MnZn-BASED FERRITE

Abstract

An MnZn-based ferrite includes, as major components, 50 mol % to 53 mol % Fe.sub.2O.sub.3, 8 mol % to 10 mol % ZnO, and 37 mol % to 42 mol % MnO on an oxide basis. The MnZn-based ferrite includes, as minor components, less than or equal to 120 ppm SiO.sub.2, 100 ppm to 500 ppm Nb.sub.2O.sub.5, 0 ppm to 200 ppm ZrO.sub.2, 2000 ppm to 4000 ppm Co.sub.3O.sub.4, and 0 ppm to 1500 ppm SnO.sub.2 on an oxide basis.

Claims

1. An MnZn-based ferrite comprising: as major components, 50 mol % to 53 mol % Fe.sub.2O.sub.3, 8 mol % to 10 mol % ZnO, and 37 mol % to 42 mol % MnO on an oxide basis; as minor components, 100 ppm to 300 ppm CaO, less than or equal to 120 ppm SiO.sub.2, 100 ppm to 500 ppm Nb.sub.2O.sub.5, 0 ppm to 200 ppm ZrO.sub.2, 2000 ppm to 4000 ppm Co.sub.3O.sub.4, and 0 ppm to 1500 ppm SnO.sub.2 on an oxide basis.

2. The MnZn-based ferrite of claim 1, wherein: the MnZn-based ferrite comprises, as the minor components, 150 ppm to 250 ppm CaO, 50 ppm to 150 ppm ZrO.sub.2, 2000 ppm to 3000 ppm Co.sub.3O.sub.4, and 500 ppm to 1000 ppm SnO.sub.2 on an oxide basis.

Description

DESCRIPTION OF EMBODIMENTS

[0015] An aspect for implementing the present invention will be described below. The description of a preferable embodiment below is substantially a mere example and does not intend to limit the present invention, the application method thereof, or the application thereof.

[0016] First of all, MnZn-based ferrite according to an embodiment of the present invention will be described.

[0017] The MnZn-based ferrite according to the present embodiment contains, as major components, 50 mol % to 53 mol % Fe.sub.2O.sub.3, 8 mol % to 10 mol % ZnO, and 37 mol % to 42 mol % MnO on an oxide basis. When the contents of Fe.sub.2O.sub.3, ZnO, and MnO fall out of their respective content ranges, the core loss may increase.

[0018] Further, the MnZn-based ferrite according to the present embodiment contains, as minor components, 100 ppm to 300 ppm CaO, less than or equal to 120 ppm SiO.sub.2, 100 ppm to 500 ppm Nb.sub.2O.sub.5, 0 ppm to 200 ppm ZrO.sub.2, 2000 ppm to 4000 ppm Co.sub.3O.sub.4, and 0 ppm to 1500 ppm SnO.sub.2 on an oxide basis.

[0019] In the content ranges of the minor components, when CaO is less than 100 ppm, the core loss may increase, whereas when CaO exceeds 300 ppm, abnormal grain growth of a crystal easily occurs at the time of sintering, and as a result, the core loss may increase. Preferably, the content of CaO falls within the range of from 185 ppm to 280 ppm, and more preferably, the content of CaO falls within the range of from 220 ppm to 280 ppm.

[0020] In the content ranges of the minor components, when SiO.sub.2 exceeds 120 ppm, abnormal grain growth of a crystal easily occurs at the time of sintering, and as a result, the core loss may increase. More preferably, the content of SiO.sub.2 is less than or equal to 117 ppm.

[0021] In the content ranges of the minor components, when Nb.sub.2O.sub.5 is less than 100 ppm, the effect of reducing the core loss may be reduced, whereas when Nb.sub.2O.sub.5 exceeds 500 ppm, abnormal grain growth of a crystal easily occurs at the time of sintering, and the core loss may increase. Preferably, the content of Nb.sub.2O.sub.5 falls within the range of from 300 ppm to 400 ppm.

[0022] In the content ranges of the minor components, when Co.sub.3O.sub.4 is less than 2000 ppm, the temperature dependence of the core loss increases, and the effect of reducing the core loss may be reduced, whereas when Co.sub.3O.sub.4 exceeds 4000 ppm, the core loss may increase. Preferably, the content of Co.sub.3O.sub.4 falls within the range of from 2650 ppm to 3100 ppm.

[0023] In the content ranges of the minor components, when SnO.sub.2 and ZrO.sub.2 fall out of their respective content ranges, the core loss may increase. Preferably, the content of SnO.sub.2 falls within the range of from 0 ppm to 1000 ppm, and the content of ZrO.sub.2 falls within the range of from 0 ppm to 110 ppm.

