CN114206805B

CN114206805B - MnZn ferrite

Info

Publication number: CN114206805B
Application number: CN202180004188.5A
Authority: CN
Inventors: 吉田裕史; 中村由纪子; 平谷多津彦; 田川哲哉
Original assignee: JFE Steel Corp; JFE Chemical Corp
Current assignee: JFE Steel Corp; JFE Chemical Corp
Priority date: 2020-07-14
Filing date: 2021-06-10
Publication date: 2023-06-06
Anticipated expiration: 2041-06-10
Also published as: TW202202467A; JP7185791B2; TWI793645B; CN114206805A; WO2022014218A1; JPWO2022014218A1

Abstract

The present invention provides a MnZn ferrite, which has the following functions: the fracture toughness value of the flat magnetic core measured according to JISR 1607 is 1.10 MPa.m ^1/2 The excellent mechanical properties and the loss value of the toroidal core manufactured under the same conditions at 100 ℃, 300kHz and 100mT are 450kW/m ³ The following good magnetic properties were obtained. The MnZn ferrite is composed of a basic component, an auxiliary component and unavoidable impurities, wherein the content of P, B, na, mg, al and K in the unavoidable impurities are respectively controlled as follows: p: less than 10 mass ppm, B: less than 10 mass ppm, na: less than 200 mass ppm, mg: less than 200 mass ppm, al: less than 250 mass ppm and K: less than 100 mass ppm.

Description

MnZn ferrite

Technical Field

The present disclosure relates to MnZn ferrite particularly suitable for a magnetic core of an automobile-mounted component.

Background

MnZn ferrite is widely used as a material for a noise filter such as a switching power supply, a transformer, and a core of an antenna. The following advantages can be cited: among soft magnetic materials, there are high permeability and low loss in kHz region, and are cheaper than amorphous metals and the like.

In recent years, with the progress of hybrid and electrification of automobiles, mnZn ferrite, which is provided to a magnetic core of an electronic component for automobile mounting applications, is required to have a high fracture toughness value. This is because MnZn ferrite is ceramic, is a brittle material, and is easily broken, and in addition, is continuously used in an environment where vibration is continuously applied and easily broken in an automotive mounting application, as compared with a conventional household electrical appliance application. However, in addition to the high fracture toughness value, it is also important to have suitable magnetic properties similar to those of the conventional applications in addition to the light weight and space saving in the automobile applications.

As MnZn ferrite used for automobile mounting applications, various developments have been made in the past, and patent document 1 and patent document 2 are cited as examples of MnZn ferrite having good magnetic properties. As MnZn ferrite having an improved fracture toughness value, patent documents 3 and 4, for example, have been reported.

Prior art literature

Patent literature

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

Patent document 2: japanese patent application laid-open No. 2012-76983

Patent document 3: JP-A-4-318904

Patent document 4: JP-A-4-177808

Disclosure of Invention

(technical problem to be solved by the invention)

However, for example, patent document 1 and patent document 2 refer to compositions for achieving desired magnetic characteristics, but do not refer to fracture toughness values at all, and are not suitable for use as magnetic cores of electronic components for automobile use. On the other hand, patent document 3 and patent document 4 mention improvement of fracture toughness values, but the magnetic properties are insufficient as a core of an electronic component for automobile use, and are still unsuitable for this purpose.

The present disclosure has been made in view of the above-described facts, and an object thereof is to provide MnZn-based ferrite having both: the flat magnetic core is according toFracture toughness value measured in JIS R1607 was 1.10 MPa.m ^1/2 The excellent mechanical properties and the loss value of the toroidal core manufactured under the same conditions at 100 ℃, 300kHz and 100mT are 450kW/m ³ The following good magnetic properties were obtained.

(technical means for solving the technical problems)

The present inventors have made intensive studies to accomplish the above-mentioned problems, and as a result, have found the following.

The inventors have found that Fe of MnZn ferrite can reduce the loss value at 100 ℃ and 300kHz ₂ O ₃ The optimum composition of the amount and ZnO. If the composition is within this range, the magnetic anisotropy and magnetostriction are small, and therefore, the temperature characteristic of the loss can be kept to a minimum while maintaining the resistivity, and the secondary peak can be caused to appear at around 100 ℃.

Next, it was found that by adding an appropriate amount of SiO as a nonmagnetic component segregated at the grain boundaries ₂ CaO and Nb ₂ O ₅ Even grain boundaries can be generated, and the resistivity is improved, whereby the loss value can be further reduced.

In addition, when the inventors studied factors effective for improving fracture toughness values, the following two findings can be obtained.

