JP6010843B2 - Method for producing particulate α-alumina - Google Patents

Description

  The present invention relates to a method for producing fine particle α-alumina. Specifically, the present invention relates to a simple method for producing α-alumina having a high α conversion rate, a small average particle size, and a narrow particle size distribution.

  α-Alumina is a substance used for abrasives and cutting tools. As a manufacturing method of α-alumina, for example, the following is known.

  A method of producing particles finer than 1 μm by adding very fine α-alumina as a seed crystal to alumina gel and firing at a temperature lower than 1400 ° C. (Patent Document 1).

  Stearic acid is added to α-alumina obtained by calcining aluminum hydroxide and pulverized in a vibration mill pot. A process for further pulverizing α-alumina after firing to obtain 0.5 μm α-alumina (Patent Document 2).

  A method for producing ultrafine aluminum oxide, in which a mixed gas of aluminum trichloride vapor and hydrogen and an oxygen-containing gas are mixed and burned, and the fine powder produced is separated from combustion exhaust gas at 90 ° C. or lower (Patent Document 3).

  A method for producing a readily sinterable alumina powder by baking aluminum ammonium carbonate hydroxide at a temperature of 1350 ° C. or less under normal pressure or reduced pressure (Patent Document 4).

  The powder of aluminum compound is coated with a carbonaceous material, heated and fired in a non-oxidizing atmosphere, subjected to α-aluminization treatment, and then the carbonaceous material is burned and removed in an oxidizing atmosphere to produce α-alumina. Method (Patent Document 5).

  A method for producing submicron microcrystalline powder in which alumina is electrophoretically deposited on an electrode from a suspension containing organic α-alumina, and the electrode is taken out, dried and sintered (Patent Document 6).

  A process for producing abrasive particles in which alpha ferric oxide is added to a dispersion of alpha aluminum oxide gel and the dried solid is calcined (Patent Document 7).

  After recovering aluminum hydroxide hydrate obtained by mixing an aqueous solution of aluminum chloride and an aqueous solution of ammonium carbonate, fine silica powder is baked by adding 0.5 to 5% by mass with respect to aluminum oxide. A method for obtaining an α-alumina powder (Patent Document 8).

  A process for producing α-alumina particles in which a substance that forms a barrier around boehmite particles is dispersed in a boehmite gel, dried, and fired (Patent Document 9).

  A method of agglomerating an anhydrous alumina product obtained from a mixture of an aqueous medium and an anhydrous alumina precursor at 250 ° C. or higher to obtain a submicron anhydrous alumina powder having an average particle size of about 1 μm or less (Patent Document 10).

  Α-alumina which is converted to α-alumina upon firing is added to α-alumina precursor sol or gel as seed crystals to obtain a mixture, and the mixture is treated at 900 ° C to 1350 ° C. (Patent Document 11).

  A method for producing fine α-alumina, in which aluminum hydroxide and fine α-alumina are mixed, and a halogen compound is added and fired (Patent Document 12).

  A method for producing α-alumina ultrafine particles, in which γ-alumina ultrafine particles produced by a vapor phase method are fired at 1200 ° C. to 1300 ° C. until they are transformed into an α-alumina phase (Patent Document 13).

  Water is removed from an aqueous compound containing an α-alumina precursor and seed crystal particles, and further containing 2.8 mol to 3.3 mol of nitrate ions per 1 mol of the metal-converted aluminum component, and an obtained powder mixture is obtained. A method for producing fine alumina to be fired (Patent Document 14).

  A method for producing fine-grained alumina in which a mixture obtained by dispersing an aluminum hydrolyzate together with seed crystal particles in an aqueous medium having a hydrogen ion concentration of 5 or less is dried and fired (Patent Document 15).

  A method of removing moisture from an aqueous mixture containing an α-alumina precursor and seed crystal particles and having a nitrate ion content of 2.7 moles per mole of aluminum and firing the resulting powder mixture (Non-patent Document 1) .

European Patent Publication No. 0152768 JP-A-55-113615 Japanese Patent Laid-Open No. 57-1445026 JP-A-61-201619 JP-A-5-105425 JP-A-3-28120 Japanese Patent Laid-Open No. 4-12908 JP-A-4-260612 JP-A-5-345611 JP-A-6-500068 JP-A-7-1000060 JP-A-8-183612 JP 2001-199718 A JP-A-2005-1984 JP-A-2005-179116

Key Engineering Materials, Vol. 53 53-55 (1991) 462-468

  However, the conventional α-alumina production method cannot easily produce α-alumina having a high α conversion ratio, a small average particle diameter, and a narrow particle size distribution.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that α-alumina obtained from an aqueous mixture containing alumina sol, tetraol, and seed crystal particles has a high α conversion ratio and an average particle size. Was found to be small and the particle size distribution was narrow, and the present invention was completed. That is, the present invention relates to the following 1 to 9.

