JPH0321489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cyclic iron oxide powder having a novel particle shape and a method for producing the same.

More specifically, the present invention provides an annular shaped α
-It relates to iron oxide powders such as _{Fe 2} O ₃ , Fe ₃ O ₄ and γ-Fe ₂ O ₃ and their manufacturing method.

The cyclic iron oxide powder of the present invention can be used as electronic materials such as magnetic powder and raw materials thereof, pigments for reinforcing paint films, reinforcing materials for composite materials, medical materials, etc.

[Conventional technology]

Conventionally, α-
Many iron oxide powders such as Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and their manufacturing methods are known, and iron oxide powders are used as magnetic powders, their raw materials, pigments, reinforcing materials, etc. ing. Furthermore, in recent years, attempts have been made to develop uses for ferromagnetic iron oxide powder as a medical material, such as using it in combination with magnetic drugs and using it as a medium to transport drugs to necessary locations within the body.

[Problem that the invention seeks to solve]

However, conventionally, no iron oxide powder having ring-shaped particles and a method for producing the same have been proposed.

If cyclic iron oxide powder can be obtained instead of iron oxide powder whose particle shape is acicular or grain-like, it will be possible to obtain properties based on the cyclic shape in the fields of electronic materials, pigments, reinforcing materials, medical materials, etc. It is expected that new applications will be developed.

An object of the present invention is to provide a cyclic iron oxide powder such as α-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ or the like having an unprecedented shape, and a method for producing the same.

A further object of the present invention is to provide an annular iron oxide powder having a particle size in the range of 0.03 to 0.5 μm and a method for producing the same.

[Means for solving problems]

As a result of research aimed at developing iron oxide powder with a new shape, the inventors of the present invention obtained hydroxylated iron oxide powder by reacting a ferric salt with an alkali in an aqueous medium in the presence of an oxyalkylamine. When ferric hydroxide is generated and the resulting slurry of ferric hydroxide is hydrothermally treated, goethite with a new plate-like particle shape can be obtained; after this goethite is treated with a silicon compound, it is heated and dehydrated. Then, the cyclic α−Fe ₂ O ₃
However, when this is reduced after heating and dehydration, a cyclic
The inventors have discovered that Fe _{3 O 4} can be further reoxidized to obtain cyclic γ-Fe ₂ O ₃ , leading to the present _invention .

In the present invention, the particles have an annular shape and a particle diameter of 0.03.
The present invention relates to a cyclic iron oxide powder characterized in that the particle size is in the range of ~0.5 μm.

The present invention also involves reacting a ferric salt and an alkali in an aqueous medium in the presence of an oxyalkylamine to produce ferric hydroxide, and hydrothermally treating the resulting slurry of ferric hydroxide. The particle size is 0.03~0.5μ
m, thickness is 0.1μm or less, plate ratio (particle size/thickness)
A step of obtaining a disc-shaped α-FeOOH with 2 or more, (a)
After treating disc-shaped α-FeOOH with a silicon compound, heat dehydration is performed to obtain cyclic α-Fe ₂ O ₃ powder, (b) α-Fe ₂ O ₃ powder obtained in step (a) is A step of reducing to obtain a cyclic Fe ₃ O ₄ powder, and oxidizing the Fe ₃ O ₄ powder obtained in steps (c) and (b) to obtain a cyclic γ-
Selected from the group consisting of the process of obtaining Fe ₂ O ₃ powder
The present invention relates to a method for producing cyclic iron oxide powder, characterized by comprising steps (a) to (c).

The cyclic iron oxide powder of the present invention will be explained in detail along with its manufacturing method.

In the process of obtaining α-FeOOH of the present invention, the ferric salts generally include ferric sulfate, ferric chloride,
Ferric nitrate and the like are used, and among these, ferric chloride is preferred. As the alkali, alkali hydroxides such as sodium hydroxide and potassium hydroxide are preferably used.

As a method for reacting a ferric salt and an alkali in an aqueous medium, it is generally preferable to carry out the reaction using an aqueous ferric salt solution and an aqueous alkali hydroxide solution. At that time, the concentration of ferric salt in the aqueous solution is
It is appropriate to adjust the concentration of the alkali hydroxide to 0.1 to 1 mol/, and it is also appropriate to adjust the concentration of alkali hydroxide to 0.3 to 5 mol/. Also, the amount of alkali hydroxide used for ferric salt is
It is suitable that the amount is about 1 to 5 times equivalent.

