Dust core, inductor, and dust core manufacturing method

Abstract

A dust core (12) comprises: a magnetic powder formed of a plurality of magnetic particles (15); and a binder (18) that binds the plurality of magnetic particles (15) to each other and contains elemental Si. The plurality of magnetic particles (15) each have a metal particle (16) and an oxide layer (17) that covers the surface of the metal particle (16) and that contains elemental Si. The elemental Si concentration of the oxide layer (17) is higher than the elemental Si concentration of the binder (18).

Description

Powder magnetic core, inductor, and method for manufacturing powder magnetic core

[0001] The present disclosure relates to a powder magnetic core, an inductor, and a method for manufacturing a powder magnetic core.

[0002] In various electronic devices, a step-up / step-down circuit for adjusting a power supply voltage, a DC / DC converter circuit, and the like are used as drive circuits for the electronic devices. Inductors such as choke coils and transformers are used in these circuits. Further, in order to cope with the size reduction and large current of electronic devices, there has been known an inductor using a powder magnetic core produced by pressure-molding metal magnetic powder having a higher saturation magnetic flux density than ferrite as an inductor. For example, since an AI server consumes large power, an inductor used in the AI server is required to have higher conversion efficiency.

[0003] In order to improve the conversion efficiency of an inductor, a powder magnetic core used for the inductor is required to have high magnetic permeability and low magnetic loss. For example, when particles of metal magnetic powder come into contact with each other, magnetic loss increases due to eddy current loss, so it is required to suppress contact between particles of metal magnetic powder.

[0004] Patent Document 1 discloses a magnetic core characterized in that a Si-containing layer exists in grain boundaries present between Fe—Si—Al-based alloy particles or Fe—Si—Cr-based alloy particles.

[0005] Japanese Unexamined Patent Publication No. 2014-143301

[0006] In the technique described in Patent Document 1, forming the Si-containing layer at the grain boundaries suppresses contact between particles of the metal magnetic powder, so that a reduction in magnetic loss of the powder magnetic core can be expected. However, further improvement in performance of powder magnetic cores requires an increase in the magnetic permeability of the powder magnetic core.

[0007] Therefore, the present disclosure provides a powder magnetic core or the like having high magnetic permeability and low magnetic loss.

[0008] A compacted magnetic core according to one aspect of the present disclosure comprises a magnetic powder composed of a plurality of magnetic particles and a binder containing Si elements that binds the plurality of magnetic particles together, wherein each of the plurality of magnetic particles has a metal particle and an oxide layer containing Si elements that covers the surface of the metal particle, and the Si element concentration of the oxide layer is higher than the Si element concentration of the binder.

[0009] An inductor according to one aspect of the present disclosure comprises the powdered magnetic core and a coil portion.

[0010] A method for manufacturing a compacted magnetic core according to one aspect of the present disclosure includes the steps of: forming an oxide layer containing Si elements on the surface of a plurality of metal particles constituting a metal powder using tetraalkoxysilane to obtain magnetic powder; mixing the obtained magnetic powder with a silicone resin to obtain granulated powder; pressure molding the obtained granulated powder to obtain a molded body; and annealing the obtained molded body.

[0011] According to this disclosure, it is possible to provide a powder core with high magnetic permeability and low magnetic loss.

[0012] Figure 1A is a perspective view showing the configuration of an inductor according to an embodiment. Figure 1B is an exploded perspective view showing the configuration of an inductor according to an embodiment. Figure 2 is an enlarged view of a part of the cross-section of a compacted magnetic core according to an embodiment. Figure 3 is a cross-sectional view of magnetic powder according to an embodiment. Figure 4 is a schematic diagram showing an example of the molecular structure of a fluorine-based oligomer. Figure 5 is a flowchart showing the method for manufacturing a compacted magnetic core according to an embodiment. Figure 6 is a flowchart showing the method for manufacturing magnetic powder according to an embodiment. Figure 7 is a perspective view showing the configuration of an inductor according to a modified example of the embodiment. Figure 8 is a cross-sectional view showing the configuration of an inductor according to a modified example of the embodiment. Figure 9 is another cross-sectional view showing the configuration of an inductor according to a modified example of the embodiment. Figure 10 is a cross-sectional view for explaining the method for manufacturing an inductor according to a modified example of the embodiment. Figure 11 is a diagram showing a STEM image of a compacted magnetic core in an example. Figure 12 is a diagram showing the measurement results of the elemental concentration distribution of the compacted magnetic core in an example. Figure 13 is a diagram showing the measurement results of each elemental concentration in the silicon oxide layer. Figure 14 is an enlarged view showing the measurement results of the F element concentration in the silicon oxide layer. Figure 15 shows the relationship between applied pressure and volume resistivity in magnetic powder using Fe-Si-Cr alloy metal powder. Figure 16 shows the relationship between applied pressure and volume resistivity in magnetic powder using Fe-Ni alloy metal powder. Figure 17 shows the relationship between silicon oxide content and volume resistivity in magnetic powder. Figure 18 shows the relationship between fluorine-based oligomer content and volume resistivity in magnetic powder using Fe-Si-Cr alloy metal powder. Figure 19 shows the relationship between fluorine-based oligomer content and volume resistivity in magnetic powder using Fe-Ni alloy metal powder.

[0013] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0014] The embodiments described below are all specific examples of this disclosure. The numerical values, shapes, materials, components, arrangement positions of components, connection configurations, steps (processes), and the order of steps (processes) shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, any components in the following embodiments that are not described in an independent claim will be described as optional components.

[0015] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, for example, the scale may not necessarily match in each figure. Also, in each figure, substantially identical components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0016] Furthermore, in this specification, terms indicating relationships between elements such as parallel or orthogonal, terms indicating the shape of elements such as rectangles or cuboids, and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as differences of a few percent.

[0017] (Embodiments) The following describes the magnetic powder according to the embodiment, the compacted magnetic core using the magnetic powder, and the inductor using the compacted magnetic core.

[0018] [Configuration] First, the configuration of the inductor according to this embodiment will be explained with reference to Figures 1A, 1B, and 2.

[0019] Figure 1A is a perspective view showing the configuration of the inductor 1 according to this embodiment. Figure 1B is an exploded perspective view showing the configuration of the inductor 1 according to this embodiment. Figure 2 is an enlarged view of a part of the cross-section of the compacted magnetic core 12 according to this embodiment.

[0020] The inductor 1 according to this embodiment consists of a magnetic core (dust core) formed from a powdered magnetic core 12 and a coil portion arranged inside the magnetic core. In this embodiment, the inductor 1 is described as one example of the use of the powdered magnetic core 12, but the powdered magnetic core 12 can be used simply as a magnetic material, and its use is not limited to the inductor 1 according to this embodiment.

[0021] As shown in Figures 1A and 1B, the inductor 1 comprises two powdered magnetic cores 12, a conductor 13, and two coil supports 14. The two powdered magnetic cores 12, which are two divided magnetic cores, form a magnetic core, and the conductor 13 and the two coil supports 14 form a coil portion.

[0022] The compacted magnetic core 12 comprises a base 12a and a cylindrical core portion 12b formed on one side of the base 12a. Furthermore, two opposing sides of the four sides constituting the base 12a have wall portions 12c that rise from the edge of the base 12a. The core portion 12b and the wall portions 12c are at the same height from one side of the base 12a. Each of the two compacted magnetic cores 12 is a compacted molded body formed by pressurizing magnetic powder into a predetermined shape.

