JPH08165117A - Spindlelike geothite particulate powder containing cobalt and its production - Google Patents

Abstract

PURPOSE: To obtain the subject fine particulate powder having a uniform particle size without any dendritic particles mixed therein by adding an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide to an aqueous solution of a ferrous salt, adding a compound containing Si, etc., to a suspension containing the resultant precipitate, adding a Co compound and further adding a compound of Al, etc., to a solution in the course of oxidizing reaction. CONSTITUTION: An aqueous solution of an alkali hydroxide is added to an aqueous solution of an alkali carbonate at 0.2-1.2 molar ratio to the aqueous solution of the alkali carbonate and the total amount of the alkali is 1.3-2.5 equiv. based on the total Fe in an aqueous solution of a ferrous salt. A compound containing Si, etc., is referred to as a compound containing one or more of Si, Nd, Y, La, Ce, Pr and Tb and added in an amount of 0.1-1.0 atomic % based on the total Fe. A Co compound is added in an amount of 8-50 atomic % (expressed in terms of Co) based on the total Fe. A compound of Al, etc., is added to the solution in the course of oxidizing reaction at 20-50% oxidation ratio of Fe<2+> based on the total Fe. The compound of Al etc., is a compound containing one or more of Al, Si, Nd, Y, La, Ce, Pr and Tb and added in an amount of 0.1-10.0 atomic % based on the total Fe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to fine particles, in particular, having an average major axis diameter of 0.05 to 0.15 μm and an axial ratio (major axis diameter / minor axis diameter, −hereinafter, simply referred to as “axial ratio”). ) Is 4-8,
X-ray particle size ratio (D ₀₂₀ / D ₁₁₀ -Below, simply "(D ₀₂₀ /
D ₁₁₀ ) ". ) Is in the range of 2.0 to 3.5,
The present invention also relates to a spindle-shaped goethite particle powder containing cobalt having a uniform particle size and containing no dendritic particles, and a method for producing the same.

The spindle-shaped goethite particle powder containing cobalt according to the present invention is suitable as a starting raw material powder for magnetic particle powder, and in particular, a spindle containing cobalt and iron, which are fine particles and have high coercive force, as main components. It is excellent as a starting material powder from which powdery metal magnetic particles are obtained.

[0003]

2. Description of the Related Art In recent years, video recording and audio magnetic recording / reproducing devices have been recorded for a long time and have been reduced in size and weight. In particular, the spread of VTRs (video tape recorders) has been remarkable and long. Development of VTRs aiming at time recording and reduction in size and weight is being actively conducted.
On the other hand, there is a demand for high performance and high density recording for a magnetic tape which is a magnetic recording medium.

That is, it is required to improve the high image quality of the magnetic recording medium, the high output characteristics, especially the frequency characteristics.
Improvement of residual magnetic flux density Br, high coercive force and dispersibility,
It is necessary to improve the filling property and the smoothness of the tape surface.
Improvement of N ratio is required.

Although these various characteristics of the magnetic recording medium have a close relationship with the magnetic particle powder used in the magnetic recording medium, in recent years, they have been kept higher than the conventional iron oxide magnetic particle powder. Metal magnetic particle powder containing iron as a main component having a magnetic force and a large saturation magnetization has attracted attention and has been put to practical use as a magnetic recording medium such as digital audio tape (DAT), 8 mm video tape, and Hi-8 tape. . However, it is strongly desired to further improve the characteristics of these metal magnetic particle powders.

Now, the relationship between various characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail below.

To obtain high image quality as a magnetic recording medium for video, "Nikkei Electronics" (1976)
As is clear from the record of No. 133, pages 82 to 105,
Improvement of video S / N ratio, chroma S / N ratio, and video frequency characteristics is required.

In order to improve the video S / N ratio and the chroma S / N ratio, the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film and the filling property are improved, and It is important to improve the surface smoothness of the magnetic recording medium, and as such magnetic particle powder, fine particles, and the particle size is uniform, dendritic particles are not mixed, and, It is required to have an appropriate axial ratio.

Next, in order to improve the video frequency characteristics, it is necessary for the magnetic recording medium to have a high coercive force and a large residual magnetic flux density Br. In order to increase the coercive force of the magnetic recording medium, the coercive force of the magnetic particle powder is required to be as high as possible.

Since the coercive force of magnetic particle powder is generally caused by its shape anisotropy, a high coercive force can be obtained by making the particles as fine as possible or by increasing the axial ratio of the particles. . For example, in Japanese Patent Publication No. 1-18961, "... Coercive force increases as the axial ratio increases, while the coercive force is affected by the particle size, and the particle size is larger than the particle size at which superparamagnetism appears. Becomes smaller, the target coercive force is
It is obtained by appropriately selecting the particle size and its axial ratio. "..." is as described.

Further, the coercive force distribution (SFD: Swi)
tching Field Distributio
n) is required to be excellent.

This fact is shown in FIG. 1 of Japanese Patent Laid-Open No. 63-26821 which shows the relationship between the SFD and the recording / reproducing output measured for the above magnetic disk. The relationship between the SFD and the recording / reproducing output is a straight line, as is apparent from FIG.
F. D. It can be seen that the recording / reproducing output can be increased by using a ferromagnetic powder having a small value. That is, in order to increase the recording / reproducing output, the S. F. D. The smaller the S.I., the smaller the S. F. D. is necessary. "..." is as described.

Further, the demand for these metal magnetic particle powders is not limited to the above, and it is also required that the fine particles mentioned above have a high coercive force and a large saturation magnetization value.
For example, in Japanese Patent Laid-Open No. 5-98321, "... In order to achieve high density of magnetic recording medium, the metal magnetic powder used is fine particles, high coercive force, high saturation magnetic flux density, In addition, it must have excellent dispersibility and oxidation stability .... The saturation magnetic flux density changes depending on the composition of the magnetic metal powder, the size of the particles, and the thickness of the oxide film. Considering the alloys mentioned above, the addition of cobalt is effective.
The saturation magnetic flux density also naturally increases. However, the axial ratio greatly affects the coercive force, so it cannot be made extremely small. "..." is as described.

