JPH0616426A - Production of spindle-shaped goethite granular powder - Google Patents

Abstract

PURPOSE:To obtain a fine-grain goethite having uniform grain size, in which dendritic grains are not included and with the axial ratio increased by adding an aq. soln. of alkali carbonate to a mixture of green rust with a goethite nucleus grain and introducing an oxygen-contg. gas into the soln. CONSTITUTION:An aq. ferrous salt soln. is allowed to react with the aq. solns. of alkali hydroxide and alkali carbonate or the mixed aq. soln. of alkali hydroxide and alkali carbonate in the amt. (0.15-0.85 equivalent) less than the equivalent to the Fe<2+> in the soln. to obtain a ferrous salt reaction soln. contg. a ferrous hydroxide colloid or iron-contg. precipitate. An oxygen-contg. gas is introduced into the reaction soln. to oxidize the colloid to obtain a ferrous salt reaction soln. contg. green rust and a goethite nucleus grain generated via the green rust. An aq. alkali carbonate soln. in the amt. more than the equivalent to the Fe<2+> in the soln. is added to the reaction soln. contg. 10-30% Fe<2+>, and an oxygen-contg. gas is introduced to grow the goethite nucleus grain.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to fine particles which are suitable as a starting material for producing magnetic particle powders for magnetic recording and which have a uniform particle size and do not contain dendritic particles. It is an object of the present invention to provide a spindle-shaped goethite particle powder having a large ratio (major axis diameter / minor axis diameter-the same applies hereinafter), in particular, having an axial ratio of 10 or more.

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization and weight reduction of magnetic recording / reproducing equipment, there is an increasing need to improve the performance of recording media such as magnetic tapes and magnetic disks. That is, high recording density, high sensitivity characteristics and high output characteristics are required. The characteristics of the magnetic material particle powder required to satisfy the above requirements for the magnetic recording medium are high coercive force and excellent dispersibility.

That is, in order to increase the sensitivity and output of the magnetic recording medium, it is necessary that the magnetic particle powder be as fine as possible and have a high coercive force. Issued "... Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology" (1982), page 310, "The direction of improving magnetic tape performance was to improve sensitivity, output and noise. The focus was on high coercive force and fine particle formation of the powdery γ-Fe ₂ O ₃ particles.
... "is as described.

As described in the above-mentioned “Development of Magnetic Materials and Highly Dispersion of Magnetic Particles”, page 312, “... noise decreases as particle size becomes finer ...” Can be reduced to provide a high quality magnetic recording medium.

Further, in order to achieve a high recording density of the magnetic recording medium, the above-mentioned "Development of Magnetic Materials and Highly Dispersion Technique of Magnetic Powder", No. 3,
The condition for high-density recording on the coated tape on page 12 is that it can maintain high output characteristics with low noise for short wavelength signals. For that purpose, coercive force Hc and residual magnetization Br are required. As described above, it is necessary for the magnetic recording medium to have a high coercive force and a large remanent magnetization Br. It is required that the magnetic particle powder is fine particles, has a high coercive force, and has excellent dispersibility in a vehicle, orientation in a coating film, and filling property.

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

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles, which are currently used as magnetic particles for magnetic recording, and metallic magnetic particles containing iron as a main component, have different shapes. A relatively high coercive force is obtained by utilizing the derived anisotropy, that is, by increasing the axial ratio.

[0008] These known magnetic particle powders include goethite particles as a starting material or needle-like 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, or by oxidizing the magnetite particles in air to form maghemite particles.

The remanent 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 1 is fine particles, the particle size is uniform, dendritic particles are not mixed, and the axial ratio is large.

As described above, a magnetic particle powder which is a fine particle, has a uniform particle size, does not contain dendritic particles, and has a large axial ratio is currently most demanded. In order to obtain magnetic particle powder having characteristics, the starting material goethite particle powder is fine particles and the particle size is uniform and dendritic particles are not mixed,
Moreover, a large axial ratio is required.