[0023] The two compacted magnetic cores 12 are arranged so that their respective core portions 12b and wall portions 12c are in contact with each other. At this time, a conductor 13 is arranged so as to surround the core portion 12b. The conductor 13 is incorporated into the compacted magnetic cores 12 via a coil support 14 and is enclosed within the two compacted magnetic cores 12.

[0024] As shown in Figure 1B, the two coil supports 14 each comprise an annular base portion 14a and a cylindrical portion 14b. The core portion 12b of the compacted magnetic core 12 is placed inside the cylindrical portion 14b, and the conductor 13 is placed on the outer circumference of the cylindrical portion 14b.

[0025] As shown in Figure 2, the compacted magnetic core 12 comprises magnetic powder composed of a plurality of magnetic particles 15 and a binder 18. Each of the plurality of magnetic particles 15 has a metal particle 16 and an oxide layer 17 that covers the surface of the metal particle 16. In the compacted magnetic core 12, the magnetic powder is pressure-molded, and the binder 18 is formed in a film-like manner on the surface of each magnetic particle 15 of the magnetic powder. The binder 18 covering the surface of adjacent magnetic particles 15 of the magnetic powder are bonded to each other. The binder 18 is placed between each magnetic particle 15 of the magnetic powder, and the metal particles 16 of each magnetic particle 15 of the magnetic powder are insulated from each other by the oxide layer 17 and the binder 18. Since the metal particles 16 are insulated not only by the binder 18 but also by the oxide layer 17, the magnetic loss of the compacted magnetic core 12 can be reduced.

[0026] Here, the magnetic powder according to this embodiment will be described with reference to Figure 3. Figure 3 is a cross-sectional view of the magnetic powder 10 according to this embodiment.

[0027] As shown in Figure 3, the magnetic powder 10 is composed of a plurality of magnetic particles 15. Each of the plurality of magnetic particles 15 has a metal particle 16 and an oxide layer 17 that covers the surface of the metal particle 16.

[0028] The metal particles 16 contain the element Fe. The metal particles 16 are useful for use under high currents because they have a higher saturation magnetic flux density compared to magnetic particles made of ferrite or the like. The metal particles 16 may contain, for example, 20 wt% or more of the element Fe. The metal particles 16 may also contain 50 wt% or more of the element Fe. For the metal particles 16, for example, pure metal Fe or a metallic magnetic material of the Fe-Ni or Fe-Co alloy system can be used. Among these, from the viewpoint of increasing the magnetic permeability of the compacted magnetic core 12, the metal particles 16 may be pure metal Fe particles or Fe-Ni alloy particles containing the elements Fe and Ni. When the metal particles 16 are Fe-Ni alloy particles, the constituent elements consist of Ni in an amount of 35 wt% to 80 wt%, and the remaining constituent elements are Fe and unavoidable impurities. Here, unavoidable impurities include, for example, Mn, P, S, C, etc. Furthermore, the metal particles 16 may also be Fe-Si-Cr alloy particles. When the metal particles 16 are Fe-Si-Cr alloy particles, the constituent elements consist, for example, Si in an amount of 1 wt% to 8 wt%, Cr in an amount of 2 wt% to 8 wt%, and Fe and unavoidable impurities as the remaining constituent elements.

[0029] Furthermore, the metallic magnetic material used for the metal particles 16 is not particularly limited, and the metal particles 16 may be made of metallic magnetic materials such as Fe-Si, Fe-Si-Al, Fe-Si-Cr-B, or Fe-Si-Cr-B-C alloys.

[0030] The method for producing the metal particles 16 according to this embodiment is not particularly limited, and various atomization methods and various grinding methods can be used.

[0031] The median diameter D50 of the metal particles 16 is, for example, 5 μm or more and 35 μm or less. By making the median diameter D50 of the metal particles 16 small in order to mitigate electric field concentration between particles, the insulating properties can be improved. Furthermore, by setting the median diameter D50 of the metal particles 16 to 35 μm or less, high packing efficiency and handling properties can be ensured. In addition, by setting the median diameter D50 of the metal particles 16 to 35 μm or less, eddy current losses can be reduced. The median diameter D50 of the metal particles 16 is the particle size when the cumulative value reaches 50% of the total particle size distribution of a metal powder composed of multiple metal particles 16 measured by laser diffraction scattering method, counting from the smallest particle size.

[0032] The oxide layer 17 covers the entire surface of the metal particles 16. The oxide layer 17 is formed directly on the surface of the metal particles 16. The oxide layer 17 contains the element Si. As will be described in detail later, the oxide layer 17 is a silicon oxide layer containing silicon oxide formed by, for example, the sol-gel method.

[0033] Furthermore, from the viewpoint of improving the insulating properties of the oxide layer 17 when the magnetic powder 10 is used under pressure, the oxide layer 17 may contain element F. The oxide layer 17 contains, for example, a fluorine-based oligomer, and the element F contained in the oxide layer 17 is derived from the fluorine-based oligomer. The fluorine-based oligomer is an oligomer of a fluorine compound that contains a fluorine-containing functional group such as a fluoroalkyl group. In this embodiment, from the viewpoint of effectively improving the insulating properties of the oxide layer 17, the relative permittivity of the fluorine-based oligomer is, for example, greater than 5. Also, from the viewpoint of suppressing eddy currents due to electric field concentration in the compacted magnetic core 12, the relative permittivity of the fluorine-based oligomer may be 15 or less, or 10 or less.

[0034] Figure 4 is a schematic diagram showing an example of the molecular structure of a fluorine-based oligomer. As shown in Figure 4, a fluorine-based oligomer has a molecular structure in which a fluorine-containing group Rf and a hydrophilic group Rh are bonded as side chains to a main chain, which is shown by the horizontal lines in Figure 4. The main chain is, for example, a hydrocarbon chain such as a methylene chain.

[0035] The fluorine-containing group Rf is a functional group containing fluorine, such as a fluoroalkyl group. A fluoroalkyl group is, for example, a fluoroalkyl group in which all hydrogen atoms of the alkyl group are replaced with fluorine. The number of carbon atoms in a fluoroalkyl group is, for example, 6 or less. When the number of carbon atoms in a fluoroalkyl group increases, the molecular chains of the fluoroalkyl group align and aggregate, canceling out the polarization. By keeping the number of carbon atoms in the fluoroalkyl group to 6 or less, the polarization is less likely to be canceled out, and the dielectric constant of the fluorine-based oligomer can be increased. The number of carbon atoms in the fluoroalkyl group may also be 3 or less. Furthermore, the fluorine-based oligomer may contain fluoroalkyl groups with different numbers of carbon atoms.

[0036] The hydrophilic group Rh is, for example, a functional group containing a hydroxyl group (-OH). This allows for a higher dielectric constant of the fluorine oligomer, and enables hydrogen bonding between the fluorine oligomer and the silicon oxide in the oxide layer 17, thereby increasing the stability of the oxide layer 17. In addition, in the oxide layer 17, the fluorine oligomer and the silicon alkoxide, which is a raw material for the silicon oxide, may undergo dehydration condensation via the hydrophilic group Rh, resulting in a bond between the fluorine oligomer and the silicon oxide.

[0037] Furthermore, the hydrophilic group Rh may have a silanol structure (Si-OH). Alternatively, the hydrophilic group Rh may have a siloxane chain (Si-O-Si). This further enhances the affinity between the fluorine-based oligomer and the silicon oxide in the oxide layer 17.

