JPH01261237A - Plate magnetite particle powder and production thereof - Google Patents

Abstract

PURPOSE:To obtain a pore-free plate magnetite particle powder having average diameter and specific surface area being in the prescribed range, free from sintering and having excellent dispersibility in a resin, by subjecting an alkaline suspension containing water-containing iron(III)oxide particle and iron(II) hydroxide to hydrothermal treatment in the presence of sulfuric acid radical at a specific temperature. CONSTITUTION:An alkaline suspension containing water-containing iron(III)oxide and iron(II)hydroxide is subjected to hydrothermal treatment in the presence of a sulfuric acid radical at 200-300 deg.C to provide the plate magnetite particle. Thereby the aimed pore-free plate magnetite particle powder having 0.5-5mum average diameter and 1.5-6m<2>/g specific surface area and free from sintering is obtained. The obtained particle is preferably used as a material powder for electromagnetic absorption and shield material because of having excellent dispersibility in a vehicle or resin and being >=0.5mum particle.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a non-porous and unburned material with an average diameter of 0.5 to 2.0 μm and a specific surface area of 1.5 to 6.0 m2/g. The present invention relates to a plate-shaped magnetite particle powder made of plate-shaped magnetite particles and a method for producing the same.

The main uses of the plate-shaped magnetite particle powder according to the present invention are:
Material powder for electromagnetic wave absorbing materials, shielding materials, etc.

[Conventional technology]

Magnetite particle powder is used as material powder for electromagnetic wave absorbing materials and shielding materials.

This fact can be seen, for example, in JP-A No. 54-110496, by elucidating the radio wave absorption characteristics of "Magnetite" (FesQa) by comparing it with conventional composite ferrite.
In the microwave range of ~1 OGI+2, it can be made thinner than composite ferrite, has improved workability, and has excellent radio wave absorption... It is as described in J. , electromagnetic wave absorption, and seal L' are achieved by applying a paint obtained by dispersing and mixing magnetite particles in a vehicle to buildings, ships, aircraft, etc. that reflect radio waves, and equipment that is a source of electromagnetic waves. It is being said.

Magnetite particles used as material powder for electromagnetic wave absorption and shielding materials are plate-shaped particles with excellent dispersibility in a vehicle, and have a large particle size, especially 0.5 μm or more. particles.

That is, in terms of particle morphology, for example, JP-A-61
``Plate-shaped ferrite particles exhibit excellent properties as a radio wave absorbing material and an electromagnetic shielding material in the low frequency range, which cannot be achieved with ordinary ferrite particles.''

'' and, for example, in JP-A-55-104923, ``...an extremely pronounced parallel orientation of the individual particles occurs in the coating material. possible, resulting in, for example, increased corrosion protection, effective shielding against electromagnetic interference groups, and high electrical conductivity. ) There are other uses for iron oxides...a very pronounced parallel orientation (orientation) of the individual particles occurs.Therefore,
...It is possible to have a significantly high packing density.
As described in "...", it is necessary that the particles have a plate-like shape.

Next, regarding the particle size,
No. 77626 [...The average major axis d of the particles is 0
．． 5 μm or more... ” as stated.

Conventionally, as a method for producing plate-shaped magnetite particles, for example, alkaline L containing ferric hydroxide or goethite has been used.
%? A method of producing plate-shaped matite particles from an aqueous solution by hydrothermally treating a f& using an autoclave, and heating and reducing the plate-shaped hematite particles in a reducing gas, and an alkaline suspension containing ferrous hydroxide. Ferric hydroxide is produced by rapidly oxidizing the suspension with a strong oxidizing agent or by reacting a ferric salt with an alkali in an aqueous medium in the presence of specific additives, and the water A known method is to generate plate-shaped goethite particles from an aqueous solution by hydrothermally treating ferric oxide, heat dehydrate the plate-shaped goethite particles, and then reduce the plate-shaped goethite particles by heating in a reducing gas.

Examples of methods belonging to the former method include the method described in the above-mentioned Japanese Patent Application Laid-Open No. 51-28700, and the method described in the above-mentioned Japanese Patent Application Laid-Open No. 55-1989.
There is a method described in Japanese Patent Publication No. 104923, and examples of the latter method include, for example, the method described in Japanese Unexamined Patent Publication No. 61-266 mentioned above.
There are methods described in Japanese Patent Application Publication No. 311 and Japanese Patent Application Laid-open No. 104923/1983.

