CN112041952B - MnZn ferrite and method for producing same - Google Patents

Abstract

The invention provides a MnZn ferrite with high initial permeability and high fracture toughness value. The basic component and the auxiliary component of the MnZn ferrite are adjusted to an appropriate range, and the amounts of P and B as inevitable impurities are respectively suppressed to be P: less than 10 mass ppm and B: less than 10 ppm by mass, the number of voids in the grains is less than 55% relative to the total number of voids in the MnZn ferrite, the initial permeability at 23 ℃ and 100kHz is 4000 or more, and the fracture toughness value measured according to JIS R1607 is 1.00MPa m^1/2The above.

Description

MnZn ferrite and method for producing same

Technical Field

The present invention relates to a MnZn-based ferrite suitable for a magnetic core particularly for use in automobile-mounted parts, and a method for producing the same.

Background

MnZn ferrite is widely used as a material for magnetic cores of noise filters, transformers, and antennas such as switching power supplies. As the advantages, there are mentioned that the soft magnetic material has high magnetic permeability and low loss in the kHz region, and is inexpensive as compared with amorphous metals and the like.

Among them, in recent years, with the development of hybrid and electric vehicles, there is an increasing demand for magnetic cores for electronic devices for vehicle-mounted applications, and MnZn-based ferrites used for the magnetic cores are required to have high fracture toughness values. This is because: the MnZn ferrite is ceramic and is a brittle material, and therefore is easily broken, and is used for automobile mounting applications, that is, is continuously used in an environment where vibration is constantly applied and breakage is easily caused, as compared with the use of conventional household electric appliances.

At the same time, however, in automotive applications, weight reduction and space saving are also required, and therefore, it is important to have appropriate magnetic properties in addition to a high fracture toughness value as in conventional applications.

Various studies have been made on MnZn-based ferrites for automobile mounting applications.

As ferrites having the mentioned excellent magnetic properties, patent documents 1 and 2 and the like are reported, and as MnZn-based ferrites having improved fracture toughness values, patent documents 3 and 4 and the like are reported.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2007-51052;

patent document 2: japanese laid-open patent publication No. 2012 and 76983;

patent document 3: japanese patent laid-open publication No. 4-318904;

patent document 4: japanese patent laid-open No. 4-177808.

Disclosure of Invention

Problems to be solved by the invention

In general, in order to increase the initial permeability of MnZn-based ferrite, it is effective to reduce the magnetic anisotropy and magnetostriction. In order to achieve this, Fe, which is a main component of MnZn-based ferrite, needs to be added₂O₃The amounts of ZnO and MnO are set to appropriate ranges.

Further, by applying sufficient heat in the sintering step to appropriately grow the crystal grains in the ferrite, the magnetic domain walls in the crystal grains in the magnetization step can be easily moved, and further, a component that causes segregation in the grain boundaries is added to generate grain boundaries of an appropriate and uniform thickness, thereby achieving high initial permeability even in the 100kHz region while maintaining the specific resistance and suppressing attenuation of the initial permeability accompanying the increase in frequency.

In addition to the above magnetic properties, a high fracture toughness value is required for a magnetic core of an electronic component mounted on an automobile, which is not broken even in an environment where vibrations are constantly applied. When the MnZn ferrite as the core is damaged, the inductance is greatly reduced, and thus the electronic component cannot exhibit a desired function, and the entire automobile cannot be operated under the influence of the inductance.

As described above, both good magnetic properties represented by high initial permeability and high fracture toughness values are required for MnZn-based ferrites to be supplied to electronic components for automobile mounting.

However, although patent documents 1 and 2 mention compositions for achieving desired magnetic properties, they do not describe the fracture toughness value at all, and are considered to be unsuitable as magnetic cores for electronic components mounted on automobiles.

In addition, although patent documents 3 and 4 mention improvement of fracture toughness, their magnetic properties are not sufficient as a magnetic core for electronic components mounted on automobiles, and thus they are not suitable for such applications.

Accordingly, an object of the present invention is to provide a MnZn ferrite having excellent magnetic characteristics such that the initial permeability at 23 ℃ and 100kHz is 4000 or more, and further having a fracture toughness value of 1.00MPa m.m.measured in accordance with JIS R1607 for a flat plate-like sample^1/2The above mechanical properties.

Means for solving the problems

Therefore, as a basic component of MnZn ferrite capable of improving initial permeability at 23 ℃ and 100kHz in a toroidal core, the inventors first conducted Fe₂O₃And the appropriate amount of ZnO were investigated.

As a result, an appropriate range of the basic component was found, and if within this composition range, the magnetic anisotropy and magnetostriction were reduced, the resistivity was also maintained, and the second peak showing the maximum value of the temperature characteristic of the initial permeability could also appear in the vicinity of 23 ℃.

Next, it was found that SiO, which is a nonmagnetic component that segregates in grain boundaries, is added in an appropriate amount₂、CaO、Nb₂O₅And Bi₂O₃As an auxiliary component, it is possible to form grain boundaries of uniform thickness, increase the resistivity, and suppress the attenuation accompanying the frequency increase of the initial permeability.

