JPH10259026A - Production of fine particle of acicular 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 shapes as acicular fine particles, by adding a solution of alkali carbonate to a suspended resultant mixture of ferric salt solution and strong alkaline solution so as to contain a specific concentration of carbonate ion. 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 alkaline solution, i.e., ferric hydroxide and/or FeOOH with a little water therein. In the production, a solution of alkali carbonate is added to the suspension so that the molar ratio of carbonate ion to ferric ion may be 6.0 to 10.0 and the aging is conducted preferably at 35 to 80 deg.C. Preferably, the concentration of the ferric salt solution in the suspension is 0.01 to 0.10 mol/l and the suspension is at pH12.6 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, the particle morphology of the acicular goethite fine particles fluctuates greatly depending on the setting of the aging conditions, and it has been difficult to stably synthesize fine particles having excellent acicularity.

[0005] Therefore, as a method for producing acicular goethite fine particles having an excellent particle size distribution and excellent branch-free acicularity in the aging method, an alkali hydroxide is added to a ferric salt solution and the pH is adjusted to a neutral range of 6 to 8. A method has been proposed in which a ferric hydroxide colloid is produced by adding the alkali metal carbonate to the colloid solution, followed by aging. However, there are also cases where granular or cubic α-Fe ₂ O ₃ particles are produced as by-products and mixed in the acicular goethite fine particles produced by this method. When the powder is produced, a granular magnetic powder is mixed in addition to the acicular magnetic powder, which is not preferable as a magnetic powder for a magnetic recording medium. In addition, since the pH of the suspension at the time of precipitation of the gelled ferric hydroxide colloid is as low as 6 to 8, crystallization into α-FeOOH particles is inhibited, and the resulting needle-like goethite fine particles are crystallized. A gel-like amorphous substance of ferric hydroxide that has not been converted is likely to be mixed.

Further, as a method for improving these disadvantages, a ferric salt solution is added to an alkali hydroxide solution to adjust the pH to 9.0.
A ferric hydroxide colloid is precipitated and formed in an alkali region of about 12.0, and alkali carbonate is added to the ferric hydroxide colloid suspension at a molar ratio of CO ₃ ²⁻ / Fe ³⁺ of 0.4. ~ 4.
JP-A-59-119704 proposes a method for obtaining needle-like goethite microparticles after adding so as to obtain a fine particle having a particle size of 8. However, even in this method, the fineness of the acicular goethite fine particles to be generated is insufficient, which is not preferable as a magnetic powder for a recent high-density magnetic recording medium. As described above, it can be said that a method of producing fine acicular goethite fine particles which is fine and excellent in acicularity and excellent in thermal stability in any method has not yet been established.

[0007]

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.

[0008]

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. Method for producing needle-like goethite microparticles obtained by aging the resulting suspension containing at least one gel-like amorphous substance of ferric hydroxide and FeOOH containing a trace amount of water therein At
An alkali carbonate solution is added to the suspension so that the molar ratio of carbonate ion to ferric ion becomes 6.0 or more and 10.0 or less, and the suspension is aged. If the molar ratio of carbonate ion to ferric ion, that is, the molar ratio of CO ₃ ²⁻ / Fe ³⁺ is less than 6.0, the resulting fine needle-like goethite particles are insufficiently refined, and the monodisperse particles Cannot take form. CO ₃ ^2-
If the molar ratio of / Fe ³⁺ exceeds 10.0, the effect of miniaturizing the acicular goethite fine particles is saturated, and it is meaningless to add excessive carbonate ions.

In the present invention, it is desirable that the suspension be fermented with the ferric salt concentration in the range of 0.01 mol / l to 0.10 mol / l. If 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 if the ferric salt concentration is less than this range, the needle Since the yield of the goethite-like fine particles decreases, it is unsuitable as an industrial production method.

The pH of this suspension, ie, the suspension mother liquor,
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, the pH should be 12.6 or more and 1
By selecting the range of 3.5 or less, it is possible to obtain needle-like goethite fine particles having a small particle size and a sharp particle size distribution, and having no twins which are branched crystals and having excellent needle-like properties.

It is preferable that the aging is performed in a temperature range of 35 ° C. or more and 80 ° C. or less. If the aging temperature exceeds 80 ° C., particulate α-Fe ₂ O ₃ is easily formed, which is not preferable. If the aging temperature is lower than 35 ° C., crystallization of the acicular goethite fine particles is not sufficient, and unreacted particles composed of a gel-like amorphous substance are likely to remain.

As the ferric salt used in the present invention, any one 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 mixed with the ferric salt solution is not particularly limited either.
It is used by dissolving an alkali metal hydroxide such as potassium hydroxide or lithium hydroxide in a solvent such as water.

The carbonate used as the carbonate ion source is not particularly limited either. For example, an alkali carbonate such as sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate is dissolved in a solvent such as water. Used.

