JP2003309008A - Oxide magnetic material and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the loss caused by the eddy current loss by improving resistivity without lowering the magnetic characteristics of MnZn ferrite. <P>SOLUTION: A mold formed by pressing MnZn ferrite powder is immersed in water solution including Fe ion, Ni ion, Zn ion and added with oxidizing agent, and NiZn ferrite is produced in a clearance of the powder constituting the mold. Since the NiZn ferrite has high resistivity, the loss can be reduced without lowering the magnetic characteristics when compared by a conventional method for precipitating nonmagnetic oxide in the grain boundary of ferrite. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

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

[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 supply both in terms of volume and power loss, downsizing and higher efficiency are required.

When the loss of the transformer material is large, not only the efficiency as a power source is low, but also a problem occurs due to self-heating. MnZn ferrite, which has a relatively high saturation magnetic flux density, is mainly used as a power transformer material, but MnZn ferrite has a DC specific resistance of 10 ¹ to ¹ 1.
Since it is as low as 0 ³ Ω · cm, eddy current loss occurs and the total loss is increased.

In order to reduce this eddy current loss, it is generally practiced to add a highly non-resistive oxide to precipitate it at the grain boundaries to increase the specific resistance, but this additive is non-magnetic. However, there is also a possibility that the deterioration of magnetic characteristics is promoted.
Further, since MnZn ferrite has a low specific resistance, it is usually wound around these magnetic cores via a bobbin in order to eliminate problems such as a short circuit, and in order to promote miniaturization, weight reduction and cost reduction. It is an obstacle.

On the other hand, NiZn ferrite generally has a high DC specific resistance of 10 ⁸ to 10 ¹⁰ Ω · cm and does not require a bobbin for winding, but its power loss is significantly higher than that of MnZn ferrite. As a result, when NiZn ferrite is used, a large amount of heat is generated, and defects such as shortening the life of peripheral circuit components may occur, resulting in low reliability. Further, since the power efficiency is lowered, it may be an obstacle to energy saving of electric products.

[0006]

Therefore, the technical object of the present invention is to prevent MnZn from being deteriorated in magnetic properties.
By improving the specific resistance of ferrite, the eddy current loss is reduced and the total loss is reduced.

[0007]

As a means for solving the above problems, the present invention has been made as a result of studying filling the gaps between MnZn ferrite crystal grains with NiZn ferrite having a high specific resistance.

[0008] That is, the present invention is an oxide magnetic material comprising a compact made of MnZn ferrite powder and NiZn ferrite formed in the voids of the MnZn ferrite powder of the compact.

In the present invention, the composition of the MnZn ferrite is 52.0 to 54.0 mol% Fe ₂ O ₃ , 3
The oxide magnetic material is characterized in that 4.0 to 43.0 mol% of MnO and the balance ZnO.

Further, according to the present invention, a MnZn ferrite powder is press-molded to obtain a molded body, and the molded body is plated with an aqueous solution containing Fe ions, Ni ions, Zn ions and an oxidizing agent. The method for producing an oxide magnetic material is characterized in that NiZn ferrite is generated in voids in the molded body.

[0011]

FUNCTION The magnetic loss (Pcv) of ferrite consists of hysteresis loss, eddy current loss and residual loss. The eddy current loss is proportional to the reciprocal of the specific resistance. Hysteresis loss is
It mainly depends on the crystal structure and the crystal magnetic anisotropy energy.
According to the present invention, MnZn ferrite powder is press-molded, and the voids inside the molded body are filled with NiZn ferrite in an aqueous solution by a ferrite plating method.
A low loss magnetic material is obtained.

The cause has not been fully clarified, but NiZn having a high specific resistance fills the voids of the green compact of MnZn ferrite, whereby MnZ in the sintered body is obtained.
It is understood that the NiZn ferrite is present in the gap between the crystal grains of the n-ferrite and the eddy current loss is reduced.

Further, in the prior art, the specific resistance was increased by adding a non-magnetic oxide having a high specific resistance and precipitating it at the grain boundary. However, in the present invention, it is replaced with a magnetic NiZn ferrite. Therefore, there is a possibility that the magnetic interaction between the MnZn ferrite particles or between the MnZn ferrite and the NiZn ferrite may act to reduce the loss.

In the present invention, the composition of MnZn ferrite is 52.0 to 54.0 mol% Fe ₂ O ₃ , 34.0 to 34.0.
The reason why the MnO content is 43.0 mol% and the balance is ZnO is that the loss increases remarkably outside the range.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. The MnZn ferrite compact in the present invention is obtained by pressure-molding a calcined powder of MnZn ferrite prepared by a usual method using a mold.
Usually, in order to obtain a ferrite molded body by pressure molding, considering the filling property into the mold, etc., the calcined powder is molded as granules by using polyvinyl alcohol or the like as a binder. It is necessary to remove the binder before filling the voids. As the binder removal method, a usual method of thermally decomposing the binder by heating and volatilizing it can be used.