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 has a pH of 11. As described above, a method of forming needle-shaped goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 80 ° C. or lower (Japanese Patent Publication No. 39-39
No. 5610), a suspension containing FeCO ₃ obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali carbonate is passed through an oxygen-containing gas to carry out an oxidation reaction to obtain spindle-shaped goethite particles. Method for generating (Japanese Patent Laid-Open No. Sho 5
0-80999), an oxygen-containing gas is aerated in an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an equivalent amount of an aqueous alkali hydroxide solution or an aqueous solution of alkali carbonate to the aqueous ferrous salt solution. To generate acicular goethite core particles by performing an oxidation reaction, and then, in an aqueous ferrous salt solution containing the acicular goethite core particles, an equivalent amount or more based on the amount of Fe ^{2+ in} the ferrous salt aqueous solution. A method of growing the acicular goethite nucleus particles by adding an aqueous solution of alkali hydroxide and then aerating an oxygen-containing gas (Japanese Patent Publication No. 59-48766, Japanese Patent Publication No. 59-128293, and Japanese Patent Publication No. 59-128293).
No. 128294 / JP-A-59-128295) and an aqueous solution of a ferrous salt and an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate in an amount less than the equivalent amount of the ferrous hydroxide colloid solution. A method of generating acicular goethite nucleus particles by carrying out an oxidation reaction by passing an oxygen-containing gas, and then growing the acicular goethite nucleus particles in an acidic to neutral region (Japanese Patent Publication No. 51-17518).
JP-A-55-149136, JP-A-58-58
-60506, JP-A-60-11300,
JP-A-61-140110, JP-A-62-128
No. 929) is known.

[0012]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, fine particles having a uniform particle size and no dendritic particles are mixed,
Moreover, magnetic particle powders having a large axial ratio are currently most demanded, but in the case of the above-described method for producing goethite particle powder as a starting material, a large axial ratio, particularly, Although acicular goethite particles having a ratio of 10 or more can be generated, dendritic particles are mixed and it is hard to say that the particles have a uniform particle size. still,
“Needle-like” refers to a shape in which the ridge lines in the major axis direction are substantially parallel.

According to the above-mentioned method, it is possible to produce spindle-shaped goethite particles having a uniform particle size and no dendritic particles mixed therein, but the axial ratio is at most 7.
However, there is a drawback that particles with a large axial ratio are difficult to be generated, and in particular, this phenomenon tends to become more remarkable as the major axis diameter of the generated particles becomes smaller.

The above-mentioned method includes various characteristics of needle-shaped goethite particles obtained by the above-mentioned method and
That is, although the purpose is to improve the particle size, the axial ratio, the presence or absence of dendritic particles, etc., goethite particle powders having various properties that are sufficiently satisfactory have not yet been obtained.

In the case of the above-mentioned method, acicular goethite particles having a uniform particle size are obtained, but the acicular goethite particles obtained in the acidic or neutral region contain impurities such as sulfur and chlorine on the particle surface. Due to the residual adhesion, sintering occurs during heating and reduction, and the particle shape is likely to collapse, making it difficult to obtain magnetic particle powder with an appropriate axial ratio.

Therefore, according to the present invention, the spindle-shaped goethite has a fine particle size, is uniform in particle size, does not contain dendritic particles, and has a large axial ratio, in particular, an axial ratio of 10 or more. It is a technical subject to obtain a particle powder.

[0017]

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

That is, the present invention is obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate or a mixed solution of an alkali hydroxide and an alkali carbonate which is less than the equivalent amount of Fe ^{2+ in the} solution. A ferrous salt reaction solution containing a ferrous hydroxide colloid or an iron-containing precipitate colloid is aerated to oxidize the ferrous hydroxide colloid or the iron-containing precipitate colloid to obtain a green solution. A ferrous salt reaction solution containing a mixture of the last and goethite nucleus particles produced via the green last, and then the degree of oxidation of Fe ²⁺ in the ferrous salt reaction solution containing the mixture is increased. in the liquid in the range of 10-30%, row the growth reaction of the goethite nucleus particles by passing an oxygen-containing gas after the addition of more equivalents of aqueous alkali carbonate solution to Fe ²⁺ in the solution A method for producing goethite particles exhibited fusiform consisting.

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

The ferrous salt aqueous solution used in the present invention may be a ferrous sulfate aqueous solution, a ferrous chloride aqueous solution or the like.

The alkali hydroxide aqueous solution used in the reaction for producing green last in the present invention includes sodium hydroxide aqueous solution and potassium hydroxide aqueous solution, and the alkali carbonate aqueous solution includes sodium carbonate aqueous solution, potassium carbonate aqueous solution and ammonium carbonate aqueous solution. Etc. can be used, and a mixed aqueous solution of these can also be used.

