MnZn-BASED FERRITE AND METHOD FOR PRODUCING SAME

Abstract

A MnZn-based ferrite that can suppress both reduction of the loss at a high frequency and a change in magnetic properties in a high magnetic field and a method for producing the same are provided. A MnZn-based ferrite including Fe.sub.2O.sub.3, ZnO, and MnO as main components, in which Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components, the MnZn-based ferrite includes 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of CO.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, as auxiliary components, per 100% by mass of the main components, an average crystal grain diameter is 4 m or less, and a sintering density is 4.8 g/cm.sup.3 or more.

Claims

1. A MnZn-based ferrite comprising Fe.sub.2O.sub.3, ZnO, and MnO as main components, wherein Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components, the MnZn-based ferrite comprises 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, as auxiliary components, per 100% by mass of the main components, an average crystal grain diameter is 4 m or less, and a sintering density is 4.8 g/cm.sup.3 or more.

2. The MnZn-based ferrite according to claim 1, further comprising 0.010 to 0.100% by mass of ZrO as an auxiliary component.

3. The MnZn-based ferrite according to claim 1, wherein a unit volume magnetic core loss (Pcv) at 25 C., 2 MHz, and 50 mT is 1500 mW/cm.sup.3 or less.

4. The MnZn-based ferrite according to claim 1, wherein a rate of change of a unit volume magnetic core loss (Pcv) at 25 C., 2 MHz, and 50 mT represented by the following expression (1) to that before a magnetic field is applied is 100% or less:
(PcvPcv.sub.0)/Pcv.sub.0100Expression (1) where Pcv.sub.0 is a unit volume magnetic core loss before a magnetic field is applied.

5. A method for producing the MnZn-based ferrite according to claim 1, the method comprising: a step of mixing raw materials comprising the main components, respectively, such that Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components, after sintering; a step of adding raw materials comprising the auxiliary components, respectively, such that the MnZn-based ferrite comprises 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, per 100% by mass of the main components, after sintering; and a step of disintegrating a mixed powder obtained until the mixed powder becomes a disintegrated powder having a D90 particle diameter of 1.2 m or less.

6. The method for producing the MnZn-based ferrite according to claim 5, further comprising a step of molding the disintegrated powder and heat-treating a resulting molded product at 1050 to 1150 C.

Description

DESCRIPTION OF EMBODIMENTS

[0026] Hereinafter, the MnZn-based ferrite and the method for producing the same according to the present invention will be described.

[0027] Unless otherwise specified, the numerical range represented by using to includes the lower limit value and the upper limit value thereof.

[0028] [MnZn-Based Ferrite]

[0029] The MnZn-based ferrite according to the present invention (hereinafter, also referred to as the present MnZn-based ferrite) [0030] includes Fe.sub.2O.sub.3, ZnO, and MnO as main components, in which [0031] Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components, [0032] the MnZn-based ferrite includes 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, as auxiliary components, per 100% by mass of the main components, [0033] an average crystal grain diameter is 4 m or less, and [0034] a sintering density is 4.8 g/cm.sup.3 or more.

[0035] The present inventor has obtained the finding that by adjusting the MnZn-based ferrite such that each metal oxide is included in the above specific proportion as described above, the average crystal grain diameter is 4 m or less, and the sintering density is 4.8 g/cm.sup.3 or more, it is possible to reduce the loss at a high frequency (particularly 1 MHz to 3 MHz) and also suppress a change in magnetic properties after a high magnetic field is applied, and has completed the present invention.

[0036] The present inventor had obtained the finding that it is possible to reduce the loss at a high frequency by using a MnZn-based ferrite in which the hysteresis loop has a perminvar property. For the MnZn-based ferrite having a perminvar property, the residual loss associated with domain wall displacement is reduced by suppressing the displacement (pinning) of a domain wall. However, when a high magnetic field is applied, the pinning of a domain wall becomes insufficient and the mobility of the domain wall increases, and thereby the reduction of the loss may become insufficient. On the other hand, the MnZn-based ferrite contains each component in the above specific proportion and the crystal grain diameter is reduced to 4 m or less to thereby reduce the number of domain walls in the crystal grains and reduce the residual loss associated with domain wall displacement. Specifically, the present MnZn-based ferrite can suppress the unit volume magnetic core loss (Pcv) at 25 C., 2 MHz, and 50 mT to 1500 mW/cm.sup.3 or less. Further, the present MnZn-based ferrite can set, for example, the rate of change of the unit volume magnetic core loss (Pcv) at 25 C., 2 MHz, and 50 mT represented by the following expression (1) to that before a magnetic field is applied, to 100% or less.

