JPS61183125A - Production of fine gamma-iron oxide particle - Google Patents

Abstract

PURPOSE:To obtain fine gamma-iron oxide particles having superior dispersibility in water and various org. solvents by uniformly dispersing dehydrated fine magnetite particles in a nonaqueous solvent and oxidizing them by heating at a specified temp. or above. CONSTITUTION:Fine magnetite particles are dehydrated by washing with a hydrophilic solvent such as acetone or alcohol. Methanol, ethanol or propanol is preferably used as the alcohol. The dehydrated fine magnetite particles are uniformly dispersed in a nonaqueous solvent such as decyl alcohol, kerosene or silicone oil and the resulting dispersion is heat treated at >=100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the production of γ-iron oxide (γ-Fe2), which is useful as a magnetic material.
O3) This relates to a method for producing fine particles. More specifically, the present invention has excellent dispersibility in water and various organic solvents, and excellent thermal and magnetic stability, making it suitable as a magnetic material used particularly for the separation and recovery of magnetic fluids and various useful substances. The present invention relates to a method for effectively producing γ-iron oxide fine particles.

Conventional technology Since magnetite and γ-iron oxide, which are iron oxides, have ferromagnetic properties, their powders have been used as magnetic materials, such as magnetic recording materials such as magnetic tapes, magnetic disks, and magnetic tickets. It is widely used in ferrite materials such as magnetic cores, permanent magnets, and memory elements.

In particular, γ-iron oxide has superior chemical and magnetic stability at room temperature compared to magnetite, so demand for it has increased with the development of audio equipment such as stereos, tape decks, and car stereos, as well as video tape recorders. d It is growing rapidly.

However, recently, the use of magnetite particles and γ-iron oxide particles as magnetic fluids has attracted attention as a new application, such as various sealing materials, lubricating bearings, oil and water capture and separation, dampers, magnetic ink, Applications are being considered for sensors, medicines, agricultural chemicals, etc.

Furthermore, magnetite particles and γ-iron oxide particles are also used for the separation and recovery of various useful substances. For example, heavy metal adsorbents or various ion adsorbents are immobilized on the surface of the particles to selectively capture desired useful substances, which are then used for purposes such as efficient recovery and separation using a magnetic field. There is.

By the way, magnetite particles and γ-iron oxide particles used as magnetic materials for magnetic recording materials such as magnetic tapes are
Hitherto, acicular iron oxyhydroxide obtained by a wet method has been produced by heating and oxidizing it in an all-electric furnace. For example, as a general method for producing magnetite particles, ferric salt is dissolved in water, added to this solution in alkali IJ', and heated and oxidized as it is to produce acicular α-iron oxyhydroxide particles. After washing with water and drying, put it in an electric furnace for 600 hrs.
α-Iron oxide (α-Fe
203) There is a method in which magnetite particles are obtained by forming particles and then reducing them (Japanese Patent Application Laid-Open No. 58-60632).

Furthermore, γ-iron oxide particles are produced by heating the magnetite particles obtained in this way, gradually raising the temperature, and holding the temperature at 200° C. for about 1 hour.

By the way, the magnetite particles and γ-iron oxide particles produced by such a method have a length in the major axis direction of 0.3 to 0.
．． It has an acicular shape with a length ratio of 5 μm/major axis/minor axis of 8 to 10 and has excellent magnetic properties, but the magnetite particles and γ-iron oxide particles obtained by the above method can be used as a magnetic fluid. Alternatively, when used as a carrier for separating and recovering useful substances, the particles are too large and have poor dispersion stability in solvents.

Further, there are problems such as a small specific surface area.

The method for producing iron oxide fine particles (particle size of several 100 oi) used as carriers for magnetic fluids and materials for separation and recovery of useful substances is as follows:
Co-precipitation method for obtaining fine magnetite particles by adding all alkali to an aqueous solution containing ferrous salt and ferric salt
75754) is known. However, since the magnetite fine particles produced in such a dispersed state in an aqueous solution cannot completely remove hydration water and adsorbed water, they have poor dispersibility in low polar solvents, and It has drawbacks such as being magnetically unstable in air.

