JP2001006916A - Low loss oxide magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low loss oxide magnetic material wherein power loss is reduced. SOLUTION: Main component of this magnetic material is composed of Fe2O3 of 43-50 mol%, NiO of 10-40 mol%, CuO of 0.1-15 mol% and residue ZnO. At least one kind out of CaO, Cr2O3, MgO, Al2O3 and P2O5 of 0.005-0.1 wt.% is contained as additive. In this case, the mean crystal grain diameter of a baked member is at least 5 μm, and the ratio of pores in crystal grains to the whole pores is 5-60%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a low-loss oxide magnetic material used for a power transformer.

[0002]

2. Description of the Related Art In recent years, electronic devices, such as portable devices, have been rapidly reduced in size. And the power supply used for them is in the same flow. The transformer in the power supply
Since they occupy a large position in terms of both volume and power loss, their miniaturization and high efficiency are required.

[0003] The characteristics required of a ferrite material used for a power transformer include a low loss at a driving frequency, a high saturation magnetic flux density, a high Curie temperature, and a high specific resistance. If the loss is large, not only efficiency as a power source is poor, but also a problem of self-heating occurs. Therefore, it is desirable that the ferrite material has a low loss and a negative temperature characteristic of the loss. As these materials, low-cost Mn-Zn-based ferrite having a high saturation magnetic flux density (about 500 mT) is used.

However, the conventional Mn-Zn based ferrite has a small specific resistance and must be wound through a bobbin in order to secure insulation, and there is a limit to miniaturization.

On the other hand, Ni—Zn-based ferrite has a high specific resistance and can be wound directly. Further, in addition to the high specific resistance, since the low-temperature sintering is possible by adding Cu, the conductor and the magnetic body can be integrally sintered, and an unlimited size reduction can be realized.

However, conventional Ni-Zn ferrites have a high loss and are inefficient, and due to the problem of self-heating, it has been difficult to commercialize them as ferrite materials used for power transformers.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a low-loss oxide magnetic material with reduced power loss.

[0008]

According to the present invention, the main component is 43%.
５０50 mol% of Fe ₂ O ₃ , 10 to 40 mol% of N
iO, 1 to 15 mol% CuO, balance ZnO, 0.005 to 0.1 wt% CaO, C as an additive
It is a low-loss oxide magnetic material containing at least one of r ₂ O ₃ , MgO, Al ₂ O _{3 and} P ₂ O ₅ .

Further, the present invention provides the low-loss oxide magnetic material, wherein the sintered body has an average crystal grain size of 5 μm or more, and the ratio of pores in the crystal grains to all pores is 5 to 60%.
Is a low-loss oxide magnetic material.

The present invention also relates to the low-loss oxide magnetic material, wherein the temperature at which the power loss is minimized is 100 ° C. or higher.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various studies, the present inventors have found that as a main component composition, 43 to 50 mol% of Fe ₂
O _3, 10~40mol% of NiO, 1~15mol%
Of CuO, with the balance being ZnO, with 0.00 as an additive.
5～0.1Wt% of _{CaO, Cr 2 O 3, MgO} , Al
By containing at least one of ₂ O _{3 and} P ₂ O ₅ , the sintered body has an average crystal grain size of 5 μm or more, and the proportion of the pores in the crystal grains to all the pores is 5 to 60%, the low It has been found that a lossy oxide magnetic material for a power transformer can be obtained.

In the present invention, the reason why the specific resistance is remarkably higher than that of the conventional Mn-Zn ferrite is Fe ₂ O.
_This is because by setting ₃ to 43 to 50 mol%, the generation of Fe ^{2+ that} causes electric conduction was suppressed. Since the specific resistance is high, the winding can be wound directly, and a bobbin is not required. Therefore, cost can be reduced and downsizing can be achieved. Further, since the specific resistance is high, it is possible to integrally mold the conductor.

