EP1301434A2 - Nanoscale corundum powders, sintered compacts produced from these powders and method for producing the same - Google Patents

Nanoscale corundum powders, sintered compacts produced from these powders and method for producing the same

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Publication number
EP1301434A2
EP1301434A2 EP01960526A EP01960526A EP1301434A2 EP 1301434 A2 EP1301434 A2 EP 1301434A2 EP 01960526 A EP01960526 A EP 01960526A EP 01960526 A EP01960526 A EP 01960526A EP 1301434 A2 EP1301434 A2 EP 1301434A2
Authority
EP
European Patent Office
Prior art keywords
corundum
precursor
aluminum
temperatures
powders
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.)
Withdrawn
Application number
EP01960526A
Other languages
German (de)
French (fr)
Inventor
Robert Drumm
Christian Goebbert
Kai Gossmann
Ralph Nonninger
Helmut Schmidt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Leibniz-Institut fur Neue Materialien Gemeinnuet
Original Assignee
Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
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Application filed by Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH filed Critical Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Publication of EP1301434A2 publication Critical patent/EP1301434A2/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
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    • 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
    • C01F7/34—Preparation of aluminium hydroxide by precipitation from solutions containing aluminium salts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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    • 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
    • C01F7/44—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water
    • C01F7/441—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination
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    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/62605—Treating the starting powders individually or as mixtures
    • C04B35/62645—Thermal treatment of powders or mixtures thereof other than sintering
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    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
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Definitions

  • NANOSKAL1GE COROD POWDER SINTER BODIES MADE THEREOF AND METHOD FOR THE PRODUCTION THEREOF
  • the invention relates to nanoscale corundum powder, a process for their production and their processing into sintered bodies.
  • Powdered corundum ( ⁇ - Al 2 O 3 ) is an important raw material for the production of aluminum oxide ceramics, which can basically be done in two ways.
  • One way starts with shaped bodies that are made directly from corundum powder ( ⁇ -AI 2 0 3 powder), the other from shaped bodies that consist of an -AI 2 0 3 precursor (for example, the ⁇ or ⁇ phase) , which is then converted in situ into the ⁇ -AI 0 3 phase.
  • the sintering temperature of the corundum is between 1300 and 1600 ° C, depending on the size of the starting particles used.
  • the most important obstacle to this is the high activation energy of the homogeneous nucleation, which is kinetically strongly delayed, so that the other Al 2 0 3 phases (e.g.
  • US-A-4657754 describes nanoscale corundum having an average particle size of 20 and 50 nm (jr nanocorundum "), which is produced by seeding, so that the synthesis temperature may be reduced so that at 1000 ° C ⁇ -AI 2 0 3 -Powder with a density of 3.78 g / cm 3 (corresponds to 95% of the theoretical density) is present.
  • Weng et al. describe another method from salt solutions in CN-A-085187, which likewise gives nanocorundus with a diameter of 10 to 15 nm at synthesis temperatures of 1100 to 1300 ° C.
  • a synthesis temperature of 1000 ° C is too high for many purposes, in particular for cofiring processes in microelectronics with foils or the sealing sintering of pastes.
  • the synthesis temperature can be reduced to values below 1000 ° C. by means of a special process technology, an only weakly agglomerated nanoscale corundum powder being obtained which can be sintered at lower sintering temperatures.
  • This seemingly minor improvement is of eminent technical importance, since it enables a much broader field of application to be worked on.
  • new multi-layer systems can be processed in a single cofiring step (which previously required several sintering steps at higher temperatures), since all the multilayer elements contained can now be compressed at the lower sintering temperature.
  • the invention relates to a process for the preparation of nanoscale corundum powders, in which one first produces an Al 2 0 3 precursor by adding an aqueous solution of an aluminum compound with seed crystals and adding a base and the Al 2 O 3 precursor then by calcining at elevated temperatures The temperature is converted to corundum, which is characterized in that the salts present in addition to the Al 2 O 3 precursor are separated off before the calcination, the product obtained is calcined at temperatures from 700 to 975 ° C. and any fines present ( ⁇ 40 nm) are removed ,
  • Aluminum compounds suitable for producing the Al 2 O 3 precursor are preferably water-soluble aluminum salts such as aluminum (IH) nitrate, aluminum (III) chloride, aluminum (III) acetate or aluminum (III) ethylate. These aluminum compounds are dissolved, for example, in deionized water and seed crystals are added, which preferably have a particle size ⁇ 100 nm. Examples of suitable germs are corundum or diasporic germs.
  • the desired Al 2 O 3 precursor which is required for conversion to corundum at temperatures below 1000 ° C., is formed during a ripening period.
  • bases which can be used are inorganic or organic bases, such as sodium, potassium, calcium or magnesium hydroxide, ammonia, urea, aliphatic and aromatic amines, thermally separable bases such as ammonia being particularly preferred.
  • the precipitation or ripening usually takes place at temperatures of 50 to 100 ° C., preferably 70 to 90 ° C. and particularly preferably 80 to 90 ° C., over a period of 20 to 145 hours, preferably 60 to 90 hours and particularly preferably 70 to 80 hours.
  • the n-corundum is preferably produced using the following two alternative methods.
  • the aqueous solvent is preferably removed by freeze-drying and the salts contained as impurities are thermally decomposed at temperatures of 150 to 500 ° C., for example 400 ° C.
  • the product obtained is mechanically comminuted and converted into ⁇ -Al 2 O 3 by calcining at temperatures from 700 to 975 ° C., preferably 750 to 950 ° C. and in particular 800 to 900 ° C.
  • Caicination is usually carried out over a period of 1 to 3 hours.
  • the corundum powder obtained by method 1 is characterized by a high
  • Corundum content but as a secondary phase still contains a small fine fraction ( ⁇ 40 nm), which mainly consists of non- ⁇ -Al 2 0 3 phases. It is essential to the invention to at least largely remove this fine fraction by a later one To enable compaction of the nanoscale corundum powder at sintering temperatures ⁇ 1200 ° C.
  • the fine fraction is preferably removed by centrifugation.
  • the corundum powder produced is dispersed in aqueous solution with the aid of a dispersant (surface modifier) and then centrifuged one or more times.
  • Suitable dispersants are, for example, inorganic acids (preferably HNO 3 ), aromatic or aliphatic mono-, di- or polycarboxylic acids, aromatic or aliphatic oxacarboxylic acids, such as trioxadecanoic acids (TODS), ⁇ -dicarbonyl compounds and amino acids.
  • the dispersant concentration is adapted to the specific surface of the synthesized corundum powder, so that, for example, 4-5 ⁇ mol of dispersant are available per m 2 Al 2 O 3 surface.
