DE19629690C2 - Process for the production of sintered alpha-AL¶2¶0¶3¶ bodies and their use - Google Patents
Process for the production of sintered alpha-AL¶2¶0¶3¶ bodies and their useInfo
- Publication number
- DE19629690C2 DE19629690C2 DE1996129690 DE19629690A DE19629690C2 DE 19629690 C2 DE19629690 C2 DE 19629690C2 DE 1996129690 DE1996129690 DE 1996129690 DE 19629690 A DE19629690 A DE 19629690A DE 19629690 C2 DE19629690 C2 DE 19629690C2
- Authority
- DE
- Germany
- Prior art keywords
- sintering
- slip
- solids content
- weight
- suspension
- 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.)
- Expired - Fee Related
Links
- 238000000034 method Methods 0.000 title claims description 49
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 238000005245 sintering Methods 0.000 claims description 39
- 239000008187 granular material Substances 0.000 claims description 22
- 239000000725 suspension Substances 0.000 claims description 20
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 19
- 238000000227 grinding Methods 0.000 claims description 17
- 239000013078 crystal Substances 0.000 claims description 14
- 239000007787 solid Substances 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 11
- 238000009826 distribution Methods 0.000 claims description 10
- 239000007858 starting material Substances 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 7
- 230000035939 shock Effects 0.000 claims description 7
- 239000007921 spray Substances 0.000 claims description 7
- 239000000654 additive Substances 0.000 claims description 5
- 239000000843 powder Substances 0.000 claims description 5
- 230000002902 bimodal effect Effects 0.000 claims description 4
- 229910001593 boehmite Inorganic materials 0.000 claims description 4
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 claims description 4
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 4
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 4
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 3
- 238000005520 cutting process Methods 0.000 claims description 3
- 229910052749 magnesium Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 239000003381 stabilizer Substances 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 229910052725 zinc Inorganic materials 0.000 claims description 3
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- 239000004375 Dextrin Substances 0.000 claims description 2
- 229920001353 Dextrin Polymers 0.000 claims description 2
- 229920000084 Gum arabic Polymers 0.000 claims description 2
- 229920001732 Lignosulfonate Polymers 0.000 claims description 2
- 241000978776 Senegalia senegal Species 0.000 claims description 2
- 229920002472 Starch Polymers 0.000 claims description 2
- 235000010489 acacia gum Nutrition 0.000 claims description 2
- 239000000205 acacia gum Substances 0.000 claims description 2
- 235000010443 alginic acid Nutrition 0.000 claims description 2
- 229920000615 alginic acid Polymers 0.000 claims description 2
- 229910052796 boron Inorganic materials 0.000 claims description 2
- 235000019425 dextrin Nutrition 0.000 claims description 2
- 239000006185 dispersion Substances 0.000 claims description 2
- 150000002334 glycols Chemical class 0.000 claims description 2
- 229910052735 hafnium Inorganic materials 0.000 claims description 2
- 239000003112 inhibitor Substances 0.000 claims description 2
- 229920000609 methyl cellulose Polymers 0.000 claims description 2
- 239000001923 methylcellulose Substances 0.000 claims description 2
- 235000010981 methylcellulose Nutrition 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229920002689 polyvinyl acetate Polymers 0.000 claims description 2
- 239000011118 polyvinyl acetate Substances 0.000 claims description 2
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims description 2
- 235000019353 potassium silicate Nutrition 0.000 claims description 2
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 2
- 235000019698 starch Nutrition 0.000 claims description 2
- 239000008107 starch Substances 0.000 claims description 2
- 235000000346 sugar Nutrition 0.000 claims description 2
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims 1
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims 1
- 229910052593 corundum Inorganic materials 0.000 description 13
- 239000010431 corundum Substances 0.000 description 13
- 238000003980 solgel method Methods 0.000 description 12
- 230000008901 benefit Effects 0.000 description 8
- 239000002994 raw material Substances 0.000 description 7
- 239000006061 abrasive grain Substances 0.000 description 6
- 238000005469 granulation Methods 0.000 description 6
- 230000003179 granulation Effects 0.000 description 6
- 239000000047 product Substances 0.000 description 5
- 239000002002 slurry Substances 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 239000003082 abrasive agent Substances 0.000 description 4
- 230000006641 stabilisation Effects 0.000 description 4
- 238000011105 stabilization Methods 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 description 3
- 239000002253 acid Substances 0.000 description 3
- 239000012736 aqueous medium Substances 0.000 description 3
- 238000001354 calcination Methods 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- 238000001238 wet grinding Methods 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000007900 aqueous suspension Substances 0.000 description 2
- 244000052616 bacterial pathogen Species 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000001962 electrophoresis Methods 0.000 description 2
- 238000001652 electrophoretic deposition Methods 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 150000007522 mineralic acids Chemical class 0.000 description 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- 229920002845 Poly(methacrylic acid) Polymers 0.000 description 1
- 229920000954 Polyglycolide Polymers 0.000 description 1
- 229920002125 Sokalan® Polymers 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000004581 coalescence Methods 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- WMWXXXSCZVGQAR-UHFFFAOYSA-N dialuminum;oxygen(2-);hydrate Chemical compound O.[O-2].[O-2].[O-2].[Al+3].[Al+3] WMWXXXSCZVGQAR-UHFFFAOYSA-N 0.000 description 1
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 229910001679 gibbsite Inorganic materials 0.000 description 1
- 239000003966 growth inhibitor Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 150000002484 inorganic compounds Chemical class 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000010327 methods by industry Methods 0.000 description 1
- 238000009768 microwave sintering Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052863 mullite Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000001694 spray drying Methods 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
Classifications
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- 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
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- 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
- C04B35/1115—Minute sintered entities, e.g. sintered abrasive grains or shaped particles such as platelets
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- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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- C04B35/62605—Treating the starting powders individually or as mixtures
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- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
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- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
- C04B2235/3217—Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
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- C04B2235/34—Non-metal oxides, non-metal mixed oxides, or salts thereof that form the non-metal oxides upon heating, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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Description
Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung gesinterter, mikrokristalliner Körper auf Basis von α-Al2O3 sowie deren Verwendung.The present invention relates to a method for producing sintered, microcrystalline bodies based on α-Al 2 O 3 and the use thereof.
