JP2005310919A - Composite magnetic material and magnetic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite magnetic material and a magnetic component manufactured thereof, having high electric resistance, and keeping high magnetic permeability up to a high frequency region. <P>SOLUTION: The composite magnetic material involves ferrite coated metal magnetic particles obtained by coating particles of a metal magnetic material with Ni-Zn ferrite, and the trace amount of an element having third ionization energy larger than Fe but smaller than Ni is added to the Ni-Zn ferrite. The magnetic component is obtained by rendering the composite magnetic material to compression molding and heat treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a composite magnetic material in which metal magnetic particles are coated with ferrite and a magnetic component produced by compression molding thereof. More specifically, the present invention relates to a magnetic component such as a transformer or a reactor mounted on a switching power supply.

  In recent years, various electronic devices have been reduced in size and weight, and there has been a demand for lower power consumption. Along with this, there is an increasing demand for highly efficient and compact switching power supplies as power supplies mounted on electronic devices. In particular, switching power supplies used in small information devices such as notebook computers and mobile phones, thin CRTs, and flat panel displays are strongly required to be small and thin.

  In conventional switching power supplies, magnetic components such as transformers and reactors, which are the main components, occupy a large volume. To reduce the size and thickness of switching power supplies, the volume of these magnetic components can be reduced. It was indispensable. Conventionally, a metal magnetic material such as Sendust or Permalloy or an oxide magnetic material such as ferrite has been used for the magnetic core of such a magnetic component.

  Metallic magnetic materials generally have a high saturation magnetic flux density and magnetic permeability, but have low electrical resistivity, so that eddy current loss is particularly large in the high frequency region. Switching power supplies tend to be highly efficient and miniaturized by driving the circuit at high frequency, but it is not possible to use metal magnetic materials as magnetic cores for magnetic components for switching power supplies due to the effects of eddy current loss. Have difficulty.

  On the other hand, an oxide magnetic material typified by ferrite has a higher electrical resistivity than a metal magnetic material, and therefore, an eddy current loss generated even in a high frequency region is small. However, when the transformer or the reactor is downsized, the magnetic flux density applied to the magnetic core increases even if the current flowing through the coil is the same. In general, since the saturation magnetic flux density of ferrite is smaller than that of a metal magnetic material, the magnetic flux is saturated in the magnetic core. For this reason, when an oxide magnetic material such as ferrite is used as a magnetic core of a magnetic component, there is a limit to downsizing.

  That is, regardless of which material is used, it has been difficult to satisfy both the high frequency driving and the miniaturization required for the magnetic components of the switching power supply. Recently, as a magnetic material having the advantages of both a metal magnetic material and an oxide magnetic material, a coating layer of an oxide magnetic material having a high electrical resistivity is formed on the surface of a metal magnetic material having a high saturation magnetic flux density and a high magnetic permeability. Magnetic materials have been proposed.

  For example, a high magnetic permeability material in which a coating layer of a high magnetic permeability metal oxide is formed on the surface of a metal magnetic material powder has been proposed (see Patent Document 1).

Further, the surface of the metallic magnetic material consisting of 1~10μm particles coated with _M-Fe x _{O 4} (where M = Ni, Mn, Zn, x ≦ 2) metal oxide magnetic material of the spinel composition represented by A high-density sintered magnetic body is proposed (see Patent Document 2).

  Further, a ferromagnetic fine particle powder of a metal or an intermetallic compound having a ferrite layer coating formed by ultrasonic excitation ferrite plating on the surface is compression-molded, and a magnetic path is formed between the ferromagnetic particles via the ferrite layer. There has been proposed a composite magnetic material that is characterized by forming (see Patent Document 3).

JP-A-53-91397 JP-A-56-38402 WO03 / 015109 pamphlet Powder metallurgy, 47 (7), 757 (2000)

  In a magnetic part formed by compression-molding the ferrite-coated metal magnetic particles, two things are required to achieve high magnetic permeability in a high frequency range. One is to increase the electrical resistivity in order to prevent eddy current loss, and the other is to not prevent magnetic path formation between the metal magnetic particles.