The amount of the aqueous alkali hydroxide solution or aqueous alkali carbonate solution used is less than the equivalent amount to Fe ²⁺ in the aqueous ferrous salt solution. When the amount is more than the equivalent, the particle size is asymmetric and the dendritic particles are mixed, and the spindle-shaped goethite particles having a large axial ratio cannot be obtained. Further, granular magnetite particles may be mixed together. The preferred amount used is in the range of 0.15 to 0.85 equivalent, and
When the amount is less than 15 equivalents, goethite core particles are generated in an extremely short time, and it is difficult to control the degree of oxidation. If it exceeds 0.85 equivalents, granular magnetite may be mixed, and the proportion of iron carbonate in the growth reaction decreases, so that the reaction becomes non-uniform and the obtained goethite particles have an uneven particle size. Becomes

In the present invention, the Fe ²⁺ oxidation degree of the ferrous salt reaction solution containing a mixture of green last and goethite nucleus particles produced via the green last is 10 or ^less.
An aqueous solution of alkali carbonate in an amount equal to or more than that of Fe ²⁺ in the liquid is added to the liquid in the range of ˜30%. Degree of oxidation is 1
When it is less than 0%, only goethite particles having a spindle-like shape with a small axial ratio can be obtained even by the growth reaction because the formation of goethite nucleus particles is insufficient. When the degree of oxidation exceeds 30%, since the particle size of the goethite nucleus particles has already grown large, the particle size of the obtained spindle-shaped goethite particles also becomes large, and it cannot be called fine particles.

The degree of oxidation is determined by the following formula by measuring the Fe ²⁺ content in the reaction solution. (A−B) ÷ A × 100 = oxidation degree (%) However, A is the Fe ²⁺ content in the reaction solution immediately after mixing the ferrous salt aqueous solution and the alkaline aqueous solution of less than the equivalent amount B includes the mixture. Fe ²⁺ content in ferrous salt reaction solution

The amount of the aqueous alkali carbonate solution used is at least equivalent to Fe ²⁺ in the ferrous salt reaction solution containing the mixed solution. When the amount is less than the equivalent, the particle size of the obtained goethite particles becomes asymmetric, and spherical magnetite particles are mixed.

As the alkali carbonate aqueous solution used in the growth reaction of goethite nucleus particles in the present invention, the above alkali carbonate aqueous solution can be used.

The reaction temperature in the present invention is usually 80 ° C. or lower at which goethite particles are formed. 8
When the temperature exceeds 0 ° C, granular magnetite particles are mixed in the goethite particles.

The oxidizing means in the present invention is carried out by bubbling 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, the reaction for producing green last and the reaction for growing goethite nuclei particles can be carried out in the same reaction tower, and even if separate reaction towers are used, the object of the present invention is to be achieved. Goethite particles are obtained.

Further, in the present invention, in order to improve the characteristics of the magnetic particle powder and the like, different elements other than Fe, such as Co, Ni, Zn, P, Al and Si, which are usually added during the formation reaction of goethite particles, are used. It can be added, and the same effect can be obtained in this case as well.

[0031]

In the present invention, a ferrous salt reaction solution containing a mixture of the green last and acicular goethite core particles produced via the green last is produced, and the ferrous salt reaction containing the mixture is produced. The degree of oxidation of Fe ^{2+ in} the solution is 10
By adding an aqueous solution of an alkali carbonate equivalent to or more than Fe ²⁺ in the liquid to a liquid in the range of ˜30% and then aerating an oxygen-containing gas to carry out the growth reaction of the goethite nucleus particles, Spinel-shaped goethite particles having an axial diameter of 0.25 μm or less, a uniform particle size and no mixed dendritic particles, and a large axial ratio, particularly, an axial ratio of 10 or more. You are getting powder.

The above reaction system will be described in detail below. First of all, as for the green last, for example, “The sample is 0.7 equivalent of N ferrous sulfate to N.
The pH is measured while oxidizing the basic salt produced by adding aOH, and the oxidation is stopped when the pH reaches 5.5. The compound obtained at this time is green rus
t. The pH at which green last is produced, although it depends on the equivalent ratio of alkali.
Is 6.5 to 5.5, and when all of the green last is changed to goethite core particles, the pH sharply drops to 4 or less.