Eine bevorzugte Anwendung von α-Al2O3-Sinterkörpern ist deren Einsatz als Schleifmittel. Neben geschmolzenen Korundschleifmitteln sind solche aus gesin tertem Material schon seit mehr als 50 Jahren bekannt.A preferred application of α-Al 2 O 3 sintered bodies is their use as an abrasive. In addition to molten corundum abrasives, those made of sintered material have been known for more than 50 years.
In der US-A 3 909 991 werden polykristalline α-Al2O3-Körper beschrieben, deren Kristallitgröße im Submicron-Bereich liegt und deren Dichte über 95% der theo retischen Dichte beträgt. Die Herstellung erfolgt durch Heißpressen aus einer Mischung aus Ruß und granulierten α-Al2O3-Körpern, die nach der US-A 3 079 243 durch Zerkleinern kaltgepreßter α-Al2O3-Formkörper gewonnen werden.US Pat. No. 3,909,991 describes polycrystalline α-Al 2 O 3 bodies whose crystallite size is in the submicron range and whose density is above 95% of the theoretical density. The production takes place by hot pressing from a mixture of carbon black and granulated α-Al 2 O 3 bodies, which are obtained according to US Pat. No. 3,079,243 by crushing cold-pressed α-Al 2 O 3 shaped bodies.
In der neueren Zeit wurden ähnliche gesinterte Schleifmittel auf α-Al2O3-Basis be kannt, die aufgrund ihrer mikrokristallinen Struktur Vorteile gegenüber den be kannten Korundschleifmitteln aufweisen. So wird in der EP-B 0 152 768 ein Schleifmittel offenbart, das über die Sol-Gel-Technik bei Sintertemperaturen von ca. 1.400°C hergestellt wird. Als Sinterhilfe werden Kristallisationskeime zuge setzt. Ähnliche Verfahren und Stoffe gehen aus der EP-A 0 024 099, DE-A 32 19 607, US-A 4 518 397, US-A 4 574 003, US-A 4 623 364, EP-A 0 168 606, EP-A 0 200 487, EP-A 0 228 856, EP-A 0 209 084 und der EP-A 0 263 810 hervor.More recently, similar sintered abrasives based on α-Al 2 O 3 have been known, which have advantages over the known corundum abrasives due to their microcrystalline structure. For example, EP-B 0 152 768 discloses an abrasive which is produced using the sol-gel technique at sintering temperatures of approximately 1,400 ° C. Crystallization nuclei are added as a sintering aid. Similar processes and substances are known from EP-A 0 024 099, DE-A 32 19 607, US-A 4 518 397, US-A 4 574 003, US-A 4 623 364, EP-A 0 168 606, EP -A 0 200 487, EP-A 0 228 856, EP-A 0 209 084 and EP-A 0 263 810.
Allen letztgenannten Verfahren ist gemeinsam, daß sie über ein Sol-Gel-Verfahren mit feinstdispersem Aluminiumoxidmonohydrat des Typs Böhmit durchgeführt werden. Die verhältnismäßig teuren Rohstoffe, die über die Hydrolyse von Aluminium-organischen Verbindungen gewonnen werden, und die energieaufwen dige Verfahrenstechnik lassen die Kosten des Sol-Gel-Korundes auf ein Vielfaches der herkömmlichen Korunde ansteigen. Ein weiterer Nachteil dieser Verfahren ist, daß die kolloidalen Lösungen meist mit relativ großen Mengen leicht flüchtiger anorganischer Säuren stabilisiert sind, was verfahrens- und umwelttechnische Probleme mit sich bringt. All of the latter methods have in common that they have a sol-gel method with finely dispersed aluminum oxide monohydrate of the boehmite type become. The relatively expensive raw materials that are involved in the hydrolysis of Aluminum-organic compounds are obtained, and the energy expenditure process engineering, the costs of sol-gel corundum are many times over of conventional corundum. Another disadvantage of these methods is that the colloidal solutions are usually more volatile with relatively large amounts inorganic acids are stabilized, which is procedural and environmental Brings problems.
In der DE-C 36 04 848 wird ein Verfahren beschrieben, eine Dispersion aus tonerdehaltigen Rohstoffen, kieselsäurehaltigen Verbindungen und weiteren Zu sätzen (z. B. Verbindungen der Metalle Co, Ni, Mg, Cr, Zr, Zn, Si oder Ti) zu einem sinterfähigen Schlicker zu vermahlen, aus dem durch stufenweises Trocknen und Sintern bei Temperaturen bis 1.700°C ein Schleifmittel hergestellt werden kann, dessen Korundprimärkristallite einen Durchmesser von weniger als 5 µm haben. Das so erhaltene Produkt hat mit einer Kristallitgröße kleiner 5 µm noch nicht die Feinstruktur eines Stoffes, der über die Sol-Gel-Methode mit entsprechenden Sinteradditiven hergestellt wird.DE-C 36 04 848 describes a method of dispersing alumina-containing raw materials, silicic acid-containing compounds and other additives add (e.g. compounds of the metals Co, Ni, Mg, Cr, Zr, Zn, Si or Ti) to grind a sinterable slurry, from which by gradual drying and sintering at temperatures up to 1,700 ° C can, whose primary corundum crystallites have a diameter of less than 5 microns to have. The product obtained in this way has a crystallite size of less than 5 μm not yet the fine structure of a substance using the sol-gel method corresponding sintering additives is produced.
