JPH06333726A - Manufacture of high-density mn-zn ferrite - Google Patents

Abstract

PURPOSE:To provide a Mn-Zn ferrite of uniform magnetic characteristics without residual hematite or residual pores by sintering ferrite material with reducing agent in an inert atmosphere. CONSTITUTION:Materials for Mn-Zn ferrite, 62-68mol.% Fe2O3, 16-28mol.% MnO, and 10-16mol.% CoO, are mixed in a ball mill and baked in a nitrogen atmosphere. After CaO, SiO2, ZrO2 and CoO are added as additives, all the materials are pulverized in a ball mill. The resulting powder and a reducing agent are mixed at a ratio of 0.05-2.0% by weight in a mortar, and the mixture is compressed into a compact. After heated to 200 deg.C in a nitrogen atmosphere, the compact is sintered at 1200 deg.C in a nitrogen atmosphere containing 0.1% oxygen. This sinter is worked on a hot isostatic press, and then heat-treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency low-loss Mn-Zn ferrite used in a high-frequency transformer and a high-density Mn-Zn ferrite having a high magnetic flux density and a high frequency and a high magnetic permeability used in a magnetic head core. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Mn-Zn ferrite has been widely used as a transformer material in a switching power supply, but in recent years, the power supply has become smaller and lighter, and its operating frequency is 5
It has been used at a high frequency of 00KHZ to 1MHZ, and it is considered that the frequency will further increase to 1MHZ or more in the future. The transformer material used for such a power source is also required to have a low loss at high frequencies, and the conventional Fe2 O3 content is 50 to 55 mol%.
If Mn-Zn ferrite containing is used, there is a problem that the loss is large and heat is generated.

FDD (floppy disk drive),
As a recent magnetic head material used for RDD (fixed disk drive), VTR (video tape recorder), etc., high density Mn-Zn ferrite is mainly used. However, as the recording density in magnetic recording has been improved in recent years, a metal medium having a higher coercive force has been widely used as a recording medium used for this instead of an iron oxide type, and a conventional Fe2 O3 content of 50 to 55 mol. %, It was difficult to use a head using a high-density Mn-Zn ferrite containing it because of its low saturation magnetic flux density. In order to improve these problems, Mn-Zn ferrite containing Fe2 O3 in an amount of 60 mol% or more and having a high saturation magnetic flux density is known. Due to the high saturation magnetic flux density, the initial permeability is high up to high frequencies, It has a feature of low loss.

However, if Mn-Zn ferrite containing a large amount of Fe2 O3 is to be calcined, crushed and fired by a conventional ceramic technique, the spinelization reaction of Fe2 O3 will occur during firing. Due to the release of excess oxygen due to the above, there are problems that a large amount of pores and unreacted hematite remain in the fired body, and the magnetic properties become nonuniform in the fired body. Further, even if an attempt is made to densify such a fired body by hot isostatic pressing (hereinafter referred to as HIP treatment), it does not densify due to the residual pores, and due to unreacted hematite. Magnetic properties deteriorate and become non-uniform.

In order to prevent such a large amount of pores and hematite from remaining in the fired body, calcination is performed at a high temperature of 1100 ° C. or higher in an inert gas for a plurality of times and for a long time,
Although the oxygen released during firing can be reduced by sufficiently increasing the spinelization degree of the powder, the effect becomes insufficient as the fired body becomes larger, and the above-mentioned problems still occur. Further, in this case, since the calcination temperature is high, the powder is sintered and the subsequent pulverization becomes difficult, and the firing in an oxidizing atmosphere causes the spinel structure to dissociate, which requires a deashing step. Can not use organic binder. Further, there is a problem that the higher the degree of spinelization, the easier the dissociation of the spinel structure due to reoxidation during the temperature rising process during firing.

In Japanese Patent Publication No. 4-33756, Fe2
In a method for producing a ferrite containing a large amount of O3, a method has been proposed in which firing is performed in a plurality of steps and firing is performed at a temperature higher than 1250 ° C. However, since the firing step is complicated and the firing temperature is high, There is a problem that abnormal growth of crystal grains occurs.

