JPH11329816A - Manufacture of co containing needle like goethite fine particles and co containing needle like magnetic fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve needle like property as a fine particle shape by specifying Co/Fe ratio in Co containing needle-like goethite fine particle, adding alkali carbonate to soil suspension thereof to specify the mole ratio of carbonate ion to ferric ion and aging it. SOLUTION: A ferric salt solution containing Co salt is adjusted by dissolving Co salt and ferric salt to water. In the process, the ratio of Co salt to ferric salt is selected to make Co/Fe ratio in finally obtained Co containing needle like goethite fine particles which does not exceed about 15 at%. Then, strong akalline solution is mixed with the Co salt containing ferric salt solution and is agitated, and soil suspension is formed. Alkali carbonate is added to the soil suspension to make the mole ratio of carbonate ion to ferric ion to be about 6.0 or more and about 10.0 or less and is aged. Thereby, twin-free Co containing needle-like goethite fine particles which have fine grain diameter and are superior in needle-like property is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing Co-containing acicular goethite fine particles and Co-containing acicular magnetic fine particles. The present invention relates to a method for producing ac-containing acicular goethite fine particles, and to Co-containing acicular magnetic fine particles obtained by heat-treating the obtained ac-containing acicular goethite fine particles.

[0002]

2. Description of the Related Art As a starting material for Co-containing acicular γ-Fe ₂ O ₃ , Fe ₃ O ₄ or Fe—Co alloy fine particles used for a coating type high density magnetic recording medium, a Co-containing acicular goethite is used. (Goethite; α-FeOOH) fine particles are widely used. The magnetic properties, powder properties, paint properties, and the like of these Co-containing needle-like magnetic fine particles are determined by the starting material C
It is greatly affected by the particle shape of the o-containing acicular goethite. Therefore, in order to obtain a magnetic powder having excellent magnetic properties and rheological properties, it is necessary to use fine particles and excellent needle-like properties, and that their distribution is sharp, that there is no branching shape, that is, there are no twins, and that they are added in a later step. Monodisperse Co that exhibits durability against various heat treatments such as dehydration, reduction and oxidation, and satisfies the conditions such as that the shape of the acicular fine particles is well preserved.
It is necessary to prepare containing needle-like goethite particles.

Heretofore, several methods have been proposed for producing needle-like goethite fine particles. For example, (1) a method of oxidizing a ferrous hydroxide colloid obtained by adding an alkali solution to a ferrous salt solution in an acidic, neutral, or alkaline suspension; Hydrothermal synthesis method in which a colloid of ferric hydroxide obtained by adding a solution is subjected to high-temperature and high-pressure treatment in a strong alkali turbid solution. (3) Ferric hydroxide obtained by adding an alkaline solution to a ferric salt solution A method of aging a colloid at a relatively low temperature in a strong alkaline suspension is known.

Among these methods, the method (1) of oxidizing a ferrous hydroxide colloid tends to broaden the particle size distribution and to easily generate particles having a twin structure forming an angle of about 120 °. Magnetic powder starting from such irregular Co-containing acicular goethite fine particles tends to cause sintering between the particles, and when this is applied to the magnetic recording layer of a magnetic recording medium, the dispersibility and filling of the magnetic powder can be improved. Inferior in properties and orientation, it is difficult to improve the electromagnetic conversion characteristics. Further, in the hydrothermal synthesis method (2), since the synthesis is performed at a high temperature of 100 ° C. or more, cubic crystals of α-Fe ₂ O ₃ are often generated and mixed into the Co-containing acicular goethite fine particles, or The needle-containing goethite-containing fine particles are agglomerated with each other and the needle-like property is deteriorated. Further, the method (3) of aging the ferric hydroxide colloid at a relatively low temperature in a strong alkali turbid solution is a method proposed to improve the above-mentioned conventional method. For example, Japanese Patent Publication No. 55-4695 No. 6,086,045. However, the particle morphology of the acicular goethite fine particles varies greatly depending on the setting of the aging conditions, and it is difficult to stably synthesize fine particles having excellent acicularity.