The oxyalkylamine is dissolved in a solvent,
For example, the oxylalkylamine may be added dissolved in a solvent such as water, dissolved in an aqueous alkali hydroxide solution, or directly added to the system, but the amount of oxylalkylamine is usually 30-80 for iron salts
It is advisable to adjust the amount to twice the molar amount, preferably 35 to 75 times the molar amount. If the amount of oxyalkylamine is too small, it tends to become granular or have a wide particle size distribution, and if the amount is too large, it is not economical.

As the oxyalkylamine, those having an alkyl group of 2 to 6 carbon atoms are suitable, and representative examples thereof include monoethanolamine, γ-propanolamine, β-propanolamine, diethanolamine, triethanolamine, and isobutanolamine. Among them, ethanolamine is preferred.

The reaction temperature for producing ferric hydroxide by reacting a ferric salt with an alkali in the presence of an oxyalkylamine is 50°C or less, preferably 0 to 45°C.
It is preferable to increase the effect of the oxyalkylamine and to control the thickness, plate ratio, particle morphology, etc. of the α-FeOOH particles. If the temperature is too high, the α-FeOOH particles will become longer,
It is easy for granular α-Fe ₂ O ₃ to coexist or for the α-FeOOH particle morphology to vary widely, and there is no particular advantage in lowering the temperature too much. The reaction time is not particularly limited, but is generally 0.01~
Appropriately selected from a range of 20 hours.

A slurry of ferric hydroxide obtained by the reaction of a ferric salt with an alkali can produce plate-shaped goethite even if it is immediately hydrothermally treated, but it must be aged prior to the hydrothermal treatment. This makes it easier to obtain disk-shaped particles with uniform morphology. As a maturing method, generally employed is a method of leaving the product at 0 to 80°C for about 5 to 50 hours with or without stirring.

In addition, in order to enhance the hydrothermal treatment effect, it is necessary to
It is desirable to conduct the hydrothermal treatment at a pH of 10 or higher, preferably 10.5 to 14. To adjust the pH of the slurry to 10 or higher, for example, the slurry containing ferric hydroxide may be filtered, washed, or after removing the supernatant liquid, an alkali such as sodium hydroxide or potassium hydroxide may be added to the slurry. It is convenient to use this method for adjustment.

Hydrothermal treatment temperature is 100~250℃, preferably 120~
230°C is preferred. If the hydrothermal treatment temperature is too low, it will take a long time to convert ferric hydroxide into goethite, and the goethite particles may become elongated or have a large variation in morphology, and the hydrothermal treatment temperature is too high. and granular α-Fe ₂ O ₃ are generated. The hydrothermal treatment time is not particularly limited, but is generally about 0.5 to 5 hours.

Further, an autoclave is generally suitably employed for the hydrothermal treatment.

By the hydrothermal treatment, the ferric hydroxide in the slurry is converted into disk-shaped goethite with an unprecedented particle morphology and good dispersibility, specifically into hexagonal disk-shaped or similar goethite.

As a method for recovering plate-shaped goethite particles from the slurry after hydrothermal treatment, conventional methods such as washing with water, filtration, drying, etc. can be employed.

In the present invention, the plate-shaped goethite particles recovered after hydrothermal treatment are found to have α
-It is confirmed that it is a crystal of FeOOH.

The particle diameter (disc diameter), particle thickness, disc ratio (particle diameter/thickness), etc. can be varied over a fairly wide range within the range of the above manufacturing conditions, but in order to obtain cyclic iron oxide, the particle Diameter is 0.03-0.5μm, thickness is 0.1μm
Below, the normal size is 0.1 to 0.01 μm, the plate ratio is 2 or more,
Normally it is controlled to 3-6 as appropriate. If the particles are too thick or the platelet ratio is too small, it will be difficult to form them into a ring in the next step. Measurement of particle diameter, particle thickness, etc. can be performed using a transmission electron microscope (TEM).

In the present invention, it has been discovered that the cyclic α-Fe ₂ O ₃ iron oxide powder can be obtained by treating disc-shaped goethite (α-FeOOH) with a silicon compound and then heating and dehydrating it.