1. A method for producing particulate α-alumina,
A process of obtaining an aqueous mixture by dispersing alumina sol and seed crystal particles in an aqueous medium containing tetraol, wherein the concentration of the tetraol is 0.05% by mass or more based on the total mass of the aqueous mixture. A process,
Adjusting the pH of the aqueous mixture to 0.1 to 5.0,
Drying the aqueous mixture to obtain a powder mixture;
Baking the powder mixture at a temperature of 950 ° C. or higher and 1200 ° C. or lower;
A step of pulverizing the fired product obtained by the firing to obtain fine particle α-alumina,
A method comprising the steps of:

2. 2. The method for producing fine particle α-alumina according to 1 above, wherein the tetraol is diglycerin and / or pentaerythritol.

3. 3. The method for producing fine particle α-alumina according to 1 or 2 above, wherein the tetraol content in the aqueous mixture is 8.0% by mass or less.

4). 4. The method for producing fine particle α-alumina according to any one of 1 to 3, wherein the alumina sol is a product obtained by peptizing α-alumina monohydrate.

5. The method for producing particulate α-alumina according to any one of 1 to 4, wherein the content of the alumina sol in the aqueous mixture is 5% by mass or more and 30% by mass or less in terms of α-alumina with respect to the total mass of the aqueous mixture. .

6). 6. The method for producing fine particle α-alumina according to any one of 1 to 5, wherein the seed crystal particles are a corundum type metal oxide.

7). 7. The method for producing fine particle α-alumina according to 6 above, wherein the corundum type metal oxide is α-alumina.

8). 8. The method for producing fine particle α-alumina according to any one of 1 to 7, wherein the seed crystal particles have an average particle diameter of 0.01 μm or more and 0.2 μm or less.

9. The method for producing fine particle α-alumina according to any one of 1 to 8, wherein the amount of the seed crystal particles used is 1 to 20 parts by mass per 100 parts by mass of the alumina sol.

  According to the production method of the present invention, α-alumina having a high α conversion rate, a small average particle size, and a narrow particle size distribution can be easily produced as shown in Examples described later.

  The fine particle α-alumina production method of the present invention is a step of dispersing an alumina sol and seed crystal particles in an aqueous medium containing tetraol to obtain an aqueous mixture, wherein the concentration of the tetraol is the total amount of the aqueous mixture. The step of 0.05% by mass or more with respect to the mass, the step of adjusting the pH of the aqueous mixture to 0.1 to 5.0, the step of drying the aqueous mixture to obtain a powder mixture, and the powder mixture of 950 A step of firing at a temperature of from ℃ to 1200 ° C., and a step of pulverizing the fired product obtained by the firing to obtain fine particle α-alumina.

The alumina sol used in the production method of the present invention is a product obtained by peptizing α-alumina monohydrate such as boehmite. Specifically, it is a sol obtained by peptizing α-alumina monohydrate at a temperature of 100 ° C. or lower in an aqueous solution of pH 4 or lower using a peptizer. The concentration of α-alumina monohydrate in the alumina sol is 2 to 30% by mass, preferably 15 to 20% by mass, based on the mass of the alumina sol. As the peptizer, a monovalent inorganic acid or a monovalent organic acid can usually be used. Examples of the monovalent inorganic acid include nitric acid and hydrochloric acid. Examples of monovalent organic acids include formic acid, acetic acid, and monochloroacetic acid. The peptizer is preferably acetic acid, which has few problems of equipment corrosion and environmental pollution. The amount of the peptizer used is preferably adjusted so that the pH of the aqueous medium is in the range of 0.5 to 5.0. Preferably it is the range of pH 1.0-4.5, More preferably, it is the range of 1.5-4.0. For example, the amount of the monovalent inorganic acid used is such that the molar ratio of the acid radical of the inorganic acid / α-alumina monohydrate is preferably 0.005 to 0.30. The amount of the monovalent organic acid used is such that the molar ratio of the acid radical of the organic acid / α-alumina monohydrate is preferably 0.01 to 0.80.
If the content of the alumina sol in the aqueous mixture is 5% by mass or more in terms of α-alumina with respect to the total mass of the aqueous mixture, the production efficiency is increased, and if it is 30% by mass or less, the viscosity of the aqueous mixture does not become too high. From the viewpoint of easy handling, it is preferably 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 18% by mass or less, in terms of α-alumina, based on the total mass of the aqueous mixture. .

  The following known α-alumina sols can also be used in the present invention.

  B. E. Yoldas, Amer. Ceram. Soc. Bull. 54, 289 (1975), an alumina sol which hydrolyzes aluminum isopropoxide and peptizes by adding an acid.

  A pseudo boehmite sol obtained by reacting a dilute aqueous solution of hydrochloric acid, acetic acid or the like with metal aluminum powder as described in JP-B-39-20150.