Therefore, it has been desired to develop ferromagnetic iron oxide fine particles that have good magnetic stability and excellent dispersibility in various solvents.

Problems to be Solved by the Invention - The purpose of the present invention is to meet these demands by producing particles with a particle size of approximately several hundred λ, excellent dispersibility in water and various M solvents, and thermal and magnetic stability. The object of the present invention is to provide fine ferromagnetic iron oxide particles with excellent properties.

Means for Solving the Problems As a result of intensive research, the inventors of the present invention have found that γ-oxidation, which is obtained by uniformly dispersing dehydrated magnetite fine particles in a non-aqueous solvent and heating and oxidizing them at a predetermined temperature. It was discovered that iron fine particles were suitable for the above purpose, and based on this knowledge, the present invention was completed.That is, in the present invention, after uniformly dispersing dehydrated magnetite fine particles in a non-aqueous solvent, The present invention provides a method for producing γ-iron oxide fine particles, which is characterized by heating and oxidizing at a temperature of 100° C. or higher.

The magnetite particles used in the method of the present invention have a particle size of several 10
It is necessary that the particles be of the order of 0>, and are usually obtained by a coprecipitation method from an aqueous solution containing a ferrous salt and a ferric salt, as described above. These magnetite fine particles are used after being washed with ion-exchanged water, but before being heated and oxidized in a non-aqueous solvent, it is necessary to remove the moisture adsorbed on the surface of the fine particles. , the following two methods are suitable.

That is, the first method is to wash magnetite fine particles with ion-exchanged water and then wash them with acetone, methanol, ethanol,
This method removes adsorbed water by cleaning with a highly polar lower alcohol such as propatool. The magnetite fine particles from which the adsorbed water has been removed in this manner are uniformly dispersed in a non-aqueous solvent and heated and oxidized. The second method is to add magnetite fine particles washed with ion-exchanged water to a non-aqueous solvent, and then heat and dehydrate the particles. The magnetite fine particles heated and dehydrated in this manner are heated to a higher temperature and oxidized while being uniformly dispersed in the non-aqueous solvent.

In the method of the present invention, a nonaqueous solvent having a boiling point of 100° C. or higher is preferably used as a medium for uniformly dispersing magnetite fine particles and heating and oxidizing them. Suitable examples of this nonaqueous solvent include decyl alcohol, kerosene, and silicone oil. Particularly, a solvent having a hydrophilic group such as decyl alcohol is preferable because the hydrophilic group adsorbs to the hydroxyl group present on the surface of the iron oxide fine particles, thereby increasing the dispersion stability of the particles. Also, solvents like silicone oil, which have a higher oxygen solubility than kerosene, accelerate the oxidation rate.

The generation time of r-iron oxide becomes shorter.

In this way, the desired γ-iron oxide particles can be obtained by uniformly dispersing the magnetite fine particles in a non-aqueous solvent and then heating and oxidizing them. At this time, if necessary, heating oxidation may be performed while blowing oxygen or air. The reaction temperature is selected from 100°C or higher, preferably from 100 to 180°C.

In addition, the heating time until γ-iron oxide fine particles are generated is
This depends on the particle size of the magnetite particles, the type of dispersion medium, the degree of agitation, the heating temperature, whether oxygen or air is blown, etc., but in general, the smaller the particle size of the magnetite particles, the higher the oxygen solubility. The stronger the stirring of the solvent and the higher the heating temperature, the shorter the heating time until the formation of γ-iron oxide fine particles.

Note that magnetite particles obtained by heating and oxidizing in an electric furnace or the like in open air are not thermally stable, and it is difficult to convert them into γ-iron oxide by the method of the present invention.

The γ-iron oxide fine particles thus obtained may be separated from the solvent and filtered out by a conventional method, or they may be aggregated using a magnet to remove the solvent. These γ-iron oxide fine particles are not only uniformly dispersed in the above-mentioned non-aqueous solvent, but also uniformly dispersed in an aqueous medium by washing with acetone.