When Co is further added to these needle-like goethite fine particles, it becomes more difficult to control the shape of the needle-like fine particles, and a method for producing stable Co-containing needle-like goethite fine particles has not yet been established. You can say no.

[0006]

DISCLOSURE OF THE INVENTION The present invention is based on such a technical background, and it is proposed that fine particles have excellent acicularity and that their distribution is sharp.
Co-containing needle that has no branched shape, ie, twins, and has durability against various heat treatments such as dehydration, reduction, and oxidation added in a later step, and is capable of favorably preserving the shape of acicular fine particles. It is an object of the present invention to provide a method of producing fine goethite fine particles.

Another object of the present invention is to provide a Co-containing acicular goethite fine particle obtained by such a production method,
An object of the present invention is to provide Co-containing needle-like magnetic fine particles for a high-density magnetic recording medium which are obtained by heat treatment in a predetermined atmosphere and have excellent fine particle shape and magnetic properties.

[0008]

Means for Solving the Problems The method of the present invention for producing Co-containing acicular goethite fine particles is proposed to solve the above-mentioned problems, and comprises a ferric salt solution containing a Co salt, A method for producing Co-containing acicular goethite fine particles comprising a step of preparing a suspension by mixing and stirring with an alkali solution, and a step of aging the suspension. Is added to the suspension so that the molar ratio of carbonate ion to ferric ion is 6.0 or more and 10.0 or less. It is characterized by doing.

In the Co-containing acicular goethite fine particles, Co /
If the Fe ratio exceeds 15 at%, Co is not doped into the acicular goethite fine particles, and granular Co ferrite particles are generated and mixed in addition to the Co-containing acicular goethite fine particles. As inappropriate. C
The lower limit of the o / Fe ratio is not particularly limited. However, C
The purpose of adding o to the acicular magnetic fine particles is to control the magnetic properties, and is a design matter determined by the desired magnetic properties. However, even if a small amount of Co is added, the effect of controlling the magnetic properties is small, so a value of 0.5% or more is usually adopted.

The Co salt is not particularly limited, and a water-soluble salt such as Co sulfate, Co nitrate, Co chloride or Co bromide is employed.

In the present invention, it is also possible to produce acicular goethite fine particles containing a metal other than Co, for example, Zn, Cr or Ti. For example, acicular goethite fine particles containing Zn can be obtained by aging a suspension containing a gel-like amorphous substance of ferric hydroxide containing Zn using zinc sulfate or the like. Needle-like goethite fine particles containing another metal can be obtained in the same manner.

The strong alkali mixed with the ferric salt solution containing a Co salt is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide. Is used by dissolving in a solvent such as water.

If the molar ratio of carbonate ion to ferric ion, that is, the molar ratio of carbonate ion / ferric ion is less than 6.0, the resulting fine Co-containing needle-like goethite particles are insufficiently refined, Further, it cannot take a monodisperse particle form. If the molar ratio of carbonate ion / ferric ion exceeds 10, the effect of refining the Co-containing needle-like goethite fine particles is saturated, so that it is meaningless to add excessive carbonate ions and the production cost is reduced. Invite a rise.

The carbonate used as the carbonate ion source is not particularly limited. For example, alkali carbonates such as sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate can be used alone or in combination.

The concentration of ferric iron in the suspension is 0.01 mol
It is desirable that the ripening be performed in a range of not less than 0.10 mol / l and not more than 0.10 mol / l. The suspension may be a Co-containing ferric hydroxide colloid or a Co-containing FeO containing a trace amount of water therein.
OH colloid is suspended in the reaction mother liquor. If the concentration of ferric iron in this suspension exceeds 0.10 mol / l, the generated needle-like goethite fine particles are likely to aggregate with each other, making it difficult to obtain a monodispersed state. Also 0.01mol
If the ratio is less than / l, the yield of needle-like goethite fine particles decreases, which is unsuitable as an industrial production method.