(1) The inventors first found that abnormal grain growth must be suppressed. Abnormal grain growth is a phenomenon in which grain growth is unbalanced during firing due to the presence of impurities or the like, and coarse particles having a size corresponding to about 100 normal particles are locally present. When abnormal grain growth occurs, the strength of the abnormal grain growth portion is extremely low, and the core is broken starting from the portion. Therefore, suppression of abnormal grain growth is essential for improving fracture toughness values.

(2) Next, although abnormal crystal grains were not confirmed, even in the samples prepared under the same conditions, samples having abnormally low toughness values were obtained in some cases, and the cause thereof was investigated. As a result, it was found that impurities of specific components were present on fracture surfaces of samples having low toughness values, and it was confirmed that the fracture toughness values of MnZn ferrite materials could be improved by preventing these impurities from being mixed into the raw materials and water and suppressing these impurities from being mixed into the raw materials and water.

(3) Further, na, mg, al, K among the impurities was found to adversely affect cracking of the molded article. It is found that MnZn ferrite can be industrially produced efficiently by reducing these impurities.

The present invention has been made based on the above findings. Namely, the main technical scheme of the invention is as follows.

[1] A MnZn ferrite composed of a basic component, an auxiliary component, and unavoidable impurities, characterized in that:

the basic component is Fe ₂ O ₃ The sum of iron, zinc and manganese is 100mol percent based on ZnO and MnO:

iron: by Fe ₂ O ₃ From 51.5mol% to 55.5mol%,

zinc: 5.0mol% to 15.5mol% based on ZnO, and

manganese: the balance;

the auxiliary components are, relative to the basic components:

SiO ₂ :50 to 300 mass ppm of a catalyst,

CaO:100 to 1300 mass ppm, and

Nb ₂ O ₅ :100 to 400 mass ppm;

the contents of P, B, na, mg, al and K in the unavoidable impurities are respectively controlled as follows:

p: less than 10 mass ppm of the catalyst is used,

b: less than 10 mass ppm of the catalyst is used,

na: less than 200 mass ppm of the catalyst,

mg: less than 200 mass ppm of the catalyst,

al: less than 250 mass ppm, and

k: less than 100 mass ppm.

[2] The MnZn ferrite according to the above [1], characterized in that the auxiliary component further contains one or two selected from the group consisting of: coO:3500 mass ppm or less and NiO:15000 mass ppm or less.

[3]According to [1] above]Or [2]]The MnZn ferrite is characterized by having a fracture toughness value of 1.10 MPa.m as measured according to JIS R1607 ^1/2 The loss value at 100 ℃, 300kHz and 100mT is 450kW/m ³ The following is given.

(effects of the invention)

According to the present invention, it is possible to provide MnZn ferrite having both of the following properties, in which the crack occurrence rate of the molded article is reduced to 3.5% or less and the yield is excellent: the flat plate-shaped magnetic core has a fracture toughness value of 1.10 MPa.m measured according to JIS R1607 ^1/2 The excellent mechanical properties and the loss value of the toroidal core manufactured under the same conditions at 100 ℃, 300kHz and 100mT are 450kW/m ³ The following good magnetic properties were obtained.

Detailed Description

In general, in order to reduce the loss value of MnZn ferrite, it is effective to reduce magnetic anisotropy and magnetostriction. To achieve this, it is necessary to select Fe as a main component of MnZn ferrite within an appropriate range ₂ O ₃ Compounding amount of ZnO and MnO. In addition, by applying sufficient heat in the firing step to appropriately grow crystal grains in ferrite, movement of magnetic domain walls in the crystal grains in the magnetizing step can be facilitated. Also, by adding a component segregated at the grain boundary and forming it into a grain boundary of an appropriate and uniform thickness, it is possible to maintain the resistivity to reduce the eddy current loss, and achieve low loss in the region of 100 to 500 kHz.

In addition to the magnetic characteristics described above, a magnetic core of an electronic component for use in an automobile is required to have a high fracture toughness value so as not to be damaged even in an environment in which vibration is continuously applied. If MnZn ferrite as a magnetic core is broken, inductance may be greatly lowered, and thus electronic components may be difficult to operate as desired, and the entire automobile may be disabled due to the influence thereof.

As described above, mnZn ferrite provided to electronic components for automobile use is required to have both low-loss magnetic characteristics and high fracture toughness. According to the present disclosure, mnZn ferrite having both good magnetic characteristics and high fracture toughness value can be provided.

