CA2110961A1 - Process for preparing aluminum oxide particles, an aluminum oxide powder prepared according to this process, as well as its use - Google Patents
Process for preparing aluminum oxide particles, an aluminum oxide powder prepared according to this process, as well as its useInfo
- Publication number
- CA2110961A1 CA2110961A1 CA002110961A CA2110961A CA2110961A1 CA 2110961 A1 CA2110961 A1 CA 2110961A1 CA 002110961 A CA002110961 A CA 002110961A CA 2110961 A CA2110961 A CA 2110961A CA 2110961 A1 CA2110961 A1 CA 2110961A1
- Authority
- CA
- Canada
- Prior art keywords
- aluminum
- aluminum oxide
- accordance
- oxide powder
- metallic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000002245 particle Substances 0.000 title claims abstract description 42
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 27
- 239000000843 powder Substances 0.000 title claims abstract description 17
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 28
- 229910052782 aluminium Inorganic materials 0.000 claims description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 12
- 239000007789 gas Substances 0.000 claims description 12
- -1 aluminum carbides Chemical class 0.000 claims description 9
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 230000003647 oxidation Effects 0.000 claims description 8
- 238000007254 oxidation reaction Methods 0.000 claims description 8
- 239000003638 chemical reducing agent Substances 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 238000010891 electric arc Methods 0.000 claims description 4
- 230000008020 evaporation Effects 0.000 claims description 4
- 238000001704 evaporation Methods 0.000 claims description 4
- 150000001247 metal acetylides Chemical class 0.000 claims description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 3
- 239000011230 binding agent Substances 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 230000001590 oxidative effect Effects 0.000 claims description 3
- 229910052760 oxygen Inorganic materials 0.000 claims description 3
- 239000001301 oxygen Substances 0.000 claims description 3
- 238000005498 polishing Methods 0.000 claims description 3
- 239000003054 catalyst Substances 0.000 claims description 2
- 229910010293 ceramic material Inorganic materials 0.000 claims description 2
- 239000003795 chemical substances by application Substances 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 claims description 2
- 239000000945 filler Substances 0.000 claims description 2
- 239000011214 refractory ceramic Substances 0.000 claims description 2
- 239000000443 aerosol Substances 0.000 claims 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 14
- 229910052593 corundum Inorganic materials 0.000 description 13
- 229910001845 yogo sapphire Inorganic materials 0.000 description 13
- 238000005245 sintering Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 4
- 229910002804 graphite Inorganic materials 0.000 description 3
- 239000010439 graphite Substances 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000005979 thermal decomposition reaction Methods 0.000 description 3
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000003082 abrasive agent Substances 0.000 description 2
- 229910000287 alkaline earth metal oxide Inorganic materials 0.000 description 2
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical group Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 239000012467 final product Substances 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 229910016384 Al4C3 Inorganic materials 0.000 description 1
- 238000004131 Bayer process Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229940037003 alum Drugs 0.000 description 1
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical group [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 description 1
- CAVCGVPGBKGDTG-UHFFFAOYSA-N alumanylidynemethyl(alumanylidynemethylalumanylidenemethylidene)alumane Chemical compound [Al]#C[Al]=C=[Al]C#[Al] CAVCGVPGBKGDTG-UHFFFAOYSA-N 0.000 description 1
- LCQXXBOSCBRNNT-UHFFFAOYSA-K ammonium aluminium sulfate Chemical compound [NH4+].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O LCQXXBOSCBRNNT-UHFFFAOYSA-K 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 230000009970 fire resistant effect Effects 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000010405 reoxidation reaction Methods 0.000 description 1
- 150000003839 salts Chemical group 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K3/00—Materials not provided for elsewhere
- C09K3/14—Anti-slip materials; Abrasives
- C09K3/1409—Abrasive particles per se
- C09K3/1418—Abrasive particles per se obtained by division of a mass agglomerated by sintering
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
- B01J21/04—Alumina
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/30—Preparation of aluminium oxide or hydroxide by thermal decomposition or by hydrolysis or oxidation of aluminium compounds
- C01F7/302—Hydrolysis or oxidation of gaseous aluminium compounds in the gaseous phase
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/42—Preparation of aluminium oxide or hydroxide from metallic aluminium, e.g. by oxidation
- C01F7/422—Preparation of aluminium oxide or hydroxide from metallic aluminium, e.g. by oxidation by oxidation with a gaseous oxidator at a high temperature
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
- C04B35/111—Fine ceramics
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
- B01J35/61—Surface area
- B01J35/613—10-100 m2/g
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/30—Particle morphology extending in three dimensions
- C01P2004/32—Spheres
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/10—Solid density
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Thermal Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Structural Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Ceramic Products (AREA)
- Catalysts (AREA)
- Filtering Materials (AREA)
Abstract
Abstract of the Disclosure The present invention pertains to a process for preparing aluminum oxide particles, as well as to an aluminum oxide powder prepared according to this process, and to its use.
