Coated magnetic material and method of producing the same

Abstract

To provide a magnetic material with a coating exhibiting superior heat resistance and a method of producing the same.SOLUTION: A method of producing a coated magnetic material includes: a coating step of mixing an aqueous solution containing a phosphate compound and a rare earth compound with a magnetic material, which is a soft magnetic material, to form a coating containing a phosphorus compound containing a rare earth metal 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 method for producing a magnetic material having a coating with excellent heat resistance. [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 rare earth compound with a magnetic material that is a soft magnetic material, and forming a coating containing a phosphorus compound containing a rare earth metal element on the surface of the magnetic material.

[0006] A coated magnetic material according to one embodiment of the present disclosure includes a magnetic material that is a soft magnetic material, and a coating that contains a rare earth metal element, phosphorus, and oxygen and is provided on a surface of the magnetic material. Effect of the Invention

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

[0008] [Figure 1] 1 shows a STEM (scanning transmission electron microscope) image of the coated magnetic material produced in Example 10. [Diagram 2] 1 shows the results of line analysis of the coated magnetic material produced in Example 10. [Diagram 3] 1 shows the results of line analysis of the coated magnetic material produced in Example 10. [Figure 4A] FIG. 11 is a distribution diagram of Mn by STEM-EDX analysis of the coated magnetic material produced in Example 16. [Figure 4B] 13 is a histogram showing the distribution of the Mn content of the coated magnetic material produced in Example 16. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiments of the present disclosure are described in detail below. However, the embodiments described 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 rare earth compound with a magnetic material that is a soft magnetic material, and forming a coating containing a phosphorus compound containing a rare earth metal 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] 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%.

[0018] 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.

[0019] <Coating process> In the coating process, an aqueous solution containing a phosphate compound and a rare earth compound is mixed with a magnetic material, which is a soft magnetic material. As a result, the metal component contained in the magnetic material reacts with the phosphate component contained in the phosphate compound to form a coating. The coating may be a coating containing a phosphorus compound containing a rare earth metal element, or a coating containing a rare earth 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 phosphate may be obtained by heating after the coating containing the rare earth phosphate is formed.

[0020] 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.

[0021] 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.

[0022] The rare earth metal element derived from the rare earth compound contained in the aqueous solution in the coating process adheres to the magnetic material. The amount of the rare earth compound contained in the aqueous solution is preferably an amount that makes the content of the rare earth metal element relative to the coated magnetic material 0.0001% by mass or more, more preferably an amount that makes the content of the rare earth metal element relative to the coated magnetic material 0.01% by mass or more, and even more preferably an amount that makes the content of the rare earth metal element relative to the coated magnetic material 0.0001% by mass or more tends to stabilize the coating amount of the coating, and if it is 0.01% by mass or more, the loss tends to be further reduced, and if it is 0.1% by mass or more, the heat resistance tends to be further improved. The upper limit of the content of the rare earth metal element in the coated magnetic material can be 50% by mass or less, and preferably 10% by mass or less. By making the content of the rare earth metal element contained in the coated magnetic material 50% by mass or less, the decrease in the magnetic permeability of the coated magnetic material can be suppressed, and the decrease in the characteristics can be suppressed. The rare earth metal element precipitates on the surface of the magnetic material as a phosphorus compound containing the rare earth metal element, or as a phosphate containing the rare earth element.

[0023] Rare earth metal elements tend to have a small Gibbs energy change (ΔG) in the oxidation reaction in the temperature range when the coated magnetic material is heated (approximately 400°C to 700°C), so by using rare earth compounds in the coating process, a coated magnetic material with excellent heat resistance can be obtained. Table 1 shows the Gibbs energy change in the oxidation reaction of rare earth oxides at 600°C. [Table 1]

[0024] The rare earth compound contains a rare earth metal element. The rare earth metal element is preferably Ce, Nd, Sm, La, Dy, Y, or Pr, more preferably Ce, Nd, Sm, La, or Dy, even more preferably Ce, Sm, La, or Dy, and particularly preferably Sm or Dy. The rare earth compound is preferably a compound that generates rare earth ions in an aqueous solution, such as a rare earth oxide, a rare earth hydroxide, a rare earth chloride, a rare earth sulfate, a rare earth nitrate, or a rare earth acetate, and more preferably a rare earth chloride. Specific examples of preferred rare earth compounds include one or more rare earth chlorides selected from the group consisting of Ce, Nd, Sm, La, and Dy. These may be used alone or in combination of two or more. Rare earth chlorides tend to be easily soluble, so the aqueous solution used in the coating process can be easily obtained by using rare earth chlorides.