As disclosed in Japanese Patent Laid-Open No. 63-252929, there has been proposed a method of using coprecipitated ferrite containing a large amount of divalent iron in the powder used for the ferrite material. Since it is originally made spinel, it is not necessary to perform calcination, and the amount of oxygen released during firing is small, but there is a problem that the process of obtaining the coprecipitated powder is complicated and the raw material cost is high.

[0008]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to produce residual Mn-Zn ferrite containing a large amount of Fe2 O3 by the conventional ceramic method. It is intended to provide a manufacturing method for obtaining Mn-Zn ferrite which does not include residual pores and has uniform magnetic properties in a product. More specifically, even a powder having a relatively low spinelization degree is 1200 ° C.
It is an object of the present invention to obtain a high-frequency low-loss Mn-Zn ferrite having uniform magnetic properties, which is obtained in a state where a relatively large fired body at a low firing temperature before and after does not contain residual hematite and has few remaining pores. Furthermore, this Mn-Zn ferrite is added to H
It is an object of the present invention to obtain a high-density ferrite having a high saturation magnetic flux density and a high initial permeability at a high frequency, which does not contain residual hematite and pores, by IP and heat treatment.

[0009]

According to the present invention, the main components are 62 to 68% of Fe2 O3 and 16 to 28% in molar ratio.
Of MnO and 10 to 16% ZnO, and a ferrite material containing at least one of CaO, SiO2, ZrO2 and CoO as a subcomponent to obtain a Mn-Zn ferrite in a weight ratio to the ferrite material. A reducing agent is added in an amount of 0.05 to 2.0%, the temperature is raised in an inert gas, and firing is performed. Also, the high density M obtained in this way
High-density Mn-Zn ferrite is obtained by HIP heat treatment of n-Zn ferrite.

The main component of the ferrite material used in the present invention is 62 to 68% of Fe2 O3 and MnO 16 to 28 in molar ratio.
% And ZnO 10 to 16%, and a sintered body having a saturation magnetic flux density of 5800 G or more can be obtained. These main components are weighed, mixed, and then calcined. It is necessary to properly select the temperature and atmosphere for the calcination so that the spinelization degree of the powder progresses to about 60 to 90%. If the spinelization degree is further increased, the sintering proceeds excessively and it becomes difficult to grind, and if the spinelization degree is lower than this, the effect of the reducing agent does not work sufficiently.

After calcination, CaO, SiO2,
A predetermined amount of at least one of ZrO2 and CoO is added and crushed. Of these, CaO, SiO2 and ZrO2 have the effect of increasing the resistivity of the fired body, and CoO is Fe2 O3.
There is an effect of adjusting the anisotropy constant K1 in accordance with the amount of, and any of them can improve the initial permeability at high frequency.

The reducing agent is not particularly limited, but it is preferable to use an organic binder which can be uniformly mixed with the ferrite material. The organic binder can be selected from polyacrylamide, methyl cellulose, polyvinyl alcohol, glycerin, polyethylene oxide, oleic acid and the like. The reducing agent can be added either during pulverization, sizing, or molding, but in any case, it must be sufficiently mixed with the powder. For example, at the time of sizing, it can be added after being sufficiently kneaded with the powder in a mortar or the like. The amount of addition is 0.05 to 2.0 wt% with respect to the ferrite material, depending on the spinelization of the powder. If the added amount is 2.0 wt% or more, a different phase such as wustite occurs in the fired body and the magnetic properties are deteriorated, and if it is 0.05 wt% or less, the effect as a reducing agent does not sufficiently work, and hematite and a large amount are added. Porosity remains.

It is known that such a reducing agent is added also to the conventional Mn-Zn ferrite containing 50 to 55 mol% of Fe2 O3. The purpose is to add a microcrystalline sintered body. Is about to get 10
It aims to completely react hematite even at low temperature firing below 00 ° C., and Mn containing a large amount of Fe 2 O 3 according to the present invention.
The purpose is different from the case of -Zn ferrite.

