JPH0597507A - Ferrite material - Google Patents

Abstract

PURPOSE:To provide a polycrystalline ferrite material or a joined ferrite material excellent in productivity and mass productivity. CONSTITUTION:Ferrite raw material powder 2 is calcined by a discharge plasma sintering method to produce a ferrite material composed of a polycrystalline substance. A coprecipitated ferrite material is preferred as the above-mentioned ferrite raw material powder 2. At this time, the ferrite raw material powder is preferably subjected to heat treatment (calcining) at >=900 deg.C temperature in calcining. The calcining by the discharge plasma sintering method is carried out in a state of a single crystal ferrite material brought into contact with the coprecipitated ferrite material or embedded in the coprecipitated ferrite material. Thereby, the coprecipitated ferrite material is calcined and converted into the polycrystalline ferrite material and the joining and integration of the polycrystalline ferrite material with the single crystal ferrite material are simultaneously carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite material used as a material for electronic parts typified by electroceramics, and more particularly to a ferrite material excellent in high frequency characteristics.

[0002]

2. Description of the Related Art In recent years, under the circumstances where demands for downsizing and high performance of electronic devices are increasing, the same applies to various parts constituting the electronic devices and eventually various materials. Demand is a big issue. For example, in ferrite materials that compose SW power supplies (switching power supplies), magnetic heads, and the like, it is desired to develop materials having superior high-frequency characteristics in order to achieve downsizing of SW power supplies and high performance of magnetic heads. It is rare.

As such a ferrite material having a fine particle size and excellent high frequency characteristics, for example, a fine coprecipitated ferrite material which is wet-synthesized by a coprecipitation reaction in an aqueous solution is used as a raw material powder. A ferrite material made of a polycrystalline body obtained by firing is known. Since the coprecipitated ferrite material is already in the spinel phase, it does not require a calcination step as in the conventional ceramic process, and a sintered body can be formed by a simple process of drying, molding and firing. It is suitable as a raw material powder of the above ferrite material because it can be manufactured and has advantages such as excellent composition uniformity.

[0004]

However, when a ferrite material is produced from the above co-precipitated ferrite material, fine cracks occur in the final product because the spinel type crystals are easily decomposed during firing, resulting in mechanical failure. There is a problem that durability and magnetic characteristics are deteriorated.

Therefore, in order to obtain a ferrite material having excellent characteristics by using a coprecipitated ferrite material as a raw material powder, a special firing method is required, for example, JP-A-60-141669. And JP-A-1-152707
Techniques disclosed in Japanese Patent Publications and the like are known. The technique described in JP-A-60-141669 mentioned above is one in which firing is performed after heating to a temperature having a constant temperature rising rate in a mixed gas atmosphere of N ₂ gas and H ₂ gas. The technique described in Kaihei 1-152707 is to perform firing at a constant temperature rising rate in a vacuum or in an atmosphere of an inert gas such as N ₂ gas or Ar gas.

[0006] However, these techniques are satisfactory in terms of productivity and mass productivity because they require maintaining a special firing atmosphere and strictly controlling the temperature rising rate during firing. It is hard to say.

On the other hand, in a magnetic head such as a video head, in order to reduce sliding noise and improve the CN ratio, a single crystal ferrite material and a polycrystalline ferrite material are used instead of the conventional single crystal ferrite head. It is being switched to a composite type magnetic head. This composite type magnetic head has a single structure ferrite having a high saturation magnetic flux density on the front gap side and a polycrystalline ferrite having a high magnetic permeability on the back gap side. And has the advantage of exhibiting excellent electromagnetic conversion efficiency.

Conventionally, a composite ferrite material used as a magnetic core in such a composite magnetic head is
For example, it is obtained by producing a single crystal ferrite material and a polycrystal ferrite material, respectively, and then thermocompression bonding both of them. As described above, the conventional method for manufacturing a bonded ferrite material requires many steps, and thus is extremely disadvantageous in terms of cost reduction.