[Problem 3 to be solved by the invention: Excellent dispersibility and large particle size, especially 0.5 μm
The above-mentioned plate-shaped magnetite particles are currently most in demand, but when using the known method as described above, it is necessary to reduce the plate-shaped particles generated from an aqueous solution by heating in a reducing gas. As a result, sintering between particles and particles occurs, resulting in difficulty in dispersion in a vehicle or resin, resulting in a disadvantage that the packing density decreases and the orientation deteriorates.

In addition, in the case of the latter method among the known methods, water in the goethite crystal particles is dehydrated when the plate-shaped goethite particles are heated, so there are many voids on the surface and inside of the obtained plate-shaped magnetite particles. There will be holes.

When such porous plate-shaped magnetite particles are dispersed in a vehicle or resin, other fine particles are attracted to the area where the surface magnetic poles are formed, and as a result, many particles aggregate. Agglomerates of considerable size are formed,
For this reason, dispersion becomes difficult, the packing density decreases, and the orientation deteriorates.

In view of the above-mentioned prior art, the present inventors have determined that by directly producing plate-shaped magnetite particles from an aqueous solution,
A method for obtaining non-porous and non-sintered plate-shaped magnetite particles has already been developed (Japanese Patent Application No. 62-34141, Japanese Patent Application No. 62-332467). However, by this method, it was not possible to obtain plate-shaped magnetite particles having a large particle size, especially 0.5 μm or more.

Therefore, there is a strong demand for a method for directly producing plate-shaped magnetite particles with a large particle size, especially 0.5 μm or more, from an aqueous solution.

[Means to solve the problem]

The present inventor has arrived at the present invention as a result of various studies on a method for directly producing plate-shaped magnetite particles with a large particle size, particularly 0.5 μm or more, from an aqueous solution.

That is, the present invention provides plate-shaped magnetite particles consisting of non-porous and non-sintered plate-shaped magnetite particles having an average diameter of 0.5 to 2.0 μm and a specific surface area of 1.5 to 6.0 rti/g. A powder and an alkaline suspension containing hydrated ferric oxide particles and ferrous hydroxide were heated to 200 to 300 ml in the presence of sulfuric acid.
Plate-shaped magnetite particles are generated from the water-soluble solution by hydrothermal treatment in the temperature range of 1.5 to 2.0 µm, and have an average diameter of 0.5 to 2.0 µm and a specific surface area of 1.5 to 6.0 µm.
This is a method for producing plate-shaped magnetite particle powder consisting of non-porous and non-sintered plate-shaped magnetite particles having a particle size of 0 m2/g.

[For production]

First, the most important point in the present invention is that an alkaline suspension containing hydrous ferric oxide particles and ferrous hydroxide is hydrothermally treated in the temperature range of 200 to 300°C in the presence of sulfate. The fact is that when plate-shaped magnetite particles are generated from an aqueous solution, plate-shaped magnetite particles with a large particle size, especially 0.5 μm or more, can be directly generated from water.

Although it is not yet clear why magnetite particles exhibiting a plate-like shape are generated in the uninvented system, the present inventor has found that plate-like particles are formed in the absence of sulfate groups, as shown in the comparative example below. This suggests that the sulfate radicals are involved in the particle morphology of the produced magnetite particles.

Furthermore, although it is not yet clear why plate-like magnetite particles with large particle sizes are produced in the present invention, the inventors have discovered that plate-like magnetite particles When producing magnetite particles, it is impossible to produce particles with a large particle size, especially particles larger than 0.5 μm, so it is thought that conditions such as high temperature and high pressure are involved in the particle size of the magnetite particles produced. There is.

The plate-shaped magnetite particles in the present invention have a particle size of 0.5
They are large particles of ~2.0 μm, and because they are directly produced from an aqueous solution, they are non-porous and non-sintered.

1 The present magnetite particles in the present invention are large particles and are non-porous, so they have a specific surface area of 6, Ord/
Because it is small (less than 100 g), and has a plate-like form that is non-porous and non-sintered, it is easy to make into paints, has excellent dispersibility and orientation, and can be packed at high density into vehicles or resins. It is.

Saraotoko, the plate-shaped magnetite particle powder in the present invention is
It is characterized by a low n force of 50 to 700e.

Therefore, it is easy to obtain a large i3 magnetic coefficient (μ) and can be particularly advantageously used as material powder for electromagnetic wave absorbing materials and shielding materials.

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

The hydrous ferric oxide particles in the present invention include α-1β
-17-FeOOH etc. can be used.

The ferrous hydroxide in the present invention can be produced by reacting a ferrous salt with an alkali.

As the ferrous salt, ferrous sulfate or ferrous chloride can be used, and as the alkali, sodium hydroxide or the like can be used.

