JPH0314782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a Ba. ferrite fine particle powder exhibiting a hexagonal plate shape, and it is possible to easily produce a plate-shaped Ba. ferrite fine particle powder suitable for perpendicular magnetic recording. The purpose is to manufacture it economically.

Conventionally, the manufacturing method of plate-shaped Ba. ferrite particles includes:
Hydrothermal methods, glass crystal methods, flux methods, etc. have been reported. Among these methods, the hydrothermal method can produce Ba. ferrite with a large plate ratio (particle size/thickness), but on the other hand, the particles tend to grow and produce relatively large particles, and it is not a method suitable for mass production. Furthermore, although the glass crystal method can produce fine particles with uniform particle diameters, the production method is complicated and cannot be said to be an economically advantageous method. The last flux method is considered to be the most advantageous method industrially, but in this case as well, the particle size of the particles obtained is considerably larger than the value required for magnetic particles for perpendicular magnetic recording media. There are many occasions.

However, Japanese Patent Publication No. 1987-41727 discloses an interesting method for synthesizing fine Ba. ferrite powder by a flux method. That is,
Aqueous barium chloride solution and aqueous iron chloride () solution and optionally aqueous metal chloride (Me: zinc, nickel and/or cobalt) expressed as MeCl ₂ and optionally titanium chloride (). In addition, the resulting mixture is reacted with an aqueous sodium carbonate solution and consists of the poorly soluble precipitated product in the sodium chloride solution, and the dried salt mixture is subsequently heated to a temperature above the melting point of the sodium chloride, but at a temperature above the melting point of the sodium chloride.
This method involves heating the material to a temperature not higher than 950°C, and then leaching the resulting fine plate-like hexagonal ferrite with water.

Therefore, the present inventors have developed Ba. ferrite fine powder suitable for use as a high-density magnetic recording medium by the above method, that is, the particle size is 0.3 μm or less, the particle size distribution is narrow, and the size and shape of individual particles are well-defined. However, due to the following problems, it was not possible to synthesize Ba. ferrite suitable for high-density magnetic recording media. That is, although it is possible to synthesize Ba. ferrite with an average particle size of about 0.1 μm, Ba. ferrite with a size of 0.3 μm or more is mixed in this, resulting in a double distribution. Ordinary Ba. ferrite has a high coercive force and the head is saturated during recording, so
By replacing some of the constituent atoms with specific other atoms, it is necessary to reduce the coercive force to a value suitable for perpendicular magnetic recording.
Ba. Some of the Fe ³⁺ ions in ferrite are converted to Co ²⁺ −
A method of replacing with Ti ⁴⁺ ions has been adopted, but when attempting to synthesize Co ²⁺ −Ti ⁴⁺ substituted Ba. ferrite using the above synthesis method, non-magnetic Ba. Co. ferrite (Ba ₂ Co ₂ Fe ₁₂ O ₂₂ ) is mixed in, which lowers the saturation magnetization. When the particle size is smaller than 0.1 μm, only Ba. ferrite having a platelet ratio of 2 or less can be synthesized. It has become clear that there are problems such as poor reproducibility of magnetic properties, especially coercive force.

Therefore, the present inventors conducted intensive research on a method for synthesizing Ba. ferrite fine particle powder suitable for high-density magnetic recording media, and found that after adding water-soluble silicate to an aqueous alkali carbonate solution, iron chloride () ,
A mixed aqueous solution of cobalt chloride (), titanium chloride (), and barium chloride is added to form a coprecipitate, and the slurry is aged under carbon dioxide gas pressure, dried, and then calcined at 850 to 950°C, rapidly cooled, and washed. Drying/
Plate-shaped particles with a particle size of 0.2μm or less are produced through the pulverization process.
The present invention was completed by discovering that Ba. ferrite fine particle powder can be produced with good reproducibility.

Next, the configuration of the present invention will be explained.

In the present invention, a mixed aqueous solution of iron chloride (), cobalt chloride (), titanium chloride (), and barium chloride is added to a mixed aqueous solution of an alkali carbonate and a water-soluble silicate until the pH becomes 4.5 to 5.5. A method for producing a plate-shaped Ba. ferrite fine particle powder, which comprises producing a precipitate, aging the coprecipitate under pressure with carbon dioxide gas, drying it, then calcining it at 850 to 950°C, and then rapidly cooling it. It is.

In the present invention, the alkali carbonate refers to sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, and the like. Although the concentration of the aqueous solution of these salts is not particularly limited, it is preferable from an industrial standpoint that it be as concentrated as possible. Furthermore, water-soluble silicate refers to sodium silicate, potassium silicate, and the like. Silicate has the effect of reducing the particle size of the Ba. ferrite produced and increasing the plate-like ratio, but the addition ratio is 0.3 to 2.0 as SiO ₂ to Ba. ferrite.
% is preferably in the range of 0.5-1.5%. i.e. 0.3%
In the case of the following addition ratio, plate-like Ba with a narrow particle size distribution.
Fine ferrite particles cannot be obtained, and the plate-like ratio is also small. In addition, when the addition ratio is 2.0% or more, the added SiO ₂ reacts with other components to generate compounds other than Ba. ferrite, which not only significantly reduces the saturation magnetization but also causes the formation of Ba. ferrite. The particle size becomes larger.

