JPH06290927A - Soft ferrite magnetic material excellent in magnetic property - Google Patents

Abstract

PURPOSE:To prevent the components of magnetic material powder from segregating so as to obtain a soft ferrite magnetic material low in power loss by a method wherein hydrothermal synthetic powder is used as material powder. CONSTITUTION:Hydrothermal synthetic ferrite powder, which is 0.3 to 8mum in average grain diameter, equal in composition, so uniform in grain diameter and so optionally controlled in grain size as to make a figure obtained by dividing its standard deviation by average grain diameter smaller than 0.20 and to satisfy formulas, log (d10/d)>=-0.38 and log (d90/d)<=0.30, (d denotes average diameter of ferrite powder, and d10 and d90 represent diameters of ferrite powder which amounts to 1094 and 90% of total amount of ferrite powder in a grain diameter cumulative distribution), is used as soft ferrite magnetic material. By this setup, a soft ferrite magnetic material uniform in grain diameter, fine in crystalline structure, less segregated, small in number of voids, uniform in void distribution, and low in power loss can be 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 soft ferrite magnetic material having excellent magnetic properties.

[0002]

2. Description of the Related Art In recent years, with the increasing switching frequency of switching power supplies, soft ferrite magnetic materials used for magnetic cores such as transformers are required to have low loss even at high frequencies. A soft ferrite magnetic material having a low loss even at such a high frequency is required to have a structure in which crystal grains are fine and regular, there are few pores that hinder the domain wall movement, and there is little component segregation.

Conventionally, in order to obtain a soft ferrite magnetic material having such a structure, Japanese Patent Laid-Open No. 1-296602 has been proposed.
No. 1-136309, No. 1-111270
No. 7, JP-A-1-179756, and the like have been tried. However, with this method using a small amount of additive, it is difficult to weigh it due to the small amount of additive, and it is difficult to mix and disperse easily with a method using a ball mill or the like, and homogeneous calcination / crushed powder cannot be obtained. Therefore, under the present circumstances, abnormal grain growth occurs or component segregation remains, and the originally obtained magnetic characteristics cannot be obtained in many cases. Further, in order to adjust the crystal grain size and reduce the segregation of components, it has been studied to classify the calcined / crushed powder. However, this method has a problem that component segregation occurs for each classified particle size.

[0004]

DISCLOSURE OF THE INVENTION The present invention uses a homogeneous raw material ferrite powder which cannot be obtained by a conventional method, and has a fine structure with a uniform crystal grain size, a small component segregation, and pores. It is an object of the present invention to provide a method for obtaining a soft ferrite magnetic material having a uniform pore distribution and excellent loss characteristics.

[0005]

The inventors have found that the average particle size is 0.3 to 8 μm and the value obtained by dividing the standard deviation by the average particle size is 0.
20 or less and log (d _10% /d)≧−0.38,
log (d _90% /d)≦0.30, (where d is the average particle size of the ferrite powder, d _10% and d _90% are 10% and 90%, respectively, in the cumulative distribution of the particle size of the ferrite powder. When using a homogeneous hydrothermally synthesized ferrite powder with a uniform particle size and a composition whose size is arbitrarily controlled, the soft ferrite magnetism excellent in the loss characteristics of the above problems is obtained. Got the material. The hydrothermally synthesized ferrite powder used here is obtained by adding divalent metal ions of Mn and Zn to an aqueous solution containing ferrous ions disclosed in Japanese Patent Application No. 4-66426, and a pH of 8 to 160 ° C. to 300 ° C. It is obtained by a method of producing MnZn ferrite particles having a uniform particle size by heating to and by a hydrolysis reaction.