(PcvPcv.sub.0)/Pcv.sub.0100Expression (1)

As described above, the present MnZn-based ferrite has the following characteristic: even when a high magnetic field is applied, the loss at a high frequency can be reduced as in the state where no high magnetic field is applied.

[0037] The present MnZn-based ferrite includes Fe.sub.2O.sub.3, ZnO, and MnO as main components. In the present MnZn-based ferrite, Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance (33.0 to 43.8 mol %) of MnO, in 100 mol % of the main components.

[0038] By setting Fe.sub.2O.sub.3 to 53.2 mol % or more, preferably 53.5 mol % or more, a MnZn-based ferrite having a high magnetic flux density can be obtained. On the other hand, by setting Fe.sub.2O.sub.3 to 56.0 mol % or less, preferably 55.0 mol % or less, more preferably 54.8 mol % or less, a combination thereof with other components suppresses the formation of a MnZn-based ferrite into a perminvar to make it possible to reduce the loss when a high magnetic field is applied.

[0039] By setting ZnO to 3 mol % or more, preferably 6 mol % or more, a combination thereof with other components can suppress the formation of a MnZn-based ferrite into a perminvar, and the sinterability is excellent, and it is easy to adjust the crystal density to 4.8 g/cm.sup.3 or more. On the other hand, by setting ZnO to 12.0 mol % or less, preferably 11.0 mol % or less, a MnZn-based ferrite having a high magnetic flux density can be obtained.

[0040] In addition, the present MnZn-based ferrite includes at least SiO.sub.2, CaO, Co.sub.2O.sub.3, and TiO.sub.2 as auxiliary components.

[0041] By setting SiO.sub.2 to 0.005% by mass or more, preferably 0.010% by mass or more, a grain boundary phase having a high specific resistance is sufficiently formed to suppress the generation of eddy current at a high frequency. In addition, by containing SiO.sub.2, the mechanical strength of the MnZn-based ferrite is improved. On the other hand, by setting SiO.sub.2 to 0.060% by mass or less, preferably 0.050% by mass or less, it is possible to suppress the generation of enlarged SiO.sub.2 and suppress the deterioration of the loss.

[0042] By setting CaO to 0.010% by mass or more, preferably 0.030% by mass or more, a grain boundary phase having a high specific resistance is sufficiently formed to suppress the generation of eddy current at a high frequency. On the other hand, by setting CaO to 0.050% by mass or less, preferably 0.045% by mass or less, it is possible to suppress CaO remaining as an impurity and suppress the deterioration of the loss.

[0043] By setting Co.sub.2O.sub.3 to 0.10% by mass or more, preferably 0.20% by mass or more, the loss in a high temperature environment can be suppressed. On the other hand, by setting Co.sub.2O.sub.3 to 0.40% by mass or less, preferably 0.30% by mass or less, perminvar formation is suppressed to make it possible to reduce the loss when a high magnetic field is applied.

[0044] On the other hand, by setting TiO.sub.2 to 0.05% by mass or more, preferably 0.10% by mass or more, perminvar formation is suppressed to make it possible to reduce the loss when a high magnetic field is applied. On the other hand, by setting TiO.sub.2 to 0.30% by mass or less, preferably 0.25% by mass or less, perminvar formation is suppressed to make it possible to reduce the loss when a high magnetic field is applied.

[0045] The present MnZn-based ferrite may further include a further component as long as the effects of the present invention are exhibited. Examples of the further component include further metal oxide added if necessary, and an element inevitably included.

[0046] Examples of the further metal oxide include ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3, and MoO.sub.3, and among these, ZrO.sub.2 is preferable. In addition, examples of the element inevitably included include C (carbon atom), P (phosphorus atom), and B (boron atom).

[0047] By setting ZrO.sub.2 to 0.01% by mass or more, preferably 0.04% by mass or more, a grain boundary phase having a high specific resistance is sufficiently formed to suppress the generation of eddy current at a high frequency. On the other hand, by setting ZrO.sub.2 to 0.1% by mass or less, preferably 0.08% by mass or less, it is possible to suppress ZrO.sub.2 remaining as an impurity and suppress the deterioration of the loss.

