Mn-Zn ferrite and method for producing the same

Abstract

To provide Mn-Zn ferrite having high impedance in a wide frequency band and a method for producing the same.SOLUTION: The Mn-Zn ferrite comprises a principal component consisting of 48.0-51.0 mol% of Fe2O3, 20.0-25.0 mol% of ZnO, and the remainder of MnO in 100 mol%, a CaO of 0.015 pt.mass or less, and a SiO2 of 0.005 pt.mass or less based on 100 pts.mass of the principal component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to Mn-Zn ferrite and a method for producing the same. [Background technology]

[0002] Ferrite materials have high electrical resistance and suppress eddy current losses even with high-frequency currents, making them widely used as core materials for transformers and coils, as well as noise filters. Ni-Zn ferrite and Mn-Zn ferrite are the most widely known types of ferrite materials.

[0003] For example, noise filters use ferrite materials that have high impedance in the noise frequency band to block noise. Currently, when comparing Mn-Zn ferrite and Ni-Zn ferrite, Mn-Zn ferrite tends to have lower impedance at high frequencies, while Ni-Zn ferrite tends to have lower impedance at low frequencies, and they are used differently depending on the application.

[0004] Patent Document 1 discloses a specific Mn-Co-Zn ferrite to which a specific amount of SrO and / or BaO is added, as a method for improving the normalization impedance in the high-frequency range while maintaining a high normalization impedance in the low-frequency range.

[0005] Furthermore, Patent Document 2 discloses a method for promoting grain growth by adding specific by-components to Mn-Zn ferrite having a high initial permeability of 100 or more at 10 MHz. However, this method is prone to abnormal grain growth and the resulting generation of pores, and the movement of magnetic domain walls is suppressed by the pores generated within the crystal grains, which can suppress the improvement of relative permeability. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-213531 [Patent Document 2] Japanese Patent Publication No. 2001-220221 [Overview of the project] [Problems that the invention aims to solve]

[0007] There is a need for noise filters that can be used across a wide frequency band, and therefore, ferrite materials that have high impedance characteristics across a wide frequency band, from low to high frequencies, are required. [Means for solving the problem]

[0008] This disclosure has been made in view of the above circumstances and provides a Mn-Zn ferrite having high impedance over a wide frequency band, and a method for manufacturing the same.

[0009] The Mn-Zn ferrite relating to this disclosure has as its main component 48.0-51.0 mol% Fe2O3, 20.0-25.0 mol% ZnO, and the remainder being MnO, out of 100 mol%. The above-mentioned main component contains 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2 per 100 parts by mass of the main component.

[0010] One embodiment of the above Mn-Zn ferrite has an average crystal grain size of 12 μm or more.

[0011] One embodiment of the above-mentioned Mn-Zn ferrite has a real part μ' of the complex relative permeability at 10 kHz of 6200 or more.

[0012] One embodiment of the above Mn-Zn ferrite has a real part μ' of the complex relative permeability at 10 MHz of 200 or more.

[0013] One embodiment of the above-mentioned Mn-Zn ferrite has an impedance of 1100Ω or more at 1MHz.

[0014] One embodiment of the above-mentioned Mn-Zn ferrite has an impedance of 1850Ω or more at 10MHz.

[0015] One embodiment of the above Mn-Zn ferrite has a Curie temperature Tc of 100°C or higher.

[0016] One embodiment of the above Mn-Zn ferrite is such that the main component further contains 0.2 to 2 mol% of CoO.

[0017] The Mn-Zn ferrite according to the present disclosure has a real part μ' of the complex relative permeability at 10 kHz of 6200 or more and a real part μ' of the complex relative permeability at 10 MHz of 200 or more.