  • the existing salt load is reduced or removed by dialysis.
  • the solution containing the AI 2 0 3 precursor is filled into dialysis tubes and stored in deionized water.
  • the dialyzed solution is then frozen and freeze-dried.
  • the powder obtained can, if necessary, be calcined at 150 to 500.degree. C. (for example 400.degree. C.) to completely remove the salt content still present.
  • the powder is converted into ⁇ -Al 2 O 3 by calcining at temperatures from 700 to 975 ° C., preferably 750 to 950 ° C. and in particular 800 to 900 ° C.
  • ⁇ -Al 2 0 3 powder obtained after surface modification with suitable surface modifiers such as inorganic acids (preferably HN0 3 ), .aromatic or aliphatic mono-, di- or polycarboxylic acids, aromatic or aliphatic oxacarboxylic acids, for example trioxadecanoic acids (TODS), ⁇ -dicarbonyl compounds or amino acids, can be compressed directly at sintering temperatures ⁇ 1200 ° C.
  • suitable surface modifiers such as inorganic acids (preferably HN0 3 ), .aromatic or aliphatic mono-, di- or polycarboxylic acids, aromatic or aliphatic oxacarboxylic acids, for example trioxadecanoic acids (TODS), ⁇ -dicarbonyl compounds or amino acids
  • the amount of surface modifier is the specific surface of the synthesized corundum powder adapted so that, for example, 4-5 ⁇ mol of dispersant are available per m 2 Al 2 O 3 surface.
  • the surface can be modified, for example, using a ball mill (3-4 h, aluminum oxide grinding balls ⁇ 1 mm), mortar mills, three-roller mill or kneading unit, adapted to the subsequent shaping technique.
  • the average primary particle size is usually 30 to 150 nm, preferably 40 to 100 nm and particularly preferably 50 to 70 nm.
  • the corundum powder is only slightly agglomerated in the redispersed state. It has a phase purity (content of ⁇ -Al 2 0 3 ) of> 80, preferably> 90 and in particular> 95% by weight and a density of> 3.90 g / cm 3 , preferably 3 3.93 g / cm 3 , particularly preferably> 3.95 g / cm 3 .
  • the corundum powder produced according to the invention is used for further shaping with conventional processing aids, e.g. organic solvents, binders, plasticizers, mixed.
  • suitable solvents are e.g. Ethylene glycol, diethylene glycol monobutyl ether and diethylene glycol monoethyl ether, individually or as mixtures.
  • binders which can be used are cellulose derivatives such as hydroxypropyl cellulose, polyvinylpyrrolidone, acrylate polymers and oligomers,
  • Methacrylates such as tetraethylene glycol dimethacrylate and polyethylene glycoidimethacrylate. The following are used e.g. 15% by weight of binder, based on the weighed solid.
  • binder e.g. 15% by weight of binder, based on the weighed solid.
  • polyethylene glycol dimethacrylates, polyethylene glycols e.g. PEG 600, PEG 800, PEG 1000, PEG 2000, PEG 6000
  • plasticizers e.g. PEG 600, PEG 800, PEG 1000, PEG 2000, PEG 6000
  • 25% by weight based on the weighed-in binder.
  • the nanoscale corundum powders according to the invention are suitable for producing dense Al 2 O 3 sintered bodies in the form of components or constituents of multilayer structures.
  • Special application areas of these components and Multi-layer systems are (micro) electronics, sensors (gas, pressure, piezo sensors), microsystem technology (eg microreactors), ceramic filter elements and catalyst carriers.
  • the solution obtained is frozen (for example at -30 ° C.) and then dried (freeze-drying).
  • the powder is then heated to 400 ° C. (air atmosphere) at a heating rate of 2 K / min and kept at this temperature for 1 h.
  • the powder is ground dry in a mortar mill for 1 hour.
  • the powder is then brought to 800 ° C. at a heating rate of 10 K / min and immediately heated to 900 ° C. at a heating rate of 2 K / min and kept at this temperature for 1 hour.
  • the powder produced in this way has a specific surface area of approximately 20-60 m 2 / g and a density of 3.6-3.9 g / cm 3 , depending on the germs used.
  • the powder After cooling, the powder is dispersed for 3-4 hours in a ball mill with aluminum oxide grinding balls ( ⁇ 1 mm) and an organic acid (TODS) as a dispersant / surface modifier.
  • the dispersant content is adapted to the specific surface of the synthesized aluminum oxide powder, so that 4-5 ⁇ mol TODS per m 2 Al 2 O 3 surface are contained.
  • the fine fraction of the aluminum oxide powder obtained is separated off by repeated centrifugation.
  • the separation limit for centrifugation is arithmetically a particle size of approximately 40 nm.
  • the fine fraction consists predominantly (> 90%) of non- ⁇ -Al 2 0 3 particles.
  • the centrifugate is freeze-dried to remove the solvent.
  • the resulting solution is purified by dialysis in portions containing approximately 400 g ammonium nitrate to remove the dissolved ammonium nitrate ions.
  • the solution is poured into a dialysis tube (pore size 2.5 - 3 nmj and approx.
  • a hold period of 1 is inserted at 900 ° C.
  • the powder thus produced has a specific surface area of approx. 18-22 m 2 / g and a density of 3.95-3.98 g / cm 3 .
  • the primary particle size is between 40-70 nm, the powder is weakly agglomerated in the redispersed state.
  • Example 1 10.5 g of the ⁇ -Al 2 0 3 prepared in Example 1 are homogeneously mixed together with 2.8 g of a 1: 1 solvent mixture of ethylene glycol and diethylene glycol monobutyl ether and 0.5 g of polyvinylpyrrolidone as a binder. Mortars, kneaders or mortar mills can be used as mixing units. The paste obtained is applied several times to a three-roll mill for the final homogenization.
  • the aluminum oxide paste is applied using a thick-film process (screen printing) to already sintered corundum substrates or green (unsintered) substrates made of yttrium-stabilized (3 mol% Y 2 0 3 ) zirconium dioxide in dry layer thicknesses of up to 30 ⁇ m and dried without cracks in a circulating air drying cabinet at 80 ° C.
  • the printed layers on the corundum substrates are thermally compacted at 1200 ° C (heating rate 5K / min) with a holding time of 1 hour.
  • the compression of the ⁇ -Al 2 0 3 layers printed on green (unsintered) substrates made of yttrium-stabilized zirconium dioxide takes place in two stages.
  • the organic matter contained in the composite is removed in a protective gas atmosphere (nitrogen) at temperatures up to 450 ° C by thermal decomposition.
