JP4595383B2 - Production method of 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 finer α-alumina.

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 light-transmitting tubes. Yes. Such fine α-alumina is required to have a high α conversion ratio and finer in that a sintered body having excellent strength can be obtained.

As a method for producing such fine α-alumina, Patent Document 1 (Japanese Patent Application Laid-Open No. Sho 62-128918) includes an α-alumina precursor and seed crystal particles, and the content of the seed crystal particles is an α-alumina precursor in terms of oxide. A method of firing a mixture of less than 5 parts by mass with respect to 100 parts by mass of the total amount of the body and seed crystal particles is disclosed.

JP-A-62-128918

However, the fine α-alumina obtained by such a conventional production method could not be said to have a sufficiently small particle size.

Therefore, as a result of intensive studies to develop a method capable of producing a fine α-alumina having a smaller particle diameter, the present inventor results in a decrease in the particle diameter of the obtained fine α-alumina when more seed crystal particles are used. And found the present invention.

That is, the present invention includes a powder mixture containing an α-alumina precursor and seed crystal particles, and the content of the seed crystal particles is 25 parts by mass or more per 100 parts by mass of the total amount of the α-alumina precursor and seed crystal particles in terms of oxide. A method for producing fine α-alumina, which is characterized in that is fired.

According to the production method of the present invention, it is possible to easily produce fine α-alumina having a smaller particle diameter.

In the production method of the present invention, a powder mixture containing an α-alumina precursor and seed crystal particles is fired.

The α-alumina precursor contained in the powder mixture is a compound that becomes α-alumina upon firing, and examples thereof include aluminum salts, aluminum alkoxides, transition aluminas, aluminum hydroxides, and aluminum hydrolysis products.

The aluminum salt usually includes inorganic salts of aluminum, and specifically includes aluminum nitrates such as aluminum nitrate and ammonium nitrate, aluminum alum, aluminum carbonate, ammonium carbonate aluminum, aluminum sulfate, and ammonium sulfate aluminum. Moreover, the organic salt of aluminum is mentioned, Specifically, an aluminum oxalate, an aluminum acetate, an aluminum stearate, an aluminum lactate, an aluminum laurate etc. are mentioned.

Examples of the aluminum alkoxide include aluminum isopropoxide, aluminum ethoxide, aluminum s-butoxide, aluminum t-butoxide and the like.

Examples of the transition alumina include γ-alumina, χ-alumina, χ-alumina, θ-alumina, ρ-alumina, and κ-alumina whose crystal phases are γ-phase, χ-phase, θ-phase, ρ-phase, κ-phase, and the like.

Examples of aluminum hydroxide include amorphous aluminum hydroxide in addition to crystalline aluminum hydroxide such as gibbsite, boehmite, pseudoboehmite, bayerite, norstrandide, and diaspore.

Examples of the aluminum hydrolysis product include those obtained by hydrolyzing a water-soluble aluminum compound by reacting with water.

Examples of the water-soluble aluminum compound include the same aluminum salts as described above. In order to hydrolyze such a water-soluble aluminum compound in water, for example, an aqueous aluminum compound solution may be obtained by dissolving the water-soluble aluminum compound in water. The concentration of the aluminum compound in the water-soluble 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.

By hydrolyzing the water-soluble aluminum compound in the aqueous aluminum compound solution, the aluminum compound contained in the aqueous solution is hydrolyzed to produce an aluminum hydrolysis product. In order to hydrolyze the water-soluble aluminum compound, a base is usually added. 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.

The amount of the base to be added may be such that the pH of the aqueous aluminum compound solution is 3 or more. For example, the base is added until the pH becomes 3 or more while measuring the hydrogen ion concentration using a hydrogen ion meter (pH meter). That's fine. Further, the base may be added in a large excess to such an extent that the pH cannot be measured. However, it is preferable to add the base so that the pH does not exceed 5 in that fine α-alumina with little necking can be easily obtained.

The hydrolysis temperature is usually higher than the freezing temperature of the aqueous solution, preferably 0 ° C. or higher, and usually 100 ° C. or lower, but 60 ° C. or lower in that fine α-alumina with little necking can be easily obtained. Further, it is preferably carried out at 50 ° C. or lower, particularly 45 ° C. or lower.

After adding the base, the hydrolysis temperature may be maintained, for example, for 1 hour or more and usually 72 hours or less for sufficient hydrolysis.

By hydrolyzing the aluminum compound in an 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 hydrolysis product thus obtained is usually used as it is without being taken out from the reaction mixture after hydrolysis.

