JP4251124B2 - Method for producing fine α-alumina - Google Patents

Description

The present invention relates to a method for producing a fine α-alumina, and more particularly to a method for producing fine α-alumina having a small α-necking particle, a high α conversion ratio and a large BET specific surface area.

Fine α-alumina is a fine particle of alumina [Al ₂ O ₃ ] whose main crystal phase is α-phase, and is widely used as a raw material for producing sintered bodies such as light-transmitting tubes. Yes. Such fine α-alumina is required to have a high α conversion rate, a large BET specific surface area, and a small number of particles that are necked in that a sintered body having excellent strength can be obtained.

Non-Patent Document 1 [A. Krell, NanoStructured Materials, Vol. 11, 1141 (1999)] describes a method for producing fine α-alumina with a high α conversion ratio and a large BET specific surface area. Water is distilled off from an aqueous mixture containing the product to obtain a dry powder mixture containing an aluminum hydrolyzate and seed crystal particles, and a method for firing the obtained dry powder mixture is disclosed. No description regarding the preparation of seed crystal particles can be found.

A. Krell, Nano Structured Materials, Vol. 11, 1141 (1999)

However, the fine α-alumina obtained by such a conventional production method has a problem that there is much necking between particles.

Therefore, the present inventor has intensively studied to develop a method for producing a fine α-alumina having a high α-ratio and a large BET specific surface area with little particle-necking, and as a result, an unground metal compound is used as a seed crystal particle. The half-value width (H) of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum obtained by pulverizing the particles is 1.06 times or more than the half-value width (H ₀ ) before pulverization. It was found that by using the above, fine α-alumina having a high α conversion rate and a large BET specific surface area can be obtained, and the present invention has been achieved.

That is, in the present invention, the following seed crystal particles are dispersed, water is removed from the aqueous mixture containing the aluminum compound to obtain a dry powder mixture, and the obtained dry powder mixture is heated at 600 ° C. to 1000 ° C. in the atmosphere or A method for producing fine α-alumina having a particle size of 0.01 μm or more and 0.1 μm or less, characterized by firing in an inert gas for a firing time of 10 minutes to 24 hours .
Seed crystal particles: obtained by pulverizing unground metal compound particles made of alumina, iron oxide, chromium oxide or diaspore, and the half-value width (H of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum (H ) Is 1.06 times or more of the half width before grinding (H ₀ )

According to the production method of the present invention, it is possible to obtain fine α-alumina having a high BET specific surface area with a high α conversion rate, with less necking between particles.

The aqueous mixture used in the present invention is one in which seed crystal particles are dispersed and an aluminum compound is contained.

The seed crystal particles are obtained by pulverizing unground metal compound particles. As the unground metal compound particles, for example, particles made of a metal oxide such as alumina, iron oxide or chromium oxide, metal hydroxide particles such as diaspore, etc. are usually used. As such seed crystal particles, those having a particle size of usually about 0.01 μm or more and 0.5 μm or less are used, and preferably 0.05 μm or more. The BET specific surface area is preferably about 12 m ² / g or more and about 150 m ² / g or less, more preferably 15 m ² / g or more. As the seed crystal particles, those having a crystal structure of corundum type are preferably used, and those having no crystal water are preferably used. Examples of seed crystal particles having a corundum crystal structure and no crystal water include α-alumina particles, α-iron oxide particles, and α-chromium oxide particles. Alumina particles are preferably used because they are the same metal component as the fine α-alumina obtained.

The pulverization may be dry pulverization in which a liquid such as water is added without drying, or may be wet pulverization in which a liquid such as water is added and pulverized in a wet state. For pulverization by dry pulverization, for example, a ball mill such as a rolling mill, a vibration ball mill or a planetary mill, a high-speed rotary pulverizer such as a pin mill, a pulverizer such as a medium stirring mill or a jet mill can be used. For pulverization by wet pulverization, for example, a pulverizer such as a ball mill, a high-speed rotary pulverizer, a medium stirring mill, and the like can be used.

In dry pulverization, unmilled metal compound particles may be pulverized alone, but it is preferable to increase the pulverization efficiency by adding a deflocculant, a pulverization aid, and the like. Therefore, it is preferable to add a grinding aid. Examples of the grinding aid include alcohols such as ethanol and propanol, glycols such as propylene glycol, polypropylene glycol and ethylene glycol, amines such as triethanolamine, higher fatty acids such as palmitic acid, stearic acid and oleic acid, aluminum Metal alkoxides such as alkoxide, carbon materials such as carbon black and graphite, and mixtures thereof are used. When a peptizer, a grinding aid, etc. are added, the addition amount is 0.01 to 10 parts by weight, preferably 0.5 to 5 parts by weight, more preferably 0 per 100 parts by weight of the metal compound particles. .75 parts by mass to about 2 parts by mass.

