JPH0651574B2 - Manufacturing method of spindle-shaped magnetic iron oxide particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing magnetic iron oxide particle powder for magnetic recording, which has substantially no pores on the surface or inside the particle. Magnetic iron oxide composed of spindle-shaped magnetite particles or maghemite particles with high density, uniform particle size, no mixed dendritic particles, and a small axial ratio (major axis: minor axis) The purpose is to provide a particle powder.

[Prior art]

In recent years, with the progress of longer-time recording and smaller size and lighter weight of magnetic recording / reproducing devices, there is an increasing need for higher performance of recording media such as magnetic tapes and magnetic disks.

That is, high recording density, high sensitivity characteristics, high output characteristics, and low noise characteristics are required.

The characteristics of the magnetic particle powder required to satisfy the above requirements for the magnetic recording medium are that it has excellent dispersibility and high coercive force, and that the axial ratio (major axis: minor axis) is small. Is.

This fact is, for example, "Development of magnetic materials and high dispersion technology of magnetic powder" (1982) published by Sogo Gijutsu Center Co., Ltd. With respect to signals, it is possible to maintain high output characteristics with low noise, but for that purpose it is necessary that both coercive force Hc and residual magnetization Br are large and that the thickness of the coating film be thinner. " Also, in Japanese Patent Laid-Open No. 57-183626, "The concept of perpendicular magnetization recording has been introduced in recent years, and there is a proposal to effectively use the residual magnetization component in the direction perpendicular to the surface of the magnetic recording medium. And the recording density defined above becomes higher, and the particle size becomes shorter than the vertical / axial ratio of more than 1 and 3 or less. In-plane orientation and coating by reducing the thickness of the coating in the thickness direction It is characterized in that it suppresses the tendency of particles to lie in the plane, such as orientation in the casting direction due to the flow of time, and positively takes a large remanent magnetization positively if necessary. ".

Further, the remanent magnetization Br of the magnetic recording medium depends on the dispersion lasting of the magnetic particle powder in the vehicle, the orientation lasting in the coating film, and the filling lasting. In order to improve these characteristics, The magnetic particle powder to be dispersed in the particle surface is substantially high density with no pores present on the surface and inside the particle, and,
Particles having a uniform particle size and no dendritic particles coexisting, and in terms of particle shape, spindle-shaped particles are required.
As is well known, the magnitude of the coercive force of the magnetic particle powder depends on any of shape anisotropy, crystal anisotropy, strain anisotropy and exchange anisotropy, or their interaction. Current,
The acicular magnetite particle powder or the acicular maghemite particle powder used as the magnetic particle powder for magnetic recording uses anisotropy derived from its shape, that is, the axial ratio (long axis: short axis). A relatively high coercive force is obtained by increasing the (axis).

Thus, the known acicular magnetite particle powder or acicular maghemite particle powder obtains a relatively high coercive force by utilizing its shape anisotropy.
By adding Co, by utilizing its crystal anisotropy,
Further, it is generally known to improve the coercive force.

These known acicular magnetite particle powders, or maghematite particle powders are generally pH containing ferrous hydroxide particles obtained by reacting an aqueous ferrous salt solution with an alkali.
Needle crystal goethite particles obtained by air-oxidizing an aqueous solution of 11 or more colloids (usually called "wet reaction") are heated and dehydrated in air at around 300 ° C to form hematite particles. It is reduced in a reducing gas such as hydrogen at 300 to 400 ° C. to give needle-shaped magnetite particles, or subsequently,
It is obtained by oxidization in air at 200-300 ℃ to form acicular maghemite particles.

[Problems to be solved by the invention]

There are no pores on the surface of the particle and inside the particle, and the density is substantially high, and the particle size is uniform and dendritic particles are not mixed, and the axial ratio (long axis: short axis) is The magnetic iron oxide particle powder exhibiting a small spindle shape is the most demanded at present, and in order to obtain the magnetic particle powder having such characteristics, the starting material particles themselves are naturally the particle surface and the particle. Spindle type that has no pores inside, is of substantially high density, has a uniform particle size, does not contain dendritic particles, and has a small axial ratio (major axis: minor axis). However, the particle powder obtained by the above-mentioned known method for producing needle-shaped goethite particles as a starting material has an axial ratio (long axis: short axis) of 10: 1. The particles have the above needle-like morphology, are mixed with dendritic particles, and Speaking, hard to say that a particle having a uniformity of particle size.