[0038] The F element concentration in the oxide layer 17 is highest on the surface of the oxide layer 17 (i.e., the surface opposite to the metal particle 16 side) within the oxide layer 17. As will be described in detail later, this results in a high concentration of hydrophobic components such as fluorine-based oligomers present on the surface of the oxide layer 17, thereby improving the insulating properties of the oxide layer 17. Furthermore, the improvement in the insulating properties of the oxide layer 17 makes it possible to increase magnetic permeability and reduce magnetic loss in the dust core 12. In the present specification, when comparing element concentrations within the oxide layer 17, the element concentration in the magnetic particles 15 is measured by performing elemental analysis every 2 nm in the depth direction from the surface of the oxide layer 17 in the state of the magnetic particles 15 before forming the dust core 12, using an X-ray Photoelectron Spectroscopy (XPS) analyzer. In addition, in the present specification, the element concentration measured using an XPS analyzer is the ratio (atomic %) of the amount of the element to be measured relative to the total amount of O element, Si element, and F element, and elements other than these are ignored in the calculation of element concentration.

[0039] In the oxide layer 17, the distribution of F element concentration in the depth direction may have a maximum inside the oxide layer 17. That is, the oxide layer 17 may include a portion where F element is localized not only on the surface but also inside the oxide layer 17.

[0040] Furthermore, the O element concentration in the oxide layer 17 is lowest on the surface of the oxide layer 17 within the oxide layer 17. This reduces the hydrophilicity of the surface of the oxide layer 17, increases hydrophobicity, and improves the insulating properties of the oxide layer 17.

[0041] In the oxide layer 17, the ratio of the weight of the fluorine-based oligomer to the weight of silicon oxide is, for example, 0.125 or more and 5 or less. This ratio may be 0.5 or more and 5 or less.

[0042] Furthermore, the weight ratio of silicon oxide in the oxide layer 17 relative to the metal particles 16 is, for example, 0.01 wt% or more and 1 wt% or less.

[0043] Referring again to Figure 2, in the compacted magnetic core 12, the thickness of the oxide layer 17 is, for example, 5 nm to 60 nm. By having an oxide layer thickness of 5 nm or more, contact between metal particles 16 can be suppressed, thereby suppressing the increase in magnetic loss due to the increase in eddy currents. Also, by having an oxide layer thickness of 60 nm or less, magnetic saturation of the metal particles 16 in the compacted magnetic core 12 can be suppressed, thereby improving the DC superposition characteristics of the compacted magnetic core 12. Alternatively, the thickness of the oxide layer 17 may be 5 nm to 40 nm. By having an oxide layer thickness of 40 nm or less, the proportion of metal particles 16 in the compacted magnetic core 12 can be increased, thereby increasing the magnetic permeability of the compacted magnetic core 12. The thickness of the oxide layer 17 can be adjusted, for example, by the amount of silicon alkoxide added to form the oxide layer 17, which will be described later.

[0044] The binder 18 is formed to cover the entire surface of the magnetic particles 15. The binder 18 contains the element Si. The Si element contained in the binder 18 originates from the silicone resin. The binder 18 includes the residue of the silicone resin after degreasing, as described later, as a component containing the element Si.

[0045] In the compacted magnetic core 12, the Si element concentration in the oxide layer 17 is higher than the Si element concentration in the binder 18. This suppresses the diffusion of oxygen components from outside the magnetic particles 15, such as oxygen components in the binder 18, into the metal particles 16 via the oxide layer 17, thereby suppressing the decrease in magnetic permeability due to oxidation of the metal particles 16 and increasing the magnetic permeability. In the compacted magnetic core 12, the Si element concentration in the oxide layer 17 is, for example, 28 atomic percent or more.

[0046] In this specification, when comparing the element concentration between the oxide layer 17 and the binder 18, the element concentration in the dust core 12 refers to the maximum value in the element concentration distribution of each of the oxide layer 17 and the binder 18 in the thickness direction of the oxide layer 17, which is measured by EDX (Energy Dispersive X-ray) on the cut surface of the dust core 12. However, when determining the maximum value in the oxide layer 17, the portion where the element concentration changes sharply near the interface between the oxide layer 17 and other adjacent constituent elements is excluded. Also, when determining the maximum value in the binder 18, the portion where the element concentration changes sharply near the interface between the binder 18 and other adjacent constituent elements is excluded. The element concentration distribution is measured by, for example, a STEM (Scanning Transmission Electron Microscope)-EDX analyzer. In addition, in this specification, the element concentration measured by EDX is the ratio (atomic %) of the amount of the element to be measured to the total amount of Si element, O element, C element and the metal elements contained in the metal particles 16, and elements other than these elements are ignored in the calculation of element concentration.

[0047] Furthermore, in the dust core 12, the O element concentration of the oxide layer 17 may be higher than the O element concentration of the binder 18. This can also suppress the decrease in magnetic permeability caused by oxidation of the metal particles 16 and increase the magnetic permeability. In the dust core 12, the O element concentration of the oxide layer 17 is, for example, 53 atomic % or more.

[0048] [Manufacturing Method] Next, the manufacturing method of the above dust core 12 will be described.

[0049] FIG. 5 is a flowchart showing the manufacturing method of the dust core 12 according to the present embodiment.

[0050] As shown in FIG. 5, in the manufacturing method of the dust core 12 according to the present embodiment, first, an oxide layer 17 containing Si element is formed on the surfaces of a plurality of metal particles 16 constituting metal powder, to prepare magnetic powder 10 composed of a plurality of magnetic particles 15 (step S10).

[0051] Here, an example of a method for manufacturing the magnetic powder 10 in step S10 will be described in detail. Figure 6 is a flowchart showing the method for manufacturing the magnetic powder 10 according to this embodiment.

[0052] As shown in Figure 6, in the production of the magnetic powder 10 according to this embodiment, first, a metal powder, a silicon alkoxide, and a fluorine-based oligomer are mixed in a solution to form an oxide layer 17 containing the fluorine-based oligomer on the surface of a plurality of metal particles 16 constituting the metal powder, thereby obtaining a slurry containing the magnetic powder 10 (step S11). In step S11, for example, the oxide layer 17 is formed on the surface of each metal particle 16 by the sol-gel method. In the example shown in Figure 6, step S11 includes the steps of adding a catalyst and a fluorine-based oligomer to the solvent (step S12), further adding the metal powder to the solvent (step S13), and further adding the silicon alkoxide to the solvent (step S14).

[0053] In step S12, for example, a base catalyst such as aqueous ammonia and a fluorine-based oligomer are added to an organic solvent such as ethanol or isopropyl alcohol and stirred. Details of the fluorine-based oligomer are as described above. For example, a liquid or semi-solid fluorine-based oligomer is used. After step S12, in step S13, for example, a metal powder composed of multiple metal particles 16 is further added to the organic solvent and stirred. After step S13, in step S14, for example, a tetraalkoxysilane as a silicon alkoxide is further added to the organic solvent and stirred. As a result, the hydrolyzed tetraalkoxysilane undergoes dehydration condensation, and an oxide layer 17 is formed on the surface of the metal particles 16. Examples of tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane. Through these steps, a slurry of magnetic powder 10 composed of multiple magnetic particles 15 is obtained. The oxide layer 17 thus formed contains a fluorine-based oligomer that tends to localize on the surface of the oxide layer 17, thus improving the insulating properties of the oxide layer 17.

