JP2003109813A - Low loss oxide magnetic material and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide magnetic material having high resistivity and low loss. SOLUTION: A method for manufacturing the low loss oxide magnetic material containing Fe2 O3 , NiO, ZnO, and CuO as main components is characterized in that the oxygen partial pressure of the atmosphere of a temperature rising part and a temperature keeping part is 10% or lower and the oxygen partial pressure of a cooling part is 10% or more in a baking step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low loss oxide magnetic material used for a power transformer or a choke coil.

[0002]

2. Description of the Related Art In recent years, electronic devices such as portable devices have been rapidly reduced in size. Since the transformer occupies a large position in the power source in terms of volume and power loss, downsizing and high efficiency are required. If the loss of the material for the transformer is large, not only the efficiency as a power source is poor, but also self-heating occurs.

As a power transformer material, Mn-Zn ferrite, which has a relatively high saturation magnetic flux density and a small power loss, is mainly used. Mn-Zn-based ferrite has a low DC specific resistance of 10 to 10 ³ Ωcm. Therefore, in order to eliminate problems such as a short circuit, windings are usually wound around these magnetic cores via a bobbin, which is an obstacle to further miniaturization, weight reduction and cost reduction.

On the other hand, Ni--Zn type ferrite generally has a high DC specific resistance of 10 ⁸ to 10 ¹⁰ Ωcm and does not require a bobbin for winding, but has a power loss of Mn-.
Remarkably higher than Zn-based ferrite. As a result, Ni
When a Zn-based ferrite is used, a large amount of heat is generated, and there is a possibility that problems such as shortening the life of peripheral circuit parts may occur, and the reliability is low. In addition, it lowers power efficiency, which may be an obstacle to energy saving of electric products.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an oxide magnetic material having a high specific resistance and a low loss.

[0006]

Means for Solving the Problems Fe ₂ O ₃ , NiO, Z
The Ni-Zn-Cu-based ferrite containing nO and CuO as the main components is generally fired in the air (oxygen partial pressure = about 20%). As a result of various studies, the present inventors have found that Fe _{2
O 3, NiO, ZnO, Ni} -Z mainly composed of CuO
In the firing process of the n-Cu ferrite, the oxygen partial pressure of the atmosphere of the temperature raising part and the temperature holding part is 10% or less, and the oxygen partial pressure of the cooling part is 10% or more. It has been found that a low loss oxide magnetic material having an intragranular pore number in the cut surface of 8000 / mm ² or less can be obtained, and the above problems can be solved.

That is, according to the present invention, Fe ₂ O ₃ , NiO, Z
In the method for producing a low-loss oxide magnetic material containing nO or CuO as a main component, the oxygen partial pressure of the atmosphere of the temperature raising portion and the temperature holding portion in the firing step is 10% or less, and the oxygen partial pressure of the cooling portion is It is a method for producing a low-loss oxide magnetic material, which is 10% or more.

Further, the present invention is the above-mentioned low-loss oxide magnetic material, characterized in that the number of pores in the grains in the cut surface of the sintered body is 8000 / mm ² or less.

Further, according to the present invention, the saturation magnetic flux density is 450 m.
The above low-loss oxide magnetic material is characterized in that it is T or more and the loss at 50 kHz, 150 mT and 80 ° C. is 270 kW / m ³ or less.

The magnetic loss (Pcv) of ferrite is
It consists of a loss of teresis, an eddy current loss and a residual loss. Ni
In general, a Zn-based ferrite has a DC specific resistance of 10⁸~
10 ¹⁰Ωcm is high, and eddy current loss is negligible.
Sai. Hysteresis loss is mainly due to the difference between crystal structure and crystal magnetic
Directional energy (K₁) And the loss due to domain wall motion
It is a loss. The pores (intragranular pores) existing in the crystal grains are domain walls.
It is considered to hinder the movement and deteriorate the hysteresis loss.
available.

In the present invention, Fe ₂ O ₃ , NiO, Z
In the Ni—Zn—Cu-based ferrite firing process containing nO and CuO as the main components, the oxygen partial pressure in the atmosphere of the temperature raising portion and the temperature holding portion is 10% or less, and the oxygen partial pressure in the cooling portion is 10% or less.
% Or more, a low-loss oxide magnetic material having a crystal structure in which the number of intragranular pores is smaller than that of conventional materials can be obtained. Oxygen partial pressure of the atmosphere of the temperature rising part and the temperature holding part is 10%
The reason for this is that the oxygen partial pressure exceeding that value does not make much difference in the number of intragranular pores and loss with the conventional product. The oxygen partial pressure in the cooling part is set to 10% or more because the specific resistance is significantly reduced when the oxygen partial pressure is less than 10%.