Description
~ ~9~1 ......
l E-1452 Proc~s~ for Preparing ~lumi~m oxi~e Particle~, an Aluminum O~ide Powder Prepaxed ~caor~i~g to thi~ Proce~, as well as i~s ~se ~ :
8pe~ifi~atio~
The present invention pertains to a process for preparing sinter-active, very extensively spherical aluminum oxide particles with a mean particle diameter of < 1.0 ~m, to an aluminum oxide powder prepared according to this process, as well as to its use.
Aluminum oxide powders are used as pigments, abrasives and polishing agents, in refractory or fire-resistant products, in ceramics, as catalyst materials, or as fillers~ as well as for coatings.
The chemical resistance, good mechanical strengths, especially its favorable wear property, its high electrical resistance, and its good temperature resistance are decisive for the industrial application of aluminum oxide.
. Especially the following properties are required for the preparation of high quality ceramic, especially re~ractory products:
- high sintering activity (especially due to small particle sizes), - minimization of the impurities that inhibit the sintering process or promote an undesirable particle . .
growth, - lowest possible content of melt phase~forming ~ :
`` 2 2 ~ 1 9 ~ ~ E-14 5 2 accompanying substances, - good processability (pressability), and ~ ;
- high green strength.
Low porosity of the individual particles (powder particles) is also necessary for reaching high green `-~
strengths (green densities). ;
Various thermal, wet-chemical, mechanical, and physical processes for preparing sinter-active, microcrystalline Al2O3 particles and powders have been known.
They include the thermal decomposition and subsequent calcination of purified alum (ammonium aluminum sulfate), or the thermal decomposition of aluminum chloride according to the so-called spray roasting processO The disadvantages of such thermal decompositions of aluminum salts are the high price of the corresponding plants and the salt residues remaining in the oxide, which may contribute to an increased particle growth during the sintering process.
It has also been known that an alumina prepared according to the so-called Bayer process can be ground to prepare finely dispersed aluminum oxide. However, this fine grinding is very expensive, and the more finely the material is to be ground, the more time-consuming is the process, so that particles finer than 1 ~m can be prepared, if at all, with an extrem~ly high technical effort only. In addition, the morphology of the powder particles thus prepared is splintery and granular. This ~ - -21i 0.9~:l may cause disadvantages in terms of the rheological behavior.
The preparation of spherical Al2O3 particles according to a process, in which water-containing aluminum oxide is subjected to a special, multistep, heat treatment, has been known ~rom U.S.-A-4,818,515. The process reguires a starting material that can be prepared at a considerable cost only because of the required purity.
Finally, finely dispersed calcinates can be prepared by the hydrolysis of aluminum alkoxides; however, depending on the degree of calcination, these calcinates sometimes have a considerable microporosity, which leads to a corresponding (undesired) shrinkage during a subsequent sintering process.
The above-described processes have therefore not become successful for many large-scale applications for technical and economic reasons.
Therefore, the basic task of the present invention is to provide a process which makes it possible to prepare ver~ fine aluminum oxide particles in the submicron range (< 1.0 ~m) in a relatively inexpensive manner, wherein very extensively spherical particle shape, low porosity, and consequently good compaction and sintering properties are desirable in order to make possible or optimize application for the purposes mentioned in the introduction.
