JPS63288913A - Production of zinc oxide - Google Patents

Abstract

PURPOSE:To stably produce the superfine particles of ZnO by allowing an aq. slurry contg. ZnO to react with gaseous CO2 to obtain basic zinc carbonate which is then pulverized, and thermally decomposing the pulverized material. CONSTITUTION:Gaseous CO2 is blown at the rate of 0.5-5l/min per kg Zn and at 10-70 deg.C into an aq. slurry contg. 100-800g/l ZnO, and allowed to react with the ZnO to obtain basic zinc carbonate. The obtained basic zinc carbonate is pulverized, and then heated and decomposed at 250-1,000 deg.C to obtain ZnO having 0.02-0.1mum particle diameter.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to rubber vulcanization accelerators, paints, cosmetics, inks, pigments, pharmaceuticals, etc., as well as varistors, electrophotographic photosensitive materials, and gas sensors. , relates to a method for producing zinc oxide used in applications such as catalysts.

[Prior Art] As a conventional method for producing zinc oxide, an oxidative combustion method of metal zinc vapor, such as the so-called French method, is known. The particle size of zinc oxide obtained by such a method is 0, even if it is fine.
．． 2 μm, on average 0.5 to 0.8 μm.

Due to the viscosity and cohesiveness of these zinc oxides, it is difficult to further refine them by mechanical grinding. However, in addition to the applications that have been used for a long time as mentioned above, in applications such as varistors that have been developed in recent years, higher purity and ultra-fine grains are required than ever before.

Therefore, methods for producing ultrafine zinc oxide can be roughly divided into two types: a thermal decomposition method in which a fine zinc compound is generated and then thermally decomposed, and a gas phase reaction method in which zinc vapor is directly oxidized and burned. .

The first example of the thermal decomposition method is to add oxalic acid, alkali oxalate, or ammonium oxalate solution to a zinc ion solution such as zinc chloride, zinc sulfate, or zinc nitrate to generate fine crystals of zinc B-acid, and then filter the solution. Separately, after drying, the zinc oxide is thermally decomposed to form zinc oxide (see Japanese Patent Application No. 56-90782@), and the particle size of the obtained zinc oxide is said to be about 0.03 μm.

The second example of the thermal decomposition method is a method in which alkali hydroxide or alkali carbonate is added to a zinc salt solution, one zinc hydroxide or one m-based zinc carbonate is filtered, dried, and then thermally decomposed. The particle size of zinc oxide produced by thermal decomposition of zinc hydroxide is up to 0.1 μm, and in the case of thermal decomposition of basic zinc carbonate, a particle size of 0.07 to 0.1 μm is possible.

The third example of the pyrolysis method is to react a water slurry of zinc oxide with CO2 gas in a closed container to produce basic zinc carbonate, and then pyrolyze this basic zinc carbonate to form zinc oxide. Zinc oxide obtained by the method (see Japanese Patent Application No. 59-111720) has a specific surface area of 15II12/g, which gives an average particle diameter of 0.07 μm.

In addition, as an example of a gas phase reaction method, after spouting metallic zinc vapor into an oxygen-containing atmosphere to oxidize and burn zinc,
Acicular zinc is produced by rapidly cooling the immediately generated zinc oxide, and desired properties (particle size,
particle size distribution, bulk density, adsorption properties, etc.)
(See Japanese Patent Application No. 55-23516).

[Problems to be Solved by the Invention] In the first and second examples of the pyrolysis method described above, for example, by diluting the concentration of zinc salt and the concentration of alkali carbonate to be added, the basicity produced can be reduced. Suppressing the enlargement of zinc carbonate particles to 0.1μmPi! Although it is possible to obtain finely divided zinc atomized, there is a limit to how finely atomized zinc can be obtained by simply adjusting the reaction conditions, and in both methods, the desired reaction product (
A process for washing and removing zinc salts (e.g., zinc chloride, zinc UA acid, etc.) remaining in the reaction system and a1 products (e.g., sodium chloride, Glauber's salt, etc.) of the production system from the basic zinc carbonate) is avoided. Since the products are so fine that they cannot be washed easily, this is a major economic disadvantage. If cleaning is insufficient, naturally Na, S, etc. will be mixed into the zinc oxide as impurities, resulting in a problem that high purity requirements cannot be met.

The third example of the pyrolysis method discloses a method for producing basic zinc carbonate that does not contain impurities, and although it is possible to make zinc oxide by pyrolyzing it free of impurities, it is possible to make zinc oxide free from impurities; There is a problem that requires the use of containers.

In the example of the gas phase method, the purpose is essentially to produce acicular zinc oxide, and there is no disclosure of production of ultrafine zinc oxide.

[Means for Solving the Problems] The present invention aims to solve the above-mentioned conventional problems and to produce highly purified and ultra-fine zinc oxide. CO2 in water slurry containing zinc
This is a method for producing zinc oxide, which is characterized by reacting gas to produce zinc carbonate, then pulverizing the zinc carbonate, and then thermally decomposing it.

