CN110178191B - MnCoZn-based ferrite and method for producing same - Google Patents

Abstract

The invention provides a MnCoZn ferrite, which contains the following components as basic components: with Fe₂O₃45.0 mol% or more and less than 50.0 mol%, zinc: 15.5 to 24.0 mol% in terms of ZnO, cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: the balance, with respect to the above basic component, as a subcomponent, contains SiO₂: 50-300 mass ppm and CaO: 300 to 1300 ppm by mass, and the balance being made up of unavoidable impurities, wherein the amounts of Cd, Pb, Sb, As and Se in the unavoidable impurities are each suppressed to less than 20 ppm by mass, and wherein the abrasion value is less than 0.85%, the coercive force at 23 ℃ is 15A/m or less, the resistivity is 30 Ω & m or more, and the Curie temperature is 100 ℃ or more, whereby the magnetic properties are excellent, such As high resistance and low coercive force, and the mechanical strength is excellent.

Description

MnCoZn-based ferrite and method for producing same

Technical Field

The present invention relates to a MnCoZn ferrite having a high resistivity, a small coercive force and a low tendency to defect, and a method for producing the same.

In this specification, the coercive force refers to a value at 23 ℃.

Background

As a representative example of the soft magnetic oxide magnetic material, MnZn ferrite is cited. The conventional MnZn ferrite contains about 2 mass% or more of Fe having positive magnetic anisotropy²⁺By reaction with Fe having negative magnetic anisotropy³⁺、Mn²⁺The cancellation is achieved thereby achieving high initial permeability, low losses in the kHz region.

The MnZn ferrite is inexpensive compared to amorphous metals and the like, and therefore is widely used as a noise filter of a switching power supply and the like, a transformer, and a magnetic core of an antenna.

However, Fe of MnZn ferrite²⁺In large amounts, therefore, Fe is liable to occur³⁺-Fe²⁺Transfer of electrons between them and a low resistivity of 0.1. omega. m. Therefore, when the frequency region to be used is increased, the loss due to eddy current flowing in the ferrite is sharply increased, the initial permeability is greatly reduced, and the loss is also increased. Therefore, the durable frequency of MnZn ferrite is limited to about several hundred kHz, and NiZn ferrite is mainly used in the MHz level. The NiZn ferrite has a resistivity of 10⁵Since the ferrite is about 1 ten thousand times as high as the MnZn ferrite in terms of (. omega. m) or more and has a small eddy current loss, the properties of high initial permeability and low loss are hardly lost even in a high-frequency region.

However, the NiZn ferrite has a big problem. This is a problem in that the soft magnetic material is required to be sensitive to a change in external magnetic field, and therefore the coercive force Hc is preferably small, but the NiZn ferrite is made up of only ions having negative magnetic anisotropy, and therefore the value of the coercive force is large. The coercive force is defined in JIS C2560-2.

As a method for obtaining a ferrite having a large resistivity in addition to a NiZn ferrite, there is a method of reducing Fe contained in a MnZn ferrite²⁺And increasing the resistivity.

For example, patent documents 1, 2, and 3 report the use of Fe₂O₃Less than 50 mol% of the component, reduced Fe²⁺MnZn ferrite with increased resistivity. However, they are also composed of only ions having negative magnetic anisotropy, as with NiZn ferrite, and therefore the problem of reduced coercivity is not solved at all.

Accordingly, patent documents 4, 5, and 6 disclose addition of Fe²⁺Co having positive magnetic anisotropy other than²⁺Such techniques, however, do not aim at reducing the coercive force. Further, the measures against abnormal crystal grains described later are insufficientAnd thus is also poor in cost and manufacturing efficiency.

In contrast, patent document 7 reports a high-resistance MnCoZn ferrite which can be stably produced by suppressing the occurrence of abnormal crystal grains by specifying the impurity composition and has a low coercive force.

The abnormal grain growth is a phenomenon that occurs when the balance of grain growth is locally disrupted for some reason, and is often observed in production by the powder metallurgy method. Since a substance that largely hinders the movement of a magnetic domain wall, such as an impurity or a lattice defect, is mixed in the abnormally grown grains, the soft magnetic properties are lost, and the coercive force is increased. At the same time, grain boundary formation becomes insufficient, and thus the resistivity decreases.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 7-230909

Patent document 2: japanese patent laid-open No. 2000-277316

Patent document 3: japanese patent laid-open No. 2001-220222

Patent document 4: japanese patent No. 3418827

Patent document 5: japanese patent laid-open No. 2001 and 220221

Patent document 6: japanese patent laid-open publication No. 2001 and 68325

Patent document 7: japanese patent No. 4554959

Patent document 8: japanese patent laid-open publication No. 2006-44971

Disclosure of Invention

Problems to be solved by the invention

By the development of the above-mentioned patent document 7, a MnCoZn ferrite having satisfactory magnetic characteristics has been obtained.