Effects of the Invention According to the method of the present invention, in order to carry out the oxidation reaction of magnetite fine particles to γ-iron oxide fine particles in a non-aqueous solvent,
It becomes easy to stir the magnetite particles and control the temperature of the reaction system, and as a result, the oxidation reaction can proceed uniformly. Furthermore, since the oxidation reaction is carried out with the particles uniformly dispersed in the medium, it is possible to prevent non-uniformity and loss of particles due to agglomeration of the particles and adhesion to the reaction vessel.

The particle morphology of the γ-iron oxide fine particles obtained by the method of the present invention is achieved by using fine magnetite particles obtained by, for example, a coprecipitation method, in order to maintain the shape of the magnetite fine particles dispersed in the solvent. Fine γ-iron oxide particles can be obtained.

The γ-iron oxide fine particles obtained by the method of the present invention have excellent dispersibility in water and various organic solvents, and excellent thermal and magnetic stability, and can be used as magnetic materials such as magnetic recording materials and ferrite materials. Of course, the scales used for
It is particularly useful as a carrier for magnetic fluids and materials for separating and recovering useful substances.

EXAMPLES Next, the present invention will be explained in more detail with reference to examples.0 Example 1 After washing magnetite particles 202 produced by coprecipitation method by repeating decantation several times with acetone, they were forcibly precipitated with a magnet. After removing acetone, the mixture was uniformly dispersed in 500-decyl alcohol. Next, this dispersion was stirred while being heated and maintained at a temperature of 150° C., and after 30 minutes, the black particles dispersed in decyl alcohol changed to brown particles. The particles were taken out, washed with acetone, and dried in vacuum to obtain a powder sample.

According to a scanning electron microscope, this material retained the particle morphology of the magnetite particles before heat treatment, but it was found that the fine particles aggregated to form lumpy particles with a particle size of 700 Å or more. Ta. In addition, X-ray diffraction analysis was performed and the results are shown in the table. From this table, it is clear that the obtained sample is γ-iron oxide; Example 2 By washing a commercially available magnetic fluid with acetone, oleic acid is partially removed and magnetite fine particles are recovered. The fine particles were uniformly dispersed in 20 tf of 500 ml of decyl alcohol, heated, and stirred while maintaining the temperature at 170° C. while passing air at a rate of SOZ per hour. After 1 hour, the color of the fine particles changed from black to brown, so the fine particles were taken out, washed with acetone, and vacuum dried to obtain a powder sample.

This product had a particle morphology similar to that obtained in Example 1, and formed agglomerated particles with a particle size of 7001 mm or more. In addition, X-ray diffraction analysis was performed, and the results are shown in the table. As can be seen from this table, the obtained sample was confirmed to be γ-iron oxide.

Example 3 Magnetite particle-like 20ff obtained in the same manner as Example 2
After uniformly dispersing it in r500mj kerosene, it was heated and stirred while maintaining the temperature at 170℃.
After 1 hour, the black particles dispersed in kerosene turned brown. The particles were taken out, washed with acetone, and dried in vacuum to obtain a powder sample.

This product had a particle morphology similar to that obtained in Example 1, and formed agglomerated particles with a particle size of 700 or more. In addition, X-ray diffraction analysis was performed and the results are shown in the table. From this table, it is clear that this is γ-iron oxide.

Claims (1)

[Scope of Claims] 1. A method for producing γ-iron oxide fine particles, which comprises uniformly dispersing dehydrated magnetite fine particles in a non-aqueous solvent and then heating and oxidizing them at a temperature of 100° C. or higher. 2. The manufacturing method according to claim 1, wherein the dehydration is carried out by washing with a hydrophilic solvent such as acetone or alcohol. 3. The manufacturing method according to claim 2, wherein the alcohol is methanol, ethanol, or propanol. 4. The manufacturing method according to claim 1, wherein the dehydration is carried out by heating in a non-aqueous solvent.