[0025] In the aqueous solution containing a phosphoric acid compound and a rare earth compound, the content of the rare earth compound is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass. In these ranges, the rare earth compound tends to have high solubility in water and high storage stability.

[0026] 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.

[0027] 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, phosphates having smaller particle sizes are 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.

[0028] In the coating process, the pH of the aqueous solution may increase as phosphoric acid derived from the phosphoric acid compound adheres to the 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 precipitation rate of the phosphorus compound containing a rare earth metal element can be reduced compared to when the pH is less than 1, making it easier to control the thickness of the coating to be formed. If the pH is 7 or more, the amount of phosphate precipitation decreases, which tends to result in insufficient coating and increased loss, so the pH is preferably less than 7. By setting the pH to 4.5 or less, the precipitation rate of the phosphate can be set to a level that is not too slow. 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. 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 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.

[0029] In the coating step, the content of the magnetic material in the mixture of the aqueous solution containing the phosphoric acid compound and the rare earth compound and the magnetic material can be 0.0001% by mass to 70% by mass, preferably 0.01% by mass to 10% by mass. Within these ranges, the thickness of the coating tends to be stable.

[0030] For the purpose of improving the water resistance and corrosion resistance by the coating and the magnetic properties of the magnetic powder, oxoacid salts such as molybdate, tungstate, vanadate, and chromate, oxidizing agents such as sodium nitrate and sodium nitrite, and chelating agents such as EDTA may be further added. When the aqueous solution contains an oxoacid salt, the concentration is preferably 0.0001% by mass to 10% by mass, and more preferably 0.01% by mass to 1% by mass. When the aqueous solution contains an oxidizing agent, the concentration is preferably 0.0001% by mass to 10% by mass, and more preferably 0.01% by mass to 1% by mass. When the aqueous solution contains a chelating ...

[0031] In the coating process, as long as the aqueous solution containing the phosphoric acid compound and the rare earth compound can be mixed with the magnetic material, which is a soft magnetic material, in the end, the order of mixing the components does not matter. In the coating process, it is preferable to first mix the aqueous solution containing the rare earth compound with the magnetic material, and then mix the phosphoric acid compound. By mixing the aqueous solution containing the rare earth compound with the magnetic material in advance, the rare earth compound is easily attached or bonded to the surface of the magnetic material, and the amount of the coating containing the phosphorus compound can be increased. When the aqueous solution containing the rare earth compound and the magnetic material are mixed in advance, the aqueous solution containing the rare earth compound can be mixed with the magnetic material in advance, and then the aqueous solution containing the phosphoric acid compound can be added after mixing the aqueous solution containing the rare earth compound and the magnetic material, preferably under conditions of pH 2 to 12, more preferably pH 4 to 10, and even more preferably pH 5 to 8, and stirring for preferably 1 minute or more, more preferably 5 minutes or more.

[0032] In the method for producing a coated 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 phosphorus compound containing a rare earth metal element can be formed on the surface of the magnetic material. The upper limit of the number of coating steps can be, for example, 10 times or less, or may be 5 times or less. The number of coating steps may be two times.

[0033] When the coating step is performed two or more times, the magnetic material may be purified between the coating steps. The magnetic material on which the coating is formed can be purified, for example, by heating at 100°C to 800°C, filtering, or the like.

[0034] When the coating step is performed two or more times, it is preferable that the aqueous solution in the n-th coating step is obtained by adding a rare earth compound to the aqueous solution in the n-1-th coating step. In this case, the n-th coating step can be performed without purifying the magnetic material after the n-1-th coating step. n is an integer of 2 or more, but when the coating step is performed k times, it is preferable that n is any integer of 2 to k. When n is any integer of 2 to k, the aqueous solution obtained by adding a rare earth compound to the aqueous solution in the coating step is used in all coating steps from the second time onwards.

[0035] The type of rare earth compound added to the aqueous solution in the (n-1)th coating step may be the same as or different from the rare earth compound contained in the aqueous solution in the nth coating step.

[0036] The concentration of the rare earth compound added to the aqueous solution in the n-1th coating step may be appropriately determined depending on the reaction time of the nth coating step and the type of rare earth compound. The concentration of the rare earth compound added to the aqueous solution in the n-1th coating step is preferably 0.01 to 50 times, more preferably 0.1 to 10 times, the content of the rare earth compound contained in the aqueous solution in the nth coating step. Within these ranges, unevenness in the thickness of the coating film can be reduced.

