JP2005047783A - Hexagonal system z-type ferrite and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hexagonal Z-type ferrite having few heterogeneous phase and high volume resistivity. <P>SOLUTION: In the hexagonal Z type ferrite, Fe<SP>2+</SP>contained in a sintered compact is ≤0.2% of Fe<SP>3+</SP>, the production ratio of a W phase in the sintered compact is ≤5% and the production ratio of BaFe<SB>2</SB>O<SB>4</SB>phase is ≤2% and the volume resistivity is ≥3×10<SP>3</SP>Ω×m. In the manufacturing method, the pulverized powder or the granulated powder of the hexagonal Z-type ferrite consisting essentially of iron oxide (Fe<SB>2</SB>O<SB>3</SB>), barium oxide (BaO) and cobalt oxide (CoO) is incompletely mixed with the pulverized powder or the granulated powder of at least one kind of Mn-Zn-based ferrite or Ni-Zn-based ferrite and the mixture is fired. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic material for high frequency, and particularly relates to a hexagonal Z-type ferrite used for electronic components such as choke coils and noise removing elements and radio wave absorbers in a high frequency band from several MHz to several GHz.

  In recent years, with the increase in the frequency of mobile phones, wireless LANs, personal computers, etc., the elements used inside the apparatus are also required to have a higher frequency. In response to such a requirement, conventionally used spinel ferrite cannot be used because there is a frequency limit called a snake limit in a high frequency band. Therefore, hexagonal ferrite having an easy magnetization surface and a hexagonal crystal structure has been studied as a high frequency material exceeding the frequency limit. Among hexagonal ferrites, it is known that the Z-type containing Co, in particular, has a relatively high magnetic permeability and exhibits excellent high-frequency characteristics. When hexagonal ferrite is used for electronic parts such as coil parts, high volume resistivity is required at the same time from the viewpoint of ensuring insulation as well as high magnetic permeability and good frequency characteristics.

In order to meet the above-mentioned requirements, in Patent Document 1, as a study of high magnetic permeability and high frequency, CaO and SiO ₂ are precipitated at grain boundaries to form a high-resistance glass layer, and eddy current loss is suppressed to suppress high-frequency permeability. It is disclosed to improve the magnetic susceptibility. Patent Document 2 describes that the permeability at low frequencies is improved by replacing iron with divalent and tetravalent metal ions. Patent Document 3 describes that by replacing Co with Cu and Ba with Sr and Pb, firing can be performed at a temperature lower than the melting point of silver, and the magnetic permeability can be improved in a high frequency region.

In addition, among the above requirements, Patent Document 4 discloses that high resistance and high resistance can be achieved while maintaining magnetic permeability by simultaneously adding Mn ₃ O ₄ and Bi ₂ O ₃ or CuO after calcination as a study of increasing resistance. In Patent Document 5, it is stated that a ferrite with high specific resistance can be obtained by providing a low-temperature temperature decrease region in which the temperature decrease rate is 0 ° C./min or more and less than 1 ° C./min in the temperature decrease process of the sintering process. It has been. Patent Document 6 describes the content of increasing the resistance by blending ₁ to 10 wt% of Ba carbonate or Sr carbonate or both and 0.5 to 5 wt% of SiO2.

There are various methods for improving the properties of the hexagonal ferrite as described above, but there are Patent Documents 7 and 8 as examples in which compositions having other crystal structures are mixed. In Patent Document 7, planar type ferrite is added to Ni—Zn—Co ferrite to improve high frequency characteristics. In Patent Document 8, Ba—O is added to Li—Ni—Mg ferrite in the form of hexagonal ferrite. Thus, the temperature coefficient of initial permeability is reduced. In such a form, spinel type ferrite is the main composition, and hexagonal ferrite is included therein.
JP-A-9-129433 JP 2000-235916 A JP 2002-252108 A JP 2001-39718 A JP 2002-362968 A JP 2003-2656 A Japanese Patent Publication No.49-30435 Japanese Patent Publication No.55-19043

However, it is difficult to achieve both good frequency characteristics that can be originally possessed by hexagonal Z-type ferrite and high volume resistivity even if the improvement methods of Patent Documents 1 to 6 are used.
Further, in Patent Documents 7 and 8, in order for a mixture of two kinds of crystals to exhibit desirable characteristics, it is essential that microcrystals of hexagonal ferrite are scattered in the resulting sintered spinel ferrite. ing. That is, it is essential that these two types of crystal systems do not dissolve in each other but each exist as a single phase. However, when another crystal system exists as a single phase in this way, it becomes difficult for the hexagonal Z-type ferrite to obtain desired high frequency characteristics.
In other words, even with these conventional improvement methods, the hexagonal ferrite cannot simultaneously satisfy the desired high frequency characteristics and high volume resistivity. Therefore, an object of the present invention is to solve this point.