This goal is achieved by a process of the class ' , 9 fi :1 -4 E~1452 described in the introduction, which is characterized by the following steps: :
- introduction of an aluminum carrier, such as Al or :~
Al203, into a furnace unit, - heating the aluminum carrier, ~-~
- reduction of the aluminum carrier, unless it is introduced as metallic aluminum, into metallic aluminum and/or aluminum carbides (including aluminum oxicarbides), - increasing the furnace temperature to a value at which the metallic aluminum or the aluminum carbides evaporate, - subsequent oxidation of the metallic aluminum or its carbides into aluminum oxide in a gas ~low, and ~ introduction of the gas flow into a filter, wherein - the temperature, the atmosphere, and the hold time of the aluminum oxide particles in the gas flow are adjusted ~:
according to the desired particle size.
Consequently, using, e.g., lumpy aluminum oxide as the starting product, this aluminum oxide is first reduced into metallic aluminum and/or aluminum carbides, these are subsequently or simultaneously evaporated, and finally reoxidizPd in a suitable manner, before the aluminum oxide particles thus formed secondarily are separated in a filter. .
What is very important for reaching the fine particle size of the aluminum oxide particles, which was formiulated according to the task, is to introduce the Alz03 particles, carried in the gas flow, in the gas flow -2~9~
into the subsequent filter. The shorter the hold time of the Al2O3 particles in the gas flow, the smaller is the particle size, which can also be controlled secondarily ~ia the tempera~ure and the (oxidizing) atmosphere of the gas flow.
To obtain the fineist Al203 particles possible, the filter is consequently connected directly to the above-described oxidation step.
An electric arc furnace proved to be particularly advantageous as a furnace unit. According to an embodiment of the present invention, it is operated at current densities between 10 and 50 A/cm2l and in the preferred range between 15 and 30 A/cm2.
It proved to be advantageous to add a reducing agent (such as carbon) during the reduction reaction of aluminum oxide, aluminum carbide, or aluminum oxicarbide in order to reach the effective evaporation capacity. It is also possible to use carbon-releasing compounds in this sense.
The subsequent oxidation of the vapor-form aluminum and/or condensed aluminum particles can be accelerated by feeding in ex~ernal oxygen. This makes it possible to subsequently separate the particles, which have a short hold time in the oxidation step, in a suitable filter, e.g., a bag filter.
As an alternative, the oxidation step may be designed such that aluminum particles are introduced into a furnace section, in which oxidizing atmosphere is :
fi ~
present.
Sinter-active, spherical aluminum oxide particles with a density of up to 3.97 g~cm3 and a specific surface between 0.5 and 60 m2/g can be prepared by the process according to the present invention.
The process makes it possible to form aluminum oxide particles with a mean particle size of marXedly less than 1 ~m, and even as small as 0.10 ~m, by correspondingly adjusting the process parameters, such as the temperature, the atmosphere, and the hold time of the Al2O3 particles in the gas flow.
One particular advantage is the fact that the Al2O3 particles prepared according to the process described have a nearly ideal spherical (ball-shaped~
configuration, so that the material can be used particularly advantageously for, e.g., abrasives and polishing agants, or in refractory ceramic materials (in which latter it is used as a binder or binder component).
The sphsrical shape is the major factor for the contribution of the particles to the exc llent rheological properties of corresponding systems.
If an electric arc furnace is used, the charge may readily be in the lumpy form. The evaporation capacity of the arc generated depends on its energy content and the local arc temperature. The evaporation capacity is in the range of 40 to 100 g of Al2O3 per kWh at current densities in the range of 10 to 50 A/cm2.
The composition of the Al2~3 particles obtainad .
-according to this process depends on the aluminum-containing raw material (aluminum carrier) charged in and the reducing agent used. If the raw material and/or the reducing agent contain alkali and/or alkaline earth oxides, sio2, iron oxide, or the like, these impurities can be found in the final product nearly quantitatively.