Further, the inventors investigated factors effective for improving the fracture toughness value, and as a result, analyzed the observed image after polishing and etching the cross section of the MnZn-based ferrite, found that there is a correlation between the ratio of voids remaining in the grains and the fracture toughness value among the voids (void) in the material.

That is, it was found that voids include voids present in grain boundaries and voids present in grains, and that by reducing the voids remaining in the grains (hereinafter also referred to as "intra-grain voids"), crack propagation of MnZn-based ferrite, which is a brittle material, can be suppressed, and as a result, the fracture toughness value of the material is improved.

Based on this viewpoint, the inventors further investigated and found 2 methods for reducing voids in the crystal grains.

First, when sintering ferrite, abnormal particles, which contain a large number of voids in the particles, occur due to the break of the balance of particle growth. In order to suppress the generation of abnormal particles and reduce the number of voids in the crystal grains, the content of impurities needs to be reduced. In addition, since the occurrence of abnormal particles increases the loss, it is also required to avoid abnormal particles from the viewpoint of magnetic characteristics.

In another method, in the production of a general MnZn-based ferrite, a precalcination process is performed, and the maximum temperature of precalcination and the speed or environment at the time of cooling are appropriately controlled, whereby the material is prevented from absorbing excessive oxygen, and the amount of oxygen released at the time of reduction reaction at the time of sintering is reduced, thereby reducing the number of voids and reducing the voids in the crystal grains.

By appropriately controlling these two methods, the fracture toughness value of the material can be increased.

As described above, in order to obtain MnZn ferrite having a high initial permeability and a high fracture toughness value, Fe as a basic component is required₂O₃And ZnO, and SiO as a nonmagnetic component₂、CaO、Nb₂O₅And Bi₂O₃The amount of (b) is adjusted to an appropriate amount and the voids in the crystal grains are reduced.

In addition, in the above-mentioned patent documents 1 and 2, the fracture toughness value is not mentioned, and the improvement is not possible.

In patent documents 3 and 4, although toughness is improved, desired magnetic characteristics cannot be achieved because an appropriate composition range cannot be selected.

Therefore, only by these findings, it is not possible to produce a practically useful MnZn-based ferrite suitable for a magnetic core of an electronic component for automobile mounting.

The present invention is based on the above findings.

That is, the main structure of the present invention is as follows.

1. A MnZn-based ferrite comprises a basic component, an auxiliary component and inevitable impurities,

in the presence of Fe₂O₃And ZnO and MnO, wherein the total of Fe, Zn and Mn is 100 mol%, and the essential components are as follows:

iron: with Fe₂O₃51.5 to 55.5 mol% in terms of;

zinc: more than 15.5 mol% and not more than 26.0 mol% in terms of ZnO; and

manganese: 22.0 to 32.0 mol% in terms of MnO;

the auxiliary components are as follows relative to the basic components:

SiO₂: 50 to 250 mass ppm;

CaO: 100 mass ppm or more and less than 1000 mass ppm;

Nb₂O₅: 100 to 300 mass ppm; and

Bi₂O₃: 50 to 300 mass ppm of a nitrogen-containing compound,

the amounts of P and B in the above-mentioned inevitable impurities are suppressed to

P: less than 10 mass ppm, and

b: less than 10 mass ppm of a water-soluble polymer,

the number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn ferrite, and the Mn-Zn ferrite is further processed to have a high thermal conductivity

The MnZn ferrite has an initial permeability of 4000 or more at 23 ℃ and 100kHz,

the fracture toughness value measured according to JIS R1607 was 1.00MPa m^1/2The above.

2. The MnZn ferrite according to the above 1, further comprising, as the auxiliary component, a ferrite

And (3) CoO: 3500 ppm by mass or less.

3. A method for producing a MnZn ferrite from which the MnZn ferrite of 1 or 2 is obtained, comprising:

a pre-calcination step of subjecting the mixture of the above-mentioned basic components to pre-calcination and cooling to obtain pre-calcined powder;

a mixing-pulverizing step of adding the auxiliary component to the pre-calcined powder, mixing and pulverizing the mixture to obtain a pulverized powder;

a granulation step of adding a binder to the pulverized powder, mixing the powders, and granulating the mixture to obtain granulated powder;

a molding step of molding the granulated powder to obtain a molded body; and

a sintering step of sintering the molded body to obtain a MnZn ferrite,

the highest temperature of the pre-calcination in the pre-calcination procedure is in the range of 800-950 ℃,

and at least one of a cooling rate of 800 ℃/hour or more from the maximum temperature to 100 ℃, and an oxygen concentration of 5 vol% or less in an environment at the time of cooling from the maximum temperature to 100 ℃.

4. A method for producing a MnZn ferrite from which the MnZn ferrite of 1 or 2 is obtained, comprising:

a precalcination step, in which the mixture of the basic components is precalcined and cooled to obtain precalcined powder;

a mixing-pulverizing step of adding the auxiliary component to the pre-calcined powder, mixing and pulverizing the mixture to obtain a pulverized powder;

a granulation step of adding a binder to the pulverized powder, mixing, and granulating to obtain granulated powder;

a molding step of molding the granulated powder to obtain a molded body; and

a sintering step of sintering the molded body to obtain a MnZn ferrite,

the pre-calcined powder has a peak intensity ratio (X) represented by the following formula (1) of 0.80 or more.

