JP2009196841A - Manganese-zinc ferrite and manganese-zinc ferrite core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manganese-zinc ferrite core having high initial magnetic permeability in a wide frequency range. <P>SOLUTION: Manganese-zinc ferrite comprises MnO, ZnO and Fe<SB>2</SB>O<SB>3</SB>as principal components, 0-0.005 wt.% SiO<SB>2</SB>, 0.02-0.2 wt.% CaO, 0.05-0.5 wt.% MoO<SB>3</SB>, 0.01-0.2 wt.% K<SB>2</SB>O, 0.005-0.1 wt.% Bi<SB>2</SB>O<SB>3</SB>, and 0.005-0.05 wt.% Nb<SB>2</SB>O<SB>5</SB>as assistant components and at least one of 0.001-0.1 wt.% B<SB>2</SB>O<SB>3</SB>and 0.001-0.1 wt.% P<SB>2</SB>O<SB>5</SB>. When a precipitation phase containing MoO<SB>3</SB>and CaO is formed on the surface of a fired body of the obtained manganese-zinc ferrite and the average crystal grain size of the resulting fired body is made to be 30-100 μm and the specific resistance of the resulting fired body is made to be 20-100 Ωcm, the manganese-zinc ferrite core having ≥12,000 initial magnetic permeability when the frequency is 1 kHz and ≥12,500 initial magnetic permeability when the frequency is 150 kHz can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high magnetic permeability MnZn ferrite and MnZn ferrite core, and more particularly to a MnZn ferrite suitable as a ferrite core for a noise filter.

  2. Description of the Related Art In recent years, technological innovations for downsizing and high performance of electronic devices have been remarkable, and there has been a demand for high performance, for example, high magnetic permeability and low loss of Mn—Zn ferrite used therewith. Especially, the ferrite core for noise filters is required to exhibit a high initial permeability over a wide frequency band.

  In order to obtain a high initial permeability, it is necessary to reduce the crystal magnetic anisotropy and increase the average crystal grain size.

In order to reduce the magnetocrystalline anisotropy, it is necessary to select a composition that minimizes the magnetocrystalline anisotropy constant at the operating environment temperature. In order to reduce the magnetocrystalline anisotropy constant, it is generally known that the ZnO content of the main component composition is the rich composition. Specifically, 52.0 mol% to 52.5 mol% of Fe ₂ O ₃ , 24.0 mol% to 28.0 mol% of MnO, and the composition in the vicinity of the balance ZnO are manufactured as a high magnetic permeability material.

In order to increase the crystal grain size, a technique of adding appropriate amounts of various grain growth additives has been used for the purpose of promoting grain growth. In addition, a method of promoting grain growth by increasing the firing holding temperature is used. Patent Document 1 proposes that Bi ₂ O ₃ is added to increase the crystal grain size.

  On the other hand, in order to obtain a high initial permeability in a wide frequency band up to a high frequency band, it is necessary to increase the specific resistance of the material.

  Eddy current loss increases with increasing frequency, and the initial permeability decreases in the high frequency band. An effective means for preventing this is to increase the resistance of the material, thereby improving the frequency characteristics of the initial permeability in the high frequency band.

  For this reason, generally, a method is used in which an additive that precipitates at the grain boundary is added to increase the specific resistance of the grain boundary and to obtain a high initial permeability in a wide frequency band.

JP 2000-327333 A

  As described above, the method using various grain growth additives is effective for increasing the crystal grain size and obtaining high initial permeability. However, the grain growth additive is also an abnormal grain growth promoting factor, and abnormal grains are easily generated. Abnormal grains increase eddy current loss and lead to a decrease in specific resistance, resulting in a decrease in initial permeability in a high frequency band.

  In addition, as described above, it is effective to increase the firing temperature in order to increase the crystal grain size. However, if the firing temperature is too high, ZnO volatilizes from the surface of the fired body, resulting in distortion due to the resulting composition gradient, leading to a decrease in initial permeability.

