JPWO2020158335A1 - MnZn-based ferrite and its manufacturing method - Google Patents

Abstract

Provided is an MnZn-based ferrite having a high initial magnetic permeability and a high fracture toughness value. The basic and sub-components of MnZn-based ferrite are adjusted to an appropriate range, and the amounts of unavoidable impurities P and B are suppressed to less than P: 10 mass ppm and B: less than 10 mass ppm, respectively, and all voids in the MnZn-based ferrite are suppressed. The number of voids in the crystal grains relative to the number shall be less than 55%, the initial magnetic permeability at 23 ° C. and 100 kHz shall be 4000 or more, and the fracture toughness value measured in accordance with JIS R 1607 shall be 1.00 MPa · m 1/2 or more.

Description

The present invention relates to an MnZn-based ferrite that is particularly suitable for magnetic cores of automobile-mounted parts and a method for producing the same.

MnZn-based ferrite is a material widely used as a magnetic core of 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.

Of these, MnZn-based ferrites used for the magnetic cores of electronic devices for automobile mounting applications, whose needs are expanding due to the recent hybridization and electrical equipment of automobiles, are required to have a high fracture toughness value. This is because MnZn-based ferrites are ceramics and are brittle materials, so they are easily damaged. In addition, compared to conventional home appliances, they are constantly vibrated and easily damaged in automobile mounting applications. This is because it will continue to be used.
However, at the same time, in automobile applications, weight reduction and space saving are also required. Therefore, it is important to have a suitable magnetic property as in the conventional application in addition to a high fracture toughness value.

Various developments have been carried out in the past as MnZn-based ferrites for automobile mounting applications.
Patent Documents 1 and 2 and the like are reported as references 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.

JP-A-2007-51052 Japanese Unexamined Patent Publication No. 2012-76983 Japanese Unexamined Patent Publication No. 4-318904 Japanese Unexamined Patent Publication No. 4-177808

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 set the blending amounts of Fe ₂ O ₃ , ZnO and MnO, which are the main components of the MnZn-based ferrite, in a suitable range.
Further, by applying sufficient heat in the firing step to appropriately grow the crystal grains in the ferrite, the movement of the domain wall in the crystal grains in the magnetization step is facilitated, and a component segregating at the grain boundary is added to obtain an appropriate amount. By generating grain boundaries of uniform thickness and maintaining the specific resistance, the attenuation of the initial magnetic permeability due to the frequency rise is suppressed, and a high initial magnetic permeability is realized even in the 100 kHz region.

In addition to the above magnetic properties, the magnetic core of electronic components for automobiles is required to have a high fracture toughness value so that it will not be damaged even in an environment subject to constant vibration. If the MnZn-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 becomes inoperable.
From the above, MnZn-based ferrites used in electronic components for automobiles are required to have both good magnetic properties such as high initial magnetic permeability and high fracture toughness values.

However, 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 the magnetic core of the electronic component for automobiles is used. It seems unsuitable.
Further, although Patent Documents 3 and 4 mention the improvement of the fracture toughness value, the magnetic characteristics are insufficient as the magnetic core of the electronic component for automobiles, and it can be said that it is also unsuitable for this application.

Therefore, the present invention has a good magnetic property that the initial magnetic permeability value at 23 ° C. and 100 kHz is 4000 or more, and the fracture toughness value measured in accordance with JIS R 1607 of a flat sample is 1.00 MPa · m. ^An object of the present invention is to provide an MnZn-based ferrite having a mechanical property of ^1/2 or more.

Therefore, the inventors first examined the appropriate amounts of Fe ₂ O ₃ and Zn O, which are the basic components of MnZn-based ferrite, which can increase the initial magnetic permeability at 23 ° C. and 100 kHz in the toroidal-shaped core.
As a result, within this composition range, the magnetic anisotropy and magnetostriction are small, the specific resistance is maintained, and the secondary peak showing the maximum value of the temperature characteristic of the initial magnetic permeability can be made to appear in the vicinity of 23 ° C. As a result, we found an appropriate range in which a high initial magnetic permeability can be realized under the same conditions.

Next, by adding an appropriate amount of SiO ₂ , CaO, Nb ₂ O ₅ and Bi ₂ O ₃ which are non-magnetic components segregating at the grain boundaries as subcomponents, grain boundaries of uniform thickness are generated and the specific resistance is increased. As a result, it was found that the attenuation due to the frequency increase of the initial permeability can be further suppressed.