As the ferric salt used in preparing the suspension, any ferric salt that is usually used for producing needle-like goethite fine particles can be used, and examples thereof include ferric chloride and sulfuric acid sulfate. Examples thereof include ferric iron and ferric nitrate. These ferric salts are dissolved in a solvent such as water and used for the reaction as a ferric salt solution.

During aging, the pH of the suspension is 11.0
It is desirable that it is not less than 13.5. pH 13.
If it exceeds 5, the major axis of the needle-like goethite fine particles grows remarkably, and therefore the particle shape becomes extremely elongated, and aggregation of the particles easily occurs, which is not preferable. Also the pH of the suspension
If it is less than 11.0, the crystallinity of the acicular goethite fine particles decreases, and the heat resistance to various heat treatments in the subsequent steps becomes poor. Further, generation of granular α-Fe ₂ O ₃ is likely to occur.
Therefore, by selecting the pH within this range, it is possible to obtain needle-like goethite fine particles having a small particle size, a sharp particle size distribution, and excellent twin crystal-free crystallinity.

The aging is preferably performed at a temperature in the range of 45 ° C. to 80 ° C. If the aging temperature exceeds 80 ° C., particulate α-Fe ₂ O ₃ is generated, which is not preferable in terms of magnetic properties. When the aging temperature is 45 ° C. or lower, the crystallization of the acicular goethite fine particles is not sufficient, and unreacted particles composed of a gel-like amorphous substance tend to remain.

In the present invention, the order of mixing the ferric salt solution containing the Co salt with the strong alkali solution and the alkali carbonate may be any method. That is, a ferric salt solution containing a Co salt may be dropped into a strong alkaline solution and mixed, or vice versa. The alkali carbonate may be added at any stage.
Alternatively, both solutions may be continuously mixed in a fixed amount by a mixing means such as a line mixer. Acetic goethite fine particles having no difference in particle morphology can be obtained by any of the mixing methods. The time required from the start to the end of the mixing of the ferric salt solution containing the Co salt with the strong alkali solution and the alkali carbonate is preferably short, for example, within 5 minutes. If the mixing time is long, ferric hydroxide containing Co that has been mixed previously or a trace amount (for example, 10
(% By weight) of a suspension containing a gel-like amorphous material of FeOOH containing water therein sometimes progresses from the nucleation of acicular goethite fine particles to the stage of nucleus growth. The particle size distribution of the goethite fine particles expands, making it difficult to obtain monodisperse particles.

The ferric salt solution containing a Co salt is mixed with a strong alkali solution and alkali carbonate at room temperature.
As a pretreatment for aging, it is desirable to continue mixing of a suspension containing a gel-like amorphous substance of ferric hydroxide containing Co while maintaining room temperature to make the dispersion uniform.
By performing such a pretreatment, the crystallization of the acicular goethite fine particles becomes uniform, and this has an excellent effect on the particle size distribution.

The time required for aging depends on the aging temperature.
In general, the higher the aging temperature, the shorter the required reaction time. Therefore, the ripening temperature may be selected within a range that does not adversely affect the shape of the generated needle-like goethite fine particles and in consideration of the yield and the like.

Next, the Co-containing acicular magnetic fine particles of the present invention are characterized by being obtained by subjecting the Co-containing acicular goethite fine particles produced by such a production method to a heat treatment in a predetermined atmosphere. Examples of the Co-containing needle-like magnetic fine particles include Co
Content γ-Fe ₂ O ₃ , Co content Fe ₃ O ₄ , Co content γ
_{-Fe 2 O 3 / Fe 3 O} 4 Intermediate (berthollide compound), Co-containing iron nitride or Fe-Co alloy fine particles and the like.

