WO2022014219A1

WO2022014219A1 - Mncozn-based ferrite

Info

Publication number: WO2022014219A1
Application number: PCT/JP2021/022202
Authority: WO
Inventors: 裕史吉田; 由紀子中村; 多津彦平谷; 哲哉田川
Original assignee: Ｊｆｅケミカル株式会社; Ｊｆｅスチール株式会社
Priority date: 2020-07-14
Filing date: 2021-06-10
Publication date: 2022-01-20
Also published as: CN114269709A; TW202214543A; TWI796712B; JPWO2022014219A1; JP7182016B2; CN114269709B

Abstract

Provided is an MnCoZn-based ferrite having an excellent mechanical property, that is to say, a fracture toughness value of 1.00 MPa·m^1/2 or greater as measured according to JIS R1607 for a flat-plate-shaped core, combined with excellent magnetic properties, that is to say, a specific resistance of 30 Ω·m or greater, a Curie temperature of 100°C or higher, a magnetic coercivity of 15.0 A/m or less for a toroidal shape core produced under the same conditions, and an initial permeability value of 150 or greater at 23°C and 10 MHz.　The MnCoZn-based ferrite comprises a fundamental ingredient, a secondary ingredient, and unavoidable impurities. In the MnCoZn-based ferrite, the contents of P, B, Na, Mg, Al, and K in the unavoidable impurities are limited to less than 10 mass ppm for P, less than 10 mass ppm for B, less than 200 mass ppm for Na, less than 200 mass ppm for Mg, less than 250 mass ppm for Al, and less than 100 mass ppm for K, respectively.

Description

MnCoZn-based ferrite

The present disclosure relates to MnCoZn-based ferrites that are particularly suitable for the magnetic cores of automobile-mounted parts.

MnZn-based ferrite is a material widely used as a magnetic core for noise filters such as switching power supplies, transformers, and antennas. Among the soft magnetic materials, it has high magnetic permeability and low loss in the kHz region, and is cheaper than amorphous metals and the like.

On the other hand, ordinary MnZn-based ferrites have low resistivity, and it is difficult to maintain magnetic permeability in the 10 MHz region due to attenuation due to eddy current loss. As a countermeasure, a region of less than 50 mol% is selected as the amount of _{Fe 2} O _{3, and} positive and negative magnetic anisotropy is achieved by the presence of ^{Fe 2+ ions having positive magnetic anisotropy in ordinary MnZn-based ferrites.} MnCoZn-based ferrites are known in which the cancellation of the above is ^{replaced by Co 2+ ions, which also exhibit positive magnetic anisotropy.} This MnCoZn-based ferrite has a high specific resistance and is characterized by maintaining the initial magnetic permeability up to the 10 MHz region.

By the way, high fracture toughness is required for the magnetic core of electronic devices for automobile mounting, whose needs are expanding due to the recent hybridization and electrification of automobiles. This is because oxide magnetic materials such as MnZn-based ferrite are ceramics and are easily damaged because they are brittle materials. In addition, they are constantly vibrated in automobile-mounted applications compared to conventional home appliance applications. This is because it will continue to be used in a fragile environment. However, at the same time, since weight reduction and space saving are also required for automobile applications, it is important to have suitable magnetic properties as well as conventional applications in addition to high fracture toughness value.

Various developments have been made in the past as MnZn-based ferrites for automobile mounting applications. Patent Documents 1 and 2 and the like are reported as long as they refer to good magnetic properties, and Patent Documents 3 and 4 and the like are reported as MnZn-based ferrites having an increased fracture toughness value. Further, Patent Documents 5 and 6 and the like have been reported as high-resistance MnCoZn-based ferrites that maintain the initial magnetic permeability up to the 10 MHz region.

Japanese Unexamined Patent Publication No. 2007-51052 Japanese Unexamined Patent Publication No. 2012-76983 Japanese Unexamined Patent Publication No. 4-318904 Japanese Unexamined Patent Publication No. 4-177808 Japanese Patent No. 4508626 Japanese Patent No. 4554959

However, for example, in Patent Document 1 and Patent Document 2, although the composition for realizing the desired magnetic properties is mentioned, the fracture toughness value is not mentioned at all, and it is used as a magnetic core of an electronic component for an automobile. Is unsuitable. Similarly, Patent Documents 5 and 6 do not mention the fracture toughness value, and are unsuitable as a magnetic core of an in-vehicle electronic component. On the other hand, while Patent Documents 3 and 4 refer to the improvement of the fracture toughness value, the magnetic properties are insufficient as the magnetic core of an electronic component for an automobile vehicle, which is also unsuitable for this application.

