WO2020189035A1

WO2020189035A1 - MnCoZn FERRITE AND METHOD FOR PRODUCING SAME

Info

Publication number: WO2020189035A1
Application number: PCT/JP2020/003151
Authority: WO
Inventors: 由紀子中村; 裕史吉田; 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: 2019-03-18
Filing date: 2020-01-29
Publication date: 2020-09-24
Also published as: TWI761757B; CN112041275B; CN112041275A; TW202035336A

Abstract

Provided is a MnCoZn ferrite that has excellent magnetic characteristics and mechanical characteristics and that is suitable for use in electronic components to be mounted to an automobile. In the MnCoZn ferrite, basic components and secondary components are adjusted to appropriate ranges, and the amounts of unavoidable impurities, namely, P, B, and Ti are controlled so that P is less than 10 mass ppm, B is less than 10 mass ppm, and Ti is less than 50 mass ppm. In addition, the surface residual stress is set to a value of less than 40 MPa.

Description

MnCoZn-based ferrite and its manufacturing method

The present invention relates to MnCoZn-based ferrite and a method for producing the same, which are particularly suitable for magnetic cores of automobile-mounted parts.

MnZn 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, MnZn ferrite has high magnetic permeability and low loss in the kHz region, and is cheaper than amorphous metals and the like.

On the other hand, in the 10 MHz region, in the case of ordinary MnZn ferrite, the specific resistance is low and it is difficult to maintain its magnetic permeability due to attenuation due to eddy current loss. As a countermeasure, the content range of Fe ₂ O ₃ is selected to be less than 50 mol%, and the positive and negative magnetic anisotropy caused by the presence of Fe ²⁺ ions having positive magnetic anisotropy in ordinary MnZn ferrite is canceled out. Is replaced by Co ²⁺ ions, which also exhibit positive magnetic anisotropy, and MnCoZn-based ferrite is known. This MnCoZn-based ferrite is characterized by having a high specific resistance and maintaining a good initial magnetic permeability up to the 10 MHz region.

By the way, as the magnetic core of electronic devices for automobile mounting, whose needs are expanding due to the recent hybridization and electrification of automobiles, it is required that they are not damaged during their use, that is, they have a particularly high fracture toughness value (Kic). Be done. This is because oxide magnetic materials such as MnZn 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, in automobile applications, weight reduction and space saving are also required at the same time. Therefore, it is important that MnZn ferrite and MnCoZn ferrite have not only high fracture toughness value but also suitable magnetic properties as in the conventional application.

Various developments have been made in the past as MnZn 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 ferrite 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 their initial magnetic permeability even in the 10 MHz region.

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 Japanese Patent No. 4508626 Japanese Patent No. 4554959

Generally, in order to increase the initial magnetic permeability of conventional MnZn 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 MnZn ferrite, in an appropriate range.
Further, there are the following methods as a method for increasing the initial magnetic permeability of MnZn ferrite in the high frequency region. That is, 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 that segregates at the grain boundaries is further added. Produces grain boundaries of appropriate and uniform thickness. By this method, the specific resistance of MnZn ferrite is maintained, the attenuation due to the frequency increase of the initial magnetic permeability is suppressed, and a high initial magnetic permeability is realized even in the 100 kHz region.
However, since the specific resistance of MnZn ferrite is limited to about 20Ω · m at the maximum, it is impossible to maintain a high initial magnetic permeability up to 10 MHz with such specific resistance. Therefore, the above-mentioned MnCoZn-based ferrite may be used in the 10 MHz region.

On the other hand, regarding the magnetic core of electronic components for automobiles, 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, and the electronic component cannot perform the desired function. Then, as a result, the entire automobile becomes inoperable.
From the above, the magnetic core of an electronic component for an automobile is required to have both good magnetic properties typified by high initial magnetic permeability and high fracture toughness value. As a specific example, the specific resistance is 30Ω · m or more, the initial magnetic permeability value at 23 ° C. and 10MHz is 150 or more, the coercive force at 23 ° C. is 15.0A / m or less, and the Curie temperature is 100 ° C. or more. In addition, excellent mechanical properties such as a fracture toughness value of 1.00 MPa · m ^1/2 or more in the fracture toughness measurement based on JIS R 1607 of a flat plate sample are required.

