JP3975513B2 - Continuous production of alpha alumina - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a continuous process for the production of alpha alumina. More specifically, the present invention relates to a continuous production method of α-alumina having a spherical alumina particle and a sharp particle size distribution.
[0002]
[Prior art]
α-alumina is molded, sintered and used as various mechanical parts and electrical parts because of its excellent chemical stability, excellent mechanical strength, and physical properties. In these applications, alumina powder having a spherical shape and a sharp particle size distribution is required because it is inexpensive and requires dimensional stability and high sintering density.
[0003]
As a method for producing alumina by firing aluminum hydroxide obtained by the Bayer method, various production methods have been proposed for the purpose of controlling characteristics such as particle size, particle size distribution, and BET specific surface area. For example, (1) a method of adding and firing at least one of fluorine, chlorine and boron as a mineralizer, (2) a method of using a silica-based compound such as cinnabar sand or a chlorine-based compound as a soda removing agent, (3) A method of using a combination of a mineralizer and a soda remover, and further (4) a method of adding alumina fine particles to aluminum hydroxide at the time of firing, and firing by combining this with the above method ( (Japanese Patent Publication No. 6-104570, Japanese Patent Laid-Open No. 7-41318).
[0004]
However, when a halogen compound such as a chlorine compound and / or a fluorine compound is used as a mineralizer, the halogen remaining in α-alumina is proportional to the amount of the halogen compound added as a mineralizer to the raw material. The amount of the system compound increases, and the aggregates generated during firing increase. As a countermeasure, there has been proposed a method of dehalogenating the composition after firing in a halogen-containing gas atmosphere of 0.1% by volume or more (Japanese Patent Laid-Open No. 7-206432). According to this method, α-alumina having a low halogen content and a sharp particle size distribution can be obtained, but it has a problem that a new dehalogenation treatment is necessary. In addition, when a silica compound as a soda removing agent is added, silica contamination increases in proportion to the fluorine compound added to the raw material.
[0005]
[Problems to be solved by the invention]
In view of such circumstances, the present inventor used inexpensive aluminum hydroxide obtained by the Bayer method, and continuously baked it, and as a result of earnest examination to obtain an α-alumina powder having a spherical shape and a sharp particle size distribution Using a specific firing device, alumina having specific physical properties is added to aluminum hydroxide as a raw material, mixed and fired, and the abundance of fluorine compounds contained in the alumina after firing is within a specific range. As can be seen, when the addition of a specific amount of a fluorine-based compound and the amount of collected powder to be recycled are prepared and calcined, the above-mentioned target α-alumina can be continuously produced. The invention has been completed.
[0006]
[Means for Solving the Problems]
That is, the present invention includes an aluminum hydroxide supply line (1), a firing furnace (2) for firing the supplied aluminum hydroxide, a line (3) for discharging the fired alumina out of the system, and a firing furnace (2). ) The exhaust gas line (4) for introducing the gas discharged from the dust collector (5), the dust collector (5) for collecting powder contained in the exhaust gas, and collecting the exhaust gas after collecting the powder In a method of continuously producing α- alumina using a firing apparatus comprising a line (6) for discharging from the apparatus (5) and a line (7) for discharging collected powder out of the system, A line (8) for circulating and supplying the powder collected by the dust device (5) to the firing furnace (2) is provided, and at least a part of the powder collected by the dust collector (5) is provided in the firing furnace (2). While circulating into the baking furnace (2), the aluminum hydroxide obtained by the buyer method and (110) plane {2θ = 37.7 °}, (300) plane {2θ = 68.2 °}, (116) plane {2θ = 57.5 ° measured by X-ray diffraction method with a particle diameter of 15 μm to 150 μm } The line strength of
(I ₍₁₁₀₎ + I ₍₃₀₀₎ ) / (2 × I ₍₁₁₆₎ ) Equation 1
Alumina assignment with values obtained is 0.3 to 1.0 in (referred to as alumina A), 5 to 150% by weight relative to the aqueous aluminum oxide (Al ₂ O ₃ in terms) (Al ₂ O ₃ in terms of ) And aluminum hydroxide (Al ₂ O ₃ equivalent) and the total amount of alumina A, fluorine compound is added and prepared in the range of 20 to 200 ppm (F equivalent), and discharged from the line (3) after firing. It is another object of the present invention to provide a continuous production method of α-alumina, characterized in that it is fired so that the fluorine-based compound content in the alumina becomes 1 to 200 ppm (F conversion).