[0037] When the coating step is performed two or more times, the pH of the mixture of the aqueous solution and the magnetic material in the m-th coating step is preferably lower than the pH of the mixture of the aqueous solution and the magnetic material in the m-1-th coating step, and the difference is preferably 0.1 or more, more preferably 1 or more. In addition, the free phosphoric acid in the aqueous solution may decrease with the reaction between the phosphoric acid compound and the magnetic material, and the pH of the mixture of the aqueous solution and the magnetic material may increase. When the pH fluctuates during the reaction, the pH of the mixture of the aqueous solution and the magnetic material in the m-1-th coating step refers to the pH at the end of the m-1-th coating step. When the pH of the mixture of the aqueous solution and the magnetic material in the m-th coating step is lower than the m-1-th coating step, the efficiency of forming a coating containing a phosphorus compound on the magnetic material can be improved.

[0038] Although m is an integer of 2 or more, when the coating step is performed k times, m may be any integer between 2 and k. When m is any integer between 2 and k, in the second and all subsequent coating steps, an aqueous solution having a lower pH than the mixed solution in which the aqueous solution and the magnetic material are mixed in the previous coating step is used. Alternatively, when k is 3 or more, the pH in the first and second coating steps may be different, and the pH in the third and subsequent coating steps may be adjusted to be in the same pH range as in the second coating step.

[0039] In the m-th coating step, 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 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 adjusting the pH to 1 or more, the precipitation rate of the phosphorus compound containing a rare earth metal element can be reduced compared to the case of a pH lower than that, and the thickness of the coating film to be formed can be easily controlled. When the pH is 7 or higher, 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 adjusting the pH to 4.5 or lower, the precipitation rate of the phosphate can be made 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 can be used in combination depending on the purpose. A mixture of an inorganic acid and an organic acid may be used. When adjusting the pH, an inorganic acid or an organic acid may be added as needed during the coating process so that the pH falls within the above range. Since the pH rises rapidly in the initial stage of the coating process, it is preferable to shorten the interval at which the inorganic acid or organic acid for pH control is added.

[0040] 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, and is preferably adjusted 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 coating progresses, the pH fluctuation gradually becomes gentler, and the intervals between additions of inorganic or organic acid become longer, so that the end point of the reaction can be determined.

[0041] The n-th coating step may also serve as the m-th coating step, that is, in the n-th coating step, the pH adjustment may be carried out as the m-th coating step.

[0042] After the coating step, coating may be performed using an aqueous solution containing a phosphoric acid compound and a compound of a non-rare earth metal element. In this case, it is preferable that the method for producing a coated magnetic material includes a first coating step, and a second coating step after the first coating step, in which an aqueous solution containing a phosphoric acid compound and a compound of a non-rare earth metal element is mixed with the magnetic material to form a coating containing phosphoric acid and the non-rare earth metal element on the surface of the magnetic material. By performing the second coating step, the amount of the coating containing phosphorus formed on the surface of the magnetic material can be increased. Also, by performing the second coating step, the rare earth metal element can be biased toward the side of the coating closer to the magnetic material.

[0043] The type and concentration of the phosphoric acid compound in the aqueous solution used in the second coating step are as described above for the coating step. The non-rare earth metal element may be any other than the rare earth metal elements, and may include metal elements other than the rare earth metal elements and metalloid elements. Metal elements other than the rare earth metal elements may include alkali metal elements such as Li, Na, K, Rb, and Cs, alkaline earth metal elements such as Ca, Sr, Ba, and Mg, 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, Zn, Cd, and Al. Metalloid elements may include B, Al, Si, and Ge. Among these, metal elements are preferred, and in order to obtain a coated magnetic material with excellent heat resistance, metal elements whose Gibbs energy change (ΔG) of the oxidation reaction is -300 kJ / mol O2 or less in the temperature range when the coated magnetic material is heated (approximately 400°C or higher and approximately 700°C or lower) are more preferred, with transition metals being even more preferred, and Cr, W, Mn, Mo, Nb, and V being particularly preferred. Table 2 shows the Gibbs energy change of the oxidation reaction of metal oxides other than rare earths at 600°C. [Table 2]

[0044] Examples of the compound of the non-rare earth metal element include oxoacids, heteroacids, chlorides, hydroxides, nitrides, oxides, borides, etc. of the non-rare earth metal element, and oxoacids are preferred. The oxoacid may be a polyacid. Among these, metal oxoacid compounds are preferred, transition metal oxoacid compounds are more preferred, and oxoacid compounds of Cr, W, Mn, Mo, Nb, and V are even more preferred. The compounds of the non-rare earth metal elements listed above may be used alone or in combination of two or more.

