JP2002128523A - Method of manufacturing ferrite fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a manufacture of ferrite fine particles possible about room temperature or the lower temperature when the pH of a reactive aqueous solution is nearly neutral value, nurse resources and economize in energy, and make a formation of ferrite possible without changing in the quality of substances which are sensitive to temperature and pH as environment conditions. SOLUTION: The ferrite fine particles are manufactured by dissolving oxygen in the aqueous water containing divalent ferrous ion as an indispensable component and metal ions having the pH value of 7-9 and 40 deg.C or less, and oxidizing the divalent ferrous ion for changing to trivalent ferric ion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing ferrite fine particles, and more particularly to a method for producing ferrite fine particles from an aqueous solution and recovering the same.

[0002]

2. Description of the Related Art Ferrites used in ordinary electronic parts are prepared by mixing raw material powders and pre-baking to obtain predetermined magnetic properties while securing crystallinity.
It is manufactured by a method in which the temperature is raised to at least ℃ and sintering.

On the other hand, a coprecipitation method is known as a method for directly producing ferrite fine particles from an aqueous solution without using such a high temperature. Regarding this coprecipitation method, a study by Sato, Sugihara and Saito was published in Industrial Chemistry Magazine 65 (196
2) It is described on p.1748, and research by Takada and Kiyama is based on the Proceedings of the International Conference of Ferrites (Proc. ICF (197
0)) It is described on page 69.

[0004] The coprecipitation method is a method in which an alkali is added to an aqueous solution containing Fe ²⁺ and Fe ³⁺ to precipitate the aqueous solution by raising the pH of the aqueous solution. Ferrite fine particles could not be synthesized at room temperature and in a pH range near neutrality, being limited to a strong alkali region of 10 or more (J. Oh: Proceedings of the Sixths).・ International Conference of
Ferrite (Proc. ICF6 (1992)) p. 211, O. Perales P
erez et al .: Hydrometallurgy 50
(1998) 223.).

On the other hand, as a method for producing a ferrite thin film instead of a method for producing ferrite fine particles, there is a ferrite plating method (Abe and Tamura: Japanese Shanar of Applied Physics (Jpn. J. Appl. Phys.) 22
(1983) L 511, Masaki Abe: Journal of the Japan Society of Applied Magnetics, Vol. 22,
No. 9 (1998) p1225).

Ferrite plating involves binding divalent iron ions on a substrate and oxidizing a portion thereof to trivalent Fe in an aqueous solution at a pH of about 60 to 100 ° C. at a weakly acidic or neutral pH. Thus, a method for forming a spinel ferrite film has been developed by one of the present inventors.
This ferrite plating method has an excellent feature that it can form a ferrite thin film with good crystallinity and magnetic properties comparable to bulk crystals without heat treatment.
The ferrite film can be formed in an aqueous solution at a temperature of 60 to 100 ° C. in a weakly acidic to near neutral temperature, and the formed ferrite film has magnetic properties comparable to a bulk sample without requiring heat treatment.
Even if the substrate is a non-heat-resistant one such as plastic, a device can be formed by providing a ferrite thin film thereon.

[0007] Recently, as a result of research on ferrite plating, the temperature at which a ferrite film is formed has a temperature of 60 to 100 ° C.
Instead, it was possible to form a ferrite film even at temperatures around or below room temperature (Nishimura, Ohara,
Kitamoto, Abe: Journal of the Japan Society of Applied Magnetics, Vol 24, No. 4-2, (200
0) See p.515). As a result of research on the phase equilibrium diagram of the potential and pH of Fe in the ferrite plating reaction, if the pH of the aqueous solution was increased compared to the conventional ferrite plating, this improvement had to be performed at 60 to 100 ° C. They found that ferrite plating of magnetite (Fe ₃ O ₄ ), which had to be done, could be performed at room temperature, and through detailed experiments it was possible to obtain a magnetite film with good crystallinity and magnetic properties at room temperature 25 ° C. It was done.

[0008]

SUMMARY OF THE INVENTION Ferrite fine particles
It is desirable that it can be produced at a temperature around room temperature or lower and at a pH around neutral. If ferrite fine particles can be produced under such conditions, it is preferable not only from the viewpoint of resource saving and energy saving, but also from many other viewpoints. For example, in the presence of a substance such as a biological substance that needs to maintain predetermined conditions such as temperature and pH to maintain its activity, the ferrite fine particles are generated even at room temperature or lower while maintaining the activity of the substance. It becomes possible.