As the liquid used in the wet pulverization, water is usually used. Moreover, it is preferable to grind by adding a dispersant because it can be pulverized with good dispersibility. Examples of the dispersant include acids such as nitric acid, acetic acid, oxalic acid, hydrochloric acid and sulfuric acid, alcohols such as methanol, ethanol and isopropyl alcohol, aluminum salts such as aluminum chloride, aluminum oxalate, aluminum acetate and aluminum nitrate, and surfactants. Etc.

The lining of the pulverizer is preferably made of high-purity alumina from the viewpoint of hardly contaminating the seed crystal particles obtained. The diameter of the medium beads used for pulverization is not particularly limited as long as pulverization proceeds.

Milling is the half width (H) of pre-crushed half width of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in X-ray diffraction spectrum (H ₀₎ with respect to 1.06 times or more, preferably 1. It is carried out until it becomes 08 times or more, and usually it is 3 times or less in terms of time required for grinding. The half width (H) of the main peak increases with the progress of pulverization.

As the seed crystal particles, those obtained by pulverization may be used as they are, but it is preferable to use those obtained by pulverizing and removing coarse particles by classification. In the case of using the classified one, the coarse particles are usually removed in an accumulated percentage of 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

Examples of the aluminum compound contained in the aqueous mixture include an aluminum hydrolyzate obtained by hydrolyzing a water-soluble aluminum salt in water, particularly when the pulverization degree of seed crystal particles is 1.15 or less. A solution obtained by hydrolyzing an aqueous aluminum compound solution at a temperature of 60 ° C. or less at a hydrogen ion concentration of pH 5 or less is preferably used.

An aluminum compound aqueous solution is an aqueous solution in which a water-soluble aluminum compound is dissolved in water. As the water-soluble aluminum compound, one containing no metal component other than aluminum is used, for example, an aluminum salt. It may be aluminum alkoxide.

Examples of the aluminum salt include aluminum nitrates such as aluminum nitrate and ammonium ammonium nitrate, aluminum inorganic salts such as ammonium alum and ammonium carbonate, aluminum organic salts such as aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate, and aluminum laurate. Of these, aluminum inorganic salts are preferred, and aluminum nitrates are more preferred. Examples of the aluminum alkoxide include aluminum isopropoxide, aluminum ethoxide, aluminum s-butoxide, aluminum t-butoxide and the like.

The aluminum compound concentration in the aluminum compound aqueous solution is usually 0.01 mol / L or more and a saturation concentration or less in terms of aluminum. It is preferable that the aluminum compound is completely dissolved in the aluminum compound aqueous solution to be used. For this reason, the hydrogen ion concentration pH of the aluminum compound aqueous solution is usually 2 or less, and usually 0 or more.

The aluminum compound aqueous solution may contain a solvent that volatilizes or disappears at least at the firing temperature. Examples of such solvents include polar organic solvents such as alcohols such as methanol, ethanol, propanol and isopropanol, and organic solvents such as nonpolar organic solvents such as carbon tetrachloride, benzene and hexane.

In order to hydrolyze such an aluminum compound aqueous solution, a base is usually added to obtain a hydrogen ion concentration of pH 3 or higher. As the base, for example, those containing no metal component such as ammonia are used. When ammonia is used, it may be added in a gaseous state, but it is preferably added as an aqueous ammonia solution. When using an aqueous ammonia solution, the concentration is usually 0.01 mol / L or more and saturated concentration or less in terms of aluminum.

In order to hydrolyze such an aluminum compound aqueous solution at a hydrogen ion concentration of pH 5 or less, for example, a base may be added so that the hydrogen ion concentration of the aluminum compound aqueous solution does not exceed pH 5. For example, by adjusting the amount of base used, pH 5 An amount of base that gives the following hydrogen ion concentration may be added, or a base may be added so as not to exceed pH 5 while measuring the hydrogen ion concentration using a hydrogen ion meter (pH meter). If the base is added excessively to exceed pH 5, fine α-alumina with many necking particles can be easily obtained.