Therefore, the present invention has been proposed in view of such circumstances, and an object thereof is to provide a polycrystalline ferrite material or a junction type ferrite material excellent in productivity and mass productivity. ..

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies as a result of achieving the above-mentioned objects, and as a result, if a spark plasma sintering method is adopted when firing a coprecipitated ferrite material, special firing is performed. It is not necessary to strictly control the atmosphere or the temperature rising rate during firing, and it is possible to produce a sintered body with a fine grain size and excellent high frequency characteristics in a very short time. When performing firing, if the coprecipitated ferrite material and the single crystal ferrite material are in contact with each other, or if the single crystal ferrite material is embedded in the coprecipitated ferrite material, the coprecipitated ferrite material is fired, They have found that they can be thermocompression bonded together, and have completed the present invention.

That is, the present invention is characterized in that the ferrite raw material powder is composed of a polycrystalline body obtained by firing by a discharge plasma sintering method. Further, the present invention is obtained by sintering the ferrite raw material powder in a state of being in contact with the single crystal ferrite material by a discharge plasma sintering method, and a polycrystalline ferrite material which is a sintered body of the ferrite raw material powder and the single crystal. It is characterized by being joined and integrated with a ferrite material.

As the ferrite raw material powder, any of conventionally known materials can be used, and a raw material powder synthesized by a solid phase reaction may be used, but especially by a coprecipitation reaction in an aqueous solution. Co-precipitated ferrite materials that are synthesized are preferred. This co-precipitated ferrite material is, for example, Mn ²⁺ , Z
A water-soluble salt such as n ²⁺ , Fe ²⁺ , or Fe ³⁺ is used, and a coprecipitation reaction by addition of an alkaline solution in an aqueous solution adjusted so that the water-soluble salt has a predetermined composition, or the co-precipitation reaction It is synthesized from the oxidation reaction of precipitation.

The water-soluble salt is not particularly limited,
For example, sulfate, hydrochloride, etc. can be used.

The ferrite material of the present invention is obtained by molding the above ferrite raw material powder and then firing it by a discharge plasma sintering method. The spark plasma sintering method is a novel sintering method that uses discharge plasma for the sintering reaction. When performing this spark plasma sintering method, as shown in FIG. 1, ferrite raw material powder 2 is filled in a cylindrical mold 1 having heat resistance and impact resistance, and made of a conductive heat resistant material. Then, the protrusions of the electrodes 3, 3 having the protrusions that fit in the mold 1 are inserted through the openings of the mold 1 and a predetermined pressure is applied to the ferrite raw material powder 2. Then, a voltage is applied to the electrodes 3 and 3 to generate discharge plasma in the ferrite raw material powder 2. As a result, the surface of the ferrite raw material powder 2 is activated, and at the same time, it is electrically heated to be fired. By firing the ferrite raw material powder 2 by the discharge plasma sintering method,
It becomes possible to obtain a bulk sintered body in an extremely short time of 3 minutes.

Before firing the ferrite raw material powder by such a discharge plasma sintering method, it is desirable to preliminarily heat-treat at a temperature of 900 ° C. or higher. As a result, the magnetic characteristics of the obtained polycrystalline ferrite material are significantly improved. At this time, it is preferable that the processing time is appropriately selected. If the heat treatment temperature is lower than 900 ° C, a sufficient effect cannot be expected.

Further, in the present invention, in the firing step by such a discharge plasma sintering method, the sintered body and the single crystal ferrite material are joined and integrated simultaneously with the production of the sintered body as described above. be able to. In this case, firing is performed by the discharge plasma sintering method in a state where the single crystal ferrite material is brought into contact with the ferrite raw material powder or in a state where the single crystal ferrite material is embedded in the ferrite raw material powder. This greatly simplifies the manufacturing process and reduces the cost, and since the thermocompression bonding of polycrystalline ferrite material and single crystal ferrite material is performed at low temperature and in a short time, the interface between the two Separation is very good, and the controllability of the interface is improved such that the undulation of the interface is extremely small.