In addition to these, the inventors investigated factors effective in improving the fracture toughness value, and found that the crystal grains among the voids in the material were analyzed from the analysis of the images observed after polishing and etching the fracture surface of MnZn-based ferrite. It was found that there is a correlation between the ratio of voids remaining inside and the fracture toughness value.
That is, voids include those existing at grain boundaries and those existing inside crystal grains, but are brittle materials by reducing the voids remaining in the crystal grains (hereinafter, also referred to as intra-crystal voids). It has been clarified that the crack propagation of a certain MnZn-based ferrite is suppressed, and as a result, the fracture toughness value of the material is improved.

From this point of view, the inventors further investigated and found two means for reducing intragranular voids.
First, abnormal grains may appear due to the imbalance of grain growth during firing of ferrite, and these abnormal grains contain a large number of voids in the grains. In order to suppress the generation of abnormal grains and reduce the number of voids in the crystal grains, it is necessary to reduce the content of impurities. Since the appearance of abnormal grains increases the loss, it is required to avoid the abnormal grains from the viewpoint of magnetic characteristics.
The other is that the normal MnZn-based ferrite is manufactured through a calcining process. By properly controlling the maximum temperature of calcining and the speed or atmosphere during cooling, the material becomes excessively oxygenated. This is a method of reducing the number of voids appearing and reducing the voids in the crystal grains by preventing the absorption of oxygen and reducing the amount of oxygen desorbed during the reduction reaction during firing.
Only by properly controlling these two means can the fracture toughness value of the material be increased.

As described above, the amounts of the basic components Fe ₂ O ₃ and Zn O and the amounts of the non-magnetic components SiO ₂ , Ca O, Nb ₂ O ₅ and Bi ₂ O ₃ are adjusted to appropriate amounts, and crystals are formed. It is necessary to reduce intragranular voids in order to obtain MnZn-based ferrite having high initial magnetic permeability and high fracture toughness value.
It should be noted that Patent Document 1 and Patent Document 2 described above do not mention the fracture toughness value, and it can be said that this improvement is impossible.
Further, in Patent Document 3 and Patent Document 4, although the toughness is improved, a satisfactory magnetic property cannot be realized because an appropriate composition range cannot be selected.
Therefore, it is not possible to produce MnZn-based ferrite suitable for the magnetic core of electronic components for automobiles, which is practically useful only by these findings.
The present invention is based on the above findings.

That is, the gist structure of the present invention is as follows.
1. 1. MnZn-based ferrite consisting of basic components, sub-components and unavoidable impurities.
Assuming that the total of the basic components, iron, zinc, and manganese in terms of Fe ₂ O ₃ , ZnO, and MnO is 100 mol%,
Iron: 51.5 to 55.5 mol% in terms of Fe ₂ O ₃
Zinc: more than 15.5 mol% in terms of ZnO, 26.0 mol% or less, and manganese: 22.0 to 32.0 mol% in terms of MnO
And
With respect to the basic component, the sub-component is
SiO ₂ : 50-250 massppm,
CaO: 100 massppm or more, less than 1000 massppm,
Nb ₂ O ₅ : 100 to 300 mass ppm and Bi ₂ O ₃ : 50 to 300 mass ppm
And
The amounts of P and B in the unavoidable impurities, respectively,
P: less than 10 mass ppm and B: less than 10 mass ppm,
The number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn-based ferrite, and the initial magnetic permeability at 23 ° C. and 100 kHz is 4000 or more.
MnZn-based ferrite having a fracture toughness value of 1.00 MPa · m ^1/2 or more measured in accordance with JIS R 1607.

2. 2. The MnZn-based ferrite according to 1 above, which further contains CoO: 3500 mass ppm or less as the sub-component.

3. 3. The method for producing an MnZn-based ferrite, which obtains the MnZn-based ferrite according to 1 or 2 above.
A calcining step of calcining a mixture of the basic components and cooling the mixture to obtain a calcined powder.
A mixing-crushing step of adding the sub-ingredient to the calcined powder, mixing and crushing to obtain crushed powder, and
A granulation step of adding and mixing a binder to the pulverized powder and then granulating to obtain a granulated powder.
The molding process of molding the granulated powder to obtain a molded product, and
It has a firing step of calcining the molded product to obtain MnZn-based ferrite.
The maximum temperature of calcining in the calcining step is in the range of 800 to 950 ° C.
MnZn-based ferrite that satisfies at least one of a cooling rate of 800 ° C./hr or more from the maximum temperature to 100 ° C. or an oxygen concentration of 5% by volume or less in the atmosphere during cooling from the maximum temperature to 100 ° C. Manufacturing method.

