Metal powder

Abstract

To provide metal powder capable of being formed into a green compact usable as a magnetic core for an inductor with a low-level eddy current loss even when the green compact is produced with metal powder whose average particle diameter is 1.50 μm or less.SOLUTION: Metal powder contains, by mass concentration, 1.0 to 13.0% Si, 0.10 to 8.00% Cr and the balance Fe with inevitable impurities. The metal powder has an electrical insulation coating sheet of a metal oxide on a surface thereof. In the metal powder, if D50 of a number-based primary particle diameter by a SEM measurement is X (μm) and D50 of a volume-based secondary particle diameter by a laser diffraction grain size measurement is Y (μm), X is 0.10 to 1.50 μm and a ratio of Y and X (Y / X) is 1.50 or less. Thus, the metal powder having a low coercive force, high saturation magnetization and excellent rust resistance can be obtained, and furthermore, a green compact with a low core loss can easily be obtained.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to metal powders, and particularly to metal powders made of an iron alloy suitable for inductors.

Background Art

[0002] In recent years, small portable devices typified by smartphones and tablet PCs have been advancing in high functionality and multifunctionality. Along with this, there has been an increasing demand for inductors in power circuits to cope with an increase in the number of mounted units and a large current due to the high functionality of integrated circuit ICs. In addition, in response to the demand for further miniaturization and thinning of portable devices, there has also been an increasing demand for miniaturization and low profile of inductors.

[0003] Conventionally, ferrite materials have been used for the magnetic cores of inductors. However, since the saturation magnetic flux density of ferrite is low, when miniaturized, the DC superposition characteristics deteriorate due to saturation magnetism, and a large current cannot flow. For this reason, recently, metal powders, which are iron-based metal magnetic fine particles with a high saturation magnetic flux density, have attracted attention as magnetic core materials for small inductors. Furthermore, in order to achieve miniaturization and weight reduction of passive elements including inductors and to reduce noise due to magnetostriction of inductors, etc., the operating frequency of electric circuits is being increased. Along with this, it is important to improve the core loss (also referred to as "magnetic core loss") due to an increase in eddy current loss in inductors using compacted powders made by compression molding of metal powders as magnetic cores.

[0004] For example, Patent Document 1 discloses "soft magnetic alloy powders". It is described that by forming an insulating layer by attaching a silica film or fine silica particles obtained by hydrolysis of alkyl silicate to the powder surface, the specific resistance of the compacted powder made by compression molding of the soft magnetic alloy powder increases, and the eddy current loss is reduced.

[0005] In addition, Patent Document 2 discloses "Si oxide film-coated soft magnetic powder". In this Si oxide film-coated soft magnetic powder, a SiOx (x = 1 to 2) deposited oxide film is formed on the surface of iron powder through a diffusion layer of a Si-Fe-O ternary oxide composed of Si, Fe, and O. The diffusion layer of the Si-Fe-O ternary oxide has a concentration gradient where the Fe concentration is high and the Si concentration is low at the interface with the iron powder, and the Fe concentration is low and the Si concentration is high at the interface with the SiOx (x = 1 to 2) deposited oxide film. By having this concentration gradient, the oxide film adheres firmly to the surface of the soft magnetic powder, solving the drawback that in the process of manufacturing a soft magnetic material by press-forming and firing soft magnetic powder coated with a conventional silicate film, the silicate film peels off or breaks during press-forming, unable to exhibit a sufficient insulation effect and unable to obtain a sufficient high specific resistance.

[0006] In addition, Patent Document 3 discloses "soft magnetic powder material". This soft magnetic powder material is characterized by having a coating layer mainly composed of silicon oxide coated on the surface of iron powder particles mainly composed of Fe. Thereby, it is described that the specific resistance of a soft magnetic molded body using the soft magnetic powder material can be increased, the eddy current generated in the soft magnetic molded body can be suppressed even when used in an alternating magnetic field, and the energy loss due to eddy current can be suppressed.

