JPS5919162B2 - Method for producing iron-cobalt alloy ferromagnetic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing iron-cobalt alloy ferromagnetic powder.

Ferromagnetic alloy powder, which is a magnetic recording material, has several times better magnetic properties than conventional oxide-based powder.

Therefore, its usage is expected to increase significantly in the future. As a production method on a commercial basis, a low-temperature (350 to 500° C.) hydrogen reduction method of iron-based oxides using goethite, which is acicular ferric hydroxide, as a starting material is considered to be effective.

The problem with this process is the effective use of the reducing agent in the reduction step. Low-temperature reduction is desired because the reduction maintains the acicular nature of the raw material goethite.
Since the reduction temperature is low, the reaction rate between the reducing agent and the iron oxide is slow, and the amount of reducing agent D consumed is large. Currently, there are two main methods to deal with this problem: 1, Sn,
The so-called oxides of Ag, Co, Ni, Cu, etc. contain elements that are more easily reduced by hydrogen gas than iron oxide in iron hydroxide or iron oxide to increase the reduction rate.

152, the goethite particles are enriched with a metal compound, such as hydroxide of silicic acid, aluminum or titanium, to maintain their acicularity and prevent sintering during the reduction step, and are reduced by raising the temperature.

The method of the present invention is similar to method 1, in which gator 20ite is obtained, suspended in an aqueous solution containing primary cobalt ions, and a neutralizing agent is added to hydrolyze the cobalt ions.
Cobaltous hydroxide (Co(OH)O) is uniformly deposited on the goethite surface.

Although this is known, the methods known so far25 use an alkaline aqueous solution (including aqueous ammonia) as a neutralizing agent; Cobalt hydroxide was often produced, and cobaltous hydroxide was deposited on the goethite surface in the form of particles and did not completely cover the goethite surface. A neutralization reaction method using ammonia produced by adding urea and decomposing it at high temperature has better uniformity of the neutralization reaction than the method using an alkaline aqueous solution, but it is not economical because the utilization rate of urea is poor and the price is high. do not have. 35 This method uses ammonia gas as a neutralizing agent, and blows it into the suspension either alone or in a mixture with an inert gas or air to cause a neutralization reaction and generate cobalt hydroxide. It is deposited uniformly and directly on the goethite surface.

That is, according to the present invention, an alkali is added to an aqueous medium containing dispersed goethite particles and cobalt ions, and cobalt hydroxide is deposited on the goethite particles to form iron hydroxide cobalt hydroxide composite particles. This is converted into oxide composite particles, and the oxide composite particles are reduced with hydrogen to obtain iron-
A method for obtaining a cobalt alloy ferromagnetic powder, which uses ammonia gas or a mixture of ammonia gas and an inert gas as an alkali in the step of depositing cobalt hydroxide, and supplies this in the form of bubbles into the aqueous medium. A method is provided which is characterized in that:

In the method of the present invention, the cobalt (auto)ion source may be either a mineral acid salt or an inorganic acid salt of cobalt, but cobaltous sulfate is easily used due to its availability, price, stability, etc. . It is not necessary to use a particularly expensive gas to dilute the ammonia gas, and nitrogen or air may be used.

According to this method, the reaction occurs through gas-liquid contact, and the gas can be introduced as fine bubbles, which increases the uniformity of the neutralization reaction in the solution, and neutralizes by changing the amount of gas. The speed can be controlled, and the equipment and handling are extremely simple. Furthermore, when this method is used, cobaltous hydroxide (CO(0H)2) is precipitated uniformly and evenly on the goethite surface, so that during reduction, the reduction rate is fast and the amount of hydrogen consumed is small.

This is thought to be because cobalt becomes the nucleus of the reaction during hydrogen reduction, and cobalt is uniformly distributed over the entire particle surface. Next, examples of the method of the present invention will be shown.
The present invention is not limited to this.

Example 1700g of ferrous sulfate (FeSO4.7H20)
1 of water and mixed with 121 of water in which 200 g of sodium hydroxide was dissolved.

Air at 1000ce//T while maintaining temperature at 50℃
Acicular goethite was obtained by blowing at a speed of 10 min. After washing this separately with F and dispersing it in water 201, 298 g (CO/(Fe+
Add a solution of CO) (15 mol% by mol%) dissolved in water 411 and mix with ammonia gas/air 1:10 at room temperature (20°C).
A mixed gas by volume ratio was blown into the solution at a flow rate of 1100 cc/Mm, and when the pH of the solution reached 9, the blowing of gas was stopped, and the precipitate was washed separately and dried.

FIG. 1 shows an electron micrograph of the hydroxide crystal thus obtained at a magnification of 20,000 times. As seen there, cobaltous hydroxide is uniformly attached to thin acicular goethite crystals. Under the same conditions as the previous example, but,
Figure 2 shows a 20,000x electron micrograph of a composite hydroxide produced by pouring 14% ammonia water into air-diluted ammonia gas with stirring until the pH reached 9.

In this case, spherical cobaltous hydroxide is attached to the needle-shaped goethite crystals, which is not preferable. The above composite hydroxide was calcined at 600° C. for 2 hours to prepare a sample for reduction.

For reduction, place 50 mg of the sample on a thermobalance and set the reduction temperature to 400°C.
The hydrogen gas was flowed at a flow rate of 500 cc/Nin.

The same applies to simple hematite (αFe2O3) particles and complex oxide particles obtained from cobalt hydroxide (auto)coated goethite produced under the same conditions as in the present invention by adding NaOH solution instead of ammonia gas. Hydrogen reduction was performed and the results are summarized in Table 1 and Figure 3. As seen in Table 1 and Figure 3, the iron oxide cobalt oxide composite particles obtained by the method of the present invention can be reduced in a significantly shorter time than the iron oxide cobalt oxide composite particles obtained by the conventional method. It doesn't have to be too small.

The products obtained by the method of the present invention obtained in Example-1 above are as follows:
Hc measured in a magnetic field of 77KOe: 1050.0e. B
m: 170 emu/g1 Square ratio: 43%.

On the other hand, the magnetic properties of the particles obtained by the conventional method, i.e., precipitated using an alkaline aqueous solution and treated under the same conditions, are approximately the same as the products produced by the method of the present invention in terms of coercive force and squareness ratio. ,
Bm was 160 emu/g.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph of a composite hydroxide produced using ammonia gas according to the method of the present invention.

Claims (1)

[Claims] 1. Add an alkali to an aqueous medium containing dispersed goethite particles and cobalt ions to adhere cobalt hydroxide onto the goethite particles to obtain iron hydroxide cobalt hydroxide composite particles, which are then converted into oxide composite particles. A method of obtaining iron-cobalt alloy ferromagnetic powder by converting the oxide composite particles into particles and reducing the oxide composite particles with hydrogen, using ammonia gas or ammonia gas and an inert gas or air as an alkali in the step of attaching cobalt hydroxide. A method characterized in that the neutralization reaction is allowed to proceed slowly by using a mixture of and supplying the mixture in the form of bubbles to the aqueous medium.