JPH01176233A - Production of plate magnetite particle powder - Google Patents

Abstract

PURPOSE:To obtain the title non-porous non-sintered powder having fine particle size and excellent dispersibility, etc., by reacting an aqueous solution of a ferrous salt with a aqueous solution of an alkali carbonate at a specific equivalent ratio to form FeCO3 and passing an oxygen-containing gas through the system in the presence of a specific amount of tartaric acid (salt), thereby oxidizing the compound. CONSTITUTION:An aqueous solution containing FeCO3 is produced by reacting (A) an aqueous solution of a ferrous salt with (B) an aqueous solution of an alkali carbonate keeping the equivalent ratio of the alkali carbonate in the component B to the ferrous salt in the component A to >=1 and below the value defined by the formula. Tartaric acid (or its salt) is added to the component A or component B or added to the FeCO3-containing aqueous solution in an amount of 0.01-2mol.% based on Fe and the reaction product is oxidized by passing an oxygen-containing gas to obtain non-porous non-sintered plate magnetite particle powder having an average particle diameter of 0.03-0.5mum and a specific surface area of 7-30m<2>/g.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a non-porous and non-sintered material having an average diameter of 0.03 to 0.5 μm and a specific surface area of 7 to 30 r+?/g. The present invention relates to a method for producing plate-shaped magnetite particle powder made of plate-shaped magnetite particles.

The main uses of the plate-shaped magnetite particle powder according to the present invention are:
These include material powders for electromagnetic wave absorbing materials, shielding materials, magnetic material powders for magnetic recording, black pigment powders for paints, and colorants for rubber and plastics.

(Prior art) Magnetite particle powder is used as material powder for electromagnetic wave absorbing materials and shielding materials.
Shielding is carried out by applying a paint obtained by dispersing and mixing magnetite particles in a vehicle to equipment and the like that are sources of electromagnetic waves.

Moreover, magnetite particle powder is widely used as a magnetic material powder for magnetic recording. That is, magnetic recording media such as magnetic tapes and magnetic disks are manufactured by applying a magnetic paint obtained by mixing magnetic particle powder such as magnetite particle powder and a vehicle to the disk or tape.

Furthermore, since magnetite particle powder exhibits a black color,
It is widely used as a pigment powder for paints when mixing pigments and vehicles to produce paints, and it is also used as a coloring agent when mixed and dispersed in rubber and plastics.

As mentioned above, magnetite particle powder is used in various fields, but the properties commonly required in all fields are that it is easy to make into a paint, and it can be used in a vehicle or resin. It has a high packing density, excellent dispersibility and orientation, and a high contact rate between particles.

This fact is explained, for example, in Japanese Patent Application Laid-open No. 55-104923, which states, ``...a very 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 the conductivity becomes high. ”, JP-A-51-2
Publication No. 8700 states, ``...The magnetic powder used in the present invention has the characteristic that it can ensure sufficiently good coating properties even if the packing density in the organic binder is high.
It has a high magnetic flux density because the packing density has been dramatically improved. ” and PETRO
TECll) Volume 9, No. 6 (Published in 1986) No. 494
This is a classification of material technology for electromagnetic shielding on the page. It is a conductive coating method that is currently mainstream. Fine nickel particles are placed in the paint.・
...Of course, contact between metals is essential, and...
Those with a high mutual contact rate are selected...''.

Magnetite particles that satisfy the above-mentioned characteristics need to be fine particles with a plate-like shape.

This fact can be seen, for example, in the above-mentioned Japanese Unexamined Patent Publication No. 51-28700, which states, ``...By applying magnetic powder that essentially has a plate-like shape, the filling rate of the magnetic powder is high and uniform.
and provides a magnetic film with excellent magnetic properties...'', in the above-mentioned Japanese Patent Application Laid-Open No. 55-104923, ``...''
- There are other applications for hexagonal flake-shaped (plate-like) iron oxides with magnetite or magnetite structure. ...
- A very pronounced parallel orientation (orientation) of the individual particles occurs. Therefore, it is possible to have an extremely high packing density...'' and JP-A-61-266
Publication No. 311 states, ``...If a fine plate-shaped cobalt-containing iron oxide ferromagnetic powder of 1μ or less is used, due to its plate-like shape, magnetic properties with excellent dispersibility and filling properties of the powder and surface smoothness of the tape can be obtained. It is possible to provide a recording medium.''

