Ferrite powder

Abstract

To provide a ferrite powder excellent in stability of magnetic permeability with time while maintaining high fillability and high magnetic permeability and low loss at high frequencies.SOLUTION: A ferrite powder contains 56.0 mass% or more and 63.0 mass% or less iron (Fe), 7.0 mass% or more and 13.0 mass% or less manganese (Mn), and 1.0 mass% or more and 3.0 mass% or less zinc (Zn).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to ferrite powder. [Background technology]

[0002] Composite materials consisting of ferrite powder and resin are widely used in various applications, including inductors. Such composite materials are manufactured by kneading ferrite powder and resin. The composite material is then molded into a sheet or other shape to form a composite (molded body). When the particles constituting the ferrite powder are nearly spherical, the fluidity during molding increases, leading to a higher packing density of ferrite powder within the composite. This results in improved moldability and better magnetic properties. From this perspective, ferrite powders (particles) composed of spherical or polyhedral particles have been proposed.

[0003] For example, Patent Document 1 describes a Mn-Zn ferrite powder comprising at least spherical or polyhedral ferrite particles with a spinel phase as the main phase, wherein the ferrite particles have a step structure on their surface with a convex polygonal contour, and the ferrite powder has a BET specific surface area of ​​0.35 m². 2 / g or more 10.00m 2 A ferrite powder is disclosed that has a density of less than or equal to / g and has a zinc oxide (ZnO) phase content of 0% by mass or more and 0.8% by mass or less (Claim 1 of Patent Document 1). Furthermore, Patent Document 1 states that the ferrite powder can suppress magnetic loss at high frequencies and can suppress particle shedding without impairing moldability and packing properties when applied to composite materials or composites (

[0024] of Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2022 / 209640 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Thus, it has been conventionally proposed to improve the moldability and filling properties of composite materials and composites by using spherical or polyhedral ferrite powder. However, the present inventors have found that when conventional ferrite powder is compounded with resin and then heated and molded to produce a resin molded body (composite), a problem occurs in which the magnetic permeability of the resin molded body gradually decreases over time (disaccommodation).

[0006] Further investigations by the inventors revealed that the time-dependent change in magnetic permeability is greatly influenced by γ-Fe2O3, which has vacancies among the ferromagnetic iron (Fe) oxides contained in the ferrite. They then found that by suppressing the formation of γ-Fe2O3 and controlling the vacancy ratio, it is possible to obtain a ferrite powder with excellent time-dependent stability of magnetic permeability while maintaining high packing, high magnetic permeability at high frequencies, and low losses.

[0007] Therefore, the present invention aims to provide a ferrite powder that exhibits excellent temporal stability of magnetic permeability while maintaining high packing capacity, high magnetic permeability at high frequencies, and low loss. [Means for solving the problem]

[0008] The present invention encompasses the following embodiments (1) to (4). In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0009] (1) Ferrite powder containing iron (Fe) in a proportion of 56.0% to 63.0% by mass, manganese (Mn) in a proportion of 7.0% to 13.0% by mass, and zinc (Zn) in a proportion of 1.0% to 3.0% by mass.

[0010] (2) The ferrite powder contains spherical ferrite particles mainly composed of the spinel phase, The spinel phase has an iron (Fe) content that is excessive compared to the stoichiometric ratio and a vacancy ratio of 0 mol% or more and 90 mol% or less. The ferrite powder has a shape factor SF-1 of 100 or more and 110 or less and a volume average particle diameter (D50) of 2.0 μm or more and 20 μm or less. The ferrite powder of (1) above.

[0011] (3) The ferrite powder of (1) or (2) above, having an α-iron oxide (α-Fe2O3) content of 0.0 mass% or more and 3.0 mass% or less.

[0012] (4) The ferrite powder of any one of (1) to (3) above, having a copper (Cu) content of 0.0 mass% or more and 0.5 mass% or less.

Advantages of the Invention

[0013] According to the present invention, there is provided a ferrite powder that is excellent in the temporal stability of magnetic permeability while maintaining high packing density, high magnetic permeability at high frequencies, and low loss.

Brief Description of the Drawings

[0014] [Figure 1] (Example 1) showing the time change of the real part of the magnetic permeability (μ’) of the ferrite powder. [Figure 2] (Example 5) showing the time change of the real part of the magnetic permeability (μ’) of the ferrite powder. [[ID=第32]]】

Embodiments for Carrying Out the Invention

[0015] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described. Note that the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

[0016] [[ID=第42]]】<<1. Ferrite Powder>> The ferrite powder of this embodiment contains iron (Fe) in a proportion of 56.0% to 63.0% by mass, manganese (Mn) in a proportion of 7.0% to 13.0% by mass, and zinc (Zn) in a proportion of 1.0% to 3.0% by mass.

[0017] Ferrite powder (hereinafter sometimes simply referred to as "powder") is composed of multiple ferrite particles (hereinafter sometimes simply referred to as "particles"). In other words, ferrite powder is an aggregate of multiple ferrite particles. Furthermore, the ferrite particles that make up ferrite powder are basically independent. Therefore, ferrite powder exhibits fluidity as a whole. However, as long as it exhibits fluidity as a whole, this does not exclude cases where some particles contained in the ferrite powder have bonded together to form aggregated particles (secondary particles).

[0018] The ferrite powder (particles) of this embodiment has a spinel phase as its main phase. That is, the spinel phase content is 50.0% by mass or more. The spinel phase is an iron oxide compound having a basic composition represented by MFe2O4 (where M is a metal element such as a transition metal element or a vacancy), and most of them are ferromagnetic. Therefore, ferrite powder with a spinel phase as its main phase exhibits excellent magnetic properties.

[0019] Furthermore, the ferrite powder of this embodiment has a Mn-Zn ferrite composition containing iron (Fe), manganese (Mn), and zinc (Zn). Mn-Zn ferrites generally have high magnetic permeability. Therefore, when ferrite powder is applied to elements such as inductors, it becomes possible to obtain excellent magnetic properties.

[0020] The iron (Fe) content of the ferrite powder is 56.0% by mass or more and 63.0% by mass or less. If the Fe content falls below 56.0% by mass, the Mn and / or Zn content increases relatively. In this case, depending on the composition ratio, the loss coefficient (tanδ) tends to increase from relatively low frequencies around 50 MHz. Due to the large loss, it is unsuitable for use in high-frequency applications such as inductors. The Fe content is preferably 57% by mass or more, and more preferably 58% by mass or more. On the other hand, if the Fe content exceeds 63.0% by mass, the Mn and / or Zn content decreases relatively. The real part of the complex permeability (real part of permeability; μ') is low, and a high saturation magnetic flux density cannot be obtained. Therefore, it is also unsuitable for use in applications such as inductors. The Fe content is preferably 62.5% by mass or less, and more preferably 62% by mass or less.