The present inventors have studied the production of ferrite fine particles by oxidizing ferrous ions by applying the above method of forming a thin film by ferrite plating, and as a result, have found that ferrite fine particles can be produced. The present invention has been completed based on the findings.

[0010]

According to the present invention, there is provided a method for producing ferrite fine particles, which comprises converting an aqueous solution containing ferrous metal ions as essential components and containing metal element ions constituting ferrite into a liquid phase at 40 ° C. or lower. While maintaining the temperature shown, at least a part of the divalent iron ions is oxidized to trivalent iron ions by an oxidizing agent, and a pH adjusting solution is mixed to adjust the pH to 7 to 9.
And collecting and collecting ferrite fine particles.

The present invention makes it possible to produce ferrite fine particles at a pH around neutral, at the temperature of an aqueous solution or at around room temperature or lower. In the present invention, the temperature of the aqueous solution is set at 40 ° C. or lower. The ferrite fine particles with good crystallinity and magnetic properties are manufactured by maintaining ferrite fine particles by maintaining the temperature of the liquid phase of the aqueous solution and maintaining the pH of the aqueous solution at 7 to 9 to oxidize ferrous iron ions. Is what you can do. If the pH of the aqueous solution is less than 7, ferrite fine particles cannot be produced, and if the pH exceeds 9, the advantage that the aqueous solution is near neutrality is lost, and the effect of alkali becomes strong, and ferrite particles are oxidized. The characteristics of generation are lost.

Similarly, in the present invention, the temperature of the aqueous solution is preferably 40 ° C. or less, and the temperature at which the liquid phase is maintained is good.
The above is more preferred. According to the present invention, for example, ferrite fine particles can be easily produced at an aqueous solution temperature of about 5 ° C.

In the present invention, it is preferable that a substance serving as a nucleus exists for the production of the ferrite fine particles. For this reason, a fine substance serving as a nucleus can be contained in the aqueous solution, and ferrite fine particles can be generated in the fine substance. As such a nucleus substance, a precipitate of ferrous hydroxide or ferric hydroxide which easily precipitates from an aqueous solution may be used as a nucleus, or a nucleation substance such as an organic substance such as saccharose may be previously dissolved in a solution. It can also be contained in it. Further, by stirring the aqueous solution and taking oxygen gas into the solution, nuclei for ferrite fine particle generation can be generated in the aqueous solution.

Here, the method of stirring the aqueous solution in the present invention is not particularly limited, and a method of rotating a stirrer blade in a container containing the aqueous solution to apply a rotational flow to the aqueous solution, a method of mixing gas such as oxygen or air with the aqueous solution, And a method in which an aqueous solution is flowed through a flow path provided therein, or a method in which the aqueous solution is agitated by being dropped and provided with a flow path.

In the present invention, it is preferable that the aqueous solution containing metal element ions constituting ferrite contains trivalent iron ions together with divalent iron ions. By containing trivalent iron ions, the generation of ferrite fine particles can be remarkably accelerated and the particle size can be reduced. The reason why the particles can be made finer by trivalent iron ions is thought to be that the addition of trivalent iron ions generates fine particles of a substance such as ferric hydroxide, which becomes the core of ferrite fine particles. Can be

In the present invention, in addition to Fe, Co, Ni, Mn, Zn, Cu, Mg Al
And at least one of Ti and Ti. In addition, various other elements that can constitute ferrite can be appropriately contained. By doing so, the ferrite fine particles contain these metals, and various properties such as magnetic properties and resistivity can be controlled.

The oxidizing agent used in the present invention is not particularly limited. For example, oxygen in the atmosphere can be taken into an aqueous solution and used. It is preferable to use atmospheric oxygen as the oxidizing agent because it is not necessary to procure the oxidizing agent and resources can be saved.

In the present invention, pH is adjusted by using a pH adjuster, since hydrogen ions are generated by ferri-oxidation and formation reaction of ferrous iron ions to generate hydrogen ions, and the pH is lowered as it is. The pH adjuster is not particularly limited, and a pH buffer and various alkaline aqueous solutions can be used. As the alkali aqueous solution, various alkalis such as a NaOH aqueous solution and a KOH aqueous solution can be used. Among them, an aqueous ammonia solution containing no alkali metal ion is particularly preferable because there is no problem of alkali metal ion remaining in the ferrite fine particles.