On the other hand, in recent years, the trend toward electrical installation of automobiles has been remarkable, and the number of cases where MnCoZn ferrite is mounted on automobiles has also been increasing. Since vibration occurs during traveling in an automobile as compared with electric products and industrial equipment which have been mainly used so far, it is also required that MnCoZn ferrite which is a ceramic for use in an automobile is not damaged by impact due to vibration.

However, Fe₂O₃Since MnCoZn ferrite having a composition of less than 50 mol% has a small amount of oxygen vacancies and thus sintering easily proceeds during firing, vacancies easily remain in the grains and the grain boundary is easily unevenly generated. As a result, there are the following problems: when an external impact is applied, defects are more likely to occur than in the conventional MnCoZn ferrite.

That is, in the technique disclosed in patent document 7, the obtained magnetic properties are sufficient, but on the other hand, a problem remains in that the mechanical strength against the defect is not necessarily sufficient.

As a technique for improving the strength of defect, patent document 8 discloses a technique of adding TiO in a range of 0.01 to 0.5 mass%₂The technique of (1).

On the other hand, however, TiO is added₂Will form a solid solution in the crystal grains to produce Ti⁴⁺Some Fe due to valence balance³⁺Is reduced to Fe²⁺Therefore, there is a disadvantage of causing a large decrease in resistivity.

The purpose of the present invention is to provide MnCoZn ferrite that has both mechanical strength, such as fracture resistance expressed by an abrasion value, and mechanical strength, by suppressing abnormal grain growth while generating uniform grain boundaries, while maintaining excellent magnetic properties, such as conventional high resistance and low coercive force, and to provide an advantageous method for manufacturing the MnCoZn ferrite.

Means for solving the problems

The present inventors first conducted experiments on Fe of MnCoZn ferrite required for obtaining desired magnetic characteristics₂O₃As a result of studies on appropriate amounts of ZnO and CoO, it was found that an appropriate range in which all of the characteristics of high resistivity, small coercive force and high curie temperature can be simultaneously achieved.

In the present specification, as described above, the coercivity is a value at 23 ℃. This is because MnZn ferrite cores used for antennas and noise filters are often used at a position away from a power transformer or a semiconductor as a heat source, and they operate at normal temperature (5 to 35 ℃). Therefore, it is important that the magnetic properties at 23 ℃ which is a representative value in the range of room temperature (5 to 35 ℃) are good, that is, the coercive force is small.

Next, focusing on the microstructure, it was found that by reducing the voids in the grains and regulating the grain size and realizing a grain boundary of an appropriate thickness, the defect of the sintered core expressed by the abrasion value can be suppressed. Here, in order to realize a desired crystal structure, SiO, which is a component segregated in the grain boundary₂And the amount of CaO added have a great influence, and therefore, appropriate ranges of these components have been successfully determined. Within this range, the abrasion value can be kept low.

Further, as a result of studies focusing on production conditions at the time of occurrence of abnormal crystal grains with respect to suppression of occurrence of abnormal crystal grains, which is essential for achieving both appropriate magnetic properties and mechanical strength against defects, it was found that the SiO layer described above has excellent magnetic properties and excellent mechanical strength against defects₂And abnormal crystal grains appear when CaO is excessive, or when Cd, Pb, Sb, As, Se, and other components, which are impurities present in natural ore or mixed during smelting, are contained at a certain value or more.

The present invention is based on the above findings.

As described above, patent documents 1, 2, 3 and the like refer to high resistivity, and patent documents 4, 5, and 6 refer to Co having positive magnetic anisotropy²⁺But there is no description about the coercivity, and in patent document 5, there is more conversely specified: instead, Pb is actively added. In addition, in these patent documents 1 to 6, since there is no description at all about measures against abnormal crystal grains, it is inferred that the mechanical strength is insufficient. In addition, even patent document 7, which is mentioned about the low coercive force, does not provide sufficient additives, and thus sufficient mechanical strength for suppressing the defect cannot be expected. Furthermore, even patent document 8, which is mentioned about improvement of the defect strength, cannot avoid electricityThe resistivity is greatly reduced.

The gist of the present invention is as follows.

