JPH08259315A - Production of ferrite sintered compact - Google Patents

Abstract

PURPOSE: To provide a method for producing a ferrite sintered compact having slight dimensional change in baking and excellent magnetic characteristics in the ferrite sintered compact used for various electronic parts. CONSTITUTION: This method for producing a ferrite sintered compact comprises the first step for heat-treating at least one or more oxides constituting the ferrite composition and pulverizing the heat-treated oxides, the second step for replacing all or a part of at least the one or more of the oxides constituting the ferrite with a metallic powder and mixing the oxides with the metallic powder, the third step for adding an organic binder to the prepared mixed powder and forming a granulated powder, the fourth step for compression- forming the granulated powder and providing a compact and the fifth step for baking the resultant compact and forming the ferrite crystalline body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferrite sintered body used in various electronic parts.

[0002]

2. Description of the Related Art Conventional ferrite sintered bodies have been manufactured as follows.

First, MnO, NiO, and C are used as starting materials.
After measuring and mixing oxides such as uO, ZnO, and Fe ₂ O ₃ , the mixture is calcined at about 800 to 900 ° C., and then the calcined powder is crushed and granulated, and then molded to about 1100 to 100 ° C. It was manufactured by firing at 1300 ° C.

However, the ferrite sintered body produced in this way shrinks by about 10 to 30% during the main firing as is well known. Shrinkage during the sintering process occurs due to the following reasons. A compact compacted by simply pressurizing the calcined powder has a low compacting density because a powder having a particle size of about 1 to 5 μm or less is used, and although the particles are in contact with each other, there are still many voids. When heated at a temperature equal to or higher than the firing temperature, mutual diffusion occurs at the contact portion between particles and sintering starts.
As the sintering progresses, the voids between the particles decrease, resulting in 10-30% shrinkage. Therefore, when the ferrite material is actually fired, the molded body is manufactured so as to be slightly larger than the required size of the ferrite sintered body in consideration of this dimensional change rate and deformation. Therefore, in order to obtain a ferrite sintered body that requires high dimensional accuracy, a cutting process for forming the obtained ferrite sintered body into the required size and shape was necessary. Further, since the ferrite sintered body after firing is extremely hard, the cutting blade used in this cutting process is significantly worn, and the number of processing steps is large, resulting in a high cost.

Although many studies have been carried out so far to improve the shrinkage of ferrite due to sintering, it is the actual situation that some shrinkage is inevitable in order to secure the various characteristics of ferrite. For example, JP-A-58-135
As described in JP-A No. 133 and JP-A-58-135606, when the calcined ferrite powder and the glass powder are mixed and then fired at a temperature at which ferrite sintering proceeds, the glass powder becomes ferrite particles. By covering the periphery of the ferrite, it is possible to partially suppress the densification of the ferrite and obtain a ferrite sintered body with a low shrinkage ratio. However, since the calcination powder preparation temperature is lower than the main calcination temperature, mutual diffusion between ferrite particles in direct contact with each other is unavoidable during the main calcination, and in reality, shrinkage of several% occurred.

[0006]

As described above, in the conventional ferrite sintered body, the shrinkage increases as the sintering proceeds to obtain the desired characteristics, and conversely, if the shrinkage is suppressed, the characteristics decrease. However, it is very difficult to achieve both.
However, ferrite sintered bodies are widely used as electronic parts and device materials, and their characteristics and high dimensional accuracy are becoming more and more important.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for producing a ferrite sintered body having a small dimensional change rate during firing and excellent magnetic properties.

[0008]

In order to achieve the above-mentioned object, a method for producing a ferrite sintered body of the present invention comprises a first step of heat-treating and pulverizing at least one kind of oxide constituting a ferrite composition, A second step of substituting and mixing at least one or more kinds of oxides constituting the ferrite with metal powders wholly or partly, and a second step of adding and mixing at least one or more kinds of metal powders of elements, and this mixing A third step of forming a granulated powder by adding an organic binder to the powder to form a granulated powder, a fourth step of compression-molding the granulated powder to obtain a molded body, and firing the molded body to obtain a ferrite crystal body. And a fifth step for forming a ferrite sintered body.

Further, MnO, NiO, Cu as oxides
O, ZnO, Fe ₂ O ₃ at least one kind, and Mn, Ni, Cu, Zn, Fe at least one kind as a metal powder are used, and the heat treatment temperature is 500 to 1100 ° C., and the firing temperature is 800 to 1300 ° C. The present invention relates to a manufacturing method.

