JPH10259025A - Production of fine particle of acicuiar goethite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain fine particles of acicular goethite excellent in acicularity, sharp in size distribution and having no twin crystal, and additionally having durability against various heat treatments in its post-process and retaining its shape as acicular fine particles by aging a suspended resultant mixture of ferric salt solution and strong alkali solution while limiting the concentration of the ferric salt. SOLUTION: This method is to produce fine particles of acicular goethite by aging a suspension containing at least one gelatinized amorphous substance obtained from a mixture of ferric salt solution and strong alkali solution, i.e., ferric hydroxide and/or FeOOH with a little water therein. In the production, the aging is conducted, preferably at 35 to 80 deg.C, so that the concentration of the ferric salt in the suspension may fall into the range of 0.10 to 0.10mol/l, and preferably the suspension is at PH 12.6 to 13.5.

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 acicular goethite microparticles, and more particularly, to a method of producing acicular goethite microparticles suitable as a pigment or the like as a magnetic powder raw material for a coating type high density magnetic recording medium. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Needle-like γ-Fe ₂ O ₃ and Fe ₃ O ₄ used for a coating type magnetic recording medium, and iron oxide-based magnetic powder obtained by coating Co on them, or acicular Fe or Fe- C
As starting materials for metal-based magnetic powders such as o-alloys, acicular goethite (α-FeOOH) fine particles are widely used. The magnetic properties, powder properties, and coating properties of these magnetic powders are greatly affected by the particle shape of acicular goethite, which is the starting material. Therefore, to obtain a magnetic powder with excellent magnetic and rheological properties,
Fine needles with excellent needle-like properties, sharp distribution of these, no branching, that is, no twins, and durability against various heat treatments such as dehydration, reduction, and oxidation added in the subsequent process. It is necessary to prepare monodisperse needle-like goethite fine particles satisfying conditions such as good preservation of the shape of the fine fine particles.

Hitherto, several methods have been proposed as a method for producing acicular goethite fine particles. For example, a ferrous hydroxide colloid obtained by adding an alkali solution to a ferrous salt solution is converted into an acidic, medium, A method of oxidizing in a neutral or alkaline suspension, a hydrothermal synthesis method in which a ferric hydroxide colloid obtained by adding an alkali solution to a ferric salt solution is subjected to high-temperature and high-pressure treatment in a strong alkali turbid solution, and A method is known in which a ferric hydroxide colloid obtained by adding an alkali solution to a ferrous salt solution is aged at a relatively low temperature in a strong alkali turbid solution.

Of these methods, the first method of oxidizing ferrous hydroxide colloids tends to broaden the particle size distribution and easily produce particles having a twin structure forming an angle of about 120 °. Magnetic powder starting from such irregular needle-like 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 orientation of the magnetic powder can be reduced. And it is difficult to improve the electromagnetic conversion characteristics. In the second hydrothermal synthesis method, 100 ° C.
Because of the synthesis at the above high temperature, cubic crystals of α-Fe ₂ O ₃ are often generated and mixed into the acicular goethite fine particles, or the acicular goethite fine particles aggregate to deteriorate the acicularity. Therefore, it is not suitable as a raw material of a magnetic powder for a high-density magnetic recording medium. The third method of aging ferric hydroxide colloid in a strong alkaline turbid solution at a relatively low temperature is a method proposed to improve the above-mentioned conventional method. For example, Japanese Patent Publication No. 55-4695 It is disclosed in the gazette. However, it can be said that the particle morphology of the acicular goethite fine particles greatly fluctuates depending on the setting of the aging conditions, and a method for stably synthesizing fine particles having excellent acicularity has not yet been established.

[0005]

DISCLOSURE OF THE INVENTION The present invention is based on such a technical background, and is intended to provide fine and fine needle-like properties, a sharp distribution of the fine particles, and a bifurcated shape, that is, a double shape. Manufacture of needle-like goethite fine particles having no crystals and exhibiting durability against various heat treatments such as dehydration, reduction and oxidation added in a later step, and capable of favorably preserving the shape of the needle-like fine particles. The task is to provide a method.

