JPS5846841B2 - Manufacturing method of ferromagnetic iron oxide powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ferromagnetic iron oxide powder suitable as a recording element of a magnetic recording medium.

The inventors have already discovered that when βFe00H, which is normally obtained by hydrolyzing FeCl3 and contains several weight coefficients of chlorine atoms, is reduced with a reducing gas in a state where the chlorine atoms are contained, the following reaction occurs in a reducing atmosphere. 2FeCA3 (gas) + H242FeC12 (solid) +
2HC7 (gas) 3FeC12 (solid) + 4H20-'F e 30
4 (Solid) + 6HC1 (Gas) + H2 As a result of the vapor phase growth of Fe304, the generation of particle pores and branches that are likely to occur during dehydration is suppressed, and Fe3O4 magnetic powder with a smooth surface is formed. The γ-Fe203 magnetic powder obtained by oxidation does not impair the above-mentioned characteristics and shape. Therefore, when these magnetic powders are kneaded with a binder resin, the magnetic powders are uniformly dispersed and a magnetic material with good orientation is obtained. It has been found that a recording material can be obtained.

However, for this method, if the β-FeOOH powder containing chlorine atoms to be subjected to reduction is composed of a large number of rod-shaped particles arranged in a layered manner, the vapor phase growth mainly occurs between adjacent particles. Fe3O is generated and grows in the vapor phase.
4, each particle is bonded and integrated with each other, resulting in the formation of large Fe 304 magnetic powder in the particle.Also, if there is a variation in the number of rod-shaped particles arranged in layers, this variation will occur. may be transmitted into the particles of Fe3O4 magnetic powder formed.

Therefore, it is preferable that the β-FeOOH powder containing chlorine atoms used in the above method does not have a layered structure, and even if it does have a layered structure, the number of rod-shaped particles constituting it should be as small as possible. It is preferable to use a powder with a small number of particles and a small variation in the number of particles among each powder.

However, it is very difficult to obtain such β-Fe00H powder. For example, the usual method of hydrolyzing FeCl3 to obtain β-Fe00H containing chlorine atoms, washing it with water, filtering it, and then drying it is difficult to synthesize. Immediately after, some rod-shaped particles are already arranged in a layer, and when washed with water and filtered, they grow further to form a tactoid consisting of many particles.The number of particles differs depending on each tactoid, and by drying, the shape and becomes difficult to dissociate.

Therefore, no matter how finely pulverized the particles are after drying, the number of particles cannot be reduced below a certain value, but is generally large and fluctuates, and fluctuations in the number of particles are further exacerbated by non-uniform pulverization.

As described above, in the previously proposed method, the enlargement button in the particles of the Fe304 magnetic powder formed due to the arrangement structure of the particles of β-Fe00H used or the γFe2O3 magnetic powder obtained by oxidizing the same is Non-uniformity is inevitable, and enlargement in the grains deteriorates the axial ratio and the acicular ratio, lowering the coercive force, and the non-uniformity has an adverse effect on other magnetic properties.

The present invention aims to provide a method for producing ferromagnetic iron oxide powder, which improves the proposed method from the above viewpoint and suppresses enlargement and non-uniformity of the particles.

In other words, this invention provides β-containing chlorine atoms immediately after synthesis.
Fe00H was dispersed in an ammonium carbonate aqueous solution, and after the β-Fe00H particles contained chlorine atoms in the state of 11, the ammonium carbonate was interposed between the particles, and then dried, and then dried with a reducing gas. F e 304 or γ-Fe2O3 which is thermally reduced or subsequently oxidized
The present invention relates to a method for producing ferromagnetic iron oxide powder consisting of:

β-Fe00H used for this invention needs to contain at least one chlorine atom or more in order to carry out the vapor phase growth, and usually FeCl3
It can be synthesized by the hydrolysis method.

Looking at the particle arrangement structure of β-Fe00H containing chlorine atoms immediately after synthesis, rod-shaped particles are already arranged in a partial layer, but the number of particles is generally small.

In this invention, βFe0O containing chlorine atoms immediately after synthesis
H is subjected to a dispersion treatment in an aqueous ammonium carbonate solution.

As a result of this dispersion process, the layered arrangement is once dissociated and then rearranged, or it further grows to produce tactoids with a large number of particles.

The purpose of the dispersion treatment is to generate such tactoids in a state in which chlorine atoms are contained in β-Fe00H rod-shaped particles, and the particles are brought into direct contact with each other by intervening ammonium carbonate between the rod-shaped particles. The goal is to prevent the formation of tactoids and reduce the number of particles that come into direct contact with each other as much as possible.

The dispersion treatment can be carried out by, for example, adding an excessive amount of ammonium carbonate aqueous solution to β-FeOOH containing chlorine atoms immediately after synthesis, which is charged in a funnel, stirring and dispersing it, and filtering while dispersing it. The preferred method is to add it to an aqueous ammonium carbonate solution, stir and disperse it, allow it to settle, and then filter and separate it.

In the latter case, powdered ammonium carbonate may be immediately added to water in which β-FeOOH is dispersed.

The temperature during dispersion treatment should be maintained at a temperature at which ammonium carbonate does not decompose, and the amount of ammonium carbonate used varies depending on the concentration of the aqueous solution, but usually β-FeOOH
It is preferable that the amount is at least 5% by weight relative to the total amount.

Prior to this dispersion treatment, there is no problem in washing the β-FeOOH containing chlorine atoms immediately after synthesis according to Tsunehiro with water, which is rather preferable for the purpose of obtaining magnetic powder in the form of needle-like crystals.

