EP1651583A1 - Method for producing a precursor ceramic - Google Patents

Method for producing a precursor ceramic

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Publication number
EP1651583A1
EP1651583A1 EP04738504A EP04738504A EP1651583A1 EP 1651583 A1 EP1651583 A1 EP 1651583A1 EP 04738504 A EP04738504 A EP 04738504A EP 04738504 A EP04738504 A EP 04738504A EP 1651583 A1 EP1651583 A1 EP 1651583A1
Authority
EP
European Patent Office
Prior art keywords
carbon
precursor
ceramic
carbon nanotubes
precursor ceramic
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.)
Ceased
Application number
EP04738504A
Other languages
German (de)
French (fr)
Inventor
Martin Koehne
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.)
Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of EP1651583A1 publication Critical patent/EP1651583A1/en
Ceased legal-status Critical Current

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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
    • C04B35/71—Ceramic products containing macroscopic reinforcing agents
    • C04B35/78—Ceramic products containing macroscopic reinforcing agents containing non-metallic materials
    • C04B35/80—Fibres, filaments, whiskers, platelets, or the like
    • 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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Definitions

  • the invention relates to a method for producing a precursor ceramic according to the preamble of the independent claim.
  • amorphous SiOC ceramics are obtained by pyrolysis of element-organic precursors.
  • Advantages of this precursor thermolysis process compared to conventional manufacturing processes for ceramics (sintering) are the significantly lower process temperatures and the easy processability and formability of the elemental organic precursors, e.g. of polysiloxane resins.
  • the filler components used include those made from chromium, molybdenum, silicon and intermetallic compounds from representatives of the fourth to sixth subgroups of the periodic table with boron, silicon or aluminum. These fillers are necessary, otherwise shrinkage cracks and excessive pores occur during pyrolysis. With the help of these fillers it is possible to get certain Properties such as coefficient of thermal expansion, thermal conductivity or the specific electrical resistance of the composite can be set precisely.
  • a polysiloxane ie, a polymer based on Si, C, O and H, being used as the starting material, for example, can be selected accordingly Fillers cut the electrical or physical property profile of the ceramic composite material resulting after pyrolysis exactly to the respective requirement profile, for example a ceramic glow plug. In particular, it is possible in this way to set the electrical conductivity from very good to insulating.
  • Crack toughness K ⁇ c ⁇ 2 MPa m can, however, only be improved to a limited extent by fillers with a low aspect ratio, ie a low ratio of length to diameter of ⁇ 5. Fillers with a high aspect ratio of> 10, such as fibers, provide significantly better results.
  • Precursor ceramic is porous due to the gaseous decomposition products that arise during pyrolysis.
  • the pore size is in the range from approximately 300 to approximately 800 nm.
  • the connection of whiskers, typically with a diameter of approximately 1 ⁇ m and lengths of approximately 100 ⁇ m, and fibers to the precursor ceramic is impaired by these pores, since the pores cause the reduce the effective whisker / fiber surface adhering to the precursor ceramic.
  • the reinforcing effect of whiskers and fibers in components made of precursor ceramic is reduced.
  • carbon nanotubes / fibers carbon nanotubes - in the following as
  • Carbon nanotubes) for reinforcing precursor ceramics has advantages due to the much smaller dimensions with the same aspect ratio.
  • Typical dimensions of carbon nanotubes are diameters from approximately 20 to approximately 120 nm with a length of approximately 0.5 to approximately 200 ⁇ m.
  • carbon nanotubes are very insensitive to the mechanical stresses in the Production (mixing, kneading, grinding, sieving) of the composite of organic precursor, fillers and possibly carbon nanotubes, since even when the carbon nanotubes are comminuted, for example by halving, the aspect ratio is still large enough.
  • Carbon nanotubes as fiber reinforcement in composites are of great interest due to their outstanding properties and are already used in plastic composites and sintered ceramics.
  • WO 01/92381 A1 describes a method for forming a composite of embedded nanofibers in a polymer matrix. The process includes that
  • nanofiber-reinforced polymer composite system which has a plurality of nanofibers embedded in polymer matrices.
  • One method of making nanotube-reinforced fibers involves mixing a nanofiber into a polymer and inducing an orientation of the nanofiber that enables it to be used to improve mechanical, thermal, and electrical properties.
  • WO 02/18296 discloses a ceramic matrix nanocomposite with improved mechanical behavior. This consists of a filler made of carbon nanotubes and a ceramic matrix, which is composed of a nanocrystalline ceramic oxide. By sintering the article formed from it, ceramic materials with improved fracture toughness can be obtained.
  • MWNT multiwall carbon nanotubes carbon nanotubes
  • the object of the invention is to improve the properties of composites made of precursor ceramics.
  • the method according to the invention for producing ceramic composite materials from element-organic precursor polymers has the advantage over the prior art that the properties of the composite materials produced can be significantly improved.
  • connection of the carbon nanotubes to the precursor ceramic is decisive for the reinforcing effect of the carbon nanotubes. Without an appropriate connection, the force that acts on the precursor ceramic cannot be absorbed by the carbon nanotubes.
  • the connection of the carbon tubes to the precursor ceramic can be considerably improved by the present invention insofar as the connection connects the carbon nanotubes to the precursor ceramic in a non-positive manner.
  • the connection to the precursor ceramic takes place by adjusting the content of free carbon which is formed during the decomposition of the polymer precursor of the precursor ceramic, ie the element-organic precursors.