[0018] The manufacturing method of the Mn-Zn ferrite according to the present disclosure In 100 mol%, a main component composed of 48.0 to 51.0 mol% of Fe2O3, 20.0 to 25.0 mol% of ZnO, and the balance being MnO, and raw materials are mixed so as to contain 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2 with respect to 100 parts by mass of the main component, and a step of preparing a mixed powder A step of crushing the mixed powder <00…​​​​​​​​​​​​​​​​​​​​​​​According to the present invention, it is possible to provide a Mn-Zn ferrite having high impedance over a wide frequency band, and a method for manufacturing the same. [Modes for carrying out the invention]

[0024] The following describes Mn-Zn ferrite and its manufacturing method. Unless otherwise specified, the "~" symbol indicating a numerical range includes both the lower and upper limits.

[0025] [Mn-Zn ferrite] The Mn-Zn ferrite disclosed herein has as its main component 48.0-51.0 mol% Fe2O3, 20.0-25.0 mol% ZnO, and the remainder being MnO, in 100 mol%. The present invention is characterized by containing 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2 per 100 parts by mass of the main component.

[0026] This Mn-Zn ferrite is based on a Mn-Zn ferrite with high μ' in the low-frequency range. Furthermore, by lowering the proportion of Fe2O3 in the main component, the resistivity is increased, the dielectric constant ε is reduced, and μ' is improved in the high-frequency range. As a result, it becomes a Mn-Zn ferrite with high impedance characteristics over a wide frequency range, for example, 1kHz to 1GHz, and especially 10kHz to 10MHz.

[0027] The complex relative permeability μ is expressed by the following equation (1). Equation (1): μ = μ'-jμ” Here, μ' is the real part (inductance component) of the complex relative permeability, μ'' is the imaginary part (resistive component) of the complex relative permeability, and j is the imaginary unit.

[0028] The impedance Z (Ω) is expressed by the following equation (2). Equation (2): Z = (R 2 +X 2 ) 1 / 2 Here, R and X are expressed by equations (3) and (4), respectively.

[0029] Equation (3): R = (μ”·2πfn 2 A e μ 0 ) / L e Equation (4): X = (μ’·2πfn 2 A e μ 0 ) / L e Here, f is the frequency (kHz), n is the number of turns of the coil, A e is the effective cross-sectional area of the ferrite (mm 2 ), L e is the magnetic path length of the ferrite (mm), μ 0 is the permeability of free space (4π×10 -7 (H / m)).

[0030] In addition, in the present disclosure, the impedance Z is the value measured using an annular core with an outer diameter of 25 mm, an inner diameter of 10 mm, a thickness of 5 mm, and a rectangular cross-sectional shape (7.5 mm×5 mm) for the ferrite material to be measured, and with the number of turns of the coil being 10 times.

[0031] This Mn-Zn based ferrite has high μ’ in a wide frequency band, and thus has high impedance characteristics in a wide frequency band.

[0032] Next, the composition of this Mn-Zn based ferrite will be described. This Mn-Zn based ferrite has Fe2O3, ZnO, and MnO as main components, and may further contain CoO. The ratio of the main components is preferably such that, in 100 mol% of the main components, Fe2O3 is 48.0 to 51.0 mol%, ZnO is 20.0 to 25.0 mol%, and when CoO is included, the CoO is 0.2 to 2 mol%, and the balance is MnO.

[0033] By setting Fe2O3 to 51.0 mol% or less, preferably 50.0 mol% or less, μ’ in the high frequency band is improved. Also, by setting Fe2Oз to 48.0 mol% or more, preferably 49.0 mol% or more, μ’ in the low frequency band is improved.

[0034] By setting the ZnO content to 25.0 mol% or less, preferably 24.0 mol% or less, the Curie temperature Tc can be increased. Furthermore, by setting the ZnO content to 20.0 mol% or more, preferably 22.0 mol% or more, μ' in the low-frequency band is improved.

[0035] It may also contain CoO as the main component. If CoO is included, 0.2 to 2 mol% is preferred, and 1.0 to 1.5 mol% is more preferred. Including CoO within the above range improves μ' in the low-frequency band.

[0036] Furthermore, this Mn-Zn ferrite contains, as minor components, 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2, per 100 parts by mass of the main component.