In the present invention, it is possible to produce needle-like 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, the strong alkali solution and the alkali carbonate 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 with the strong alkali solution and the alkali carbonate solution is preferably short, for example, within 5 minutes. If the mixing time is long, ferric hydroxide, which has been mixed earlier,
Alternatively, a suspension containing a gel-like amorphous substance of FeOOH containing a small amount (for example, about 10% by weight) of water therein may proceed from the nucleation of needle-like goethite fine particles to the nucleus growth stage, and the final formation may occur. The particle size distribution of the acicular goethite fine particles, which is the product, is widened, and it is difficult to obtain monodisperse particles.

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

[0019]

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 3 show the amounts of alkali carbonate added to a suspension containing a gelled amorphous substance of ferric hydroxide and / or FeOOH containing a trace amount of water, In this example, needle-like goethite fine particles are prepared by changing the amount of alkali carbonate solution and changing the molar ratio of carbonate ion to ferric ion. Ferric chloride hexahydrate (FeCl _3.
6H ₂ O) was dissolved in distilled water to prepare 2500 ml of a 0.075 mol / l ferric chloride solution. While stirring the ferric chloride solution, sodium hydroxide (NaOH)
Was dissolved in distilled water and 1625 ml of a 0.375 mol / l sodium hydroxide solution was dropped and mixed, and a suspension containing a gel-like amorphous substance of ferric hydroxide and / or FeOOH containing a trace amount of water therein was added. Prepared. At this point the pH of the suspension was 13.0. Subsequently, 300 ml of a solution obtained by dissolving sodium carbonate (Na ₂ CO ₃ ) in distilled water to a concentration of 3.75 mol / l was added to the suspension, followed by stirring and mixing. The concentration of ferric salt in this suspension was 0.042 mol / l by simple calculation, and the pH was 1
3.1. The molar ratio of CO ₃ ^2- / Fe ³⁺ is 6.
It was 0. Thereafter, the suspension is transferred to an aged incubator,
Aging was conducted at an aging temperature of 35 ° C. for 96 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 obtain a 0.375 mol / l sodium hydroxide solution 1650.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 13.0. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, followed by stirring and mixing. The ferric salt concentration in this suspension was 0.04 by simple calculation.
It was 1 mol / l and the pH was 13.1. The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 8.0. 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 2.

Example 3 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 1650.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 13.0. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, and the mixture was further stirred and mixed. The concentration of ferric salt in this suspension was 0.0
It was 40 mol / l and the pH was 13.1.
The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 10.0. Thereafter, the suspension was transferred to an aging incubator, and an aging temperature of 35 ° C.
For 96 hours to obtain needle-like goethite fine particles of Example 3.

Example 4 The following Examples 4 and 5 are examples in which the molar ratio of carbonate ion to ferric ion was changed to produce needle-like goethite fine particles as in Examples 1 to 3 above. This is an example in which the aging temperature is higher than in Examples 1 to 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. While stirring the ferric chloride solution, sodium hydroxide (Na
OH) dissolved in distilled water is mixed dropwise with 1690 ml of a 0.375 mol / l sodium hydroxide solution, and ferric hydroxide and / or FeOOH containing a trace amount of water therein.
A suspension containing the gelled amorphous material of was prepared. At this point the pH of the suspension was 13.0. Subsequently, 300 ml of a solution obtained by dissolving sodium carbonate (Na ₂ CO ₃ ) in distilled water to 3.75 mol / l was added to this suspension.
Was added and further mixed by stirring. The concentration of ferric salt in this suspension was 0.042 mol / l by simple calculation, and p
H was 13.1. The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 6.0. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 55 ° C. for 44 hours to obtain needle-like goethite fine particles of Example 4.

Example 5 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, a 0.375 mol / l sodium hydroxide solution 1720 in which sodium hydroxide (NaOH) was dissolved in distilled water was used.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 13.0. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, followed by stirring and mixing. The ferric salt concentration in this suspension was 0.04 by simple calculation.
It was 1 mol / l and the pH was 13.1. The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 8.0. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 55 ° C. for 44 hours to obtain needle-like goethite fine particles of Example 5.

Example 6 In the following Examples 6 to 7, the molar ratio of CO ₃ ²⁻ / Fe ³⁺ was kept constant, and the pH of the suspension was slightly lowered from that of the previous example, which was kept constant. This is an example in which the temperature is changed. Dissolved ferric chloride hexahydrate and (FeCl ₃ · 6H ₂ O) in distilled water,
2500 ml of a 0.075 mol / l ferric chloride solution was prepared. While stirring the ferric chloride solution, 0.289 of sodium hydroxide (NaOH) dissolved in distilled water was added.
A 1950 ml mol / l sodium hydroxide solution was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension is 12.5
Met. Subsequently, sodium carbonate (Na ₂
300 ml of a solution obtained by dissolving CO ₃ ) in distilled water was adjusted to 3.75 mol / l, and the mixture was further stirred and mixed. The concentration of ferric salt in this suspension was 0.040 mol / l by simple calculation.
And the pH was 12.6. CO ₃ ^2- /
The molar ratio of Fe ³⁺ was 6.0. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 35 ° C. for 162 hours to obtain needle-like goethite fine particles of Example 6.

