JPS62207720A - Manufacturing method of barium ferrite powder - Google Patents

Abstract

PURPOSE:To obtain barium ferrite powder having small tabular ratio and high dispersibility by adding alkali hydroxide to soln. of metal salts contg. specified amt. of Ba, Fe, Si, etc., and calcining the soln. after mixing a chloride with formed precipitate. CONSTITUTION:Aq. soln. of metal salts contg. 5-11g atom Fe and 0.001-1g atom Si and Ca per 1g atom Ba is prepd. Alkali hydroxide such as NaOH, etc., is added to the heated above described aq. soln. to cause reaction. The amt. of the alkali hydroxide is regulated to above equivalent amt. of neutralization so as to obtain >=3mol/l concn. of alkali hydroxide in the soln. after the reaction. NaCl and BaCl2 are added to the precipitate contg. formed metal hydroxide, and the mixture is aged, then free alkali is removed by neutralization, etc. After drying and calcining the precipitate at 700-950 deg.C, the product is washed to remove impurities. By this method, barium ferrite powder having sufficient crystal condition and small mean particle size is obtd. without requiring any pressure resistant vessels.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a method for producing hexagonal plate-shaped magnetoblanbite-type barium ferrite powder.

In recent years, with the demand for higher density magnetic recording, development of perpendicular magnetic recording systems using barium ferrite (magnetobrambite type) as a magnetic material for magnetic recording has been progressing.

Barium ferrite used in the perpendicular magnetic recording system has a coercive force of an appropriate value (600 to 15,000e),
It is desired that the saturation magnetization is as high as possible, the magnetic properties of each particle are uniform, the particles are small and uniform, there is no agglomeration or sintering of single particles, and there is good dispersibility with an appropriate plate ratio. .

[Conventional technology]

Conventionally, various methods have been known for producing barium ferrite, such as coprecipitation method, flux method, hydrothermal synthesis method, and glass crystallization method. Public notice.

Regarding the flux method, see 9. For example, Japanese Patent Publication No. 60-1557.
For example, Japanese Patent Publication No. 46-1 for hydrothermal synthesis method.
3545, JP-A-56-149-28, JP-A-56-160-28, JP-A-58-2224
No. 161002, JP 59-161002, JP 59-1989
-164640, JP 59-164641, JP 60-1297, JP 60-15
This has been proposed in Publication No. 576, etc.

[Problem that the invention seeks to solve]

Barium ferrite produced by hydrothermal synthesis generally has less agglomeration of particles and relatively good dispersibility.

Requires autoclaving. Furthermore, conventionally known methods can only produce particles with a large particle size.

The particle size distribution was wide and not uniform6. When attempting to crystallize barium ferrite into particles with a solid shape, sintering between particles tends to occur, making it difficult to make paints (inks). ), the dispersibility and smoothness of the coating film may deteriorate, and the saturation magnetization may be 50 emu/? However, even if one tried to obtain a product with a small plate-like ratio of 5 or less, it was difficult to obtain a product with a small plate-like ratio of 5 or less.

In addition, barium ferrite produced by the coprecipitation method generally has fine particles and a small plate-like ratio, but has the drawback that the particles are not well aligned and there are many aggregates and sintered bodies.

An object of the present invention is to provide a method for producing barium ferrite powder with fine particles, a low plate-like ratio, and good dispersibility, which can improve the above-mentioned difficulties in hydrothermal synthesis and coprecipitation.

[Failure to solve the problem]

In the present invention, 5 to 1 iron is added to 1 gram atom of barium.
1 gram atom, silicon and/or calcium, O,
To a solution of a metal salt containing 1 to 1 gram atom of OO, add alkali hydroxide in an amount equal to or more than the neutralization equivalent so that the concentration of alkali hydroxide in the solution after reacting with the alkali hydroxide becomes mol/l or more. 1 Then, sodium chloride and/or barium chloride were mixed with the resulting precipitate, and 7
The present invention relates to a method for producing barium ferrite powder, which is characterized in that the fired product is washed after firing at a temperature of 00 to 950°C.

In the present invention, a solution of a metal salt containing 5 to 11 gram atoms of iron and 0.001 to 1 gram atom of silicon and/or calcium per 1 gram atom of barium is
In general, water-soluble and relatively highly soluble metal salts such as ferric nitrate, ferric chloride, barium nitrate, barium chloride, sodium silicate, and calcium nitrate are combined with barium and iron, barium and silicon and/or calcium. It is prepared by appropriately dissolving it in water so that the atomic ratio falls within the above range. At that time, various elements 2 such as Co, Ni, Mn, which are added to conventional barium ferrite, are added.

Zn, Ca, P'b, E3r, Ti, Engineering
Nb, La+Ce+Pr.

