JP6982853B2 - Magnetic particles and their manufacturing method - Google Patents

Description

The present invention relates to magnetic particles and a method for producing the same, and more specifically, to an efficient method for producing magnetic particles having a uniform shape and size, and magnetic particles obtained by the production method.

In recent years, the fields of use of magnetic particles have expanded, and are widely used in magnetic fluids, magnetic viscous fluids, contrast media, electromagnetic wave shielding materials, induction heating materials for cancer treatment, and the like. Here, goethite (goethite, α-FeOOH) is inexpensive, and a method for producing magnetic particles using the goethite as a raw material is very attractive in terms of cost. In fact, needle-shaped magnetic particles obtained by reducing goethite with hydrogen are used as magnetic particles for magnetic tape.

For example, Non-Patent Document 1 (Inorganic Chemistry, American Chemical Society, 45 (2006) pp. 5196-5200) discloses a method for producing nanorod-shaped hematite, which thermally decomposes and crystallizes goethite in the atmosphere. , The resulting hematite lacks uniformity and widens the size distribution.

Further, Patent Document 1 (Japanese Unexamined Patent Publication No. 2014-94838) is characterized in that goethite particles having a plate-like shape and / or hematite particles having a plate-like shape are dispersed in polyhydric alcohol and heat-treated. A method for producing ferromagnetic iron oxide particles has been proposed.

In the method for producing ferromagnetic iron oxide particles described in Patent Document 1, iron hydroxide particles such as gateite particles having a plate-like shape and hematite particles are dispersed in polyhydric alcohol and heat-treated. It is said that the magnetite particles can be converted into magnetite particles having excellent heat generation characteristics without causing deformation of the plate-like shape of the particles, and the magnetite particles are excellent in dispersion stability with respect to an injection medium.

Japanese Unexamined Patent Publication No. 2014-94838

Inorganic Chemistry, American Chemical Society, 45 (2006) pp. 5196-5200

However, in the non-patent documents and the methods for producing magnetic particles described in the patent documents, the shape of the magnetic particles cannot be arbitrarily controlled, and the size of the obtained magnetic particles becomes non-uniform. As for nanoparticles, many methods for producing relatively homogeneous particles have been proposed, but micromagnetic particles having the same shape and size (magnetic particles having an average diameter of about 1 μm to 10 μm) can be stably produced. There is no cheap and easy way to do this. In addition, the shape of the magnetic particles obtained by the conventional manufacturing method is basically limited to a spherical shape, a plate shape, a rod shape, or the like.

In view of the above problems in the prior art, an object of the present invention is an inexpensive and simple manufacturing method capable of stably obtaining micromagnetic particles having the same shape and size, and a unique shape obtained by the method. And / or to provide magnetic particles having a size. Another object of the present invention is to provide magnetic particles having a novel shape and / or size.

As a result of diligent research on a method for producing magnetic particles in order to achieve the above object, the present inventor has made magnetic particles in a mixed solution using iron hydroxide as a raw material in a mixed solution containing an appropriate reducing solvent and water. We have found that it is extremely effective to directly precipitate iron and the like, and have reached the present invention.

That is, the present invention is characterized in that iron hydroxide is heated and pressurized in a mixed solution containing 1,2-glycol and water to precipitate magnetic particles having different shapes using the dissolved iron hydroxide as a raw material. Provided is a method for producing magnetic particles.

The heating and pressurizing methods are not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known methods can be used. For example, magnetic particles can be obtained by heating and pressurizing a mixed solution containing 1,2-glycol and water and iron hydroxide in a pressure-resistant container such as an autoclave. In addition, 1,2-glycol is used as a reducing solvent.

The amounts of 1,2-glycol, water and iron hydroxide to be sealed in the pressure-resistant container may be appropriately determined depending on the shape, size, production amount and the like of the magnetic particles. In the method for producing magnetic particles of the present invention, the addition of water is indispensable, and the presence of the water under heating and pressurizing conditions makes the size of the magnetic particles almost uniform, and the amount of water added and the amount of water added. It has been clarified that magnetic particles having various shapes can be obtained depending on the heating and pressurizing conditions. In addition, magnetite can be produced from the raw material goethite by the reducing action of 1,2-glycol.

Further, the heating conditions differ depending on the type of 1,2-glycol used, the amount of water added, etc., and may be appropriately determined in consideration of the shape, size, production amount, etc. of the magnetic particles. By setting it near the boiling point, the synthetic reaction can proceed smoothly. Here, since 1,2-glycol, water, and iron hydroxide are sealed in the pressure-resistant container, the pressure becomes higher than the normal pressure by heating.

