JP3186929B2 - Method for producing spherical hematite particles with uniform particle size - Google Patents

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]

2. Description of the Related Art Ferric oxide is used as a coloring agent for paints, inks, synthetic resins, building materials, ceramics, and the like, and has a functional property such as a phosphor, an ultraviolet absorber, and a magnetic material. It is widely used for applications that make good use of it. 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. In the coprecipitation method, an alkali is applied as a precipitant to a single or a mixture of ferrous ions or ferric ions to generate a precipitate, which is calcined to obtain ferric oxide particles. In order to obtain iron oxide particles having a uniform particle size by this coprecipitation method, precise control of precipitation conditions was required, and there was an industrial difficulty. The wet oxidation method is a method of producing ferrous hydroxide particles and iron oxide particles by oxidizing ferrous ions with an oxidizing gas such as air in an alkaline solution. Although ordered acicular iron oxide is obtained, spherical hematite is hardly obtained. 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.
Although hematite particles having a certain shape such as a plate shape can be obtained, conditions such as temperature, pressure, alkali concentration and the like are strictly set, and there is a problem in industry. Furthermore, hydrolysis is a method of obtaining hematite particles by using a trivalent iron salt as a raw material and hydrolyzing it in a dilute concentration state in an acidic region for several hours to several days to obtain hematite particles. Although spherical hematite with a uniform particle size can be obtained, the production solution must be made dilute, and it takes a long time to produce the solution.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is easy to control the size of particles, and it is excellent in dispersibility. 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 provides the following:
Divalent iron salt having an iron salt concentration of 1 × 10 ⁻⁶ to 1 × 10 ⁻² mol / l or iron powder having an iron salt concentration of 0.01 to 0.1 g / l, and further adding urea And then heating after dissolving and mixing in water.

[0005]

By using urea as a precipitant using a trivalent iron salt to which a trace amount of a ferrous salt or iron powder is added, first, a hydroxide precipitate of trivalent iron is generated. Next, a small amount of ferrous salt or iron powder accelerates the dehydration reaction of this hydroxide, so that spherical hematite particles having a uniform particle diameter 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 conditions such as the urea concentration of the iron salt and the precipitant, the rate of temperature rise, and the temperature. Therefore, the spherical hematite particles obtained by this method have a uniform particle size and are excellent in dispersibility. For example, when used as a pigment, when used as a pigment, it can be used for conventional coatings, inks, synthetic resins, building materials, and ceramics. In addition to being used as an agent, for phosphors,
It is useful in a wide range of fields utilizing its functionality, such as for ultraviolet absorbers and magnetic materials.

Next, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, the iron salt mainly used is a trivalent iron salt, and any trivalent iron salt such as a chloride salt, a nitrate salt, and a sulfate salt may be used. Iron salts produced by the steel industry may be used. In addition, any salts can be similarly used as a divalent iron salt added in a trace amount. A predetermined amount of these salts is measured together with urea in a reaction tank having a reflux function such as a separable flask equipped with a condenser. However, the trivalent iron salt concentration is 0.03 to 0.3 mol.
/ L, divalent iron salt concentration is 1 × 10 ⁻⁶ to 1 × 10 ⁻² mol /
l, iron powder 0.01-0.1 g / l, urea concentration 0.3
It is good in the range of 4.0 mol / l. Preferably, the number of moles of the divalent iron salt is about 1/100 with respect to the number of moles of the trivalent iron ion, and the urea is urea having a molar concentration of 10 times or more that of the trivalent iron salt. However, even when the concentration is outside the above range, precipitation of iron can be obtained, but spherical hematite particles having a uniform particle size of the present invention cannot be obtained with hydroxide precipitation. 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 decomposes, and is preferably 70 ° C. or higher. Further, the heating rate affects the grain growth, and the slower the temperature, the more the generated precipitate tends to be relatively large. In this way, spherical hematite particles having a uniform particle diameter of 0.01 to 1.0 μm can be easily obtained.