That is, the magnetic material powder for the high density magnetic recording medium is fine particles, has a uniform particle size and does not contain dendritic particles, has a high coercive force, an excellent coercive force distribution and a large saturation magnetization. Value, and also excellent in oxidative stability.

Generally, the magnetic metal particle powder is obtained by heating, as necessary, goethite particles as a starting material, hematite particles obtained by heating and dehydrating the particles, or particles containing a different metal other than iron in these particles, In reducing gas,
It is obtained by heat reduction.

Conventionally, as a method of producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution has a pH of 11. As described above, a method of forming needle-shaped goethite particles by aerating an oxygen-containing gas at a temperature of 80 ° C. or less to carry out an oxidation reaction (Japanese Patent Publication No. 39-5).
No. 610, etc.-hereinafter "iron hydroxide-based goethite particles"
Say. -), A method of generating spindle-shaped goethite particles by passing an oxygen-containing gas through a suspension containing FeCO ₃ obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali carbonate to carry out an oxidation reaction (special feature KAISHO 50-80999, etc.-Hereinafter referred to as "iron carbonate-based goethite particles."-)
And a suspension containing FeCO ₃ or an iron-containing precipitate obtained by reacting an aqueous solution of a ferrous salt with an aqueous mixed solution of an alkali carbonate and an alkali hydroxide, by passing an oxygen-containing gas to perform an oxidation reaction Methods for producing goethite particles (Japanese Patent Laid-Open No. 2-51429, etc.-hereinafter referred to as "alkaline-based goethite particles"-) and the like are known.

As a prior art for obtaining metal magnetic particle powders using these goethite particle powders such as iron hydroxide-based goethite particles, iron carbonate-based goethite particles and alkali-based goethite particles as starting raw material particles, Japanese Patent Publication No. 55-29577.
Japanese Patent Publication No. 1-18961, Japanese Patent Publication No. 2-57
No. 122, Japanese Patent Publication No. 3-43323, and Japanese Patent Laid-Open No.
JP-A-3-222404, JP-A-3-49026, JP-A-4-63210, and JP-A-5-6216.
No. 6, JP-A-5-98321, and JP-A-6-2.
5702, JP-A-6-36265, JP-A-6-139553, JP-A-6-140222 and JP-A-6-215360.

[0018]

In the iron hydroxide-based goethite particles described above, needle-shaped goethite particles having a large axial ratio, particularly 10 or more, are produced, but dendritic particles are mixed.
Moreover, it cannot be said that the particle sizes are uniform. For example, it is produced by air-oxidizing a hydrolyzate of a ferrous salt with an alkali hydroxide described in JP-A-5-62166. According to this method, goethite particles are miniaturized. In order to achieve this, for example, water-soluble silicate is added to the reaction system .... Branches are likely to be generated in the particles .... The particle size distribution of the metal magnetic powder is broadened. Moreover, the above-mentioned alkali hydroxide method has a limit when trying to make the particle size distribution uniform.
Is as described. In addition, when a metal magnetic particle powder is used, a high coercive force is easily obtained, but it is difficult to reduce the particle size, and it is also difficult to obtain a uniform particle size. Hard to get.

The iron carbonate-based goethite particles described above are uniform in particle size, and spindle-shaped particles in which dendritic particles are not mixed are produced. On the other hand, the axial ratio is at most about 7, and the axial ratio Large particles are difficult to generate. For example, the above-mentioned Japanese Patent Laid-Open No. 5-6
No. 2166, “... Spindle-type goethite particles obtained by hydrolyzing ferrous salt with alkali carbonate and then air-oxidizing the particles to make the spindle-shaped goethite particles finer and uniform in particle size distribution. It is considered that it is difficult to increase the coercive force due to the small ratio and the shape anisotropy. Further, when the metal magnetic particle powder is used, there is a problem that it is difficult to obtain a high coercive force.

The above-mentioned alkali-based goethite particles can produce spindle-shaped particles having a uniform particle size and a large axial ratio. For example, in Japanese Patent Laid-Open No. 2-51429, "...
A spindle-shaped goethite particle having a large axial ratio (major axis diameter / minor axis diameter) can be obtained. "..." is as described. Further, it is easy to obtain metal magnetic particle powder having a higher coercive force than iron carbonate-based goethite particles.

Therefore, first, the above-mentioned respective prior arts in the case of obtaining metal magnetic particle powder using iron hydroxide-based goethite particles and iron carbonate-based goethite as starting material particles were examined.

Japanese Patent Publication No. 55-29577, Japanese Patent Publication No. 1-18961, and Japanese Patent Publication No. 2-5712.
No. 2, JP-B-3-43323, JP-A-3-49026, JP-A-5-62166, JP-A-5-98321 and JP-A-6-36265. In the technical means described in the publication,
In all cases, the coercive force Hc of the obtained metal magnetic particle powder was 18
It is 50 Oe or less.

According to the technical means described in JP-A-6-139553, the coercive force H of the obtained metal magnetic particle powder is obtained.
An example in which c exceeds 1850 Oe is also shown, but the particle size is 0.
It is a large one exceeding 2 μm.

In the technical means described in JP-A-63-222404 and JP-A-6-215360, which method is used for producing goethite particles is not described because no specific method is described. Unknown. However, when iron carbonate-based goethite particles are used as a starting material as described in the above-mentioned respective publications, fine particles of metal magnetic particles having a coercive force Hc exceeding 1850 Oe have not been obtained. It can be estimated that a coercive force Hc of 1850 Oe or more is obtained by using the system goethite particles.

Next, each of the above-mentioned prior arts was examined for the case where metal magnetic particle powder was obtained by using alkali-based goethite particles as starting material particles.

According to the technique described in JP-A-4-63210, an iron-containing precipitate obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkaline carbonate and an aqueous solution of an alkaline hydroxide as an alkaline aqueous solution. The axial ratio can be further improved when a zinc compound is present in a suspension containing the above. In particular, spindle-shaped goethite particles having an axial ratio of 15 or more (Applicant's note: iron carbonate-based goethite Particles) and the coercive force of the obtained metal magnetic particle powder can be increased, but it is still 185.
Nothing exceeding 0 Oe has been obtained.

