JPS63162535A - Production of powdery acicular hematite particle - Google Patents

Abstract

PURPOSE:To produce powdery acicular hematite particles having high density and uniform grain size and having no hole on the surface and in the inside of the particles, by treating acidic suspension contg. beta-FeOOH hydrothermally after adding a P compd. thereto. CONSTITUTION:Aq. suspension having <=7pH is obtd. by adding alkaline aq. soln. to aq. suspension contg. <=1mol/l beta-FeOOH obtd. by heat-treating and hydrolyzing aq. soln. of FeCl3 and adjusting the pH of the mixture to >=8, and adding hydrochloric acid thereto. Then, 0.1-2.0atom% P compd. expressed in terms of P and based on the amt. of Fe(III) in the suspension (e.g. metaphosphoric acid) is added to the suspension, and the mixture is treated hydrothermally at 100-130 deg.C to form powdery acicular hematite particles.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing acicular hematite particles used as a starting material in producing magnetic iron oxide particles for high-density recording. More specifically, it consists of acicular hematite particles that have no pores on the particle surface or inside the particle, are substantially high-density, have uniform particle size, and do not contain dendritic particles. The present invention relates to a method for producing acicular hematite particle powder.

[Conventional technology]

BACKGROUND ART In recent years, as magnetic recording and reproducing equipment has become longer recording time and has become smaller and lighter, demands for higher performance and higher density recording of magnetic recording media have been increasing.

In order to improve the performance and increase the recording density of magnetic recording media, it is necessary to improve the residual magnetic flux density B. It depends on the properties, orientation in the coating, and filling properties.

In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, it is necessary to prevent the presence of pores on the surface and inside of the magnetic iron oxide particles to be dispersed in the vehicle. Particles are required to have substantially high density, uniform particle size, and no dendritic particles.

Currently, acicular magnetite particles or acicular maghemite particles are mainly used as magnetic particles for magnetic recording. These reactions are generally called "wet reactions" in which an aqueous colloid solution of 11111 or more containing ferrous hydroxide particles obtained by reacting an aqueous ferrous salt solution with an alkali is oxidized with air. ) obtained with acicular α-
Fe0011 particles are heated and dehydrated in air at around 300°C to form hematite particles, and further reduced in a reducing gas such as hydrogen at 300 to 400°C to form acicular magnetite particles, or this is then heated and dehydrated in air at 200°C. It is obtained by oxidizing at ~300°C to obtain acicular maghemite particles.

[Problem that the invention seeks to solve]

There is a current demand for magnetic iron oxide particle powder that has no pores on the particle surface or inside the particle, has a substantially high density, has a uniform particle size, and does not contain dendritic particles. However, the particle powder obtained by the above-mentioned known method for producing acicular goethite particles as a starting material contains dendritic particles, and in terms of particle size,
It is difficult to say that the particles have a uniform particle size.

In addition, when magnetic iron oxide particles are obtained using the goethite particles as a starting material by a conventional method, the hematite particles obtained by heating and dehydrating the goethite particles have many pores on the particle surface and inside the particles due to dehydration. Then, it is observed that the magnetite particles or maghemite particles obtained by reducing or further oxidizing the hematite particles also have a large number of pores distributed on the particle surface and inside the particles.

As described above, magnetic iron oxide particles having a large number of pores on the particle surface and inside the particles have a low coercive force lie, and moreover, have poor dispersion in a vehicle.

Attempts to eliminate pores generated on the surface and inside of magnetic iron oxide particles have been made, for example, as described in Japanese Patent Publication No. 38-26156 and 2-6 of the Abstracts of Presentations at the 1960 Spring Conference of the Powder and Powder Metallurgy Association. Both methods require heating at high temperatures to eliminate pores generated on the particle surface and inside the particles, and as a result, sintering occurs between the particles and between the particles. The coercive force of the magnetic iron oxide particle powder obtained by reducing and oxidizing the magnetic iron oxide particles is extremely low, and the dispersion into a vehicle when manufacturing a magnetic paint is also poor.

