JPH11131274A - Production of zinc oxide fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and inexpensively producing a zinc oxide fine powder having <=0.1 μm, preferably <=0.05 μm average particle diameter without the need for any heating. SOLUTION: A coating film consisting of a black zinc oxide fine particle is formed on the surface of metallic zinc by anodization, then a coating film consisting of a white zinc oxide fine particle is formed by anodization on the surface of the metallic zinc below the coating film consisting of the black zinc oxide fine particle to release the black zinc oxide fine particle in the form of micropieces, and the micropieces are recovered and crushed. Otherwise, metallic zinc is anodized at >=10 V electrolyzing voltage in an electrolyte contg. 0.05-0.4 M alkali metal hydroxide and 0.05-0.4 M nitrate to form a suspension of a zinc oxide fine particle, and the zinc oxide fine particle is recovered from the suspension.

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 zinc oxide fine powder, and more particularly, to a method for producing zinc oxide fine powder using a technique of anodizing zinc oxide.

[0002]

2. Description of the Related Art As a method for producing zinc oxide powder,
A method of obtaining zinc oxide powder by oxidizing zinc vapor (dry synthesis method) and a method of neutralizing zinc ions to precipitate zinc hydroxide and then calcining to obtain zinc oxide powder (wet synthesis method) are widely used. Used. Further, JP-A-2-311
As disclosed in Japanese Patent Publication No. 314, a method for thermally decomposing zinc sulfide to obtain zinc oxide powder is also known.

[0003] Zinc oxide is obtained as a black powder depending on the production method. For example, as disclosed in Japanese Patent Publication No. 5-55451, black zinc oxide powder can be obtained by heating metallic zinc in a heated oxygen atmosphere. However, this method cannot obtain a powder having an average particle size of 0.1 μm or less.

Japanese Patent Application Laid-Open No. 7-289913 discloses that a zinc oxide film composed of particles having an average particle size of 0.2 μm or less is produced by an anodizing method, and that this zinc oxide film is effective as a photocatalyst. Have been. Further, in the example described in the publication, anodization of zinc was carried out at an electrolytic voltage of 10 V in an electrolytic solution consisting of 20 g of sodium hydroxide, 10 g of sodium nitrate and 1 liter of water to obtain a thickness of about 3 mm.
A plate with a black zinc oxide coating of μm is obtained.
However, the coating obtained by this method is a strong coating as described in the publication, and it is difficult to separate the zinc oxide fine particles constituting the coating into individual fine particles.

[0005] Further, it is known that a zinc oxide film is obtained by anodizing a zinc plate in an alkaline solution, and it becomes a white film or a black film depending on the electrolysis conditions at this time. For example, in Electrochemistry, Vol. 64, No. 5, pp. 373-374, the lower the concentration of sodium hydroxide and the higher the applied voltage, the more the white film tends to be. It is reported that there is a tendency.

[0006] Zinc oxide is a semiconductor and can only absorb ultraviolet rays of 380 nm or less. Utilizing this ultraviolet absorption function, fine zinc oxide is kneaded or mixed with resin or paint as an ultraviolet absorber. In addition, since it can protect human skin and has high transparency, it is also used in cosmetics.

When zinc oxide powder is added to a resin as an ultraviolet absorber and used, the transparency of the resin tends to be lost as the particle size increases. It is reported that a zinc oxide powder having a particle size of is preferred.

[0008]

Such zinc oxide fine particles can be produced by a wet synthesis method. In the wet synthesis method, zinc hydroxide is calcined to obtain zinc oxide powder. At the time, zinc oxide is easy to sinter,
It is not easy to obtain the above zinc oxide fine powder.

On the other hand, if a dry synthesis method is employed, it is possible to produce zinc oxide particles with little aggregation, but the average particle diameter is 0.1%.
It is difficult to produce fine particles of μm or less. JP-A-7-28
According to the method disclosed in Japanese Patent No. 9913, a zinc oxide coating composed of fine particles can be produced, but a zinc oxide powder composed of fine particles cannot be obtained.