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, a sodium hydroxide solution (1870) of 0.321 mol / l sodium hydroxide (NaOH) was dissolved in distilled water.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 12.5. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, followed by stirring and mixing. The ferric salt concentration in this suspension was 0.04 by simple calculation.
It was 0 mol / l and the pH was 12.6. The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 6.0. Thereafter, the suspension was transferred to an aging incubator and aged at an aging temperature of 55 ° C. for 71 hours to obtain needle-like goethite fine particles of Example 7.

Comparative Example 1 The following Comparative Examples 1 to 3 are examples in which the molar ratio of CO ₃ ²⁻ / Fe ³⁺ deviates from the scope of the present invention. Dissolved ferric chloride hexahydrate and (FeCl ₃ · 6H ₂ O) in distilled water, 0.07
2500 ml of a 5 mol / l ferric chloride solution was prepared. 0.375 mol of sodium hydroxide (NaOH) dissolved in distilled water while stirring the ferric chloride solution.
A suspension containing a ferric hydroxide and / or a gel-like amorphous substance of FeOOH containing a trace amount of water therein was prepared by dropwise mixing 1625 ml of a 1 / l sodium hydroxide solution. At this point the pH of the suspension was 13.0. Subsequently, sodium carbonate (Na ₂ CO 3) was added to this suspension.
₃ ) was dissolved in distilled water, and 100 ml of a solution having a concentration of 3.75 mol / l was added thereto, followed by stirring and mixing. The ferric salt concentration in this suspension was 0.044 mol / l by simple calculation, and the pH was 13.1. CO ₃ ^2- / Fe
^{The 3+} molar ratio was 2.0. 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 Comparative Example 1.

Comparative 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 this ferric chloride solution, a 0.375 mol / l sodium hydroxide solution 1625 in which sodium hydroxide (NaOH) was dissolved in distilled water was used.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 13.0. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, followed by stirring and mixing. The ferric salt concentration in this suspension was 0.04 by simple calculation.
It was 3 mol / l and the pH was 13.1. The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 4.0. 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 Comparative Example 2.

Comparative Example 3 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 this ferric chloride solution, a 0.375 mol / l sodium hydroxide solution 1625 in which sodium hydroxide (NaOH) was dissolved in distilled water was used.
The resulting mixture was dropped and mixed to prepare a suspension containing ferric hydroxide and / or a gelled amorphous substance of FeOOH containing a trace amount of water therein. At this point the pH of the suspension
Was 13.0. Subsequently, sodium carbonate (Na ₂ CO ₃ ) was dissolved in distilled water to give 3.75 mol of the suspension.
/ L of the solution was added, and the mixture was further stirred and mixed. The concentration of ferric salt in this suspension was 0.0
It was 40 mol / l and the pH was 13.2.
The molar ratio of CO ₃ ²⁻ / Fe ³⁺ was 12.0. Thereafter, the suspension was transferred to an aging incubator, and an aging temperature of 35 ° C.
For 96 hours to obtain needle-like goethite fine particles of Comparative Example 3.

Examples 1 to 7 and Comparative Examples 1 to 3
The aging conditions for the ten types of needle-like goethite microparticles are summarized in [Table 1].

[0031]

[Table 1]

Examples 1 to 7 and Comparative Example 1 obtained above
The powder properties of 10 types of acicular goethite fine particles of Nos. 1 to 3 were measured. The cumulative average diameter and its standard deviation were determined by Doppler scattered light analysis. The crystallite diameter is
It was determined by the rr 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].

[0033]

[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 Comparative Examples 1 and 2. Observation with a TEM showed that twins and aggregation were small. Further, it exhibited durability against various heat treatments such as dehydration, reduction, and oxidation added in a later step, and the shape of the acicular fine particles was well preserved. Further, the needle-like goethite fine particles of Comparative Example 3 are comparable to the examples in that fine particles can be obtained, but the effect of the fineness is saturated, and it is less meaningful to add a large excess of alkali carbonate.

Although the present invention has been described in detail above, the present invention is not limited to these embodiments. For example, it is possible to adopt various compounds other than the sodium carbonate of the examples as the kind of the alkali carbonate. The type of ferric salt and the type of strong alkali can also be selected from various compounds other than ferric chloride and sodium hydroxide of the examples, 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.

[0036]

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 (4)

[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 molar ratio of carbonate ions to ferric ions in the suspension is 6.0 or more and 10.0 or less. A method for producing acicular goethite fine particles, comprising adding an alkali carbonate solution to the mixture and aging the mixture. 2. The ferric salt concentration in the suspension is set at 0.0
2. The method for producing needle-like goethite fine particles according to claim 1, wherein the ripening is performed in a range of 1 mol / l to 0.10 mol / l. 3. 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. 4. 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.