DD293799A5 - PROCESS FOR THE PYROGENIC PREPARATION OF ALPHA ALUMINUM OXIDE - Google Patents

Abstract

The invention relates to a process for the pyrogenic production of α-alumina with an α-alumina content of 20 to 80 parts by weight in% with a BET specific surface area (DIN 66 131) of 5 to 40 m 2 / g, virtually isolated primary particles and a primary particle distribution from about 20 to 500 nanometers, is produced by pyrogenic means by vaporizing aluminum trichloride, mixed with a traeger gas, this mixture burns in an oxygen / fuel gas flame in a flame tube in the flame tube a temperature of 1 200 to 1 500C holds or increased to 1 700C and the reaction effluents and the resulting product passed through a cooling section of known type and separates the product in a known manner from the reaction offgases. {a-alumina production, pyrogenic; Primary particles, almost isolated present}

Description

For this 3 pages drawings

Field of application of the invention

The invention relates to a process for the pyrogenic production of α-rtluminiumoxid.

Characteristic of the known state of the art

a-alumina is a well-known commercial product. It has coarse particles with diameters of several micrometers and a low specific surface area of ώ 15m ² / g.

The known a-alumina has the disadvantage that it is too coarse for some applications, such as polishing of sensitive surfaces or electronic packaging.

In the earlier application according to DE 3827898 describes how to produce a finely divided a-alumina by thermal aftertreatment of a-alumina.

A direct synthesis of α-alumina on pyrogeiiem way is not known.

Object of the invention

The invention provides a process for producing α-alumina, the advantage of the process being in the direct synthesis of α-alumina on AICI ₃ with a fine particle distribution.

Explanation of the essence of the invention

The present invention has for its object to provide a novel process for the synthesis of alumina. The invention relates to a process for the preparation of α-alumina, which is characterized by an α-alumina content of 20 to 80 parts by weight in%, a BET specific surface area (DIN 66131) of 5 to 40m ² / g, almost completely present primary particles and a primary particle distribution of about 20 to 500 nanometers. The α-alumina prepared according to the invention may have the following composition: 20 to 80 parts by weight in% crystalline α-alumina 10 to 50 parts by weight in% delta-aluminum oxide 10 to 30 parts by weight in% -A -aluminum oxide

In a preferred embodiment of the invention, the α-aluminum oxide may have the primary particle distribution according to FIG.

The a-aluminum oxide according to the invention can be used because of its particle fineness as a polishing agent for sensitive surfaces, such as in contact lenses or in so-called memory discs (hard disks) in computers.

The invention thus provides a process for the pyrogenic preparation of the α-alumina with an α-alumina content of 20 to 80 parts by weight in%, with a BET specific surface area (DIN 66131) of 5 to 40m ² / g, almost completely present primary particles and a primary particle distribution of about 20 to 500 nanometers, which is characterized in that aluminum trichloride is evaporated, mixed with an inert carrier gas, passed through a heated to a temperature of about 25O ⁰ C tube, immediately before a burner with a fuel gas in one Mixed mixing chamber, the mixture is fed to the burner and burned in a flame tube, while maintaining a temperature of 1200 ⁰ C to 1500 ⁰ C, preferably from 1200 ⁰ C to 1300 ⁰ C in the flame tube or optionally increased to 1700 ⁰ C, then to the flame tube, the reaction exhaust gases and the resulting product passes through a cooling section of known design and the product on b Separated manner from the reaction gases.

Such a cooling section and separation method are used in the pyrogenic production of metal oxide or metal oxides (cf .. Ulimann's Encyclopedia of Industrial Chemistry, 4th edition, Volume 21, p.464).

As fuel gas can be used hydrogen or carbon monoxide, carbon monoxide is preferred.

As the inert carrier gas can be used nitrogen or argon or other noble gases.

As burner, a system of three coaxial tubes can be used, through the middle tube of the vaporized aluminum trichloride is conducted in a mixture with the fuel gas, while oxygen is passed through the middle tube and through the outer tube further fuel gas.

As a flame tube can use a steel pipe, which is poured inside with alumina cement, the temperature in the flame tube can be by means of afterburners, which consist of annularly arranged in the flame tube nozzles or annular nozzles through which additional fuel gas is introduced, in the area from 1200 ⁰ C to 1500 ⁰ C maintained or increased up to 1700 ° C.

In the flame tube can be arranged 1 to 4 annularly arranged nozzles or annular nozzles.

The inventive method has the advantage that it allows the direct synthesis of α-alumina on AICI ₃ with a fine particle distribution.

The primary particles of the product are almost isolated and have a distribution of about 20 to 500 nanometers.

embodiment

The method according to the invention or the flame tube used according to the invention is explained in the drawing.

FIG. 1: solid aluminum trichloride is fed via the metering system 1 to the evaporation plant 2. The vaporized aluminum trichloride is mixed in the mixing chamber 3 with the fuel gas and in the burner 4, which consists of three concentrically arranged tubes out. The flame flows in the combustion of the mixture in the fed by oxygen and further fuel gas flame in the flame tube. 5

The flame tube 5 consists of the steel jacket 6, which is poured with alumina cement 7 such that a concentric tube 8 is formed.