1. A MnCoZn-based ferrite material which is,

as essential components, iron: with Fe₂O₃45.0 mol% or more and less than 50.0 mol%, zinc: 15.5 to 24.0 mol% in terms of ZnO, cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: the balance of the weight percentage is as follows,

SiO is contained as a subcomponent with respect to the above-mentioned basic component₂: 50-300 mass ppm and CaO: 300 to 1300 ppm by mass of a catalyst,

the balance being made up of unavoidable impurities, wherein,

the amounts of Cd, Pb, Sb, As and Se in the above-mentioned inevitable impurities are suppressed to less than 20 mass ppm respectively,

the MnCoZn ferrite has a wear value of less than 0.85%, a coercive force at 23 ℃ of 15A/m or less, a resistivity of 30 [ omega ] m or more, and a Curie temperature of 100 ℃ or more.

2. The MnCoZn ferrite according to claim 1, wherein the sintered density of the MnCoZn ferrite is 4.85g/cm³The above.

3. The MnCoZn-based ferrite according to claim 1 or 2, wherein the MnCoZn-based ferrite is a MnCoZn-based ferrite formed from a green compact of a granulated powder having a particle size distribution d90 value of 300 μm or less.

4. The MnCoZn ferrite according to any one of the above 1 to 3, wherein the MnCoZn ferrite is formed of a formed-sintered body of a granulated powder having a crushing strength of less than 1.50 MPa.

5. A method for producing a MnCoZn ferrite, comprising:

a pre-firing step of pre-firing a mixture of basic components weighed so as to have a predetermined component ratio;

a mixing-grinding step of adding an accessory ingredient adjusted to a predetermined ratio to the calcined powder obtained in the above-mentioned calcining step, and mixing and grinding the mixture; and

a calcination step of adding a binder to the pulverized powder obtained in the mixing-pulverizing step, mixing the mixture, granulating the granulated powder so that the value of the particle size distribution d90 of the granulated powder is 300 μm or less and/or the crushing strength is less than 1.50MPa, molding the obtained granulated powder, and then calcining the molded powder at a maximum holding temperature of 1290 ℃ or more for a holding time of 1 hour or more to obtain the MnCoZn-based ferrite described in the above 1 or 2.

6. The method for producing a MnCoZn ferrite according to claim 5, wherein the granulation is a spray drying method.

Effects of the invention

According to the present invention, a MnCoZn ferrite having not only excellent magnetic properties such as high electric resistance and low coercive force but also mechanical strength such as excellent defect resistance by suppressing abnormal grain growth while generating uniform grain boundaries can be obtained.

The MnCoZn ferrite of the present invention has excellent magnetic properties such that the initial permeability at 23 ℃ and 1kHz is 3000 or more, the initial permeability at 23 ℃ and 1MHz is 2000 or more, and the initial permeability at 23 ℃ and 10MHz is 150 or more.

Detailed Description

The present invention will be specifically described below.

First, the reason why the composition of the MnCoZn ferrite is limited to the above range in the present invention will be described. In addition, iron, zinc, cobalt, and manganese contained as the basic components in the present invention are all converted into Fe₂O₃Values of ZnO, CoO, and MnO. In addition, regarding these Fe₂O₃The contents of ZnO, CoO and MnO are expressed in mol%, and the contents of subcomponents and impurity components are expressed in mass ppm with respect to the entire ferrite.

Fe₂O₃: 45.0 mol% or more and less than 50.0 mol%

Fe₂O₃Containing excess of, sometimes, Fe²⁺The amount increases, whereby the resistivity of the MnCoZn ferrite decreases. To avoid this, Fe₂O₃Volume demandThe suppression is less than 50 mole%. However, if it is too small, the coercive force increases and the curie temperature decreases, so that Fe is used as Fe₂O₃The conversion is to contain a minimum of 45.0 mol%. Preferred Fe₂O₃Is 47.1 mol% or more and less than 50.0 mol%, and more preferably 47.1 to 49.5 mol%.

ZnO: 15.5 to 24.0 mol%

ZnO has an effect of increasing the saturation magnetization of ferrite, increasing the sintered density due to a low saturation vapor pressure, and increasing the saturation magnetic flux density, and is an effective component for reducing the coercive force. Therefore, zinc is contained at least 15.5 mol% in terms of ZnO. On the other hand, if the zinc content is more than an appropriate value, the Curie temperature is lowered, which is problematic in practical use. Therefore, the upper limit of zinc is set to 24.0 mol% in terms of ZnO. The ZnO is preferably 15.5 to 23.0 mol%, more preferably 17.0 to 23.0 mol%.

And (3) CoO: 0.5 to 4.0 mol%

Co in CoO²⁺Is an ion having positive magnetic anisotropy energy, and the absolute value of the sum of the magnetic anisotropy energies decreases with the addition of an appropriate amount of CoO, resulting in a decrease in coercive force. For this purpose, 0.5 mol% or more of CoO needs to be added. On the other hand, the addition of a large amount results in a decrease in resistivity, induces abnormal grain growth, and excessively corrects the sum of magnetic anisotropy energy, thus conversely resulting in an increase in coercivity. To prevent this, CoO was added in an amount of 4.0 mol% at most. The preferred range of CoO is 1.0 to 3.5 mol%, more preferably 1.0 to 3.0 mol%.

