JPS6015573B2 - Method for producing cobalt-containing magnetic iron oxide particles - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for producing cobalt-containing magnetic iron oxide particles, and more specifically, the present invention relates to a method for producing cobalt-containing magnetic iron oxide particles, which has a high coercive force that shows little change over time and also has excellent erasing characteristics when used as a magnetic recording medium. The present invention relates to a method for producing cobalt-containing magnetic iron oxide particles having a ratio of Fe/Fe of 0.2 to 0.3.

Conventionally, magnetic iron oxide particles used in magnetic recording media have been developed to have high coercive force in order to meet the demands for high recording density and the like.

One method for this purpose is to incorporate cobalt into magnetic iron oxide particles. On the other hand, by making iron oxide particles with an oxidation degree intermediate between magnetite and maghemite, in other words, iron oxide particles with the Fe/Te ratio appropriately controlled within the range of 0 to 0.5. Methods of obtaining magnetic iron oxide particles with high coercive force have also been considered. As is well known, there are various methods for incorporating cobalt into magnetic iron oxide particles, but they can be roughly divided into: (1) Reacting a ferrous salt aqueous solution containing a predetermined amount of cobalt with an alkali;
Cobalt-containing goethite particles are obtained through a wet reaction in which cobalt-containing ketide particles are generated by air oxidation of an aqueous solution on PHI sand, which is then dehydrated.
A method usually called "doping method J" in which cobalt-containing magnetic iron oxide particles are obtained by reduction and further oxidation if necessary, and
There is a method usually called the "observed method" in which magnetite particles or maghemite particles are obtained by various general manufacturing methods, and a cobalt layer or a cobalt ferrite layer is formed on the surface of the particles to obtain cobalt-containing magnetic iron oxide particles. is well known.

Cobalt-containing magnetic iron oxide particles produced by the former doping method are
Although it has the advantage of superior erasing characteristics when used as a magnetic recording medium such as magnetic tape, compared to the latter method, it is difficult to use magnetic recording media because the coercive force changes over time. It is difficult to say that it is suitable for use as a recording medium.

The change in coercive force over time can be seen, for example, in "Powders and Powder Metallurgy", Vol. 2, P. As clarified by the literature of 4 ships and others, this phenomenon is thought to occur because the cobalt contained in the iron oxide particles moves within the iron oxide particles. If Fe particles are present in the particles, they become active due to the influence of the nuclear Fe particles, causing a significant change in coercive force over time. Therefore, in cobalt-containing magnetic iron oxide particles produced by the doping method, it is extremely difficult to obtain a magnetic iron oxide particle powder that combines the effects of controlling the FeH/Fe ratio described above and improving the coercive force by controlling the Fe/Few ratio. It is.

The present invention aims at improving cobalt-containing magnetic iron oxide particles by a doping method, and uses cobalt-containing goethite particles obtained by the above-mentioned wet reaction as a starting material. That is, the present inventor has conducted research for many years in order to control the FeH/Fe ratio of cobalt-containing magnetic iron oxide using the above-mentioned doping method, to make it have a high coercive force, and to eliminate changes in coercive force over time.

In order to eliminate the change in coercive force of the cobalt-containing magnetic iron oxide over time, in other words, to prevent the cobalt in the iron oxide from moving, it is effective to eliminate Fe in the iron oxide.
However, if we eliminate the Fe day, one Fe/Fe
The effect of improving coercive force by controlling the river cannot be expected.
Therefore, the present inventor developed magnetite (Fe
In order to complete the movement of cobalt by further heat treatment in the state of H / Fe state = 0.5), that is, in a state where cobalt is easy to move, at the same time the value of Fe juice / Fe day should be set to an appropriate value. Various considerations were made regarding the conditions.
When heat-treating cobalt-containing magnetite, one of the conditions that must be considered first is the heating temperature. In terms of facilitating the movement of cobalt, it seems that the higher the temperature, the greater the effect. On the other hand, in order to bring the value of the FeH/Fe ratio to a predetermined value by oxidizing the Fe in magnetite and reducing the Fe content, it is easier to control the oxidation gradually at a low temperature. In addition, the Fe/Fe value, which is the highest area of coercive force, is from "Powder Metallurgy Association 1973 Spring Conference Lecture Summary Collection P.126-127"
It is in the range of 0.2 to 0.3 as reported in .

