JP5086529B2 - Method for producing fine α-alumina - Google Patents

Description

The present invention relates to a method for producing fine α-alumina, and more particularly, to a method for producing fine α-alumina with a small amount of necking particles, 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 the α-phase, and is widely used as a raw material for producing sintered bodies such as translucent glazes. 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 necked particles in that a sintered body having excellent strength can be obtained.

Non-Patent Document 1 (Key Engineering Materials, Vols. 53-55, 462-468 (1991)) describes a method for producing fine α-alumina having a high α conversion rate and a large BET specific surface area. Hydrolysis is performed by adding ammonia to the aqueous aluminum salt solution to adjust the hydrogen ion concentration to pH 9, and then distilling off water to obtain a mixture of the hydrolyzate and seed crystal particles, and this mixture is fired. A method is disclosed.

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

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

Therefore, the present inventor has intensively studied to develop a method capable of producing fine α-alumina with a small amount of necking between particles, a high α conversion ratio, and a large BET specific surface area, and has reached the present invention.

That is, the present invention
A method for producing fine α-alumina by firing a mixture of a hydrolyzate obtained by hydrolyzing an aqueous solution of an aluminum compound at a temperature exceeding 60 ° C. or a hydrogen ion concentration exceeding pH 5 and seed crystal particles. Yes,
In the seed crystal particles, the half-value width (H) of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum is 1.06 times or more of the half-value width (H ₀ ) before pulverization. Furthermore, the present invention provides a method for producing fine α-alumina, which is obtained by grinding an unground metal compound.

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

The hydrolyzate used in the production method of the present invention is obtained by hydrolyzing an aqueous solution of an aluminum compound at a temperature exceeding 60 ° C. or a hydrogen ion concentration exceeding pH 5. Examples of the aluminum compound include aluminum salts and aluminum alkoxides.

Examples of the aluminum salt include aluminum chlorides such as aluminum chloride,
Aluminum nitrates such as aluminum nitrate, ammonium aluminum nitrate,
Ammonium alum,
Inorganic salts of aluminum, such as ammonium aluminum carbonate etc
Examples thereof include organic salts of aluminum such as aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate, and aluminum laurate.

Examples of the aluminum alkoxide include aluminum isopropoxide, aluminum ethoxide, aluminum s-butoxide, and aluminum t-butoxide. Aluminum chloride is preferable in that fine α-aluminum with high whiteness can be easily obtained.

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

The aqueous solution of the aluminum compound may be specified to contain at least a solvent that volatilizes or burns off upon firing. Examples of such a solvent include polar organic solvents including 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 an aqueous solution of an aluminum compound, it is usually sufficient to add a base to adjust the hydrogen ion concentration to pH 3 or higher. As the base, those not containing metal components such as ammonia, ammonium hydrogen carbonate, and ammonium carbonate are usually used. When ammonia is used, it may be added by blowing it into the aqueous solution in the form of a gas, but it is preferable to add it as an aqueous ammonia solution dissolved in water. When the aqueous ammonia solution is used, the concentration is usually 0.01 mol / L or more and the saturation concentration or less.

The hydrolysis is carried out at a temperature above 60 ° C., usually below 100 ° C., or above pH 5 and usually at pH 13 or below, preferably pH 11 or below, at a temperature above 60 ° C. Alternatively, hydrolysis may be performed at a hydrogen ion concentration exceeding pH 5. In order to hydrolyze at a hydrogen ion concentration exceeding pH 5, the amount of base used may be increased.

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

The seed crystal particles used in the production method of the present invention are obtained by pulverizing an unground metal compound. Examples of the unpulverized metal compound include metal oxides such as alumina (aluminum oxide), iron oxide, and chromium oxide, and metal hydroxides such as diaspore (aluminum hydroxide). The crystal type is preferably a corundum type. More preferably, there is no crystal water. Examples of the corundum-type metal compound having no crystal water include α-alumina, α-iron oxide, α-chromium oxide and the like, and α-alumina is preferably used because it is the same component as the intended fine α-alumina.

