JP3087778B2 - Method for producing acicular goethite particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing magnetic particles for magnetic recording which has a uniform particle size suitable as a starting material, no dendritic particles, and a large axial ratio (long length). An object of the present invention is to provide acicular goethite particle powder having a shaft diameter / a short axis diameter (hereinafter the same).

[0002]

2. Description of the Related Art In recent years, as the size and weight of magnetic recording / reproducing devices have been reduced, the need for higher performance for recording media such as magnetic tapes and magnetic disks has been increasing. That is, high recording density, high sensitivity characteristics, high output characteristics, and the like are required. The characteristics of the magnetic material particles required to satisfy the above requirements for the magnetic recording medium are to have high coercive force and excellent dispersibility.

That is, in order to increase the sensitivity and output of a magnetic recording medium, it is necessary that the magnetic particle powder has a coercive force as high as possible. "Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder" (1982), p. 310, "‥‥ Improvement of magnetic tape performance was due to high sensitivity, high output and low noise. The emphasis was on increasing the coercive force and reducing the particle size of the Fe ₂ O ₃ particles.

In order to achieve a high recording density of a magnetic recording medium, the aforementioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder”, No. 3
The condition for high-density recording on a coated tape is to maintain high output characteristics with low noise for a short wavelength signal on page 12. For this purpose, the coercive force Hc and the residual magnetization Br Are required to be large, and the thickness of the coating film must be small. As described in {}, the magnetic recording medium needs to have a high coercive force and a large remanent magnetization Br. It is required that the magnetic particle powder has a high coercive force and is excellent in dispersibility in a vehicle, orientation and filling in a coating film.

As is well known, the magnitude of the coercive force of a magnetic particle powder depends on one of shape anisotropy, crystal anisotropy, strain anisotropy and exchange anisotropy, or their interaction. I have.

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles used as magnetic particles for magnetic recording, and metal magnetic particles containing iron as a main component are formed into a shape. A relatively high coercive force is obtained by utilizing the derived anisotropy, that is, by increasing the axial ratio.

[0007] These known magnetic particle powders are obtained by reducing goethite particles as a starting material or acicular hematite particles obtained by heat-treating the goethite particles in a reducing gas such as hydrogen to reduce magnetite particles or iron. It is obtained by using metal particles as a main component and by oxidizing the magnetite particles in air to form maghemite particles.

The residual magnetization Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. It is required that the magnetic particle powder to be dispersed in the powder has a uniform particle size, does not contain dendritic particles, and has a large axial ratio.

As described above, magnetic particle powders having a uniform particle size, containing no dendritic particles, and having a large axial ratio are currently being most demanded. In order to obtain the provided magnetic particle powder, it is necessary that the particle size of the goethite particle powder as a starting material is uniform, no dendritic particles are mixed, and the material has a large axial ratio.

Conventionally, as a method for 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 is used. A method of producing needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower to carry out an oxidation reaction (Japanese Patent Publication No.
No. 5610), spindle-shaped goethite particles are formed by passing an oxygen-containing gas through a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution to carry out an oxidation reaction. Generation method (JP-A-5
No. 0-80999), an oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding a less than equivalent amount of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to an aqueous ferrous salt solution. To form needle-like goethite core particles by performing an oxidation reaction, and then, to an aqueous ferrous salt solution containing the needle-like goethite core particles, an amount of water equivalent to or more than Fe ²⁺ in the aqueous ferrous salt solution. A method of growing the needle-like goethite nucleus particles by passing an oxygen-containing gas after adding an aqueous alkali oxide solution (JP-B-59-48766, JP-A-59-128293, JP-A-59-1).
No. 28294, JP-A-59-128295)
And carrying out an oxidation reaction by passing an oxygen-containing gas through a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate less than the equivalent of the aqueous ferrous salt solution. To produce acicular goethite nucleus particles, and then growing the acicular goethite nucleus particles in an acidic to neutral region (Japanese Patent Publication No. 51-1751).
No. 8, JP-A-55-149136, and JP-A-5-149136.
JP-A-8-60506, JP-A-60-11300, JP-A-61-140110, JP-A-62-1
No. 28929) is known.

