KR100270077B1 - A method of preparing repidocrocite - Google Patents

Abstract

PURPOSE: Provided is a method for preparing a lepidocrocite which has good acicular property and uniform particles. CONSTITUTION: The method comprises steps of: (i) adding an alkali aqueous solution less than equivalent to ferrous chloride aqueous solution to prepare ferrous hydroxide; (ii) oxidizing the ferrous hydroxide to prepare a seed crystal of lepidocrocite with regulating the oxidation speed of the ferrous hydroxide to 0.4-0.6 mol per minute; and (iii) after increasing the temperature of the reaction suspension of the step (ii) at a certain degree, oxidizing the reaction suspension to grow the seed crystal to prepare lepidocrocite with regulating the oxidation speed of the ferrous hydroxide to 0.15-0.4 mol per minute.

Description

Method of manufacturing lepidocrocite

The present invention relates to a method for producing lepidocrocite (γ-FeOOH), and more particularly, a method for producing lepidocrocite excellent in acicularness suitable for use as a starting material for magnetic iron oxide for magnetic recording media such as audio and video. It is about.

Generally, iron oxides for magnetic recording such as audio and video include gamma iron oxide produced by heat treatment of repidocrosite by dehydration, reduction, and oxidation, and cobalt gamma iron oxide having cobalt deposited on its surface.

Since the magnetic properties of the magnetic iron oxide are highly dependent on the acicular properties of the starting material repidocrosite, it is essential to use the repidocrosite having excellent acicular properties in order to produce a good magnetic iron oxide for a magnetic recording medium. Therefore, it is very important to control the particle characteristics of acicular repidocrosite.

Conventional repidocrosite is prepared as follows.

That is, an aqueous alkali solution such as NaOH or NH ₄ OH is added to the ferrous chloride solution to make equivalent ferrous hydroxide, followed by oxidation with an oxygen-containing gas to form a lepidocrocite seed crystal. The falcon becomes 3.0-3.8.

Thereafter, the temperature of the reaction suspension is increased to 30 ° C.-50 ° C. and prepared by a crystal growth reaction in which an oxygen-containing gas is added while adding an alkaline aqueous solution to pH 3-4.

When the growth reaction is complete, the pH is raised. At this time, the reaction was terminated when the pH reached 5.5 to prepare acicular repidocrosite.

In this regard, Japanese Patent Laid-Open Publication Nos. Hei 2-55382 and Hei 3-29011 disclose a method of proceeding a growth reaction after ripening at a constant temperature for a certain time after seed crystal formation reaction, and in Japanese Patent Application Laid-Open No. 62-119117 Japanese Patent Laid-Open Publication Nos. 62-65937 and 62-167222 disclose a method of controlling the oxidizing gas flow rate in three stages according to the oxidation reaction process. Disclosed are a method of controlling the pH increase rate of the reaction solution.

It is an object of the present invention to provide a further improved method of producing rapid dockcrosite.

Furthermore, another object of the present invention is to provide a method for producing repidocrosite having excellent acicularity and uniform particles.

Figure 1a is a TEM picture of the particles prepared under the conditions of Comparative Example 1 of Example 1 of the present invention, Figure b is a TEM picture of the particles prepared by the preparation of Example 2 of Example 1 of the present invention, Figure c is a view of the present invention TEM photograph of the particles prepared under the conditions of Comparative Example 3 in Example 1.

Figure 2a is a TEM photograph of the particles prepared under the conditions of Comparative Example 3 of Example 2 of the present invention, Figure b is a TEM photograph of the particles prepared under the conditions of Example 5 of Example 2 of the present invention, Figure c is a view of the present invention TEM picture of the particles prepared under the conditions of Comparative Example 4 in Example 2.

According to the present invention, ferrous hydroxide is prepared by adding an aqueous alkali solution to an aqueous ferrous chloride solution in an equivalent amount, and then oxidizing it to produce a lepidocrocite seed crystal. In the wet oxidation method for preparing a site, the oxidation rate of ferrous hydroxide when the ferric hydroxide aqueous solution is added to the ferric chloride aqueous solution to prepare ferrous hydroxide, and then oxidized to produce a repidocrosite seed crystal. Generating seed crystals by adjusting the mixture to 0.4-1.6 mol / min; and after the seed crystals are produced, the temperature of the reaction suspension is raised to a predetermined temperature, followed by an academia reaction to grow crystals, wherein the oxidation rate of ferrous hydroxide is increased. There is provided a method for preparing lepidocrocite comprising the step of growing seed crystals by adjusting to 0.15-0.4 mol / min.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is excellent in acicular properties and uniform particles by controlling the oxidation rate of ferrous hydroxide in the seed crystal production step and the crystal growth step, respectively, in the method of producing the process of rapid oxidation by the wet oxidation reaction. It relates to a method for producing crosite. In seed crystal formation reaction, ferric chloride is added to an aqueous alkali solution such as NaOH and NH ₄ OH to form ferrous hydroxide, and then oxidized ferrous hydroxide to form lepidocrocite (γ-FeOOH). At this time, by adjusting the oxidation rate of ferrous hydroxide to O.4-1.6 mol / min, the needle-like particles are small, uniform, such as Goatite (α-FeOOH) and Icaganite (β-FeOOH) Redodocrocite seed crystals are produced that do not incorporate other phases. When the oxidation rate of ferrous hydroxide is less than 0.4 mol / min, the reaction rate is slowed, so that gothite (α-FeOOH) is mixed and seed crystal grains of repidocrosite (γ-FeOOH) are coarse, and 1.6 mol / min In the above case, it becomes a fast oxidation condition, and other phases, such as acaganite, are formed and mixed.