[0007] Furthermore, Patent Document 4 discloses "soft magnetic material powder". This soft magnetic material powder has a core containing an Fe-based soft magnetic material and an insulating film covering its surface. The insulating film contains an inorganic oxide and a water-soluble polymer and includes soft magnetic material particles. It is described that by molding this soft magnetic material powder into a magnetic core, sufficient density can be obtained, the magnetic permeability of the magnetic core can be increased, and a magnetic core having a high electrical resistance can be obtained by the insulating film and binder contained in the soft magnetic material powder.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

[0009] In order to further miniaturize an inductor that uses a compacted powder made by compression-molding metal powder as a magnetic core, it is important to reduce the particle size of the metal powder used. Conventionally, metal powder with an average particle size of 2 to 50 μm has been used to produce a compacted powder for the magnetic core of an inductor. For example, in a multilayer inductor, a small inductor with a size of 1.0 mm in length × 0.5 mm in width × 0.5 mm in height has been manufactured. However, for the manufacture of an inductor with an even smaller size, fine metal powder with a particle size of 1 μm or less is required.

[0010] However, in the technologies described in Patent Documents 1 to 4, when producing a compacted powder, metal powder with an average particle size of 1 μm or less is likely to aggregate, and once aggregated, it is difficult to disperse. Therefore, when surface coating is applied to metal powder with insufficient dispersion, the surface coating is formed on the aggregates. When a compacted powder is manufactured using metal powder with a surface coating on the aggregates, the aggregates are broken up by the pressure during press molding, and the surfaces of the particles that are not surface-coated come into contact with each other, resulting in electrical conduction. Thus, there is a problem that eddy current loss cannot be reduced.

[0011] An object of the present invention is to solve such problems of the prior art and provide metal powder that can be used as a magnetic core for an inductor with low eddy current loss even when a compacted powder is manufactured using metal powder with an average particle size of 1.50 μm or less. Here, the "average particle size" refers to the number-based D50 obtained by observing and imaging the particles of the metal powder using a scanning electron microscope (SEM), measuring 1000 to 2000 particles at a magnification of 20,000 times, and performing SEM image analysis, as described later.

Means for Solving the Problems

[0012] In order to achieve the above object, the inventors of the present invention earnestly studied the composition of metal powder mainly composed of iron powder, the amount of oxide coating for the purpose of insulating particles from each other, and the particle size of metal powder. As a result, it was found that it is important to contain an appropriate amount of Si and Cr in Fe, coat the metal powder with an appropriate amount of oxide, and further make the particle size of the aggregate of the metal powder coated with oxide be below a certain size. In particular, by making the particle size of the aggregate of the metal powder coated with oxide be below a certain size, it is possible to suppress a decrease in the electrical resistance of the compact due to the disintegration of the aggregate caused by pressing when forming the compact, thereby ensuring the electrical resistance due to the oxide coating and facilitating the production of a compact with less core loss due to eddy current. This is a newly found knowledge.

[0013] The present invention has been completed through further studies based on such findings. That is, the gist of the present invention is as follows. (1) A metal powder containing Si: 1.0 to 13.0% and Cr: 0.10 to 8.00% by mass concentration, with the balance being Fe and inevitable impurities, having an insulating film of metal oxide on the surface of the metal powder. When the D50 of the primary particle size based on the number in SEM measurement is X (μm) and the D50 of the secondary particle size based on volume by laser diffraction particle size measurement is Y (μm), X is 0.10 to 1.50 μm and the ratio of Y to X (Y / X) is 1.50 or less. (2) The metal powder according to (1), further containing S (sulfur): 100 to 2000 ppm by mass concentration. (3) The metal powder according to (1) or (2), further containing Ni: 10.0% or less and / or Al: 5.0% or less by mass concentration. (4) In any one of (1) to (3), at least one element of Si, Ti, and Al is contained in the insulating film of the metal oxide in an amount of 0.001 to 0.100 mol / m 2 per unit surface area of the metal powder. (5) In any one of (1) to (4), the metal powder is characterized in that the number ratio of spherical particles to the total number of observed particles in the SEM measurement of the metal powder is 45% or more.