That is, the present applicant has previously disclosed a method for producing basic zinc carbonate which is particularly useful as a zinc supply source for electrogalvanizing.
(see Japanese Patent Publication No. 2003-11), a method was developed to obtain a highly pure product without any impurity removal process; however, in the present invention, the basic zinc carbonate obtained by this method is thermally decomposed. The resulting zinc oxide can be obtained as is with the high purity of basic zinc carbonate. Since the particle size of the basic zinc carbonate obtained in the above-mentioned prior invention is about 1 to 10 μm, crystal growth and secondary agglomeration occur, so even if it is directly thermally decomposed, the obtained zinc oxide can be reduced to the desired particle size. Since it was determined that it would be difficult to reduce the zinc carbonate to a fine particle size of 0.05 μm, in the present invention, zinc carbonate is pulverized by mechanical pulverization, and then heated to reduce the average particle size to 0.05 μm.
It was possible to achieve ultra-fine grain size of less than m.

The thermal decomposition temperature is the decomposition temperature of basic zinc carbonate2
The temperature should be 18°C or higher, but in consideration of shortening the decomposition time and various physical properties required of the produced zinc oxide, such as particle size, bulk specific gravity, color development, lattice defects, etc., the temperature should be set at 250 to 1000°C.
be selected as appropriate within the range. A particularly preferred range is 500 to 700° C. from the viewpoint of shortening the decomposition time and preventing the zinc oxide particles from becoming enlarged due to sintering during high-temperature heating.

The atmosphere during heating may be either air or an oxygen-enriched atmosphere, but if it is an oxygen-enriched atmosphere, even if very fine canned amium is mixed in during the reaction or crushing process, this substance will be completely decomposed. It is extremely effective.

In addition, the zinc oxide used in the production of basic bamboo charcoal M zinc is Wa! l! Lead or high purity Nitrous oxide) (
It is preferable to use zinc oxide obtained by oxidative combustion in the Seinuma tower In for the purpose of tJ construction (purest zinc).

In addition, the water slurry containing zinc oxide at 11 degrees is 100 to 8
00 (1/β, preferably in the range of 150 to 380 G/J2. If the slurry concentration is less than 100 g/J2, the production efficiency will decrease, and if it exceeds 800 a/J2, a uniform product will not be produced. .

The reaction between the water slurry and CO2 gas is carried out by blowing COz gas into the slurry using a device such as an aeration tube immersed in the slurry. In this case, the carbon dioxide source used is high tkm compressed carbon dioxide, purified combustion exhaust gas, or the like. In order to speed up the reaction time and to improve the fluidity of the slurry, it is preferable that the water be saturated with CO2 before slurry preparation.

The reaction temperature is set in the range of 10 to 10°C. When the temperature is lower than 10°C, the reaction rate is slow and the slurry becomes highly viscous, and when the temperature exceeds 70°C, there are many disadvantages in terms of cost from the viewpoint of thermal compensation and COzm decomposition. A more preferable range is 30 to 40°C. The appropriate rate of injection of CO2 gas is 0.5 to 5j2/min per kg of zinc (dry ffi standard), and the appropriate reaction time is in the range of 60 to 180 minutes.

[Example] Next, examples and comparative examples will be described.

Example 1 Using high purity zinc oxide obtained by the French method,
A G/J Zn0 grain water slurry was placed in a reaction vessel, and CO2 gas was blown in at a rate of 1 i/min from the lower center of the vessel through an aeration tube. After 2 hours of reaction, remove the high purity lII basic zinc carbonate.

The obtained basic carbon M curved lead was crushed to the extent that it could be easily crushed by mechanical crushing, 300℃, SOO℃, 7
It was heated and decomposed at a temperature of 00°C and 900°C. The heating atmosphere was air. The results are summarized in a table. In addition, Figure 1 shows the particle structure after thermal decomposition at 500°C for 30 minutes.
The micrograph, FIG. 2, shows a micrograph showing the particle structure after thermal decomposition at 900° C. for 30 minutes.

table *P was extracted from decarbonization.

Comparative Example 1 Commercially available fine powder basic zinc carbonate (0.3 μm or less) was
Thermal decomposition was carried out at 00°C. The particle size of the obtained zinc oxide was 0.
The particle diameter was 1 to 0.03 μm, and the atomization was sufficiently satisfied, but the impurity element Na was 1200 (IEI plow, S was aoopp-).Also, the color of oxidized! IIi lead was different from that in the example. The yellow color was stronger than that of No. 1 heated to 500° C. or more.

Comparative Example 2 Zinc carbonate described in 1) of Japanese Patent Application No. 58-2291884 was thermally decomposed at 700° C. for 30 minutes without being pulverized. The obtained zinc oxide has a small amount of particles of 0.1 μm or less, but
Most had a diameter of 1 μm.

Comparative Example 3 13L of zinc carbonate was roughly pulverized in Example fIA7, and 500
Thermal decomposition was carried out at ℃. The particle size of the obtained zinc oxide is 0.3~
It lacked uniformity as 0.02 μm. Moreover, the color of zinc oxide was comparable to that of Example 1.

] R-light effect fi] According to the present invention, the purity is high and as shown in the drawing, 0.0
2-0,1. It is possible to stably obtain ultrafine zinc oxide having an average particle size of approximately czm, particularly 0.05 μm or less.

[Brief explanation of the drawing]

FIGS. 1 and 2 are micrographs showing the particle structure in Examples of the present invention.

Claims (2)

[Claims] (1) A water slurry containing zinc oxide is reacted with CO_2 gas to produce basic zinc carbonate (hereinafter abbreviated as zinc carbonate), and then the zinc carbonate is pulverized and then thermally decomposed. Method for manufacturing zinc oxide. (2) The method for producing zinc oxide according to claim (1), wherein the heating temperature is 250 to 1000°C.