In order to solve the problem, the first invention is a hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO), and cobalt oxide (CoO), and in particular, sintered. A high volume resistivity is realized by setting the production rate of Fe ²⁺ contained in the body to 0.2% or less.

The second invention is a hexagonal Z-type ferrite containing iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO) as main components, wherein the W phase in the sintered body is A hexagonal Z-type ferrite having a generation ratio of 5% or less, a BaFe ₂ O ₄ phase generation ratio of 2% or less, and a volume resistivity of 3 × 10 ³ Ω · m or more. .

Further, the third invention relates to a pulverized hexagonal Z-type ferrite composed mainly of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO), and cobalt oxide (CoO), and Mn—Zn ferrite or Ni— A method for producing a hexagonal Z-type ferrite characterized by mixing at least one pulverized powder of Zn-based ferrite or garnet-based ferrite, and the volume resistivity is 3 × 10 ³ Ω · m or more by such a method. Thus, a hexagonal Z-type ferrite can be obtained.

Furthermore, the fourth invention relates to a pulverized hexagonal Z-type ferrite composed mainly of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO), and Mn—Zn ferrite or Ni—. A method for producing a hexagonal Z-type ferrite comprising mixing at least one kind of granulated powder of Zn-based ferrite or garnet-based ferrite, and the volume resistivity is reduced to 3 × 10 ³ Ω · m by such a method. A hexagonal Z-type ferrite characterized by the above can be obtained.

Further, the fifth invention relates to a granulated powder of hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO), and Mn—Zn ferrite or Ni. -Zn-based ferrite or garnet-based ferrite is mixed with at least one type of granulated powder, which is a method for producing hexagonal Z-type ferrite, and the volume resistivity is reduced to 3 × 10 ³ Ω · A hexagonal Z-type ferrite characterized by being m or more can be obtained.

Further, a sixth invention is a hexagonal crystal comprising iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO) as main components in the third invention, the fourth invention or the fifth invention. Z type ferrite pulverized powder or granulated powder and at least one pulverized powder or granulated powder of Mn-Zn type ferrite, Ni-Zn type ferrite or garnet type ferrite were mixed using a dry mixing means. This is a method for producing a hexagonal Z-type ferrite.

According to the present invention, a hexagonal Z-type ferrite having an excellent volume resistivity can be provided. That is, the volume resistivity can be greatly improved by setting the production rate of Fe ²⁺ in the sintered body sample within a predetermined range. By using the hexagonal Z-type ferrite of the present invention, high magnetic permeability can be obtained, and high quality choke coils, radio wave absorbers and the like can be manufactured.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the present invention, the raw materials are mixed with, for example, a wet ball mill and calcined using an electric furnace or the like to obtain calcined powder. The obtained calcined powder is pulverized using a wet ball mill or the like, and the obtained pulverized powder is molded by a press machine and subjected to main firing by using, for example, an electric furnace to obtain hexagonal Z-type ferrite.

The hexagonal Z-type ferrite needs to have a somewhat high sintered density in order to obtain a high magnetic permeability. However, the resistance of a sample exhibiting a high sintered density can be greatly reduced. Presence of Fe ²⁺ generated in the sintered body sample can be expected as a cause of such a decrease in resistance. Although the hexagonal Z-type ferrite normally does not contain Fe ²⁺ in its composition, it tends to easily generate internal Fe ²⁺ when sintered at high density. That is, by suppressing the Fe ²⁺ generation rate, a high volume resistivity can be obtained while maintaining a high sintered density.

Conventionally, the generation of heterogeneous phases in hexagonal ferrite has been regarded as undesirable because it impairs performance, and in many studies, efforts have been made to completely eliminate heterogeneous phases. However, in the present invention, it is not always necessary to completely eliminate the heterogeneous phase. Rather, Fe ²⁺ is reduced in the range where the W phase and the BaFe ₂ O ₄ phase are present, and as a result, a high electric resistivity is found. It was. The mechanism of high resistance in such a state is not yet clear, but it is presumed that the main reason is that the balance of charge in the hexagonal ferrite, which has a complicated relationship between the generation of complex phases and the charge, is favorable. Is done.