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

In the present disclosure, the composition of MnZn-based ferrite is defined. First, in the present disclosure, the reason why the composition of MnZn ferrite (hereinafter, simply referred to as "ferrite") is limited to the above-described range will be described. In addition, the iron, zinc and manganese contained in the present disclosure as essential components are all produced by the method of adding Fe ₂ O ₃ Values of ZnO and MnO meter. And, for these Fe ₂ O ₃ Content of ZnO, mnO relative to Fe ₂ O ₃ The mol% of the total amount of iron, zinc and manganese, expressed as 100mol% in terms of ZnO and MnO, is expressed in terms of mass ppm relative to the basic components with respect to the content of the auxiliary components and unavoidable impurities.

First, the basic components will be described.

Fe ₂ O ₃ :51.5mol% to 55.5mol%

Whether Fe in the essential component ₂ O ₃ If the amount is smaller or larger than the appropriate amount, the loss increases due to the increase in magnetic anisotropy or magnetostriction. Thus Fe ₂ O ₃ The content of (2) is at least 51.5mol% and is at the upper limit of 55.5 mol%. Fe (Fe) ₂ O ₃ The content of (2) is preferably 55.3mol% or less.

ZnO:5.0mol% to 15.5mol%

When ZnO is small, an excessive increase in Curie temperature leads to an increase in loss at 100℃and thus, at a minimum, znO is contained in an amount of 5.0mol% or more. However, when the ZnO content is equal to or more than a proper amount, the minor peak temperature at which the loss value exhibits the minimum value also decreases, resulting in an increase in the loss value at 100 ℃. Therefore, the upper limit of the content of ZnO is set to 15.5mol%. The ZnO content is preferably 5.5mol% or more.

MnO: allowance of

The present disclosure relates to a MnZn ferrite, the balance of which is MnO. The reason is that if the excitation temperature is not MnO, the excitation temperature of 100 ℃, 300kHz and 100mT cannot be realized, and the loss value is 450kW/m ³ The following is given. The content of MnO is preferably 29.0mol% or more, more preferably 30.0mol% or more, and still more preferably 30.5mol% or more. The content of MnO is preferably 43.0mol% or less, more preferably 42.0mol% or less.

The basic components are described above, and the auxiliary components are as follows.

SiO ₂ :50 to 300 mass ppm

SiO is known to be ₂ The homogenization of the ferrite crystal structure is facilitated, and the abnormal grain growth is suppressed by adding an appropriate amount, and the resistivity is also improved. Along with SiO ₂ The addition of a proper amount of (C) can reduce the loss value under excitation conditions of 100 ℃, 300kHz and 100mT, and can improve the fracture toughness value. Therefore, siO is contained at least 50 mass ppm ₂ . However, in SiO ₂ If the content of (C) is too large, abnormal grains which locally become low in strength, which cause a significant decrease in fracture toughness and a significant deterioration in loss value, are formed, and SiO is formed ₂ The content of (2) is controlled to 300 mass ppm or less. SiO (SiO) ₂ The content of (2) is preferably 55 mass ppm or more, more preferably 60 mass ppm or more. SiO (SiO) ₂ The content of (2) is preferably 275 mass ppm or less, more preferably 250 mass ppm or less.

CaO:100 to 1300 mass ppm

CaO segregates at grain boundaries of MnZn ferrite and has an effect of suppressing crystal grain growth, and by adding an appropriate amount, the loss value under excitation conditions of 100 ℃, 300kHz, and 100mT can be reduced with an increase in resistivity. In addition, since the effect of suppressing the growth of crystal grains is also exhibited, the fracture toughness value can be improved by adding a proper amount of CaO. Therefore, caO is contained at least in an amount of 100 mass ppm. However, if the CaO content is too large, abnormal grains are generated, the fracture toughness value is lowered, and the loss value is also lowered, so that the CaO content is controlled to 1300 mass ppm or less. The CaO content is preferably 120 mass ppm or more, more preferably 150 mass ppm or more. The CaO content is more preferably 200 mass ppm or more. The CaO content is preferably 1200 mass ppm or less, more preferably 1100 mass ppm or less.

Nb ₂ O ₅ :100 to 400 mass ppm

Known Nb ₂ O ₅ Segregation at the grain boundaries of MnZn ferrite has the effect of slowly suppressing the crystal grain growth and relaxing such stress. Accordingly, with the addition of an appropriate amount thereof, the loss value can be reduced, and abnormal grain growth which locally becomes low in strength can be suppressed, whereby the fracture toughness value can also be improved, and thus Nb is contained at least 100 mass ppm ₂ O ₅ . However, in Nb ₂ O ₅ If the content of (B) is too large, abnormal grains are generated, and the fracture toughness value is significantly lowered and the loss value is deteriorated, so that Nb is added ₂ O ₅ The content of (2) is controlled to 400 mass ppm or less. Nb (Nb) ₂ O ₅ The content of (2) is preferably 120 mass ppm or more, more preferably 130 mass ppm or more. In addition, nb ₂ O ₅ The content of (C) is preferably less than 380 mass ppm. When ferrite is produced, nb is added to properly disperse Nb so as to properly prevent the variation of the temperature characteristic of the loss value and to properly prevent the increase of the loss value at 100 DEG C ₂ O ₅ The content of (2) is more preferably 375 mass ppm or less, and still more preferably 350 mass ppm or less.

