JPS61141627A - Production of alpha-feooh needles - Google Patents

Abstract

PURPOSE:When a hydroxide suspension resulting from the reaction of a ferrous salt solution with an aqueous alkali is oxidized at a specific pH, the temperature of the suspension and the oxidation rate are specified to give fine and branching- free needles of alpha-FeOOH with highly narrow particle size distribution. CONSTITUTION:An aqueous solution of ferrous compound such as ferrous sulfate is mixed with an aqueous alkali such as sodium hydroxide to precipitate ferrous hydroxide. When the resultant suspension is oxidized by bringing it into contact with an oxygen-containing gas at a pH over 12, the temperature of the suspension and the oxidation rate are set to 5-18 deg.C, and 10-100%/hr, respectively. Further, the addition of nickel at an atomic ratio of 0.005-0.10 to the iron in the suspension can stabilize the inhibition of needles branching. Thus, alpha- FeOOH suitable for use as a metallic magnetic powder for magnetic recording is obtained.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to a method for producing magnetic metal powder containing iron as a main component, and more specifically to a method for producing magnetic metal powder containing iron as a main component. The present invention relates to a method for producing α-F e OOH.

Acicular α- used as raw material for metal magnetic powder for magnetic recording
FeOOH is required to have high density recording and good electromagnetic exchangeability, and its powder properties are said to require fine particles with uniform particle size, excellent acicularity, and little branching.

(Prior art) Conventionally, the method for producing α-FeOOH powder is to add an alkaline aqueous solution to a ferrous salt aqueous solution to form a ferrous hydroxide precipitate, which is then heated with air at a temperature of 20 to 80°C. Although it is basically oxidized, it has a uniform particle size,
Various methods have been proposed to obtain α-FeOOH with less branching.

For example, a water-soluble silicate is added in advance to a solution containing ferrous hydroxide obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution, or a ferrous salt aqueous solution and zinc hydroxide (Zn
A method of adding a water-soluble silicate to a solution containing (OH)2) and then oxidizing it (see Japanese Patent Publication No. 58-53686, Japanese Patent Publication No. 58-5368JF, etc.); A method of obtaining goethite by intermittently supplying an oxidizing gas to a solution containing ferrous hydroxide obtained by reacting an aqueous solution (for example, JP-A-57-2098
34 Publication), etc., but there are no branching of α-Fe00H and the particle size is highly adjusted, for example, particle size distribution width (maximum and minimum of 50 particles selected from electron micrograph). It is not possible to obtain highly uniform values such as a value difference of 0.15μ.

(Object of the Invention) In view of the above circumstances, the present inventors have developed a method that has excellent acicularity and
As a result of intensive studies to obtain α-Fe00H with fine particles and highly uniform particle size, it was discovered that the above object could be achieved by setting the reaction temperature and reaction rate during oxidation treatment within a specific range, and the present invention I was able to complete it.

(Summary of the Invention) That is, the present invention provides a method for obtaining acicular α-FeOOH by oxidizing a suspension with a hydroxide obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution at a pH of 12 or higher. Acicular α-F e OOH characterized by oxidizing a suspension at a temperature of 5 to 18°C and an oxidation rate of 10 to 100%/hour.
To provide a manufacturing method.

(Example of the invention) The method of the present invention will be explained in more detail below.

The ferrous salt used in carrying out the method of the present invention may be any water-soluble iron salt, such as ferrous sulfate, ferrous chloride, or ferrous nitrate.
Iron, etc. may be used alone or as long as it is produced. For example, an aqueous solution of sodium hydroxide or potassium hydroxide is used, and the preferred blending amount is the equivalent amount necessary to precipitate ferrous hydroxide. Any above is sufficient.

In the method of the present invention, a ferrous salt aqueous solution and an alkaline solution are mixed to precipitate ferrous hydroxide, and then a suspension containing the precipitate is oxidized at a pH of 12 or more at a temperature of 5 to 18°C, preferably 7°C. It is brought into contact with an oxygen-containing gas under oxidation conditions of ~15°C and an oxidation rate of 10-100%/hr, preferably 15-60%/hr.

If the pH of the suspension during the oxidation treatment is less than 12, goethite will have many branches, which is not preferable. In addition, when the oxidation temperature exceeds 18℃, fine particles α-F with no difference in technique are used.
When trying to obtain eOOH crystals, it is not possible to obtain crystals with highly uniform grain size, and on the other hand, when the oxidation temperature is less than 5°C, the oxidation rate must be significantly slowed down to obtain crystals without branching. (Actually 5%/hr) Must be L,
The reaction takes a long time and requires cooling of the oxidation reaction vessel, which is economically unfavorable.

