JP4572576B2 - 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 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 [Key Engineering Materials, Vol. 53-55 (1991), 462-468] describes a method for producing a fine α-alumina having a high α conversion ratio and a large BET specific surface area. A method is disclosed in which water is removed from an aqueous mixture containing crystal grains and having a nitrate ion (NO ₃ ⁻ ) content of 2.7 moles per mole of aluminum, and the resulting powder mixture is fired.

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

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

Therefore, the present inventor has intensively studied to develop a method for producing a fine α-alumina having a small Beck specific surface area, a high α conversion rate, and a large BET specific surface area. When water was removed from an aqueous mixture containing 3.3 mol of nitrate ions and the resulting powder mixture was fired, it was found that fine α-alumina with little necking was obtained, and the present invention was achieved.

That is, the present invention provides a powder obtained by removing water from an aqueous mixture containing an α-alumina precursor and seed crystal particles and containing 2.8 mol to 3.3 mol of nitrate ions per mol of metal in terms of metal. The present invention provides a method for producing fine α-alumina characterized by firing a mixture.

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.

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

The α-alumina precursor contained in the aqueous 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 reacting a water-soluble aluminum compound with water, and examples of the water-soluble aluminum compound include aluminum inorganic salts, aluminum organic salts, and aluminum similar to those described above. An alkoxide etc. are mentioned.

As such an aluminum compound, an aluminum salt, an aluminum inorganic salt, particularly an aluminum nitrate is preferable.

Such an aluminum compound is preferably present dissolved in an aqueous mixture, but may be present as an insoluble matter. When it is an insoluble material, it may be dispersed as fine particles. For example, it is preferably dispersed in a sol form or a gel form.

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 the seed crystal particles used is about 5 to 50 parts by mass, preferably about 10 to 30 parts by mass, in terms of oxide, per 100 parts by mass of the total amount of α-alumina precursor and seed crystal particles. is there.

The aqueous mixture used in the present invention is a mixture containing such α-alumina precursor and seed crystal particles, and is a mixture of these and water. The water content in the aqueous mixture is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and usually 10 parts by mass or less, preferably 5 parts per 1 part by mass of the total amount of α-alumina precursor and seed crystal particles. It is below mass parts.

The aqueous mixture contains nitrate ions. The nitrate ions may be generated by dissolving the α-alumina precursor in water when a compound containing nitrate ions as the α-alumina precursor, such as aluminum nitrate, is used. Also, non-metal nitrates such as ammonium nitrate, urea nitrate, hydroxylammonium nitrate, propyl nitrate, nitrate ester, ethanol nitrate, ethyl nitrate, ethylene nitrate, etc. may be added and dissolved in water. Good.

The content of nitrate ion is 2.8 mol or more and 3.3 mol or less per 1 mol of metal in terms of metal contained in the aqueous mixture in that fine α-alumina with little necking is obtained. Here, the aluminum content includes the aluminum content contained in the α-alumina precursor, as well as the aluminum content contained in the seed crystal particles when α-aluminum particles are used as the seed crystal particles. This is the total amount of aluminum in the body and aluminum in the seed crystal particles.

In the production method of the present invention, water is removed from such an aqueous mixture. 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. When an α-alumina precursor or a nonmetallic nitrate is used, the α-alumina precursor may precipitate from the nonmetallic nitrate and the reaction product depending on the type.

In the production method of the present invention, the powder mixture thus obtained is fired. The firing temperature is usually 600 ° C. or higher, preferably 700 ° C. or higher in that the α conversion rate tends to be high, and is usually 1000 ° C. or lower in that necking is reduced or the BET specific surface area is likely to increase. Preferably it is 950 degrees C or less. 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. Moreover, it may be performed while keeping the partial pressure of water vapor 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 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 15 m ² / g or more and 50 m ² / g or less, preferably 17 m ² / g or more and 40 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 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 ) × 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.