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 described at all. Similarly, in Patent Document 5 and Patent Document 6, there is no reference to the fracture toughness value, and it is considered unsuitable as a magnetic core of an in-vehicle electronic component.
On the other hand, although Patent Document 3 and Patent Document 4 mention the improvement of the fracture toughness value, the magnetic characteristics are insufficient as the magnetic core of the in-vehicle electronic component, and it can be said that it is also unsuitable for this application.

Therefore, the present inventors first, among the basic components of MnCoZn-based ferrite capable of realizing high initial magnetic permeability at 23 ° C. and 10 MHz of a toroidal-shaped core, iron (Fe ₂ O ₃ conversion) and cobalt (CoO conversion). And the appropriate amount of zinc (ZnO equivalent) was examined.
As a result, the present inventors can maintain a high specific resistance to some extent because they contain almost no Fe ²⁺ ions that cause a decrease in electrical resistance, and because magnetic anisotropy and magnetostriction are small, they are soft magnetic materials. We have found an appropriate range of basic components that can maintain a low coercive force, a high Curie temperature that does not pose a problem in practice, and a high initial magnetic permeability in the 10 MHz region.

Next, the present inventors can generate grain boundaries having a uniform thickness in MnCoZn-based ferrite by adding appropriate amounts of SiO ₂ and CaO, which are non-magnetic components segregating to the grain boundaries, and as a result, are effective in improving the magnetic characteristics. It was found that in addition to further increase in resistivity, it is possible to prepare a crystal structure that is effective in improving the fracture toughness value.

Furthermore, when the present inventors investigated factors effective in improving the fracture toughness value, the following two findings could be obtained.
First, the present inventors have found that suppression of abnormal grain growth is essential. Abnormal grain growth referred to in the present invention means coarse particles having a size of about 100 normal particles (abnormal particles in the present invention) due to the imbalance of grain growth during firing due to the presence of impurities or the like. (Also known as) appears. When this abnormal grain growth occurs, the strength of the portion is extremely low, so that the ferrite core is likely to break from this portion. Therefore, suppressing the growth of abnormal grains in ferrite is indispensable for improving the fracture toughness value of ferrite.

Next, the present inventors measured and considered the residual stress of the ferrite material from the X-ray diffraction of the ferrite surface. As a result, the present inventors have found that there is a correlation between the residual stress value and the fracture toughness value. That is, the brittle material breaks due to tensile stress, but if the residual stress on the surface is compressive stress or tensile stress below a certain value, crack propagation during fracture can be suppressed, so MnCoZn. The fracture toughness value of the ferrite material is improved.

From this point of view, the inventors further investigated and found a means for reducing the tensile stress remaining on the surface.
It is a method of immersing a fired product after firing in the process of producing a ferrite core in an oxidizing liquid having a concentration of 10 N or more, for example, nitric acid, sulfuric acid, hydrochloric acid, or the like for more than 0.50 hours. The surface of the conventional MnCoZn ferrite is slightly oxygen-deficient due to the reduction reaction during firing, which causes tensile stress. However, when the above-mentioned chemical oxidation with the oxidizing liquid is performed, oxygen is applied to the ferrite surface portion, and the tensile stress of the ferrite surface portion can be reduced.
Then, in the production method of the present invention, it is possible to effectively increase the fracture toughness value of the material by using this means.

Note that Patent Document 7 and Patent Document 8 disclose a process of immersing a ferrite fired product in an acid. However, in Patent Document 7, the acid concentration is 1 to 5% (corresponding to about 0.2 to 1.1 N for sulfuric acid, about 0.2 to 0.8 N for nitric acid, and about 0.3 to 1.5 N for hydrochloric acid). In Patent Document 8, the immersion time is as short as 6 to 30 minutes, so that the surface residual stress cannot be sufficiently reduced in any case. Further, in these documents, the purpose of immersing the ferrite is to elute Cu and adjust the inductance L value, respectively, and neither of them describes the surface residual stress.

Japanese Unexamined Patent Publication No. 2003-286072 Japanese Unexamined Patent Publication No. 9-20554

In Patent Document 1 and Patent Document 2 described above, the fracture toughness value is not mentioned, and it can be said that improvement of such a value is impossible. Similarly, Patent Documents 5 and 6 mention good magnetic properties such as high initial permeability at 23 ° C. and 10 MHz, but do not mention fracture toughness values.
Further, in Patent Documents 3 and 4, although the toughness is improved, the desired magnetic properties cannot be realized because an appropriate composition range cannot be selected.

