JPH07176419A - Method of manufacturing pre-baked powder for high frequency low loss magnetic material - Google Patents

Abstract

PURPOSE:To improve power loss and magnetic characteristics by producing pre-baked powders by heating a solution of complex of amino acid that contains Fe, Mn and Zn and drying it, in a method of manufacturing pre-baked powders for a high frequency low loss magnetic material. CONSTITUTION:In the method of manufacturing pre-baked powders for the high frequency low loss magnetic material, pre-baked powders of Fe, Mn and Zn are produced by heating the solution of the complex of the amino acid that contains Fe, Mn and Zn and drying it. The method of manufacturing the pre-baked powders comprises the heating temperature of the solution of the complex of the amino acid that contains Fe, Mn and Zn that is higher than the boiling temperature of the solution and not more that 400 deg.C. Slurry is produced by mixing binder with the powders produced by this manufacturing method. The method of manufacturing a high frequency low loss magnetic sintered body comprises the production of a compact by granulating and compacting the slurry and then the sintering of the compact. By this procedure, pre-baked powders with less power loss at high frequency range and lower heat generation are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pre-calcined powder which is a raw material for Mn-Zn ferrite to be mounted on a switching power supply or the like.

[0002]

2. Description of the Related Art Conventionally, M is used as a magnetic material used for a core or the like used in a transformer of a switching power supply.
An n-Zn ferrite was used, and its driving frequency was about 200 kHz or less. On the other hand, with the recent miniaturization and weight reduction, the drive frequency is 300 kHz to 50 kHz.
Studies are underway to increase the frequency to 0 kHz and further to 1 MHz.

However, in this high frequency region, the conventional M
When the n-Zn ferrite is used, there is a drawback that heat generation due to an increase in power loss of the ferrite is extremely large and that the function cannot be achieved in the high frequency region as described above.

Generally, ferrite is produced by mixing iron, manganese, and zinc oxide powders in a ball mill or the like, followed by pre-baking, fine pulverization, granulation and pressing to produce a powder compact. The target ferrite fired body is obtained by firing this compressed powder.

The magnetic characteristics in the high frequency region are mainly eddy current loss, and how to reduce this eddy current loss (Pe) has become an extremely important issue. In order to reduce this eddy current loss, it is essential to improve the electrical resistance (R) of the grain boundary phase or spinel phase of the sintered body.

As a method for improving the electric resistance of the spinel phase itself, from the viewpoint of how to reduce the electron hopping phenomenon between Fe ²⁺ and Fe ^3+, by increasing the oxygen partial pressure under the sintering conditions, Fe There is a method of suppressing the occurrence of the hopping phenomenon of electrons by reducing ²⁺ or substituting Fe ³⁺ by containing Ti ⁴⁺ and Sn ⁴⁺ .

However, the former causes a remarkable deterioration of the initial magnetic permeability μi and an increase of the coercive force Hc due to the extreme decrease of Fe ²⁺ , resulting in deterioration of the magnetic characteristics. In addition, addition of Ti ⁴⁺ , Sn ^4+, etc. is not preferable because the temperature at which the power loss value becomes minimum in the temperature characteristic of power loss (called minimum point) is significantly deteriorated to the low temperature side. Furthermore, even if the electrical resistance of the spinel phase itself is improved by either method, the greatest drawback is that the electrical resistance of the sintered body does not increase as much as expected.

As a method for improving the electric resistance of the grain boundary phase,
A general method is to form a high-resistance grain boundary phase by adding a third element in addition to SiO ₂ and CaO.

This method is the most effective and the most widely used method for improving the resistance of the ferrite sintered body. At this time, the crystal grain size is reduced to reduce the eddy current generated in each grain, and even if the eddy current flows beyond the grain boundary phase, the crystal grain is small, that is, the grain boundary phase. It is possible to effectively utilize the high resistance grain boundary phase and to achieve a remarkable effect by adopting a method of blocking by increasing the number of As a method of reducing the crystal grain size, it is essential to reduce the powder grain size and sinter at a temperature as low as possible.

In the conventional method for producing Mn-Zn ferrite, as described above, fine oxides must be obtained by mixing oxides of Fe, Mn and Zn, calcining and finely pulverizing them. I won't. However, since the particle size of the calcined powder obtained by this method is 0.5 to 1 μm or more and is quite large, it requires a long time pulverization to obtain a fine powder to obtain a sintered body. Must be manufactured. This method is not preferable because it requires a long time of crushing, which not only increases the cost, but also causes significant contamination from the inner wall of the crusher or balls during crushing and causes significant deterioration of magnetic properties due to the inclusion of impurities. Further, since the calcined powder obtained by the conventional manufacturing method has a coarse powder particle size when molded as it is, when sintered at a low temperature, the density of the sintered body is low and the magnetic properties are also low. is there.

Further, if the sintering temperature is raised to improve the density of the sintered body, the crystal grain size becomes large and the eddy current loss becomes large, which is not preferable.