[0007]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Parts in the examples are on a weight basis unless otherwise specified. Example 1 102.3 parts of reagent grade 1 ferric chloride hexahydrate, ferrous sulfate heptahydrate 0.17 in a separable flask equipped with a condenser
Weigh 400 parts of urea as a precipitant in each part and add dissolved water to this to dissolve it so that the total amount becomes 1,700 parts. This is set on a mantle heater to enable heating. The temperature is raised to 100 ° C. at a rate of 5 ° C./min while thoroughly stirring and thoroughly dissolving and stirring each component. After a while, a precipitate starts to be deposited. After that, heating and stirring are continued for 2 hours, and then the reactant is taken out and sufficiently washed with water by decantation to remove residual salts. This was filtered and dried at 120 ° C. for 10 hours. The product thus obtained was observed by X-ray diffraction and transmission electron microscopy. As a result, it was confirmed that the product was spherical hematite particles having a diameter of about 0.1 μm and a uniform particle diameter. Example 2 In a separable flask with a condenser, 51.1 parts of reagent grade 1 ferric chloride hexahydrate, ferrous sulfate heptahydrate 0.17
Urea, 300 parts of urea as a precipitant, and dissolving water added thereto to dissolve so that the total amount becomes 1,700 parts. This is set on a mantle heater to enable heating. The product obtained by the same method as in Example 1 was subjected to X-ray diffraction. As a result, a crystal peak of hematite particles clearly appeared 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 diameter. Example 3 In a separable flask equipped with a condenser, 34.1 parts of reagent-grade ferric chloride hexahydrate, and 0.1 part of iron powder, 150 parts of urea as a precipitant were weighed, and dissolved water was added thereto. So that the total is 1,700 copies. This is set on a mantle heater to enable heating. The temperature was raised to 100 ° C. at a rate of 1 ° C./min, and the product obtained in the same manner as in Example 1 was confirmed to be spherical hematite particles having a diameter of about 0.7 μm and having a uniform particle diameter. did it. Comparative Example 1 In the same manner as in Example 1 except that a trace amount of ferrous sulfate was added, 102.3 parts of a reagent first-grade ferric chloride hexahydrate and 400 parts of urea as a precipitant were weighed, and this was taken. Add dissolved water and dissolve to a total of 1,700 parts. This is set on a mantle heater to enable heating. The product obtained by the same method as in Example 1 was subjected to X-ray diffraction, and as a result, as shown in FIG. 2, the product was amorphous ferric hydroxide and no crystal peak of hematite particles appeared. Comparative Example 2 In a separable flask equipped with a condenser, 34.1 parts of reagent grade 1 ferric chloride hexahydrate, 5.0 parts of ferrous sulfate heptahydrate 150 parts of urea was measured as a precipitant and dissolved therein. Add water and dissolve to make a total of 1,700 parts.
This is set on a mantle heater to enable heating. The product obtained in the same manner as in Example 1 was a mixture of magnetite, α-oxoferric hydroxide and hematite, and spherical hematite particles having a uniform particle size could not be obtained.

[0008]

According to the method for producing hematite of the present invention, it is easy to control the size of the particles, and it is also easy to industrially produce spherical hematite particles having excellent dispersibility and a uniform particle diameter. There are advantages that can be manufactured.

[Brief description of the 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 the amorphous ferric hydroxide obtained in Comparative Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akira Nishio 1-7-6, Nihonbashi Bakurocho, Chuo-ku, Tokyo Inside Dainichi Seika Kogyo Co., Ltd. (56) References JP-A-53-115698 JP-A-63-64925 (JP, A) JP-A-1-141823 (JP, A) JP-A-6-211524 (JP, A) JP-A-7-257930 (JP, A) (58) Int.Cl. ⁷ , DB name) C01G 49/06 C09C 1/24

Claims (4)

(57) [Claims] An iron salt concentration of 1.times.10.sup.- ⁶ to 1.times.1
0 ^-2 mol / l ferrous salt or iron salt concentration 0.01 to 0.1
g / l iron powder, further adding urea, dissolving and mixing in water, and then heating the mixture. 2. The dissolution concentration of the trivalent iron salt is 0.03-0.3 mol.
The method for producing spherical hematite particles having a uniform particle size according to claim 1, wherein the ratio is 1 / l. 3. The method according to claim 1, wherein the concentration of urea is 0.3 to 4.0 mol / l. 4. The spherical hematite particles having a particle diameter of 0.01 to
The method for producing spherical hematite particles having a uniform particle diameter according to claim 1, which has a diameter of 1.0 µm.