[0010]

According to the above-described method for producing a ferrite sintered body of the present invention, the added metal powder is oxidized and expanded during the firing process to fill the voids between the particles, thereby suppressing the dimensional change during firing. By heat-treating at least one oxide of the starting material, the sinterability of ferrite is remarkably improved, the dimensional change rate is small, and a ferrite sintered body having excellent magnetic properties can be obtained.

[0011]

EXAMPLES Examples of the present invention will be described below.

That is, the basis of the method for producing a ferrite sintered body of the present invention is that the first step of heat-treating and pulverizing at least one or more kinds of oxides constituting the ferrite composition, and the oxidation constituting the ferrite. A second step of substituting and mixing at least one kind or more of all or part of the metal powder with a metal powder, a second step of adding and mixing at least one kind of metal powder of the element, and an organic binder to the mixed powder. A third step of adding and mixing to form a granulated powder, a fourth step of compression molding the granulated powder to obtain a molded body, and a fifth step of firing the molded body to form a ferrite crystal body. It is equipped with and.

At this time, the heat treatment temperature is 500 to 1000 ° C.
It is preferable that the temperature is 100 ° C. or more lower than the firing temperature. This means that when heat treatment is performed at a high temperature equal to or higher than the firing temperature, the reactivity during the main firing is significantly reduced.
This is because it is difficult to obtain excellent magnetic properties.

Further, the effect of the heat treatment is greater when the main baking temperature is 1300 ° C. or lower. When fired at 1300 ° C. or higher, magnetic properties start to deteriorate. On the other hand, when the main firing temperature is 800 ° C. or lower, the reaction does not proceed sufficiently,
Since it is not made 100% spinel, various characteristics are significantly deteriorated.

The effect obtained by heat-treating each oxide is that NiO undergoes a phase transition at around 250 ° C. (Electrochemical Handbook, 4th edition, Electrochemical Society, Maruzen).
It is known that the heat treatment causes a phase transition of NiO, which enhances the reactivity during the main firing and improves the magnetic properties. For other oxides, although the reason is not clear, it may be possible to increase the reactivity with the metal powder or remove impurities by performing heat treatment in advance, and the same effect with varying degrees. Was recognized.

The average particle size of the metal powder is the minimum condition that all the metal powder is oxidized during the firing process, and varies greatly depending on various conditions such as firing temperature and temperature rising rate.
It is desirable that the thickness is about 20 μm. If the particle size of the metal powder is too small, oxidative expansion will proceed rapidly in a certain temperature range, and the oxygen concentration in the sample will become non-uniform and a sound structure will not be obtained, or cracks will occur in the sintered body. This is because such a problem occurs.

Next, specific examples will be described based on experimental results. (Example 1) The starting material was calcined at 800 ° C. for 2 hours, the average particle size was 1 μm, the composition ratio was NiO = 15 mol%, and Z was Z.
nO = 30 mol%, CuO = 5 mol%, Fe ₂ O ₃ =
A 50 mol% Ni-Zn-Cu-based ferrite calcined powder was used. Further, as oxides, NiO, ZnO, CuO,
As the metal powder, a metal Fe powder having an average particle size of 6 μm was used. Here, the oxide and the metal powder are collectively referred to as a filler. The composition of this filler was blended so as to have the same composition as the above-mentioned ferrite calcined powder. The oxides and metal powders that compose the ferrite calcined powder and the filler were weighed so that the volume ratio of the calcined ferrite powder and the filler was 6: 4. Among these, at least one kind of oxides NiO, ZnO, and CuO is 800 ° C. as shown in (Table 1),
It was replaced with one that was heat-treated for 2 hours.

The above calcined ferrite powder, oxide, heat-treated oxide and metal powder were mixed, 10% by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added, and the mixture was passed through a 30 # sieve to granulate. did. 1 t / cm of this granulated powder
^After uniaxial die molding in ² , the molded body was bound out at 350 ° C. for 1 hr in air, and then fired at 1000 ° C. for 5 hr in air.

To measure the characteristics, a toroidal core having an outer diameter of 15 mm, an inner diameter of 10 mm, and a thickness of 3 mm was cut out from the obtained ferrite sintered body, and a 0.5 mmφ enamel wire was cut into 20 pieces.
Turn, 1M using an impedance analyzer
The magnetic permeability at Hz was measured. The density, dimensional change rate, and magnetic permeability of each ferrite core are shown in (Table 1).