Advantages of the Invention

[0014] According to the present invention, since the metal powder having an average particle diameter of 1.50 μm or less has its surface coated with an oxide in a state with less aggregation, by molding it into a compact, a magnetic core for an inductor having a small size and a high electrical resistance can be obtained.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] [Composition and Characteristics of Metal Powder] The metal powder of the present invention is a metal powder (Fe alloy powder) mainly composed of Fe. That is, the metal powder of the present invention contains Si: 1.0 to 13.0% and Cr: 0.10 to 8.00% in terms of mass concentration, and the balance is Fe and inevitable impurities. And it has an insulating film of metal oxide on the surface of the metal powder. Further, when the D50 of the number-based primary particle diameter in the SEM measurement is X (μm) and the D50 of the volume-based secondary particle diameter by laser diffraction particle size measurement is Y (μm), X is 0.10 to 1.50 μm, and the ratio of Y to X (Y / X) is 1.50 or less. Here, the "primary particle diameter" refers to the size of particles whose contours can be identified in the SEM image, and the "secondary particle diameter" refers to the size of aggregates in which primary particles aggregate and behave like one particle. Also, the "number-based" is a standard for creating a particle size distribution, showing the distribution of the percentage of the number in each range in the total number of particles, and the "volume-based" similarly shows the distribution of the percentage of the volume in each range in the total volume of particles.

[0017] Further, it is preferable that the metal powder contains S (sulfur) at a mass concentration of 100 to 2000 ppm. And in the insulating film of the metal oxide, at least one element among Si, Ti, and Al is 0.001 to 0.100 mol / m per unit surface area of the metal powder 2 It is preferably contained. Further, it is preferable that the number ratio of spherical particles to the total number of observed particles in the SEM measurement of the metal powder is 50% or more. Hereinafter, % and ppm in the composition mean mass concentration.

[0018] Next, the reasons for the composition limitations will be described.

[0019] [Si: 1.0 to 13.0%] In the metal powder mainly composed of Fe, Si is an element that dissolves in the base Fe and contributes to the decrease in the coercive force of the metal powder. In order to achieve a desired low coercive force, Si needs to be contained at 1.0% or more. On the other hand, when it exceeds 13.0%, the coercive force increases and the saturation magnetization decreases. For this reason, Si is limited to the range of 1.0 to 13.0%. Preferably, it is 3.0 to 11.0%. More preferably, it is 6.0 to 9.0%.

[0020] [Cr: 0.10 to 8.00%] Cr is an element that deteriorates the magnetic properties of the metal powder but improves the corrosion resistance. In the metal powder of the present invention, it needs to be contained at 0.10% or more. When Cr is less than 0.10%, rust is likely to occur on the particle surface. On the other hand, when it is contained in a large amount exceeding 8.00%, the saturation magnetization decreases. For this reason, Cr is limited to the range of 0.10 to 8.00%. Preferably, it is 0.50 to 6.00%. More preferably, it is 0.70 to 4.00%. Here, the corrosion resistance means the rust resistance described later.

[0021] [Optional elements] Furthermore, examples of the optional elements that can be mixed include S (sulfur), Ni, and Al.