[0021] The manganese (Mn) content of the ferrite powder is 7.0% by mass or more and 13.0% by mass or less. If the Mn content falls below 7.0% by mass, the Fe and / or Zn content increases relatively. In this case, the real part of the magnetic permeability (μ') becomes low, making it unsuitable for use in applications such as inductors. The Mn content is preferably 7.3% by mass or more, and more preferably 7.5% by mass or more. On the other hand, if the Mn content exceeds 13.0% by mass, the Fe and / or Zn content decreases relatively. Depending on the composition ratio, the loss coefficient (tanδ) tends to increase from relatively low frequencies around 50 MHz. Therefore, it is also unsuitable for use in high-frequency applications such as inductors. The Mn content is preferably 12% by mass or less, and more preferably 11% by mass or less.

[0022] The zinc (Zn) content of the ferrite powder is between 1.0% by mass and 3.0% by mass. If the Zn content falls below 1.0% by mass, the effect of Zn addition becomes less pronounced, and the real part of the magnetic permeability (μ') decreases. On the other hand, if the Zn content exceeds 3.0% by mass, the loss coefficient (tanδ) at 50 MHz increases. Furthermore, if there is an excess of Zn, particulate zinc oxide (ZnO) may adhere to the surface of the ferrite particles constituting the ferrite powder. This is because some of the excess Zn volatilizes during the high-temperature heat treatment process (thermal spraying process, etc.) in the ferrite powder manufacturing process and re-deposits as particulate ZnO on the surface of the ferrite particles. When ZnO adheres to the surface of ferrite particles, the viscosity of the composition may increase rapidly when mixing and kneading the ferrite powder with resin to produce a composite material, potentially making the manufacturing process difficult.

[0023] Preferably, the ferrite powder contains spherical ferrite particles mainly composed of the spinel phase. Here, spherical ferrite particles include not only spherical particles but also polyhedral particles. By controlling the shape of the particles contained in the ferrite powder to be spherical (spherical or polyhedral), the moldability and packing properties of the ferrite powder can be improved. This is because spherical particles can smoothly avoid contact with other particles during molding. Therefore, fluidity during molding is improved, and dense packing is possible. In contrast, particles with anisotropic or irregular shapes, such as plate-like or needle-like shapes, have poor moldability and packing properties.

[0024] The ferrite particles constituting the ferrite powder may consist of some spherical ferrite particles, or all of them may consist of spherical ferrite particles. However, from the viewpoint of improving moldability and packing properties, a higher proportion of spherical ferrite particles is preferable. Specifically, a proportion of spherical ferrite particles of 50% or more is preferable.

[0025] Polyhedral particles basically have a shape formed by the three-dimensional combination of multiple polygons. The polygons that make up the polyhedron typically consist of triangles, quadrilaterals, hexagons, octagons, decagons, or combinations thereof, reflecting the crystal structure of the ferrite particles. An example of such a polyhedron is the truncated cuboctahedron, which is a combination of quadrilaterals, hexagons, and octagons. Furthermore, the more faces a polyhedron has, the closer it becomes to a sphere. Therefore, polyhedral particles preferably have a shape of 10 faces or more, more preferably 12 faces or more, and even more preferably 14 faces or more. Also, polyhedral particles typically have a shape of 100 faces or less, more typically 72 faces or less, and even more typically 24 faces or less.

[0026] Furthermore, particles in which one or more of the straight lines constituting the polygon are broken, or particles in which part of the straight lines are curved, are also included in polyhedral particles if they can be recognized as polyhedral when viewed as a whole. Particles with finely jagged lines constituting the polygon are also included in polyhedral particles. In addition, spherical-like step particles may have a step structure on their surface. In this case, strictly speaking, they may not be perfectly spherical or polyhedral. However, this step structure is significantly smaller than the particle's dimensions. Therefore, even if a particle has such a microscopic step structure, if it has a spherical or polyhedral shape macroscopically, it is considered a spherical or polyhedral particle.

[0027] Preferably, the ferrite powder contains ferrite particles (spherical-like step particles) that have a step structure on their surface. The inclusion of such step-structured particles improves adhesion to the resin and suppresses particle shedding when the ferrite powder is applied to composite materials or composites. While the detailed mechanism is unknown, it is presumed that the presence of the step structure increases the surface area of ​​the particles, i.e., the contact area with the resin, resulting in a higher chemical bond between the particles and the resin. It is also presumed that the interlocking of particles and resin at the step structure creates an anchoring effect on the resin, increasing the physical bond between the particles and the resin.

[0028] The step structure has a convex polygonal contour on the surface of the ferrite particle. That is, when the particle is viewed from the surface, the step structure has a convex polygonal shape. In other words, the step structure is provided so as to surround a region of the particle surface with a combination of straight lines. By providing such a step structure, it is possible to more effectively prevent the particle from falling off. Here, a convex polygon is a polygon in which any interior angle is 180° or less. It can also be defined as a polygon in which no line segment connecting any two points inside or on the boundary extends outside. That is, it is not a concave polygon (non-convex polygon) such as a star shape. The contour of the step structure is not limited as long as it is a convex polygon. However, reflecting the crystal structure of ferrite, the contour is typically a triangle, square, hexagon, octagon, or decagon. Furthermore, ferrite particles may have multiple step structures on their surface. This can more effectively prevent the particle from falling off.

[0029] Preferably, the spinel phase contained in the ferrite powder has an excess of iron (Fe) compared to the stoichiometric composition. In other words, the spinel phase has a composition with an excess of iron (Fe) compared to the stoichiometric composition. As mentioned above, the spinel phase has a basic composition represented by MFe2O4 (where M is a metallic element such as a transition metal or a vacancy). Therefore, in the stoichiometric composition where M is an element other than Fe, the molar ratio of Fe to the total amount of M and Fe contained in the spinel phase is 2 / 3. If the proportion of Fe is greater than 2 / 3, Fe is incorporated into the M sites, and the composition of the spinel phase becomes (M,Fe)Fe2O4. By increasing the amount of Fe contained in the spinel phase compared to the stoichiometric composition, the loss coefficient (tanδ) at high frequencies can be lowered, and as a result, low loss of the ferrite powder is achieved.