  A pseudo-boehmite sol obtained by hydrothermally treating an aqueous slurry of alumina gel with an acid / aluminum molar ratio of 0.5 to 2.4 described in JP-B-40-14292.

  As disclosed in JP-A-54-116398, JP-A-55-23034 and JP-A-55-27824, by reacting a basic aluminum salt with an acid or alkali, or an acidic aluminum salt An alumina sol obtained by peptizing an alumina gel obtained by reacting an alkali with an acid with an acid.

  An alumina sol obtained by peptizing alumina monohydrate obtained by hydrolyzing aluminum alkoxide, as described in JP-A-57-88074.

  An alumina sol obtained by hydrolyzing metal aluminum in the presence of acetic acid, as described in JP-A-59-78925.

  Alumina sol described in JP-A-62-56321, peptized by adding a peptizer of nitric acid to boehmite obtained by hydrolyzing aluminum alkoxide in a dilute acetic acid aqueous solution.

  An alumina sol obtained by treating an aluminum hydroxide gel obtained by neutralization of an aluminum chloride aqueous solution and a sodium carbonate aqueous solution described in JP-A-57-77026 in the presence of an acid.

  An alumina sol obtained by peptizing an aluminum alkoxide with an organic acid or an inorganic acid, as described in JP-A-4-27517.

  Tetraol used in the production method of the present invention is an alcohol having four hydroxy groups. Specific examples include diglycerin, pentaerythritol, bis (2,3-dihydroxypropyl) ether, 1,2,7,8-octanetetraol. Preferred tetraols for use in the present invention are diglycerin and pentaerythritol. Tetraol is a known substance and can be easily obtained in the market or can be prepared. Said tetraol may be used independently and may be used in combination of 2 or more type. The concentration of tetraol is 0.05% by mass or more based on the total mass of the aqueous mixture. There is no particular upper limit, but 8.0 mass% is sufficient. The concentration of tetraol is more preferably 0.1 to 5.0% by mass, still more preferably 0.5 to 3.0% by mass. When the amount of tetraol used is 0.05% by mass or more, a sufficient aggregation suppressing effect between the alumina sol and the alumina particles can be obtained.

  In the present invention, tetraol is considered to contribute to the suppression of aggregation of α-alumina particles generated by alumina firing. The action mechanism is presumed as follows. Tetraol is coordinated around the alumina particles of the alumina sol to form a very thin film, which is obtained in the process of obtaining a powder mixture from an aqueous mixture and the firing process of the powder mixture. It is presumed that the movement of the particles along the axis is suppressed, and thus the formation of aggregates when the alumina particles transition to the α phase is prevented or at least substantially suppressed.

  Due to the action of the tetraol, the baked product of the aqueous mixture forms an aggregate with relatively loose bonds. Therefore, the fired product can be easily made into fine particles by manual pulverization.

  The seed crystal particles used in the production method of the present invention are metal oxides having a crystal structure of corundum type. Specific examples include α-alumina, α-iron oxide, and α-chromium oxide without crystal water. Α-alumina, which is the same metal component as the obtained fine particle α-alumina, is preferred. In order to obtain fine particle α-alumina, it is desirable that the seed crystal particles that are the core of α-alumina crystal growth have a smaller particle size, and preferably 0.01 μm or more and 0.2 μm or less. Furthermore, it is preferable that they are 0.01 micrometer or more and 0.1 micrometer or less. The particle diameter of the seed crystal particles can be measured with a transmission electron microscope. The amount of seed crystal particles used is preferably 1 part by mass to 20 parts by mass, more preferably 5 parts by mass to 15 parts by mass, and still more preferably 7 parts by mass to 13 parts by mass, per 100 parts by mass of the alumina sol.

  The crystal form of the alumina seed crystal used in the present invention is α-alumina which is an α phase. Such α-alumina seed crystals can be obtained by wet pulverization or dry pulverization of normal α-alumina powder. More preferred is wet pulverization.

  In order to obtain seed crystals by wet pulverization, α-alumina powder is mixed with an aqueous solvent to form a slurry and pulverized using a pulverizer such as a ball mill. As the aqueous solvent, pure water, ion-exchanged water or tap water can be used, and can be appropriately selected depending on the application. The usage-amount of an aqueous solvent is 100 mass parts-1000 mass parts normally with respect to 100 mass parts of alpha alumina powder.

  By centrifuging the pulverized product after wet pulverization, the seed crystal α-alumina particles and the aqueous solvent can be separated. In addition, for separation of the seed crystal α-alumina particles and the solvent, a cartridge separator filter may be used. A centrifugal separation system is preferred.

