JPH08119727A - Method for sintering oxide magnetic material - Google Patents

Abstract

PURPOSE: To obtain an oxide magnetic material having a high permeability, a low iron loss and prescribed characteristics by avoiding the compositional regulation such as addition of accessory components as much as possible and specifying sintering conditions in an Mn-Zn-based ferrite. CONSTITUTION: An oxide magnetic material consisting essentially of Fe2 O3 , MnO and ZnO is sintered. When the oxygen partial pressure in a cooling process of the sintering step is PO2 and the temperature is T, with the proviso that A and B are constants in the process, the oxygen partial pressure PO2 of the atmosphere in the cooling process is controlled according to the formula represented by logPO2 =-(A/T) × 10<-4> + B corresponding to the respective temperatures in the cooling process from the sintering temperature. The constant A is set within the range of 2000-50000 in the case of the oxide magnetic material for a high permeability and within the range of 2000-80000 in the case of the oxide magnetic material for a low iron loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention shows an oxide magnetic material having a high magnetic permeability which is used as a magnetic core in a transformer for communication and the like and a low loss characteristic which is used as a magnetic core of a power source element of an electronic device. The present invention relates to a method for sintering an oxide magnetic material.

[0002]

2. Description of the Related Art Conventionally, oxide magnetic materials have been widely used as magnetic core materials for signal transformers and electric power transformers of various communication equipments and electronic equipments, and particularly, high magnetic permeability and low loss at several 100 kHz. It is used by taking advantage of its characteristics. Conventional Mn-
In order to improve the initial magnetic permeability (μ) value of Zn-based oxide magnetic material and its temperature characteristic, and improve the iron loss (P _cv ) and its temperature characteristic, the μ-T curve characteristic of the material is obtained, and The temperature showing the second peak of μ and the magnitude of μ, and P _cv −
The T-curve characteristics were obtained, and the composition was changed with reference to the temperature at which P _cv was the lowest and the size of P _cv . In particular, by changing the composition due to the addition of trace amounts, mu and P _cv,
And its temperature characteristics have been improved.

Signal transformers in communication equipment are required to be compact and have high performance. For this reason, Mn-Zn type ferrite having a large initial magnetic permeability is particularly used. As described above, if the temperature at which the second peak of the initial magnetic permeability shows and the initial magnetic permeability at that temperature can be controlled, the magnitude of μ and the temperature characteristic can be controlled. In the conventional control of the temperature characteristics of the magnetic core material, the temperature of the second peak of the initial magnetic permeability and the value of the peak have been used as a guide for the control, but the method is mainly based on the composition including addition of a subcomponent. Although we have obtained products that meet the required characteristics by controlling, it is extremely difficult and under extremely strict control,
There is a problem that it is not suitable for mass production because it requires a great deal of labor and a low yield.

On the other hand, in addition to low loss characteristics, oxide magnetic materials used for power transformers and the like have to control the temperature characteristics of iron loss (P _cv ) according to the environmental temperature of the equipment in which they are incorporated and used. However, Mn—Zn-based ferrite containing CaO and SiO ₂ as subcomponents is used, and Al ₂ O ₃ and SnO are further added depending on required temperature characteristics.
_A general method is to add auxiliary components such as ₂ , TiO ₂ , V ₂ O ₅ , Nb ₂ O ₅ and the like. In this case as well, the temperature was shown to be the minimum P _cv of the P _cv -T curve characteristic of the material and the value of P _cv was used as a standard for improvement. For this reason, the composition of ferrite has been adjusted according to the temperature characteristics based on individual requirements. In order to satisfy various required characteristics, it is necessary to prepare powders of various compositions under extremely strict control, as in the case of the high magnetic permeability material, which requires complicated control and low yield. For,
There was a problem that it was forced to work inefficiently.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a Mn-Zn-based ferrite which has a predetermined temperature characteristic and a high magnetic permeability characteristic and a low loss characteristic. The temperature showing the second peak of the initial magnetic permeability in the μ-T curve characteristic, which is a standard for improving the above-mentioned various properties, and the value of the initial magnetic permeability at that temperature, which is a measure for improving the above-mentioned various properties, by avoiding relying on preparation as much as possible , Or P _cv −
And the magnitude of the temperature and P _cv where P _cv in T curve characteristic exhibits a minimum as a guide, in providing sintering process the oxide magnetic material can be realized having a predetermined temperature characteristic with high magnetic permeability and low core loss is there.

[0006]

In order to solve the above-mentioned problems, the present invention provides a method for sintering an oxide magnetic material containing Fe ₂ O ₃ , MnO and ZnO as main components. The oxygen partial pressure of the atmosphere in the process is P _O2 , the temperature is T, A and B are constants, and log P _O2 =-(A / T) according to each temperature in the cooling process from the sintering temperature.
Provided is a method for sintering an oxide magnetic material, which controls an oxygen partial pressure P _O2 of an atmosphere in a cooling process according to a formula represented by × 10 ^-4 + B.

A method of sintering an oxide magnetic material, characterized in that the value of A is in the range of 2000 to 50,000 in the method of sintering an oxide magnetic material described above.