4. The method for producing an MnZn-based ferrite according to claim 1 or 2, wherein the MnZn-based ferrite is obtained.
A calcining step of calcining a mixture of the basic components and cooling the mixture to obtain a calcined powder.
A mixing-crushing step of adding the sub-ingredient to the calcined powder, mixing and crushing to obtain crushed powder, and
A granulation step of adding and mixing a binder to the pulverized powder and then granulating to obtain a granulated powder.
The molding process of molding the granulated powder to obtain a molded product, and
It has a firing step of calcining the molded product to obtain MnZn-based ferrite.
A method for producing an MnZn-based ferrite in which the peak intensity ratio (X) represented by the following formula (1) of the calcined powder is 0.80 or more.
X = (peak intensity of spinel compound analyzed by X-ray diffraction) / (peak intensity of α-Fe ₂ O ₃ analyzed by X-ray diffraction) ... (1)

5. The maximum temperature of calcining in the calcining step is in the range of 800 to 950 ° C.
4. The above 4, wherein the cooling rate from the maximum temperature to 100 ° C. satisfies at least one of 800 ° C./hr or more or the oxygen concentration of the atmosphere at the time of cooling from the maximum temperature to 100 ° C. is 5% by volume or less. MnZn-based ferrite manufacturing method.

The MnZn-based ferrite of the present invention has a good magnetic property of an initial magnetic permeability of 4000 or more at 100 kHz at 23 ° C., and further has a fracture toughness value measured in accordance with JIS R 1607 of a flat sample. It also has mechanical characteristics of 00 MPa ・ m ^1/2 or more.

Hereinafter, the present invention will be specifically described. 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.
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, iron, zinc, and manganese contained in the present invention as basic components are all shown as values converted into Fe ₂ O ₃ , ZnO, and MnO. These _Fe 2 _O 3, ZnO, for the content of _MnO, Fe ₂ O 3, ZnO, iron in terms of MnO, zinc, in mol% relative to the total amount 100 mol% of manganese, whereas subcomponent and inevitable impurities The content of is expressed in mass ppm with respect to the basic component.

Fe ₂ O ₃ : 51.5 to 55.5 mol%
Of the basic components, whether Fe ₂ O ₃ is less than the appropriate range or more, the magnetic anisotropy becomes large and the magnetostriction also becomes large, which causes a decrease in the initial magnetic permeability. Therefore, at least Fe ₂ O ₃ is contained in an amount of 51.5 mol% or more, and the upper limit is 55.5 mol%.

ZnO: More than 15.5 mol%, 26.0 mol% or less When the amount of ZnO is small, the Curie temperature becomes excessively high, and the initial magnetic permeability at 23 ° C. decreases. Therefore, at least 15.5 mol% or more is contained. I will do it. However, even when the content exceeds an appropriate amount, the secondary peak temperature at which the initial magnetic permeability shows a maximum value decreases, which causes a decrease in the initial magnetic permeability at 23 ° C. Therefore, the upper limit is set to 26.0 mol%. The ZnO content is preferably in the range of 16.0 to 25.5 mol%.

MnO: 22.0 to 32.0 mol%
The present invention is an MnZn-based ferrite, and the balance of the main component composition must be MnO. This is because it is not possible to achieve an initial magnetic permeability of 4000 or more at 23 ° C. and 100 kHz without MnO. The MnO content is preferably in the range of 22.5 to 31.0 mol%.
Needless to say, the total amount of the basic components Fe ₂ O ₃ , ZnO, and MnO is 100 mol%.

The basic components have been described above, but the sub-components are as follows.
SiO ₂ : 50-250 massppm
SiO ₂ is known to contribute to homogenization of the crystal structure of ferrite, reduces the number of voids in the crystal grains remaining in the crystal grains with addition, and also increases the specific resistance, so that the amount is appropriate. By the addition, the initial magnetic permeability at 23 ° C. and 100 kHz can be increased, and the fracture toughness value can be increased. Therefore, it is assumed that at least 50 massppm of SiO ₂ is contained. However, when the amount added is excessive, on the contrary, abnormal grains containing a large number of intragranular voids appear, which significantly lowers the fracture toughness value and at the same time significantly deteriorates the initial magnetic permeability. Therefore, it is necessary to suppress the amount to 250 mass ppm or less. is there. The content of SiO ₂ is preferably in the range of 60 to 230 mass ppm.