  • the addition of reactive additives or pyrolysis in a hydrogen-containing atmosphere results in an approximately stoichiometric to moderately substoichiometric carbon content of the precursor ceramic in the range of, for example, approximately 15% carbon excess to approximately 50%.
  • Carbon deficit set The preferred carbon content is in the range of ⁇ 5% around the stoichiometric carbon content.
  • the resulting good connection through the resulting chemical bond between carbon nanotubes and precursor ceramic is responsible for the improvement of the mechanical and thermal properties.
  • This principle can be applied to all precursor ceramics made from carbonaceous element organic polymeric precursors, e.g. Polysilazanes, polycarbosilanes, polysiloxanes, polysilanes, polyborazanes and the like.
  • carbon nanotubes according to the invention By using carbon nanotubes according to the invention, the above-mentioned. Improve properties. In contrast to the use of fibers or whiskers, there is no deterioration in the structural unit, since the carbon nanotubes, in contrast to whiskers, for example, are smaller than the filler articles.
  • the amount of free carbon, as it arises during the decomposition of the polymer precursors of the precursor ceramic, can be controlled in two ways.
  • suitable reactive additives can be added, whereby the formation of free carbon is suppressed or a carbon deficit is generated. This forces the precursor ceramic to bind to the carbon nanotubes.
  • Suitable additives are those which react with a) the oxygen and / or b) with the carbon of the precursor ceramic.
  • the additives react with the oxygen of the precursor ceramic (case a)) correspondingly more carbon remains in the precursor ceramic, since the carbon replaces the oxygen in the precursor ceramic occurs.
  • the additives react with the carbon of the precursor ceramic (case b)) the formation of free carbon can be prevented or carbon can be withdrawn from the precursor ceramic.
  • Al, Si, Fe, Mo, Cr, SiO 2 , B, V, Ti, Zr, Ni, Cu, Co or all elements or their compounds which are thermally stable (at least up to 1300 ° C.) can be added as additives.
  • the nanometal powders produced by electrical wire explosion are particularly advantageous here, since these powders have a particularly high reactivity even at low temperatures. As a result, the precursor ceramic is extracted from carbon and / or oxygen even at low temperatures during the pyrolysis.
  • a connection to the precursor ceramic through the additive can also take place by bridging, which means that particles of the additive are connected on one side to the precursor ceramic and on the other side to the carbon nanotube. The particle reacts with the precursor ceramic on one side and with the carbon nanotube on the other side.
  • the free carbon content of organic precursors can also be adjusted during pyrolysis under a defined hydrogen-containing atmosphere. If, for example, methyl groups are present as a carbon source in the element-organic precursor, the carbon concentration is influenced via the methane gas balance. The higher the hydrogen concentration in the pyrolysis atmosphere, the stronger the equilibrium of the methane gas reaction C + 2H -i CH 4 on the product side (methane side).
  • the methane / methane radical which splits off during the pyrolysis of the elementary precursor, which contains methyl groups, is prevented from decomposing into hydrogen and carbon, and can thus diffuse out of the precursor ceramic.
  • MWNT multi wall carbon nanotubes
  • the electrical and thermal conductivity of the precursor ceramic can also be improved by carbon nanotubes. Percolation occurs in carbon nanotubes that are dispersed in plastics from 0.2% by weight.
  • polysiloxane (contains 0-3 mass% zirconium acetylacetonate)
  • the required amount of aluminum in the composite material is defined by the following relationship. Oxidation during pyrolysis removes so much oxygen from the precursor ceramic that the remaining amount of the elements Si, O and C, which originate from the polysiloxane, can only be present in the precursor ceramic as Si02 and SiC and therefore no free carbon can exist , or a carbon deficit is present. This forces the reaction of the precursor ceramic with the carbon nanotubes.
  • Step 2 Mixing The ingredients mentioned in step 1 are mixed in a high-speed mixer at 1500 min '1
  • 3rd step kneading The mixture from the 2nd step is kneaded in the extruder until there are no more agglomerates.
  • 4th step shaping The shaping is done by hot pressing at 160 ° C for 20 minutes.
  • 5th step Pyrolysis heating with 100 Kh '1 to 1300 ° C; Hold at 1300 ° C for 1 hour; Cool with 300 Kh "1 until room temperature is reached.

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Abstract

The invention relates to a method for producing a precursor ceramic by pyrolysis of element-organic precursor polymers. According to said method, carbon nanotubes are linked to the precursor ceramic in such a way that the quantity of free carbon that forms during the decomposition of the element-organic precursor polymers is adjusted such that the carbon content of the precursor ceramic is stoichiometric or moderately substoichiometric.

Description

Verfahren zur Herstellung einer Precursor-KeramikProcess for producing a precursor ceramic
Die Erfindung betrifft ein Verfahren zur Herstellung einer Precursor-Keramik nach dem Oberbegriff des unabhängigen Anspruchs.The invention relates to a method for producing a precursor ceramic according to the preamble of the independent claim.