On the other hand, as a method for producing goethite particles, JP-A-50-809
There is a method described in Japanese Patent Publication No. 99. That is, the method described in JP-A-50-80999 is a method in which an oxygen-containing gas is passed through an aqueous solution containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution with an alkali carbonate to oxidize the aqueous solution. . According to this method, goethite particles having a uniform particle size and no spindle-shaped dendritic particles and a spindle-shaped goethite particle are obtained.

However, when magnetic iron oxide particle powder is obtained by a conventional method using the needle-shaped goethite particle powder obtained by the known method or the method described in JP-A-50-80999, heating the goethite particles The hematite particles obtained by dehydration produce a large number of pores on the particle surface as well as the inside of the particle by dehydration, and then the magnetite particles or maghemite particles obtained by reducing or further oxidizing the hematite particles are also particles. It is observed that many pores are distributed on the surface as well as inside the particles.

As described above, the magnetic iron oxide particle powder having a large number of pores on the particle surface and inside the particle has a low coercive force Hc and is poorly dispersed in the vehicle.

This fact is because, for example, in Japanese Patent Laid-Open No. 55-47227, "γ-Fe ₂ CO ₃ (maghemite) particles are widely used as magnetic powder for magnetic recording, and high coercive force has been conventionally measured. In order to do so, the produced γ-Fe ₂ CO ₃ retains the needle-like morphology of its mother salt, iron oxyhydroxide (α, β, γ-FeOOH), as well as the dehydration hole (Pore). This dehydration hole (vacancy) is generated when the mother salt iron oxyhydroxide is dehydrated and remains in the product γ-Fe ₂ CO ₃ particles. Decrease coercive force. "And electrochemical and industrial physical chemistry
Volume 38, No. 7 (1970), p. 544, "... Various dispersion techniques in vehicles have been considered, but nonetheless, dispersion in γ-Fe ₂ CO ₃ tapes produced is poor. Γ-
Fe ₂ CO ₃ has holes (holes) as shown in Fig. 17, and magnetic poles appear at the edges of the holes to generate Lorentz magnetic field. It is clear from the description that the magnetostatic energy is reduced to form chestnut-shaped aggregates.

As described above, a magnetic iron oxide particle powder suitable for high-density recording is required to have a small axial ratio (major axis: minor axis). Magnetic iron oxide particles with a small size cannot utilize the anisotropy derived from the shape, so that only coercive force Hc of about 200 Oe or less can be obtained. It is particularly strongly desired to improve the coercive force as much as possible by eliminating this.

Attempts have been made to eliminate the pores generated on the surface of the magnetic iron oxide particles as well as inside the particles.For example, in Japanese Examined Patent Publication No. 38-26156, the composition changes after being reduced to magnetite at low temperature. In order to prevent this, a method of annealing at a temperature of 800 ° C. or higher and 1000 ° C. or lower in a vacuum, hydrogen stream, or carbon gas stream is described.

In addition, the powder and powder metallurgical association 1968 spring conference lecture summary 2-6 shows that as the dehydration temperature of acicular goethite rises, the number of voids on the surface and inside of acicular hematite particles decreases. However, it has been reported that when the dehydration temperature is higher than 700 ° C., the voids disappear but the sintering progresses and the acicular crystal particles collapse.

In any of the above methods, it is necessary to heat at a high temperature in order to eliminate the voids generated on the surface of the particle and inside the particle, and as a result, sintering occurs between the particles and between the particles, which is reduced and oxidized. The coercive force of the magnetic iron oxide particle powder obtained as described above is extremely lowered, and the dispersibility in the vehicle during the production of the magnetic coating is also deteriorated.

On the other hand, a method of obtaining magnetic iron oxide particles by using particles having no pores on the particle surface and inside the particle as a starting material is also attempted, instead of eliminating the pores once generated on the surface of the magnetic iron oxide particle and inside the particle. ing.