As the α-alumina precursor, those that become α-alumina via amorphous alumina, such as an aluminum hydrolysis product and an aluminum salt, are preferably used.

As the seed crystal particles, a metal compound is usually used, and specifically, metal oxide particles such as alumina, iron oxide, chromium oxide and the like are used. The metal oxide is preferably a corundum-type metal oxide whose crystal type is a corundum type. Examples of the corundum-type metal oxide include those having no crystal water such as α-alumina, α-iron oxide, α-chromium oxide, and the like. preferable. The seed crystal particles usually have a particle size of about 0.01 μm or more and 0.5 μm or less, preferably 0.05 μm or more. The BET specific surface area of the seed crystal particles is preferably about 12 m ² / g or more and 150 m ² / g or less, more preferably 15 m ² / g or more.

The amount of seed crystal particles used is 25 parts by mass or more and usually about 50 parts by mass or less per 100 parts by mass of the total amount of α-alumina precursor and seed crystal particles in terms of oxide.

Such a powder mixture may be obtained by mixing α-alumina precursor powder and seed crystal particles. The α-alumina precursor and the seed crystal particles may be mixed by dry mixing without using water. However, water may be added from an aqueous mixture in which the α-alumina precursor and seed crystal particles are dissolved or dispersed in water. It is easy to uniformly mix the α-alumina precursor and the seed crystal particles by removing the mixture to obtain a powder mixture containing the α-alumina precursor and the seed crystal particles, so-called wet mixing. preferable.

When mixing by wet mixing, the content of water in the aqueous mixture is usually 0.5 parts by mass or more, preferably 1 part by mass or more per 1 part by mass of the total amount of α-alumina precursor and seed crystal particles. It is 5 parts by mass or less, preferably 5 parts by mass or less.

When an aluminum hydrolysis product is used as the α-alumina precursor, water and an aluminum hydrolysis product are contained in the reaction mixture after the hydrolysis, so that this can be used as it is.

The seed crystal particles may be added after mixing water and the α-alumina precursor, or may be added in advance to water. Moreover, when obtaining an aluminum hydrolyzable substance, you may add beforehand to aluminum compound aqueous solution. The seed crystal particles may be added after being dispersed in water in advance.

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.

Alternatively, the water may be removed by a method of filtering off water by a normal filtration operation and then drying the filtration residue. The filtration temperature is usually 100 ° C. or lower. The filtration residue after filtration may be dried by air drying, or may be dried by heating. The drying temperature is usually 100 ° C. or lower. Drying may be performed in the atmosphere, may be performed in an inert gas such as nitrogen gas, or may be performed under reduced pressure.

Thus, by removing water from the aqueous mixture, the α-alumina precursor is deposited as it is or while reacting with water to obtain a powder mixture containing seed crystal particles.

In the production method of the present invention, such a powder mixture is fired. The powder mixture is usually 600 ° C. or higher, preferably 700 ° C. or higher in that the α-alumination rate of the fine α-alumina obtained is likely to be high, and is usually 1000 ° C. or lower in that the BET specific surface area tends to increase. Baking is preferably performed at 950 ° C. or lower. The firing time is usually 10 minutes or longer, preferably 30 minutes or longer in terms of the pregelatinization rate, and is usually 24 hours or shorter, preferably 10 hours or shorter.

Firing may be performed in the air, or may be performed in an inert gas atmosphere such as nitrogen gas or argon gas, or may be performed while maintaining the partial pressure of water vapor in the atmosphere. However, in the production method of the present invention, the firing is preferably performed in an atmosphere substantially free of an active gas such as a halogen gas or a hydrogen halide gas, for example, in the air or in an inert gas atmosphere.

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.

Thus, the desired fine α-alumina can be obtained. The fine α-alumina has a small particle size, a high α conversion rate and a large BET specific surface area. For example, the particle size is about 10 nm to 60 nm, Is 90% or more, preferably 95% or more, and the BET specific surface area is 15 m ² / g or more and 150 m ² / g or less.

The obtained fine α-alumina may be pulverized. In order to pulverize the fine α-alumina, 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 this Example.

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 ) × 100 (%) (1)
Calculated by
The BET specific surface area was determined by a nitrogen adsorption method using a specific surface area measuring device. 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 a 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.

Example 1
[Production of seed crystal slurry]
After 20 parts by mass of α-alumina particles (seed crystal particles) having a BET specific surface area of 16.0 m ² / g and a particle diameter of about 100 nm were added to and dispersed in 80 parts by mass of an aqueous nitric acid solution (pH = 4), alumina beads (diameter 2 mm) ) Wet-dispersed for 3 hours using a ball mill filled with 350 g to obtain a seed crystal slurry.