[0017]

When a voltage is directly applied to the ferrite raw material powder, as shown in FIG. 2, a micro discharge occurs in the gap 4a of the powder particle 4 and plasma is generated. The impact of the plasma evaporates and removes the oxide film on the surface of the powder particles 4 and impurities such as adsorbed gas, and at the same time, heat and strain energy are accumulated on the surfaces of the powder particles 4 to activate them. To be done. As a result, many vacancies are generated, the diffusion constant of atom transfer is increased to several hundred times that of a normal atom, Joule heat is generated between the powder particles 4, and thermal diffusion actively occurs. This makes it possible to complete the sintering in an extremely short time.

Further, when a voltage is applied in the state where the single crystal ferrite material is brought into contact with the ferrite raw material powder or in the state where the single crystal ferrite material is embedded in the ferrite raw material powder, the same as described above is obtained. According to the principle, plasma is generated between the ferrite raw material powder and the single crystal ferrite material, the surfaces of these are activated, and the joining and integration of the two are completed at low temperature and in a short time.

[0019]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples. Example 1 This example is an example of producing a polycrystalline ferrite material by firing the Mn—Zn based ferrite raw material powder wet-synthesized by a coprecipitation reaction in an aqueous solution by a discharge plasma sintering method.

First, as a raw material, an Fe raw material (for example, FeS) is used.
_{O 4 · 7H 2 O),} Mn raw material (e.g. MnSO ₄ · 5H
₂ O) and a Zn raw material (for example, ZnSO ₄ .7H ₂ O), and MnO: ZnO: Fe ₂ O ₃ = 28: 20: 52.
An aqueous solution containing the following proportions was prepared. Then, potassium hydroxide was added to this aqueous solution as an alkaline component to adjust the pH of the solution to 11.

Then, while sufficiently stirring this solution, for example potassium chlorate KClO ₃ was added as an oxidant,
The temperature of the reaction solution was set to 100 ° C. and maintained for 1 hour to allow the reaction to proceed. After the reaction was completed, the obtained reaction product was thoroughly washed with water, filtered and dried to obtain coprecipitated Mn-Zn ferrite fine particle powder. Then, this coprecipitated Mn-Zn ferrite fine particle powder was calcinated at 1000 ° C. for 2 hours in an N ₂ gas atmosphere. It was confirmed that 10 to 20% of α-hematite (Fe ₂ O ₃ ) was produced during this calcination.

Then, the coprecipitated Mn-Zn ferrite fine particle powder was fired in the atmosphere for 5 minutes by a discharge plasma sintering method to obtain a polycrystalline Mn-Zn ferrite material. At this time, the pressure was 500 kgf / cm ² , and the current was 2000 A.
Was thrown in. Next, the polycrystalline Mn thus obtained
The —Zn ferrite material was annealed at 900 ° C. for 6 hours in a N ₂ gas atmosphere.

The polycrystalline Mn-Zn thus obtained
When the grain structure of the ferrite material was examined by X-ray diffraction, it was found that it was a spinel single phase despite being fired in the air, and its density was sufficiently densified to 99% or more of the true density. It was In addition, this polycrystalline Mn-Zn
The ferrite material has a very fine grain structure with a grain size of about 1 to 2 μm, and it takes only 5 minutes to complete the sintering reaction.
It can be seen that the particles of the -Zn ferrite material hardly grew. In addition, such a result did not depend on the temperature rising rate during firing.

On the other hand, when the coprecipitated Mn-Zn ferrite fine particle powder is fired by the conventional firing method (referred to as Comparative Example 1), the grain size of the obtained polycrystalline Mn-Zn ferrite material is obtained. Was 10 to 15 μm, and it was not possible to obtain a polycrystalline ferrite material having a good fine grain size.

Next, the polycrystalline Mn--Zn of the above-mentioned embodiment is used.
Using the ferrite material and Comparative Example 1 described above, an outer diameter of 6 mm,
When ring-shaped samples having an inner diameter of 3 mm and a thickness of 1 mm were produced and the frequency dependence of their magnetic permeability was examined, the results shown in FIGS. 3 and 5 were obtained.