This method is a method of directly producing acicular hematite particles from an aqueous solution, and reducing and oxidizing the acicular hematite particles as a starting material to obtain acicular magnetic iron oxide particles.

That is, as described above, the pores on the particle surface and inside the particles are generated by dehydration when the needle-shaped goethite particles are heated and dehydrated to form needle-shaped hematite particles. If crystallized hematite particles are generated, the dehydration step can be omitted. Therefore, needle-shaped magnetite particles having no pores on the particle surface and inside can be obtained, and the hematite particles can be used as a starting material for reduction. The acicular crystalline iron oxide particles obtained by oxidation also have no pores on the particle surface and inside the particle.

As a method for directly producing acicular hematite particles from an aqueous solution, for example, there is a method described in JP-B-55-22416. That is, the method described in JP-B-55-22416 is a method of heat-treating an aqueous slurry in which three components of ferric hydroxide, citric acid or / and its salt, and an alkali compound coexist. 3 at 25 ℃
The needle-like hematite particles are obtained by adjusting the pH of the component-coexisting aqueous slurry to 10 to 13 and the heat treatment temperature to 100 to 250 ° C.

However, in the case of this method, a high temperature of 100 ° C. or higher is required, and a special device called an autoclave is required, which is not industrial or economical.

As a method for producing hematite particles from an aqueous solution at a temperature of 100 ° C. or lower, there is a method described in JP-A-51-8193. That is, in the method described in JP-A-51-8193, the pH of the ferrous salt solution is adjusted to pH 7 by adding alkali hydrogen carbonate alone or by adding both alkali hydrogen carbonate and alkali carbonate or alkali hydroxide. The oxidation reaction is performed at a temperature of -11 to 65 ° C to 100 ° C.

According to this method, the shape of the generated hematite particles is spherical, and particles of other types other than the hematite particles are generated and mixed.

As is clear from the above, there are no pores on the particle surface and inside the particle, and the particle density is substantially high,
Moreover, the probability of a method for producing a spindle-shaped magnetic iron oxide particle powder in which the particles are uniform and dendritic particles are not mixed and the axial ratio (long axis: short axis) is small is strongly demanded. .

[Means for solving problems]

The present inventors have found that the surface of the particle and the inside of the particle do not have pores and have a substantially high density, and the particle size is uniform and dendritic particles are not mixed, and the axial ratio (long axis : Short axis)
As a result of various studies to obtain a magnetic iron oxide particle powder exhibiting a small spindle shape, a ferrous salt aqueous solution and carbon in a ratio of 1.8 equivalent or more in terms of CO ₃ with respect to Fe in the ferrous salt aqueous solution. Before oxygenating the oxygen-containing gas by aerating the aqueous solution containing FeCO ₃ obtained by reacting with the alkaline aqueous solution, the aforesaid ferrous salt solution, the alkaline carbonate aqueous solution and the oxygen-containing gas are aerated before oxidation. When 0.1 to 1.5 mol% of citric acid or a salt thereof with respect to Fe is added to any one of the aqueous solutions containing FeCO ₃ , the starting material has a uniform particle size and dendritic particles are mixed. The present invention has been completed based on the novel finding that it is possible to directly generate spindle-shaped hematite particles having a small axial ratio (major axis: minor axis) from an aqueous solution at 100 ° C or less. is there.