The present invention has been made in view of such circumstances, and has ^{excellent mechanical properties such as a fracture toughness value of 1.00 MPa · m 1/2} or more measured in accordance with JIS R1607 of a flat plate core, and a specific resistance of 30 Ω ·. Excellent magnetic properties such as m or more, Curie temperature of 100 ° C or more, coercive force of toroidal shape core manufactured under the same conditions of 15.0 A / m or less, and initial magnetic permeability of 150 or more at 23 ° C and 10 MHz. It is an object of the present invention to provide MnCoZn-based ferrite having both.

The present inventors have obtained the following findings as a result of repeated diligent studies in order to achieve the above-mentioned problems.

The inventors first selected an appropriate composition _{of Fe 2} O ₃ amount, Zn O and CoO amount of MnCoZn-based ferrite capable of achieving high initial magnetic permeability at 23 ° C. and 10 MHz of the toroidal shape core. Within this composition range, since it ^{contains almost no Fe 2+} ions that cause a decrease in electrical resistance, it is possible to maintain a high specific resistance to some extent, and since magnetic anisotropy and magnetostriction are small, it is soft. It is possible to obtain a low coercive force, which is important as a magnetic material, and a high Curie temperature, which is not a problem in practice, and to maintain a high initial magnetic permeability even in the 10 MHz region.

_{Next, the inventors can generate a uniform grain boundary by adding an appropriate amount of SiO 2} and CaO, which are non-magnetic components segregating at the grain boundary, further increase the specific resistance, and prepare the crystal structure. I found the facts that would be possible.

In addition to these, the inventors investigated factors effective in improving the fracture toughness value, and obtained two findings.

(1) The inventors first found that suppression of abnormal grain growth was essential. Abnormal grain growth is a phenomenon in which the balance of grain growth during firing is lost due to the presence of impurities or the like, and coarse particles having a size of about 100 normal particles appear in some parts. When abnormal grain growth appears, the abnormal grain growth site has extremely low strength, and the core breaks from this site. Therefore, suppressing abnormal grain growth is indispensable for improving the fracture toughness value.

(2) Next, although no abnormal grains were confirmed, even if the sample was prepared under the same conditions, a sample with an abnormally low toughness value could occasionally be obtained, and the cause of this was investigated. As a result, it was found that impurities of specific components were present on the fracture surface in the sample with low toughness value, and that these impurities were mixed from the raw materials and water, and by suppressing the mixing of these impurities, the MnCoZn-based ferrite material was used. It was possible to verify that the fracture toughness value can be improved.

(3) Further, it was found that among the impurities, Na, Mg, Al and K had an adverse effect on the cracking of the molded product. It was found that by reducing these impurities, MnCoZn-based ferrite can be industrially and efficiently produced.

This disclosure is based on the above findings. That is, the gist structure of the present invention is as follows.

[1] MnCoZn-based ferrite composed of basic components, sub-components and unavoidable impurities.
The basic component is Fe ₂ O ₃ , ZnO, CoO, and iron, zinc, cobalt, and manganese in terms of MnO, assuming that the total is 100 mol%.
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of _{Fe 2} O _3,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5-4.0 mol% in terms of CoO and manganese: balance.
With respect to the basic component, the sub-component
SiO ₂ : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
And
The contents of P, B, Na, Mg, Al and K in the unavoidable impurities, respectively.
P: less than 10 mass ppm,
B: less than 10 mass ppm,
Na: less than 200 mass ppm,
Mg: less than 200 mass ppm,
MnCoZn-based ferrite that suppresses Al: less than 250 mass ppm and K: less than 100 mass ppm.

[2] The fracture toughness value measured in accordance with JIS R1607 is 1.00 MPa · m ^1/2 or more, and the initial magnetic permeability at 23 ° C. and 10 MHz is 150 or more.
Specific resistance is 30Ω ・ m or more,
Coercive force at 23 ° C is 15.0 A / m or less,
The MnCoZn-based ferrite according to the above [1], wherein the Curie temperature is 100 ° C. or higher.

According to the present invention, the plate-shaped core ^{has excellent mechanical properties with a breaking toughness value of 1.00 MPa · m 1/2} or more measured in accordance with JIS R1607, a specific resistance of 30 Ω · m or more, and a Curie temperature of 100 ° C. As described above, a MnCoZn-based ferrite having an excellent magnetic property of a coercive force of 15.0 A / m or less and an initial magnetic permeability of 150 or more at 23 ° C. and 10 MHz of a toroidal-shaped core manufactured under the same conditions is formed. The crack occurrence rate can be reduced to less than 2.0% to provide a good yield.

Generally, in order to increase the initial magnetic permeability of MnZn-based ferrite, it is effective to reduce the magnetic anisotropy and magnetostriction. In order to realize these, it is necessary to select the blending amount of _{Fe 2} O ₃ , ZnO and MnO, which are the main components of the MnZn-based ferrite, from a suitable range. Further, by applying sufficient heat in the firing step to appropriately grow the crystal grains in the ferrite, it is possible to facilitate the movement of the domain wall in the crystal grains in the magnetization step. Moreover, by adding a component that segregates to the grain boundaries and generating grain boundaries of appropriate and uniform thickness, the specific resistance is maintained and the attenuation due to the frequency increase of the initial permeability is suppressed, and the initial permeability is high even in the 100 kHz region. Has been realized.