[0037] The inclusion of CaO allows for the formation of grain boundaries with high resistivity, suppressing the generation of eddy currents in the high-frequency range and improving μ' in the high-frequency range. To suppress the decrease in μ' in the low-frequency range, the CaO content is preferably 0.015 parts by mass or less, and more preferably 0.012 parts by mass or less, per 100 parts by mass of the main component. To obtain high resistivity, the CaO content is preferably 0.001 parts by mass or more, and more preferably 0.002 parts by mass or more.

[0038] The inclusion of SiO2 allows for the formation of grain boundaries with high resistivity, improving μ' in the high-frequency range. To suppress the decrease in μ' in the low-frequency range, the SiO2 content is preferably 0.005 parts by mass or less, and more preferably 0.004 parts by mass or less, per 100 parts by mass of the main component. To obtain high resistivity, the SiO2 content is preferably 0.0001 parts by mass or more, and more preferably 0.0005 parts by mass or more.

[0039] This Mn-Zn ferrite may contain other components to the extent that it achieves the effects of the present invention. Other components include other metal oxides added as needed, and elements that are inevitably present. Other metal oxides include, for example, ZrO2, TiO2, Ta2O5, Nb2O5, Bi2O3, and MoO3. Elements that are inevitably present include C (carbon atoms), P (phosphorus atoms), and B (boron atoms). The total content of other components is preferably 0.1 parts by mass or less, more preferably 0.01 parts by mass or less, and even more preferably 0.001 parts by mass or less, per 100 parts by mass of the main component.

[0040] The average grain size of this Mn-Zn ferrite is preferably 12 μm or more, more preferably 14 μm or more, and even more preferably 15 μm or more. By setting the average grain size to 12 μm or more, the μ' can be improved, especially in the low-frequency band. On the other hand, the average grain size is preferably 100 μm or less, more preferably 80 μm or less, and more preferably 50 μm or less. Furthermore, grains having a grain size of 100 μm or more preferably account for 1% or less of the total grains, and more preferably 0.1% or less. The grain size can be determined by mirror-polishing the ferrite sample to be measured, dissolving the grain boundary phase by etching, and then analyzing the image obtained by microscopic observation. The grain size is determined using the longest diameter, and the average grain size is the average value of the grain sizes of 100 grains.

[0041] The real part μ' of the complex relative permeability of this Mn-Zn ferrite at 10 kHz can be 6200 or higher, and is preferably 6500 or higher. The real part μ' of the complex relative permeability of this Mn-Zn ferrite at 10 MHz can be 200 or more, preferably 240 or more, and more preferably 250 or more.

[0042] This Mn-Zn ferrite can achieve an absolute impedance of 1100Ω or more at 1MHz, preferably 1200Ω or more, and more preferably 1500Ω or more. This Mn-Zn ferrite can achieve an absolute impedance of 1850Ω or more at 10MHz, preferably 2000Ω or more, and more preferably 2200Ω or more. The impedance mentioned above can be achieved, for example, by using this Mn-Zn ferrite as an annular core with an outer diameter of 25 mm, an inner diameter of 10 mm, a thickness of 5 mm, and a rectangular cross-sectional shape (7.5 mm x 5 mm). However, it is not limited to this shape, and other shapes may be used as a reference.

[0043] This Mn-Zn ferrite can be used suitably even in high-temperature environments, and therefore, a Curie temperature Tc of 100°C or higher is preferable, 110°C or higher is more preferable, and 115°C or higher is even preferable. The Curie temperature is the temperature at which a ferromagnetic material changes to a paramagnetic material.

[0044] Furthermore, this disclosure can provide a Mn-Zn ferrite in which the real part μ' of the complex relative permeability at 10 kHz is 6200 or more, and the real part μ' of the complex relative permeability at 10 MHz is 200 or more.

[0045] Because this Mn-Zn ferrite has high impedance over a wide frequency range, it can be suitably used as an electromagnetic noise suppression component, such as a noise filter, that can be used over a wide frequency range.