That is, the present invention is an aqueous solution containing FeCO ₃ obtained by reacting an aqueous solution of a ferrous salt and an aqueous solution of an alkali carbonate having a ratio of 1.8 equivalent or more in terms of CO ₃ with respect to Fe in the aqueous solution of the ferrous salt. In passing oxygen to the oxygen-containing gas for oxidation, the ferrous salt aqueous solution in advance, to the solution in any one of the aqueous solutions containing FeCO ₃ before oxidizing the alkali carbonate aqueous solution and oxygen-containing gas to oxidize. On the other hand, 0.1 to 1.5 mol% of citric acid or a salt thereof was added, and then oxygen-containing gas was aerated in the temperature range of 70 to 100 ° C. to oxidize it to generate spindle-shaped hematite particles from the aqueous solution. A spindle type comprising heating and reducing the spindle-shaped hematite particles in a reducing gas to form spindle-shaped magnetite particles, or further oxidizing the spindle-shaped hematite particles to form spindle-shaped maghemite particles Magnetic oxidation A method for producing magnetic iron oxide particles consisting of iron particles, and reacting a ferrous salt aqueous solution with an aqueous solution of alkali carbonate having a ratio of 1.8 equivalent or more in terms of CO ₃ with respect to Fe in the ferrous salt aqueous solution. When the oxygen-containing gas is aerated to oxidize the obtained FeCO ₃ -containing aqueous solution, the ferrous iron salt aqueous solution, the alkali carbonate aqueous solution, and the FeCO ₃ -containing aqueous solution before the oxygen-containing gas is aerated and oxidized. In either liquid, 0.1 to 1.5 mol% citric acid or a salt thereof with respect to Fe and 0.5 to 10 in terms of Co with respect to Fe.
Add 0 atom% water-soluble cobalt salt, then 70-1
A spindle-shaped hematite particle containing Co was generated from an aqueous solution by aerating and oxidizing an oxygen-containing gas in the temperature range of 00 ° C, and the spindle-shaped hematite particle containing Co was reducible. Spindle-shaped magnetic properties obtained by heating and reducing in gas to form spindle-shaped hematite particles containing Co, or by further oxidizing them to form spindle-shaped maghemite particles containing Co. This is a method for producing magnetic iron oxide particle powder composed of iron oxide particles.

[Action]

First, the most important point in the present invention is that the surface of the particle and the inside of the particle have substantially no high density of pores, and the particle size is uniform and dendritic particles are not mixed,
Moreover, when manufacturing the magnetic iron oxide particle powder of spindle type having a small axial ratio (major axis: minor axis), no pores are present as the starting material on the surface of the particle and inside the particle, and the density is substantially high. In addition, the spindle-shaped hematite particle powder has a uniform particle size, does not contain dendritic particles, and has a small axial ratio (major axis: minor axis).

In the present invention, the fusiform hematite particles are
We have obtained hematite particles that do not have pores on the particle surface and inside by directly generating from an aqueous solution at 0 ° C or less.
It does not require a special device such as.

Further, in the present invention, only spindle-shaped hematite particles can be produced from an aqueous solution at 100 ° C. or lower.

In the present invention, it is not yet clear why the spindle-shaped hematite particles having a small axial ratio can be produced, but the present inventors have found that the ferrous salt aqueous solution and the ferrous salt aqueous solution are When citric acid or a salt thereof is added under the condition of less than 1.8 equivalents in terms of CO _{3 with} respect to Fe in the
Since granular magnetite particles are mixed in the spindle-shaped hematite particles, it is considered to be due to the synergistic effect of alkali carbonate and citric acid or its salt.

In the present invention, the magnetic iron oxide particle powder having a higher coercive force produces a spindle-shaped hematite particle containing Co by adding a water-soluble cobalt salt in the production reaction of the spindle-shaped hematite particle. Let the Co
Or reduce the spindle-shaped hematite particles containing
If necessary, it can be further oxidized to obtain a spindle-shaped magnetic iron oxide particle containing Co, and the obtained spindle-shaped magnetic iron oxide particle containing Co has a uniform shape. It is not only directional but also magnetically isotropic, and is suitable as a magnetic iron oxide particle powder for magnetic recording.

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

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

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

The ferrous salt aqueous solution and the alkali carbonate may be added first or at the same time.

The reaction temperature in the present invention is 70 to 100 ° C. When the temperature is lower than 70 ° C, goethite particles are mixed in the hematite particles. When the temperature exceeds 100 ° C, the object of the present invention can be achieved, but it requires a special device such as an autoclave and is not economical.

The amount of alkali carbonate used in the present invention is based on Fe.
It is 1.8 equivalents or more in terms of CO ₃ . If the amount is less than 1.8 equivalents, granular magnetite particles will be mixed in the spindle-shaped hematite particles.