Stand der TechnikState of the art
Bei der Herstellung von keramischen Glühstiftkerzen aus Keramik- Verbundwerkstoffen werden durch die Pyrolyse von elementorganischen Precursoren amorphe SiOC-Keramiken (Precursor-Keramiken) gewonnen. Vorteile dieses Precursor-Thermolyse- Verfahrens gegenüber den konventionellen Herstellungsverfahren für Keramiken (Sintern) sind die wesentlich niedrigeren Prozesstemperaturen und die einfache Verarbeitbarkeit und Formbarkeit der elementorganischen Precursoren wie z.B. von Polysiloxanharzen.In the manufacture of ceramic glow plugs from ceramic composites, amorphous SiOC ceramics (precursor ceramics) are obtained by pyrolysis of element-organic precursors. Advantages of this precursor thermolysis process compared to conventional manufacturing processes for ceramics (sintering) are the significantly lower process temperatures and the easy processability and formability of the elemental organic precursors, e.g. of polysiloxane resins.
Um mechanisch stabile Keramikkörper aus siliziumorganischen Polymeren herzustellen, genügen bereits Temperaturen von etwa 800°C, während Sinterpulver meist erst bei Sintertemperaturen oberhalb von 1200°C mechanisch stabile Körper ergeben. Die Herstellung keramischer Festkörper aus gefüllten siliziumorganischen Polymeren erfordert also wesentlich niedrigere Temperaturen als das Sintern keramischer Pulver. Ein solches Verfahren ist beispielsweise aus der EP 0 412 428 B1 bekannt. Dabei wird dem Ausgangspolymeren ein metallischer Füller zugemischt, der mit den bei der Pyrolyse der Polymerverbindungen entstehenden Zersetzungsprodukten reagiert. Bei der Pyrolyse wird bei einer Temperatur im Bereich zwischen 600 bis 1800°C und häufig in einer Inertgasatmosphäre gearbeitet. Als Füllerkomponenten werden u.a. solche aus Chrom, Molybdän, Silizium und intermetallische Verbindungen von Vertretern der vierten bis sechsten Nebengruppe des Periodensystems mit Bor, Silizium oder Aluminium eingesetzt. Diese Füllstoffe sind notwendig, da sonst Schwindungsrisse und übermäßig viele Poren während der Pyrolyse auftreten. Mit Hilfe dieser Füllstoffe ist es möglich, bestimmte Eigenschaften wie z.B. Wärmeausdehnungskoeffizient, Wärmeleitfähigkeit oder den spezifischen elektrischen Widerstand des Komposits genau einzustellen.Temperatures of around 800 ° C are sufficient to produce mechanically stable ceramic bodies from organosilicon polymers, while sintered powders usually only give mechanically stable bodies at sintering temperatures above 1200 ° C. The production of ceramic solids from filled organosilicon polymers therefore requires significantly lower temperatures than the sintering of ceramic powders. Such a method is known for example from EP 0 412 428 B1. A metallic filler is added to the starting polymer and reacts with the decomposition products formed during the pyrolysis of the polymer compounds. Pyrolysis is carried out at a temperature in the range from 600 to 1800 ° C. and often in an inert gas atmosphere. The filler components used include those made from chromium, molybdenum, silicon and intermetallic compounds from representatives of the fourth to sixth subgroups of the periodic table with boron, silicon or aluminum. These fillers are necessary, otherwise shrinkage cracks and excessive pores occur during pyrolysis. With the help of these fillers it is possible to get certain Properties such as coefficient of thermal expansion, thermal conductivity or the specific electrical resistance of the composite can be set precisely.
Bei der Herstellung eines Keramik- Verbund- Werkstoffes aus einer Precursor-Keramik, wobei als Ausgangsmaterial bspw. ein Polysiloxan, d.h., ein Polymer auf der Basis von Si, C, O und H, verwendet wird, lässt sich demnach durch die Wahl der entsprechenden Füllstoffe das elektrische bzw. physikalische Eigenschaftsprofil des nach der Pyrolyse resultierenden Keramik- Verbund- Werkstoffes exakt auf das jeweilige Anforderungsprofil, bspw. einer keramischen Glühstiftkerze, zuschneiden. Insbesondere ist es auf diese Weise möglich, die elektrische Leitfähigkeit von sehr gut leitend bis isolierend einzustellen.In the production of a ceramic composite material from a precursor ceramic, a polysiloxane, ie, a polymer based on Si, C, O and H, being used as the starting material, for example, can be selected accordingly Fillers cut the electrical or physical property profile of the ceramic composite material resulting after pyrolysis exactly to the respective requirement profile, for example a ceramic glow plug. In particular, it is possible in this way to set the electrical conductivity from very good to insulating.
Die mechanischen Eigenschaften von Precursorkeramiken (Biegfestigkeit < 350 MPa,The mechanical properties of precursor ceramics (bending strength <350 MPa,
Risszähigkeit Kιc < 2 MPa m lassen sich jedoch durch Füllstoffe mit einem niedrigen Aspektverhältnis, d.h., einem niedrigen Verhältnis von Länge zu Durchmesser von < 5, nur begrenzt verbessern. Wesentlich bessere Ergebnisse liefern Füllstoffe mit einem hohen Aspektverhältnis von > 10, wie zum Beispiel Fasern.Crack toughness Kι c <2 MPa m can, however, only be improved to a limited extent by fillers with a low aspect ratio, ie a low ratio of length to diameter of <5. Fillers with a high aspect ratio of> 10, such as fibers, provide significantly better results.