However, the specific resistance of MnZn-based ferrite is about 20 Ωm at the maximum, which makes it impossible to maintain the initial magnetic permeability up to 10 MHz. Therefore, as described above, MnCoZn-based ferrite may be used in automobile-mounted applications.

On the other hand, regarding the magnetic core of in-vehicle electronic components, in addition to the above magnetic characteristics, a high fracture toughness value is required so as not to be damaged even in an environment subject to constant vibration. If the MnCoZn-based ferrite, which is the magnetic core, is damaged, the inductance is greatly reduced, so that the electronic component cannot perform the desired function, and as a result, the entire automobile may become inoperable.

From the above, MnCoZn-based ferrites used in electronic components for automobiles are required to have both good magnetic properties represented by high initial permeability and high fracture toughness values.

Hereinafter, embodiments of the present disclosure will be described. The present disclosure is not limited to the following embodiments. Further, in the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

In the present disclosure, the composition of MnCoZn-based ferrite is limited. First, in the present disclosure, the reason why the composition of MnCoZn-based ferrite (hereinafter, also simply referred to as ferrite) is limited to the above range will be described. Incidentally, it indicated by value converted iron, zinc, all the manganese Fe ₂ O _3, ZnO, of MnO contained in the present disclosure as a basic component. These Fe ₂ O _3, ZnO, for the content of MnO, Fe ₂ O _3, ZnO, CoO, iron in terms of MnO, zinc, cobalt, in mol% relative to the total amount 100 mol% of manganese, whereas subcomponent And the content of unavoidable impurities is expressed in mass ppm with respect to the basic component.

First, the basic components will be described.
Fe ₂ O ₃ : 45.0 mol% or more and less than 50.0 mol% When Fe ₂ O ₃ is excessively contained, the ^{amount of Fe 2+} increases, which lowers the specific resistance of MnCoZn-based ferrite. In order to avoid this, the _{amount of Fe 2} O ₃ should be suppressed to less than 50 mol%. However, _{if the amount of Fe 2} O ₃ is too small, the coercive force will increase and the Curie temperature will decrease. Therefore, iron should be contained at least 45.0 mol% in terms of _{Fe 2} O _3. The content of Fe ₂ O ₃ is preferably 47.1 mol% or more. The content of Fe ₂ O ₃ is preferably 49.5 mol% or less.

ZnO: 15.5 mol% to 24.0 mol%
ZnO has a function of increasing the saturation magnetization of ferrite and a function of increasing the sintering density because the saturated vapor pressure is relatively low, and is an effective component for lowering the coercive force. Therefore, it is assumed that at least zinc is contained in 15.5 mol% in terms of ZnO. On the other hand, when the zinc content is higher than the appropriate value, the Curie temperature is lowered, which causes a practical problem. Therefore, zinc should be 24.0 mol% or less in terms of ZnO. The ZnO content is preferably 23.0 mol% or less, more preferably 22.0 mol% or less.

CoO: 0.5 mol% to 4.0 mol%
Co ²⁺ in CoO is an ion having positive magnetic anisotropy energy, and as a result of the addition of an appropriate amount of CoO, the absolute value of the total magnetic anisotropy energy decreases, and as a result, the coercive force decreases. Therefore, 0.5 mol% or more of CoO is added. On the other hand, when a large amount of CoO is added, the resistivity is lowered, abnormal grain growth is induced, and the total magnetic anisotropy energy is excessively positively inclined, which conversely leads to an increase in coercive force. In order to prevent these, CoO shall be added only at a maximum of 4.0 mol% or less. The CoO content is preferably 0.8 mol% or more, more preferably 1.0 mol% or more. The CoO content is preferably 3.8 mol% or less, more preferably 3.5 mol% or less.

MnO: Remaining This disclosure relates to MnCoZn-based ferrite, and the balance of the basic composition is MnO. This is because if it is not MnO, good magnetic characteristics typified by low coercive force and high magnetic permeability at 10 MHz cannot be obtained. The MnO content is preferably 25.0 mol% or more, more preferably 26.0 mol% or more. The MnO content is preferably 33.0 mol% or less, more preferably 32.0 mol% or less.