[0054] Furthermore, by adding the catalyst and fluorine-based oligomer to the solvent before the silicon alkoxide, the fluorine-based oligomer is more easily incorporated into the oxide layer 17 during the process of forming the oxide layer 17 by the dehydration condensation of the silicon alkoxide, thereby improving the insulating properties of the oxide layer 17.

[0055] In step S11, the ratio of the weight of the fluorine oligomer added to the solution to the weight of the silicon oxide in the silicon alkoxide added to the solution is, for example, 0.125 or more and 5 or less. This ratio may also be 0.5 or more and 5 or less. Here, the weight of the silicon oxide in the silicon alkoxide is the weight assuming that all of the silicon alkoxide is converted to silicon oxide by dehydration condensation. In other words, the weight of the silicon oxide in the silicon alkoxide is the weight of the silicon alkoxide minus the theoretical weight of water that is lost due to dehydration condensation.

[0056] Furthermore, in step S11, the ratio of the weight of silicon oxide in the silicon alkoxide added to the solution to the weight of the metal powder added to the solution is, for example, 0.01 wt% or more and 1 wt% or less.

[0057] In step S11, as long as the oxide layer 17 can be formed, the order in which the materials are added to the solvent is not particularly limited. For example, steps S12 to S14 may be performed in parallel, with two or more of these steps being carried out in parallel, and the order may be changed.

[0058] Next, the slurry obtained in step S11 is subjected to solid-liquid separation to obtain magnetic powder 10 (step S15). For example, the slurry obtained in step S11 is filtered to separate the magnetic powder 10. Then, the magnetic powder 10 obtained in step S15 is dried (step S16). Through the above steps, the magnetic powder 10 according to this embodiment is manufactured. By manufacturing the magnetic powder 10 through steps S11, S15, and S16, a magnetic powder 10 in which an oxide layer 17 is formed on the surface of metal particles 16 can be obtained.

[0059] In this embodiment, by using tetraalkoxysilane to form the oxide layer 17, substantially only Si and O elements remain in the oxide layer 17 as components derived from tetraalkoxysilane due to hydrolysis, thus allowing for high concentrations of Si and O in the oxide layer 17. In forming the oxide layer 17, for example, only tetraalkoxysilane is used as the Si-containing material, but other materials such as trialkoxysilane may be further included in the Si-containing material, as long as the Si concentration in the oxide layer 17 does not fall below the Si concentration in the binder 18.

[0060] Referring again to Figure 5, next, the magnetic powder obtained in step S10 and the silicone resin are mixed to produce granular powder (step S20). This yields granular powder in which the magnetic powder and the silicone resin, which is a binder component for binding the magnetic particles 15 of the magnetic powder, are mixed. In the production of granular powder, resins other than silicone resin, such as acrylic resin, may be further mixed as a binder component. In addition, materials other than binder components, such as metal soap, may be further mixed as needed. Furthermore, the granular powder may be classified to obtain granular powder with particle sizes within a predetermined range.

[0061] Furthermore, when mixing magnetic powder and silicone resin, a solvent may be added and mixed. If a solvent is added, the solvent can be evaporated after mixing by heating at a temperature of, for example, 30°C to 100°C, and the granulated powder can be obtained by removing the solvent from the mixture. Examples of solvents include toluene, xylene, ethanol, isopropyl alcohol, acetone, or methyl ethyl ketone.

[0062] In the preparation of granulated powder, the ratio of silicone resin to magnetic powder is, for example, 0.5 wt% to 5 wt%.

[0063] The silicone resin has a polysiloxane skeleton as its main chain and hydrocarbon groups such as methyl groups as side chains. Therefore, although the silicone resin becomes a binder 18 through degreasing and annealing as described later, components containing element C remain in the binder 18, so the concentrations of element Si and element O in the binder 18 are lower than those in the oxide layer 17.

[0064] After step S20, the granulated powder produced in step S20 is pressure-molded into a predetermined shape to obtain a molded body (step S30). Specifically, in step S30, the granulated powder is placed in a molding die and compressed to produce a molded body. At this time, for example, 4 ton / cm ２ More than 12ton / cm ２ Uniaxial molding is performed under the following constant pressure. After molding, the silicone resin is cured as needed. Note that the silicone resin may not be cured at this point, and may be cured before degreasing, as described later, or by heating during degreasing.

[0065] The shape of the molded body is, for example, the shape of the compacted magnetic core 12 shown in Figure 1B. However, the shape of the molded body is not limited to this, and for example, the core portion 12b of the compacted magnetic core 12 may be a separate component.

[0066] Next, the molded body obtained in step S30 is degreased (step S40). In degreasing, for example, the molded body is heated at a temperature of 250°C to 450°C in a non-oxidizing atmosphere such as under nitrogen gas. This removes at least some of the organic components of the silicone resin contained in the molded body. Degreasing may also be performed under a predetermined oxygen partial pressure. The heating time in degreasing (the time spent processing at the target temperature) is, for example, 10 minutes to 120 minutes.

[0067] Next, the molded body degreased in step S40 is annealed (step S50). This yields the compacted magnetic core 12. The annealing in step S50 may be performed immediately after the degreasing in step S40.

[0068] By performing annealing, the strain in the molded body caused by the compression during pressure molding in step S30 is relieved. As a result, the magnetic properties can be improved.

[0069] In step S50, the molded body is heated to a temperature of, for example, 400°C to 1000°C. The heating temperature in annealing is higher than the heating temperature in degreasing. The heating temperature in annealing may be 600°C or higher. This effectively removes the distortion of the compacted magnetic core 12. Alternatively, the heating temperature in annealing may be 900°C or lower. This suppresses the decrease in electrical resistance due to the crystallization of silicon oxide.

[0070] Furthermore, in step S50, annealing is performed under a non-oxidizing atmosphere. Annealing may be performed under a hydrogen gas or under a mixed gas of hydrogen gas and an inert gas such as nitrogen gas, under a non-oxidizing atmosphere containing hydrogen gas. This suppresses the oxidative diffusion of metal elements contained in the metal particles 16 into the oxide layer 17 and binder 18, thereby reducing, for example, the Fe element concentration in the oxide layer 17 and binder 18. As a result, the insulating properties of the oxide layer 17 and binder 18 can be improved. In the compacted magnetic core 12, the Fe element concentration in the oxide layer 17 and binder 18 is, for example, 3 atomic percent or less. The heating time in annealing (the time spent processing at the target temperature) is, for example, 10 minutes or more and 120 minutes or less.

[0071] Alternatively, step S40 may be omitted, and annealing may be performed in step S50 on the molded body that has not been degreased.

[0072] When manufacturing the inductor 1, the obtained powdered magnetic core 12 is assembled with the conductor 13 and coil support 14 described above to complete the inductor 1. In assembling the inductor 1, for example, first a coil is formed by winding the conductor 13 a predetermined number of times. Next, the powdered magnetic core 12, conductor 13 and coil support 14 are assembled. As shown in Figure 1B, the conductor 13 is arranged to surround the core portion 12b of the two powdered magnetic cores 12. At this time, the cylindrical portions 14b of the two coil support 14 are positioned between the conductor 13 and the respective core portions 12b of the two powdered magnetic cores 12. Also, the annular base portions 14a of the two coil support 14 are positioned between the conductor 13 and the respective bases 12a of the two powdered magnetic cores 12. At this time, the ends of the cylindrical portions 14b of the two coil support 14, opposite to the side where the annular base portion 14a is formed, are positioned to abut each other.