As described above, in the conventional ferrite manufacturing process, Mn-Zn ferrite having a fine crystal grain size and exhibiting excellent magnetic characteristics in a high frequency region could not be obtained.

In addition to the above reduction of overcurrent loss, various magnetic characteristics such as hysteresis loss, initial permeability μi, saturation magnetic flux density Bs, residual magnetization Br, coercive force Hc, etc. are important as ferrite materials for power supplies. It is a characteristic item. It is important for these properties to make the texture of the sintered body uniform up to the atomic level. In the conventional method, since the pre-calcined powder is obtained by the solid-phase reaction, the diffusion of atoms is insufficient, and the pre-calcined powder obtained is only non-uniform, resulting in excellent magnetic properties. It had the drawback of not being able to.

Further, as a method for solving this problem,
There is a so-called Lusner method in which a pre-calcined powder is obtained from a hydrochloric acid solution of Fe, Mn, and Zn by a spray roasting method. In this method, since each element can be mixed in a solution state, uniform mixing can be performed at the atomic level. However, the compositional deviation due to the high vapor pressure of ZnCl ₂ is significant, and it is not possible to produce a compositional powder that meets the purpose. Further, in this method, since the temperature inside the furnace is kept high and atomization is carried out, the obtained powder particle size is large, and pulverization for a long time as described above is required, so the same drawbacks as described above occur. Furthermore, a large-scale plant was required, and mass production could not be performed easily.

As described above, Mn-Z has excellent magnetic characteristics in the high frequency range regardless of which conventional technique is used.
It was difficult to obtain an n-ferrite material.

[0016]

DISCLOSURE OF THE INVENTION The present invention is designed for use with several hundred kHz.
It is an object of the present invention to provide a method for producing a pre-calcined powder for a low loss magnetic material, which has a small power loss even in a high frequency region up to about 1 MHz and can suppress the amount of heat generation.

[0017]

As a result of various studies to solve the above-mentioned problems, the present inventor found that Fe, Mn,
It has been found that a solution of a complex of an amino acid containing Zn is heated and dried to obtain a pre-calcined powder suitable for a high frequency low loss magnetic material.

Using this powder as a raw material, mixing, granulation, molding,
By sintering, a sintered body having an extremely fine structure having an average crystal grain size of 6 μm or less can be obtained. This sintered body has extremely high electric resistance and excellent magnetic characteristics in a high frequency region.

[0019]

In the case of the present invention, each element of Fe, Mn and Zn is
Since the amino acid complex can be mixed in a solution state, uniform mixing can be performed at the atomic level. When the solvent of the solution is removed by further heating and drying this solution, the residue causes self-combustion. Since this combustion is completed within a very narrow range and in a short time, and is completed, it is possible to obtain a powder having a very fine and uniform particle size. Further, it was found that a spinel single phase was obtained by analyzing the produced phase of the obtained powder by X-ray diffraction. According to the present invention, since spraying can be performed without maintaining the temperature inside the furnace at a high temperature as in the Rusner method, a large-scale plant is not required for mass production and the industrial value is high. Further, water is industrially inexpensive for the solution containing the amino acid, which is preferable in terms of cost. Further, industrially, by using spray drying as a heating method like spray granulation, the obtained powder properties become suitable for handling.

In the second aspect of the invention, the reason why the heating temperature is set to 400 ° C. or lower is that if the heating temperature is set to 400 ° C. or higher, fine powder particles cannot be obtained. . In the invention of claim 5, the reason why the average particle size of the sintered body is 6 μm or less is 6 μm.
This is because the eddy current loss becomes large as described above in the region exceeding m.

[0021]

EXAMPLES Examples of the present invention will be shown below.

Example 1 High-purity Fe (NO ₃ ) ₃ ,
Mn (NO ₃ ) ₂ and Zn (NO ₃ ) ₂ are replaced with Fe ₂ O ₃ and M
53 mol% -39 mol% -8 in terms of nO and ZnO
It was weighed to be mol% and dissolved in pure water. Aminoacetic acid was added to this solution by adding Fe (NO ₃ ) ₃ , Mn (N
20 wt% based on the total weight of O ₃ ) ₂ and Zn (NO ₃ ) ₂ .
And mixed well. Next, this solution was sprayed into a furnace in which the temperature in the furnace was kept at 300 ° C. afterwards,
The product obtained by the reaction in the furnace was in powder form.

When the generated phase of this powder was examined by X-ray diffraction, it was found to be a Mn-Zn ferrite spinel single phase. Moreover, as a result of analyzing the composition of this powder, 52.9F
_{e 2 O 3 -39.0MnO-8.1ZnO (} mol%)
It was found that there was almost no deviation in the composition.
0.04SiO ₂ , 0.08CaO (wt
%) And 0.06 wt% V ₂ O ₅ were added and mixed in a ball mill. Then, polyvinyl alcohol was added as a binder, and the binder was mixed. The resulting slurry was dried and granulated, and then shaped into a toroidal shape of φ25 × φ15 × t5 at a pressure of 2 t / cm 2. The obtained molded body was placed in a nitrogen stream with a controlled oxygen partial pressure.
Sintered at a temperature of 0 to 1200 ° C.