For the combined use of an aqueous solution of alkali carbonate and an aqueous solution of alkali hydroxide, the above-mentioned JP-A-6-2570 is used.
There is Example 9 in the technical means described in Japanese Patent Publication No. 2 and Example 6 and 7 in the technical means described in Japanese Unexamined Patent Publication No. 6-140222, and in particular, Japanese Unexamined Patent Publication No. 6-2570.
In Example 9 of Japanese Patent Laid-Open No. 2 and Japanese Patent Application Laid-Open No. 6-140222, it is unclear because the axial ratio is not described, but in the case of using an alkaline carbonate aqueous solution and an alkaline hydroxide aqueous solution together. Since spindle-shaped goethite particles having a relatively large axial ratio are easily obtained, the use of spindle-shaped goethite particles having a large axial ratio does not give a metallic magnetic powder of about 1800 to 1850 Oe. It can be estimated that

From these results, when the above-mentioned conventional goethite particles were used as the starting material particles to obtain the metal magnetic particle powder, the particles were fine particles, the particle sizes were uniform, and the dendritic particles were not mixed, A metal magnetic particle powder having an appropriate axial ratio, a high coercive force, an excellent coercive force distribution and a large saturation magnetization value, and excellent oxidative stability and well-balanced properties is obtained. Absent.

Therefore, the present invention provides a magnetic particle powder, in particular,
It is a fine particle, has a uniform particle size, does not contain dendritic particles, and has a high coercive force, especially a coercive force Hc of 18
Starting material particles from which a spindle-shaped metal magnetic particle powder having 50 to 2500 Oe and a saturation magnetization value of 135 emu / g or more, that is, iron carbonate-based goethite particles in which alkali carbonate and alkali hydroxide are used in combination, In particular, the average major axis diameter is 0.05 to 0.15 μm, the axial ratio is 4 to 8, the X-ray particle size ratio is in the range of 2.0 to 3.5, and
A technical object is to obtain a spindle-shaped goethite particle powder containing cobalt having a uniform particle size and containing no dendritic particles.

[0030]

The above technical problems can be achieved by the present invention as follows.

That is, in the present invention, cobalt is contained in the spindle-shaped goethite particle powder in an amount of 8 to 50 atomic% in terms of Co based on the total Fe, and the average major axis diameter is 0.05 to 0.15 μm and the average minor axis is. Diameter is 0.010 to 0.025 μm, axial ratio is 4 to 8
And (D ₀₂₀ / D ₁₁₀ ) is in the range of 2.0 to 3.5, which is a spindle-shaped goethite particle powder containing cobalt.

In the present invention, a suspension containing an iron-containing precipitate obtained by reacting an aqueous solution of an alkaline carbonate and an aqueous solution of an alkaline hydroxide with an aqueous solution of a ferrous salt is used under a non-oxidizing atmosphere. After maintaining and stirring for aging, an oxygen-containing gas is passed through the suspension to carry out an oxidation reaction to produce spindle-shaped goethite particles, thereby producing a spindle-shaped goethite particle powder. In any one of the suspensions containing the iron-containing precipitate before aging,
The molar ratio to the alkali carbonate aqueous solution is 0.2 to 1.
The total amount of the alkali carbonate aqueous solution and the alkali hydroxide aqueous solution is set to 1.3 to 2.5 equivalents relative to the total Fe in the ferrous iron salt aqueous solution by adding the alkali hydroxide aqueous solution of 2. S in an aqueous solution of an iron salt solution, an aqueous solution of alkali carbonate, an aqueous solution of alkali hydroxide, or a suspension containing an iron-containing precipitate before the aging,
One or two or more compounds selected from the elements of i, Nd, Y, La, Ce, Pr and Tb are added in an amount of 0.1 to 1.0 in terms of elements with respect to all Fe in the aqueous solution of ferrous salt. The Co compound is added in the range of atomic% and in any one of the aqueous solution of the ferrous salt, the suspension containing the iron-containing precipitate before the aging and the suspension in the course of aging. Is 8 to 50 atom% in terms of Co with respect to all Fe in the aqueous solution of the ferrous salt.
In the range of 20 to 50% of the total Fe in the aqueous solution of ferrous salt, the oxidation rate of Fe ²⁺ in the oxidation reaction solution is 20 to 50%, and Under the same conditions as Al, Si, Nd, Y, La, Ce, P
One or two or more compounds selected from the elements of r and Tb are added in the range of 0.1 to 10.0 atomic% in terms of elements with respect to the total Fe in the ferrous salt aqueous solution. This is a method for producing a spindle-shaped goethite particle powder containing cobalt.

The structure of the present invention will be described in detail below.

First, the spindle-shaped goethite particle powder containing cobalt according to the present invention will be described.

The spindle-shaped goethite particle powder according to the present invention has an average major axis diameter of 0.05 to 0.15 μm, an average minor axis diameter of 0.010 to 0.025 μm, and an axial ratio of 4 to 8,
Further, it is a spindle-shaped goethite particle powder containing Co, which has a (D ₀₂₀ / D ₁₁₀ ) in the range of 2.0 to 3.5.

The average major axis diameter is 0.05 to 0.15 μm. When it is less than 0.05 μm, the particle size of the metal magnetic particle powder is also small, and the particle size is close to the superparamagnetic region, so that the saturation magnetization value is decreased and the coercive force is also decreased. 0.
When it exceeds 15 μm, a large saturation magnetization value is easily obtained, but it is difficult to obtain a high coercive force within the range of the axial ratio in the present invention. The preferred range is 0.05 to 0.1
It is in the range of 2 μm.

The minor axis diameter is 0.010 to 0.025 μm. When it is less than 0.010 μm, the particle size of the metal magnetic particle powder is also small, and the particle size is close to the superparamagnetic region, so that the saturation magnetization value is decreased and the coercive force is also decreased.
When it exceeds 0.025 μm, it becomes difficult to obtain a high coercive force within the range of the axial ratio in the present invention. A preferred range is 0.010 to 0.020 μm.

The axial ratio is in the range of 4-8. When it is less than 4, it becomes difficult to obtain a metal magnetic particle powder having a high coercive force. When it exceeds 8, a high coercive force tends to be obtained, but a large saturation magnetization value is difficult to obtain.