X ═ (peak intensity of spinel compound analyzed by X-ray diffraction)/(α -Fe analyzed by X-ray diffraction₂O₃Peak intensity of) … … (1)

5. The method for producing a MnZn ferrite according to the above 4, wherein a maximum temperature of the preliminary calcination in the preliminary calcination step is in a range of 800 to 950 ℃,

and at least one of a cooling rate of 800 ℃/hour or more from the maximum temperature to 100 ℃ and an oxygen concentration of 5 vol% or less in an environment at the time of cooling from the maximum temperature to 100 ℃.

Effects of the invention

The MnZn ferrite of the present invention has excellent magnetic characteristics such that the initial permeability value at 23 ℃ and 100kHz is 4000 or more, and further has a fracture toughness value of 1.00MPa m.m.measured according to JIS R1607 for a flat plate-like sample^1/2The above mechanical properties.

Detailed Description

The present invention will be specifically described below. In the present specification, the range of numerical values expressed by the term "to" is meant to include ranges in which the numerical values recited before and after the term "to" are the lower limit value and the upper limit value.

First, in the present invention, the reason why the composition of MnZn-based ferrite (hereinafter, also simply referred to as ferrite) is limited to the above range will be described. In addition, as the basic components, iron, zinc and manganese contained in the present invention are all in terms of Fe₂O₃Values of ZnO and MnO. In addition, for these Fe₂O₃ZnO and MnO in an amount corresponding to Fe₂O₃The total amount of iron, zinc and manganese calculated as ZnO and MnO is expressed as mol% of 100 mol%, while the contents of the auxiliary components and inevitable impurities are expressed as mass ppm with respect to the base components.

Fe₂O₃：51.5～55.5mol％

In the basic composition, in Fe₂O₃When the amount is smaller or larger than the appropriate range, the initial permeability is lowered because the magnetic anisotropy and the magnetostriction are increased. Therefore, it contains Fe at least 51.5 mol% or more₂O₃The upper limit is 55.5 mol%.

ZnO: more than 15.5 mol% and not more than 26.0 mol%

In the case where the ZnO content is small, the Curie temperature becomes too high, and therefore the initial permeability at 23 ℃ is lowered, so that it is contained at least more than 15.5 mol%. However, in the case where the content exceeds an appropriate amount, the temperature of the second peak at which the initial permeability shows a maximum value is lowered, thus resulting in a decrease in the initial permeability at 23 ℃. Therefore, the upper limit is 26.0 mol%. The content of ZnO is preferably within a range of 16.0 to 25.5 mol%.

MnO：22.0～32.0mol％

The present invention is a MnZn ferrite, and the remainder of the basic component must be MnO. This is because if the remaining portion is not MnO, the initial permeability of 100kHz at 23 ℃ cannot be achieved at 4000 or more. The MnO content is preferably in the range of 22.5 to 31.0 mol%.

In addition, Fe as a basic component₂O₃The total amount of ZnO and MnO is of course 100 mol%.

The basic components are described above, and the auxiliary components are described below.

SiO₂: 50 to 250 mass ppm

SiO is known₂Contributes to the homogenization of the crystal structure of ferrite accompanied by SiO₂Since the addition of an appropriate amount of (3) reduces the number of voids remaining in the grains and also increases the resistivity, the initial permeability at 23 ℃ and 100kHz can be increased and the fracture toughness value can be increased by the addition of an appropriate amount of (3). Therefore, SiO is contained at least in an amount of 50 mass ppm₂. However, in the case where the addition amount is too large, rather abnormal particles containing a large number of intra-grain voids appear, which significantly lowers the fracture toughness value and at the same time significantly deteriorates the initial permeability, and therefore SiO is significantly deteriorated₂The content of (B) is required to be suppressed to 250 mass ppm or less. SiO 2₂The content of (b) is preferably in the range of 60 to 230 mass ppm.

CaO: 100 mass ppm or more and less than 1000 mass ppm

CaO has a function of suppressing grain growth by causing segregation in the grain boundary of MnZn ferrite, and by adding an appropriate amount, the resistivity is increased, and the initial permeability at 23 ℃ and 100kHz can be increased. Further, the fracture toughness value can also be improved by reducing the voids in the grains with the suppression of the grain growth. Therefore, CaO is contained at least in an amount of 100 mass ppm. However, in the case where the amount is excessively added, abnormal particles occur, resulting in a decrease in fracture toughness value and deterioration in initial permeability, and therefore the content of CaO needs to be limited to less than 1000 mass ppm. The content of CaO is preferably in the range of 130 to 850 mass ppm.

Nb₂O₅: 100 to 300 mass ppm

Nb₂O₅The MnZn ferrite has the effects of generating segregation in grain boundaries, gradually suppressing grain growth, and relaxing the stress. Therefore, by adding Nb in an appropriate amount₂O₅Since the initial permeability can be increased and the fracture toughness value can be increased by reducing the number of voids in the grains, 100 ppm by mass of Nb is contained at minimum₂O₅. However, it is not limited toWhen the amount of addition is too large, abnormal grains occur, which cause a decrease in fracture toughness value and deterioration in initial permeability, so Nb₂O₅The content of (B) is limited to 300 mass ppm or less. Nb₂O₅The content of (B) is preferably in the range of 120 to 280 mass ppm.