An object of the present invention is to provide a method for easily and inexpensively producing a zinc oxide fine powder having an average particle size of 0.1 μm or less, preferably 0.05 μm or less, without requiring any heating. And In addition, the present invention has a black average particle diameter of 0.1 μm or less, preferably 0.05 μm.
It is an object of the present invention to provide a production method capable of easily and inexpensively producing the following zinc oxide fine powder.

[0011]

Means for Solving the Problems The present inventors anodized metallic zinc using electrolytic solutions of various compositions and various electrolytic voltages, and examined the growth rate of the film and the color of the film. As a result, the black zinc oxide film and the white zinc oxide film can be separately formed by changing the electrolytic voltage even when the electrolytic solution composition is the same. The black zinc oxide coating and the white zinc oxide coating can be separately formed by changing the composition, and the black zinc oxide coating and the white zinc oxide coating can be formed by appropriately adjusting the electrolyte composition and the electrolytic voltage. And found that they can be made separately.

In order to obtain a black zinc oxide coating, it is better to add sodium nitrate to an alkaline electrolytic bath containing sodium hydroxide, potassium hydroxide and the like as a main component;
On the other hand, it has been found that in order to obtain a white zinc oxide film, it is better to add sodium carbonate to an alkaline electrolytic bath containing sodium hydroxide, potassium hydroxide or the like as a main component. It has also been found that when these reagents are added, the film grows faster and the color developability is better than when they are not added.

Further, when a white zinc oxide film is formed after a black zinc oxide film is formed, the black zinc oxide film and the white zinc oxide film have poor adhesion. The white zinc oxide film generated at the interface with the metallic zinc extrudes the black zinc oxide film, and as a result, only the black zinc oxide film disintegrates into fine particles, peels off, and is suspended in the electrolytic solution. Was found. In addition, the inventors have found that the exfoliated fine flake zinc oxide can be easily disintegrated into fine particles because the fine particles are only loosely aggregated.

The reason why the black zinc oxide film is disintegrated and exfoliated in the form of fine flakes and that the separated fine flake zinc oxide can be easily disintegrated into fine particles because the fine particles are only loosely aggregated. It is considered that the reason for the crushing was that zinc oxide was deposited while simultaneously generating both oxygen and eluting zinc on the surface of the metallic zinc. in this way,
Since this method does not result in a passive film as represented by anodic oxidation of aluminum, a large amount of fine zinc oxide can be generated on a zinc metal plate by performing electrolysis for a long time.

That is, according to the method for producing a zinc oxide fine powder of the present invention, a coating made of black zinc oxide fine particles is formed on the surface of metallic zinc by anodic oxidation, and then the lower side of the coating made of the black zinc oxide fine particles is formed. Forming a coating composed of white zinc oxide fine particles by anodic oxidation on the surface of metallic zinc, thereby peeling the black zinc oxide fine particles into fine flakes, collecting and crushing the fine flake zinc oxide. It is characterized by. By this production method, black zinc oxide fine powder having an average particle size of 0.1 μm or less, usually 0.05 μm or less can be obtained.

Further, when the present inventors anodize metallic zinc using a specific electrolytic solution composition and a specific electrolytic voltage, white fine zinc oxide precipitates on the metallic zinc surface, and oxygen is removed from the metallic zinc surface. It has been found that fine particles of zinc oxide are detached together with bubbles and dispersed in the electrolytic solution because they are generated in large amounts, so that the electrolytic solution becomes cloudy, that is, no zinc oxide film is formed.

That is, the method for producing a zinc oxide fine powder of the present invention is carried out in an electrolytic solution having an alkali metal hydroxide concentration of 0.05 to 0.4 M and a nitrate concentration of 0.05 to 0.4 M in an electrolytic voltage of 10 to 10 M.
The method is characterized in that metallic zinc is anodically oxidized at V or more to form a suspension of zinc oxide fine particles, and the zinc oxide fine particles are recovered from the suspension. By this production method, white zinc oxide fine powder having an average particle size of 0.1 μm or less, usually 0.05 μm or less can be obtained.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The metal zinc used in the present invention may be a zinc metal or a zinc alloy. In the present invention, it is essential to form a coating made of black zinc oxide fine particles by anodic oxidation on the surface of metallic zinc,
Such a black coating is obtained by appropriately adjusting the composition and voltage of the electrolytic solution, and the composition and voltage of the electrolytic solution are not limited to specific ranges.
Further, in the present invention, it is essential to form a film made of white zinc oxide fine particles by anodic oxidation on the surface of metallic zinc under the film made of black zinc oxide fine particles. The coating is also obtained by appropriately adjusting the composition and voltage of the electrolytic solution, and the composition and voltage of the electrolytic solution are not limited to specific ranges.