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a block diagram of an aluminum hydroxide continuous firing apparatus used in the method of the present invention, wherein (1) is an aluminum hydroxide supply line, (2) is a firing furnace, and (3) is alumina after firing. (4) is an exhaust gas line for introducing gas discharged from the firing furnace (2) into the dust collector (5), and (5) is for collecting powder contained in the exhaust gas. (6) is a line for discharging exhaust gas after collecting powder from the dust collector (5), (7) is a line for discharging collected powder out of the system, (8) is dust collecting The line which circulates and supplies the powder collected by the apparatus (5) to a baking furnace (2) is shown.
[0008]
In the practice of the present invention, in the firing furnace (2), the aluminum hydroxide obtained by the Bayer method and the average particle size is about 15 μm to about 150 μm and measured by the X-ray diffraction method (110) plane. The linear intensity of {2θ = 37.7 °}, (300) plane {2θ = 68.2 °}, (116) plane {2θ = 57.5 °}
(I ₍₁₁₀₎ + I ₍₃₀₀₎ ) / (2 × I ₍₁₁₆₎ ) Equation 1
Substituted in the alumina A value is 0.3 to 1.0 as determined, 5-150 wt% relative to the aqueous aluminum oxide (Al ₂ O ₃ conversion) (Al ₂ O ₃ basis) and hydroxide A fluorine-based compound is added in a range of 20 to 200 ppm (F conversion) with respect to the total amount of aluminum (Al ₂ O ₃ conversion) and alumina A and fired. The exhaust gas from the firing furnace (2) is introduced into the dust collector (5) through the exhaust gas line (4), the alumina powder in the exhaust gas is collected, and at least a part of the collected powder is collected in the line (8 ) Is circulated and supplied to the firing furnace (2) for firing.
[0009]
In the method of the present invention, the product alumina after firing is taken out from the system through the line (3) from the firing furnace (2), but the fluorine compound content in the product alumina taken out from the system from the line (3) Is 1 to 200 ppm (F conversion). Product alumina containing such a range of fluorine compounds can be adjusted by the amount of fluorine compound added to the firing furnace (2) and the amount of powder circulated from the line (8) to the firing furnace (2). it can.
[0010]
As alumina A added to aluminum hydroxide at the time of firing, α-alumina is used. Alumina A is an X-ray diffraction method.
(110) plane {2θ = 37.7 °}, in Formula 1, X-ray intensity is above (300) plane {2θ = 68.2 °}, ( 116) plane {2θ = 57.5 °}, 0 The average particle size (average secondary particle size) is about 15 μm to about 150 μm, preferably about 30 μm to about 70 μm. used.
[0011]
The amount added is about 5 to about 150% by weight, preferably about 10% to about 100% by weight, based on aluminum hydroxide (in terms of Al ₂ O ₃ ). When the amount of alumina A added is less than the above range, the particle size distribution of the resulting alumina is not sharp. If alumina A does not satisfy the range described above In Formula 1, i.e., as was the case the value according to the formula 1 is less than about 0.3 (particle shape, flaky) was added alumina A predetermined amount However, α-alumina having a sharp particle size distribution cannot be obtained. Further, even when the value according to the above formula 1 exceeds about 1.0, α-alumina having a sharp particle size distribution cannot be obtained.