The basic components have been described above, but the sub-components are as follows.
SiO ₂ : 50-300 mass ppm
SiO ₂ is known to contribute to the homogenization of the crystal structure of ferrite, and by adding an appropriate amount, abnormal grain growth is suppressed and specific resistance is also increased. Therefore, the coercive force can be lowered and the fracture toughness value can be increased. Therefore, it is _{assumed that the SiO 2} is contained at least 50 mass ppm or more. On the other hand, when _{the content of SiO 2} is excessive, abnormal particles appear on the contrary, and the abnormal particles significantly reduce the fracture toughness value, and at the same time, the initial magnetic permeability and coercive force at 10 MHz are also significantly deteriorated. The content of SiO ₂ is limited to 300 mass ppm or less. The content of SiO ₂ is preferably 55 mass ppm or more, more preferably 60 mass ppm or more, and further preferably 180 mass ppm or more. The content of SiO ₂ is preferably 275 mass ppm or less, more preferably 250 mass ppm or less.

CaO: 300-1300 mass ppm
CaO has a function of segregating into the grain boundaries of MnZn-based ferrite and suppressing the growth of crystal grains, and with the addition of an appropriate amount, the resistivity increases, the coercive force decreases, and the fracture toughness value can also increase. .. Therefore, it is decided to contain at least 300 mass ppm of CaO. On the other hand, when the CaO content is excessive, abnormal particles appear and both the fracture toughness value and the coercive force are deteriorated. Therefore, the CaO content is limited to 1300 mass ppm or less. The CaO content is preferably 325 mass ppm or more, more preferably 350 mass ppm or more, and further preferably more than 500 mass ppm. The CaO content is most preferably 600 mass ppm or more and 700 mass ppm or more. In particular, when the CaO content is 600 mass ppm or more, or 700 mass ppm or more, a particularly excellent fracture toughness value can be obtained. The CaO content is preferably 1150 mass ppm or less, more preferably 1000 mass ppm or less.

P: less than 10 mass ppm, B: less than 10 mass ppm P and B are mainly components inevitably contained in the raw material iron oxide. There is no problem if these contents are in a very small amount, but if they are contained in a certain amount or more, abnormal grain growth of ferrite is induced, and the fracture toughness value decreases because the abnormal grain growth site becomes the starting point of fracture. It increases the coercive force and lowers the initial magnetic permeability, which has a serious adverse effect. Therefore, the contents of P and B are both limited to less than 10 mass ppm. The content of P is preferably 8 mass ppm or less, more preferably 5 mass ppm or less. Further, the content of B is preferably 8 mass ppm or less, more preferably 5 mass ppm or less. The lower limit of the contents of P and B is not particularly limited, and may be 0 mass ppm, respectively.

Na: less than 200 mass ppm Mg: less than 200 mass ppm Al: less than 250 mass ppm K: less than 100 mass ppm Na, Mg, Al, K are low-purity iron oxide, manganese oxide, and zinc oxide that are raw materials for MnCoZn-based ferrite. It is contained in water and is present as a dissolved component in water such as tap water. Further, in the ferrite manufacturing process, components such as a dispersant containing these metal ions may be added. Further, those containing these components are mainly used as refractories of the furnace used for calcining and firing in the ferrite manufacturing process, and it is conceivable that these components may be mixed due to the furnace falling off or contact wear. If some of these components remain at the time of molding, they may react with iron oxide during firing to form a spinel structure and dissolve in MnCoZn-based ferrite. These components themselves do not induce abnormal grain growth and do not adversely affect the magnetic properties, but the solid solution of these components has lower toughness than ordinary MnCoZn-based ferrites. Therefore, the presence of these components causes MnCoZn. The toughness of the system ferrite may be significantly reduced. Therefore, in order to suppress the decrease in toughness, the content of these four components is limited.

Specifically, Na: less than 200 mass ppm, Mg: less than 200 mass ppm, Al: less than 250 mass ppm, K: less than 100 mass ppm. The Na content is preferably 130 mass ppm or less, more preferably 90 mass ppm or less. The Mg content is preferably 150 mass ppm or less, more preferably 125 mass ppm or less. The Al content is preferably 200 mass ppm or less, more preferably 180 mass ppm or less. Further, the content of K is preferably 85 mass ppm or less, and more preferably 75 mass ppm or less. The lower limits of Na, Mg, Al, and K are not particularly limited and may be 0 ppm, respectively. From the viewpoint of production technology, the Na content is preferably 10 mass ppm or more. From the viewpoint of production technology, the Mg content is preferably 10 mass ppm or more. From the viewpoint of production technology, the Al content is preferably 15 mass ppm or more. Further, from the viewpoint of production technology, the K content is preferably 5 mass ppm or more.

As a secondary effect obtained by reducing the Na, Mg, Al and K components, there is an improvement in yield in the molding process. The MnCoZn-based ferrite will be described in detail later, but is produced by molding a granulated powder containing a binder by a powder compression method and then firing it. In this molding process, the molded body may be cracked mainly when the mold is removed from the mold. If cracks occur at this point, the product will be defective and its value as a product will be lost. When the Na, Mg, Al and K components have a composition within the above-mentioned specified range, the crack generation rate of the molded product can be suppressed. We are investigating the details of this mechanism, but the present inventors speculate as follows. It is known that a cross-linking reaction occurs between an organic binder such as polyvinyl alcohol, which is mainly used as a binder, and metal ions such as Na, Mg, Al and K. Therefore, it is considered that metal ions such as Na, Mg, Al and K have a function of inhibiting the uniform dispersion of the binder. Therefore, the present inventors consider that this can be suppressed by setting the contents of Na, Mg, Al and K. By reducing the Na, Mg, Al and K components, the crack generation rate of the molded product can be reduced to less than 2.0%, and MnCoZn-based ferrite can be produced with good yield.