CaO: 100 massppm or more and less than 1000 massppm CaO segregates at the grain boundaries of MnZn-based ferrite and has a function of suppressing the growth of crystal grains. When an appropriate amount is added, the specific resistance increases and the initial permeability at 23 ° C. and 100 kHz. The magnetic coefficient can be increased. In addition, the fracture toughness value can be increased by reducing the number of voids in the crystal grains as the crystal grain growth is suppressed. Therefore, it is assumed that CaO is contained at least 100 mass ppm. However, if the amount added is excessive, abnormal particles will appear, leading to a decrease in fracture toughness value and deterioration of initial magnetic permeability. Therefore, it is necessary to limit the CaO content to less than 1000 mass ppm. The CaO content is preferably in the range of 130-850 mass ppm.

Nb ₂ O ₅ : 100-300 massppm
Nb ₂ O ₅ segregates at the crystal grain boundaries of MnZn-based ferrite, and has the effect of gently suppressing the crystal grain growth and relaxing the stress. Therefore, the initial magnetic permeability can be increased by adding an appropriate amount, and the fracture toughness value can be increased by reducing the number of voids in the crystal grains. Therefore, at least 100 mass ppm of Nb ₂ O ₅ is contained. To do. However, when the amount added is excessive, abnormal particles appear, which induces a significant decrease in fracture toughness value and deterioration of initial magnetic permeability. Therefore, it is necessary to suppress the content of Nb ₂ O ₅ to 300 mass ppm or less. The content of Nb ₂ O ₅ is preferably in the range of 120 to 280 mass ppm.

Bi ₂ O ₃ : 50-300 massppm
Bi ₂ O ₃ has the effect of slowly promoting the crystal grain growth of MnZn-based ferrite, and unlike conventional grain growth promoting additives, it homogenizes the crystal structure with the addition of an appropriate amount, and thus has fracture toughness. Since the value can be increased and the initial magnetic permeability can be increased, at least 50 mass ppm of Bi ₂ O ₃ is contained. However, when the amount added is excessive, abnormal particles appear, which induces a significant decrease in fracture toughness value and deterioration of initial magnetic permeability. Therefore, it is necessary to suppress the Bi ₂ O ₃ content to 300 mass ppm or less. The content of Bi ₂ O ₃ is preferably in the range of 75 to 275 mass ppm, more preferably 100 to 250 mass ppm.

Next, the unavoidable impurities to be suppressed will be described.
P: less than 10 mass ppm, B: less than 10 mass ppm P and B are components inevitably contained mainly in the raw material iron oxide. There is no problem if these contents are very small, but if they are contained above a certain level, abnormal grain growth of ferrite is induced and the void ratio in the crystal grains is increased, so that the fracture toughness value is lowered and the fracture toughness value is lowered for the first time. Permeability is reduced, which has a serious adverse effect. Therefore, the contents of P and B are both limited to less than 10 mass ppm. Preferably, both P and B are 8 mass ppm or less.

Further, various characteristics of the MnZn-based ferrite are greatly affected by various parameters regardless of the composition. Therefore, in the present invention, the following provisions are provided in order to secure more preferable magnetic characteristics and strength characteristics.
Fracture toughness value measured in accordance with JIS R 1607: 1.00 MPa · m ^1/2 or more MnZn-based ferrite is a ceramic and is a brittle material, so 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 making a Vickers indentation in the center of the flat sample and performing a bending test with a pre-crack. The MnZn-based ferrite of the present invention is intended for use in automobiles where high toughness is required, and the fracture toughness value is required to be 1.00 MPa · m ^1/2 or more.
In order to satisfy this condition, in the MnZn-based ferrite produced by powder molding, voids remain in the material, but after polishing the fracture surface and etching the grain boundary with fluorine nitric acid, the observation was performed in a 200 to 500 times field of view. It is necessary to analyze the image and divide the total number of intragranular voids by the total number of residual voids in the field of view so that the intragranular void ratio is less than 55%. The void ratio in the crystal grains is preferably 50% or less, more preferably 45% or less. This is because the cracks in the MnZn-based ferrite propagate mainly through the voids in the crystal grains, so when the void ratio in the crystal grains is high, the cracks easily propagate and the toughness value is low, so that they break. This is because the toughness value: 1.00 MPa · m ^1/2 or more cannot be satisfied.

In order to keep the void ratio in the crystal grains below 55%, it is necessary to satisfy two conditions.
The first is to suppress the amount of unavoidable impurities P and B to less than 10 mass ppm. This is because these components are components that induce the appearance of abnormal grains containing a large number of intragranular voids, and increase the intragranular void ratio.