The mixing ratio of iron chloride (), cobalt chloride (), titanium chloride () and barium chloride is (Fe
+Co+Ti)/Ba (atomic ratio) is preferably in the range of 9.0 to 11.5. If the (Fe+Co+Ti)/Ba ratio is less than 9.0, non-magnetic Ba.Co. ferrite (Ba ₂ Co ₂ Fe ₁₂ O ₂₂ ) is generated, and as a result, the saturation magnetization decreases significantly. Also, the (Fe+Co+Ti)/Ba ratio is
When it is larger than 11.5, hematite (α-Fe ₂ O ₃ ) is mixed into the product, which not only lowers the saturation magnetization but also increases the particle size of Ba. ferrite.

The liquid temperature when adding the mixed aqueous solution of iron chloride (), cobalt chloride (), titanium chloride (), and barium chloride to the mixed aqueous solution of an alkali carbonate and a water-soluble silicate is preferably 20°C or lower. If the liquid temperature is higher than this, reproducibility will be poor and hematite may be mixed depending on the conditions.

Further, the mixed aqueous solution of iron chloride (2), cobalt chloride (2), titanium chloride (2), and barium chloride is added to the mixed aqueous solution of an alkali carbonate and a water-soluble silicate until the pH reaches 4.5 to 5.5. In other words, if the addition reaches a pH lower than 4.5, hematite will be mixed into the product, and if the addition is stopped at a pH higher than 5.5, Ba.Co.
Ferrite or having a size of 0.3 μm or more
Ba. Ferrite is mixed.

By aging the coprecipitate under pressure of carbon dioxide gas, the particle size distribution of Ba. ferrite produced is significantly improved, and the formation of non-magnetic Ba. Co. ferrite and hematite is suppressed, but the pressure at this time The appropriate gauge pressure is 0.5 Kg/cm ² or more, preferably about 1 Kg/cm ² , and increasing the pressure higher than this has no particular effect. Also, a suitable aging time is 0.5 to 1 hour.

For drying after completion of ripening, spray drying, thin film drying, etc. are effective. Furthermore, the firing temperature after drying is 850-950℃.
It is appropriate to do this for 0.5 to 1.5 hours. That is,
At temperatures lower than 850℃, Ba. has low saturation magnetization.
Only ferrite can be synthesized, and if the temperature is higher than 950°C, the particle size becomes large, making it impossible to synthesize Ba. ferrite fine particle powder suitable for high-density recording media.

The rapid cooling operation after firing has the effect of significantly improving the magnetic properties of the produced Ba. ferrite, particularly the reproducibility of the coercive force, and narrowing the coercive force distribution. That is, since the coercive force varies significantly depending on the cooling rate, the rapid cooling operation is essential for improving reproducibility and narrowing the coercive force distribution.

Examples are provided below to more fully illustrate the invention.

Example 1 317 g/Fe ₂ O ₃ in 5 glass beakers
1275 ml of iron chloride () aqueous solution, 234 as CoO
g/146 ml of cobalt chloride () aqueous solution, TiO ₂
99.6g/titanium chloride () aqueous solution 341
ml and 370 ml of a barium chloride aqueous solution containing 224 g/BaO.

100g/in 20 stainless steel containers
After separating Na ₂ CO ₃ aqueous solution 9, 76g/SiO ₂ was collected.
Add 73 ml of sodium silicate aqueous solution. While stirring this mixed aqueous solution with a homogenizer,
Add the above mixed aqueous solution of iron chloride, etc. until the pH reaches 4.9. At this time, cool the reaction solution so that the temperature does not exceed 20°C. After the addition of the mixed aqueous solution of iron chloride, etc. is completed, the reaction slurry is transferred to a closed container, the air in the container is replaced with carbon dioxide gas, and then the pressure is increased to 1 kg/cm ² with carbon dioxide gas. After 1 hour the slurry is removed and spray dried.
The dried product is placed in a platinum container and baked at 860℃ for 1 hour. After firing, the fired product is put into water and rapidly cooled. After washing, the mixture was subjected to filtration, drying, and bantam milling to obtain a fine powder. When this fine powder was examined using an electron microscope and X-ray diffraction, the average particle size was 0.06 μm.
It was found to be a single phase of plate-like Ba. ferrite with an average plate ratio of 3. Also, the magnetic properties of this thing are
Coercive force Hc: 6530e Saturation magnetization σs: 55.9emu/g with an external magnetic field of 10Kgauss, and specific surface area is 28.1m ² /
It was hot at g.

Example 2 Into the glass-lined container of 5, 1335 ml of an aqueous solution of iron chloride () containing 303 g as Fe ₂ O ₃ and CoO
as 234g/cobalt chloride () aqueous solution 143
99.6g/titanium chloride (as ml, _TiO2 )
333 ml of aqueous solution and 405 ml of barium chloride aqueous solution containing 224 g/BaO are separated.