During thermal dehydration, if the thickness of goethite is too thick, the disc ratio is too small, or the treatment with silicon compounds is insufficient, the cyclic α-
Instead of becoming Fe ₂ O ₃ powder, it becomes granular α-Fe ₂ O ₃ .

Heat dehydration is performed in a non-reducing atmosphere such as nitrogen or air.
It is suitable to conduct the reaction at a temperature of 300 to 900°C, preferably 400 to 700°C. If the heating dehydration temperature is too low, the cyclic α-
Fe ₂ O ₃ does not become a particle, but cyclic Fe ₃ O ₄ ,
This causes the shape to become more distorted when obtaining γ-Fe ₂ O ₃ and the like. On the other hand, if the heating and dehydration temperature is too high, it may cause deformation of particles, sintering between particles, etc.

In the present invention, the cyclic α-Fe ₂ O ₃ iron oxide powder is obtained by treating the disc-shaped goethite powder with a silicon compound and then heating and dehydrating it.

When obtaining cyclic α-Fe ₂ O ₃ , treatment with a silicon compound prior to heat dehydration improves the sintering prevention effect and shape retention effect, and furthermore, the annular shape is formed due to the growth of dehydration pores, resulting in improved crystallinity. α-Fe ₂ O ₃ powder with an increased degree of oxidation and inheriting and retaining the annular shape can be obtained. The treatment method with a silicon compound is not particularly limited, but in general, disk-shaped goethite particles are suspended in water, the suspension is made acidic or alkaline, and dispersed, and SiO ₂ is added to α-Fe ₂ O ₃ . in terms of
A method of adding 0.3-5.0% water-soluble silicate such as sodium silicate, followed by treatment and coating with SiO ₂ by adjusting the pH value to 7-8, using an organosilicon compound such as tetraalkoxysilane. A method of bringing the materials into contact with each other in a gas phase is preferably employed.

In the present invention, the cyclic α-Fe ₂ O ₃ powder obtained by treatment with a silicon compound and thermal dehydration is treated in a reducing gas atmosphere such as hydrogen or a mixed gas of hydrogen and nitrogen at a temperature of 250 to 500 ℃, preferably 300-450℃
When reduced with , cyclic Fe ₃ O ₄ is obtained. At this time, water vapor may be included in order to prevent excessive reduction. If the reduction temperature is too low, the reduction reaction will proceed slowly and take a long time; if it is too high, the reduction reaction will proceed rapidly and the resulting annular Fe ₃ O ₄ particles will be likely to be deformed, sintered, etc.

Furthermore, in the present invention, the cyclic γ-Fe ₂ O ₃ powder is
It has been found that it can be obtained by oxidizing the cyclic Fe ₃ O ₄ powder.

Oxidation of the cyclic Fe ₃ O ₄ powder is carried out in an oxidizing gas atmosphere such as oxygen or a mixed gas of oxygen and nitrogen, generally in an air atmosphere at a temperature of 200 to 400°C, preferably 250 to 350°C.
It is preferable to carry out the Cyclic γ- by oxidation
Fe ₂ O ₃ powder is obtained, but if the temperature is too low, oxidation will not proceed sufficiently, and if the temperature is too high, the shape will easily collapse, and α-Fe ₂ O ₃ may be mixed, resulting in cyclic γ-
It becomes difficult to obtain Fe ₂ O ₃ .

In the present invention, a plate-shaped goethite is first obtained _{, and then treated with a silicon compound and then heated and dehydrated to produce cyclic α-Fe 2 O 3 .} and then reduced to form a cyclic α-
Cyclic Fe ₃ O ₄ , which inherited the form of Fe ₂ O ₃ , is also treated with a silicon compound and then heated and dehydrated to form cyclic α-
Fe ₂ O ₃ is converted into Fe 2 O 3, then reduced to form cyclic Fe ₃ O ₄ , and then oxidized to obtain cyclic γ-Fe ₂ O ₃ , which inherits the form of cyclic α-Fe ₂ O ₃ . The particle size of the iron oxide powder is almost the same as that of platy goethite, and the particle size is in the range of 0.03 to 0.5 μm. In addition, the particle thickness, platelet ratio, etc. are almost the same as those of platy goethite.