Further, the content of Ti as an unavoidable impurity is preferably less than 50 mass ppm. When the Ti content is less than 50 mass ppm, fluctuations in the temperature characteristics of the initial magnetic permeability can be suitably suppressed, and a decrease in the initial magnetic permeability at 23 ° C. and 10 MHz can be suitably prevented. The lower limit of the Ti content is not particularly limited and may be 0 mass ppm. _{The content of Nb 2} O ₅ as an unavoidable impurity is preferably 50 mass ppm or less, and more preferably 10 mass ppm or less. When _{the content of Nb 2} O ₅ is preferably 50 mass ppm or less, more preferably 10 mass ppm or less, fluctuations in the temperature characteristics of the initial magnetic permeability are preferably suppressed, and a decrease in the initial magnetic permeability at 23 ° C. and 10 MHz is preferable. Can be prevented. The lower limit of the content of Nb ₂ O ₅ is not particularly limited and may be 0 mass ppm.

The total amount of P, B, Na, Mg, Al, and K is preferably 675 mass ppm or less, and more preferably 400 mass ppm or less. The smaller the total amount of these, the larger the fracture toughness value.

The contents of P, B, Na, Mg, Al, K, and other unavoidable impurities are quantified according to JIS K 0102 (ICP mass spectrometry).

In addition, various characteristics of MnZn-based ferrite are greatly affected by various parameters, not limited to the composition. Among them, in the present disclosure, it is preferable to provide the following provisions in order to obtain more preferable magnetic characteristics and mechanical characteristics.

Since MnCoZn-based ferrite is a ceramic and is a brittle material, it hardly undergoes plastic deformation. Therefore, the fracture toughness value is measured by the SEBP method (Single-Edge-Precracked-Beam method) specified in JIS R 1607. In the SEBP method, the fracture toughness value is measured by imprinting a Vickers indenter in the center of the flat plate core and performing a bending test with a pre-crack. The MnCoZn-based ferrite of the present disclosure is intended for use in automobiles where high toughness is required, and has a fracture toughness value of 1.00 MPa · m ^1/2 or more. In order to satisfy this condition, it is necessary to control the component composition within the specified range as described above. The fracture toughness value is preferably 1.05 MPa · m ^1/2 or more, and more preferably 1.10 MPa · m ^1/2 or more.

Next, a method for producing the MnCoZn-based ferrite of the present disclosure will be described.
The method for producing MnCoZn-based ferrite of the present disclosure is as follows.
A calcination step of calcifying a mixture of the basic components and cooling to obtain a calcination powder.
The mixing-crushing step of adding the sub-ingredient to the calcination powder, mixing and crushing to obtain crushed powder, and
A granulation step of adding a binder to the pulverized powder, mixing the mixture, and then granulating to obtain a granulated powder.
The molding process of molding the granulated powder to obtain a molded body, and
It can be a method for producing MnZn-based ferrite, which comprises a firing step of calcining the molded body to obtain MnCoZn-based ferrite.

In the production of MnCoZn-based ferrite, first, Fe ₂ O ₃ , ZnO, CoO and MnO powder, which are the basic components, are weighed so as to have the above-mentioned ratio, and these are sufficiently mixed to form a mixture, and then the mixture is obtained. (Turning process). At this time, unavoidable impurities are limited to the above-mentioned range.

Next, the sub-ingredients specified in the present disclosure are added to the obtained calcined powder at a predetermined ratio, mixed with the calcined powder, and pulverized (mixing-crushing step). In this step, the powder is sufficiently homogenized so that the concentration of the added component is not biased, and at the same time, the calcined powder is refined to the target average particle size to obtain a pulverized powder.

Next, a known organic binder such as polyvinyl alcohol is added to the pulverized powder, and granulation is performed by a spray-drying method or the like to obtain granulated powder (granulation step). After that, if necessary, it is subjected to a step such as sieving for adjusting the particle size, and then pressure is applied by a molding machine to form a molded product (molding step). If cracks occur in the molded body in this molding step, cracks remain in the final product MnCoZn-based ferrite. MnZn-based ferrite containing cracks is inferior in strength and is synonymous with containing a gap, so that it is a defective product that cannot satisfy the desired magnetic characteristics. Therefore, the molded product containing cracks is removed at this point. Next, the molded product is fired under known firing conditions to obtain MnCoZn-based ferrite (firing step).

