JP2007297232A - Method for producing oxide magnetic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an oxide magnetic material having a low loss and a high saturation magnetic flux density by further enhancing the density of a sintered compact by reducing the releasing amount of oxygen in a temperature-raising step of a sintering process. <P>SOLUTION: In a mixing process, Fe<SB>2</SB>O<SB>3</SB>is mixed in an amount less than a desired Fe<SB>2</SB>O<SB>3</SB>amount so as to completely convert Fe<SB>2</SB>O<SB>3</SB>and Mn<SB>3</SB>O<SB>4</SB>into (MnZn)Fe<SB>2</SB>O<SB>4</SB>about 900°C and to complete releasing of oxygen in a following calcining process. Further, the composition is adjusted by adding Fe<SB>3</SB>O<SB>4</SB>and ZnO for adjusting the shortage amount of Fe<SB>2</SB>O<SB>3</SB>in a pulverization process, and after granulating, forming is performed. Thereby, the releasing amount of oxygen in the sintering process can be reduced. Consequently, it becomes possible to control the oxygen partial pressure in the temperature-raising step of the sintering process to be ≤0.1% of atmospheric pressure, and a sintered compact having a higher density can be obtained and a Mn-Zn-based ferrite having a low loss and a high saturation magnetic flux density can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an oxide magnetic material which is a magnetic core material used for a power transformer or the like and has a low loss up to a high frequency and a high saturation magnetic flux density.

  In recent years, downsizing of electronic devices has been progressing rapidly including portable devices. And the power source used for them is in the same flow. Since transformers occupy a large proportion in power supply components in terms of volume and power loss, miniaturization and high efficiency are urgently needed.

  Characteristics required as a transformer material for power supply include a low loss at a driving frequency, a high saturation magnetic flux density, and a high initial permeability. It is known that the saturation magnetic flux density depends on the main component composition and the sintered body density. The loss is composed of eddy current loss, hysteresis loss, and residual loss. When the loss is particularly large, not only the efficiency as a power source is bad but also a problem of self-heating occurs.

The eddy current loss mainly depends on the direct current resistance, and in order to reduce the eddy current loss, subcomponents such as SiO ₂ and CaO are added and precipitated at the grain boundaries to increase the resistance (for example, Patent Document 1).

  Hysteresis loss mainly depends on the crystal structure, and in order to reduce hysteresis loss, it is important to obtain a high sintered body density while obtaining a uniform grain size distribution with an appropriate grain size. (For example, Patent Document 2).

Therefore, in order to obtain a Mn—Zn-based ferrite having a low loss and a high saturation magnetic flux density, it is necessary to select an appropriate powder composition and obtain a dense and dense sintered body. Densification progresses most at the temperature rising part in the sintering process, and by lowering the oxygen partial pressure in the temperature rising part, solid solution of MnO, Fe ₂ O ₃ , ZnO is promoted, and a denser sintered body is obtained. Obtained (for example, Patent Document 3). Further, although the density is further increased by increasing the holding temperature, it is not preferable because the crystal grain size becomes too large, and the grain size distribution of the crystal grain size becomes wide and loss increases.

JP 2004-22619 A JP 2001-126911 A JP 2003-109813 A

In the conventional method for producing Mn—Zn ferrite, the raw materials are mixed in the mixing process so that the powder composition after the granulation process becomes a desired composition, and then calcined, pulverized, granulated, Sintering is performed. Further, an N ₂ flow is performed in order to reduce the oxygen partial pressure in the temperature raising portion in the sintering process. However, when N ₂ is flowed and the temperature rising part of the sintering process is to be reduced in oxygen partial pressure, at 800 ° C. to 1050 ° C., Mn ₃ O ₄ and Fe ₂ O shown in the formulas (1) and (2) _Since a reduction reaction of ₃ occurs and O ₂ is released, it is difficult to reduce the oxygen partial pressure to a desired level without flowing a large flow rate of N ₂ . In particular, in the vicinity of the product in the sintering furnace, even if a large flow rate of N ₂ is flowed, the released oxygen cannot be completely removed and the oxygen partial pressure becomes high. Furthermore, when firing in large quantities at once, such as firing in a mass production continuous furnace, the oxygen partial pressure rises remarkably, the oxygen partial pressure becomes unstable, and it is difficult to control the oxygen partial pressure.

Mn ₃ O ₄ → 3MnO + (1/2) O ₂ (1)
3Fe ₂ O ₃ → 2Fe ₃ O ₄ + (1/2) O ₂ (2)

  The object of the present invention is to solve the above-mentioned problems, reduce oxygen release at the temperature rising part in the sintering process, and further improve the sintered body density, thereby reducing the oxidation with low loss and high saturation magnetic flux density. The object is to provide a method for producing a magnetic material.