[0045] The content of the compound of the non-rare earth metal element in the aqueous solution used in the second covering step is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass.

[0046] In the second covering step, 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.

[0047] In the second coating step, it is preferable to adjust the pH by adding an inorganic acid or an organic acid to the aqueous solution. The pH range when adjusting the pH can be 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 precipitation rate of the phosphate can be reduced compared to when it is less than that, and the thickness of the coating to be formed can be easily controlled. If the pH is 7 or more, the amount of phosphate precipitation decreases, which tends to result in insufficient coverage and increased loss, so it is preferable to set the pH below 7. By setting the pH to 4.5 or less, the precipitation rate of the phosphate can be set to a level that is not too slow. The acid to be added can 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 can be used in combination depending on the purpose. A mixture of an inorganic acid and an organic acid may be used. When adjusting the pH, an inorganic acid or an organic acid may be added as needed during the coating process so that the pH falls within the above range. Since the pH rises rapidly in the initial stage of the coating process, it is preferable to shorten the interval at which the inorganic acid or organic acid for pH control is added.

[0048] 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, and is preferably adjusted 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 coating progresses, the pH fluctuation gradually becomes gentler, and the intervals between additions of inorganic or organic acid become longer, so that the end point of the reaction can be determined.

[0049] After the coating step and, if necessary, the second coating step described above, a purification step of the coated magnetic material may be performed. In the purification step of the coated magnetic material, liquid components can be removed, for example, by heating at 100°C to 500°C or by filtering.

[0050] In addition, after the coating step and, if necessary, the above-mentioned second coating step, a coating fixing step may be performed. In the coating fixing step, the purified coated 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 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.

[0051] <<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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] When pressing, the coated magnetic material may be pressed alone. When pressing, the coated 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 magnetic material. When the amount of binder used is within the above range, a molded product having excellent mechanical strength and small losses such as iron loss can be obtained.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] <<Coated magnetic materials>> The coated magnetic material of this embodiment is characterized by having a magnetic material that is a soft magnetic material, and a coating containing a rare earth metal element, phosphorus, and oxygen provided on the surface of the magnetic material. The coating can contain a phosphorus compound containing a rare earth metal element, and the phosphorus compound may be a phosphate. The coating may have an oxide that does not contain a rare earth metal element, and in that case, the phosphorus compound containing a rare earth metal element does not have to be a phosphate. Examples of rare earth metal elements include Ce, Nd, Sm, La, Dy, Y, and Pr, and Ce, Nd, Sm, La, and Dy are preferred. The coated magnetic material of this embodiment can be obtained, for example, by the manufacturing method of the coated magnetic material described above, but may also be obtained by other manufacturing methods.

[0060] The particle diameter D50 of the coated 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 coated magnetic powder corresponds to 50%.

[0061] The thickness of the coating containing rare earth metal elements, phosphorus, and oxygen is preferably 2 nm to 10 μm, more preferably 5 nm to 500 nm, from the viewpoint of the insulating property and heat resistance of the coated magnetic material. 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.

[0062] It is preferable that the coating contains more oxygen than phosphorus. In this case, there is at least a portion of the coating in the thickness direction where oxygen is more than phosphorus. The portion of the coating in which oxygen is more than phosphorus is preferably 10% or more of the coating in the thickness direction, 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 may be 2 times or more, or may be 3 times or more. The upper limit of the oxygen content may be, for example, 10 times or less that of phosphorus.

[0063] The coating may contain non-rare earth metal elements other than phosphorus and oxygen, in addition to rare earth metal elements, phosphorus, and oxygen. Non-rare earth metal elements other than phosphorus and oxygen include metal elements other than rare earth metal elements, metalloid elements, H, C, N, O, F, P, S, Cl, Br, I, etc. Metal elements other than rare earth metal elements include alkali metal elements such as Li, Na, K, Rb, Cs, alkaline earth metal elements such as Ca, Sr, Ba, transition metal elements such as Fe, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Ru, Co, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al. Metalloid elements include B, Al, Si, Ge, etc. Among these, metal elements are preferred, and in order to obtain a coated magnetic material with excellent heat resistance, metal elements whose Gibbs energy change (ΔG) in the oxidation reaction is -300 kJ / mol O2 or less in the temperature range when the coated magnetic material is heated (approximately 400°C or higher and approximately 700°C or lower) are more preferred, with transition metals being even more preferred, and Cr, W, Mn, Mo, Nb, and V being particularly preferred. These elements contained in the coating may be derived from the magnetic material to be coated, or may be elements that were present during the coating formation reaction.