[0022] [S (sulfur): 100~2000 ppm] The metal powder of the present invention may contain S (sulfur) at 100 to 2000 ppm as an optionally selectable element that can be mixed. The metal powder (Fe-Si-Cr alloy powder) mainly composed of Fe of the present invention and containing Si and Cr as described above is a metal magnetic fine particle having a D50 of the number-based primary particle diameter measured by SEM of 0.10 to 1.50 μm, and can be mainly produced by the CVD method or the PVD method described later. The CVD method and the PVD method are methods of forming particles in the gas phase at a high temperature. However, when the metal powder flies in the gas and crystal growth occurs, polyhedral particles in which specific crystal planes preferentially grow are mixed. S (sulfur) is concentrated on the surface of the generated particles. This surface enrichment layer of S suppresses the preferential growth of specific crystal planes, so that crystal growth is uniform in all directions, and the abundance ratio of particles grown into a spherical shape can be increased. If S is less than 100 ppm, the suppressing effect on the generation of this polyhedron is insufficient. If it exceeds 2000 ppm, the amount of S enrichment on the surface of the particles becomes excessive, and the growth of the particles is extremely suppressed, and only particles finer than the target particle size range can be obtained. For this reason, it is preferable to contain S (sulfur) at 100 to 2000 ppm. More preferably, it is 300 to 1500 ppm, and still more preferably, it is 500 to 1000 ppm.

[0023] [Ni: 10.0% or less] The metal powder of the present invention may contain Ni at 10.0% or less (excluding 0%) as an optionally selectable element that can be mixed. Ni is an element that reduces the saturation magnetization of the metal powder when mixed with the metal powder and the Fe content decreases. Although it is preferably reduced as much as possible, Ni has an effect of suppressing the heat generation due to the oxidation of the Fe alloy powder compared to other elements, can ensure the safety of handling the Fe alloy powder, and the action of reducing the saturation magnetization is slow, so it is acceptable if the content is 10.0% or less. In addition, for the purpose of improving the saturation magnetic flux density as the core, it is more preferably 5.0% or less. Still more preferably, it is 3.0% or less.

[0024] [Al: 5.0% or less] In addition, as an optional element that can be mixed, Al may be added in an amount of more than 0% and 5.0% or less (excluding 0%). Similar to Ni, when Al is mixed into the metal powder and the Fe content decreases, the saturation magnetization of the metal powder will decrease, and it is preferably reduced as much as possible. However, since Al has an effect of suppressing the heat generation due to the oxidation of the Fe alloy powder compared to other elements, in order to ensure the safety of handling the Fe alloy powder, it is acceptable if the content is 5.0% or less. More preferably, it is 1.0% or less. Even more preferably, it is 0.5% or less.

[0025] [Remaining composition] The remainder other than the above-described composition is Fe and inevitable impurities. Examples of inevitable impurity elements include elements such as C, N, P, Mn, and Cu. These elements are elements that reduce the saturation magnetization of the metal powder. If the total content is 3% or less, a practically fatal decrease in magnetic properties does not occur, so it is acceptable. From the viewpoint of improving the saturation magnetic flux density of the core, it is more preferable that the total content of the above-described elements is 1% or less. Even more preferably, it is 0.5% or less.

[0026] [Particle size (average particle diameter) of metal powder] [D50 of the primary particle diameter based on the number of SEM measurements: 0.10 to 1.50 μm] The metal powder was observed and imaged using a scanning electron microscope (SEM), and the D50, which is the cumulative 50% primary particle diameter based on the number of particles measured at a magnification of 20,000 times with 1000 - 2000 measured particles (hereinafter also referred to as "SEM measurement"), was limited to the range of 0.10 - 1.50 μm. The reason for this limitation is that when D50 is less than 0.10 μm, the coercive force becomes too large, and it becomes difficult to disperse aggregation in the subsequent surface coating process. Also, in order to manufacture an inductor with further miniaturization compared to a conventional inductor using a metal powder with an average particle diameter of 1.50 - 50 μm as the magnetic core material, the D50 of the primary particle diameter of the metal powder used for the magnetic core needs to be 1.50 μm or less in order to reduce the size of the magnetic core. Preferably, it is 0.20 - 1.00 μm. More preferably, it is 0.30 - 0.90 μm.