[0020]

[Table 1]

Since NiO has the lowest reactivity among the oxides used in this example, the characteristics of NiO heat-treated are particularly improved. In addition, NiO, ZnO,
Even if CuO is mixed and heat-treated, no compound is formed, so magnetic properties,
No difference is seen in any of the microstructures.

Combinations other than the combinations shown in (Table 1) are conceivable, but it goes without saying that they are also effective.

Example 2 The starting material has an average particle size of 1 to
Using NiO, ZnO, CuO, Fe ₂ O _{3 of} 4 μm and metallic Fe powder having an average particle size of 6 μm, the composition ratio is NiO = 8mo.
1%, ZnO = 32 mol%, CuO = 12 mol%,
A ferrite containing Fe ₂ O ₃ = 48 mol% was prepared.

First, NiO, ZnO and CuO were mixed in a molar ratio of 8:32:12 and heat-treated for 2 hours at the temperature shown in (Table 2). In addition to this, Fe ₂ O ₃ and metal F
The e powder was weighed and mixed so that the weight ratio was 1: 1 and the mixture was added so as to have the above composition ratio. Then, a molded body was prepared by the same method as in Example 1, bound at 350 ° C. for 1 hr in the air, and then fired at 1200 ° C. for 4 hr.

The density, dimensional change rate and magnetic permeability of the thus obtained ferrite sintered body are shown in (Table 2).

[0026]

[Table 2]

It can be seen that when the heat treatment temperature is 480 ° C., the density and magnetic permeability are remarkably lower than those of the samples heat-treated at other temperatures, and the sinterability is clearly inferior to the case of heat treatment at 500 ° C. or higher. . On the other hand, when the heat treatment temperature is equal to or lower than the firing temperature, the reactivity is rather lowered by the heat treatment and the sintering does not proceed, so that it is considered that the density and magnetic permeability are not improved. This can also be explained from the fact that the shrinkage during sintering is small and the dimensional change rate tends to expand. The heat treatment temperature is lower than the firing temperature, and the magnetic permeability shows a good value when the heat treatment temperature is in the range of 500 to 1100 ° C. However, in consideration of the density and the dimensional change rate, the heat treatment is further performed in the range of 600 to 1000 ° C. desirable.

It is also conceivable to change the main firing temperature, but it goes without saying that there is no problem if it is at or above the temperature at which spinelization progresses.

(Example 3) The starting material has an average particle size of 1 to 3
Using NiO, ZnO, CuO, Fe ₂ O ₃ of μm and metallic Fe powder having an average particle size of 6 μm, the composition ratio is NiO = 8 mol
%, ZnO = 32 mol%, CuO = 12 mol%, F
A ferrite of e ₂ O ₃ = 48 mol% was prepared.

First, NiO, ZnO and CuO were mixed at a molar ratio of 8:32:12, and the mixture was heated at 600 ° C. for 2 hours.
Heat treated in. Fe ₂ O ₃ and metallic Fe powder were weighed and mixed so that the weight ratio was 1: 1 and added to the above composition ratio so as to prepare a molded body in the same manner as in Example 1. After binding out at 350 ° C. for 1 hr in the atmosphere, firing was performed in the atmosphere for 6 hr at the temperature shown in (Table 3).

Table 3 shows the density, dimensional change rate, and magnetic permeability when the firing temperature was changed. For comparison, the magnetic permeability of the sample of the same composition without heat treatment is also shown in parentheses.

[0032]

[Table 3]

The firing temperature and the magnetic permeability have a positive correlation up to 1300 ° C. regardless of the presence or absence of the heat treatment, but the one heat treated at 600 ° C. has a considerably improved magnetic permeability at a low temperature of 800 ° C. It can be seen that the reactivity was improved by performing the heat treatment. However, the firing temperature is 1320
It is considered that the characteristics deteriorate as the temperature rises above ° C.
On the other hand, the sample that has not been subjected to the pretreatment has insufficient reactivity, and therefore the magnetic permeability does not improve even in the sample fired at a high temperature.

Although the optimum firing temperature was slightly changed by changing the composition, firing time, and heat treatment temperature, no difference was observed in the characteristics as compared with those obtained in this example. 950 to 1200 in terms of density, dimensional change rate and magnetic permeability
The effect of the present invention is maximized by firing at a temperature between ° C.