The powder to which the reducing agent is added is molded and then fired. During firing, the release of excess oxygen due to the spinelization reaction occurs in the range of 300 to 1100 ° C., but this released oxygen is effectively absorbed by the decomposition of the reducing agent evenly contained in the inside of the molded body, resulting in large molding. The fired body is uniform both inside and outside the body. The firing is performed in an atmosphere of an inert gas so that the effect of the reducing agent is sufficient. When firing in an oxidizing gas such as air, the added reducing agent is oxidatively decomposed and does not function as a reducing agent. It is preferable to introduce the inert gas at 200 ° C. At a temperature higher than this, oxidative combustion of the reducing agent partially occurs and absorption of released oxygen becomes insufficient, and at a temperature lower than this, a part of the inert gas is wasted. Will end up. The inert gas can be selected from argon, helium, nitrogen and the like. After that, the firing temperature is maintained in the range of 1150 to 1250 ° C. in an inert gas, or more preferably in an inert gas whose oxygen concentration is controlled, and then the temperature is lowered.

When the ferrite fired body thus obtained is to be a high-density ferrite, the fired body is subjected to HIP treatment. The conditions of the HIP treatment are not particularly limited, but in order to increase the density while suppressing the growth of crystal grains, the temperature is 30 to 100 ° C. lower than the firing temperature and the pressure is 500 to 1
It is preferably carried out in the range of 500 kg / cm 2. The HIP-treated high-density ferrite is heat-treated to remove internal strain by the HIP treatment. The condition of heat treatment is not particularly limited as long as the internal strain is removed, but in order to prevent reproduction of pores inside the ferrite or deterioration of the surface portion,
700 to 10 in an inert gas atmosphere with controlled oxygen concentration
It is preferably carried out in the range of 00 ° C.

[0016]

According to the above-described method for producing Mn-Zn ferrite containing a large amount of Fe2 O3, there is no residual hematite and there are few residual pores by the conventional ceramic method, so that the magnetic characteristics are uniform and the high frequency Thus, a relatively large ferrite fired body with low loss can be obtained. Further, by subjecting this fired body to HIP treatment and heat treatment, high density ferrite free of residual hematite and pores, having uniform magnetic properties in the product, high saturation magnetic flux density and high initial permeability at high frequency. Can be provided with good mass productivity.

[0017]

EXAMPLES Examples of the present invention will be described below. Fe2 O3, MnO and ZnO were selected as the main components within the composition range shown in FIG.
It was calcined at 0 to 1000 ° C. for 5 hours. CaO, SiO2, ZrO2 and CoO were added as auxiliary components in the range shown in FIG. 1 and pulverized with a ball mill. A reducing agent was mixed and added to this ferrite raw material powder in the types and ranges shown in FIG. 2 using a mortar, and 50 × 50 × 1
It was molded into a 0 mm block shape. Then, the temperature of this formed body was raised from 200 ° C. in a nitrogen atmosphere, and the formed body was fired at 1200 ° C. for 6 hours in a nitrogen atmosphere containing 0.1% oxygen to obtain a fired body. The presence or absence of residual foreign phase and residual pores inside the block of this fired body was examined. Also, from the center and the surface of the block, the outer diameter is 5 mmφ, the inner diameter is 3 mmφ, and the thickness is 0.5 mmt.
The ring was processed and the initial magnetic permeability μi and the relative loss coefficient tan δ / μi at 5 MHZ were measured. The results are shown in FIG.

Further, this fired body was subjected to HIP treatment in an argon atmosphere at 1130 ° C. and 1000 kg / cm 2 for 3 hours, and further heat-treated in an atmosphere containing 20 ppm of oxygen at 850 ° C. for 6 hours. The presence or absence of residual foreign phase, residual pores and cracks inside the block of the thus obtained high density ferrite was examined. Further, a ring having an outer diameter of 5 mmφ, an inner diameter of 3 mmφ and a thickness of 0.5 mmt is machined from the center of the block, and the saturation magnetic flux density Bs and 1 at 10 Oe are
With respect to the initial magnetic permeability μi at MHZ and 10 MHZ, a ring was similarly processed from the surface portion, and the initial magnetic permeability μi was measured. The results are shown in FIG.