In the present invention, the black coating is conveniently formed by anodizing the surface of metallic zinc in a nitrate-containing alkaline solution in which the concentration of alkali metal hydroxide in the electrolytic solution is 0.3 mol or more. In addition, the white film is formed in a carbonate-containing alkaline solution in which the concentration of the alkali metal hydroxide in the electrolytic solution is 0.05 mol or more and 0.5 mol or less under the condition that the electrolytic voltage is 15 V or more. It can be conveniently prepared by anodizing the surface of metallic zinc.

That is, in a preferred embodiment of the present invention,
The method for producing zinc oxide fine powder is a method comprising: anodizing the surface of metallic zinc in a nitrate-containing alkaline solution having an alkali metal hydroxide concentration of 0.3 mol or more in an electrolytic solution to form a coating made of black zinc oxide fine particles. Then, in a carbonate-containing alkali solution having an alkali metal hydroxide concentration of 0.05 mol or more and 0.5 mol or less, the electrolytic voltage is 15 V
Under the conditions described above, the surface of the metallic zinc under the coating made of the black zinc oxide fine particles is anodized under the condition of forming a coating made of the white zinc oxide fine particles, whereby the black zinc oxide fine particles are formed. Can be exfoliated in the form of fine pieces. In this case, the anodic oxidation treatment time varies depending on electrolysis conditions such as the thickness of the coating made of the black zinc oxide fine particles and the distance between the electrodes, but may be about 30 seconds to several minutes. The fine flakes are collected, for example, by filtration, dried, and the fine flake zinc oxide is crushed to obtain fine zinc oxide powder.

In a preferred embodiment of the present invention, the concentration x (mol) of alkali metal hydroxide in the electrolytic solution is set to 0.1.
When 05 ≦ x ≦ 0.5, the electrolysis voltage y (V) is y <50x +
Under the condition of 7, the surface of the metallic zinc is anodized to form a coating composed of black zinc oxide fine particles, and then the alkali metal hydroxide concentration x (mol) of the electrolyte is 0.05 ≦ x
Under a condition of ≦ 0.5 and an electrolysis voltage y (V) of y> 50x + 8, the surface of the metallic zinc under the coating of the black zinc oxide fine particles is anodized to remove the white zinc oxide fine particles. The black zinc oxide fine particles are exfoliated as individual fine particles by forming a coating film, and the zinc oxide fine particles are recovered from the resulting suspension and dried to obtain zinc oxide fine powder.

In another embodiment of the present invention, the concentration of the alkali metal hydroxide is 0.05 to 0.4 M, preferably 0.1 to 0.4 M.
Anodizing metal zinc at an electrolysis voltage of 10 V or more, preferably 15 V or more, more preferably 20 V or more in an electrolyte having a concentration of 0.3 M and a nitrate concentration of 0.05 to 0.4 M, preferably 0.05 to 0.2 M. Thus, a suspension of zinc oxide fine particles is formed, and the zinc oxide fine particles are recovered from the suspension, for example, by filtration, and dried to obtain zinc oxide fine powder.

The zinc oxide fine powder obtained by the production method of the present invention has an average particle size of 0.1 μm or less, usually 0.02 μm.
Since it is 5 μm or less, it can be used very effectively for various uses requiring transparency and dispersibility, such as kneading into resins, mixing into fats and oils, and mixing into cosmetics.