In the method for producing magnetic particles of the present invention, it is not always clear why magnetic particles having extremely uniform shape and size can be obtained. However, in the presence of water, goethite (α-FeOOH) dissolves as trivalent iron ions, which are partially reduced in 1,2-glycol to precipitate as _{a magnetite phase (Fe 3} O _4). It is probable that a self-organizing action worked in the process of doing so. By completely consuming iron hydroxide as a raw material, only magnetic particles can be obtained.

As the reducing solvent that can be used in the method for producing magnetic particles of the present invention, polyhydric alcohols such as dihydric alcohols and trihydric alcohols can be mentioned as candidates. There are many types of dihydric alcohols, but the use of 1,2-glycol can efficiently promote the synthetic reaction of magnetic particles. The 1,2-glycol has a hydroxyl group bonded to adjacent carbons, and ethylene glycol, 1,2-propanediol and the like can be exemplified. The reason why the synthetic reaction of magnetic particles proceeds efficiently when 1,2-glycol is used is not always clear, but the two hydroxyl groups (-OH) in the molecule of 1,2-glycol It is considered that the fact that the distance between the two is shorter than that of other glycols contributes to the promotion of this synthetic reaction. For example, when 1,3-glycol having a structure in which the distance between two hydroxyl groups (−OH) is longer is used, the synthetic reaction of magnetic particles cannot proceed efficiently. Further, diethylene glycol, triethylene glycol, and tetraethylene glycol obtained by dehydration condensation of ethylene glycol have a structure in which the distance between hydroxyl groups (-OH) is longer than that of 1,2-glycol, and the synthesis reaction of magnetic particles is efficient. Cannot be advanced.

Further, since trihydric alcohols such as glycerin have a high viscosity, they are difficult to handle and impractical, and it is also difficult to control the reaction conditions for obtaining magnetic particles.

In the method for producing magnetic particles of the present invention, magnetic particles having the same shape and size can be obtained only with 1,2-glycol, water and iron hydroxide, which is simple and low cost. When iron hydroxide as a raw material is completely consumed after the production process is completed, most of the residue in the pressure-resistant container is 1,2-glycol and water, and the magnetic particles can be easily recovered.

In the method for producing magnetic particles of the present invention, it is preferable that the iron hydroxide is goethite, the magnetic particles are magnetite, and the magnetite is directly formed from the goethite as a raw material.

More specifically, by using goethite (α-FeOOH) as a raw material, magnetite (Fe ₃ O ₄ ) can be directly obtained _{without passing through hematite (Fe 2} O _3). Although there is a method for producing magnetite from goethite via hematite, the production method of the present invention has a simpler magnetite production route than the production method, and the shape and size can be easily controlled by the reaction rate, reaction time, etc. can do.

In addition to goethite, iron hydroxide contains goethite (β-FeOOH) and lepidocrocite (γ-FeOOH), but in order to form magnetite particles with a uniform shape and size, goethite is used as a raw material. Is preferable. When lepidocrocite is used as a raw material, nano-sized magnetite particles are basically generated, and it is difficult to obtain micro-sized magnetite particles.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the iron hydroxide is needle-shaped. Goethite is inexpensive and easily available, and is suitable for mass production of magnetic particles.

Further, in the manufacturing method of the magnetic particles of the present invention, the specific surface area of the goethite is ^{10m 2} / ^g~100m 2 / g, it is preferred. By setting the specific surface area of goethite to 10 m ² / g or more, a sufficient amount of iron hydroxide can be dissolved for smooth synthesis of magnetic particles, and by setting it to 100 m ² / g or less, dissolution from goethite can be achieved. It is possible to prevent the magnetic particles from becoming nanoparticles due to the fact that the amount is too large and the dissolution rate is too fast.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the content of the water in the mixed solution is 1% by volume to 15% by volume. By setting the water content to 1% by volume or more, magnetic particles having a shape different from that of the raw material iron hydroxide can be synthesized, and by setting the water content to 15% by volume or less, the shape is adjusted. It is possible to synthesize uniform magnetic particles.

Here, if the water content is less than 1% by volume, the synthetic reaction becomes non-uniform, it is difficult to use only magnetite as magnetic particles, and it tends to be a mixture of magnetite and hematite. Further, when the water content is larger than 15% by volume, the precipitation of magnetite is delayed, and the raw material goethite is likely to remain.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the boiling point of the 1,2-glycol is higher than that of water and the heating temperature is −20 ° C. to + 35 ° C. of the boiling point. The reduction reaction rate of 1,2-glycol depends on the temperature. By setting the heating temperature to −20 ° C. or higher, which is the boiling point of 1,2-glycol, the synthesis of magnetite can be promoted, and the shape and size of the obtained magnetite particles can be made uniform. On the other hand, when the heating temperature is set to + 35 ° C. or higher, which is the boiling point of 1,2-glycol, the reduction reaction is remarkably accelerated, and the controllability of the shape and size of the magnetite particles is lowered.