Conventionally, as a method for producing plate-shaped magnetite particles, for example, plate-shaped hematite particles are generated from an aqueous solution by hydrothermally treating an alkaline suspension containing ferric hydroxide or goethite using an autoclave. By heating and reducing the plate-shaped hematite particles in a reducing gas and rapidly oxidizing an alkaline suspension containing ferrous hydroxide with a strong oxidizing agent, or in the presence of specific additives. A ferric salt and an alkali are reacted in an aqueous medium to produce ferric hydroxide, and the ferric hydroxide is hydrothermally treated to produce plate-shaped goethite particles from the aqueous solution. A method is known in which goethite particles are heated to dehydrate and then heated and reduced 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 that the invention seeks to solve]

There is currently a demand for single-grain plate-shaped magnetite powder with high packing density and excellent dispersibility and orientation, but when using the known method as described above, plate-shaped particles produced from an aqueous solution can be used. Because it is necessary to reduce the particles by heating in a reducing gas, sintering of particles and particles occurs, which makes dispersion in a vehicle or resin difficult, reducing packing density and reducing orientation. The disadvantage is that the properties deteriorate.

Furthermore, in the case of the former method among known methods, it is difficult to produce plate-shaped hematite fine particles with an average diameter of 1 μm or less, especially 0.5 μm or less from an aqueous solution, and cough hematite particles Of course, it is difficult to obtain plate-like magnetite particles obtained by thermal reduction with an average diameter of 1 μm or less, particularly 0.5 μm or less. This fact can be seen, for example, in the above-mentioned Japanese Unexamined Patent Publication No. 51-28700:
It occurs naturally as aceous iron oxide and is known as an inorganic rust-preventing paint, but recently it has become possible to synthesize it artificially...Synthesized iron oxide has a shape that is The plate diameter is approximately 1 to 40 μm, and is as described in the following.

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.

As is clear from the above, in order to obtain a non-porous and non-sintered plate-shaped magnetite fine particle powder, there is a strong demand for a method of directly producing plate-shaped magnetite fine particles 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 methods for directly producing plate-shaped magnetite fine particles from an aqueous solution.

That is, in the present invention, when an aqueous solution containing FeCO3 obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution is oxidized by passing an oxygen-containing gas through the aqueous solution containing the ferrous salt and the aqueous alkali carbonate solution, The equivalent ratio of the alkali carbonate to the ferrous salt in the salt aqueous solution is 1 equivalent or more, and the amount of the alkali carbonate aqueous solution is equal to or less than the value expressed by the general formula. Tartaric acid or its salt in an amount of 0.01 to 2.0 mol% based on Fe is added to any of the aqueous solution, the alkali carbonate aqueous solution, and the FeCO5-containing aqueous solution before oxidation by passing the oxygen-containing gas through the aqueous solution, and then oxygen It is characterized by producing plate-shaped magnetite particles from an aqueous solution by aerating and oxidizing the contained gas.The average particle size is 0.03 to 0.5 μm and the specific surface area is 7 to 30n (/g). This is a method for producing non-porous and non-sintered plate-shaped magnetite particles.

[For production]

First, the most important point in the present invention is that FeCO obtained by reacting a ferrous salt aqueous solution and an alkali carbonate aqueous solution
5 is oxidized by passing an oxygen-containing gas through the aqueous solution containing 5, the equivalent ratio of the alkali carbonate to the ferrous salt in the ferrous salt aqueous solution is 1 equivalent or more, - The FeCO3 is reacted with the aqueous alkali carbonate solution in an amount that is less than or equal to the value expressed by formula a, and contains the FeCO3 before being oxidized by aerating the aqueous ferrous iron solution, the aqueous alkali carbonate solution, and an oxygen-containing gas in advance. When 0.01 to 2.0 mol% of tartaric acid or its salt is added to any of the aqueous solutions based on Fe, and then oxidized by passing oxygen-containing gas, plate-shaped magnetite particles are generated directly from the aqueous solution. The fact is that it can be done.

The plate-shaped magnetite particles in the present invention have a particle size of 0.5
Since they are fine particles of micrometers or less in size and are produced directly from an aqueous solution, they are non-porous and non-sintered.

Although the plate-shaped magnetite particles in the present invention are fine particles, they are non-porous and have a specific surface area of 30i/
It is small, less than 25nr/g, especially less than 25nr/g, and is plate-like, non-porous, and non-sintered, so it is easy to make into a paint, has excellent dispersibility and orientation, and can be used in vehicles or resins. High-density filling inside is possible.

In the present invention, when a non-oxidizing gas such as nitrogen gas is blown into an aqueous solution containing FeCO5, stirring is performed as necessary, and aging treatment is performed, a plate having a large plate ratio (plate diameter: thickness) is obtained. magnetite particles are easily obtained.