FIG. 1 shows the most excellent temperature characteristic of the power loss characteristic among the sintered bodies produced by changing these conditions. Table 1 shows various magnetic properties of this sintered body. The average crystal grain size of the sintered body at this time was 4 μm.

[0025]

[Table 1]

Example 2 A powder was obtained by the same manufacturing method as in Example 1, and the relationship between the average crystal grain size of each sintered body obtained by changing the sintering conditions and the power loss of the sintered body was shown. Figure 2
Shown in. The measurement condition at this time is 1 MHz-500G-
It is 80 ° C. From the drawings, it can be seen that this embodiment is superior.

[Embodiment 3] By changing the temperature condition of spraying,
Under other conditions, powder was obtained by the same manufacturing method as in Example 1, and the power loss characteristics of the sintered body obtained under the same sintering conditions are shown in FIG. From the drawings, it can be seen that this embodiment is superior.

[Embodiment 4] Similar to Embodiment 1, high-purity Fe (NO ₃ ) ₃ , Mn (NO ₃ ) ₂ , Zn (NO ₃ )
₂ is 53 mol% in terms of Fe ₂ O ₃ , MnO, ZnO
It was weighed to be −39 mol% −8 mol% and dissolved in pure water. Aminoacetic acid was added to this solution as acid Fe (N
O ₃ ) ₃ , Mn (NO ₃ ) ₂ and Zn (NO ₃ ) ₂ were added to the total weight of 20 wt% and mixed well. Next, this solution was put into a beaker and heated to evaporate water to cause a reaction. After that, the product obtained was found to be powdery.

This product was molded and sintered in the same manner as in Example 1, and the power loss characteristics of the obtained sintered body are shown in FIG.

Comparative Example 53 Fe ₂ O ₃ -39MnO-8 was prepared by using high-purity iron oxide, manganese oxide, and zinc oxide.
ZnO (mol%) was weighed, mixed with a ball mill, and then pre-baked at about 1000 ° C.

This pre-calcined powder was made into Si in the same manner as in Example 1.
O ₂ , CaO and V ₂ O ₅ were added, granulated, molded and sintered in the same manner as in Example 1.

Among the sintered bodies in which these conditions are changed,
The temperature characteristics of the most excellent power loss characteristics are shown in FIG. Table 1 shows various magnetic properties of this sintered body.

[0033]

As described above, the present invention provides a method for producing a pre-calcined powder for high frequency low loss magnetic material, comprising Fe, M
A solution of an amino acid complex containing n and Zn is heated and dried to obtain a pre-calcined powder. The powder obtained by this method is used as a raw material for mixing, granulating, molding and sintering. By this, a sintered body having an extremely fine structure can be obtained, and power loss and various magnetic characteristics can be improved,
When mounted on a switching power supply or the like, the amount of heat generated is reduced, and an excellent low loss magnetic material can be obtained.

This is because the average crystal grain size in the Mn-Zn ferrite sintered body was refined, and when the elements in the solution of the amino acid complex were uniform at the atomic level, diffusion produced good characteristics. Inferred.

[Brief description of drawings]

FIG. 1 shows power loss characteristics with respect to respective temperatures of sintered bodies according to Example 1 and a comparative example.

FIG. 2 shows the relationship between the average crystal grain size and the power loss of the sintered body according to Example 2.

FIG. 3 shows the relationship between the temperature condition during spraying and power loss in Example 3.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area C04B 35/38 C04B 35/38 Z

Claims (5)

[Claims] 1. A method for producing a pre-calcined powder for a high frequency low loss magnetic material, wherein a solution of an amino acid complex containing Fe, Mn and Zn is heated and dried to obtain the pre-calcined powder of Fe, Mn and Zn. A method for producing a pre-calcined powder for high-frequency low-loss magnetic material, characterized by being obtained. 2. The temperature for heating the solution of the amino acid complex containing Fe, Mn, and Zn is 400 or higher than the boiling point of the solution.
The method for producing a pre-calcined powder for a high frequency low loss magnetic material according to claim 1, wherein the temperature is not higher than ° C. 3. The method according to claim 1 or 2, wherein the step of heating and drying the solution of the amino acid complex containing Fe, Mn, and Zn is performed by a spray heat drying method.
A method for producing a pre-calcined powder for a high frequency low loss magnetic material according to claim 1. 4. A binder is mixed with the powder obtained by the method for producing a pre-calcined powder for a high frequency low loss magnetic material according to claim 1 to obtain a slurry, and the slurry is granulated and then molded. The method for producing a high-frequency low-loss magnetic sintered body is characterized in that the molded body is obtained by sintering, and the molded body is sintered to obtain a sintered body. 5. A sintered body obtained by the method for producing a high-frequency low-loss magnetic sintered body according to claim 4, wherein the average crystal grain size of the sintered body is 6 μm or less. High frequency low loss magnetic sintered body.