JPS62297216A - Production of fine particle of ba ferrite - Google Patents

Abstract

PURPOSE:To obtain fine particles of Ba ferrite having very small particles and improved magnetic characteristics and powder characteristics free from sintering between particles, by obtaining coprecipitation from an aqueous solution containing both ions of Fe and Ba having a specific ratio of Fe/Ba, washing the coprecipitation with water, drying and calcining the coprecipitation with a specific flux. CONSTITUTION:Fine particles of Ba ferrite are obtained by the following method. Namely, (1) an aqueous solution containing Fe ion and Ba ion having a molar ratio of Fe/Ba of 10-13 is blended with an alkali aqueous solution and precipitate is obtained at pH >=10. (2) the precipitate is washed with water until the pH becomes 6-9 and dried. (3) the dried precipitate is incorporated with >=5wt% based on total amount of one or more of chloride or sulfate of Na or K and calcined at 600-1,200 deg.C.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing Ba ferrite fine particles, particularly for use in permanent magnet materials such as rubber or plastic magnets incorporated into electrical equipment, etc. The present invention relates to a method for producing Ba ferrite fine particles suitable as magnetic powder.

<Prior art and its problems> Characteristics required of magnetic powder used in rubber, plastic magnets, etc. include good powder characteristics and magnetic characteristics.

In other words, the powder properties are that it has good kneadability with resin, that is, the particle size is approximately a single domain diameter,
It is required that the particle size be uniform, that there is no sintering between the particles, and that the particles are easily dispersed in the resin, and that the magnetic properties are high, such as saturation magnetization and coercive force.

By the way, as a conventional method for obtaining particles without sintering, fusion, etc. between particles, there is a known method of adding a fluxing agent when firing raw materials. As a result, barium chloride and strontium chloride are used for firing. However, although these fluxes prevent sintering and fusion due to contact between particles, they promote crystal growth of the particles by condensing the ferrite component in the melt phase onto the ferrite particles, making it difficult to reduce the size of the particles.

In addition, in the method of Japanese Patent Publication No. 57-21517, Ba,
NaCf1, BaCf1 in ferrite particle powder such as Sr
The particle shape is controlled by adding a flux such as 2 to control the particle shape, but since powder obtained by pulverizing the calcined product is used as the raw material, the particle size of the fired product is large and the coercive force is 3 KOe.
The degree is low.

<Objective of the Invention> The object of the present invention is to respond to the miniaturization, density, and performance improvement of permanent magnets accompanying the miniaturization of electrical equipment, and in order to respond to the miniaturization, density, and performance improvement of permanent magnets, the particles are minute, there is no sintering between the particles, and The object of the present invention is to provide a method for producing Ha mitzerite particles having uniform particle sizes, excellent magnetic properties, and excellent kneading properties when compounded with a resin.

<Structure of the Invention> When producing Ba ferrite, powders of barium carbonate and iron oxide are generally used as raw materials, which are mixed and then reacted. However, since this reaction occurs due to the diffusion of barium ions from the surface of the iron oxide powder particles into the interior, the generated Ba ferrite particles cannot be made smaller than the iron oxide particles in principle.

By the way, when Fe ions and Ba ions are precipitated at the same time in an aqueous solution, the precipitate becomes amorphous or very small particles, and Fe and Ba are adjacent to each other in ion units, and diffusion for reaction is minimal. The reaction can be completed before grain growth progresses.

However, when particles are actually produced using this precipitate, the coagulation between the particles becomes strong, so the particles are extremely susceptible to sintering, causing fusion and binding, making it impossible to separate the particles. Therefore, a fluxing agent is added to the coprecipitate to prevent sintering between particles.

It is desirable that the flux used at this time has properties that suppress grain growth and promote the reaction.

In consideration of the above, the present invention was achieved as a result of selecting a flux and performing production under various conditions.