Darüber hinaus müssen nach den in der DE-C 36 04 848 offenbarten Verfahren kieselsäurehaltige Verbindungen zugegeben werden, die als Sinterhilfe fungieren. Bei der Sinterung entsteht daraus durch Reaktion mit dem Aluminiumoxid Mullit. Es ist bekannt, das durch die Anwesenheit silikatischer Phasen die Leistungsstärke eines Schleifkorns herabgesetzt wird.In addition, the method disclosed in DE-C 36 04 848 silicic acid compounds are added, which act as a sintering aid. During sintering, mullite is formed from this by reaction with the aluminum oxide. It is known that due to the presence of silicate phases the performance of an abrasive grain is reduced.
Zahlreiche schleiftechnische Untersuchungen an Sinterkorunden in den letzten Jahren haben gezeigt, daß die Schleifleistung umgekehrt proportional zur Größe der Primärkristalle ist. Das heißt, je feiner das Gefüge ist, umso höher ist in der Regel die Schleifleistung.Numerous grinding tests on sintered corundums in recent years Years have shown that grinding performance is inversely proportional to size is the primary crystals. That is, the finer the structure, the higher the Rule grinding performance.
Die EP-A 0 524 436 offenbart ein Verfahren, wobei statt der teuren Böhmite andere preiswerte Vorstufen des Aluminiumoxids (z. B. Hydrargillit) eingesetzt werden. Durch Vermahlen und anschließende Desagglomeration werden Suspen sionen mit einem Feststoffgehalt zwischen 10 und 40 Gew.-% erhalten, die analog zu den Sol-Gel-Verfahren weiterverarbeitet werden können. Auch bei diesem Ver fahren muß mit sehr viel Energieaufwand das restliche Wasser entfernt werden. Mit Ausnahme des teuren Rohstoffes weist das in der EP-A 0 524 436 be schriebene Verfahren alle verfahrenstechnischen Nachteile der Sol-Gel-Methode auf.EP-A 0 524 436 discloses a method whereby instead of the expensive boehmite other inexpensive precursors of aluminum oxide (e.g. hydrargillite) are used become. By grinding and subsequent deagglomeration Suspen Sions with a solids content between 10 and 40 wt .-% obtained, the analog can be further processed into the sol-gel process. Even with this ver the remaining water has to be removed with a lot of energy. With the exception of the expensive raw material, this is demonstrated in EP-A 0 524 436 Process described all procedural disadvantages of the sol-gel method on.
Im Vergleich zu den Sol-Gel-Verfahren haben jedoch alle bisher bekannten Alter nativ-Verfahren zur Herstellung mikrokristalliner Sinterkorunde, die von preiswer ten Rohstoffen ausgehen, den Nachteil, daß nach der Sinterung deutlich gröbere Strukturen vorliegen als bei den über die Sol-Gel-Verfahren gewonnenen Pro dukten. Die Grunde dafür sind offensichtlich. Die Sol-Gel-Verfahren gehen von besonders feinteiligen Ausgangsstoffen aus, die unter Zugabe von Sinterhilfen ver fahrensbedingt bei sehr niedrigen Temperaturen dichtgesintert werden können. Da durch wird das Kristallwachstum unterdrückt. Die Alternativ-Verfahren benötigen grundsätzlich höhere Sintertemperaturen, die zu einem verstärkten Kristall wachstum führen. Darüber hinaus wird durch die bei der Sinterung stattfindenden Phasenumwandlungen zum α-Al2O3 ein homogenes und unkontrolliertes Kristall wachstum initiiert. Die Leistungsstärke der über die Alternativ-Verfahren ge wonnenen Sinterkorunde liegt somit deutlich unter denen der Sol-Gel-Korunde.Compared to the sol-gel process, however, all previously known alternative processes for the production of microcrystalline sintered corundum, which are based on inexpensive raw materials, have the disadvantage that after sintering there are significantly coarser structures than in the case of the sol-gel processes. Processed products. The reasons for this are obvious. The sol-gel processes are based on particularly finely divided starting materials that can be densely sintered with the addition of sintering aids due to the process at very low temperatures. As a result, crystal growth is suppressed. The alternative processes generally require higher sintering temperatures, which lead to increased crystal growth. In addition, a homogeneous and uncontrolled crystal growth is initiated by the phase conversions to α-Al 2 O 3 which take place during the sintering. The performance of the sintered corundum obtained via the alternative process is therefore significantly lower than that of the sol-gel corundum.
In der EP-A 0 402 G86 wird ein Verfahren aufgezeigt, mikrokristallinen Korund über die elektrophoretische Abscheidung aus einer α-Al2O3-haltigen organischen Suspension zu gewinnen. Es gelingt so, einen relativ dichten Grünkörper zu er halten, der allerdings - trotz der dichten und homogenen Packung - erst bei Temperaturen von 1.600°C dichtgesintert werden kann, so daß es auch hier wieder zu einem verstärkten Kristallwachstum kommt. Das Gefüge eines über die elektro phoretische Abscheidung gewonnen Sinterkorundes ist deutlich gröber als das der über das Sol-Gel-Verfahren hergestellten Sinterkotunde. Entsprechend geringer ist auch die Leistungsstärke der über die Elektrophorese gewonnenen Sinterkorunde.EP-A 0 402 G86 shows a process for extracting microcrystalline corundum from an α-Al 2 O 3 -containing organic suspension by electrophoretic deposition. It is thus possible to maintain a relatively dense green body, which - despite the dense and homogeneous packing - can only be densely sintered at temperatures of 1,600 ° C, so that there is increased crystal growth again. The structure of a sintered corundum obtained by means of electrophoretic deposition is significantly coarser than that of the sintered layer produced using the sol-gel process. The performance of the sintered corundum obtained by electrophoresis is correspondingly lower.
Aufgabe dieser Erfindung ist es somit, ein Verfahren zur Herstellung eines mikrokristallinen α-Al2O3-Sinterkörpers aufzuzeigen, welches die beschriebenen Nachteile des Standes der Technik nicht aufweist, und deren Verwendung anzugeben.It is therefore the object of this invention to provide a method for producing a microcrystalline α-Al 2 O 3 sintered body which does not have the disadvantages of the prior art described, and to indicate the use thereof.