[0027] [Ratio of the volume-based secondary particle diameter by laser diffraction particle size measurement to the primary particle diameter of the SEM measurement] The particle size obtained by a laser diffraction particle size distribution measuring device (hereinafter also referred to as "laser diffraction particle size measurement") is the secondary particle diameter in the state where the metal powder is aggregated. When the D50, which is the cumulative 50% secondary particle diameter based on volume by this laser diffraction particle size measurement, is defined as Y (μm), and the D50 of the number-based primary particle diameter of the aforementioned SEM measurement is defined as X (μm), the ratio of Y to X (Y / X) was limited to the range of 1.50 or less. When Y / X exceeds 1.50, aggregates break up under the pressure of the press that forms the metal powder coated with an oxide into a green compact, and a phenomenon occurs where the surfaces of the uncoated particles come into contact with each other and electrical conduction occurs in many places within the green compact. Therefore, the electrical resistance of the green compact decreases and the eddy current loss of the inductor cannot be reduced. Preferably, it is 1.45 or less. More preferably, it is 1.40 or less.

[0028] [Number ratio of spherical particles] Further, it is preferable that the metal powder of the present invention has a spherical particle number ratio of 45% or more with respect to the total number of observed particles obtained by the above-described SEM measurement. The "spherical particle number ratio" referred to herein is the ratio (%) of the number of particles visually observed and determined to be spherical out of 1000 particles by imaging the metal powder with SEM. If the shape of each particle of the metal powder is a polyhedron, aggregates (aggregated particles) formed by the contact of the flat portions of the polyhedra between the particles are difficult to disperse because the binding force is strong. In order to easily disperse the particles, it is desirable that the abundance ratio (number ratio) of spherical particles is high. When the number ratio of spherical particles is less than 45%, measures such as extending the time for dispersion are required to disperse the aggregates, which becomes complicated. For this reason, the number ratio of spherical particles of the metal powder of the present invention is preferably in the range of 45% or more. More preferably, it is 60% or more. Even more preferably, it is 70% or more.

[0029] [Insulating film] The surface of the metal powder of the present invention is coated with an insulating film made of an inorganic oxide. In the film, at least one element of Si, Ti, and Al is contained in an amount of 0.001 to 0.100 mol / m per unit surface area of the metal powder. 2 It is preferable to contain. Si, Ti, or Al is an element that can be easily and inexpensively coated as an oxide on the metal surface. If the amount of these elements is less than 0.001 mol / m per unit surface area of the metal powder, the amount of the film is insufficient and the insulating effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.100 mol / m, adhesion between particles may occur during coating, and aggregates that are difficult to disperse may be formed. A more preferable range is 0.002 to 0.080 mol / m. 2 If it is less than, the amount of the film is insufficient and the insulating effect cannot be obtained sufficiently. Also, if it exceeds 0.100 mol / m, 2 particle adhesion during coating may occur, and aggregates that are difficult to disperse may be formed. A more preferable range is 0.002 to 0.080 mol / m. 2 Even more preferably, it is 0.005 to 0.070 mol / m. 2 is.

[0030] In addition, as agents for surface coating with the above-mentioned oxides, ethyl silicate, alkoxysilane, etc. for oxides containing Si, titanate coupling agents, organic titanates, etc. for oxides containing Ti, and Al-based coupling agents, etc. for oxides containing Al can be applied.

[0031] [Method for manufacturing metal powder] Next, the method for manufacturing the metal powder of the present invention will be described. The metal powder of the present invention is preferably manufactured using chemical vapor deposition (hereinafter also referred to as CVD). In CVD, alloy elements such as Fe, Si, and Cr are reacted with high-temperature chlorine gas to generate chloride gases of each element, or chloride gases obtained by heating chlorides of each element such as Fe, Si, and Cr to a high temperature and vaporizing them are mixed in a predetermined ratio with a mixed gas, and further a gas obtained by vaporizing S (sulfur) at a high temperature is mixed in a predetermined ratio. At appropriate temperatures, hydrogen is reacted to reduce the chlorides, and a metal powder having a desired composition containing Si, Cr, S (sulfur), etc. is obtained. In the method for manufacturing the metal powder of the present invention, it is preferable to adjust the concentration of the chloride gas, the reaction temperature, and the reaction time so as to obtain a desired particle diameter.