Here, Patent Document 9 and Patent Document 10 describe that the residual stress affects the bending strength. However, the bending strength in Patent Documents 9 and 10 is a means for evaluating those in which the strength on the outermost surface is particularly important, and is a case where no pre-crack is formed in order to evaluate the strength of the portion on the outermost surface. This is to evaluate the bending strength.
On the other hand, the improvement of fracture toughness, which is a subject of the present invention, utilizes treatment with a predetermined acid. Therefore, it is necessary to evaluate the strength at a certain depth from the surface. Therefore, the fracture toughness value in the present specification is evaluated by a bending test after making a pre-crack on the surface of the test piece.
As described above, in the MnCoZn-based ferrite in the present specification, the strength of a portion different from the above-mentioned Patent Documents 9 and 10 is important, and in order to evaluate such a different portion, Patent Document 9 and Patent Document 10 are different from each other. Evaluating differently. That is, it can be seen that there is a large technical difference between the above-mentioned Patent Documents 9 and 10 and the MnCoZn-based ferrite in the present specification from the strength evaluation method.

Japanese Unexamined Patent Publication No. 2015-178442 Japanese Unexamined Patent Publication No. 2015-178443

Therefore, it is not possible to produce MnCoZn-based ferrite suitable for the magnetic cores of automobile-mounted parts, particularly in-vehicle electronic parts, which are practically useful only by these known techniques.
The present invention has been made to solve such a problem, and is based on the above-mentioned new findings.

That is, the gist structure of the present invention is as follows.
1. 1. MnCoZn-based ferrite consisting of basic components, sub-components and unavoidable impurities.
As the above basic ingredients
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: including the balance
As a sub-ingredient to the above basic ingredient
SiO ₂ : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
Including
The amounts of P, B and Ti in the above unavoidable impurities, respectively.
P: less than 10 mass ppm,
B: suppressed to less than 10 mass ppm and Ti: less than 50 mass ppm,
The MnCoZn-based ferrite having a surface residual stress value of less than 40 MPa.

2. 2. Of the MnCoZn-based ferrite,
The fracture toughness value of the fracture toughness measurement based on JIS R1607 is 1.00 MPa · m ^1/2 or more, and the initial magnetic permeability value 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 1 above, wherein the Curie temperature is 100 ° C. or higher.

3. 3. 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 sub-ingredients to the temporary baking powder obtained in the above temporary baking step, mixing and crushing to obtain crushed powder, and
A granulation step of adding a binder to the crushed powder obtained in the above mixing-crushing step, mixing, and then granulating.
The method for producing MnCoZn-based ferrite according to 1 or 2 above, which comprises a firing step of molding and then firing the granulated powder obtained in the above-mentioned granulation step and a dipping step of immersing in an acid. hand,
The dipping step is a method for producing MnCoZn-based ferrite in which the fired product obtained in the firing step is immersed in an oxidizing liquid having a concentration of 10 N or more for more than 0.50 hours.

4. The method for producing an MnCoZn-based ferrite according to 3 above, wherein the oxidizing liquid is nitric acid, sulfuric acid or hydrochloric acid.

The MnCoZn-based ferrite of the present invention has both excellent magnetic properties and excellent mechanical properties at a level not possible with conventional MnCoZn-based ferrites, and is particularly suitable for use in the magnetic core of electronic components mounted on automobiles. .. Excellent magnetic characteristics include, for example, a specific resistance of 30 Ω · m or more, an initial magnetic permeability value of 150 or more at 23 ° C. and 10 MHz, a coercive force of 15.0 A / m or less at 23 ° C., and a Curie temperature of 100 ° C. or more. Is. Further, as an excellent mechanical property, for example, the fracture toughness value in the fracture toughness measurement based on JIS R 1607 of a flat plate sample is 1.00 MPa · m ^1/2 or more.

Hereinafter, the present invention will be specifically described.
First, in the present invention, the reason why the composition of MnCoZn-based ferrite is limited to the above-mentioned range will be described. The iron, zinc, cobalt, and manganese contained in the present invention as basic components are all shown as values converted into Fe ₂ O ₃ , ZnO, CoO, and MnO, respectively. The contents of Fe ₂ O ₃ , ZnO, CoO, and MnO are expressed in mol%, while the contents of sub-components and impurity components are expressed in mass ppm with respect to the basic component.

