JPS6046525B2 - Method for producing granular magnetite particle powder containing high coercive force and magnetic stability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing Co-containing granular magnetite particles, and more specifically, Co-containing granular magnetite particles having magnetic stability and high coercive force. This invention relates to a method for manufacturing powder using a wet method.

Recently, magnetite particles have been regarded as important as magnetic recording media materials because of their high coercive force (Hc), high saturation magnetism (σs), and high electrical conductivity. Attempts are being made to use materials exhibiting this as materials for magnetic cards, floppy disks, etc.

In general, the following "wet method" is well known as a typical manufacturing method for magnetite particle powder exhibiting a granular particle shape.

That is, Fe obtained by adding an equivalent amount or more of a basic substance (alkali) to the acid radical in an aqueous solution of ferrous salt such as ferrous sulfate.
60% of an aqueous solution containing (OH)O colloid with a pH of 10 or more.
A granular magnetite is produced by maintaining the temperature in a temperature range of ℃ to 1000℃ and carrying out an oxidation reaction while stirring and passing an oxidizing isotropic gas to produce a granular black precipitate, which is then filtered, washed with water, and dried. A granular powder is obtained.

However, the coercive force of the granular magnetite particle powder obtained by the above wet method is about 1450e at most.
This material had a low coercive force and was not satisfactory for use as a magnetic recording medium material for magnetic cards, floppy disks, etc.

Therefore, various methods have been proposed to increase the coercive force of granular magnetite particles. Conventionally, the technical means widely used for this purpose is to coexist Co(OH)2 with Fe(OH)O in the solution before the oxidation reaction when obtaining granular magnetite particle powder by the wet method. There is a method of allowing Co to be contained in the granular magnetite particles produced by the oxidation reaction by leaving the magnetite to stand.

This method utilizes the crystal magnetic anisotropy of CO ions and is intended to be used in magnetic recording media materials that increase coercive force by incorporating CO into granular magnetite particles.

That is, the coercive force is adjusted by the amount of CO added, and by increasing the amount added, the coercive force can be improved. However, since the temperature coefficient of the anisotropy constant Ku of CO, which is effective in improving the coercive force, is large, there is a problem that magnetic instability of the coercive force occurs, and the magnetic instability of the coercive force is caused by temperature factors. It is known that the magnetic instability is affected by changes over time, and the current subject of development of CO-containing granular magnetite particles is how to improve this magnetic instability. In this way, CO-containing granular magnetite particles have a high coercive force, and as the CO content increases, a high coercive force can be obtained more efficiently. This is a cause of increased magnetic instability due to changes over time. In view of the above-mentioned current situation, the present inventor has been conducting research for many years in order to obtain a CO-containing granular magnetite particle powder which has excellent magnetic stability and in particular has as small a change in coercive force as possible over time.

The present inventor has been conducting studies in the direction of obtaining a CO-containing granular magnetite particle powder with a small change in coercive force over time by reducing the CO content. but,
Although the change in coercive force over time can be reduced by reducing the CO content, it has not been possible to obtain CO-containing granular magnetite particles having a high coercive force. The inventor believes that the reason for this is that when obtaining granular magnetite particles containing a small amount of CO, naturally the amount of CO compound added to the ferrous salt aqueous solution is also small, and in this case, CO is present in individual magnetite particles. I thought that it might be because it was not uniformly contained in the particles. The present inventor has discovered that CO(0H)2 and Fe(0H)2 in the solution before the oxidation reaction can be sufficiently uniformly dispersed even when the amount of the added CO compound is relatively small. It was thought that if possible, a CO-containing granular magnetite particle powder having a high coercive force and containing CO uniformly in each particle would be obtained.

Therefore, the present inventor investigated CO in the solution before the oxidation reaction.
As a result of various studies on methods for sufficiently uniformly dispersing (0H)2 and Fe(0H)2, it was discovered that phosphate is the most effective dispersant.

However, in this industry, (1) a method of increasing coercive force by coating granular iron oxide with phosphate, (Journal of the Chemical Society of Japan 1)
976, (8), Pl3l9-1321) (2) A method of adsorbing CO to iron oxide powder containing silicon and phosphorus (Japanese Unexamined Patent Publication No. 55-149137) is known.