  • the heating up time is 10 hours, holding time 3 hours.
  • the thermal compression up to the dense material composite takes place in an atmosphere furnace at temperatures of
  • Example 2 5 2 g of the -Al 2 0 3 powder produced in Example 1 are homogeneously mixed with 1 g of a solvent mixture of ethylene glycol / diethylene glycol monobutyl ether (1: 1) and 0.15 g of a cellulose binder and dried at 100 ° C. 200 mg of the mixture are compressed in a uniaxial pressing tool with an inner diameter of 5 mm at a pressure of 200 MPa. Then ⁇ Q is post-compressed in a cold isostatic press at 400 MPa. The compact is thermally compressed at 1200 ° C (1h) in an air atmosphere. After sintering, the shaped body has a density of 3.85 g / cm 3 (96.5% of theory).

Abstract

Nanoscale corundum powders are obtained by first producing an Al2O3 precursor by adding seed crystals to an aqueous solution of an aluminium compound and adding a base and then converting the Al2O3 precursor into corundum by calcination at a high temperature. Before the calcination, the salts that are present in addition to the Al2O3 precursor are separated off. The resulting product is calcinated at temperatures of 700 to 975 DEG C and any fines that may be present are removed. The resulting corundum powders can be sintered at temperatures ≤ 1200 DEG C to produce compacts or components of multiple layer systems.

Description

NANOSKAL1GE KORUNDPULVER, DARAUS GEFERTIGTE SINTERKÖRPER UND VERFAHREN ZU DEREN HERSTELLUNG NANOSKAL1GE COROD POWDER, SINTER BODIES MADE THEREOF AND METHOD FOR THE PRODUCTION THEREOF
Die Erfindung betrifft nanoskaiige Korundpulver, ein Verfahren zu deren Herstellung und deren Verarbeitung zu Sinterkörpern.The invention relates to nanoscale corundum powder, a process for their production and their processing into sintered bodies.
Pulverförmiger Korund (α- AI2O3) ist ein wichtiger Rohstoff zur Herstellung von Aluminiumoxidkeramik, die grundsätzlich auf zwei Wegen erfolgen kann. Ein Weg geht aus von Formkörpern, die direkt aus Korundpulver (α-AI203-Pulver) gefertigt sind, der andere von Formkörpern, die aus einer -AI203-Vorstufe (beispielsweiise der γ- oder Θ-Phase) bestehen, welche dann in situ in die α-AI 03-Phase umgewandelt wird.Powdered corundum (α- Al 2 O 3 ) is an important raw material for the production of aluminum oxide ceramics, which can basically be done in two ways. One way starts with shaped bodies that are made directly from corundum powder (α-AI 2 0 3 powder), the other from shaped bodies that consist of an -AI 2 0 3 precursor (for example, the γ or Θ phase) , which is then converted in situ into the α-AI 0 3 phase.
Bei der Verarbeitung üblicher Korundpulver zu dichten Sinterkörpern liegt die Sintertemperatur des Korund, je nach verwendeter Ausgangsteilchengröße, zwischen 1300 und 1600°C. Es hat vielfache Versuche gegeben, die Sintertemperatur von Korund zu reduzieren bzw. die thermodynamisch stabile α- AI 03.Phase bei wesentlich niedrigen Temperaturen zu erreichen. Wichtigster Hinderungsgrund dabei ist die hohe Aktivierungsenergie der homogenen Nukleation, die kinetisch stark verzögert ist, so dass sich aus den anderen Al203-Phasen (z. B.When conventional corundum powder is processed to form dense sintered bodies, the sintering temperature of the corundum is between 1300 and 1600 ° C, depending on the size of the starting particles used. There have been numerous attempts to reduce the sintering temperature of corundum or to achieve the thermodynamically stable α-AI 0 3 phase at significantly lower temperatures. The most important obstacle to this is the high activation energy of the homogeneous nucleation, which is kinetically strongly delayed, so that the other Al 2 0 3 phases (e.g.
- der γ- oder Θ-Phase) eine solche Nukleation nur bei höheren Temperaturen erreichen lässt, da hier die Diffusionskoeffizienten höher liegen. Es hat daher nicht an Versuchen gefehlt, durch Zugabe von Keimen die Umwandlungstemperatur deutlich zu erniedrigen; siehe EP-A-554908, US-A-4657754 und WO 98/55400.- the γ- or Θ-phase) can only achieve such nucleation at higher temperatures, since the diffusion coefficients are higher here. There has therefore been no lack of attempts to significantly lower the transition temperature by adding germs; see EP-A-554908, US-A-4657754 and WO 98/55400.
Beispielsweise beschreibt die US-A-4657754 nanoskaligen Korund mit einer mittleren Partikelgröße von 20 und 50 nm (jrNanokorund"), der durch Bekeimen hergestellt wird, wodurch die Synthesetemperatur so reduziert werden kann, dass bei 1000°C α-AI203-Pulver mit einer Dichte von 3,78 g/cm3 (entspricht 95 % der theoretischen Dichte) vorliegt. Weng et al. beschreiben in der CN-A- 085187 ein anderes Verfahren aus Salzlösungen, das ebenfalls Nanokorund von 10 bis 15 nm Durchmesser bei Synthesetemperaturen von 1100 bis 1300°C ergibt.For example, US-A-4657754 describes nanoscale corundum having an average particle size of 20 and 50 nm (jr nanocorundum "), which is produced by seeding, so that the synthesis temperature may be reduced so that at 1000 ° C α-AI 2 0 3 -Powder with a density of 3.78 g / cm 3 (corresponds to 95% of the theoretical density) is present. Weng et al. describe another method from salt solutions in CN-A-085187, which likewise gives nanocorundus with a diameter of 10 to 15 nm at synthesis temperatures of 1100 to 1300 ° C.
Eine Synthesetemperatur von 1000°C ist jedoch für viele Zwecke zu hoch, insbesondere für Cofiringprozesse in der Mikroelektronik mit Folien oder das Dichtsintern von Pasten. Gleiches gilt für die relativ hohe Sintertemperatur herkömmlicher Korundpulver von 1300 bis 1600°C.However, a synthesis temperature of 1000 ° C is too high for many purposes, in particular for cofiring processes in microelectronics with foils or the sealing sintering of pastes. The same applies to the relatively high sintering temperature of conventional corundum powder from 1300 to 1600 ° C.