As the metal compound of the unmilled, usually particle size 0.01Myuemu～0.5Myuemu, preferably used is 0.05μm or more particles, preferably a BET specific surface area of 12m ² / g~150m ² / g, more preferably The thing of 15 m < ² > / g or more is used.

The metal compound may be pulverized by dry pulverization that is pulverized in a dry state without adding a liquid such as water, or may be pulverized by wet pulverization that is pulverized in a wet state with a liquid added.

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.

In dry pulverization, the unground metal compound may be pulverized alone, but it is preferable to increase the pulverization efficiency by adding additives such as pulverization aids and peptizers, and the seed crystal particles after pulverization are dispersible. It is preferable to add a dispersion aid because it can be dispersed without careful observation. As the grinding aid, for example, alcohols such as methanol, ethanol, propanol,
Glycols such as propylene glycol, polypropylene glycol, ethylene glycol,
Amines such as triethanolamine,
Higher fatty acids such as palmitic acid, stearic acid, oleic acid,
Metal alkoxides such as aluminum alkoxide,
Examples thereof include carbon materials such as carbon black and graphite, and these are used alone or in combination of two or more. When additives such as grinding aids and peptizers are added, the amount added is usually 0.01 parts by weight to 10 parts by weight, preferably 0.5 parts by weight to 5 parts by weight, per 100 parts by weight of the metal compound. Preferably it is about 0.75 part by mass to 2 parts by mass.

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. As the liquid used for wet grinding, 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, isopropanol,
Examples thereof include aluminum salts such as aluminum chloride, aluminum oxalate, aluminum acetate, and aluminum nitrate, surfactants, and the like. These may be used alone or in combination of two or more. When using a dispersing agent, the usage-amount is about 0.1 mass part-20 mass parts per 100 mass parts of liquids normally.

In the pulverizer, it is preferable that the surface in contact with the metal compound is made of high-purity alumina in that the obtained seed crystal particles are less contaminated. It is preferable that the pulverizing medium used when pulverizing with a medium stirring mill is also made of high-purity alumina.

In the pulverization of the metal compound, the half-value width (H) of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum is preferably 1.06 times or more the half-value width (H ₀ ) before pulverization. Is 1.1 times or more, more preferably 1.2 times or more, and usually 3 times or less in terms of time required for pulverization. Since the half-value width (H) of the main peak usually increases with the progress of pulverization, the pulverization may be continued until the half-value width (H) falls within the range specified in the present invention.

In the production method of the present invention, the seed crystal particles thus obtained are used. These seed crystal particles may be used as they are without being pulverized and classified, or may be used after removing coarse particles by classification. Good. Classification can be performed by, for example, a centrifugal separation process. In the case of classification, the coarse particles are usually removed at a cumulative percentage of 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and particularly preferably 99% by mass or more.

The amount of seed crystal particles used is that when a metal oxide or metal hydroxide is used as the metal compound, a fine α-alumina having a high α conversion rate can be easily obtained. It is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 4 parts by mass or more per 100 parts by mass of the total amount of seed crystal particles. Further, the amount of seed crystal particles used may exceed 50 parts by mass, but is usually 50 parts by mass or less, preferably 40 parts by mass or less, more preferably in view of increasing the pregelatinization rate corresponding to the amount of use. Is 25 parts by mass or less.

The production method of the present invention is a method for firing a mixture of such a hydrolyzate and seed crystal particles. The mixture can be prepared by a method in which the hydrolyzate and seed crystal particles obtained separately are mixed and stirred, but it is easy to obtain a mixture in which the hydrolyzate and seed crystal particles are uniformly mixed. Therefore, it is preferable to add seed crystal particles to the aqueous solution of the aluminum compound in advance and hydrolyze the aqueous solution. The seed crystal particles may be added to the aqueous solution in a dry state, or may be added in the form of a dispersed dispersion that has been dispersed in water in advance.

