JPH0881638A - Production of spherical hematite particle with even diameter - Google Patents

Abstract

PURPOSE: To obtain in an industrially advantageous way fine spherical hematite particles easy to control the size thereof, excellent in dispersibility, by adding a ferrous salt, etc., and urea to a ferric salt followed by mixing to effect dissolution in water and then by heating the resultant solution. CONSTITUTION: (A) A ferric salt having a concentration of pref. 0.03-0.3mol/L when dissolved is incorporated with about 0.01 molar times of (B) (i) a ferrous salt 1×10-<6> to 1×10-<2> in concentration or (ii) iron powder 0.01-0.1g/L in iron salt concentration followed by addition, as precipitant, of (C) at least 10 molar times of urea pref. 0.3-4mol/L in concentration, and the resultant system is mixed in water into an aqueous solution, which is, in turn, heated to 70 deg.C or higher, thus obtaining the objective spherical hematite particles 0.01-1.0μm in diameter. The particles can be used as a colorant for coating materials, ink, synthetic resins, construction materials and the ceramic industry, and is also useful for fluophors, ultraviolet absorbers and magnetic materials, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spherical hematite particles having a uniform particle size, fine particles and excellent dispersibility.

[0002]

BACKGROUND OF THE INVENTION Ferric oxide is used as a coloring agent for paints, inks, synthetic resins, building materials, ceramics, etc., as well as its functionality for phosphors, ultraviolet absorbers, magnetic materials, etc. It is widely used for various purposes. Conventionally, as a wet production method of iron oxide particles, a coprecipitation method, a wet oxidation method, a hydrothermal method, a hydrolysis method and the like are known. The coprecipitation method is a method in which an alkali or a mixture of ferrous ions and ferric ions is caused to act as a precipitant to generate a precipitate, and the precipitate is fired to obtain ferric oxide particles. When trying to obtain iron oxide particles having a uniform particle size by this coprecipitation method, it is necessary to precisely control the precipitation conditions, which is an industrial problem. The wet oxidation method is a method for producing iron oxide hydroxide particles and iron oxide particles by oxidizing ferrous ions with an oxidizing gas such as air in an alkaline solution. Although regular needle-shaped iron oxide can be obtained, it is difficult to obtain spherical hematite. In addition, the hydrothermal method is
Hematite particles are obtained by an oxidative hydrolysis reaction of ferrous ions in an alkaline solution at 150 ° C. or higher using an autoclave. According to this hydrothermal method, spherical particles,
Although it is possible to obtain hematite particles having a certain degree of regularity such as a plate shape, the conditions such as temperature, pressure and alkali concentration are severely set, which is a problem in industrial terms. Further, hydrolysis is a method in which a trivalent iron salt is used as a raw material, and this is hydrolyzed in a dilute concentration state in an acidic region for several hours to several days to obtain hematite particles. According to this hydrolysis method, Although spherical hematite having a uniform particle size can be obtained, the manufacturing solution has to be made into a dilute state, and it takes a long time to generate it, which is an industrially difficult point.

[0003]

The present invention has been made against the background of the above-mentioned problems of the prior art, and it is easy to control the size of particles, and spherical particles having a uniform particle size excellent in dispersibility are provided. An object of the present invention is to provide a production method capable of easily producing hematite particles industrially.

[0004]

That is, the present invention has three features.
Add divalent iron salt with iron salt concentration of 1 × 10 ^-6 to 1 × 10 ^-2 mol / l or iron powder with iron salt concentration of 0.01 to 0.1 g / l, and further add urea The method is a method for producing spherical hematite particles having a uniform particle size, which is characterized in that the solution is dissolved and mixed in water and then heated.

[0005]

By using urea containing a trivalent iron salt to which a small amount of divalent iron salt or iron powder is added as a precipitant, a hydroxide precipitate of trivalent iron is first produced. Next, a small amount of divalent iron salt or iron powder accelerates the dehydration reaction of the hydroxide, so that spherical hematite particles having a uniform particle size can be easily obtained in this solution in a short time. At this time, the shape and particle size can be changed depending on the urea concentration of the iron salt and the precipitating agent, and the conditions such as the temperature rising rate and the temperature. Therefore, since the spherical hematite particles obtained by this method have a uniform particle size and excellent dispersibility, when used as a pigment, for example, conventional paints, inks, synthetic resins, building materials, coloring for ceramics are used. Besides being used as an agent, for phosphors,
It is useful in a wide range of fields such as UV absorbers and magnetic materials that make the most of its functionality.

The present invention will be described in more detail with reference to the preferred embodiments. In the present invention, the iron salt mainly used is an iron salt having a valence of 3, and any salt such as chloride salt, nitrate salt, and sulfate salt may be used as long as it is a trivalent iron salt. An iron salt produced as a by-product in the steel industry may be used. Further, as the divalent iron salt added in a trace amount, any salt can be used as well. A predetermined amount of these salts is measured together with urea into a reaction tank having a reflux function such as a separable flask equipped with a condenser. However, the concentration of trivalent iron salt is 0.03 to 0.3 mol
/ L, the divalent iron salt concentration is 1 × 10 ^-6 to 1 × 10 ^-2 mol /
1, iron powder 0.01-0.1g / l, urea concentration 0.3
Good in the range of up to 4.0 mol / l. It is preferable that the divalent iron salt has a molar ratio of about 1/100, and the urea has a urea concentration of 10 times or more that of the trivalent iron salt. However, even if the concentration is out of the above range, iron precipitation can be obtained, but hydroxide precipitation remains and the spherical hematite particles of the present invention having a uniform particle size cannot be obtained. Since this reaction is a precipitation reaction due to the decomposition of urea, the reaction temperature needs to be higher than the temperature at which urea is decomposed, and is preferably 70 ° C. or higher. In addition, the rate of temperature rise affects grain growth, and the slower the rate, the larger the precipitation that forms. In this way, spherical hematite particles having a uniform particle size of 0.01 to 1.0 μm can be easily obtained.