  In the method for producing fine particle α-alumina using the alumina sol of the present invention as a raw material, the action mechanism of the seed crystal particles will be described by taking the seed crystal of α-alumina as an example. The seed α-alumina particles act as transition nuclei at the transition from the θ phase to the α phase in the firing process of alumina. The nucleus dynamically increases the transition rate and lowers the transition temperature. Lowering the transition temperature brings about an effect of suppressing the crystal growth of α-alumina.

  When α-alumina seed crystal particles are used, the transition temperature can be lowered by about 170 ° C. as compared with the case where α-alumina seed crystal particles are not used. The transition temperature of α-alumina using alumina sol as a raw material is 1150 ° C to 1250 ° C. Therefore, the α-alumina has a transition temperature of 980 ° C. to 1080 ° C. when fired in the presence of α-alumina seed crystal particles (J. Am. Ceram. Soc., 68 [9] 500-505 ( 1985)).

  In the method for producing fine particle α-alumina using the alumina sol of the present invention as a raw material, the effect of suppressing aggregation between α-alumina particles by tetraol, and the transition temperature reduction of α-alumina to α phase by using seed particles of α-alumina Thus, fine particle α-alumina can be easily obtained by a synergistic effect with the effect of suppressing the crystal growth of α-alumina.

  The aqueous medium used in the present invention is mainly composed of water. Specific examples include ultrapure water, pure water, tap water, well water, and the like, preferably ultrapure water or pure water.

  For the dispersion of the alumina sol and seed crystal particles in the aqueous mixture of the present invention, any means can be used that results in the state that they are uniformly diffused and mixed in the aqueous mixture. For example, there are motor stirring, homomixer, and ultrasonic dispersion.

  The hydrogen ion concentration of the aqueous mixture of the present invention is in the range of pH 0.1 to 5.0. Preferably it is pH 1.0-4.0, More preferably, it is pH 1.5-3.5. When the pH is 0.1 or more, the problem of corrosion of the apparatus can be avoided. When the pH is 5.0 or less, aggregation of α-alumina particles can be suppressed. For pH adjustment, acetic acid, nitric acid, hydrochloric acid, formic acid or monochloroacetic acid can be used, and acetic acid, nitric acid or hydrochloric acid is preferably used.

[Drying the aqueous mixture]
In the method for producing fine particle α-alumina of the present invention, a powder mixture containing alumina sol, seed crystal α-alumina particles and tetraol is obtained by distilling off the aqueous medium from the aqueous mixture. The distillation temperature of the aqueous solvent is preferably 70 ° C. or higher and 100 ° C. or lower. In the drying step, for example, usual methods such as constant temperature drying, freeze drying, vacuum drying, and high frequency drying can be used. Specific drying equipment includes a shelf dryer, a spray dryer, a slurry dryer, and the like.

[Baking powder mixture]
The calcination temperature of the powder product of the aqueous mixture by the method for producing fine particle α-alumina of the present invention is 950 ° C. to 1200 ° C., preferably 1000 ° C. to 1150 ° C. When the temperature is 950 ° C. or higher, the alpha conversion rate of the particulate α-alumina can be increased, and when it is 1200 ° C. or lower, necking of the α-alumina congruents can be suppressed. The rate of temperature increase until reaching the firing temperature is not particularly limited as long as it has a sufficient time for the alumina sol to transfer to α-alumina. The firing time varies depending on the particle diameter of the seed crystal α-alumina, the ratio of the seed crystal α-alumina / alumina sol, the type and type of the firing furnace, the firing temperature, the firing atmosphere, etc., but is usually 10 hours to 12 hours. The firing atmosphere may be air or an inert gas such as nitrogen gas, helium gas, or argon gas. Usually performed in air.

  For firing an aqueous mixture, a stationary material firing furnace (batch-type aerated flow type, batch-type parallel flow type, box-type firing furnace), tunnel kiln, rotary kiln, tubular electric furnace, far-infrared furnace, microwave heating furnace, A reflection furnace or the like can be used.

  As a baking method for the aqueous mixture, any of a batch baking method, a continuous baking method, a stationary baking method, and a fluidized baking method can be used.

[Crushing of fired product of aqueous mixture]
The baked product of the aqueous mixture has a loose bond of aggregates. For example, it is possible to easily obtain fine-particle α-alumina by hand grinding with a magnetic mortar. Accordingly, fine particles α-alumina is obtained by pulverization with a jet mill or a vibration mill.

The alpha conversion rate of α-alumina indicates the proportion of alumina that is α-alumina. In the present specification, the “high α conversion rate” means that the α conversion rate is 80% or more. The alpha conversion rate of α-alumina appears at a position of 2θ = 25.6 ° from the diffraction spectrum of fine particle α-alumina obtained using an X-ray diffractometer (for example, X-ray diffractometer MINIFLEX manufactured by Rigaku Corporation). α- alumina α phase (012 plane) peak height I _25.6 and 2 [Theta] = 46 ° of appearing at position γ phase, eta phase, chi-phase, kappa phase from θ phase and δ-phase peak heights I ₄₆ Metropolitan ( It can be calculated by equation (1).
_Alphaation rate = I _25.6 / (I _25.6 + I ₄₆ ) × 100 (Formula 1)

In the present specification, the average particle size means a particle size [D ₅₀ ] equivalent to a cumulative percentage of 50% obtained on a mass basis.