By removing water from the hydrolyzed aqueous solution by, for example, a method of volatilizing water, a mixture in which the hydrolyzate and seed crystal particles are uniformly dispersed can be obtained. The temperature at which the water is volatilized is usually 100 ° C. or less, but the water may be rapidly removed at a temperature exceeding this. By removing water, a dry mixture can be obtained.

In the production method of the present invention, such a mixture is 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 is easily obtained, and is usually 1000 ° C. or lower in terms of less necking between particles. Preferably it is 950 degrees C or less.

The temperature of the mixture is raised to the firing temperature, for example, at a heating rate of 60 ° C./hour to 1200 ° C./hour, but a temperature range of at least 150 ° C. to 600 ° C. in that fine α-alumina with less necking can be easily obtained. Then, it is preferable to raise the temperature at a heating rate of 500 ° C./hour or less, more preferably 200 ° C./hour or less, and usually 60 ° C./hour or more.

Depending on the type of aluminum compound used as a raw material, the gaseous by-product due to the aluminum compound is generated along with the temperature rise, but after maintaining the temperature below 600 ° C. until the generation of such by-product stops, It is preferable to mute to the firing temperature.

The mixture may be fired in the air or in an inert gas such as nitrogen gas or argon gas. Further, it may be fired in a dry atmosphere having a low water vapor partial pressure.

For firing, for example, a normal firing furnace such as a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a far-infrared furnace, a microwave heating furnace, a shaft furnace, a reflection furnace, a rotary furnace, a roller hearth furnace or the like can be used. The mixture may be fired batchwise or continuously. Further, it may be fired in a static manner or may be fired in a fluid manner.

The firing time may be a time sufficient for the hydrolyzate to be α and fine α-alumina having a pore α conversion rate to be obtained, the type of aluminum compound to be used, the usage ratio of the aluminum hydrolyzate and seed crystal particles, Although it differs depending on the type of firing furnace, firing temperature, firing atmosphere, etc., for example, it is 10 minutes to 24 hours.

The fine α-alumina thus obtained has a particle size of about 0.01 μm to 0.1 μm and exhibits a high α conversion rate and a large BET specific surface area. For example, the α conversion rate is 90% or more, preferably 95% or more. The BET specific surface area is usually 10 m ² / g or more, preferably 13 m ² / g or more, more preferably 15 m ² / g or more, usually 150 m ² / g or less, preferably 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.

The obtained fine α-alumina is used as a cosmetic additive, a brake lining additive, a catalyst carrier, and a material such as a conductive sintered body and a thermally conductive sintered body.

The obtained fine α-alumina can be added to the ceramic powder and used as a sintering aid for facilitating sintering when a sintered body is produced by sintering a ceramic powder that is difficult to sinter.

By using the obtained fine α-alumina as a raw material, fine aluminum nitride powder, yttrium-alumina-garnet (YAG) powder, powdered phosphor and the like can be produced.

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 the alumina α phase (012) appearing at 2θ = 25.6 ° from the diffraction spectrum of the fine α-alumina obtained using a powder X-ray diffractometer. since the peak of the surface) height and _{(I 25.6), 2θ = 46} ° of appearing at position γ phase, eta phase, chi-phase, kappa phase, the peak height of the θ-phase and δ-phase and (I _46), wherein ( 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 for 20 or more arbitrary particles in the transmission electron micrograph of 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 width (H (116)) of the X-ray diffraction peak [2θ = 57.5 °] of the α-phase (116) surface and the seed crystal (α From the half-value width (H ₀ (116)) of the X-ray diffraction peak of the α phase (116) surface of (alumina), 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.

To 100 parts by mass of the α-alumina particles, 1 part by mass of a grinding aid [propylene glycol] was added, a powder medium (alumina beads having a particle diameter of 15 mm) was added, and the mixture was pulverized with a vibration mill for 12 hours. The BET specific surface area of the α-alumina particles after pulverization was 16.6 m ² / g, and the pulverization degree was 1.10.