[0064] When the coating contains non-rare earth metal elements other than phosphorus and oxygen, the content of the non-rare earth metal elements and the rare earth metal elements in the coating preferably shows the maximum value of the non-rare earth metal elements and then the maximum value of the rare earth metal elements in the direction from the surface of the coating to the magnetic material. At this time, the insulation tends to be improved. When the thickness of the coating is T, the distance between the position showing the maximum value of the non-rare earth metal elements and the position showing the maximum value of the rare earth metal elements in the direction from the surface of the coating to the magnetic material is preferably 0.001×T or more and 0.99×T or less, and more preferably 0.1×T or more and 0.9×T or less. In the range of 0.1×T or more and 0.9×T or less, the insulation tends to be further improved.

[0065] The content of the non-rare earth metal element preferably decreases after reaching a maximum value in the direction from the surface of the coating toward the magnetic material, and then starts to increase. Such a distribution tends to improve the heat resistance of the coating. When forming the coating, the coating process is performed two or more times, and in the second or subsequent coating processes, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less, so that the coating can be formed so that the content of the non-rare earth metal element shows this distribution. 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 can be 0.001 times or more of the maximum value.

[0066] In the coating, each of the above elements may be present in either a crystalline or amorphous form. The concentration (atomic %) of each element in the coating can be measured by performing a composition analysis on the coated 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.

[0067] The soft magnetic material included in the coated magnetic material of this embodiment can be one described in the manufacturing method of the coated magnetic material, and includes oxide-based soft magnetic materials and metal-based soft magnetic materials. The 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. Metal-based soft magnetic materials include pure iron, Fe-X alloy (X: Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, 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. Fe-X alloys are made by reducing ferrite powder, which contains X components that are difficult to reduce with hydrogen, in a reducing gas containing hydrogen gas, and generating the first and second phases through a disproportionation reaction. Therefore, the surface area is large, and there is a fine compositional fluctuation on the surface. It is presumed that this special microstructure makes it easy to form a dense phosphate film or a passivation film with phosphorus compounds containing rare earth metal elements and non-rare earth metal elements such as Cr, W, Mn, Mo, Nb, and V. Compared to pure iron, for example, Fe-X alloys tend to have lower hysteresis loss and eddy current loss, and significantly improved iron loss.

[0068] The content of the rare earth metal element in the coated 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 product 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. By making the content of the rare earth metal element contained in the coated magnetic material 50% by mass or less, it is possible to suppress the decrease in the magnetic permeability of the coated magnetic material and the decrease in the characteristics. The content of the rare earth metal element in the coated magnetic material is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0069] The phosphorus content in the coated 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 magnetic material is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0070] The iron loss W of the compact containing the coated magnetic material can be 150 W / kg or less, preferably 100 W / kg or less, and more preferably 80 W / kg or less. The lower limit of the iron loss W may be 4 W / kg or more. The hysteresis loss W of the coated magnetic material h can be 70 W / kg or less, preferably 60 W / kg or less, and more preferably 45 W / kg or less. Hysteresis loss W h The lower limit of the eddy current loss W of the coated magnetic material may be 3.9 W / kg or more. e The eddy current loss W can be 90 W / kg or less, preferably 40 W / kg or less, and more preferably 35 W / kg or less. eThe lower limit of may 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.

[0071] <<Molded body>> The molded body of this embodiment is characterized by including the coated 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 powder magnetic 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 also be used as a soft magnetic part incorporated into 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.

[0072] The present disclosure includes the following aspects. (Section 1) A method for producing a coated magnetic material, comprising a coating step of mixing an aqueous solution containing a phosphate compound and a rare earth compound with a magnetic material that is a soft magnetic material, and forming a coating containing a phosphorus compound containing a rare earth metal element on the surface of the magnetic material.

[0073] (Section 2) The rare earth compound comprises one or more chlorides selected from the group consisting of Ce, Nd, Sm, La, and / or Dy; Item 1. A method for producing the covered magnetic material according to item 1.