[0011]

A magnetic particle powder having a uniform particle size, containing no dendritic particles, and having a large axial ratio is currently the most required, but it is a starting material. When a certain goethite particle powder is produced by the above-mentioned method, the axial ratio is large, especially the axial ratio is 1
Even if 0 or more needle-like goethite particles can be produced, dendritic particles are mixed, and it cannot be said that the particles have uniform particle size. The term "needle-like" refers to a shape in which ridges in the long axis direction are substantially parallel.

In the case of the method described above, spindle-shaped particles having a uniform particle size and containing no dendritic particles can be produced, but the axial ratio is at most about 7 and the axial ratio is at most about 7. The disadvantage is that particles with a large ratio are difficult to generate,
In particular, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases.

The above-mentioned method is characterized by various properties of the acicular goethite particles obtained by each of the above-mentioned methods and
That is, although it is intended to improve the particle size, the axial ratio, the presence or absence of dendritic particles, and the like, goethite particle powder having sufficiently satisfactory properties has not yet been obtained.

According to the above-mentioned method, acicular goethite particles having a uniform particle size can be obtained, but the axial ratio is not yet sufficient.

Accordingly, an object of the present invention is to obtain acicular goethite particles having a uniform particle size, containing no dendritic particles, and having a large axial ratio.

[0016]

The above technical object can be achieved by the following method of the present invention.

That is, the present invention relates to an aqueous solution of a ferrous salt and an aqueous solution of an alkali hydroxide selected from an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate or a mixed aqueous solution of an alkali hydroxide and an alkali carbonate with respect to Fe ^{2+ in the} solution. Oxygen-containing gas is passed through a ferrous hydroxide reaction solution containing a ferrous hydroxide colloid or an iron-containing precipitate colloid obtained by reacting the ferrous hydroxide colloid or the iron-containing precipitate colloid. Thereby producing acicular goethite nucleus particles via green blast, and then producing acicular goethite particles by growing the acicular goethite nucleus particles. passing an oxygen-containing gas and said aqueous alkaline solution in the range of Fe ²⁺ to 0.3 to 0.7 equivalents to the ferrous salt reaction solution obtained by reacting in the liquid Oxidation of the Fe ²⁺ in the liquid Te 30%
The following is a ferrous salt reaction solution in a state containing a mixture of needle-like goethite core particles and green rust, and the sum of the amount of the alkali aqueous solution reacted with the ferrous salt aqueous solution. Is added to the aqueous solution of the alkali in an amount that is less than the equivalent to Fe ²⁺ in the aqueous ferrous salt solution, and then the major axis diameter obtained by performing a growth reaction of the acicular goethite nucleus particles is obtained. 0.35 to 0.45 μm
This is a method for producing acicular goethite particle powder having an axial ratio of 15 to 25 .

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

As the aqueous ferrous salt solution used in the present invention, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution and the like can be used.

The aqueous solution of alkali hydroxide used in the present invention may be an aqueous solution of sodium hydroxide or potassium hydroxide, and the aqueous solution of alkali carbonate may be an aqueous solution of sodium carbonate, an aqueous solution of potassium carbonate, ammonium carbonate, or the like. Alternatively, a mixed aqueous solution thereof can be used.

In the present invention, the amount of the alkali aqueous solution used as a ferrous salt reaction solution containing a mixture of acicular goethite core particles and green rust is determined by the amount of Fe ^{2+ in the} ferrous salt aqueous solution. Range from 0.3 to 0.7 equivalent. If it is less than 0.3 equivalent, acicular goethite particles having a large axial ratio cannot be obtained, and if it exceeds 0.7 equivalent, it is difficult to obtain acicular goethite particles having a uniform particle size, and magnetite is mixed. Sometimes it comes.

In the present invention, the degree of oxidation of Fe ²⁺ in the ferrous salt reaction solution containing the mixture is 30%.
One of the above aqueous alkali solutions is added to the following liquid. When the degree of oxidation exceeds 30%, the effect of adding an aqueous alkali solution cannot be obtained because a large number of goethite core particles already exist.

The preferred range is 5 to 30%. When the content is less than 5%, the particle size becomes uneven as in the case where the aqueous alkali solution exceeds 0.7 equivalent from the beginning of the reaction. Therefore, the content is preferably set to 5% or more.