The second is to optimize the calcining conditions in the manufacturing process of MnZn-based ferrite.
Firing of MnZn-based ferrite, which is basically a metal oxide, is a reduction reaction, and excess oxygen retained by the material is released in this process. In the molding process before firing, an organic binder is added to the granulated powder to be molded in order to maintain the shape of the powder-compressed molded product, and this binder is burnt, decomposed and removed in the initial stage of firing. To. The reducing atmosphere at the time of decomposition and removal may be accompanied by a chemical reaction that deprives the ferrite material, which is an oxide, of oxygen, and this chemical reaction is accompanied by volume expansion, which damages the molded product. Therefore, in order to prevent this, the MnZn-based ferrite intentionally absorbs and retains oxygen in excess of the stoichiometric ratio in the calcining step. However, as a matter of course, when oxygen is excessively retained, the amount of oxygen released in the firing step increases. Oxygen is released to the outside of the material as the grains grow during firing, but the greater the amount of oxygen released, the greater the amount of intragranular voids, and when the intragranular void ratio is 55% or more, fracture toughness The value is lower than the desired 1.00 MPa · m ^1/2 . Therefore, in the calcining step, it is necessary to treat the MnZn-based ferrite under an appropriate temperature and atmosphere range.
Specifically, the maximum temperature of calcining should be in the range of 800 to 950 ° C (preferably in the range of 850 to 950 ° C), and the cooling rate from the maximum temperature to 100 ° C should be 800 ° C / h or more, or It is necessary to carry out the treatment under the condition that the oxygen concentration at the time of cooling from the maximum temperature to 100 ° C. satisfies at least one of 5% by volume or less (preferably 4% or less).
When the oxygen concentration during cooling from the maximum temperature to 100 ° C. is 5% by volume or less, the maximum temperature of calcining is 800 to 950 ° C. (more preferably 850 to 930 ° C.), and the calcining atmosphere is in the air. It is preferable to do so.

The amount of oxygen retained by the calcined powder can be quantified by analysis by X-ray Diffraction (XRD) using Cu-Kα rays having a wavelength of 1.542 Å. The peak intensity ratio (X) represented by the following formula (1) may be set to 0.80 or more by the treatment under the 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 method) / (peak intensity of α-Fe ₂ O ₃ analyzed by X-ray diffraction method) ... (1)
The meaning of the above formula (1) is that the peak intensity of the spinel compound appearing at about 35 ° among the appearing peaks when XRD analysis is performed using Cu-Kα rays having a wavelength of 1.542 Å. It is a ratio divided by the peak intensity of α-Fe ₂ O ₃ appearing at 33 °, and if this value is 0.80 or more, it means that a good toughness value can be obtained.

The MnZn-based ferrite of the present invention may further contain the following additives as subcomponents.
CoO: 3500 massppm or less CoO is a component containing Co ²⁺ ions having positive magnetic anisotropy, and the addition of this component can widen the temperature range of the secondary peak showing the maximum temperature of the initial magnetic permeability. However, when the amount added is excessive, the negative magnetic anisotropy of other components cannot be offset, resulting in a significant decrease in the initial magnetic permeability. Therefore, when added, the CoO content needs to be limited to 3500 mass ppm or less. The CoO content is more preferably 3000 mass ppm or less, still more preferably 2500 mass ppm or less.

Next, the method for producing the MnZn-based ferrite of the present invention will be described.
In the production of MnZn-based ferrite, first, the basic components Fe ₂ O ₃ , ZnO and MnO powder are weighed so as to have the above-mentioned ratios, and these are sufficiently mixed to form a mixture, and then the mixture is temporarily prepared. Bake (temporary baking process). At this time, in order to have suitable magnetic properties and fracture toughness value, the maximum temperature of calcining is set in the range of 800 to 950 ° C, and the cooling rate from the maximum temperature to 100 ° C is set to 800 ° C. Cu- having a wavelength of 1.542 Å is satisfied by satisfying at least one of the following: / h or more, or the oxygen concentration at the time of cooling from the maximum temperature to 100 ° C. is 5% by volume or less. When analyzed by XRD using Kα rays, the ratio of the peak intensity of the spinel compound appearing at about 35 ° divided by the peak intensity of α-Fe ₂ O ₃ appearing at 33 ° is 0.80 or more, preferably 0. It is in the range of .90 or more, more preferably 0.95 or more. Here, the spinel compound is (a compound having a spinel-type crystal structure existing in ferrite calcined powder, and is represented by the general formula AFe ₂ O ₄ (A is Mn, Zn).