Bi₂O₃: 50 to 300 mass ppm

Bi₂O₃Has an effect of slowly promoting the grain growth of MnZn ferrite, and is accompanied by Bi, unlike conventional grain growth promoting additives₂O₃Since the addition of an appropriate amount can homogenize the crystal structure, the fracture toughness value can be improved and the initial permeability can be improved, and therefore, Bi is contained at least 50 mass ppm₂O₃. However, when the amount is too large, abnormal grains occur, which causes a significant decrease in fracture toughness value and deterioration in initial permeability, so that Bi₂O₃The content of (B) is limited to 300 mass ppm or less. Bi₂O₃The content of (B) is preferably in the range of 75 to 275 mass ppm, and more preferably in the range of 100 to 250 mass ppm.

Next, inevitable impurities that should be suppressed will be described.

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. If the content is extremely small, there is no problem, but if the content is more than a certain amount, abnormal grain growth of ferrite occurs and the intra-grain porosity increases, so that the fracture toughness value decreases and the initial permeability decreases, which has a significant adverse effect. Thus, the contents of both P and B are limited to less than 10 mass ppm. Preferably P, B are all 8 mass ppm or less.

In addition, not only the composition but also various properties of MnZn-based ferrite are greatly affected by various parameters. Therefore, in the present invention, the following regulations are provided in order to ensure more preferable magnetic properties and strength properties.

Fracture toughness value measured according to JIS R1607: 1.00MPa m^1/2The above

Since MnZn ferrite is ceramic and a brittle material, plastic deformation hardly occurs. Therefore, the fracture toughness value is measured by the SEPB method (Single-Edge-Precracked-Beam method) prescribed in JIS R1607. In the SEPB method, a vickers indentation is applied to the center of a flat plate-like specimen, and a bending test is performed in a state where a pre-crack is applied, thereby measuring a fracture toughness value. The MnZn ferrite of the present invention is expected to be used for automobile-mounted applications requiring high toughness, and the fracture toughness value is required to be 1.00MPa · m^1/2The above.

In order to satisfy this condition, although voids remain in the material of the MnZn-based ferrite produced by powder molding, the fracture surface is polished and the grain boundary portion is etched with nitric fluoride, and then an image observed with a view field of 200 to 500 times is analyzed, and the intra-grain void ratio obtained by dividing the total number of intra-grain voids by the total number of total remaining voids in the view field needs to be less than 55%. The intra-grain porosity is preferably 50% or less, more preferably 45% or less. This is because cracks in the MnZn ferrite propagate mainly along the voids in the crystal grains, and therefore when the porosity in the crystal grains is high, the cracks easily propagate, and the toughness value is low, and therefore the fracture toughness value is not satisfied: 1.00MPa m^1/2The above.

In order to ensure that the intra-grain porosity is less than 55%, two conditions need to be satisfied.

First, the amount of P, B, which is an inevitable impurity, is suppressed to less than 10 mass ppm. This is because these components are components that cause the occurrence of abnormal particles containing a large number of intra-grain voids, and increase the intra-grain void ratio.

Second, the pre-firing conditions in the production process of the MnZn-based ferrite are optimized.

Sintering of MnZn-based ferrite as a metal oxide is basically a reduction reaction, and in this process, excess oxygen held by the material is released. In the molding step before sintering, in order to maintain the shape of the molded body obtained by compressing the powder, an organic binder is added to the molded granulated powder, and the binder is decomposed by combustion at the initial stage of sinteringIs removed. The reducing environment during decomposition removal is accompanied by a chemical reaction of taking oxygen from the ferrite material as an oxide, and the chemical reaction is accompanied by volume expansion, thereby damaging the molded body. Therefore, in order to prevent this, it is possible to intentionally absorb and hold more oxygen than the stoichiometric ratio in the MnZn-based ferrite in an excessive amount in the precalcination step. However, it is a matter of course that in the case of excessively holding oxygen, the amount of oxygen released in the sintering process increases. Oxygen is released out of the material along with grain growth during sintering, but the more the amount of oxygen released increases, the more the amount of intragranular voids increases, and when the intragranular porosity becomes 55% or more, the fracture toughness value becomes higher than the desired value of 1.00MPa · m^1/2Low. Therefore, in the pre-firing step, it is necessary to treat the MnZn-based ferrite at an appropriate temperature and in an environmental range.

Specifically, the pre-calcination is performed under conditions such that the maximum temperature of the pre-calcination is in the range of 800 to 950 ℃ (preferably 850 to 950 ℃), and at least one of the cooling rate from the maximum temperature to 100 ℃ is 800 ℃/h or more, and the oxygen concentration during cooling from the maximum temperature to 100 ℃ is 5 vol% or less (preferably 4% or less).