In the method for producing MnCoZn-based ferrite of the present disclosure, a raw material having a reduced amount of impurities is used. Further, during mixing, pulverization, and granulation, pure water or ion-exchanged water having a reduced amount of impurities is used as a solvent for the slurry containing the basic component or the sub-component. Also, as the binder and the surfactant to be added to reduce the viscosity of the slurry, select one having reduced metal ions. Further, the refractories of the furnace used in the calcining process and the firing process often contain these components. For this reason, Na, Mg, Al and K can be obtained by appropriately sieving in order to suppress contamination of these elements and by adopting a bedding powder at the time of firing in order to reduce the contact area between the molded body and the refractory material. Prevents contamination.
The obtained MnCoZn-based ferrite may be appropriately subjected to surface polishing or other processing.

The MnCoZn-based ferrite thus obtained is an excellent machine ^{with a breaking toughness value of 1.00 MPa · m 1/2} or more measured in accordance with JIS R1607 of a flat plate core, which was not possible with conventional MnCoZn-based ferrites. Not only has the characteristics, the specific resistance is 30Ω ・ m or more, the Curie temperature is 100 ℃ or more, the coercive force of the toroidal shape core manufactured under the same conditions is 15.0A / m or less, and the initial magnetic permeability at 23 ℃ and 10MHz. At the same time, it realizes excellent magnetic characteristics of 150 or more. The specific resistance is preferably 40 Ω · m or more, preferably 50 Ω · m or more. The Curie temperature is preferably 150 ° C. or higher. The coercive force of the toroidal shape core is preferably 13.0 A / m or less, more preferably 12.6 A / m or less. The initial magnetic permeability at 23 ° C. and 10 MHz is preferably 160 or more, more preferably 170 or more.

The initial magnetic permeability of the toroidal shape core is calculated based on the impedance and the phase angle measured by applying a winding of 10 turns to the toroidal shape core and using an impedance analyzer (4294A manufactured by Keysight Co., Ltd.).

In addition, the coercive force Hc is measured at 23 ° C. in accordance with JIS C 2560-1.

The specific resistance is measured by the 4-terminal method.

The Curie temperature is calculated from the temperature characteristic measurement result of the inductance measured using an LCR meter (4980A manufactured by Keysight).

The fracture toughness value of the flat plate core is in accordance with JIS R1607, and after making a pre-crack in the sample dented in the center by the Vickers indenter, it breaks in a three-point bending test, and the breaking load and the dimensions of the test piece are determined. Calculated based on.

(Example 1)
Fe contained, Zn, all Co and Mn Fe ₂ O _3, ZnO, when calculated as CoO and MnO, each Fe ₂ O _3, ZnO, CoO, and MnO were weighed so that the ratio shown in Table 1 The raw material powder was mixed for 16 hours using a ball mill, then calcined in the air at 900 ° C. for 3 hours, and cooled to room temperature in the air for 1.5 hours to obtain a calcined powder. Next, SiO ₂ and CaO were weighed equivalent to 150,700 mass ppm, respectively, and then added to the calcined powder, and pulverized with a ball mill for 12 hours to obtain pulverized powder. Polyvinyl alcohol was added to the pulverized powder to perform spray-dry granulation, and a pressure of 118 MPa was applied to form a toroidal-shaped core and a flat plate-shaped core. After that, it was visually confirmed that these molded bodies were not cracked, and the molded bodies were placed in a firing furnace and fired at a maximum temperature of 1320 ° C. for 2 hours in a gas stream in which nitrogen gas and air were appropriately mixed. A sintered toroidal-shaped core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm and a sintered flat plate-shaped core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained.

By using a high-purity raw material as a raw material, using pure water when mixing and crushing auxiliary components, and by not adding components such as a lubricant containing metal ions to the slurry, Na, Mg, Al and K can be obtained. Since contamination was suppressed, the amounts of P and B contained in the sintered toroidal-shaped core and the sintered flat plate-shaped core were 4 and 3 mass ppm, respectively, and Na, Mg, Al, and K were 80 and 75, respectively. It was 120 and 30 mass ppm. The contents of P, B, Na, Mg, Al, and K were quantified according to JIS K 0102 (ICP mass spectrometry) as described above.

According to the method described above, the initial magnetic permeability of the sintered toroidal-shaped core, the coercive force Hc, the Curie temperature, and the fracture toughness value of the sintered flat plate-shaped core were measured. The results obtained are shown in Table 1.

As shown in the table, in Examples 1-1 to 1-7, which are examples of the invention, the specific resistance is 30 Ωm or more, the coercive force at 23 ° C. is 15.0 A / m or less, the Curie temperature is 100 ° C. or more, and 23 ° C. The initial magnetic permeability at 10 MHz is 150 or more and the fracture toughness value is 1.00 MPa · m ^1/2 or more, and it has both suitable magnetic properties and high toughness.