If carbon is used as the reducing agent, or sometimes also due to carbon from the furnace electrodes, small amounts of carbon are released, or carbides or oxicarbides are formed. If the reoxidation does not take place completely, low carbon contents of up to ca. 0.5 wt.%, which can be further reduced, if needed, by heat aftertreatment (eOg., annealing treatment), may occur in the final product in this case~
The present invention will be described in greater detail below on the basis of an exemplary embodiment:
A mixture of 85 parts by weight of lumpy aluminum oxide and 15 parts by weiyht of graphite chips were charged into an electric arc furnace equipped with ;
graphite electrodes. After the arc had been ignited, a melt sump o~ aluminum oxide, Al404C and Al4C3, which is advantayeous as a protective layer for the bottom lining of the ~urnace (which consisted of carbon bricks in this case), was initially formed. The capacity of the arc was 2~ in the range of 150-180 kVA. The current density was between 16 and 23 A/cm2.
The lumpy starting material subsequently ~vaporated, and metallic aluminum and aluminum carbides were formed;
9 ~ 1 the metallic aluminum and the aluminum carbides were subsequently reoxidized into Al203 particles in the atmosphere or by supplying oxygen, before these were introduced into a fabric filter, where they were separated at a rate exceeding 99 wt.%. The mean size of the predominantly spherical aluminum oxide powder particles obtained was 0.2 ~m. The density of the material was 3.8 g/cm3. The specific surface was 9.8 m2/g -In the case of an Al2O3 charge of the composition of 0.03 wt.% Na2O ~ K2O, 0.014 wt.% Fe2O3, 0~03 wt.% MgO, 0.03 wt.% sio2, remainder Al2O3, `
an Al2O3 powder of the following particle composition was obtained:
0.037 wt.% Na2O ~ K2O, 0.03 wt.% Fe2O3, 0.05 wt~% MgO, 0.08 wt.% SiO2, `
0.37 wt.~ C, remainder Al2O3.
The increase in the impurity level was due to the percentage of ash in the graphite used for the reduction, as well as to the furnace electrodes.
l E-1452 Proc~s~ for Preparing ~lumi~m oxi~e Particle~, an Aluminum O~ide Powder Prepaxed ~caor~i~g to thi~ Proce~, as well as i~s ~se ~ :
8pe~ifi~atio~
The present invention pertains to a process for preparing sinter-active, very extensively spherical aluminum oxide particles with a mean particle diameter of < 1.0 ~m, to an aluminum oxide powder prepared according to this process, as well as to its use.
Aluminum oxide powders are used as pigments, abrasives and polishing agents, in refractory or fire-resistant products, in ceramics, as catalyst materials, or as fillers~ as well as for coatings.
The chemical resistance, good mechanical strengths, especially its favorable wear property, its high electrical resistance, and its good temperature resistance are decisive for the industrial application of aluminum oxide.
. Especially the following properties are required for the preparation of high quality ceramic, especially re~ractory products:
- high sintering activity (especially due to small particle sizes), - minimization of the impurities that inhibit the sintering process or promote an undesirable particle . .
growth, - lowest possible content of melt phase~forming ~ :
`` 2 2 ~ 1 9 ~ ~ E-14 5 2 accompanying substances, - good processability (pressability), and ~ ;
- high green strength.
Low porosity of the individual particles (powder particles) is also necessary for reaching high green `-~
strengths (green densities). ;
Various thermal, wet-chemical, mechanical, and physical processes for preparing sinter-active, microcrystalline Al2O3 particles and powders have been known.
They include the thermal decomposition and subsequent calcination of purified alum (ammonium aluminum sulfate), or the thermal decomposition of aluminum chloride according to the so-called spray roasting processO The disadvantages of such thermal decompositions of aluminum salts are the high price of the corresponding plants and the salt residues remaining in the oxide, which may contribute to an increased particle growth during the sintering process.
It has also been known that an alumina prepared according to the so-called Bayer process can be ground to prepare finely dispersed aluminum oxide. However, this fine grinding is very expensive, and the more finely the material is to be ground, the more time-consuming is the process, so that particles finer than 1 ~m can be prepared, if at all, with an extrem~ly high technical effort only. In addition, the morphology of the powder particles thus prepared is splintery and granular. This ~ - -21i 0.9~:l may cause disadvantages in terms of the rheological behavior.
The preparation of spherical Al2O3 particles according to a process, in which water-containing aluminum oxide is subjected to a special, multistep, heat treatment, has been known ~rom U.S.-A-4,818,515. The process reguires a starting material that can be prepared at a considerable cost only because of the required purity.