[0073] Furthermore, the two powder cores 12 are arranged so that their respective core portions 12b and wall portions 12c are in contact with each other. In this way, the inductor 1 is assembled by incorporating the conductor 13 into the powder core 12 via the coil support 14. This completes the configuration in which the conductor 13 is wound around the core portion 12b of the powder core 12. In other words, the powder core 12 becomes a magnetic core in which the core portion 12b penetrates the conductor 13 in the direction of the winding axis of the conductor 13. Furthermore, the assembled inductor 1 may be molded with a resin material.

[0074] As described above, the method for manufacturing the compacted magnetic core 12 according to this embodiment includes the steps of: forming an oxide layer 17 containing Si elements on the surface of a plurality of metal particles 16 constituting the metal powder using tetraalkoxysilane to obtain magnetic powder (step S10); mixing the obtained magnetic powder with a silicone resin to obtain granulated powder (step S20); pressure molding the obtained granulated powder to obtain a molded body (step S30); and annealing the obtained molded body (step S50).

[0075] This results in a compacted magnetic core 12 in which magnetic particles 15 are bound together by a binder 18 containing Si elements. Furthermore, by using tetraalkoxysilane to form the oxide layer 17, the Si element concentration of the oxide layer 17 can be increased. As a result, the diffusion of oxygen components from outside the magnetic particles 15, such as oxygen components in the binder 18, to the metal particles 16 via the oxide layer 17 is suppressed, thereby suppressing the decrease in magnetic permeability due to oxidation of the metal particles 16 and increasing the magnetic permeability of the compacted magnetic core 12. In addition, the magnetic particles 15 of the magnetic powder, in which the metal particles 16 are covered with an oxide layer 17 that does not utilize the alloy components of the metal particles 16, are bound together by the binder 18. As a result, contact between the metal particles 16 is suppressed, reducing the eddy current loss of the compacted magnetic core 12 and lowering the magnetic loss of the compacted magnetic core 12.

[0076] [Modified Version] Next, an inductor according to a modified version of the embodiment will be described. The inductor according to the modified version of the embodiment uses a powdered magnetic core 12 as the magnetic core, similar to the inductor 1 according to the embodiment. In the following description of the modified version, the differences from the embodiment will be explained in detail, and the explanation of the common points will be omitted or simplified.

[0077] Figure 7 is a perspective view showing the configuration of the inductor 2 according to this modified example. Figures 8 and 9 are cross-sectional views showing the configuration of the inductor 2 according to this modified example. Figure 8 shows a cross-section when the inductor 2 is cut along the line VIII-VIII in Figure 7. Figure 9 shows a cross-section when the inductor 2 is cut along the line IX-IX in Figure 7.

[0078] As shown in Figures 7 to 9, the inductor 2 comprises a powdered magnetic core 12, a coil conductor 21, and a terminal portion 26.

[0079] The coil conductor 21 is a coil portion having a metal conductor such as a copper plate. The coil conductor 21 is formed in a single layer, for example, by punching a metal plate in a straight line. An insulating coating may be formed on the surface of the coil conductor 21. The coil conductor 21 is enclosed within the compacted magnetic core 12.

[0080] The terminal portion 26 is the ends of the coil conductor 21 that is led out from the powdered magnetic core 12. The outer circumference of the terminal portion 26 is solder-plated and is formed by bending it along the side and bottom of the powdered magnetic core 12.

[0081] Inductor 2 can be manufactured through steps S10 to S50 in the same way as inductor 1, except that in step S30, the coil conductor 21 is insert molded so that it is placed inside the compacted magnetic core 12.

[0082] Figure 10 is a cross-sectional view illustrating a method for manufacturing the inductor 2 according to this modified example. As shown in Figure 10, in the manufacturing of the inductor 2, in step S30, a flat coil conductor 21 and the granulated powder 22 obtained in step S20 are placed in a molding die 29 so as to sandwich the coil conductor 21. Then, the upper and lower punches 20 are used to press-mold the molded body in the direction of the arrows in Figure 10. After the obtained molded body is degreased and annealed (steps S40 and S50) to obtain a powder core 12, solder plating is applied to both ends of the coil conductor 21 led out from the powder core 12 as appropriate, and the terminal portion 26 is formed by bending it along the bottom surface from the side of the powder core 12. This gives rise to the inductor 2.

[0083] [Evaluation of Compacted Magnetic Cores] Next, the evaluation results of the compacted magnetic cores according to the embodiment will be described. Specifically, compacted magnetic cores were manufactured as shown below, and the manufactured compacted magnetic cores were evaluated. Note that this embodiment is not limited in any way to the evaluation described below.

[0084] <Preparation of Compacted Magnetic Cores> First, we will explain how the compacted magnetic core samples used in the evaluation were prepared.

[0085] (1) Examples In the preparation of the compacted magnetic core sample in the example, first, 5 g of 9% aqueous ammonia and 0.1 g of fluorine-based oligomer were added to 15 g of ethanol and stirred for 5 minutes. Then, 100 g of Fe-Ni alloy (Ni is 50 wt%) metal powder (D50 = 10 μm) was added and stirred for another 5 minutes. 1 g of tetraethoxysilane was then added to the solution and stirred for 60 minutes to form a silicon oxide layer containing silicon oxide on the surface of the metal particles of the metal powder, thereby preparing a magnetic powder slurry. The magnetic powder obtained from the resulting slurry was then filtered and dried to obtain the magnetic powder. The fluorine-based oligomer used had a structure in which the fluorine-containing group Rf (see Figure 4) was a fluoroalkyl group with 3 or fewer carbon atoms, and the hydrophilic group Rh (see Figure 4) had a siloxane chain containing a silanol structure.

[0086] Next, the obtained magnetic powder was mixed with 1 wt% silicone resin relative to the magnetic powder and toluene. Then, the mixture was heated to remove the toluene, and then pulverized to produce granular powder.

[0087] The prepared granulated powder was heated at room temperature at a rate of 8 ton / cm². ２ A ring core with an outer diameter of 14.4 mm, an inner diameter of 10.3 mm, and a thickness of 4.4 mm was fabricated by pressure molding with the specified pressure, followed by curing of the resin. Furthermore, the obtained ring core was degreased by heating it under nitrogen gas at 400°C for 30 minutes, and then annealed by heating it under hydrogen gas at 750°C for 30 minutes to produce a sample of a ring-shaped compacted magnetic core.

[0088] (2) Comparative Example In the preparation of the compacted magnetic core sample in the comparative example, granulated powder was prepared in the same manner as in the example, except that metal powder (D50 = 10 μm) of Fe-Si alloy (Si content 2.5 wt%) was used as the magnetic powder. Then, using the granulated powder, a ring-shaped compacted magnetic core sample was prepared in the same manner as in the example, except that an oxide layer containing silicon oxide containing Si elements derived from the metal particles was formed on the surface of the metal particles of the metal powder by annealing in an air atmosphere.

[0089] <Method for Calculating Permeability> The permeability was determined by measuring the inductance L of a ring-shaped powder core at an applied magnetic field of 0 Ørsted (Oe) using an LCR meter, and calculating the initial permeability (the permeability μi shown below) from the following equation (1) (measurement frequency 100 kHz).