MnO: balance of

The invention is MnCoZn ferrite, and the rest of the basic component needs MnO. The reason for this is that if MnO is not used, good magnetic characteristics such as high saturation magnetic flux density, low loss, and high magnetic permeability cannot be obtained. The preferable MnO content is in the range of 26.5 to 32.0 mol%.

The basic components are explained above, and the subcomponents are as follows.

SiO₂：50～300 mass ppm

SiO₂It is known that the addition of an appropriate amount of the ferrite contributes to uniformization of the crystal structure of the ferrite, and reduces the residual voids in the crystal grains, thereby lowering the residual magnetic flux density and thus lowering the coercive force. In addition, SiO₂Since the grain boundaries are segregated to increase the resistivity and reduce the coarse-grain size crystals, the wear value, which is an index of the defects of the sintered body, can be reduced. Therefore, SiO is contained in an amount of at least 50 mass ppm₂. On the other hand, when the amount is too large, abnormal crystal grains are produced, which become starting points of defects, and hence the wear value is increased, and the coercive force is also increased, and hence SiO is produced₂The content of (B) is limited to 300 mass ppm or less. More preferred SiO₂The content of (B) is in the range of 60 to 250 mass ppm.

CaO: 300 to 1300 mass ppm

CaO segregates at the grain boundary of MnCoZn ferrite, has an effect of suppressing grain growth, and also has an effect of reducing vacancies remaining in the grains. Therefore, with the addition of an appropriate amount, the resistivity is increased, the coercive force is also decreased, and coarse crystals are reduced, so that the abrasion value can also be decreased. Therefore, CaO is contained at least in an amount of 300 mass ppm. On the other hand, when the amount is too large, abnormal crystal grains occur, and the wear value and coercive force are also increased, so that the CaO content needs to be limited to 1300 mass ppm or less. More preferably, the content of CaO is in the range of 350 to 1000 mass ppm.

Next, the impurity components to be suppressed will be described.

Cd, Pb, Sb, As and Se are respectively less than 20 mass ppm

These components are components that are contained in natural ore or are inevitably contained in raw materials due to mixing in during smelting or the like. When the amount of these compounds is too small, there is no problem, but when the amount is more than a certain amount, abnormal grain growth of the ferrite is induced, and each property of the obtained ferrite is seriously adversely affected. Containing only less than 50 mol% Fe as in the present invention₂O₃The ferrite of (4) is crystalline as compared with the case where 50 mol% or more is containedSince grain growth easily progresses, abnormal grain growth easily occurs when the amounts of Cd, Pb, Sb, As, and Se are large. In this case, not only the coercivity is increased but also the generation of grain boundaries is insufficient, so that the resistivity is lowered and becomes a starting point of a defect, so that the abrasion value is also increased.

Therefore, in the present invention, the contents of Cd, Pb, Sb, As, and Se are suppressed to less than 20 mass ppm, respectively.

The allowable amount of unavoidable impurities, including Cd, Pb, Sb, As, and Se, needs to be set to 50 mass ppm or less As a whole. The allowable amount of the unavoidable impurities is preferably 40 mass ppm or less.

Therefore, it is preferable to suppress as much as possible the mixing of impurities in the base component and the subcomponent used as the raw materials. The total amount of impurities in the base component and the subcomponent used As the raw materials, including Cd, Pb, Sb, As, and Se, is preferably 50 mass ppm or less, and more preferably 40 mass ppm or less.

In addition, not limited to the composition, each characteristic of the MnCoZn ferrite is also greatly influenced by various parameters. Therefore, in the present invention, the following conditions are preferably satisfied in order to have desired magnetic properties and strength properties.

Sintered density: 4.85g/cm³The above

The MnCoZn ferrite is subjected to sintering and grain growth by a calcination treatment, and constitutes crystal grains and grain boundaries. In order to realize a crystal structure capable of realizing a low coercive force, that is, a form in which a nonmagnetic component to be present in a grain boundary is appropriately segregated in the grain boundary, and the grain is made of a component having uniform magnetic properties while maintaining an appropriate grain size, it is necessary to sufficiently progress a sintering reaction. Further, from the viewpoint of preventing chipping, insufficient sintering is not preferable because strength is reduced.