  As described above, in general, a material having a high initial permeability in a low frequency band has a problem that it is difficult to maintain a high initial permeability up to a high frequency band, and a high initial permeability in a wide frequency band. It is desired to obtain magnetic permeability.

  The present invention has been made to solve such problems, and a technical problem thereof is to provide a MnZn ferrite core having a high initial permeability in a wide frequency band.

As a result of various investigations, in the MnZn ferrite whose main component is MnO, ZnO, Fe ₂ O ₃ , SiO ₂ is 0 to 0.005 parts by weight and CaO is a secondary component with respect to 100 parts by weight of the main component. 0.02 part by weight to 0.2 part by weight, MoO ₃ by 0.05 part by weight to 0.5 part by weight, K ₂ O by 0.01 part by weight to 0.2 part by weight, and Bi ₂ O ₃ by 0.2 part by weight. 005 to 0.1 parts by weight, Nb ₂ O5 contains 0.005 to 0.05 parts by weight, and B ₂ O ₃ contains 0.001 to 0.1 parts by weight, P ₂ O ₅ has a precipitated phase containing MoO ₃ and CaO on the surface of the sintered body of the obtained MnZn ferrite containing at least one of 0.001 to 0.1 parts by weight, and the average crystal grain size is 30 μm or more 100 μm or less, and the specific resistance of the fired body is 20 Ωcm or more and 100 Ωcm or less. Thus, it has been found that an MnZn ferrite core having an initial permeability of 12,000 or more at a frequency of 1 kHz and an initial permeability of 12,500 or more at a frequency of 150 kHz can be obtained. Hereinafter, the “parts by weight” of the additive as a subsidiary component when the main component is 100 parts by weight will be simply expressed by “wt%”.

That is, according to the present invention, in the MnZn ferrite whose main components are MnO, ZnO and Fe ₂ O ₃ , SiO ₂ is 0 to 0.005 wt% and CaO is 0.02 wt% as subcomponents with respect to the main components. 0.2 wt%, MoO ₃ 0.05 wt% -0.5 wt%, K ₂ O 0.01 wt% -0.2 wt%, Bi ₂ O ₃ 0.005 wt% -0.1 wt%, Nb ₂ O ₅ is contained in an amount of 0.005 wt% to 0.05 wt%, B ₂ O ₃ is 0.001 wt% to 0.1 wt%, and P ₂ O ₅ is 0.001 wt% to 0.1 wt%. MnZn ferrite characterized in that it contains s is obtained.

Further, it is a MnZn ferrite core made of a sintered body of MnZn ferrite, having a precipitated phase containing MoO ₃ and CaO on the surface of the sintered body, and having an average crystal grain size of 30 μm or more and 100 μm or less. A MnZn ferrite core is obtained.

  Moreover, it is a MnZn ferrite core which consists of a sintered body of MnZn ferrite, The specific resistance of the said sintered body is 20 ohm-cm or more and 100 ohm-cm or less, The MnZn ferrite core characterized by the above-mentioned is obtained.

  The MnZn ferrite core is a sintered body of MnZn ferrite, wherein the sintered body has an initial permeability of 12,000 or more at a frequency of 1 kHz and an initial permeability of 12,500 or more at a frequency of 150 kHz. A MnZn ferrite core characterized by the following can be obtained.

According to the product of the present invention, SiO ₂ added to MnZn ferrite is 0 to 0.005 wt%, CaO is 0.02 wt% to 0.2 wt%, and Nb ₂ O ₅ is 0.005 wt% to 0.05 wt%. As a result, a high-resistance grain boundary layer can be formed without inhibiting crystal grain growth, and eddy current loss can be reduced. As a result, a MnZn ferrite core having a high initial permeability even in a high frequency band can be obtained.

Further, the _{MoO 3 0.05wt% ~0.5wt%, K} 2 O and 0.01~0.2wt%, Bi ₂ O ₃ to 0.005wt% ~0.1wt%, a B ₂ O ₃ 0. By using MnZn ferrite containing at least one kind of 001 wt% to 0.1 wt% and P ₂ O ₅ of 0.001 wt% to 0.1 wt%, at a firing temperature at which ZnO does not volatilize from the surface of the fired body. Since the crystal grain size can be increased, a MnZn ferrite core having a high initial permeability can be obtained.