Next, sub-ingredients are added to the obtained calcined flour at a predetermined ratio so as to have the above-mentioned content, mixed with the calcined flour, 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.
Then, a known organic binder such as polyvinyl alcohol is added to the pulverized powder, and the powder is granulated by a spray-drying method or the like to obtain a granulated powder (granulation step). After that, if necessary, a step such as sieving for adjusting the particle size is performed, and then pressure is applied by a molding machine to form a molded product (molding step). Next, the molded product is fired under known firing conditions to obtain MnZn-based ferrite (firing step).
The obtained MnZn-based ferrite may be appropriately subjected to surface polishing or other processing.

The MnZn-based ferrite thus obtained not only has good magnetic properties with an initial magnetic permeability of 4000 or more at 23 ° C. and 100 kHz, but also has JIS of a flat sample, which was impossible with conventional MnZn-based ferrites. It has excellent mechanical properties with a fracture toughness value of 1.00 MPa · m ^1/2 or more measured in accordance with R 1607.

(Example 1)
Each raw material powder weighed so that the amounts of Fe ₂ O ₃ , ZnO and MnO have the ratios shown in Table 1 are mixed for 16 hours using a ball mill, and then calcined in air at 900 ° C. for 3 hours. went. The cooling atmosphere from the maximum temperature of calcining to 100 ° C. was in air, and the cooling rate was 1600 ° C./h. Next, SiO ₂ , CaO, Nb ₂ O ₅ and Bi ₂ O ₃ were weighed equivalent to 130, 450, 200 and 100 mass ppm, respectively, and then added to the calcined powder, and the mixture was pulverized with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained pulverized powder for spray-dry granulation, and a pressure of 118 MPa was applied to form a toroidal core and a flat core. Then, these compacts were charged into a firing furnace and fired at a maximum temperature of 1350 ° C. for 2 hours in a gas stream in which nitrogen gas and air were appropriately mixed, and the outer diameter was 25 mm, the inner diameter was 15 mm, and the height was increased. A 5 mm sintered toroidal core and a sintered flat plate core (also referred to as a rectangular core) having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained.
Since high-purity raw materials are used as raw materials and media such as ball mills are thoroughly washed before use to suppress contamination of components from other materials, P is an unavoidable impurity contained in toroidal cores and rectangular parallelepiped cores. The amounts of and B were 4 and 3 mass ppm, respectively. The contents of P and B were quantified according to JIS K 0102 (IPC mass spectrometry).

The initial magnetic permeability of the obtained toroidal core was calculated based on the impedance and the phase angle measured by winding the toroidal core with 10 turns and using an impedance analyzer (4294A manufactured by Keysight Co., Ltd.).
Regarding the void ratio in the crystal grains, the obtained toroidal core was broken, the fracture surface was polished and then etched with fluoric nitric acid, and then observed with an optical microscope at a magnification of 500 times, and within a visual field of 120 μm in length and 160 μm in width. It was calculated by counting the voids that appeared in the crystal grains and dividing the number of voids remaining in the crystal grains by the total number of voids that appeared.
For the peak intensity ratio of the calcined powder, XRD analysis (UltimaIV manufactured by Rigaku) was performed on the calcined powder using Cu-Kα rays having a wavelength of 1.542 Å, and the peak intensity of the spinel compound appearing at about 35 ° was 33 °. It was calculated by dividing by the peak intensity of α-Fe ₂ O ₃ appearing in.
Regarding the fracture toughness value of the rectangular parallelepiped core, according to JIS R 1607, a sample that was dented in the center by a Vickers indenter was cracked and then broken by a three-point bending test, and the breaking load and the size of the sample were determined. Calculated based on. The results obtained are shown in Table 1.

As shown in the table, in Examples 1-1 to 1-5, which are examples of the invention, the initial magnetic permeability at 23 ° C. and 100 kHz is 4000 or more, and the fracture toughness value is 1.00 MPa · m ^1/2 or more. Yes, suitable magnetic properties and high toughness are both obtained.
In contrast, in the _Fe 2 _{O 3} Comparative Example 1-1 comprises less than 51.5Mol% a and _Fe 2 _{O 3} Comparison is more than 55.5Mol% Example 1-2, although the high toughness is realized, Since the magnetic anisotropy and magnetostriction have increased, the initial magnetic permeability has decreased, and the initial magnetic permeability at 23 ° C. and 100 kHz does not satisfy 4000 or more.
Further, in Comparative Example 1-3 in which ZnO was insufficient, the Curie temperature rose excessively, while in Comparative Example 1-4 in which ZnO was contained in a larger amount than the appropriate range, the secondary peak showing the maximum value of the initial magnetic permeability decreased. , The initial magnetic permeability at 23 ° C. and 100 kHz does not satisfy 4000 or more.