The X-ray particle size (D ₀₂₀ ) is 160 to 300Å. When it is less than 160Å, it is difficult to obtain a metal magnetic particle powder having a high coercive force. If it exceeds 300Å, the minor axis diameter becomes too large and the axial ratio decreases, making it difficult to obtain metal magnetic particle powder with high coercive force. The preferred range is 18
It is 0 to 280Å.

The X-ray particle size (D ₁₁₀ ) is 70 to 200Å. When it is less than 70Å, it is difficult to obtain a metal magnetic particle powder having a high coercive force. If it exceeds 200 Å, the minor axis diameter becomes too large and the axial ratio decreases, making it difficult to obtain a metal magnetic particle powder having a high coercive force. The preferred range is 80-1
It is 50Å.

(D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5. When it is less than 2.0, the effect for obtaining the metal magnetic particle powder having a high coercive force is not sufficient. When it exceeds 3.5, the minor axis diameter becomes too large and the axial ratio decreases, and it becomes difficult to obtain a metal magnetic particle powder having a high coercive force. A preferred range is 2.1 to 3.1.

The content of cobalt in the spindle-shaped goethite particle powder according to the present invention is in the range of 8 to 50 atomic% in terms of element based on the total Fe in the spindle-shaped goethite particle powder. A preferred range is 9 to 43 atomic%. It is more preferably in the range of 9 to 36 atomic%.

Al, Si, Nd, Y, La, Ce and P contained in the spindle-shaped goethite particle powder according to the present invention.
The content of one or more compounds selected from the elements of r and Tb is 10.0 atom% or less in terms of element based on the spindle-shaped goethite particle powder.

Next, generation of the spindle-shaped goethite particle powder according to 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.

Examples of the alkali carbonate aqueous solution used in the present invention include sodium carbonate aqueous solution, potassium carbonate aqueous solution and ammonium carbonate aqueous solution.

Examples of the aqueous alkali hydroxide solution used in the present invention include sodium hydroxide and potassium hydroxide.

In the present invention, the alkali carbonate aqueous solution and the alkali hydroxide aqueous solution are used together. When the alkaline carbonate aqueous solution is used alone, it is difficult to obtain metal magnetic particles having a large coercive force Hc. Further, when the aqueous solution of alkali hydroxide is used alone, it is difficult to obtain goethite particles having a uniform particle size and, in addition, dendritic particles may be mixed. It is difficult to obtain powder.

For the alkali hydroxide aqueous solution, an alkali hydroxide aqueous solution having a molar ratio of 0.2 to 1.2 is added to the alkali carbonate aqueous solution. When it is less than 0.2 mol, the coercive force H is the same as when the alkali carbonate aqueous solution is used alone.
It is difficult to obtain metal magnetic particles having a large c. When the amount exceeds 1.2 mol, it is difficult to obtain goethite particles having a fine particle size and a uniform particle size, and dendritic particles may coexist as in the case of using the alkali hydroxide aqueous solution alone. However, granular particles may be mixed. Therefore, it is difficult to obtain a metal magnetic particle powder having fine particles and a uniform particle size. A preferred range is 0.3 to 1.0 mol.

The total amount of the alkali carbonate aqueous solution and the alkali hydroxide aqueous solution was 1.
When the amount is 3 to 2.5 equivalents and less than 1.3 equivalents, granular particles may coexist. When it exceeds 2.5 equivalents, it is difficult to obtain goethite particles having a uniform particle size. A preferred range is 1.4 to 2.4 equivalents.

Therefore, the pH value of the reaction solution is 7.0 to 1 as in the case of the usual iron carbonate-based goethite particle formation reaction.
It is in the range of 1.0, and more preferable pH value is 8.0 to 1.
It is 0.0.

In the present invention, the aqueous alkali hydroxide solution is added in any one of the suspensions containing the aqueous alkali carbonate solution and the iron-containing precipitate before aging. It is particularly preferable to add it to the aqueous solution of alkali carbonate.

The aging in the present invention is carried out by maintaining and stirring in the range of 2.0 to 7.0 hours in a non-oxidizing atmosphere.
When the aging time is less than 2.0 hours, it is difficult to obtain fine goethite particles, and when it exceeds 7.0 hours,
The goethite particles that are the object of the present invention can be obtained, but there is no point in making them longer than necessary. The preferred range is 3 to 5 hours.

The aging temperature in this case is in the range of 40 to 60 ° C. When the temperature is lower than 40 ° C., the size of the goethite particles is small, but it is difficult to obtain the one having an appropriate axial ratio. When it exceeds 60 ° C, it is difficult to obtain goethite particles having small particles. A preferred range is 45 to 55 ° C.

The non-oxidizing atmosphere can be formed by ventilating an inert gas (N ₂ gas or the like) into the suspension reaction vessel.

In the present invention, Si, Nd, is added to any one of a ferrous salt aqueous solution, an alkali carbonate aqueous solution, an alkali hydroxide aqueous solution, and a suspension containing an iron-containing precipitate before the aging. One or more compounds selected from the elements Y, La, Ce, Pr and Tb are added. The reason for the addition timing is that the grain shape and the crystal plane growth property of the present invention are taken into consideration. Specifically, the axial ratio is 4 to 8, and (D ₀₂₀ / D ₁₁₀ ) is 2.0-
This is to obtain 3.5 goethite particles.

Examples of the Si compound in this case include sodium silicate, potassium silicate, and water glass.

As the elements of Nd, Y, La, Ce, Pr and Tb, water-soluble salts such as sulfate, chloride and nitrate of each element can be used.

Si, Nd, Y, La, Ce, Pr, Tb
The addition amount of one or more compounds selected from the above elements is in the range of 0.1 to 1.0 atomic% with respect to the total Fe in the aqueous ferrous salt solution. When it is less than 0.1 atomic%, it becomes difficult to obtain the high coercive force and the large saturation magnetization value which are the objects of the present invention. When it exceeds 1.0 atom%, the ratio becomes too smaller than the axial ratio aimed at by the present invention, and it becomes difficult to obtain a metal magnetic particle powder having a high coercive force. The preferable range of the Si compound is 0.1 to 0.5 atom%, and more preferably 0.1 to 0.3 atom%. Also, N
The preferable range of the compound selected from the elements of d, Y, La, Ce, Pr and Tb is 0.1 to 0.5 atom%.