Precursorkeramik ist aufgrund der gasförmigen Zersetzungsprodukte, die während der Pyrolyse entstehen, porös. Die Porengröße liegt im Bereich von ungefähr 300 bis ungefähr 800 nm. Die Anbindung von Whiskern, typischerweise mit einem Durchmesser von ca. 1 μm und Längen von ca. 100 μm, und Fasern an die Precursorkeramik wird durch diese Poren verschlechtert, da die Poren die effektive, in der Precursorkeramik haftende Whisker- /Faseroberfläche herabsetzen. Die verstärkende Wirkung von Whiskern und Fasern in Bauteilen aus Precursorkeramik wird dadurch reduziert.Precursor ceramic is porous due to the gaseous decomposition products that arise during pyrolysis. The pore size is in the range from approximately 300 to approximately 800 nm. The connection of whiskers, typically with a diameter of approximately 1 μm and lengths of approximately 100 μm, and fibers to the precursor ceramic is impaired by these pores, since the pores cause the reduce the effective whisker / fiber surface adhering to the precursor ceramic. The reinforcing effect of whiskers and fibers in components made of precursor ceramic is reduced.
Der Einsatz von Kohlenstoffnanoröhren/-fasern (carbon nanotubes - im folgenden alsThe use of carbon nanotubes / fibers (carbon nanotubes - in the following as
Kohlenstoffnanoröhren bezeichnet) zur Verstärkung von Precursorkeramik bringt aufgrund der wesentlich kleineren Dimensionen bei gleichem Aspektverhältnis Vorteile. Typische Abmessungen von Kohlenstoffnanoröhren sind Durchmesser von ungefähr 20 bis ungefähr 120 nm bei einer Länge von ungefähr 0,5 bis ungefähr 200 μm. Darüber hinaus sind Kohlenstoffnanoröhren sehr unempfindlich gegenüber den mechanischen Belastungen bei der Herstellung (Mischen, Kneten, Mahlen, Sieben) des Verbunds aus elementorganischem Precursor, Füllstoffen und ggf. Kohlenstoffnanoröhren, da selbst bei einer Zerkleinerung der Kohlenstoffnanoröliren, z.B. einer Halbierung, das Aspektverhältnis immer noch groß genug ist.Carbon nanotubes) for reinforcing precursor ceramics has advantages due to the much smaller dimensions with the same aspect ratio. Typical dimensions of carbon nanotubes are diameters from approximately 20 to approximately 120 nm with a length of approximately 0.5 to approximately 200 μm. In addition, carbon nanotubes are very insensitive to the mechanical stresses in the Production (mixing, kneading, grinding, sieving) of the composite of organic precursor, fillers and possibly carbon nanotubes, since even when the carbon nanotubes are comminuted, for example by halving, the aspect ratio is still large enough.
Kohlenstoffnanoröhren als Faserverstärkung in Verbundstoffen sind aufgrund ihrer herausragenden Eigenschaften von großem Interesse und werden in Kunststoffverbunden und Sinterkeramiken bereits eingesetzt.Carbon nanotubes as fiber reinforcement in composites are of great interest due to their outstanding properties and are already used in plastic composites and sintered ceramics.
So beschreibt bspw. die WO 01/92381 AI ein Verfahren zur Bildung eines Verbundstoffes von eingebetteten Nanofasern in einer polymeren Matrix. Das Verfahren umfasst dasFor example, WO 01/92381 A1 describes a method for forming a composite of embedded nanofibers in a polymer matrix. The process includes that
Einarbeiten von Nanofasern in eine Kunststoffmatrix unter Bildung von Agglomeraten, und das einheitliche Verteilen der Nanofasern, indem die Agglomerate hydrodynamischen Spannungen ausgesetzt werden. Ebenfalls offenbart ist ein nanofaserverstärktes polymeres Verbundsystem, das eine Mehrzahl von in polymeren Matrices eingebetteten Nanofasern aufweist. Ein Verfahren zur Herstellung von durch Nanoröhren verstärkten Fasern umfasst das Einmischen einer Nanofaser in ein Polymer und das Induzieren einer Orientierung der Nanofaser, die diese in die Lage versetzt, dazu verwendet zu werden, die mechanischen, thermischen und elektrischen Eigenschaften zu verbessern.Incorporation of nanofibers into a plastic matrix to form agglomerates, and the uniform distribution of the nanofibers by exposing the agglomerates to hydrodynamic stresses. Also disclosed is a nanofiber-reinforced polymer composite system which has a plurality of nanofibers embedded in polymer matrices. One method of making nanotube-reinforced fibers involves mixing a nanofiber into a polymer and inducing an orientation of the nanofiber that enables it to be used to improve mechanical, thermal, and electrical properties.
In der WO 02/18296 wird ein keramischer Matrix-Nanoverbundstoff mit verbessertem mechanischen Verhalten offenbart. Dieser besteht aus einem Füllstoff aus Kohlenstoffnanoröhren und einer keramischen Matrix, die aus einem nanokristallinen keramischen Oxid zusammengesetzt ist. Durch Sintern des daraus geformten Artikels lassen sich keramische Werkstoffe mit verbesserter Bruchzähigkeit erhalten.WO 02/18296 discloses a ceramic matrix nanocomposite with improved mechanical behavior. This consists of a filler made of carbon nanotubes and a ceramic matrix, which is composed of a nanocrystalline ceramic oxide. By sintering the article formed from it, ceramic materials with improved fracture toughness can be obtained.
