JP4534524B2 - Method for producing fine α-alumina - Google Patents

Description

The present invention relates to a method for producing fine α-alumina.

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. As the production method thereof, Non-Patent Document 1 [Journal of Mineral Society, Vol. 19, No. 1, page 21 to page 41] and Patent Document 1 (Japanese Patent Laid-Open No. Sho 62-128918) disclose alumina hydrate. A method of firing as it is (Non-patent Document 1) and a method of firing alumina hydrate in the presence of seed crystals (Patent Document 1) are disclosed.

However, the conventional method for firing alumina hydrate cannot produce fine α-alumina having a high BET specific surface area with a high α conversion rate.

JP-A-62-128918 Journal of the Mineralogical Society, Vol. 19, No. 1, pp. 21-41

Therefore, the present inventor has intensively studied to develop a method capable of producing a fine α-alumina having a high α conversion rate and a large BET specific surface area. As a result, if the aluminium salt is fired in the presence of seed crystals, Fine α-alumina having a high α conversion rate was obtained, and the fine α-alumina was found to have a sufficiently large BET specific surface area, leading to the present invention.

That is, the present invention provides a method for producing fine α-alumina, which comprises firing an aluminum salt in the presence of seed crystals.

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

The aluminum salt used in the production method of the present invention 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. May be. 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.

Examples of seed crystals include metal oxides such as α-alumina, diaspore, iron oxide, chromium oxide, and titanium oxide. These seed crystals are used alone or in combination of two or more. Particle size of such seed crystals is small, it is usually preferably are used is of the order or 0.5μm or less 0.01 [mu] m, BET specific surface area is preferably 12m ² / g or more, the degree 150 meters ² / g or less, more preferably Is 15 m ² / g or more.

The amount of the seed crystal 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 oxide of the metal component, in that a fine α-alumina having a high α conversion rate can be easily obtained. 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.

In order to fire the aluminum salt in the presence of the seed crystal, for example, the aluminum salt may be mixed with the seed crystal and then fired. In order to mix the aluminum salt with the seed crystal, for example, the aluminum salt is mixed with a solvent to form a solution or slurry, the seed crystal is added, and then the solvent is distilled off. By distilling off the solvent, the aluminum salt in the solvent is precipitated while the seed crystals are uniformly dispersed. By firing the precipitated aluminum salt in a state where the seed crystals are uniformly dispersed, the desired fine α-alumina can be obtained. The seed crystal may be added in the form of powder or may be added in a state dispersed in a solvent.

Also, seed crystals may be added to the aluminum salt and mixed with stirring. By firing the mixture after mixing, the desired fine α-alumina can be obtained. For the mixing, for example, a mixer such as a vertical granulator or a Henschel mixer can be used. The seed crystal may be added in a powder state or may be added in a state dispersed in a solvent.

Firing is usually performed at 600 ° C. or higher, preferably 700 ° C. or higher, usually 1000 ° C. or lower, preferably 950 ° C. or lower, more preferably 890 ° C. or lower. Beyond 1000 ° C, BE
The T specific surface area tends not to be large. If it is less than 600 ° C., the pregelatinization rate tends to be low.

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 is, for example, a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a far-infrared furnace, a microwave heating furnace,
A normal firing furnace such as a shaft furnace, a reflection furnace, a rotary furnace, or a roller hearth furnace can be used. 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 a time sufficient for the aluminum salt to be α-ized to obtain a high α-granulation fine α-alumina, and varies depending on the type, amount, type of firing furnace, firing temperature, and firing atmosphere of the aluminum salt used. For example, it is about 10 minutes or more and 24 hours or less.

The fine α-alumina thus obtained has a particle diameter of about 0.05 μm or more and 1 μm or less, a high α conversion rate and a large BET specific surface area, for example, an α conversion rate of 90% or more, preferably 95% or more, The BET specific surface area is 8 m ² / g or more, preferably 13 m ² / g or more, more preferably 15 m ² / g or more, and usually about 30 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 to improve the head cleaning property and body wearability by adding it to the coating layer of the coating type magnetic media in the same manner as normal α-alumina powder as it is. Can do. 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 a transmission electron micrograph of fine α-alumina.

Example 1
[Preparation of seed crystal slurry]
After adding 20 parts by mass of alpha alumina particles having a BET specific surface area of 16.0 m ² / g (particle size is about 0.1 μm) to 80 parts by mass of aqueous nitric acid (pH = 4), alumina beads (diameter 2 mm) are dispersed. Was wet-classified using a ball mill filled with 3 to obtain a seed crystal slurry.

[Production of fine α-alumina]
Aluminum nitrate nonahydrate _{[Al (NO 3) 3 · 9H} 2 O ] (Wako Pure Chemical Industries, Ltd., guaranteed reagent) 375.13G (1 mol) was dissolved in pure water, nitric acid volume 1 dm ³ (1000 cm ³⁾ An aqueous aluminum solution was obtained. To 100 cm ^{3 of} this aluminum nitrate aqueous solution, 2.83 g of the seed crystal slurry obtained above (0.566 g of α-alumina particles) was added, and water was distilled off under reduced pressure by a rotary evaporator in a 75 ° C. warm bath to obtain aluminum nitrate. Of powder was obtained. This powder contains 10 parts by mass of seed crystals (α-alumina) per 100 parts by mass in terms of oxide of the metal component.