When adding each of the above compounds, it is possible to quickly stir the solution by adding it as an aqueous solution dissolved in water.
It is preferable because it can be dispersed.

Examples of the Co compound used in the present invention include cobalt sulfate, cobalt acetate, cobalt chloride and cobalt nitrate.

The amount of the Co compound is 8 to 50 atom% in terms of Co based on the total Fe in the aqueous ferrous salt solution. When it is less than 8 atomic%, it becomes difficult to form fine particles, and it becomes difficult to obtain a metal magnetic particle powder having a high coercive force, a large saturation magnetization value and an oxidation stability. When it exceeds 50 atomic%, the saturation magnetization value is lowered. A preferred range is 9 to 43 atomic%. More preferably 9 to 3
It is in the range of 6 atom%.

The Co compound is added at any one of the aqueous solution of the ferrous salt, the suspension containing the iron-containing precipitate before aging, and the suspension during aging. If added after starting the oxidation reaction, fine goethite particles cannot be obtained. A preferred range is from immediately after the start of aging to 120 minutes after the start of aging.

When the Co compound is added, it is preferable to add it as an aqueous solution dissolved in water because it can be rapidly stirred and dispersed in the solution.

The temperature range of the oxidation reaction in the present invention is 40.
~ 60 ° C. If the temperature is lower than 40 ° C., fine goethite particles can be obtained, but the ratio is smaller than the axial ratio targeted by the present invention. When the temperature exceeds 60 ° C., fine goethite particles as the object of the present invention are obtained, but granular particles may coexist. A preferred range is 45 to 55 ° C.

In the present invention, one or more compounds selected from the elements of Al, Si, Nd, Y, La, Ce, Pr and Tb are added to the liquid in the middle of the oxidation reaction. In this case, the addition timing is such that the oxidation rate of Fe ²⁺ in the oxidation reaction liquid is 20 relative to the total Fe in the ferrous salt aqueous solution.
The solution is in the middle of the oxidation reaction in the range of 50%. When the oxidation rate is less than 20%, the ratio becomes lower than the axial ratio aimed at by the present invention, and it becomes difficult to obtain high coercive force metal magnetic particles. When it exceeds 50%, it becomes impossible to obtain a metal magnetic particle powder satisfying the high coercive force and the large saturation magnetization value which are the objects of the present invention. The preferred range is 30 to 5
It is in the range of 0%.

As the Al compound, aluminum sulfate,
Examples thereof include aluminum chloride, aluminum nitrate, sodium aluminate, potassium aluminate, ammonium aluminate and the like.

Further, Si, Nd, Y, La, Ce, P
One or more compounds selected from the elements of r and Tb are the same as the above compounds.

Al, Si, Nd, Y, La, Ce, P
The addition amount of one or more compounds selected from the elements of r and Tb is 0.1 to 10.0 atomic% with respect to the total Fe in the aqueous ferrous salt solution. If it is less than 0.1 atom%, it becomes difficult to obtain the effect of preventing sintering in the heat treatment step. If it exceeds 10.0 atomic%, the ratio becomes smaller than the axial ratio aimed at by the present invention, and it becomes impossible to obtain a metal magnetic particle powder having a high coercive force. Further, when the number of compounds that do not participate in magnetization increases, the saturation magnetization value also decreases. A preferable range is 0.5 to 6.0 atomic%.

The preferable amount of Al compound added is 0.1.
To 3.0 at%, and the preferable addition amount of the Si compound is 0.5 to 2.0 at%. Also, N
1 selected from elements of d, Y, La, Ce, Pr and Tb
The preferable addition amount of one kind or two or more kinds of compounds is 1.0 to
It is in the range of 2.0 atom%.

When these compounds are added in combination, the total amount of the compounds added is 0.1 to 10.0 atomic% with respect to the total Fe in the aqueous ferrous salt solution.
Can be added in an amount in the range. 0.1
If it is less than atomic%, the effect of preventing sintering is not sufficient,
When the metal magnetic particles containing iron as the main component are used, the oxidation stability and coercive force cannot be improved sufficiently. If it exceeds 10.0 atomic%, the ratio becomes smaller than the axial ratio aimed at by the present invention, and it becomes impossible to obtain a metal magnetic particle powder having a high coercive force. Further, when the number of compounds that do not participate in magnetization increases, the saturation magnetization value also decreases. Further, the reduction time may be long. A preferable range is 0.5 to 6.0 atomic%.

It is preferable that the Al compound is solid-dissolved on the surface of the goethite particles, which is excellent in shape retention and oxidation stability when the magnetic metal particles containing iron as a main component are used. Not only that, when used as a magnetic recording medium, the compatibility with the binder resin is improved, and the dispersibility and durability are also excellent. Therefore, A
It is preferable to use the 1 compound and the above compounds other than the Al compound in combination.

Further, when the Si element is used, the sintering preventing effect is particularly excellent, and when the compound of the rare earth element such as Nd is used, the sintering preventing effect can be exhibited and the base Since it is a volatile substance, it is used for magnetic recording media.
COOM, -SO ₃ M (M is a metal) can be improved conformability also good dispersibility with the binder resin having an acidic functional group, such as.

Therefore, it is preferable that the addition of each of the above-mentioned compounds is appropriately combined with the combination of the above-mentioned each compound and the addition amount thereof in accordance with the purpose in the range where the oxidation rate of the oxidation reaction is in the range of 20 to 50%.

When adding each compound, it is preferable to add it as an aqueous solution dissolved in water because it can be rapidly stirred and dispersed in the solution.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid, and mechanical stirring may be used together.

The spindle-shaped goethite particles produced in the present invention are filtered, washed with water and dried by a conventional method to obtain a particle powder.

[0078]

The operation of the present invention having the above-described structure is as follows.

Conventionally, in the case of obtaining a magnetic particle powder, particularly a metal magnetic particle powder having a high coercive force, the coercive force of the magnetic particle powder is caused by its shape anisotropy as described above. Therefore, it is necessary to make the particles as fine as possible or to increase the axial ratio of the particles.