The ferrite fine particles produced in the present invention can be recovered from the aqueous solution by filtration or precipitation, but can be easily performed by magnetic separation by applying a magnetic field.

The method for producing ferrite fine particles of the present invention comprises:
An aqueous solution containing a metal element ion constituting ferrite containing divalent iron ions as an essential component is added to a pH-adjusting solution and water containing oxygen, and oxygen is supplied to the water to supply the divalent iron. It can be carried out by oxidizing the ions to trivalent iron ions and generating and collecting ferrite fine particles while maintaining the pH of the solution at 7 to 9 using the pH adjusting solution. The water used here is not particularly limited, but pure water is preferable because it is not affected by impurities. According to this method, it is possible to produce ferrite fine particles having stable characteristics.

In the present invention, the generation of ferrite fine particles is considered to be generated according to the following reaction, taking as an example a case where a divalent metal element M is included as a metal element constituting ferrite.

1/2 (Fe ²⁺ + 3Fe ³⁺ ) + (1-x) Fe ²⁺ + x M
²⁺ +1/4 [O] + 15 / 4H ₂ O + 1 / 22H ⁺ → 2Fe ³ ++ (1-x) Fe 2 ^{++
_{x M 2+ + 4H 2 O →}} M x Fe 3-x O 4 + 8H + here [O] is an oxygen for the oxidation is supplied by way to push dissolved oxygen in the aqueous solution. For example, it can be performed by a method in which oxygen in the atmosphere is further supplied by using pure water in which oxygen is dissolved by stirring in the air in advance and stirring is performed during the reaction. Here, it is preferable to keep the dissolved oxygen at a saturated value in order to obtain reproducibility of fine particle production. In addition, hydrogen ions H ⁺ generated by the above reaction
Can be maintained at a predetermined value by adjusting the pH with, for example, an NH ₄ OH solution.

The method for producing ferrite fine particles of the present invention comprises:
Since it does not require heating to a high temperature, it is essentially an energy-saving manufacturing method, and the manufacturing method of the present invention does not require high temperature or high pressure, nor does it require a seal or evacuation for vacuum, Moreover, since oxygen in the atmosphere can be taken in by stirring the aqueous solution and used without the need for an oxidizing agent, this is an essentially resource-saving method for producing ferrite fine particles.

The radio wave absorber can be formed by dispersing and molding the ferrite fine particles produced by the energy-saving and resource-saving production method of the present invention in a binder, and can be formed by cold press or hot press molding. By doing so, various cores can be manufactured.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described based on examples.

(Example 1) As schematically shown in FIG.
FeCl was placed in a beaker 1 containing 100 ml of pure water 2 at room temperature of 25 ° C.
₂ and the pH-adjusted NH ₄ OH solution at temperature / pH
Both are 50m in volume while being managed using the controller 4.
l, The reaction was performed by pouring at a constant flow rate of 5 ml / min. Pure water was used in which the amount of dissolved oxygen had almost reached saturation by stirring in advance with the stirrer 3 in the atmosphere.
Further, the stirring rate of the aqueous solution during the reaction by the stirrer 3 was changed to control the amount of oxygen taken in the atmosphere.

The sample thus prepared was subjected to magnetic separation, washed three times, and then collected and dried in the air for several days. The crystal structure of the sample was measured by a Cu-Kα X-ray diffractometer, the magnetic properties were measured by a vibrating sample magnetometer, the composition was analyzed by ICP composition analysis, and the particle size was measured by a transmission electron microscope (TEM).

FIG. 2 shows only the Fe ²⁺ ions in this way.
The figure shows the results of determining the spinel ferrite (Fe ₃ O ₄ ) phase formation region with respect to pH and stirring speed for each Fe ²⁺ concentration when particles were formed using an aqueous solution to which Fe ³⁺ ions were not added. is there. In FIG. 2, a circle indicates a single phase of the spinel ferrite phase, and a cross indicates γ-FeO in addition to the spinel ferrite phase.
A phase containing OH or Fe (OH) ₃ and △ indicate Fe (OH) ₂ .