2.8 g of the powder obtained above is put in an alumina crucible, put in a box-type electric furnace at room temperature (about 25 ° C.), heated to 850 ° C. at 300 ° C./hour, and held at that temperature for 3 hours. To obtain fine α-alumina (Example 1). This fine α-alumina powder had an α conversion of 95%, a BET specific surface area of 15.9 m ² / g, and an average primary particle size of 96 nm.

Example 2
A fine α-alumina was obtained by firing in the same manner as in Example 1 except that the amount of aluminum nitrate powder obtained in Example 1 was 3.3 g and the firing temperature was 890 ° C. Table 1 shows the gelatinization rate and BET specific surface area of the fine α-alumina.

Example 3
A fine α-alumina was obtained by firing in the same manner as in Example 1 except that the amount of aluminum nitrate powder obtained in Example 1 was 5.0 g and the firing temperature was 925 ° C. Table 1 shows the gelatinization rate and BET specific surface area of the fine α-alumina.

Table 1
━━━━━━━━━━━━━━━━━
Example α conversion rate BET specific surface area
(%) (M ² / g)
─────────────────
Example 1 98 15.9
Example 2 97 13.3
Example 3 99 10.1
━━━━━━━━━━━━━━━━━

Example 4
100 g of aluminum nitrate nonahydrate [Al (NO ₃ ) ₃ .9H ₂ O] (special grade, manufactured by Wako Pure Chemical Industries, Ltd.) and α-alumina powder having a BET specific surface area of 16.0 m ² / g (particle size is about 0.00). 1 μm) 1.5 g was added and mixed in a mortar. The mixture after mixing contains 10 parts by mass of seed crystals (α-alumina) per 100 parts by mass in terms of oxide of the metal component.

4.5 g of this mixture is placed in an alumina crucible, placed in a box-type electric furnace at room temperature (about 25 ° C.), heated to 870 ° C. at 300 ° C./hour, and calcined by maintaining the same temperature for 3 hours. Thus, fine α-alumina was obtained (Example 4). The α-alumina conversion rate of this fine α-alumina was 96%, the BET specific surface area was 17.4 m ² / g, and the average primary particle size was 110 nm.

Example 5
A fine α-alumina was obtained in the same manner as in Example 4 except that the amount of the mixture obtained in Example 4 was 3.9 g and the firing temperature was 850 ° C. Table 2 shows the gelatinization rate and BET specific surface area of the fine α-alumina.

Table 2
━━━━━━━━━━━━━━━━━
Example α conversion rate BET specific surface area
(%) (M ² / g)
─────────────────
Example 4 96 17.4
Example 5 97 18.9
━━━━━━━━━━━━━━━━━

Comparative Example 1
Aluminum nitrate nonahydrate _{[Al (NO 3) 3 · 9H} 2 O ] (manufactured by Wako Pure Chemical Industries, special grade, powdered) in without adding a seed crystal, put into an alumina crucible, room temperature (approximately 25 ° C.) Then, it was put into a box-type electric furnace, heated to 870 ° C. at 300 ° C./hour, and calcined by maintaining the same temperature for 3 hours to obtain alumina powder. The alumina powder had a BET specific surface area of 111 m ² / g, but no peak of the alumina α phase was observed in the X-ray diffraction spectrum, and the α conversion was 0%.

Comparative Example 2
Alumina powder was obtained in the same manner as in Comparative Example 1 except that the amount of aluminum nitrate nonahydrate used was 7.5 g and the firing temperature was 900 ° C. Table 3 shows the alpha conversion rate and BET specific surface area of the alumina powder.

Comparative Example 3
Alumina powder was obtained in the same manner as in Comparative Example 1 except that the amount of aluminum nitrate nonahydrate used was 8.0 g and the firing temperature was 950 ° C. Table 3 shows the alpha conversion rate and BET specific surface area of the alumina powder.

Comparative Example 4
Alumina powder was obtained in the same manner as in Comparative Example 1 except that the amount of aluminum nitrate nonahydrate used was 8.1 g and the firing temperature was 970 ° C. Table 3 shows the alpha conversion rate and BET specific surface area of the alumina powder.

Table 3
━━━━━━━━━━━━━━━━━
Example α conversion rate BET specific surface area
(%) (M ² / g)
─────────────────
Comparative Example 1 0 111
Comparative Example 2 0 107
Comparative Example 3 91 41
Comparative Example 4 98 9.9
━━━━━━━━━━━━━━━━━

Claims (7)

A method for producing fine α-alumina, comprising mixing an aluminum salt and a seed crystal to obtain a mixture, and then firing the mixture in an inert gas or air selected from the group consisting of nitrogen gas and argon gas . The production method according to claim 1, wherein the aluminum salt is an aluminum inorganic salt. The production method according to claim 2, wherein the aluminum inorganic salt is aluminum nitrate. The manufacturing method in any one of Claims 1-3 baked at 600 degreeC or more. The production method according to claim 1, wherein the seed crystal is α-alumina, diaspore, iron oxide, chromium oxide, or titanium oxide. The production method according to claim 1, wherein the seed crystal has a BET specific surface area of 12 m ² / g or more. The production method according to claim 1, wherein the amount of the seed crystal 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 oxide of the metal component.