Die Eigenschaften von Kohlenstoffnanoröhren des Typs MWNT (multiwall carbon nanotubes) sind wie folgt:The properties of MWNT (multiwall carbon nanotubes) carbon nanotubes are as follows:
Thermische Leitfähigkeit: > 2000 W/mK Zugfestigkeit: > 10 GPaThermal conductivity:> 2000 W / mK tensile strength:> 10 GPa
Young's Modulus: bis 1200 GPa Elektrische Leitfähigkeit: Halbleiter oder metallischYoung's modulus: up to 1200 GPa Electrical conductivity: semiconductor or metallic
Aspektverhältnis: 100-1000Aspect ratio: 100-1000
Die Zahl der Hersteller von Kohlenstoffnanoröhren nimmt stetig zu. Die großtechnische Produktion mit über 100 t/Jahr ist inzwischen realisiert, was dazu führt, dass der Preis für solche Kohlenstoffnanoröhren deutlich sinkt.The number of manufacturers of carbon nanotubes is steadily increasing. Large-scale production with over 100 t / year has now been realized, which means that the price for such carbon nanotubes drops significantly.
Aufgabe der Erfindung ist es, die Eigenschaften von Verbundstoffen aus Precursorkeramiken zu verbessern.The object of the invention is to improve the properties of composites made of precursor ceramics.
Vorteile der ErfindungAdvantages of the invention
Das erfindungsgemäße Verfahren zur Herstellung von Keramik- Verbund- Werkstoffen aus elementorganischen Precursor-Polymeren hat gegenüber dem Stand der Technik den Vorteil, dass die Eigenschaften der hergestellten Verbundstoffe deutlich verbessert werden können.The method according to the invention for producing ceramic composite materials from element-organic precursor polymers has the advantage over the prior art that the properties of the composite materials produced can be significantly improved.
Weiterhin ist vorteilhaft, dass es im Gegensatz zur Verwendung von Fasern oder Whiskern nicht zu einer Verschlechterung der Gefügefeinheit kommt.It is also advantageous that, in contrast to the use of fibers or whiskers, there is no deterioration in the structural unit.
AusfuhrungsbeispieleExemplary embodiments
Durch den Einsatz von Kohlenstoffnanoröhren können Keramiken aus Precursorkeramik bzgl. ihrer Festigkeit, Schlagfestigkeit, elektrischer und thermischer Leitfähigkeit verbessert werden. Dabei ist die Qualität der Anbindung der Kohlenstoffnanoröhren an die Precursorkeramik entscheidend für die verstärkende Wirkung der Kohlenstoffnanoröhren. Ohne eine entsprechende Anbindung kann die Kraft, die auf die Precursorkeramik wirkt, nicht von den Kohlenstoffnanoröhren aufgenommen werden. Durch die vorliegende Erfindung kann jedoch die Anbindung der Kohlenstoffröhren an die Precursorkeramik insoweit erheblich verbessert werden, als durch die Anbindung die Kohlenstoffnanoröhren kraftschlüssig mit der Precursorkeramik verbunden werden. Die Anbindung an die Precursorkeramik geschieht durch Einstellung des Gehalts an freiem Kohlenstoff, der sich bei der Zersetzung des polymeren Vorläufers der Precursorkeramik, d.h., der elementorganischen Precursoren, bildet. Dabei wird durch die Zugabe reaktiver Zuschlagstoffe bzw. durch Pyrolyse in einer wasserstoffhaltigen Atmosphäre ein annähernd stöchiometrischer bis mäßig unterstöchiometrischer Kohlenstoffgehalt der Precursorkeramik im Bereich von bspw. ungefähr 15% Kohlenstoffüberschuss bis ungefähr 50%By using carbon nanotubes, ceramics made of precursor ceramic can be improved with regard to their strength, impact resistance, electrical and thermal conductivity. The quality of the connection of the carbon nanotubes to the precursor ceramic is decisive for the reinforcing effect of the carbon nanotubes. Without an appropriate connection, the force that acts on the precursor ceramic cannot be absorbed by the carbon nanotubes. However, the connection of the carbon tubes to the precursor ceramic can be considerably improved by the present invention insofar as the connection connects the carbon nanotubes to the precursor ceramic in a non-positive manner. The connection to the precursor ceramic takes place by adjusting the content of free carbon which is formed during the decomposition of the polymer precursor of the precursor ceramic, ie the element-organic precursors. The addition of reactive additives or pyrolysis in a hydrogen-containing atmosphere results in an approximately stoichiometric to moderately substoichiometric carbon content of the precursor ceramic in the range of, for example, approximately 15% carbon excess to approximately 50%.
Kohlenstoffunterschuss eingestellt. Der bevorzugte Kohlenstoffgehalt bewegt sich dabei im Bereich von ± 5% um den stöchiometrischen Kohlenstoffgehalt. Dadurch wird eine Reaktion zwischen Precursorkeramik und Kohlenstoffnanoröhren insoweit erzwungen, als das Si aus der SiO-Matrix mit den Kohlenstoffnanoröhren reagiert. Die daraus resultierende gute Anbindung durch die entstehende chemische Bindung zwischen Kohlenstoffnanoröhren und Precursorkeramik ist für die Verbesserung der mechanischen und thermischen Eigenschaften verantwortlich. Diese Prinzip kann auf alle Precursorkeramiken angewendet werden, die aus kohlenstoffhaltigen elementorganischen polymeren Vorläufern hergestellt werden, z.B. Polysilazane, Polycarbosilane, Polysiloxane, Polysilane, Polyborazane und dgl.Carbon deficit set. The preferred carbon content is in the range of ± 5% around the stoichiometric carbon content. This forces a reaction between the precursor ceramic and the carbon nanotubes insofar as the Si from the SiO matrix reacts with the carbon nanotubes. The resulting good connection through the resulting chemical bond between carbon nanotubes and precursor ceramic is responsible for the improvement of the mechanical and thermal properties. This principle can be applied to all precursor ceramics made from carbonaceous element organic polymeric precursors, e.g. Polysilazanes, polycarbosilanes, polysiloxanes, polysilanes, polyborazanes and the like.