Therefore, the present inventor examined the degree of oxidation of green last in the reaction system and the state of goethite nucleus particles produced through the green last, and the green last and the goethite nucleus passed through the green last were examined. To a ferrous salt reaction solution containing a mixture with particles, at an oxidation degree of Fe ²⁺ of 0 to 50%, an aqueous solution of an alkaline carbonate equivalent to or more than the Fe ^{2+ in the} solution is added to grow. When the reaction was performed to produce spindle-shaped goethite particles, the following results were obtained.

When the degree of oxidation is less than 10%, as shown in Comparative Example 1 below, goethite core particles are not sufficiently formed, and thus the spindle-shaped particles having a small axial ratio are obtained even by the growth reaction with the aqueous solution of alkali carbonate. Only goethite particles exhibiting the above are obtained. When the degree of oxidation exceeds 30%, needle-shaped goethite particles are obtained and the particle size is large because the particle size of the goethite nucleus particles becomes large as shown in Comparative Example 2 below. Further, when the degree of oxidation is 0%, goethite core particles are not generated at all as shown in Comparative Example 3 below, and thus, a spindle-shaped goethite having a small axial ratio similar to the method described above is obtained. Only particles can be obtained.

Then, as shown in Examples described later, when the degree of oxidation is in the range of 10 to 30%, a major axis diameter of 0. It is possible to obtain spindle-shaped goethite particles having a particle size of 25 μm or less, a uniform particle size, and a large axial ratio, in particular, an axial ratio of 10 or more.

It is generally considered that fine goethite nucleus particles are produced from green last, and the remaining green last grows fine goethite nucleus particles, and in the above reaction system, green of pH 6.5 to 5.5 is also used. If the degree of oxidation exceeds 30% in the last region, the particles are aged by a dissolution precipitation reaction and grow to a large particle size.

On the other hand, FeCO obtained by reacting the aqueous solution of ferrous salt and the aqueous solution of alkali carbonate by the above-mentioned method.
_When spindle-shaped goethite particles are produced by carrying out an oxidation reaction by passing an oxygen-containing gas through a suspension containing ₃ , FeCO ₃ has a very low viscosity and high-speed oxidation is carried out, so that fine particles are obtained. Is obtained, but the axial ratio is small. However, in the above reaction system, the presence of fine goethite nucleus particles in FeCO ₃ makes the particles finer, and moreover, the crystal habit of the acicular crystals of the nucleus particles produced from green last is taken over, so that the axial ratio becomes large.

Therefore, the present inventor added an equivalent amount or more of the aqueous solution of alkali carbonate at the time when the fine goethite core particles were produced, and immediately added FeCO ₃ produced by the remaining Fe ²⁺ and the aqueous solution of alkali carbonate. It is considered that the goethite particles which are fine particles and have a uniform particle size and have a spindle shape with a large axial ratio can be obtained because the growth reaction of fine goethite nucleus particles can be performed.

In the present invention, since the growth reaction is carried out by adding an equivalent amount or more of the alkali carbonate aqueous solution, impurities such as sulfur and chlorine do not remain on the surface of the particles.
Therefore, since the sintering does not occur during heating and reduction and the particle shape is not disturbed, it is possible to obtain a magnetic particle powder having a uniform particle size and an appropriate axial ratio.

When an aqueous solution of alkali hydroxide is used in place of the aqueous solution of alkali carbonate to be added to the aqueous solution of ferrous salt containing the mixture, an equivalent amount or more of the aqueous solution of alkali hydroxide or the aqueous solution of alkali carbonate is used in the reaction for producing goethite nucleus particles. In any of the cases, the goethite particle powder, which is the object of the present invention, has a uniform particle size and does not contain dendritic particles, and has a large axial ratio cannot be obtained.

Further, in the technical means for carrying out the growth reaction in the presence of green rust in the acidic to neutral region after the goethite core particles are produced by an aqueous solution of an alkali hydroxide or an alkali carbonate having an equivalent amount or less, as described above, Even if a uniform particle size is obtained, the axial ratio is still insufficient, and impurities such as sulfur and chlorine remain on the particle surface, causing sintering to occur during heat reduction, resulting in a particle shape It is easily crumbled, and thus it is difficult to obtain a magnetic particle powder having a large axial ratio.

[0042]

The present invention will be described below with reference to Examples and Comparative Examples. The major axis diameter and the axial ratio of the particles in the following examples and comparative examples are all shown by the average value of the numerical values measured from electron micrographs.