P: less than 10 mass ppm, B: less than 10 mass ppm

P and B are mainly components which are inevitably contained in the raw material iron oxide. If these components are contained in a very small amount, there is no problem, but if these components are contained in a certain amount or more, abnormal grain growth of ferrite is caused, and abnormal grain growth sites become the starting points of fracture, resulting in a decrease in fracture toughness value, and also, with respect to magnetic characteristics, a loss value is increased, with serious adverse effects. Therefore, the content of both P and B needs to be limited to less than 10 mass ppm. The content of P is preferably 8 mass ppm or less, more preferably 5 mass ppm or less. The content of B is preferably 8 mass ppm or less, more preferably 5 mass ppm or less. The lower limits of the contents of P and B are not particularly limited, and may be 0 mass ppm, respectively.

Na: less than 200 mass ppm

Mg: less than 200 mass ppm

Al: less than 250 mass ppm

K: less than 100 mass ppm

The iron oxide, manganese oxide, and zinc oxide, which are raw materials of MnZn ferrite, contain Na, mg, al, K having low purity, and Na, mg, al, K is present as a dissolved component in water such as tap water. In addition, in the ferrite production process, components such as a dispersant containing these metal ions may be added. Further, it is considered that substances containing these components are mainly used as a refractory material for a furnace used in calcination and firing in a ferrite production process, and these components are mixed due to falling off of the furnace, contact wear, and the like. If some of these components remain during molding of the molded body, they may react with iron oxide during firing to form a spinel structure and be solid-dissolved in MnZn ferrite. Although these components do not cause abnormal grain growth and do not adversely affect magnetic properties, the toughness of solid solution portions of these components is lower than that of ordinary MnZn ferrite, and therefore the presence of these components causes significant decrease in toughness of MnZn ferrite. Therefore, in order to suppress the decrease in toughness, the contents of these four components are limited.

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

In addition, as a secondary effect obtained by reducing Na, mg, al, and K components, there is an improvement in yield in the molding process. The MnZn ferrite is produced by molding a granulated powder containing a binder by a powder compaction method and then firing the powder, and details thereof will be described later. In this molding step, cracks are mainly generated in the molded article when the molded article is released from the mold. In this case, if cracks are generated, the product is a defective product, and the value as a product is lost. If the Na, mg, al and K components have a composition within the above-mentioned predetermined range, the occurrence of cracks in the molded article can be suppressed. Details of this mechanism are under investigation, and the inventors of the present application have speculated as follows. It is known that a crosslinking reaction occurs between an organic binder such as polyvinyl alcohol mainly used as a binder and metal ions such as Na, mg, al, and K. Thus, it is considered that metal ions such as Na, mg, al, and K have an effect of inhibiting uniform dispersion of the binder. Therefore, the present inventors considered that limiting the content settings of Na, mg, al, and K can suppress the occurrence of this phenomenon. By reducing the Na, mg, al and K components, the crack occurrence rate of the molded article can be reduced to 3.5% or less, and MnZn ferrite can be produced at a high yield.

In addition, the content of Ti as an unavoidable impurity is preferably less than 50 mass ppm. If the Ti content is less than 50 mass ppm, the variation in the temperature characteristic of the loss value can be appropriately prevented, and the increase in the loss value at 100℃can be appropriately suppressed. The lower limit of the Ti content is not particularly limited, and may be 0 mass ppm. From the viewpoint of production technology, the Ti content is preferably 5 mass ppm or more.

The total amount of P, B, na, mg, al, K is preferably 675 mass ppm or less, more preferably 400 mass ppm or less. If the total amount of these elements is reduced, the fracture toughness value becomes greater.

Further, the content of P, B, na, mg, al, K and other unavoidable impurities was quantified according to JIS K0102 (ICP mass spectrometry).

In addition, various characteristics of MnZn ferrite are not limited to composition, and are greatly affected by various parameters. In the present disclosure, the following is preferably set to obtain suitable magnetic properties and mechanical properties.

Fracture toughness value measured according to JIS R1607 was 1.10 MPa.m ^1/2 The above.