The present invention is a method for producing a Mn—Zn ferrite, the composition of which is 50.0 to 51.0 mol% in terms of Fe ₂ O ₃ , 3.0 to 8.0 mol% in terms of ZnO, and the balance is MnO. When starting materials adjusted to be mixed and pulverized through calcining, the main component composition is 54.0 to 60.0 mol% in terms of Fe ₂ O ₃ and 3.0 to 8 in terms of ZnO. The composition is adjusted by adding Fe ₃ O ₄ and ZnO so that the remaining amount is MnO, and 0.005 to 0.05 wt% of SiO ₂ in terms of weight ratio to the main component as an auxiliary component, 0 .01 to 0.1 wt% CaO, 0.005 to 0.06 wt% Nb ₂ O ₅ is added, pulverized, granulated, molded, and heated at a temperature of 300 ° C. or higher in the sintering step Sintering with oxygen partial pressure of 0.1% or less It allows to improve the sintered density and uniform crystal structure is obtained, to provide a method of manufacturing an oxide magnetic material having a high saturation magnetic flux density with low loss.

According to the present invention, by mixing the Fe ₂ O ₃ amount less than the desired Fe ₂ O ₃ amount in the mixing step, all Fe ₂ O ₃ and Mn ₃ are mixed in the next pre-baking step. O ₄ becomes (MnZn) Fe ₂ O ₄ around 900 ° C., and the release of oxygen is completed. Furthermore, after adjusting the composition of the deficient Fe ₂ O ₃ with Fe ₃ O ₄ and ZnO in the crushing process, oxygen release in the sintering process can be reduced by granulating and molding. As a result, it becomes possible to control the oxygen partial pressure in the temperature raising part of the sintering process to 0.1% or less, and a higher sintered body density is obtained, and Mn—Zn having a low saturation and a high saturation magnetic flux density. -Based ferrite can be obtained. Further, by adding SiO ₂ , CaO, Nb ₂ O ₅ and concentrating it in the grain boundary layer, the specific resistance increases and eddy current loss, which is one of the loss components, can be reduced.

In order to achieve a low loss with the composition of the main component and subcomponents in the above desired ranges, and to adjust the composition of the main component, the amount of Fe ₂ O ₃ of the main component of the starting material is changed to the desired Fe ₂ after sintering. By blending less than the amount of O _3, the release of oxygen at the heating part of the sintering process is reduced, the oxygen partial pressure is 0.1% or less, and the sintering density is improved, resulting in low loss and high saturation. Realized the magnetic flux density.

The reason why Fe ₂ O ₃ is 50.0 to 51.0 mol% and ZnO is 3.0 to 8.0 mol% is that Fe ₂ O ₃ is more than 51.0 mol% and ZnO is less than 3.0 mol%. This is because oxygen release in the calcination step is not sufficient. This is because if Fe ₂ O ₃ is less than 50.0 mol% and ZnO is more than 8.0, the amount of composition adjustment by Fe ₃ O ₄ in the crushing process increases and the magnetic properties deteriorate. To that of SiO ₂ and 0.005 to 0.05% may not provide a sufficient resistivity less than 0.005 wt%, it is because the loss increases, abnormal grain growth is more than 0.05 wt% This is because the loss increases rapidly.

The reason why CaO is set to 0.01 to 0.1 wt% is that if it is less than 0.01 wt%, a sufficient specific resistance cannot be obtained and loss increases. This is because the loss decreases and the loss increases rapidly. The reason why Nb ₂ O ₅ is 0.005 to 0.06 wt% is that if it is less than 0.005 wt%, sufficient resistivity cannot be obtained and loss increases, and if it exceeds 0.06 wt%, abnormal particles This is because it grows and the loss increases rapidly.

  The reason why the temperature at which the oxygen partial pressure is set to 0.1% or less with respect to the atmospheric pressure in the temperature raising part of the sintering process is set to 300 ° C. or higher is to be less than 300 ° C. in order to decompose the binder added for molding. This is because a certain oxygen partial pressure is required. In addition, the oxygen partial pressure was set to 0.1% or less with respect to the atmospheric pressure at the temperature rising portion of 300 ° C. or higher. This is because low loss and high saturation magnetic flux density cannot be obtained.

Weighed so that the main components were Fe ₂ O ₃ : 49.5 to 51.5 mol%, ZnO: 7.5 to 10.5 mol%, and the balance: MnO, mixed using a ball mill, and 950 ° C in an air atmosphere. And calcined for 2 hours.