In the present invention, the sulfate group may be formed by a reaction between ferrous sulfate and an alkali, or may be formed by sulfates such as sodium sulfate, manganese sulfate, zinc sulfate, nickel sulfate, etc. in the anti-[F] solution. This may be the case in which the sulfate of the metal is separately added.

The hydrothermal treatment in the present invention can be performed using a high-temperature, high-pressure container such as an autoclave.

The temperature of the hydrothermal treatment in the present invention is 200 to 300°C.

When the temperature is 200° C. or lower, plate-like magnetite particles are also produced, but the particle size distribution becomes wider.

Although it is possible to generate plate-shaped magnetite particles at temperatures above 300°C, when considering the safety of the equipment, etc.
The upper temperature limit is 300'C.

〔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 and comparative examples,
The plate ratio (ratio of plate surface diameter to thickness) is shown by the average value of numerical values measured from electron micrographs, and the specific surface area is measured by the BET method. Magnetic measurements were carried out using a vibrating sample magnetometer VSMP-1 model (manufactured by Toei Kogyo) at a measurement magnetic field of 10 KOe.

Example 1 cr-Fe00HO, 093 mol and FeSO40,
046 mol and Na0HO, 7 mol were mixed to make a total volume of 0.7β, and after putting it into an autoclave, '22
Heat to 0°C and keep at this temperature with mechanical stirring for 2 hours.
The mixture was held for a period of time to form a black precipitate. After cooling to room temperature,
The black precipitate was separated in a furnace, washed with water, dried, and crushed in a conventional manner.

As a result of transmission electron microscopy observation, this black particle powder has an average diameter of 1.0 μm, and as is clear from the scanning electron micrograph (xlo, 000) shown in FIG. The particles had a plate-like morphology with a ratio of 7:l, and no pores were present on the surface or inside the particles.

In addition, each particle of this particle powder is in a disjointed state (unsintered), and its BET specific surface area is 2.8n (/
g, the squareness ratio (σr/σS) was 0.078, and the particles had excellent orientation. Coercive force Hc was 580e. The X-ray diffraction diagram of this particle powder is shown in FIG. Figure 2
As is clear from the figure, peak A is a peak indicating magnetite, and it can be seen that it consists only of magnetite.

Example 2 α-FeOOHO, 093 mol and FeSO40,0
Mix 46 mol and 4.2 mol of NaOH to make a total volume of 1
0.74! After binding and putting into the autoclave, 250
'C and held at this temperature for 2 hours with mechanical stirring to form a black precipitate. After cooling to room temperature, the black precipitate was separated in a furnace, washed with water, dried, and crushed in a conventional manner.

As a result of transmission electron microscopy observation, this black particle powder has an average diameter of 1.5 μm, and as is clear from the scanning electron micrograph (xlo, 000) shown in FIG. The particles had a plate-like shape with a ratio of 21:1, and there were no pores on the surface or inside the particles.

In addition, this particle powder has a shape Q in which each particle is disjointed.
(gfA sintered), and its BET specific surface area is 5.5M
/g, the squareness ratio (σr/σS) was 0.087, and the particles had excellent orientation. Coercive force 11c is 640e
Met.

As a result of X-ray diffraction, only a peak indicative of magnetite was observed in this particle powder, indicating that it was composed only of magnetite.

Example 3 α-FeOOHO, 093 mol and Pe5Oa 0.
046 mol and Na0HO, 35 mol were mixed, the total volume was 0.7 IV, the mixture was sealed, and the mixture was charged into an autoclave, heated to 280° C., and maintained at this temperature for 2 hours with mechanical stirring to form a black precipitate. After cooling to room temperature, the black precipitate was separated in a furnace, washed with water, dried, and crushed in a conventional manner.

As a result of transmission electron microscopy observation, this black particle powder has an average diameter of 0.7 μm, and as is clear from the scanning electron micrograph (x 10,000) shown in FIG. The particles had a plate-like shape with a ratio of thickness to thickness of 6:1, and there were no pores on the surface or inside the particles.

In addition, each particle of this particle powder is in a disjointed state (unsintered), and its BET specific surface area is 3.5rrr.
/g, squareness ratio Car/as) was 0.092, and the particles had excellent orientation. coercive force) 1c is 570e
Met.

As a result of X-ray diffraction, only a peak indicative of magnetite was observed in this particle powder, indicating that it was composed only of magnetite.