Überraschenderweise wurde nun gefunden, dass über eine besondere Verfahrenstechnik die Synthesetemperatur auf Werte unter 1000°C abgesenkt werden kann, wobei ein nur schwach agglomeriertes nanoskaliges Korundpulver erhalten wird, das bei niedrigeren Sintertemperaturen gesintert werden kann. Diese gering erscheinende Verbesserung ist von eminenter technischer Bedeutung, da hierdurch ein deutlich breiteres Anwendungsfeld bearbeitet werden kann. Beispielsweise können neuartige Merhschichtsysteme in einem einzigen Cofiring-Schritt verarbeitet werden (wozu zuvor mehrere Sinterschritte bei höheren Temperaturen erforderlich waren), da nun alle enthaltenen Mehrschichtelemente bei der niedrigeren Sintertemperatur verdichtet werden können.Surprisingly, it has now been found that the synthesis temperature can be reduced to values below 1000 ° C. by means of a special process technology, an only weakly agglomerated nanoscale corundum powder being obtained which can be sintered at lower sintering temperatures. This seemingly minor improvement is of eminent technical importance, since it enables a much broader field of application to be worked on. For example, new multi-layer systems can be processed in a single cofiring step (which previously required several sintering steps at higher temperatures), since all the multilayer elements contained can now be compressed at the lower sintering temperature.
Gegenstand der Erfindung ist ein Verfahren zur Herstellung von nanoskaligen Korundpulvern, bei dem man zunächst einen AI203-Precursor herstellt durch Versetzen einer wässrigen Lösung einer Aluminiumverbihdung mit Keimkristallen und Zugabe einer Base und den AI2O3-Precursor dann durch Calcinieren bei erhöhter Temperatur in Korund überführt, das dadurch gekennzeichnet ist, daß man vor der Calcinierung die neben dem AI2O3-Precursor vorhandenen Salze abtrennt, das erhaltene Produkt bei Temperaturen von 700 bis 975°C calciniert und gegebenenfalls vorhandene Feinanteile (< 40 nm) entfernt.The invention relates to a process for the preparation of nanoscale corundum powders, in which one first produces an Al 2 0 3 precursor by adding an aqueous solution of an aluminum compound with seed crystals and adding a base and the Al 2 O 3 precursor then by calcining at elevated temperatures The temperature is converted to corundum, which is characterized in that the salts present in addition to the Al 2 O 3 precursor are separated off before the calcination, the product obtained is calcined at temperatures from 700 to 975 ° C. and any fines present (<40 nm) are removed ,
Zur Herstellung des AI2O3-Precursors geeignete Aluminiumverbindungen sind vorzugsweise wasserlösliche Aluminiumsalze wie Aluminium(IH)nitrat, Aluminium(lll)chlorid, Aluminium(lll)acetat oder Aluminium(lll)ethylat. Diese Aluminiumverbindungen werden z.B. in deionisiertem Wasser gelöst und mit Keimkristallen versetzt, die vorzugsweise eine Partikelgröße < 100 nm aufweisen. Beispiele für geeignete Keime sind Korund- oder Diaspor-Keime.Aluminum compounds suitable for producing the Al 2 O 3 precursor are preferably water-soluble aluminum salts such as aluminum (IH) nitrate, aluminum (III) chloride, aluminum (III) acetate or aluminum (III) ethylate. These aluminum compounds are dissolved, for example, in deionized water and seed crystals are added, which preferably have a particle size <100 nm. Examples of suitable germs are corundum or diasporic germs.
Durch Zugabe einer Base bildet sich während einer Reifezeit der gewünschte AI2O3- Precursor, der zur Umwandlung in Korund bei Temperaturen unter 1000°C erforderlich ist. Beispiele für verwendbare Basen sind anorganische oder organische Basen, wie Natrium-, Kalium-, Calcium- oder Magnesiumhydroxid, Ammoniak, Harnstoff, aliphatische und aromatische Amine, wobei thermisch abtrennbare Basen wie Ammoniak besonders bevorzugt sind. ,By adding a base, the desired Al 2 O 3 precursor, which is required for conversion to corundum at temperatures below 1000 ° C., is formed during a ripening period. Examples of bases which can be used are inorganic or organic bases, such as sodium, potassium, calcium or magnesium hydroxide, ammonia, urea, aliphatic and aromatic amines, thermally separable bases such as ammonia being particularly preferred. .
Die Ausfällung bzw. Reifung erfolgt gewöhnlich bei Temperaturen von 50 bis 100°C, vorzugsweise 70 bis 90°C und besonders bevorzugt 80 bis 90°C, über einen Zeitraum von 20 bis 145 Stunden, bevorzugt 60 bis 90 Stunden und besonders bevorzugt 70 bis 80 Stunden.The precipitation or ripening usually takes place at temperatures of 50 to 100 ° C., preferably 70 to 90 ° C. and particularly preferably 80 to 90 ° C., over a period of 20 to 145 hours, preferably 60 to 90 hours and particularly preferably 70 to 80 hours.
Nach dieser Reifung erfolgt die n-Korund-Herstellung vorzugsweise nach den folgenden beiden alternativen Methoden.After this ripening, the n-corundum is preferably produced using the following two alternative methods.
Bei der Methode 1 wird das wässrige Lösungsmittel vorzugsweise durch Gefriertrocknung entfernt und die als Verunreinigungen enthaltenen Salze werden bei Temperaturen von 150 bis 500°C, beispielsweise 400°C, thermisch zersetzt. Das erhaltene Produkt wird mechanisch zerkleinert und durch Calcinieren bei Temperaturen von 700 bis 975°C, vorzugsweise 750 bis 950°C und insbesondere 800 bis 900°C in α-AI2O3 umgewandelt. Die Caicinierung erfolgt gewöhnlich über einen Zeitraum von 1 bis 3 Stunden.In method 1, the aqueous solvent is preferably removed by freeze-drying and the salts contained as impurities are thermally decomposed at temperatures of 150 to 500 ° C., for example 400 ° C. The product obtained is mechanically comminuted and converted into α-Al 2 O 3 by calcining at temperatures from 700 to 975 ° C., preferably 750 to 950 ° C. and in particular 800 to 900 ° C. Caicination is usually carried out over a period of 1 to 3 hours.
Das nach der Methode 1 erhaltene Korundpulver zeichnet sich durch einen hohenThe corundum powder obtained by method 1 is characterized by a high
Korundanteil aus, enthält jedoch als Nebenphase noch ein geringen Feinanteil (< 40 nm), der hauptsächlich aus Nicht-α-AI203-Phasen besteht. Erfindungswesentlich ist es, diesen Feinanteil zumindest weitgehend zu entfernen, um eine spätere Verdichtung der nanoskaligen Korundpulver bei Sintertemperaturen < 1200 °C zu ermöglichen.Corundum content, but as a secondary phase still contains a small fine fraction (<40 nm), which mainly consists of non-α-Al 2 0 3 phases. It is essential to the invention to at least largely remove this fine fraction by a later one To enable compaction of the nanoscale corundum powder at sintering temperatures <1200 ° C.