Among these, Fe—Co alloy fine particles are particularly desirable as a high-density magnetic recording medium. When producing Fe—Co alloy fine particles, for example, after heating and dehydrating in a non-reducing atmosphere such as nitrogen or air to convert them into Co-containing needle-like hematite fine particles, this is converted to 40% in a reducing atmosphere such as hydrogen.
0 ° C or more and 700 ° C or less, more preferably 500 ° C or more and 6
It is obtained by heat treatment in a temperature range of 50 ° C. or less. If the heat treatment temperature is lower than 400 ° C., the reduction reaction is insufficient and magnetite is mixed. On the other hand, when the temperature exceeds 700 ° C., sintering of the obtained Fe—Co alloy fine particles within and between the particles proceeds, which is not preferable from the viewpoint of magnetic properties, dispersibility, orientation and the like. Other iron oxide-based or iron nitride-based Co
In the case of the acicular magnetic fine particles containing Co, the heat treatment conditions in a predetermined atmosphere conventionally used are directly applied to the Co-containing acicular goethite fine particles obtained by the method for producing the Co-containing acicular goethite fine particles of the present invention. Can be manufactured.

According to the method for producing ac-containing acicular goethite fine particles of the present invention, by setting the Co / Fe ratio, carbonate ion concentration and the like to optimum conditions, fine acicular particle shapes and excellent crystallinity are obtained. Thus, Co-containing needle-like goethite fine particles can be produced. In particular, by adding a large amount of carbonate ions, the particle size of the Co-containing needle-like goethite fine particles can be reduced without increasing the axial ratio. The reason for this is not necessarily clear, but is presumed as follows. That is, anions such as chloride ion, sulfate ion, phosphate ion and hydroxyl ion have strong adsorptivity. Among them, chloride ion and hydroxyl ion are the surfaces parallel to the c-axis direction (length direction) of the goethite fine particles, that is, It has the property of specifically adsorbing to the b-axis direction (width direction) and a-axis direction (thickness direction) of the site fine particles (the goethite fine particles are described as needle-shaped for convenience, but strictly speaking, they are shaped like bamboo leaves). Close plate-like particles). For this reason, in general, the growth of the goethite fine particles in the lateral direction is suppressed, and the longitudinal direction is selectively grown, resulting in an excessive axial ratio. On the other hand, carbonate ions originally have lower adsorptivity than chloride ions and hydroxyl ions, and have no selective adsorption to a specific crystal plane.
Therefore, by adding the carbonate ion in a larger amount than the chlorine ion or the hydroxyl group ion, the carbonate ion is preferentially and uniformly adsorbed on each crystal face. Therefore, the growth of the goethite particles in the a-axis, b-axis and c-axis directions becomes uniform,
Micronization is achieved without growing only the major axis.

The Co-containing acicular magnetic fine particles of the present invention are
By heat-treating the Co-containing acicular goethite fine particles obtained by such a production method in a predetermined atmosphere, that is, an atmosphere such as a reducing or oxidizing atmosphere, excellent acicularity and crystallinity can be obtained. It is possible to provide magnetic particles suitable for the above.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process flow chart illustrating a method for producing Co-containing acicular goethite fine particles of the present invention.

[SP1] Step of Preparing a Ferric Salt Solution Containing a Co Salt, a Strongly Alkaline Solution, and an Alkaline Carbonate The Co salt and the ferric salt are dissolved in water to prepare a ferric salt solution containing a Co salt. I do. The ratio of the Co salt to the ferric salt (Co ²⁺ / Fe ³⁺ ) is selected so that the Co / Fe ratio in the finally obtained Co-containing acicular goethite fine particles is 15 at% or less. Generally, the Co / Fe ratio in the Co-containing acicular goethite fine particles is determined by the C / Fe ratio in the ferric solution containing the Co salt.
It is slightly higher than the o ²⁺ / Fe ³⁺ ratio, that is, within a range of about 5% to 15%. Meanwhile, an alkali metal hydroxide or the like is dissolved in water to separately prepare a strong alkali solution. further,
The alkali carbonate is dissolved in water to separately prepare an alkali carbonate solution.

[SP2] Mixing and Stirring Step A ferric salt solution containing a Co salt, a strong alkali solution and an alkali carbonate solution are mixed and stirred.

[SP3] Step of forming suspension A suspension is formed as a result of the mixing and stirring step of SP2. In this suspension, Co-containing ferric hydroxide and C
o-containing FeOOH and the like, all of which are in a colloidal state. It is desirable that the concentration of ferric iron in the suspension be 0.01 mol / l or more and 0.10 mol / l or less. Further, the pH of the suspension is desirably 11.0 or more and 13.5 or less.