The maximum temperature of the preliminary calcination is preferably 800 to 950 ℃ (more preferably 850 to 930 ℃) when the oxygen concentration during cooling from the maximum temperature to 100 ℃ is 5 vol% or less, and the preliminary calcination environment is preferably in air.

Further, the amount of oxygen held by the pre-calcined powder can be controlled by using the wavelength of

The peak intensity ratio (X) represented by the following formula (1) can be made 0.80 or more by the treatment under the above conditions. The peak intensity ratio (X) is preferably 0.90 or more, more preferably 0.95 or more.

X ═ (peak intensity of spinel compound analyzed by X-ray diffraction)/(α -Fe analyzed by X-ray diffraction method₂O₃Peak intensity of) … … (1)

The meaning of the above formula (1) is,at the wavelength of use of

When XRD analysis is performed on the Cu-K.alpha.ray of (C), among the peaks appearing, the peak intensity of the spinel compound appearing at about 35 ℃ is divided by the α -Fe appearing at 33 ℃₂O₃If the ratio obtained by the peak intensity of (a) is 0.80 or more, it means that a good toughness value can be obtained.

The MnZn ferrite of the present invention may further contain the following additives as auxiliary components.

And (3) CoO: 3500 mass ppm or less

CoO is a compound containing Co having positive magnetic anisotropy²⁺The temperature width of the second peak at which the initial permeability shows the maximum temperature can be widened by adding the ionic component. However, in the case where the CoO addition amount is too large, it cannot be offset by the negative magnetic anisotropy of other components, thus resulting in a significant decrease in initial permeability. Therefore, when CoO is added, the CoO content needs to be limited to 3500 mass ppm or less. The CoO content is more preferably 3000 ppm by mass or less, and still more preferably 2500 ppm by mass or less.

Next, a method for producing the MnZn-based ferrite of the present invention will be described.

In the production of MnZn-based ferrite, first, Fe as a basic component is weighed so as to have the above-described ratio₂O₃And ZnO and MnO powder, and the above are thoroughly mixed to prepare a mixture, and the mixture is precalcined (precalcination step). In this case, in order to have both good magnetic properties and fracture toughness values, the maximum temperature of the precalcining is set to be in the range of 800 to 950 ℃, and at least one of the cooling rate from the maximum temperature to 100 ℃ is set to be 800 ℃/h or more, or the oxygen concentration at the time of cooling from the maximum temperature to 100 ℃ is set to be 5 vol% or less is satisfied, thereby the pre-firing is performed at a wavelength of the pre-firing

When XRD analysis is performed on the Cu-K alpha ray of (1), the peak intensity of the spinel compound appearing at about 35 DEG isDivided by the alpha-Fe occurring at 33 deg. -%₂O₃The ratio obtained by the peak intensity of (a) is in the range of 0.80 or more, preferably in the range of 0.90 or more, and more preferably in the range of 0.95 or more. The spinel compound is a compound having a spinel crystal structure present in the pre-calcined ferrite powder and represented by the general formula AFe₂O₄(A is Mn, Zn).

Next, the auxiliary component is added to the obtained calcined powder at a predetermined ratio so that the auxiliary component is contained in the above-mentioned amount, and the calcined powder is mixed with the auxiliary component and pulverized (mixing-pulverizing step). In this step, the pre-calcined powder is pulverized to a size of a target average particle diameter while sufficiently homogenizing the powder so that the concentration of the added component does not deviate.

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). Thereafter, if necessary, a molding machine applies pressure to the mixture through a step such as sieving for adjusting the particle size to mold the mixture, thereby forming a molded article (molding step). Next, the compact is sintered under known sintering conditions to obtain a MnZn-based ferrite (sintering step).

The obtained MnZn-based ferrite can be subjected to appropriate surface finishing or the like.

The MnZn ferrite thus obtained not only has such excellent magnetic properties that the initial permeability at 23 ℃ and 100kHz is 4000 or more, but also has a fracture toughness value of 1.00MPa m measured in accordance with JIS R1607 for a flat plate-like sample, which has not been realized by conventional MnZn ferrites^1/2The above excellent mechanical properties.

Examples

(example 1)

In the presence of Fe in a ball mill₂O₃The respective raw material powders weighed so that the amounts of ZnO and MnO became the ratios shown in table 1 were mixed for 16 hours, and then precalcined at 900 ℃ for 3 hours in air. In addition, the cooling environment from the highest temperature of the precalcination to 100 ℃ is in air and the cooling is carried outThe speed was 1600 ℃/h. Next, the equivalent amounts of SiO were weighed at 130, 450, 200, and 100 mass ppm, respectively₂、CaO、Nb₂O₅And Bi₂O₃Then, the calcined powder was added to the calcined powder, and pulverized for 12 hours by a ball mill. Then, polyvinyl alcohol was added to the obtained pulverized powder, followed by spray drying granulation and molding into a toroidal core and a flat core under a pressure of 118 MPa. Then, these molded bodies were charged into a sintering furnace and sintered at a maximum temperature of 1350 ℃ for 2 hours in a gas flow appropriately mixed with nitrogen and air to obtain an outer diameter: 25mm, inner diameter: 15mm, height: 5mm sintered body toroidal core and width: 4mm, length: 35mm, thickness: a 3mm sintered body flat plate-shaped magnetic core (also referred to as a rectangular parallelepiped magnetic core).