Finally, finely dispersed calcinates can be prepared by the hydrolysis of aluminum alkoxides; however, depending on the degree of calcination, these calcinates sometimes have a considerable microporosity, which leads to a corresponding (undesired) shrinkage during a subsequent sintering process.
The above-described processes have therefore not become successful for many large-scale applications for technical and economic reasons.
Therefore, the basic task of the present invention is to provide a process which makes it possible to prepare ver~ fine aluminum oxide particles in the submicron range (< 1.0 ~m) in a relatively inexpensive manner, wherein very extensively spherical particle shape, low porosity, and consequently good compaction and sintering properties are desirable in order to make possible or optimize application for the purposes mentioned in the introduction.
This goal is achieved by a process of the class ' , 9 fi :1 -4 E~1452 described in the introduction, which is characterized by the following steps: :
- introduction of an aluminum carrier, such as Al or :~
Al203, into a furnace unit, - heating the aluminum carrier, ~-~
- reduction of the aluminum carrier, unless it is introduced as metallic aluminum, into metallic aluminum and/or aluminum carbides (including aluminum oxicarbides), - increasing the furnace temperature to a value at which the metallic aluminum or the aluminum carbides evaporate, - subsequent oxidation of the metallic aluminum or its carbides into aluminum oxide in a gas ~low, and ~ introduction of the gas flow into a filter, wherein - the temperature, the atmosphere, and the hold time of the aluminum oxide particles in the gas flow are adjusted ~:
according to the desired particle size.
Consequently, using, e.g., lumpy aluminum oxide as the starting product, this aluminum oxide is first reduced into metallic aluminum and/or aluminum carbides, these are subsequently or simultaneously evaporated, and finally reoxidizPd in a suitable manner, before the aluminum oxide particles thus formed secondarily are separated in a filter. .
What is very important for reaching the fine particle size of the aluminum oxide particles, which was formiulated according to the task, is to introduce the Alz03 particles, carried in the gas flow, in the gas flow -2~9~
into the subsequent filter. The shorter the hold time of the Al2O3 particles in the gas flow, the smaller is the particle size, which can also be controlled secondarily ~ia the tempera~ure and the (oxidizing) atmosphere of the gas flow.
To obtain the fineist Al203 particles possible, the filter is consequently connected directly to the above-described oxidation step.
An electric arc furnace proved to be particularly advantageous as a furnace unit. According to an embodiment of the present invention, it is operated at current densities between 10 and 50 A/cm2l and in the preferred range between 15 and 30 A/cm2.
It proved to be advantageous to add a reducing agent (such as carbon) during the reduction reaction of aluminum oxide, aluminum carbide, or aluminum oxicarbide in order to reach the effective evaporation capacity. It is also possible to use carbon-releasing compounds in this sense.
The subsequent oxidation of the vapor-form aluminum and/or condensed aluminum particles can be accelerated by feeding in ex~ernal oxygen. This makes it possible to subsequently separate the particles, which have a short hold time in the oxidation step, in a suitable filter, e.g., a bag filter.
As an alternative, the oxidation step may be designed such that aluminum particles are introduced into a furnace section, in which oxidizing atmosphere is :
fi ~
present.
Sinter-active, spherical aluminum oxide particles with a density of up to 3.97 g~cm3 and a specific surface between 0.5 and 60 m2/g can be prepared by the process according to the present invention.
The process makes it possible to form aluminum oxide particles with a mean particle size of marXedly less than 1 ~m, and even as small as 0.10 ~m, by correspondingly adjusting the process parameters, such as the temperature, the atmosphere, and the hold time of the Al2O3 particles in the gas flow.
One particular advantage is the fact that the Al2O3 particles prepared according to the process described have a nearly ideal spherical (ball-shaped~
configuration, so that the material can be used particularly advantageously for, e.g., abrasives and polishing agants, or in refractory ceramic materials (in which latter it is used as a binder or binder component).
The sphsrical shape is the major factor for the contribution of the particles to the exc llent rheological properties of corresponding systems.
If an electric arc furnace is used, the charge may readily be in the lumpy form. The evaporation capacity of the arc generated depends on its energy content and the local arc temperature. The evaporation capacity is in the range of 40 to 100 g of Al2O3 per kWh at current densities in the range of 10 to 50 A/cm2.