[0046] [Manufacturing method for Mn-Zn ferrite] Next, an embodiment of the method for manufacturing Mn-Zn ferrite (hereinafter also referred to as "this manufacturing method") will be described. This manufacturing method is suitable for manufacturing the above-mentioned Mn-Zn ferrite. A process to prepare a mixed powder by mixing raw materials such that the main component consists of 48.0-51.0 mol% Fe2O3, 20.0-25.0 mol% ZnO, and the remainder being MnO in 100 mol%, and that the mixture contains 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2 per 100 parts by mass of the main component, The process of crushing the aforementioned mixed powder, The process includes a step of sintering the powder after crushing, and may further include other steps.

[0047] In the process of preparing the above mixed powder, as an example, first, the main components are mixed so that the main components after sintering have the same composition as the Mn-Zn ferrite. The form of the main components before mixing is not particularly limited, but it is preferable to use a powder form because it is easy to handle and can be mixed uniformly. The raw material powders of the main components are mixed and crushed as necessary to make a mixed powder. The mixing and crushing method can be appropriately selected from known methods. Specifically, examples include attritors and bead mills. The particle size of the mixed powder is adjusted so that the median diameter d50 is preferably 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.6 μm or less, from the viewpoint of uniformity. The lower limit of d50 is not particularly limited, but it is usually 0.1 μm or more, and 0.2 μm or more is preferable. The particle size distribution of the mixed powder and other powders can be measured with a particle size distribution analyzer, and the particle size at which the cumulative frequency is 50% is defined as d50. If necessary, a drying and granulation process may be carried out on the mixed powder of the above main components. In the drying and granulation process, for example, granules can be obtained by adding 0.5 to 1 part by mass of a binder such as polyvinyl alcohol to the mixed powder, when the total mass of the mixed powder is 100 parts by mass, and spraying it using a spray dryer or the like. The obtained granules may be calcined to a calcined product by calcining at 750°C in an air atmosphere for about 1 hour (calcination process).

[0048] Next, the auxiliary components are added to the mixed powder so that the auxiliary components after sintering have the same composition as the Mn-Zn ferrite. The form of the auxiliary components before addition is not particularly limited, but it is preferable that they be particulate for ease of handling and uniform mixing. In particular, from the viewpoint of uniformity, the median diameter d50 is preferably 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.6 μm or less. The lower limit of d50 is not particularly limited, but it is usually 0.1 μm or more, and 0.2 μm or more is preferable.

[0049] After adding the auxiliary components, the resulting mixed powder is crushed to obtain crushed powder. Specifically, in the crushing process, it is preferable that the median diameter D50 of the particle size after crushing be 0.8 μm or less, and more preferably 0.1 μm or more and 0.7 μm or less.

[0050] A granulation process may be carried out on the powder after crushing. For example, granules can be obtained by adding 0.5 to 1.0 parts by mass of a binder such as polyvinyl alcohol to the crushed powder, assuming a total mass of 100 parts by mass of the crushed powder, and spraying it with a spray dryer or the like.

[0051] Next, the obtained granules are molded into a predetermined shape. The predetermined shape can be designed according to the intended use. For example, they may be molded into an annular shape with an outer diameter of 25 mm, an inner diameter of 10 mm, and a thickness of 5 mm.

[0052] A sintered body (this Mn-Zn ferrite) is obtained by firing the molded granules. The firing temperature can be, for example, around 1300°C. The firing time can be, for example, 1 to 24 hours, and should be adjusted to achieve the desired average crystal grain size. In this manufacturing method, it is preferable to perform sintering in an atmosphere with an oxygen concentration of 5% or higher. Sintering in an atmosphere with an oxygen concentration of 5% or higher suppresses the volatilization of Zn on the surface of the raw material powder, thereby suppressing the decrease in μ' in the low frequency band, and also promotes oxidation of the surface of the raw material powder, thereby increasing the resistivity of the sintered body and increasing μ' in the high frequency band. The oxygen concentration is preferably 8% or higher, and more preferably 10% or higher.