Durch die erfindungsgemäße Verwendung von Kohlenstoffnanoröhren lassen sich die o.g. Eigenschaften verbessern. Dabei kommt es im Gegensatz zur Verwendung von Fasern oder Whiskern nicht zu einer Verschlechterung der Gefügefeinheit, da die Kohlenstoffnanoröhren im Gegensatz bspw. zu Whiskern kleiner als die Füllstof artikel sind.By using carbon nanotubes according to the invention, the above-mentioned. Improve properties. In contrast to the use of fibers or whiskers, there is no deterioration in the structural unit, since the carbon nanotubes, in contrast to whiskers, for example, are smaller than the filler articles.
Eine Kontrolle der Menge an freiem Kohlenstoff, wie er bei der Zersetzung der polymeren Vorläufer der Precursorkeramik entsteht, kann auf zwei Arten geschehen. Zum einen können geeignete reaktive Zuschlagstoffe zugegeben werden, wodurch die Bildung von freiem Kohlenstoff unterdrückt bzw. ein Kohlenstoffunterschuss erzeugt wird. Dadurch wird die Precursorkeramik gezwungen, an die Kohlenstoffnanoröhren anzubinden. Durch dieThe amount of free carbon, as it arises during the decomposition of the polymer precursors of the precursor ceramic, can be controlled in two ways. On the one hand, suitable reactive additives can be added, whereby the formation of free carbon is suppressed or a carbon deficit is generated. This forces the precursor ceramic to bind to the carbon nanotubes. Through the
Abspaltung gasförmiger Zersetzungsprodukte werden Valenzen frei (freie Elektronen). Diese Valenzen der Precursorkeramik sind die Triebkraft für die Reaktion mit den Kohlenstoffnanoröhren. Geeignete Zuschlagstoffe sind solche, die eine Reaktion mit a) dem Sauerstoff und/oder b) mit dem Kohlenstoff der Precursorkeramik eingehen. Bei der Reaktion der Zuschlagstoffe mit dem Sauerstoff der Precursorkeramik (Fall a)) verbleibt entsprechend mehr Kohlenstoff in der Precursorkeramik, da der Kohlenstoff an die Stelle des Sauerstoffs in der Precursorkeramik tritt. Bei der Reaktion der Zuschlagstoffe mit dem Kohlenstoff der Precursorkeramik (Fall b)) kann die Bildung von freiem Kohlenstoff verhindert bzw. der Precursorkeramik Kohlenstoff entzogen werden.Elimination of gaseous decomposition products releases valences (free electrons). These valences of the precursor ceramic are the driving force for the reaction with the carbon nanotubes. Suitable additives are those which react with a) the oxygen and / or b) with the carbon of the precursor ceramic. When the additives react with the oxygen of the precursor ceramic (case a)), correspondingly more carbon remains in the precursor ceramic, since the carbon replaces the oxygen in the precursor ceramic occurs. When the additives react with the carbon of the precursor ceramic (case b)), the formation of free carbon can be prevented or carbon can be withdrawn from the precursor ceramic.
Als Zuschlagstoffe können z.B. AI, Si, Fe, Mo, Cr, SiO2, B, V, Ti, Zr, Ni, Cu, Co bzw. alle Elemente oder deren Verbindungen zugegeben werden, die thermisch stabile (mindestens bis 1300°C) Kohlenstoff- oder Sauerstoffverbindungen bilden. Hier sind insbesondere die durch elektrische Drahtexplosion hergestellten Nanometallpulver vorteilhaft, da bei diesen Pulvern bereits bei niedrigen Temperaturen eine besonders hohe Reaktivität vorliegt. Dadurch wird die Precursorkeramik bereits bei niedrigen Temperaturen während der Pyrolyse Kohlenstoff und/oder Sauerstoff entzogen.Al, Si, Fe, Mo, Cr, SiO 2 , B, V, Ti, Zr, Ni, Cu, Co or all elements or their compounds which are thermally stable (at least up to 1300 ° C.) can be added as additives. Form carbon or oxygen compounds. The nanometal powders produced by electrical wire explosion are particularly advantageous here, since these powders have a particularly high reactivity even at low temperatures. As a result, the precursor ceramic is extracted from carbon and / or oxygen even at low temperatures during the pyrolysis.
Eine Anbindung an die Precursorkeramik durch den Zuschlagstoff kann auch durch Brückenbildung geschehen, was bedeutet, dass Partikel des Zuschlagsstoffs auf der einen Seite mit der Precursorkeramik und auf der anderen Seite mit der Kohlenstoffhanoröhre verbunden sind. Der Partikel reagiert also auf der einen Seite mit der Precursorkeramik und auf der anderen Site mit der Kohlenstoffhanoröhre.A connection to the precursor ceramic through the additive can also take place by bridging, which means that particles of the additive are connected on one side to the precursor ceramic and on the other side to the carbon nanotube. The particle reacts with the precursor ceramic on one side and with the carbon nanotube on the other side.