[0030] Preferably, the spinel phase has a vacancy ratio of 0 mol% or more and 90 mol% or less. The vacancy ratio is the ratio of γ-Fe2O3 (magnetite) to the total number of moles of Fe3O4 (magnetite) and γ-Fe2O3 (maghematite) contained in the ferrite powder (spinel phase). 3のIt is defined as the molar ratio (number of moles of γ-Fe2O3 / (number of moles of Fe3O4 + number of moles of γ-Fe2O3)). By suppressing the vacancy rate, it becomes possible to reduce the temporal change in the magnetic permeability of the ferrite powder. On the other hand, when the vacancy rate exceeds 90 mol%, the long-term temporal change in the magnetic permeability becomes large. Therefore, when the ferrite powder is used as a filler for the magnetic core of an inductor, the performance of the inductor changes over time. In this case, it becomes difficult to obtain the performance at the initial design stage, which leads to malfunction of electronic devices.

[0031] To explain this point, as described above, the spinel phase with excess iron (Fe) has a composition of (M,Fe)Fe2O4. That is, the crystal of the spinel phase as an oxide contains a large amount of Fe. By the way, there are various forms of iron oxides such as α-Fe2O3 (hematite), γ-Fe2O3 (maghemite), and Fe3O4 (magnetite). Among these, α-Fe2O3 and FeO are antiferromagnets and do not exhibit ferromagnetic properties. Also, they do not have a spinel structure.

[0032] On the other hand, Fe3O4 (magnetite) and γ-Fe2O3 (maghemite) are ferromagnets. Also, the composition formula of Fe3O4 can be rewritten as Fe 3+ (Fe 2+ ,Fe 3+ )2O4, and the composition formula of γ-Fe2O3 can be rewritten as Fe 3+ (Fe 3+ 5 / 6 V 1 / 6 )2O4 (where V is a vacancy). Therefore, these have a spinel structure. Thus, it can be said that the spinel phase with excess iron (Fe) contains one or both of Fe3O4 (magnetite) and γ-Fe2O3 (maghemite).

[0033] Fe3O4 (magnetite), which has a spinel structure, does not have vacancies in its crystal structure, whereas γ-Fe2O3 (maghematite) does have vacancies (V). Therefore, ferrite powder containing γ-Fe2O3 has vacancies (V) in the spinel phase, and the number of vacancies increases as the amount of γ-Fe2O3 increases. Furthermore, the more vacancies there are, that is, the greater the amount of γ-Fe2O3, the greater the change in magnetic permeability over time. We believe that this is related to the interaction between the vacancies present in the ferrite crystal lattice moving within the crystal lattice over time and settling into an energetically stable state (position), and the fact that the presence of vacancies hinders the movement of magnetic domain walls.

[0034] Therefore, the time variation of the permeability can be reduced by lowering the amount of γ-Fe2O3 in the spinel phase, i.e., the vacancy ratio. From the viewpoint of suppressing the time variation of the permeability, a smaller vacancy ratio is desirable. A vacancy ratio of 90 mol% or less is more preferable, and 85 mol% or less is even more preferable. On the other hand, by increasing the vacancy ratio to a certain extent, the loss coefficient (tanδ) can be kept low. A vacancy ratio of 20 mol% or more is preferable, 30 mol% or more is more preferable, and 40 mol% or more is even more preferable.

[0035] As mentioned earlier, the vacancy ratio is the ratio of moles of γ-Fe2O3 to the total number of moles of Fe3O4 and γ-Fe2O3. The ferromagnetic Fe oxides are two types of spinel compounds, Fe3O4 and γ-Fe2O3, and it is thought that these two types of Fe oxides exist as unstoichiometric compounds in spinel. Therefore, by using the proportion of vacancy-containing Fe oxide (γ-Fe2O3) in ferromagnetic Fe oxides (Fe3O4, γ-Fe2O3) (vacancy ratio) as an indicator, the vacancy ratio in spinel can be estimated.

[0036] The vacancy ratio is determined as follows. First, the ferrite powder is subjected to chemical analysis to determine the amounts of Fe, Mn, Zn, and Cu in the powder as mass percentages (mass%). Separately, the amount of divalent iron (Fe) contained in the ferrite powder is determined by redox titration. 2+The amount of ) is determined. Furthermore, the ferrite powder is subjected to X-ray diffraction (XRD) analysis to determine the amount of α-Fe2O3 (hematite) in the powder.

[0037] Next, using the atomic weights of Fe (55.85), Mn (54.94), Zn (65.39), Cu (63.55), and α-Fe2O3 (159.70), the amount of Fe A, Mn B, Zn C, and Fe were converted to moles according to equations (1) to (6) below. 2+ The amounts D, E (α-Fe2O3), and F (Cu) are calculated. Then, the excess Fe amount G (in moles) and the amount H (in moles) of Fe compound (γ-Fe2O3) with vacancies are determined according to equations (7) and (8) below. Finally, the vacancy fraction I (mol%) is calculated according to equation (9) below.

[0038]

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[0039]

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[0040] Note that ferrite powder may contain α-Fe2O3 (hematite). Also, if the ferrite powder contains copper (Cu), CuOFe5O8 (copper-iron composite oxide) may be formed. α-Fe2O3 and CuOFe5O8 are not ferromagnetic materials with a spinel structure. Therefore, when calculating the excess Fe amount in the spinel phase using equation (7) above, the Fe content contained in α-Fe2O3 and CuOFe5O8 is excluded. Also, Fe3O4 (magnetite) contains divalent iron ions (Fe 2+ ) contains Fe, whereas γ-Fe2O3 (maghematite) contains Fe 2+ It does not include. Therefore, when calculating the amount of γ-Fe2O3 using equation (8) above, the Fe contained in Fe3O4 is not included. 2+ Minutes have been excluded.

[0041] Furthermore, the excess Fe amount obtained according to equation (7) above should be greater than zero (0). In this case, the spinel phase contained in the ferrite powder will have an excess of iron (Fe) compared to its stoichiometric composition.

[0042] Preferably, the excess iron (Fe) ratio of the ferrite powder is 25 mol% or more and 70 mol% or less. If the excess Fe ratio is less than 25 mol%, the actual permeability part (μ') increases, but the loss coefficient (tanδ) increases. Therefore, ferrite powder is unsuitable for use as a filler for the magnetic core of an inductor. Also, if the excess Fe ratio exceeds 70 mol%, the loss coefficient (tanδ) decreases, but the actual permeability part (μ') also decreases. Therefore, ferrite powder is also unsuitable for use as a filler for the magnetic core of an inductor. An excess Fe ratio of 35 mol% or more and 70 mol% or less is more preferable, and 40 mol% or more and 70 mol% or less is even more preferable. The excess Fe ratio is the ratio of the amount of excess Fe to the total amount of Fe, and is calculated according to equation (10) below.