The composition of the Al2~3 particles obtainad .
-according to this process depends on the aluminum-containing raw material (aluminum carrier) charged in and the reducing agent used. If the raw material and/or the reducing agent contain alkali and/or alkaline earth oxides, sio2, iron oxide, or the like, these impurities can be found in the final product nearly quantitatively.
If carbon is used as the reducing agent, or sometimes also due to carbon from the furnace electrodes, small amounts of carbon are released, or carbides or oxicarbides are formed. If the reoxidation does not take place completely, low carbon contents of up to ca. 0.5 wt.%, which can be further reduced, if needed, by heat aftertreatment (eOg., annealing treatment), may occur in the final product in this case~
The present invention will be described in greater detail below on the basis of an exemplary embodiment:
A mixture of 85 parts by weight of lumpy aluminum oxide and 15 parts by weiyht of graphite chips were charged into an electric arc furnace equipped with ;
graphite electrodes. After the arc had been ignited, a melt sump o~ aluminum oxide, Al404C and Al4C3, which is advantayeous as a protective layer for the bottom lining of the ~urnace (which consisted of carbon bricks in this case), was initially formed. The capacity of the arc was 2~ in the range of 150-180 kVA. The current density was between 16 and 23 A/cm2.
The lumpy starting material subsequently ~vaporated, and metallic aluminum and aluminum carbides were formed;
9 ~ 1 the metallic aluminum and the aluminum carbides were subsequently reoxidized into Al203 particles in the atmosphere or by supplying oxygen, before these were introduced into a fabric filter, where they were separated at a rate exceeding 99 wt.%. The mean size of the predominantly spherical aluminum oxide powder particles obtained was 0.2 ~m. The density of the material was 3.8 g/cm3. The specific surface was 9.8 m2/g -In the case of an Al2O3 charge of the composition of 0.03 wt.% Na2O ~ K2O, 0.014 wt.% Fe2O3, 0~03 wt.% MgO, 0.03 wt.% sio2, remainder Al2O3, `
an Al2O3 powder of the following particle composition was obtained:
0.037 wt.% Na2O ~ K2O, 0.03 wt.% Fe2O3, 0.05 wt~% MgO, 0.08 wt.% SiO2, `
0.37 wt.~ C, remainder Al2O3.
The increase in the impurity level was due to the percentage of ash in the graphite used for the reduction, as well as to the furnace electrodes.
Claims (16)
1. Process for preparing sinter-active, very extensively spherical aluminum oxide particles with a mean particle diameter of < 1.0 µm, preferably < 0.5 µm, comprising the following steps:
1.1. introduction of an aluminum carrier, such as metallic aluminum or aluminum oxide, into a furnace unit, 1.2. heating of the aluminum carrier, 1.3. reduction of the aluminum carrier, if it was not introduced as metallic aluminum, into metallic aluminum and/or aluminum carbides, 1.4. increasing the furnace temperature to a value at which the metallic aluminum or the metallic carbides evaporate, 1.5. subsequent oxidation of the metallic aluminum or its carbides into aluminum oxide in a gas flow, and 1.6. introduction of the gas flow into a filter, wherein 1.7. the temperature, the atmosphere, and the hold time of the aluminum oxide particles in the gas stream are adjusted corresponding to the desired particle size.
1.1. introduction of an aluminum carrier, such as metallic aluminum or aluminum oxide, into a furnace unit, 1.2. heating of the aluminum carrier, 1.3. reduction of the aluminum carrier, if it was not introduced as metallic aluminum, into metallic aluminum and/or aluminum carbides, 1.4. increasing the furnace temperature to a value at which the metallic aluminum or the metallic carbides evaporate, 1.5. subsequent oxidation of the metallic aluminum or its carbides into aluminum oxide in a gas flow, and 1.6. introduction of the gas flow into a filter, wherein 1.7. the temperature, the atmosphere, and the hold time of the aluminum oxide particles in the gas stream are adjusted corresponding to the desired particle size.
2. Process in accordance with claim 1, characterized in that the aluminum carrier is charged in in the lumpy form.
3. Process in accordance with claim 1 or 2, characterized in that the evaporation takes place in an electric arc furnace.