[0090] μi=(L×le) / (μ0×Ae×n ２ ) ... (1)

[0091] Note that le represents the effective magnetic path length, μ0 represents the permeability of vacuum, Ae represents the cross-sectional area, and n represents the number of turns of the measuring coil.

[0092] <Method for Calculating Magnetic Loss> Magnetic loss was measured for a ring-shaped powder core using a B-H analyzer under the conditions of Bm = 25 mT and frequency = 1 MHz.

[0093] <Measurement of elemental concentration distribution and oxide layer thickness> The elemental concentration distribution and oxide layer thickness were measured for the compacted magnetic cores prepared in the examples and comparative examples. The elemental concentration distribution in the thickness direction of the oxide layer formed on the surface of the metal particles was measured using STEM-EDX. The thickness of the oxide layer was also measured using STEM images.

[0094] The measurement results of the specific elemental concentration distribution will be explained using the compacted magnetic core in the example as an example. Figure 11 is a STEM image of the compacted magnetic core in the example. Figure 11 shows a STEM image of the cross-section of the compacted magnetic core in the example. Figure 12 is a diagram showing the measurement results of the elemental concentration distribution of the compacted magnetic core in the example. Figure 12 shows the distribution of elemental concentrations in the thickness direction of the oxide layer near the surface of the metal particles shown in Figure 11. In Figure 12, the horizontal axis shows the position in the thickness direction of the oxide layer with a predetermined position within the metal particle as the reference (0 nm), and the vertical axis shows the elemental concentration of each element. The measured elemental concentrations are the ratio (atomic %) of the amount of each element to the total amount of Fe, Ni, Si, O, and C. Furthermore, the elemental concentrations were measured every 0.35 nm in the thickness direction of the oxide layer.

[0095] As shown in Figure 12, in the compacted magnetic core of the example, the Si element concentration in the oxide layer is higher than the Si element concentration in the binder. Furthermore, in the compacted magnetic core of the example, the O element concentration in the oxide layer is higher than the O element concentration in the binder.

[0096] <Evaluation Results> The permeability and magnetic loss of the compacted magnetic cores fabricated in the examples and comparative examples were evaluated using the method described above. The results are shown in Table 1. Some of the conditions for fabricating the compacted magnetic cores are also shown in Table 1. The elemental concentrations in Table 1 are the maximum values ​​in the distribution of elemental concentrations in the oxide layer and the binder in the thickness direction of the oxide layer. However, when determining the maximum value in the oxide layer, the portion near the interface with other adjacent components where the elemental concentration changes abruptly is excluded. Similarly, when determining the maximum value in the binder, the portion near the interface with other adjacent components where the elemental concentration changes abruptly is excluded. In Figure 12, a dashed line extends vertically from the portion where the elemental concentration distribution is considered to have a maximum value.

[0097]

[0098] As shown in Table 1, the permeability of the compacted magnetic core in the example is higher than that of the compacted magnetic core in the comparative example. This is thought to be because the high concentrations of Si and O in the oxide layer of the compacted magnetic core in the example suppress the diffusion of oxygen into the metal particles, thereby suppressing the decrease in permeability due to oxidation of the metal particles. Furthermore, the magnetic loss of the compacted magnetic core in the example is lower than that of the compacted magnetic core in the comparative example. This is thought to be because the metal particles are covered with an oxide layer that does not utilize the alloy components of the metal particles, suppressing contact between the metal particles and reducing eddy current loss.

[0099] [Elemental Concentration of Silicon Oxide Layer] Next, the measurement results of the elemental concentration of the silicon oxide layer in the magnetic powder according to this embodiment will be described. Specifically, magnetic powder was prepared as shown below, and the elemental concentration of the silicon oxide layer in the obtained magnetic powder was measured. Note that this embodiment is not limited in any way to the measurement results shown below.

[0100] <Preparation of Magnetic Powder> The magnetic powder used for the measurement was prepared as follows.

[0101] First, 10% aqueous ammonia and a fluorinated oligomer were added to isopropyl alcohol and stirred for 5 minutes. Then, metal powder of Fe-Ni alloy (Ni content 50 wt%) (D50 = 12 μm) was added and stirred for another 5 minutes. Tetraethoxysilane was then added to the solution and stirred for 60 minutes. Through these steps, a silicon oxide layer was formed on the surface of the metal particles of the metal powder, and a slurry containing magnetic powder, each consisting of multiple magnetic particles having a metal particle and a silicon oxide layer, was prepared. The magnetic powder from the obtained slurry was then filtered and dried to obtain magnetic powder. In this process, the weight ratios of aqueous ammonia, fluorinated oligomer, and silicon oxide in the silicon alkoxide to the weight of the metal powder were 5 wt%, 0.375 wt%, and 0.3 wt%, respectively. Furthermore, the fluorine-based oligomers used were those in which the fluorine-containing group Rf (see Figure 4) is a fluoroalkyl group having 3 or fewer carbon atoms, and the hydrophilic group Rh (see Figure 4) has a siloxane chain containing a silanol structure.

[0102] <Measurement of Elemental Concentration in Silicon Oxide Layer> The magnetic powder prepared as described above was analyzed using an XPS analyzer (PHI 5000) manufactured by ULVAC-PHI. The elemental concentrations of oxygen (O), silicon (Si), and fluorine (F) in the silicon oxide layer were measured by performing elemental analysis at 2 nm intervals from the surface in the depth direction. The measured elemental concentrations are expressed as the percentage (atomic %) of each element relative to the total amount of oxygen, silicon, and fluorine.

[0103] The measurement results are shown in Table 2, Figure 13, and Figure 14. Figure 13 shows the measurement results of the elemental concentrations in the silicon oxide layer. Figure 14 is a magnified view of the measurement results of the elemental concentration of the silicon oxide layer. In Figures 13 and 14, the vertical axis represents elemental concentration, and the horizontal axis represents the distance from the surface (i.e., depth relative to the surface). A distance of zero from the surface represents the elemental concentration at the surface of the silicon oxide layer.

[0104]

[0105] As shown in Table 2, Figures 13 and 14, the concentration of element F in the silicon oxide layer is highest at the surface of the silicon oxide layer. Therefore, it can be seen that fluorine-based oligomers within the silicon oxide layer are locally distributed on the surface. This is thought to be because the fluorine-containing group Rf (see Figure 4) of the fluorine-based oligomer is easily migrated to the surface of the silicon oxide layer due to the difference in surface free energy. In addition, the hydrophilic group Rh (see Figure 4) of the fluorine-based oligomer can bond with the silicon oxide by hydrogen bonding or dehydration condensation. Therefore, it is thought that the fluorine-based oligomer is immobilized on the surface of the silicon oxide layer so that the fluorine-containing group Rf is oriented outward. For these reasons, the hydrophobicity of the surface of the silicon oxide layer is increased by the fluorine-containing group Rf, and the insulating properties of the silicon oxide layer can be improved. Furthermore, because fluorine-based oligomers are present on the surface of the silicon oxide layer, the flexibility of the surface of the silicon oxide layer is increased, and even when magnetic powder is used under pressure, the silicon oxide layer is less likely to be damaged, thereby improving the insulating properties of the silicon oxide layer.