The present invention also provides a magnetic powder comprising substantially spherical magnetite particles, wherein the magnetite particles have an average diameter of 1.0 μm to 1.5 μm.

Approximately spherical magnetite particles have existed for some time, but are nanoparticles with an average diameter of less than 1.0 μm. On the other hand, the magnetite particles constituting the magnetic powder of the present invention have an average diameter of 1.0 μm to 1.5 μm, and can be suitably used for a magnetic viscous fluid, an electromagnetic wave sealing material, or the like.

Further, the present invention is a powder made of magnetite particles having an octahedral shape, and the magnetic powder is characterized in that the average length of the longest piece of the magnetite particles is 1.0 μm to 1.5 μm. , Also provides.

Magnetite particles having an octahedral shape have existed for a long time, but are nanoparticles having an average particle size of less than 1.0 μm. On the other hand, the magnetite particles constituting the magnetic powder of the present invention have an average length of 1.0 μm to 1.5 μm, which is the longest piece, and can be suitably used for a magnetic viscous fluid, an electromagnetic wave sealing material, or the like.

Further, the present invention also provides magnetite particles having an icosahedron shape composed of 8 triangles and 12 hexagons. The icosahedron-like magnetite particles composed of eight triangles and twelve hexagons have never existed and have a very peculiar shape. Here, the average diameter of the magnetite particles is preferably 1.0 μm to 1.5 μm.

These magnetic powders and magnetic particles of the present invention can be suitably obtained by using the method for producing magnetic particles of the present invention.

According to the present invention, there is provided an inexpensive and simple manufacturing method capable of stably obtaining micromagnetic particles having a uniform shape and size, and magnetic particles having a unique shape and / or size obtained thereby. Can be done. Further, according to the present invention, it is possible to provide magnetic particles having a novel shape and / or size.

It is a schematic diagram of a magnetic powder composed of spherical particles. It is a schematic diagram of the magnetic powder composed of octahedral magnetite particles. It is a schematic diagram of icosahedron magnetite particles. It is an SEM photograph of goethite used as a raw material in Example 1. It is an XRD pattern of the powder obtained in Example 1. 6 is an SEM photograph of the powder obtained in Example 1. 6 is an SEM photograph of the powder obtained in Example 2. 6 is an SEM photograph of the powder obtained in Example 3. 6 is an SEM photograph of the powder obtained in Example 4. 6 is an SEM photograph of the powder obtained in Example 5. 6 is an SEM photograph of the powder obtained in Example 6. 6 is an SEM photograph of the powder obtained in Example 7. It is an SEM photograph of the powder obtained in Example 22. It is an SEM photograph of the powder obtained in Example 23. It is an SEM photograph of the powder obtained in Example 24. 6 is an SEM photograph of the powder obtained in Comparative Example 1. 6 is a high-magnification SEM photograph of the powder obtained in Example 6. 6 is a high-magnification SEM photograph of the powder obtained in Example 17.

Hereinafter, the method for producing magnetic particles and typical embodiments of magnetic particles of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts may be designated by the same reference numerals, and duplicate description may be omitted. Further, since the drawings are for conceptually explaining the present invention, the dimensions of each component represented and their ratios may differ from the actual ones.

(1) Method for producing magnetic particles In the method for producing magnetic particles of the present invention, iron hydroxide is heated and pressurized in a mixed solution containing 1,2-glycol and water, and has a shape different from that of the iron hydroxide. It is characterized by precipitating magnetic particles in a mixed solution.

In the method for producing magnetic particles of the present invention, the reason why magnetic particles having a shape different from that of iron hydroxide used as a raw material is precipitated is not always clear. In the process of dissolving goethite (FeOOH) as a trivalent iron ion in the presence of water and partially reducing it in 1,2-glycol to precipitate as _{a magnetite phase (Fe 3} O _4). It is probable that a self-organizing action worked.

The amounts of 1,2-glycol, water and iron hydroxide to be sealed in the pressure-resistant container may be appropriately determined depending on the shape, size, production amount and the like of the magnetic particles. In the method for producing magnetic particles of the present invention, addition of water is indispensable, and the presence of the water under heating and pressurizing conditions makes the size of the magnetic particles uniform, and the amount of water added and heating. It has been clarified that magnetic particles having various shapes can be obtained depending on the pressurizing conditions. In addition, the raw material goethite can be made into magnetite by the reducing action of 1,2-glycol.