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

Examples of the ferrous salt aqueous solution used in the present invention include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution.

As the alkali carbonate used in the present invention, sodium carbonate, potassium carbonate, ammonium carbonate, etc. can be used alone or in combination.

The ferrous salt aqueous solution and the alkali carbonate may be added either first or simultaneously.

The reaction temperature in the present invention is 75 to 100°C.

When the temperature is 75° C. or lower, spindle-shaped hematite particles and acicular goethite particles are mixed in the plate-shaped magnetite particles. Although the object of the present invention can be achieved when the temperature is 100° C. or higher, it requires a special equipment such as an autoclave, which is not economical.

The amount of alkali carbonate used in the present invention is such that the equivalent ratio of alkali carbonate to ferrous salt in the ferrous salt aqueous solution is 1.
It is more than equivalent and less than the value expressed by the general formula. If it is more than the above specific value, spindle-shaped hematite will be mixed in the plate-shaped magnetite particles. In addition, in consideration of productivity, the lower limit of the iron concentration is preferably about 0.1 i+ol/Il.

In the present invention, tartaric acid or a salt thereof can be used. Here, the salt includes sodium tartrate, potassium tartrate, lithium tartrate, ammonium tartrate, and the like.

The amount of tartaric acid or its salt added in the present invention is 0.01 to 2.0 mol% based on Fe. If it is 0.01 mol% or less, granular hematite particles and acicular goethite particles will be mixed in the plate-shaped magnetite particles. When the content is 2.0 mol % or more, magnetite particles are produced, but the saturation magnetization decreases significantly.

Tartaric acid or its salt in the present invention affects the type and form of the generated particles through a synergistic effect with the alkali carbonate, and therefore, it is added before the reaction for producing plate-shaped magnetite particles starts. If necessary, it can be added to any of the ferrous salt aqueous solution, the aqueous alkali carbonate solution, and the aqueous solution containing FeCO3 before being oxidized by bubbling oxygen-containing gas.

〔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 the values measured from the electron microscope W1 mirror photograph, and the specific surface area is measured by the BET method. [The magnetic field was measured using a vibrating sample magnetometer VSMP-1 model (manufactured by Toei Kogyo Co., Ltd.) at a measurement magnetic field of 10 Oe.

Example 1 Ferrous sulfate 1.08 mol/j aqueous solution 0.834,
Under a N8 gas flow, 0.67 g of tartaric acid was added to contain 0.5 mol% of Fe prepared in the reactor. = 2.0 equivalent.) FeCQs was produced at a temperature of 60°C. The iron concentration at this time is 0.201101 in terms of Fe.
/ It was J. The above aqueous solution containing pecOs was subjected to aging treatment at 90°C for 30 minutes while blowing Hz gas at a rate of 10ffi per minute, and then air was passed through at 90°C at a rate of 101 per minute for 2.5 hours to generate particles. .

The end point of the oxidation reaction was determined by extracting a portion of the reaction solution and adjusting the 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 generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As a result of transmission electron microscopy observation, this particle powder has an average diameter of 0.30 μm, and as is clear from the scanning electron micrograph (x30,000) shown in Figure 1, the plate-like ratio (plate surface diameter and thickness The particles had a plate-like morphology with a ratio of 8:1 and no pores were present on the surface or inside the particles.

In addition, the BET specific surface area of this particle powder is 8.8ran
g, the coercive force) 1c is 1150e, and the saturation magnetization σS is 87. Oemu/g, squareness ratio (σr/σS)
was 0.125.

As is clear from FIG. 2, which shows the X-ray diffraction diagram of this particle powder, peak A is a peak indicating magnetite, and it can be seen that it consists only of magnetite.

Example 2 Ferrous sulfate 1.35+sol/J aqueous solution 0.3:l,
Under a flow of N2 gas, 0.33 g of tartaric acid was added to contain 0.5 mol% of the Fe prepared in the reactor, resulting in a 0.221 Iol/1 NazCOs aqueous solution 4.17j! (corresponding to C03/Fe = 2.0 equivalent), FeC01 was generated at a temperature of 60°C. The iron concentration at this time is 0.1 moI in terms of Fe.
/l. While continuously blowing Nt gas into the FeCO3-containing aqueous solution at a rate of 15n/min, the temperature was increased to 85°C.
After aging for 30 minutes at 85°C,
Particles were generated by bubbling 81 air for 1.0 hour.