Die Abtrennung des Feinanteils erfolgt vorzugsweise durch Zentrifugation. Hierzu wird das hergestellte Korundpulver mit Hilfe eines Dispergiermittels (Oberflächen- modifikator) in wässriger Lösung dispergiert und anschließend ein- oder mehrmals zentrifugiert. Geeignete Dispergiermittel sind z.B. anorganische Säuren (vorzugsweise HNO3), aromatische oder aliphatische Mono- Di- oder Polycarbonsäuren, aromatische oder aliphatische Oxacarbonsäuren, wie Trioxadecansäre (TODS), ß- Dicarbonylverbindungen und Aminosäuren. Die Dispergiermittelkonzentration wird der spezifischen Oberfläche des synthetisierten Korundpulvers angepasst, so dass beispielsweise 4-5 μmol Dispergiermittel pro m2 AI203-Oberfläche zur Verfügung stehen.The fine fraction is preferably removed by centrifugation. For this purpose, the corundum powder produced is dispersed in aqueous solution with the aid of a dispersant (surface modifier) and then centrifuged one or more times. Suitable dispersants are, for example, inorganic acids (preferably HNO 3 ), aromatic or aliphatic mono-, di- or polycarboxylic acids, aromatic or aliphatic oxacarboxylic acids, such as trioxadecanoic acids (TODS), β-dicarbonyl compounds and amino acids. The dispersant concentration is adapted to the specific surface of the synthesized corundum powder, so that, for example, 4-5 μmol of dispersant are available per m 2 Al 2 O 3 surface.
Bei der Methode 2 wird die vorhandene Salzbeladung durch Dialyse reduziert oder entfernt. Dazu wird die den AI203-Precursor enthaltende Lösung in Dialyseschläuche gefüllt und in deionisiertem Wasser eingelagert. Die dialysierte Lösung wird anschließend eingefroren und gefriergetrocknet. Das erhaltene Pulver kann zur vollständigen Entfernung des noch vorhandenen Salzgehaltes gegebenenfalls noch bei 150 bis 500°C (z.B. 400 °C) calciniert werden. Die Umwandlung des Pulvers in α-AI2O3 erfolgt wie bei Methode 1 durch Calcinieren bei Temperaturen von 700 bis 975°C, vorzugsweise 750 bis 950°C und insbesondere 800 bis 900°C.In method 2, the existing salt load is reduced or removed by dialysis. For this purpose, the solution containing the AI 2 0 3 precursor is filled into dialysis tubes and stored in deionized water. The dialyzed solution is then frozen and freeze-dried. The powder obtained can, if necessary, be calcined at 150 to 500.degree. C. (for example 400.degree. C.) to completely remove the salt content still present. As in method 1, the powder is converted into α-Al 2 O 3 by calcining at temperatures from 700 to 975 ° C., preferably 750 to 950 ° C. and in particular 800 to 900 ° C.
Bei dieser Methode 2 entsteht während der Synthese kein oder nur eine geringe Menge Feinanteil aus Nicht-α-AI203-Phasen, so dass das erhaltene α-AI203-Pulver nach einer Oberflächenmodifizierung mit geeigneten Oberflächenmodifikatoren, wie anorganischen Säuren (vorzugsweise HN03), .aromatischen oder aliphatischen Mono-, Di- oder Polycarbonsäuren, aromatischen oder aliphatischen Oxacarbonsäuren, z.B. Trioxadecansäre (TODS), ß-Dicarbonylverbindungen oder Aminosäuren, direkt bei Sintertemperaturen < 1200 °C verdichtet werden kann. Die Menge des Oberflächenmodifikators wird der spezifischen Oberfläche des synthetisierten Korundpulvers angepasst, so dass beispielsweise 4-5 μmol Dispergiermittel pro m2 AI203-Oberfläche zur Verfügung stehen. Die Oberflächenmodifizierung kann z.B. mittels Kugelmühle (3-4 h, Aluminiumoxid- Mahlkugeln < 1 mm), Mörsermühlen, Dreiwalzenstuhl oder Knetaggregat erfolgen, angepasst an die darauf folgende Formgebungstechnik.In this method 2, no or only a small amount of fine fraction is formed from non-α-Al 2 0 3 phases during the synthesis, so that the α-Al 2 0 3 powder obtained after surface modification with suitable surface modifiers, such as inorganic acids ( preferably HN0 3 ), .aromatic or aliphatic mono-, di- or polycarboxylic acids, aromatic or aliphatic oxacarboxylic acids, for example trioxadecanoic acids (TODS), β-dicarbonyl compounds or amino acids, can be compressed directly at sintering temperatures <1200 ° C. The amount of surface modifier is the specific surface of the synthesized corundum powder adapted so that, for example, 4-5 μmol of dispersant are available per m 2 Al 2 O 3 surface. The surface can be modified, for example, using a ball mill (3-4 h, aluminum oxide grinding balls <1 mm), mortar mills, three-roller mill or kneading unit, adapted to the subsequent shaping technique.
Danach liegt ein redispergierbares Korundpulver vor, dass über unterschiedliche Formgebungsverfahren wie Foliengießen, Siebdruck, Tampondruck, Elektrophorese, Schlickerguß, Extrusion, Spritzguß, weiterverarbeitet werden kann. Die mittlere Primärpartikelgröße beträgt gewöhnlich 30 bis 150 nm, vorzugsweise 40 bis 100 nm und besonders bevorzugt 50 bis 70 nm. Das Korundpulver ist im redispergierten Zustand nur schwach agglomeriert. Es hat eine Phasenreinheit (Gehalt an α-AI203 ) von > 80, vorzugsweise > 90 und insbesondere > 95 Gew.-% und eine Dichte von > 3,90 g/cm3, vorzugsweise ≥ 3,93 g/cm3, besonders bevorzugt > 3,95 g/cm3.Thereafter, there is a redispersible corundum powder which can be processed further using various shaping processes such as film casting, screen printing, pad printing, electrophoresis, slip casting, extrusion, injection molding. The average primary particle size is usually 30 to 150 nm, preferably 40 to 100 nm and particularly preferably 50 to 70 nm. The corundum powder is only slightly agglomerated in the redispersed state. It has a phase purity (content of α-Al 2 0 3 ) of> 80, preferably> 90 and in particular> 95% by weight and a density of> 3.90 g / cm 3 , preferably 3 3.93 g / cm 3 , particularly preferably> 3.95 g / cm 3 .