[0043]

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[0044] Preferably, the mass ratio of iron (Fe) to manganese (Mn) in the ferrite powder (Fe / Mn mass ratio) is between 5.5 and 8.0. If the Zn content is within the range of 1% to 3% by mass, and the Fe / Mn mass ratio is between 5.5 and 8.0, it is possible to achieve a good balance between high permeability and low loss in the ferrite powder. Therefore, it becomes possible to increase the μ'Q product.

[0045] Preferably, the copper (Cu) content of the ferrite powder is 0% by mass or more and 1.0% by mass or less. Cu is prone to segregation in ferrite particles. If segregation occurs, the magnetic properties of the ferrite powder may deteriorate. By limiting the amount of Cu to 1.0% by mass or less, it is possible to suppress the formation of segregation that causes deterioration of magnetic properties. On the other hand, Cu has the effect of stabilizing the valence state of Fe. Depending on the manufacturing method of the ferrite powder, adding Cu in an appropriate amount can suppress the formation of vacancies and suppress the change in magnetic permeability over time. A Cu content of 0% by mass or more and 0.50% by mass or less is more preferable, and 0% by mass or more and 0.35% by mass or less is even more preferable.

[0046] The ferrite powder may contain iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and oxygen (O), with the remainder being unavoidable impurities. Alternatively, it may contain other elemental components besides Fe, Mn, Zn, Cu, and O. Examples of such elemental components include lithium (Li), magnesium (Mg), aluminum (Al), titanium (Ti), chromium (Cr), cobalt (Co), and nickel (Ni). However, from the viewpoint of utilizing the excellent magnetic properties of Mn-Zn ferrite, it is preferable that it does not contain large amounts of other elemental components besides Fe, Mn, Zn, Cu, and O. The content of other elemental components is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0047] Preferably, the spinel phase content in the ferrite powder (ferrite particles) is 80.0% by mass or more. The spinel phase, being a ferromagnetic material, is the crystalline phase that is the main component responsible for the magnetic properties of the ferrite powder. Increasing the spinel phase content makes it possible to increase the saturation magnetization (σs) and permeability (μ) of the ferrite powder. A spinel phase content of 85.0% by mass or more is more preferable, 90.0% by mass or more is even more preferable, 95.0% by mass or more is particularly preferable, and 99.0% by mass or more is most preferable.

[0048] Preferably, the zinc oxide (ZnO) content in the ferrite powder is 0.0% by mass or more and 1.0% by mass or less. Zinc oxide (ZnO) is a separate phase derived from zinc (Zn) that did not ferrite. Ferrite powder containing a large amount of ZnO has poor magnetic properties. Furthermore, this ferrite powder can cause problems such as increasing the viscosity of the resin composition when applied to it. Therefore, the less ZnO separate phase there is, the better. A ZnO content of 0.0% by mass or more and 0.8% by mass or less is more preferable, and 0.0% by mass or more and 0.5% by mass or less is even more preferable.

[0049] Preferably, the α-iron oxide (α-Fe2O3) content in the ferrite powder is 0.0% by mass or more and 3.0% by mass or less. α-Fe2O3 is an antiferromagnetic phase. If the amount of α-Fe2O3 is excessive, the magnetic properties of the ferrite powder will deteriorate. If the amount of α-Fe2O3 is within the aforementioned range, the effect on the magnetic properties will be minimal. Therefore, by keeping the amount of α-Fe2O3 within this range, it is possible to prevent a decrease in magnetic properties, especially a decrease in saturation magnetization (σs), and a decrease in saturation magnetic flux density when used in an inductor.

[0050] The particles constituting the ferrite powder may be single-crystal or polycrystalline. However, polycrystalline particles are preferred. Furthermore, the average crystallite diameter of the particles constituting the ferrite powder is preferably between 150 nm and 220 nm.

[0051] Preferably, the volume-average particle size (D50) of the ferrite powder is 2.0 μm or more and 20 μm or less. Here, the volume-average particle size is the cumulative 50% diameter (D50) in the volume particle size distribution. By increasing D50 to 2.0 μm or more, aggregation of the ferrite powder can be suppressed, and moldability and packing properties can be further improved. Also, depending on the manufacturing conditions, the vacancy rate of the ferrite powder can be controlled by increasing the particle size to a certain extent. That is, ferrite particles with small particle sizes have a large specific surface area. Therefore, oxidation tends to progress easily in high-temperature heat treatment processes such as thermal spraying during ferrite powder production, and γ-Fe2O3 with vacancies tends to be easily generated. From the viewpoint of improving moldability and packing properties and controlling the vacancy rate, a D50 of 2.3 μm or more is more preferable, 2.5 μm or more is even more preferable, 2.8 μm or more is particularly preferable, and 3.0 μm or more is most preferable. On the other hand, by keeping D50 below 20 μm, the generation of interparticle voids can be suppressed, resulting in better packing performance. From the viewpoint of improving packing performance, D50 is more preferably 12 μm or less, even more preferably 10 μm or less, particularly preferably 8.0 μm or less, and most preferably 7.0 μm or less.

[0052] Preferably, the shape factor SF-1 of the ferrite powder is 100 or more and 110 or less. SF-1 is an index of the sphericity of the particles constituting the powder. For perfectly spherical particles, SF-1 is 100, and it increases as the particle deviates from sphere. By keeping SF-1 below 110, the fluidity of the powder is increased, and moldability and packing properties are improved, regardless of whether the particles are spherical or polyhedral. SF-1 is more preferably 105 or less, and even more preferably 103 or less.

[0053] Preferably, the shape factor SF-2 of the ferrite powder is between 100 and 110. SF-2 is an index indicating the degree of surface irregularity of the particles constituting the powder. If there is no surface irregularity, SF-2 is 100, and it increases as the irregularity deepens. If the ferrite powder has a microscopic step structure on the particle surface, this improves adhesion with the resin when it is made into a composite material or composite, and suppresses particle shedding. Therefore, SF-2 should be moderately high, more preferably 101 or higher. On the other hand, if SF-2 is excessively high, the fluidity of the powder decreases, which may lead to a decrease in moldability and packability. SF-2 is more preferably 105 or lower, and even more preferably 103 or lower.

[0054] Preferably, the BET specific surface area of ​​the ferrite powder is 0.2 m². 2 / g or more 2.0m 2 It is less than / g. The specific surface area of ​​BET is 0.2m². 2 By increasing the BET specific surface area to over 0.3 m², the generation of interparticle voids is suppressed, making it possible to further improve packing performance. Furthermore, by keeping the BET specific surface area within the above range, the adhesion between the ferrite powder and the resin is improved when applied to composite materials or composites. From the viewpoint of improving packing performance and adhesion, the BET specific surface area is 0.3 m². 2 A value of 2.0 m² or more is preferable. On the other hand, a BET specific surface area of ​​2.0 m² is preferable. 2 By keeping the BET specific surface area below 1.5 m², aggregation of ferrite powder is suppressed, which leads to improved moldability and packability. Furthermore, depending on the manufacturing conditions, reducing the BET specific surface area to a certain extent makes it possible to control the vacancy ratio of the ferrite powder within an appropriate range. From the viewpoint of improving moldability and packability and controlling the vacancy ratio, the BET specific surface area is 1.5 m². 2 More preferably less than / g, and 1.0m 2 A value of less than / g is even more preferable.