〔Example〕

Example 1 [Production of cyclic α-Fe ₂ O ₃ powder] 500 g of ferric chloride [FeCl ₃ 6H ₂ O] was mixed with 10 g of distilled water.
750g of sodium hydroxide and 55g of monoethanolamine
(45 times the mole relative to ferric chloride) was added dropwise to a solution at 8°C in which 20% of distilled water was dissolved, and the mixture was stirred and reacted while being maintained at about 10°C to obtain a ferric hydroxide slurry.

After aging the slurry at 25°C for about 20 hours, remove the supernatant liquid, wash with a 10% sodium hydroxide aqueous solution to bring the pH of the slurry to 11, and reduce the slurry to a content of 15.
The slurry was placed in an autoclave and subjected to hydrothermal treatment at 150°C to obtain a hexagonal disk or a plate-like goethite slurry similar to it.

The plate-shaped goethite slurry was washed with water to obtain plate-shaped goethite.

After adding acetic acid to the platy goethite to adjust the pH to 3.5, 3.35 g of sodium silicate (Na ₂ SiO ₃ ) (equivalent to 1.0 wt% as SiO ₂ to goethite) was added to water.
It was dissolved in 200ml and added. After stirring for 60 minutes,
Adjust the pH of the suspension to 8 with ammonia water (concentration 28wt%)
After aging overnight, the mixture was washed, filtered, and dried to obtain disc-shaped goethite particles treated with a silicon compound.

Plate-like goethite is α-
It was confirmed that it has a FeOOH structure. In addition, the particle size was determined using a transmission electron microscope (TEM).
The plate ratio, thickness, etc. were measured. The specific surface area was also measured. These results are shown below. Note that the average particle diameter, average platelet ratio, and average thickness are average values for 30 particles.

Particle size: 0.07 to 0.13 μm (average value 0.10 μm) Platy ratio: 3 to 4.1 (average value 3.3) Thickness: 0.019 to 0.035 μm (average value 0.028 μm) Specific surface area 34 m ² /g Next is platy goethite 50g was heated and dehydrated in air at 650℃ for 1 hour in a fluidized bed calcining furnace to form a cyclic α-Fe ₂ O ₃
A powder was obtained.

A transmission electron micrograph (60,000 times) of annular α-Fe ₂ O ₃ powder particles is shown in FIG. cyclic α−
The particle size of Fe ₂ O ₃ is 0.06 to 0.12 μm (average value 0.095 μm
m), and the disc ratio was 2.8 to 3.9 (average value 3.2).

Example 2 [Manufacture of cyclic Fe ₃ O ₄ powder] 20 g of cyclic α-Fe ₂ O ₃ obtained by treatment with the silicon compound obtained in Example 1 and heat dehydration was heated in a fluidized bed calcining furnace. Hydrogen gas was reduced at 1/min (containing 5% water vapor) at a reduction temperature of 350°C for 3 hours, and α-Fe ₂ O ₃
A cyclic Fe ₃ O ₄ powder was obtained which inherited the cyclic shape of .

The particle size of cyclic Fe ₃ O ₄ is 0.05 to 0.12 μm (average value
(0.10 μm) disk ratio was 2.5 to 3.6 (average value 30).

Example 3 [Manufacture of cyclic γ-Fe ₂ O ₃ powder] 15 g of the cyclic Fe ₃ O ₄ powder obtained in Example 2 was passed through a fluidized bed calcining furnace at a rate of 1/min to 250 g of cyclic Fe 3 O 4 powder.
Oxidation was carried out at ℃ for 2 hours to obtain cyclic γ-Fe ₂ O ₃ powder.

Cyclic γ-Fe ₂ O ₃ powder particles are cyclic Fe ₃ O ₄
It inherits the particle morphology of powder, with annular γ-
The particle size of Fe ₂ O ₃ is 0.05 to 0.13 μm (average value 0.10 μm
m), and the disc ratio was 2.6 to 3.8 (average value 3.1).

FIG. 2 shows a transmission electron micrograph (60,000 times) of annular γ-Fe ₂ O ₃ powder particles.