20 parts by mass of α-alumina particles after pulverization as described above are mixed with 80 parts by mass of an aqueous aluminum chloride solution (aluminum chloride concentration 0.01 mol / L), and 2.9 kg of alumina beads (bead diameter 0.65 mm) are wet-dispersed. After being continuously wet-dispersed with an average residence time of 15 minutes using “Dynomill” (manufactured by Ajisawa Co., Ltd.), the mixture is centrifuged for 40 minutes at a rotational speed of 4000 rpm (centrifugal acceleration of about 2100 G) to obtain a solid-liquid By the separation, a seed crystal slurry (solid content concentration 1.1% by mass) containing α-alumina fine particles [pulverization degree 1.4] was obtained as a supernatant.

[Production of aluminum hydrolyzate]
128.8 g of the seed crystal slurry obtained above (1.4 g of α-alumina fine particles) is aluminum chloride hexahydrate [AlCl ₃ .6H ₂ O] (Wako Pure Chemical Industries, Ltd., special grade, powder) 60 .4 g (0.25 mol) and 79.9 g of pure water were mixed at room temperature (about 25 ° C.) to obtain an aqueous solution, and 25% ammonia water [manufactured by Wako Pure Chemical Industries, Ltd.] using a micro rotary pump while stirring at the same temperature. , Special grade] 45.9 g (ammonia 11.5 g) was added at a feed rate of about 4.5 g / min.
At the end of the addition, the hydrolyzate precipitated and became a gel, and the hydrogen ion concentration was pH 6.5. It dried over 1 day using a 60 degreeC thermostat, and obtained the mixture of the hydrolyzate and seed crystal particle. This mixture contains 10 parts by mass of seed crystal particles per 100 parts by mass in terms of oxide of the metal component.

[Baking]
The mixture is pulverized using an alumina mortar to form a powder, put in an alumina crucible, heated to 500 ° C. in a box-type electric furnace at a heating rate of 150 ° C./hour in the atmosphere, and held at that temperature for 1 hour. And then cooled to room temperature (about 25 ° C.). Thereafter, the mixture was again heated in the atmosphere from room temperature to 900 ° C. at a heating rate of 300 ° C./hour using the electric furnace, and baked at the same temperature for 3 hours to obtain fine α-alumina. This fine α-alumina had high whiteness, a pregelatinization rate of 98%, and a BET specific surface area of 18.8 m ² / g. When the fine α-alumina was observed with a transmission electron microscope (TEM), no particles that were necked and connected to the adjacent particles were found. A TEM photograph of the obtained fine α-alumina is shown in FIG.

Example 2
[Production of aluminum hydrolyzate]
94.4 g of seed crystal slurry obtained by the same operation as in Example 1 (1.4 g of α-alumina fine particles) was aluminum chloride hexahydrate [AlCl ₃ .6H ₂ O] (manufactured by Wako Pure Chemical Industries, Ltd.). , Special grade, powdered) 60.4 g (0.25 mol) and 108 g of pure water were mixed at room temperature (about 25 ° C.) to obtain an aqueous solution, and the mixture was stirred using a micro rotary pump while stirring in a 75 ° C. water bath. % Aqueous ammonia (made by Wako Pure Chemical Industries, special grade) 46.6 g (ammonia 11.5 g) was added at a supply rate of about 4 g / min, and then cooled to room temperature. At the end of the addition, the slurry was a hydrolyzate deposit, and the hydrogen ion concentration after cooling was pH 7.2. Subsequently, it dried over 1 day using a 60 degreeC thermostat, and obtained the mixture of the hydrolyzate and seed crystal particle. This mixture contains 10 parts by mass of seed crystal particles per 100 parts by mass in terms of oxide of the metal component.

