JPH01143306A - Preparation of barium ferrite powder - Google Patents

Abstract

PURPOSE:To suppress the particle size growth of barium ferrite powders and to shorten a washing time by adding magnesium ions to barium ferrite powders synthesized by a wet method and by performing surface treatment on barium ferrite particles. CONSTITUTION:Magnesium ions are added to a barium ferrite product obtained by reacting a water solution containing Fe<3+> and Ba<2+> or its suspension using a wet method in highly concd. alkalis at room temperatures to neutralize a barium ferrite product. After that, washing, filtering and heat treatment are performed. A water solution containing starting materials, Fe<3+> and Ba<2+>, is prepared by dissolving water soluble Fe<3+> salts and water soluble Ba<2+> salts in pure water. The mole ratio (Fe/Ba) of Fe and Ba is preferably 9-12. This enables the particle size growth of barium ferrite particles to be suppressed and a washing time to be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing barium ferrite powder used as a permanent magnet material or magnetic powder for perpendicular magnetic recording media.

[Summary of the invention]

In the present invention, after adding magnesium ions to a barium ferrite product obtained by wet-reacting an aqueous solution containing Fe ff + and Ba24 or a suspension thereof in a highly concentrated alkali at room temperature, washing, filtration,
It is an object of the present invention to provide a method for producing barium ferrite powder that can suppress particle size growth of obtained barium ferrite particles and simplify the production process by performing heat treatment.

[Conventional technology]

Barium ferrite is widely known as a permanent magnet material, and permanent magnets of various shapes are made by molding and firing its fine powder.

Furthermore, it is also a material that is used as a so-called rubber magnet by mixing it with rubber or the like.

On the other hand, barium ferrite powder has recently attracted attention as a magnetic powder for magnetic recording media for perpendicular magnetic recording, and is a material that is being actively researched and developed.

In other words, the barium ferrite powder has a hexagonal plate-like particle shape, and the axis of easy magnetization is perpendicular to the plate surface, making it indispensable for developing coated perpendicular magnetic recording media. ing.

With the progress of high-density recording, the usefulness of the barium ferrite powder is being reconsidered even in ordinary longitudinal recording magnetic recording media. It is also being considered for use as magnetic powder in (slave tape) and high-density floppy disks.

Coating-type magnetic recording media using barium ferrite powder not only have excellent high-density recording properties, but also can be mass-produced using conventional continuous coating equipment, and because it is an oxide magnetic material. It has many advantages over metal thin film magnetic recording media (so-called vapor-deposited tapes), such as fewer problems such as corrosion and the ability to apply conventional magnetic head-medium interface technology.

Incidentally, as a method for manufacturing barium ferrite powder used as a magnetic powder for these permanent magnet materials and magnetic recording media, a dry method has conventionally been generally used. However, with this dry method, there is a limit to the ability to refine the particle size of the barium ferrite powder due to the manufacturing method.
Furthermore, there were other problems such as poor particle size distribution, unavoidable inclusion of coarse particles, and unavoidable inclusion of impurities.

Therefore, in recent years, as methods for solving the above-mentioned problems, studies have been conducted on glass crystallization methods, hydrothermal synthesis methods using autoclaves, methods using organic metal salts such as alkoxides, and the like. However, all of these methods have problems such as complicated operation, poor productivity, and high manufacturing costs.

Therefore, in Japanese Patent Application No. 163601/1982, the applicant of the present application has developed a barium ferrite product by wet-reacting an aqueous solution containing Fe3+ and Ba2'' or a suspension thereof in a highly concentrated alkali at room temperature. A so-called wet synthesis method is proposed [Problems to be solved by the invention] The barium ferrite powder obtained by the above wet synthesis method has a very fine particle shape at the time of synthesis.
It is very suitable as a magnetic powder for coated magnetic recording media. However, in terms of magnetic properties, the magnetization amount σ9 is very small, and therefore, after the synthesis of barium ferrite a powder, it is necessary to heat-treat the synthesized barium ferrite powder to increase the magnetization amount σ9 to a necessary and sufficient amount. There is.

As mentioned above, by performing heat treatment to increase the magnetization amount σ9 of barium ferrite powder to a necessary and sufficient amount, the particles of barium ferrite powder grow large due to sintering etc. The fine barium ferrite powder becomes meaningless and becomes unsuitable as a coated magnetic powder.