In the present invention, citric acid or its salt can be used. Here, the salt includes sodium citrate, potassium citrate, lithium citrate, ammonium citrate and the like.

The addition amount of citric acid or a salt thereof in the present invention is 0.1 to 1.5 mol% with respect to Fe. If less than 0.1 mol%,
Spindle-shaped goethite particles and granular hematite particles are mixed. If it exceeds 1.5 mol%, fine amorphous particles are generated. Considering the particle morphology of the produced hematite particles, 0.1 to 1.0 mol% is preferable.

Citric acid or a salt thereof in the present invention affects the type and morphology of the produced particles by a synergistic action with alkali carbonate, and therefore, before the initiation of the production reaction of spindle-shaped hematite particles. It must be added in advance, and it can be added to any of the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the aqueous solution containing FeCO ₃ before being oxidized by aeration with an oxygen-containing gas.

As the water-soluble cobalt salt in the present invention, cobalt sulfate, cobalt chloride or the like can be used.

The amount of water-soluble cobalt salt added is 0.5 with respect to Fe in terms of Co.
~ 10.0 atomic%.

If the content is less than 0.5 atom%, the effect of improving the coercive force of the obtained spindle-shaped magnetite particles or maghemite particles cannot be sufficiently achieved.

If it exceeds 10.0 atomic%, the temperature stability of the obtained spindle-shaped magnetite particles or maghemite particles becomes poor.

The water-soluble cobalt salt in the present invention is required to be contained in the produced spindle-shaped hematite particles, and therefore, is added before the production reaction of the spindle-shaped hematite particles is started. However, it can be added to any one of the aqueous ferrous salt solution, the aqueous alkali carbonate solution, and the aqueous solution containing FeCO ₃ before being oxidized by aeration with an oxygen-containing gas.

Further, in the present invention, it is possible to add a metal other than Fe such as Mg, Al, Cr, Zn, and Ni which are conventionally added in the generation of the starting material particles in order to improve various properties of the magnetic iron oxide particles. it can.

The heat reduction treatment and the oxidation treatment in the reducing gas in the present invention can be carried out by a conventional method.

In addition, the starting material, hematite particles, is a spindle type with more excellent dispersibility by being pre-coated with a substance that has a sintering-preventing effect such as Si, Al, and P compounds that are usually performed prior to heat treatment. It is possible to obtain powder of magnetic iron oxide particles exhibiting

〔Example〕

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

The axial ratios (long axis: short axis) and long axis of the particles in the following Examples and Comparative Examples are all represented by the average of the numerical values measured from electron micrographs.

The magnetic characteristics of the magnetic iron oxide particle powder are as follows:
Using SMP-1 type (manufactured by Toei Industry), measuring magnetic field 5KO
It was measured by e.

<Production of Spindle-Shaped Hematite Particle Powder> Examples 1 to 14 and Comparative Examples 1 to 3; Example 1 Sodium citrate 3.3 so as to contain 0.5 mol% with respect to Fe.
1.5 mol of ferrous sulfate obtained by adding g / aqueous solution 1.5
Was added to 1.54 mol / 3.0 Na ₂ CO ₃ aqueous solution (CO ₃ / Fe =
This corresponds to 2.0 equivalents. ), And FeCO ₃ was generated at a temperature of 80 ° C.

Particles were generated by passing 20 air per minute at a temperature of 80 ° C. for 4.5 hours into the aqueous solution containing FeCO ₃ .

The end point of the oxidation reaction was determined by extracting a part of the reaction solution, adjusting the acidity to hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue color reaction of Fe ²⁺ .

The produced particles were separated by a conventional method, washed with water, dried and pulverized.
This particle powder is an electron micrograph (× 20,00 shown in FIG.
As is clear from (0), it is composed of spindle-shaped particles having an average value of a long axis of 0.25 μm and an axial ratio (major axis: minor axis) of 3.5: 1. No
The particle size was uniform and dendritic particles were not mixed.

The X-ray diffraction pattern of this particle is shown in FIG. As is clear from FIG. 2, peak A is a peak showing hematite, and it can be seen that it consists of hematite only.