[0048] The total content of the further metal oxide other than ZrO.sub.2 and the element is preferably 0.1% by mass or less, and further preferably 0.01% by mass or less, per 100% by mass of the main components.

[0049] The present MnZn-based ferrite can be suitably used, for example, as a core material of an inductor used in a switching power supply circuit having a switching frequency of a high frequency (for example, 1 to 3 MHz). In addition, the present MnZn-based ferrite suppresses a change in magnetic properties even when a high magnetic field is applied, and thus can be suitably used for, for example, a transformer or a choke coil through which a large current may flow.

[0050] [Method for Producing MnZn-Based Ferrite]

[0051] Next, one embodiment of the method for producing a MnZn-based ferrite (hereinafter, also referred to as the present production method) will be described.

[0052] The present production method may be a production method that can suitably produce the present MnZn-based ferrite, including at least: a step (mixing step) of mixing raw materials including the main components, respectively, such that Fe.sub.2O.sub.3 is 53.2 to 56.0 mol % and ZnO is 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components, after sintering; a step (addition step) of adding raw materials including the auxiliary components, respectively, such that the present MnZn-based ferrite includes 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, per 100% by mass of the main components, after sintering; and a step (disintegration step) of disintegrating a mixed powder obtained until the mixed powder becomes a disintegrated powder having a D90 particle diameter of 1.2 m or less. The present production method may further include a step such as a drying/granulation step of adding a binder to the mixed powder of the main components after the mixing step to obtain a granule; a calcination step of calcining the obtained granule; a drying/granulation step of the disintegrated powder; a molding step of molding the disintegrated powder or a granule thereof; or a heat treatment step (sintering step) of heat-treating the resulting molded product.

[0053] In the above mixing step, the main components are mixed such that the main components after sintering have the composition of the present MnZn-based ferrite. The form of the main components before mixing is not particularly limited, and is preferably the form of a powder because the powder is easy to handle and can be mixed uniformly. The raw material powders of the main components, respectively, are mixed and if necessary disintegrated to obtain a mixed powder. The mixing and disintegration methods may be appropriately selected from known methods. Specific examples thereof include an attritor and a bead mill. The particle diameter of the mixed powder is not particularly limited, and it is preferable to adjust the median diameter D50 to 0.5 m to 1.5 m from the viewpoint of uniformity or the like. The particle diameters D50 and D90 described later are the particle diameter (D50) where the cumulative particle diameter frequency is 50% and the particle diameter (D90) where the cumulative particle diameter frequency is 90%, respectively, when the particle size distribution of the target particle is measured. The particle size distribution of the mixed powder can be measured by using a particle size distribution measuring apparatus.

[0054] A drying/granulation step may be applied to the mixed powder of the above main components. In the drying/granulation step, a granule can be obtained, for example, by adding 0.5 to 1 part by mass of a binder such as polyvinyl alcohol when the total mass of the mixed powder is 100 parts by mass to the mixed powder obtained in the mixing step, and spraying the resulting mixture by using a spray dryer or the like.

[0055] Next, the obtained granule may be calcined at 750 C. for about 1 hour in an air atmosphere to obtain a calcined product (calcination step).

[0056] Next, the auxiliary components are added to the calcined product such that the auxiliary components after sintering have the composition of the present MnZn-based ferrite. The form of the auxiliary components before addition is not particularly limited, and is preferably the form of a particle because the particle is easy to handle and can be mixed uniformly.

[0057] After adding the auxiliary components, the resulting mixed powder is disintegrated to obtain a disintegrated powder. The disintegration may be appropriately adjusted such that the average crystal grain diameter of the MnZn-based ferrite obtained is 4 m or less. Examples of a method therefor include a method involving disintegrating the calcined product until the particle diameter D90 after disintegration becomes 1.2 m or less.

[0058] In the drying/granulation step, a granule is obtained by adding 0.5 to 1.0 part by mass of a binder such as polyvinyl alcohol when the total mass of the disintegrated powder is 100 parts by mass to the disintegrated powder obtained in the disintegration step, and spraying the resulting mixture by using a spray dryer or the like. At this time, the median diameter D50 of the granule is desirably 40 m or more and 200 m or less.

[0059] In the molding step, the granule obtained in the drying/granulation step is molded into a predetermined shape. The predetermined shape may be designed according to the application or the like. For example, the granule is molded into a toroidal type core having an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 11 mm.