[SP4] Aging step The suspension obtained in the preceding step is aged. Aging is desirably performed in a temperature range of 45 ° C. or more and 80 ° C. or less. The required aging time depends on the aging temperature, but is usually selected from several tens to several hundred hours.

[SP5] Step of forming Co-containing acicular goethite fine particles As a result of the aging step, finally, Co-containing acicular goethite fine particles are obtained. The Co / Fe ratio in the Co-containing needle-like goethite fine particles is selected in a range of 15 at% or less.

In the subsequent steps, a Co-containing needle-like goethite fine particle powder is obtained through washing and drying steps according to a conventional method.
If necessary, a sintering inhibitor applying step may be added after the cleaning step. As the sintering inhibitor, any of conventionally known agents such as water glass and aluminum hydroxide can be used.

The Co-containing acicular goethite fine particles thus obtained can be converted into Co-containing acicular magnetic fine particles such as a Co—Fe alloy by heating in a predetermined atmosphere.

[0034]

EXAMPLES Hereinafter, the method for producing Co-containing acicular goethite fine particles and the Co-containing acicular magnetic fine particles of the present invention will be described in more detail with reference to Examples along with Comparative Examples. However, the following examples are exemplifications to facilitate understanding of the present invention, and the present invention is not limited to these examples.

Example 1 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.00
375 mol was dissolved in distilled water to make 350 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2850 ml of a ferric salt solution containing a Co salt. The Co ²⁺ / Fe ³⁺ ratio in this mixed solution is 2.0 at%. While stirring this mixed solution, 0.375 mol /
1850 ml of sodium hydroxide solution and 3.75
300 ml of a mol / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension is a suspension of a Co-containing ferric hydroxide colloid and a Co-containing FeOOH colloid containing a trace amount of water therein in a reaction mother liquor. The concentration of ferric iron in this suspension was 0.040 mol /
1, pH was 12.0.

The obtained suspension was stirred by a high-speed rotating blade at 8000 rpm for 10 minutes, and then the stirring was stopped.
Aging was performed at 60 ° C. for 209 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 2.2 at%.

The Co-containing needle-like goethite fine particles obtained were filtered and washed, and then surface-treated with water glass in a state of high-speed dispersion in water, to thereby perform a sintering prevention treatment. Surface treated C
The o-containing acicular goethite fine particles were filtered and dried under a drying condition at 80 ° C to obtain a Co-containing acicular goethite fine particle powder.

The Co-containing acicular goethite fine particles were heated and dehydrated at 550 ° C. for 1 hour in a nitrogen atmosphere to obtain Co-containing acicular hematite fine particles. Subsequently, reduction was carried out by heating at 550 ° C. for 3 hours in a hydrogen atmosphere. After the reduction was completed, the reduction furnace was cooled and gradually oxidized at room temperature with nitrogen containing a trace amount of oxygen to form and stabilize a surface oxide film, thereby obtaining needle-like FeCo alloy fine particles.

Example 2 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.00
75 mol was dissolved in distilled water to make 50 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2550 ml of a ferric salt solution containing a Co salt. The Co ²⁺ / Fe ³⁺ ratio in this mixed solution is 4.0 at%. While stirring the mixed solution, 1840 ml of a separately prepared 0.375 mol / l sodium hydroxide solution and 3.75 mol
300 ml of a 1 / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension contains a Co-containing ferric hydroxide colloid or a Co-containing F containing a small amount of water therein.
The eOOH colloid is suspended in the reaction mother liquor.
The concentration of ferric iron in this suspension was 0.040 mol / l, p
H was 12.0.

The obtained suspension was stirred by a high-speed rotating blade at 8000 rpm for 10 minutes, and then the stirring was stopped.
Aging was performed at 60 ° C. for 209 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 4.3 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying, and heat treatment in a predetermined atmosphere according to Example 1 to obtain FeCo alloy acicular fine particles.