'ndem flame tube 5 are at predetermined intervals, the annular nozzles 9; 10; 11 and 12, via the additional fuel gas in the concentric tube 8 of the flame tube 5 is introduced.

The reaction gases and the product are passed through the cooling section 13.

example

In an evaporator 1 kg / h of AICI _{3 are} evaporated and conveyed to the burner with 300 l / h of nitrogen. The AICI ₃ is premixed in the burner core with 2m ³ / h carbon monoxide. In the I.Mantel 1.5 m ³ / h of oxygen, in a second coat again 1 m ³ / h carbon monoxide fed into the flame. The reaction flame burns in a flame tube according to FIG 1. By introducing further fuel gas and oxygen through the annular nozzles 9,10 and 11, the flame tube is maintained at a temperature level of 1200 ⁰ C to 1400 ° C.

The gas-solid mixture is cooled in a cooling section of known type and the solid separated by filtration or cyclone. The yield is 0.38 kg Al ₂ O ₃ per hour. This gives an aluminum oxide having a BET surface area (DIN 66131) of 21% by volume and the following phase distribution:

about 70% a-alumina

about 20% δ-alumina

about 10% O-alumina

no gamma and amorphous alumina

The size of the primary particles is preferably in the range of 50 to 200 nm.

The electron micrograph (TEM) according to FIG. 3 shows almost exclusively isolated, ie. h., unaggregated spherical primary particles. These primary particles have - measured with the Cilas granulometer - the following particle size distribution:

Total particle number (N) 2059

Particle diameter, Arithm. Medium (DN) 104.54 (NM)

Particle diameter, over surface area, averaged (DA) 146.45 (NM)

Percentage distribution

number Number % total total diameter N N% · Number % Weight% D (NM) 15 0.729 SN% SND 3% 29.780 43 2,083 0.729 0,010 40.820 123 5,974 2,817 0.086 51.860 199 9,665 8.791 0.529 62.900 276 13.405 18.456 1,808 • 73,940 216 10.491 31.860 4,689 84.980 251 12.190 42.351 8.113 96.020 212 10,296 54.541 13.852 107.060 181 8.791 64.837 2C.571 118.100 138 6,702 73.628 28.271 129.140 118 5,731 80.330 35,947 140.180 76 3,691 86.061 44.341 151.220 54 2,623 89.752 51.129 162.260 51 2,477 92.375 57.087 173.300 29 1,408 94.852 63.942 184.340 18 0,874 96.260 68.634 195.380 15 0.729 97.135 72,101 206.420 5 0.243 97.863 75.509 217.460 6 0.291 98.106 76.837 228.500 7 0.340 98.397 78.685 239.540 5 0.243 98.737 81.170 250.580 2 0.097 98.980 83.202 261.620 7 0.340 99.077 84.127 272.660 2 0.097 99.417 87.792 283.700 1 0,049 99.514 88.971 294.740 2 0.097 99.563 89.632 305.780 2 0.097 99.660 91109 316.820 2 0.097 99.757 92.752 327.860 1 0,049 99.854 94.572 338.900 1 0,049 99.903 97.577 405.140 1 0,049 99.951 97.295 471.380 100000 100000

Claims (6)

1. A process for the pyrogenic production of a-alumina with an a-alumina content of 20 to 80 parts by mass in%, with a BET specific surface area (DIN 66131) of 5 to 40m ² / g, almost completely present primary particles and a primary particle distribution of approx 20 to 500 nanometers, characterized in that aluminum trichloride evaporated, mixed with an inert gas carrier stream, passed through a heated to a temperature of about 250 ⁰ C tube immediately before a burner mixed with a fuel gas in a mixing chamber, the mixture Burner feeds and burns in a flame tube, while maintaining a temperature of 1200 ⁰ C to 1500 ⁰ C, preferably from 1 200 ⁰ C to 1300 ⁰ C in the flame tube or optionally increased to 1700 ⁰ C, following the flame tube, the reaction gases and passing the resulting product through a cooling line of known type and separating the product from the reaction offgas in a known manner. 2. The method according to claim 1, characterized in that one uses carbon monoxide as the fuel gas. 3. The method according to claim 1 or 2, characterized in that the burner used is a system of three coaxial tubes, through the central tube, the vaporized aluminum trichloride is passed in admixture with the fuel gas, while through the middle tube oxygen and further through the outer tube Fuel gas is guided. 4. The method according to claim 1 to 3, characterized in that the flame tube used is a steel tube, which is poured inside with aluminum oxide cement. 5. The method according to claim 1 to 4, characterized in that the temperature in the flame tube by means of afterburners, each consisting of annularly arranged in the flame tube nozzles or annular nozzles, is introduced by the additional fuel gas, in the range of 1200 ⁰ C. to 1 500 ⁰ C maintained or optionally increased to 1700 ⁰ C. 6. The method according to claim 5, characterized in that arranged in the flame tube 1 to 4 annularly arranged nozzles or annular nozzles.