[0006]

The calcined powder of soft ferrite calcined in air is usually composed of a spinel phase of ferrite, a hematite phase and a phase of another oxide. The size of various substances forming these calcined powders varies depending on the condition of phase equilibrium and the difference in growth rate. Further, when a trace amount of the additive is added, the sintering reactivity differs between the portion where the concentration of the additive is high and the portion where the concentration of the additive is low, and therefore the particle size of the calcined powder is different. Therefore, it is considered that the difference in the particle size of the particles forming the calcined powder represents the difference in the components. Furthermore, due to the difference in particle size immediately after calcination and the difference in the strength of various substances constituting the calcinated powder against crushing, it is considered that the particle size distribution of crushed powder represents some kind of component distribution. The inventors conducted an experiment based on this idea,
It has already been found that component segregation can be reduced by classifying the calcined and crushed powder.

The sintering reaction proceeds due to the migration of cations and the migration of anions. Ion migration easily occurs where the difference in ion distribution is large, and sintering proceeds easily, and progresses where the difference in ion distribution is small. Hateful. Therefore, if the composition distribution at the time of main sintering is not uniform, a sintered body with a uniform crystal grain size cannot be obtained because there are portions where the rate of the sintering reaction is fast and portions where the rate of the sintering reaction is slow. Since the hydrothermal synthetic powder is produced by a homogeneous reaction in an aqueous solution, it is advantageous in the homogeneity of the composition. Also, by increasing the firing temperature and taking sufficient time, the crystal grain size of the fired body tends to be adjusted if the crystal grains are enlarged, but in order to reduce the eddy current loss at high frequency, Organization is desirable. Therefore, it is effective to suppress grain growth by low temperature firing, and for that purpose, it is necessary to adjust the grain size of the raw material powder. It has also been confirmed that there is a correlation between the size of the raw material powder and the size of the obtained fired body.

[0008] Here, using the powder obtained by the classification method, the conditions for sufficiently bringing out the sizing effect are:
(D _10% /d)≧−0.38, log (d _90% / d) ≦
It is required to be 0.30. d is the average particle size of the calcined / crushed powder after classification, d _10% and d _90% are the cumulative distributions of the calcined / crushed powder after classification, which are the particle sizes at 10% and 90%, respectively. Show. The area was defined by d, d _10% and d _90% without taking the full width at half maximum because the fine powder which affects the sintering at full width at half maximum,
This is because no restrictions can be set for coarse powder. This relationship applies to calcined and crushed powders having a particle size of 20 μm or less, and no difference is observed between calcinated and crushed powder having a particle size of 20 μm or more before and after classification. It is considered that this is because the particle size of the calcined / crushed powder of 20 μm or more is too large, and thus the sintering of the fired body does not proceed sufficiently under normal firing conditions.

Log (d _10% / d) ≧ −0.38 is a condition relating to fine powder, and if the fine powder deviating from this condition increases, abnormal crystal grains are generated and the magnetic characteristics deteriorate. Also,
The condition of log (d _90% / d) ≤ 0.30 relates to coarse powder, and if the amount of coarse powder deviating from this condition increases, the component composition of the sintered body will become inhomogeneous and the classification effect will not be seen. . Hydrothermal synthetic powder sufficiently satisfies the conditions of this particle size distribution, therefore, by using a homogeneous hydrothermal synthetic ferrite powder having a composition with a uniform particle size as a raw material, a uniform crystal particle size, It is possible to obtain a soft ferrite magnetic material having a fine structure, a small amount of component segregation, a small number of pores, a uniform pore distribution, and excellent magnetic characteristics.

[0010]

【Example】

Example 1 A divalent metal ion of Zn and Mn was added to an aqueous solution containing ferrous iron shown in Japanese Patent Application No. 4-66426, and PH was added.
MnZn ferrite particles having three types of ordered particle sizes were manufactured by a manufacturing method in which a hydrolysis reaction was carried out by heating to 160 to 300 ° C. at 8 or higher. Component analysis value, average crystal grain size, log (d
The values of _10% / d) and log (d _90% / d) are shown in Table 1.

