-mentioned method. The results are shown in Table 2.

[0091] [Table 2]

[0092] In Comparative Example 1 (without a coating process) and Comparative Example 2 (without a metal oxo acid compound), the iron loss was large. In Comparative Example 3, in which chromium chloride was used, the iron loss was reduced in Examples 2, 3, 11, and 12, in which a chromium oxo acid compound was used. In Comparative Example 4, in which vanadium chloride was used, the iron loss was reduced in Examples 4 and 13, in which a vanadium oxo acid compound was used. In Comparative Example 5, in which manganese chloride was used, the iron loss was reduced in Examples 6 and 14, in which a manganese oxo acid compound was used. In Comparative Example 6, in which molybdenum chloride was used, the iron loss was reduced in Examples 7 and 15, in which a molybdenum oxo acid compound was used as the metal oxo acid compound while using the same soft magnetic material. In Examples 1 to 7, in which samarium chloride was used in combination, the iron loss was significantly reduced.

[0093] In comparison with Example 17, in which a coating process was performed on a commercially available iron powder, Example 7, in which a similar coating process was performed on an Fe-X alloy, showed smaller iron loss, hysteresis loss, and eddy current loss. In addition, in comparison with Example 18, in which a coating process was performed on a commercially available iron powder, Example 1, in which a similar coating process was performed on an Fe-X alloy, showed smaller iron loss, hysteresis loss, and eddy current loss. Thus, it was found that the coating process is more effective when performed on an Fe-X alloy.

[0094] The surface of the molded body for coating evaluation using the coated magnetic material of Example 15 was observed by STEM-EDX. The obtained STEM image is shown in FIG. 1B. The line analysis results in FIG. 1A were measured along the white line in FIG. 1B. It can be seen that an M composition gradient phase in which the Mo content, which is an M component, decreases from the passive film composition exists between 100 nm and 180 nm in the direction from the surface of the coating toward the base material of the magnetic material. It is considered that this gradual M composition gradient phase over 80 nm allows the coating to maintain its bond without peeling off from the base material (soft magnetic material) even when thermal stress or mechanical stress is applied, and thus high heat resistance can be obtained.

[0095] The beginning of the M composition gradient phase can be easily identified when there is a component that is contained in the soft magnetic material but not in the coating, such as Ni in Example 15. In Fig. 1A, the M composition gradient phase begins at the position (168 mm) where the Ni composition becomes 0.

[0096] The surface of a molded body for coating evaluation using the coated magnetic material of Example 7 was observed by STEM-EDX. The obtained STEM image is shown in FIG. 2. FIG. 3 includes element mapping (EDS) images of O, P, Fe, Ni, Mo, and Sm. Line analysis results for the metal elements, P, and O in the white line in the image labeled "Grey" in FIG. 2 are shown in FIGS. 3 and 4. FIG. 4 is an enlarged view of the 0 to 40 atomic % region in FIG. 3.

[0097] In Figures 2 to 4, the thickness of the coating on the magnetic material surface was approximately 200 nm. In Figure 4, O was more abundant than P over the entire range of the coating. In the direction from the surface of the coating toward the magnetic material, maximum values ​​of Mo and Fe were observed, followed by a maximum value of Sm. It is believed that Mo originates from sodium molybdate added in the coating process, and Fe originates from the soft magnetic material (base material).

[0098] When the aqueous solution during the coating reaction contains a rare earth metal element, Ni may also be contained in the coating. In this case, it is not appropriate to identify the M composition gradient phase by focusing on the Ni content. In this case, it can be determined from the change in the content of Mo, which is the M component. From the results of the line analysis in Figures 3 and 4, it can be seen that an M composition gradient phase is formed in which the content of Mo, which is the M component, decreases from the passive film composition between 100 nm and 180 nm. In Example 7, the M component and rare earth metal elements, which have low ΔG and whose oxides and phosphate compounds are thermodynamically stable, are present in the inner layer of the passive film phase with high Fe and M component contents. This makes it possible to obtain a coated soft magnetic material with excellent heat resistance and oxidation resistance. The Fe-X alloy of Example 7 was prepared by reducing ferrite powder containing X component, which is difficult to reduce mainly with hydrogen, in a reducing gas containing hydrogen gas, and generating the first and second phases by a disproportionation reaction. This makes it possible to obtain a structure with a large surface area and fine composition fluctuations. It is believed that this structure makes it easier for the metal to form a passive film with metal oxyacids, especially M oxyacids.