  The particle size distribution is a variation in particle diameter.

The average particle size and particle size distribution of α-alumina correspond to a cumulative percentage of 10% obtained on a mass basis by a laser diffraction particle size distribution analyzer (for example, “Microtrac HRA (X-100) manufactured by Nikkiso Co., Ltd.)” The particle size [D ₁₀ ], the particle size [D ₅₀ ] corresponding to a cumulative percentage of 50% obtained on a mass basis, and the particle size [D ₉₀ ] equivalent to a cumulative percentage of 90% obtained on a mass basis can be obtained.

  The particulate α-alumina produced by the method of the present invention comprises abrasives, cutting tools, semiconductor manufacturing equipment parts, electronic parts (oxygen sensors, etc.), translucent tubes (sodium lamps, metal halide lamps, etc.), ceramic filters (foods). Etc.), gas selective permeation filters, cosmetic additives, catalyst carriers, conductive sintered bodies, ignition plug insulators for internal combustion engines, and wear-resistant ceramics.

  Hereinafter, the production method of the fine particle α-alumina of the present invention will be described with reference to examples. The present invention is not limited to the following examples, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[Sample preparation for measuring average particle size and particle size distribution of α-alumina]
In order to measure the average particle size and particle size distribution of α-alumina, the α-alumina powder was diluted with distilled water to a concentration (mass) of 1%, and then treated with ULTRASONIC CLEANERRC20D for 3 minutes, uniformly. An aqueous solution dispersed in was prepared.
[Measurement of average particle size and particle size distribution of α-alumina]
The average particle size and particle size distribution of α-alumina were determined by a laser diffraction particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., “Microtrac HRA (X-100)). ₁₀ ], particle size [D ₅₀ ] equivalent to 50% cumulative percentage determined on a mass basis, and particle size [D ₉₀ ] equivalent to 90% cumulative percent determined on a mass basis.
[Transition ratio to crystalline α phase]
The α-alumina conversion rate of the fine particle α-alumina of the present invention is expressed by α-alumina α appearing at 2θ = 25.6 ° from the diffraction spectrum of the fine particle α-alumina obtained using an X-ray diffractometer MINIFLEX manufactured by Rigaku Corporation phase (012 plane) peak height I _25.6 and 2 [Theta] = 46 ° of appearing at position γ phase, eta phase, chi-phase, kappa phase, by the θ-phase and δ-phase peak heights I ₄₆ Metropolitan (equation 1) Calculated.
_Alphaation rate = I _25.6 / (I _25.6 + I ₄₆ ) × 100 (Formula 1)
[Bulk specific gravity]
It measured according to JIS-Z-9301.

(Preparation Example 1)
(Preparation of alumina sol)
850 g of pure water and 15 g of acetic acid (made by Kishida Chemical Co., Ltd., special grade reagent) in a 2 L beaker equipped with a stirrer (three-one motor manufactured by Shinto Kagaku Co., Ltd., rotation speed: 650 rpm), thermometer and reflux condenser. ), Stirred and mixed. 150 g of boehmite (SB Pural manufactured by Condea Corp.) was continuously added to the aqueous solution over 1.5 hours. Furthermore, aging was carried out for 1 hour. The reaction temperature was 25 ° C to 27 ° C. Thereafter, the reaction mass was allowed to stand for 5 hours. 3 g of unreacted boehmite was fractionated by a gradient method to obtain 950 g of alumina sol (concentration: 14.7%).

(Preparation Example 2)
[Preparation of alumina sol powder]
950 g of alumina sol obtained in Preparation Example 1 of alumina sol was placed in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a constant temperature dryer Model DX402 manufactured by Yamato Scientific Co., Ltd. 140 g was obtained.

(Preparation Example 3)
(Preparation of seed crystal α-alumina particles)
In a ball mill in which 20 parts by mass of commercially available α-alumina powder [Taimicron “TM-D] manufactured by Daimei Chemical Industry Co., Ltd.) is mixed with 80 parts by mass of pure water and 100 parts by mass of alumina beads (bead diameter 0.50 mm) are filled. The resulting pulverized mixture was allowed to stand to obtain 80 parts by mass of a supernatant, the concentration was 2.0%, and the average particle size was 100 nm. The solution was concentrated to a concentration of 30% using a machine model SB-1100).