The degree of oxidation can be determined by measuring the Fe ²⁺ content in the reaction solution and using the following equation. (AB) ÷ A × 100 = degree of oxidation (%) where A is the Fe ²⁺ content in the reaction solution immediately after mixing with the aqueous ferrous salt solution and an aqueous solution having less than the equivalent amount. B contains the mixture. Fe ²⁺ content in ferrous salt reaction solution

In the present invention, the amount of the aqueous alkali solution to be added to the ferrous salt reaction solution containing the mixture is the sum of the amount of the aqueous alkali solution reacted with the aqueous ferrous salt solution. The amount is within a range that is less than the equivalent to Fe ²⁺ in the aqueous ferrous salt solution. If the equivalent amount is exceeded, the particle size may be uneven, dendritic particles may be mixed, or particulate magnetite may be mixed.

The preferred amount of the aqueous alkali solution is as follows:
It is an amount in the range of 0.05 to 0.3 equivalent. If the amount is less than 0.05 equivalent, it is difficult to obtain the effect of the addition, and if it exceeds 0.3 equivalent, since the existence time of the green rust becomes long, the sulfate ions enter the goethite lattice and become magnetic. When iron oxide is used, the magnetic properties may be impaired.

The alkaline aqueous solution to be added includes:
Although any of the alkaline aqueous solutions may be used, it is preferable to add the same alkaline aqueous solution used for the ferrous salt reaction solution.

The method of adding the aqueous alkali solution to the ferrous salt reaction solution containing the mixture may be added at once, or may be added in two or more portions. The effect remains the same.

In the growth reaction of the acicular goethite nucleus particles according to the present invention, the ferrous salt reaction solution containing the acicular goethite nucleus particles may be added with a ferrous salt, if necessary, while maintaining the pH at 3 to 6 while maintaining the pH. Method of aerating the containing gas, if necessary for the ferrous salt reaction solution containing the acicular goethite core particles,
After the addition of the ferrous salt, an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution is added to adjust the pH to 8 to 10.
If necessary for the method of aerating an oxygen-containing gas in the range and the ferrous salt reaction solution containing the acicular goethite core particles,
After the addition of the ferrous salt, any method of adding an aqueous alkali hydroxide solution and passing an oxygen-containing gas at pH 11 or higher may be used.

As the alkaline aqueous solution used in the growth reaction of the acicular goethite core particles in the present invention, the above-mentioned alkaline aqueous solution can be used.

The reaction temperature in the present invention may be usually at a temperature of 80 ° C. or less at which goethite particles are formed. 8
When the temperature exceeds 0 ° C., granular magnetite particles may be mixed in the acicular goethite particles.

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

In the present invention, in order to improve the properties of the magnetic particles, etc., different elements other than Fe, such as Co, Ni, Zn, P, Al, and Si, which are usually added during the reaction of forming goethite particles, are used. It can be added, and in this case, the same effect can be obtained.

[0034]

According to the present invention, there is provided a ferrous hydroxide colloid or an iron-containing colloid obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution in an amount of 0.3 to 0.7 equivalents to Fe2 ^{+ in the} aqueous solution. Oxygen-containing gas was passed through the ferrous salt reaction solution containing the precipitate colloid to oxidize the solution, whereby the degree of oxidation of Fe ^{2+ in} the solution was 30% or less and the solution was formed via green rust. A ferrous salt reaction solution containing a mixture of needle-like goethite core particles and green rust, and the sum of the used amount of the alkali aqueous solution reacted with the ferrous salt aqueous solution is the first ferrous salt aqueous solution. By adding an aqueous alkali solution in an amount that is less than the equivalent to Fe ²⁺ in the aqueous iron salt solution to generate acicular goethite core particles, and then performing a growth reaction of the acicular goethite core particles, Dendritic particles with uniform particle size Not mixed, moreover, the axial ratio is obtained acicular goethite particles have come large <br/>.

The above reaction system is described in detail as follows. First, as for the green rust, for example, "‥‥ Sample is 0.7 equivalent of N in ferrous sulfate on p.
The pH is measured while air oxidizing the basic salt formed by adding aOH, and the oxidation is stopped when the pH reaches 5.5. The compound obtained at this time is green rus
t. ‥‥ ”, and the pH at which green rust is generated is 6.5 to 5.5, although it varies depending on the equivalent ratio of alkali hydroxide. When all the green rust is converted into acicular goethite particles, the pH becomes It drops sharply to 4 or less.