In addition, since a high-purity raw material is used as a raw material and a medium such as a ball mill is sufficiently washed before use to suppress mixing of components derived from other materials, the amounts of P and B contained as inevitable impurities in the toroidal core and the rectangular parallelepiped core are 4 mass ppm and 3 mass ppm, respectively. The contents of P and B were determined in accordance with JIS K0102 (ICP mass spectrometry).

Initial permeability of the obtained toroidal core a winding of 10 turns was applied to the toroidal core, and calculated from impedance and phase angle measured using an impedance analyzer (Keysight Technologies, manufactured by 4294A).

The void fraction in the crystal grain was calculated by breaking the obtained toroidal core, polishing the cross section, etching the core with fluoronitric acid, observing the core at a magnification of 500 times using an optical microscope, counting the voids appearing in a field of view having a width of 120 μm and a length of 160 μm, and dividing the number of voids remaining in the crystal grain by the total number of the voids appearing.

For the peak intensity ratio of the pre-calcined powder, a wavelength of

XRD analysis (ultimaIV manufactured by Rigaku Corporation) of the pre-calcined powder was performed, and the peak intensity of the spinel compound occurring at about 35 ℃ was divided by α -Fe occurring at 33 °₂O₃The peak intensity of (c) was calculated.

The fracture toughness value of the rectangular parallelepiped core was calculated based on the fracture load and the size of the sample by applying a pre-crack to the sample punched in the center portion by a vickers indenter in accordance with JIS R1607, and then breaking the sample by a three-point bending test. The results obtained are shown in Table 1.

[ Table 1]

As shown in the table, in examples 1-1 to 1-5 which are inventive examples, the initial permeability at 23 ℃ and 100kHz was 4000 or more, and the fracture toughness value was 1.00MPa · m^1/2As described above, preferable magnetic properties and high toughness are obtained.

In contrast, only Fe of less than 51.5 mol% is contained₂O₃Comparative example 1-1 and Fe₂O₃In comparative example 1-2 in which the initial permeability is not less than 4000 at 23 ℃ and 100kHz, the initial permeability is lowered because the magnetic anisotropy and magnetostriction become large, although high toughness can be achieved.

In comparative examples 1 to 3 in which ZnO was insufficient, the curie temperature increased excessively, while in comparative examples 1 to 4 in which ZnO was included in an amount larger than the appropriate range, the second peak of the maximum initial permeability was lowered, and therefore the initial permeability at 23 ℃ and 100kHz could not satisfy 4000 or more.

(example 2)

With Fe₂O₃The raw materials were weighed so that the amount was 53.0 mol%, the amount of ZnO was 20.0 mol%, and the balance was MnO, and mixed for 16 hours using a ball mill, and then precalcined at 900 ℃ for 3 hours in air. In addition, the pre-calcination was carried out in an atmosphere of cooling from the maximum temperature to 100 ℃ at a cooling rate of 1600 ℃/h in air. Next, SiO was added to the calcined powder in the amount shown in Table 2₂、CaO、Nb₂O₅、Bi₂O₃And CoO was added to a part of the sample, and pulverized for 12 hours by a ball mill. Then, polyvinyl alcohol was added to the obtained powder, and spraying was performedThe pellets were dried and granulated, and a pressure of 118MPa was applied to the pellets to mold them into a toroidal core and a flat core. These shaped bodies were then charged into a sintering furnace and sintered at a maximum temperature of 1320 ℃ for 2 hours in a gas flow suitably mixed with nitrogen and air, giving the external diameter: 25mm, inner diameter: 15mm, height: 5mm sintered body toroidal core and width: 4mm, length: 35mm, thickness: 3mm rectangular parallelepiped magnetic core of sintered body. In addition, the amounts of P and B contained as inevitable impurities in the obtained toroidal core and the rectangular parallelepiped core were 4 mass ppm and 3 mass ppm, respectively.

The properties of each of these samples were evaluated by the same method and apparatus as in example 1. The results are shown in Table 2.

[ Table 2]

As shown in the table, in SiO₂、CaO、Nb₂O₅、Bi₂O₃And CoO in an appropriate range, the initial permeability at 23 ℃ and 100kHz of examples 2-1 to 2-9 was 4000 or more, and the fracture toughness was 1.00M Pa.m^1/2As described above, both preferable magnetic properties and high toughness can be achieved.

On the other hand, in SiO₂、CaO、Nb₂O₅And Bi₂O₃In comparative examples 2-1, 2-3, 2-5 and 2-7 in which only 1 of the 4 components was smaller than a predetermined amount, the resistivity was lowered due to insufficient grain boundary formation, or the fracture toughness was lowered due to the lowering of initial permeability and the increase of the intra-grain porosity caused by insufficient homogenization of the crystal structure. In addition, in comparative examples 2-2, 2-4, 2-6 and 2-8 in which 1 of these components was excessive, the initial permeability was significantly deteriorated due to the occurrence of abnormal particles, and since abnormal particles included a large number of intra-granular voids, the void ratio was high, and as a result, the fracture toughness value was also significantly reduced.