Example 4 α-PeOOtl O, 093 mol and FeC1z
0.046 mol and 5.6 mol of Na OIt were mixed, and further 0.1 mol of NazSOa was added to bring the total volume to 10. 'l, and after putting it into the autoclave, 2
Heat to 20”C and keep at this temperature with delicate stirring for 2 hours.
The mixture was held for a period of time to form a black precipitate. After cooling to room temperature,
The black precipitate was separated in a furnace, washed with water, dried, and crushed in a conventional manner.

As a result of transmission electron microscopy observation, this black particle powder has an average diameter of 2.0 μ(7), and as is clear from the scanning electron micrograph (X 15,000) shown in FIG. The particles had a plate-like shape with a ratio of surface diameter to thickness of 25:1, and there were no pores on the surface or inside the particles.

Also, each particle of this powder is in pieces!
IJH (g sintered), and its BET specific surface area is 4.8
rd/g, squareness ratio <or/1ts) was 0.082, and the particles had excellent orientation. Coercive force Hc is 53
It was 0e.

As a result of X-ray diffraction, only a peak indicative of magnetite was observed in this particle powder, indicating that it was composed only of magnetite.

Comparative Example 1 A black precipitate was produced in the same manner as in Example 1, except that FeC1 was used instead of FeS0g.

After cooling to room temperature, the black precipitate was separated in a furnace, washed with water, dried, and crushed in a conventional manner.

As a result of transmission electron microscopy observation, this black particle powder has an average diameter of 0.25 μm, and as is clear from the transmission electron micrograph (X30,000) shown in FIG. 6, it consists of particles exhibiting isotropic layers. There were no pores on the surface or inside the particles.

Reference example 1 Ferrous sulfate 1.35 mol/l aqueous solution 0.83 f! N! Under gas flow, 1.65 g of trisodium citrate dihydrate was added to contain 0.5 mol% of Fe prepared in the reactor, resulting in 0.62 mol/
l of Na2COs water) volume/&3.61! Power ■e (C
This corresponds to Os/Fe = 2.0 equivalent. ) temperature 60'
FeCO3 was produced at C.

The iron concentration at this time was 0.25 mol/l in terms of Fe.

Subsequently, N2 gas was blown into the FeC0z-containing aqueous solution at a rate of 15j2 per minute, and the particles were then heated at 85°C for 30 minutes. generated.

The end point of the oxidation reaction was determined by extracting a portion of the reaction solution, adjusting it to acidity with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe''.

The produced particles were separated in a furnace, washed with water, dried, and crushed in a conventional manner. As a result of observation with a transmission electron microscope, this particle powder has an average diameter of 0.39μ, and as a result of observation with a scanning electron microscope,
It consisted of particles exhibiting a plate-like morphology with a plate-like ratio (ratio of plate surface diameter to thickness) of 8:1, and no pores were present on the particle surface or inside.

In addition, the BET specific surface area of this particle powder is 8.5n (/
As for magnetism, the coercive force He was 1100e, the saturation magnetization as was 87.8 emu/g, and the squareness ratio (ar/as> was 0.168).

As a result of X-ray diffraction, only a peak indicative of magnetite was observed in this particle powder, indicating that it was composed only of magnetite.

[Effect] As shown in the above-mentioned example, the magnetite particles according to the present invention are plate-shaped particles, and due to the particle shape and non-porous and non-sintered nature, the magnetite particles are not easily absorbed in the vehicle. Or, since they are particles with excellent dispersibility in resin and are large, especially particles of 0.5 μm or more, they can be used for absorbing electromagnetic waves.
It is suitable as a material powder for shielding materials.

[Brief explanation of the drawing]

1 and 3 to 6 are electron micrographs, and FIGS. 1 and 3 to 5 are examples 1 to 4, respectively.
The plate-shaped magnetite particle powder obtained in FIG. 6 is the magnetite particle powder exhibiting an isotropic layer obtained in Comparative Example 1 (1). FIG. 2 is an X-ray diffraction diagram of the plate-shaped magnetite particles obtained in Example 1.

Claims (2)

[Claims] (1) Plate-shaped magnetite particle powder consisting of non-porous and non-sintered plate-shaped magnetite particles with an average diameter of 0.5 to 2.0 μm and a specific surface area of 1.5 to 6.0 m^2/g . (2) Platy magnetite particles are removed from the aqueous solution by hydrothermally treating an alkaline suspension containing hydrous ferric oxide particles and ferrous hydroxide at a temperature range of 200 to 300°C in the presence of sulfuric acid. The average diameter is 0.
．． 5 to 2.0 μm and specific surface area of 1.5 to 6.0 m
A method for producing plate-shaped magnetite particle powder consisting of non-porous and non-sintered plate-shaped magnetite particles having a particle size of ^2/g.