[Baking]
Except that the firing temperature was 920 ° C., the same operation as in Example 1 was performed, and the mixture obtained above was fired to obtain fine α-alumina. This fine α-alumina had high whiteness, a pregelatinization rate of 98%, and a BET specific surface area of 17.7 m ² / g. When the fine α-alumina was observed by TEM, no particles that were necked and connected to the adjacent particles were found. A TEM photograph of the obtained fine α-alumina is shown in FIG.

Comparative Example 1
[Production of seed crystal slurry]
20 parts by mass of α-alumina particles having a BET non-surface area of 14 m ² / g obtained in Example 1 were added and dispersed in 80 parts by mass of an aqueous aluminum chloride solution (pH = 2) without being pulverized, and then alumina beads (diameter 2 mm) was wet dispersed for 3 hours using a ball mill filled with 700 g to obtain a seed crystal slurry. The degree of pulverization of the α-alumina particles contained in the seed crystal slurry was measured and found to be 0.90.

[Production of fine α-alumina]
241.3 g (1 mol) of aluminum chloride hexahydrate [AlCl ₃ .6H ₂ O] (manufactured by Wako Pure Chemical Industries, special grade, powder) is dissolved in pure water, and the volume is 1 L (1000 cm ³ ) of aluminum chloride. An aqueous solution was obtained. To this aluminum chloride aqueous solution 250 cm ³ , 7.1 g (including α-alumina particles 1.4 g) of the seed crystal slurry obtained above was added, and 25% ammonia water [Wako Pure Chemical Industries, Ltd.] was used with a micro rotary pump while stirring at 75 ° C. 42.8 g (ammonia 9.8 g) was added at a feed rate of about 4 g / min. At the end of the addition, the slurry was a hydrolyzed precipitate (aluminum hydrolysate), and the pH was 4.8. The slurry was allowed to stand at room temperature (about 25 ° C.) for gelation, and then water was volatilized using a 60 ° C. thermostat to obtain a dry powder mixture.

This mixture contains 10 parts by mass of α-alumina particles per 100 parts by mass in terms of oxide of the metal component. This hydrolyzed precipitate was crushed in a mortar, placed in an alumina crucible, heated in a box-type electric furnace from room temperature to 1000 ° C. at a temperature rising rate of 300 ° C./h, and kept at the same temperature for 3 hours. Firing was performed to obtain fine α-alumina. This fine α-alumina had an α-formation rate of 98% and a BET specific surface area of 12.1 m ² / g. When this fine α-alumina was observed with a transmission electron microscope (TEM), a number of particles that were necked and connected to adjacent particles were found.

2 is a transmission electron micrograph (magnification 100,000 times) of the fine α-alumina obtained in Example 1. FIG. 4 is a transmission electron micrograph (magnification of 100,000 times) of the fine α-alumina obtained in Example 2.

Claims (3)

A mixture of a hydrolyzate obtained by hydrolyzing an aqueous solution of an aluminum compound with a hydrogen ion concentration exceeding pH 5 and 13 or less, and seed crystal particles at 600 ° C. or more and 1000 ° C. or less in the atmosphere or in an inert gas It is a method for producing fine α-alumina having a particle size of 0.01 μm to 0.1 μm by firing for a firing time of 10 minutes to 24 hours,
In the seed crystal particles, the half-value width (H) of the main peak in the range of 45 ° ≦ 2θ ≦ 70 ° in the X-ray diffraction spectrum is 1.06 times or more of the half-value width (H ₀ ) before pulverization. Obtained by pulverizing an unground metal compound composed of alumina, iron oxide, chromium oxide or diaspore ,
The metal compound unmilled The method of manufacturing the fine α-alumina, wherein the <br/> having a BET specific surface area of the particle diameter and 12m ² / g~150m ² / g of 0.01μm~0.5μm . The manufacturing method according to claim 1, wherein the hydrolysis is performed at 25 to 75 ° C. The production method according to claim 1 or 2 , wherein the aluminum compound is aluminum chloride.