[0012]
The alumina A may be any alumina having an average particle (secondary) diameter of about 15 μm to about 150 μm and a value according to Formula 1 of about 0.3 to about 1.0, and the production method is not particularly limited. However, it can be obtained, for example, by baking aluminum hydroxide C-12 (manufactured by Sumitomo Chemical Co., Ltd.) in a batch static oven at about 1250 ° C. for 2 hours.
[0013]
In the present invention, the fluorine compound to be applied is not particularly limited, but usually at least one selected from aluminum fluoride, hydrogen fluoride, ammonium fluoride, sodium fluoride, magnesium fluoride and calcium fluoride. Use seeds.
[0014]
Although it does not restrict | limit especially as a dust collector applied to this invention, For example, a cyclone, an electric dust collector, a bag filter, a scrubber etc. are mentioned. Moreover, as a kiln, a rotary kiln, SP rotary kiln, NSP rotary kiln, and a fluidized bed furnace can be used. In order to increase the thermal efficiency, it is recommended to use an internal combustion furnace in which the combustion gas as the heat medium and the alumina powder are countercurrent.
[0015]
The firing conditions of aluminum hydroxide are not unambiguous depending on the type of firing furnace used, the amount of firing, the required degree of firing of aluminum hydroxide, etc., but usually the firing temperature is about 1100 ° C. to about 1500 ° C. in the firing furnace. The alumina residence time is about 1 hour to about 10 hours.
[0016]
Further, within a range that does not impair the effect of the method of the present invention, when the silica-based compound as the soda removal agent is fired, it is in the range of about 1 to about 20% by weight with respect to aluminum hydroxide (as Al ₂ O ₃ ). It can also be added and used. Other additives can be used in combination.
[0017]
【The invention's effect】
As described above in detail, in the method of the present invention, inexpensive aluminum hydroxide obtained by the Bayer method is used, and alumina having specific physical properties is added thereto as a firing aid, and collected by an agent dust collector. By adjusting the addition amount of at least a part of the powder and the fluorine compound to the firing furnace, the continuous production method of alumina that makes the content of the fluorine compound contained in the fired product a specific range is inexpensive. In addition, it has been found that alumina having a spherical shape and a sharp particle size distribution (usually D90 / D10 is less than 4.0, preferably less than 3.5) can be obtained, and supplies raw materials for various mechanical parts and electrical parts. In terms of its industrial value, its industrial value is enormous.
[0018]
【Example】
EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples. In addition, the measurement shown in an Example employ | adopted the following method.
[0019]
(1) Value of alumina A: (110) by powder X-ray diffraction method (CuKα, tube voltage 40 kV, tube current 20 mA, scanning speed 2 ° / min, divergence slit 1 °, scattering slit 1 °, light receiving slit 0.6 mm) ) Surface {2θ = 37.7 °}, (300) surface {2θ = 68.2 °}, and (116) surface {2θ = 57.5 °} are measured and assigned to Equation 1. .
(I ₍₁₁₀₎ + I ₍₃₀₀₎ ) / (2 × I ₍₁₁₆₎ ) Equation 1
[0020]
(2) BET specific surface area: Measured by the BET method by nitrogen adsorption.
[0021]
(3) Composition analysis Fluorine (F): Measured by a steam distillation-ion electrode method.
Sodium oxide (Na ₂ O): Conforms to JIS H1901.
Silicon dioxide (SiO ₂ ): Conforms to JIS H1901.
[0022]
(4) Particle size distribution: Measured using Microtrac HRA X-100.
[0023]
(5) Grinding test method 1: 3 kg of alumina balls having a diameter of 15 mm and 400 g of sample α-alumina were placed in a 3.3 L alumina pot and treated at a rotational speed of 80 rpm for 12 hours.
Method 2: 3 kg of alumina balls with a diameter of 15 mm in a 3.3 L alumina pot, 400 g of sample α-alumina, 8 g of silicon dioxide (manufactured by Wako Pure Chemical), 7 g of magnesium hydroxide (manufactured by Wako Reagent), 2 g of calcium carbonate (manufactured by Wako Reagent) The mixture was crushed at a rotation speed of 80 rpm.