Furthermore, when barium ferrite powder is synthesized, it is in a highly concentrated alkali state, and a step is provided to reduce the alkali concentration to about pH 12 to 13 by decantation. Because the particle size is extremely small, approximately 0.01 to 0.1 μm, the sedimentation rate is very slow, and in some cases, they may be dispersed in the filtrate and no longer sediment, reducing the time required for decantation. There are also problems in the manufacturing process, such as an extremely large amount of time and effort.

Therefore, the present invention was proposed in view of the above-mentioned conventional situation, and it is possible to produce barium ferrite powder that can suppress the particle size growth of the obtained barium ferrite particles and shorten the cleaning time. The purpose is to provide a method.

[Means for solving problems]

The present inventors have conducted intensive research to develop a method for obtaining barium ferrite powder with excellent magnetic properties and particle size by effectively utilizing the fine barium ferrite powder obtained by the wet synthesis method. By treating the surface of the barium ferrite powder obtained by the synthesis method with magnesium ions, cleaning time can be shortened, and the grain size growth can be suppressed without sintering of the barium ferrite powder even after heat treatment. We have come to the conclusion that it is possible, and have completed the present invention.

That is, the present invention provides an aqueous solution containing Fe" and Ba2+,
Alternatively, magnesium ions are added to a barium ferrite product obtained by wet-reacting its suspension in a highly concentrated alkali at room temperature, followed by washing, filtration, and heat treatment. .

Here, the aqueous solution containing Fe3+ and Ba@+, which is the starting material, contains water-soluble Fe3+ salts such as ferric chloride FeC1z·nH2O, ferric nitrate Fe(NOs) i·6HzO, and barium chloride BaC1z-28zO, barium nitrate B
a(NOz)z, barium acetate Ba(CH+C00)2
・HzO, barium hydroxide Ba (OH) z.

It is prepared by dissolving water-soluble Ba 2 + salts such as 8H20 and Ba(OH)z in pure water. Note that the starting material is not limited to an aqueous solution of these water-soluble salts, but may also be a suspension containing a water-insoluble hydroxide such as iron hydroxide. Alternatively, it may be a combination of a water-soluble salt and a water-insoluble hydroxide.

The molar ratio of Fe to Ba (Fe/Ba) contained in the aqueous solution or suspension is preferably from 9 to 12, more preferably from 10.5 to 11.8.

In the wet reaction, an alkali is added so that the alkali concentration in the liquid is 6 to 20 moles, and then the mixture is heated to the boiling point under normal pressure. In this case, Fe'+ and B a
An alkali may be gradually added to an aqueous solution or suspension containing 2+, or, conversely, an aqueous solution or suspension containing Fe'3+ and Ba2° may be gradually added to an alkaline solution. The type of alkali used does not matter, but sodium hydroxide is usually used.

Alkali metal hydroxides such as potassium hydroxide and lithium hydroxide are used. Further, these alkalis may be dissolved in pure water and added as an alkaline solution, or may be added as is, or both may be used in combination.

The alkali concentration (OH-) is determined from the experimental results of the present inventors.
A range of 6 to 20 mol/Il is suitable for the progress of the reaction.

Magnesium ions are added to the barium ferrite product obtained by the above wet reaction, followed by washing,
After filtering, the barium ferrite product is subjected to heat treatment for the purpose of improving magnetic properties such as the magnetization amount σ9.

Here, the barium ferrite powder is surface-treated by adding magnesium ions to the barium ferrite product synthesized by the wet method as described above. Even when the barium ferrite powder subjected to the above-described treatment is heat-treated, the particles do not sinter and maintain a fine particle state. This is because when magnesium ions are added to a highly concentrated alkaline solution, they become colloidal and are adsorbed on the surface of the barium ferrite powder particles, forming a protective film on each particle.

Since the surface is thus protected by the magnesium colloid, the barium ferrite powder does not disperse and can be easily washed and filtered.

Here, the magnesium ion is preferably added as a water-soluble salt, and may be added in the form of, for example, a halide excluding fluorine, an acetate, a nitrate, or the like. The amount of magnesium ions to be added is about 1 to 10% by weight, preferably about 1 to 6% by weight, based on the barium ferrite powder when calculated as MgO. Addition amount is 1
If the amount is less than 10% by weight, the effect of adding magnesium ions will not appear, and if it is more than 10% by weight, the magnesium ions themselves will aggregate.