[0024] Further, in the present embodiment, as the minor components, 150 ppm to 250 ppm CaO, 50 ppm to 150 ppm ZrO.sub.2, 2000 ppm to 3000 ppm Co.sub.3O.sub.4, and 500 ppm to 1000 ppm SnO.sub.2 on an oxide basis are preferably included. In this case, MnZn-based ferrite with more effectively reduced core loss over a wide temperature range of 25 C. to 120 C. can be obtained. More preferably, the content of CaO is within the range of from 185 ppm to 215 ppm, the content of ZrO.sub.2 is within the range of from 90 ppm to 110 ppm, the content of Co.sub.3O.sub.4 is within the range of from 2650 ppm to 2750 ppm, and the content of SnO.sub.2 is within the range of from 900 ppm to 1000 ppm.

[0025] Further, in the present embodiment, the ratio (Nb.sub.2O.sub.5/CaO) of Nb.sub.2O.sub.5 and CaO as the minor components preferably falls within the range of from 1.0 to 2.5. Setting the ratio of Nb.sub.2O.sub.5 and CaO within this range enables the temperature dependence of the core loss to be reduced.

[0026] Further, the present embodiment preferably contains substantially none of TiO.sub.2, V.sub.2O.sub.5, MoO.sub.3, and Bi.sub.2O.sub.3 as the minor components.

[0027] Next, a preferred method of producing the MnZn-based ferrite according to the embodiment of the present invention will be described.

[0028] First of all, raw materials (Fe.sub.2O.sub.3, ZnO, MnO) being the major components in powder form are wet blended, are then calcined at a predetermined temperature within the range of from 800 C. to 900 C., and are ground, thereby obtaining a ground product. Then, to the ground product, raw materials (CaO, SiO.sub.2, Nb.sub.2O.sub.5, ZrO.sub.2, Co.sub.3O.sub.4, SnO.sub.2) being the minor components are added at their respective predetermined amounts, thereby obtaining mixture powder.

[0029] The mixture powder thus obtained and including the major components and the minor components is first granulated into granules for being molded into a desired shape. For this purpose, for example, a small amount of polyvinyl alcohol as an appropriate binder is added to the mixture powder, and then the mixture powder is spray-dried.

[0030] The granules thus obtained are molded into the desired shape, thereby obtaining molded bodies, which are then subjected to a sintering step. The sintering step is performed by being separated into a temperature rising step, a maintaining step, and a cooling step. In particular, in the maintaining step, the granules are maintained at a maintenance temperature of from 1200 C. to 1300 C. for 2 hours to 5 hours. At this time, the atmospheric oxygen concentration is adjusted within the range of from 1% to 5%, and is adjusted, in the cooling step, by using an equilibrium oxygen partial pressure method. Thus, MnZn-based ferrite molded into the desired shape can be manufactured.

EXAMPLES

[0031] Examples and their comparative examples to which the present invention has been applied will be described below. The examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention.

(Production of Samples)

[0032] First of all, samples of MnZn-based ferrite of Examples 1 and 2 and Comparative Examples 1 to 4 were produced by the following method. Specifically, for the sample of each of the examples and the comparative examples, raw materials (Fe.sub.2O.sub.3, MnO, ZnO) being the major components were measured to achieve the composition shown in Table 1 and were then wet blended with each other, thereby obtaining a slurry. The slurry obtained by the wet blending was dried, was then calcined at a temperature of from 800 C. to 900 C., and was then ground, thereby obtaining calcined powder. Then, to the calcined powder thus obtained, appropriate amounts of CaO, Nb.sub.2O.sub.5, Co.sub.3O.sub.4, ZrO.sub.2, SnO.sub.2, TaO.sub.2 and the like being the minor components were added to achieve the composition shown in Table 1, and a binder was then added to obtain a mixture, and the mixture was then pulverized and spray-dried, thereby obtaining granules. The granules thus obtained were molded into a predetermined shape and were then sintered.

[0033] The sintering step was performed by being separated into the temperature rising step, the maintaining step, and the cooling step. The temperature rising step was performed in an atmosphere to rise the temperature from 600 C. to 800 C. and then in a reducing atmosphere to further rise the temperature to the maintenance temperature. At this time, the rate of temperature rise was 150 C./h250 C./h. The temperature for the maintaining step was from 1200 C. to 1300 C. and was maintained for 2 hours to 5 hours. At this time, the atmospheric oxygen concentration was adjusted within the range of from 1% to 5%. In the cooling step, cooling was performed at the rate of cooling of 60 C./h-100 C./h, and the atmospheric oxygen concentration was adjusted by using an equilibrium oxygen partial pressure method. Through the sintering step described above, a sample having an outer diameter of 25 mm, an inner diameter of 17 mm, and a height of 11 mm was obtained.