[0053] According to the above manufacturing method, Mn-Zn ferrite having high impedance over a wide frequency band can be suitably produced. [Examples]

[0054] The present invention will be specifically described below with reference to examples and comparative examples. However, this description is not intended to limit the present invention.

[0055] [Example 1] Each raw material powder was weighed and mixed so that the main component composition after sintering was 52.5 mol% Fe2O, 18.0 mol% ZnO, and 29.5 mol% MnO, and then crushed in an attritor. The median diameter d50 of the mixed powder was 0.8 μm. Next, 0.5 parts by mass of polyvinyl alcohol was added to 100 parts by mass of the total mass of the above mixture, and granules were obtained by spraying with a spray dryer. Next, the granules were calcined in an air atmosphere at 750°C for 1 hour to obtain a calcined product. Next, SiO2 and Ca(OH)2 were added to 100 parts by mass of the main component, in an order of 0.003 parts by mass of SiO2 and 0.010 parts by mass of CaO. Note that the SiO2 and Ca(OH)2 particles used each had an average particle diameter of 0.1 μm or larger. Next, in the crushing step, the above mixed powder was crushed in a crusher so that the median diameter d50 of the particle size after crushing was 0.7 μm to obtain crushed powder. Next, in the drying and granulation step, 1 part by mass of polyvinyl alcohol was added to the crushed material, assuming a total mass of 100 parts by mass of the crushed material, and granules were obtained by spraying with a spray dryer. Next, these granules were formed into rings with an outer diameter of 25 mm, an inner diameter of 10 mm, and a thickness of 5 mm, and fired at 1300°C for 10 hours in an atmosphere with an oxygen concentration of 10% to obtain a sintered body (ferrite).

[0056] <Measurement> (1) Impedance, complex relative permeability The sintered body obtained in Example 1 was wound with a winding 10 times, and the impedance and inductance were measured using an impedance analyzer while changing the frequency, and the complex relative permeability was calculated. The measurement results at 25°C are shown in Table 1. (2) Curie temperature The sintered body obtained in Example 1 was wound with a winding 10 times, and the inductance was measured in the temperature range of 20°C to 250°C. The relative initial permeability at each temperature was calculated. Then, from the relationship between the obtained temperature and relative initial permeability, the temperature at which the relative initial permeability was 1 was defined as the Curie temperature. (3) Average grain size The surface of the sintered body obtained in Example 1 was mirror-polished, the grain boundary phase was dissolved by etching, and the grain size of 100 crystal grains was determined from the images observed under a microscope using image analysis, and the average value was calculated. The results are shown in Table 1.

[0057] [Examples 2-33] In Example 1, a sintered body was manufactured in the same manner as in Example 1, except that the composition, the particle size of the mixed powder in the manufacturing process, the particle size of the crushed powder, and the oxygen concentration during firing were changed as shown in Table 1. In addition, impedance, complex relative permeability, Curie temperature, and average grain size were measured, similar to Example 1. The results are shown in Table 1.

[0058] [Table 1]