[0013] The loss of ferrite is the hysteresis loss,
It can be roughly divided into eddy current loss and residual loss. The present invention and the conventional N
Comparing the loss of the i-Zn ferrite, it was found that the loss was reduced mainly due to the reduction of the hysteresis loss. The hysteresis loss is a loss caused by irreversible movement of the domain wall. In order to reduce the hysteresis loss, it is necessary to reduce inclusions that hinder domain wall movement. However, if the inclusions are reduced too much, the domain wall will travel a long distance, and conversely increase the hysteresis loss. Further, the number of domain walls depends on the average crystal grain size. Therefore, it is desirable that the crystal grain size is large. As described above, in order to reduce the hysteresis loss, the average crystal grain size is large, and the crystal grains are
It seems that it is desirable that there be moderately obstacles that hinder domain wall movement.

The reason for the small loss of the product of the present invention is that, in addition to the large average crystal grain size of 5 μm or more, the ratio of pores in the crystal grains is large, or CaO, Cr ₂ added as an additive. O ₃ , MgO, Al ₂ O ₃ or P
It is presumed that ₂ O ₅ was present as inclusions in the crystal grains, and the hysteresis loss was reduced by the pinning action of the domain wall. In addition, the temperature at which the loss is minimized is 100 ° C. or higher regardless of the composition of the present invention. The exact cause is unknown.

The main component composition is 43 to 50 mol% of Fe ₂
O _3, 10~40mol% of NiO, 1~15mol%
Of CuO and the balance of ZnO were Fe ₂ O ₃ of 43 m
If the amount is less than 0.1 mol%, or if the content of NiO exceeds 40 mol%, or if the content of CuO exceeds 15 mol%, the loss at room temperature is significantly deteriorated. Also, when the content of Fe ₂ O ₃ exceeds 50 mol%, the specific resistance is remarkably reduced due to generation of Fe ²⁺ . If the NiO content is less than 10 mol%, the Curie temperature and the maximum magnetic flux density decrease, and the reliability as a power transformer material is poor. If CuO is less than 1 mol%, firing at a low temperature cannot be performed, and the specific resistance is significantly reduced due to generation of Fe ²⁺ by firing at a high temperature.

As an additive, 0.005 to 0.1 wt% of C
aO, Cr ₂ O ₃ , MgO, Al ₂ O ₃ or P ₂ O ₅
At least one of CaO, Cr ₂ O ₃ , M
If the content of gO, Al ₂ O ₃ or P ₂ O ₅ is less than 0.005 wt%, hysteresis loss increases to cause deterioration of the loss, and CaO, Cr ₂ O ₃ , MgO, Al
_This is because when the content of ₂ O ₃ or P ₂ O ₅ exceeds 0.1 wt%, the density becomes low. The same effect can be obtained by adding these additives alone or in combination.

The reason why the average crystal grain size of the fired body is set to 5 μm or more is that if the average crystal grain size of the fired body is less than 5 μm, the loss is deteriorated due to an increase in hysteresis loss. The proportion of pores in the crystal grains to all pores is 5-60%
The reason is that the ratio of the pores in the crystal grains to all the pores is 5
% Or more than 60% increases the hysteresis loss.

[0018]

EXAMPLES (Example 1) Samples having different main component compositions were prepared. 41.5 to 50.5 mol% of F as a main component
e ₃ O _4, 8.0~42.0mol% of NiO, 0~1
6.0 mol% CuO, balance ZnO, 0.1% as additive
01 wt% CaO is weighed, and 2 wt.
Mix for hours. After mixing, the mixture 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, the mixture was granulated by a spray dryer, pressed into a toroidal shape, and fired at a firing temperature of 1150 ° C.

As a conventional product, the main component composition is 49 mol%
Of Fe ₂ O ₃ , 25 mol% of NiO, and the balance of ZnO, Ni—Zn-based ferrite, were weighed and mixed using an attritor for 2 hours. After mixing, the mixture 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, the mixture was granulated by a spray dryer, pressed into a toroidal shape, and fired at a firing temperature of 1250 ° C.

Table 1 shows the ratio of the pores in the crystal grains to the total pores of the invention product, the comparison product (the sample whose main component composition is outside the scope of the claims) and the conventional product when the main component composition was changed, and the average crystal grain. Diameter, specific resistance and 50kHz-150mT-room temperature, 50k
Hz-150mT-80 ° C, 50kHz-150mT-
Indicates a loss of 120 ° C.