[0011]

[Table 1]

The three types of hydrothermal powders will be referred to as hydrothermal powder A, hydrothermal powder B, and hydrothermal powder C in order of decreasing average particle size.
As for the component analysis value, 5g of each powder was sampled,
It was obtained by quantitative luminescence analysis. Conventional process powder, hydrothermal powder A, hydrothermal powder B, and hydrothermal powder C at 1250 ° C
It was baked in. Looking at the texture of the etched surface of the fired body after cutting, polishing, and etching, hydrothermal powder A, hydrothermal powder B, and hydrothermal powder C
There is no abnormal grain growth and there are few pores. 1
Table 2 shows the average grain size and standard deviation of the grain size of 000 crystals measured.

[0013]

[Table 2]

It can be seen that, when the hydrothermal synthetic powder is used, the standard deviation is small and the crystal grain size is uniform as compared with the conventional process powder. Table 3 shows the results of similarly measuring the diameters of the pores and determining the average diameter and the standard deviation.

[0015]

[Table 3]

It can be seen that the standard deviation of the pores of the hydrothermal powder is small and uniform. Fe ₂ O obtained by irradiating a 50 mm × 50 mm area on the polished surface of a fired body using the conventional process powder and hydrothermal powder B with an electron beam having a spot diameter of 2 μm × 2 μm and examining characteristic X-rays ₃ , M
FIG. 1 shows how the components of nO and ZnO vary. The horizontal axis of the figure shows the component value detected most often as the origin, and the deviation from the component value is expressed as a percentage, and the vertical axis shows the detection frequency on an arbitrary scale. As is clear from FIG. 1, the calcined body using the powder of the hydrothermal powder B is homogeneous with less variation in components than the calcined body using the conventional process powder. Similar results were obtained using hydrothermal powder A and hydrothermal powder C.

Comparative Example 1 MnZn soft ferrite powder (conventional process powder) calcinated in air at 950 ° C. and crushed by a ball mill.
Were classified into three types of powders having different average particle sizes according to the conditions of the present invention. There are various classification methods such as a method using centrifugal force and a method using a filter. In this example, a classifier using the Coanda effect was used.

Component analysis values of the powder before classification (conventional process powder) and the three kinds of powder after classification, average crystal grain size, log (d
The values of _10% / d) and log (d _90% / d) are shown in Table 4.

[0019]

[Table 4]

The three types of powders after classification will be referred to as A after classification, B after classification, and C after classification, in order of decreasing average particle size.
As for the component analysis value, 5g of each powder was sampled,
It was obtained by quantitative luminescence analysis. The composition ratio of Fe ₂ O ₃ , MnO, and ZnO of the powder before classification (conventional process powder) is the same as the weighing ratio before mixing, but the composition ratio of all powders with different average particle sizes after classification is the same. It is out of alignment.
This suggests that powders with different particle sizes have different composition. Since the target is powder, it is difficult to examine the microscopic segregation of the composition, but as will be shown later, the segregation of the components of the fired body using the powders after classification A, after classification B, and after classification C It is shown that the powder after classification indirectly has less component segregation than the powder using the process powder).

The powders before classification (conventional process powder), after classification A, after classification B, and after classification C were fired at 1250 ° C. Looking at the texture of the etched surface of the fired body after cutting, polishing, and etching, those using the powders after classification A, after classification B, and after classification C did not show abnormal grain growth and had few pores. 10
Table 5 shows the average grain size and standard deviation obtained by measuring the grain size of 00 crystals.