Überraschend wurde gefunden, daß diese Anforderungen erfüllt werden durch ein Verfahren zur Herstellung gesinterter, mikrokristalliner Körper auf Basis von α- Al2O3, dadurch gekennzeichnet, daß als Ausgangsstoff ein α-Al2O3-Pulver mit einer mittleren Korngröße ≦ 3 µm zu einem Schlicker mit einer Partikelgröße < 1 µm vermahlen oder desagglomeriert wird, der Schlicker mit Hilfe eines Wirbelschicht-Sprühgranulators zu Grünkörper mit einer Dichte ≧ 40% der theoretischen Dichte und einer Restfeuchte von ≦ 6 Gew.-% granuliert und anschließend einer Schocksinterung bei Temperaturen im Bereich von 1300 bis 1550°C unterzogen wird.Surprisingly, it was found that these requirements are met by a process for producing sintered, microcrystalline bodies based on α-Al 2 O 3 , characterized in that an α-Al 2 O 3 powder with an average grain size ≦ 3 µm is used as the starting material is ground or deagglomerated into a slurry with a particle size of <1 µm, the slurry is granulated with the aid of a fluidized bed spray granulator into green bodies with a density ≧ 40% of the theoretical density and a residual moisture content of ≦ 6% by weight and then a shock sintering at temperatures in the range from 1300 to 1550 ° C.
Der erste Verfahrensschritt besteht aus einer Naßvermahlung oder einer Desagglo merierung eines bereits möglichst feinteiligen α-Al2O3-Pulvers. Ziel der Naßver mahlung oder Desagglomerierung ist es, eine noch feinere, sehr homogene α- Al2O3-Suspension mit einer extrem feinen Kornverteilungskurve zu erhalten. Die Naßvermahlung und Desagglomerierung wird vorteilhaft im wäßrigen Medium durchgeführt. Im zweiten Schritt wird anschließend die bei der Mahlung oder Des agglomerierung erhaltene wäßrige Suspension in einem Wirbelschichtgranulator zu kugelförmigen Granulaten mit einem Durchmesser zwischen 1 und 10 mm granuliert.The first process step consists of wet grinding or disagglomeration of an α-Al 2 O 3 powder that is already as finely divided as possible. The aim of wet grinding or deagglomeration is to obtain an even finer, very homogeneous α-Al 2 O 3 suspension with an extremely fine particle size distribution curve. The wet grinding and deagglomeration is advantageously carried out in an aqueous medium. In the second step, the aqueous suspension obtained during grinding or de-agglomeration is granulated in a fluidized bed granulator into spherical granules with a diameter between 1 and 10 mm.
Die DE-A 35 07 376 beschreibt ein Verfahren und eine Vorrichtung zur Herstel lung von Granulaten mit enger Kornverteilung, bei denen das zu granulierende Produkt in flüssiger Form in ein Wirbelbett eingesprüht und dort auf entspre chende Keime aufgetragen wird. Die Granulatgröße wird durch die Stärke des Sichtgasstromes eines Zick-Zack-Sichters eingestellt. Ähnliche Verfahren bzw. Weiterentwicklungen der sogenannten Wirbelschicht-Sprühgranulation werden in der DE-A 38 08 277 und der DE-A 43 04 405 beschrieben.DE-A 35 07 376 describes a method and an apparatus for the manufacture development of granules with a narrow particle size distribution, in which the granulate to be granulated Product in liquid form sprayed into a fluidized bed and there on correspond germs are applied. The granule size is determined by the strength of the Visible gas flow of a zigzag classifier set. Similar procedures or Further developments of the so-called fluidized bed spray granulation are in DE-A 38 08 277 and DE-A 43 04 405.
Im dritten Schritt werden die Granulate einer Schocksinterung unterzogen.In the third step, the granules are subjected to shock sintering.
Die Granulate können vor oder nach der Sinterung auf die gewünschte Kornform und -größe zerkleinert werden. Die Aufbereitung und Klassifizierung zur fertigen Schleifkörnung erfolgt nach den üblichen Methoden.The granules can be cut to the desired grain shape before or after sintering size and size. The preparation and classification for the finished Abrasive grains are made using the usual methods.
Nach dem erfindungsgemäßen Verfahren können überraschenderweise, ausgehend von kostengünstigen Rohstoffen, Sinterkorunde gewonnen werden, die in ihren Eigenschaften vergleichbar mit den Sol-Gel-Korunden sind. Da die Kristallitgröße im gesinterten Endprodukt wesentlich von der mittleren Korngröße und der Kornverteilung im Ausgangsmaterial abhängt, ist es zweckmäßig, möglichst feinteilige α-Al2O3-Typen einzusetzen, die dann auf die gewünschte Korngröße vermahlen bzw. desagglomeriert werden.Surprisingly, sintered corundum can be obtained from the method according to the invention, starting from inexpensive raw materials, and its properties are comparable to that of sol-gel corundum. Since the crystallite size in the sintered end product essentially depends on the average grain size and the grain distribution in the starting material, it is expedient to use α-Al 2 O 3 types which are as finely divided as possible and which are then ground or deagglomerated to the desired grain size.