The barium ferrite powder that has been surface-treated by adding magnesium ions as described above is subjected to heat treatment in order to improve its magnetization amount σ. However, because the surface of barium ferrite powder is protected by magnesium colloid, the particles do not sinter during heat treatment, and the heat treatment can be performed in the fine particle state obtained by wet synthesis, resulting in good improvement in magnetic properties such as magnetization σ9. be done.

Further, a coagulation aid may be added so that the obtained barium ferrite powder can be filtered well. As this agglomeration remover, polyacrylamide such as Separan 8 P-30 manufactured by Dow Chemical Company can be used, and the amount added is preferably in the range of 0.01 to 0.1 g. When adding the above-mentioned flocculant, it is preferable to dissolve the flocculant in water and then add it.

[Effect]

By adding magnesium ions to barium ferrite powder synthesized by a wet method, the magnesium ions become colloidal in a highly concentrated alkaline solution and are adsorbed on the surface of the barium ferrite powder particles, forming particles on the sides. This causes a protective film to form on the surface. Therefore, even if the barium ferrite particles are subjected to heat treatment, the barium ferrite particles do not sinter, that is, the particle size does not grow, and only the magnetic properties of the barium ferrite can be improved.

In addition, since the surface is protected by magnesium colloid, the powder can be easily washed and filtered without being dispersed, which eliminates the enormous amount of time and effort required for decantation. , there is no need for equipment, etc., and there are great advantages in terms of the manufacturing process.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Implemented coal water supply 500m j! A solution of 800 g of NaOH dissolved in was placed in a 21-volume stirrer-equipped reaction vessel with external heating.

While heating the container and constantly stirring the contents, add BaCIz.21 (go
36.65g.

401.4g of FeC13J)120, CoCIg・6
A solution in which 8.55 g of HzO and 22.77 g of TiCl4 were dissolved was added and maintained at the boiling point for 8 hours to synthesize barium ferrite.

Put the barium ferrite synthesized as described above into a 5β beaker and add water to bring the total amount to 57! Closed.

To this solution, 1.5% by weight of Mg(N(h)z aqueous solution in the form of MgO based on the barium ferrite particles was added with stirring, and 2 g of a coagulation aid (Separan AP-30, manufactured by Dow Chemical Company) was added. 20ml of /β solution was added, left to stand, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left to settle to precipitate the barium ferrite powder.This operation was repeated until the p of the solution
The barium ferrite powder was washed repeatedly until H was around 7. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

57 barium ferrites synthesized by the same method as in Example 1! Pour into a beaker and add water to bring the total volume to 5.
7! Closed. To this solution, 2.5% by weight of Mg(NO3)z aqueous solution was added in the form of MgO based on the barium ferrite particles while stirring, and a coagulation aid (Separan A) was added to the solution while stirring.
P-30. 20m of 2g/l molten liquid (manufactured by Dow Chemical Company)
1 was added, the mixture was allowed to stand, the supernatant was discarded, water was added again, and the mixture was stirred and allowed to stand to precipitate the barium ferrite powder. This operation was repeated until the pn of the solution reached around 7 to wash the barium ferrite powder. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

A solution of 800 g of NaOH dissolved in 500 m of water was placed in a reaction vessel with external heating and a 2j2 volume stirrer.

While heating the container and constantly stirring the contents, add 36.65 g of BaCl 1 g.2H2O to 700 mj+ of water in this solution.

FeCl3.6HgO at 401.48. CoC1z・
28.55g of 6HzO, 22.77g of TiCl4
Add a solution in which Mg(N(L+)z,
96ml of 6F120 aqueous solution (50ml as MgOO form)
g/j! ) and then maintained at the boiling point for 8 hours to synthesize barium ferrite.

The barium ferrite synthesized as described above is 5j!
The mixture was placed in a beaker and water was added to make the total volume 51.

To this solution, 20ml of 2g/β melt of coagulation aid (Separan AP-30, manufactured by Dow Chemical Company) was added, and after standing still, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left standing to powder barium ferrite. was allowed to settle. This operation was repeated until the pH of the solution reached around 7 to wash the barium ferrite powder. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

A solution of 800 g of NaOH dissolved in 500 m (l) of water was placed in a 21-volume reaction vessel with external heating and a stirrer.