(Example 2)
The raw materials were weighed so that the composition of Fe ₂ O ₃ was 53.0 mol%, the amount of Zn O was 20.0 mol%, and the balance was MnO, mixed for 16 hours using a ball mill, and then in the air at 900 ° C. for 3 hours. It was calcined. The cooling atmosphere from the maximum temperature of calcining to 100 ° C. was in air, and the cooling rate was 1600 ° C./h. Next, the amounts of SiO ₂ , CaO, Nb ₂ O ₅ , Bi ₂ O ₃ and some samples were added to the calcined powder as shown in Table 2, and the mixture was pulverized with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained pulverized powder for spray-dry granulation, and a pressure of 118 MPa was applied to form a toroidal core and a flat core. Then, these compacts were charged 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, and the outer diameter was 25 mm, the inner diameter was 15 mm, and the height was increased. A 5 mm sintered toroidal core and a sintered rectangular parallelepiped core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained. The amounts of unavoidable impurities P and B contained in the obtained toroidal core and rectangular parallelepiped core were 4 and 3 mass ppm, respectively.
The characteristics of each of these samples were evaluated using the same method and equipment as in Example 1. The results obtained are also shown in Table 2.

As shown in the table, in Examples 2-1 to 2-9 in which the amounts of SiO ₂ , CaO, Nb ₂ O ₅ , Bi ₂ O ₃ and CoO are within the appropriate range, the initial magnetic permeability at 23 ° C. and 100 kHz The value is 4000 or more, and the fracture toughness value is 1.00 MPa · m ^1/2 or more, and both suitable magnetic properties and high toughness can be achieved.
On the other hand, in Comparative Examples 2-1, 2-3, 2-5 and 2-7 in which even one of the four components of SiO ₂ , CaO, Nb ₂ O ₅ and Bi ₂ O ₃ is contained in an amount less than an appropriate amount, the grains are grains. The specific resistance decreases due to insufficient field formation, or the crystal structure homogenization is insufficient, resulting in a decrease in the initial magnetic permeability and a decrease in the fracture toughness value due to an increase in the intragranular void ratio. Be looked at. Further, in Comparative Examples 2-2, 2-4, 2-6 and 2-8 in which even one of the same components is excessive, the initial magnetic permeability is significantly deteriorated due to the appearance of abnormal grains, and the abnormal grains are present. As a result of the high void ratio due to the large amount of intra-grain voids, the fracture toughness value is also significantly reduced.

(Example 3)
By the method shown in Example 1, raw materials in which the basic component and the sub-component have the same composition as in Example 1-2, but the amounts of P and B, which are unavoidable impurities contained, are variously different. The granulated flour obtained by using the product was obtained. A pressure of 118 MPa was applied to the granulated powder to form a toroidal core and a flat core. Then, these compacts were charged 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. Outer diameter: 25 mm, inner diameter: 15 mm, height: A 5 mm sintered toroidal core and a sintered rectangular parallelepiped 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 results obtained are shown in Table 3.

As shown in the table, in Example 3-1 in which the impurities P and B components are within the specified range, the initial magnetic permeability value at 23 ° C. and 100 kHz is 4000 or more, and the fracture toughness value is 1.00 MPa. The m is ^1/2 or more, and both suitable 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 are contained in excess of the specified value, the initial magnetic permeability deteriorates due to the appearance of abnormal grains, and at the same time, intragranular voids. Since the rate increases, the fracture toughness value also decreases, and both the initial magnetic permeability and the fracture toughness value are not obtained.

(Example 4)
Granulated powder was prepared in the same manner as in Example 1-2 except that the heat treatment temperature, cooling rate, and cooling atmosphere in the calcining step were changed to the conditions shown in Table 4. A pressure of 118 MPa was applied to the granulated powder to form a toroidal core and a flat core. Then, these compacts were charged 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. Outer diameter: 25 mm, inner diameter: 15 mm, height: A 5 mm sintered toroidal core and a sintered rectangular parallelepiped 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 results obtained are also shown in Table 4.