Bevorzugt werden die Feststoffe auf eine mittlere Teilchengröße von kleiner als 1 µm, besonders bevorzugt kleiner als 0,4 µm, herabgemahlen und/oder desagglomeriert, um die gewünschte Ausgangskorngröße zu erhalten bzw. vorliegende Agglomerate in Einzelkristallite zu zerteilen. Die Vermahlung bzw. Desagglomeration wird vorzugsweise naß in Vibrationsmühlen, Attritoren oder Kugelmühlen durchgeführt. Die Mahldauer hängt von der Ausgangskorngröße und dem eingesetzten Mühlentyp ab. Obwohl es naheliegend sein sollte, ein möglichst feinteiliges Ausgangsmaterial zu wählen, sprechen vielfach wirtschaftliche Überle gungen dagegen; denn die superfeinen α-Aluminiumoxide sind häufig so teuer, daß einer der wesentlichen Vorteile des erfindungsgemäßen Verfahrens, nämlich der Einsatz eines kostengünstigen Rohstoffes, verloren geht. Beim erfindungsge mäßen Verfahren können hingegen vorteilhaft auch gröbere α-Al2O3-Aus gangspulver eingesetzt werden.The solids are preferably ground down and / or deagglomerated to an average particle size of less than 1 μm, particularly preferably less than 0.4 μm, in order to obtain the desired starting grain size or to break up the agglomerates present into individual crystallites. The grinding or deagglomeration is preferably carried out wet in vibration mills, attritors or ball mills. The grinding time depends on the starting grain size and the type of mill used. Although it should be obvious to choose a starting material that is as fine as possible, economic considerations often speak against it; because the superfine α-aluminum oxides are often so expensive that one of the essential advantages of the process according to the invention, namely the use of an inexpensive raw material, is lost. In the method according to the invention, however, coarser α-Al 2 O 3 starting powder can advantageously also be used.
Da die Schleifleistung sich umgekehrt proportional zur Primärkristallgröße im Schleifkorn verhält, kann es vorteilhaft sein, das Ausgangsmaterial mit zusätzlichen Komponenten, Sinterhilfen und/oder Kristallwachstumsinhibitoren zu versetzen. Geeignete zusätzliche Komponenten, Sinterhilfen und Kristallwachs tumsinhibitoren sind die Oxide der Elemente Mg, Co, Ni, Zn, Hf, Ti, Zr, Cu, Li, Sr, Ba, K, Nb, Si, B und/oder Seltene Erden.Since the grinding power is inversely proportional to the primary crystal size in Abrasive grain behaves, it may be advantageous to use the starting material additional components, sintering aids and / or crystal growth inhibitors offset. Suitable additional components, sintering aids and crystal wax inhibitors are the oxides of the elements Mg, Co, Ni, Zn, Hf, Ti, Zr, Cu, Li, Sr, Ba, K, Nb, Si, B and / or rare earths.
Die Flüssigkeitsmenge bei der Vermahlung wird vorzugsweise so gewählt, daß die entstehende Suspension einen Feststoffgehalt von 15 bis 80 Gew.-%, bevorzugt 30 bis 70 Gew.-%, aufweist. Als Lösungsmittel wird vorzugsweise Wasser eingesetzt. Gegen andere Lösungsmittel wie z. B. Alkohole, Aceton, die ebenfalls eingesetzt werden können, sprechen vor allem ökologische Überlegungen.The amount of liquid during grinding is preferably chosen so that the resulting suspension has a solids content of 15 to 80% by weight, preferably 30 up to 70% by weight. Water is preferably used as the solvent. Against other solvents such as. B. alcohols, acetone, which are also used ecological considerations speak above all.
Da besonders bevorzugt ein Sinterkörper mit einer mittleren Primärkristallgröße unter 0,4 µm angestrebt wird und bei richtiger Wahl der Sintertemperatur im Falle des erfindungsgemäßen Verfahrens das Kristallwachstum unterdrückt werden kann, reicht es häufig aus, die Mahlung solange fortzusetzen, bis die mittlere Korngröße in der Suspension unter 0,4 µm fliegt.Since a sintered body with an average primary crystal size is particularly preferred less than 0.4 µm is desired and if the sintering temperature is selected correctly In the case of the method according to the invention, crystal growth can be suppressed , it is often sufficient to continue grinding until the middle one Grain size in the suspension flies below 0.4 µm.
Vorteilhaft können Suspensionen, deren Feststoffpartikel eine bimodale Korn verteilungskurve aufweisen, eingesetzt werden.Suspensions whose solid particles have a bimodal grain can be advantageous have distribution curve, are used.
Die besten Ergebnisse können mit Schlicker erzielt werden, deren bimodale Korngrößenverteilung ein Maximum im Bereich zwischen 0,1 und 0,3 µm und ein weiteres Maximum im Bereich zwischen 0,2 und 1,0 µm aufweisen. Die Korngrößenverteilung wird mit Hilfe einer Laser-Dispersion-Methode (Microtrac Type MIC 2, Micromeritics) in einer wäßrigen Lösung und Na4P2O7 als Dispergierhilfe gemessen.The best results can be achieved with slip whose bimodal grain size distribution has a maximum in the range between 0.1 and 0.3 µm and a further maximum in the range between 0.2 and 1.0 µm. The particle size distribution is measured using a laser dispersion method (Microtrac Type MIC 2, Micromeritics) in an aqueous solution and Na 4 P 2 O 7 as a dispersing aid.
Die Suspension kann sterisch oder elektrostatisch durch anorganische oder organische Verbindungen stabilisiert werden. Im Falle der sterischen Stabilisierung können sämtliche bekannten Dispergierhilfen eingesetzt werden. Als solche eignen sich besonders Polyacrylsäuren, Polyglykolsäuren, Polymethacrylsäuren, organi sche Basen wie Triethylamin oder Carbonsäuren wie Essigsäure oder Propion säure. Bevorzugt enthält die Suspension zwischen 0,5 und 5 Gew.-% entspre chender organischer Stabilisatoren. Im Falle der elektrostatischen Stabilisierung können vorteilhaft flüchtige anorganische Säuren wie Salpetersäure oder Salzsäure sowie Ammoniak als Base eingesetzt werden.The suspension can be steric or electrostatic by inorganic or organic compounds are stabilized. In the case of steric stabilization all known dispersing aids can be used. Suitable as such especially polyacrylic acids, polyglycolic acids, polymethacrylic acids, organi bases such as triethylamine or carboxylic acids such as acetic acid or propion acid. The suspension preferably contains between 0.5 and 5% by weight organic stabilizers. In the case of electrostatic stabilization can advantageously volatile inorganic acids such as nitric acid or hydrochloric acid and ammonia can be used as the base.