[0021]

[Table 1]

According to Table 1, the main component composition was 43 to 50 mol.
% Fe ₂ O ₃ , 10-40 mol% NiO, 1-1
It can be seen that the specific resistance is high and the loss is small in the range of 5 mol% of CuO and the balance of ZnO.

FIG. 1 shows the product 4 of the present invention and 50 kHz of the conventional product.
4 shows the temperature characteristics of a loss of −150 mT. FIG. 1 shows that the product 4 of the present invention has a smaller loss over the entire temperature range than the conventional product, and the temperature at which the power loss is minimized is 120 ° C. or higher.

Example 2 The type and amount of additives were changed.
A sample was prepared. 49.5mol as main component
% Fe₂O₃, 15 mol% NiO, 5 mol%
CuO, balance ZnO, 0.001-0.2 w as additive
t% CaO, Cr₂O₃, MgO, Al ₂O₃Or
P₂O₅Are weighed and mixed using an attritor for 2 hours.
Was. After mixing, the mixture was granulated with a spray dryer. Granulated
The powder was calcined in a rotary kiln. A.
Disintegrated using a triter. After crushing, spray dry
Granulated in a towel and pressed to toroidal shape.
It was fired at a firing temperature of ° C.

Tables 2 to 6 show that CaO, Cr ₂ O ₃ , Mg
When the amount of O, Al ₂ O ₃ or P ₂ O ₅ was changed, the ratio of the pores in the crystal grains to the total pores of the invention product, the comparison product, and the conventional product (prepared in Example 1), the average crystal grain size, Specific resistance and 5
0kHz-150mT-room temperature, 50kHz-150mT
The loss at -80 ° C, 50kHz-150mT-120 ° C is shown.

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

[Table 5]

[0030]

[Table 6]

According to Tables 2 to 6, 0.005 to 0.1 wt%
CaO, Cr ₂ O ₃ , MgO, Al ₂ O ₃ or P ₂
Inventions containing O ₅ has a high specific resistance, it can be seen that loss is small.

Example 3 A sample was prepared in which the average crystal grain size was changed. 49.5 mol% of Fe ₂ as a main component
O ₃ , 15 mol% NiO, 5 mol% CuO, the balance ZnO, and 0.01 wt% CaO as an additive were weighed and mixed for 2 hours using an attritor. After mixing, the mixture 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, the mixture is granulated by a spray dryer, pressed into a toroidal shape, and subjected to 1050 to 1250 ° C.
At the firing temperature of

Table 7 shows the ratio of the pores in the crystal grains to the total pores of the invention product, the comparative product, and the conventional product (made in Example 1) when the average crystal grain size was changed, the average crystal grain size, and the ratio. Resistance and 50kHz-150mT-room temperature, 50kHz-150m
The loss at T-80 ° C, 50kHz-150mT-120 ° C is shown.

[0034]

[Table 7]

From Table 7, it can be seen that the inventions having an average crystal grain size of 5 μm or more have high specific resistance and small loss.

[0036]

As described above, according to the present invention,
A low-loss oxide magnetic material with reduced power loss can be provided.

[Brief description of the drawings]

FIG. 1 shows a product 4 of the present invention and a conventional product of 50 kHz-150 mT.
The figure which shows the temperature characteristic of the loss of FIG.

[Explanation of symbols]

 A Product of the present invention 4 B Conventional product

Claims (3)

[Claims] 1. An Fe ₂ O containing 43 to 50 mol% of a main component.
₃ , composed of 10 to 40 mol% of NiO, 1 to 15 mol% of CuO, and balance of ZnO, and 0.005 as an additive.
～0.1Wt% of _{CaO, Cr 2 O 3, MgO} , Al 2
A low-loss oxide magnetic material containing at least one of O _{3 and} P ₂ O ₅ . 2. The low-loss oxide magnetic material according to claim 1, wherein an average crystal grain size of the fired body is 5 μm or more, and a ratio of pores in crystal grains to all pores is 5 to 60%. Characterized low-loss oxide magnetic material. 3. The low-loss oxide magnetic material according to claim 2, wherein the temperature at which the power loss is minimized is 100 ° C. or higher.