In addition, in general, the faster the reaction rate of the oxidation reaction, the more uniform the particle size distribution can be, but if the reaction rate exceeds 100%/hr, fine particles of unbranched α-FeO
It is not possible to obtain OH crystals, which is not preferable, and on the other hand, 10%
If it is slower than /hr, there will be less branching, but it will be difficult to make the particle size distribution uniform and the oxidation time will be long, so it is not practical.

In the present invention, the oxidation rate refers to the concentration of iron in the suspension, which is measured by titration with potassium permanganate.
The oxidation rate R (%) was calculated using the first equation, the time until R reached 30% was set as t (hr), and the calculation was performed using the second equation.

Oxidation rate = -(2) When a known branching inhibitor, especially a nickel salt, is added in a specific range amount when carrying out the method of the present invention, α-FeOO
A more stable branching prevention effect can be exhibited without deteriorating the powder properties of H.

As a method for obtaining nickel component-containing α-FeOOH crystals, ferrous hydroxide and nickel hydroxide are co-precipitated by mixing a mixed solution of ferrous salt and nickel salt with an alkaline solution, or ferrous hydroxide and nickel hydroxide are co-precipitated. An alkaline solution may be added to each of the salt solution and the nickel salt solution to precipitate ferrous hydroxide and nickel hydroxide separately, and then mixed. The amount of nickel salt added that has the effect of suppressing branching is such that the atomic ratio of nickel to iron in the ferrous salt is 0.005 to 0.10, preferably 0.
．． It is used in the range of 0.01 to 0.08. If the amount of nickel added to iron is less than 0.005, there is no effect of suppressing branching, and if it exceeds 0.10, some nickel hydroxide precipitates exist alone, and α-
This is not preferable because it deteriorates the powder characteristics of FeOOH.

Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited by these Examples.

Example 1 Aqueous sodium hydroxide with a concentration of 5.60 mol/1? A ferrous sulfate aqueous solution 21 having a concentration of 0.70 mol/l was added to &5β and reacted while being maintained at 10° C. to obtain a white precipitate of ferrous hydroxide.

(The pH of this suspension was 13.) Next, this suspension was maintained at 10°C while maintaining a pH of 0. Air was blown into the mixture at a rate of 4β/min, and the mixture was oxidized with stirring for 24 hours to obtain a brownish yellow precipitate. The oxidation rate at this time was 43%/hr.

After the precipitate thus obtained was filtered and washed with water,
It was dried at 5°C to obtain α-FeOOH powder.

The major axis diameter of this powdered α-FeOOH was 0.16μ, the particle size distribution width was 0.09μ, and the acicular ratio was 30 with little branching.

Examples 2 to 4 and Comparative Examples 1 to 5 α-FeOOH Reference Examples α- obtained in Examples and Comparative Examples in the same manner as in Example 1 except that the raw material liquid composition and reaction conditions were changed as shown in Table 1. FeOOH powder 40.1
g was dehydrated at 300°C and pre-calcined at 700°C.

The obtained α-F e 20336. Og to volume 20
Place it in a double cone retort container and add 1 H gas.
Aerate at a rate of 12/min and reduce the temperature to 450
The mixture was reduced at ℃ for 2 hours to obtain needle-shaped magnetic iron particle powder. Table 2 shows the coercive force, saturation magnetization, and squareness ratio of the acicular magnetic iron particles thus obtained.

Table 2 (Effects of the Invention) According to the method of the present invention detailed above, a precipitated suspension of ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution is simply heated at a specific temperature and speed. By oxidizing it with , we succeeded in obtaining acicular α-FeOOH with fine particles, highly uniform particle size distribution, and no branching, and its industrial value is extremely great.

Claims (1)

[Claims] 1) A method for obtaining acicular α-FeOOH by oxidizing a hydroxide suspension obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution at a pH of 12 or higher, liquid at temperature 5
A method for producing acicular α-FeOOH, characterized by oxidizing at ~18°C and an oxidation rate of 10 to 100%/hour. 2) Acicular α-FeOOH according to claim 1, in which a nickel component is present in an atomic ratio of 0.005 to 0.10 with respect to iron present in the suspension during the oxidation reaction.
manufacturing method.