[0059] The Mn-Zn ferrites in Examples 1 and 4, which contain a large amount of Fe2O3, exhibit low μ' values ​​in the high-frequency range. The Ni-Zn ferrite in Example 2 exhibits low μ' values ​​in the low-frequency range. The Mn-Zn ferrite in Example 9, which contains little ZnO, exhibits low μ' values ​​in the low-frequency range. The Mn-Zn ferrite in Example 10, which contains a large amount of ZnO, exhibits good μ' values ​​across a wide frequency range, but its Curie temperature is lower. The Mn-Zn ferrites in Examples 17-18 and 21-22, which contain a large amount of the minor components CaO or SiO2, exhibit low μ' values ​​in the low-frequency range. In contrast, the Mn-Zn ferrites of Examples 5-8, 11-16, 19-20, and 23-33 (Examples), which consist of a main component of 48.0-51.0 mol% Fe2O3, 20.0-25.0 mol% ZnO, and the remainder MnO, and containing 0.015 parts by mass or less of CaO and 0.005 parts by mass or less of SiO2 per 100 parts by mass of the main component, achieved a μ' of 6200 or more at 10 kHz and 200 or more at 10 MHz, demonstrating high μ' over a wide frequency band. Furthermore, as a result of having high μ' over a wide frequency band, it was shown that high impedance characteristics were obtained over a wide frequency band, with an impedance of 1100 Ω or more at 1 MHz and 1850 Ω or more at 10 MHz. In addition, it was shown that the Mn-Zn ferrites of the Examples have a high Curie temperature, with a Curie temperature Tc of 100°C or higher. Next, we will compare the examples within the given context. From a comparison of Examples 26, 27, and 32, it was observed that the larger the average grain size of the crystal grains, the higher the μ' in the low-frequency band tended to be. Furthermore, from a comparison of Examples 28-30 and 32, it was observed that the smaller the median system of the mixed powder raw materials, the higher the μ' of the resulting Mn-Zn ferrite tended to be. Additionally, from a comparison of Examples 31-33, it was observed that the higher the oxygen concentration during firing, the higher the μ' of the resulting Mn-Zn ferrite tended to be.

Claims

1. In 100 mol%, Fe ２ O ３ The main component consists of 48.0-51.0 mol% of ZnO, 20.0-25.0 mol%, 0.2-2 mol% of CoO, and the remainder being MnO. With respect to 100 parts by mass of the main component, 0.008 parts by mass to 0.015 parts by mass of CaO and 0.002 parts by mass to 0.005 parts by mass of SiO ２ and Mn-Zn ferrite, in which the total content of other components is 0.01 parts by mass or less per 100 parts by mass of the main component.

2. The Mn-Zn ferrite according to claim 1, wherein the average crystal grain size is 12 μm or more.

3. The Mn-Zn ferrite according to claim 1 or 2, wherein the real part μ' of the complex relative permeability at 10 kHz is 6200 or more.

4. The Mn-Zn ferrite according to claim 3, wherein the real part μ' of the complex relative permeability at 10 MHz is 200 or more.

5. The Mn-Zn ferrite according to claim 1 or 2, wherein the impedance at 1 MHz is 1100 Ω or more.

6. The Mn-Zn ferrite according to claim 5, wherein the impedance at 10 MHz is 1850 Ω or more.

7. The Mn-Zn ferrite according to claim 1 or 2, wherein the Curie temperature Tc is 100°C or higher.

8. The real part μ' of the complex relative permeability at 10 kHz is 6200 or more. A Mn-Zn ferrite having a real part μ' of the complex relative permeability at 10 MHz of 200 or more.

9. A method for producing Mn-Zn ferrite according to claim 1 or 8, In 100 mol%, Fe ２ O ３ The main component consists of 48.0 to 51.0 mol% of phosphate, 20.0 to 25.0 mol% of ZnO, 0.2 to 2 mol% of CoO, and the remainder being MnO. Per 100 parts by mass of the main component, it contains 0.008 to 0.015 parts by mass of CaO and 0.002 to 0.005 parts by mass of SiO. ２ The process involves mixing the raw materials, including the main component, such that the total content of other components is 0.01 parts by mass or less per 100 parts by mass of the main component, to prepare a mixed powder. The process of crushing the aforementioned mixed powder, A method for producing Mn-Zn ferrite, comprising the step of sintering the powder after crushing.

10. The method for producing Mn-Zn ferrite according to claim 9, wherein the median diameter d50 of the mixed powder is 1.5 μm or less.

11. The method for producing Mn-Zn ferrite according to claim 9, wherein the median diameter d50 of the powder after crushing is 0.8 μm or less.

12. The method for producing Mn-Zn ferrite according to claim 9, wherein the main component further contains 0.2 to 2 mol% of CoO.

13. A method for producing Mn-Zn ferrite according to claim 9, wherein sintering is performed in an atmosphere with an oxygen concentration of 5% or more.

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