  In order to prevent the generation of eddy current, it is effective to use a ferrite having a high electrical resistivity (for example, Ni—Zn ferrite). Further, in order to improve the magnetic path formation between the metal magnetic particles, it is necessary that there are no voids at the interface between the metal magnetic particles and the ferrite coating layer and that they are chemically bonded.

  As a method of coating metal magnetic particles with ferrite, there is an ultrasonic excitation ferrite plating method (see Patent Document 3). In this method, the reaction is caused by adsorption of ions such as Fe using OH groups on the surface of the metal particles as nuclei. As the process proceeds, the chemical bond between the metal magnetic particles and the ferrite coating layer is low. In addition, since the growth form of ferrite is not a complete film, and is in a state where fine particles are attached, there are not a few voids at the interface. Therefore, a magnetic component in which ferrite-coated particles are simply compression-molded cannot achieve a significantly higher magnetic permeability than conventional materials.

When the ferrite coated particles are compression molded and then heat treated, the magnetic permeability is greatly improved. This is because an interfacial layer is formed by interdiffusion of atoms between the metal magnetic particles and the ferrite coating layer, voids are reduced, and chemical bonding is improved, so that magnetic path formation is facilitated. Conceivable. However, when electrons are lost together with the cations in the ferrite coating layer due to this interdiffusion, the remaining Ni ²⁺ causes electron emission / bonding as shown in the formula (I).

In addition, when Fe ²⁺ flows into the Ni or Zn site from the metal particles, the transfer of electrons as shown in the formula (II) occurs, including the originally existing Fe ³⁺ . When such electron movement occurs, the insulation of the ferrite coating layer decreases, and the magnetic permeability decreases due to eddy currents in the high frequency range, so it cannot be put into practical use.

  The present invention has been made in view of such problems, and the object of the present invention is to suppress the transfer of electrons of Ni and Fe ions by adding a trace element to the ferrite coating layer, and to resist resistance by heat treatment. An object of the present invention is to provide a composite magnetic material that suppresses a decrease in the rate and maintains a high magnetic permeability even in a high frequency range.

  In order to achieve such an object, the composite magnetic material of the first embodiment of the present invention includes ferrite-coated metal magnetic particles in which particles of a metal magnetic material are coated with Ni—Zn ferrite, and is third than Fe. A trace element having a large ionization energy and a third ionization energy smaller than that of Ni is added to Ni—Zn ferrite. The trace element may be Mn or Co, and the addition amount may be 0.1 mol% to 10 mol% based on the total metal elements in the Ni-Zn ferrite.

  The magnetic component according to the second embodiment of the present invention is formed by compression-molding the ferrite-coated metal magnetic particles of the first embodiment and then heat-treating at a temperature of 500 ° C. or higher. The magnetic component of this embodiment is useful as a magnetic core for a transformer and a reactor.

  As described above, with the composite magnetic material of the present invention, it is possible to produce a magnetic component that maintains a high magnetic permeability up to a high frequency range and has high electrical resistance and can operate in a high frequency range. This makes it possible to produce highly functional, small and thin magnetic components for switching power supplies such as notebook computers, small portable devices, and thin displays.

  The composite magnetic material according to the first embodiment of the present invention includes ferrite-coated metal magnetic particles in which particles of a metal magnetic material are coated with Ni—Zn ferrite, has a third ionization energy higher than that of Fe, and is higher than that of Ni. 3 A trace element having a small ionization energy is added to Ni—Zn ferrite.

  Metallic magnetic materials that can be used in the present embodiment include various soft magnetic materials such as pure iron, iron-silicon alloy, iron-nickel alloy, sendust alloy, cobalt and cobalt alloy, nickel and nickel alloy, and various amorphous alloys. Can be used. The particles of the metal magnetic material can take various shapes such as a spherical shape, a disc shape, a flake shape, a needle shape, and a granular shape. From the viewpoint of preventing the occurrence of stress during pressure molding, it is preferable to use substantially spherical particles with little shape anisotropy. The metal magnetic material desirably has an average particle diameter of 20 nm or more, preferably 50 nm or more, and 100 μm or less, preferably 30 μm or less. By having an average particle size within such a range, it is possible to prevent damage to the ferrite coating layer during pressure forming and achieve high electrical resistivity, while at the same time achieving high magnetic permeability.