Fe ₂ O ₃ : 45.0 mol% or more and less than 50.0 mol% When iron (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 iron needs to be suppressed to less than 50.0 mol% in terms of Fe ₂ O ₃ . On the other hand, if the amount of iron is too small, the coercive force of ferrite increases and the Curie temperature decreases. In order to prevent such a problem, iron shall be contained at least 45.0 mol% in terms of Fe ₂ O ₃ . It is preferably in the range of 47.1 mol% or more and less than 50.0 mol%. More preferably, it is in the range of 47.1 to 49.5 mol%. The amount of Fe ₂ O ₃ is preferably 47.1 mol% or more, preferably less than 50.0 mol%, and more preferably 49.5 mol% or less.

ZnO: 15.5 to 24.0 mol%
Zinc 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 poses a practical problem. Therefore, the upper limit of zinc is 24.0 mol% in terms of ZnO. The preferred range of ZnO amount is 15.5 to 23.0 mol%, more preferably 17.0 to 23.0 mol%. The amount of ZnO is preferably 17.0 mol% or more, preferably 23.0 mol% or less.

CoO: 0.5-4.0 mol%
Co ²⁺ ions in cobalt (CoO) are ions with positive magnetic anisotropy energy, and as a result of the addition of an appropriate amount of this CoO, the absolute value of the total magnetic anisotropy energy decreases, resulting in a decrease in coercive force. can get. For that purpose, it is necessary to add 0.5 mol% or more of CoO. On the other hand, the addition of a large amount of cobalt causes a decrease in resistivity, induction of abnormal grain growth, and an excessively positive sum of magnetic anisotropy energies, resulting in an increase in coercive force. In order to prevent this, CoO shall be added only at a maximum of 4.0 mol%. The preferred CoO range is 1.0 to 3.0 mol%. The amount of CoO is preferably 1.0 mol% or more, and preferably 3.0 mol% or less.

MnO: Remaining portion The present invention is MnCoZn-based ferrite, and the remaining portion of the principal component composition is manganese (MnO). The reason is that it is difficult to obtain good magnetic properties typified by low coercive force and high magnetic permeability at 10 MHz unless manganese is used. The preferred range of MnO is 25.0 to 32.0 mol%. It is more preferably in the range of 26.0 to 33.0 mol%, still more preferably in the range of 26.5 to 32.0 mol%. The amount of MnO is preferably 25.0 mol% or more, more preferably 26.0 mol% or more, further preferably 26.5 mol% or more, preferably 33.0 mol% or less, and even 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 massppm
SiO ₂ is known to contribute to the homogenization of the ferrite crystal structure. Therefore, by adding an appropriate amount of SiO ₂ , abnormal grain growth is suppressed and the specific resistance is also increased, so that the coercive force can be lowered and the fracture toughness value can be increased. Therefore, at least 50 massppm of SiO _{2 is} to be contained. On the other hand, when the amount of SiO ₂ added is excessive, abnormal grain growth occurs on the contrary. This significantly reduces the fracture toughness value, and at the same time, significantly deteriorates the initial magnetic permeability and coercive force at 10 MHz. Therefore, the content of SiO ₂ needs to be limited to 300 mass ppm or less. The amount of SiO ₂ is preferably in the range of 60 to 250 mass ppm, preferably 60 mass ppm or more, preferably 250 mass ppm or less, and more preferably 190 mass ppm or less.

CaO: 300-1300 massppm
CaO segregates at the grain boundaries of MnCoZn-based ferrite and has a function of suppressing the growth of crystal grains. Therefore, with the addition of an appropriate amount of CaO, the specific resistance can be increased, the coercive force can be decreased, and the fracture toughness value can be increased. Therefore, at least 300 massppm of CaO is contained. On the other hand, when the amount of CaO added is excessive, abnormal particles appear, which deteriorates both the fracture toughness value and the coercive force. Therefore, the content of CaO needs to be limited to 1300 mass ppm or less. The preferred CaO content is in the range of 350 to 1200 mass ppm, more preferably 350 to 1000 mass ppm. The amount of CaO is preferably 350 mass ppm or more, more preferably 500 mass ppm or more, preferably 1200 mass ppm or less, and more preferably 1000 mass ppm or less.