Example 3 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.01
125 mol was dissolved in distilled water to make 80 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2580 ml of a ferric salt solution containing a Co salt. The Co ²⁺ / Fe ³⁺ ratio in this mixed solution is 6.0 at%. While stirring this mixed solution, 0.375 mol / l separately prepared
Sodium hydroxide solution of 1840 ml and 3.75 m
300 ml of an ol / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension is a suspension of a Co-containing ferric hydroxide colloid and a Co-containing FeOOH colloid containing a trace amount of water therein in a reaction mother liquor. The concentration of ferric iron in this suspension was 0.040 mol /
1, pH was 12.0.

The obtained suspension was stirred by a high-speed rotating blade at 8000 rpm for 10 minutes, and then the stirring was stopped.
Aging was performed at 60 ° C. for 144 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 6.4 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying, and heat treatment in a predetermined atmosphere according to Example 1, to obtain FeCo alloy acicular fine particles.

Example 4 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.01
5 mol was dissolved in distilled water to make 80 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2580 ml of a ferric salt solution containing a Co salt. C in this mixed solution
The o ²⁺ / Fe ³⁺ ratio is 8.0 at%. While stirring the mixed solution, 1840 ml of a separately prepared 0.375 mol / l sodium hydroxide solution and 3.75 mol of a sodium hydroxide solution were prepared.
A 300 ml / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension contains a Co-containing ferric hydroxide colloid or a Co-containing F containing a small amount of water therein.
The eOOH colloid is suspended in the reaction mother liquor.
The concentration of ferric iron in this suspension was 0.040 mol / l, p
H was 12.0.

The obtained suspension was stirred for 10 minutes by a high-speed rotating blade at 8000 rpm, and then the stirring was stopped.
Aging was performed at 60 ° C. for 144 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 8.7 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying, and heat treatment in a predetermined atmosphere according to Example 1 to obtain FeCo alloy acicular fine particles.

Example 5 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.03
75 mol was dissolved in distilled water to make 50 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2550 ml of a ferric salt solution containing a Co salt. The Co ²⁺ / Fe ³⁺ ratio in this mixed solution is 2.0 at%. While stirring the mixed solution, 1580 ml of a separately prepared 0.375 mol / l sodium hydroxide solution and 3.75 mol
300 ml of a 1 / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension contains a Co-containing ferric hydroxide colloid or a Co-containing F containing a small amount of water therein.
The eOOH colloid is suspended in the reaction mother liquor.
The concentration of ferric iron in this suspension was 0.042 mol / l, p
H was 11.3.

The obtained suspension was stirred by a high-speed rotating blade at 8000 rpm for 10 minutes, and then the stirring was stopped.
Aging was performed at 45 ° C. for 165 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 2.2 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying and heat treatment in a predetermined atmosphere according to Example 1 to obtain FeCo alloy acicular fine particles.

Example 6 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.00
75 mol was dissolved in distilled water to make 50 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 2550 ml of a ferric salt solution containing a Co salt. The Co ²⁺ / Fe ³⁺ ratio in this mixed solution is 3.8 at%. While stirring the mixed solution, 1700 ml of a separately prepared 0.375 mol / l sodium hydroxide solution and 3.75 mo were prepared.
300 ml of a 1 / l sodium carbonate solution was added dropwise and mixed to prepare a suspension. This suspension contains a Co-containing ferric hydroxide colloid or a Co-containing F containing a small amount of water therein.
The eOOH colloid is suspended in the reaction mother liquor.
The concentration of ferric iron in this suspension was 0.041 mol / l, p
H was 11.5.

The obtained suspension was stirred for 10 minutes by a high-speed rotating blade at 8000 rpm, and then the stirring was stopped.
Aging was performed at 45 ° C. for 165 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 4.3 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying and heat treatment in a predetermined atmosphere according to Example 1 to obtain FeCo alloy acicular fine particles.

Comparative Example 1 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 mol
2500 l / l ferric chloride solution was prepared. While stirring this solution, 0.469 mol / l separately prepared
Was added dropwise and mixed to prepare a suspension. The concentration of ferric iron in this suspension was 0.044 mol / l, and the pH was 12.5.