On the other hand, instead of the method of eliminating the pores once generated on the particle surface and inside of the magnetic iron oxide particles, a method of obtaining magnetic iron oxide particles using particles without pores on the particle surface and inside the particles as a starting material has also been attempted. ing.

This method is disclosed in, for example, Japanese Patent Publication No. 55-22416,
Japanese Patent Publication No. 55-4694, Japanese Patent Publication No. 57-92527
As described in Japanese Patent Publication No. 51-8193, needle-shaped matite particles are directly generated from an aqueous solution, and the needle-shaped hematite particles are reduced and oxidized as a starting material to produce needle-shaped crystals. This is a method for obtaining magnetic iron oxide particles.

That is, as mentioned above, the pores on the particle surface and inside the particles are generated by dehydration when acicular goethite particles are heated and dehydrated to form acicular hematite particles.
If acicular hematite is produced directly from an aqueous solution, the dehydration step can be omitted, and therefore acicular hematite particles with no pores on the particle surface or inside the particles can be obtained. Reduction using matite particles as a starting material,
The acicular crystal magnetic iron oxide particles obtained by oxidation also have no pores on the particle surface or inside the particle.

As is clear from the above, the acicular magnetic oxide has substantially no pores on the particle surface or inside the particle, has a substantially high density, has uniform particles, and does not contain dendritic particles. In order to obtain iron particle powder, there is a strong demand for a method of directly producing acicular hematite particles, which have uniform particles and do not contain dendritic particles, from an aqueous solution.

[Means for Solving the Problems] The present inventor has conducted various studies on a method for directly producing acicular hematite particles with uniform particle size and no dendritic particle force 9 from an aqueous solution, and has developed the present invention. The invention was achieved.

That is, in the present invention, an alkaline aqueous solution is added to a water-suspended F4 solution containing β-FeO011 to form an aqueous suspension having a pH of 8 or more, and then hydrochloric acid is added to the aqueous suspension to obtain the -Into an aqueous suspension containing pl (7 or less), 0.0% in terms of P is added to Fe(III) in the suspension.
After adding 1-2.0% or less of phosphorus compound, 100-2.0%
This is a method for producing acicular hematite particle powder consisting of acicular hematite particles by generating acicular hematite particles by hydrothermal treatment in a temperature range of 130°C.

[For production]

First, the most important point in the present invention is to prepare an aqueous suspension of β-Fe00H 9118 or more, and then add hydrochloric acid to the aqueous suspension to obtain the p-containing β-Fe0OII.
117 or less, Fe(II
When a phosphorus compound of 0.1 to 2.0% or less (calculated as P) is added to I) and then hydrothermally treated in a temperature range of 100 to 130°C, the particle size is uniform and dendritic particles are mixed. The fact is that free acicular hematite particles can be produced directly from an aqueous solution.

Regarding the reason why acicular hematite particles are generated in the present invention, the present inventor believes that, as shown in the comparative example below, isotropic hematite particles are generated when no phosphorus compound is added. , concerning the particle morphology of hematite particles produced by phosphorus compounds! 7. I think that I am doing it.

In the present invention, an aqueous suspension with a pH of 9118 or higher is
When using hydrochloric acid as the acid used to prepare the following aqueous suspended EJ solution, hematite particles can be generated, but when using acids other than hydrochloric acid, such as sulfuric acid, acetic acid, phosphoric acid, etc. cannot produce hematite particles.

Next, various conditions for implementing the present invention will be described.

In the present invention, it is necessary to use β-FeOOH as the iron raw material. β-Fe0011 can be obtained by a method of heating and hydrolyzing a ferric chloride aqueous solution, a method of performing an oxidation reaction by passing an oxygen-containing gas through a ferrous chloride aqueous solution, etc. Any particle shape, such as needle-like or spindle-like, can be used.