Die Stabilisierung der Suspension erfolgt entweder schon während oder nach der Vermahlung mit Hilfe eines Dispergators, wodurch eine schnelle und gleichmäßige Verteilung des Stabilisators gewährleistet ist. Bevorzugt vor, aber auch während oder nach der Vermahlung bzw. Stabilisierung können der Suspension Sinteradditive und Bindemittel zugesetzt werden. Als Sinteradditive kommen sämtliche für Al2O3 bekannten Sinterhilfen bzw. deren Vorstufen in Frage.The suspension is stabilized either during or after grinding with the aid of a disperser, which ensures that the stabilizer is distributed quickly and evenly. Sintering additives and binders can preferably be added to the suspension before, but also during or after grinding or stabilization. All sintering aids known for Al 2 O 3 or their precursors are suitable as sintering additives.
Bevorzugt enthält die erfindungsgemäße Suspension 0,5 bis 10 Gew.-% eines oder mehrerer Bindemittel aus der Gruppe Alginate, Dextrin, Glykole, Gummiarabicum, Ligninsulfonat, Methylcellulose, Polyvinylacetat, Polyvinylalkohol, Polyvinylpyrro lidon, Stärke und Zucker, bezogen auf den Feststoffgehalt der Suspension. Ebenso vorteilhaft kann die Suspension 0,5 bis 10 Gew.-% eines oder mehrere Bindemittel aus der Gruppe Böhmit-Sol, Kieselsol und Wasserglas enthalten.The suspension according to the invention preferably contains 0.5 to 10% by weight of one or several binders from the group alginates, dextrin, glycols, gum arabic, Lignin sulfonate, methyl cellulose, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrro lidon, starch and sugar, based on the solids content of the suspension. As well The suspension can advantageously be 0.5 to 10% by weight of one or more binders from the group boehmite sol, silica sol and water glass.
Die Trocknung der Suspension und Verdichtung des Feststoffes erfolgt in einem Schritt in einem Wirbelschichtgranulator. Die Granulation wird vorzugsweise an Luft durchgeführt und kann in einer Wirbelbettapparatur angefahren werden, die bereits Startgranulat enthält. Es ist jedoch auch möglich, die Granulation in einer leeren Apparatur zu starten, wobei die Wirbelbettgranulation als Sprühtrocknung beginnt und in situ Keime erzeugt werden.The suspension is dried and the solid is compacted in one Step in a fluidized bed granulator. The granulation is preferably on Air is carried out and can be started in a fluidized bed apparatus that already contains starting granules. However, it is also possible to do the granulation in one empty apparatus to start, the fluidized bed granulation as spray drying begins and germs are generated in situ.
Die zu granulierende Suspension wird durch Sprühdüsen in das Wirbelbett einge bracht. Besonders vorteilhaft ist die Verwendung von Zweistoffdüsen. Als Zer stäubungsgas kann jedes unter den Arbeitsbedingungen inerte Gas verwendet wer den. Die Menge an Zerstäubergas kann innerhalb eines größeren Bereiches variiert werden und richtet sich im allgemeinen nach den Apparate-Dimensionen und nach der Art und Menge des einzusprühenden Produktes. Die Temperatur des Zerstäu bergas-Stromes bzw. die Lufteintrittstemperatur ist ebenfalls innerhalb eines grö ßeren Bereiches variabel. Im allgemeinen arbeitet man bei Temperaturen zwischen 20 und 350°C. Auch die Sichtgas-Temperaturen sind in einem größeren Bereich variabel. Auch hier arbeitet man bevorzugt in einem Bereich zwischen 20 und 350°C. Die Menge und Geschwindigkeit des Sichtgases richtet sich nach der Dichte und der gewünschten Korngröße des Granulats.The suspension to be granulated is sprayed into the fluidized bed brings. The use of two-component nozzles is particularly advantageous. As Zer Dust gas can be any gas that is inert under the working conditions the. The amount of atomizing gas can vary within a wide range are and generally depends on the dimensions of the apparatus and the type and quantity of the product to be sprayed. The temperature of the atomization Bergas current or the air inlet temperature is also within a gr variable range. Generally one works at temperatures between 20 and 350 ° C. The sight gas temperatures are also in a larger range variable. Here, too, it is preferred to work in a range between 20 and 350 ° C. The amount and speed of the sight gas depends on the Density and the desired grain size of the granulate.
Die Korngröße wird primär durch Gasstrom und Geschwindigkeit des Sichtergases gesteuert. Mit dem in der DE-A 35 07 376 beschriebenem Zick-Zack-Sichter ist es möglich, gezielt ein enges Kornband im Korngrößenbereich zwischen 0,01 und 10 mm mit einer Bandbreite ≦ 1 mm einzustellen. Das fertige Granulat kann direkt - oder nach einem Kalzinier-Zwischenschritt bei Temperaturen zwischen 300 und 600°C - gesintert werden.The grain size is primarily determined by the gas flow and velocity of the classifying gas controlled. With the zigzag sifter described in DE-A 35 07 376 it is possible, a narrow grain band in the grain size range between 0.01 and 10 mm with a bandwidth of ≦ 1 mm. The finished granulate can be used directly - or after an intermediate calcining step at temperatures between 300 and 600 ° C - to be sintered.