The hydrolysis is preferably performed at a temperature of 60 ° C. or lower, more preferably 50 ° C. or lower, particularly 45 ° C. or lower, and is usually performed at a temperature higher than the freezing temperature of the aqueous aluminum compound solution, preferably 0 ° C. or higher. When hydrolyzed at a temperature exceeding 60 ° C., the resulting fine α-alumina tends to have many necked particles.

After adding the base, preferably 60 ° C. or lower, more preferably 50 ° C. or lower, particularly preferably 45 ° C. or lower, usually at a freezing temperature or higher, preferably 0 ° C. or higher, for example 1 hour or longer, usually 72 hours or less. The degree may be maintained.

By hydrolyzing the aluminum compound aqueous solution, a hydrolysis mixture containing water and an aluminum hydrolyzate is obtained. Since the aluminum hydrolyzate is usually insoluble in water, in such a hydrolysis mixture, the aluminum hydrolyzate is in the form of a sol or gel, or is precipitated as a precipitate.

The aqueous mixture in which the seed crystal particles are dispersed and containing the aluminum hydrolyzate may be obtained by a method of adding the aluminum hydrolyzate and seed crystal particles to water, or the hydrolysis mixture after hydrolyzing the aluminum compound aqueous solution. Contains water and aluminum hydrolysates, so seed crystal particles may be added to the hydrolysis mixture. Alternatively, seed crystal particles may be added in advance to the aluminum compound aqueous solution and hydrolyzed in the presence of the seed crystal particles to obtain an aqueous mixture containing water, an aluminum hydrolyzate, and seed crystal particles.

For example, the seed crystal particles may be added to the hydrolysis mixture or the aqueous aluminum compound solution in a powder state, or may be added in a state of being dispersed in a solvent such as water. In order to disperse the seed crystal particles in the solvent, for example, the seed crystal particles may be mixed with the solvent.

The content of the seed crystal particles in the aqueous mixture is such that, when metal oxide particles are used, the aluminum hydrolyzate and seed crystal particles in terms of metal oxide are obtained in that a fine α-alumina with a high α conversion rate can be easily obtained. It is preferable that it is 1 part by mass or more, further 2 parts by mass or more, and particularly 4 parts by mass or more per 100 parts by mass of the total amount. The amount of seed crystal particles may exceed 50 parts by mass, but since the pregelatinization rate does not increase in accordance with the amount of use, it is usually 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 25. It is about the mass part or less.

The amount of water used is about 150 parts by mass or more and 1000 parts by mass or less, preferably about 200 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the total amount of the aluminum hydrolyzate and seed crystal particles.

An aluminum salt is also mentioned as an aluminum compound. The aluminum salt is a salt of aluminum and a base, and may be an aluminum inorganic salt of aluminum and an inorganic base, or an aluminum organic salt of aluminum and an organic base. Examples of the aluminum inorganic salt include aluminum nitrate, ammonium aluminum nitrate, ammonium aluminum carbonate, aluminum sulfate, and aluminum ammonium sulfate. Examples of the aluminum organic salt include aluminum oxalate, aluminum acetate, aluminum stearate, ammonium alum, aluminum lactate, and aluminum laurate.

The aqueous mixture in which the seed crystal particles are dispersed and containing the aluminum salt can be obtained, for example, by mixing the aluminum salt with water to form an aqueous solution or slurry and adding the seed crystal particles. The seed crystal may be added in the form of powder or may be added in a state dispersed in a solvent.

The amount of the seed crystal particles used is 1 part by mass or more per 100 parts by mass of the total amount of the aluminum salt and the seed crystal, in terms of the oxide of the metal component, in terms of easily obtaining fine α-alumina having a high α conversion rate. Further, it is preferably 2 parts by mass or more, particularly 4 parts by mass or more. The amount of seed crystals used may exceed 50 parts by mass, but since the pregelatinization rate does not increase in accordance with the amount used, it is usually 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass. Part or less.

The amount of water used is about 150 parts by mass or more and 1000 parts by mass or less, preferably about 200 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the total amount of the aluminum hydrolyzate and seed crystal particles.

In order to remove water from the aqueous mixture, for example, water may be volatilized and evaporated to dryness. Water can be volatilized by an ordinary method such as a freeze drying method or a vacuum drying method. The temperature at which water is volatilized is usually 100 ° C. or lower.

Thus, by removing water from the aqueous mixture, a dry powder mixture in which the seed crystal particles are uniformly dispersed in the aluminum compound can be obtained.