The obtained suspension was stirred by a high-speed rotating blade at 8000 rpm for 10 minutes, and then the stirring was stopped.
Aging was performed at 60 ° C. for 209 hours. By this aging step, acicular goethite fine particles were generated.

The obtained needle-like goethite fine particles were subjected to washing, surface treatment, drying and heat treatment in a predetermined atmosphere according to Example 1 to obtain Fe metal needle-like fine particles.

Comparative Example 2 Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.75 mol /
1 ml of a ferric chloride solution was prepared. Separately, cobalt chloride hexahydrate (CoCl ₂ .6H ₂ O) 0.0187
5 mol was dissolved in distilled water to make 50 ml, and a cobalt chloride solution was prepared. The two solutions were mixed to prepare 300 ml of a ferric salt solution containing a Co salt. Co in this mixed solution
^{The 2 +} / Fe3 ⁺ ratio is 10.0 at%. While stirring this mixed solution, 176 ml of a separately prepared 3.75 mol / l sodium hydroxide solution was dropped and mixed, and further, a 0.75 mol / l sodium hydroxide solution 13 was added.
ml was added dropwise and mixed to prepare a suspension. This suspension is a suspension of a Co-containing ferric hydroxide colloid and a Co-containing FeOOH colloid containing a trace amount of water therein in a reaction mother liquor. The concentration of ferric iron in this suspension was 0.3
83 mol / l, pH was 12.5.

The obtained suspension was stirred for 10 minutes by a high-speed rotating blade at 8000 rpm, and then the stirring was stopped.
Aging was performed at 60 ° C. for 120 hours. By this aging step, Co-containing acicular goethite fine particles were generated. Co
Co content in needle-containing goethite microparticles containing
The / Fe ratio was 10.6 at%.

The obtained Co-containing acicular goethite fine particles were subjected to washing, surface treatment, drying and heat treatment in a predetermined atmosphere according to Example 1 to obtain FeCo alloy acicular fine particles.

The above Examples 1 to 6 and Comparative Examples 1 and 2
The production conditions of the Co-containing needle-like goethite fine particles or the needle-like goethite fine particles obtained by the above are summarized in [Table 1].

[0061]

[Table 1]

Similarly, the powder characteristics of the Co-containing acicular goethite fine particles or the acicular goethite fine particles obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were as follows:
The results are shown in [Table 2]. Among these, the shape of the acicular particles, that is, the major axis, the minor axis, and the axial ratio were determined by dimension measurement from a TEM (transmission electron microscope) photograph. The crystallite diameter was determined from the (110) plane by the Debye-Scherrer method.

[0063]

[Table 2]

From the results shown in Table 2, the Co-containing acicular goethite fine particles obtained by the method for producing the Co-containing acicular goethite fine particles of the present invention have the major axis and the minor axis in an appropriate range. At the same time, it is understood that the axial ratio is also within an appropriate range. In addition, the presence of twins was not recognized, and the particles were in a monodispersed state. On the other hand, the needle-like goethite fine particles of Comparative Example 1 and the Co-containing needle-like goethite fine particles of Comparative Example 2 have an axial ratio of 4.0.
And 3.5, which is small. Fine particles having twins were slightly mixed, and aggregation was observed.

Next, the FeCo alloy needle-like magnetic fine particles obtained in the above Examples 1 to 6 and Comparative Examples 1 and 2,
The powder characteristics of the Fe metal needle-shaped magnetic fine particles are summarized in [Table 3]. The shape of each acicular magnetic particle, that is, the major axis, minor axis, and axial ratio were determined by measuring the dimensions from a TEM photograph.

[0066]

[Table 3]

From the results shown in Table 3, the FeCo alloy needle-like fine particles obtained from the Co-containing needle-like goethite fine particles obtained by the method for producing the Co-containing needle-like goethite fine particles of the present invention have long axis and short axis. The particle diameter is in an appropriate range for use in a high density magnetic recording medium, and the axial ratio is 13.0.
２８28.5, which is within an appropriate range. On the other hand, Fe metal needle-shaped magnetic fine particles of Comparative Example 1 and FeC of Comparative Example 2
The o-alloy acicular magnetic fine particles have small axial ratios of 7.3 and 3.6, and may leave problems in the orientation and the coercive force distribution.