Der Gehalt an freiem Kohlenstoff kann bei elementorganischen Precursoren aber auch während der Pyrolyse unter definierter wasserstoffhaltiger Atmosphäre eingestellt werden. Liegen im elementorganischen Precursor z.B. Methylgruppen als Kohlenstoffquelle vor, so wird die Kohlenstoffkonzentration über das Methangasgleichgewicht beeinflusst. Je höher die Wasserstoffkonzentration in der Pyrolyseatmosphäre ist, um so stärker liegt das Gleichgewicht der Methangasreaktion C + 2H -i CH4 auf der Produktseite (Methanseite).The free carbon content of organic precursors can also be adjusted during pyrolysis under a defined hydrogen-containing atmosphere. If, for example, methyl groups are present as a carbon source in the element-organic precursor, the carbon concentration is influenced via the methane gas balance. The higher the hydrogen concentration in the pyrolysis atmosphere, the stronger the equilibrium of the methane gas reaction C + 2H -i CH 4 on the product side (methane side).
Durch die hohe Wasserstoff konzentration wird das Methan/Methanradikal, das sich während der Pyrolyse vom elementorganischen Precursor, der Methylgruppen enthält, abspaltet, an der Zersetzung zu Wasserstoff und Kohlenstoff gehindert, und kann so aus der Precursorkeramik heraus diffundieren.Due to the high hydrogen concentration, the methane / methane radical, which splits off during the pyrolysis of the elementary precursor, which contains methyl groups, is prevented from decomposing into hydrogen and carbon, and can thus diffuse out of the precursor ceramic.
Besonders gut geeignet für die Verstärkung von Precursorkeramiken sind sogenannte multi wall carbon nanotubes (MWNT). Beim Anbinden der Precursorkeramik und/oder der Zuschlagstoffe an die äußere Kohlenstoffnanoröhre bzw. -röhren der MWNT bleiben die inneren Kohlenstoffnanoröhren erhalten.So-called multi wall carbon nanotubes (MWNT) are particularly well suited for the reinforcement of precursor ceramics. When connecting the precursor ceramic and / or the Additives to the outer carbon nanotube or tubes of the MWNT remain in the inner carbon nanotubes.
Neben der Verstärkung kann durch Kohlenstoffnanoröhren auch die elektrische und thermische Leitfähigkeit der Precursorkeramik verbessert werden. Perkolation tritt bei Kohlenstoffnanoröhren, die in Kunststoffen dispergiert sind, bereits ab 0,2 Gew.-% auf.In addition to the reinforcement, the electrical and thermal conductivity of the precursor ceramic can also be improved by carbon nanotubes. Percolation occurs in carbon nanotubes that are dispersed in plastics from 0.2% by weight.
Ein Beispiel für einen Verbundwerkstoff zur Herstellung von mit Kohlenstoffnanoröhren verstärkter Precursorkeramik ist wie folgt:An example of a composite material for producing precursor ceramic reinforced with carbon nanotubes is as follows:
50-80 Vol.-% Polysiloxan (enthält 0-3 Masse-% Zirkonacetylacetonat)50-80 vol .-% polysiloxane (contains 0-3 mass% zirconium acetylacetonate)
0-10 Vol-% SiC0-10 vol% SiC
0-20 Vol.-% A1203 0-20% by volume A1 2 0 3
0-20 Vol-% MoSi2 0-20% by volume MoSi 2
0-10 Vol.-% Aluminium 0-20 Vol.-% Kohlenstoffnanoröhren0-10 vol .-% aluminum 0-20 vol .-% carbon nanotubes
Die notwendige Menge an Aluminium im Verbundwerkstoff ist durch folgenden Zusammenhang definiert. Durch Oxidation während der Pyrolyse wird der Precursorkeramik soviel Sauerstoff entzogen, dass die verbleibende Menge der Elemente Si, O und C, die aus dem Polysiloxan stammen, in der Precursorkeramik rechnerisch nur noch als Si02 und SiC vorliegen können und somit rechnerisch kein freier Kohlenstoff existieren kann, bzw. ein Kohlenstoffunterschuss vorliegt. Dadurch wird die Reaktion der Precursorkeramik mit den Kohlenstoffnanoröhren erzwungen.The required amount of aluminum in the composite material is defined by the following relationship. Oxidation during pyrolysis removes so much oxygen from the precursor ceramic that the remaining amount of the elements Si, O and C, which originate from the polysiloxane, can only be present in the precursor ceramic as Si02 and SiC and therefore no free carbon can exist , or a carbon deficit is present. This forces the reaction of the precursor ceramic with the carbon nanotubes.
Im folgenden wird ein detailliertes Ausführungsbeispiel angegeben.A detailed embodiment is given below.