Example 4 MnO, ZnO, Fe ₂ O ₃ as oxides and Mn, Fe as metal powders were used as starting materials for Mn-Zn ferrite, and the composition ratio was MnO: Zn.
O: Fe ₂ O ₃ = 24: 24: 52 mol% ferrite was produced. As shown in (Table 4), in Example 18, M
nO, and Fe ₂ O ₃ in Example 19 at 800 ° C.,
Heat treatment was performed in the atmosphere for 2 hours, and as the metal powder, Fe was used in Example 18 and Mn and Fe were used in Example 19. The oxide and the metal powder were added at a weight ratio of 1: 1. These were granulated in the same manner as in Example 1 to prepare a molded body, which was bound out in the atmosphere at 350 ° C. for 1 hr, and then fired at 1200 ° C. for 6 hr in an N ₂ —O ₂ atmosphere. The density, dimensional change rate and magnetic permeability of the obtained ferrite sintered body are shown in (Table 5) as Comparative Example 8, Example 23,
Shown as 24.

On the other hand, the starting material for the Ni-Zn-Cu ferrite is Ni having an average particle size of 1 to 4 μm as an oxide.
O, ZnO, CuO, Fe ₂ O ₃ and Ni, Zn, Cu, Fe metal powder having an average particle size of 3 to 8 μm as a metal powder were used, and the composition ratio was NiO = 10 mol%, ZnO = 30 mol.
%, CuO = 12 mol%, Fe ₂ O ₃ = 48 mol% ferrite was produced. In addition to the above starting materials, NiO,
ZnO and Fe ₂ O ₃ were individually heat-treated at 800 ° C. for 2 hours, and NiO, ZnO, and CuO were mixed and simultaneously heat-treated at 800 ° C. for 2 hours. These were weighed with the combinations shown in (Table 4) so as to have the above composition ratio, and granulated powder was produced in the same manner as in Example 1. The oxide and the metal powder were mixed in a weight ratio of 1: 1. A molded body was produced from the above-mentioned granulated powder by the same method as in Example 1, bound out at 350 ° C. for 1 hr in air, and then fired at 1000 ° C. for 6 hr in air. The density, dimensional change rate and magnetic permeability of the obtained ferrite sintered body are shown in (Table 5) as Comparative Example 9 and Examples 25 to 27.
As shown.

[0037]

[Table 4]

[0038]

[Table 5]

As shown in (Table 5), good characteristics were obtained in combination with various oxides and metal powders. However, it can be seen that the reactivity of the sample in which the oxide was not heat-treated was clearly reduced.

Needless to say, even with the combinations not shown in this embodiment, sufficiently good characteristics can be obtained.
However, it should be noted that a substance such as Mn metal powder which is rapidly oxidized at a low temperature cannot obtain a uniform structure unless the temperature rising rate is controlled or the atmosphere is controlled. Also, since the oxidation start temperature and melting point of the metal powder have a great influence on the characteristics of the sintered body, the same caution is required.

[0041]

As described above, according to the method for producing a ferrite sintered body of the present invention, the added metal powder oxidatively expands during the firing process and fills the voids between the particles, thereby suppressing the dimensional change during firing. Suppressing, and further heat treating at least one kind of oxide as a starting material, the sinterability of ferrite is significantly improved, the dimensional change rate is small, and the ferrite sintered body with excellent magnetic properties can be manufactured at low cost. You can

Claims (4)

[Claims] 1. A first step of heat-treating at least one or more kinds of oxides constituting a ferrite composition and pulverizing, and substituting at least one or more kinds of oxides constituting the ferrite with metal powders wholly or partly. A second step of mixing, a third step of forming a granulated powder by adding an organic binder to the mixed powder, and a fourth step of obtaining a molded product by compression molding the granulated powder, A fifth step of firing a molded body to form a ferrite crystal body, the method for producing a ferrite sintered body. 2. The heat treatment temperature of the first step is 500 to 110.
The method for producing a ferrite sintered body according to claim 1, wherein the temperature is 0 ° C. 3. The main firing temperature in the fifth step is 800 to 130.
It is 0 degreeC, The manufacturing method of the ferrite sintered compact of Claim 1 or 2. 4. Mn, Ni, Cu, Z as a metal powder
2. At least one of n and Fe is used.
A method for producing the ferrite sintered body described.