The degree of oxidation is determined by charging a ferrous salt aqueous solution or a reaction solution into a flask, substituting it with an inert gas, and adding and dissolving a mixed acid of sulfuric acid and phosphoric acid while heating, and then dissolving Fe ^{2 in the} solution. ⁺ Was measured by a redox titration method, and was calculated from the Fe ²⁺ content by the following formula. (A−B) ÷ A × 100 = oxidation degree (%) However, A is the Fe ²⁺ content in the reaction solution immediately after mixing the ferrous salt aqueous solution and the alkaline aqueous solution of less than the equivalent amount B includes the mixture. Fe ²⁺ content in ferrous salt reaction solution

Example 1 Ferrous Sulfate Aqueous Solution Containing 1.5 mol / l Fe ²⁺ 13.
3 l and 26.7 l of 0.75N NaOH aqueous solution (corresponding to 0.5 equivalent to Fe ^{2+ in} ferrous sulfate aqueous solution) were mixed, and F was added at pH 7.4 and temperature 39 ° C.
An aqueous ferrous sulfate solution containing e (OH) ₂ was produced.

The ferrous sulfate aqueous solution containing Fe (OH) ₂ was aerated with 150 l / min of air for 30 minutes at a temperature of 42 ° C. to separate the green rust and the goethite core particles produced through the green rust. A ferrous salt reaction solution containing the mixture was produced. A part of the reaction solution was sampled and the measured degree of oxidation was 25%.

To the ferrous salt reaction solution containing the mixture with the above-mentioned goethite core particles, a 1.33N Na ₂ CO ₃ aqueous solution 15 was added.
1 (corresponding to 2.0 equivalents to Fe ²⁺ in the residual ferrous sulfate aqueous solution) was added, and 100 l / min of air was aerated for 5 hours at pH 9.2 and a temperature of 42 ° C. to obtain goethite particle powder. Was generated. The produced goethite particles were filtered, washed with water and dried by a conventional method.

As shown in the electron micrograph (× 30000) of FIG. 1, the obtained goethite particle powder had a uniform particle size and did not contain dendritic particles, and had a major axis diameter of 0.21.
The particles were spindle-shaped particles having a diameter of μm and an axial ratio of 13.

Examples 2 to 5, Comparative Examples 1 to 4 Kind, concentration and amount of ferrous salt aqueous solution, kind, concentration and amount of alkaline aqueous solution at the time of producing a mixture of greenlast and goethite core particles, Different types and amounts of different elements, pH during mixing, reaction temperature during formation, degree of oxidation when adding alkaline aqueous solution, type, concentration and amount of alkaline aqueous solution for growth reaction, pH during reaction, and reaction temperature Goethite particles were produced in the same manner as in Example 1 except that the above was used.

The main production conditions and various characteristics of the produced goethite particles at this time are shown in Tables 1 and 2.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

EFFECTS OF THE INVENTION According to the method for producing spindle-shaped goethite particle powder according to the present invention, as shown in the above Examples,
Goethite in the form of spindles having a major axis diameter of 0.25 μm or less, a uniform particle size, no dendritic particles mixed in, and a large axial ratio, in particular, an axial ratio of 10 or more. A particle powder can be obtained.

Spindle-shaped magnetite particle powder obtained by heating and reducing the spindle-shaped goethite particle powder according to the present invention as a starting material, and spindle-shaped powder obtained by heating and then oxidizing The maghemite particle powder exhibiting the above is also a fine particle and does not have dendritic particles mixed in which the particle size is uniform, and moreover, since it is a spindle-shaped particle having a large axial ratio, high recording density, high sensitivity, It is suitable as a magnetic particle powder for high output.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 1.
0).

2 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 3. FIG.
0).

3 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 1. FIG.
0).

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

5 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 3. FIG.
0).

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 4.

Claims (1)

[Claims] 1. A hydroxide hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate or a mixed 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 salt reaction solution containing a ferrous colloid or an iron-containing precipitate colloid to oxidize the ferrous hydroxide colloid or the iron-containing precipitate colloid, whereby the green last and the green are obtained. A ferrous salt reaction solution containing a mixture with goethite core particles produced via the last is produced, and then the degree of oxidation of Fe ²⁺ in the ferrous salt reaction solution containing this mixture is 10 to 30%. In a liquid in the range of 1), Fe ²⁺ in the liquid is added with an aqueous solution of an alkali carbonate having an equivalent amount or more, and then an oxygen-containing gas is passed through to carry out the growth reaction of the goethite nucleus particles. A method for producing a goethite particle powder having a spindle shape.