From the above viewpoint, the MnCoZn ferrite of the present invention is preferably set to have a sintered density of 4.85g/cm³The above. By satisfying the above conditions, the coercive force is lowered and the abrasion value can be suppressed to be low. It should be noted that, in the following description,in order to achieve this sintered density, it is necessary to perform the calcination while setting the maximum holding temperature at the time of calcination to 1290 ℃ or higher and setting the holding time at that temperature to 1 hour or longer. Preferably, the maximum holding temperature is 1290-1400 ℃ and the holding time is 1-8 hours. In addition, when abnormal grain growth occurs, the sintering density is not increased, and therefore, in order to prevent abnormal grain, it is necessary to manufacture the sintered body by limiting the amount of the additive and the amount of impurities to appropriate ranges.

The granulated powder is produced by using a granulated powder having a particle size distribution d90 of 300 μm or less.

The granulated powder having a crushing strength of less than 1.50MPa is used for the production.

Generally, a MnCoZn ferrite is obtained by a powder molding step of filling a mold with granulated powder, then compressing the powder at a pressure of about 100MPa, and calcining and sintering the obtained compact. On the surface of the ferrite, fine irregularities due to the gaps between the granulated powders remain even after sintering, and this becomes a starting point of fracture at the time of impact, and therefore, the wear value is improved with an increase in the remaining fine irregularities. Therefore, in order to reduce the gaps between the granulated powders, it is preferable to remove the granulated powder having a coarse particle size and to suppress the crushing strength of the granulated powder to a certain value or less.

As an effective means for satisfying this condition, it is effective to adjust the particle size by sieving the obtained granulated powder. On the other hand, in order to reduce the crushing strength of the granulated powder, it is effective to increase the temperature without excessively increasing the temperature when granulation is performed by applying heat as in the spray granulation method. The particle size distribution was measured by particle size analysis based on a laser diffraction scattering method described in JIS Z8825. "d 90" represents a particle diameter of 90% in volume accumulation from the small particle diameter side in the particle size distribution curve. The crushing strength of the granulated powder was measured by the method specified in JIS Z8841.

When the value of the particle size distribution d90 is too small, the flowability decreases due to an increase in the number of contact points between the granulated powders, which causes problems such as a failure in filling the powder into a mold during powder molding and an increase in molding pressure during molding, and therefore the lower limit of d90 is preferably set to 75 μm. Further, when the crushing strength of the granulated powder is greatly reduced, the granulated powder is crushed and the flowability is reduced at the time of transportation and mold filling of the powder, and thus a defect at the time of mold filling of the powder and a problem of an increase in molding pressure at the time of molding still occur, and therefore, the lower limit of the crushing strength is preferably set to 0.50 MPa.

Next, a method for producing a MnCoZn ferrite of the present invention will be described.

Regarding the production of MnCoZn ferrite, Fe is first weighed so as to attain a predetermined ratio₂O₃And ZnO, CoO, and MnO powders were thoroughly mixed and then calcined. Next, the obtained calcined powder is pulverized to obtain a pulverized powder. At this time, the subcomponents specified in the present invention are added at a predetermined ratio and pulverized together with the calcined powder. In this step, the calcined powder is pulverized to a size of a target average particle diameter while sufficiently homogenizing the powder so that the concentration of the added component does not vary. Here, the average particle diameter of the target pulverized powder is 1.4 to 1.0. mu.m.

Next, an organic binder such as polyvinyl alcohol is added to the powder having the desired composition, and granulated powder is prepared by granulation by a spray drying method or the like under appropriate conditions in order to obtain a sample having a desired particle size and crushing strength. In the spray drying method, it is preferable to set the exhaust temperature to less than 270 ℃. Here, the preferred particle size of the granulated powder is 75 to 300 μm in terms of the particle size distribution d 90. The granulated powder preferably has a crushing strength of 0.50MPa or more and less than 1.50 MPa.

Next, after a step of sieving for particle size adjustment or the like is performed as necessary, the resultant is molded by applying pressure by a molding machine, and then, the resultant is calcined under appropriate calcination conditions. It is preferable to pass through a sieve having a 350 μm mesh and remove coarse powder on the sieve.

The suitable calcination conditions mean that the maximum holding temperature is 1290 ℃ or more and the holding time is 1 hour or more, as described above.

The obtained ferrite sintered body may be subjected to a surface polishing or the like.

As a result, MnCoZn ferrite satisfying all the excellent characteristics described below, which has not been possible in the past, can be obtained.