After the seed crystals have been formed, the temperature of the reaction suspension is raised to a constant temperature, and then the oxidation reaction proceeds to allow the crystals to grow on the resulting seed crystal surface. In the crystal growth step, it is preferable to adjust the oxidation rate of ferrous hydroxide to 0.15-0.4 mol / min.

When the oxidation rate of ferrous hydroxide is less than 0.15 mol / min in the crystal growth stage, the reaction rate is slowed, so that gothite may be mixed and the ferrous hydroxide may be sludged without being oxidized, and faster than 0.4 mol / min. Redodocrocite grown under oxidation reaction conditions is formed in unstable particles, and may be redissolved with Fe ²⁺ and OH-.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

Oxidation Rate Control During Seed Formation

After ferrous hydroxide was prepared by adding 10 L of an aqueous sodium hydroxide solution having a concentration of 1.6 M / L to 40 L of ferrous chloride solution having a concentration of 0.8 M / L, oxidation was performed at a reaction temperature of 25 ° C. At this time, seed crystal formation reaction was carried out by varying the oxidation rate of ferrous hydroxide.

The materials produced according to the conditions were examined in XRD and TEM, and the crystal phases and electron microscopic structures were shown in Table 1 and FIG. 1.

As shown in FIG. 1, in Comparative Example 1 in which the oxidation rate of ferrous hydroxide was 0.4 mol / min or less in the seed crystal forming step, gothite formed at a slow oxidation rate was formed and mixed, and particles were coarse and uniform. In contrast, Comparative Example 2, which is 1.6 mol / min or more, also does not form the redodocrocite seed crystals in the form of needles with uniform particle size, Inventive Example 2 is formed in the form of needle-like repidocrosite seed crystals with a uniform particle size It became.

Example 2

Oxidation Rate Control in Crystal Growth

After subjecting the seed pydochrosite seed crystals under the conditions of Inventive Example 2, the temperature of the reaction suspension was raised to 40 ° C., followed by oxidation to proceed the crystal growth reaction. At this time, the crystals were grown by varying the oxidation rate of ferrous hydroxide. The materials produced according to the conditions were examined in XRD and TEM, and the crystal phases and electron microscopic structures were shown in Table 2 and FIG. 2.

As shown in FIG. 2, in Comparative Example 3 in which the oxidation rate of ferrous hydroxide was 0.15 mol / min or less, fine and long particles were formed, indicating that α-FeOOH having a different crystal structure was formed, and a circular aggregate was formed. Indicates that ferrous hydroxide is not oxidized but is sludged, and Comparative Example 4 having an oxidation rate of 0.4 mol / min or more indicates a cloud-like structure rather than acicular shape, indicating that the crystal structure is not stabilized. On the contrary, when the crystals were grown by oxidizing within the oxidation rate range according to the present invention, as shown in Inventive Example 5, fine and clear rod-shaped particles were formed.

In the preparation of repidocrosite, in the seed crystal generation step and the crystal growth step, the repirocrosite produced by adjusting the oxidation rate of ferrous hydroxide to the oxidation rate range of the present invention is used for audio, video, magnetic recording It is suitable to be used as a starting material for magnetic iron oxide for the medium, and is made of repidocrosite having good acicularity and uniform particle size without incorporation of goatite and acaganite.

Claims (1)

Wet oxidation method in which ferric hydroxide is prepared by adding an aqueous alkali solution to ferrous chloride solution in an equivalent amount or less and then oxidizing it to produce a seed crystals of repidocrosite, and growing the seed crystals to produce repidocrosite. In preparing ferrous hydroxide by adding an aqueous alkali solution to the ferric chloride aqueous solution, and then oxidizing the ferric chloride to produce a repidocrosite seed crystal, the oxidation rate of ferrous hydroxide is 0.4-1.6 mol / min to produce seed crystals; and after the seed crystals are produced, the temperature of the reaction suspension is raised to a constant temperature, followed by oxidation to grow crystals, wherein the oxidation rate of ferrous hydroxide is 0.15-0.4 mol / min. Controlling to grow seed crystals; Lepidocrosite production method comprising a.