[0022]

[Table 5]

As with hydrothermal powder, it can be seen that when the classified powder is used, the dispersion is small and the crystal grain size is uniform as compared with the conventional process powder. Further, the diameters of the pores were measured in the same manner, and the average diameter and the standard deviation were obtained and the results are shown in Table 3 for comparison with the hydrothermal powder. It can be seen that the standard deviation of the pores after classification is small and well arranged. It was obtained by irradiating an electron beam having a spot diameter of 2 μm × 2 μm on a region of 50 mm × 50 mm on the polished surface of the fired body using A before classification (conventional process powder) and after classification by characteristic X-rays FIG. 2 shows the variation of the components of Fe ₂ O ₃ , MnO, and ZnO together with the results of hydrothermal powder. The horizontal axis of the figure shows the component value detected most often as the origin, and the deviation from the component value is expressed as a percentage, and the vertical axis shows the detection frequency on an arbitrary scale. As is clear from FIG. 2, the calcined body using the powder of A after classification has less variation in the components and is homogeneous as compared with the result of the hydrothermal powder as compared with the calcined body using the powder before classification (conventional process powder). It can be seen that it is. Similar results were obtained for post-classification B and post-classification C.

Comparative Example 2 In order to show that the effect of classification is not due to the difference in composition, the composition of the powder after classification should be the same as that of the powder before classification (conventional process powder). The baked and crushed powder was classified. The classified calcined / crushed powder is that described in Comparative Example 1. The classified powder, the powder before classification (conventional process powder), and the hydrothermal synthetic powder described in Example 1 were 1200
FIG. 3 shows the result of measuring the temperature dependence of loss by firing at ℃. The numbers in the figure are the measured frequency and magnetic flux density.
As is clear from FIG. 3, the loss of the fired body obtained from the powder having a uniform grain size is low, and under the conditions of a frequency of 500 kHz and a magnetic flux density of 50 mT, it is about half of the loss of the fired body using the conventional process powder. Losses have been improved.

Although the loss was remarkably improved by using the hydrothermal synthetic powder having a uniform particle size, the particle size distribution effect was confirmed by the powder obtained by classification.
With the same composition of components, log (d _10% /
FIG. 4 shows the change in the minimum loss when the values of d) and log (d _90% / d) are changed. However, when changing the conditions on the fine powder side, the conditions on the coarse powder side were satisfied, and when changing the conditions on the coarse powder side, the conditions on the fine powder side were satisfied. It can be seen from FIG. 4 that the improvement effect cannot be seen if the particle size distribution is out of the above range.

It has been shown that the hydrothermal synthetic powder of the present invention satisfies the above conditions, and that a soft ferrite magnetic material having more excellent loss characteristics than the powder obtained by sizing by classification is obtained.

[0027]

EFFECT OF THE INVENTION By using the hydrothermal synthetic powder of the present invention as a raw material powder, segregation of powder components is eliminated, and the crystal grain size is excellent, which is excellent in loss characteristics even at high frequencies used for electronic parts such as switching power supplies, It is possible to obtain a soft ferrite magnetic material having a fine structure, less segregation of components, and less pores and a uniform pore size distribution.

[Brief description of drawings]

FIG. 1 is a diagram showing component segregation of a fired body using conventional process powder and a fired body using hydrothermal powder.

FIG. 2 is a diagram showing component segregation of a fired body using a conventional process powder, a fired body using hydrothermal powder, and a fired body using classified powder.

FIG. 3 is a diagram showing temperature dependence of loss at a frequency of 100 kHz, a magnetic flux density of 200 mT, a frequency of 500 kHz, and a magnetic flux density of 50 mT.

FIG. 4 is a diagram showing a relationship between a particle size distribution range and a loss value.

Front page continuation (72) Inventor Koji Watanabe 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation Advanced Technology Research Laboratories

Claims (1)

[Claims] 1. An average particle size of 0.3 to 8 μm, a value obtained by dividing a standard deviation by the average particle size is 0.20 or less, and a particle size satisfying the following mathematical formula is adjusted and an arbitrary size is set. A soft ferrite magnetic material with excellent loss characteristics, characterized by using a homogeneous hydrothermally synthesized ferrite powder having a controlled composition. log (d _10% / d) ≧ −0.38, log (d _90% / d) ≦ 0.30 where d is the average particle diameter of the ferrite powder, d _10% , d _90%
Is 1 in the cumulative distribution of the particle size of the ferrite powder.
It represents the particle size when it becomes 0% or 90%.