Abrasion value less than 0.85%

A coercive force at 23 ℃ of 15A/m or less

Resistivity of 30. omega. m or more

Curie temperature of 100 ℃ or higher

Examples

Example 1

Fe is added to the iron, zinc, cobalt and manganese contained in the alloy₂O₃Converting the forms of ZnO, CoO and MnO to Fe₂O₃Each raw material powder was weighed so that the amounts of ZnO, CoO, and MnO became the ratios shown in table 1, and after mixing the raw material powders for 16 hours using a ball mill, the mixture was calcined in air at 925 ℃ for 3 hours. Next, the calcined powder was weighed to obtain SiO powders in an amount of 150 ppm by mass and 700 ppm by mass, respectively₂CaO was added thereto, and the mixture was pulverized for 12 hours by a ball mill. Then, polyvinyl alcohol was added to the obtained pulverized slurry, spray-dried and granulated at an air discharge temperature of 250 ℃, coarse powder was removed by a sieve having a mesh size of 350 μm, and then a pressure of 118MPa was applied to form a ring core and a rectangular parallelepiped core. The granulated powder used in the molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

Then, the compact was charged into a calciner, and calcined in a gas flow obtained by appropriately mixing nitrogen gas and air at a maximum temperature of 1350 ℃ for 2 hours, to obtain a sintered body annular core having an outer diameter of 25mm, an inner diameter of 15mm, and a height of 5mm, and 5 sintered body cylindrical cores having a diameter of 10mm and a height of 10 mm.

Since a high-purity raw material was used, the sintered body core contained impurities Cd, Pb, Sb, As and Se in an amount of 3 mass ppm.

The contents of Cd, Pb, Sb, As and Se were determined by JIS K0102 (IPC mass spectrometry).

With respect to the obtained sample, the sintered density was measured by the Archimedes method at 23 ℃ for a ring core and the resistivity was measured by the four-terminal method based on JIS C2560-2. Regarding the initial permeability of the toroidal core, 10-turn windings were applied to the toroidal core, the inductance was measured using an LCR tester (4980A manufactured by Keysight corporation), and calculation was performed based on the measured inductance. The curie temperature is calculated from the measurement result of the temperature characteristics of the inductor. With respect to the abrasion value, the measurement was carried out in accordance with the method defined in JPMAP 11-1992. The coercive force Hc was measured at 23 ℃ in accordance with JIS C2560-2.

The results obtained are also shown in table 1.

As shown in the table, in examples 1-1 to 1-7 which are inventive examples, MnCoZn ferrites having high strength with a wear value of less than 0.85% and excellent magnetic properties with a resistivity of 30. omega. m or more at 23 ℃, a coercive force of 15A/m or less and a Curie temperature of 100 ℃ or more were obtained.

On the other hand, the Fe content is 50.0 mol% or more₂O₃Comparative examples 1-1 and 1-2 in which Fe was accompanied²⁺The resistivity is greatly reduced. On the other hand, in Fe₂O₃In comparative examples 1 to 3 in which the amount was less than 45.0 mol%, an increase in coercive force and a decrease in curie temperature were observed.

In comparative examples 1 to 4 in which the amount of ZnO exceeded the appropriate range, a decrease in the Curie temperature was observed. On the other hand, in comparative examples 1 to 5 in which the ZnO amount did not satisfy the appropriate range, the coercive force was increased, and the preferable magnetic properties could not be achieved.

In comparative examples 1 to 6 in which the CoO amount does not fall within the appropriate range, the coercive force is high due to insufficient positive magnetic anisotropy, while in comparative examples 1 to 7 in which the CoO amount exceeds the appropriate range, the coercive force is increased due to excessive increase in positive magnetic anisotropy, and the coercive force is out of the preferred range.

Example 2

Fe is added to the iron, zinc, cobalt and manganese contained in the alloy₂O₃Conversion of ZnO, CoO and MnOTo form Fe₂O₃The raw materials were weighed so as to have a composition of 49.0 mol% of ZnO, 21.0 mol% of CoO, and the balance MnO, mixed by a ball mill for 16 hours, and then calcined in air at 925 ℃ for 3 hours. Next, SiO was added to the calcined powder in the amount shown in Table 2₂CaO was pulverized in a ball mill for 12 hours. Then, polyvinyl alcohol was added to the obtained pulverized slurry, spray-dried and granulated at a discharge temperature of 250 ℃, coarse powder was removed by a sieve having a mesh size of 350 μm, and then a pressure of 118MPa was applied to form a ring core and a cylindrical core. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

Then, the compact was charged into a calciner, and calcined in a gas flow obtained by appropriately mixing nitrogen gas and air at a maximum temperature of 1350 ℃ for 2 hours, to obtain a sintered body annular core having an outer diameter of 25mm, an inner diameter of 15mm, and a height of 5mm, and 5 cylindrical cores having a diameter of 10mm and a height of 10 mm.