Example 1
[Production of seed crystal slurry]
After the α-alumina particles (seed particles) 20 parts by weight of the particle diameter of about 0.1μm was added to 80 parts by weight aqueous nitric acid solution (pH = 4) dispersed in a BET specific surface area of 16.0 m ² / g, alumina beads ( Using a ball mill filled with 350 g (diameter 2 mm), it was wet dispersed over 3 hours 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.), 2.83 g of the seed crystal slurry obtained above (alpha alumina particle content is 0.57 g) is added to 100 mL (100 cm ³ ) of this aluminum nitrate aqueous solution, and 2.64 g of ammonium nitrate is further added. An aqueous mixture was obtained. This aqueous mixture contains 10% by mass of seed crystal particles (α-alumina particles) in terms of oxide of the metal component, and 3.0 moles per mole of aluminum nitrate and seed crystal particles in terms of aluminum. nitrate ion (NO ₃ ^-) are included.

Thereafter, this aqueous mixture was heated to 75 ° C. by a rotary evaporator and dried under reduced pressure with stirring to obtain a powder mixture. The hydrolyzed precipitate was crushed with a mortar, placed in an alumina crucible, and fired in the box-type electric furnace in the atmosphere at 890 ° C. for 3 hours to obtain fine α-alumina. The α ratio of fine α-alumina is 97%, BET specific surface area of 14.1 m ² / g, average primary particle size was 70 nm. When the fine α-alumina was observed with a transmission electron microscope (TEM), there was little necking between the particles.

Example 2
[Production of fine α-alumina]
An aqueous mixture was obtained in the same manner as in Example 1 except that the amount of ammonium nitrate used was changed to 4.16 g. This aqueous mixture contains 10% by mass of seed crystal particles (α-alumina) in terms of oxide of the metal component, and 3.2 moles per mole of the total amount of aluminum nitrate and seed crystal particles in terms of aluminum. Contains nitrate ions.

Thereafter, a powder mixture was obtained in the same manner as in Example 1, and fine α-alumina was obtained in the same manner as in Example 1 except that the firing temperature was 930 ° C. The α ratio of fine α-alumina is 96%, BET specific surface area of 13.8 m ² / g, average primary particle size was 84 nm. When this fine α-alumina was observed by TEM, there was little necking between the particles.

Comparative Example 1
[Production of fine α-alumina]
An aqueous mixture was obtained in the same manner as in Example 1 except that ammonium nitrate was not added. This aqueous mixture contains 10% by mass of seed crystal particles (α-alumina particles) in terms of metal component oxide, and 2.7 moles per mole of aluminum nitrate and seed crystal particles in terms of aluminum. Nitrate ions are included, and these nitrate ions are derived from aluminum nitrate.

Thereafter, a powder mixture was obtained in the same manner as in Example 1, and fine α-alumina was obtained in the same manner as in Example 1 except that the firing temperature was 850 ° C. The α-alumina conversion rate of this fine α-alumina was 95%, the BET specific surface area was 15.9 m ² / g, and the average primary particle size was 96 nm. When this fine α-alumina was observed with TEM, many neckings were observed between the particles.

Comparative Example 2
[Production of fine α-alumina]
An aqueous mixture was obtained in the same manner as in Example 1 except that the amount of ammonium nitrate used was 6.24 g. This aqueous mixture contains 10% by mass of seed crystal particles (α-alumina) in terms of oxide of the metal component, and 3.4 moles per mole of the total amount of aluminum nitrate and seed crystal particles in terms of aluminum. Contains nitrate ions.

Thereafter, a powder mixture was obtained in the same manner as in Example 1, and fine α-alumina was obtained in the same manner as in Example 1 except that the firing temperature was 930 ° C. The α-alumina conversion rate of this fine α-alumina was 97%, the BET specific surface area was 14.0 m ² / g, and the average primary particle size was 115 nm. When this fine α-alumina was observed with TEM, many neckings were observed between the particles.

Claims (5)

Water is removed from an aqueous mixture containing aluminum nitrate and seed crystal particles and containing 2.8 mol to 3.3 mol of nitrate ions per mol of metal component in terms of metal, and the obtained powder mixture is fired. A method for producing fine α-alumina. The production method according to claim 1, wherein the seed crystal particles are corundum-type metal oxide particles. 2. The production method according to claim 1, wherein the amount of seed crystal particles used is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total amount of aluminum nitrate and seed crystal particles in terms of oxide. The production method according to claim 1, wherein the content of water in the aqueous mixture is 0.5 parts by mass or more and 10 parts by mass or less per 1 part by mass of the total amount of aluminum nitrate and seed crystal particles. The manufacturing method according to claim 1, wherein baking is performed at 600 ° C. or more and 1000 ° C. or less.