In the present invention, the cause of the decrease in loss is not clear, but it may be caused by the decrease in the number of pores in the grain. In the present invention, Fe ₂ O ₃ , NiO, Zn
O, CuO was the main component, but Fe ₂ O ₃ , NiO, Z
The same effect can be obtained with a Ni-Zn ferrite containing nO as a main component.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

Fe ₂ O containing 49 mol 1% as a main component composition
₃ , 19mo1% NiO, 25mo1% ZnO, b
Weigh a predetermined amount of alCuO and use an attritor to
Mixed for hours. After mixing, it was granulated with a spray dryer. The granulated powder was calcined in a rotary kiln. The obtained powder was crushed using an attritor. After crushing, it was granulated with a spray dryer, pressed into a toroidal shape, and fired at 900 to 1050 ° C.

In Table 1, the firing holding temperatures are 900, 950,
1000, 1050 ° C., average crystal grain size when the oxygen partial pressure of the temperature rising part and the holding part was changed to 0.01 to 15% when the oxygen partial pressure of the cooling part was 20%, cutting of the sintered body Number of pores in the grain per unit area of the surface, 50 kHz, 150 mT, 8
Loss at 0 ° C (Pcv), resistivity and saturation magnetic flux density (B
s) is shown.

[0016]

[Table 1]

From Table 1, the product of the present invention has a smaller number of pores in the grain per unit area of the cut surface of the sintered body than the conventional product,
It can be seen that the loss is low, and the changes in the specific resistance and the saturation magnetic flux density (Bs) are practically negligible. Further, it can be seen that the number of intragranular pores present in the cut surface of the product of the present invention is 8000 / mm ² or less. Although the loss is high at 900 ° C firing, it is considered that the cause is that the crystal grain growth is not sufficient. Although the loss is high at 1050 ° C. firing, it is considered that the cause is an abnormal composition length.

In Table 2, the average crystal grain size when the oxygen partial pressure in the cooling part is changed when the holding temperature is 1000 ° C., the number of intragranular pores per unit area of the cut surface of the sintered body, 50 kH
z, 150 mT, loss at 80 ° C. (Pcv), specific resistance and saturation magnetic flux density (Bs) are shown.

[0019]

[Table 2]

From Table 2, the product of the present invention has a smaller number of pores in the grain per unit area of the cut surface of the sintered body than the conventional product,
It can be seen that the loss is low, and the changes in the specific resistance and the saturation magnetic flux density (Bs) are practically negligible. Further, it can be seen that the number of intragranular pores present in the cut surface of the product of the present invention is 8000 / mm ² or less. The reason why the specific resistance is low when the oxygen partial pressure is lower than 10% is considered to be that a large amount of Fe ²⁺ remains and contributes to electric conduction.

FIG. 1 shows 50 kHz of the conventional product and the invention product 7,
The temperature characteristic of a loss of 150 mT is shown. It can be seen from FIG. 1 that the product of the present invention has a lower loss in a practical temperature range than the conventional product.

Therefore, since the product of the present invention has a remarkably high specific resistance as compared with the conventional Mn-Zn type ferrite, it is possible to directly wind the winding, and the bobbin and other winding parts are not required, and the cost is reduced. It can be reduced. In addition, since it has a high specific resistance, it can be integrally fired with a magnetic material, and can be infinitely downsized. Further, it has a low loss as compared with the conventional Ni-Zn ferrite.

[0023]

As described above, according to the present invention,
It was possible to provide an oxide magnetic material having high specific resistance and low loss.

[Brief description of drawings]

FIG. 1 shows temperature characteristics of the invention product 7 and a conventional product with loss of 50 kHz and 150 mT.

[Explanation of symbols]

A invention 7 B Conventional product

Claims (3)

[Claims] 1. A method for producing a low-loss oxide magnetic material containing Fe ₂ O ₃ , NiO, ZnO, and CuO as a main component, wherein the oxygen partial pressure in the atmosphere of the temperature raising portion and the temperature holding portion in the firing step is 10%. The method for producing a low-loss oxide magnetic material is the following, and the oxygen partial pressure in the cooling part is 10% or more. 2. The number of intragranular pores in the cut surface of the sintered body is 800.
The low loss oxide magnetic material according to claim 1, wherein the number is 0 / mm ² or less. 3. The saturation magnetic flux density is 450 mT or more,
And the loss at 50kHz, 150mT, 80 ℃ is 2
The low loss oxide magnetic material according to claim 1 or 2, wherein the magnetic loss is 70 kW / m ³ or less.