Since a high-purity raw material was used As the raw material, the sintered body core contained impurities Cd, Pb, Sb, As, and Se in an amount of 3 mass ppm.

For each of these samples, the characteristics were evaluated by the same method and apparatus as in example 1.

The results obtained are also shown in Table 2.

As shown in the table, in SiO₂And examples 2-1 to 2-4 in which the amount of CaO was within an appropriate range, high strength with a wear value of less than 0.85% and excellent magnetic properties in which the resistivity at 23 ℃ was 30. omega. m or more, the coercive force was 15A/m or less, and the Curie temperature was 100 ℃ or more were obtained.

In contrast, in SiO₂Comparative examples 2-1 and 2-3 in which either CaO or CaO did not satisfy the appropriate range had insufficient generation of grain boundaries, and thus the grains were not sufficiently generatedSince the particle size is not uniform, the abrasion value is higher than 0.85%, and the grain boundary thickness is insufficient, so that the resistivity is less than 30 Ω · m.

In addition, in the level of comparative examples 2-2, 2-4 and 2-5, which have too much one of the components, abnormal crystal grains are generated and sintering is inhibited, so that the sintering density is low and the abrasion value is high. In addition, the generation of grain boundaries is insufficient, and therefore, the resistivity is low and the coercivity is also high.

Example 3

Using the raw materials containing the same basic components and subcomponents in the same composition ratio as in example 1-2 but containing different amounts of impurities, the method shown in examples 1 and 2 was used to produce a sintered body annular core having an outer diameter of 25mm, an inner diameter of 15mm and a height of 5mm and 5 cylindrical cores having a diameter of 10mm and a height of 10mm, and characteristics were evaluated by the same method and apparatus as in example 1, and the results are shown in table 3. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

As shown in the table, in example 3-1 in which the contents of Cd, Pb, Sb, As, and Se were equal to or less than the predetermined values, the strength indicated by the wear value and the magnetic properties indicated by the coercive force, the resistivity, and the curie temperature were all good values.

On the other hand, in comparative examples 3-1 to 3-7 in which one or more of the 5 levels exceeded the predetermined value, abnormal crystal grains appeared, and sintering was inhibited, and therefore, the sintering density was low, and therefore, the abrasion value was high, and the generation of grain boundaries was insufficient, and therefore, the specific resistance was low, and further, the coercive force was also high.

Example 4

Compacts prepared in such proportions that the basic components, subcomponents, and impurity components had the same compositions as in examples 1-2 were calcined under various temperature conditions shown in table 4 by the methods shown in examples 1 and 2.

For each of these samples, the characteristics were evaluated by the same method and apparatus as in example 1. The results obtained are also shown in Table 4. The granulated powder used for molding had a particle size distribution d90 of 230 μm and a crushing strength of 1.29 MPa.

As shown in the table, the firing was carried out at a maximum holding temperature of 1290 ℃ or more and a holding time of 1 hour or more at the time of firing to obtain a sintered density of 4.85g/cm³In examples 3-1 to 3-5, the strength represented by the abrasion value, and the magnetic properties represented by the resistivity, coercive force, and Curie temperature were all good.

On the other hand, the sintering density is less than 4.85g/cm at a calcination temperature of less than 1290 ℃ or at a holding time of less than 1 hour³In comparative examples 3-1 to 3-6, since the sintered density was low, the abrasion value was high, and the crystal grain growth was insufficient, so that the hysteresis loss was large, and as a result, the coercive force was high, which was not preferable from the viewpoint of both strength and magnetic properties.

Example 5

By the methods shown in examples 1 and 2, a ring-shaped core and a cylindrical core were molded by applying a pressure of 118MPa to a sample (crushing strength: 1.29MPa) having a particle size distribution d90 shown in table 5, which was prepared by changing the sieving conditions, with respect to a granulated powder having the same composition as in example 1-2 and obtained under the same spray drying conditions. Then, the compact was charged into a calciner, and calcined in a gas flow obtained by appropriately mixing nitrogen gas and air at a maximum temperature of 1350 ℃ for 2 hours, to obtain a sintered body annular core having an outer diameter of 25mm, an inner diameter of 15mm, and a height of 5mm, and 5 cylindrical cores having a diameter of 10mm and a height of 10 mm.

For each of these samples, the characteristics were evaluated by the same method and apparatus as in example 1. The results obtained are also shown in Table 5.

As shown in the table, in example 5-1 in which the value of the granulated powder particle size distribution d90 was 300 μm or less, the abrasion value was suppressed to 0.85% or less because the remaining of voids between the granulated powders was small and the starting points of chipping were small.