Fe ₂ O ₃ , MnO, and ZnO are contained as main components, and CaO and SiO ₂ are contained as at least subordinate components. The content ratios of CaO are 0.02 to 0.15% by weight, and SiO ₂ is 0. In the sintering method of the oxide magnetic material of 005 to 0.1% by weight, the oxygen partial pressure of the atmosphere in the cooling process of the sintering process is P _O2 and the temperatures are T, A and B.
Is a constant, and the oxygen partial pressure P _O2 of the atmosphere during the cooling process is controlled according to the expression log P _O2 = − (A / T) × 10 ⁻⁴ + B according to each temperature in the cooling process from the sintering temperature. , A of the oxide magnetic material in the range of 2000 to 80,000 is provided.

[0009]

As a method of improving the temperature characteristics of μ and P _cv in Mn-Zn system ferrite, the present invention continuously changes the oxygen partial pressure of the atmosphere during the sintering process, particularly the cooling process, as a function of the cooling temperature. By controlling to, the target μ-T curve characteristic and P _cv -T curve characteristic are obtained, and the target temperature characteristic is realized.

[0010]

The present invention will be described below with reference to examples. FIG. 1 shows the relationship between the temperature in the sintering process, particularly in the cooling process, and the oxygen partial pressure controlled in conjunction with the temperature in the sintering process in Examples 1 and 2 described below. FIG. 2 (a) shows the relationship between the constant A in the formula shown by the present invention and the temperature showing the second peak in the μ-T curve in Example 1,
FIG. 2B shows the relationship between the constant A and the magnitude of the initial magnetic permeability at the second peak. FIG. 3A shows the relationship between the constant A in the formula shown by the present invention and the temperature at which the minimum iron loss (P _cv ) is obtained in Example 2, and FIG. The relationship with the minimum iron loss (P _cv ) is shown.

(Embodiment 1) In this embodiment, M for high magnetic permeability is used.
It is an example of an n-Zn ferrite. Fe ₂ O ₃ , MnO
In the Mn-Zn-based ferrite composed mainly of ZnO and ZnO, the composition ratio is Fe ₂ O ₃ 52.0 mol%, M
nO25.0 mol% and the balance ZnO.

The powder having the above composition ratio is mixed by a ball mill, pre-baked, granulated and molded and sintered. Molded body has an outer diameter of 3
It was molded into 0 mm, inner diameter 18 mm, and height 5 mm. It is known that a desirable sintering condition for this material is to hold at a sintering temperature of 1300 to 1400 ° C. for 2 to 10 hours in a nitrogen atmosphere containing 0.5 to 3.5% of oxygen. The sintering retention conditions in this example were such that the sintering temperature was maintained at 1350 ° C. for 2 hours in a nitrogen atmosphere containing 1.5% oxygen.

Next, the oxygen partial pressure P _{O2 is set} to 1 with respect to the temperature T in the cooling process of sintering, which is indicated by a cooling program separately defined.
The value of the constant A was variously set according to the expression represented by ogP _O2 =-(A / T) × 10 ^-4 + B. It should be noted that B is a constant determined by the temperature and slope at which the control of the oxygen partial pressure of the atmosphere during the cooling process is started. The temperature of the electric furnace, which is the heating means, was controlled by the program controller. The oxygen partial pressure was controlled by using a mass flow controller linked to the program controller and adjusting the flow rates of air and nitrogen.

FIG. 1 shows the relationship between each temperature in the cooling process according to the value of the set constant A and the oxygen partial pressure to be controlled corresponding to the temperature. The magnetic core of the sintered body obtained under the above sintering conditions was used as a sample. FIG. 2 (a) shows the dependence of the temperature showing the second peak of the initial permeability when the sample was measured at a frequency of 1 kHz for each value of the constant A in the above equation.
(B) shows the dependence of the initial magnetic permeability at the second peak on each value of the constant A. A = 2000
And when A = 50000, the temperatures showing the second peak are −10 ° C. and 50 ° C., respectively, and the initial magnetic permeability is 7200 and 11800, respectively. The value of A is 2000
In the range of up to 50,000, as is apparent from FIGS. 2A and 2B, the temperature showing the second peak becomes higher with the increase of A at the frequency of 1 kHz.
Similarly, the peak value, that is, the initial magnetic permeability, monotonically increases with A. From this result, the temperature showing the second peak,
It can be seen that the control of the initial magnetic permeability at that temperature and the temperature thereof are stably obtained under the above sintering conditions.

However, in the sample obtained by setting the value of A to 2000 or less, the result shows the low magnetic property which is considered to be caused by the abnormal grain growth, and it is difficult to control the temperature showing the second peak. It was also found that when the value of A was set to exceed 50,000, the loss (tan δ / μ) increased.