Bi ₂ O ₃ , B ₂ O ₃ , and P ₂ O ₅ are additives for generating abnormal grains as well as crystal grain growth additives. MoO ₃ and K ₂ O ₃ have a sizing action, and have the effect of enlarging crystal grains while suppressing abnormal grain growth caused by Bi ₂ O ₃ , B ₂ O ₃ , and P ₂ O ₅ .

Further, the obtained sintered body of MnZn ferrite has a precipitated phase containing MoO ₃ and CaO on its surface, the average crystal grain size is 30 μm or more and 100 μm or less, and the specific resistance of the sintered body is 20 Ωcm or more and 100 Ωcm or less. Therefore, an MnZn ferrite core having an initial permeability of 12000 or more at a frequency of 1 kHz and an initial permeability of 12500 or more at a frequency of 150 kHz can be obtained. Since the above-mentioned product of the present invention is a MnZn ferrite core having a high initial permeability in a wide frequency band, it provides a high-performance noise filter that is small and exhibits high impedance characteristics when used as a ferrite core for a noise filter. it can.

As a result of various investigations, in the MnZn ferrite whose main component is MnO, ZnO, Fe ₂ O ₃ , the outer frame with respect to the main component, SiO ₂ is 0 to 0.005 wt% as a secondary component, and CaO is 0.02wt% ~0.2wt%, MoO ₃ is 0.05wt% ~0.5wt%, K ₂ O is _{0.01wt% ~0.2wt%, Bi 2 O} 3 is 0.005wt% ~0.1wt %, Nb ₂ O ₅ is 0.005 wt% to 0.05 wt%, B ₂ O ₃ is 0.001 wt% to 0.1 wt%, and P ₂ O ₅ is 0.001 wt% to 0.1 wt%. The MnZn ferrite containing at least one kind has a precipitated phase containing MoO ₃ and CaO on the surface of the fired body of the obtained MnZn ferrite, the average crystal grain size is 30 μm or more and 100 μm or less, and the specific resistance of the fired body is 20Ωcm or more, 100Ωcm With lower frequency initial permeability at 1kHz is over 12,000, the initial permeability at a frequency 150kHz has been found that the resulting MnZn ferrite core is 12,500 or more.

The reason why SiO ₂ is set to 0 to 0.005 wt% as a subcomponent is that when it is 0.005 wt% or more, crystal grain growth is inhibited and the initial permeability is remarkably lowered.

  The reason why the CaO content is 0.02 wt% to 0.2 wt% is 0.02 wt% or less, since the grain boundary layer formation is insufficient, the specific resistance is lowered, and the eddy current loss is increased to increase the high frequency band. This is because the initial magnetic permeability at the time is reduced and a high initial magnetic permeability cannot be obtained in a wide frequency band. Moreover, it is because excess CaO will inhibit a crystal grain growth and it cannot obtain sufficient initial permeability as it is 0.2 wt% or more.

The reason why Nb ₂ O _{5 is set} to 0.005 wt% to 0.05 wt% is that when Nb ₂ O _{5 is set} to 0.005 wt% or less, the grain boundary layer is not sufficiently formed, so that the specific resistance is lowered and the eddy current is decreased. This is because the initial permeability in the high frequency band is reduced due to the increase in loss, and a high initial permeability cannot be obtained in a wide frequency band. Further, if it is 0.05 wt% or more, Nb ₂ O ₅ inhibits crystal grain growth, and sufficient initial permeability cannot be obtained.