Die Sinterung erfolgt bei Temperaturen zwischen 1300°C und 1550°C. Damit liegt die notwendige Sintertemperatur zwar deutlich unter den sonst für das Sintern von konventioneller α-Al202-Keramik üblichen Temperaturen von ca. 1600°C, ist aber gleichzeitig immer noch wesentlich höher, als die beim Sol-Gel-Prozeß erfor derliche Temperatur, die vorzugsweise unter 1300°C liegt. Um so überraschender ist es, daß es bei dem erfindungsgemäßen Verfahren gelingt, das Kristallwachstum nahezu vollständig zu unterdrücken. Dazu muß neben der Feinteiligkeit und sehr engen Kornverteilung des Ausgangspulvers und der hohen Dichte des Grünkörpers als weitere Voraussetzung ein sehr schnelles Erreichen der notwendigen Sinter temperatur gewährleistet sein. Das heißt, daß der Grünkörper möglichst schnell in die heißeste Zone des Sinterofens gelangen sollte. Durch diese Schocksinterung gelingt es, den Sinterprozess abzuschließen, bevor das Kristallwachstum einsetzt. Gleichzeitig wird der Sinterprozess durch die gute Vorverdichtung beschleunigt. Die homogene Kornverteilung und die Feinheit des Ausgangsstoffes begünstigt ein gleichmäßiges Dichtsintern, wobei ein Zusammenwachsen der Primärkristalle zu größeren Kristalliten vermieden werden kann.Sintering takes place at temperatures between 1300 ° C and 1550 ° C. Thus, the necessary sintering temperature is significantly lower than the usual temperatures for the sintering of conventional α-Al 2 0 2 ceramics of approx. 1600 ° C, but at the same time it is still significantly higher than that required for the sol-gel process Temperature, which is preferably below 1300 ° C. It is all the more surprising that the process according to the invention succeeds in almost completely suppressing crystal growth. In addition to the fine particle size and very narrow particle size distribution of the starting powder and the high density of the green body, a further requirement is that the required sintering temperature be reached very quickly. This means that the green body should get into the hottest zone of the sintering furnace as quickly as possible. This shock sintering enables the sintering process to be completed before crystal growth begins. At the same time, the good pre-compression speeds up the sintering process. The homogeneous grain distribution and the fineness of the starting material favors a uniform dense sintering, whereby a coalescence of the primary crystals into larger crystallites can be avoided.
Für die Sinterung eignen sich sämtliche Ofentypen bzw. Sintetverfahren, die ein schlagartiges Aufheizen des Grünkörpers ermöglichen. Vorteilhaft können direkt oder indirekt beheizte Drehrohröfen, Pendelöfen, Durchschuböfen, Wirbelschicht sinteröfen oder Mikrowellensinteröfen eingesetzt werden. Vorteilhaft erfolgt die Schocksinterung so, daß der Grünkörper in ≦ 60 Sekunden, bevorzugt ≦ 10 Sekunden, besonders bevorzugt ≦ 3 Sekunden, auf die erforderliche Sinter temperatur gebracht wird. Die Haltezeit bei der Sinterung beträgt ≦ 60 Minuten, bevorzugt ≦ 30 Minuten, besonders bevorzugt ≦ 15 Minuten. All types of furnaces or sinting processes are suitable for sintering allow sudden heating of the green body. Can be beneficial directly or indirectly heated rotary kilns, pendulum furnaces, push-through furnaces, fluidized beds sintering ovens or microwave sintering ovens are used. This is advantageous Shock sintering so that the green body in ≦ 60 seconds, preferably ≦ 10 Seconds, particularly preferably ≦ 3 seconds, on the required sintering temperature is brought. The holding time during sintering is ≦ 60 minutes, preferably ≦ 30 minutes, particularly preferably ≦ 15 minutes.
Die Zerkleinerung der Granulate zur gewünschten Körnung erfolgt aus energeti schen Gründen vorteilhaft direkt nach der Granulation. Je nach Einsatzzweck kann es jedoch auch vorteilhaft sein, daß nach dem Kalzinierschritt oder nach der Sinte rung die Zerkleinerung der Granulate durchgeführt wird, um besonders scharfe Schneidkanten zu erhalten.The granules are crushed to the desired grain size from energeti reasons immediately after granulation. Depending on the application however, it may also be advantageous that after the calcining step or after the sine The crushing of the granules is carried out to make them particularly sharp Get cutting edges.
Gegenüber der Elektrophorese hat das erfindungsgemäße Verfahren den Vorteil, daß bei vergleichbaren Korngrößen der Ausgangsstoffe feinere Kristallitgefüge im gesinterten Endprodukt erhalten werden können.The method according to the invention has the advantage over electrophoresis that that with comparable grain sizes of the starting materials finer crystallite structure in sintered end product can be obtained.
Da die Feinheit des Kristallitgefüges in direkter Relation zur Leistungsstärke des Schleifkorns steht, kann nach dem erfindungsgemäßen Verfahren ein Schleifkorn mit einer höheren Abtragsleistung zur Verfügung gestellt werden. Ein weiterer Vorteil aus ökologischer Sicht besteht darin, daß in wäßrigem Medium gearbeitet werden kann und eine Umweltbelastung durch organische Lösungsmittel vermieden wird.Since the fineness of the crystallite structure is directly related to the performance of the Abrasive grain stands, can be an abrasive grain according to the inventive method with a higher stock removal rate. Another An advantage from an ecological point of view is that it works in an aqueous medium and environmental pollution from organic solvents is avoided.
Gegenüber den Sol-Gel-Verfahren ergeben sich ebenfalls - neben dem ökonomischen Vorteil durch den Einsatz von preiswerten Rohstoffen - nicht zu unterschätzende ökologische Vorteile. So werden beim Sol-Gel-Verfahren zur Stabilisierung der Suspension relativ große Mengen an leicht flüchtigen Säuren eingesetzt, die während des Trocknens und vor allem während des Kalzinierens verdampft werden müssen. Bei den Säuren handelt es sich vorzugsweise um Salpeter- oder Salzsäure.Compared to the sol-gel process, there are also - in addition to the economic advantage through the use of inexpensive raw materials - not too underestimated environmental benefits. So in the sol-gel process Stabilization of the suspension of relatively large amounts of volatile acids used during drying and especially during calcining need to be evaporated. The acids are preferably Nitric or hydrochloric acid.
Dabei treten Umweltbelastungen auf, die trotz aufwendiger Technik noch nicht vollständig vermieden werden können. Ein weiterer Vorteil gegenüber den Sol-Gel-Verfahren besteht in der Einfachheit des erfindungsgemäßen Verfahrens, wodurch die Fertigung im kontinuierlichen Produktionsbetrieb erleichtert wird, was letztendlich wieder wirtschaftliche Vorteile mit sich bringt.There are environmental impacts that, despite the complex technology, are not yet can be completely avoided. Another advantage over the Sol-gel method consists in the simplicity of the method according to the invention, whereby the production in the continuous production operation is facilitated, what ultimately brings economic benefits again.
