JP2890866B2 - Method for producing fine α-alumina powder - 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 a uniform and fine .alpha.-alumina powder excellent in hardness and abrasiveness.

[0002]

2. Description of the Related Art Alumina (Al ₂ O ₃ ) is currently widely used as an abrasive or abrasive as one of its uses. As the alumina for the abrasive, α-alumina having a high hardness (Mohs hardness 9) is used. With regard to the alumina powder for the abrasive, recently, with the demand for precise polishing, a powder which is more uniform and finer than the conventional one is required. Specifically, the specific surface area is 10 m ² / g or more,
A fine α-alumina powder having a specific surface area of 0.15 μm or less has been demanded. However, conventionally, such a fine α-
It was difficult to produce alumina.

In a conventional method for producing α-alumina powder, sodium hydroxide, which is called the Bayer method, is neutralized with an acid to form aluminum hydroxide, which is heated to a high temperature (1200 ° C. or higher).
It is common to bake with. However, in this manufacturing method, aluminum hydroxide is generated and is heated and calcined at 1200 ° C. or more for a long time, so that the size of the obtained alumina particles is not uniform, and the particles are mutually sintered. , It becomes coarse with a specific surface area of less than 10 m ² / g. As another production method, there is known a method of producing aluminum hydroxide by hydrolysis of aluminum alkoxide, for example, aluminum isopropoxide, and subjecting this to heat treatment at a high temperature to obtain α-alumina particles. However, even in this method, the particles are fired at a high temperature,
The powder particle size increases. In addition, since the abrasiveness of alumina particles is exhibited by α-alumina having a high hardness, most of the alumina particles must be α-alumina and have high crystallinity in order to have excellent abrasiveness. It is. Therefore, in X-ray diffraction, even if only the α-alumina phase is detected, the polishing property is poor unless the X-ray intensity is high. Thus, at present, the specific surface area is 10 m ² / g or more,
Fine α-alumina powder having a specific surface area diameter of 0.15 μm or less and excellent in polishing properties has not been obtained.

[0004]

[MEANS FOR SOLVING PROBLEMS: Structure of the Invention]
An object of the present invention is to provide a method for producing α-alumina powder having a fine surface property of not less than m ² / g and a specific surface area of not more than 0.15 μm and excellent in polishing properties. According to the present invention, after collecting an aluminum oxide hydrate or aluminum hydroxide obtained by mixing an aluminum chloride aqueous solution and an ammonium carbonate aqueous solution or an ammonium hydrogen carbonate aqueous solution, the aluminum oxide hydrate or the aluminum hydroxide is finely divided. A fine silica powder is added to aluminum oxide in an amount of 0.5 to 5.0 wt%, followed by heating and calcining to produce fine α-alumina powder.

[0005] The following table shows an example of the preferred ranges of the concentrations of the aqueous aluminum chloride solution and the aqueous ammonium carbonate solution, the molar mixture ratio of the two solutions, the reaction temperature, and the dropping time of the aqueous aluminum chloride solution used in the present invention. Aluminum chloride concentration: 0.5-3.0 mol / l Ammonium carbonate concentration: 0.5-3.0 mol / l Mixture molar ratio of ammonium carbonate / aluminum chloride:
1-2 Reaction temperature: room temperature to 80 ° C Aluminum chloride aqueous solution dripping time: 10 minutes to 1
time

When aluminum oxide hydrate or aluminum hydroxide is converted to α-alumina, α-alumina nuclei are first formed, and the α-alumina grows in the form of α-alumina. -Alumina particles are inevitably large. On the other hand, when silica is added, coarsening of α-alumina is prevented. This is considered that silica also becomes a nucleus, and it is presumed that the grain growth of α-alumina is suppressed due to the presence of many silica nuclei. When the amount of silica added in the present invention is 0.5 wt% or less, there is no effect, and when it becomes α-alumina, its specific surface area diameter becomes 0.15 μm or more. The amount of silica added is 5.0
If the content is not less than wt%, a specific surface area diameter of 0.15 μm or less can be obtained, but the crystallinity is poor, and a high temperature of 1300 ° C. or more is required to convert to α-alumina. Is also not preferred.