[0055] Preferably, the tap density of the ferrite powder is 0.50 g / cm³. 3 More than 3.50g / cm 3The following is the result: By mixing small and large particle sizes, the tap density can be increased, resulting in better overall packing of the ferrite powder. The tap density is 1.00 g / cm³. 3 More than 3.00g / cm 3 The following are preferable.

[0056] Preferably, the true specific gravity of the ferrite powder is 5.00 g / cm³. 3 That concludes the explanation. By increasing the true specific gravity, it is possible to improve the magnetic properties of ferrite powder, particularly the saturation magnetization (σs) and permeability (μ). The true specific gravity is 5.05 g / cm³. 3 The above is preferable.

[0057] Preferably, the real permeability part (μ') of the ferrite powder at 50 MHz is 7.0 or higher. Increasing μ' can improve the magnetic properties of elements such as inductors containing ferrite powder. A μ' of 7.5 or higher is more preferable, and 8.0 or higher is even more preferable.

[0058] Preferably, the μ'Q product of the ferrite powder at 50 MHz is 400 or higher. Increasing the μ'Q product makes it possible to achieve a good balance between high permeability and low loss in the ferrite powder. A μ'Q product of 450 or higher is more preferable, and 500 or higher is even more preferable. The μ'Q product is determined using the real part (μ') and loss factor (tanδ) of the complex permeability of the ferrite powder according to equation (11) below. The loss factor (tanδ) is determined using the real part (μ') and imaginary part (μ'') of the complex permeability according to equation (12) below.

[0059]

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[0060] Preferably, the rate of change of permeability of the ferrite powder at 50 MHz is 0.040 or less. The rate of change of permeability is an indicator of the degree of change of permeability over time, and the smaller it is, the smaller the change of permeability over time, meaning that it has excellent temporal stability. Changes in permeability over long periods of time are considered to be one of the relaxation phenomena and are approximated by power measurements. Therefore, the permeability μ'(t) after elapsed time t (unit: hr) has an approximate linear relationship with the natural logarithm ln(t) of time t, as shown in equation (13) below. In equation (13) below, A represents the slope of the line and B represents the intercept. Then, as shown in equation (14) below, the absolute value of the slope A of the line is defined as the rate of change of permeability.

[0061]

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[0062] If the rate of change of magnetic permeability is 0.040 or less, it can be judged that the change in magnetic permeability over a long period of time is small. On the other hand, if the rate of change of magnetic permeability is greater than 0.040, the performance of the inductor will change over time when ferrite powder is used as the magnetic core filler of the inductor. This makes it difficult to obtain the performance (output) that was initially designed, and may lead to malfunction of electronic equipment.

[0063] <<2. Method for producing ferrite powder>> The ferrite powder of this embodiment is not limited in its manufacturing method, as long as it satisfies the requirements described above. However, it is preferably manufactured by thermal spraying a mixture of ferrite raw materials under predetermined conditions, followed by rapid cooling, as shown below.

[0064] <Raw material mixture> First, the ferrite raw materials are mixed to form a raw material mixture. Known ferrite raw materials such as oxides, carbonates, hydroxides, and / or chlorides can be used as the ferrite raw materials. The raw materials can be mixed using a known mixer such as a Henschel mixer, either dry or wet, or both.

[0065] <Castration and crushing> Next, the raw material mixture is calcined to produce a calcined product. Calcination can be carried out by known methods. For example, it can be done using a furnace such as a rotary kiln, a continuous furnace, or a batch furnace, under known conditions. For example, conditions include holding the mixture at a temperature of 700°C to 1300°C for a period of 2 to 12 hours in an atmosphere such as air.

[0066] <Granulation> Subsequently, the calcined material is crushed and granulated to form granules. The crushing method is not particularly limited. For example, known crushing machines such as vibratory mills, ball mills, or bead mills may be used, and the process may be carried out either dry or wet, or both. The granulation method may also be a known method. For example, water and, if necessary, additives such as a binder such as polyvinyl alcohol (PVA), a dispersant, and / or an antifoaming agent may be added to the crushed calcined material to adjust the viscosity, and then granulation may be carried out using a granulator such as a spray dryer.

[0067] In the conventional production of ferrite powder (particles), binder components are generally removed before the final firing. In contrast, in the manufacturing method of this embodiment, it is preferable not to perform a binder removal treatment. By performing thermal spraying with the binder components still present and controlling the amount of carbon contained in the granules, the vacancy ratio of the final ferrite powder can be adjusted to an appropriate range.

[0068] Preferably, the carbon content in the granules is between 0.08% by mass and 0.20% by mass. Depending on the thermal spraying conditions, limiting the carbon content of the granules to the aforementioned range allows the vacancy ratio of the ferrite powder to be controlled to a desired value. Conversely, if the carbon content is too low, the oxygen concentration in the environment surrounding the particles passing through the flame will increase in the subsequent thermal spraying process. As a result, oxidation of the ferrite powder will progress, promoting the formation of γ-Fe2O3, which may lead to an increase in the vacancy ratio. On the other hand, if the carbon content is too high, the decomposition of the binder components in the granules will not proceed sufficiently. As a result, there is a risk of generating particles with excessively large particle sizes and non-uniform shapes.

[0069] <Thermal spraying> Next, the obtained granules are thermal sprayed to form a sprayed material. In thermal spraying, the granules, transported by gas, are melted and ferrite as they pass through the spray flame. Subsequently, the ferrite particles are rapidly cooled and solidified with a cooling gas, and recovered using a cyclone or filter. The cooling gas may be ambient air at room temperature, or to prevent rapid cooling and oxidation, air or an inert gas (nitrogen gas, helium gas, argon gas, etc.) at a temperature lower than room temperature may be used. If necessary, the recovered ferrite particles may be classified. In classification, existing methods such as wind classification, mesh filtration, sieve classification, and sedimentation are used to adjust the particle size to the desired size. It is also possible to separate and recover large particle sizes in a single process using airflow classification such as a cyclone.