Example 1
In a 2 L polyethylene beaker, 950 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 32.7 g of seed crystal α-alumina particle mixture obtained in Preparation Example 3 (concentration: 30%), diglycerin ( Sakamoto Yakuhin Kogyo Co., Ltd.) (14 g) and pure water (3 g) were added, stirred and mixed uniformly, and adjusted to pH 3.0 with acetic acid. The obtained mixture was placed in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer Model DX402) to obtain 149 g of alumina sol powder. The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1150 ° C. for 8 hours and at 1150 ° C. for 3 hours. The alumina fired product was pulverized in a porcelain mortar. The resulting alumina had an alpha conversion of 97% and an average particle size of 260 nm.

(Example 2)
140 g of the alumina sol powder obtained in Preparation Example 2 in a 2 L polyethylene beaker, 47 g (concentration: 30%) of the seed crystal α-alumina particle mixed solution obtained in Preparation Example 3, and 20 g of diglycerin (manufactured by Sakamoto Pharmaceutical Co., Ltd.) Then, 793 g of pure water was added and stirred and mixed uniformly, and the pH was adjusted to 2.9 with nitric acid. The obtained mixture was put in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer Model DX402) to obtain 153 g of alumina sol powder. The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1150 ° C. for 8 hours and at 1150 ° C. for 3 hours. The alumina fired product was pulverized in a porcelain mortar. The obtained alumina had an alpha conversion of 96% and an average particle size of 232 nm.

(Example 3)
Same as Example 1, except that the amount of diglycerin used was changed to 5 g, the amount of seed crystal α-alumina particles mixed solution used was changed to 30 g, the amount of pure water used was changed to 15 g, and the pH was changed to 3.2. Fine α-alumina was obtained by the procedure. The obtained alumina had a pregelatinization rate of 96% and an average particle size of 275 nm.

Example 4
140 g of the alumina sol powder of Preparation Example 2 is used, the amount of diglycerin used is 30 g, the amount of seed crystal α-alumina particles mixed solution is 60 g, the amount of pure water is 770 g, and the pH is 3.2. Except for the change, fine particle α-alumina was obtained by the same procedure as in Example 1. The obtained alumina had a pregelatinization rate of 96% and an average particle size of 220 nm.

(Example 5)
Same as Example 1, except that the amount of diglycerin used was changed to 25 g, the amount of seed crystal α-alumina particles mixed solution used was changed to 23 g, the amount of pure water used was changed to 2 g, and the pH was changed to 3.1. Fine α-alumina was obtained by the procedure. The resulting alumina had an alpha conversion of 95% and an average particle size of 300 nm.

(Example 6)
The amount of alumina sol used was changed to 900 g, the amount of diglycerin used was changed to 45 g, the amount of seed crystal α-alumina particles mixed solution was changed to 10 g, the amount of pure water used was changed to 45 g, and the pH was changed to 3.4. Except for the above, fine particle α-alumina was obtained by the same procedure as in Example 1. The alumina obtained had an α-formation ratio of 93% and an average particle size of 430 nm.

(Example 7)
The amount of alumina sol used was changed to 900 g, the amount of diglycerin used was changed to 70 g, the amount of seed crystal α-alumina particles mixed solution was changed to 15 g, the amount of pure water used was changed to 15 g, and the pH was changed to 3.3. Except for the above, fine particle α-alumina was obtained by the same procedure as in Example 1. The alumina obtained had an α-formation rate of 94% and an average particle size of 370 nm.

(Example 8)
The amount of alumina sol used was changed to 900 g, the amount of diglycerin used was changed to 10 g, the amount of seed crystal α-alumina particles mixed solution was changed to 57 g, the amount of pure water used was changed to 33 g, and the pH was changed to 3.5. Except for the above, fine particle α-alumina was obtained by the same procedure as in Example 1. The alumina obtained had an α-formation ratio of 93% and an average particle size of 230 nm.

Example 9
In a 2 L beaker made of polyethylene, 950 g of the alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 32.7 g of the seed crystal α-alumina particle mixture obtained in Preparation Example 3 (concentration: 30%), pentaerythritol ( 14 g for Kishida Chemical Co., Ltd. and 3 g of pure water were uniformly stirred and mixed, and adjusted to pH 3.0 with nitric acid. The obtained mixture was put in a stainless steel tray (prepared to a thickness of about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model DX402) to obtain 152 g of alumina sol powder. . The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1150 ° C. for 8 hours and at 1150 ° C. for 3 hours. The alumina fired product was pulverized in a porcelain mortar. The obtained alumina had an alpha conversion of 95% and an average particle size of 275 nm.