[0060] The granule after molding is heat-treated to obtain a sintered body (the present MnZn-based ferrite). The heat treatment (sintering) conditions are preferably heating at 1050 to 1150 C. for several hours. By heat-treating at 1050 C. or more, it becomes easy to achieve a sintering density of 4.8 g/cm.sup.3 or more. On the other hand, by heat-treating at 1150 C. or less, it becomes easy to achieve an average crystal grain diameter of 4 m or less.

[0061] According to the above production method, a MnZn-based ferrite having an average crystal grain diameter of 4 m or less and a sintering density of 4.8 g/cm.sup.3 or more is preferably produced.

EXAMPLES

[0062] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited by the descriptions thereof.

Example 1

[0063] Each raw material powder was weighed and mixed such that after sintering, the Fe.sub.2O.sub.3 content was 54.0 mol %, the ZnO content was 10.0 mol %, and the MnO content was 36.0 mol % to make a total of 100 mol %. To the above mixture, polyvinyl alcohol was added in an amount equivalent to 0.5 parts by mass per 100 parts by mass in total of the mixture, and the resulting mixture was sprayed by using a spray dryer to obtain a granule. Next, the granule was calcined at 750 C. for 1 hour in an air atmosphere to obtain a calcined product. Next, raw material powders of auxiliary components, respectively, were added such that SiO.sub.2 was 0.03% by mass, CaO was 0.04% by mass, Co.sub.2O.sub.3 was 0.2% by mass, TiO.sub.2 was 0.2% by mass, and ZrO.sub.2 was 0.08% by mass, per 100% by mass of the main components.

[0064] Next, as a disintegration step, a mixture of the calcined product and the additives was disintegrated by using a disintegrator such that the particle diameter D90 after disintegration was 1.2 m or less, to obtain a disintegrated powder. Next, as a drying/granulation step, when the total mass of the disintegrated powder was 100 parts by mass, 1 part by mass of polyvinyl alcohol was added to the disintegrated powder, and the resulting mixture was sprayed by using a spray dryer to obtain a granule. Next, as a molding step and a sintering step, the granule was molded into a toroidal type core having an outer diameter of 16 mm, an inner diameter of 10 mm, and a height of 5 mm, and sintered at 1100 C. to obtain a sintered body (MnZn-based ferrite).

Examples 2 to 16

[0065] MnZn-based ferrites of Examples 2 to 16 were obtained in the same manner in Example 1 except that in Example 1, the raw materials were mixed and added such that the content proportions of the main components and the auxiliary components after sintering were as shown in Table 1.

Comparative Example 1

[0066] A MnZn-based ferrite of Comparative Example 1 was obtained in the same manner in Example 1 except that in Example 1, the disintegration time was shortened and the particle diameter D90 of the powder after disintegration was 4.82 m.

Comparative Examples 2 to 12

[0067] MnZn-based ferrites of Comparative Examples 2 to 12 were obtained in the same manner in Example 1 except that in Example 1, the raw materials were mixed and added such that the content proportions of the main components and the auxiliary components after sintering were as shown in Table 1.

[0068] <Evaluation>

[0069] The disintegration particle diameter D90 was determined by measuring the slurry of the disintegrated powder obtained in the production process of each of the above Examples and Comparative Examples by using a wet particle size distribution measuring apparatus.

[0070] The average crystal grain diameter was calculated by image analysis from an image obtained by mirror-polishing the MnZn-based ferrite obtained in each of the Examples and the Comparative Examples and then dissolving the grain boundary phase by etching followed by observation under a microscope. The measurement was carried out on 100 crystal grains for each.

[0071] The sintering density was measured by the Archimedes method.

[0072] In addition, Pcv and Pcv.sub.0 of the MnZn-based ferrite were measured by using a BH analyzer, and the Pcv change rate was calculated by the above expression (1). Results thereof are shown in Table 1.