In the present invention, as described above, in order to reduce the Fe ²⁺ generation rate, the pulverized powder or granulated powder of hexagonal Z-type ferrite is at least one of Mn—Zn ferrite, Ni—Zn ferrite, and garnet ferrite. The powder is mixed in the state of pulverized powder or granulated powder and then fired. While such additives are not yet clear in terms of reducing the yield of Fe ²⁺ Mn, Ni, resulting in solid solution preferentially to sites that metal having a valency of Zn such as +2 to generate a Fe ²⁺ It can be predicted that the production of Fe ²⁺ is suppressed.

  Still further, in the present invention, a powder of Mn-Zn ferrite, Ni-Zn ferrite, or garnet ferrite is mixed in the state of pulverized powder or granulated powder with hexagonal Z-type ferrite ground powder or granulated powder. In this case, it is not preferable to make the degree of mixing perfect, but on the contrary, it is better to keep it in an incompletely mixed state. Complete mixing is undesirable because it reduces the volume resistivity. It can be considered that this is because the W phase, which is a stable phase, is very easily generated by performing more uniform addition. Further, it is known that Mn and Ni which are one type of additive element are preferentially dissolved in the W phase, and the generation of the W phase greatly reduces the effect of the addition.

  In the present invention, hexagonal ferrite is the main composition, and the oxide magnetic material of different crystal system is mixed in the middle of the manufacturing process in the same way as the conventional example, but the mixing method is And thus the overall phase production that occurs during the calcination stage is quite different. That is, in the present invention, it is important that both hexagonal crystals and other crystal systems mixed with them are mixed at least once having undergone a calcination step and most of which have become a predetermined crystal system. Even if it mixes in a step, the effect of the present invention is not expressed. Specifically, mixing with a powder pulverized or granulated after calcination produces an effect.

  Furthermore, in the present invention, it is not necessary that pulverized powder or granulated powder of hexagonal crystal and Mn—Zn ferrite, Ni—Zn ferrite, or garnet ferrite exist as a single phase in the sintered body.

As a result of further various studies, at least one pulverized powder or granulated powder of Mn—Zn ferrite, Ni—Zn ferrite, or garnet ferrite is crushed or granulated into hexagonal ferrite, or a dry ball mill or It has been found that the desired high characteristics can be obtained only by mixing and baking using some dry mixing means such as a mixer. However, the production conditions of Mn—Zn ferrite, Ni—Zn ferrite, and garnet ferrite used in the present invention do not affect the effect of the present invention, and Mn—Zn ferrite, Ni—Zn ferrite having various compositions and production conditions, The same effect is exhibited with garnet ferrite.
Examples will be described in detail below.

As described above, in the present invention, it is found that the amount of Fe ²⁺ has a great influence on the resistivity, and a desired volume resistivity can be obtained when the production rate is 0.2% or less. The reason for limitation will be described below. The reason why it is 0.2% or less is that a volume resistivity of 10 ³ Ω · m or more is obtained, and when it exceeds 0.2%, the volume resistivity is extremely lowered.
Furthermore, in the present invention, it is found that the production rate of Fe ²⁺ greatly depends on the production rate of the heterogeneous phase, and when the production rate of the W phase is 5% or less and the production rate of the BaFe ₂ O ₄ phase is 2% or less, The production rate of Fe ²⁺ is suppressed to 0.2% or less, and as a result, a volume resistivity of 10 ³ Ω · m or more is obtained. The reason for limitation will be described below. The reason why the generation rate of the W phase is 5% or less and the generation rate of the BaFe ₂ O ₄ phase is 2% or less is that the volume resistivity of 10 ³ Ω · m or more is obtained when the generation rate of the different phase is within such a range. This is because when the generation rate of the heterogeneous phase is outside the above range, the volume resistivity is extremely lowered.

The hexagonal Z-type ferrite according to the present invention will be specifically described below.
First, 70.2 wt% of Fe ₂ O ₃ , 24.8 wt% of BaO (using BaCO ₃ ) and 5.0 wt% of CoO were weighed and mixed for 16 hours in a wet ball mill, and this was mixed at 1200 ° C. for 2 hours. It was calcined.
Next, it was pulverized with a wet ball mill for 18 hours. To the prepared pulverized powder, pulverized powders of Mn—Zn ferrite, Ni—Zn ferrite and garnet ferrite were added by mixing for 30 minutes using a 3.6 wt% V-type mixer, and a binder was further added to granulate. After granulation, it was compression molded into a ring shape, and then sintered at 1340 ° C. for 3 hours in an oxygen atmosphere. The initial permeability and volume resistivity at 25 ° C. of the obtained ring-shaped sintered body having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm were measured.