In FIG. 2, when the Fe ²⁺ concentration becomes high, the Fe ₃ O
_The region where the _four particles are formed moves to the low pH region and the region with high stirring speed (high oxygen supply). The region where single-phase spinel ferrite fine particles could be synthesized was a pH region near neutrality (pH 7 to 9). In addition, the diameter of each of the prepared particles was about 15 nm.

Example 2 Next, pure water at room temperature of about 25 ° C. was added to 10
An aqueous solution in which FeCl ₂ and FeCl ₃ were dissolved and a pH-adjusted NH ₄ OH solution were both poured into a beaker containing 0 ml at a constant flow rate of 5 ml / min. As in Example 1, pure water was previously stirred in the atmosphere,
The amount of dissolved oxygen was almost saturated, and the stirring rate of the aqueous solution during the reaction was changed to control the amount of oxygen taken in the atmosphere. Thus, the Fe ²⁺ ion concentration is kept constant, and the Fe ³⁺ ion is added to increase the Fe ³⁺ / Fe ²⁺ ratio.
0, 0.5, 1.0, 1.5, 2.0, 2.5, Fe ₃ O ₄
Particles were made.

By adding Fe ³⁺ ions, the synthesis time of the sample was shortened, and it took more than 20 hours for Fe ²⁺ ions alone, whereas 10 minutes for Fe ³⁺ / Fe ²⁺ 1.0 or more. I knew it could be done within. It was also found that the addition of Fe ³⁺ ions makes the spinel ferrite phase stable up to the high pH range and the spinel ferrite phase up to the high stirring speed range (high oxygen supply range).

The particle size of the synthesized Fe ₃ O ₄ fine particles was reduced by adding Fe ³⁺ and decreased from 15 nm to 10 nm or less. The saturation magnetization of each of the synthesized Fe ₃ O ₄ particles was about 76 emu / cm ³ , and the coercive force was about 50 Oe.

The synthesis was performed with the ratio of Fe ³⁺ / Fe ²⁺ larger than 2.0. As a result, generation of Fe (OH) ₃ particles was observed. This, Fe ³⁺ / Fe ²⁺ composition ratio in Fe ₃ O ₄ whereas a 2.0, the ratio of oxidized Fe ³⁺ / Fe ²⁺ by oxygen in the air
This is because it is larger than 2.0.

Example 3 In the method of synthesizing the magnetite fine particles of Example 2 described above, a part (percentage) of Fe ²⁺
x) M ²⁺ (M = Co, Ni and Zn ) by replacing, the spinel ferrite Fe ²⁺ ions in a solid solution M _x Fe _3-x O
_Four fine particles could be synthesized in the neutral region.

In a 200 ml beaker containing 100 ml of pure water at about 25 ° C., FeCl ₂ having a total metal ion concentration of 25 mol / m ^{3 was} fixed.
(Min air _{oxidation) + 3FeCl 3 + 2MCl 2 (} M = Fe, Co, N
i, and Zn) aqueous solution and N adjusted to pH 8
The H ₄ OH solution was poured at a volume of 50 ml and a constant flow rate of 5 ml / min, and the stirring was performed at 500 rpm for 10 minutes. The pure water used here reached a saturated dissolved oxygen amount by stirring in the air. The prepared sample was subjected to magnetic separation, washed three times, collected, and dried in the air for several days.

As shown in FIG. 3, the composition x (x in reaction solution) contained in the aqueous solution and the composition x (x in powder) contained in the particles were almost equal. Also,
When the composition x of Co and Ni ions was 0.75 or more, no spinel ferrite was formed, but the Zn ions maintained the spinel structure. The shape of the ferrite fine particles prepared as shown in Fig. 2 was almost spherical, and the particle size was less than 10 nm.

As shown in FIG. 4, in the case of Co and Ni substitution, when the substitution amount x (x in powder) in the particles increases, the saturation magnetization (s
aturation magnetization) decreased. In addition, the saturation magnetization increased in the Zn ion substitution, and reached a maximum when the substitution amount x = 0.25. This is a characteristic peculiar to ferrimagnetism, and is due to a decrease in the magnetization at the A site that has canceled the magnetization at the B site when nonmagnetic Zn ²⁺ ions enter the A site.

The saturation magnetization of the synthesized ferrite fine particles is
All have the same saturation magnetization as the bulk and have a coercive force
(coercive force) was about 50 Oe.