(example 3)

Granulated powders were obtained by the method shown in example 1 using raw materials having the same composition ratios of the basic components and the auxiliary components as in example 1-2, but different amounts of P, B contained as inevitable impurities. The granulated powder was pressed at 118MPa to form a toroidal core and a flat core. Then, these molded bodies were charged into a sintering furnace and sintered at a maximum temperature of 1320 ℃ for 2 hours in a gas flow appropriately mixed with nitrogen and air to obtain an outer diameter: 25mm, inner diameter: 15mm, height: 5mm sintered body toroidal core and width: 4mm, length: 35mm, thickness: 3mm rectangular parallelepiped magnetic core of sintered body.

The properties of each of these samples were evaluated by the same method and apparatus as in example 1. The results obtained are shown in Table 3.

[ Table 3]

As shown in the table, in example 3-1 in which the impurities P and B are in the predetermined ranges, the initial permeability at 23 ℃ and 100kHz is 4000 or more, and the fracture toughness value is 1.00MPa · m^1/2As described above, both preferable magnetic properties and high toughness can be achieved.

On the other hand, in comparative examples 3-1, 3-2 and 3-3 in which one or both of the two components were the predetermined values or more, the initial permeability was deteriorated due to the presence of abnormal particles, and the fracture toughness value was lowered due to the increase of the intra-grain porosity, so that the initial permeability and the fracture toughness value could not be obtained at desired values.

(example 4)

Granulated powders were produced in the same manner as in example 1-2, except that the heat treatment temperature, cooling rate, and cooling environment in the preliminary calcination step were changed to the conditions shown in table 4. The granulated powder was pressed at 118MPa to form a toroidal core and a flat core. Then, these molded bodies were charged into a sintering furnace and sintered at a maximum temperature of 1320 ℃ for 2 hours in a gas flow appropriately mixed with nitrogen and air to obtain an outer diameter: 25mm, inner diameter: 15mm, height: 5mm sintered body annular core and width: 4mm, length: 35mm, thickness: 3mm rectangular parallelepiped magnetic core of sintered body.

The properties of each of these samples were evaluated by the same method and apparatus as in example 1. The results are shown in Table 4.

[ Table 4]

In the precalcination process, in

1) The highest temperature is in the range of 800-950 ℃;

2) and examples 4-1 to 4-6, which were manufactured under the condition that at least either the cooling rate from the maximum temperature to 100 ℃ was 800 ℃/h or more or the oxygen concentration at the time of cooling from the maximum temperature to 100 ℃ was 5 vol% or less, were able to suppress excessive oxygen absorption at the time of cooling, and therefore spinel compound/α -Fe observed by XRD was able to be inhibited₂O₃The peak ratio of (A) is maintained at 0.80 or more, and the oxygen release amount during sintering is reduced, so that the intra-grain porosity is lowered, and as a result, a fracture toughness value of 1.00MPa · m is obtained^1/2The above good fracture toughness values.

In contrast, in comparative examples 4-1 to 4-8 prepared outside the above range, in 4-1 to 4-4, 4-6 and 4-8, the amount of spinel compound produced in the precalcination step was insufficient, or the amount of oxygen absorption during cooling was increased, and α -Fe in the obtained precalcined powder was₂O₃The amount increases. Therefore, the amount of oxygen released during sintering increases, and the intra-grain porosity increases, resulting in a fracture toughness value smaller than a desired value.

When attention is paid to comparative examples 4-5 and 4-7 in which the precalcining temperature exceeded the appropriate range, although the fracture toughness value was high, the initial permeability of the magnetic core became poor. This is presumably because excessive heat is applied during the precalcination, the reaction proceeds excessively, the particle size of the precalcined powder becomes coarse and solidified, and therefore sufficient pulverization cannot be performed in the subsequent pulverization step, and therefore the sintering reaction between the powders is hindered during sintering, and the reaction is insufficient, and thus desired magnetic properties cannot be obtained.

Claims (7)

1. A MnZn-based ferrite comprises a basic component, an auxiliary component and inevitable impurities,

in the presence of Fe₂O₃And ZnO and MnO, wherein the basic components are as follows when the total of Fe, Zn and Mn calculated as 100 mol%:

iron: with Fe₂O₃51.5 to 55.5 mol% in terms of;

zinc: more than 15.5 mol% and not more than 26.0 mol% in terms of ZnO; and

manganese: 22.0 to 32.0 mol% in terms of MnO;

relative to the basic components, the auxiliary components are:

SiO₂: 50 to 250 mass ppm;

CaO: 100 mass ppm or more and less than 1000 mass ppm;

Nb₂O₅: 100 to 300 mass ppm; and

Bi₂O₃: 50 to 150 ppm by mass of a catalyst,

the amounts of P and B in the inevitable impurities are suppressed to

P: less than 10 mass ppm; and

b: less than 10 mass ppm of a water-soluble polymer,

the number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn ferrite, and the MnZn ferrite further contains

The initial permeability of the MnZn ferrite at 23 ℃ and 100kHz is more than 4000,

the fracture toughness value measured according to JIS R1607 was 1.00MPa m^1/2The above.