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 generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

This particle powder is shown in the transmission electron micrograph (X
50,000), the average diameter is 0.16μ, and as a result of scanning electron microscopy observation, the plate-like ratio (
The particles had a plate-like shape with a ratio of plate surface diameter to thickness of 6:1, and there were no pores on the particle surface or inside the particle.

In addition, the BET specific surface area of this particle powder is 12.8rd
/g, and the magnetism is such that the coercive force Hc is 1050e, the saturation magnetization σS is 86.8emu/g, and the squareness ratio (σr/σS
) was 0.165.

As a result of X-ray diffraction, this particle powder consisted of only a peak indicating magnetite, and it consisted only of magnetite.Example 3 Ferrous sulfate 1.35 + mol/j aqueous solution 1.00 fi
was prepared in the reactor under Nt gas flow.
In addition to 3.50 Il of a 0.78 mo1/-1 NagCO3 aqueous solution obtained by adding 1.01 g of tartaric acid so as to contain 0.5 mol% (corresponding to C03/Fe = 1.5 equivalent). , FeCO5 was produced at a temperature of 85°C. The iron concentration at this time is 0.3 mo in terms of Fe.
It was l/l. Particles were generated by blowing 181 air per minute into the FeCO3-containing aqueous solution for 2.5 hours at a temperature of 85°C.

The end point of the oxidation reaction was determined by extracting a portion of the reaction solution, acidifying it 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 generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As a result of observation with a transmission electron microscope, this particle powder has an average diameter of 0.35 μm, and as a result of observation with a scanning electron microscope, it has a plate-like shape with a plate-like ratio (ratio of plate surface diameter to thickness) of 8:l. It consisted of particles exhibiting the following properties, and there were no pores on the surface or inside the particles.

Moreover, the BET specific surface area of this particle powder is 8.5r+?
/g, and the magnetism is as follows: coercive force Hc is 1200e, saturation magnetization σS is 88.2e biased u/g, squareness ratio (σr/σS
) was 0.135.

As a result of X-ray diffraction, this particle powder was found to consist only of magnetite, with only a peak indicating magnetite.

Example 4 0.61 g of tartaric acid to contain 0.5 mol% based on Fe
0.60 n of a 1.35 mol/l aqueous solution of ferrous sulfate obtained by adding ( corresponding to C03/Fe=3.5 equivalents), and FeCO5 was generated at a temperature of 85°C. The iron concentration at this time is 0.18 mol/Fe equivalent.
It was f. 85°C while continuously blowing N2 gas into the FeCO5-containing aqueous solution at a rate of tSX per minute.
After aging for 30 minutes at 85°C,
Particles were generated by bubbling 8 Il of air for 2.0 hours.

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 generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As a result of observation with a transmission electron microscope, this particle powder has an average diameter of 0.21μ■, and as a result of observation with a scanning electron microscope, it has a plate-like shape with a plate-like ratio (ratio of plate surface diameter to thickness) of 6:1. It consisted of particles exhibiting the following properties, and there were no pores on the surface or inside the particles.

In addition, the BET specific surface area of this particle powder is 10.5 rJ
/g, and the magnetism is such that the coercive force Hc is 1150e, the saturation magnetization as is 87.8emu/g, and the squareness ratio (σr/σS
) was 0.155.

As a result of X-ray diffraction, this particle powder contained only a peak indicating magnetite, and was composed only of magnetite.

Example 5 Ferrous sulfate 1.35 sol/l aqueous solution 1.331
Under N-rich gas flow, 0.70% sodium tartrate was added to contain 0.2 mol% of Fe prepared in the reactor.
0.71 sol/j of Na, C obtained by adding g
In addition to 3.17j of O3 aqueous solution (COs/Fe"1.
This corresponds to 25 equivalents. ), FeCO at a temperature of 60°C
5 was produced. The iron concentration at this time is 0.
It was 4 axes or/l. The FeCO3-containing aqueous solution was then aged at 90°C for 30 minutes while blowing Nt gas at a rate of 157/min, and then air was bubbled through at 90°C for 3.0 hours at a rate of 181/min to generate particles. .

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 generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As a result of observation with a transmission electron microscope, this particle powder has an average diameter of 0.25μ, and as a result of observation with a scanning electron microscope, it has a plate-like shape with a plate-like ratio (ratio of plate surface diameter to thickness) of 5:1. It consisted of particles exhibiting the following properties, and there were no pores on the surface or inside the particles.

In addition, the BET specific surface area of this particle powder is 10.5 i/
g, and the magnetism is as follows: coercive force Hc is 1050e, saturation magnetization σS is 87.2ewu/g-, squareness ratio (σr/σ3)
was 0.123.