On the other hand, in comparative examples 5-1 to 5-3 in which the value of d90 was larger than 300. mu.m, the number of voids between granulated powders was large, and the number of starting points of defects was large, so that the abrasion value was high and the strength was low.

Example 6

Slurries having the same compositions as those of examples 1 and 2 produced by the methods shown in examples 1 and 2 were spray-dried at the discharge air temperature conditions shown in table 6 to obtain granulated powders having different crushing strengths, and after coarse powders were removed by a sieve having a mesh size of 350 μm, the granulated powders were molded into a ring core and a cylindrical core by applying a pressure of 118 MPa. In this case, the particle size distribution d90 of the granulated powder was 230. mu.m.

Then, the compact was charged into a calciner, and calcined in a gas flow obtained by appropriately mixing nitrogen gas and air at a maximum temperature of 1350 ℃ for 2 hours, to obtain a sintered body annular core having an outer diameter of 25mm, an inner diameter of 15mm, and a height of 5mm, and 5 cylindrical cores having a diameter of 10mm and a height of 10 mm.

The characteristics of these samples were evaluated by the same method and apparatus as in example 1, and the results are shown in table 6.

As shown in the table, in examples 1-2 and 6-1 in which the exhaust air temperature for spray drying granulation was not excessively high, the crushing strength of the granulated powder was less than 1.5MPa, and the granulated powder was sufficiently crushed during molding, so that no gaps between the granulated powders remained, and the starting points of the defects were small, and therefore, the abrasion value could be suppressed to less than 0.85%.

On the other hand, in comparative examples 6-1 to 6-3 in which the crushing strength of the granulated powder is 1.5MPa or more due to an excessively high discharge air temperature, the abrasion value is increased and the strength is lowered because many starting points of the defects are generated due to the crushing failure of the granulated powder.

Claims (4)

1. A MnCoZn-based ferrite material which is,

as essential components, iron: with Fe₂O₃45.0 mol% or more and less than 50.0 mol%, zinc: 15.5 to 24.0 mol% in terms of ZnO, cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: the balance of the weight percentage is as follows,

SiO is contained as a subcomponent with respect to the basic component₂: 50-300 mass ppm and CaO: 300 to 1300 ppm by mass of a catalyst,

the balance being made up of unavoidable impurities, wherein,

the amounts of Cd, Pb, Sb, As and Se in the unavoidable impurities are suppressed to less than 20 mass ppm respectively,

wherein the MnCoZn ferrite has a wear value of less than 0.85%, a coercive force at 23 ℃ of 15A/m or less, a resistivity of 30 [ omega ] m or more, and a Curie temperature of 100 ℃ or more,

the MnCoZn ferrite is formed by a formed-sintered body of a granulated powder having a particle size distribution d90 of 230 to 300 [ mu ] m and a crushing strength of 1.18 to less than 1.50 MPa.

2. The MnCoZn-based ferrite according to claim 1, wherein the sintered density of the MnCoZn-based ferrite is 4.85g/cm³The above.

3. A method for producing a MnCoZn ferrite, comprising:

a pre-firing step of pre-firing a mixture of basic components weighed so as to have a predetermined component ratio;

a mixing-grinding step of adding an accessory component adjusted so as to achieve a predetermined component ratio to the calcined powder obtained in the calcining step, and mixing and grinding the mixture; and

a calcination step of adding a binder to the pulverized powder obtained in the mixing-pulverizing step, mixing the mixture, granulating the granulated powder so that the particle size distribution d90 of the granulated powder is 230 to 300 μm and the crushing strength is 1.18 to less than 1.50MPa, molding the obtained granulated powder, and calcining the molded powder at a maximum holding temperature of 1290 ℃ or more for a holding time of 1 hour or more to obtain a MnCoZn-based ferrite,

the MnCoZn-based ferrite is characterized in that,

as essential components, iron: with Fe₂O₃45.0 mol% or more and less than 50.0 mol%, zinc: 15.5 to 24.0 mol% in terms of ZnO, cobalt: 0.5 to 4.0 mol% in terms of CoO and manganese: the balance of the weight percentage is as follows,

SiO is contained as a subcomponent with respect to the basic component₂: 50-300 mass ppm and CaO: 300 to 1300 ppm by mass of a catalyst,

the balance being made up of unavoidable impurities, wherein,

the amounts of Cd, Pb, Sb, As and Se in the unavoidable impurities are suppressed to less than 20 mass ppm respectively,

the MnCoZn ferrite has a wear value of less than 0.85%, a coercive force at 23 ℃ of 15A/m or less, a resistivity of 30 [ omega ] m or more, and a Curie temperature of 100 ℃ or more.

4. The method for producing a MnCoZn ferrite according to claim 3, wherein the granulation is a spray drying method.