4. Process in accordance with claim 3, characterized in that the current density is 10 to 50 A/cm2.
5. Process in accordance with claim 4, characterized in that the current density is 15 to 30 A/cm2.
6. Process in accordance with one of the claims 1 through 5, characterized in that carbon or carbon-releasing compounds are used as the reducing agent.
7. Process in accordance with one of the claims 1 through 6, characterized in that oxygen is blown into the gas flow in the oxidation step.
8. Process in accordance with one of the claims 1 through 6, characterized in that the oxidation of the vapor-form aluminum or aluminum carbides into aluminum oxide is performed by introducing the aerosol into a furnace section with oxidizing atmosphere.
9. Process in accordance with one of the claims 1 through 8, characterized in that the aluminum oxide particles are separated in a bag filter.
10. Sinter-active, very extensively spherical aluminum oxide powder, prepared by the process according to one of the claims 1 through 9, characterized in that it has a density of 2.5 to 3.97 g/cm3 and a specific surface of 0.5 to 60 m2/g.
11. Aluminum oxide powder in accordance with claim 10, characterized in that it has a density between 3.2 and 3.97 g/cm3 and a specific surface between 4 and 20 m2/g.
12. Aluminum oxide powder in accordance with claim 10 or 11, with a mean particle size between 0.05 and 0.3 µm.
13. Use of an aluminum oxide powder in accordance with one of the claims 10 through 12 as an abrasive and polishing agent.
14. Use of an aluminum oxide powder in accordance with one of the claims 10 through 12 as a binder in refractory ceramic materials.
15. Use of an aluminum oxide powder in accordance with one of the claims 10 through 12 as a filler.
16. Use of an aluminum oxide powder in accordance with one of the claims 10 through 12 as a catalyst material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4241625.6 | 1992-12-10 | ||
| DE4241625A DE4241625C1 (en) | 1992-12-10 | 1992-12-10 | Process for the production of sinter-active, largely spherical aluminum oxide and its use |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2110961A1 true CA2110961A1 (en) | 1994-06-11 |
Family
ID=6474898
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002110961A Abandoned CA2110961A1 (en) | 1992-12-10 | 1993-12-08 | Process for preparing aluminum oxide particles, an aluminum oxide powder prepared according to this process, as well as its use |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0601453A3 (en) |
| JP (1) | JPH07309618A (en) |
| CA (1) | CA2110961A1 (en) |
| CZ (1) | CZ260493A3 (en) |
| DE (1) | DE4241625C1 (en) |
| HU (1) | HUT68748A (en) |
| PL (1) | PL301393A1 (en) |
| SI (1) | SI9300649A (en) |
| SK (1) | SK138493A3 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO337267B1 (en) * | 2014-02-10 | 2016-02-29 | Elkem As | Process for the production of alumina particles |
| EP3110900A4 (en) * | 2014-02-27 | 2017-10-04 | 3M Innovative Properties Company | Abrasive particles, abrasive articles, and methods of making and using the same |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19520614C1 (en) * | 1995-06-06 | 1996-11-07 | Starck H C Gmbh Co Kg | Microcrystalline sintered abrasive grains based on a-AI¶2¶O¶3¶ with high wear resistance, process for its production and its use |
| DE19605556C1 (en) * | 1996-02-15 | 1997-09-11 | Vaw Silizium Gmbh | Reactive spherical metal oxide powder particles |
| US5856254A (en) * | 1996-02-15 | 1999-01-05 | Vaw Silizium Gmbh | Spherical metal-oxide powder particles and process for their manufacture |
| KR19990023544A (en) * | 1997-08-19 | 1999-03-25 | 마쯔모또 에이찌 | Aqueous dispersion of inorganic particles and preparation method thereof |