While heating the container and constantly stirring the contents, add BaCl 2 .2H20 to 700 mA of water to this solution.
399g of 36.658°FeCIa・6HzO,
A solution in which 29.62 g of CoC1z.68zO and 23.62 g of TiC1m were dissolved was added and maintained at the boiling point for 8 hours to synthesize barium ferrite.

The barium ferrite synthesized as described above is 5j!
The mixture was placed in a beaker and water was added to make the total volume 51.

To this solution, 2.5% by weight of Mg(NO3)z aqueous solution was added in the form of MgO based on the barium ferrite particles while stirring, and 2g/l of a coagulation aid (Separan AP-30, manufactured by Dow Chemical Company) was added. After adding 20 ml of the solution and allowing it to stand, the supernatant liquid was discarded, water was added again, and the mixture was stirred and allowed to stand to precipitate the barium ferrite powder. This operation is performed at the p of the solution.
The barium ferrite powder was washed repeatedly until H was around 7. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

Barium ferrite synthesized by the same method as in Example 4 was placed in a beaker 51, and water was added to bring the total amount to 5p.
And so. To this solution, 5% by weight of Mg (No. 3) z aqueous solution was added in the form of hgo to the barium ferrite particles while stirring, and a coagulation aid (Separan AP) was added to the barium ferrite particles.
-30. 20ml of 2g/β solution (manufactured by Dow Chemical Company)
After addition, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left to stand to precipitate the barium ferrite powder. This operation was repeated until the pH of the solution reached around 7 to wash the barium ferrite powder. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

A solution of 800 g of NaOH dissolved in 500 m of clean water II was placed in a 21-volume stirred reaction vessel with external heating.

While heating the container and constantly stirring the contents, add 3 liters of BaC1z.2HJ to 700ml of water into the solution.
6.65g.

401.4 g of FeCl,-5H2Q, CoCl.・
A solution in which 8.55 g of 6H20 and 22.77 g of T+C]a were dissolved was added and maintained at the boiling point for 8 hours to synthesize barium ferrite.

The barium ferrite synthesized as described above is 57!
The mixture was placed in a beaker and water was added to make the total volume 51.

After stirring this solution, a flocculation aid (Separan AP
-30. Dow Chemical Company) 2g/l solution in 2011
The barium ferrite powder is then allowed to settle.

This operation is repeated several times until the pH of the washing solution becomes around 12 to 13, followed by filtration and washing.

A sample barium ferrite powder was obtained by drying.

Le comparison flame 1 water 500m j! A solution in which 800 g of Na1 was dissolved was placed in a 21-volume stirrer-equipped reaction vessel with external heating.

While heating the container and constantly stirring the contents, 36.65 g of BaCIz.2HzO was added to 700 ml of water in this solution.

399g of FeCl3・68zO, GOC12・6H
A solution in which 29.62 g of 20 and 23.62 g of TiCl4 were dissolved was added and maintained at the boiling point for 8 hours to synthesize barium ferrite.

The barium ferrite synthesized as described above was placed in a 5β beaker, and water was added to make the total amount 572.

After stirring this solution, a flocculation aid (Separan AP
-30. 20ml of 2g/l solution of Dow Chemical Company)
The barium ferrite powder is then allowed to settle.

This operation is repeated several times until the pH of the washing solution becomes around 12 to 13, followed by filtration and washing.

A sample barium ferrite powder was obtained by drying.

Barium ferrite synthesized by the same method as in Comparative Example 1 was placed in a 51 beaker, and water was added to bring the total amount to 5β.
And so. To this solution, 5% by weight of Na25iO□ aqueous solution was added as SjO□O form to the barium ferrite particles while stirring, and a coagulation aid (Separan AP-30
．． Add 20ml of 2g/β solution (manufactured by Dow Chemical Company),
After standing still, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left standing to precipitate the barium ferrite powder. This operation was repeated until the pl+ of the solution reached around 7 to wash the barium ferrite powder. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

Comparative example↓ Barium ferrite synthesized by the same method as Comparative Example 1 was placed in a 5β beaker, and water was added to make the total amount 5β.
And so. To this solution, 5% by weight of ZrCl4 aqueous solution was added in the form of ZrO2 based on the barium ferrite particles while stirring, and 20ml of a flocculation aid (Separan AP~30. manufactured by Dow Chemical Company) at 2g/j2'fJ was added.
After addition, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left to stand to precipitate the barium ferrite powder. This operation was repeated until the pH of the solution reached around 7 to wash the barium ferrite powder.