Next, the unavoidable impurity components to be suppressed will be described.
P: less than 10 mass ppm, B: less than 10 mass ppm, Ti: less than 50 mass ppm These are components inevitably contained mainly in the raw material iron oxide. There is no problem if the content of P and B is very small. However, when P and B are contained above a certain level, abnormal grain growth of ferrite is induced, and this site becomes the starting point of fracture, so that the fracture toughness value decreases, the coercive force increases, and the initial magnetic permeability increases. It causes a decline and has a serious adverse effect. Therefore, the contents of P and B were both suppressed to less than 10 mass ppm. Preferably, both the amounts of P and B are 8 mass ppm or less. The content of P is preferably 8 mass ppm or less, and the content of B is preferably 8 mass ppm or less.
Further, when the Ti content is high, not only the fracture toughness but also the specific resistance of ferrite, the coercive force, and the initial magnetic permeability deteriorate. Therefore, the Ti content is controlled to less than 50 mass ppm. The Ti content is preferably less than 40 mass ppm, more preferably less than 30 mass ppm.

Further, various characteristics of MnCoZn-based ferrite are greatly affected by various parameters regardless of the composition. Therefore, in the present invention, the following provisions can be further provided in order to have more preferable magnetic characteristics and strength characteristics.
Fracture toughness value of fine ceramics based on JIS R 1607: 1.00 MPa · m ^1/2 or more MnCoZn-based ferrite is a ceramic and is a brittle material, so it hardly plastically deforms. Therefore, the SEBP method specified in JIS R 1607 is used for the evaluation of fracture toughness. In this SEBP method, the fracture toughness value (Kic) is measured by imprinting a Vickers indentation in the center of the object to be measured and performing a bending test with a pre-crack added. The MnCoZn-based ferrite of the present invention is intended for use in automobiles where high toughness is required, and it is desirable that the fracture toughness value obtained by the SEBP method is 1.00 MPa · m ^1/2 or more.

In order to satisfy the condition of the fracture toughness value, the surface residual stress value of the obtained MnCoZn-based ferrite needs to be less than 40 MPa. Here, the value of the surface residual stress is minute from the shift of the (551) plane peak appearing at 148.40 ° by X-ray diffraction, assuming that the surface of the MnCoZn-based ferrite (ferrite core) is MnFe ₂ O _4. This is the result of calculating the stress.
Since MnCoZn-based ferrite is a brittle material, it breaks due to tensile stress. Similarly, for glass, which is a brittle material, tempered glass in which compressive stress is applied to the surface in advance is known in order to cancel the tensile stress that causes this fracture. Inspired by this, the present inventors thought that the fracture toughness value could be improved by controlling the surface stress even in MnCoZn-based ferrite, and repeated diligent research. As a result, tensile stress generated due to a slight oxygen deficiency due to the reduction reaction during firing remains on the surface of normal MnCoZn-based ferrite, and by reducing this tensile stress, MnCoZn-based ferrite as a material can be used. It was found that the fracture toughness value can be increased. There is a correlation between the fracture toughness value and the surface residual stress, and in order to obtain a desirable fracture toughness value of 1.00 MPa · m ^1/2 or more, the surface residual stress must be less than 40 MPa, and 38 MPa. The value is preferably 36 MPa or less, and more preferably 36 MPa or less.

In order to keep the surface residual stress value of MnCoZn-based ferrite less than 40 MPa, it is necessary to immerse the fired product after firing in the ferrite core manufacturing process in an oxidizing liquid having a concentration of 10 N or more for more than 0.50 hours. The immersion temperature is preferably in the range of 20 to 60 ° C. The surface of the conventional MnCoZn-based ferrite is slightly oxygen-deficient due to the reducing action during firing, so that tensile stress is generated, and the surface residual stress is 40 MPa or more. Therefore, in the production method of the present invention, ferrite as a fired product is chemically oxidized by immersing it in an oxidizing liquid having a predetermined concentration. As a result of oxygen being applied to the ferrite surface portion by this method, the tensile stress on the surface is reduced and the residual stress becomes less than 40 MPa.
Here, the oxidizing liquid is preferably nitric acid, sulfuric acid or hydrochloric acid from the viewpoint of easy availability, ease of handling and the like.