[0032] After the reaction (reduction reaction), the obtained metal powder is further subjected to a dechlorination process. The dechlorination process is a process of washing the obtained metal powder with a solvent to reduce and adjust the chlorine concentration. As the solvent to be used, it is preferable to use a solvent that dissolves unreacted chlorides and by-products generated by the reduction reaction. Examples of such solvents include water-soluble inorganic solvents such as water, or organic solvents such as aliphatic alcohols such as ethyl alcohol. A slurry containing the metal powder is formed at the end of the dechlorination process.

[0033] Note that instead of the above-mentioned CVD, it may also be manufactured using PVD (Physical Vapor Deposition). PVD includes vacuum evaporation, sputtering, and ion plating, which are techniques for heating and evaporating a raw material substance under vacuum or ionizing it to generate fine particles. In PVD, a dechlorination process is not required, but metal powder is put into a solvent to make a slurry before proceeding to the surface coating process.

[0034] Next, in the surface coating process with an oxide, the slurry containing the metal powder formed at the end of the previous process is dispersed by a wet disperser, and then a chemical for surface coating with an oxide is added to the slurry and dispersed while stirring for a predetermined time by the wet disperser. Then, the solvent is discharged and dried in a vacuum. Since dry aggregation occurs when it becomes dry metal powder, it is passed through a dry disperser (for example, a pin mill or a dry jet mill can be applied) or a classifier (for example, a dry cyclone can be applied) to break up or remove coarse aggregates. As the wet disperser used in this process, a disperser with higher dispersing power than ultrasonic dispersers such as a thin-film swirling high-speed mixer (trade name: Filmix, manufactured by Primix Corporation) or a wet jet mill (trade name: Starburst, manufactured by Sugino Machine Limited) is preferable.

Examples

[0035] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited thereto.

[0036] As raw materials, chloride of Fe, chloride of Si, chloride of Cr, and S (sulfur) were prepared respectively. Then, these chlorides and S (sulfur) were heated to a high temperature (1100 °C) in a reaction apparatus to vaporize the chlorides and S (sulfur), generating chloride gases of each element and S (sulfur) gas. The generated chloride gases of each element were mixed with varying mixing ratios to achieve the composition of each metal powder described in Table 1 shown below, resulting in various mixed gases. The obtained mixed gases were reacted with hydrogen at a predetermined reaction temperature (1100 - 1200 °C) to reduce the chloride gases and produce metal powders (Fe - Si - Cr alloy powders), while incorporating S (sulfur) into the metal powders. Then, a dechlorination process of washing the obtained various metal powders with pure water was carried out to remove the remaining chlorides.

[0037] Next, after dispersing the water slurry of the metal powder after the dechlorination process with a wet jet mill, as agents for surface coating with oxides, ethyl silicate for oxides containing Si, titanate - based coupling agent for oxides containing Ti, or Al - based coupling agent for oxides containing Al were added to the water slurry of the above - mentioned metal powder. While dispersing the metal powder with a wet jet mill or an ultrasonic disperser, the slurry was stirred for a predetermined time, then dehydrated and dried while heating to 50 °C in a vacuum to form a film of Si, Ti, or Al oxide on the surface of the metal powder. After that, the various dried metal powders were dispersed with a dry jet mill and then classified with a dry cyclone to remove coarse aggregates.

[0038] Regarding the obtained various metal powders, the element content of the metal powder, the content in the insulating film, particle size D50, spherical particle ratio, magnetic properties, rust resistance, and further the core loss of the compacted powder were investigated. The investigation methods were as follows.