MnZn ferrite is a ceramic, and is a brittle material, so plastic deformation hardly occurs. Therefore, fracture toughness was measured according to the SEPB method (Single-Edge-pre-cracked-Beam method) specified in JIS R1607. In the SEPB method, the fracture toughness value is measured by pressing a vickers indenter into the center portion of a flat magnetic core and performing a bending test in a state where a pre-crack is applied. The MnZn ferrite of the invention is set for the vehicle-mounted application requiring high toughness, and the fracture toughness value of the MnZn ferrite meets 1.10 MPa.m ^1/2 The above. In order to satisfy this condition, the composition of the components needs to be controlled within a predetermined range. The fracture toughness value is preferably 1.12 MPa.m ^1/2 The above.

The MnZn-based ferrite of the present disclosure may further contain the following additive substances as auxiliary components.

CoO:3500 mass ppm or less

CoO is a material containing Co having positive magnetic anisotropy ²⁺ The temperature range of the secondary peak of the minimum temperature indicating the loss value can be widened by adding the component of the ion. Further, when the CoO content is 3500 mass ppm or less, negative magnetic anisotropy of the other components can be canceled, and an increase in loss value at 100 ℃ can be further prevented. The lower limit of CoO is not particularly limited, and may be 0 mass ppm, but preferably exceeds500 mass ppm. The CoO content is preferably 2500 mass ppm or less.

NiO:15000 mass ppm or less

The NiO is selectively doped into the B site of the spinel lattice, which has the following effect: the curie temperature of the material is increased, thereby increasing the saturation magnetic flux density, with the result that the loss value is reduced. Further, by setting the content of NiO to 15000 mass ppm or less, it is possible to further prevent an increase in magnetostriction and an increase in loss value at 100 ℃. Therefore, in the case of addition, it is necessary to limit the content of NiO to 15000 mass ppm or less. The content of NiO is preferably 12000 mass ppm or less. The lower limit of NiO is not particularly limited and may be 0 mass ppm, but is preferably 1200 mass ppm or more, more preferably 1500 mass ppm or more, and still more preferably 2000 mass ppm or more.

Next, a method for producing MnZn ferrite according to the present invention will be described.

The method for producing MnZn ferrite of the present disclosure is a method for producing MnZn ferrite having the steps of:

a calcination step of calcining and cooling the mixture of the basic components to obtain a calcined powder;

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

a granulating 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

and a firing step in which the molded body is fired to obtain MnZn ferrite.

In the production of MnZn ferrite, fe as a basic component is first weighed in the above-mentioned ratio ₂ O ₃ ZnO, and MnO powder, and mixing them thoroughly to obtain a mixture, and then calcining the mixture (calcining step). At this time, the unavoidable impurities are limited to the above range.

Next, the auxiliary component specified in the present disclosure is added to the obtained calcined powder in a specified ratio, and the mixture is mixed with the calcined powder and pulverized (mixing-pulverizing step). In this step, the powder is sufficiently homogenized so that the concentration of the added component does not vary, and the calcined powder is pulverized to a target average particle size to produce a pulverized powder.

Next, a known organic binder such as polyvinyl alcohol is added to the pulverized powder, and the mixture is granulated by a spray drying method or the like to obtain a granulated powder (granulating step). Then, the particle size is adjusted by a process such as sieving, if necessary, and then the molded article is obtained by molding by applying pressure by a molding machine (molding process). In this molding step, when cracks are generated in the molded article, cracks remain in the MnZn ferrite of the final product. The cracked MnZn ferrite has poor strength and is a defective product which does not reach the desired magnetic properties, similar to the cracked product. Therefore, the cracked molded article is removed at this time. Subsequently, the molded body is fired under known firing conditions to obtain MnZn ferrite (firing step).

In addition, in the method for producing MnZn ferrite of the present disclosure, a raw material having a reduced impurity content is used. In addition, when mixing, pulverizing, and granulating, pure water or ion-exchanged water having a reduced impurity content is used as a solvent for a slurry containing a basic component or further containing an auxiliary component. In addition, a surfactant or the like added to reduce the viscosity of the binder and the slurry also selects a surfactant that reduces metal ions. Further, these components are often contained in the refractory materials of the furnaces used in the firing step and the firing step. Therefore, in order to suppress contamination of these elements, screening is suitably performed, or a mat powder is used at the time of firing to reduce the contact area of the mixture or the molded body with the refractory, thereby preventing contamination of Na, mg, al, and K.

The MnZn ferrite obtained may be subjected to a suitable surface grinding or other processing.

The MnZn ferrite thus obtained has not only the presentSome MnZn ferrite cannot achieve a fracture toughness value of 1.10MPa m of a flat plate-shaped magnetic core measured according to JIS R1607 ^1/2 The excellent mechanical properties are achieved, and the loss value of the toroidal magnetic core manufactured under the same conditions at 100 ℃ under 300kHz and 100mT is 450kW/m ³ The following good magnetic properties were obtained. The loss value of the toroidal core at 100 ℃, 300kHz and 100mT is preferably 440kW/m ³ The following is given.