[0034] Then, each sample thus obtained was evaluated in terms of the core loss, the saturated magnetic flux density, and the magnetic permeability. Evaluation methods are as described below.

(Temperature Dependence of Core Loss)

[0035] The core loss was evaluated by using model SY-8217 manufactured by IWATSU ELECTRIC CO., LTD. by winding primary and secondary side windings each three turns around the sample thus obtained for each of the examples and comparative examples, at a frequency of 100 kHz, a maximum magnetic flux density of 200 mT, and a temperature within the range of from 25 C. to 140 C.

(Saturated Magnetic Flux Density)

[0036] The saturated magnetic flux density was evaluated by using model SY-8217 manufactured by IWATSU ELECTRIC CO., LTD. by winding primary and secondary side windings each eighteen turns around the sample thus obtained for each of the examples and comparative examples, at 1 kHz, 1194 A/m, 25 C., and 100 C.

(Magnetic Permeability)

[0037] The magnetic permeability was evaluated by using model E4990A manufactured by Keysight Technologies by winding ten turns around the sample thus obtained for each of the examples and comparative examples, at 1 kHz, 1 V, and a room temperature.

[0038] Evaluation results of the core loss, the saturated magnetic flux density, and the magnetic permeability of each sample are shown in Table 2.

TABLE-US-00001 TABLE 1 Major Component Minor Component Fe.sub.2O.sub.3 MnO ZnO NiO CaO SiO.sub.2 Nb.sub.2O.sub.5 Nb.sub.2O.sub.5/ (mol %) (mol %) (mol %) (ppm) (ppm) (ppm) (ppm) CaO Example 1 52.32 38.26 9.42 0 250 <117 360 1.44 Example 2 52.03 37.98 9.99 0 195 <110 350 1.79 Comparative 51.82 37.17 11 0 400 <110 270 0.68 Example 1 Comparative 52.22 39.76 8.02 0 125 0 330 2.64 Example 2 Comparative 51.44 37.45 11.1 0 250 <115 380 1.52 Example 3 Comparative 54.68 35.86 7.35 2.1 240 0 200 0.83 Example 4 Minor Component ZrO.sub.2 Co.sub.3O.sub.4 TiO.sub.2 SnO.sub.2 V.sub.2O.sub.5 MoO.sub.3 Bi.sub.2O.sub.3 (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) Example 1 0 3050 0 0 0 0 0 Example 2 100 2700 0 950 0 0 0 Comparative 0 0 0 0 400 0 0 Example 1 Comparative 230 800 0 0 0 0 0 Example 2 Comparative 0 0 5000 0 0 0 0 Example 3 Comparative 0 0 0 0 0 360 260 Example 4

TABLE-US-00002 TABLE 2 Saturated Magnetic Core Loss Flux Density (mW/cc, 100 kHz-200 mT) Magnetic (mT, 1 kHz-1194 A/m) 25 C. 80 C. 100 C. 110 C. 120 C. 140 C. Permeability 25 C. 100 C. Example 1 306 308 344 374 404 471 3137 517 416 Example 2 325 261 305 329 348 410 3396 531 416 Comparative 619 440 492 535 591 750 2400 511 392 Example 1 Comparative 655 429 446 465 485 530 2500 530 420 Example 2 Comparative 848 680 721 775 835 973 1970 490 370 Example 3 Comparative 775 417 395 434 506 700 1965 566 475 Example 4

[0039] Table 2 reveals that the MnZn-based ferrite of each example satisfying the composition range of the present invention has high magnetic permeability and has, in particular, in the temperature range of from 25 C. to 120 C., low core loss as well as a high saturated magnetic flux density as compared with the MnZn-based ferrite of each comparative example not satisfying the composition range of the present invention. Therefore, when the MnZn-based ferrite of each example is used, MnZn-based ferrite with reduced core loss in the temperature range of from 25 C. to 120 C. can be obtained.

[0040] Thus, the MnZn-based ferrite according to the present invention containing, as the major components, 50 mol % to 53 mol % Fe.sub.2O.sub.3, 8 mol % to 10 mol % ZnO, and 37 mol % to 42 mol % MnO on an oxide basis, and as the minor components, 100 ppm to 300 ppm CaO, less than or equal to 120 ppm SiO.sub.2, 100 ppm to 500 ppm Nb.sub.2O.sub.5, 0 ppm to 200 ppm ZrO.sub.2, 2000 ppm to 4000 ppm Co.sub.3O.sub.4, and 0 ppm to 1500 ppm SnO.sub.2 on an oxide basis has reduced core loss over a wide temperature range of from 25 C. to 120 C. and is thus useful.