However, method (1) involves depositing phosphate on the surface of granular iron oxide once generated, and method (2) involves a step of heat-treating the hydrous oxide to form iron oxide powder. Silicon and phosphorus are used to prevent particles from sintering, and the final product is intended to adsorb CO to obtain a high coercive force as gamma ferric oxide. Various methods for obtaining high coercive force have been studied, as shown in the conventional methods listed above, but none of these methods is sufficiently effective in obtaining CO-containing granular magnetite particles having high coercive force. However, the effect of reducing the change in the coercive force of the particles over time as much as possible was not sufficient.

In view of the above-mentioned facts, the present inventor has conducted extensive research in order to obtain a CO-containing granular magnetite particle powder that has high coercive force and magnetic stability with small changes in coercive force over time. As a result, the present invention was achieved.

That is, in the present invention, an equivalent amount or more of alkali is added to an aqueous ferrous salt solution, and the solution temperature is 70 to 10% in the presence of CO ions.
In a method of manufacturing CO-containing granular magnetite particle powder by an oxidation reaction by passing an oxidizing gas through the oxidizing gas at 0°C, the amount of Fe in the solution before passing the oxidizing gas is 0 in terms of CO.
．． 1-8. (1) High coercive force CO-containing granular magnetite with magnetic stability characterized by adding a CO compound of RnOl% and a P compound of 0.5 to 6.0r1101% in terms of P to Fe This is a method for producing particulate powder.

Next, the configuration and effects of the present invention will be explained in detail.

First, the CO compound used in the method of the present invention may be a water-soluble cobalt salt such as cobalt sulfate or cobalt chloride. The amount of added CO compound is 0 in terms of CO compared to Fe.
．． It must be in the range of 1 to 8.0n101%.

If it is less than 0.1m01%, granular macnetite particles with high coercive force cannot be obtained, and if it is less than 8.0n101%,
If the above amount is used, the rate of increase in coercive force is small, and furthermore, the change in coercive force over time becomes large.

From the magnetic characteristics and economical point of view, 0.5 to 5.0 r1
A range of 101% is preferred. Next, referring to the P compound, a water-soluble lyso acid salt such as phosphoric acid or sodium phosphate can be used as the P compound.

The amount of P compound added is 0.5 to 6.0 in terms of P to Fe.
An rT range of 101% is required. If it is less than 0.5m01%, sufficient dispersion effect cannot be obtained and 6.0
If the rT is 101% or more, it is not preferable because α-FeOOH particles will be mixed into the target CO-containing granular magnetite particle powder.

Preferably it is in the range of 1.0 to 5.0 rT101%.
The CO compound and the P compound may be added before the oxidation reaction occurs; for example, in the starting solution, the desired CO compound and P compound may be added in advance to the ferrous salt aqueous solution. The temperature of the aqueous solution must be maintained in the range of 70 to 100°C during the oxidation reaction, and if it is lower than 70°C, α-FeOOH particles will be generated, which is not preferable.

Further, temperatures of 100°C or higher are not practical from an industrial standpoint.
As the alkali to be used, sodium hydroxide, potassium hydroxide, etc. can be used.

Note that the means for venting the oxidizing gas (for example, air) may be any well-known means used in carrying out the wet method.

Next, the effects of the present invention will be described below.

The CO-containing granular magnetite particle powder obtained by the method of the present invention has the following effects.

That is, as mentioned above, the CO-containing granular magnetite particle powder obtained by the conventional method has a high CO content in order to obtain a high coercive force, so magnetic instability increases and changes over time are large. It has become a thing.

On the other hand, as shown in FIG. 1, the CO-containing granular magnetite particles obtained by the method of the present invention have a high coercive force with a composition having a low CO content.

Figure 1 shows the relationship between CO content and coercive force Hc of CO-containing granular magnetite particle powder, and curve 1 in the figure shows the relationship between CO content and coercive force Hc.
Curve 2 represents particles produced by the method of the present invention (Examples 2, 3, and 5), and curve 2 represents particles obtained by the conventional method (Comparative Examples 1, 2, and 3). Further, the CO-containing granular magnetite particles obtained by the method of the present invention are CO-containing granular magnetite particles that hardly change over time and have magnetic stability, as shown in FIG. Figure 2 shows the coercive force Hc of each powder shown in Figure 1 when left at room temperature (25°C) for 60 days.
The graph shows the change over time between the CO content and the increase rate (%) of Hc. In the figure, curve 1 is the particles produced by the method of the present invention, and curve 2 is the particles obtained by the conventional method. . As mentioned above, the CO-containing granular magnetite particle powder obtained by the method of the present invention has excellent magnetic stability and high coercive force, so it can be used not only as a magnetic card but also as a magnetic recording medium material for floppy disks and the like. I can do it.