  The particles of the metal magnetic material used in this embodiment are a method of reducing a metal oxide or the like by a gas reduction method or a solid reduction method, a method of thermally decomposing a carbonyl complex or the like, a method by electrolysis, a method by mechanical pulverization, a spray Can be produced by any method known in the art, such as the method according to (Atomization method).

In the present embodiment, as the ferrite for forming the ferrite coating layer, it is preferable to use NiZn ferrite having a high saturation magnetization and a high electrical resistivity of 10 ⁴ to 10 ⁶ Ω · m.

  It is desirable that the ferrite coating layer has a sufficient thickness to be maintained in the compact after compression molding of the composite magnetic material to give a high electric resistivity, and usually has a thickness of 20 nm or more, more preferably 50 nm or more. It is desirable. Further, the ratio of ferrite in the composite magnetic material is desirably 1% by volume or more and 50% by volume or less, preferably 1% by volume or more and 20% by volume or less, based on the volume of the composite magnetic material. By using ferrite within such a ratio range, it is possible to obtain a composite magnetic material having both large saturation magnetization and high electrical resistivity.

  Furthermore, the ferrite coating layer in the present invention further includes a trace element having a third ionization energy larger than the third ionization energy of Fe and smaller than the third ionization energy of Ni. Trace elements that can be used include Mn and Co as shown in Table 1, for example.

  When such a trace element (Met) is added to the ferrite coating layer, Met emits electrons instead of Ni as shown in formula (III) even if electrons are lost in mutual diffusion with the metal magnetic material. Therefore, the transfer of electrons of Ni element as in the formula (I) can be suppressed. This is due to the fact that the third ionization energy of Met is smaller than the third ionization energy of Ni.

In addition, even if Fe ²⁺ flows into the Ni or Zn site from the metal magnetic material due to interdiffusion, Met ³⁺ takes electrons from Fe ²⁺ and stabilizes it to Fe ³⁺ as shown in formula (IV). Transfer of electrons as in formula (II) can be suppressed. This is due to the fact that the third ionization energy of Met is larger than the third ionization energy of Fe.

  If a trace element having an appropriate third ionization energy is added to the ferrite coating layer in this way, even if atoms are interdiffused at the boundary between the metal magnetic material particles and the ferrite coating layer by the heat treatment, the insulating properties of the ferrite coating layer are reduced. The decrease can be suppressed. As a result, it is possible to realize a composite magnetic material that does not flow eddy current even in a high frequency range and maintains high magnetic permeability.

  The addition amount of the trace element is 0.1 to 10 mol%, preferably 1 to 10 mol%, based on the total metal elements in the ferrite coating layer. By using an addition amount within this range, composite magnetic material particles having high magnetic permeability and high electrical resistivity, suppressing the transfer of Ni and Fe electrons in interdiffusion during heat treatment and the resulting decrease in electrical resistivity. Can be obtained.

The metal magnetic material particles can be coated with the ferrite coating layer by, for example, a ferrite plating method. When the Ni—Zn ferrite coating layer is formed by a ferrite plating method, for example, an iron (II) salt such as FeCl ₂ , a nickel (II) salt such as NiCl ₂ , a Zn (II) salt such as ZnCl ₂ , a trace element source While dispersing metal magnetic material particles in a ferrite plating reaction solution in which a salt such as Met-Cl ₂ and, if necessary, an iron (III) salt such as FeCl ₃ is dissolved in water, the pH and temperature are controlled. It is carried out by adding an oxidizing agent (NaNO ₂ or the like) aqueous solution. The pH of the reaction mixture is preferably adjusted to neutral to alkaline, for example, about 7 to 11. The preferred reaction temperature is room temperature to 100 ° C, preferably 80 ° C. Furthermore, by applying ultrasonic waves to the reaction mixture using an ultrasonic horn or the like, the reaction mixture may be vigorously vibrated to promote coating layer formation. The film thickness and volume ratio of the ferrite coating layer in the produced composite magnetic material particles can be adjusted by controlling the reaction time. After completion of the coating, the produced composite magnetic material particles may be processed by operations such as drying and classification as necessary.

