JPS6081029A - Manufacture of goethite - Google Patents

Abstract

PURPOSE:To manufacture needlelike goethite for a magnetic recording medium such as a magnetic tape in a short time by subjecting an alkaline Fe(OH)2 suspension to oxidation treatment with a gas contg. oxygen in two steps under specified conditions. CONSTITUTION:An aqueous soln. of a ferrous salt such as FeSO4 or FeCl2 is mixed with an aqueous soln. of an alkali such as NaOH to prepare an alkaline Fe(OH)2 suspension, and a gas contg. oxygen such as air is blown into the suspension in 2-3 ratio of alkali:Fe at 10-30 deg.C to produce seed crystals of goethite. An aqueous alkali soln. is added to the suspension and heated, and a gas contg. oxygen is blown again into the suspension in >=3 ratio of alkali:Fe at 40-60 deg.C to grow the seed crystals of goethite by oxidation. Fine and uniform needlelike goethite by oxidation. Fine and uniform needlelike goethite of 0.02- 0.05mum particle size can be manufactured in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic material for magnetic recording media, and more particularly to a method for producing acicular goethite.

Sword-shaped iron particles of γ-ferric oxide (γ-Fe2O3), which are excellent in wide moments, are expected to be used as magnetic recording media such as magnetic tapes or magnetic tapes.

In order to improve the performance of magnetic recording media, fine (long axis: 0.
1 to 0.4 lm) and a uniform particle size distribution with little branching is required, and the raw material nail-shaped goethite particles must also be fine and have a uniform particle size IIJ. .

A conventionally known method for producing acicular goethite is to add alkali to a ferrous salt solution such as ferrous sulfate to make it strongly alkaline, and then blow an oxidizing gas such as air into the solution to cause an oxidation reaction. . However, this method requires a long time to produce, and the resulting nail-like goethite particles are large and branched, and the particle size distribution is uneven. This method provides the ability to eliminate defects and obtain fine, unbranched, sword-shaped goethite particles with a uniform particle size distribution in a short time.

According to the present invention, goethite is produced through a two-step process of producing a seed crystal and growing the seed crystal. Seed crystal production at this time is performed at a low temperature of 10 to 30°C and an alkali-to-iron ratio of 2 to 3 or more, and crystal growth is performed at a temperature of 40 to 60°C and an alkali-to-iron ratio of 3 or more.
-The reaction is carried out under the following conditions.

Goethite (α-ferric oxyhydroxide α-Fe”00)1), which is the raw material for γ-ferric oxide, is produced by adding a caustic sorter to an aqueous solution of ferrous salts such as ferrous sulfate and ferrous chloride. A basic solution such as alkali or carbonate is added to generate ferrous hydroxide or a poorly soluble salt as a nucleus through a neutralization reaction, and then a butyric acid-containing residue such as air is blown in to cause an oxidative hydrolysis reaction. Goethite.

Oxygen-containing gas refers to oxygen diluted with inert gas such as nitrogen or argon, and air is generally used in goethite production.

When creating goethite particles, the lower the liquid temperature and the lower the alkali/iron ratio, the faster the nucleation rate or the crystal growth rate, resulting in extremely fine and uniformly distributed seed crystals (long axis 0).
．． 0.05 lm or less).

Conversely, by raising the water temperature and increasing the alkali/iron ratio, only crystal growth occurs on this seed crystal, resulting in fine and uniformly distributed Geitai I (Length IIi + 0.2□”0.4
gm) can be obtained.

The alkali/iron ratio is the number of moles of alkali (01('-) such as sodium hydroxide used and the added ferrous iron (F
It refers to the ratio of the number of moles of e2+).

The inventors of the present invention have investigated various crystal growth conditions for JZ goethite and have found that nucleation and crystal growth can be effectively controlled by appropriately selecting the liquid temperature and the amount of alkali relative to iron, leading to the present invention.