[0099] A part of the cross section of the molded body for coating evaluation using the coated magnetic material of Example 16 was observed by STEM-EDX. The obtained results are shown in Figures 5A and 5B. Figure 5A is a distribution diagram of Mn using characteristic X-rays by STEM-EDX analysis. Black parts indicate low Mn content, and white parts indicate high Mn content. This EDX analysis was performed by dividing the screen into 512 x 512 pixels with a side of 3 nm, narrowing the electron beam diameter to 1 nm for the center of each pixel, and measuring the amount of characteristic X-rays. Figure 5B is a histogram showing the distribution of Mn content. In Fig. 5B, the Mn content at all measurement points is divided into five categories: 0 atomic % or more and less than 0.05 atomic % (shown as 0-0.05 on the horizontal axis in the figure), 0.05 atomic % or more and less than 0.1 atomic % (shown as 0.05-0.1 on the horizontal axis in the figure), 0.1 atomic % or more and less than 0.15 atomic % (shown as 0.1-0.15 on the horizontal axis in the figure), 0.15 atomic % or more and less than 0.2 atomic % (shown as 0.15-0.2 on the horizontal axis in the figure), and 0.2 atomic % or more (shown as 0.2+ on the horizontal axis in the figure), and the number of pixels having each composition is shown as a percentage (called the abundance ratio), thereby showing the distribution of the Mn content. From Fig. 5B, it can be seen that the abundance ratio of pixels corresponding to the first phase, which have a Mn composition of 0 atomic % or more and less than 0.05 atomic %, is about 10% of the total. The percentage of pixels having a Mn content of 0.1 atomic % or more was about 50% of the total, which can be said to be the percentage of the second phase having a Mn content higher than that of the first phase. From Figures 5A and 5B, it was found that the Fe-X alloy, which was the soft magnetic material used in the coated magnetic material of Example 16, was phase-separated into the first and second phases.

Claims

1. A method for producing a coated soft magnetic material, comprising a coating step of mixing an aqueous solution containing a phosphoric acid compound and a metal oxoacid compound with a soft magnetic material, and forming a coating containing a metal phosphorus compound on the surface of the soft magnetic material.

2. The metal oxoacid compound is an oxoacid compound of Cr, W, Mn, Mo, Nb, or V; A method for producing the coated soft magnetic material according to claim 1.

3. The method for producing a coated soft magnetic material according to claim 1 or 2, wherein the pH of the aqueous solution is adjusted to 1 or more and 4.5 or less by adding an inorganic acid.

4. The method for producing a coated soft magnetic material according to claim 3 , wherein the conditioning is carried out for 10 minutes or more.

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

6. The method for producing a coated soft magnetic material according to claim 1 or 2, wherein the coating step is carried out two or more times.

7. The aqueous solution in the k-th coating step (where k is an integer of 2 or more) is The metal oxoacid compound is added to the aqueous solution in the (k-1)th coating step. A method for producing the coated soft magnetic material according to claim 6.

8. The metal oxo acid compound in the m-th coating step (where m is an integer of 2 or more) is different from the metal oxo acid compound in the (m-1)th coating step; A method for producing the coated soft magnetic material according to claim 6.

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

10. A soft magnetic material and a coating provided on a surface of the soft magnetic material, the coating has an M component main phase mainly containing an M component, and an M composition gradient phase located between the M component main phase and the soft magnetic material, in which the content of the M component decreases in a direction toward the soft magnetic material, the thickness of the M composition gradient phase in a direction from the M component main phase toward the soft magnetic material is 20 nm or more; The coated soft magnetic material, wherein the M component is Cr, W, Mn, Mo, Nb, or V.

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