(Example 10)
In a 2 L beaker made of polyethylene, 950 g of the alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 32.7 g of the seed crystal α-alumina particle mixture obtained in Preparation Example 3 (concentration: 30%), pentaerythritol ( 14 g of Kishida Chemical Co., Ltd. and 3 g of pure water were uniformly stirred and mixed, and adjusted to pH 3.0 with acetic acid. The obtained mixture was put into a stainless steel tray (prepared to a thickness of about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model DX402) to obtain 150 g of alumina sol powder. . The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1150 ° C. for 8 hours and at 1150 ° C. for 3 hours. The alumina fired product was pulverized in a porcelain mortar. The resulting alumina had an alpha conversion of 95% and an average particle size of 290 nm.

(Example 11)
In a 2 L polyethylene beaker, 950 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 32.7 g of seed crystal α-alumina particle mixture obtained in Preparation Example 3 (concentration: 30%), diglycerin ( 14 g of Sakamoto Pharmaceutical Co., Ltd.) and 3 g of pure water were uniformly stirred and mixed, and the pH was adjusted to 3.0 with nitric acid. The obtained mixture was put into a stainless steel tray (prepared to a thickness of about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model DX402) to obtain 149 g of alumina sol powder. . The dried alumina sol was put in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1050 ° C. for 8 hours and 1050 ° C. for 1.5 hours. The alumina fired product was pulverized in a porcelain mortar. The obtained alumina had an alpha conversion of 98% and an average particle size of 225 nm.

(Example 12)
In a 2 L polyethylene beaker, 950 g (concentration: 14.7%) of the alumina sol obtained in Preparation Example 1, 32.7 g (concentration: 30%) of the seed crystal α-alumina particle mixture obtained in Preparation Example 3, and diglycerin ( Sakamoto Yakuhin Kogyo Co., Ltd.) (14 g) and pure water (3 g) were added, stirred and mixed uniformly, and adjusted to pH 3.0 with acetic acid. The obtained mixture was put in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model SX402) to obtain 149 g of alumina sol powder. The dried alumina sol was put in a crucible and baked in an electric furnace (Kyoei Electric Furnace Model TK-3N) at room temperature to 1200 ° C. for 8 hours and 1200 ° C. for 3 hours. The calcined alumina was pulverized with a magnetic mortar. The obtained alumina had a pregelatinization rate of 98% and an average particle size of 295 nm.

(Example 13)
In a 2 L polyethylene beaker, 950 g (concentration: 14.7%) of the alumina sol obtained in Preparation Example 1, 32.7 g (concentration: 30%) of the seed crystal α-alumina particle mixture obtained in Preparation Example 3, and diglycerin ( Sakamoto Yakuhin Kogyo Co., Ltd.) (14 g) and pure water (3 g) were added, stirred and mixed uniformly, and adjusted to pH 3.0 with acetic acid. The obtained mixture was put in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model SX402) to obtain 149 g of alumina sol powder. The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Model TK-3N) at room temperature to 1000 ° C. for 8 hours and at 1000 ° C. for 3 hours. The calcined alumina was pulverized with a magnetic mortar. The resulting alumina had an alpha conversion of 85% and an average particle size of 252 nm.

(Example 14)
In a 2 L polyethylene beaker, 950 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 32.7 g of seed crystal α-alumina particle mixture obtained in Preparation Example 3 (concentration: 30%), diglycerin ( 14 g of Sakamoto Pharmaceutical Co., Ltd.) and 3 g of pure water were uniformly stirred and mixed, and the pH was adjusted to 3.0 with nitric acid. The obtained mixture was put into a stainless steel tray (prepared to a thickness of about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model DX402) to obtain 149 g of alumina sol powder. . The dried alumina sol was put in a crucible and baked in an electric furnace (Kyoei Electric Furnace Model TK-3N) at room temperature to 950 ° C. for 8 hours and at 950 ° C. for 1.5 hours. The alumina fired product was pulverized in a porcelain mortar. The obtained alumina had a gelatinization rate of 89% and an average particle size of 205 nm.

(Comparative Example 1)
It carried out according to Example 1 except for diglycerin. The obtained alumina had a pregelatinization rate of 93% and an average particle size of 479 nm.

(Comparative Example 2)
In order to investigate the effect when seed crystal particles are not used, 950 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%), 14 g of diglycerin (manufactured by Sakamoto Pharmaceutical Co., Ltd.), pure, in a 2 L polyethylene beaker 36 g of water was uniformly stirred and mixed, and adjusted to pH 2.9 with nitric acid. The obtained mixture was put into a stainless steel tray (prepared to a thickness of about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model DX402) to obtain 149 g of alumina sol powder. . The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Co., Ltd. Model TK-3N) at room temperature to 1150 ° C. for 8 hours and at 1150 ° C. for 3 hours. The calcined alumina was pulverized with a magnetic mortar. The obtained alumina had an alpha conversion of 65% and an average particle size of 723 nm.