[0106] Furthermore, in the silicon oxide layer, the distribution of element fluorine concentration in the depth direction shows a maximum within the silicon oxide layer. Therefore, it can be said that there are areas within the silicon oxide layer where fluorine-based oligomers exist locally. This is thought to be because the fluorine-containing groups Rf of the fluorine-based oligomers that remained inside the silicon oxide layer without migrating to the surface of the silicon oxide layer aggregate, forming micelles of fluorine-based oligomers with hydrophilic groups Rh facing outward within the silicon oxide layer. In such micelles, the hydrophilic groups Rh can bond with the silicon oxide through hydrogen bonding or dehydration condensation. This reduces defects within the silicon oxide layer and improves the strength and insulation properties of the silicon oxide layer.

[0107] Furthermore, the concentration of element O in the silicon oxide layer is lowest at the surface of the silicon oxide layer. As a result, the hydrophilicity of the silicon oxide layer surface decreases and its hydrophobicity increases, thereby improving the insulating properties of the silicon oxide layer.

[0108] [Evaluation of Magnetic Powder] Next, the evaluation results of the magnetic powder according to the embodiment will be described. Specifically, magnetic powder was prepared as shown below, and the volume resistivity was measured as an evaluation of the prepared magnetic powder. Note that this embodiment is not limited in any way to the evaluation described below.

[0109] <Preparation of Magnetic Powder> Samples of magnetic powder to be used for evaluation were prepared as follows.

[0110] First, 10% aqueous ammonia and a fluorinated oligomer, or 10% aqueous ammonia, were added to isopropyl alcohol and stirred for 5 minutes. Then, metal powder was added and stirred for another 5 minutes. Tetraethoxysilane was further added to the solution and stirred for 60 minutes. Through these steps, a silicon oxide layer was formed on the surface of the metal particles of the metal powder, and a slurry containing magnetic powder, each consisting of multiple magnetic particles having a metal particle and a silicon oxide layer, was prepared. The magnetic powder obtained from the resulting slurry was then filtered and dried to obtain magnetic powder. In this process, the weight ratio of aqueous ammonia to the weight of metal powder was set to 5 wt%. Furthermore, the weight ratio of fluorinated oligomer to the weight of metal powder and the weight ratio of silicon oxide in the silicon alkoxide for each sample are shown in Tables 3 to 6 below. Hereafter, the weight ratio of fluorinated oligomer to the weight of metal powder may be simply referred to as "amount of fluorinated oligomer." Similarly, the weight ratio of silicon oxide in the silicon alkoxide to the weight of metal powder may be simply referred to as "amount of silicon oxide."

[0111] Furthermore, the fluorine-based oligomers used had a fluorine-containing group Rf (see Figure 4) that was a fluoroalkyl group with 3 or fewer carbon atoms, and a hydrophilic group Rh (see Figure 4) that had a siloxane chain containing a silanol structure. The metal powders used were Fe-Si-Cr alloy (3.5 wt% Si, 4.5 wt% Cr) metal powder (D50 = 11 μm) or Fe-Ni alloy (50 wt% Ni) metal powder (D50 = 12 μm). The metal powders used for each sample are shown in Tables 3 to 6 below.

[0112] In Tables 3 to 6, samples marked with "X" are magnetic powders prepared using Fe-Si-Cr alloy metal powder without the addition of fluorine-based oligomers. Samples marked with "Y" are magnetic powders prepared using Fe-Ni alloy metal powder without the addition of fluorine-based oligomers. Samples marked with "A" are magnetic powders prepared using Fe-Si-Cr alloy metal powder with the addition of fluorine-based oligomers. Samples marked with "B" are magnetic powders prepared using Fe-Ni alloy metal powder with the addition of fluorine-based oligomers. Furthermore, in Tables 3 to 6, samples shown in the same table were prepared and evaluated on the same day. Additionally, in Tables 3 to 6, samples prepared and evaluated on different days, even if they have the same metal particle, silicon oxide, and fluorine-based oligomer content, are shown with different markings.

[0113] <Measurement of Volume Resistivity> For each sample of magnetic powder prepared as described above, the volume resistivity was measured using an automatic powder resistance measurement system (MCP-PD600) and a high-resistivity resistivity meter (High Resta-UX, MCP-HT800) manufactured by Nitto Seiko Analytech Co., Ltd. The volume resistivity was measured using the double-ring electrode method while applying a predetermined pressure to 4 g of magnetic powder. A higher volume resistivity indicates higher insulating properties of the silicon oxide layer in the magnetic powder.

[0114] <Evaluation Results 1> First, we evaluated whether the insulating properties of the silicon oxide layer were susceptible to stress depending on whether or not a fluorine-based oligomer was added during the formation of the silicon oxide layer. Specifically, the volume resistivity was measured under the pressure conditions shown in Table 3 when applying pressure to the magnetic powder. The results are shown in Table 3, Figure 15, and Figure 16. Figure 15 is a diagram showing the relationship between applied pressure and volume resistivity for a magnetic powder sample using Fe-Si-Cr alloy metal powder from the samples shown in Table 3. Figure 16 is a diagram showing the relationship between applied pressure and volume resistivity for a magnetic powder sample using Fe-Ni alloy metal powder from the samples shown in Table 3. Figures 15 and 16 are semi-logarithmic graphs, and the vertical axis showing volume resistivity in Figures 15 and 16 is a logarithmic axis.

[0115]

[0116] As shown in Table 3 and Figure 15, when using Fe-Si-Cr alloy metal powder, sample A1 with added fluorine-based oligomer shows improved insulation compared to sample X1 without added fluorine-based oligomer, with less decrease in volume resistivity even when the applied pressure is increased. Similarly, as shown in Table 3 and Figure 16, when using Fe-Ni alloy metal powder, sample B1 with added fluorine-based oligomer shows improved insulation compared to sample Y1 without added fluorine-based oligomer, with less decrease in volume resistivity even when the applied pressure is increased. Thus, in samples A1 and B1 with added fluorine-based oligomer, the insulation of the silicon oxide layer is improved when used under pressure. These results are considered to be due to the effect of including fluorine-based oligomer in the silicon oxide layer, as explained above.

[0117] <Evaluation Results 2> Next, the effect of adding fluorine-based oligomers on improving insulation was examined, specifically the influence of silicon oxide content. The results are shown in Table 4 and Figure 17. Figure 17 is a diagram showing the relationship between silicon oxide content and volume resistivity for the magnetic powder samples shown in Table 4. Figure 17 is a semi-logarithmic graph, and the vertical axis showing volume resistivity in Figure 17 is a logarithmic axis. The volume resistivity measurement results shown in Table 4 and Figure 17 are the measurement results when the applied pressure is 63.7 MPa.

[0118]

[0119] As shown in Table 4 and Figure 17, regardless of the amount of silicon oxide, the addition of fluorine-based oligomers increases the volume resistivity and improves the insulating properties of the silicon oxide layer. Furthermore, the results shown in Table 4 and Figure 17 confirm that the effect of improving the insulating properties of the silicon oxide layer is observed when the ratio of fluorine-based oligomers to silicon oxide is in the range of 0.5 to 5.