Nach dem erfindungsgemäßen Verfahren gelingt die Herstellung von hochdichten gesinterten, mikrokristallinen Körpern mit einer hohen Härte, deren Kristallitgröße zwischen 0,1 und 10 µm einstellbar ist. Aufgrund dieser Eigenschaften eignen sich diese Sinterkörper hervorragend als Schleifmittel, wobei hier die Kristallitgrößen zwischen 0,1 bis 3 µm betragen. The process according to the invention enables high-density to be produced sintered, microcrystalline bodies with a high hardness, their crystallite size is adjustable between 0.1 and 10 µm. Because of these properties are suitable these sintered bodies are excellent as abrasives, with the crystallite sizes here be between 0.1 and 3 µm.
Gegenstand dieser Erfindung ist somit auch die Verwendung der erfindungsgemäß hergestellten gesinterten mikrokristallinen Körper als Schleifmittel und für die Herstellung von Schleif- und Schneidwerkzeugen.This invention therefore also relates to the use of the invention produced sintered microcrystalline body as an abrasive and for the Manufacture of grinding and cutting tools.
Da die Schleifeigenschaften wesentlich von der Kristallitstruktur des jeweiligen Schleifkorns abhängen, gelingt es nach dem erfindungsgemäßen Verfahren für die verschiedensten Anwendungszwecke Schleifkörnungen mit einem für die jeweilige Anwendung optimalen Kristallitgefüge bereitzustellen.Because the grinding properties differ significantly from the crystallite structure of each Depend on abrasive grain, it succeeds in the inventive method for the Various applications with one grit for the To provide optimal crystallite structure for each application.
Im folgenden wird die Erfindung beispielhaft erläutert, ohne daß darin eine Einschränkung zu sehen ist. In the following the invention will be explained by way of example without one Restriction can be seen.
α-Aluminiumoxid mit einer mittleren Korngröße (d50) von 1,5 µm wurde in einer Rührwerkskugelmühle (Typ PMC 25 TEX, Fa. Drais) auf eine mittlere Korngröße (d50) von 320 nm in wäßrigem Medium vermahlen. Die entstehende Slurry mit einem Feststoffgehalt von 30 Gew.-% und einem d90 von 630 nm wurde mit einer 10%igen wäßrigen Suspension eines Polyvinyl alkohols als Binder (Mowiol 8/88, Hoechst AG, Deutschland) vermischt, so daß der Anteil des Binders ca. 4 Gew.-% betrug, bezogen auf den Feststoffgehalt der Slurry.α-Alumina with an average grain size (d 50 ) of 1.5 μm was ground in an agitator ball mill (type PMC 25 TEX, Drais) to an average grain size (d 50 ) of 320 nm in an aqueous medium. The resulting slurry with a solids content of 30 wt .-% and ad 90 of 630 nm was mixed with a 10% aqueous suspension of a polyvinyl alcohol as a binder (Mowiol 8/88, Hoechst AG, Germany), so that the proportion of Binder was approximately 4% by weight, based on the solids content of the slurry.
Anschließend wurde die Suspension in einem Wirbelschicht- Sprühgranulator (AGT 400, Fa. Glatt Deutschland) bei einer Lufteintrittstemperatur von 320°C, einer Schichttemperatur von 75°C und einer Sprührate von 2,4 kg/min zu Grünkörpern mit einer Dichte von ≧ 40% der theoretischen Dichte verarbei tet. Zur Keimbildung wurde eine feine Granulatfraktion mit einer mittleren Granulatgröße zwischen 0,5 und 1 mm, die bei einer vorangegangenen Wirbelschicht-Sprühgranulation über eine in-situ-Keimbildung gewonnen worden war, eingesetzt.The suspension was then placed in a fluidized bed Spray granulator (AGT 400, Glatt Germany) at one Air inlet temperature of 320 ° C, a layer temperature of 75 ° C and a spray rate of 2.4 kg / min to green bodies with a density of ≧ 40% of the theoretical density tet. A fine granulate fraction was used to nucleate an average granule size between 0.5 and 1 mm, which at a previous fluidized bed spray granulation in situ nucleation was used.
Die Abtrennung des gewünschten Granulats erfolgte über einen Zick-Zack-Sichter. 60 Gew.-% des so gewonnenen Granulats hatten einen Durchmesser zwischen 3 und 5 mm, ca. 30 Gew.-% der Granulate hatten eine Durchmesser zwischen 1 und 3 mm und ca. 10 Gew.-% der Granulate hatten einen Durchmesser von < 5 mm. Die Restfeuchte der Granulate lag unter 1%.The desired granules were separated off using a Zigzag sifter. 60% by weight of the granules obtained in this way had a diameter between 3 and 5 mm, approx. 30% by weight the granules had a diameter between 1 and 3 mm approx. 10% by weight of the granules had a diameter of <5 mm. The residual moisture of the granules was less than 1%.
Die Granulate wurden zerkleinert und anschließend bei 1480°C in einem beheizten Drehrohr reiner Schocksinterung bei Temperaturen von 1300 bis 1550°C unterzogen.The granules were crushed and then at 1480 ° C shock sintering in a heated rotary tube Subjected to temperatures from 1300 to 1550 ° C.
Das erhaltene Produkt hat eine Vickershärte (HV 0,2) von 20,1 GPa und eine mittlere Primärkristallitgröße von 0,38 µm. Die Dichte liegt bei 98,7% der theoretischen Dichte. The product obtained has a Vickers hardness (HV 0.2) of 20.1 GPa and an average primary crystallite size of 0.38 µm. The Density is 98.7% of the theoretical density.
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EP3384980A1 (en) | 2017-04-06 | 2018-10-10 | SASOL Germany GmbH | Process for production of attrition stable granulated material |
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