On the other hand, in the reaction for producing acicular goethite nucleus particles via green rust, if the alkali equivalent ratio is reduced, acicular goethite nucleus particles having a uniform particle size can be obtained, but the axial ratio becomes smaller, and the alkali equivalent When the ratio is increased, the axial ratio of the acicular goethite core particles increases, but the particle size becomes uneven.

Therefore, when trying to obtain acicular goethite nucleus particles having a uniform particle size and a large axial ratio, it is possible to obtain a large axial ratio by using acicular goethite nucleus particles having a uniform particle size. Is the point. Therefore, the present inventors examined the state in green rust, the ferrous salt reaction solution in a state containing a mixture of needle-like goethite core particles and green rust generated via the green rust, At each oxidation degree where the degree of oxidation of Fe ^{2+ in} the liquid is 20 to 50%, the sum of the amount of the aqueous alkali solution reacted with the aqueous ferrous salt solution with respect to the amount of Fe ²⁺ in the liquid is An aqueous alkali solution in an amount that is less than the equivalent to Fe ²⁺ in the aqueous ferrous salt solution is added to generate acicular goethite core particles, and then a growth reaction of the acicular goethite core particles is performed. When the needle-like goethite particles were generated by the above method, the following phenomena were confirmed.

When the degree of oxidation exceeds 30%, the axial ratio of the goethite core particles decreases, so that the axial ratio of the acicular goethite particles obtained by the growth reaction is also small.

As shown in the examples below, when the degree of oxidation is in the range of 30% or less, the needle-like particles having a uniform particle size formed in the ferrous salt reaction solution containing the mixture. The axial ratio can be increased by maintaining goethite core particles.

In the technical means disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-149136, the pH value of the reaction solution is adjusted to 5.5 to 7.5 for most of the time from the start to the end of the oxidation reaction. In other words, when the reaction is performed all the time in the green rust region, a large axial ratio cannot be obtained, and the formation reaction of obtaining goethite core particles after the reaction in the green rust region is completed is performed. is necessary.
In other technical means for generating needle-like goethite nucleus particles from the green rust described above and then performing a growth reaction, it is necessary to satisfy both characteristics of uniform particle size and large axial ratio. difficult.

The growth reaction of the acicular goethite nucleus particles in the present invention includes, as described above, a method of passing an oxygen-containing gas while maintaining the ferrous salt reaction solution containing the acicular goethite nucleus particles at pH 3 to 6. An aqueous solution of alkali carbonate or an aqueous solution of alkali carbonate / alkali hydroxide is added to the ferrous salt reaction solution containing the acicular goethite core particles to adjust the pH to 8 to 1.
Any method of passing an oxygen-containing gas in the range of 0 and a method of adding an aqueous alkali hydroxide solution to the ferrous salt reaction solution containing the acicular goethite core particles to pass the oxygen-containing gas at pH 11 or more. Good.

Among them, a preferred method is a pH of 8 to 1
In the method of performing the growth reaction in the range of 0 or in the alkaline region of pH 11 or more, impurities such as sulfur and chlorine do not remain on the particle surface, and therefore, sintering occurs during heat reduction and the particle shape is broken. As a result, acicular goethite particles having a uniform particle size and a large axial ratio, particularly having an axial ratio of 15 or more, can be obtained.

The most preferable method is to oxidize the needle-like core particles by adding an aqueous alkali carbonate solution to the ferrous salt reaction solution and passing an oxygen-containing gas in a pH range of 8 to 10 to carry out an oxidation reaction. Is Fe ²⁺ remaining in the ferrous salt reaction solution and Fe 2
The axial ratio can be further increased by taking over the habit of needle-like crystals of the core particles generated from the green blast by CO ₃ , so that the particle size is uniform and the axial ratio is large.
The above needle-like goethite particle powder is obtained.

[0044]

Next, the present invention will be described with reference to examples and comparative examples. In addition, the major axis diameter and the axial ratio of the particles in the following Examples and Comparative Examples are all shown as average values of the numerical values measured from electron micrographs.