The reason why MoO ₃ is 0.05 wt% to 0.5 wt% and K ₂ O is 0.01 wt% to 0.2 wt% is that MoO ₃ is 0.05 wt% or less and K ₂ O is 0.01 wt% or less. If present, the grain size adjusting action of MoO ₃ and K ₂ O is inhibited, and abnormal grain growth caused by Bi ₂ O ₃ , B ₂ O, and P ₂ O ₅ becomes remarkable, leading to a decrease in initial permeability and a decrease in specific resistance. It is. If MoO ₃ is 0.5 wt% or more and K ₂ O is 0.2 wt% or more, the grain growth effect brought about by Bi ₂ O ₃ , B ₂ O, and P ₂ O ₅ cannot be obtained. This is to reduce the magnetic susceptibility.

Bi ₂ O ₃ is 0.005 wt% to 0.1 wt%, B ₂ O ₃ is 0.001 wt% to 0.1 wt%, and P ₂ O ₅ is 0.001 wt% to 0.1 wt%. Crystals produced by Bi ₂ O ₃ , B ₂ O, and P ₂ O ₅ when ₂ O ₃ is 0.005 wt% or less, B ₂ O ₃ is 0.001 wt% or less, and P ₂ O ₅ is 0.001 wt% or less. This is because the grain growth effect cannot be obtained, and the initial permeability is reduced. Further, when Bi ₂ O ₃ is 0.1 wt% or more, B ₂ O ₃ is 0.1 wt% or more, and P ₂ O ₅ is 0.1 wt% or more, Bi ₂ O ₃ , B ₂ O, P ₂ O _This is because the abnormal grain growth brought about by ₅ becomes remarkable, and the initial permeability is reduced and the specific resistance is reduced.

  In addition, in the obtained MnZn ferrite, the average grain size of the fired body was set to 30 μm or more and 100 μm or less because when the average crystal grain size is 30 μm or less, the crystal grain size is small and sufficient initial permeability can be obtained. It is because it is not possible. In addition, when the average crystal grain size is 100 μm or more, the grain boundary layer formation is insufficient and the specific resistance is lowered, and the increase in eddy current loss reduces the initial permeability in the high frequency band. This is because high initial permeability cannot be obtained.

  The specific resistance of the fired body is set to 20 Ωcm or more and 100 Ωcm or less. When the specific resistance is 20 Ωcm or less, the initial permeability in the high frequency band is reduced due to the increase in eddy current loss, and the high initial permeability in a wide frequency band. This is because the magnetic susceptibility cannot be obtained. The reason why the specific resistance is set to 100 Ωcm or less is that when it is 100 Ωcm or more, the crystal grain size is small and sufficient initial permeability cannot be obtained.

Although it is unknown in detail about the precipitation phase containing MoO ₃ and CaO present on the surface of the sintered body of MnZn ferrite, MoO ₃ is a volatile additive and is a eutectic mixture between CaO as a grain boundary component and the surface of the sintered body. It is presumed that In the experimental results of the present inventors, in the case of the invention product showing a high initial permeability, a precipitated phase containing MoO ₃ and CaO is found on the surface. It is desirable that a precipitated phase containing MoO ₃ and CaO exists on the surface of the body.

Example 1
As an invention, 52.5 mol% Fe ₂ O ₃ , 22.5 mol% ZnO, and the rest MnO, with respect to these main components, 0 to 0.006 wt% SiO ₂ as an outer frame and subcomponent 0.01 wt% to 0.25 wt% CaO, 0.004 wt% to 0.06 wt% Nb ₂ O ₅ , 0.04 wt% to 0.6 wt% MoO ₃ , 0.005 wt% to 0.3 wt% Of K ₂ O, 0.004 wt% to 0.15 wt% Bi ₂ O ₃ , and 0 to 0.11 wt% B ₂ O ₃ and 0 to 0.11 wt% P ₂ O ₅ are added. And mixed for 2 hours using an attritor.

  After mixing, the mixture was granulated with a spray dryer and pre-fired in the air at 850 ° C. for 2 hours. The pre-baked powder obtained was pulverized with an attritor. After pulverization, it was granulated with a spray dryer, pressed into a toroidal shape of φ25 mm-φ15 mm-12 mm, and fired at 1350 ° C.