The dry powder mixture thus obtained is heated and fired. The firing temperature is usually 600 ° C. or higher, preferably 700 ° C. or higher in that fine α-alumina having a high α conversion rate can be easily obtained, and 1000 ° C. or lower, preferably 950 ° C. or lower in terms of less necking between particles. It is. The powder mixture is heated to a firing temperature at a temperature rising rate of, for example, 60 ° C./h to 1200 ° C./h. However, it is 150 at a temperature range of at least 150 ° C. to 500 ° C. in that fine α-alumina particles with little necking are obtained. It is preferable to heat at a rate of temperature increase of from ° C / h to 500 ° C / h.

Firing may be performed in the air or in an inert gas such as nitrogen gas or argon gas. Further, it may be fired while keeping the water vapor partial pressure in the atmosphere low.

Firing can be performed using a normal firing furnace such as a tubular electric furnace, box-type electric furnace, tunnel furnace, far-infrared furnace, microwave heating furnace, shaft furnace, reflection furnace, rotary furnace, roller hearth furnace, or the like. . Firing may be performed batchwise or continuously. Moreover, you may carry out by a stationary type and may carry out by a fluid type.

The firing time may be sufficient as long as the aluminum hydrolyzate is turned into α to obtain fine α-alumina having a high α conversion rate, depending on the type, amount, type of firing furnace, firing temperature, and firing atmosphere of the aluminum compound used. Although it differs, it is about 10 minutes or more and 24 hours or less, for example.

The fine α-alumina thus obtained has a particle diameter of about 0.01 μm or more and 0.1 μm or less, a high α conversion and a large BET specific surface area, for example, an α conversion of 90% or more, preferably 95% or more. The BET specific surface area is 10 m ² / g or more, preferably 13 m ² / g or more and 150 m ² / g or less, more preferably 15 m ² / g or more and 100 m ² / g or less.

The obtained fine α-alumina may be pulverized. In order to pulverize the fine α-alumina, for example, a medium pulverizer such as a vibration mill, a ball mill, or a jet mill can be used. The obtained fine α-alumina may be classified.

The α-alumina thus obtained is useful as a raw material for producing an α-alumina sintered body, for example. Examples of the α-alumina sintered body include those requiring high strength such as cutting tools, bioceramics, and bulletproof plates. Examples include semiconductor manufacturing equipment parts such as wafer handlers and electronic parts such as oxygen sensors. Light-transmitting tubes such as sodium lamps and metal halide lamps are also included. Also included are ceramic filters used for removing solids contained in gases such as exhaust gas, filtering molten aluminum, and filtering food such as beer. Examples of the ceramic filter include a selective permeation filter for selectively permeating hydrogen in a fuel cell or selectively permeating gas components generated during petroleum refining, carbon monoxide, carbon dioxide, nitrogen, oxygen, and the like. These permselective filters may be used as a catalyst carrier for supporting a catalyst component on the surface thereof.

Using the resulting fine α-alumina as a raw material, it is used as a cosmetic additive, brake lining additive, catalyst carrier, and as a material for conductive sintered bodies, thermally conductive sintered bodies, etc. Is done.

The obtained fine α-alumina is used as an additive for improving the head cleaning property and wear resistance by being added to the coating layer of the coating type magnetic media in the same manner as the normal α-alumina powder in the form of powder. be able to. It can also be used as a toner. It can also be used as a filler added to the resin. It can also be used as an abrasive, for example, it can be used as a slurry dispersed in a solvent such as water, and can be used for polishing semiconductor CMP, polishing a hard disk substrate, etc. It can be used for precision polishing of magnetic heads.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these Examples.

Note that the alpha conversion rate of the fine α-alumina obtained in each example is determined by the alumina α phase (012) appearing at a position of 2θ = 25.6 ° from the diffraction spectrum of the fine α-alumina obtained using a powder X-ray diffractometer. Surface) peak height (I _25.6 ) and peak heights (I ₄₆ ) of γ phase, η phase, χ phase, κ phase, θ phase and δ phase appearing at 2θ = 46 °, 1)
α conversion rate = I _25.6 / (I _25.6 + I ₄₆ ) x 100 (%) (1)
Calculated by
The BET specific surface area was determined by a nitrogen adsorption method.
The average primary particle diameter was determined as the number average value of the measured values by measuring the maximum diameter in the fixed direction of each primary particle with respect to 20 or more arbitrary particles in the transmission electron micrograph of the fine α-alumina.
The neck ratio was determined as the ratio of the particles that were necked and connected to the adjacent particles for 20 or more arbitrary particles in the transmission electron micrograph of the fine α-alumina.
The degree of pulverization of the seed crystal (α-alumina) depends on the half-value width (H (116)) of the X-ray diffraction peak of the α-phase (116) surface and the α-phase (116) of the seed crystal (α-alumina) before pulverization. Half width of the X-ray diffraction peak of the surface (
H ₀ (116)) and the formula (2)
Grinding degree = H (116) / H ₀ (116) (2)
Determined by