On the other hand, in the _{comparative example (Comparative Examples 1-1 and 1-2) containing 50.0 mol% or more of Fe 2} O ₃ , the specific resistance is significantly reduced, and the first 10 MHz due to the increase in eddy current loss. The magnetic permeability has also deteriorated significantly. On the other hand, in _{Comparative Example (Comparative Example 1-3) in which Fe 2} O ₃ was less than 45.0 mol%, although high toughness was realized, the coercive force increased due to the increase in magnetic anisotropy and magnetostriction. And the Curie temperature is decreasing.

In Comparative Example (Comparative Example 1-4) in which ZnO is excessive, the Curie temperature is lowered to less than 100 ° C. On the contrary, in the comparative example (Comparative Example 1-5) in which ZnO is less than the specified range, the coercive force increases and is out of the desirable range.

Focusing on CoO, in Comparative Example (Comparative Example 1-6) in which the content is less than the specified range, the coercive force is high and excessively because the cancellation of the positive and negative magnetic anisotropy is insufficient. In the comparative example (Comparative Example 1-7) including, on the contrary, since the positive magnetic anisotropy is excessively increased, the coercive force is increased and the initial magnetic permeability at 10 MHz is also decreased.

(Example 2)
Fe contained, Zn, all Co and Mn Fe ₂ O _3, ZnO, when calculated as CoO and _{_{MnO, Fe 2 O 3: 49.0mol}} %, CoO: 2.0mol%, ZnO: 21.0mol% , MnO: Weigh the raw materials to 28.0 mol%, mix for 16 hours using a ball mill, perform calcining at 900 ° C. in the air for 3 hours, and cool to room temperature in the air for 1.5 hours. And obtained the calcined powder. Next, the amounts of SiO ₂ and CaO shown in Table 2 were added to the calcined powder, and the mixture was pulverized with a ball mill for 12 hours to obtain pulverized powder. Polyvinyl alcohol was added to the pulverized powder to perform spray-dry granulation, and a pressure of 118 MPa was applied to form a toroidal-shaped core and a flat plate-shaped core. After that, it was visually confirmed that these molded bodies were not cracked, and the molded bodies were inserted into a firing furnace and fired at a maximum temperature of 1320 ° C. for 2 hours in a gas stream in which nitrogen gas and air were appropriately mixed. A sintered toroidal-shaped core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm and a sintered flat plate-shaped core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained. The amounts of P and B contained in the obtained sintered toroidal-shaped core and the sintered flat plate-shaped core were 4 and 3 mass ppm, respectively, and Na, Mg, Al, and K were 80, 75, 120, and 30 mass ppm, respectively. Met.

The characteristics of each of these samples were evaluated using the same method and equipment as in Example 1. The obtained results are shown in Table 2.

As shown in the table, in _{Examples 2-1 to 2-4 in which the amounts of SiO 2} and CaO are within the specified range, the specific resistance is 30 Ωm or more, the coercive force is 15.0 A / m or less, and the Curie temperature. Has good magnetic properties of 100 ° C. or higher and an initial magnetic permeability of 150 or higher at 23 ° C. and 10 MHz, and a fracture toughness value of 1.00 MPa · m ^1/2 or higher, achieving both high toughness.

On the other hand, in _{Comparative Examples 2-1, 2-3 in which even one of the two components of SiO 2} and CaO is contained in less than the specified amount, the specific resistance is lowered due to insufficient grain boundary formation, and the crystal grains are crystallized. The fracture toughness value is less than the desired value because some low-strength coarse grains appear due to insufficient suppression of growth. On the contrary, in Comparative Examples 2-2, 2-4 and 2-5 in which even one of the same components is excessive, the magnetic characteristics such as the initial magnetic permeability at 23 ° C. and 10 MHz deteriorate due to the appearance of abnormal grains. In addition, since the abnormal grains contain many intragranular voids, the void residual ratio is high, and as a result, the fracture toughness value is also greatly reduced.

(Example 3)
By the method shown in Example 1, the ratio of the basic component and the sub-ingredients is the same as that of Example 1-2, but the amount of P and B contained is different. Got The granulated powder was formed into a toroidal-shaped core and a flat plate-shaped core by applying a pressure of 118 MPa. After that, it was visually confirmed that these compacts were not cracked, and the compacts were inserted into a firing furnace and fired at a maximum temperature of 1320 ° C. for 2 hours in a gas stream in which nitrogen gas and air were appropriately mixed. A sintered toroidal-shaped core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm and a sintered flat plate-shaped core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained.
The characteristics of each of these samples were evaluated using the same method and equipment as in Example 1. The obtained results are shown in Table 3.

In addition, 1000 molded bodies were manufactured under the same conditions, and the presence or absence of cracks was visually observed. As for the judgment of cracks, those in which the molded body was completely broken, cracks of 0.5 mm or more, or those in which partial deprivation was confirmed were judged to be cracked cores. Table 3 shows the crack occurrence rate.

