JP3711318B2 - Method for producing alumina particles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing alumina particles, particularly plate-like alumina particles. More specifically, plate-like alumina particles provide plate-like alumina particles having a large aspect ratio and a smooth particle surface with a narrow particle size distribution. In addition, an abrasive, a filler, a cosmetic material, a ceramic raw material, a pigment, and a material useful as a bright pigment can be provided by coating the surface with a metal oxide.
[0002]
[Prior art]
Conventionally, as a method for producing alumina particles, particularly alumina particles having a plate-like form, a hydrothermal treatment method (hereinafter referred to as hydrothermal synthesis method) as disclosed in Japanese Patent No. 2654276 and a method disclosed in JP-A-9-227337 are disclosed. A method of firing in the presence of such a fluorine-based mineralizer is known.
[0003]
However, the hydrothermal synthesis method is disadvantageous because it requires a high-temperature reaction treatment apparatus from the viewpoint of the production method, and the capital investment is large and disadvantageous, and the production method is also a synthesis under high temperature and high pressure. There was a problem that powder became expensive. In addition, the method of firing aluminum hydroxide in the presence of a halogen-based gas has a problem of treating halogen gas generated during firing.
Furthermore, there is a method in which an alkaline carbonate is used for the acidic aluminum salt, but this method has a problem that a large amount of carbonic acid is generated during neutralization and is difficult to handle.
[0004]
[Problems to be solved by the invention]
The present invention aims to ameliorate many of the problems in the prior art, and provides a simple method for producing alumina particles having a sharp particle size distribution without aggregation and plate-like alumina particles containing these particles and having a smooth surface. The purpose is to provide.
[0005]
[Means for Solving the Problems]
The present invention has the following configuration.
[0006]
(1) A mixture containing alumina or / and alumina hydrate and a neutralized metal salt is produced by reacting an aluminate and an acidic aluminum salt in a state containing water, and this mixture is produced at 1000 to 1600 ° C. A method for producing alumina particles, comprising firing at
[0007]
(2) The method for producing alumina particles according to the above (1), wherein the alumina or / and the alumina hydrate is amorphous or / and crystalline.
(3) The method for producing alumina particles according to (1), wherein the aluminate, acidic aluminum salt and phosphate are reacted in a state containing water.
[0008]
(4) The method for producing alumina particles as described in (1) above, wherein a mixture of an aluminate added with an alkaline phosphate and an acidic aluminum salt is reacted in a state containing moisture.
(5) The method for producing alumina particles according to (1), wherein an aluminate and an acidic aluminum salt added with an acidic phosphate are reacted in a state containing moisture.
(6) Production of alumina particles according to any one of (3) to (5) above, wherein the hydrogen ion concentration when the aluminate, acidic aluminum salt, and phosphate are mixed is in the range of pH = 6-10. Method.
[0009]
(7) Any one of the above (3) to (6) for producing plate-like alumina particles having an average particle diameter of 0.2 to 100 μm, a thickness of 3 μm or less, and an aspect ratio (particle diameter / thickness) of 5 or more. The manufacturing method of the alumina particle of description.
[0010]
The aluminate used in the present invention is not particularly limited as long as aluminum or aluminum hydroxide is dissolved in an alkali hydroxide solution. For example, MAlO ₂ such as NaAlO ₂ or KAlO ₂ (M is a monovalent metal). alkali metal salts and NaAlO ₂ · 5 / 4H ₂ O take structural _{formula, NaAlO 2 · 3H 2 O,} MAlO 2 · nH 2 O such as _{KAlO 2 · 3 / 2H 2 O} (M is a monovalent metal) of The structural formula is taken, and the general formula is xM ₂ O.yAl ₂ O ₃ .zH ₂ O (M is a monovalent metal, including z = 0). The acidic aluminum salt may be anything as long as aluminum or aluminum hydroxide is dissolved in an acidic solution. Examples of acidic solutions include mineral acids such as phosphoric acid and sulfuric acid, and organic acids such as oxalic acid, maleic acid, and malonic acid. Examples include acids. Specific examples include aluminum sulfate and aluminum chloride.
[0011]
Phosphate has a function as a crystal growth agent and is necessary for producing plate-like alumina. Phosphoric acid, sodium phosphate, potassium phosphate, ammonium phosphate, sodium pyrophosphate, potassium pyrophosphate, sodium tripolyphosphate, tripolyphosphate An ammonium phosphate etc. can be mentioned. The amount of phosphate added is preferably 0.01% by weight or more in terms of alumina. An aqueous solution in which an acidic aluminum salt or a phosphate salt is mixed with an aluminate is mixed to obtain a suspension or gel containing a hydrolysis product and a neutralized salt. The neutralized salt is in a molten state at the time of firing, and has the effect of promoting aluminization and plate formation of alumina. The amount of neutralization is preferably 0.1 to 7 times the weight of alumina. If it is less than 0.1 times, sufficient effects for aluminization and plate formation of alumina cannot be exhibited, and if it exceeds 7 times, a considerable burden is applied during cleaning.
[0012]
Thereafter, if the dry powder is fired at 1000 to 1600 ° C., the firing temperature is less than 1000 ° C., it takes a long time to aluminate (particularly plate-like alumina), which is not economical and exceeds 1600 ° C. This is because particles of alumina and alumina (particularly plate-like alumina) are sintered. In order to prevent such sintering more reliably, the firing temperature is more preferably set to 1400 ° C. or lower.
[0013]
When the hydrogen ion concentration is in the range of pH 6 to 10, precipitation of alumina hydrate is efficiently performed, and alumina (particularly plate-like alumina) can be produced efficiently. The mixture of amorphous alumina and / or crystalline alumina particles and neutralized metal salt is preferably transpiration-dried before firing, and then the mixture is unraveled in order to prevent aggregation of particles produced after firing. . In addition, after firing, it is preferable to obtain a solid content by treatment with a molten salt, then wash the solid content with water, filter and dry it.