Further, the needle-like magnetic fine particles of the FeCo alloy obtained in the above Examples 1 to 6 and Comparative Examples 1 and 2,
The magnetic properties of the Fe metal needle-shaped magnetic fine particles are summarized in [Table 4]. The magnetic properties were measured using a VSM (sample vibrating magnetometer).

[0069]

[Table 4]

From the results in Table 4, it can be seen that FeCo obtained by the method for producing Co-containing acicular goethite fine particles of the present invention was obtained.
The alloy needle-shaped fine particles satisfy the coercive force Hc and the saturation magnetization moment σs required for a high-density magnetic recording medium, and the squareness ratio σr / σs is also good as a measured value in a magnetic powder state. On the other hand, the needle-like magnetic fine particles of Fe metal of Comparative Example 1 and the needle-like magnetic fine particles of FeCo alloy of Comparative Example 2
In any case, the coercive force is smaller than that of the embodiment, and there is a problem in the application of the high-density magnetic recording medium.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to these embodiments.

For example, as the type of the ferric salt, the type of the Co salt, or the type of the strong alkali and the alkali carbonate, various compounds other than the ferric chloride and the cobalt chloride of the embodiment or the sodium hydroxide and the sodium carbonate are selected. And the combination is arbitrary. In addition, various modes are also possible for a method of mixing a ferric salt solution containing a Co salt with a strong alkali.

As the Co-containing acicular magnetic fine particles, FeC
Although o-alloy acicular fine particles are exemplified, a Co-containing acicular γ-Fe
_{The present} invention can be applied to various materials suitable for high-density magnetic recording media, such as ₂ O ₃ , Co-containing acicular Fe ₃ O ₄ or an intermediate thereof (beltride compound), and Co-containing acicular iron nitride.

[0074]

As is apparent from the above description, according to the method for producing Co-containing acicular goethite fine particles of the present invention,
It is possible to provide Co-containing needle-like goethite fine particles having a fine particle diameter, excellent needle-like properties, and no twinning. Further, according to the Co-containing acicular magnetic fine particles of the present invention, it is possible to provide Co-containing acicular magnetic fine particles having a fine particle diameter, excellent acicularity, and excellent magnetic properties. Therefore, it is possible to provide a high-density coating type magnetic recording medium having excellent magnetic properties such as coercive force, residual magnetic flux density, squareness ratio, and the like, or excellent surface properties.

[Brief description of the drawings]

FIG. 1 is a process flow chart showing steps of a method for producing Co-containing acicular goethite fine particles of the present invention.

Claims (5)

[Claims] 1. A step of preparing a suspension by mixing and stirring a ferric salt solution containing a Co salt and a strongly alkaline solution, and a step of aging the suspension. 5. A method for producing fine particles, wherein the Co / Fe ratio in the Co-containing acicular goethite fine particles is 15 at% or less, and the molar ratio of carbonate ions to ferric ions in the suspension is 6. A method for producing Co-containing acicular goethite fine particles, characterized by adding an alkali carbonate so as to be 0 or more and 10.0 or less and aging. 2. The ferric iron concentration in the suspension is 0.01
2. The method for producing Co-containing needle-like goethite fine particles according to claim 1, wherein the ripening is performed in the range of from 0.1 mol / l to 0.10 mol / l. 3. The pH of the suspension is 11.0 or more and 1 or more.
2. The Co according to claim 1, wherein said Co is not more than 3.5.
Method for producing fine needle-containing goethite particles. 4. The method according to claim 1, wherein the aging is performed in a temperature range of 45 ° C. or more and 80 ° C. or less. 5. A Co-containing needle obtained by subjecting Co-containing acicular goethite fine particles produced by the method for producing Co-containing acicular goethite fine particles according to claim 1 to heat treatment in a predetermined atmosphere. Magnetic fine particles.