[0074] (Section 3) In the coating step, an aqueous solution containing the rare earth compound is mixed with the magnetic material, and then the phosphoric acid compound is mixed therewith. Item 3. A method for producing a covered magnetic material according to item 1 or 2.

[0075] (Section 4) 4. The method for producing a covered magnetic material according to any one of items 1 to 3, wherein the covering step is carried out two or more times.

[0076] (Section 5) The aqueous solution in the n-th (n is an integer of 2 or more) coating step is The rare earth compound is added to the aqueous solution in the n-1th coating step. Item 5. A method for producing a covered magnetic material according to item 4.

[0077] (Section 6) The pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the m-th (where m is an integer of 2 or more) coating step is lower than the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the m-1-th coating step. Item 6. A method for producing a covered magnetic material according to item 4 or 5.

[0078] (Section 7) Item 7. The method for producing a covered magnetic material according to item 6, wherein in the m-th covering step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less.

[0079] (Section 8) Item 8. The method for producing a covered magnetic material according to item 7, wherein the adjustment is carried out for 10 minutes or more.

[0080] (Section 9) The coating step is a first coating step, and after the first coating step, A second coating step of mixing the magnetic material with an aqueous solution containing a phosphoric acid compound and a compound of a non-rare earth metal element to form a coating containing phosphorus and the non-rare earth metal element on the surface of the magnetic material, Item 4. A method for producing a covered magnetic material according to any one of items 1 to 3.

[0081] (Section 10) Item 10. The method for producing a covered magnetic material according to item 9, wherein the compound of the non-rare earth metal element is a metal oxo acid compound.

[0082] (Section 11) Item 11. The method for producing a covered magnetic material according to item 9 or 10, wherein in the second covering step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less.

[0083] (Section 12) Obtaining a coated magnetic material by the method according to any one of items 1 to 11; and a heating step of heating the covered magnetic material.

[0084] (Section 13) a step of pressing the coated magnetic material to obtain a pressed product before the heating step, The heating step is a step of heating the pressure-molded product. Item 13. A method for producing a molded article according to item 12.

[0085] (Section 14) A coated magnetic material comprising a magnetic material that is a soft magnetic material, and a coating that contains a rare earth metal element, phosphorus, and oxygen and is provided on the surface of the magnetic material.

[0086] (Section 15) Item 15. The coated magnetic material of item 14, wherein the coating contains more oxygen than phosphorus.

[0087] (Section 16) Item 16. The coated magnetic material according to item 14 or 15, wherein the coating further contains iron.

[0088] (Section 17) the coating contains phosphorus and a non-rare earth metal element other than oxygen; the contents of the non-rare earth metal elements and the rare earth metal elements in the coating, in a direction from the surface of the coating toward the magnetic material, exhibit a maximum value for the non-rare earth metal elements and then a maximum value for the rare earth metal elements; Item 17. The coated magnetic material according to any one of items 14 to 16.

[0089] (Section 18) Item 18. The coated magnetic material according to item 17, wherein the content of the non-rare earth metal element decreases after showing the maximum value in the direction from the surface of the coating toward the magnetic material, and then starts to increase.

[0090] (Section 19) Item 19. A molded body comprising the coated magnetic material according to any one of items 14 to 18. EXAMPLES

[0091] Examples will be described below. Unless otherwise specified, "%" is by weight.

[0092] (1) Evaluation method (1-1) Iron loss The coated magnetic material was charged into 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 heated in an Ar atmosphere at 600 ° C for 1 hour to produce a toroidal compact. In Example 16, 0.2 mass% of lubricant (1,2-bis (stearoylamino) ethane, zinc stearate) was added to the magnetic powder, charged into the same die, molded at 200 ° C and a pressure of 1.5 GPa, and then heat-treated at 520 ° C in an air atmosphere, and then heat-treated at 600 ° C for 1 hour in an Ar atmosphere 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.

[0093] (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 determined by line analysis from the outside to the inside of the coated magnetic material in steps of 0.791 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.

[0094] (2) Examples 1 to 15 and Comparative Examples 1 to 13 (2-1) Manufacturing of coated magnetic materials (ii) Preparation of soft magnetic materials: Example 1, Comparative Examples 1 and 3 As the soft magnetic materials (magnetic materials) of Example 1 and Comparative Examples 1 and 3, commercially available water-atomized iron powder was prepared.