In the method for producing magnetic particles of the present invention, it is considered that iron hydroxide is basically dissolved in a mixed solvent and partially reduced to produce magnetic particles. Here, the reducing power varies depending on the heating and pressurizing conditions, the amount of water, the amount of iron hydroxide added, and the type of 1,2-glycol. That is, in the method for producing magnetic particles of the present invention, the shape and size finally obtained can be controlled by changing these conditions.

The heating conditions vary depending on the type of 1,2-glycol used, the amount of water added, etc., and may be appropriately determined in consideration of the desired shape, size, production amount, etc. of the magnetic particles, but have a boiling point higher than that of water. By setting the boiling point of 1,2-glycol to be close to that of 1,2-glycol, the synthesis reaction can be smoothly promoted. Here, since 1,2-glycol, water, and iron hydroxide are sealed in the pressure-resistant container, the pressure becomes higher than the normal pressure by heating. Under such circumstances, iron hydroxide is considered to be efficiently dissolved, and the reducing power of 1,2-glycol can be efficiently expressed.

In the method for producing magnetic particles of the present invention, the reason why extremely uniform magnetic particles are obtained in terms of shape and size is not always clear, but in the presence of water, getite (FeOOH) is used as a trivalent iron ion. It is considered that a self-organizing action was exerted in the process of dissolving and partially reducing it in 1,2-glycol to _{precipitate as a magnetite phase (Fe 3} O _4). By completely consuming iron hydroxide as a raw material, only magnetic particles can be obtained.

In the method for producing magnetic particles of the present invention, magnetic particles having the same shape and size can be obtained only with 1,2-glycol, water and iron hydroxide, which is simple and low cost. When iron hydroxide as a raw material is completely consumed after the production process is completed, most of the residue in the pressure-resistant container is 1,2-glycol and water, and the magnetic particles can be easily recovered.

In the method for producing magnetic particles of the present invention, iron hydroxide is goethite and magnetic particles are magnetite. By selecting appropriate reaction conditions, magnetite (Fe ₃ O ₄ ) can be directly obtained _{without passing through hematite (Fe 2} O _3).

In addition to goethite, iron hydroxide contains goethite (β-FeOOH) and lepidocrocite (γ-FeOOH), which have different crystal structures. However, in order to form magnetite particles with a uniform shape and size, goethite is used. Is preferable as a raw material. When lepidocrocite is used as a raw material, nano-sized magnetite particles are basically generated, and it is difficult to obtain micro-sized magnetite particles.

Further, in the method for producing magnetic particles of the present invention, 1,2-glycol is used as a reducing solvent. 1,2-Glycol has a hydroxyl group bonded to adjacent carbons, respectively, and is composed of 1,2-ethanediol (ethylene glycol, 2 carbon atoms), 1,2-propanediol (3 carbon atoms), and the like. And 1,2-butanediol (4 carbon atoms) and the like can be exemplified. However, 1,2-glycol having 5 or more carbon atoms is difficult to use because of its high viscosity.

By using 1,2-glycol as the reducing solvent, the synthetic reaction of magnetic particles can be efficiently promoted. The reason why the synthetic reaction of magnetic particles proceeds efficiently when 1,2-glycol is used is not always clear, but the two hydroxyl groups (-OH) in the molecule of 1,2-glycol It is considered that the fact that the distance between the two is shorter than that of other glycols contributes to the promotion of this synthetic reaction. For example, when 1,3-glycol having a structure in which the distance between two hydroxyl groups (−OH) is longer is used, the synthetic reaction of magnetic particles cannot proceed efficiently. Further, diethylene glycol, triethylene glycol, and tetraethylene glycol obtained by dehydration condensation of ethylene glycol have a structure in which the distance between hydroxyl groups (-OH) is longer than that of 1,2-glycol, and the synthesis reaction of magnetic particles is efficient. Cannot be advanced.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the iron hydroxide is needle-shaped. By using needle-shaped iron hydroxide, a network structure in which iron hydroxides are entangled with each other is easily formed, and local aggregation and growth of magnetic particles deposited on the surface of iron hydroxide can be effectively suppressed. Can be done. In addition, goethite is inexpensive and easily available, and is suitable for mass production of magnetic particles.