In the present invention, pi of the water-suspended Shu solution containing β-Fe00H
is about 6.0 at most, and the amount of outside water 7 in the suspension is
By adding 8 liquids, it becomes 1118 or more.

As the alkaline aqueous solution in the present invention, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. can be used. p of aqueous suspension after addition of alkaline aqueous solution
When H is 8 or less, a mixture of hematite and β-FGOOH is produced.

In the present invention, it is necessary to use hydrochloric acid in order to turn an aqueous suspension with a pH of 9118 or higher into an aqueous suspension with a pH of 7 or lower. When the pH of the aqueous suspension after addition of hydrochloric acid is 7 or higher, hematite particles are not produced because β-Fe0011 is stably produced in the temperature range of 100 to 130°C.

In the present invention, it is possible to produce hematite particles even at a high temperature where the concentration of the aqueous suspension containing β-FeOOH is about 1.0 moI/l. 1.0 mo
Although hematite particles are generated when the ratio is 1/2 or more, the particle size becomes asymmetric.

As the phosphorus compound in the present invention, inorganic phosphorus compounds such as metaphosphoric acid, hypophosphorous acid, phosphorous acid, orthophosphoric acid, pyrophosphoric acid, and salts thereof can be used.

The amount of the phosphorus compound added is 0.1 to 2.0% in terms of P based on Fe(III) in the suspension. If the content is 0.1% or less, the acicular hematite particles targeted by the present invention cannot be obtained. If the content is 2.0% or more, acicular hematite is produced, but the reaction takes a long time.

The reaction temperature in the present invention is 100 to 130°C.

If the temperature is below 100°C, hematite particles will not be generated because the dissolution of β-Fe0011 will not proceed sufficiently.1
Although hematite particles are produced when the temperature is 30° C. or higher, this is not industrially or economically viable because it requires special equipment such as a high-pressure container.

〔Example〕

Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the average diameter of particles in the following examples is the average value of numerical values measured from electron micrographs, and the specific surface area is BE
This is a value measured by the T method.

Example 1 500 m of an aqueous suspension of ρ115.5 containing β-Fe0011 particles (specific surface area 58 n?/g) of O,4 mo1/Il
An aqueous solution of Na01l was added to the resulting solution to obtain an aqueous suspension with a pH of 9.0.

β obtained by adding IIcI aqueous solution to the above aqueous suspension
- an aqueous suspension at pH 2.0 containing Fe0011 particles;
Orthophosphoric acid 0.20g (1 in terms of P for Fe(III))
．． This corresponds to 0 atom%. ), the mixture was placed in a closed container and hydrothermally treated at 125° C. for 15 hours to form a reddish-brown precipitate. The particles obtained by washing the reddish-brown precipitate with water, filtration, and drying were hematite as shown in the X-ray diffraction shown in Figure 1, and the electron micrograph (x 20 , 0
00), the particles were acicular particles with an average particle diameter of 0.8 μm, the particle size was uniform, and each particle was an independent particle.

Example 2 Aqueous suspension 500III at pH 5.0 containing 0.5 mol/It β-Fe0011 particles (specific surface area 110 rrr/g). , an aqueous N 114011 solution was added to obtain an aqueous suspension with a pl+8.5.

β obtained by adding llCl aqueous solution to the above aqueous suspension
- an aqueous suspension of pH 1.5 containing Fe0011 particles;
After adding 0.125 g of orthophosphoric acid (corresponding to 0.5 at% in terms of P based on Fe(III)), the mixture was placed in a sealed container and hydrothermally treated at 125°C for 15 hours to form a reddish brown precipitate. I let it happen. The particles obtained by washing the reddish-brown precipitate with water, filtering, and drying were found to be hematite as a result of X-ray diffraction, as shown in Figure 3.
As is clear from the electron micrograph (X20.000) shown in , the particles were acicular particles with an average particle diameter of 0.5 μm, the particle size was uniform, and each particle was an independent particle.