[0024]
(6) Molding density: Measured by the mercury Archimedes method.
[0025]
(7) Sintering density: Measured by the underwater Archimedes method.
[0026]
Example 1
Aluminum hydroxide C-12 (center particle size 50 μm, Na ₂ O 0.2%, F 20 ppm, manufactured by Sumitomo Chemical Co., Ltd.) 6950 g obtained by the Bayer method, average particle size 50 μm, value in the above formula 1 Is added to and mixed with 455 g of alumina (trade name: Alumina A-26, manufactured by Sumitomo Chemical Co., Ltd.) and 1.1 g of aluminum fluoride (manufactured by Wako Pure Chemical Industries). (Inner diameter 7 cm, length 140 cm, 1300 ° C. uniform temperature zone 60 cm, inclination angle 45 °, rotation speed 2 rpm, glass fiber filter is installed on the upper part of the firing furnace for recovery of alumina, and the recovered alumina is removed from the filter by a vibrator. After the removal, it was returned to the kiln) and continuously fed at a feed rate of 100 g / h. The residence time of alumina in the firing furnace was 6 hours.
The BET specific surface area of the α-alumina obtained after firing was 0.9 m ² / g, and the fluorine content was 170 ppm. The center particle diameter of the alumina pulverized by Method 1 was 1.6 μm, and D90 / D10 was 3.0. The alumina pulverized by Method 2 for 9 hours was CIP molded at a molding pressure of 300 kg / cm ² and then sintered at 1650 ° C. for 2 hours. The mean particle diameter of the milled alumina 2.2 .mu.m, D90 / D10 was 3.1, the molding density of 2.12 g / cm ^3, the sintered density was 3.84 g / cm ^3.
[0027]
Example 2
Example 1 Example 1 except that 3830 g of aluminum hydroxide C-12, 2500 g of alumina A-26 having an average particle diameter of 50 μm and an index of 0.4 were mixed with 1.1 g of aluminum fluoride (manufactured by Wako Pure Chemical Industries). The same operation was performed. The α-alumina obtained had a BET specific surface area of 2.1 m ² / g and a fluorine content of 180 ppm. The center particle diameter of the alumina pulverized by Method 1 was 1.0 μm, and D90 / D10 was 3.5.
[0028]
Example 3
In Example 1, the same operation as in Example 1 was performed, except that the aluminum fluoride was changed to 0.1 g. The calcined α-alumina obtained had a BET specific surface area of 2.3 m ² / g and a fluorine content of 25 ppm. The center particle diameter of the alumina pulverized by Method 1 was 1.0 μm, and D90 / D10 was 3.5.
[0029]
Example 4
In Example 1, 500 g of cinnabar sand having a particle diameter of about 1 mm was newly mixed, and after calcination, the same operation as in Example 1 was performed except that cinnabar sand was sieved from alumina with a sieve having a mesh size of 149 μm. The obtained calcined α-alumina had a BET specific surface area of 0.9 m ² / g, a fluorine content of 165 ppm, Na ₂ O 0.06% and SiO ₂ 0.04%. The center particle diameter of the alumina pulverized by Method 1 was 1.7 μm, and D90 / D10 was 3.0.
[0030]
Comparative Example 1
In Example 1, the same operation as in Example 1 was performed except that α-alumina A-26 having an average particle diameter of 50 μm was not mixed. The calcined α-alumina obtained had a BET specific surface area of 0.5 m ² / g and a fluorine content of 190 ppm. The center particle diameter of the alumina pulverized by Method 1 was 2.3 μm, and D90 / D10 was 4.8.