130g/in 20 stainless steel containers
After separating Na ₂ CO ₃ aqueous solution 7, 81 g/SiO ₂ was obtained.
Add 69 ml of an aqueous solution of sodium silicate. While stirring this mixed aqueous solution with a homogenizer,
Add the above mixed aqueous solution of iron chloride, etc. until the pH reaches 5.2. At this time, cool the reaction solution so that the temperature does not exceed 20°C. After the addition of the mixed aqueous solution of iron chloride, etc. is completed, the reaction slurry is transferred to a closed container, the air in the container is replaced with carbon dioxide gas, and the pressure is increased to 0.6 Kg/cm ² with carbon dioxide gas. After 40 minutes, remove the slurry and spray dry.
The dried product is placed in a platinum container and baked at 900℃ for 1 hour. After firing, the fired product is placed in water and rapidly cooled. After washing, the mixture was filtered, dried, and pulverized in a bantam mill to obtain a plate-like Ba. ferrite fine particle powder. This material had an average particle diameter of 0.08 μm, an average platelet ratio of 5, and a specific surface area of 27.0 m ² /g. Also, the magnetic properties are coercive force Hc: 6620e, saturation magnetization σs:
It was 57.5 emu/g.

Comparative Example 1 In a glass-lined container of 5, 1335 ml of an aqueous solution of iron chloride () containing 303 g/Fe ₂ O ₃ and CoO
as 234g/cobalt chloride () aqueous solution 143
ml and 405 ml of a barium chloride aqueous solution containing 224 g/BaO.

130g/in 20 stainless steel containers
After fractionating the Na ₂ CO ₃ aqueous solution 7, the aqueous solution of iron chloride, etc. was added thereto while stirring with a homogenizer, and then 333 ml of a titanium chloride () aqueous solution containing 99.6 g/g as TiO ₂ was added. The pH at this time was 4.9. Next, 50 g/aqueous Na ₂ CO ₃ solution was added to adjust the pH to 5.8. After spray drying, dry matter is 900
It was baked at ℃ for 1 hour. After slow cooling, the same treatment as in Example 2 was carried out to obtain a fine powder. When this material was examined by electron microscopy and X-ray diffraction, it was found that although the average particle diameter was 0.10 μm and the average platelet ratio was 2, there were also particles with a size of 0.3 μm or more mixed in, and other than Ba. ferrite. Ba.Co. ferrite (Ba ₂ Co ₂ Fe ₁₂ O ₂₂ ) was generated. The specific surface area was 11.6 m ² /g, and the magnetic properties were coercive force Hc: 480 Oe and saturation magnetization σs: 47.0 emu/g.

Further, FIG. 1 shows an electron micrograph of the product of Example 2, and FIG. 2 shows an electron micrograph of the product of Comparative Example 1. From this, the product of Comparative Example 1 contains
It can be seen that particles having a size of 0.3 μm or more are mixed. The magnification for both images is 100,000x. Figure 3 is an X-ray diffraction chart of the product of Example 2, and Figure 4 is an X-ray diffraction chart of the product of Comparative Example 1. The product of Comparative Example 2 is Ba.
It can be seen that it is a two-phase mixture of ferrite Ba.Co. ferrite.

[Brief explanation of drawings]

FIG. 1 shows an electron micrograph of the particle structure of the Ba. ferrite powder obtained in Example 2. Second
The figure shows an electron micrograph of the particle structure of Ba. ferrite powder obtained in Comparative Example 1. FIG. 3 is an X-ray diffraction chart of the product of Example 2. Fourth
The figure is an X-ray diffraction chart of the product of Comparative Example 1.

Claims (1)

[Claims] 1. Iron chloride (), cobalt chloride (), cobalt chloride (),
A second mixed aqueous solution containing titanium chloride () and barium chloride is added until the pH of both mixed solutions is 4.5 to 4.5.
5.5 to form a solid coprecipitate in the combined liquid, then the combined liquid was pressurized under a carbon dioxide atmosphere to ripen the coprecipitate, and then the aged coprecipitate was Platy Ba is produced by separating it from the body liquid, drying it, then firing it at 850-950℃, rapidly cooling the resulting fired product, and then crushing it into a fine powder.
A method for producing ferrite fine particle powder. 2. The method according to claim 1, characterized in that in the solid coprecipitate production step, the temperature of the combined liquid does not exceed 20°C. 3. Claim 1 or 2, characterized in that in the pressurizing step under carbon dioxide atmosphere, the gauge pressure under pressurization is 0.5 Kg/cm ² or more, preferably about 1 Kg/cm ² The method described in any of the paragraphs. 4 Claim 1, characterized in that the firing time in the firing step is 0.5 to 1.5 hours.
3. The method according to any one of items 3 to 3. 5 The alkali carbonate is at least one member selected from the group consisting of sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate, and the water-soluble silicate is at least one member selected from the group consisting of sodium silicate and potassium silicate. 5. The method according to any one of claims 1 to 4, wherein at least one member is selected. 6. The method according to claim 5, wherein the alkali carbonate is sodium carbonate and the water-soluble silicate is sodium silicate.