Das erfindungsgemäß hergestellte Korundpulver wird zur weiteren Formgebung mit üblichen Verarbeitungshilfsmitteln, z.B. organischen Lösungsmitteln, Bindemitteln, Weichmachern, vermischt. Als Lösungsmittel eignen sich z.B. Ethylenglycol, Diethylenglycolmonobutylether und Diethylenglycolmonoethylether, einzeln oder als Gemische. Beispiele für verwendbare Bindemittel sind Cellulosederivate wie Hydroxypropylcellulose, Polyvinylpyrrolidon, Acrylat-Polymere und -Oligomere,The corundum powder produced according to the invention is used for further shaping with conventional processing aids, e.g. organic solvents, binders, plasticizers, mixed. Suitable solvents are e.g. Ethylene glycol, diethylene glycol monobutyl ether and diethylene glycol monoethyl ether, individually or as mixtures. Examples of binders which can be used are cellulose derivatives such as hydroxypropyl cellulose, polyvinylpyrrolidone, acrylate polymers and oligomers,
Methacrylate wie Tetraethylenglycol-dimethacrylat und Polyethylenglycoi- dimethacrylat. Eingesetzt werden dabei z.B. 15 Gew.% Bindemittel, bezogen auf den eingewogenen Feststoff. Als Weichmacher werden beispielsweise Polyethylen- glycol-dimethacrylate, Polyethyienglycole (z.B. PEG 600, PEG 800, PEG 1000, PEG 2000, PEG 6000) verwendet. Eingesetzt werden z.B. 25 Gew.%, bezogen auf das eingewogene Bindemittel.Methacrylates such as tetraethylene glycol dimethacrylate and polyethylene glycoidimethacrylate. The following are used e.g. 15% by weight of binder, based on the weighed solid. For example, polyethylene glycol dimethacrylates, polyethylene glycols (e.g. PEG 600, PEG 800, PEG 1000, PEG 2000, PEG 6000) are used as plasticizers. For example, 25% by weight, based on the weighed-in binder.
Die erfindungsgemäßen nanoskaligen Korundpulver eignen sich zur Herstellung von dichten Al203-Sinterkörpern in Form von Bauteilen oder Bestandteilen von mehrschichtigen Strukturen. Spezielle Anwendungsgebiete dieser Bauteile und Mehrsschichtsysteme sind die (Mikro)Elektronik, Sensorik (Gas-, Druck-, Piezosensoren), Mikrosystemtechnik (z.B. Mikroreaktoren), keramische Filterelemente und Katalysatorträger.The nanoscale corundum powders according to the invention are suitable for producing dense Al 2 O 3 sintered bodies in the form of components or constituents of multilayer structures. Special application areas of these components and Multi-layer systems are (micro) electronics, sensors (gas, pressure, piezo sensors), microsystem technology (eg microreactors), ceramic filter elements and catalyst carriers.
Die folgenden Beispiele erläutern die Erfindung.The following examples illustrate the invention.
Beispiel 1example 1
Herstellung des n-KorundsProduction of the n-corundum
In einem Glasrührbehälter werden 16 I deionisiertes Wasser vorgelegt, in die 4 kg AI(N03)3 . 6H20 unter Rühren zugegeben werden. Danach werden 60 g Aluminiumoxidkeime (α-Aluminiumoxid oder Diaspor) in Form einer 5-20 gew.-%igen wässrigen Suspension (pH-Wert > 3) zugesetzt. Die Lösung wird auf eine Temperatur von 85°C ± 5°C erwärmt. Mittels wässriger Ammoniaklösung (25 Gew.- %) wird der pH-Wert der Lösung auf pH = 4,8 + 0,1 eingestellt. Die Lösung wird 72 h bei einer Temperatur von 85°C ± 5°C unter Rühren gehalten. Nach den 72 h können zwei alternative Wege zur Herstellung von nanoskaligem Korund eingeschlagen werden.16 I of deionized water are placed in a glass stirred container, into which 4 kg of Al (NO 3 ) 3 . 6H 2 0 are added with stirring. Then 60 g of aluminum oxide seeds (α-aluminum oxide or diaspore) in the form of a 5-20% strength by weight aqueous suspension (pH> 3) are added. The solution is heated to a temperature of 85 ° C ± 5 ° C. The pH of the solution is adjusted to pH = 4.8 + 0.1 using aqueous ammonia solution (25% by weight). The solution is kept under stirring for 72 h at a temperature of 85 ° C ± 5 ° C. After the 72 h, two alternative ways of producing nanoscale corundum can be taken.
Methode 1Method 1
Die erhaltene Lösung wird eingefroren (beispielsweise bei -30°C) und anschließend getrocknet (Gefriertrocknung). Danach wird das Pulver mit einer Aufheizrate von 2 K/min auf 400°C aufgeheizt (Luftatmosphäre) und 1 h bei dieser Temperatur gehalten. Nach dem Abkühlen wird das Pulver 1 h in einer Mörsermühle trocken zerkleinert. Anschließend wird das Pulver mit einer Aufheizrate von 10 K/min auf 800°C gebracht und sofort mit einer Aufheizrate von 2 K/min auf 900°C erwärmt und 1 h bei dieser Temperatur gehalten. Das so hergestellte Pulver hat eine spezifische Oberfläche von circa 20-60 m2/g und eine Dichte von 3,6-3,9 g/cm3, jeweils abhängig von den eingesetzten Keimen. Nach dem Abkühlen wird das Pulver 3-4 h in einer Kugelmühle mit Aluminiumoxidmahlkugeln (< 1 mm) und einer organischen Säure (TODS) als Dispergiermittel/Oberflächenmodifikator dispergiert. Der Dispergiermittel-Gehalt wird der spezifischen Oberfläche des synthetisierten Aluminiumoxidpulvers angepasst, so dass 4-5 μmol TODS pro m2 AI203-Oberfläche enthalten sind. Nach dem Mahlprozeß wird der Feinanteil des erhaltenen Aluminiumoxidpulvers durch mehrmalige Zentrifugation abgetrennt. Die Trenngrenze bei der Zentrifugation liegt rechnerisch bei einer Partikelgröße von ca. 40 nm. Der Feinanteil besteht zu einem überwiegenden Anteil (> 90%) aus nicht α-AI203-Partikeln. Das Zentrifugat wird zur Entfernung des Lösungsmittels gefriergetrocknet.The solution obtained is frozen (for example at -30 ° C.) and then dried (freeze-drying). The powder is then heated to 400 ° C. (air atmosphere) at a heating rate of 2 K / min and kept at this temperature for 1 h. After cooling, the powder is ground dry in a mortar mill for 1 hour. The powder is then brought to 800 ° C. at a heating rate of 10 K / min and immediately heated to 900 ° C. at a heating rate of 2 K / min and kept at this temperature for 1 hour. The powder produced in this way has a specific surface area of approximately 20-60 m 2 / g and a density of 3.6-3.9 g / cm 3 , depending on the germs used. After cooling, the powder is dispersed for 3-4 hours in a ball mill with aluminum oxide grinding balls (<1 mm) and an organic acid (TODS) as a dispersant / surface modifier. The dispersant content is adapted to the specific surface of the synthesized aluminum oxide powder, so that 4-5 μmol TODS per m 2 Al 2 O 3 surface are contained. After the grinding process, the fine fraction of the aluminum oxide powder obtained is separated off by repeated centrifugation. The separation limit for centrifugation is arithmetically a particle size of approximately 40 nm. The fine fraction consists predominantly (> 90%) of non-α-Al 2 0 3 particles. The centrifugate is freeze-dried to remove the solvent.