Further, as for the loss value of the toroidal core, the loss values of 300kHz and 100mT at 100℃were measured by applying a primary winding of 5 turns and a secondary winding of 5 turns to the core and then using a core loss measuring instrument (rock-through measurement: SY-8232).

The fracture toughness value of the flat magnetic core was calculated from the fracture load and the size of the test piece by the three-point bending test after the precracking was applied to the sample pressed into the center portion by the vickers indenter according to JIS R1607.

Examples

Example 1

In the process, all of Fe, zn and Mn contained are contained as Fe ₂ O ₃ In the case of ZnO and MnO meter, each raw material powder was weighed to obtain Fe ₂ O ₃ The proportions of the amounts of ZnO and MnO are shown in table 1, and each raw material powder was mixed for 16 hours using a ball mill, and then calcined in air at 900 ℃ for 3 hours, and cooled to room temperature in air for 1.5 hours to obtain a calcined powder. Next, 150 mass ppm, 700 mass ppm and 250 mass ppm equivalent of SiO were weighed out respectively ₂ CaO and Nb ₂ O ₅ Then, it was added to the calcined powder, and pulverized for 12 hours using a ball mill, thereby obtaining a pulverized powder. Polyvinyl alcohol was added to the pulverized powder to carry out spray-drying granulation, and a pressure of 118MPa was applied to form a toroidal core and a flat core. After confirming visually that these molded bodies were free from cracks, the molded bodies were charged into a firing furnace, and fired in a stream of nitrogen and air properly mixed at a maximum temperature of 1320 ℃ for 2 hours to obtain an outer diameter: 25mm; inner diameter: 15mm; height: 5mm sintered body toroidal core and length: 4mm; width: 35mm; thickness: firing of 3mmA knot body plate-shaped magnetic core.

Further, since a high purity raw material is used as a raw material, pure water is used at the time of mixing and pulverizing of auxiliary components, and further, a component such as a lubricant containing metal ions is not added to the slurry, contamination of Na, mg, al, and K is suppressed, whereby the amounts of P and B contained in the sintered body toroidal core and the sintered body flat plate-shaped core are 4 mass ppm and 3 mass ppm, respectively, and Na, mg, al, and K are 80 mass ppm, 75 mass ppm, 120 mass ppm, and 30 mass ppm, respectively. Further, as described above, the contents of P, B, na, mg, al and K were quantified according to JIS K0102 (ICP mass spectrometry).

The loss value of the sintered annular magnetic core and the fracture toughness value of the sintered flat magnetic core were obtained by the above-described method. The results obtained are shown in Table 1.

TABLE 1

As shown in the table, in examples 1-1 to 1-5 as examples of the invention, the loss value at 100℃at 300kHz at 100mT was 450kW/m ³ Below, and fracture toughness value of 1.10 MPa.m ^1/2 The above-mentioned materials have both suitable magnetic properties and high toughness.

In contrast, the alloy contains less than 51.5mol% Fe ₂ O ₃ Comparative example (comparative example 1-1) and Fe ₂ O ₃ In the comparative examples (comparative examples 1 to 2) having more than 55.5mol%, although high toughness was achieved, the loss value increased due to the increase of magnetic anisotropy and magnetostriction, so that the loss value at 100℃at 300kHz and 100mT could not satisfy 450kW/m ³ The following is given. In the comparative examples (comparative examples 1 to 3) in which ZnO was insufficient, the Curie temperature was excessively increased, whereas in the comparative examples (comparative examples 1 to 4) in which ZnO was contained in a larger amount than the claimed range, the loss value showed the decrease of the minor peak of the minimum value, and therefore, the loss value at 100℃at 300kHz and 100mT could not satisfy 450kW/m ³ The following is given.

Example 2

In the process, all of Fe, zn and Mn contained are contained as Fe ₂ O ₃ In the case of ZnO and MnO meters, the raw materials were weighed to form a composition of Fe ₂ O ₃ :53.0mol percent ZnO:12.0mol%, mnO:35.0mol% was mixed for 16 hours using a ball mill, and then calcined in air at 900℃for 3 hours, and cooled to room temperature in air for 1.5 hours to obtain a calcined powder. Next, siO was added to the calcined powder in the amount shown in Table 2 ₂ CaO and Nb ₂ O ₅ And adding CoO or NiO to a part of the sample, and pulverizing for 12 hours using a ball mill, thereby obtaining pulverized powder. Polyvinyl alcohol was added to the pulverized powder to carry out spray-drying granulation, and a pressure of 118MPa was applied to form a toroidal core and a flat core. After confirming visually that these molded bodies were free from cracks, the molded bodies were inserted into a firing furnace, and fired for 2 hours at a maximum temperature of 1320 ℃ in a gas flow in which nitrogen and air were properly mixed, to obtain an outer diameter: 25mm; inner diameter: 15mm; height: 5mm sintered body toroidal core and length: 4mm; width: 35mm; thickness: 3mm sintered body flat magnetic core. The amounts of P and B contained in the obtained sintered annular magnetic core and sintered flat magnetic core were 4 mass ppm and 3 mass ppm, respectively, and Na, mg, al and K were 80 mass ppm, 75 mass ppm, 120 mass ppm and 30 mass ppm, respectively.