[0007] Usually, the conversion of aluminum oxide hydrate or aluminum hydroxide to α-alumina is 1100
It is performed by firing at a high temperature of ~ 1300 ° C. The time required for sintering is long at low temperatures, and short at high temperatures. However, when silica is not added in any case, when α-alumina is formed, α-alumina particles grow and the specific surface area becomes 0.15 μm or more. Even if the specific surface area becomes 0.15 μm or less, the crystallinity is poor. When calcined for a short time at a low or high temperature of 1100 ° C or less, a specific surface area diameter of 0.15 μm or less is obtained, but this is not completely α-formed and remains in a form other than α-alumina, or Low crystallinity and poor polishing. That is, it is difficult to obtain a powder having a high specific surface area of 0.15 μm or less in the peak of α-alumina in X-ray diffraction. Although the α-alumina powder after sintering is in a weakly agglomerated state, a required fine α-alumina powder can be obtained by lightly loosening.

In the present invention, as described above, silica is added to a hydrate of aluminum oxide or aluminum hydroxide obtained by mixing an aqueous solution of aluminum chloride and an aqueous solution of ammonium carbonate or ammonium hydrogen carbonate, followed by drying and firing. Thus, the growth of α-alumina particles is suppressed, α-alumina crystallinity is high, and a fine powder having a specific surface area of 0.15 μm or less can be obtained.

A hydrate of aluminum oxide or aluminum hydroxide can be obtained by a method of neutralizing sodium aluminate with an acid or a method of adjusting aluminum chloride with an alkali such as sodium hydroxide or potassium hydroxide. It is. However, in the method of neutralizing sodium aluminate with an acid, a residue of sodium cannot be avoided, and there is no effect of controlling the grain growth when silica is added. In addition, even if aluminum chloride is used as a starting material, according to the method of adjusting with alkali such as sodium hydroxide or potassium hydroxide, the generated particles include not only uneven and fine particles but also coarse particles. . For polishing, α-alumina powder having a specific surface area diameter of 0.15 μm or more has a large particle diameter and the surface to be polished is easily damaged. Therefore, the particle diameter of the powder needs to be 0.15 μm or less in terms of specific surface area. When a metal aluminum plate was polished using alumina powder which had not been pregelatinized, the polishing rate was low. When the powder had a specific surface area of 0.15 μm or more, the surface to be polished was damaged. On the other hand, when the fine α-alumina powder according to the present invention was used, the polishing rate was doubled, and the surface to be polished was not damaged and a smooth surface was obtained. The α-alumina according to the present invention inevitably contains silica, so that it is not used as a ceramic raw material requiring high purity, but there is no problem even if silica is contained for an abrasive.

Examples of the present invention and comparative examples are shown below.

EXAMPLE A solution of 89 g of commercially available aluminum chloride in 300 ml of water, added to a solution of 108 g of ammonium carbonate in 1000 ml of water, and then subjected to solid-liquid separation to obtain a hydrate of aluminum oxide or aluminum hydroxide And 0.6g of silica (Aerosil N, manufactured by Nippon Aerosil Co., Ltd.)
o.200), kneaded well, dried at 120 ° C, placed in an alumina crucible, and placed in an electric furnace at 1200 ° C for 6 hours.
Fired for hours. The specific surface area diameter of the obtained powder was 0.08 μm, and only a peak of α phase was obtained by X-ray diffraction.
The linear strength was 80% of those having a particle size of 0.2 μm or more.

Comparative Example 89 g of commercially available aluminum chloride was dissolved in 300 ml of water, added to a solution of 108 g of ammonium carbonate in 1000 ml of water, and then subjected to solid-liquid separation to obtain a hydrate of aluminum oxide or aluminum hydroxide. Was put in an alumina crucible dried at 120 ° C.
It was baked at 1200 ° C. for 6 hours in an electric furnace. The resulting powder is
In X-ray diffraction, only the peak of the α phase was obtained, but the specific surface area diameter was 0.19 μm.

[0011]

According to the production method of the present invention, silica is added to aluminum oxide hydrate or aluminum hydroxide obtained by mixing an aqueous solution of aluminum chloride and an aqueous solution of ammonium carbonate or ammonium hydrogen carbonate, followed by drying. By firing, the grain growth of the generated α-alumina powder is suppressed, and the specific surface area of the α-alumina powder is 0.07 to 0.15 μm, and the fine α-
Alumina powder can be obtained.

Claims (2)

(57) [Claims] An aluminum oxide hydrate or aluminum hydroxide obtained by mixing an aqueous solution of aluminum chloride and an aqueous solution of ammonium carbonate or aqueous ammonium hydrogen carbonate is recovered, and then finely divided into the aluminum oxide hydrate or aluminum hydroxide. A method characterized in that a fine α-alumina powder is produced by adding 0.5 to 5.0 wt% of silica powder to aluminum oxide and calcining by heating. 2. The method according to claim 1, wherein the heating and firing temperature is from 1,100 to 1,300 ° C.