As a conventional product, the main component of 52.5 mol% Fe ₂ O ₃ , 22.5 mol% ZnO, and the balance MnO, and the main component of these, the outer frame and 0.015 wt% SiO as an accessory component ₂ , 0.015 wt% CaO and 0.015 wt% Bi ₂ O ₃ were added and mixed for 2 hours using an attritor. After mixing, the mixture was granulated with a spray dryer and pre-fired in the air at 850 ° C. for 2 hours. The pre-baked powder obtained was pulverized with an attritor. After pulverization, it was granulated with a spray dryer, pressed into a toroidal shape of φ25 mm-φ15 mm-12 mm, and fired at 1350 ° C.

  For magnetic properties, the obtained MnZn ferrite fired body was wound with 10 turns and the initial permeability was measured. The specific resistance was measured by applying a Ga-In paste on the upper and lower surfaces of the sample. Moreover, the analysis of the surface precipitation phase was performed by SEM-EDX and X-ray diffraction.

Table 1 shows the average crystals of conventional products and invention products with different amounts of addition of SiO ₂ , CaO, Nb ₂ O ₅ , MoO ₃ , K ₂ O, Bi ₂ O ₃ , B ₂ O ₃ , and P ₂ O _5. Particle diameter, specific resistance, initial permeability at frequencies of 1 kHz and 150 kHz (indicated by μ in the table) are shown. In Table 1, the amount of addition was within the scope of the present invention, and the outside of the range was the comparative product.

As shown in Table 1, SiO ₂ is 0 to 0.005 wt%, CaO is 0.02 wt% to 0.2 wt%, MoO ₃ is 0.05 wt% to 0.5 wt%, and K ₂ O is 0.01 wt%. 0.2 wt%, Bi ₂ O ₃ is 0.005 wt% to 0.1 wt%, Nb ₂ O ₅ is 0.005 wt% to 0.05 wt%, and B ₂ O ₃ is 0.001 wt% to 0 wt%. 1 wt%, P ₂ O ₅ is an invention containing at least one of 0.001 wt% to 0.1 wt%, the sintered body has an average crystal grain size of 30 μm to 100 μm, a specific resistance of 20 Ωcm to 100 Ωcm, a frequency It can be seen that the initial permeability at 1 kHz is 12,000 or more, and the initial permeability at a frequency of 150 kHz is 12,500 or more. Moreover, as a result of performing compositional analysis on the surface of the fired body by SEM-EDX analysis and further performing X-ray diffraction, it was confirmed that the precipitated phases of MoO ₃ and CaO were present in all invention products.

  FIG. 1 shows the frequency characteristics of the complex magnetic permeability μ ′ and μ ″ of the inventive product 7 and the conventional product. The inventive product has a complex magnetic permeability μ ′ in the low frequency band to the high frequency band as compared with the conventional product. , Μ ″ both showed high values, and it was confirmed that a high initial permeability was obtained. That is, according to the MnZn ferrite of the present invention, it was found that a ferrite core having high initial permeability and high impedance characteristics over a wide frequency band was obtained, which was very useful as a noise filter material.

(Example 2)
As an invention product, 52.5 mol% Fe ₂ O ₃ , 22.5 mol% ZnO, and the balance MnO with respect to these main components, 0.001 wt% SiO ₂ , 0 0.07 wt% CaO, 0.01 wt% Nb ₂ O ₅ , 0.2 wt% MoO ₃ , 0.05 wt% K ₂ O, 0.05 wt% Bi ₂ O _3, and 025 wt% B ₂ O ₃ and 0.02 wt% P ₂ O ₅ were added and mixed for 2 hours using an attritor.

  After mixing, the mixture was granulated with a spray dryer and pre-fired in the air at 850 ° C. for 2 hours. The pre-baked powder obtained was pulverized with an attritor. After pulverization, it was granulated with a spray dryer, pressed into a toroidal shape of φ25 mm-φ15 mm-12 mm, and fired at 1250 ° C. to 1450 ° C.