[0007]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. The parts in the examples are based on weight unless otherwise specified. Example 1 102.3 parts of reagent grade ferric chloride hexahydrate, ferrous sulfate heptahydrate 0.17 in a separable flask equipped with a condenser
400 parts of urea as a precipitating agent is weighed in 1 part, and dissolved water is added to this to dissolve it, so that the total amount becomes 1,700 parts. Set this on the mantle heater so that it can be heated. While stirring well, each component is completely dissolved and stirred, the temperature is raised to 100 ° C. at a temperature rising rate of 5 ° C./min, and when the temperature rises, it is kept constant and kept as it is. After a while, a precipitate begins to precipitate, but after that, heating and stirring are continued and after 2 hours, the reaction product is taken out and thoroughly washed with water by decantation to wash out the residual salt. This was filtered and dried at 120 ° C. for 10 hours. The product thus obtained was observed by X-ray diffraction and a transmission electron microscope, and as a result, it was confirmed that the product was spherical hematite particles having a diameter of about 0.1 μm and a regular particle size. Example 2 In a separable flask equipped with a condenser, 51.1 parts of reagent grade ferric chloride hexahydrate and ferrous sulfate heptahydrate 0.17
Parts, 300 parts of urea as a precipitant is weighed, and dissolved water is added to this to dissolve it, so that the total amount becomes 1,700 parts. Set this on the mantle heater so that it can be heated. As a result of X-ray diffraction of the product obtained by the same method as in Example 1 below, a crystal peak of hematite particles clearly appears as shown in FIG. Further, as a result of observation with a transmission electron microscope, it was confirmed that the particles were spherical hematite particles having a diameter of about 0.3 μm and a uniform particle size. Example 3 In a separable flask equipped with a condenser, 34.1 parts of ferric chloride hexahydrate of the first grade reagent and 0.1 part of iron powder were weighed with 150 parts of urea as a precipitating agent, and dissolved water was added thereto to dissolve. The total number of copies will be 1,700. Set this on the mantle heater so that it can be heated. The temperature was raised to 100 ° C. at a temperature rising rate of 1 ° C./min, and it was confirmed that the product obtained by the same method as in Example 1 below was spherical hematite particles having a diameter of about 0.7 μm and a regular particle size. did it. Comparative Example 1 102.3 parts of ferric chloride hexahydrate of reagent grade 1 and 400 parts of urea as a precipitating agent were weighed in the same manner as in Example 1 except that a small amount of ferrous sulfate was added. Dissolved water is added and dissolved to make a total of 1,700 parts. Set this on the mantle heater so that it can be heated. The product obtained by the same method as in Example 1 was subjected to X-ray diffraction. As a result, it was amorphous ferric hydroxide and no crystal peak of hematite particles appeared as shown in FIG. Comparative Example 2 In a separable flask equipped with a condenser, 34.1 parts of reagent grade ferric chloride hexahydrate, 5.0 parts ferrous sulfate heptahydrate 5.0 parts, 150 parts of urea as a precipitant were measured and dissolved. Add water to dissolve and make a total of 1,700 parts.
Set this on the mantle heater so that it can be heated. The product obtained in the same manner as in Example 1 below was a mixture of magnetite, α-ferric oxohydroxide and hematite, and spherical hematite particles having a uniform particle size could not be obtained.

[0008]

EFFECT OF THE INVENTION According to the method for producing hematite of the present invention, the size of the particles can be easily controlled, and the spherical hematite particles having an excellent dispersibility and a uniform particle size can be easily industrially produced. There are advantages that can be produced.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of hematite particles obtained in Example 2.

FIG. 2 is an X-ray diffraction diagram of amorphous ferric hydroxide obtained in Comparative Example 1.

Claims (4)

[Claims] 1. An iron salt concentration of 1 × 10 ⁻⁶ to 1 × 1 in trivalent iron salt.
0 ^-2 mol / l divalent iron salt or iron salt concentration 0.01-0.1
A method for producing spherical hematite particles having a uniform particle size, which comprises adding g / l iron powder, further adding urea, dissolving and mixing in water, and then heating. 2. The dissolved concentration of trivalent iron salt is 0.03 to 0.3 mo.
The method for producing spherical hematite particles having a uniform particle size according to claim 1, which is 1 / l. 3. The method for producing spherical hematite particles having a uniform particle size according to claim 1, wherein the concentration of urea is 0.3 to 4.0 mol / l. 4. The spherical hematite particles have a particle size of 0.01 to
The method for producing spherical hematite particles having a uniform particle size according to claim 1, which is 1.0 μm.