In Example 3-1 in which P and B are within the specified range, the desired magnetic properties such as resistivity, coercive force, initial magnetic permeability at 23 ° C. and 10 MHz are 150 or more, and fracture toughness value is 1.00 MPa · m. ^{It is more than 1/2} , and has both high toughness. On the contrary, when one or both of the two components are contained more than the specified value, the appearance of abnormal particles deteriorates a plurality of magnetic properties, and at the same time, the fracture toughness value also decreases, and the desired values are not obtained for both.

(Example 4)
By the method shown in Example 1, the basic component and the sub-component have the same composition as in Example 1-2, but raw materials containing various amounts of impurities are used, and mixed, pulverized, and produced. Regarding the water used as the solvent for the slurry at the time of granulation, unlike ordinary pure water or ion-exchanged water, tap water or mineral water with different hardness is used, or by intentionally adding a reagent, the sample is finally prepared. Using granulated powder prepared so that the amounts of Na, Mg, Al and K contained were different, a toroidal-shaped core and a flat plate-shaped core were formed by applying a pressure of 118 MPa. After that, it is visually confirmed that these compacts are not cracked, the compacts are inserted into a firing furnace, and the compacts are fired at a maximum temperature of 1320 ° C. for 2 hours in a gas stream in which nitrogen gas and air are appropriately mixed. As a result, a sintered toroidal-shaped core having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm was obtained, and a sintered flat plate-shaped core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm was obtained.
The characteristics of each of these samples were evaluated using the same method and equipment as in Example 1. The obtained results are shown in Table 4.

In addition, 1000 molded bodies were manufactured under the same conditions, and the presence or absence of cracks was visually observed. Table 4 shows the crack occurrence rate.

In Examples 4-1 to 4-9 in which the contents of Na, Mg, Al and K are within the predetermined range, ^{a good value of fracture toughness value of 1.00 MPa · m 1/2} or more is obtained. ..
On the other hand, in Comparative Examples 4-1 to 4-9 containing at least one of Na, Mg, Al and K in a specified value or more, the desired value of the magnetic property is obtained, but the fracture toughness value is 1.00 MPa.・ It has decreased to less than ^{m 1/2.} It is presumed that this decrease in toughness is due to the solid dissolution of Na, Mg, Al and K in the crystal grains, and the appearance of locally low toughness points.

Focusing on the crack occurrence rate of the molded product, the crack occurrence rate is as high as 2.0% or more in Comparative Examples 4-1 to 4-9. This is because the contents of Na, Mg, Al and K were not sufficiently suppressed in these comparative examples, so that the uniform dispersion of the binder was hindered, and the strength was weak because the amount of the binder was locally insufficient in the molded product. It is probable that this is because there are some spots and crack defects are more likely to appear.

As described above, the MnCoZn-based ferrite according to the present invention has ^{excellent mechanical properties with a breaking toughness value of 1.00 MPa · m 1/2} or more measured in accordance with JIS R1607 of a flat plate core, and a specific resistance of 30 Ω ·. It has excellent magnetic properties of m or more, Curie temperature of 100 ° C or more, coercive force of 15.0 A / m or less of toroidal shape core manufactured under the same conditions, and initial magnetic permeability of 150 or more at 23 ° C and 10 MHz. Since it is possible to reduce the cracking rate of the molded body to less than 2.0% and manufacture it with a good yield, it is particularly suitable for the magnetic core of electronic parts mounted on automobiles.

Claims

MnCoZn-based ferrite consisting of basic components, sub-components and unavoidable impurities.
The basic component is Fe 2 O 3 , ZnO, CoO, and iron, zinc, cobalt, and manganese in terms of MnO, assuming that the total is 100 mol%.
Iron: 45.0 mol% or more and less than 50.0 mol% in terms of Fe 2 O 3,
Zinc: 15.5 to 24.0 mol% in terms of ZnO,
Cobalt: 0.5-4.0 mol% in terms of CoO and manganese: balance.
With respect to the basic component, the sub-component
SiO 2 : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
And
The contents of P, B, Na, Mg, Al and K in the unavoidable impurities, respectively.
P: less than 10 mass ppm,
B: less than 10 mass ppm,
Na: less than 200 mass ppm,
Mg: less than 200 mass ppm,
MnCoZn-based ferrite that suppresses Al: less than 250 mass ppm and K: less than 100 mass ppm.
The fracture toughness value measured in accordance with JIS R1607 is 1.00 MPa · m 1/2 or more, and the initial magnetic permeability at 23 ° C. and 10 MHz is 150 or more.
Specific resistance is 30Ω ・ m or more,
Coercive force at 23 ° C is 15.0 A / m or less,
The MnCoZn-based ferrite according to claim 1, wherein the Curie temperature is 100 ° C. or higher.