As a conventional product, the main component of 52.5 mol% Fe ₂ O ₃ , 22.5 mol% ZnO, and the balance MnO, and the main component of these, the outer frame and 0.015 wt% SiO as an accessory component ₂ , 0.015 wt% CaO and 0.015 wt% Bi ₂ O ₃ were added and mixed for 2 hours using an attritor. After mixing, the mixture was granulated with a spray dryer and pre-fired in the air at 850 ° C. for 2 hours. The pre-baked powder obtained was pulverized with an attritor. After pulverization, it was granulated with a spray dryer, pressed into a toroidal shape of φ25 mm-φ15 mm-12 mm, and fired at 1350 ° C.

  As for the magnetic properties, the obtained sintered body was wound with 10 turns, and the initial permeability was measured. The specific resistance was measured by applying a Ga-In paste on the upper and lower surfaces of the sample. Moreover, the analysis of the surface precipitation phase was performed by SEM-EDX and X-ray diffraction.

  Table 2 shows the average magnetic grain size, specific resistance, initial permeability at frequencies of 1 kHz and 150 kHz (indicated by μ in the table) for the conventional product and the invention product with different firing temperatures.

  As shown in Table 2, even when the firing temperature is changed, in the case of the normal firing temperature, the initial crystallite size of the sintered body is 30 μm to 100 μm, the specific resistance is 20 Ωcm to 100 Ωcm, and the frequency is 1 kHz. It was confirmed that the initial permeability when the magnetic permeability was 12,000 or higher and the frequency was 150 kHz was 12,500 or higher. Further, it was found that when the average crystal grain size is small after firing at a low temperature, a high initial permeability cannot be obtained. However, according to the MnZn ferrite of the present invention, since the crystal grain size can be increased at a normal firing temperature at which ZnO does not volatilize from the surface of the fired body, a MnZn ferrite core having a high initial permeability can be obtained. I understood.

Moreover, as a result of performing compositional analysis on the surface of the fired body by SEM-EDX analysis and further performing X-ray diffraction, it was confirmed that MoO ₃ and CaO precipitated phases were present in all invention products.

  From the above results, it was confirmed that the MnZn ferrite core of the present invention has a high initial permeability in a wide frequency band as compared with the conventional product. Further, by adopting the MnZn ferrite of the present invention, it is possible to provide a high performance ferrite core for noise filters having high impedance characteristics.

FIG. 6 is a frequency characteristic diagram of complex permeability μ ′, μ ″ of Invention 7 and a conventional product.

Claims (4)

MnZn ferrite whose main component is MnO, ZnO, Fe ₂ O _3, with respect to 100 parts by weight of the main component, 0 to 0.005 parts by weight of SiO _{2 and} 0.02 parts by weight of CaO as subcomponents 0.2 parts by weight, MoO ₃ is 0.05 parts by weight to 0.5 parts by weight, K ₂ O is 0.01 parts by weight to 0.2 parts by weight, and Bi ₂ O ₃ is 0.005 parts by weight to 0. 1 part by weight, Nb ₂ O ₅ from 0.005 part by weight to 0.05 part by weight, B ₂ O ₃ from 0.001 part by weight to 0.1 part by weight, and P ₂ O ₅ by 0.001 MnZn ferrite characterized by containing at least one of parts by weight to 0.1 part by weight. A MnZn ferrite core comprising the sintered body of MnZn ferrite according to claim 1, wherein the sintered body has a precipitated phase containing MoO ₃ and CaO on the surface thereof, and an average crystal grain size is 30 μm or more and 100 μm or less. The MnZn ferrite core characterized by the above-mentioned.   2. A MnZn ferrite core comprising the fired body of MnZn ferrite according to claim 1, wherein the fired body has a specific resistance of 20 [Omega] cm to 100 [Omega] cm.   A MnZn ferrite core comprising the sintered body of MnZn ferrite according to claim 1, wherein the sintered body has an initial permeability of 12,000 or more at a frequency of 1 kHz and an initial permeability of 12,500 or more at a frequency of 150 kHz. A MnZn ferrite core, characterized in that

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