[0120] <Evaluation Result 3> Next, the effect of adding fluorine-based oligomers on improving insulation properties was examined by checking the influence of the amount of fluorine-based oligomers. The results are shown in Tables 5 and 6, and Figures 18 and 19. Table 5 shows the results when Fe-Si-Cr alloy metal powder was used, and Table 6 shows the results when Fe-Ni alloy metal powder was used. Figure 18 is a diagram showing the relationship between the amount of fluorine-based oligomers and volume resistivity of the magnetic powder samples shown in Table 5. Figure 19 is a diagram showing the relationship between the amount of fluorine-based oligomers and volume resistivity of the magnetic powder samples shown in Table 6. Figures 18 and 19 are semi-logarithmic graphs, and the vertical axis showing volume resistivity in Figures 18 and 19 is a logarithmic axis. The volume resistivity measurement results shown in Tables 5 and 6, and Figures 18 and 19 are the measurement results for volume resistivity when the applied pressure is 63.7 MPa.

[0121]

[0122]

[0123] As shown in Tables 5 and 6, and Figures 18 and 19, it can be seen that adding a fluorine-based oligomer increases the volume resistivity and improves the insulation properties of the silicon oxide layer, regardless of whether Fe-Si-Cr alloy metal powder or Fe-Ni alloy metal powder is used. The results shown in Tables 5 and 6, and Figures 18 and 19 confirm that the effect of improving the insulation properties of the silicon oxide layer is observed when the ratio of fluorine-based oligomer amount to silicon oxide amount is in the range of 0.125 to 4.

[0124] Furthermore, when the amount of fluorine-based oligomer exceeds a predetermined amount, the effect of improving the insulating properties of the silicon oxide layer saturates. As shown in Tables 5 and 6, and Figures 18 and 19, in both cases where Fe-Si-Cr alloy metal powder and Fe-Ni alloy metal powder are used, there is almost no difference in the insulating properties of the silicon oxide layer even when the amount of fluorine-based oligomer increases, as long as the amount of fluorine-based oligomer is 0.1 wt% or more.

[0125] Furthermore, there is a difference in the effect of adding fluorine-based oligomers to improve the insulating properties of the silicon oxide layer between the case where Fe-Si-Cr alloy metal powder is used and the case where Fe-Ni alloy metal powder is used. This is thought to be because the volume resistivity of the sample using Fe-Ni alloy metal powder is relatively high even without the addition of fluorine-based oligomers. The reason why the volume resistivity of the sample using Fe-Ni alloy metal powder is relatively high is thought to be that the thickness of the silicon oxide layer tends to be relatively larger due to the difference in alloy density, and that the contact area between metal particles in the metal powder tends to be relatively smaller due to the difference in alloy density and the difference in particle size of the metal powder.

[0126] (Other Embodiments, etc.) Although the powder core and inductor according to the embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments.

[0127] For example, electrical components using the powdered magnetic core described above are also included in this disclosure. Examples of electrical components include inductance components such as high-frequency reactors, inductors, and transformers. Power supply devices equipped with the above-mentioned electrical components are also included in this disclosure. Furthermore, magnetic powder used to form the powdered magnetic core described above is also included in this disclosure. For example, the magnetic powder described above may be used in powdered magnetic cores using a resin with a binder component other than silicone resin, or in powdered magnetic cores formed by a method different from the one described above.

[0128] Furthermore, this disclosure is not limited to the embodiments described above. Within the scope of one or more embodiments, various modifications to these embodiments that a person skilled in the art could conceive of, or forms constructed by combining components from different embodiments, may also be included, as long as they do not depart from the spirit of this disclosure.

[0129] The following are examples of the powder core, inductor, and method for manufacturing the powder core according to the present disclosure, as described based on the embodiments described above. The powder core, inductor, and method for manufacturing the powder core according to the present disclosure are not limited to the following examples.

[0130] For example, a compacted magnetic core according to a first aspect of the present disclosure comprises a magnetic powder composed of a plurality of magnetic particles, and a binder containing Si elements that binds the plurality of magnetic particles together, wherein each of the plurality of magnetic particles has a metal particle and an oxide layer containing Si elements that covers the surface of the metal particle, and the Si element concentration of the oxide layer is higher than the Si element concentration of the binder.

[0131] Furthermore, for example, the compacted magnetic core according to the second aspect of this disclosure is the compacted magnetic core according to the first aspect, wherein the metal particles are alloy particles containing Fe and Ni elements.

[0132] Furthermore, for example, the compacted magnetic core according to the third aspect of this disclosure is the compacted magnetic core according to the first or second aspect, wherein the oxygen concentration of the oxide layer is higher than the oxygen concentration of the binder.

[0133] Furthermore, for example, the compacted magnetic core according to the fourth aspect of this disclosure is a compacted magnetic core according to any one of the first to third aspects, wherein the thickness of the oxide layer is 5 nm or more and 60 nm or less.

[0134] Furthermore, for example, the compacted magnetic core according to the fifth aspect of this disclosure is a compacted magnetic core according to any one of the first to fourth aspects, wherein the oxide layer contains element F.

[0135] Furthermore, for example, an inductor according to the sixth aspect of this disclosure comprises a powder core according to any one of the first to fifth aspects and a coil portion.

[0136] Furthermore, for example, a method for manufacturing a compacted magnetic core according to a seventh aspect of the present disclosure includes the steps of: forming an oxide layer containing Si elements on the surface of a plurality of metal particles constituting a metal powder using tetraalkoxysilane to obtain magnetic powder; mixing the obtained magnetic powder with a silicone resin to obtain granulated powder; pressure molding the obtained granulated powder to obtain a molded body; and annealing the obtained molded body.

[0137] Furthermore, for example, the method for manufacturing a powdered magnetic core according to the eighth aspect of this disclosure is the method for manufacturing a powdered magnetic core according to the seventh aspect, wherein the annealing step is performed in a non-oxidizing atmosphere containing hydrogen gas.

[0138] The compacted magnetic core described herein can be applied to materials for magnetic cores in high-frequency inductors and transformers.

[0139] 1, 2 Inductor 10 Magnetic powder 12 Compacted magnetic core 12a Base 12b Core 12c Wall 13 Conductor 14 Coil support 14a Base 14b Cylindrical part 15 Magnetic particles 16 Metal particles 17 Oxide layer 18 Binder 20 Punch 21 Coil conductor 22 Granulated powder 26 Terminal part 29 Molding die

Claims

1. A compacted magnetic core comprising: a magnetic powder composed of a plurality of magnetic particles; and a binder containing Si elements that binds the plurality of magnetic particles together, wherein each of the plurality of magnetic particles has a metal particle and an oxide layer containing Si elements that covers the surface of the metal particle, and the Si element concentration of the oxide layer is higher than the Si element concentration of the binder.

2. The powdered magnetic core according to claim 1, wherein the metal particles are alloy particles containing Fe and Ni elements.

3. The oxygen concentration in the oxide layer is higher than the oxygen concentration in the binder, as described in claim 1.

4. The powdered magnetic core according to claim 1, wherein the thickness of the oxide layer is 5 nm or more and 60 nm or less.

5. The powdered magnetic core according to claim 1, wherein the oxide layer contains element F.

6. An inductor comprising a powdered magnetic core according to any one of claims 1 to 5 and a coil portion.

7. A method for manufacturing a compacted magnetic core, comprising the steps of: forming an oxide layer containing Si elements on the surface of a plurality of metal particles constituting a metal powder using tetraalkoxysilane to obtain a magnetic powder; mixing the obtained magnetic powder with a silicone resin to obtain granulated powder; pressure molding the obtained granulated powder to obtain a molded body; and annealing the obtained molded body.

8. The method for manufacturing a compacted magnetic core according to claim 7, wherein the annealing step is performed under a non-oxidizing atmosphere containing hydrogen gas.

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