That is, the present invention includes Fe ions and Ba ions,
This aqueous solution with a molar ratio (Fe/Ba) of 10 to 13 is mixed with an alkaline aqueous solution to obtain a precipitate at a pH of 10 or higher, and after washing the precipitate with water until the pH becomes 6 to 9, Na Alternatively, one or more of chloride or sulfate of crab is added at least 5 wt% of the total weight, and heated to 600℃~
Provided is a method for producing Ba ferrite particles, which is characterized by firing at a temperature of 1200°C.

The present invention will be explained in detail below.

In the method of the present invention, in order to obtain minute ferrite grains,
A coprecipitate from an aqueous solution containing Fe and Ba is used as a raw material.

The Fe raw material may be any water-soluble iron salt, and ferric chloride, ferric nitrate, ferric sulfate, etc. may be used alone or in combination.

The Ba raw material may be any water-soluble Ba salt, and barium chloride, barium nitrate, etc. may be used alone or in combination.

Molar ratio of Fe ions and Ba ions in aqueous solution (Fe/B
a) shall be 10-13. Here, when Fe/Ba is less than 10, a non-magnetic composition represented by [laO.2 Fe2O, is produced, and when it exceeds 13, Fe2O
Non-magnetic compositions such as No. 3 are produced, and neither of them can provide desirable magnetic properties.

Next, an aqueous solution containing a predetermined amount of Fe ions and Ba ions is mixed with an alkaline aqueous solution, and at a pH of 10 or more, Fe, B
Obtain a coprecipitate of a. Any alkaline aqueous solution may be used, but sodium hydroxide and sodium carbonate aqueous solutions are preferred.

When the precipitate is produced, if the pH is less than 10, Fe and Ba ions will not be sufficiently precipitated, and in this case as well, a compositional deviation will occur, making it impossible to obtain desirable magnetic properties.

In order to remove alkaline components from the above coprecipitate, p11
Wash with water until it reaches 6 to 9, and use the dried material as raw material. If alkaline components remain in the coprecipitate, Ba
Non-magnetic compositions may be formed preferentially over ferrite, and since coprecipitates are dissolved in acidic aqueous solutions, composition deviations may occur in this case as well, and Bamitzerite production Undesirable.

Next, this raw material and flux are mixed, then fired, washed with water, and dried. When a flux is used during firing, particles with a uniform diameter can be obtained without sintering between the particles.

As a fluxing agent, a chloride or sulfate of Na or Na is used alone or in combination of two or more. In particular, since these fluxes are water-soluble, they have the advantage of being easy to remove by washing with water and being inexpensive. When a flux is used alone or in combination of two or more, particles with excellent magnetic properties, with no sintering between particles and with well-uniformed particle sizes can be obtained in the firing temperature range from 600°C to 1200°C. be able to. Here, when firing at a temperature lower than 600°C, the temperature is below the melting point of the fluxing agent, and the effect of adding the fluxing agent may not be expected, or the ferrite reaction may be insufficient. When fired at a temperature higher than 0.degree. C., grain growth progresses, grain size increases, and magnetic properties are also unfavorable.

On the other hand, when firing is performed using a flux containing barium chloride, the resulting particles have unfavorable magnetic properties because of their large particle size or insufficient reaction. Also Ba
Since SO4 is poorly soluble in water, it cannot be removed by washing with water.

Regarding the mixing ratio of the fluxing agent, a fluxing agent effect is recognized when it is contained in a proportion of 5 wt % or more. Preferably, it is 5 to 70 wt%.

<Example> The invention will be specifically described below with reference to Examples.

(Example 1) Barium chloride (Ba(:12 ・21120) 15.2
5 g and ferric chloride (FeCj!3 ・6H20)
Dissolve 202.75 g in 1 U of water to make an aqueous solution. An aqueous solution containing Ba and Fe was added to an aqueous solution of 250.0 g of sodium hydroxide (Na011) and 62.5 g of sodium carbonate (Na2 CO3) dissolved in 22 of water with stirring. The precipitate obtained at pH 11 was washed with water by decantation until the pH became 8 or less, filtered, and dried.