A small amount of a water-soluble compound such as Sm, such as a hydrochloride or a nitrate, can be added, and the addition of CO and Ti compounds is particularly preferred for improving the magnetic properties and controlling the particle size.

Compounds of CO and T1 are generally chlorides.

Nitrate, alkoxide, etc. are used, and the amount added depends on the atomic ratio of metal salt to iron atoms in the solution, Co/F
It is suitable that e and Ti/Fe are respectively 0.01 to 0.20, preferably 0.02 to 0.15. Atomic ratio F of barium and iron in a solution of metal salts
When e/Ba is smaller than 5, the amount of magnetobrambite barium ferrite produced is small and the hexagonal plate shape becomes poor, and when Fe/Ba is larger than 11, α-Fe203 is not produced.

Moreover, the grain size of barium ferrite is large, and its magnetic properties are also inferior. When preparing a metal salt solution, it is desirable to keep the concentration of the barium salt in the range of 60 to 2'50 mmoA/l in order to obtain barium ferrite with a fine and uniform hexagonal plate shape. . Moreover, silicon and/or calcium have no effect if the amount is too large or too small.

Silicon and/or calcium have the effect of miniaturizing barium ferrite particles, making the two particles uniform in size and shape, and reducing the plate-like ratio. Therefore, the saturation magnetization increases and the monodispersity also improves.

The metal salt solution is heated, preferably to 50 to 160°C, and alkali hydroxide is added to react.

The amount of alkali hydroxide added is determined by the concentration of alkali hydroxide in the solution after reacting with the alkali hydroxide.
As mentioned above, it is preferably used in an amount equal to or more than the neutralizing equivalent, preferably in a range of 2 to 8 times the equivalent so that the amount becomes 5 to 8 mot/t.

In the present invention, the concentration of alkali hydroxide in the solution after adding the alkali hydroxide is low.

If the amount of alkali hydroxide is too small, the particle size may be large and the particle size distribution may be poor, and α-Fe203 may be formed, and it is not economical to increase the amount of alkali hydroxide too much.

Sodium hydroxide is an alkali hydroxide.

Potassium hydroxide and the like are suitable, and may be added after being dissolved in water or without being dissolved.

Further, the addition may be carried out either all at once or in stages, or may be added at the time of preparing a solution of the metal salt.

The precipitate containing the metal hydroxide, which is produced by adding an alkali hydroxide to a solution of a metal salt and reacting it, is aged and then the free alkali content is neutralized with a mineral acid such as hydrochloric acid or washed with water. and remove it.

Preference is given to adding barium chloride and/or sodium chloride. For aging, the slurry of the precipitate after the reaction is heated to room temperature ~9
It is appropriate to carry out the reaction at 0°C for 1 to 24 hours. Further, in order to neutralize the free alkali content, mineral acid may be added to the slurry after aging to adjust the pH to 6 to 8 without separating the precipitate.

Furthermore, when washing free alkali components with water, it is appropriate to separate the precipitate from the slurry and wash it with water.

Although the precipitate may be dried and mixed with barium chloride and/or sodium chloride, it is more effective to mix barium chloride and/or sodium chloride with the wet precipitate.

In the present invention, sodium chloride and/or barium chloride may be added as both or only one, but it is better to use barium chloride or a mixture of sodium chloride and barium chloride to form fine particles and uniform particles. You can get what you want.

If the amount of sodium chloride and/or barium chloride added is too small, sintering tends to occur.

Also, if there is too much, there is no advantage and it is not economical, so 10 to 180
% by weight, preferably from 15 to 150% by weight, is suitable.

The precipitate mixed with sodium chloride and/or barium chloride is dried and heated to 700-950°C, preferably 75°C (
Calculate at 1-900°C. Calcining promotes proper grain growth and crystallinity.

When firing, if the time required for firing is too long, the growth of the particles will be large, and the degree of growth between each particle will be different. Also, the degree of crystallinity will also be different, so the shape of each particle will change, and as a result, the retention of each particle will be affected. The magnetic properties such as magnetic force and saturation magnetization are different, and the coercive force distribution becomes wider.

Erasing characteristics tend to deteriorate. Therefore, when firing, it is preferable to rapidly raise the temperature to the firing temperature, and after firing, to rapidly lower the temperature to around room temperature. It is preferable that the temperature increase and temperature decrease rates are each 50° C./min or more.

Also, if the firing temperature is too low, the saturation magnetization will be low and crystallization will not proceed.

On the other hand, if the temperature is too high, the grains will grow too much and the grain size will become large, or sintering of one grain m1 will occur. The firing atmosphere is not particularly limited, but an air atmosphere is generally convenient.

The fired product (barium ferrite) is washed and dried appropriately to obtain the desired barium ferrite powder. Washing is impurities in the fired product.

For example, any cleaning operation may be employed as long as it can sufficiently remove impurities such as alkali metal ions and excess barium hydroxide. As the cleaning liquid, water, acetic acid, nitric acid, hydrochloric acid, etc. can be suitably used.