[0006]

The method for producing acicular goethite fine particles of the present invention is proposed to solve the above-mentioned problems, and comprises mixing a ferric salt solution with a strong alkali solution. A method for producing acicular goethite microparticles, which is obtained by aging a suspension containing at least one gelled amorphous substance of ferric hydroxide produced and FeOOH containing a trace amount of water therein. The fermentation is characterized by fermenting the suspension with the ferric salt concentration in the range of 0.01 mol / l to 0.10 mol / l. When the ferric salt concentration exceeds this range, the resulting needle-like goethite fine particles are easily aggregated and difficult to obtain in a monodispersed state, and when the ferric salt concentration is less than this range, Since the yield of needle-like goethite fine particles is reduced, it is unsuitable as an industrial production method.

At this time, p of the suspension, ie, the suspension mother liquor,
H is desirably 12.6 or more and 13.5 or less.
If the pH of the suspension exceeds 13.5, the aggregation of the acicular goethite particles tends to occur, which is not preferable. If the pH of the suspension is less than 12.6, the formation of particulate α-Fe ₂ O ₃ is likely to occur, and the heat resistance to various heat treatments in the subsequent steps will be poor. Therefore, by selecting the pH in the range of 12.6 to 13.5, the particle size is small, the particle size distribution is sharp, and there is no twin which is a branched crystal. Site fine particles can be obtained.

It is desirable that the aging is performed in a temperature range of 35 ° C. to 80 ° C. If the aging temperature exceeds 80 ° C., particulate α-Fe ₂ O ₃ is easily formed, which is not preferable. When the aging temperature is 35 ° 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.

As the ferric salt used in the present invention, any ferric salt which is usually used for producing needle-like goethite fine particles can be employed, for example, ferric chloride, ferric sulfate or nitric acid. Ferric iron and the like are exemplified. These ferric salts are dissolved in a solvent such as water and used for the reaction as a ferric salt solution.

The strong alkali to be mixed with the ferric salt solution is not particularly limited, either. Alkali metal hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide is dissolved in a solvent such as water. Used.

In the present invention, it is possible to produce acicular goethite fine particles containing a metal other than Fe, 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.

In the present invention, the order of mixing the ferric salt solution and the strong alkali solution may be any method. That is, the ferric salt solution may be dropped into the strong alkaline solution and mixed, or vice versa. 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 and the strong alkali solution is preferably short, for example, 5 minutes or less. If the mixing time is long, the suspension containing the ferric hydroxide or the gel-like amorphous substance of FeOOH containing a small amount (for example, about 10% by weight) of water therein, which has been previously mixed, In some cases, the process proceeds from the nucleation of the acicular goethite fine particles to the nucleus growth stage, and the particle size distribution of the acicular goethite fine particles, which is the final product, expands, making it difficult to obtain monodisperse particles.

The ferric salt solution and the strong alkali solution are mixed at room temperature. As a pretreatment for aging, mixing of a suspension containing a gelled amorphous substance of ferric hydroxide while maintaining room temperature is performed. It is desirable 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.

[0015]

The present invention will now be described in detail with reference to specific examples of the present invention and comparative examples, but the present invention is not limited to these examples.

Example 1 The following Examples 1 to 4 show the concentration of ferric salt in a suspension containing a gelled amorphous substance of ferric hydroxide and / or FeOOH containing a trace amount of water. This is an example in which needle-like goethite fine particles are changed. Dissolved ferric chloride hexahydrate and (FeCl ₃ · 6H ₂ O) in distilled water, 0.1
1250 ml of a 5 mol / l ferric chloride solution was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to obtain 0.75 mol /
of sodium hydroxide solution 783 ml dropwise, followed by 163 ml of 0.15 mol / l sodium hydroxide solution for pH adjustment.
Alternatively, a suspension containing a gel amorphous material of FeOOH containing a trace amount of water therein was prepared. The ferric salt concentration in this suspension was 0.085 mol / l by simple calculation, and the pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 35 ° C. for 192 hours to obtain needle-like goethite fine particles of Example 1.