  The magnetic component according to the second embodiment of the present invention is characterized in that it is formed by compression-molding the above-mentioned composite magnetic material particles and then heat-treating at a temperature of 500 ° C. or higher.

  For compression molding of composite magnetic materials, for example, uniaxial compression molding that compresses and compresses in the vertical direction using a mold, compression rolling molding, and static pressure compression molding that compresses composite magnetic material particles in a rubber mold and compresses them in all directions. (Including cold static pressure compression molding (CIP), warm static pressure compression molding (WIP), hot static pressure compression molding (HIP)) can be used. Although the temperature in the case of compression molding is not specifically limited, Preferably it is 200-500 degreeC, More preferably, 300-400 degreeC is desirable. By performing compression molding within such a temperature range, the moldability of the composite magnetic material can be improved while maintaining the ferrite coating layer. The pressure applied during compression molding is not particularly limited, but is preferably 200 to 2000 MPa, and more preferably 400 to 1000 MPa. By using a pressure within such a range, it is possible to obtain a good molded body while maintaining the ferrite coating layer. At the time of compression molding, a lubricant (stearate, wax, etc.) and / or an auxiliary agent known in the art may be used.

Next, the semi-finished product obtained by compression molding of the composite magnetic material particles is heat-treated to form a magnetic part. The heat treatment in the present invention is desirably performed at a temperature in the range of 500 ° C. to 1000 ° C., preferably 600 ° C. to 800 ° C., for 1 second to 60 seconds, preferably 1 second to 30 seconds. By performing the heat treatment under such conditions, the gap between the metal magnetic particles and the ferrite coating layer is reduced, and at the same time, the chemical bondability is improved and the formation of the magnetic path is facilitated without reducing the electrical resistivity. It is possible to achieve high magnetic permeability. Any heating means known in the art such as resistance heating, radiation heating, conduction heating with a heating medium, discharge plasma heating (see Non-Patent Document 1), induction heating, and the like can be used. It is preferably carried out in an electric furnace. The heat treatment may be performed in the air or in an inert atmosphere such as He, Ar, N ₂ or the like.

  The magnetic component of the present invention can have various shapes depending on the intended application, for example, a rod shape, a donut shape, a flat plate shape, and the like. Since the magnetic component of the present invention has a high magnetic permeability and a high electric resistivity, it is particularly useful as a magnetic core of a transformer or a reactor that operates in a high-frequency region. It is useful as a magnetic core for transformers or reactors for switching power supplies used in devices and thin displays.

(Example 1)
First, a ferrite-coated metal particle powder was produced by an ultrasonic excitation ferrite plating method. As particles of the metal magnetic material, 20 g of Ni78Mo5Fe particles (Ni is 78% by mass, Mo is 5% by mass, and the balance is Fe; the average particle diameter is 8 μm) prepared by a water atomization method. As a pretreatment for ferrite plating, these particles were placed in a solution of H ₂ O: 300 ml, 47% H ₂ SO ₄ : 1250 μl and 2 mol / l HCl: 1250 μl (liquid temperature 70 ° C.), and subjected to ultrasonic waves for 5 minutes. Applied.

Thereafter, Ni78Mo5Fe particles were transferred into a glass reaction vessel containing pure water, and 19.5 kHz ultrasonic waves were applied. In this reaction vessel, the reaction solution (H ₂ O: 500 ml, FeCl ₂ .4H ₂ O: 7.95 g, NiCl ₂ .6H ₂ O: 2.38 g, ZnCl ₂ : 1.36 g and MnCl ₂ .4H ₂ O: 0 .26 g) and an oxidizing solution (H ₂ O: 500 ml, NaNO ₂ : 1.00 g) were supplied at a rate of 3 ml / min and 2 ml / min, respectively. Here, the pH of the reaction mixture was maintained at 10.0 by appropriately dropping ammonia water. By the above plating treatment, a Ni—Zn ferrite coating layer having a Mn ratio of 3 mol% is generated. After this plating treatment was performed for 60 minutes, the particles were classified and dried.