[0031]
Comparative Example 2
In Example 1, instead of alumina A-26, alumina having an average particle size of 50 μm and a value of 0.2 in the above formula 1 (calcined with aluminum hydroxide C-12 at 500 ° C., and then added with hydrogen fluoride) The same operation as in Example 1 was performed except that 1% by weight of acid in terms of fluorine was added per Al ₂ O ₃ and alumina obtained by placing in an alumina crucible and firing at 1300 ° C. for 2 hours was used. The calcined α-alumina obtained had a BET specific surface area of 1.1 m ² / g and a fluorine content of 180 ppm. The center particle diameter of the alumina pulverized by Method 1 was 1.6 μm, and D90 / D10 was 4.3. The alumina pulverized by Method 2 for 9 hours was CIP molded at a molding pressure of 300 kg / cm ² and then sintered at 1650 ° C. for 2 hours. The mean particle diameter of the milled alumina 2.2 .mu.m, the D90 / D10 4.7, molded density of 2.08 g / cm ^3, the sintered density was 3.79 g / cm ^3.
[0032]
Comparative Example 3
In Example 1, the mixed powder was put into a chamotte container instead of being supplied to a rotary small firing furnace, and the same operation as in Example 1 was performed except that it was fired at 1300 ° C. for 6 hours in a stationary electric furnace. went. The calcined α-alumina obtained had a BET specific surface area of 4.4 m ² / g and a fluorine content of 5 ppm. The center particle diameter of the alumina pulverized by Method 1 was 0.8 μm, and D90 / D10 was 6.8.
[Brief description of the drawings]
FIG. 1 shows a schematic view of a continuous firing apparatus used in the method of the present invention.
[Explanation of symbols]
(1) is an aluminum hydroxide supply line (2) is a firing furnace (3) is a line for extracting the alumina after firing out of the system (4) is an exhaust gas line (5) is a dust collector (6) is powder A line (7) for discharging the collected exhaust gas from the dust collector shows a line (8) for discharging the collected powder out of the system, and a line (8) for circulating and feeding the collected powder to the firing furnace.

Claims (3)

Supply line (1) for aluminum hydroxide, firing furnace (2) for firing the supplied aluminum hydroxide, line (3) for discharging the alumina after firing out of the system, and gas discharged from the firing furnace (2) Exhaust gas line (4) for introducing dust into the dust collector (5), dust collector (5) for collecting the powder contained in the exhaust gas, and exhausting the exhaust gas after collecting the powder from the dust collector (5) lines (6), in the method for producing a continuous α alumina with calciner the collected powder consisting line (7) for discharging out of the system, the dust collector to the device (5) A line (8) that circulates and supplies the powder collected in the firing furnace (2) is provided, and at least a part of the powder collected by the dust collector (5) is circulated into the firing furnace (2). In the firing furnace (2), aluminum hydroxide obtained by the Bayer method and an average particle size of 15 μm to 15 Line strength of (110) plane {2θ = 37.7 °}, (300) plane {2θ = 68.2 °}, (116) plane {2θ = 57.5 °} measured by X-ray diffraction method at 0 μm With the following formula 1
(I ₍₁₁₀₎ + I ₍₃₀₀₎ ) / (2 × I ₍₁₁₆₎ ) Equation 1
Alumina assignment with values obtained is 0.3 to 1.0 in (referred to as alumina A), 5 to 150% by weight relative to the aqueous aluminum oxide (Al ₂ O ₃ in terms) (Al ₂ O ₃ in terms of ) And aluminum hydroxide (Al ₂ O ₃ equivalent) and the total amount of alumina A, fluorine compound is added and prepared in the range of 20 to 200 ppm (F equivalent), and discharged from the line (3) after firing. A continuous production method of α-alumina, characterized in that firing is performed so that the fluorine compound content in the alumina becomes 1 to 200 ppm (F conversion).   2. The α-alumina according to claim 1, wherein the fluorine compound is at least one selected from aluminum fluoride, hydrogen fluoride, ammonium fluoride, sodium fluoride, magnesium fluoride, and calcium fluoride. Continuous manufacturing method.   2. The method for continuously producing α-alumina according to claim 1, wherein 1 to 20% by weight of a silica-based compound is added as a soda remover.

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