Furthermore, according to the method of the present invention, even if the amount of very expensive CO compound used is small, C
It also has the economical effect that O-containing granular magnetite particles can be obtained. Next, the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 COSO4O. 25mOl/f aqueous solution 2.02f(CO
/Fe: corresponds to 1.5m01%.

) and H3PO4O. 50mOl/'aqueous solution 1.01e(
P/Fe: corresponds to 1.5m01%. ) and mix
The mixed aqueous solution was added to 21.3e of a 3.85 mOl/f aqueous solution of NaOH at a solution temperature of 85°C in a reaction vessel equipped with a stirrer and a vent and mixed).

Next, while maintaining the solution temperature at 85°C, 1001/Mi
A black precipitate was obtained after 19 minutes by blowing n air into the mixture.

The obtained black precipitate was filtered, washed with water, and dried at 60'C to obtain CO-containing granular magnetite particle powder. 7 The obtained particle powder was analyzed by fluorescent X-ray, and as a result, COI. O
Wt%, PO. Contains 55 Wt%, and as a result of magnetic measurement, coercive force Hc: 4440e, saturation magnetic σs: 79.4
emu/y, specific surface area 8.6d/y by BET method
It was y.

This CO-containing granular magnetite powder was prepared at room temperature (25
As a result of magnetic measurement when left at ℃) for 60 days, coercive force Hc: 4470e1 Saturation magnetism σs: 79.3emu/
(!, and was magnetically stable with no change over time. Examples 2 to 5 Amount of cobalt sulfate added, amount of phosphoric acid added, amount of sodium hydroxide used, solution temperature, and addition of phosphoric acid CO-containing granular magnetite particle powder was obtained in the same manner as in Example 1 by varying the timing.

The results of measuring the magnetic properties of the particles thus obtained are shown in the table. The table also shows the results of measuring magnetic properties when left at room temperature (25° C.) for 60 days. Like the powder particles obtained in Example 1, these were magnetically stable, high coercive force CO-containing granular magnetite particles that did not change over time. Comparative example 1! -3 CO-containing granular magnetite particle powder was obtained in the same manner as in Example 1 by varying the amount of cobalt sulfate added, the amount of sodium hydroxide used, and the solution temperature.

The results of measuring the magnetic properties of the obtained particles are shown in the table. This material had a low coercive force and was magnetically unstable due to large changes over time.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the CO content and coercive force Hc of CO-containing granular magnetite particles. In the figure, curve 1 is the powder particles obtained by the method of the present invention (Examples 2, 3, and 5), and curve 2 is the powder particles obtained by the conventional method. FIG. 2 shows the change over time in the coercive force Hc when the sample was left at room temperature (25° C.) for 60 days in terms of the relationship between the CO content and the rate of increase (%) in Hc. In the figure, curve 1 is the powder particles obtained by the method of the present invention, and curve 2 is the powder particles obtained by the conventional method.

Claims (1)

[Claims] 1. Adding an equivalent or more alkali to a ferrous salt aqueous solution
In a method for producing Co-containing granular magnetite particle powder by an oxidation reaction by passing an oxidizing gas through the solution at a temperature of 70 to 100°C in the presence of ions, Fe is added to the solution before the oxidizing gas is passed through the solution. On the other hand, in terms of Co, it is 0.1 to 8.
0.5 to 0.5 in terms of P for 0 mol% Co compound and Fe
A method for producing a granular magnetite particle powder containing high coercive force and having magnetic stability, which comprises adding 6.0 mol% of a P compound. 2 As the amount of Co compound added increases to Fe, it becomes 0.5 in terms of Co.
~5.0 mol%, and the amount of the P compound added is 1.0 to 5.0 mol% in terms of P relative to Fe. A method for producing granular magnetite particle powder.