[0039] (1) Element content of the metal powder, content in the insulating film The Si content of the alloy elements contained in the metal powder was measured using wet analysis (silicon dioxide gravimetry). The Cr content of the alloy elements was measured using ICP (inductively coupled plasma). Furthermore, S (sulfur) contained in the metal powder was measured using the combustion method. In addition, the Si content in the insulating film (content per unit surface area of the metal powder) is a value obtained by converting the difference between the Si content analysis value of the powder coated with the insulating film and the Si content analysis value of the powder before coating with the insulating film into mol / g units as the Si content in the insulating film, and dividing it by the BET specific surface area m 2 / g of the powder before coating with the insulating film. (2) Particle size D50 and sphericity ratio For the obtained metal powder, the number-based primary particle size D50 was determined by SEM observation, imaging, and image analysis, and the sphericity ratio of spherical particles was determined. In addition, the volume-based secondary particle size D50 was measured by laser diffraction particle size measurement, and the ratio to the number-based primary particle size of the SEM measurement was determined. (3) Magnetic properties For the obtained various metal powders, the coercive force and saturation magnetization were measured using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.). (4) Rust resistance The obtained various metal powders (magnetic powders) were embedded and fixed in resin, and then the cross-section was mirror-polished to obtain test pieces for rust resistance measurement. These test pieces were held in a thermostatic and humidistatic chamber for a predetermined time, and then 20 particles were randomly selected from the particles in the test pieces to observe the presence or absence of rust, and the ratio of rusted particles was calculated. The thermostatic and humidistatic chamber was maintained under the conditions of temperature: 60°C and relative humidity: 95%. The holding time in the thermostatic and humidistatic chamber was set to 2000 hours. (5) Core loss of the compacted powder The obtained various metal powders were mixed and dispersed in resin (epoxy resin) to obtain various mixed powders. These mixed powders were filled into a ring-shaped mold (outer diameter: 13 mm, inner diameter: 8 mm), press-molded, and then the resin was cured to produce a toroidal core with a thickness of 3 mm. A winding with 20 turns on the primary side and 20 turns on the secondary side was given to the obtained core, and the core loss was measured using a B-H analyzer (SY-8218 manufactured by Iwatsu Measuring Co., Ltd.) under the conditions of magnetic flux density 0.025 T and frequency 1 MHz.

[0040] The above-obtained results are listed together in Table 1.

[0041]

Table 1

[0042] All examples of the present invention are metal powders that have a low coercive force of 10 Oe or less, retain a high saturation magnetization of 180 emu / g or more, and are excellent in rust resistance. Further, when formed into a compact, they have a remarkable effect of being able to produce a compact with a low core loss of 1000 kW / m 3 as follows.

[0043] On the other hand, comparative examples outside the scope of the present invention are metal powders having a high coercive force exceeding 10 Oe, a low saturation magnetization of less than 180 emu / g, or a reduced rust resistance. When formed into a compact, they have a high core loss exceeding 1000 kW / m 3 resulting in a compact with a high core loss.

[0044] Metal powder No. 1 in Table 1 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the Si content is too low, the coercive force is large and the core loss is large.

[0045] No. 5 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the Si content is too high, the coercive force is large and the core loss is also large.

[0046] No. 6 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the Cr content is too low, rusting occurs frequently, resulting in an increase in core loss due to low resistance caused by magnetite formation and an increase in eddy current loss.

[0047] No. 9 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the Cr content is too high, the coercive force is large. Also, since the Fe content is low, the saturation magnetization is low and the core loss is large.

[0048] No.10 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the S (sulfur) content is too low and the spherical particle number ratio is low, the packing density is low and the saturation magnetization is low. Due to surface contact, the resistance is low and the core loss is large.

[0049] Note that No.21, compared with this No.10, has almost the same content except that it does not contain S (sulfur). Nevertheless, the spherical particle number ratio is high because the reaction temperature in CVD was higher (1200 °C) than that of No.10 during production. As a result, the saturation magnetization is high and the core loss is low.

[0050] No.13 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. However, the S (sulfur) content is excessive, the coercive force is large, the primary particle diameter (X) is small, and it is difficult to disperse and agglomerate fine particles. Therefore, the ratio (Y / X) with the secondary particle diameter (Y) is large, resulting in a low packing density, a low saturation magnetization, and a large core loss.