Further, in the manufacturing method of the magnetic particles of the present invention, the specific surface area of the goethite is ^{10m 2} / ^g~100m 2 / g, it is preferred. By setting the specific surface area of goethite to 10 m ² / g or more, iron hydroxide sufficient for smooth synthesis of magnetic particles can be dissolved, and by setting it to 100 m ² / g or less, the magnetic particles become nanoparticles. It can be suppressed from becoming.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the content of the water in the mixed solution is 1% by mass to 15% by mass. By setting the water content to 1% by mass or more, magnetic particles having a shape different from that of the raw material iron hydroxide can be synthesized, and by setting the water content to 15% by mass or less, the shape is adjusted. It is possible to synthesize uniform magnetic particles.

In the method for producing magnetic particles of the present invention, it is considered that the dissolved iron hydroxide is reduced by 1,2-glycol to become magnetic particles. Therefore, the concentration of the dissolved iron hydroxide and 1,2. -The balance of reducing power by glycol is important. Here, when the content of water is less than 1% by volume, it is difficult to use only magnetite as magnetic particles, and it tends to be a mixture of magnetite and hematite. Further, when the water content is larger than 15% by volume, the synthetic reaction of the magnetic particles does not proceed smoothly, and the raw material goethite tends to remain. The more preferable water content is 5% by volume to 13% by volume, and by setting the water content in the above range, more homogeneous micromagnetic particles can be obtained.

Further, in the method for producing magnetic particles of the present invention, it is preferable that the boiling point of the 1,2-glycol is higher than that of water and the heating temperature is −20 ° C. to + 35 ° C. of the boiling point. By setting the heating temperature to −20 ° C. or higher, which is the boiling point of 1,2-glycol, the synthesis of magnetite can be promoted, and the shape and size of the obtained magnetite particles can be made uniform. On the other hand, by setting the heating temperature to + 35 ° C. or lower, which is the boiling point of 1,2-glycol, hematite synthesis can be suppressed (magnetite synthesis can be promoted), and the obtained magnetite particles can be promoted. The shape and size of the can be made uniform.

(2) Magnetic particles and magnetic powder (2-1) Magnetic powder composed of spherical particles FIG. 1 shows a schematic diagram of a magnetic powder composed of spherical particles. The magnetic powder 1 is a powder composed of substantially spherical magnetite particles 2, and is characterized in that the average diameter of the substantially spherical magnetite particles 2 is 1.0 μm to 1.5 μm.

The magnetic powder 1 is an aggregate of substantially spherical magnetite particles 2, and the substantially spherical magnetite particles 2 have an average diameter of 1.0 μm to 1.5 μm. The average diameter of the substantially spherical magnetite particles 2 can be obtained, for example, by measuring and averaging the diameters of about 20 substantially spherical magnetite particles 2 from a scanning electron microscope (SEM) observation image. It can also be obtained using a scattering type particle size distribution (particle size distribution) measuring device.

(2-2) Magnetic powder made of octahedral particles FIG. 2 shows a schematic diagram of a magnetic powder made of magnetite particles having an octahedral shape. The magnetic powder 10 is a powder composed of octahedral magnetic particles 12, and is characterized in that the average length of the longest piece (L) of the octahedral magnetic particles 12 is 1.0 μm to 1.5 μm. It is a magnetic powder.

The magnetic powder 10 is an aggregate of octahedral magnetite particles 12, and the average length of the longest piece (L) of the octahedral magnetite particles 12 is 1.0 μm to 1.5 μm. The average length of the longest piece (L) can be obtained by, for example, measuring L of about 20 octahedral magnetite particles 12 from a scanning electron microscope (SEM) observation image and averaging them. ..

(2-3) Icosahedron Magnetite Particles FIG. 3 shows a schematic diagram of the icosahedron magnetite particles of the present invention. The icosahedron magnetite particles 20 have an icosahedron shape composed of eight triangles 22 and twelve hexagons 24.

The size of the icosahedron magnetite particles 20 is not particularly limited, and can be a wide range of sizes from nanoparticles to microparticles.

The magnetic powder having various shapes and sizes of the present invention and the magnetic powder composed of the magnetic particles can be suitably produced by the method for producing the magnetic particles of the present invention.

Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Will be.

<< Example 1 >>
2 g of commercially available goethite (α-FeOOH) was inserted into a 25 cc autoclave container, and the inside of the autoclave container was filled with a mixed solvent. Here, ethylene glycol (1,2-ethanediol), which is one of 1,2-glycol, was used and mixed at a ratio of ethylene glycol: 99% by volume and water: 1% by volume to prepare a mixed solvent. The boiling point of ethylene glycol is 197 ° C. Next, after heat treatment at 200 ° C. for 72 hours, the produced powder was separated. The specific surface area of goethite (α-FeOOH) used as a raw material was measured and found to be 17 m ² / g.

FIG. 4 shows an SEM photograph of goethite (α-FeOOH) used as a raw material. The goethite used as a raw material is needle-shaped with a major axis having a size of about 1 micrometer.