That is, when iron hydroxide-based goethite particles are used as a starting material, metal magnetic particle powder containing iron as a main component and having a high coercive force exceeding 1850 Oe is utilized by utilizing the characteristic large axial ratio. Has been obtained,
When iron carbonate-based goethite particles are used as the starting material, it is difficult to obtain fine metal magnetic particles having a high coercive force Hc exceeding 1850 Oe.

Therefore, the present inventor has used, as a starting material, goethite particles in combination with alkali, and has the above-mentioned balanced characteristics, in particular, an average major axis diameter of 0.05 to 0.12 μm, and a coercive force. Efforts were made to obtain a spindle-shaped metallic magnetic particle powder having an Hc of 1850 to 2500 Oe and a saturation magnetization value of 135 emu / g or more.

The above-mentioned Japanese Patent Publication No. 1-18961, "...
The coercive force increases as the axial ratio increases. On the other hand, the coercive force is affected by the particle size, and becomes larger as the particle size becomes smaller than the particle size at which superparamagnetism appears. Therefore, the target coercive force can be obtained by appropriately selecting the particle size and its axial ratio. I thought about the description "...".

As described above, the average major axis diameter is 0.
05-0.15 μm, average minor axis diameter of 0.010-0.0
25 μm, the axial ratio is 4 to 8, and (D ₀₂₀ / D
It has been found that the spindle-shaped goethite particle powder according to the present invention having a ₁₁₀ ) of 2.0 to 3.5 is suitable.

The spindle-shaped goethite particles having an axial ratio of 4 to 8 are not so different as compared with the conventional spindle-shaped goethite particles, but the conventional spindle-shaped goethite particles have the same axial ratio (D ₀₂₀ / D).
₁₁₀ ) is 1.5 to 1.9, and it is difficult to obtain metal magnetic particles having a high coercive force. However, the spindle-shaped goethite particles according to the present invention have an average major axis diameter of 0.05 to 0.1.
Even if the axial ratio is 5 μm and the axial ratio is 4 to 8, (D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5, which is a large difference.

This difference of (D ₀₂₀ / D ₁₁₀ ) is due to the fact that the crystal planes are produced with different degrees of growth. It was possible to influence the degree of growth of this crystal plane by any one of the aqueous solution of ferrous salt, aqueous solution of alkali carbonate, aqueous solution of alkali hydroxide and suspension containing iron-containing precipitate before aging. Si, Nd, Y, La, Ce, P added in
It has been found that it is an effect of one or more compounds selected from the elements of r and Tb.

Concerning the growth degree of the crystal plane, the role of increasing the axial ratio by the combined use of alkali carbonate and alkali hydroxide and the above-mentioned Si, Nd,
The addition of one or more compounds selected from the elements of Y, La, Ce, Pr, and Tb suppresses the axial ratio from increasing, and the Co compound is added. It is considered that the above acts toward the formation of fine particles, and further, the seed crystal particles of the spindle-shaped goethite particles are generated by the aging reaction for a long time.

Then, the seed crystal particles are added to Al, Si, Nd, Y, La, Ce, Pr, and T in a liquid during the oxidation reaction in which the oxidation degree in the oxidation reaction is in the range of 20 to 50%.
By adding one or more compounds selected from the element b, the effect of promoting growth in the minor axis direction rather than growth in the major axis direction overlaps, and the axial ratio according to the present invention is 4 to 4. 8 and (D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5.
It is considered that the spindle-shaped goethite particles that are

The alkali hydroxide-based goethite particles and the alkali carbonate-based goethite particles have the axial ratio (D
₀₂₀ / D ₁₁₀ ) and the average major axis diameter and (D ₀₂₀ / D
₁₁₀ )) and the goethite particles satisfying the relationship cannot be obtained, and since the spindle-shaped goethite particles according to the present invention cannot be obtained even when the kind of the compound to be added is changed or when the addition time is changed. is there.

When the spindle-shaped goethite particles according to the present invention thus obtained are used as the starting material particles and the spindle-shaped metal magnetic particles are obtained by a conventional method, the degree of crystal plane growth of the spindle-shaped goethite particles is different from that of the conventional reaction. And one or more compounds selected from the added elements of Al, Si, Nd, Y, La, Ce, Pr, and Tb are dissolved in the goethite particles to be formed, and therefore, during heat reduction It is also difficult to cause shape destruction of the above, and a high coercive force can be obtained even though the axial ratio of the obtained metal magnetic particles is as small as 4 to 7.

Further, the fact that the degree of growth of the crystal plane of the spindle-shaped goethite particles is different from that in the conventional reaction and that Co is contained in the spindle-shaped goethite particles causes the formation of primary particles in the particles in the heat reduction treatment in the case of metal magnetic particles. Since the growth can be performed easily and uniformly, a large saturation magnetization value can be obtained.

The method of introducing Co includes a method of adding it during the reaction of forming the spindle-shaped goethite particles and a method of coating the obtained spindle-shaped goethite particles, and the former method is larger. A saturated magnetization value is easily obtained, and in the latter case compared to the former case, the solid solution / diffusion inside the particles is insufficient due to the heat treatment by heat dehydration or heat reduction of Co coated / adsorbed on the surface. Moreover, I think that it may be difficult to obtain a large saturation magnetization value.

[0092]

The present invention will be described below with reference to Examples and Comparative Examples.

The major axis diameter, minor axis diameter and axial ratio of the particles in the following Examples and Comparative Examples are all shown as the average of the numerical values measured from electron micrographs, and the specific surface area of the particles is BE.
The value measured by the T method is shown.

The X-ray particle size is the grain size of crystallites measured by the X-ray diffraction method in the case of goethite particle powder (02
0) and (110) crystal planes represent the crystal grain diameters in the directions perpendicular to the (110) crystal planes in the metal magnetic particle powder, and the measurement was
From the line profile of the diffraction lines of the (020) plane and the (110) plane of the crystal, the value calculated using the following Scherrer's formula is shown.

D (X-ray particle size) = Kλ / β cos θ where β = half-width of true diffraction peak after subtracting machine width by device K = Scherrer constant (0.9) λ = wavelength of characteristic X-ray θ = Diffraction angle

The content of each element such as Co, Al, Si, Nd, Y, and Ce is "high frequency plasma emission spectroscopic analyzer ICAP-575" (Japan Jarrell Ash Co., Ltd.).
It was shown by the value measured using the product.