1. Schritt: Einwiegen 60 Vol.-% Polysiloxan (enthält 2 Masse-% Zirkonacetylacetat) 7 Vol.-% SiC 19 Vol.-% Al2O3 4 Vol.-% MoSi2 5 Vol.-% Aluminium 6 Vol.-% Kohlenstoffnanoröhren1st step: Weigh in 60% by volume of polysiloxane (contains 2% by weight of zirconium acetylacetate) 7% by volume of SiC 19% by volume of Al 2 O 3 4% by volume of MoSi 2 5 vol.% Aluminum 6 vol.% Carbon nanotubes
2. Schritt: Mischen Die im 1. Schritt genannten Bestandteile werden in einem Schnellmischer mit 1500 min'1 gemischtStep 2: Mixing The ingredients mentioned in step 1 are mixed in a high-speed mixer at 1500 min '1
3. Schritt: Kneten Die Mischung aus dem 2. Schritt wird im Extruder geknetet, bis keine Agglomerate mehr vorhanden sind.3rd step: kneading The mixture from the 2nd step is kneaded in the extruder until there are no more agglomerates.
4. Schritt: Formgebung Die Formgebung erfolgt durch Heißpressen bei 160°C für 20 Minuten.4th step: shaping The shaping is done by hot pressing at 160 ° C for 20 minutes.
5. Schritt: Pyrolyse Aufheizung mit 100 Kh'1 bis 1300°C; 1 Stunde Halten bei 1300°C; Abkühlen mit 300 Kh"1 bis zum Erreichen der Raumtemperatur. 5th step: Pyrolysis heating with 100 Kh '1 to 1300 ° C; Hold at 1300 ° C for 1 hour; Cool with 300 Kh "1 until room temperature is reached.

Claims

Ansprüche Expectations
1. Verfahren zur Herstellung einer Precursor-Keramik durch Pyrolyse von elementorganischen Precursor-Polymeren, dadurch gekennzeichnet, dass Kohlenstoffnanoröhren an die Precursor-Keramik angebunden werden und die Anbindung in der Weise geschieht, dass die Menge an freiem Kohlenstoff, der sich bei der Zersetzung der elementorganischen Precursor-Polymeren bildet, so eingestellt wird, dass ein stöchiometrischer oder mäßig unterstöchiometrischer Kohlenstoffgehalt in der Precursor- Keramik vorliegt.1. A process for producing a precursor ceramic by pyrolysis of element-organic precursor polymers, characterized in that carbon nanotubes are connected to the precursor ceramic and the connection takes place in such a way that the amount of free carbon that is present in the decomposition of the element-organic precursor polymer forms, is adjusted so that a stoichiometric or moderately substoichiometric carbon content is present in the precursor ceramic.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass als Kohlenstoffnanoröhren multiwall carbon nanotubes (MWNT) verwendet werden.2. The method according to claim 1, characterized in that multiwall carbon nanotubes (MWNT) are used as carbon nanotubes.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass der mäßig unterstöchiometrische Kohlenstoffgehalt im Bereich von 50% Kohlenstoffunterschuss bis 15% Kohlenstoffüberschuss liegt.3. The method according to claim 1 or 2, characterized in that the moderately substoichiometric carbon content is in the range of 50% carbon deficit to 15% carbon excess.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass der mäßig unterstöchiometrische Kohlenstoffgehalt im Bereich von ± 5% um den stöchiometrischen Kohlenstoffgehalt liegt.4. The method according to claim 3, characterized in that the moderately substoichiometric carbon content is in the range of ± 5% around the stoichiometric carbon content.
5. Verfahren nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die Menge an freiem Kohlenstoff durch die Zugabe von entsprechenden Zuschlagstoffen eingestellt wird. 5. The method according to any one of the preceding claims, characterized in that the amount of free carbon is adjusted by adding appropriate additives.
6. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Menge an freiem Kohlenstoff durch die Einstellung einer definierten wasserstoffhaltigen Atmosphäre während der Pyrolyse eingestellt wird.6. The method according to any one of claims 1 to 4, characterized in that the amount of free carbon is adjusted by setting a defined hydrogen-containing atmosphere during the pyrolysis.
7. Verfahren nach Anspruch 5, dadurch gekennzeichnet, dass die Zuschlagstoffe aus Elementen oder deren Verbindungen gebildet sind, die thermisch stabile Kohlenstoff- oder7. The method according to claim 5, characterized in that the additives are formed from elements or their compounds, the thermally stable carbon or
Sauer Stoffverbindungen bilden.Form acidic compounds.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass die Kohlenstoff- oder Sauerstoffverbindungen bis mindestens 1300°C thermisch stabil sind.8. The method according to claim 7, characterized in that the carbon or oxygen compounds are thermally stable up to at least 1300 ° C.
9. Verfahren nach Anspruch 7 oder 8, dadurch gekennzeichnet, dass die Zuschlagstoffe ausgewählt sind aus der Gruppe bestehend aus AI, Si, Fe, Mo, Cr, Si02, B, V, Ti, Zr, Ni, Cu und Co.9. The method according to claim 7 or 8, characterized in that the additives are selected from the group consisting of Al, Si, Fe, Mo, Cr, Si0 2 , B, V, Ti, Zr, Ni, Cu and Co.
10. Verfahren nach Anspruch 5, dadurch gekennzeichnet, dass die Anbindung durch den Zuschlagstoff durch Brückenbildung realisiert wird. 10. The method according to claim 5, characterized in that the connection is realized by the aggregate by bridging.
EP04738504A 2003-07-25 2004-05-12 Method for producing a precursor ceramic Ceased EP1651583A1 (en)

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CN102040394B (en) * 2010-11-30 2012-08-22 中国人民解放军国防科学技术大学 Silicon oxygen carbon (SiOC) micro-mesoporous ceramic and preparation method thereof
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