[0070] To obtain ferrite particles with a step structure (spherical step particles), it is important to thermal spray the granules under specific conditions. During thermal spraying, the entire granule is melted and then rapidly cooled. Although the detailed mechanism is unknown, it is speculated that a polygonal step structure reflecting the ferrite crystal structure is formed on the particle surface during high-temperature melting, and this structure is maintained by rapid cooling. In contrast, if ferrite particles are produced by firing the granules at a temperature below the melting point, it is thought that a polygonal step structure is unlikely to form, and even if it is formed, the step structure will disappear with slow cooling.

[0071] In thermal spraying, a mixture of combustion gas and oxygen can be used as the flammable gas combustion flame source. The volume ratio of combustion gas to oxygen is preferably 1:3.5 to 1:6.0, more preferably 1:4.9 to 1:6.0, and even more preferably 1:4.9 to 1:5.3. This allows the volatilized raw materials to condense, and the formation of small-particle sizes can be suitably promoted. For example, a combustion gas flow rate of 7 Nm³ 3 Total oxygen flow rate of 35 Nm / hour 3 One example of a condition is that the volume ratio of combustion gas to oxygen is 1:5 per hour.

[0072] If there is an excess of combustion gas or oxygen during combustion, the unused gas may absorb heat during combustion, potentially lowering the flame temperature. It is preferable that the amount of surplus combustion gas not used is 20% or less of the supplied combustion gas. Similarly, it is preferable that the amount of surplus oxygen not used during combustion is 20% or less of the supplied oxygen.

[0073] The amount of combustion gas relative to the amount of raw material supplied is also important. Specifically, the net fuel gas ratio should be 1.05 Nm³. 3 / kg or more 2.00Nm 3 It is preferable that the amount is less than or equal to / kg. Here, the net gas ratio is the ratio of the net combustion gas amount to the raw material supply amount, and is determined according to formula (15) below. The net combustion gas amount is the amount of combustion gas used for net combustion, and is determined according to formula (16) or (17) below.

[0074]

number

number

number

[0075] Flammable gases such as propane, propylene, and acetylene can be used as combustion gases for thermal spraying, with propane being the most preferred. To transport the granules into the flammable gas, transport gases such as nitrogen, oxygen, and air can be used. The flow rate of the transported granules is preferably 20 m / sec to 60 m / sec. The thermal spraying temperature is preferably 1000°C to 3500°C, and more preferably 2000°C to 3500°C.

[0076] The amount of raw material supplied during thermal spraying is also important. Specifically, the mechanism of step structure formation changes depending on the time it takes for the material to cool from the temperature at which it passes through the thermal spray flame (the amount of heat supplied to the raw material particles) to room temperature. In particular, step structures are formed when primary raw material particles that have passed through a high-temperature flame are rapidly cooled. Even with the same flame temperature, if the number of primary raw material particles passing per unit time (processing rate per unit time) is high, step structures are less likely to form. From the viewpoint of forming step structures, it is preferable to supply a small amount of thermal spraying raw material. For example, the supply rate is preferably 20 kg / hour or less, more preferably 10 kg / hour or less, and most preferably 7 kg / hour or less.

[0077] Ferrite powder effectively exhibits a step structure when it contains elements with high vapor pressure, such as zinc (Zn). However, not only the contained elements but also the conditions during thermal spraying are important. Specifically, the step structure is more likely to develop when the sprayed material, after passing through the thermal spray flame, cools from a high temperature at a moderate rate. In firing, which is different from thermal spraying, the cooling rate is relatively slow. Therefore, as grain boundary growth occurs, the outer circumference of the step structure becomes non-linear.

[0078] The cooling rate significantly affects the magnetic properties, particularly the frequency characteristics of permeability. Specifically, particles rapidly cooled during thermal spraying have a relatively small grain size. Therefore, the loss coefficient (tanδ) is smaller at frequencies higher than 10 MHz. On the other hand, particles slowly cooled during firing have a larger grain size, resulting in a larger loss coefficient at high frequencies.

[0079] In this way, the properties of ferrite powder can be adjusted by controlling the thermal spraying conditions. By performing thermal spraying under favorable conditions, the shape of the resulting ferrite particles can be suitably adjusted. Furthermore, the vacancy ratio of the ferrite particles can be controlled within a desired range.

[0080] <<3. Ferrite resin composite materials>> The ferrite resin composite material of this embodiment includes the ferrite powder and resin described above. This composite material suppresses the shedding of ferrite particles without impairing moldability and fillability.

[0081] Examples of resins constituting the composite material include epoxy resins, urethane resins, acrylic resins, silicone resins, polyamide resins, polyimide resins, polyamide-imide resins, fluororesins, or combinations thereof. The silicone resin may be a modified silicone resin modified with acrylic, urethane, epoxy, and / or fluorine.

[0082] The composite material may contain components other than ferrite powder and resin. Examples of such components include solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as pigments, and / or thermally conductive particles.

[0083] The proportion of ferrite powder to the total solid content in the composite material is preferably 50% to 95% by mass, and more preferably 80% to 95% by mass. The proportion of resin to the total solid content in the composite material is preferably 5% to 50% by mass, and more preferably 5% to 20% by mass. By setting the proportions of ferrite powder and resin within the above ranges, the dispersion stability of the ferrite powder in the composite material, as well as the storage stability and moldability of the composite material, are improved, and the properties such as mechanical strength and magnetic properties of the composite (molded body) obtained by molding the composite material are also improved.

[0084] <<4. Ferrite resin composite>> The ferrite resin composite of this embodiment comprises a molded body of the ferrite resin composition described above. That is, the composite is manufactured by molding the ferrite resin composition. The molding method is not particularly limited and includes, for example, compression molding, extrusion molding, injection molding, blow molding, or calendering. Alternatively, a method of forming a coating film of the composite material on a substrate may also be used.

[0085] <<5. Electronic Components>> The electronic component of this embodiment comprises the ferrite resin composite described above. The electronic component may be a known component that utilizes the magnetic properties of ferrite. Examples of such components include transformers and inductors such as communication coils. The electronic component of this embodiment has the advantage of excellent long-term stability because it contains ferrite powder with small permeability change over time. [Examples]

[0086] This embodiment will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following embodiments.

[0087] (1) Preparation of ferrite powder [Examples 1-10] <Raw material mixture> α-Iron oxide (α-Fe2O3), manganese tetroxide (Mn3O4), zinc oxide (ZnO), and copper oxide (CuO) were used as raw materials. These were weighed and mixed using a Henschel mixer. During this process, the raw materials were weighed so that their respective amounts in terms of Fe2O3, MnO, ZnO, and CuO were as shown in the molar amounts in Table 1 below.