The ferrite-coated Ni78Mo5Fe particles were filled in a cemented carbide mold and molded into a ring core shape having an inner diameter of 3 mmφ, an outer diameter of 8 mmφ, and a height of about 3 mm by uniaxial pressing of 10 tons / cm ² (980 MPa). This ring core was put in an electric furnace at 600 ° C. for 1 minute in the atmosphere to perform heat treatment. The primary and secondary windings were wound around the ring core after the heat treatment for 5 turns, respectively, and the complex permeability μ = μ ′ + iμ ”was measured in a frequency range of 10 kHz to 10 MHz with a BH analyzer. The frequency dependence of the imaginary part μ ″ is shown as A and B in FIG. 1, respectively. (In FIG. 1, the real part μ ′ and the imaginary part μ ″ of the complex permeability are shown as a ratio to the vacuum permeability. )

(Example 2)
In the same manner as described in Example 1, a sample was prepared in which the amount of MnCl ₂ .4H ₂ O added to the reaction solution was 0.52 g and the ratio of Mn in the ferrite coating layer was 6 mol%. The frequency dependence of the real part μ ′ and the imaginary part μ ″ of the complex permeability of the obtained sample is shown as C and D in FIG.

(Comparative Example 1)
In order to clarify the effect of Mn addition in the above examples, the method of Example 1 was repeated except that MnCl ₂ .4H ₂ O was not used, and a sample in which Mn was not added to the ferrite coating layer was produced. . The frequency dependence of the real part μ ′ and the imaginary part μ ″ of the complex permeability of the obtained sample is shown as E and F in FIG.

(Evaluation)
Comparing the data A, C, and E of the real part μ ′ of the complex magnetic permeability in FIG. I understand that Further, when the data B, D, and F of the imaginary part μ ″ are compared, the peak of the imaginary part μ ″ is also shifted to the high frequency side as the amount of Mn added is increased. That is, the effect of suppressing the decrease in resistivity accompanying the heat treatment is clearly shown by the addition of Mn.

  However, comparing the data A and C of the real part μ ′ of the complex permeability in the low frequency region, it can be seen that the real part μ ′ of the complex permeability is smaller for C with a larger amount of Mn added. This is presumably because the crystal structure of the ferrite coating layer was disturbed by the addition of Mn. From this, taking into account the magnitude of the real part μ ′ of the complex permeability in the low frequency range required for the intended application and the frequency at which the reduction of the real part μ ′ of the complex permeability starts, Mn It can be seen that the amount of addition should be determined.

  From the above results, in accordance with the present invention, by adding a small amount of an element having an appropriate ionization energy such as Mn or Co to the ferrite coating layer of the ferrite-coated metal magnetic material particles, the metal magnetic material and the ferrite coating during heat treatment are added. Even if interdiffusion occurs at the interface with the layer, since the transfer of electrons of Ni and Fe ions is hindered, the decrease in resistivity due to heat treatment is suppressed, and the composite magnetism that maintains high permeability up to the high frequency range It became clear that the material was obtained.

The real part μ ′ and the imaginary part μ ″ of the complex magnetic permeability of the ferrite-coated metal magnetic particles described in Example 1, Example 2 and Comparative Example 1 of the present invention with 3 mol% of Mn added, 6 mol% added and without added. Is a graph in which is plotted against frequency.

Claims (5)

  A trace element containing ferrite-coated metal magnetic particles in which particles of a metal magnetic material are coated with Ni-Zn ferrite and having a third ionization energy larger than Fe and a third ionization energy smaller than Ni is present in the Ni-Zn ferrite. A composite magnetic material characterized by being added.   The composite magnetic material according to claim 1, wherein the trace element is Mn or Co.   3. The composite magnetic material according to claim 2, wherein the addition amount of the trace element is 0.1 mol% to 10 mol% on the basis of all metal elements in the Ni—Zn ferrite.   A magnetic component formed by compression-molding the composite magnetic material according to claim 1 and heat-treating it at a temperature of 500 ° C or higher. The magnetic component according to claim 4, wherein the magnetic component is a magnetic core of a transformer or a reactor.

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