That is, in the present invention, the nucleation step is performed at 10 to 30°.
An oxidizing gas such as air is passed through a ferrous hydroxide suspension at a low temperature of C and a low alkali/iron ratio of 2 to 3 to form seed crystals. By generating crystals under the above conditions,
Nucleus crystals with a fine and uniform grain size of 0.02-0.05 g m are obtained.

In addition, the crystal growth process is 30~eo'c, alkali/iron ratio 3
That's all for now. By adding seed crystals to the ferrous hydroxide suspension under these conditions and aerating oxygen-containing gas such as air, sword-shaped goethite particles with a fine particle size distribution are obtained in a short time.

In the present invention, the temperature of the previous step is set at 10 to 30"C because below 10"C, the reaction is slow and uneconomical.
This is because the crystal growth rate is twice as high as the crystal nucleus generation rate at temperatures above 10°C and L. In addition, the temperature of the post process was set to 40 to 6
The reason for setting the temperature to 0°C was to obtain a crystal growth rate that exceeded the nucleation crystal formation rate by L, and to suppress the by-production of magnetite (Fe304), the -1-eye was set to 1liO'c.

Next, the reason for limiting the alkali/iron ratio in the present invention will be explained.

In the previous step, by adding alkali in excess of twice the amount of ferrous iron added, more nuclei are generated, resulting in seed crystals with fine and uniform grain size. The reason why the alkali/iron ratio was set to 2 to 3 is because if this ratio is less than 2,
This is because black magnetite (Fe304) is generated, and if the alkali/iron ratio is 3 or more, crystal growth progresses, resulting in seed crystals with large non-uniform grain sizes. If seed crystals with non-uniform particle size are used, the goethite obtained through the subsequent crystal growth step will be large and non-uniform in particle size, making it unsuitable as a raw material for magnetic powder.

The lower the temperature, the more nuclei are generated, and fine seed crystals can be obtained, but if the alkali/iron ratio is 2 to 3,
Furthermore, seed crystals with finer and uniform particle size can be easily obtained.

To obtain seed crystals with an alkali/iron ratio of 2 to 3, the oxygen-containing scum must be aerated into a solution at a constant temperature containing the added ferrous salt and 2 to 3 times the number of moles of alkali (OH'-). Bye.

In the post-process, by setting the alkali/iron ratio to 3 or more, the generation of nuclei is suppressed, and the fine seed crystals with a uniform grain size obtained in the previous process are allowed to grow, and the long axis length of the uniform grains is 0. 2~
0.4 km of goethite can be obtained. When the alkali/iron ratio is less than 3, more nuclei are generated, resulting in ketite with non-uniform grain size.

If the liquid temperature is 40°C or higher, crystal growth will slow down the generation of nuclei, but if the alkali/iron ratio is 3 or higher, crystal growth will be further promoted and the crystal will grow uniformly on the seed crystal. As a result, fine crystals with uniform particle size and no branching are obtained.

To grow crystals with an alkali/iron ratio of 3 or more,
A new ferrous salt solution and a solution containing an alkali (OH-) with an amount of 1- or more than three times the number of moles of ferrous iron are added to the suspension containing the seed crystals, and an oxygen-containing gas is heated at a constant temperature. Just ventilate it.

Example 1 0.5 mole of aqueous solution with FeSO4 concentration of 0.4 mole/liter and Na
0.5 ml of an aqueous solution with an OH concentration of 1.0 mol/ml is mixed,
The ferrous hydroxide suspension was removed. Keeping the liquid temperature at 20°C, stir 4 volumes of Na0)1 aqueous solution and add 1.0 mol/mm of Fe.
In addition to 5 ml of SO4 aqueous solution, air was blown at 10 ml/min while stirring to perform air oxidation at 45°C. In the second reaction, Fe(11) was no longer observed within 15 hours.

The obtained goethite had a long sleeve length and an average axis ratio between the long axis and the short axis of 0.37 g m and 13, respectively, and had a uniform particle size distribution.