Comparative Example 1 A reddish-brown precipitate was produced by hydrothermal treatment in the same manner as in Example 1, except that orthophosphoric acid was not added.

The particles obtained by washing the reddish-brown precipitate with water, filtration, and drying showed the X-ray diffraction shown in Figure 4 and the electron micrograph shown in Figure 5 (
x20,000), the average particle size is 0.3
μl of isotropic particles.

Comparative Example 2 500 pH 1.7 aqueous suspension containing 0.2 mo1/f β-Fe0011 particles (specific surface area 180 r//g)
pH!ml using Na011 aqueous solution and 11cI aqueous solution! The mixture was placed in a closed container as it was without conditioning, and subjected to hydrothermal treatment in the same manner as in Example 1 to produce a yellowish brown precipitate.

The particles obtained by washing the yellow brown precipitate with water, filtration, and drying are shown in the results of X-ray diffraction and in the electron micrograph (x
20,000), β-Fe0011
It remained as it was.

Comparative Example 3 A brown precipitate was produced by hydrothermal treatment in the same manner as in Example 1, except that an aqueous N a OIt solution was added to obtain an aqueous suspension having a pH of 6.8. As is clear from the X-ray diffraction results and the electron micrograph (x 20,000) in FIG.
It was a mixture of e0011 and hematite.

Comparative Example 4 PH7 containing β-FeOOH by adding 11cI aqueous solution
, 5 was used as an aqueous suspension, but hydrothermal treatment was carried out in the same manner as in Example 1 to produce a yellow brown precipitate. Wash the yellowish brown precipitate with water.
The particles obtained by filtration and drying remained β-Fe0011, as is clear from the results of X-ray diffraction and the electron micrograph (X50°000) shown in FIG.

Comparative Example 5 A yellow brown precipitate was produced in the same manner as in Example 1, except that the temperature of the hydrothermal treatment was 95°C. The particles obtained by washing the yellow brown precipitate with water, filtering, and drying showed the X-ray diffraction shown in Figure 9 and the electron micrograph (x 50,000) shown in Figure 10.
As is clear from this, it remained β-PeOOIl.

[Effects of the Invention] According to the method for producing acicular hematite particles of the present invention, as shown in the previous example, there are no pores on the particle surface or inside the particles, and the density of acicular hematite particles is substantially low. In addition, it is possible to obtain acicular hematite particles having a uniform particle size and containing no dendritic particles, which is suitable as a starting material for magnetic particles.

[Brief explanation of the drawing]

Figures 1, 4, and 9 are all X-ray diffraction diagrams, and Figure 1
4 is the hematite n-particle powder obtained in Example 1, FIG. 4 is the Bemata (+・particle powder) obtained in Comparative Example 1, and FIG. 9 is the β-Fef 014 particle powder obtained in Comparative Example 5. . Figures 2, 3, 5 to 8, and 10 are all electron micrographs, and Figures 2, 3, and 5 were obtained in Example 1, Example 2, and Comparative Example 1, respectively. Hematite particle powder, FIGS. 6, 8, and 10 are β-FeOQIf particles obtained in Comparative Example 2, Comparative Example 4, and Comparative Example 5, respectively, and FIG. 7 is a mixture particle powder of hematite and β-FeOOtl. It is.

Claims (1)

[Claims] (1) Add an alkaline aqueous solution to an aqueous suspension containing β-FeOOH to make an aqueous suspension with a pH of 8 or higher, and then
The β-FeO obtained by adding hydrochloric acid to the aqueous suspension
After adding a phosphorus compound of 0.1 to 2.0 atomic % in terms of P to Fe(III) in the suspension to an aqueous suspension containing OH and having a pH of 7 or less, a temperature of 100 to 130 ° C. 1. A method for producing acicular hematite particle powder comprising acicular hematite particles, characterized in that acicular hematite particles are produced by hydrothermal treatment within a range of 100 to 100 ml.