[0051] No.14 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the Si content in the insulating film on the surface is too low, the resistance is low and the core loss is large.

[0052] No.15 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. However, since the Si content in the insulating film is excessive, aggregates that are difficult to disperse are formed in the process of surface coating. The secondary particle diameter ratio (Y / X) is high, the number of aggregates increases, and the saturation magnetization is low. Contact occurs due to the new surface without an insulating film formed by the dissociation of the aggregates, resulting in a low resistance and a large core loss.

[0053] No. 16 is the result of dispersion by an ultrasonic disperser in the process of surface coating with an oxide. Although the secondary particle size ratio (Y / X) is high and there are many aggregates, this is because the ability (dispersion power) of the ultrasonic disperser during the production of metal powder was small, resulting in a large secondary particle size (Y). As a result, the packing density is low, the saturation magnetization is low, and due to the low resistance, the core loss is large.

[0054] Note that for No. 3, the content of each element, the primary particle size (X), etc. are the same as those of No. 16. Nevertheless, the reason the secondary particle size (Y) is small is that the dispersion power of the wet jet mill during the production of metal powder was large and aggregates could not be formed. As a result, it has a low coercive force and a low core loss.

[0055] No. 17 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the spherical particle number ratio is low, the packing density is low, the saturation magnetization is low, and due to surface contact, the resistance is low and the core loss is large.

[0056] No. 18 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. The primary particle size (X) is fine, the coercive force is large, and it is difficult to disperse and aggregate fine particles during the surface coating process. Therefore, due to the high secondary particle size ratio (Y / X), there are many aggregates, and the packing density is low and the saturation magnetization is low.

[0057] No. 20 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. Since the primary particle size (X) is large and the secondary particle size (Y) is also large, the core loss is large.

[0058] No. 24 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. The Ni content is excessive, the coercive force is large, and due to the low Fe content, the saturation magnetization is low, and the core loss is large.

[0059] No. 27 is the result of dispersion by a wet jet mill in the process of surface coating with an oxide. The Al content is excessive, resulting in a large coercive force. Also, due to the low Fe content, the saturation magnetization is low and the core loss is large.

[0060] No. 29 and 32 are the results of dispersion by a wet jet mill in the process of surface coating with an oxide. The surface coating amount is too small, and due to the low resistance, the core loss is large.

[0061] No. 30 and 33 are the results of dispersion by a wet jet mill in the process of surface coating with an oxide. The surface coating amount is excessive, and the number of aggregates that are difficult to disperse in the surface coating process increases, resulting in a low saturation magnetization. When the aggregates are broken up, contact occurs on new surfaces without an insulating film, resulting in a low resistance and a large core loss.

Claims

1. A metal powder containing, by mass concentration, Si: 1.0 to 13.0% and Cr: 0.10 to 8.00%, with the balance being Fe and inevitable impurities, wherein the surface of the metal powder is coated with an insulating film composed of an inorganic oxide. When the D50 of the number-based primary particle size measured by SEM is X (μm) and the D50 of the volume-based secondary particle size measured by laser diffraction particle size measurement is Y (μm), X is 0.10 to 1.50 μm and the ratio of Y to X (Y / X) is 1.50 or less.

2. The metal powder according to Claim 1, further containing, by mass concentration, S (sulfur): 100 to 2000 ppm.

3. The metal powder according to Claim 1 or 2, further containing, by mass concentration, Ni: 10.0% or less and / or Al: 5.0% or less.

4. On the insulating film of the inorganic oxide, at least one element among Si, Ti, and Al is 0.001 to 0.100 mol / m per surface area of the metal powder. ２ The metal powder according to any one of claims 1 to 3, characterized in that it contains the above.

5. The metal powder according to any one of Claims 1 to 4, wherein the number ratio of spherical particles to the total number of observed particles in the SEM measurement of the metal powder is 45% or more.

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