[0095] (i-ii) Preparation of soft magnetic material: Comparative Example 2 As a soft magnetic material (magnetic material) of Comparative Example 2, a commercially available water-atomized iron powder (coated with iron phosphate) was prepared.

[0096] (i-iii) Preparation of soft magnetic materials: Examples 2 to 15 and Comparative Examples 4 to 13 As the soft magnetic materials (magnetic materials) of Examples 2 to 15 and Comparative Examples 4 to 13, 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 250 μm. The composition of the Fe-X alloys in Examples 2 to 8 and Comparative Examples 4 to 13 was Fe. 96 Ni 3.9 Mn 0.1 The composition of the Fe-X alloys in Examples 9 to 15 was Fe 95.5 Ni 4.4 Mn 0.1 It was.

[0097] (i-iv) Preparation of soft magnetic material: Example 16 As the soft magnetic material of Example 16, an Fe-X alloy was prepared in the same manner as in Examples 2 to 8 and Comparative Examples 4 to 13, except that the raw materials were MnSO4·5H2O (manganese (II) sulfate pentahydrate), NiSO4·6H2O (nickel (II) sulfate hexahydrate, FeSO4·7H2O (iron (II) sulfate heptahydrate), and the pH adjuster was NaOH, to prepare the soft magnetic material of Example 16.

[0098] (ii) Cleaning of soft magnetic materials 10 g of the soft magnetic material shown in Table 3 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.

[0099] (iii) First coating step The rare earth compound or non-rare earth compound shown in Table 3 was added to the washed soft magnetic material as an aqueous solution containing 10 mass% of the soft magnetic material, and stirred for 15 minutes. Next, the phosphoric acid compound shown in Table 3 was added as an aqueous phosphoric acid solution of pH 2 containing 40 mass% of the soft magnetic material, and stirred for 7 minutes. The final concentrations of each component were 1.6 mass% soft magnetic material, 0.16 mass% rare earth compound or non-rare earth compound, and 0.4 mass% phosphoric acid compound (PO4 equivalent). The pH of the treatment tank increased from 3 to 5.

[0100] In Example 3, Comparative Example 3, and Comparative Example 5, an aqueous solution containing a rare earth compound or a non-rare earth compound was not added, and only an aqueous phosphoric acid solution was added.

[0101] (iv) Second coating step The rare earth compound shown in Table 3 was added as an aqueous solution containing 10% by mass of the soft magnetic material, and the reaction mixture was stirred for 30 minutes while controlling the pH of the reaction mixture to be in the range of 2.5±0.1 by adding 6% by mass of hydrochloric acid from time to time.

[0102] (v) Drying and baking The soft magnetic material after the second covering 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.

[0103] (2-2) Production of Molded Products The obtained coated magnetic material was used to manufacture a molded body for iron loss evaluation by the method described above in the iron loss evaluation method. Also, the obtained coated magnetic materials of Examples 10 and 16 were used to manufacture a molded body for coating evaluation by the method described above in the coating thickness and atomic concentration evaluation method.

[0104] The iron loss (hysteresis loss and eddy current loss) of the obtained compact for iron loss evaluation was measured. The results are shown in Table 3.

[0105] [Table 3]

[0106] In the columns for the first and second coating steps in Table 3, test examples in which these steps were performed are marked with ◯, and test examples in which these steps were not performed are marked with -. In Comparative Example 1 (without phosphate treatment), Comparative Example 2 (commercially available phosphorus-coated magnetic material), and Comparative Example 3 (without rare earth compound), the iron loss was large. In Example 1, which used the same soft magnetic material, the iron loss was reduced.

[0107] The iron loss was reduced in Examples 2 to 15 using the same soft magnetic material compared to Comparative Example 4 (without phosphate treatment), Comparative Example 5 (without rare earth compound), and Comparative Examples 6 to 13. In particular, the iron loss was significantly reduced in Examples 9 to 15, which were subjected to a coating process using a non-rare earth compound.

[0108] The surface of a molded body for coating evaluation using the coated magnetic material of Example 10 was observed by STEM-EDX. The obtained STEM image is shown in FIG. 1. FIG. 1 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. 1 are shown in FIGS. 2 and 3. FIG. 3 is an enlarged view of the 0 to 40 atomic % region in FIG. 2.

[0109] In Figures 1 to 3, the thickness of the coating on the magnetic material surface was about 200 nm. In Figure 3, O was more 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 the sodium molybdate salt added in the coating process, and Fe originates from the magnetic material.