2. The MnZn-based ferrite according to claim 1, further comprising, as the auxiliary component, a CoO: 3500 ppm by mass or less.

3. A method for producing MnZn ferrite, which is a method for producing MnZn ferrite,

the MnZn-based ferrite is composed of a basic component, an auxiliary component and unavoidable impurities,

in the presence of Fe₂O₃And ZnO and MnO, wherein the basic components are as follows when the total of Fe, Zn and Mn calculated as 100 mol%:

iron: with Fe₂O₃51.5 to 55.5 mol% in terms of;

zinc: more than 15.5 mol% and not more than 26.0 mol% in terms of ZnO; and

manganese: 22.0 to 32.0 mol% in terms of MnO;

relative to the basic components, the auxiliary components are:

SiO₂: 50 to 250 mass ppm;

CaO: 100 mass ppm or more and less than 1000 mass ppm;

Nb₂O₅: 100 to 300 mass ppm; and

Bi₂O₃: 50 to 300 mass ppm of a nitrogen-containing compound,

the amounts of P and B in the inevitable impurities are suppressed to

P: less than 10 mass ppm; and

b: less than 10 mass ppm of a water-soluble polymer,

the number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn ferrite, and the MnZn ferrite further contains

The initial permeability of the MnZn ferrite at 23 ℃ and 100kHz is more than 4000,

the fracture toughness value measured according to JIS R1607 was 1.00MPa m^1/2In the above-mentioned manner,

the method for producing a MnZn ferrite includes the following steps:

a pre-calcination step of subjecting the mixture of the basic components to pre-calcination and cooling to obtain pre-calcined powder;

a mixing-pulverizing step of adding the auxiliary component to the pre-calcined powder, mixing and pulverizing the mixture to obtain a pulverized powder;

a granulation step of adding a binder to the pulverized powder, mixing the powders, and granulating the mixture to obtain granulated powder;

a molding step of molding the granulated powder to obtain a molded body; and

a sintering step of sintering the molded body to obtain a MnZn ferrite,

the highest temperature of pre-calcination in the pre-calcination process is in the range of 800-950 ℃;

and at least one of a cooling rate of 800 ℃/hour or more from the maximum temperature to 100 ℃, and an oxygen concentration of 5 vol% or less in an environment at the time of cooling from the maximum temperature to 100 ℃.

4. A method for producing a MnZn ferrite, which is a method for producing a MnZn ferrite that is a MnZn ferrite,

the MnZn-based ferrite is composed of a basic component, an auxiliary component and unavoidable impurities,

in the presence of Fe₂O₃And ZnO and MnO, wherein the basic components are as follows when the total of Fe, Zn and Mn calculated as 100 mol%:

iron: with Fe₂O₃51.5 to 55.5 mol% in terms of;

zinc: more than 15.5 mol% and not more than 26.0 mol% in terms of ZnO; and

manganese: 22.0 to 32.0 mol% in terms of MnO;

relative to the basic components, the auxiliary components are:

SiO₂: 50 to 250 mass ppm;

CaO: 100 mass ppm or more and less than 1000 mass ppm;

Nb₂O₅: 100 to 300 mass ppm; and

Bi₂O₃: 50 to 300 mass ppm of a nitrogen-containing compound,

the amounts of P and B in the inevitable impurities are suppressed to

P: less than 10 mass ppm; and

b: less than 10 mass ppm of a water-soluble polymer,

the number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn ferrite, and the MnZn ferrite further contains

The initial permeability of the MnZn ferrite at 23 ℃ and 100kHz is more than 4000,

the fracture toughness value measured according to JIS R1607 was 1.00MPa m^1/2The above，

The method for producing a MnZn ferrite includes the following steps:

a pre-calcination step of subjecting the mixture of the basic components to pre-calcination and cooling to obtain pre-calcined powder;

a mixing-pulverizing step of adding the auxiliary component to the pre-calcined powder, mixing and pulverizing the mixture to obtain a pulverized powder;

a granulation step of adding a binder to the pulverized powder, mixing the powders, and granulating the mixture to obtain granulated powder;

a molding step of molding the granulated powder to obtain a molded body; and

a sintering step of sintering the molded body to obtain a MnZn ferrite,

the pre-calcined powder has a peak intensity ratio (X) represented by the following formula (1) of 0.80 or more,

x ═ (peak intensity of spinel compound analyzed by X-ray diffraction)/(α -Fe analyzed by X-ray diffraction₂O₃Peak intensity) … … (1).

5. The method for producing a MnZn ferrite according to claim 4, wherein a maximum temperature of the pre-firing in the pre-firing step is in a range of 800 to 950 ℃,

and at least one of a cooling rate of 800 ℃/hour or more from the maximum temperature to 100 ℃, and an oxygen concentration of 5 vol% or less in an environment at the time of cooling from the maximum temperature to 100 ℃.

6. The method for producing a MnZn ferrite according to claim 3 or 4, further comprising, as the auxiliary component, a CoO: 3500 ppm by mass or less.

7. The method for producing a MnZn ferrite according to claim 5, wherein the auxiliary component further includes a CoO: 3500 ppm by mass or less.