[0024]

【Example】

Example 1 A degreased and cleaned zinc plate (10 cm × 10 cm, thickness 1 m)
m, backside covered with vinyl tape) electrolytic solution (sodium hydroxide 0.5M, sodium nitrate 0.1M aqueous solution)
A stainless steel plate (10 cm × 10 cm) was used as a cathode, and the distance between both electrodes was 1
Anodizing was performed by applying a DC voltage of 10 V for 10 minutes to 0 cm. Thereafter, this was washed and dried to obtain a coated plate.
The surface of this coated plate was black and confirmed to be a single phase of zinc oxide by X-ray diffraction. The average particle size calculated from the half width of the diffraction peak was 20 nm. The thickness of the zinc oxide coating was about 3 μm.

The plate with the zinc oxide film obtained as described above was placed in an electrolytic solution (aqueous solution of sodium hydroxide 0.15M and sodium carbonate 0.15M), and this was used as an anode and a stainless steel plate (10 cm × 10 cm), the distance between both electrodes was 10 cm, and a DC voltage of 20 V was applied for 2 minutes. About 1 minute after the start of the electrolysis, the black film was peeled off and dropped off, and 2 minutes later, the black film was completely dropped and suspended in the electrolytic solution. The suspension was filtered, and the collected flakes were dried at 80 ° C. The dried flakes were crushed to obtain fine black powder. This fine powder was confirmed to be a single phase of zinc oxide by X-ray diffraction. The half-width of the diffraction peak and the average particle size as observed by transmission electron microscopy were 20 nm.

Example 2 A zinc plate (10 cm × 10 cm, 1 m thick) degreased and washed
m, backside covered with vinyl tape) and electrolytic solution (aqueous solution of sodium hydroxide 0.2M, sodium nitrate 0.1M)
A stainless steel plate (10 cm × 10 cm) was used as a cathode, and the distance between both electrodes was 1
0 cm and a DC voltage of 30 V was applied for 10 minutes. The electrolytic solution turned milky white by this electrolysis. The suspension was filtered, washed with water and dried at 80 ° C. to obtain a fine powder. This fine powder was confirmed to be a single phase of zinc oxide by X-ray diffraction, and had an average particle size of 20 n
m was confirmed to be a spherical powder.

[0027]

As described above, the production method of the present invention can produce zinc oxide powder having a uniform particle size without much necessity of a neutralization reaction or heat treatment, and is much easier and less expensive than the wet synthesis method. Can be manufactured. Further, the zinc oxide powder obtained by the production method of the present invention has an average particle diameter of 0.1 μm or less, usually 0.05 μm or less, so that it is kneaded into a resin, mixed into fats and oils, mixed into cosmetics. It can be used very effectively for various applications requiring transparency and dispersibility.

Claims (5)

[Claims] 1. A coating comprising black zinc oxide fine particles is formed on the surface of metallic zinc by anodic oxidation, and then a white oxide is formed by anodizing on the surface of the metallic zinc under the coating comprising black zinc oxide fine particles. A method for producing zinc oxide fine powder, comprising: forming a coating of zinc fine particles to exfoliate the black zinc oxide fine particles into fine pieces, collecting the fine pieces, and crushing the fine zinc oxide fine pieces. 2. The method according to claim 1, wherein the concentration of the alkali metal hydroxide in the electrolytic solution is 0.
The surface of the metallic zinc is anodized in a nitrate-containing alkaline solution of 3 mol or more to form a coating composed of black zinc oxide fine particles. In a carbonate-containing alkaline solution of 5 mol or less, under the condition that the electrolysis voltage is 15 V or more, the surface of the metal zinc under the coating of the black zinc oxide fine particles is anodized to form white zinc oxide. A method for producing a zinc oxide fine powder, comprising forming a coating of fine particles, thereby peeling the black zinc oxide fine particles into fine pieces, collecting the fine pieces, and pulverizing the fine flake zinc oxide. 3. An alkali metal hydroxide concentration of 0.05 to 0.4.
M, anodizing metal zinc in an electrolytic solution having a nitrate concentration of 0.05 to 0.4 M at an electrolysis voltage of 10 V or more to form a suspension of zinc oxide fine particles, and recovering the zinc oxide fine particles from the suspension A method for producing zinc oxide fine powder. 4. The production method according to claim 1, wherein the average particle diameter of each fine particle of the zinc oxide fine powder is 0.1 μm or less. 5. The method according to claim 4, wherein the average particle diameter of each fine particle of the zinc oxide fine powder is 0.05 μm or less.