The degree of oxidation was determined by adding an aqueous solution of a ferrous salt or a reaction solution to a flask, displacing with an inert gas, adding a mixed acid of sulfuric acid and phosphoric acid while heating and dissolving, and then dissolving Fe ^{2 in the} solution. ⁺ Was measured by a redox titration method, and was determined from the Fe ²⁺ content by the following equation. (AB) ÷ A × 100 = degree of oxidation (%) where A is the Fe ²⁺ content in the reaction solution immediately after mixing with the aqueous ferrous salt solution and an aqueous solution having less than the equivalent amount. B contains the mixture. Fe ²⁺ content in ferrous salt reaction solution

Example 1 An aqueous solution of ferrous sulfate containing 1.0 mol / l of Fe ²⁺ 20
was mixed with 20 l of a 1.0 N aqueous solution of NaOH (corresponding to 0.50 equivalents with ^respect to Fe ²⁺ in the aqueous ferrous sulfate solution).
H) A ferrous sulfate reaction solution containing ₂ was produced. The ferrous sulfate reaction solution containing Fe (OH) ₂ was heated to a temperature of 40 ° C.
When the degree of oxidation of the ferrous sulfate reaction solution containing a mixture of goethite core particles generated via green rust and green rust is 25%, air at 80 l / min is passed through the 4.0 L of a 1.0 N NaOH aqueous solution was dropped into the solution at one time, and air was continuously passed through the solution.
Goethite particles were produced. The pH at this time was 4.0. FIG. 1 shows an electron micrograph (× 30000) of a particle powder obtained by extracting a part of the reaction solution, filtering, washing with water, and drying by a conventional method. The obtained goethite particle powder was needle-like particles having a major axis diameter of 0.30 μm and an axial ratio of 18, as shown in FIG.

The above goethite particles are used as acicular goethite nucleus particles, and the ferrous sulfate reaction solution containing the acicular goethite nucleus particles (the amount of goethite nucleus particles corresponds to 60 mol% based on the produced goethite particles). , 2.67
6.0 L of an aqueous solution of N ₂ CO ₃ (corresponding to 2.0 equivalents to Fe ²⁺ in the remaining ferrous sulfate reaction solution) was added, and 100 L / min at pH 9.3 and a temperature of 45 ° C. For 5 hours to produce goethite particle powder.
The resulting goethite particles were filtered, washed with water and dried by a conventional method. As shown in the electron micrograph (× 30000) of FIG. 2, the obtained goethite particle powder had a uniform particle size, no dendritic particles were present, and a major axis diameter of 0.39 μm.
The particles were needle-shaped particles having an axial ratio of 25.

Example 2 An aqueous solution of ferrous sulfate containing 1.0 mol / l of Fe ²⁺ 20
l and sodium hexametaphosphate (corresponding to 0.28 mol% in terms of P with respect to Fe ²⁺ in an aqueous ferrous sulfate solution)
5.7 g and 20 l of 1.08 N Na ₂ CO ₃ aqueous solution
(Corresponding to 0.45 equivalent to Fe ²⁺ in the aqueous ferrous sulfate solution) to form a ferrous sulfate reaction solution containing Fe (OH) ₂ at pH 7.3 and a temperature of 35 ° C. Was done. At a temperature of 38 ° C., 80 l / min of air is passed through the ferrous sulfate reaction solution containing Fe (OH) ₂ to contain a mixture of goethite core particles generated via green rust and green rust. When the oxidation degree of a certain ferrous sulfate reaction solution is 20%, 1.08N of N
The a ₂ CO ₃ aq 6.7l dropwise divided into twice, to continue the air vent, to produce a goethite particles. At this time, the pH was 3.7. FIG. 3 shows an electron micrograph (× 30000) of a particle powder obtained by extracting a part of the reaction solution, filtering, washing with water, and drying by a conventional method. The obtained goethite particle powder was needle-like particles having a major axis diameter of 0.41 μm and an axial ratio of 19, as shown in FIG.

The above goethite particles are used as acicular goethite nucleus particles, and the ferrous sulfate reaction solution containing the acicular goethite nucleus particles (the amount of goethite nucleus particles corresponds to 60 mol% based on the produced goethite particles). No. 3 water glass (corresponding to 0.5 mol in terms of Si with respect to Fe ²⁺ in an aqueous ferrous sulfate solution) 8.2 g 13.1 N Na
3.3 l of OH aqueous solution (Fe in residual ferrous sulfate aqueous solution
This corresponds to 2.25 equivalents to ²⁺ . ) And pH 1
3.8, 100 liters of air per minute at a temperature of 40 ° C.
Vent for a period of time to produce goethite particle powder. The resulting goethite particles were filtered, washed with water and dried by a conventional method. As shown in the electron micrograph (× 30000) of FIG. 4, the obtained goethite particle powder has a uniform particle size, does not contain dendritic particles, has a major axis diameter of 0.45 μm, and an axial ratio of 2
0 needle-shaped particles.