Example 4 100g of ferric chloride [FeCl ₃ 6H ₂ O] was added to distilled water 2
150g of sodium hydroxide and 11g of monoethanolamine
(45 times the mole relative to ferric chloride) was added dropwise to a 15°C solution of distilled water 4 and stirred while maintaining the temperature at about 15°C to obtain a ferric hydroxide slurry.

After leaving the slurry to mature at 25℃ for about 20 hours, remove the supernatant liquid, wash with a 10% sodium hydroxide aqueous solution to adjust the pH of the slurry to 11, and charge the slurry into an autoclave with content 2. After hydrothermal treatment at 180°C to obtain a slurry of plate-shaped goethite in the shape of hexagonal disks or similar shapes, the slurry was washed with water, filtered, and dried to obtain plate-shaped goethite in powder form.

Plate-like goethite is α-
It was confirmed that it has a FeOOH structure.

The particle diameter of the platy goethite was 0.08 to 0.16 μm (average value 0.12 μm), the platy ratio was 3.7 to 5.5 (average value 4.6), and the thickness was 0.022 to 0.039 μm (average value 0.032 μm).

15 g of platy goethite powder was treated with a mixed gas of air and tetraethoxysilane at 600°C for 1 hour in a fluidized bed firing furnace, and then heated and dehydrated at 600°C for 1 hour to form cyclic α-Fe ₂ O ₃ powder. After that, hydrogen gas (5
/min) at a reduction temperature of 330℃ for 3 hours to form a cyclic Fe ₃ O ₄ powder, and then with air (1/min).
was oxidized at 250°C _for 2 hours to obtain _a cyclic γ-
_{Fe2O3 powder} was obtained.

The particle size of the cyclic γ-Fe ₂ O ₃ powder is 0.07-0.15 μm
(Average value 0.11μm) Disc ratio is 3.5 to 5.4 (Average value 4.5)
It was hot. Also, the coercive force is 230Oe, and the saturation magnetization is
It was 72 emu/g.

〔Effect of the invention〕

The present invention provides cyclic iron oxide powders such as α-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and the like having an unprecedented particle morphology, and a method for producing the same.

The cyclic iron oxide powder can be used as magnetic powder and electronic materials such as raw materials thereof, pigments, reinforcing materials, fillers, and the like. Further, by utilizing the characteristic of having a circular shape, it is possible to apply it to a base material for medical materials such as red blood cells in biochemistry, and it is also possible to make artificial red blood cells by containing hemoglobin in the circular particles.

[Brief explanation of the drawing]

Figure 1 shows the annular α obtained in Example 1 of the present invention.
- This is a transmission electron micrograph of the Fe ₂ O ₃ powder particle morphology magnified 60,000 times. Moreover, FIG. 2 is a transmission electron micrograph of the annular γ-Fe ₂ O ₃ powder particles obtained in Example 3 of the present invention, which is enlarged 60,000 times.

Claims (1)

[Claims] 1. The shape of the particles is annular, and the particle diameter is 0.03 to 0.5 μm.
Cyclic iron oxide powder, characterized in that it is in the range of. 2. The cyclic iron oxide powder according to claim 1, wherein the cyclic iron oxide powder is α-Fe ₂ O ₃ . 3. The cyclic iron oxide powder according to claim 1, wherein the cyclic iron oxide powder is Fe ₃ O ₄ . 4. The cyclic iron oxide powder according to claim 1, wherein the cyclic iron oxide powder is γ-Fe ₂ O ₃ . 5 Ferric hydroxide is produced by reacting a ferric salt and an alkali in an aqueous medium in the presence of an oxyalkylamine, and the resulting slurry of ferric hydroxide is hydrothermally treated to reduce the particle size. 0.03~0.5μm, thickness 0.1μ
m or less, and a step of obtaining a plate-like α-FeOOH with a plate-like ratio (particle size/thickness) of 2 or more;
A step of treating FeOOH with a silicon compound and then heating and dehydrating it to obtain a cyclic α-Fe ₂ O ₃ powder, (b) reducing the α-Fe ₂ O ₃ powder obtained in step (a) to obtain a cyclic
A step of obtaining Fe ₃ O ₄ powder, and a step of oxidizing the Fe ₃ O ₄ powder obtained in steps (c) and (b) to obtain a cyclic γ-Fe ₂ O ₃ powder ( 1. A method for producing cyclic iron oxide powder, comprising the steps of any one of a) to (c).