Next, the method for producing the MnCoZn-based ferrite of the present invention will be described in detail.
Regarding the production of MnCoZn-based ferrite, Fe ₂ O ₃ , ZnO, CoO and MnO are first weighed so as to have a predetermined ratio, and after sufficiently mixing these, calcining and cooling are performed to obtain calcined powder (temporary firing). Process). Fe ₂ O ₃ , ZnO, CoO and MnO are usually powders. When crushing this calcined flour, an additive as an auxiliary component specified in the present invention is added at a predetermined ratio and mixed to obtain a pulverized powder (mixing-crushing step). In this step, the powder is sufficiently homogenized so that the concentration of the added component is not biased, and the calcined powder is refined to the target average particle size. An organic binder such as polyvinyl alcohol is added to the powdered pulverized powder having the target composition thus obtained, and the granulated powder is obtained through a granulation step by a spray-drying method or the like (granulation step). After performing steps such as sieving to adjust the particle size, pressure is applied with a molding machine to mold. After such molding, firing is performed under suitable firing conditions (calcination step), and the mixture is immersed in an oxidizing liquid having a concentration of 10 N or more for more than 0.50 hours, that is, for more than 30 minutes (immersion step). Then, if necessary, it is washed with water and dried to obtain a ferrite sintered body according to the present invention, that is, MnCoZn-based ferrite.
The obtained ferrite sintered body may be subjected to surface polishing or other processing.

The MnCoZn-based ferrite thus obtained has extremely excellent characteristics that were not possible with conventional MnCoZn-based ferrites. These extremely excellent characteristics include, for example, a fracture toughness value of a flat plate sample measured by fracture toughness measurement based on JIS R1607 of 1.00 MPa · m ^1/2 or more (preferably 1.05 MPa · m ^1/2 or more). The specific resistance is 30Ω ・ m or more (preferably 40Ω ・ m or more, more preferably 50Ω ・ m or more), the Curie temperature is 100 ° C or more, and the coercive force at 23 ° C of the toughal-shaped core manufactured under the same conditions is 15.0A / It is an extremely excellent characteristic that the value of the initial magnetic permeability at 23 ° C. and 10 MHz is 150 or more at m or less (preferably 13.0 A / m or less).

(Example 1)
Each raw material powder weighed so that the amounts of Fe ₂ O ₃ , ZnO, CoO and MnO have the ratios shown in Table 1 are mixed using a ball mill for 16 hours, and then calcined in air at 900 ° C. for 3 hours. Was 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 and 700 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 pulverized powder obtained by such pulverization, spray-dried granulation was applied, and a pressure of 118 MPa was applied to form a toroidal core shape and a flat core shape to obtain a molded product. 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 fired products after firing were placed at room temperature of 23 ° C. After immersing in 13.0N (specified) nitric acid for 1.00 hours, it is taken out, washed with pure water and dried to obtain MnCoZn-based ferrite having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm. A sintered toroidal core (hereinafter, also simply referred to as a toroidal core) and a sintered flat plate-shaped core (hereinafter, simply 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 a high-purity raw material was used as the raw material and the medium such as a ball mill was thoroughly washed before use to suppress the mixing of components from other materials, impurities P, B and Ti contained in the toroidal core and the rectangular parallelepiped core were contained. The contents were 4, 3 and 15 mass ppm, respectively. The contents of P, B and Ti 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 for 10 turns and using an impedance analyzer (4294A manufactured by Keysight).
The coercive force Hc was measured at 23 ° C. based on JIS C 2560-1, and the resistivity was measured by the 4-terminal method.
The Curie temperature was calculated from the temperature characteristic measurement result of the inductance measured using an LCR meter (4980A manufactured by Keysight Co., Ltd.).
The surface residual stress was calculated by using a micro stress measuring device (AutoMATE manufactured by Rigaku), using Cr-Kα rays, and using the parallel tilt method. At this time, assuming that the ferrite surface is MnFe ₂ O ₄ , the shift of the (551) plane peak appearing at 148.40 ° was measured, and calculated using the values of Poisson's ratio 0.28 and elastic constant 147 GPa. .. For details of the above-mentioned parallel tilting method, refer to "Materials" (J. Soc. Mat. Sci., Japan), Vol. 47, No. 11, pp. 1189-1194, Nov. It is described in 1998.
The fracture toughness value of the rectangular parallelepiped core is based on JIS R 1607, which is based on the fracture load and the dimensions of the test piece after pre-cracking the sample dented in the center by Vickers and then breaking it in a three-point bending test. Calculated in.
The results obtained are also 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 Ω · m or more, the coercive force at 23 ° C. is 15.0 A / m or less, and the Curie temperature is 100 ° C. or more. The initial magnetic permeability at 23 ° C. and 10 MHz is 150 or more, and the fracture toughness value is 1.00 MPa · m ^1/2 or more, which is a combination of suitable magnetic properties and high toughness.
On the other hand, in Comparative Examples 1-1 and 1-2 containing 50.0 mol% or more of Fe ₂ O ₃ , the specific resistance was significantly reduced, and the initial magnetic permeability at 10 MHz was also significantly reduced as the eddy current loss increased. Has deteriorated. On the other hand, in Comparative Example 1-3 in which the amount of Fe ₂ O ₃ is less than 45.0 mol%, although there is no problem with the specific resistance, the coercive force increases and the Curie temperature decreases due to the increase in magnetic anisotropy and magnetostriction. Can be seen.
In Comparative Example 1-4 in which ZnO is excessive, the Curie temperature is lowered to less than 100 ° C. On the contrary, in Comparative Example 1-5 in which ZnO is less than the specified range, the coercive force increases and is out of the desired range.
Focusing on CoO, in Comparative Examples 1-6 to which CoO was not added, the coercive force was high because the cancellation of the positive and negative magnetic anisotropy was insufficient, while the CoO was excessive. In Comparative Example 1-7 including, on the contrary, since the positive magnetic anisotropy was excessively increased, the coercive force was increased and the initial magnetic permeability at 10 MHz was also decreased.