Example 2 The same procedure as in Example 1 was conducted except that the reaction temperature of the first stage reaction (seed crystal generation reaction) was changed to 10°C.

The same procedure as in Example 1 was conducted except that the wide temperature was 30°C.

Comparative Example 1 NaOH in the first stage reaction (seed crystal generation reaction) of Example 1
The same procedure as in Example 1 was carried out except that the solution concentration was 2.5 mol/cross.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the first stage reaction (seed crystal generation reaction) was carried out at 45°C.

Table 1 shows the reaction conditions of the above examples and the results of measuring the shape of the obtained goethite. Also, Example 1 and Comparative Example 1
FIG. 1 shows the results of measuring the major axis length of the goethite particles obtained in Comparative Example 2. In the figure, curve 1 represents Example 1, curve 2 represents Comparative Example 1, and curve 3 represents Comparative Example 2.

(The following is a blank space) As is clear from Table 1, the goethite obtained by the present invention is fine, has a large axial ratio, and has excellent acicularity. This is due to the fact that the seed crystals are fine and have a uniform particle size. Furthermore, it can be seen from FIG. 1 that the particle size distribution of the particles according to the present invention is sharp. Furthermore, it can be seen that in the comparative example, a long reaction time was required to obtain the same yield.

WJ micrographs showing the structure of the particles obtained in Example 1 and Comparative Example 2 are shown in FIGS. 2 and 3. As is clear from the figure, the goethite according to the present invention is finer, has an acicular shape, and has a uniform particle size distribution compared to the conventional product.

As explained above, according to the present invention, by adjusting the alkali/iron ratio, extremely fine seed crystals can be obtained, and the seed crystals can be caused to grow only, thereby easily producing fine, uniformly sized, unbranched seeds. goethite can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the length of long sleeves of goethite particles. FIG. 2 is a micrograph showing the shape of goethite according to the present invention. Figure 3 is a micrograph showing the shape of conventional goethite. Patent applicant: Showa Denko Co., Ltd. Representative: Patent attorney: Sei Kikuchi, Nakajiro, cμ′m,) Procedural amendment (method) Kazuo Wakasugi, Commissioner of the Japan Patent Office, dated July 2, 1982, 1, Indication of 4S Patent I No. 189278, 1989, 2, Title of invention: Process for manufacturing goethite 3, Amendment. Relationship with the case of the person who issued the patent Address: Shiba Daimon-13-9, Minato-ku, Tokyo Name (20
0) Showa Denko Co., Ltd. Representative Yasunori Kishimoto 4 Agent (zip code 1o5) Address 13-9 Shiba Daimon-chome, Minato-ku, Tokyo Inside Showa Denko Co., Ltd. January 31, 1980 (shipment date) "Column for brief explanation of drawings in the specification" 7. Contents of the amendment As shown in the attached sheet, "Detailed explanation of the invention" column in the specification (1) Page 1 of the specification, line 20, "Holding power" is corrected as "coercive force". (2) In the first line of page 9 of the specification, the phrase "shape" is amended to read "shape: long sleeves and axial ratio." 2. “Brief explanation of drawings” column (1) of the specification, “shape” in the first line of page 12 of the specification is corrected to “particle structure”. (2) In the second line of page 12 of the specification, "shape" is corrected to "particle structure."

Claims (1)

[Claims] By aerating oxygen-containing gas to an alkaline Fe(OH)2 suspension obtained by mixing a ferrous iron aqueous solution and an alkaline aqueous solution to perform an oxidation reaction, a nail-shaped α-FeOO)
In the method of obtaining 1 crystal, the temperature of the suspension is 10 to 3
After reacting at 0°C1 and an alkali/iron ratio of 2 to 3, the temperature was set to 40 to 60°C and an alkali/iron ratio of 3.
The method is characterized in that the reaction is carried out as described above. Goethite manufacturing method.