The obtained powder was black and adhered to the magnet surface. It was confirmed from the structural analysis of X-ray diffraction that this powder was magnetite (Fe ₃ O _4). Specifically, the measured X-ray diffraction pattern was in good agreement with the powder diffraction pattern (Magnetite, PDF # 00-019-0629) provided by the International Center for Diffraction (ICDD), and all powders were magnetite. Was identified as. The obtained XRD pattern is shown in FIG. The goethite (α-FeOOH) used as a raw material has a yellow to yellowish green color, and when hematite (Fe ₂ O ₃ ) is produced, it is reddish brown, and when magnetite (Fe ₃ O ₄ ) is produced, it is reddish brown. It becomes black.

An SEM photograph of the obtained powder is shown in FIG. It can be seen that a powder composed of magnetite particles having a relatively uniform particle size and shape is obtained.

<< Example 2 >>
A powder was obtained in the same manner as in Example 1 except that the mixing solvent was ethylene glycol: 97.5% by volume and water: 2.5% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. A substantially spherical magnetite powder was obtained. The obtained powder was black and adhered to the magnet surface.

<< Example 3 >>
A powder was obtained in the same manner as in Example 1 except that the mixed solvent was ethylene glycol: 95% by volume and water: 5% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. A substantially spherical magnetite powder was obtained. The obtained powder was black and adhered to the magnet surface.

<< Example 4 >>
A powder was obtained in the same manner as in Example 1 except that the mixing solvent was ethylene glycol: 92.5% by volume and water: 7.5% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. A substantially spherical magnetite powder was obtained. The obtained powder was black and adhered to the magnet surface.

<< Example 5 >>
A powder was obtained in the same manner as in Example 1 except that the mixing solvent was ethylene glycol: 90% by volume and water: 10% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. The obtained powder was black and adhered to the magnet surface. A magnetite powder having a substantially spherical shape and almost the same size was obtained. The magnetization curve of the powder was evaluated using a magnetic property measuring device manufactured by Quantum Design. When the saturation magnetization (300K) at room temperature was obtained from the obtained curve, it was about 85 emu / g.

<< Example 6 >>
A powder was obtained in the same manner as in Example 1 except that the mixing solvent was ethylene glycol: 87% by volume and water: 13% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. An octahedral magnetite powder was obtained. The obtained powder was black and adhered to the magnet surface.

<< Example 7 >>
A powder was obtained in the same manner as in Example 1 except that the mixing solvent was ethylene glycol: 85% by volume and water: 15% by volume and the heat treatment time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. The obtained powder had a mixed color of yellowish green and black and adhered to the magnet surface.

<< Example 8 >>
A powder was obtained in the same manner as in Example 5 except that the heat treatment time was 72 hours. The obtained powder was black and adhered to the magnet surface.

<< Example 9 >>
A powder was obtained in the same manner as in Example 6 except that the heat treatment time was 72 hours. The obtained powder was black and adhered to the magnet surface.

<< Example 10 >>
A powder was obtained in the same manner as in Example 7 except that the heat treatment time was 72 hours. The obtained powder was black and adhered to the magnet surface.

<< Example 11 >>
A powder was obtained in the same manner as in Example 5 except that the heat treatment temperature was 180 ° C. and the heat treatment time was 24 hours. The obtained powder had a mixed color of yellowish green and black and adhered to the magnet surface.

<< Example 12 >>
A powder was obtained in the same manner as in Example 5 except that the heat treatment temperature was set to 230 ° C. The obtained powder was black and adhered to the magnet surface.

<< Example 13 >>
A powder was obtained in the same manner as in Example 3 except that the heat treatment temperature was set to 230 ° C. The obtained powder was black and adhered to the magnet surface.

<< Example 14 >>
A powder was obtained in the same manner as in Example 2 except that 1,2-propanediol (boiling point: 188 ° C.), which is a kind of 1,2-glycol, was used. The obtained powder was black and adhered to the magnet surface.

<< Example 15 >>
A powder was obtained in the same manner as in Example 3 except that 1,2-propanediol (boiling point: 188 ° C.), which is a kind of 1,2-glycol, was used. The obtained powder was black and adhered to the magnet surface.

<< Example 16 >>
A powder was obtained in the same manner as in Example 5 except that 1,2-propanediol (boiling point: 188 ° C.), which is a kind of 1,2-glycol, was used. The obtained powder was yellow and black and adhered to the magnet surface.