| US6391072B1 (en) * | 2000-05-04 | 2002-05-21 | Saint-Gobain Industrial Ceramics, Inc. | Abrasive grain |
| CN100522856C (en) | 2001-08-02 | 2009-08-05 | 3M创新有限公司 | Al2O3-rare earth oxide-ZrO2/HfO2 materials and methods of making and using the same |
| WO2003011776A1 (en) | 2001-08-02 | 2003-02-13 | 3M Innovative Properties Company | Method of making articles from glass and glass ceramic articles so produced |
| JP4532898B2 (en) * | 2001-08-02 | 2010-08-25 | スリーエム イノベイティブ プロパティズ カンパニー | Abrasive particles and method for producing and using the same |
| US8056370B2 (en) | 2002-08-02 | 2011-11-15 | 3M Innovative Properties Company | Method of making amorphous and ceramics via melt spinning |
| US7811496B2 (en) | 2003-02-05 | 2010-10-12 | 3M Innovative Properties Company | Methods of making ceramic particles |
| US7292766B2 (en) | 2003-04-28 | 2007-11-06 | 3M Innovative Properties Company | Use of glasses containing rare earth oxide, alumina, and zirconia and dopant in optical waveguides |
| CN101829607B (en) * | 2010-05-17 | 2012-04-18 | 昆明珀玺金属材料有限公司 | Method for preparing catalyst carrier Al2O3 powder by activating and hydrolyzing metallic aluminium under ultrasound-electric field coupling |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL82125C (en) * | 1951-12-19 | |||
| NL197592A (en) * | 1954-05-28 | 1900-01-01 | ||
| SU967029A1 (en) * | 1965-11-20 | 1983-08-30 | Институт Химической Физики Ан Ссср | Process for preparing metal oxides |
| NL7411942A (en) * | 1973-09-10 | 1975-03-12 | Electricity Council | PROCESS FOR PRODUCING ULTRA-FINE PARTICLES OF A REFROUSIVE OXIDE. |
| BR7502067A (en) * | 1974-04-26 | 1976-03-03 | J Chevalley | PROCESS AND INSTALLATION THAT ALLOW THE TRANSPORT AND REVALUATION OF ENERGY FORMS LOCALLY AVAILABLE |
| IT1184114B (en) * | 1985-01-18 | 1987-10-22 | Montedison Spa | ALFA ALUMINATES IN THE FORM OF SPHERICAL PARTICLES, NOT AGGREGATED, WITH RESTRIBUTION GRANULOMETRIC RESTRICTED AND OF LESS THAN 2 MICRONS, AND PROCESS FOR ITS PREPARATION |
-
1992
- 1992-12-10 DE DE4241625A patent/DE4241625C1/en not_active Revoked
-
1993
- 1993-12-01 EP EP19930119343 patent/EP0601453A3/en not_active Withdrawn
- 1993-12-01 CZ CZ932604A patent/CZ260493A3/en unknown
- 1993-12-08 SK SK1384-93A patent/SK138493A3/en unknown
- 1993-12-08 CA CA002110961A patent/CA2110961A1/en not_active Abandoned
- 1993-12-09 JP JP5344621A patent/JPH07309618A/en active Pending
- 1993-12-09 PL PL93301393A patent/PL301393A1/en unknown
- 1993-12-10 HU HU9303535A patent/HUT68748A/en unknown
- 1993-12-10 SI SI9300649A patent/SI9300649A/en unknown
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO337267B1 (en) * | 2014-02-10 | 2016-02-29 | Elkem As | Process for the production of alumina particles |
| US9738540B2 (en) | 2014-02-10 | 2017-08-22 | Elkem As | Process for the production of aluminium oxide particles |
| EP3110900A4 (en) * | 2014-02-27 | 2017-10-04 | 3M Innovative Properties Company | Abrasive particles, abrasive articles, and methods of making and using the same |
| US10155892B2 (en) | 2014-02-27 | 2018-12-18 | 3M Innovative Properties Company | Abrasive particles, abrasive articles, and methods of making and using the same |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0601453A3 (en) | 1994-12-07 |
| HUT68748A (en) | 1995-04-27 |
| PL301393A1 (en) | 1994-06-13 |
| SK138493A3 (en) | 1994-07-06 |
| EP0601453A2 (en) | 1994-06-15 |
| HU9303535D0 (en) | 1994-04-28 |
| DE4241625C1 (en) | 1994-06-30 |
| JPH07309618A (en) | 1995-11-28 |
| CZ260493A3 (en) | 1994-08-17 |
| SI9300649A (en) | 1994-06-30 |
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| EEER | Examination request | ||
| FZDE | Discontinued |