[0110] 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 4A and 4B. Figure 4A 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. In this EDX analysis, the screen was divided into 512 x 512 pixels with a side of 3 nm, and the electron beam diameter was narrowed to 1 nm for the center of each pixel to measure the amount of characteristic X-rays.

[0111] Fig. 4B is a histogram showing the distribution of Mn content. In Fig. 4B, 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 Fig. 4B), 0.05 atomic % or more and less than 0.1 atomic % (shown as 0.05-0.1 on the horizontal axis in Fig. 4B), 0.1 atomic % or more and less than 0.15 atomic % (shown as 0.1-0.15 on the horizontal axis in Fig. 4B), 0.15 atomic % or more and less than 0.2 atomic % (shown as 0.15-0.2 on the horizontal axis in Fig. 4B), and 0.2 atomic % or more (shown as 0.2+ on the horizontal axis in Fig. 4B), and the distribution of Mn content is shown by showing the number of pixels having each composition as a percentage (called abundance ratio). From Fig. 4B, it can be seen that the percentage of pixels corresponding to the first phase, which has 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 is about 50% of the total, which can be said to be the percentage of the second phase, which has a Mn content higher than that of the first phase. From Fig. 4A and Fig. 4B, it can be seen that the Fe-X alloy, which is the soft magnetic material used in the coated magnetic material of Example 16, is phase-separated into the first phase and the second phase.

Claims

1. A method for producing a coated magnetic material, comprising a coating step of mixing an aqueous solution containing a phosphate compound and a rare earth compound with a magnetic material that is a soft magnetic material, and forming a coating containing a phosphorus compound containing a rare earth metal element on the surface of the magnetic material.

2. The rare earth compound includes one or more chlorides selected from the group consisting of Ce, Nd, Sm, La, and Dy; A method for producing the covered magnetic material according to claim 1.

3. In the coating step, an aqueous solution containing the rare earth compound is mixed with the magnetic material, and then the phosphoric acid compound is mixed therewith. A method for producing the covered magnetic material according to claim 1 or 2.

4. The method for producing a covered magnetic material according to claim 1 or 2, wherein the covering step is carried out two or more times.

5. The aqueous solution in the n-th coating step (where n is an integer of 2 or more) The rare earth compound is added to the aqueous solution in the n-1th coating step. A method for producing the covered magnetic material according to claim 4.

6. The pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the m-th (where m is an integer of 2 or more) coating step is lower than the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the (m-1)-th coating step. A method for producing the covered magnetic material according to claim 4.

7. 7. The method for producing a covered magnetic material according to claim 6, wherein in the m-th covering step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less.

8. The method for producing a covered magnetic material according to claim 7, wherein the conditioning is carried out for 10 minutes or more.

9. The coating step is a first coating step, and after the first coating step, A second coating step of mixing the magnetic material with an aqueous solution containing a phosphoric acid compound and a compound of a non-rare earth metal element to form a coating containing phosphoric acid and the non-rare earth metal element on a surface of the magnetic material, A method for producing the covered magnetic material according to claim 1 or 2.

10. The method for producing a covered magnetic material according to claim 9, wherein the compound of the non-rare earth metal element is a metal oxo acid compound.

11. The method for producing a covered magnetic material according to claim 9 , wherein in the second covering step, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less.

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

13. a step of pressing the coated magnetic material to obtain a pressed product before the heating step, The heating step is a step of heating the pressure-molded product. A method for producing the molded article according to claim 12.

14. A coated magnetic material comprising a magnetic material that is a soft magnetic material, and a coating that contains a rare earth metal element, phosphorus, and oxygen and is provided on the surface of the magnetic material.

15. 15. The coated magnetic material of claim 14, wherein there is more oxygen than phosphorus in the coating.

16. 16. The coated magnetic material of claim 14 or 15, wherein the coating further comprises iron.

17. the coating contains phosphorus and a non-rare earth metal element other than oxygen; the contents of the non-rare earth metal elements and the rare earth metal elements in the coating, in a direction from the surface of the coating toward the magnetic material, exhibit a maximum value for the non-rare earth metal elements and then a maximum value for the rare earth metal elements; 16. The coated magnetic material of claim 14 or 15.

18. 18. The coated magnetic material according to claim 17, wherein the content of the non-rare earth metal element decreases after exhibiting the maximum value in a direction from the surface of the coating toward the magnetic material, and then begins to increase.

19. A molded article comprising the coated magnetic material according to claim 14 or 15.

Images