The degree of oxidation was indicated by a value determined by redox titration by displacing the reaction solution with an inert gas and heating and dissolving with a mixed acid of sulfuric acid and phosphoric acid while ventilating.

The magnetic characteristics and coating characteristics of the metallic magnetic particle powder were measured by using a "vibrating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.) under an external magnetic field of 10 KOe.

Oxidation stability is the rate of decrease of the saturation magnetization value (Δσ) after standing for 1 week in an atmosphere of 60 ° C. and 90% relative humidity.
It is a value obtained by obtaining s).

The square shape of the coating film and the S.M. F. D. The measurement of
The test was performed using the sheet sample piece obtained by the method of Reference Example 1 below. Also, S. F. D. Is to obtain a differential curve of the demagnetization curve of the magnetic hysteresis curve using the differential circuit of the magnetic measuring instrument, measure the half width of this curve, and divide this value by the coercive force of the peak value of the curve. Sought by.

<Production of Goethite Particle Powder> Examples 1 to 15 and Comparative Examples 1 to 6;

Example 1 Na ₂ CO ₃ was added to a reaction vessel kept in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 50 l / min.
20 l of an aqueous solution containing 5 mol and 10 l of an aqueous solution containing 18 mol of NaOH (corresponding to a molar ratio of 0.72 with respect to Na ₂ CO ₃ .: The total amount of Na ₂ CO ₃ and NaOH corresponds to 1.70 equivalent to all Fe. And 3 No. 3 water glass so as to contain 0.25 atom% in terms of Si with respect to total Fe, and then 20 l of an aqueous ferrous sulfate solution containing 20 mol of total Fe is added and mixed (total Fe concentration is 0.4 mol /
corresponds to l. ) And an iron-containing precipitate was formed at a temperature of 47 ° C.

The above suspension containing the iron-containing precipitate was kept at a temperature of 47 ° C. for 60 minutes while continuously blowing N ₂ gas at a rate of 50 l / min.
After adding a cobalt sulfate aqueous solution so as to contain 18 atomic% in terms of conversion, it was held for another 4 hours for aging.

90 l / min of air was passed through the suspension liquid containing the iron-containing precipitate after aging at a temperature of 47 ° C., and the oxidation rate of the oxidation reaction reached 40%. No. 3 water glass solution was added so as to contain 1.75 atom% in terms of Si, and 100 was added under the same conditions as the above oxidation reaction conditions.
The oxidation reaction was continued for a minute to generate yellowish brown precipitate particles.
The pH during aeration of air is 8.0 to 9.5,
The oxidation reaction time was 220 hours.

The yellowish brown precipitated particles were separated by filtration, washed with water, dried and pulverized by a conventional method to obtain about 2 kg of yellowish brown particle powder.

The obtained yellowish brown precipitate particles were goethite, and the major axis diameter was 0.108 μm and the minor axis diameter was 0.016 μm as shown in the electron micrograph (× 30000) of FIG.
m, the axial ratio was 6.8, and (D ₀₂₀ / D ₁₁₀ ) was 2.26, and the dendritic particles were not mixed at all, and the particle size was uniform. Further, the spindle-shaped particles had a Co content of 17.94 atomic% and a Si content of 1.93 atomic%.

Examples 2 to 15 and Comparative Examples 1 to 6 In the reaction of forming FeCO ₃ or iron-containing precipitates, the amount of the alkali carbonate aqueous solution used, the amount of the alkali hydroxide aqueous solution used, the addition timing and the alkali ratio (NaOH / Na ₂ C
(O ₃ : molar ratio), presence or absence of compound to be added before aging, kind, addition amount and addition timing, temperature and time in aging step, addition amount and addition timing and time of Co compound, temperature in oxidation step, oxidation Goethite particles were generated in the same manner as in Example 1 except that the type of compound added during the process, the amount added, and the timing of addition (oxidation rate) were variously changed.

The main manufacturing conditions at this time are shown in Tables 1 to 4,
The characteristics of the produced goethite particles are shown in Tables 3 and 4.

[0108]

[Table 1]

[0109]

[Table 2]

[0110]

[Table 3]

[0111]

[Table 4]

<Production of Metallic Magnetic Particle Powder> Reference Example 1 An amount of presscake corresponding to 800 g of the spindle-shaped goethite particles obtained in Example 1 was suspended in 15 l of water.
The pH of the suspension at this time was 8.5.

Then, aluminum nitrate nonahydrate was added to the above suspension so as to be 10% by weight based on the goethite particles.
Neodymium nitrate hexahydrate and 10% to 7% by weight
Cobalt acetate tetrahydrate and so that the weight%
Further, boric acid was added to the goethite particles so as to be 15% by weight and stirred for 10 minutes. P of the suspension at this time
H was 4.5.

Further, an aqueous ammonia solution was added to adjust the pH to 9.5, and the mixture was filtered by a filter press and dried to obtain goethite particles coated with Al, Nd, Co and B compounds.

The goethite particle powder coated with Al, Nd, Co and B compounds was heat-treated in air at 400 ° C. to obtain a spindle-shaped hematite particle powder.

100 g of the obtained fusiform hematite particle powder coated with Al, Nd, Co and B compounds was charged into a fixed bed reducing apparatus having an inner diameter of 72 mm, and H ₂ gas was aerated at a rate of 35 l / min. Then, the reduction was completed when the exhaust gas dew point reached −30 ° C. at the reduction temperature of 420 ° C. At this time, the reduction time was 370 minutes.

[0117] After the reduction, once substituted with N ₂ gas, N ₂ gas 50 l / min while flowing 40 ° C. The H ₂ gas
Cooled down. Then, while maintaining the furnace temperature at 40 ° C, N
₂ gas 50l / min gas 0.2l / mi
A mixed gas of N ₂ gas and air mixed in a ratio of n was aerated. After the exothermic peak was observed due to the oxidation reaction at the mixed gas ratio, the air amount was increased to 0.4 l / min to increase the air ratio in the mixed gas. In this way, after the exothermic peak due to the oxidation reaction at the mixed gas ratio is observed, the air mixing ratio is increased stepwise by the method of increasing the ratio of air in the mixed gas, and finally 0.6 l of air is added. /
Oxidation treatment was continued with a mixed gas of a ratio of min / N ₂ gas of 50 l / min, and the heat treatment due to oxidation disappeared until the temperature of the product reached about 40 ° C., which was almost the same as the furnace temperature. During this time, the temperature of the product reached a maximum of 75 ° C.