Example 3 An aqueous solution of ferrous chloride containing 1.0 mol / l of Fe ²⁺ 20
and 20 l of a 0.72N aqueous KOH solution (corresponding to 0.45 equivalents to Fe ²⁺ in an aqueous ferrous chloride solution), and mixed with Fe (O 2) at a pH of 7.5 and a temperature of 40 ° C.
H) A ferrous chloride reaction solution containing ₂ was produced. The ferrous chloride reaction solution containing Fe (OH) ₂ was heated to a temperature of 42 ° C.
When the degree of oxidation of the ferrous chloride reaction solution containing a mixture of goethite core particles and green rust generated via green rust is 30%, the air is blown at 50 l / min. 2.2 l of a 0.72N KOH aqueous solution was dropped into the liquid over 10 minutes, and air was continuously passed through to generate goethite particles. At this time, the pH was 3.7. FIG. 5 shows an electron micrograph (× 30000) of a particle powder obtained by extracting a part of the reaction solution, filtering, washing with water, and drying by a conventional method. The obtained goethite particle powder had a major axis diameter of 0.31 μm as shown in FIG.
m, needle-like particles having an axial ratio of 15.

The above goethite particles are used as acicular goethite nucleus particles, and a ferrous chloride reaction solution containing the acicular goethite nucleus particles (the amount of goethite nucleus particles corresponds to 50 mol% based on the produced goethite particles). , 2.04
7.8 l of a KOH aqueous solution of N (corresponding to 1.0 equivalent to Fe ²⁺ in the residual ferrous chloride reaction solution) was added, and p was added.
100 liters of air per minute was passed for 15 hours at H4.2 and a temperature of 80 ° C. to produce goethite particle powder. The resulting goethite particles were filtered, washed with water and dried by a conventional method. As shown in the electron micrograph (× 30000) in FIG. 6, the obtained goethite particle powder has a uniform particle size, does not contain dendritic particles, and has a needle having a major axis diameter of 0.35 μm and an axial ratio of 15. Particles.

Comparative Example 1 Goethite nuclei were prepared in the same manner as in Example 1 except that 20 l of a 1.5N NaOH aqueous solution (corresponding to 0.75 equivalent to Fe ²⁺ in an aqueous ferrous sulfate solution) was mixed. Particles were generated, and then a growth reaction of the goethite core particles was performed to obtain acicular goethite particle powder. The obtained goethite core particles were observed by electron micrograph to find that the major axis diameter was 0.37 μm.
m, needle-like particles having an axial ratio of 22. The obtained needle-like goethite particle powder was observed as an electron micrograph, and as a result, was a needle-like particle having a major axis diameter of 0.45 μm and an axial ratio of 28. In each case, the particle size was uneven compared to Example 1, and the mixture of dendritic particles was observed.

Comparative Example 2 Goethite nuclei were prepared in the same manner as in Example 1 except that when the degree of oxidation of the ferrous sulfate reaction solution containing the mixture was 40%, an aqueous NaOH solution was added to the solution. Particles were generated, and then a growth reaction of the goethite core particles was performed to obtain acicular goethite particle powder. Observation of the obtained goethite core particles by electron micrograph showed that the major axis diameter was 0.28.
The particles were needle-shaped particles having a diameter of 13 μm and an axial ratio of 13. In addition, the obtained acicular goethite particles powder was observed as an electron micrograph,
Needle-like particles having a major axis diameter of 0.35 μm and an axial ratio of 18 were obtained. Each had a smaller axial ratio than that of Example 1.