Methode 2Method 2
Die erhaltene Lösung wird in Portionen, die ca. 400 g Ammoniumnitratenthalten, zur Entfernung der gelösten Ammoniumnitrat-Ionen durch Dialyse gereinigt. Dazu wird die Lösung in einen Dialyseschlauch (Porengröße 2,5 - 3 nmj eingefüllt und ca.The resulting solution is purified by dialysis in portions containing approximately 400 g ammonium nitrate to remove the dissolved ammonium nitrate ions. For this purpose, the solution is poured into a dialysis tube (pore size 2.5 - 3 nmj and approx.
2 Stunden in deionisiertem Wasser aufbewahrt, danach wird das Wasser ausgetauscht und erneut 2 Stunden dialysiert. Die dialysierte Lösung wird eingefroren (beispielsweise bei -30 °C) und anschließend getrocknet (Gefrier- trocknung). Gegebenenfalls kann man danach das Pulver noch mit einer Aufheizrate f von 2 K/min auf 400°C aufheizen (Luftatmosphäre) und 1 h bei dieser Temperatur halten. Dieser Schritt ist jedoch nicht unbedingt erforderlich. Anschließend wird dasStored in deionized water for 2 hours, after which the water is replaced and dialyzed again for 2 hours. The dialyzed solution is frozen (for example at -30 ° C.) and then dried (freeze-drying). If necessary, the powder can then be heated to 400 ° C. at a heating rate f of 2 K / min (air atmosphere) and kept at this temperature for 1 h. However, this step is not absolutely necessary. Then that will
Pulver mit einer Aufheizrate von 10 K/min auf 800°C gebracht und sofort mit einerPowder brought to 800 ° C with a heating rate of 10 K / min and immediately with a
Aufheizrate von 2 K/min auf 900°C erwärmt. Bei 900°C wird eine Halteperiode von 1 eingefügt.Heating rate of 2 K / min heated to 900 ° C. A hold period of 1 is inserted at 900 ° C.
Das so hergestellte Pulver hat eine spezifische Oberfläche von ca. 18-22 m2/g und eine Dichte von 3,95-3,98 g/cm3. Die Primärpartikelgröße liegt zwischen 40-70 nm, das Pulver ist im redispergierten Zustand schwach agglomeriert. Beispiel 2The powder thus produced has a specific surface area of approx. 18-22 m 2 / g and a density of 3.95-3.98 g / cm 3 . The primary particle size is between 40-70 nm, the powder is weakly agglomerated in the redispersed state. Example 2
Herstellung von gesinterten Aluminiumoxid-Schichten in MehrlagensvstemenProduction of sintered aluminum oxide layers in multi-layer systems
10,5 g des in Beispiel 1 hergestellten α-AI203 werden zusammen mit 2,8 g eines 1:1 Lösungsmittelgemisches aus Ethylenglycol und Diethylengiycolmonobutylether und 0,5 g Polyvinylpyrrolidon als Bindemittel homogen vermischt. Als Mischaggregate können Mörser, Kneter oder Mörsermühlen verwendet werden. Die dabei erhaltene Paste wird zur abschließenden Homogenisierung mehrfach auf einen Dreiwalzenstuhl aufgegeben.10.5 g of the α-Al 2 0 3 prepared in Example 1 are homogeneously mixed together with 2.8 g of a 1: 1 solvent mixture of ethylene glycol and diethylene glycol monobutyl ether and 0.5 g of polyvinylpyrrolidone as a binder. Mortars, kneaders or mortar mills can be used as mixing units. The paste obtained is applied several times to a three-roll mill for the final homogenization.
Die Aluminiumoxidpaste wird über ein Dickschichtverfahren (Siebdruck) auf bereits gesinterte Korundsubstrate bzw. grüne (ungesinterte) Substrate aus Yttriumstabilisiertem (3 Mol% Y203) Zirkondioxid in Trockenschichtdicken bis zu 30 μm aufgetragen und im Umlufttrockenschrank bei 80°C rissfrei getrocknet. Die gedruckten Schichten auf den Korundsubstraten werden bei 1200°C (Aufheizrate 5K/min) mit einer Haltezeit von 1 Stunde thermisch verdichtet. Die Verdichtung der auf grüne (ungesinterte) Substrate aus Yttrium-stabilisiertem Zirkondioxid gedruckten α-AI203-Schichten erfolgt zweistufig. In der ersten Stufe wird die im Verbund enthaltene Organik unter Schutzgasatmosphäre (Stickstoff) bei Temperaturen bis zu 450°C durch thermische Zersetzung entfernt. Die Aufheizdauer beträgt 10 Stunden, Haltezeit 3 Stunden. Die thermische Verdichtung bis zum dichten Materialverbund erfolgt in einem Atmosphärenofen bei Temperaturen vonThe aluminum oxide paste is applied using a thick-film process (screen printing) to already sintered corundum substrates or green (unsintered) substrates made of yttrium-stabilized (3 mol% Y 2 0 3 ) zirconium dioxide in dry layer thicknesses of up to 30 μm and dried without cracks in a circulating air drying cabinet at 80 ° C. The printed layers on the corundum substrates are thermally compacted at 1200 ° C (heating rate 5K / min) with a holding time of 1 hour. The compression of the α-Al 2 0 3 layers printed on green (unsintered) substrates made of yttrium-stabilized zirconium dioxide takes place in two stages. In the first stage, the organic matter contained in the composite is removed in a protective gas atmosphere (nitrogen) at temperatures up to 450 ° C by thermal decomposition. The heating up time is 10 hours, holding time 3 hours. The thermal compression up to the dense material composite takes place in an atmosphere furnace at temperatures of
1200X, Haltezeit 3 Stunden, Aufheizrate 5K/min. Beispiel 31200X, holding time 3 hours, heating rate 5K / min. Example 3
Herstellung von gesinterten Aluminiumoxid-Sinterkörper aus erfindungsgemäßem - AI?Q3 PulverProduction of sintered aluminum oxide sintered body from - AI? Q 3 powder according to the invention
5 2 g des in Beispiel 1 hergestellten -Al203-Pulvers werden mit 1 g eines Lösungsmittelgemisches aus Ethylenglycol/Diethylenglycolmonobutylether (1:1) sowie 0,15 g eines Cellulose-Bindemittels homogen vermischt und bei 100°C getrocknet. 200 mg der Mischung werden in einem uniaxialen Preßwerkzeug mit 5 mm Innendurchmesser bei einem Druck von 200 MPa verdichtet. Anschließend wird ~ Q in einer Kaltisostatpresse bei 400 MPa nachverdichtet. Der Preßling wird bei 1200°C (1h) unter Luftatmosphäre thermisch verdichtet. Der Formkörper hat nach der Sinterung eine Dichte von 3,85 g/cm3 ( 96,5 % der Theorie). 5 2 g of the -Al 2 0 3 powder produced in Example 1 are homogeneously mixed with 1 g of a solvent mixture of ethylene glycol / diethylene glycol monobutyl ether (1: 1) and 0.15 g of a cellulose binder and dried at 100 ° C. 200 mg of the mixture are compressed in a uniaxial pressing tool with an inner diameter of 5 mm at a pressure of 200 MPa. Then ~ Q is post-compressed in a cold isostatic press at 400 MPa. The compact is thermally compressed at 1200 ° C (1h) in an air atmosphere. After sintering, the shaped body has a density of 3.85 g / cm 3 (96.5% of theory).