  The initial permeability was measured at a frequency of 100 kHz using an impedance / gain phase analyzer 4194A (manufactured by Yokogawa, Hewlett, Packard) after winding the ring sintered body 20 times. The volume resistivity was measured by using an insulation resistance meter (manufactured by Advantest) after cutting the ring sintered body into two parts at the center, applying dootite as a conductive material to the cut surface.

Further, the heterogeneous phase generation rate is obtained by mirror-polishing the cross section of the ring-shaped sintered body and measuring the area occupied by the main phase Z phase and the heterogeneous phase (W phase, BaFe ₂ O ₄ phase) from a 400 times SEM image (manufactured by Hitachi, Ltd.). The area ratio was defined by the following formula.
Heterogeneous area ratio = measured heterogeneous area / total area

The amount of Fe ²⁺ formed in the sintered body was determined by titrating with potassium dichromate standard solution using diphenylamine as an indicator and determining ferrous oxide. The production rate of Fe ²⁺ was defined as follows.
Production rate of ^{Fe 2+ = Fe 2+ / (Fe} 2+ + Fe 3+)

The results of examining the magnetic permeability, volume resistivity, Fe ²⁺ formation rate, and heterogeneous phase formation rate of the obtained ring sintered body are shown in Example 1 to Example 3 in Table 2. The composition (mol%) and calcining temperature (° C.) of Mn—Zn ferrite, Ni—Zn ferrite and garnet ferrite added here are as shown in Table 1.

As shown in Table 2, in the comparative example 1 of hexagonal ferrite alone, the W phase is not generated, but there are many BaFe ₂ O ₄ phases, resulting in a low volume resistivity.

On the other hand, in Examples 1 to 3 in which pulverized powders of Mn—Zn ferrite, Ni—Zn ferrite and garnet ferrite were added, mixed in a dry ball mill and then fired, both the W phase and the BaFe ₂ O ₄ phase The production amount is small, and the production rate of Fe ²⁺ is reduced. Also, the volume resistivity is much larger than that of the comparative example. The heterogeneous state of Example 1 can be observed from an SEM image as shown in FIG. As can be seen in FIG. 1, both W phase and BaFe ₂ O ₄ phase are recognized as different phases, but no single phase of Mn—Zn ferrite, Ni—Zn ferrite, or garnet ferrite is recognized.

Comparative Examples 2 and 3 show the result of molding and firing the pulverized powder having the same composition as in Examples 1 and 2 after thoroughly mixing them for 3 hours in a wet ball mill to which water was added. It can be seen that in the case of mixing with a strong mixing degree, only the W phase is generated and the volume resistivity is extremely small. The heterogeneous state of Comparative Example 2 can be observed from the SEM image as shown in FIG. As can be seen from FIG. 2, it can be seen that only the W phase is generated as a different phase. As can be seen from the above results, according to the sample incompletely mixed for 30 minutes by the dry ball mill, the Fe ²⁺ generation rate is small, and as a result, the volume resistivity is extremely large. Both W phase and BaFe ₂ O ₄ phase exist, but the ranges are 5% or less for W phase and ₂ % or less for BaFe ₂ O ₄ phase. Under such conditions, the Fe ²⁺ generation rate is 0.2% or less, and a large volume resistivity of 3 × 10 ³ Ω · m or more is exhibited.

Next, 70.2 wt% of Fe ₂ O ₃ , 24.8 wt% of BaO (using BaCO ₃ ) and 5.0 wt% of CoO were weighed and mixed for 16 hours in a wet ball mill, and this was mixed at 1200 ° C. for 2 hours. It was calcined. Next, 3.6 wt% of the hexagonal ferrite weight was added to the pulverized powder pulverized with a wet ball mill for 18 hours and the granulated powder of Mn—Zn ferrite and Ni—Zn ferrite having the same composition as shown in Table 1. After mixing for 30 minutes using a V-type mixer, a binder was added, and after granulation, it was compression molded into a ring shape. Then, it sintered at 1340 degreeC in oxygen atmosphere for 3 hours.
The initial permeability and volume resistivity at 25 ° C. of the obtained ring-shaped sintered body having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm were measured. The measurement conditions and the like were the same as those in Example 1 described above. Table 3 shows the evaluation results of the produced ring-shaped sintered body samples. This example is an example in which the pulverized powder of hexagonal Z-type ferrite and the granulated powder of Mn—Zn ferrite or Ni—Zn ferrite are mixed. As shown in Table 3, Mn—Zn ferrite, It can be seen that by incompletely mixing the Ni—Zn ferrite granulated powder, the formation of Fe ²⁺ can be suppressed and a hexagonal Z-type ferrite having a high volume resistivity can be produced.