After washing, it was filtered and dried to obtain a sample barium ferrite powder.

Barium ferrite synthesized by the same method as in Comparative Example 1 was placed in a 511 beaker, and water was added to bring the total amount to 511.
It was set to 12. To this solution, 5% by weight of TiC1a aqueous solution in the form of TiO2 was added to the barium ferrite particles while stirring, and a coagulation aid (Separan AP-30
．． Dow Chemical Company) 2g/p, 20ml solution
After addition, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left to stand to precipitate the barium ferrite powder. This operation was repeated until the pH of the solution reached around 7 to wash the barium ferrite powder.

After washing, it was filtered and dried to obtain a sample barium ferrite powder.

Comparative Example■ Barium ferrite synthesized by the same method as Comparative Example 1 was 57! Pour into a beaker and add water to bring the total volume to 5.
It was set as ρ. To this solution, 5% by weight of Al(NO3)3 aqueous solution was added in the form of Al2O3 based on the barium ferrite particles while stirring, and further agglomeration aid (Separan AP
-30. 20ml of 2g/l solution of Dow Chemical Company)
After addition, the supernatant liquid was discarded, water was added again, and the mixture was stirred and left to stand to precipitate the barium ferrite powder. This operation was repeated until the pH of the solution reached around 7 to wash the barium ferrite powder. After washing, it was filtered and dried to obtain a sample barium ferrite powder.

In Examples 1 to 5, the sedimentation properties of the barium ferrite powder were improved by adding the coagulation aid.

However, in Comparative Examples 1 and 2, which were washed only with water, the sedimentation properties were not improved even when a coagulation aid was added.

Examples 1 to 5 and Comparative Example 1 were applied to each sample barium ferrite powder obtained as described above. For comparative example 2, at a temperature of 750°C for 2 hours or 75°C
Heat treatment was performed at 0 degrees for 4 hours, and for Example 5 and Comparative Examples 3 to 6, heat treatment was performed at a temperature of 900 degrees Celsius for 1 hour. FIG. 1 shows an electron micrograph of the barium ferrite powder obtained in Example 1. It can be seen from FIG. 1 that the barium ferrite powder treated with magnesium ions maintains a very fine particle size even after being heat treated. Examples 1 to 5 and Comparative Example 1. For Comparative Example 2, the particle size of barium ferrite powder was measured from the half-value width of the peak of Miller index (206) and C220) of the X-ray diffraction pattern of barium ferrite powder after heat treatment. The results are shown in Table 1.

(Left space below) Table 1 As is clear from Table 1, it can be seen that the barium ferrite powder treated with magnesium ions has a more suppressed particle size growth after heat treatment than the untreated barium ferrite powder.

Further, for Example 5 and Comparative Examples 3 to 6, the particle diameter, coercive force Hc, and magnetization amount σg were measured and the results are shown in Table 2.

As is clearer from Table 2, Example 5 in which barium ferrite was treated with magnesium ions maintained good fine particles with the smallest particle size. Furthermore, the magnetic properties were also favorably improved by the heat treatment. On the other hand, in Comparative Examples 3 to 6, the particle diameters were also somewhat large and lacked practicality as magnetic materials for coated magnetic recording media.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, magnesium ions are added to the barium ferrite powder synthesized by a wet method to treat the surface of the barium ferrite powder, so even heat treatment is not necessary. Fine particles obtained by wet synthesis can be maintained without particles sintering with each other.

In addition, the barium ferrite powder does not disperse even when washed, and it can be washed well, and washing and filtration can be performed in a short time, eliminating the huge time and effort required for washing with water by decantation, and manufacturing. The process can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a transmission electron micrograph of barium ferrite powder obtained by the method of the present invention. Patent Applicant: Sony Corporation Agent, Patent Attorney: Kodo Kowa, Sakae Enso - Masaru Sato, Procedural Amendment (Voluntary) Date of IO, February 1988

Claims (1)

[Claims] After adding magnesium ions to a barium ferrite product obtained by wet-reacting an aqueous solution containing Fe^3^+ and Ba^2^+ or a suspension thereof in a highly concentrated alkali at room temperature. A method for producing barium ferrite powder, comprising washing, filtration, and heat treatment.