[Production of fine α-alumina]
Aluminum nitrate nonahydrate _{[Al (NO 3) 3 · 9H} 2 O ] (manufactured by Wako Pure Chemical Industries, special grade, powdered) 375.13G (1 mol) was dissolved in pure water, the volume 1L (1000 cm ³ ) To obtain an aqueous aluminum nitrate solution (1155 g). At room temperature (about 25 ° C.), 27.32 g of the seed crystal slurry obtained above (with an α-alumina particle content of 5.46 g) was added to 250 mL (250 cm ³ ) of this aqueous aluminum nitrate solution. The amount of seed crystal particles used is 30% by mass with respect to the total amount of aluminum nitrate and seed crystal particles in terms of oxide. Thereafter, 40 g of an aqueous ammonia solution (concentration: 25 mass%, manufactured by Wako Pure Chemical Industries, Ltd., special grade) was dropped at the same temperature with a micro rotary pump at an enemy acceleration of about 2 g / min to obtain an aqueous mixture. The pH of this aqueous mixture was 4.1, and it was in the form of a slurry containing precipitates (aluminum hydrolysis products). The aqueous mixture was allowed to stand at room temperature for one day, and then dried in a vacuum dryer at 20 ° C., and the residue was crushed in a mortar to obtain a powder mixture.

The obtained powder mixture was put in an alumina crucible in the air and fired in a box-type electric furnace in the air at 940 ° C. for 3 hours to obtain fine α-alumina. The α-alumina conversion rate of this fine α-alumina was 98%, the BET specific surface area was 15.8 m ² / g, the average primary particle diameter was 50 nm, and the neck ratio was 0%.

Comparative Example 1
[Production of fine α-alumina]
A powder mixture was obtained in the same manner as in Example 1 except that the amount of seed crystal slurry used was 15.94 g. The amount of seed crystal particles used is 10% by mass with respect to the total amount of aluminum nitrate and seed crystal particles in terms of oxide.

The obtained powder mixture was put in an alumina crucible in the air and fired in a box-type electric furnace in the air at 950 ° C. for 3 hours to obtain fine α-alumina. The α-alumina conversion rate of this fine α-alumina was 98%, the BET specific surface area was 15.0 m ² / g, the average primary particle diameter was 68 nm, and the neck ratio was 0%.

Comparative Example 2
A powder mixture was obtained in the same manner as in Example 1 except that the amount of the seed crystal slurry was changed to 3.4 g. The amount of seed crystal particles used is 5% by mass with respect to the total amount of aluminum nitrate and seed crystal particles in terms of oxide.

The obtained powder mixture was put in an alumina crucible in the air, and fired at 960 ° C. for 3 hours in the air in a box-type electric furnace to obtain fine α-alumina. The α-alumina conversion rate of this fine α-alumina was 98%, the BBET specific surface area was 14.7 m ² / g, the average primary particle diameter was 112 nm, and the neck ratio was 57%.

As described above, when the amount of seed crystal particles used is 5% by mass with respect to the total amount of aluminum nitrate and seed crystal particles as shown in Comparative Example 2, the average primary particle size is as large as 112 nm, and the neck ratio as large as 57% is obtained. Show. As shown as Comparative Example 1, when the amount of seed crystal particles used is 10% by mass, the neck ratio is 0%, but the average primary particle diameter is still a relatively large value of 68 nm. As shown in Example 1, fine α-alumina with a small particle diameter of an average primary particle diameter of 50 nm can be obtained by using the seed crystal particles in an amount of 25% by mass or more.

Claims (5)

A powder mixture containing an α-alumina precursor and seed crystal particles, wherein the content of the seed crystal particles is 25 parts by mass or more per 100 parts by mass of the total amount of the α-alumina precursor and seed crystal particles in terms of oxide is nitrogen gas and argon A method for producing fine α-alumina , comprising firing in an atmosphere of an inert gas selected from the group consisting of gases or in the air . The production method according to claim 1, wherein the α-alumina precursor is an aluminum hydrolysis product. The production method according to claim 1, wherein the seed crystal particles are corundum type metal oxide particles. The production method according to claim 1, wherein water is removed from an aqueous mixture in which α-alumina precursor and seed crystal particles are dissolved or dispersed in water to obtain the powder mixture. The manufacturing method according to claim 1, wherein baking is performed at a temperature of 600 ° C. or higher and 1000 ° C. or lower.