Example 2 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water, and a 0.075 mol / l ferric chloride solution 25 was dissolved.
00 ml was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to prepare a 0.375 mol / l sodium hydroxide solution 1622.
The suspension containing the ferric hydroxide and / or the gel-like amorphous material of FeOOH containing a trace amount of water therein is added dropwise and mixed with 364 ml of a 0.075 mol / l sodium hydroxide solution. A liquid was prepared.
The ferric salt concentration in this suspension was 0.042 mol / l, and the pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 35 ° C. for 192 hours to obtain needle-like goethite fine particles of Example 2.

Example 3 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water to obtain a 0.0375 mol / l ferric chloride solution 2.
500 ml was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to prepare a 0.213 mol / l sodium hydroxide solution 176.
0 ml, followed by dropwise addition and mixing of 400 ml of 0.0375 mol / l sodium hydroxide solution to obtain ferric hydroxide and / or FeO containing a small amount of water therein.
A suspension containing a gelled amorphous material of OH was prepared. The concentration of the ferric salt in this suspension was 0.02 mol /
and the pH was 12.7. Thereafter, the suspension was transferred to an aging warmer and aged at an aging temperature of 35 ° C. for 96 hours to obtain needle-like goethite fine particles of Example 3.

Example 4 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water to obtain a 0.0249 mol / l ferric chloride solution 2.
500 ml was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to prepare a 0.126 mol / l sodium hydroxide solution 200
0 ml, followed by dropping and mixing 400 ml of a 0.0244 mol / l sodium hydroxide solution to obtain ferric hydroxide and / or FeO containing a small amount of water therein.
A suspension containing a gelled amorphous material of OH was prepared. The ferric salt concentration in this suspension was 0.013 mo
1 / l and pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 35 ° C. for 96 hours to obtain needle-like goethite fine particles of Example 4.

Example 5 In Examples 5 to 7 below, needle-shaped suspensions containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water were changed by changing the aging temperature. This is an example in which goethite fine particles were prepared. Ferric chloride hexahydrate (F
eCl ₃ · 6H the ₂ O) was dissolved in distilled water, 0.075 m
2500 ml of an ol / l ferric chloride solution were prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to obtain 0.375 mol / l.
Of sodium hydroxide solution was added dropwise, followed by 0.075 mol / l sodium hydroxide solution 36.
4 ml was dropped and mixed to prepare a suspension containing a ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. The ferric salt solution in this suspension was 0.042 mol / l and the pH was 12.7.
Met. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 45 ° C. for 71 hours to obtain needle-like goethite fine particles of Example 5.

Example 6 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water, and a 0.075 mol / l ferric chloride solution 25 was dissolved.
00 ml was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to obtain a 0.375 mol / l sodium hydroxide solution 1604.
and then 379 ml of a 0.075 mol / l sodium hydroxide solution are added dropwise and mixed to obtain a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. A liquid was prepared.
The ferric salt solution in this suspension was 0.042 mol / l and the pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 55 ° C. for 44 hours.
Acicular goethite microparticles of Example 6 were obtained.

Example 7 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water to obtain a 0.075 mol / l ferric chloride solution 25.
00 ml was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaOH) was dissolved in distilled water to prepare a 0.375 mol / l sodium hydroxide solution 1700.
of the ferric hydroxide and / or a suspension containing a gel-like amorphous substance of FeOOH containing a small amount of water therein by adding 400 ml of a 0.075 mol / l sodium hydroxide solution dropwise. A liquid was prepared.
The ferric salt concentration in this suspension was 0.041 mol / l, and the pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 80 ° C. for 22 hours.
Acicular goethite microparticles of Example 7 were obtained.