[0088] <Castration and crushing> The resulting mixture was calcined using a rotary kiln. Calcination was carried out by holding the mixture for 4 hours under the conditions (temperature and atmosphere) shown in Table 1 below. Next, the calcined material was coarsely ground using a dry bead mill (3 / 16 inch steel beads). Then, water was added and the material was finely ground using a wet bead mill (0.65 mm zirconia beads) to obtain a slurry. The particle size of the ground powder in the slurry is shown in Table 1 below.

[0089] <Granulation> Polyvinyl alcohol (PVA, 10% aqueous solution) was added as a binder to the obtained slurry. The amount of PVA added was adjusted at this time. The amount of PVA added in terms of solid content relative to the pulverized powder is shown in Table 1 below. After that, the slurry with the binder added was granulated using a spray dryer.

[0090] <Thermal spraying> The obtained granules were thermal sprayed and rapidly cooled in a flammable gas flame. Thermal spraying was performed under the conditions shown in Table 1 below (propane gas flow rate, total oxygen flow rate, raw material supply oxygen flow rate, combustion oxygen flow rate, raw material supply amount, airflow rate, and thermal spray temperature). In addition, the product was rapidly cooled by introducing cooling air into the combustion gas immediately after thermal spraying. Furthermore, the product was recovered using a cyclone installed downstream to obtain the thermal spray material. Coarse powder was removed from the obtained thermal spray material using a sieve, and then fine powder was removed using a classifier to obtain ferrite powder consisting of Mn-Zn ferrite particles.

[0091] The manufacturing conditions for the ferrite powders in Examples 1 to 10 are summarized in Table 1 below. Examples 1 and 7 to 10 are example samples, while Examples 2 to 6 are comparative examples.

[0092] [Table 1]

[0093] (2) Evaluation The ferrite powders prepared in Examples 1-10 were evaluated for various properties as follows.

[0094] <Chemical analysis> The metal content of ferrite powder was determined by chemical analysis. First, 0.2 g of ferrite powder was weighed, and 60 ml of pure water, 20 ml of 1N hydrochloric acid, and 20 ml of 1N nitric acid were added to it. The mixture was then heated to prepare an aqueous solution in which the sample was completely dissolved. The resulting aqueous solution was placed in an ICP analyzer (Shimadzu Corporation, ICPS-10001V) to measure the metal content.

[0095] <Redox titration> Redox titration revealed that the ferrite powder contains divalent iron (Fe 2+ The amount of ) was determined. Redox titration was performed in accordance with JIS M 8213, and potassium permanganate was used instead of potassium dichromate.

[0096] <xrd> The ferrite powder was analyzed by X-ray diffraction (XRD). The analysis was performed under the following conditions.

[0097] - X-ray diffractometer: Panalytical X'pertMPD (including high-speed detector) - Source: Co-Kα - Tube voltage: 45kV -Tube current: 40mA - Scan speed: 0.002° / sec (continuous scan) - Scan range (2θ): 15~90°

[0098] Based on the obtained X-ray diffraction profiles, the respective content ratios of the spinel phase, ZnO phase, and α-Fe2O3 phase in the ferrite powder were determined. Furthermore, the lattice constant of the spinel phase was estimated by Rietveld analysis of the X-ray diffraction profiles, and the crystallite size of the spinel phase was determined according to Scherrer's formula.

[0099] Furthermore, the amounts of Fe, Mn, Zn, and Cu determined by chemical analysis (unit: mass%), and the amount of divalent iron (Fe) determined by redox titration 2+ The amount of (unit: mass%) and the amount of α-Fe2O3 (unit: mass%) obtained by XRD analysis were used to calculate the vacancy fraction and Fe excess ratio of the spinel phase. Specifically, the calculations were performed according to equations (1) to (10) above.

[0100] <Particle shape and surface structure> The shape and surface structure of the particles in the ferrite powder were evaluated as follows. First, the ferrite powder was observed using a scanning electron microscope (SEM; Hitachi High-Technologies Corporation, SU-8020). The magnification was set to 50,000x. Images were taken with 1 to 30 particles, preferably 1 to 10, in the field of view. Ten random fields of view were taken to check for the presence or absence of polygonal step structures.

[0101] <Shape Factor> The shape factors (SF-1 and SF-2) of the ferrite powder were determined using a particle image analyzer (Malvern Panalytical, Morphologi G3). First, the ferrite powder was analyzed using the particle image analyzer. During the analysis, image analysis was performed for each of 30,000 particles in the powder, and circularity, perimeter, and equivalent circle diameter (CE Diameter) were automatically measured. At this time, an objective lens with a magnification of 10 times was used, and the sample amount was 3 mm 3 、and the particles were dispersed on a slide glass using a dispersion jig attached to this apparatus under the condition that the dispersion pressure was 5 bar

[0102] Among the obtained data, the average of the data of the particles within ±5% of the volume average particle diameter was determined as the average circularity, average perimeter, and average equivalent circle diameter (CE Diameter), and using these, SF-1 and SF-2 were calculated according to the following equations (18) and (19).

[0103]

Equation

Equation

[0104] <Tap density> The tap density of the ferrite powder was measured in accordance with JIS Z 2512-2012 using a USP tap density measuring device (Hosokawa Micron Corporation, Powder Tester PT-X).

[0105] <True specific gravity> The true specific gravity of the ferrite powder was measured in accordance with JIS Z8807:2012 using the gas displacement method. Specifically, the measurement was performed using a fully automatic true density measuring device (Mounttech Co., Ltd., Macpycno).

[0106] <BET specific surface area> The BET specific surface area of ​​ferrite powder was measured using a specific surface area measuring device (Macsorb HM model-1208, Mountec Co., Ltd.). First, approximately 10 g of ferrite powder was placed on weighing paper and degassed in a vacuum dryer. After confirming that the vacuum level was 0.1 MPa or less, it was heated at 200°C for 2 hours to remove moisture adhering to the particle surface. Then, the dehydrated ferrite powder (approximately 0.5-4 g) was placed in a standard sample cell dedicated to the measuring device and accurately weighed using a precision balance. Subsequently, the weighed ferrite powder was set in the measurement port of the measuring device and measured using the single-point method. The measurement atmosphere was 10-30°C and 20-80% relative humidity (no condensation).

[0107] <Particle size distribution> The particle size distribution of ferrite powder was measured as follows. First, 10 g of ferrite powder and 80 ml of water were placed in a 100 ml beaker, and 2 drops of sodium hexametaphosphate were added as a dispersant. Next, the mixture was dispersed using an ultrasonic homogenizer (SMT Corporation, UH-150 model). The output level of the ultrasonic homogenizer was set to 4, and dispersion was performed for 20 seconds. After that, the bubbles formed on the surface of the beaker were removed, and the resulting dispersion was introduced into a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7500nano) for measurement. The measurement conditions were a pump speed of 7, an internal ultrasonic irradiation time of 30, and a refractive index of 1.70-050i. From this measurement, the 10% diameter (D10), 50% diameter (volume-average particle size, D50), and 90% diameter (D90) in the volume particle size distribution were determined.