(Example 2)
The raw materials were weighed so that Fe ₂ O ₃ was 49.0 mol%, CoO was 2.0 mol%, Zn O was 21.0 mol%, and MnO was 28.0 mol%, mixed for 16 hours using a ball mill, and then in the air. , 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, which are subcomponents in the amounts shown in Table 2, were added to the calcined powder, and the mixture was pulverized with a ball mill for 12 hours. Then, polyvinyl alcohol was added to the pulverized powder obtained by such pulverization, spray-dried granulation was applied, and a pressure of 118 MPa was applied to form a toroidal core shape and a flat core shape to obtain a molded product. Then, these compacts are 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 are appropriately mixed, and the fired products after firing are placed at room temperature of 23 ° C. After immersing in 13.0 N (specified) nitric acid for 1.00 hours, it is taken out, washed with pure water and dried to obtain MnCoZn-based ferrite having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm. A sintered toroidal core and a sintered rectangular core having a length of 4 mm, a width of 35 mm, and a thickness of 3 mm were obtained. The contents of impurities P, B and Ti contained in the obtained toroidal core and rectangular parallelepiped core were 4, 3 and 15 mass ppm, respectively.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The results of the obtained evaluation are also shown in Table 2 together with the results of Example 1-2.

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 Ω · m or more and the coercive force at 23 ° C. is 15.0 A / m or less. Good magnetic properties with a Curie temperature of 100 ° C. or higher, an initial magnetic permeability of 150 ° C. or higher at 23 ° C. and 10 MHz, and high toughness with a fracture toughness value of 1.00 MPa · m ^1/2 or higher are obtained together. There is.
On the other hand, in Comparative Examples 2-1 and 2-3 in which one of the two components of SiO ₂ and CaO contained less than the specified amount, the grain boundary formation was insufficient, so that the specific resistance was lowered and the crystal was formed. The fracture toughness value is lower than 1.00 MPa · m ^1/2 because some coarse grains with low strength appear due to insufficient suppression of grain growth. On the contrary, in Comparative Examples 2-2, 2-4 and 2-5 in which at least one of the same components is excessive, a plurality of magnetic properties including the initial magnetic permeability at 23 ° C. and 10 MHz are exhibited due to the appearance of abnormal grains. As a result of deterioration and an increase in abnormal grains, the fracture toughness value is also greatly reduced.

(Example 3)
By the method shown in Example 1, the basic component and the sub-component have the same composition as in Example 1-2, while the amount of unavoidable impurities contained is different as shown in Table 3. The obtained granulated powder was molded into a toroidal core shape and a flat core shape by applying a pressure of 118 MPa to obtain a molded product. Then, these compacts are 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 are appropriately mixed, and the fired products after firing are placed at room temperature of 23 ° C. After immersing in 13.0 N (specified) nitric acid for 1.00 hours, it is taken out, washed with pure water and dried to obtain MnCoZn-based ferrite having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm. A sintered toroidal core and a sintered rectangular 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 apparatus as in Example 1. The results of the obtained evaluation are also shown in Table 3 together with the results of Example 1-2.