Comparative Example 1 The following Comparative Examples 1 and 2 are examples in which the ferric salt concentration deviated from the concentration range of the present invention. Ferric chloride hexahydrate (FeC
l ₃ · 6H the ₂ O) was dissolved in distilled water, 0.25 mol /
1 750 ml of a ferric chloride solution was prepared. While stirring the ferric chloride solution, sodium hydroxide (NaO
H) was dissolved in distilled water, and 479 ml of a 1.25 mol / l sodium hydroxide solution was dropped and mixed.
106 ml of a sodium hydroxide solution of mol / l was dropped and mixed to prepare a suspension containing a ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. The ferric salt concentration in this suspension was 0.1
It was 41 mol / l and the pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 45 ° C. for 71 hours to obtain needle-like goethite fine particles of Comparative Example 1.

Comparative Example 2 Ferric chloride hexahydrate (FeCl ₃ .6H ₂ O) was dissolved in distilled water, and a 0.75 mol / l ferric chloride solution 250 was dissolved.
ml was prepared. While stirring this ferric chloride solution,
2. Dissolve sodium hydroxide (NaOH) in distilled water;
157 ml of a 75 mol / l sodium hydroxide solution is dropped and mixed, followed by 23 ml of a 0.75 mol / l sodium hydroxide solution, and the mixture is mixed with ferric hydroxide and / or a FeOOH gel containing a trace amount of water therein. A suspension containing a crystalline amorphous material was prepared. The ferric salt concentration in the mother liquor of this suspension was 0.436 mol / l,
pH was 12.7. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 45 ° C. for 48 hours to obtain needle-like goethite fine particles of Comparative Example 2.

The aging conditions of the nine needle goethite microparticles of Examples 1 to 7 and Comparative Examples 1 and 2 are summarized in Table 1.

[0026]

[Table 1]

The obtained Examples 1 to 7 and Comparative Examples 1 and 2
The powder characteristics of the nine kinds of needle-like goethite fine particles were measured. The cumulative average diameter and its standard deviation were determined by Doppler scattered light analysis. The crystallite diameter is Scherre
It was determined by the r method. Further, the major axis and minor axis of the acicular particles and the axial ratio were determined by measuring the dimensions from a TEM (transmission electron microscope) photograph. The results are shown in [Table 2].

[0028]

[Table 2]

As is clear from the results in Table 2, the acicular goethite fine particles of the examples are finer and have a uniform particle size distribution as compared with the acicular goethite fine particles of the comparative example.
Observation by EM showed that there were few twins and aggregation.

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

For example, as the type of the ferric salt and the type of the strong alkali, various compounds other than the ferric chloride and sodium hydroxide of the embodiment can be selected, and the combination thereof is also optional. In addition, various modes are also possible for the method of mixing the ferric salt solution and the strong alkali.

[0032]

As is clear from the above description, according to the present invention, monodisperse needle-like goethite fine particles having a fine particle diameter and excellent needle-like properties, and having a sharp distribution and no twins. Can be provided. Further, the acicular goethite fine particles obtained by the present invention exhibit durability against various heat treatments such as dehydration, reduction, and oxidation added in a later step, and the shape of the acicular fine particles is well preserved. Accordingly, it is possible to provide a coating type magnetic recording medium having excellent magnetic properties such as coercive force, residual magnetic flux density, squareness ratio, etc., orientation, and surface properties. Further, since the needle-like goethite fine particles of the present invention have an excellent particle size distribution, they can be suitably used as pigments having improved chroma.

Claims (3)

[Claims] 1. A gel-like amorphous substance containing at least one of ferric hydroxide and FeOOH containing a trace amount of water therein, which is produced by mixing a ferric salt solution and a strong alkali solution. A method for producing needle-like goethite fine particles obtained by aging a suspension, wherein the ferric salt concentration in the suspension ranges from 0.01 mol / l to 0.10 mol / l. A method for producing acicular goethite microparticles, which is characterized in that: 2. The pH of the suspension is 12.6 or more and 1 or more.
2. The method for producing acicular goethite fine particles according to claim 1, wherein the particle size is 3.5 or less. 3. The method for producing acicular goethite fine particles according to claim 1, wherein the aging is performed in a temperature range of 35 ° C. or more and 80 ° C. or less.