Further, 70.2 wt% of Fe ₂ O ₃ , 24.8 wt% of BaO (using BaCO ₃ ) and 5.0 wt% of CoO were weighed and mixed for 16 hours in a wet ball mill, and this was mixed at 1200 ° C. for 2 hours. It was calcined. Next, after grinding for 18 hours in a wet ball mill, a binder was added to these and granulated. To this granulated powder, granulated powder of Mn—Zn ferrite and Ni—Zn ferrite having the same composition as in Examples 1 and 2 were mixed for 30 minutes using a V-type mixer and then compression-molded into a ring shape. Then, it sintered at 1340 degreeC in oxygen atmosphere for 3 hours. The initial permeability and volume resistivity at 25 ° C. of the obtained ring-shaped sintered body having an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm were measured. The measurement conditions and the like were the same as those in the above-described example. Table 4 shows the evaluation results of the produced ring-shaped sintered body samples. This example is an example in which a granulated powder of hexagonal Z-type ferrite and a granulated powder of Mn-Zn ferrite or Ni-Zn ferrite are mixed. As shown in Table 4, Mn-Zn ferrite is used. Incomplete mixing of the Ni-Zn ferrite granulated powder suppresses the formation of Fe ²⁺ in both the W phase and the BaFe ₂ O ₄ phase, and produces a hexagonal Z-type ferrite with a high volume resistivity. I understand that I can do it.

As described above in detail, pulverized and granulated powders of hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO ₂ ) are used as Mn—Zn. And at least one kind of pulverized powder or granulated powder out of ferrite, Ni—Zn ferrite or garnet ferrite, and then firing, both W phase and BaFe ₂ O ₄ phase exist and As a range, hexagonal ferrite having a W phase of 0 to 5% (not including 0) and a BaFe ₂ O ₄ phase of 0 to 2% (not including 0) is obtained. Also, if the degree of mixing is made strong and complete, this effect will fade. Even if mixing is strong, it is preferable to keep it within one hour with a V-type mixer.

  The hexagonal Z-type ferrite of the present invention is used for electronic components such as choke coils and noise elimination elements in a high frequency band from several MHz to several GHz.

It is a hexagonal Z-type ferrite of the present invention, and is an SEM image of Example 1 described in Table 2. 3 is a SEM image of Comparative Example 2 described in Table 2.

Explanation of symbols

1: Matrix phase (Z phase)
2: W phase 3: BaFe ₂ O ₄ phase

Claims (6)

A hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO), and cobalt oxide (CoO), and the production rate of Fe ²⁺ contained in the sintered body is 0. A hexagonal Z-type ferrite having a volume resistivity of 3 × 10 ³ Ω · m or more and 2% or less. A hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO), and cobalt oxide (CoO), wherein the W phase generation ratio in the sintered body is 5% or less and A hexagonal Z-type ferrite having a BaFe ₂ O ₄ phase generation ratio of 2% or less and a volume resistivity of 3 × 10 ³ Ω · m or more. Hexagonal Z-type ferrite pulverized powder mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO), and Mn—Zn ferrite, Ni—Zn ferrite, or garnet ferrite A method for producing a hexagonal Z-type ferrite, wherein at least one kind of pulverized powder is mixed and fired to have a volume resistivity of 3 × 10 ³ Ω · m or more. Hexagonal Z-type ferrite pulverized powder mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO), and Mn—Zn ferrite, Ni—Zn ferrite, or garnet ferrite A method for producing a hexagonal Z-type ferrite, wherein at least one kind of granulated powder is mixed and fired to have a volume resistivity of 3 × 10 ³ Ω · m or more. Granulated powder of hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO) and Mn—Zn ferrite, Ni—Zn ferrite or garnet A method for producing a hexagonal Z-type ferrite, comprising mixing at least one type of granulated powder of ferrite and then firing to make the volume resistivity 3 × 10 ³ Ω · m or more. Pulverized or granulated powder of hexagonal Z-type ferrite mainly composed of iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) and cobalt oxide (CoO), and Mn—Zn ferrite or Ni—Zn ferrite Alternatively, at least one pulverized powder or granulated powder of garnet-based ferrite is mixed using a dry mixing means, and the hexagonal Z-type ferrite according to any one of claims 3 to 5 is produced. Method.

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