JPH09309767A - Production of ferrite powder material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the labor needing to grind baked ferrite. SOLUTION: This ferrite powder material to be used as a material for e.g. wave absorbers is obtained by the following method: a ferrite stock is preliminarily baked to produce preliminarily baked powder, which is then incorporated with a binder to form a powder molding of appropriate size which is, in turn, subjected to regular baking. The regular baking is so designed that the baking temperature is gradually raised from normal temperature to a specified temperattire, then, the specified temperature is maintained and the power molding is heated for a specified time, and then gradually cooling. In this case, for the period of time from the beginning of the regular baking to the point when the specified temperature is reached, the baking is carried out in an atmosphere <=0.3wt.% of oxygen concentration. By conducting the regular baking under such conditions, ferrite granules randomly ground to some extent can be obtained as a baked ferrite. Thus, when the ferrite granules are to be ground next, labor for the grinding work can be reduced, leading to cost reduction and shortening the grinding time.

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 ferrite powder material used as a material for a radio wave absorber.

[0002]

2. Description of the Related Art As a method for producing a ferrite powder material used as a material for a radio wave absorber, a ferrite fired body of an appropriate size is first produced by a generally known production method, and then obtained. A method of pulverizing the fired ferrite body into powder is adopted. That is, first, a ferrite raw material having a predetermined mixing ratio is calcinated, and the calcinated body obtained is crushed to prepare a calcinated powder. Next, a binder is added to the preliminarily fired powder to form a powder compact having an appropriate size, and the powder compact is subjected to main firing to produce a ferrite fired body. Then, the ferrite fired body is pulverized by a mechanical means such as a pulverizing device to obtain a powder having a particle diameter of several μm to several mm, which is used as a ferrite powder material.

In the main firing of the powder compact, first, the firing temperature is gradually raised in air to remove the binder contained in the powder compact until the temperature reaches about 600 ° C. To do. After that, the firing temperature is further raised in a nitrogen atmosphere to reach a predetermined temperature, for example, about 1300 ° C., and heating is performed for a certain time while maintaining the predetermined temperature. As a result, the powder compacts are sufficiently sintered between the powders of the calcined powder, and then gradually cooled.

[0004]

However, since the ferrite fired body obtained after the main firing is usually a lump of several cm to several tens of cm, there are two types of pulverization of ferrite: coarse pulverization and fine pulverization. It had to be done in stages. For this reason, the crushing work requires a great deal of labor and time, which causes problems such as a prolonged work and an increase in cost.

Under the circumstances, the inventors of the present invention have conducted research on ferrite. As a result, the ferrite fired bodies, which are supposed to be produced as ferrite fired bodies having a predetermined shape, are scattered in the firing furnace. It was sometimes found in a shattered state. Therefore, the present inventors conducted a more detailed investigation and found that by performing the main firing under certain specific conditions, the material to be fired self-crushed during the main firing and was crushed to some extent after the main firing. It is known that a ferrite fired body in a state can be obtained.

The present invention has been made in view of the above-mentioned knowledge, and an object thereof is to obtain a crushed form of ferrite after the main calcination so that the labor for crushing the ferrite can be reduced. It is to provide a method for manufacturing a ferrite powder material.

[0007]

In order to achieve the above object, in a method for producing a ferrite powder material according to the present invention, a calcined body obtained by calcining a ferrite raw material is crushed and calcined. A method for producing a ferrite powder material by preparing a powder, adding a binder to the preliminarily calcined powder to form a powder compact, and then subjecting the powder compact to a main calcination, and pulverizing the ferrite calcination product thus obtained In the main calcination of the powder compact, the calcination temperature is gradually raised from room temperature to reach a predetermined temperature, the predetermined temperature is maintained and heated for a certain time, and then gradually cooled. Then, from the start of firing of the main firing until the temperature reaches the predetermined temperature, the firing is performed in an atmosphere having an oxygen concentration of 0.3% or less.

By carrying out the main firing under such conditions, the ferrite fired body becomes a ferrite powder granule which is self-crushed to some extent without maintaining the original shape. The reason for this is that the formation of spinel phase in the powder compact was rapidly promoted, expansion actively occurred, and cracks or cracks occurred due to the stress at this time, and in the low oxygen concentration atmosphere from the beginning of the main firing. Since some of the binder remains without being removed, oxygen in the powder compact is deprived of the waste, and
The cause is considered to be the generation of phases and distortion.

As a result, the labor required for crushing the ferrite can be reduced, the crushing efficiency can be improved, and the cost and the crushing time can be shortened.

The upper limit of the oxygen concentration is set as described above because if it exceeds 0.3%, the self-crushing in the ferrite fired body does not proceed sufficiently.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for producing a ferrite powder material according to the present invention will be described in detail below. The ferrite powder material according to the present invention is used, for example, as a material for a radio wave absorber, and its particle size is about several μm to several mm. As a typical one,
In addition to Mn-Zn ferrite, there are Ni-Zn ferrite and Mg-Zn ferrite. Of these, M
Generally, the main component of n-Zn ferrite is
Fe ₂ O ₃ is 50 to 56 mol%, MnO is 30 to 45
mol%, ZnO in each range of 5 to 20 mol%, and in a mixture set such that the total of these is 100 mol%, 0.03 to 0.1 wt% CaO, 0 as a sub-component. Up to 0.05% by weight of SiO ₂ and 0.
A ferrite raw material containing 4% by weight or less of TiO ₂ is used.