TABLE-US-00001 TABLE 1 Average Disintegration crystal Pcv Main components Auxiliary components particle grain Sintering Pcv change [mol %] [% by mass] diameter_D90 diameter density 2 MHz-50 rate Example Fe.sub.2O.sub.3 MnO ZnO SiO.sub.2 CaO ZrO.sub.2 Co.sub.2O.sub.3 TiO.sub.2 [m] [m] [g/cc] mT@25 C. [%] Comparative 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.2 4.82 4.32 4.71 1990 75 Example 1 Comparative 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.2 2.69 3.89 4.69 1710 69 Example 2 Example 1 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.2 1.12 3.95 4.92 1337 68 Example 2 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.2 1.09 3.88 4.89 1432 58 Comparative 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0 1.13 3.89 4.92 1530 112 Example 3 Example 3 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.05 1.09 3.96 4.89 1490 98 Example 4 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.1 1.15 3.87 4.90 1380 82 Example 5 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.2 1.16 3.90 4.93 1350 69 Example 6 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.3 1.08 3.91 4.95 1480 52 Comparative 54.0 36.0 10.0 0.030 0.040 0.08 0.20 0.4 1.07 3.93 4.90 1620 43 Example 4 Example 7 53.5 35.5 11.0 0.035 0.050 0.08 0.20 0.2 1.03 3.87 4.94 1400 54 Example 8 54.4 35.6 10.0 0.035 0.050 0.08 0.20 0.2 1.08 3.88 4.93 1380 68 Example 9 53.8 37.7 8.5 0.035 0.050 0.08 0.20 0.2 1.11 3.92 4.91 1420 71 Example 10 54.8 39.2 6.0 0.035 0.050 0.08 0.20 0.2 1.12 3.95 4.88 1450 88 Comparative 54.1 35.9 10.0 0.033 0.045 0.10 0.05 0.2 1.04 3.87 4.94 1820 25 Example 5 Example 11 54.1 35.9 10.0 0.033 0.045 0.10 0.10 0.2 1.07 3.87 4.94 1450 50 Example 12 54.2 35.7 10.1 0.033 0.045 0.10 0.40 0.2 1.11 3.93 4.93 1450 82 Comparative 54.3 35.6 10.1 0.033 0.045 0.10 0.45 0.2 1.13 3.93 4.92 1550 99 Example 6 Comparative 54.2 35.8 10.0 0.000 0.010 0.01 0.20 0.2 1.05 3.89 4.88 1850 75 Example 7 Example 13 54.2 35.8 10.0 0.010 0.010 0.01 0.20 0.2 1.07 3.88 4.90 1490 73 Example 14 54.3 35.6 10.1 0.050 0.010 0.01 0.20 0.2 1.10 3.96 4.94 1470 76 Comparative 54.3 35.6 10.1 0.065 0.010 0.01 0.20 0.2 1.14 4.98 1980 80 Example 8 Comparative 54.2 35.8 10.0 0.033 0.005 0.04 0.20 0.2 1.10 3.88 4.90 1600 74 Example 9 Comparative 54.3 35.6 10.1 0.033 0.065 0.04 0.20 0.2 1.14 4.98 1850 79 Example 10 Comparative 54.2 35.8 10.0 0.033 0.045 0.005 0.20 0.2 1.11 3.91 4.91 1550 73 Example 11 Comparative 54.3 35.6 10.1 0.033 0.045 0.11 0.20 0.2 1.11 3.89 4.92 1560 78 Example 12 Example 15 55.4 35.6 9.0 0.035 0.050 0.08 0.20 0.2 1.10 3.89 4.89 1428 93 Example 16 56.0 35.0 9.0 0.035 0.050 0.08 0.20 0.2 1.09 3.92 4.88 1366 98

[0073] [Summary of Results]

[0074] It was shown that the MnZn-based ferrites of Examples 1 to 16 had a unit volume magnetic core loss (Pcv) at 25 C., 2 MHz, 50 mT of 1500 mW/cm.sup.3 or less, and a rate of change of the Pcv to that before a magnetic field was applied was 100% or less, in which Fe.sub.2O.sub.3 was 53.2 to 56.0 mol % and ZnO was 3.0 to 12.0 mol %, with a balance of MnO, in 100 mol % of the main components; the MnZn-based ferrites contained 0.005 to 0.060% by mass of SiO.sub.2, 0.010 to 0.060% by mass of CaO, 0.10 to 0.40% by mass of Co.sub.2O.sub.3, and 0.05 to 0.30% by mass of TiO.sub.2, as auxiliary components, per 100% by mass of the main components; the average crystal grain diameter was 4 m or less; and the sintering density was 4.8 g/cm.sup.3 or more. From the above, it has been made clear that the present MnZn-based ferrite can suppress both reduction of the loss at a high frequency and a change in magnetic properties in a high magnetic field.

[0075] The present application claims priority based on Japanese Patent Application No. 2020-167723 filed on Oct. 2, 2020, the disclosure of which is incorporated herein by reference in its entirety.