Examples 2 to 14 type of ferrous salt, type of alkali carbonate, concentration and equivalent ratio, type of citric acid or a salt thereof, addition amount and timing of addition,
Spindle-shaped particles were produced in the same manner as in Example 1 except that the presence or absence of addition of metal ions, the addition amount, and the reaction temperature were variously changed.

As a result of X-ray diffraction, it was confirmed that all the particles obtained in Examples 2 to 14 were only hematite particles.

Table 1 shows the main production conditions and the characteristics of the produced hematite particle powder at this time.

An electron micrograph (× 20,000) of the spindle-shaped hematite particle powder containing Co obtained in Example 11 is shown in FIG.
The X-ray diffraction pattern is shown in FIG.

Comparative Example 1 Particles were produced in the same manner as in Example 1 except that 1.12 mol / Na ₂ CO ₃ aqueous solution 3.0 (corresponding to CO ₃ /Fe=1.4 equivalent) was used.

The produced particles were separated by a conventional method, washed with water, dried and pulverized.

This particle powder is an electron micrograph (× 20,00 shown in FIG.
As is clear from (0), the particles were spindle-shaped particles mixed with granular particles. As a result of X-ray diffraction, peaks of hematite and magnetite were shown.

Comparative Example 2 Particles were produced in the same manner as in Example 1 except that 13.2 g of sodium citrate (corresponding to 2.0 mol% with respect to Fe) was added.

The produced particles were separated by a conventional method, washed with water, dried and pulverized.

This particle powder is an electron micrograph (× 20,00 shown in FIG.
As is clear from 0), the particles were fine amorphous particles.

Comparative Example 3 Particles were produced in the same manner as in Example 1 except that the reaction temperature was 65 ° C.

The produced particles were separated by a conventional method, washed with water, dried and pulverized.

As is clear from the X-ray diffraction diagram shown in FIG. 7, this particle powder was particles in which hematite particles and goethite particles were mixed.

In FIG. 7, peak A is a peak showing hematite, and peak B is
Is a peak indicating goethite.

<Production of Spindle-Shaped Magnetite Particle Powder> Examples 15 to 29; Example 15 Spindle-shaped hematite particle powder obtained in Example 1
80g was put into 1 retort reduction container, and H ₂ gas was ventilated at a rate of 0.2 per minute while driving and rotating, and the reduction temperature was 3
Spindle-shaped magnetite particles were obtained by reduction at 30 ° C.

As a result of electron microscopic observation, the obtained spindle-shaped magnetite particle powder was substantially dense with no pores on the particle surface and inside the particle, and the particle size was uniform and dendritic. No particles are mixed, the long axis is 0.23μ on average
m, and the axial ratio (long axis: short axis) was 3: 1.

As a result of magnetic measurement, coercive force Hc is 272 Oe, saturation magnetization σ
s was 81.3 emu / g.

Examples 16 to 29 Spindle-shaped magnetite particles were obtained in the same manner as in Example 15 except that the type of starting material and the reduction temperature were changed. Table 2 shows the main conditions and the characteristics of the particle powder at this time.

The spindle-shaped magnetite particle powders obtained in Examples 16 to 29 are both electron microscope observation results and have a substantially high density without pores on the particle surface and inside the particle, and The particle size was uniform, and dendritic particles were not mixed.

<Production of Spindle-Shaped Maghemite Particle Powder> Examples 30 to 44; Example 30 Spindle-shaped magnetite particle powder 75 g obtained in Example 15 was oxidized in air at 300 ° C. for 60 minutes A maghemite particle powder exhibiting the above was obtained.

The obtained spindle-shaped maghemite particles, as a result of electron microscopic observation, have a substantially high density with no pores on the particle surface and inside the particles, and have a uniform particle size and dendritic particles. The average value was 0.23 μm in the major axis and the axial ratio (major axis: minor axis) was 3: 1.

As a result of magnetic measurement, coercive force Hc is 232 Oe, saturation magnetization σ
s was 73.5 emu / g.

Examples 31 to 44 Spindle-shaped maghemite particle powders were obtained in the same manner as in Example 30 except that the kind of spindle-shaped magnetite particle powder was changed. Table 3 shows the main production conditions and the characteristics of the particle powder at this time.