The baked product that has been sufficiently washed is then dried, but the drying method is not particularly limited.

〔Example〕

Example 1 Add Fe (NO3)3 ・9H2 to 75 tons of water with stirring
0 to 2Z81Kg, Ba(OH)2.8H20 to 3.
79 K7. Co(No3)2-6H20 1.45
sKp, TiC4 0.948Kf+ Na2S
i03 -o, 14bKg and NaOH 32.3
Add 9 and stir.

The mixture was neutralized to form a precipitate, which was left to mature at 60° C. for 8 hours.

Separate the precipitate by filtration and wash with water so that the weight ratio is 1:1 to the wet precipitate (dry basis) K.

A mixture of barium chloride and sodium chloride (Ba
C! A2-2H20: NaCt=1:1) was mixed and then dried.

The dried material was sized and rapidly heated in an air atmosphere in a rotary kiln, and fired at a temperature of 870''C.

After washing the fired product with water and acetic acid, it was dried with a drum dryer to obtain barium ferrite powder.

Table 1 shows the results of measuring the particle shape (particle size, thickness distribution) (average value of 50 particles) and magnetic properties of this barium ferrite powder using a transmission electron microscope (TEM). .

In addition, to check the dispersibility, the filtration rate when the ink after milling the barium ferrite powder with the binder and solvent in a sand mill was filtered through a sieve with a surface size of 1 μm (the filtration rate is 100% when the entire amount of ink passes through the sieve). )
Table 1 shows the results of measuring the glossiness of the coated film in order to examine the magnetic properties and smoothness of the coated film.

Examples 2 to 5 The amount of sodium silicate used in Example 1 was reduced to 0.073KL.
i (Example 2), calcium nitrate Ca(NO3)2 4H20 was added to 28.6
The amount of the mixture of barium chloride and sodium chloride used for the precipitate (example) was determined by weight per precipitate.
The mixture was changed to Mixture 2 (Example 4).

Mixing ratio of barium chloride and sodium chloride (weight ratio)
Barium ferrite powder was produced in the same manner as in Example 1, except that the barium chloride filter was replaced with sodium chloride 7 (Example 5), and each characteristic was measured in the same manner. The results are shown in Table 1.

In Examples 1 to 5, no agglomeration or sintering of particles occurred in the barium ferrite powder. Comparative Example 1 Except for not using the sodium silicate of Example 1,
Barium ferrite powder was produced in the same manner as in Example 1, and its properties were measured in the same manner. The results are shown in Table 1.

Comparative Example 2 Barium ferrite powder was produced in the same manner as in Example 1, except that the mixture of barium chloride and sodium chloride in Example 1 was not used, and each characteristic was measured in the same manner. The results are shown in Table 1.

Comparative Example 4. Pa(N03)3.9H20 was added to 27.8 to 75 tons of filtered water while stirring. 3.7 qKg of Ba(OH)24%O
, (:!0(No3)2-6H20 to 1.”12
K11. 0.86 Kp of T1C14 and 3Z5 of NaOH were initially added, stirred, and neutralized to form a precipitate.

Place the slurry containing the precipitate into an autoclave.

After hydrothermal treatment at a temperature of 200° C. for 5 hours, the precipitate was washed with water and dried without mixing the mixture of barium chloride and sodium chloride.

The dried material is sized and heated to 850℃ in an air atmosphere in a firing furnace.
It was fired at a temperature of

After washing the fired product with water and acetic acid, it was dried with a drum dryer to obtain barium ferrite powder.

The properties of the obtained barium ferrite powder were measured in the same manner as in Example 1. The results are shown in Table 1.

〔Effect of the invention〕

According to the present invention, it is possible to obtain barium ferrite powder with good magnetic properties, which does not require a pressure-resistant container, and is made up of minute particles of a magnetobrambite type with a good crystalline state, a small average particle size, and a narrow particle size distribution width. . In addition, this barium ferrite powder has a relatively small plate-to-plate ratio and excellent 9-dispersibility and smoothness. Furthermore, the coercive force can be freely controlled by adding the above-mentioned T1 and Co.

Claims (1)

[Claims] For 1 gram atom of barium, 5 to 11 gram atoms of iron, and 0.001 to 1 gram of silicon and/or calcium.
A reaction is carried out by adding alkali hydroxide in an amount equal to or more than the neutralization equivalent to a solution of a metal salt containing 1 gram atom so that the concentration of alkali hydroxide in the solution after reacting with the alkali hydroxide becomes 3 mol/l or more. Then, sodium chloride and/or barium chloride are mixed with the generated precipitate and the mixture is heated to 700-900 ml.
A method for producing barium ferrite powder, which comprises firing at a temperature of 50°C and then washing the fired product.