Subsequently, the composition was adjusted by adding Fe ₃ O ₄ and ZnO so that the calcined material of the main component, Fe ₂ O ₃ : 54 mol%, and ZnO: 7 mol% were added. Further, 0.02 wt% of SiO ₂ , 0.05 wt% of CaO and 0.05 wt% of Nb ₂ O ₅ were added as subcomponents expressed by weight ratio to the main component, and then pulverized by a ball mill. After fine pulverization, a binder was added and granulated with a spray dryer. Table 1 shows the powder composition when the obtained powder was measured by fluorescent X-ray analysis.

Next, it was molded into a toroidal shape of φ30 × φ25 × 5 mm and sintered. In the sintering, the temperature raising portion was heated in N ₂ , and the holding portion was sintered at 1250 ° C. for 6 hours in a reducing atmosphere in which the oxygen partial pressure was controlled. Further, as a conventional material, a main component composition of Fe ₂ O ₃ = 54.0 mol%, ZnO = 7 mol%, balance = MnO is used, and SiO ₂ is 0.03 wt% and CaO is 0.05 wt. %, Nb ₂ O ₅ was added at 0.05 wt%, and sintering was performed under the same conditions. The obtained core was wound, and a core loss of 100 kHz-200 mT was measured up to 100 ° C. from an AC BH tracer. Next, the magnetic flux density at 1194 A / m was measured up to 100 ° C. with a direct current BH tracer. Next, the sintered body density was measured by the Archimedes method.

  Table 1 shows the core loss Pcv, saturation magnetic flux density Bs, initial permeability μi, and sintered body density at 100 ° C.

  From Table 1, it can be seen that the inventive product shows superior values in all the characteristics of the core loss Pcv at 100 ° C., the saturation magnetic flux density Bs at 100 ° C., and the initial permeability μi as compared with the conventional product. Further, it can be seen that the comparative product in which the composition at the time of mixing is out of the scope of the invention is inferior or equivalent to the core loss Pcv at 100 ° C. or the saturation magnetic flux density Bs at 100 ° C. compared to the conventional product.

They were weighed so that the main components were Fe ₂ O ₃ : 50.5 mol%, ZnO: 6.0 mol%, and the balance: MnO, mixed using a ball mill, and calcined at 950 ° C. for 2 hours in an air atmosphere. Thereafter, the composition was adjusted by adding Fe ₃ O ₄ and ZnO so as to be Fe ₂ O ₃ : 54 mol% and ZnO: 7 mol%. Furthermore, 0.003~0.06wt% SiO ₂ as subcomponent, 0.005~0.11wt% of CaO, after addition of Nb ₂ O ₅ so that 0.003~0.07wt%, a ball mill And finely pulverized. After fine pulverization, a binder was added and granulated with a spray dryer.

Next, it was molded into a toroidal shape of φ30 × φ25 × 5 mm and sintered. In the sintering, the temperature raising portion was heated in N ₂ , and the holding portion was sintered at 1250 ° C. for 6 hours in a reducing atmosphere in which the oxygen partial pressure was controlled. Further, by the same method as the conventional material, Fe ₂ O ₃ = 54.0 mol%, ZnO = 7 mol%, balance = MnO, the main component composition, SiO ₂ as the subcomponent, 0.03 wt%, CaO 0.05 wt% %, Nb ₂ O ₅ was added at 0.05 wt%, and sintering was performed under the same conditions. The obtained core was wound, and a core loss of 100 kHz-200 mT was measured up to 100 ° C. from an AC BH tracer. Next, the magnetic flux density at 1194 A / m was measured up to 100 ° C. with a direct current BH tracer. Next, the sintered body density was measured by the Archimedes method.

  Table 2 shows the core loss Pcv, saturation magnetic flux density Bs, initial permeability μi, and sintered body density at 100 ° C.

  From Table 2, it can be seen that the inventive product is superior in core loss Pcv, saturation magnetic flux density Bs, and initial permeability μi at 100 ° C. compared to the conventional product. Moreover, it turns out that all the comparative products which made the content of the additive out of the scope of the invention are inferior in value of the core loss at 100 ° C. to the conventional products.

Claims (1)

A method for producing a Mn—Zn ferrite so that the composition is 50.0 to 51.0 mol% in terms of Fe ₂ O ₃ , 3.0 to 8.0 mol% in terms of ZnO, and the balance is MnO. When the adjusted starting materials are mixed and pulverized through calcination, the main component composition is 54.0 to 60.0 mol% in terms of Fe ₂ O ₃ , 3.0 to 8.0 mol% in terms of ZnO, The composition is adjusted by adding Fe ₃ O ₄ and ZnO so that the balance is MnO, and 0.005 to 0.05 wt% of SiO ₂ , 0.01 to 0.1 wt. % Of CaO, 0.005 to 0.06 wt% of Nb ₂ O ₅ , pulverization, granulation, molding, and sintering of the molded body, oxygen partial pressure at 300 ° C. or higher in the temperature rising part Oxide magnetic material characterized by containing 0.1% or less The method of production.