The spindle-shaped maghemite particle powders obtained in Examples 31 to 44 are both electron microscope observation results, and the particles have a substantially high density with no pores on the surface and inside the particles, Moreover, the particle size was uniform, and dendritic particles were not mixed.

[Effect] According to the method for producing a spindle-shaped magnetic iron oxide particle powder according to the present invention, as shown in the above-mentioned Examples, there are no pores on the particle surface and inside the particle, and Magnetic iron oxide composed of spindle-shaped magnetite particles or maghemite particles with high density, uniform particle size, no mixed dendritic particles, and a small axial ratio (major axis: minor axis) Since a particle powder can be obtained, it is suitable as a magnetic material particle powder for high recording density, high sensitivity, high output and low noise, which is currently most required.

Further, in the production of a magnetic coating material, when the magnetite particle powder or maghemite particle powder is used, the dispersibility in the vehicle is good, the orientation and filling property in the coating film are very excellent, and the preferable magnetic recording The medium can be obtained.

[Brief description of drawings]

1 and 2 are an electron micrograph (× 20,000) and an X-ray diffraction diagram, respectively, showing the particle structure of the spindle-shaped hematite particle powder obtained in Example 1. FIG. 3 and FIG. 4 are an electron micrograph (× 20,000) and an X-ray diffraction pattern, respectively, showing the particle structure of the spindle-shaped hematite particles containing Co obtained in Example 11. 5 and 6 are both electron micrographs (× 20,000)
And shows the particle structures of the particle powders obtained in Comparative Example 1 and Comparative Example 2, respectively. FIG. 7 is an X-ray diffraction diagram of the particle powder obtained in Comparative Example 3.

Claims (2)

[Claims] 1. An aqueous ferrous salt solution and Fe in the aqueous ferrous salt solution
On the other hand, in oxidizing an aqueous solution containing FeCO ₃ obtained by reacting with an aqueous solution of an alkali carbonate having a ratio of 1.8 equivalents or more in terms of CO ₃ to oxidize by passing an oxygen-containing gas, the aqueous solution of the ferrous salt in advance, the carbonate 0.1 to 1.5 mol% of citric acid or a salt thereof with respect to Fe is added to one of the aqueous solutions containing FeCO ₃ before being oxidized by aeration with an alkaline aqueous solution and an oxygen-containing gas, and then 70 to A spindle-shaped hematite particle is generated from an aqueous solution by aerating and oxidizing an oxygen-containing gas in a temperature range of 100 ° C., and the spindle-shaped hematite particle is heated and reduced in a reducing gas to form a spindle. A method for producing a magnetic iron oxide particle powder comprising spindle-shaped magnetic iron oxide particles, characterized in that it is formed into a magnetite particle exhibiting a mold, or further oxidized into a maghemite particle exhibiting a spindle shape. 2. A ferrous salt aqueous solution and Fe in the ferrous salt aqueous solution.
On the other hand, in oxidizing an aqueous solution containing FeCO ₃ obtained by reacting with an aqueous solution of an alkali carbonate having a ratio of 1.8 equivalents or more in terms of CO ₃ to oxidize by passing an oxygen-containing gas, the aqueous solution of the ferrous salt in advance, the carbonate 0.1 to 1.5 mol% citric acid or a salt thereof with respect to Fe in any one of the aqueous solutions containing FeCO ₃ before being oxidized by aeration with an alkaline aqueous solution and an oxygen-containing gas, and 0.5 in terms of Co for Fe. -10.0 atomic% of water-soluble cobalt salt was added, and then oxygen-containing gas was aerated and oxidized in the temperature range of 70-100 ° C to produce spindle-shaped hematite particles containing Co from the aqueous solution. Then, the spindle-shaped hematite particles containing Co are reduced by heating in a reducing gas to form spindle-shaped magnetite particles containing Co, or further oxidized to form Co.
A process for producing a magnetic iron oxide particle powder comprising spindle-shaped magnetic iron oxide particles, characterized in that it is a spindle-shaped maghemite particle containing.