[0108] <Magnetic Properties - Saturation Magnetization, Remanent Magnetization, and Coercivity> The magnetic properties (saturation magnetization, remanent magnetization, and coercivity) of ferrite powder were measured as follows. First, ferrite powder was packed into a cell with an inner diameter of 5 mm and a height of 2 mm, and set in a vibrating sample type magnetic measuring device (Toei Kogyo Co., Ltd., VSM-C7-10A). An applied magnetic field was swept up to 5 kOe, and then the applied magnetic field was decreased to generate a hysteresis curve. From the data of this curve, the saturation magnetization σs, remanent magnetization σr, and coercivity Hc of the ferrite powder were determined.

[0109] <Magnetic permeability> The magnetic permeability of ferrite powder was measured using an RF impedance / material analyzer (Agilent Technologies, Inc., E4991B) and a magnetic material measurement electrode (16454A). First, 9 g of ferrite powder and 1 g of binder resin (Kynar301F: polyvinylidene fluoride) were placed in a polyethylene container (capacity 100 ml) and stirred and mixed using a ball mill at a rotation speed of 100 rpm. Next, the resulting mixture (approximately 0.6 g) was filled into a die (inner diameter 4.5 mm, outer diameter 13 mm) and molded into a body by pressurizing it with a pressure of 40 MPa for 1 minute using a press machine. The resulting molded body was heat-cured at 180°C for 1 hour using a hot air dryer to prepare a sample for measurement. The obtained sample for measurement was set in the RF impedance / material analyzer, and the outer diameter, inner diameter, and height of the sample, which had been measured in advance, were input. During the measurement, the amplitude was set to 100mV, and the measurement frequency range of 1MHz to 3GHz was swept on a logarithmic scale. Then, the real part (μ') and imaginary part (μ'') of the complex permeability at a frequency of 50MHz were determined.

[0110] Furthermore, the loss coefficient (tanδ) and the μ'Q product were calculated according to equations (11) and (12) above, using the real part (μ') and imaginary part (μ'') of the complex permeability after 72 hours at 50 MHz.

[0111] Furthermore, the change in the real part of the magnetic permeability (μ') at 50 MHz was measured over time up to 17,520 hours. Then, using the obtained data, the rate of change in magnetic permeability was calculated according to equations (13) and (14) above.

[0112] (3) Evaluation results The evaluation results obtained for the ferrite powders of Examples 1 to 10 are shown in Tables 2 to 6 below. In addition, the time evolution of the real part of the magnetic permeability (μ') of the ferrite powders of Examples 1 and 5 is shown in Figure 1 (Example 1) and Figure 2 (Example 5).

[0113] The ferrite powders in comparative examples 2 and 3 had a low Fe content of 54.53 mass% or less and a high Zn content of 3.64 mass% or more (Table 2). As a result, the loss coefficient (tanδ) at 50 MHz was large (0.028 or more) and the μ'Q product was small (330 or less) (Table 5). These ferrite powders had high losses and were found to be unsuitable for high-frequency applications such as inductors.

[0114] The ferrite powder in Comparative Example 4 had a high Fe content of 63.11% by mass and zero (0) Zn content (Table 2). As a result, its real permeability (μ') was low at 6.45 (Table 5). This ferrite powder had low permeability and was found to be unsuitable for applications such as inductors.

[0115] The ferrite powder in Comparative Example 5 had a high Zn content of 3.30 mass% (Table 2). As a result, the loss coefficient (tanδ) was large at 0.024, and the μ'Q product was small at 379 (Table 5). In addition, the vacancy fraction was high at 100.0%, and the rate of change in magnetic permeability was large at 0.061 (Tables 3 and 6). This ferrite powder was found to have high losses and poor stability of magnetic permeability over time.

[0116] The ferrite powder in Comparative Example 6 contained aggregates (Table 4). As a result, the shape factors SF-1 and SF-2 were large at 126-130, and the volume-average particle size (D50) was large at 23.11 μm (Table 4). Furthermore, no step structure was observed on the particle surface (Table 4). This ferrite powder had a large loss factor (tanδ) of 0.084 and a small μ'Q product of 107 (Table 5). In addition, the rate of change of magnetic permeability was large at 0.081 (Table 6). This ferrite powder was found to have high loss and poor stability of magnetic permeability over time. Furthermore, this ferrite powder was considered to have poor packing properties when used in composite materials (composites).

[0117] In contrast, the ferrite powders of Examples 1 and 7-10 were perfectly spherical (Table 4). Therefore, SF-1 and SF-2 were small, ranging from 10¹ to 10², and they had a polygonal step structure on their surface, while D50 was relatively small, less than 9.92 μm (Table 4). The vacancy ratio was also less than 80.5 mol% (Table 3). These ferrite powders had a real part of magnetic permeability (μ') of 8.23 ​​or higher and a μ'Q product of 439 or higher (Table 5). Furthermore, the rate of change of magnetic permeability was small, less than 0.038, and in particular, the rate of change of magnetic permeability of the ferrite powder of Example 9 was extremely small, at 0.005 (Table 6). Thus, it was found that these ferrite powders have high magnetic permeability, low loss, and small change in magnetic permeability over time.

[0118] From the above results, it can be understood that, according to this embodiment, a ferrite powder with excellent permeability stability over time can be obtained while maintaining high packing, high permeability at high frequencies, and low loss.

[0119] [Table 2]

[0120] [Table 3]

[0121] [Table 4]

[0122] [Table 5]

[0123] [Table 6] < / xrd>

Claims

1. A ferrite powder containing iron (Fe) in a proportion of 56.0% to 63.0% by mass, manganese (Mn) in a proportion of 7.0% to 13.0% by mass, and zinc (Zn) in a proportion of 1.0% to 3.0% by mass, The ferrite powder contains spherical ferrite particles mainly composed of the spinel phase. The spinel phase has an iron (Fe) content that is in excess of the stoichiometric ratio, and a vacancy fraction of 0 mol% or more and 90 mol% or less. The ferrite powder is a ferrite powder having a shape factor SF-1 of 100 or more and 110 or less, and a volume-average particle size (D50) of 2.0 μm or more and 20 μm or less.

2. α-Iron oxide (α-Fe ２ O ３ The ferrite powder according to claim 1, wherein the content of ) is 0.0% by mass or more and 3.0% by mass or less.

3. The ferrite powder according to claim 1 or 2, wherein the copper (Cu) content is 0.0% by mass or more and 0.5% by mass or less.

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