(Embodiment 2) This embodiment shows an example of Mn-Zn type ferrite having low loss characteristics for a transformer.
Mn-Zn composed of 53.0 mol% Fe ₂ O ₃ , 39.0 mol% MnO, and 8.0 mol% ZnO as main components
0.02 wt% of SiO ₂ and 0.05 wt% of CaO were added as subcomponents to the system ferrite, and the molded body was sintered in the same manner as in Example 1 above. The sintering and holding conditions in this example were holding for 2 hours at a sintering temperature of 1250 to 1350 ° C. in a nitrogen atmosphere containing 0.5 to 5.0% oxygen.

In this embodiment, as in the case of Embodiment 1, the oxygen partial pressure corresponds to the cooling temperature T in the cooling process of sintering.
The value of the constant A was variously set in accordance with the expression expressing P _O2 by log P _O2 = − (A / T) × 10 ⁻⁴ + B. In FIG. 1, A = 1
The relationship of the oxygen partial pressure controlled corresponding to the temperature of the cooling process in the case of 2000 is shown. As a result, with respect to the obtained sintered body sample, the maximum excitation magnetic flux density (B _m ) = 200 mT,
FIG. 3A shows the relationship between the temperature at which P _CV measured under the condition of a frequency of 100 kHz becomes the minimum and each value of the constant A. FIG.
(B) shows the relationship between the level of P _CV and each value of the constant A. When the value of A is in the range of 2000 to 80,000, as is clear from FIG. 3, the temperature at which P _CV becomes the minimum increases monotonically as A increases. The level of P _CV is 200 for A.
It takes a minimum when it takes a value between 00 and 40,000. In the range of A = 2000 to 80,000, P _CV is 550 or less, which is the required characteristic standard, and is sufficiently satisfied. A
There time 1000, and time of 100000, P _CV in each 750 and 950, did not result in meeting the required characteristics standards.

The above facts, in the cooling process of the sintering process, by the appropriate conditions the relationship between temperature and the oxygen partial pressure, it is possible to control the temperature and P _CV which P _CV is minimum Indicates that.

[0019]

As described above, in the cooling process of the sintering process of the Mn-Zn ferrite, the oxygen partial pressure P _O2
With respect to the cooling temperature T, logP _O2 =-(A / T) × 1
By setting the value of the constant A to a predetermined value according to the expression represented by 0 ^-4 + B, the temperature at which the second peak of the initial magnetic permeability shows without relying on the preparation of the composition such as the addition of auxiliary components,
And the initial permeability at that temperature can be controlled,
It was also clarified that the temperature characteristics of iron loss can be controlled.

In the present embodiment, the temperature of the electric furnace is controlled by a program controller, and the oxygen partial pressure is controlled by using a mass flow controller linked to the program controller and adjusting the flow rates of air and nitrogen to carry out sintering. This is as already mentioned. Needless to say, the same effect can be obtained by using a so-called continuous furnace having a controlled temperature distribution and a space in which the oxygen partial pressure is maintained in association with the temperature distribution.

[Brief description of drawings]

FIG. 1 is a relationship between a temperature of a cooling process according to a value of a constant A in a relational expression between an oxygen partial pressure of an atmosphere during cooling and a cooling temperature of the present invention and an oxygen partial pressure to be controlled corresponding to the temperature. FIG.

FIG. 2 (a) is a diagram showing temperature dependence showing a second peak of the initial permeability at a frequency of 1 kHz for each value of the constant A in Example 1, and FIG. 2 (b) is Figure 2
The figure which shows the dependence with respect to the constant A of the initial magnetic permeability of the second peak measured on the same conditions as (a).

FIG. 3 (a) shows that in Example 2, B _m = 20.
FIG. 3B is a diagram showing the relationship between the temperature at which P _CV measured under the condition of 0 mT and a frequency of 100 kHz is minimum and the constant A,
P _CV level and constant A measured under the same conditions as in FIG.
The figure which shows a relationship.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01F 1/34 B

Claims (3)

[Claims] 1. A method of sintering an oxide magnetic material mainly composed of Fe ₂ O ₃ , MnO and ZnO, wherein the oxygen partial pressure of the atmosphere in the cooling process of the sintering step is P _O2 and the temperature is T, A. And B as constants, log P _O2 =-(A / T) ×, depending on each temperature in the cooling process from the sintering temperature.
A method for sintering an oxide magnetic material, comprising controlling an oxygen partial pressure P _O2 of an atmosphere in a cooling process according to an expression represented by 10 ⁻⁴ + B. 2. The method for sintering an oxide magnetic material according to claim 1, wherein the value of A is in the range of 2,000 to 50,000. 3. Fe ₂ O ₃ , MnO and ZnO as main components and at least CaO and SiO ₂ as sub-components, each content of CaO is 0.02 to 0.15 wt%, SiO ₂ is In the sintering method of the oxide magnetic material of 0.005 to 0.1 wt%, the oxygen partial pressure of the atmosphere in the cooling process of the sintering process is P _O2 , and the temperatures are T, A and B.
Is a constant, and the oxygen partial pressure P _O2 of the atmosphere during the cooling process is controlled according to the expression log P _O2 = − (A / T) × 10 ⁻⁴ + B according to each temperature in the cooling process from the sintering temperature. , A in the range of 2000 to 80,000.