In the calcination process 1) When the maximum temperature is in the range of 800 to 950 ° C,
2) Example 4 produced under the condition that the cooling rate from the maximum temperature to 100 ° C. is 800 ° C./h or more, or the oxygen concentration during cooling from the maximum temperature to 100 ° C. is at least 5% by volume or less. In -1 to 4-6, excessive oxygen absorption could be suppressed during cooling, so the peak ratio of spinel compound / α-Fe ₂ O ₃ observed by XRD was maintained at 0.80 or more. Since the amount of oxygen released during firing is reduced, the void ratio in the crystal grains is reduced, and as a result, a good fracture toughness value of 1.00 MPa · m ^1/2 or more is obtained.
On the other hand, in Comparative Examples 4-1 to 4-8 produced outside the above range, in 4-1 to 4-4,4-6.4-8, the amount of spinel compound produced in the calcining step was increased. The amount of α-Fe ₂ O ₃ in the obtained calcined powder is increasing due to the shortage or the increase in the amount of oxygen absorbed during cooling. Therefore, the amount of oxygen released during firing increases, and the void ratio in the crystal grains increases, resulting in a fracture toughness value less than a desired value.
Focusing on Comparative Examples 4-5 and 4-7 in which the calcining temperature exceeds the appropriate range, the fracture toughness value is high, but the initial magnetic permeability of the core is deteriorated. This is because the reaction proceeds excessively due to excessive heat applied during calcining, and the particle size of the calcined powder becomes coarse and hardens, so that it cannot be sufficiently pulverized in the subsequent pulverization step, and therefore the powder is powdered during calcining. It is probable that the desired magnetic properties could not be obtained because the sintering reaction between them was inhibited and insufficient.

Claims (5)

MnZn-based ferrite consisting of basic components, sub-components and unavoidable impurities.
Assuming that the total of the basic components, iron, zinc, and manganese in terms of Fe ₂ O ₃ , ZnO, and MnO is 100 mol%,
Iron: 51.5 to 55.5 mol% in terms of Fe ₂ O ₃
Zinc: more than 15.5 mol% in terms of ZnO, 26.0 mol% or less, and manganese: 22.0 to 32.0 mol% in terms of MnO
And
With respect to the basic component, the sub-component is
SiO ₂ : 50-250 massppm,
CaO: 100 massppm or more, less than 1000 massppm,
Nb ₂ O ₅ : 100 to 300 mass ppm and Bi ₂ O ₃ : 50 to 300 mass ppm
And
The amounts of P and B in the unavoidable impurities, respectively,
P: less than 10 mass ppm and B: less than 10 mass ppm,
The number of voids in the crystal grains is less than 55% of the total number of voids in the MnZn-based ferrite, and the initial magnetic permeability at 23 ° C. and 100 kHz is 4000 or more.
MnZn-based ferrite having a fracture toughness value of 1.00 MPa · m ^1/2 or more measured in accordance with JIS R 1607. The MnZn-based ferrite according to claim 1, further containing CoO: 3500 mass ppm or less as the sub-component. The method for producing an MnZn-based ferrite according to claim 1 or 2, wherein the MnZn-based ferrite is obtained.
A calcining step of calcining a mixture of the basic components and cooling the mixture to obtain a calcined powder.
A mixing-crushing step of adding the sub-ingredient to the calcined powder, mixing and crushing to obtain crushed powder, and
A granulation step of adding and mixing a binder to the pulverized powder and then granulating to obtain a granulated powder.
The molding process of molding the granulated powder to obtain a molded product, and
It has a firing step of calcining the molded product to obtain MnZn-based ferrite.
The maximum temperature of calcining in the calcining step is in the range of 800 to 950 ° C.
MnZn-based ferrite that satisfies at least one of a cooling rate of 800 ° C./hr or more from the maximum temperature to 100 ° C. or an oxygen concentration of 5% by volume or less in the atmosphere during cooling from the maximum temperature to 100 ° C. Manufacturing method. The method for producing an MnZn-based ferrite according to claim 1 or 2, wherein the MnZn-based ferrite is obtained.
A calcining step of calcining a mixture of the basic components and cooling the mixture to obtain a calcined powder.
A mixing-crushing step of adding the sub-ingredient to the calcined powder, mixing and crushing to obtain crushed powder, and
A granulation step of adding and mixing a binder to the pulverized powder and then granulating to obtain a granulated powder.
The molding process of molding the granulated powder to obtain a molded product, and
It has a firing step of calcining the molded product to obtain MnZn-based ferrite.
A method for producing an MnZn-based ferrite in which the peak intensity ratio (X) represented by the following formula (1) of the calcined powder is 0.80 or more.
X = (peak intensity of spinel compound analyzed by X-ray diffraction) / (peak intensity of α-Fe ₂ O ₃ analyzed by X-ray diffraction) ... (1) The maximum temperature of calcining in the calcining step is in the range of 800 to 950 ° C.
According to claim 4, the cooling rate from the maximum temperature to 100 ° C. is at least 800 ° C./hr or more, or the oxygen concentration in the atmosphere at the time of cooling from the maximum temperature to 100 ° C. is 5% by volume or less. The method for producing MnZn-based ferrite according to the above method.