Comparative Example 3 The ferrous sulfate reaction solution containing the mixture was added with N
Goethite core particles were generated in the same manner as in Example 1 except that the solution was not dropped into the aOH aqueous solution (the oxidation degree was 50%).
%. ) Then, a growth reaction of the goethite core particles was performed to obtain acicular goethite particle powder. The obtained goethite nucleus particles are shown in an electron micrograph of FIG.
As shown in (00), the particles were acicular particles having a major axis diameter of 0.21 μm and an axial ratio of 15. The obtained acicular goethite particle powder was acicular particles having a major axis diameter of 0.32 μm and an axial ratio of 20, as shown in the electron micrograph (× 30000) of FIG. Each had a smaller axial ratio than that of Example 1.

Comparative Example 4 The ferrous sulfate reaction solution containing the mixture was added with N
A goethite nucleus particle was produced in the same manner as in Example 2 except that the solution was not dropped into the aqueous solution of a ₂ CO ₃ (corresponding to an oxidation degree of 45%). A goethite particle powder was obtained. The obtained goethite core particles are shown in the electron micrograph of FIG. 9 (× 3
0000), the major axis diameter is 0.30 μm, and the axial ratio is 18.
Of needle-like particles. The obtained acicular goethite particle powder was acicular particles having a major axis diameter of 0.40 μm and an axial ratio of 16, as shown in the electron micrograph (× 30000) of FIG. Each had a smaller axial ratio than that of Example 2.

Comparative Example 5 The ferrous chloride reaction solution containing the mixture was mixed with K
Goethite nucleus particles were produced in the same manner as in Example 3 except that they were not dropped into the aqueous OH solution (the oxidation degree was 45%
Is equivalent to ) Then, a growth reaction of the goethite core particles was performed to obtain acicular goethite particle powder. The obtained goethite core particles were obtained by using an electron micrograph (× 300) shown in FIG.
As shown in (00), the particles were acicular particles having a major axis diameter of 0.26 μm and an axial ratio of 11. The obtained needle-like goethite particle powder has a uniform particle size without dendritic particles, a long axis diameter of 0.27 μm, and an axis as shown in the electron micrograph (× 30000) of FIG. The particles were acicular particles having a ratio of 8.
Each had a smaller axial ratio than that of Example 3.

[0057]

According to the method for producing acicular goethite particle powder according to the present invention, the particle size is uniform, dendritic particles are not mixed, and a large A needle-like goethite particle powder having a specific ratio can be obtained.

The acicular goethite particle powder according to the present invention is used as a starting material, and the acicular magnetite particle powder obtained by heat reduction or the acicular maghemite particle powder obtained by heat reduction and then oxidization are also of a particle size. Are uniform, do not contain dendritic particles, and have a large axial ratio, so that they are suitable as magnetic particles for high recording density, high sensitivity, and high output.

[Brief description of the drawings]

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

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 1.

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Example 2.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 2.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Example 3.

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 3.

FIG. 7 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Comparative Example 3.

FIG. 8 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 3.

FIG. 9 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Comparative Example 4.

FIG. 10 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 4.

FIG. 11 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Comparative Example 5.

FIG. 12 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 5.

Claims (1)

(57) [Claims] An aqueous solution of a ferrous salt is reacted with an aqueous solution of an alkali hydroxide selected from an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate or a mixed aqueous solution of an alkali hydroxide and an alkali carbonate with respect to Fe ^{2+ in the} solution. By passing an oxygen-containing gas through the resulting ferrous hydroxide colloid or iron-containing precipitate colloid-containing reaction solution containing the ferrous hydroxide colloid or the iron-containing precipitate colloid to oxidize the ferrous hydroxide colloid or the iron-containing precipitate colloid, In a method of generating acicular goethite nucleus particles via green rust, and then producing acicular goethite particles by growing the acicular goethite nucleus particles, the ferrous salt aqueous solution and the Fe ^An oxygen-containing gas is passed through the ferrous salt reaction solution obtained by reacting the aqueous alkali solution in the range of 0.3 to 0.7 equivalents with respect to A ferrous salt reaction solution having a degree of oxidation of ²⁺ of 30% or less and containing a mixture of needle-like goethite core particles and green rust, and reacted with the ferrous salt aqueous solution, An amount of the alkali aqueous solution in a range in which the total amount of the aqueous alkali solution used is less than the equivalent to Fe ²⁺ in the ferrous salt aqueous solution is added, and then the growth reaction of the acicular goethite core particles is performed. The major axis diameter is 0.35 to 0.45 μm.
And a method for producing acicular goethite particle powder having an axial ratio of 15 to 25 .