For each of these samples, each characteristic was evaluated using the same method and apparatus as in example 1. The results obtained are shown in Table 2.

TABLE 2

As shown in the table, in SiO ₂ 、CaO、Nb ₂ O ₅ To CoO toAnd the loss value at 100℃300kHz and 100mT in examples 2-1 to 2-11 in which the amount of NiO was within the prescribed range was 450kW/m ³ Below, and fracture toughness value of 1.10 MPa.m ^1/2 The above-mentioned materials have both suitable magnetic properties and high toughness.

On the other hand, in SiO ₂ CaO and Nb ₂ O ₅ In comparative examples 2-1, 2-3 and 2-5, in which one of the three components was contained in less than a predetermined amount, it was found that the resistivity was lowered due to insufficient grain boundary formation, the eddy current loss was increased, the loss value was deteriorated, and that a part of coarse grains having low strength were generated due to insufficient moderate inhibition of the growth of crystalline grains, resulting in failure to reach the desired fracture toughness value. In contrast, in comparative examples 2-2, 2-4 and 2-6, in which one of the same components was too much, the loss value was significantly deteriorated due to the occurrence of abnormal grains, and the fracture toughness value was also greatly lowered due to the locally low strength of the site where abnormal grains were generated.

Example 3

According to the method shown in example 1, granulated powders were obtained using raw materials having the same composition ratio of the essential component and the auxiliary component as in examples 1 to 2 but containing P, B in different amounts. The granulated powder was molded into a toroidal core and a flat core by applying a pressure of 118 MPa. After confirming visually that these molded bodies were free from cracks, the molded bodies were inserted into a firing furnace, and fired for 2 hours at a maximum temperature of 1320 ℃ in a gas flow in which nitrogen and air were properly mixed, to obtain an outer diameter: 25mm; inner diameter: 15mm; height: 5mm sintered body toroidal core and length: 4mm; width: 35mm; thickness: 3mm sintered body flat magnetic core.

For each of these samples, each characteristic was evaluated using the same method and apparatus as in example 1. The results obtained are shown in Table 3.

In addition, 1000 molded articles were produced under the same conditions, and whether or not there was a crack was visually observed. Further, regarding the judgment of the crack, a core in which the formed body is completely broken and cracks of 0.5mm or more or partial defects can be confirmed was judged to be cracked. The incidence of cracks is shown in table 3.

TABLE 3

In example 3-1 in which P and B are within the prescribed ranges, the loss value at 100℃at 300kHz and 100mT is 450kW/m ³ Below, and fracture toughness value of 1.10 MPa.m ^1/2 As described above, both the preferable magnetic characteristics and the high toughness can be achieved. On the other hand, when one or both of the two components contain a predetermined amount or more, abnormal crystal grains occur, which results in deterioration of the loss value, and the fracture toughness value is also lowered, and thus the desired value cannot be obtained.

Example 4

According to the method shown in example 1, raw materials having the same composition ratio of the basic component and the auxiliary component as in examples 1 to 2 but different amounts of impurities are used, and granulated powder produced by using tap water or mineral water of different hardness or the like, or intentionally adding a reagent, which is different from ordinary pure water or ion-exchanged water, as water used as a solvent for the slurry at the time of mixing, pulverizing, granulating, and applying 118MPa of pressure-molded toroidal core and tabular core to the granulated powder, which is produced by varying amounts of Na, mg, al and K contained in the final sample, are used. After confirming visually that there were no cracks on these molded bodies, these molded bodies were inserted into a firing furnace, and fired at a maximum temperature of 1320 ℃ for 2 hours in a gas flow in which nitrogen and air were properly mixed, to obtain an outer diameter: 25mm; inner diameter: 15mm; height: 5mm sintered body toroidal core and length: 4mm; width: 35mm; thickness: 3mm sintered body flat magnetic core.

For each of these samples, each characteristic was evaluated using the same method and apparatus as in example 1. The results obtained are shown in Table 4.