FIG. 3 shows the frequency dependence of the magnetic permeability of the polycrystalline Mn—Zn ferrite material of this example, and FIG. 5 shows the frequency dependence of the magnetic permeability of the polycrystalline Mn—Zn ferrite material of Comparative Example 1. .. 3 and 5, the broken line indicates
The magnetic permeability μ is a real number part (μ ′) when expressed as a complex number such as μ = μ′−jμ ″, and corresponds to a normal magnetic permeability (inductance). The solid line indicates an imaginary number part. (Μ ″), that is, the energy loss, and ideally, the lower this is, the more preferable.

From FIGS. 3 and 5, in Comparative Example 1, 100 k
While the loss was increased and the magnetic permeability was decreased in the range exceeding Hz, the loss was small in the above range and the high magnetic permeability was maintained even in the high frequency range of 1000 kHz or more in this example. Was revealed.

Further, each of these polycrystalline Mn-Zn ferrite materials and the above-mentioned coprecipitated Mn-Zn ferrite fine particle powder were wet-mixed, and then dried, pre-baked, crushed and molded, Further, with respect to the polycrystalline Mn—Zn ferrite material (referred to as Comparative Example 2) obtained by firing by the usual firing method as in Comparative Example 1, the high frequency characteristics were examined using tan δ / μ as an index. The result is shown in FIG.

As is apparent from FIG. 4, coprecipitation Mn-Zn
It has been found that a sintered body having excellent high frequency characteristics can be obtained by using ferrite fine particle powder as a raw material powder and firing the powder by a discharge plasma sintering method. In addition, when the compounded raw material powder used in Comparative Example 2 was fired by the discharge plasma sintering method, the magnetic characteristics were poor and it was not worth evaluating.

Example 2 Next, a wet-synthesized coprecipitated M was prepared in the same manner as in Example 1 above.
Using n-Zn ferrite fine particle powder, this coprecipitation Mn-
After subjecting the Zn ferrite fine particle powder to the heat treatment (temporary firing) while changing the treatment conditions as shown in Table 1, a ferrite material was manufactured by the above-mentioned discharge plasma sintering method. The relationship between the magnetic properties of the ferrite materials was investigated.

First, the Mn-Zn ferrite material powder was wet-synthesized by the coprecipitation reaction in an aqueous solution as in Example 1.

Then, the coprecipitated Mn-Zn ferrite fine particle powder was heat-treated in an N ₂ gas atmosphere under the conditions shown in Table 1 below. Then, the coprecipitated Mn-Zn ferrite fine particle powder was fired by the discharge plasma sintering method under the same conditions as in Example 1 to obtain a polycrystalline Mn-Zn ferrite material.

Polycrystalline Mn-Zn thus obtained
When the true density of the ferrite material was measured, both were 99%
It was found that the above density was sufficiently densified.

Next, using these polycrystalline Mn-Zn ferrite materials, ring-shaped samples having an outer diameter of 6 mm, an inner diameter of 3 mm and a thickness of 1 mm were prepared, and the polycrystalline Mn-Zn ferrite materials were made to pass through at a frequency of 1 MHz. The magnetic susceptibility was measured.
The results are shown in Table 1. The results obtained when the heat treatment was not performed are also shown in Table 1.

[0035]

[Table 1]

As shown in Table 1, it was found that when heat treatment was performed in advance at a temperature of 900 ° C. or higher and then firing was performed by the above-described discharge plasma sintering method, extremely high magnetic permeability was exhibited. .. On the other hand, it was revealed that when the heat treatment was not performed or the treatment temperature was less than 900 ° C., the magnetic permeability was very small and sufficient magnetic characteristics could not be obtained.

Example 3 In this example, Mn-obtained in the same manner as in Example 1 above was obtained.
Single crystal M of Zn-based ferrite raw material powder having the same composition
A polycrystalline Mn-Zn ferrite material and a single-crystal Mn-Zn ferrite material are manufactured at the same time as a polycrystalline Mn-Zn ferrite material is manufactured by performing firing by a discharge plasma sintering method while being in contact with the n-Zn ferrite material. This is an example in which a bonded ferrite is obtained by carrying out the bonding and integration with and.