Example 4 In a beaker containing pure water at room temperature of 25 ° C. and saccharose added at a concentration of 10 g / l, an aqueous solution in which FeCl ₂ was dissolved and a pH-adjusted NH ₄ OH solution were added. While controlling using the temperature / pH controller 4, the reaction was carried out at a constant flow rate under the same conditions as in Example 1. Pure water was used in which the amount of dissolved oxygen had almost reached saturation by stirring in advance with the stirrer 3 in the atmosphere. Further, the stirring rate of the aqueous solution during the reaction by the stirrer 3 was changed to control the amount of oxygen taken in the atmosphere.

The sample thus prepared was subjected to magnetic separation, washed three times, collected, dried in the air for several days, and evaluated for the crystal structure, magnetic properties, composition and particle size of the sample. . As a result, it was found that spinel ferrite (Fe ₃ O ₄ ) miniaturized to several nm was generated. This result indicates that nucleation of ferrite fine particles is performed by saccharose.

[0041]

According to the present invention, ferrite fine particles having good crystalline magnetic properties can be produced in an aqueous solution having a pH around neutral and a temperature around or below room temperature. As constituents of the ferrite fine particles, in addition to Fe, N
Various metal elements constituting ferrite such as i, Co, and Zn are contained to control magnetic properties.

According to the present invention, since the aqueous solution is brought into contact with the atmosphere to oxidize Fe ²⁺ to Fe ³⁺ by the oxygen in the atmosphere, the temperature of the aqueous solution is about room temperature or lower, and the pH is medium. The ferrite fine particles can be generated under conditions of mild oxidation by the atmosphere as well as in the vicinity of the property.

[0043] Therefore, in addition to being able to manufacture ferrite fine particles with energy saving and resource saving, in addition to the production of ferrite fine particles in the presence of a substance which is easily degraded by environmental conditions such as a biological substance, for example, Is also possible.

[Brief description of the drawings]

FIG. 1 is a view schematically showing one embodiment of a method for producing ferrite fine particles of the present invention.

FIG. 2 is a diagram showing a spinel ferrite phase on a plane composed of pH and stirring speed, with the concentration of ferrous ion in an aqueous solution as a parameter.

FIG. 3 shows the ratio of Co, Ni, Zn metal ions in the aqueous solution,
FIG. 4 is a diagram showing a relationship between the ratio of Co, Ni, and Zn metal ions in the manufactured ferrite fine particles.

Fig. 4 Co, Ni, Zn in manufactured ferrite fine particles
FIG. 4 is a diagram illustrating a relationship between a ratio of metal ions and a saturation magnetization.

[Explanation of symbols]

1 ... container 2 ... pure water / aqueous solution 3 ... stirrer 4 ... temperature / pH controller

Claims (6)

[Claims] An aqueous solution containing metal element ions constituting ferrite containing divalent iron ions as an essential component is kept at a temperature showing a liquid phase of 40 ° C. or less, and said solution is oxidized with an oxidizing agent.
Ferrite characterized by oxidizing at least a part of divalent iron ions to trivalent iron ions, mixing with a pH adjusting solution, maintaining pH 7 to 9 to generate ferrite fine particles, and collecting the ferrite particles. A method for producing fine particles. 2. The method for producing ferrite fine particles according to claim 1, wherein said aqueous solution is stirred to introduce oxygen gas into said solution. 3. The method for producing ferrite fine particles according to claim 1, wherein the aqueous solution contains a nucleating substance of ferrite fine particles. 4. An aqueous solution containing a metal element ion constituting ferrite contains trivalent iron ions together with divalent iron ions.
The method for producing ferrite fine particles according to any one of the above. 5. A pH-adjusting solution containing an aqueous solution containing metal element ions constituting ferrite containing divalent iron ions as an essential component is added to water containing oxygen, and oxygen is supplied thereto. Ferrite fine particles characterized by oxidizing the divalent iron ions to trivalent iron ions and generating ferrite fine particles while maintaining the pH of the solution at 7 to 9 using the pH adjusting solution, and collecting the ferrite fine particles. Manufacturing method. 6. An aqueous solution containing at least one metal element ion selected from the group consisting of Co, Ni, Mn, Zn, Cu, Mg, Al and Ti as a metal element ion constituting the ferrite. Item 6. The method for producing ferrite fine particles according to any one of Items 1 to 5.