As is clear from the above results, in the Mn-Zn ferrites of Examples 1 to 4 of FIG. 3 according to the present invention, since there are no different phases inside the fired product and there are few pores, the inside and the surface portion are It can be seen that the magnetic characteristics are uniform and the loss at high frequencies is small. On the other hand, in the Mn—Zn ferrite of Comparative Example 1 in which no reducing agent is added or the amount of addition of the reducing agent is not appropriate, defects such as a foreign phase are left inside the fired product, and the magnetic properties are greatly deteriorated. . Further, Comparative Examples 4 and 5 in which the composition of the main component is out of the range of the present invention.
Also, with the Mn-Zn ferrite of Comparative Example 6 containing no subcomponents of the present invention, no defects are left inside the fired product, but a decrease in initial permeability and an increase in loss occur at high frequencies.

Also, in the high density Mn-Zn ferrite obtained by treating these fired products, there are no different phases and pores inside the treated products, the high saturation magnetic flux density and the high initial magnetic permeability at high frequencies. It can be seen that there is little variation within the treated product and within the surface. On the other hand, in the high-density ferrite of Comparative Example 1 in which the reducing agent is not added, or Comparative Examples 2 and 3 in which the amount of the reducing agent is not appropriate, defects are left inside the processed product and the magnetic properties are greatly deteriorated. Further, in the high-density ferrites of Comparative Examples 4 and 5 in which the composition of the main component is out of the range of the present invention and Comparative Example 6 containing no subcomponent of the present invention,
Although no defects are left inside the processed product, the saturation magnetic flux density decreases and the initial permeability at high frequencies also decreases.

[0021]

As is apparent from the above description, in the method for producing Mn-Zn ferrite of the present invention, the main components are 62 to 68% of Fe2 O3 and 16 to 28 in molar ratio.
% MnO and 10 to 16% ZnO, and a ferrite material containing at least one of CaO, SiO2, ZrO2 and CoO as a sub-component in a weight ratio of 0.05-.
Since 2.0% of the reducing agent is added and firing is performed in an inert gas, it is possible to prevent the release of excess oxygen due to the spinelization reaction, and it is possible to obtain magnetic properties at a low firing temperature of around 1200 ° C. Relatively large Mn-Z with uniform, high frequency and low loss
An n-ferrite fired body can be obtained. Further, by subjecting this fired body to HIP treatment and heat treatment, it is possible to manufacture a high-density Mn-Zn ferrite with little variation in the product, high saturation magnetic flux density, and high initial permeability at high frequency with good mass productivity. .

[Brief description of drawings]

FIG. 1 is a diagrammatic chart comparing the components contained in an example of the present invention and a comparative example.

FIG. 2 is a chart showing the types and addition amounts of reducing agents.

FIG. 3 is a chart diagram comparing the characteristics of an example of the present invention and a comparative example.

FIG. 4 is a diagrammatic chart comparing other characteristics of the example of the present invention and the comparative example.

Claims (4)

[Claims] 1. A main component of which the molar ratio is 62 to 68% Fe.
2 O3, 16-28% MnO and 10-16% Zn
O, with CaO, SiO2, ZrO2 as subcomponents
And a high-density Mn-Zn ferrite obtained by firing a ferrite material containing at least one of CoO to obtain Mn-Zn ferrite, and adding a reducing agent to the ferrite material and firing the inert material in an inert gas. Manufacturing method. 2. In the firing according to claim 1, an inert gas atmosphere in which an inert gas atmosphere is controlled from 200 ° C., the reducing agent is gradually decomposed and released oxygen is absorbed in a range of 200 to 1100 ° C. to control the oxygen concentration. A method for producing a high-density Mn-Zn ferrite, which comprises firing in an atmosphere. 3. The reducing agent according to claim 1 is an organic binder, and the addition amount of the reducing agent is 0.
It is 0.5 to 2.0%, The manufacturing method of the high-density Mn-Zn ferrite of Claim 1 characterized by the above-mentioned. 4. A Mn-obtained by the manufacturing method according to claim 1.
A method for producing a high-density Mn-Zn ferrite, comprising performing hot isostatic pressing on Zn ferrite and then performing heat treatment.