In addition, 1000 molded articles were produced under the same conditions, and whether or not there was a crack was visually observed. The incidence of cracks is shown in table 4.

TABLE 4

In examples 4-1 to 4-9 in which the contents of Na, mg, al and K were within the predetermined ranges, fracture toughness values of 1.10 MPa.m were obtained ^1/2 The above good values.

On the other hand, in comparative examples 4-1 to 4-9 in which one of Na, mg, al and K contained a predetermined value or more, the desired magnetic properties could be obtained, but the fracture toughness value was as low as 1.10 MPa.m ^1/2 The following is given. It is presumed that this decrease in toughness is due to solid solution of Na, mg, al, and K in the crystal grains, and points of low toughness appear locally.

Regarding the crack occurrence rate of the molded article, the crack occurrence rates of comparative examples 4-1 to 4-9 were as high as 3.5% or more. The reason for this is considered that in these comparative examples, the contents of Na, mg, al and K were not sufficiently suppressed, and the uniform dispersion of the binder was hindered, and the strength weak portions where the binder amount was locally insufficient were present in the molded body, and crack defects were likely to occur.

(industrial applicability)

As described above, the MnZn ferrite of the present invention has excellent magnetic characteristics (the loss value under excitation conditions of 100 ℃ C., 300kHz and 100mT is 450 kW/m) ³ The following) and mechanical properties (fracture toughness value of 1.10 MPa.m) ^1/2 The above) can reduce the crack occurrence rate of the molded article to 3.5% or less, and can be manufactured with high yield, and therefore is particularly suitable for a magnetic core of an electronic component for mounting in an automobile.

Claims

1. A MnZn ferrite composed of a basic component, an auxiliary component, and unavoidable impurities, characterized in that:

iron: by Fe ₂ O ₃ From 51.5mol% to 55.5mol%,

zinc: 5.0mol% to 15.5mol% based on ZnO, and

manganese: the balance;

the auxiliary components are, relative to the basic components:

SiO ₂ :50 to 300 mass ppm of a catalyst,

CaO:100 to 1300 mass ppm, and

Nb ₂ O ₅ :100 to 400 mass ppm;

p: less than 10 mass ppm of the catalyst is used,

b: less than 10 mass ppm of the catalyst is used,

na:40 mass ppm or more and less than 200 mass ppm,

mg: more than 50 mass ppm and less than 200 mass ppm,

al:80 mass ppm or more, less than 250 mass ppm, and

k:20 mass ppm or more and less than 100 mass ppm.

2. A MnZn ferrite composed of a basic component, an auxiliary component, and unavoidable impurities, characterized in that:

iron: by Fe ₂ O ₃ From 51.5mol% to 55.5mol%,

zinc: 5.0mol% to 15.5mol% based on ZnO, and

manganese: the balance;

the auxiliary components are, relative to the basic components:

SiO ₂ :50 to 300 mass ppm of a catalyst,

CaO:100 mass ppm to 1300 mass ppm,

Nb ₂ O ₅ :100 to 400 mass ppm; and

CoO:3500 mass ppm or less, the CoO content being other than 0;

p: less than 10 mass ppm of the catalyst is used,

b: less than 10 mass ppm of the catalyst is used,

na:40 mass ppm or more and less than 200 mass ppm,

mg: more than 50 mass ppm and less than 200 mass ppm,

al:80 mass ppm or more, less than 250 mass ppm, and

k:20 mass ppm or more and less than 100 mass ppm.

3. A MnZn ferrite composed of a basic component, an auxiliary component, and unavoidable impurities, characterized in that:

iron: by Fe ₂ O ₃ From 51.5mol% to 55.5mol%,

zinc: 5.0mol% to 15.5mol% based on ZnO, and

manganese: the balance;

the auxiliary components are, relative to the basic components:

SiO ₂ :50 to 300 mass ppm of a catalyst,

CaO:100 mass ppm to 1300 mass ppm,

Nb ₂ O ₅ :100 to 400 mass ppm; and

NiO:15000 mass ppm or less, the content of NiO being not 0;

p: less than 10 mass ppm of the catalyst is used,

b: less than 10 mass ppm of the catalyst is used,

na:40 mass ppm or more and less than 200 mass ppm,

mg: more than 50 mass ppm and less than 200 mass ppm,

al:80 mass ppm or more, less than 250 mass ppm, and

k:20 mass ppm or more and less than 100 mass ppm.

4. The MnZn ferrite according to any one of claim 1 to 3,

the fracture toughness value measured by the single-side pre-crack beam method defined in JIS R1607 was 1.10MPa m ^1/2 The above, moreover, the loss value at 100 ℃, 300kHz and 100mT was 450kW/m ³ The following is given.