The production of such a ferrite powder material is
This is performed as follows. First, as a ferrite raw material, a mixture having a predetermined ratio is used at a temperature of 60 in an air atmosphere, for example.
Pre-baking is performed at 0 ° C. to 1000 ° C. for about 2 hours, and the pre-baked body thus obtained is pulverized to a particle size of about 0.5 to 1 μm to prepare a pre-baked powder. Next, to this calcined powder,
For example, polyvinyl alcohol or the like is added as a binder to bond the calcined powders to each other, and the dimension is 10 cm,
A powder compact having a size of about 10 cm and a height of about 5 cm is formed. Then, this powder compact is fired.

In the main firing, the firing temperature is gradually raised from room temperature to reach a predetermined temperature, and the predetermined temperature is maintained, heating is performed for a certain period of time to perform sufficient sintering, and then gradually cooled.

The predetermined temperature is set to about 1,000 to several hundreds of degrees Celsius, for example, 1300 ° C. In addition, the time from the start of the main calcination to reaching the predetermined temperature is, for example, 8 hours, the time for maintaining the predetermined temperature is, for example, 3 hours, and the slow cooling time is, for example, 8 hours. Set.

Particularly, in the present invention, this main firing is performed in a low oxygen concentration atmosphere having an oxygen concentration of 0.3% or less from the start of firing to the time when the predetermined temperature is reached. here,
The low oxygen concentration atmosphere is an atmosphere mainly composed of a gas other than oxygen, such as nitrogen. The upper limit of the oxygen concentration is set to 0.
The value of 3% is based on the test results described later.

By carrying out the main firing under such conditions, it is possible to obtain a fired ferrite body which is self-crushed to some extent. The ferrite fired body obtained here is composed of a large number of particles and powders, and the size thereof is distributed in the range of several mm to several tens of μm.

Next, such a fired ferrite body is mechanically pulverized. In this pulverization, since the ferrite fired body is sufficiently small, coarse pulverization can be omitted, and only fine pulverization can be performed using a fine pulverizing device such as a stamp mill.
The finely pulverized ferrite fired body is classified by a sieve or the like, and only the ferrite fired body having a desired particle size, that is, about several tens of μm is taken out to obtain a ferrite powder material.

From the above, according to the present invention, it is possible to obtain a ferrite fired body which is in a state of being self-crushed into pieces after the main firing, so that the labor required for the subsequent pulverization can be reduced and the pulverization efficiency can be reduced. It is possible to shorten the crushing time and reduce the cost by improving the temperature.

A comparative test conducted to confirm the effect of the present invention will be described below. In this test, especially M
This is carried out for the case of manufacturing n-Zn ferrite, and the main component of the ferrite is 53.3 mol% Fe ₂
O ₃ , 38.5 mol% MnO and 8 mol% Zn
In a mixture of O, CaO, SiO ₂ ,
Used was added and TiO _2.

Then, a ferrite fired body in a state in which the main firing according to the conventional manufacturing method is not performed and is not self-crushed into pieces, and a ferrite fired body in a state in which the main firing according to the manufacturing method of the present invention is not self-crushed into pieces Got a body and. Then, after taking 100 g of each and crushing each for 10 minutes by a stamp mill, classification was carried out by applying a sieve of 5 mm in the upper stage and 2.5 mm in the lower stage, and the weight of the obtained ferrite powder material was measured. Table 1 below summarizes the results.

[0021]

[Table 1] From Table 1, the obtained powder weight is about 30 g in the conventional production method, whereas about 90 g can be obtained in the production method of the present invention, and the production method of the present invention has better pulverization efficiency. I was able to confirm that.

Regarding the upper limit of the oxygen concentration,
It was determined as follows. That is, similar to the above test
With respect to the Mn-Zn-based ferrite, the oxygen concentration was set to 0.0%, 0.3%, and 0.4%, and the main firing according to the manufacturing method of the present invention was performed. Then, after crushing and classifying each of them in the same manner as the above test, the weight of the obtained ferrite powder material was measured and summarized in Table 2 below.

[0023]

[Table 2] From this Table 2, it is recognized that the lower the oxygen concentration, the larger the amount of powder obtained. For oxygen concentration 0.4%, 30
g is obtained, which is insufficient. From this, it is understood that the oxygen concentration is preferably set to 0.3% or less in order to sufficiently promote the self-crushing in the fired ferrite body.

As a precaution, a radio wave absorber is manufactured using the ferrite powder material manufactured by the manufacturing method of the present invention and the conventional manufacturing method. The magnetic permeability, the dielectric constant, and the specific gravity, which are the characteristics of, were examined. Table 3 below
This is a summary.

[0025]

[Table 3] From this Table 3, it was confirmed that especially when a radio wave absorber is manufactured using the ferrite powder material obtained by the manufacturing method of the present invention, characteristics almost the same as those obtained by the conventional manufacturing method can be obtained.

[0026]

As described in detail in the above embodiments of the invention, according to the method for producing a ferrite powder material according to the present invention,
By performing the main firing of the powder compact under predetermined conditions,
After the main firing, it is possible to obtain the ferrite powder particles that are self-pulverized to some extent, so that the labor required for pulverizing the ferrite can be reduced, thus reducing the cost and the pulverization time. It can be shortened.

Claims (1)

[Claims] 1. A calcinated body obtained by calcination of a ferrite raw material is pulverized to prepare a calcinated powder, a binder is added to the calcinated powder to mold a powder molded body, and then the powder molded body. In the method for producing a ferrite powder material by pulverizing the obtained calcinated ferrite and pulverizing the obtained ferrite calcinated body, the calcination temperature of the powder compact is gradually raised from room temperature to reach a predetermined temperature. Along with heating at the predetermined temperature for a certain period of time and then gradually cooling, the oxygen concentration is 0.3% or less from the start of the main calcination until the predetermined temperature is reached. A method for producing a ferrite powder material, which is performed in an atmosphere.