First, the Mn-Zn ferrite material powder was wet-synthesized by coprecipitation reaction in an aqueous solution in the same manner as in Example 1 above, and the coprecipitated Mn-Zn ferrite fine particle powder was then heated at 1000 ° C. in an N ₂ gas atmosphere. It was calcined for 2 hours.

Then, the single crystal Mn-Zn type ferrite material (the above coprecipitated Mn-Zn) produced by the Bridgman method or the like is used.
It has the same composition as the ferrite fine particle powder. Was contacted with the coprecipitated Mn-Zn ferrite fine particle powder, and was fired by the spark plasma sintering method in the same manner as described above. As a result, the coprecipitated Mn-Zn ferrite fine particle powder is fired to obtain a polycrystalline Mn-Zn ferrite material, and at the same time, the polycrystalline Mn-Zn ferrite material and the single crystal Mn-Zn ferrite material are thermocompression bonded. A bonded ferrite was obtained.

The single crystal Mn-Zn ferrite material and the polycrystalline Mn- in the thus obtained joint ferrite are
When the interface with the Zn ferrite material was observed with a scanning electron microscope, it was found that the separation of the interface was very good and the waviness of the interface was extremely small.

[0041]

As described above, in the present invention, since the ferrite raw material powder is fired by the spark plasma sintering method, it is not necessary to strictly control the special atmosphere or the temperature rising rate during firing. Thus, it is possible to obtain a ferrite material having a fine particle size and excellent high frequency characteristics. Further, in the present invention, during the firing step of the ferrite raw material powder, it is possible to complete the thermocompression bonding step of the polycrystalline ferrite material and the single crystal ferrite material, it is possible to greatly simplify the manufacturing process, The cost can be reduced easily. Moreover, according to such a discharge plasma sintering method, since the time required for completing the sintering reaction is only a few minutes, which is extremely short, the interface between the polycrystalline ferrite material and the single crystal ferrite material is The separation is very good, and the waviness of the interface is extremely small.
Excellent controllability of the interface.

Further, according to the present invention, it becomes possible to join and integrate the polycrystalline ferrite material and the single crystal ferrite material at an extremely low temperature of about 900 ° C. Therefore, productivity and mass productivity are improved accordingly. At the same time, the cost can be reduced.

[0043]

[Brief description of drawings]

FIG. 1 is a schematic perspective view for explaining a discharge plasma sintering method.

FIG. 2 is a schematic diagram for explaining a mechanism of a firing reaction by a discharge plasma sintering method.

FIG. 3 is a characteristic diagram showing frequency dependence of magnetic permeability of a polycrystalline ferrite material to which the present invention is applied.

FIG. 4 is a diagram showing a polycrystalline ferrite material to which the present invention is applied, a polycrystalline ferrite material obtained by firing a coprecipitated ferrite material by an ordinary firing method, and a polycrystalline ferrite material obtained by firing a compounding raw material by an ordinary firing method. T for frequency of crystalline ferrite material
It is a characteristic view which shows the change of an (delta) / micro.

FIG. 5 is a characteristic diagram showing frequency dependence of magnetic permeability of a polycrystalline ferrite material obtained by firing a coprecipitated ferrite material by a usual firing method.

Claims (3)

[Claims] 1. A ferrite material comprising a polycrystalline material obtained by firing a ferrite raw material powder by a discharge plasma sintering method. 2. The ferrite material according to claim 1, wherein the ferrite raw material powder is heat-treated at a temperature of 900 ° C. or higher. 3. A polycrystalline ferrite material, which is a sintered body of the above ferrite raw material powder, and the above single crystal, wherein the ferrite raw material powder is sintered by a discharge plasma sintering method while being in contact with the single crystal ferrite material. A ferrite material that is integrated with a ferrite material.