Washing with water is carried out in the same manner as described in the dispersion treatment above.
This may be carried out by means such as pouring through filtration or dispersing it in water before filtration.

It is naturally expected that during washing with water or subsequent filtration, layering of particles will progress and tactoids with a large number of particles will be generated.

However, this tactoid can be easily dissociated in the subsequent dispersion process, and new tactoids are generated in the dispersion process.

Therefore, there is almost no possibility that the presence of ammonium carbonate will be hindered by washing with water.

However, care must be taken because dissociation becomes difficult after the dispersion process is delayed and once dried.

Drying after the dispersion treatment may be performed at room temperature or under heating, but in the case of heating drying, the temperature needs to be lower than 70° C. so that the interposed ammonium carbonate does not decompose.

After this drying, it is pulverized if necessary.

When the β-Fe00H powder containing chlorine atoms, in which a plurality of rod-shaped particles prepared in this way are arranged in a layer and ammonium carbonate is interposed between the particles, is then heated and reduced with a reducing gas, the chlorine atoms are Vapor phase growth occurs based on the pores and branches that tend to occur due to dehydration, and the intervening ammonium carbonate decomposes and evaporates in the early stages of heating, creating voids between particles. Particle bonding and integration, which tends to occur during phase growth, is prevented or suppressed.

In addition, as long as ammonium carbonate is sufficiently interposed between particles on average, the above-mentioned suppressing effect will work regardless of whether there is a change in the number of particles forming a layered structure. Non-uniformity within the grain due to growth is also suppressed.

Reduction may be carried out according to a conventional method, and in order to ensure sufficient vapor phase growth, dry hydrogen gas from which water has been removed is preferably used as the reducing gas, and the reduction temperature is set at 250-400 ℃.
00'C.

The reduction time is appropriately determined depending on the gas flow rate, temperature, etc.

When oxidizing after reduction, F e s obtained by the above reduction
04 magnetic powder in a conventional manner, e.g. 200 to 300
It can be oxidized in air at a temperature of °C.

Fe3O4 magnetic powder or γ-F obtained in this way
e203 magnetic powder not only has a smooth particle surface, but also has an almost uniform inside particle, and is free from β-Fe0, which is a reductant.
It is almost the same as that of 0H or only slightly enlarged.

As detailed above, the present invention relates to β-containing chlorine atoms.
By interposing ammonium carbonate between the rod-shaped particles of Fe00H powder using a specific method, and by thermally decomposing and volatilizing this during reduction to create voids between the rod-shaped particles in a layered arrangement, particles that are easily generated by vapor phase growth are created. This suppresses the expansion and non-uniformity of Fe3O4 or γ-F, which has stable magnetic properties and less decrease in coercive force.
Ferromagnetic iron oxide powder consisting of e2O3 can be produced.

Next, the present invention will be explained in more detail with reference to Examples.

Example 549 of ferric chloride (FeCls), 27 g of ammonium chloride, and 61 of urea are dissolved in 11 of water to prepare a reaction solution.

This reaction solution is boiled for 2 hours to produce β-FeOOH, which is thoroughly washed with water and then immediately dispersed in 100 g of water, and at the same time, 4 g of reconstituted ammonium acid is added with stirring.

After being left to stand, it is filtered and dried in the usual manner (20'C).

β-F with a weight range of 3.9 in terms of chlorine content obtained by the above method
20 g of e00H powder was collected on a board and put into a reduction furnace, and hydrogen gas, which had passed through a baradium catalyst and calcium chloride to remove oxygen and moisture, was introduced into the furnace at a flow rate of 17/min. A reduction treatment was performed with C for 3 hours.

The new Fe s 04 magnetic powder has a coercive force of 360 oersted and a saturation magnetization of 82 emu/g. Observation results using an electron microscope show that it is acicular particles with a smooth surface.
It was confirmed that the inside of the particles was slightly larger than the β-FeOOH to be reduced and was almost uniform.

When this Fe3O4 magnetic powder was oxidized at 250'C with air flowing in for 1 hour, it was found that the Fe3O4 magnetic powder and
An r-Fe203 magnetic powder with no observed change in shape was obtained.

The coercive force of this powder is 340 oersted, and the saturation magnetization is 7
It was 3 emu/g.

Comparative Example: β-Fe00 after the completion of the hanging reaction without performing dispersion treatment in the ammonium carbonate aqueous solution.
After thoroughly washing H with water, it was immediately filtered and dried, and the obtained βFe0OH powder with a chlorine content of 3.9% by weight was used as a reductant and reduced in the same manner as in the example.

The Fe3O4 magnetic powder obtained by this method has a coercive force of 34
The saturation magnetization was 82 emu/g at 0 oersted.

Observation using a small-scale electron microscope revealed that the particles were acicular particles with a smooth surface, similar to the example, but on the other hand, the inside of the particles was much harsher than the reductant β-FeOOH, and the surface was uneven. Met.

Claims (1)

[Claims] 1. β-Fe00H containing a chlorine atom immediately after synthesis was dispersed in an ammonium carbonate aqueous solution, and the above β-Fe00H was dispersed.
A ferromagnetic oxide consisting of Fe3O4 or γFe2O3, which is obtained by interposing the ammonium carbonate between the FeOOH particles in the state 11 in which chlorine atoms are contained in the FeOOH particles, and then drying the particles, followed by heating reduction with a reducing gas or subsequent oxidation. Method of manufacturing iron powder.