<< Example 17 >>
A powder was obtained in the same manner as in Example 3 except that 1,2-propanediol (boiling point: 188 ° C.), which is a kind of 1,2-glycol, was used and the heat treatment time was 72 hours. The obtained powder was black and adhered to the magnet surface.

<< Example 18 >>
A powder was obtained in the same manner as in Example 3 except that 1,2-butanediol (boiling point: 196 ° C.), which is a kind of 1,2-glycol, was used. The obtained powder was black and adhered to the magnet surface.

<< Example 19 >>
A powder was obtained in the same manner as in Example 5 except that 1,2-butanediol (boiling point: 196 ° C.), which is a kind of 1,2-glycol, was used. The obtained powder had a mixed color of reddish brown and black and adhered to the magnet surface.

<< Example 20 >>
A powder was obtained in the same manner as in Example 3 except that 1,2-butanediol (boiling point: 196 ° C.), which is a kind of 1,2-glycol, was used and the heating time was 72 hours. The obtained powder was black and adhered to the magnet surface.

<< Example 21 >>
A powder was obtained in the same manner as in Example 5 except that 1,2-butanediol (boiling point: 196 ° C.), which is a kind of 1,2-glycol, was used and the heating time was 72 hours. The obtained powder was reddish brown and black and adhered to the magnet surface.

<< Example 22 >>
A powder was obtained in the same manner as in Example 5 except that lepidocrocite (γ-FeOOH) was used instead of goethite (α-FeOOH) as a raw material. The specific surface area of the lepidocrocite (γ-FeOOH) is 52 m ² / g. An SEM photograph of the obtained powder is shown in FIG. It can be seen that very fine nanoparticles are generated. The obtained powder was black and adhered to the magnet surface.

<< Example 23 >>
A powder was obtained in the same manner as in Example 22 except that the heating temperature was set to 180 ° C. An SEM photograph of the obtained powder is shown in FIG. It can be seen that very fine nanoparticles are generated. The obtained powder was black and adhered to the magnet surface.

<< Example 24 >>
A powder was obtained in the same manner as in Example 6 except that goethite (α-FeOOH) having a specific surface area of 40 m ^{2 / g was used as a raw material.} An SEM photograph of the obtained powder is shown in FIG. It can be seen that very fine nanoparticles are produced and that ^{increasing the specific surface area of goethite from 17 m 2} / g to 40 m ² / g reduces the resulting particle size. The obtained powder was black and adhered to the magnet surface.

<< Comparative Example 1 >>
A powder was obtained in the same manner as in Example 1 except that water was not added, only ethylene glycol was used as a solvent, and the heating time was 24 hours. An SEM photograph of the obtained powder is shown in FIG. The shape of the powder has not changed significantly from the state of the raw material. The obtained powder had a mixed color of yellowish green and reddish brown, and hardly adhered to the magnet surface.

<< Comparative Example 2 >>
A powder was obtained in the same manner as in Comparative Example 1 except that water was not added and only ethylene glycol was used as the solvent. The obtained powder had a mixed color of yellowish green and reddish brown, and hardly adhered to the magnet surface.

<< Comparative Example 3 >>
A powder was obtained in the same manner as in Comparative Example 1 except that water was not added and only ethylene glycol was used as a solvent and the heating temperature was set to 230 ° C. The obtained powder was dark brown and adhered to the magnet surface. No microparticle size was obtained, and shapes other than substantially spherical were observed.

<< Comparative Example 4 >>
A powder was obtained in the same manner as in Example 5 except that 1,3-propanediol (boiling point: 211 ° C.) other than 1,2-glycol was used as the divalent alcohol. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 5 >>
As the dihydric alcohol, 1,3-propanediol (boiling point: 211 ° C.) other than 1,2-glycol was used, the amount of water added was 1% by volume, and the heating temperature was 230 ° C. Similarly, a powder was obtained. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 6 >>
A powder was obtained in the same manner as in Comparative Example 5 except that 1,3-propanediol (boiling point: 211 ° C.) other than 1,2-glycol was used as the dihydric alcohol and the amount of water added was 5% by volume. rice field. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 7 >>
A powder was obtained in the same manner as in Example 5 except that diethylene glycol other than 1,2-glycol (boiling point: 244 ° C.) was used as the divalent alcohol. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 8 >>
Diethylene glycol other than 1,2-glycol (boiling point: 244 ° C.) was used as the divalent alcohol, and the powder was used in the same manner as in Comparative Example 7 except that the amount of water added was 5% by volume and the heating temperature was 230 ° C. Got The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 9 >>
Diethylene glycol other than 1,2-glycol (boiling point: 244 ° C.) was used as the divalent alcohol, and the powder was used in the same manner as in Comparative Example 8 except that the amount of water added was 5% by volume and the heating temperature was 250 ° C. Got The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 10 >>
A powder was obtained in the same manner as in Example 3 except that triethylene glycol other than 1,2-glycol (boiling point: 289 ° C.) was used as the divalent alcohol. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 11 >>
A powder was obtained in the same manner as in Example 14 except that water was not added and only 1,2-butanediol was used as the solvent. The obtained powder was yellowish green and hardly adhered to the magnet surface.