[0014]
The alumina particles according to the present invention thus obtained are granular alumina particles having an average particle diameter of 0.2 to 100 μm. In particular, the plate-like alumina particles have a large average particle diameter of 0. Plate-like alumina particles having a thickness of 2 to 100 μm and a thickness of 3 μm or less and an aspect ratio (particle diameter / thickness) of 5 or more. When dispersed and stirred in water, streamlines (suspend the flat particles in the liquid) When the dispersibility was good when stirring, a series of particles flow was observed (a phenomenon in which reflected light on the particle surface was observed as a layered stripe pattern), and the dispersibility was extremely good. As a result of analyzing the plate-like alumina particles, it is considered that phosphorus, phosphorus compounds and neutralized salts are not detected and are removed in the washing step.
[0015]
The alumina particles and plate-like alumina particles according to the present invention can be used as raw materials for ceramics as they are, or are excellent as pigments for paints, fillers for plastics, cosmetics, abrasives, glazes, etc. is there. In particular, in the case of plate-like alumina particles, it is useful for the above-mentioned applications, and the usefulness as a bright pigment is further increased by coating with a metal oxide.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
[0017]
Example 1
20 g of sodium hydroxide is made into a solution in water, and 5 g of metal aluminum and 0.25 g of disodium hydrogen phosphate are added to this solution and dissolved in the solution with stirring. Thereafter, an aqueous aluminum sulfate solution is added to the mixed solution with stirring until pH = 7. The mixture became a cloudy gel, which was directly evaporated and dried. As a result of X-ray diffraction of the transpirationally dried solid at this time, sodium sulfate was identified as crystalline. Thereafter, firing was performed at 1200 ° C. for 5 hours. Water was added to the treated product, washed and filtered, and the solid content was dried to obtain a plate-like alumina powder. When the product of the obtained plate-like alumina was identified by X-ray diffraction, it was aluminum oxide (α alumina). When observed by SEM, it was a plate-like particle. When the particle size was measured with a particle size distribution meter, the center particle size was 10 μm, and the distribution was sharp. In addition, when this powder was mixed with water, a clean flow pattern was confirmed. Example 2
20 g of sodium hydroxide is made into a solution in water at 60 ° C., and 5 g of metal aluminum and 0.25 g of disodium hydrogen phosphate are added to this solution and dissolved in the solution with stirring. Thereafter, an aluminum sulfate aqueous solution at 60 ° C. is poured into the mixed solution with stirring until pH = 9. The mixture became a cloudy gel, which was further stirred for 60 minutes and then evaporated and dried. As a result of X-ray diffraction of the transpiration-dried solid at this time, it was confirmed to be pseudoboehmite. The solid content obtained by transpiration drying was calcined at 1200 ° C. for 5 hours. Water was added to the treated product, washed and filtered, and the solid content was dried to obtain a plate-like alumina powder. When the product of the obtained plate-like alumina was identified by X-ray diffraction, it was aluminum oxide (α alumina). When observed by SEM, it was a plate-like particle. When the particle size was measured with a particle size distribution meter, the center particle size was 10 μm, and the distribution was sharp. In addition, when this powder was mixed with water, a clean flow pattern was confirmed.
[0018]
Example 3
20 g of sodium aluminate was dissolved in water at 60 ° C., and an aqueous aluminum sulfate solution was added thereto to adjust to pH = 9, followed by stirring for 60 minutes. Thereafter, transpiration drying was performed, and as a result of X-ray diffraction of the dried solid content, a diffraction peak of pseudoboehmite was confirmed. The dried solid was baked at 1200 ° C. for 5 hours, washed and filtered, and the solid was dried. As a result of identifying the obtained product by X-ray diffraction, it was aluminum oxide (α alumina). When observed by SEM, it was 0.2 μm in granular form and was not a plate-like particle. In addition, when this powder was mixed with water, no flow pattern was observed.
[0019]
【The invention's effect】
According to the present invention, alumina particles having no aggregation and having a sharp particle size distribution can be easily obtained without particularly requiring high pressure. Particularly when phosphate is used, plate-like alumina particles are produced. In addition, since no halogen-based mineralizer is used, the work environment is not contaminated.

Claims (7)

By reacting an aluminate and an acidic aluminum salt in a state containing water, a mixture containing alumina or / and alumina hydrate and a neutralized metal salt is produced, and the mixture is calcined at 1000 to 1600 ° C. A method for producing alumina particles characterized by the above. The method for producing alumina particles according to claim 1, wherein the alumina or / and the alumina hydrate are amorphous or / and crystalline. The method for producing alumina particles according to claim 1, wherein the aluminate, the acidic aluminum salt and the phosphate are reacted in a state containing water. 2. The method for producing alumina particles according to claim 1, wherein a mixture of an aluminate added with an alkaline phosphate and an acidic aluminum salt is reacted in a state containing moisture. The method for producing alumina particles according to claim 1, wherein an aluminate and an acidic aluminum salt added with an acidic phosphate are reacted in a state containing moisture. The method for producing alumina particles according to any one of claims 3 to 5, wherein the hydrogen ion concentration when the aluminate, acidic aluminum salt and phosphate are mixed is in the range of pH = 6-10. The production of alumina particles according to any one of claims 3 to 6, wherein plate-like alumina particles having an average particle diameter of 0.2 to 100 µm, a thickness of 3 µm or less, and an aspect ratio (particle diameter / thickness) of 5 or more are produced. Method.