Generally Fe/? In order to control eM, a means of oxidizing at a low temperature of 250°C or less in an oxidizing atmosphere is being explored.

However, such a low temperature is insufficient in terms of the above-mentioned movement of cobalt, and it takes a very long time to complete the movement. Therefore, the inventor decided to perform the heat treatment at a relatively high temperature of 250 to 550°C. However, in this temperature range, the normal oxidizing atmosphere,
For example, in air, it becomes overoxidized and there is a risk that Fe particles will no longer exist. Therefore, the inventors of the present invention investigated the oxidizing atmosphere and came up with the following conditions. That is, y=ax 130 (where y=air amount (so), a
=20~38 x=cobalt-containing magnetite particle amount (
If heat treatment is performed in an oxidizing atmosphere that satisfies the conditions of k9)), it is possible to complete the transfer of cobalt and at the same time set the value of Fe/Fe to within the range of 0.2 to 0.3.
The resulting cobalt-containing magnetic iron oxide particles have a high coercive force, and the coercive force does not change over time.

The present inventor has completed the invention based on the various findings detailed above.

That is, the present invention dehydrates and reduces cobalt-containing goethite particles to obtain cobalt-containing magnetite particles, and then converts the cobalt-containing magnetite particles to y=ax+30 (however, y=
Heat treatment at a temperature range of 250 to 550 q○ in an oxidizing atmosphere that is aerated with air at a rate that satisfies the amount of air (Z), a = 20 to 3 ft x = amount of cobalt-containing magnetite particles (k9)) This is a method for producing cobalt-containing magnetic iron oxide particles, characterized in that the cobalt-containing magnetic iron oxide particles have a ratio of Fe/Fe of 0.2 to 0.3.

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

First, the heat treatment conditions, which are the core technology of the present invention, will be explained. The heating temperature must be in the range of 250 to 550 qo.

If it is less than 250q○, a long time treatment is required and it is not industrially practical.

On the other hand, if the temperature is 550° C. or higher, there is a risk that the acicularity, which is the lifeblood of magnetic iron oxide, may be lost, and it becomes difficult to control the e-river to a predetermined value with FeH/, which is not preferable.
Next, regarding the heating atmosphere, the amount of air vented during the heat treatment is y=ax+30 (y=air amount (Z
), a = 20 to 35 x = amount of cobalt-containing magnetite particles (k9)). This formula was derived by the inventor from the results of numerous experiments, and when y<230, only a value of Fe/Fe state of 0.3 or more can be obtained. On the other hand, y > 3 strings 13
If it is 0, oxidation has progressed too much and the value of the FeH/Fe river is set to 0.
It becomes impossible to keep it within the range of 2 to 0.3. The amount of air expressed by the above formula is the total amount of air that is vented during the heat treatment, and the ventilation means is such that only air is vented in a predetermined amount, and the final value is the value shown by y. There are various methods such as a method of venting at a ratio of y, or a method of venting a mixed gas of air and an inert gas such as nitrogen and controlling the total amount of air in the mixed gas to the value of y. There is no difference in effectiveness no matter which method is used. When considering industrial productivity, stability, etc., it is preferable to aerate a mixed gas of air/nitrogen gas=1/0.5 to 1'2. The cobalt-containing magnetite particles to be supplied to the heat treatment, which is the most important technique of the present invention, may be any particles obtained by dehydrating and reducing the cobalt-containing goethite particles obtained by the wet method described above.

A suitable content of cobalt is 0.1 to 10 atomic % based on magnetite. The effects of the present invention described in detail above will be described below. The cobalt-containing magnetic iron oxide particles obtained by the present invention are cobalt-containing magnetic iron oxide particles originally obtained by the doping method, since the cobalt-containing goethite particles as a starting material are those obtained by the above-mentioned wet reaction. It has characteristics such as the excellent erasing property possessed by the magnetic iron oxide particles, and also eliminates the disadvantage of the change in coercive force over time of the cobalt-containing magnetic iron oxide particles produced by the doping method. In addition, the cobalt in the iron oxide particles is completely transferred, and the coercive force improvement effect due to the cobalt content is maximized. Furthermore, the value of the FeH/Fe ratio in the iron oxide particles is controlled to a range of 0.2 to 0.3, which is a region with high coercive force, and F
The effect of improving the coercive force by changing the value of eFew can also be effectively exhibited. Due to the various excellent properties described above, the cobalt-containing magnetic iron oxide particles obtained by the present invention are excellent as magnetic materials for use in magnetic recording media such as magnetic tapes. Next, the present invention will be explained with reference to Examples and Comparative Examples.