<< Comparative Example 12 >>
A powder was obtained in the same manner as in Example 3 except that 1,3-butanediol (boiling point: 207 ° C.) was used as the reducing solvent. The obtained powder was reddish brown and hardly adhered to the magnet surface.

<< Comparative Example 13 >>
A powder was obtained in the same manner as in Comparative Example 12 except that the amount of water added was 10% by volume. The obtained powder was reddish brown and hardly adhered to the magnet surface.

From the results of Examples and Comparative Examples, it can be seen that by using 1,2-glycol as the reducing solvent, magnetic particles having the same shape and size can be stably produced. On the other hand, when other polyhydric alcohols are used as the reducing solvent, good magnetic particles cannot be obtained.

Further, from the comparison between Example 7 and Example 10, it can be seen that the synthetic reaction rate of the magnetic particles becomes slow when the water content is high, but only the magnetic particles can be obtained by lengthening the heating time.

Further, from the comparison of Examples 5, 11 and 12, it can be seen that the synthetic reaction rate of the magnetic particles also depends on the heating temperature, and when the heating temperature is low, the synthetic reaction rate becomes slow.

Further, from the comparison of Examples 5, 22 and 23, when lepidocrocite (γ-FeOOH) was used as the raw material instead of goethite (α-FeOOH), micromagnetism was observed even if the heating temperature was adjusted. It turns out that particles cannot be obtained.

Further, from FIGS. 6 to 12, by heating and pressurizing iron hydroxide in a mixed solution containing 1,2-glycol and water, magnetic particles having a shape different from that of the raw material iron hydroxide are generated. You can see that there is. Further, the shape and / or size of the obtained magnetic particles depends on the amount of water added, and by setting the amount of water added to 1% by volume to 10% by volume, substantially spherical magnetic particles can be obtained, particularly 5% by volume. At 10% by volume, relatively large magnetic particles on the order of submicron to micron are obtained. From the viewpoint of producing substantially spherical micromagnetic particles having a uniform shape and size by heating and pressurizing iron hydroxide in a mixed solution containing 1,2-glycol and water, the addition of water is most preferable. The amount is 10% by volume. The powder obtained in Example 5 (FIG. 10) has a substantially spherical shape having an average diameter of 1.0 μm to 1.5 μm.

Further, when iron hydroxide is heated and pressurized in a mixed solution containing 1,2-glycol and water, octahedral magnetic particles can be obtained by setting the water content to 13% by volume to 15% by volume. Has been done. When the amount of water added is 15% by volume, residual iron hydroxide as a raw material is observed. On the other hand, from the viewpoint of producing octahedral micromagnetic particles having a uniform shape and size by heating and pressurizing iron hydroxide in a mixed solution containing 1,2-propanediol and water, it is the most. The preferred amount of water added is 5% by volume.

A high-magnification SEM photograph of the powder obtained in Example 6 is shown in FIG. Octahedral particles with extremely well-shaped shapes are generated, and the length of the longest piece is 1.0 μm to 1.5 μm.

A high-magnification SEM photograph of the powder obtained in Example 17 is shown in FIG. The obtained particles have a peculiar shape and have an icosahedron shape composed of 8 triangles and 12 hexagons.

1,10 ... Magnetic powder,
2 ... Approximately spherical magnetite particles,
12 ... octahedral magnetite particles,
20 ... icosahedron magnetite particles,
22 ... Triangle,
24 ... Hexagon.

Claims (3)

Iron hydroxide is heated and pressurized in a mixed solution containing 1,2-glycol and water, and magnetic particles having a shape different from that of the iron hydroxide are precipitated in the mixed solution.
The specific surface area of the iron hydroxide is 10m ² / g~100m ² / g,
The content of the water in the mixed solution is 1% by volume to 15% by volume.
The boiling point of 1,2-glycol is higher than that of water.
The heating temperature is −20 ° C. to + 35 ° C., which is the boiling point.
A method for producing magnetic particles. The iron hydroxide is goethite and the magnetic particles are magnetite.
The magnetite is produced from the goethite as a raw material.
The method for producing magnetic particles according to claim 1. The iron hydroxide is needle-shaped,
The method for producing magnetic particles according to claim 1 or 2.

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