Example 1
[Production of seed crystal slurry]
Aluminum hydroxide obtained by hydrolysis of aluminum isopropoxide is calcined to obtain an intermediate alumina whose main crystal phase is the θ phase and 3% by weight of the α phase, and this intermediate alumina is obtained by a jet mill. By grinding, a powder having a bulk density of 0.21 g / cm ³ was obtained.

While continuously putting the powder obtained above into an atmospheric furnace filled with dry air having a dew point of −15 ° C. (water vapor partial pressure of 165 Pa), the furnace was continuously taken out with an average residence time of 3 hours, and the maximum temperature Firing was performed at 1170 ° C. to obtain α-alumina particles having a BET specific surface area of 14 m ² / g.

The α-alumina particles 100 parts by per part by weight of the grinding aid (propylene glycol) was added, and pulverized for 12 hours with a vibration mill addition of alumina beads having a diameter of 15mm as grinding media, BET specific surface area 16.6 m ² / G, seed crystals (α alumina particles) having a pulverization degree of 1.10 were obtained.

After 37.5 g of this α-alumina particles (particle size is about 0.1 μm) are added to and dispersed in 150 g of an aluminum nitrate aqueous solution (pH = 2), it is filled into a 1 L plastic container together with 700 g of alumina beads (diameter 2 mm). After performing a dispersion treatment for 24 hours with a ball mill, the alumina beads were removed by a filtration operation to obtain a seed crystal slurry. The operation for obtaining the seed crystal slurry was repeated in the same manner as above, and the obtained seed crystal slurry was stored together.

[Production of aluminum hydrolyzate]
750.26 g (2 mol) of aluminum nitrate hydrate [Al (NO ₃ ) ₃ · 9H ₂ O] (manufactured by Kansai Catalysts Chemical Co., Ltd., first grade, powder form) was dissolved in 1555.7 g of pure water, and 1M / 1L An aqueous aluminum nitrate solution was obtained. 218.6 g (including 43.4 g of α-alumina particles) of the seed crystal slurry obtained above was added to this aqueous aluminum nitrate solution, and 25% aqueous ammonia using a micro rotary pump while stirring at room temperature (about 25 ° C.) [ Wako Pure Chemical Industries, Special Grade] 345.9 g (ammonia 86.5 g) was added at a feed rate of about 32 g / min. At the end of the addition, the slurry was a hydrolyzed product, and the pH was 3.9. The slurry was left for several tens of minutes at room temperature (about 25 ° C.). This aqueous mixture became jelly. This was dried in a constant temperature bath at 60 ° C. for 1 day and pulverized using an alumina mortar to obtain a powdery mixture. This mixture contains 30 parts by mass of seed crystal particles per 100 parts by mass in terms of oxide of the metal component. When 1 g of this powder mixture is heated to 390 ° C., a gas component of 34.7 × 10 ⁻³ is generated.

[Salt decomposition]
A rotary kiln with a length of 225 cm, an inner diameter of 212 cm and an internal volume of 79.4 L (made by Takasago Industry), made of SUS304L and provided with a discharge port with an opening area (A) of 38.5 cm ² in a laboratory with a temperature (T ₀ ) of 25 ° C. Was used, and the powder mixture obtained above was charged at 20 g / min from the charging port, and the salt-decomposed mixture was continuously taken out from the outlet and subjected to salt decomposition. The inside of the rotary kiln was replaced with nitrogen gas in advance. The furnace temperature at the outlet was 390 ° C. The furnace pressure (P) is used at atmospheric pressure (0.1 MPa), and the nitrogen gas blowing rate (V ₂ ) is 10 L / min (1.67 × 10 ⁻⁴ m ³ / sec) in terms of 25 ° C. did. The linear velocity (ρ) of the gas discharged from the discharge port was 2.8 m / sec. The rotation speed of the kiln was 2 rotations / minute.

[Baking]
The salt-decomposed mixture was placed in an alumina crucible and fired at 920 ° C. for 3 hours using a box-type electric furnace to obtain fine α-alumina. The evaluation results of this fine α-alumina are shown in Table 1.