The cobalt-containing magnetite particles used in the Examples and Comparative Examples were obtained by the following method.

Manufacturing method of raw materials 1 FeS0415. enemy hol, COS040.15hol
15 aqueous solution containing 4.65N NaOH aqueous solution 1
5. After adding soybean powder, 0 air is passed through the mixture to obtain acicular cobalt-containing goethite particles.

The obtained cobalt-containing goethite particles were separated in a furnace, washed with water, dried, dehydrated at 300° C., and reduced with 350 CO to obtain cobalt-containing magnetite particles. Cobalt content (Co/Fe) of the obtained cobalt-containing magnetite particles:
1 atomic %, average particle diameter of long axis 0.6 French m, Fujihi (long axis/
Short axis): 6/1, specific surface area by BET method: 29/g
, Fe/Fe is 0.40, and the magnetic properties are coercive force H
C:56 ratio, saturation magnetization. s:84. It was mu/g. 0 This cobalt-containing magnetite is referred to as "Raw material 1".

Manufacturing method of raw material Cobalt-containing magnetite particles were obtained in exactly the same manner as raw material manufacturing method 1 except that 2COS04 was used in 0.3 liters.

The obtained cobalt-containing magnetite particles had a cobalt content (Co/Fe) of 2 at% and an average particle diameter of 0.5 along the long axis.
rm, axial ratio (major axis/minor axis): 6'1, specific surface area by BET method: 32/g, Fe-Ti/Fe river: 0.38, and magnetic properties are similar to coercive force HC: 065. , saturation magnetization. s
:84.1 emu/g. These cobalt-containing magnetite particles are referred to as "raw material 2." Example 1 Cobalt-containing magnetite particles 15k9 of "raw material 1" were put into a retort container, and heated at a temperature of 350 pm while a gas containing a 1/1 mixture of air and nitrogen was passed through at a rate of 2 pm/side. Heat treatment was performed for a minute.

The total amount of air during the heat treatment was 58〆 (corresponding to y = 2 matsuju 30). The value of the FeH/Fe ratio in the obtained cobalt-containing magnetic 0 iron oxide particles was 0.25, and as a result of measuring the magnetic properties, coercive force HC: e of 63, saturation magnetization.
s:76. It was Mr.mu/g. In order to observe the change in the coercive force of these cobalt-containing magnetic iron oxide particles at room temperature, we measured the coercive force after 3 days, 15 days, 30 days, and 60 days.
It was 80e. Examples 2 to 6 and Comparative Examples 3 to 5 Cobalt-containing magnetic iron oxide particles were obtained in the same manner as in Example 1 except that the heat treatment conditions were changed.

The heat treatment conditions and various properties of the obtained cobalt-containing magnetic iron oxide particles are shown in the following table. In addition, in Example 6, "Raw material 2" was used as the starting material. Comparative Example 3 has y<2 30, Comparative Example 4 has y>3 30, and Comparative Example 5 has a heating temperature outside the scope of the claims of the present invention.

Comparative Examples 1 and 2 Raw materials 1 and 2 were left as they were at room temperature and changes in coercive force over time were observed, and the results were as shown in the table.

ship S S versus S ) ” cold Yield R *

Claims (1)

[Claims] 1. After dehydrating and reducing cobalt-containing goethite particles to obtain cobalt-containing magnetite particles, the cobalt-containing magnetite particles are converted to y=ax+30 (where y=air amount (l)
), a = 20 to 35, x = amount of cobalt-containing magnetite particles (kg) , Fe■/Fe■ is 0.2 to 0
．． 3. A method for producing a cobalt-containing magnetic iron oxide particle powder, characterized in that the cobalt-containing magnetic iron oxide particles are prepared as follows. 2. The method for producing a cobalt-containing magnetic iron oxide particle powder according to claim 1, wherein the cobalt content in the cobalt-containing magnetite particles is 0.1 to 10 at%. 3 Air ventilation is y = 28x + 30 (however, y = air volume (
l), x = amount of cobalt-containing magnetite particles (kg))
A method for producing cobalt-containing magnetic iron oxide particles according to claim 1 or 2. 4. The method for producing cobalt-containing magnetic iron oxide particle powder according to any one of claims 1 to 3, wherein the heating temperature range is 300 to 400°C.