For ferrite plating, Fe, N
Any water-soluble compound such as a compound of i, Zn and halogen can be used. Specific examples thereof include chlorides, but the present invention is not limited thereto. Further, it is necessary to perform a treatment for sufficiently infiltrating these aqueous solutions into the voids of the powder constituting the molded body, and it is necessary to add an oxidizing agent in order to make the components contained in the aqueous solution ferrite.

[0017]

EXAMPLES Next, the present invention will be specifically described with reference to examples.

First, Fe ₂ O ₃ is 52.0 to 54.0 mol.
%, MnO 34.0 to 43.0 mol%, balance ZnO
Of Fe ₂ O ₃ and Mn so as to obtain 6 kinds of composition within the range
₃ O ₄ and ZnO were weighed. Table 1 shows their composition.
This is shown as Examples 1 to 6.

[0019]

[Table 1]

As a comparative example, Fe ₂ O ₃ is 51.5.
mol%, 55.0 mol%, MnO 33 mol%,
Fe ₂ O ₃ , Mn ₃ O ₄ , Zn so that the balance is ZnO
Four kinds of O were weighed. In Table 1, these compositions are also shown as Comparative Examples 1 to 4.

Next, the weighed raw material powders were mixed for 2 hours using an attritor and granulated with a spray dryer. The granulated powder was calcined in a rotary kiln, the obtained calcined powder was crushed using an attritor, granulated by a spray dryer and pressed into a toroidal shape.

Each of the molded articles of Examples and Comparative Examples thus obtained was subjected to a binder removal treatment at 500 ° C. and ferrite plated to obtain a toroidal core. This treatment is performed using FeCl ₂ , NiCl ₂ , ZnCl
₂ , Fe ₂ O ₃ is 50 mol%, ZnO is 35 mol
%, NiO was added in an amount of 15 mol%, the molded body was immersed in the solution, and NaNO ₂ was gradually added as an oxidant while maintaining the temperature at 80 ° C.

At this time, an ultrasonic horn was used to allow the solution to sufficiently penetrate into the voids inside the molded body, and the pH was adjusted with NH ₄ OH by a pH controller to keep the aqueous solution substantially neutral. Further, for comparison, samples of the molded products of Examples and Comparative Examples were also prepared by sintering at 1300 ° C. in a controlled atmosphere without performing ferrite plating.

With respect to these sintered samples, the loss and the saturation magnetic flux density under the conditions of a frequency of 100 kHz, a magnetic field strength of 200 mT and a temperature of 80 ° C. were measured. In Table 1,
The measurement results of the loss and the saturation magnetic flux density for each of the examples and comparative examples are also shown.

From the results shown in Table 1, the sample plated with ferrite has lower loss than the sample sintered without ferrite plating, and the change of Bs is practically negligible. Further, it is found that the sample in which the composition of MnZn ferrite is limited to 52.0 to 54.0 mol% for Fe ₂ O ₃ , 34.0 to 43.0 mol% for MnO, and ZnO for the balance is extremely low in loss. .

[0026]

As described above, according to the present invention, M
The nZn ferrite has a lower loss than the MnZn ferrite produced by the conventional manufacturing method. In addition, since sintering is unnecessary and NiZn ferrite with a high specific resistance is plated by the ferrite plating method, it is possible to directly wire the ferrite core, and no bobbin or other winding component is required. Therefore, the cost can be reduced.

In the above-mentioned embodiment, the case where the composition of NiZn ferrite is changed is not particularly shown, but the same effect can be obtained with so-called NiZn ferrite. Also, the composition of MnZn ferrite is 52.0.
˜54.0 mol% Fe ₂ O ₃ , 34.0 to 43.0 mo
Although 1% of MnO and the balance ZnO are defined, a similar effect of lowering the loss can be obtained with a composition outside this range.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G018 AA21 AA23 AA25 AC06                 5E041 AB01 AB02 AB19 BC01 BC08                       CA02 CA03 HB14 HB17 NN01                       NN05 NN06

Claims (3)

[Claims] 1. An oxide magnetic material comprising a compact made of MnZn ferrite powder and NiZn ferrite formed in voids of the MnZn ferrite powder of the compact. 2. The oxide magnetic material according to claim 1, wherein the composition of the MnZn ferrite is 52.0 to 54.
An oxide magnetic material characterized in that 0 mol% Fe ₂ O ₃ , 34.0 to 43.0 mol% MnO, and the balance ZnO. 3. A molded body is obtained by press-molding MnZn ferrite powder, and the molded body is plated with an aqueous solution containing Fe ions, Ni ions, Zn ions, and an oxidizing agent to obtain a molded body. The method for producing an oxide magnetic material according to claim 1, wherein NiZn ferrite is generated in the voids.