Claims

Patentansprüche claims
1. Verfahren zur Herstellung von nanoskaligen Korundpulvern, bei dem man zunächst einen AI203-Precursor herstellt durch Versetzen einer wässrigen1. A process for the preparation of nanoscale corundum powders, in which one first produces an Al 2 0 3 precursor by adding an aqueous one
5 Lösung einer Aluminiumverbindung mit Keimkristallen und Zugabe einer Base und den AI203-Precursor dann durch Calcinieren bei erhöhter Temperatur in Korund überführt, dadurch gekennzeichnet, daß man vor der Caicinierung die neben dem AI203-Precursor vorhandenen Salze abtrennt, das erhaltene Produkt bei Temperaturen von 700 bis 975°C calciniert und gegebenenfalls -10 vorhandene Feinanteile (< 40 nm) entfernt.5 solution of an aluminum compound with seed crystals and addition of a base and the Al 2 0 3 precursor then converted to corundum by calcining at elevated temperature, characterized in that the salts present next to the Al 2 0 3 precursor are separated off before the caicination, the the product obtained is calcined at temperatures from 700 to 975 ° C. and any -10 fine particles present (<40 nm) are removed.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als Aluminiumverbindung Aluminium(lll)nitrat, Aluminium(lll)chlorid, Aluminium- (lll)acetat oder Aluminium(lll)ethylat verwendet.2. The method according to claim 1, characterized in that aluminum (III) nitrate, aluminum (III) chloride, aluminum (III) acetate or aluminum (III) ethylate is used as the aluminum compound.
1515
3. ~ Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß man als3. ~ Method according to claim 1 or 2, characterized in that as
Keimkristalle Korund- oder Diaspor-Keime verwendet.Seed crystals corundum or diaspore seeds are used.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß 20 man zur Herstellung des AI203-Precursors eine thermisch abtrennbare Base, vorzugsweise Ammoniak verwendet.4. The method according to any one of claims 1 to 3, characterized in that 20 a thermally separable base, preferably ammonia, is used to produce the Al 2 0 3 precursor.
5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß während und/oder nach der Herstellung des AI203-Precursors eine Reifung5. The method according to any one of claims 1 to 4, characterized in that a ripening during and / or after the preparation of the AI 2 0 3 precursor
25 bei Temperaturen im Bereich von 50 bis 100°C erfolgt.25 at temperatures in the range of 50 to 100 ° C.
6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß man vor der Caicinierung die Salze durch Dialyse und/oder thermische Zersetzung abtrennt.6. The method according to any one of claims 1 to 5, characterized in that the salts are separated by dialysis and / or thermal decomposition before the caicination.
30 30
7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß man die Caicinierung bei 800 bis 900°C durchführt.7. The method according to any one of claims 1 to 6, characterized in that one carries out the caicination at 800 to 900 ° C.
8. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß 5 man vorhandenen Feinanteil durch Dispergieren des Korundpulvers und anschließende Zentrifugation entfernt.8. The method according to any one of claims 1 to 7, characterized in that 5 one removes existing fine fraction by dispersing the corundum powder and subsequent centrifugation.
9. Nanoskaliges Korundpulver mit einem Gehalt an α- Al203 von mindestens 80 Gew.-% und einer Dichte von mindestens 3,90 g/cm3, erhältlich nach dem p Verfahren eines der Ansprüche 1 bis 8.9. Nanoscale corundum powder with a content of α-Al 2 0 3 of at least 80% by weight and a density of at least 3.90 g / cm 3 , obtainable by the p method of one of claims 1 to 8.
10. Zusammensetzungen enthaltend ein nanoskaliges Korundpulver nach Anspruch 9 und übliche Verarbeitungshilfsmittel.10. Compositions containing a nanoscale corundum powder according to claim 9 and conventional processing aids.
5 11. Verfahren zur Herstellung von dichten Al203-Sinterkörpern, dadurch gekenn- , zeichnet, daß man eine Zusammensetzung nach Anspruch 10 in einem üblichen Formgebungsverfahren zu einem Formkörper oder einem Bestandteil einer Mehrschichtenstruktur formt und dann sintert.11 process for the production of dense Al 2 0 3 sintered bodies, characterized in that a composition according to claim 10 is formed into a shaped body or a component of a multilayer structure in a conventional molding process and then sintered.
0 12. Verfahren nach Anspruch 11, dadurch gekennzeichnet, daß die Sinterung bei Temperaturen < 1200°C erfolgt. 0 12. The method according to claim 11, characterized in that the sintering takes place at temperatures <1200 ° C.
EP01960526A 2000-07-21 2001-07-20 Nanoscale corundum powders, sintered compacts produced from these powders and method for producing the same Withdrawn EP1301434A2 (en)

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