Sodium chloride (NaCIl) was added and mixed to the obtained precipitate so that the ratio of precipitate to flux was 1:1 by weight, and after baking at 1000 ° C. for 2 hours in an electric furnace, It was washed with warm water and dried.

The particles thus obtained were Ba ferrite fine particles with uniform particle sizes and no sintering between the particles. The average particle size and magnetic properties are shown in Table 1.

(Example 2) Using potassium chloride (cIL) as a flux, calcination was carried out for 8
The procedure was the same as in Example 1 except that the temperature was 00°C.

(Example 3) The same procedure as Example 1 was carried out except that sodium sulfate (Na2S04) was used as a fluxing agent.

(Example 4) Using a mixture of sodium chloride (NaC1) and sodium sulfate (Na2504) in an equimolar ratio as a flux,
The procedure was the same as in Example 1 except that the firing was performed at 700°C.

(Example 5) Sodium chloride (Nal, u), potassium chloride (nicR,) and sodium sulfate (Na2S04) were used as fluxing agents.
)'s equal moa 1/l 10-P 10 pieces Y■ 1. The procedure was the same as in Example 1, except that the heating was carried out at 600°C.

(Example 6) Barium chloride 16.65 g and ferric chloride 202.7 g
5 g was used to obtain a precipitate, and Na2S04 was used as a fluxing agent.
The procedure was the same as in Example 1 except that the firing was performed at 900°C.

(Comparative Example 1) The procedure was the same as in Example 1 except that sodium sulfate (Na2 S04) was used as a flux and the firing was performed at 1300°C.

(Comparative Example 2) A mixture of 14 g of barium carbonate (Ba CO3) powder and 52.05 g of iron oxide (a-Fe203) powder was used, and the ratio of raw material and flux was adjusted by adding sodium chloride (NaCρ) to the mixture. They were added and mixed at a weight ratio of 1=1, fired in an electric furnace at 1000°C for 2 hours, washed with warm water, and dried.

(Comparative Example 3) The same procedure as Comparative Example 2 was carried out except that potassium chloride (Cu) was used as a fluxing agent.

(Comparative Example 4) Same as Example 6 except that the firing was performed at 1100°C.

(Comparative Example 5) The same procedure as in Example 4 was carried out except that a mixture of sodium chloride (NaCl2) and barium chloride (BaCl2.) in an equimolar ratio was used as a flux.

Table 1 shows the average particle diameter and magnetic properties of the particles obtained in Examples and Comparative Examples.

Further, scanning electron micrographs of the loa ferrite particles obtained in Example 2 and Comparative Example 2 are shown in FIGS. 1 and 2, respectively.

<Effects of the Invention> As a result of scanning electron microscope observation, the particles obtained by the method of the present invention have a well-uniformed particle size with no sintering between the particles, a saturation magnetization of 55 emu/g or more, and a coercive force of 5000 0e. In summary, the fine particles have excellent properties as Ba ferrite magnetic powder for rubber and plastic magnets.

[Brief explanation of drawings]

All drawings are photographs substituted for drawings showing the crystal structure. FIG. 1 and FIG. 2 are scanning electron micrographs (6000x magnification) of Ba ferrite particles obtained in Example 2 and Comparative Example 2, respectively. Patent applicant Kawasaki Steel Co., Ltd. agent Patent attorney Nozomi Watanabe Nejiri Patent attorney Yo Ishii - No. 1
Figure 21A

Claims (1)

[Claims] (1) Contains Fe ions and Ba ions, and this molar ratio (
An aqueous solution with Fe/Ba) of 10 to 13 is mixed with an alkaline aqueous solution to obtain a precipitate at a pH of 10 or higher, and the precipitate is washed with water until the pH becomes 6 to 9, followed by chlorination of Na or Ni. 1. A method for producing Ba ferrite fine particles, which comprises adding one or more of Ba ferrite particles or sulfates in an amount of 5 wt% or more based on the total weight, and firing at a temperature of 600°C to 1200°C.