Then, the furnace temperature is set to 40 ° C. and the N ₂ gas flow rate is set to 50.
While maintaining 1 / min, the air mixing ratio was gradually increased to finally set the air amount to 10 l / min. During this time,
No fever was observed. Further, the mixture was cooled to room temperature while ventilating a mixed gas of N ₂ gas and air under the same conditions.

After the air flow rate was once stopped and the atmosphere was replaced with N ₂ gas, the thus obtained spindle-shaped metallic magnetic particle powder mainly composed of iron having an oxide film formed on the surface was recovered.

This spindle-shaped metal magnetic particle powder has an average major axis diameter of 0.085 μm, an average minor axis diameter of 0.013 μm and an axial ratio of 6.5, as shown in the electron micrograph (× 30000) of FIG. , (D ₁₁₀ ) was 148Å, and the particle size was uniform and the number of dendritic particles was small. The magnetic characteristics are
Coercive force Hc is 2032 Oe, saturation magnetization σs is 138 em
u / g, squareness ratio r / s is 0.518, Δσs is -15%
And the Co content is 20.23 atomic% (the coated Co content is 11.0% based on the total Co), and Si is 1.93.
At%, Al was 2.91 at%, Nd was 1.53 at%, and B was 1.28 at%.

<Production of Coating Film> Reference Example 2 100 parts by weight of the spindle-shaped metal magnetic particle powder obtained in Reference Example 1 and a 30 atomic% cyclohexanone solution in a vinyl chloride copolymer resin MR- having a strong polar functional group. 50 parts by weight of 110 (manufactured by Nippon Zeon Co., Ltd.) were kneaded with a 88 cc plastomill for 50 minutes to obtain a kneaded product.

This kneaded product was placed in a 140 cc glass bottle in the following proportions and mixed and dispersed for 6 hours to apply a magnetic coating material on a polyethylene terephthalate film having a thickness of 25 μm to a thickness of 50 μm using an applicator. Then, it was dried in a magnetic field of 8KGauuss to produce a coating film, and a sheet sample piece was prepared.

Kneaded product 100 parts by weight 1 mmφ glass beads 530 parts by weight Cyclohexanone 50 parts by weight Methyl ethyl ketone 57 parts by weight Toluene 57 parts by weight

The coercive force Hc of the coating film obtained from this sheet sample piece was 2114 Oe, the orientation degree SQ was 0.882, and the S.I.
F. D. Was 0.391.

[0125]

The spindle-shaped goethite particle powder containing cobalt according to the present invention has fine particles, particularly, an average major axis diameter of 0.05 to 0.15 μm and an axial ratio of 4 to 8, and (D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5.
It is possible to obtain the spindle-shaped goethite particle powder containing cobalt in which the particle size is uniform and dendritic particles are not mixed.

Therefore, it is a magnetic particle powder, in particular, a fine particle, the particle size is uniform, and dendritic particles are not mixed,
And, since it is obtained by the spindle-shaped metal magnetic particle powder containing cobalt and iron as the main components, which has a high coercive force, an excellent coercive force distribution and a large saturation magnetization value, a high recording density, a high sensitivity,
It is suitable as a starting material powder of a magnetic material powder for a high output magnetic recording medium.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 1.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 10.

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 14.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 1.

5 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 5. FIG.

6 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particle powder obtained in Reference Example 1. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01F 1/36

Claims (2)

[Claims] 1. Cobalt is contained in the spindle-shaped goethite particle powder in an amount of 8 to 50 atom% based on the total Fe in terms of Co, the average major axis diameter is 0.05 to 0.15 μm, and the average minor axis diameter is 0.
010 to 0.025 μm, axial ratio (major axis diameter / minor axis diameter) is 4
Spindle-shaped goethite particle powder containing cobalt, characterized in that the X-ray particle size ratio (D ₀₂₀ / D ₁₁₀ ) is in the range of 2.0 to 3.5. 2. A suspension containing an iron-containing precipitate obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide is stirred and maintained under a non-oxidizing atmosphere. After aging, in a method for producing a spindle-shaped goethite particle powder for generating spindle-shaped goethite particles by aerating an oxygen-containing gas in the suspension to carry out an oxidation reaction, the alkali carbonate aqueous solution and before aging By adding an aqueous solution of alkali hydroxide having a molar ratio of 0.2 to 1.2 to the aqueous solution of alkali carbonate into one of the suspensions containing the iron-containing precipitate, The total amount of the aqueous solution of alkali hydroxide is 1.3 to 2.5 equivalents relative to the total Fe in the aqueous solution of ferrous salt, and further, the aqueous solution of ferrous salt, the aqueous solution of alkali carbonate, and the aqueous solution of alkali hydroxide. And in any of the liquid in the suspension containing the iron-containing precipitate before performing the aging, Si,
0.1 to 1.0 atomic% in terms of element, based on the total Fe in the ferrous salt aqueous solution, of one or more compounds selected from the elements of Nd, Y, La, Ce, Pr, and Tb. In the liquid of any one of the ferrous salt aqueous solution, the suspension containing the iron-containing precipitate before the aging and the suspension in the course of aging, the Co compound is added in the range of Total Fe in ferrous salt solution
With respect to Co in the range of 8 to 50 atomic%, and the oxidation rate of Fe ²⁺ in the oxidation reaction solution is in the range of 20 to 50% with respect to the total Fe in the ferrous salt solution. Under the same conditions as in the above-mentioned oxidation reaction, A
1 to 2 or more compounds selected from the elements of 1, Si, Nd, Y, La, Ce, Pr, and Tb with respect to all Fe in the aqueous solution of ferrous salt in an amount of 0.1 to 10 in terms of elements. A method for producing a spindle-shaped goethite particle powder containing cobalt, characterized in that it is added in a range of 0.0 atomic%.