As a result of X, % i diffraction, this particle powder contained only a peak indicating magnetite, and was composed only of magnetite.

Comparative Example 1 Ferrous sulfate was mixed with 1.08 ol/l of N containing tartaric acid.
a1 CO8 aqueous solution 3.67 g, plus (COs/Fe
Particles were produced from an aqueous solution in the same manner as in Example 1, except that the particles were obtained from an aqueous solution. The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method. As is clear from the transmission electron micrograph (X3G, 000) shown in FIG. 4, this particle powder contained a mixture of plate-like particles and spindle-like particles. Moreover, as shown in the X&11 diffraction diagram of FIG. 5, peaks of magnetite and hematite were shown.

In FIG. 5, peak A is magnetite and peak B is hematite.

Comparative Example 2 Particles were produced from an aqueous solution in the same manner as in Example 1, except that tartaric acid was not added. The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

This particle powder is shown in the transmission electron micrograph (X) shown in Figure 6.
20.00G), plate-like particles, spindle-like particles, and needle-like particles were mixed together.

Moreover, as shown in the X-ray diffraction diagram of FIG. 7, peaks of magnetite, hematite, and goethite were shown.

In FIG. 7, peak A is magnetite, peak B is hematite, and peak C is goethite.

Comparative Example 3 Particles were produced from an aqueous solution in the same manner as in Example 1, except that the amount of tartaric acid added was 4.0 g (corresponding to 3.0 mol % based on Fe).

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

The magnetic properties of this particle powder include a coercive force Hc of 1180 eS, a saturation magnetization σS of 68.5 emu/g, and a squareness ratio (σr/σS
) was 0.123.

Comparative Example 4 Particles were produced from an aqueous solution in the same manner as in Example 1, except that the aging temperature and oxidation temperature were 70°C.

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As a result of observation using a transmission electron microscope, it was found that plate-like particles, granular particles, and needle-like particles were mixed together.

Moreover, the results of X-ray diffraction showed peaks of magnetite, hematite, and goethite.

〔effect〕

According to the method for producing magnetite particles according to the present invention, as shown in the above-mentioned examples, fine particles exhibiting a plate-like shape, particularly 0.5 μm or less, and a specific surface area of 7.
It is possible to obtain non-porous and non-sintered plate-shaped magnetite particles with a particle size of ~30 nr/g, and the packing density in the vehicle or resin is high (excellent in dispersibility and orientation, and there are no gaps between particles). It is suitable for electromagnetic wave absorption, material powder for shielding materials, magnetic material powder for magnetic recording, black pigment powder for paints, and coloring agent for rubber and plastics.

[Brief explanation of the drawing]

Figures 1, 3, 4, and 6 are all electron micrographs. Figures 1 and 3 are Example 1 and Example 2, respectively.
FIG. 4 shows a mixed powder of plate-shaped magnetite particles and spindle-shaped hematite particles obtained in Comparative Example 1, and FIG. 6 shows a plate-shaped magnetite particle obtained in Comparative Example 2. It is a mixed powder of particles, granular hematite particles, and acicular goethite particles. 2, FIG. 5, and FIG. 7 are all X-ray diffraction diagrams, and FIG. 2, FIG. 5, and FIG. 7 are the powder particles obtained in Example 1, Comparative Example 1, and Comparative Example 2, respectively.

Claims (1)

[Claims] (1) In oxidizing the FeCO_3-containing aqueous solution obtained by reacting the ferrous salt aqueous solution and the alkali carbonate aqueous solution by passing an oxygen-containing gas through the ferrous salt aqueous solution and the ferrous salt aqueous solution, The equivalent ratio of the alkali carbonate to the ferrous salt of is 1 equivalent or more, and the equivalent ratio of the general formula ([CO_3^2^-(mol)]/[Fe^2
^+(mol)])=[0.13]/[(FeCO_3
(mol/l))^2] + 0.6, and the ferrous aqueous solution, the alkali carbonate aqueous solution, and the oxygen-containing gas The Fe before being oxidized by aeration
0.01 for Fe in any of the aqueous solutions containing CO_3
It is characterized by producing plate-shaped magnetite particles from an aqueous solution by adding ~2.0 mol% of tartaric acid or its salt and then oxidizing by passing oxygen-containing gas.The average diameter is 0.03 to 0. .5μm and specific surface area is 7-3
A method for producing non-porous and non-sintered plate-shaped magnetite particles having a particle size of 0 m^2/g.