(Comparative Example 3)
In order to investigate the effect when tetraol is not used, 900 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%) in a 2 L polyethylene beaker, seed crystal α-alumina particle mixed solution 50 obtained in Preparation Example 3 0.0 g (concentration: 30%) and 50 g of pure water were uniformly stirred and mixed, and adjusted to pH 2.9 with hydrochloric acid. The obtained mixture was put in a stainless steel tray (adjusted to a thickness of about 2.5 cm) to obtain 143 g of alumina sol. The dried alumina sol was put in a crucible and heated from room temperature to 950 ° C. over 8 hours and calcined at 950 ° C. for 3 hours in an electric furnace (Kyoei Electric Furnace Model TK-3N). The obtained alumina fired product was pulverized in a magnetic mortar. The resulting alumina had an alpha conversion of 67% and an average particle size of 1590 nm.

(Comparative Example 4)
In order to examine the effect when the firing temperature was less than 950 ° C., the same procedure as in Comparative Example 2 was applied except that the firing conditions were changed from room temperature to 700 ° C. for 8 hours and at 700 ° C. for 8 hours in Comparative Example 2. Carried out. The obtained alumina had a pregelatinization rate of 0% and an average particle size of 175 nm.

(Comparative Example 5)
In order to investigate the effect when the firing temperature is lower than 950 ° C., 950 g of alumina sol obtained in Preparation Example 1 (concentration: 14.7%) in a 2 L polyethylene beaker, seed crystal α-alumina particles obtained in Preparation Example 3 32.7 g (concentration: 30%) of the mixed solution, 14 g of diglycerin (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) and 3 g of pure water were added, stirred and mixed uniformly, and adjusted to pH 3.0 with acetic acid. The obtained mixture was put in an aluminum tray (thickness: about 2.5 cm) and dried at 95 ° C. using a dryer (Yamato Scientific Co., Ltd. constant temperature dryer model SX402) to obtain 149 g of alumina sol powder. The dried alumina sol was placed in a crucible and baked in an electric furnace (Kyoei Electric Furnace Model TK-3N) at room temperature to 900 ° C. for 8 hours and at 900 ° C. for 3 hours. The calcined alumina was pulverized with a magnetic mortar. The obtained alumina had a pregelatinization rate of 30% and an average particle size of 205 nm.

Table 5 summarizes the measurement results of the alpha conversion rate, particle diameter, and bulk specific gravity of alumina obtained in Examples and Comparative Examples.

  As is clear from the measurement results of the examples and comparative examples in Table 5, the fired product obtained from the aqueous mixture containing the alumina sol, seed crystal particles, and tetraol of the present invention was obtained from the α-alumina sol of the comparative example. Compared with the calcined product, it has a high α conversion rate, a small average particle size, a narrow particle size distribution, and a large bulk specific gravity.

  According to the present invention, it is possible to easily produce fine particle α-alumina having a high α conversion rate, a small average particle size, and a narrow particle size distribution, and its industrial value is very large.

Claims (9)

A method for producing particulate α-alumina,
Dispersing alumina sol and seed crystal particles in an aqueous medium containing tetraol to obtain an aqueous mixture, wherein the tetraol is diglycerin, pentaerythritol, bis (2,3-dihydroxypropyl) ether, A step selected from the group consisting of 1,2,7,8-octanetetraol and combinations thereof, wherein the concentration of the tetraol is 0.05% by weight or more based on the total weight of the aqueous mixture;
Adjusting the pH of the aqueous mixture to 0.1 to 5.0,
Drying the aqueous mixture to obtain a powder mixture;
Baking the powder mixture at a temperature of 950 ° C. or higher and 1200 ° C. or lower;
A step of pulverizing the fired product obtained by the firing to obtain fine particle α-alumina,
A method comprising the steps of:   The method for producing fine particle α-alumina according to claim 1, wherein the tetraol is diglycerin and / or pentaerythritol.   The method for producing particulate α-alumina according to claim 1 or 2, wherein the tetraol content in the aqueous mixture is 8.0 mass% or less.   The method for producing particulate α-alumina according to any one of claims 1 to 3, wherein the alumina sol is a product obtained by peptizing α-alumina monohydrate.   The fine particle α-alumina according to any one of claims 1 to 4, wherein the content of the alumina sol in the aqueous mixture is 5% by mass or more and 30% by mass or less in terms of α-alumina with respect to the total mass of the aqueous mixture. Manufacturing method.   The method for producing fine particle α-alumina according to any one of claims 1 to 5, wherein the seed crystal particles are a corundum type metal oxide.   The method for producing fine-particle α-alumina according to claim 6, wherein the corundum-type metal oxide is α-alumina.   The method for producing fine particle α-alumina according to any one of claims 1 to 7, wherein the seed crystal particles have an average particle diameter of 0.01 µm or more and 0.2 µm or less.   The method for producing fine particle α-alumina according to any one of claims 1 to 8, wherein the amount of the seed crystal particles used is 1 to 20 parts by mass per 100 parts by mass of the alumina sol.