Example 2
[Creation of seed crystal slurry]
The seed crystal slurry prepared in the same manner as in Example 1 was centrifuged at 4000 rpm for 40 minutes, the supernatant liquid was taken out, the BET specific surface area was 38.1 m ² / g, the pulverization degree was 1.38, and the solid content concentration was 3. A 3% classified seed slurry was made.

[Preparation of aluminum hydrolyzate and salt decomposition, baking]
Aluminum nitrate hydrate [Al (NO ₃ ) ₃ · 9H ₂ O] (manufactured by Kansai Catalysts Chemical Co., Ltd., grade 1, powder) 375.13 g (2 mol) was dissolved in 777.87 g of pure water, and 1 M / 1 L An aqueous aluminum nitrate solution was obtained. To the aluminum nitrate aqueous solution, 171.7 g of the classified seed crystal slurry obtained above [α alumina particles 5.67 g] was added, and 25% aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd. 161.7 g (special grade) (40.42 g as ammonia (NH ₃ )) was added at a rate of 32 g / min. The hydrogen ion concentration of the mixture after the addition was pH 4.0. The mixture was left at room temperature, dried at 60 ° C., and pulverized in a mortar to obtain a powder mixture of aluminum hydrolyzate, seed crystal particles, and ammonium nitrate. This powder mixture contains 10 parts by mass of seed crystals (α-alumina particles) per 100 parts by mass in terms of oxide of the metal component.

[Salt decomposition and calcination]
The same procedure as in Example 1 was conducted except that the powder mixture obtained in Example 1 was used instead of the powder mixture obtained in Example 1 and the salt was decomposed by the same operation as in Example 1 and the firing temperature was set to 900 ° C. Operation and calcination gave fine α-alumina. The evaluation results of this fine α-alumina are shown in Table 1.

Comparative Example 1
The seed crystal slurry 56.67 g [α alumina particles 11.33 g] obtained in Example 1 was added to the aluminum nitrate aqueous solution obtained in the same manner as in Example 1, and the mixture was stirred at room temperature with a micro rotary pump. 340.5 g of 25% aqueous ammonia (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) (10 g as ammonia (NH ₃ )) was added at a rate of 32 g / min. The hydrogen ion concentration of the mixture after the addition was pH 3.8. The mixture was allowed to stand at room temperature, dried at 60 ° C., and pulverized in a mortar to obtain a powder mixture of aluminum hydrolyzate and ammonium nitrate. This powder mixture contains 10 parts by mass of seed crystals (α-alumina particles) per 100 parts by mass in terms of oxide of the metal component.

[Salt decomposition and calcination]
The same procedure as in Example 1 was conducted except that the powder mixture obtained in Example 1 was used instead of the powder mixture obtained in Example 1 and the salt was decomposed by the same operation as in Example 1 and the firing temperature was set to 900 ° C. Operation and calcination gave fine α-alumina. The evaluation results of this fine α-alumina are shown in Table 1.

Table 1
━━━━━━━━━━━━━━━━━━━━━━━━━━━
Alpha conversion rate BET specific surface area Particle size Neck rate
(%) (M ² / g) (nm) (%)
────────────────────────────
Example 1 98 16.9 57 8
Example 2 98 18.8 74 17
Comparative Example 1 98 15 90 31
━━━━━━━━━━━━━━━━━━━━━━━━━━━

Claims (3)

The following seed crystal particles are dispersed, water is removed from the aqueous mixture containing the aluminum compound to obtain a dry powder mixture, and the obtained dry powder mixture is at 600 ° C. to 1000 ° C. in the atmosphere or in an inert gas. A method for producing fine α-alumina having a particle size of 0.01 μm or more and 0.1 μm or less, characterized by firing at a firing time of 10 minutes to 24 hours .
Seed crystal particles: obtained by pulverizing unground metal compound particles made of alumina, iron oxide, chromium oxide or diaspore, and the half-value width (H of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum (H ) Is 1.06 times or more of the half width before grinding (H ₀ ) The production method according to claim 1, wherein the aluminum compound is an aluminum hydrolyzate. The pulverization degree of the seed crystal particles is 1.08 or less,
A base is added to the aqueous solution in which the aluminum salt is dissolved and the seed crystal particles are dispersed at 60 ° C. or lower so that the hydrogen ion concentration of the aqueous solution does not exceed pH 5 to hydrolyze the aluminum salt, and the aqueous The manufacturing method of Claim 2 which obtains a mixture.