As shown in the table, in Example 3-1 in which the unavoidable impurities P, B and Ti components are within the specified range, only the resistivity, the coercive force and the initial magnetic permeability at 23 ° C. and 10 MHz are excellent. However, an excellent fracture toughness value of 1.00 MPa · m ^1/2 or more is also obtained.
On the other hand, in Comparative Examples 3-1 to 3-4 in which any one or more of the above impurity components is contained in excess of the specified value, a plurality of magnetic properties are deteriorated due to the appearance of abnormal particles, and they are destroyed at the same time. The toughness value is also lowered, and neither of them is obtained as desired.

(Example 4)
The granulated powder obtained so as to have the same composition as that of Example 1-2 produced by the method shown in Example 1 was molded into a toroidal core shape and a flat core shape by applying a pressure of 118 MPa. And said. After that, these molded bodies were charged into a firing furnace and fired in a gas stream in which nitrogen gas and air were appropriately mixed for 2 hours at a maximum temperature of 1320 ° C., and the sintered products obtained are shown in Table 4. Under the conditions, it is immersed in nitric acid, sulfuric acid or hydrochloric acid, which is an oxidizing liquid, then taken out, washed with pure water and dried to obtain MnCoZn-based ferrite with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height. A sintered toroidal core having a length of 5 mm and a sintered rectangular core having a length of 4 mm, a width of 35 mm and a thickness of 3 mm were obtained. The amounts of P, B, and Ti components contained in the toroidal core and the rectangular parallelepiped core after immersion were 4, 3, and 15 mass ppm, respectively.
The characteristics of each of these samples were evaluated using the same method and apparatus as in Example 1. The obtained results are also shown in Table 4 together with the results of Example 1-2.

In the dipping process 1) When the concentration of the oxidizing liquid to be immersed is 10 specified (N) or more,
2) In Examples 4-1 to 4-8 produced under the immersion step conditions where the immersion time exceeds 0.50 hours (Hr) 1) and 2), the surface of the core as MnCoZn-based ferrite is Due to chemical oxidation, the surface residual stress of the core was less than 40 MPa. As a result, the tensile stress is reduced, and a good fracture toughness value of 1.00 MPa · m ^1/2 or more is obtained for the core.
On the other hand, in Comparative Examples 4-1 to 4-8 produced through a dipping step that does not satisfy the above conditions, the tensile stress remaining on the surface is not sufficiently eliminated because the chemical oxidation is insufficient. .. As a result, the desired fracture toughness value has not been obtained.

Claims

MnCoZn-based ferrite consisting of basic components, sub-components and unavoidable impurities.
As the above basic ingredients
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: including the balance
As a sub-ingredient to the above basic ingredient
SiO 2 : 50 to 300 mass ppm and CaO: 300 to 1300 mass ppm
Including
The amounts of P, B and Ti in the above unavoidable impurities, respectively.
P: less than 10 mass ppm,
B: suppressed to less than 10 mass ppm and Ti: less than 50 mass ppm,
The MnCoZn-based ferrite having a surface residual stress value of less than 40 MPa.
Of the MnCoZn-based ferrite,
The fracture toughness value of the fracture toughness measurement based on JIS R1607 is 1.00 MPa · m 1/2 or more, and the initial magnetic permeability value 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.
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 sub-ingredients to the temporary baking powder obtained in the above temporary baking step, mixing and crushing to obtain crushed powder, and
A granulation step of adding a binder to the crushed powder obtained in the above mixing-crushing step, mixing, and then granulating.
A firing step in which the granulated powder obtained in the above granulation step is molded and then fired,
The dipping process of dipping in acid and
The method for producing an MnCoZn-based ferrite according to claim 1 or 2, wherein the MnCoZn-based ferrite is obtained.
The dipping step is a method for producing MnCoZn-based ferrite in which the fired product obtained in the firing step is immersed in an oxidizing liquid having a concentration of 10 N or more for more than 0.50 hours.
The method for producing MnCoZn-based ferrite according to claim 3, wherein the oxidizing liquid is nitric acid, sulfuric acid or hydrochloric acid.