WO1997043229A1 - Procede permettant d'ajuster la porosite de materiaux composites ceramiques en polymeres organosilices - Google Patents

Procede permettant d'ajuster la porosite de materiaux composites ceramiques en polymeres organosilices Download PDF

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Publication number
WO1997043229A1
WO1997043229A1 PCT/DE1997/000276 DE9700276W WO9743229A1 WO 1997043229 A1 WO1997043229 A1 WO 1997043229A1 DE 9700276 W DE9700276 W DE 9700276W WO 9743229 A1 WO9743229 A1 WO 9743229A1
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WO
WIPO (PCT)
Prior art keywords
filler
porosity
pyrolysis
grain size
polymer
Prior art date
Application number
PCT/DE1997/000276
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German (de)
English (en)
Inventor
Jürgen OBERLE
Horst Boeder
Karl-Heinz Heussner
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 WO1997043229A1 publication Critical patent/WO1997043229A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • C04B35/589—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained from Si-containing polymer precursors or organosilicon monomers
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
    • C04B38/0022—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof obtained by a chemical conversion or reaction other than those relating to the setting or hardening of cement-like material or to the formation of a sol or a gel, e.g. by carbonising or pyrolysing preformed cellular materials based on polymers, organo-metallic or organo-silicon precursors

Definitions

  • the invention relates to a method according to the preamble of claim 1.
  • Porosity is to be understood as the apparent or open porosity, which is defined according to DIN EN 623 (Part 2) as the ratio of the total volume of the open pores of a porous body to its raw volume, with the raw volume being the sum of the volumes of solid, open pores and closed pores of a porous body is to be understood, open pores are those that are in contact with an immersion liquid or with the atmosphere in a vacuum and closed pores are such that are not penetrated by an immersion liquid or not with the immersion liquid Atmosphere.
  • the filler components used include those made of chromium, molybdenum, silicon and intermetallic compounds from representatives of the fourth to sixth subgroup of the periodic table with boron, silicon or aluminum.
  • the process is intended to produce composite bodies with properties which are suitable for uses in which they are subjected to high mechanical and thermal stresses and which have a high density. It is emphasized as an advantage that the composite bodies produced have only very small pores.
  • a significant advantage in the case of the ceramics produced by pyrolysis compared to sintered ceramics is also that the type of filler allows further functional properties, such as, for example, the electrical conductivity and the catalytic activity, to be set in a targeted manner, ie materials with a specifically adjustable property can be set ⁇ shaft profile for multi-functional applications.
  • the production of ceramic electrical resistors by pyrolysis of at least one organosilicon polymer and at least one filler containing at least one high-melting conductive or insulating component are described in DE 4435324 A1.
  • the filler component consists for example of CrSi2, MoSi2, Si3N4, graphite, Fe, Pt, A1203, Si and is used with 5 to 50 vol .-% based on the solvent-free polymer-filler mixture. Is pyrolyzed for example at a final temperature of 1200 ° C.
  • the method of the type mentioned with the features of claim 1 enables the porosity to be set within wide limits.
  • the filler Since economic considerations play a role in the selection of the filler, which can be a mixture of materials, it is advantageous if a filler that is as inexpensive as possible is first selected and then the desired porosity is set using the appropriate setting of the average grain size ( n) the filler, the filler content and the pyrolysis end temperature is controlled.
  • the filler content is also an economically important variable, in such a case it is advantageous if the type and the average grain size (s) of the filler, and also the filler content, are determined, and then the porosity is determined by the Pyrolysis end temperature is controlled.
  • the final pyrolysis temperature can also be subject to conditions, for example if the pyrolysis product is to be exposed to high temperatures when it is used, it may also be necessary, in addition to the type and the average grain size (s) of the filler determine the final pyrolysis temperature and control the porosity by adjusting the filler content. This can also be advantageous because the highest porosities can be set via the filler content.
  • the pyrolysis end temperature is set to a value in the range between approximately 780 and approximately 1200 ° C, the range between approximately 800 and about 900 ° C is particularly advantageous if a high porosity is desired.
  • the materials sintered in the low temperature range have only a low mechanical strength.
  • Fillers which are selected from the group consisting of metals, silicides, silicon, carbides, graphite, borides, boron, oxides and nitrides or combinations of two or more of these materials are not only advantageous because allows them to effectively control the porosity, but also because of their chemical resistance, because they give the ceramic good mechanical properties and, if the suitable ones are selected from them, ceramics with special, for example electrical or dielectric, properties can be produced when they are added.
  • fillers from the group consisting of molybdenum silicide, chromium silicide, silicon nitride, silicon, aluminum oxide, zirconium oxide, iron, platinum, graphite and combinations of two of these materials are particularly advantageous.
  • the filler content based on the - solvent-free - polymer-filler mixture, is preferably between about 2 and 95% by volume, since ceramics with favorable properties can be produced within this range. Contents between about 40 and about 90% by volume are particularly advantageous.
  • the particle size of the filler is preferably between approximately 0.5 and approximately 80 ⁇ m, a particle size between approximately 0.9 and approximately 20 ⁇ m resulting in particularly reproducible porosities.
  • polysiloxane polysilane, polycarbosilane or polysilazane as organosilicon polymers.
  • the polymer and the filler it is advantageous if they are in the form of a powder and are dry-mixed with one another or if the filler is dispersed in a solution of the polymer.
  • the drawing shows in diagrams the dependence of the apparent porosity 77 a on the final pyrolysis temperature Tp for a ceramic filled with CrSi2 (FIG. 2) and on the filler content Cf for ceramics filled with CrSi2 (FIG. 1) or Si3N4 (FIG. 3) .
  • a polysiloxane such as addition-crosslinked methyl-phenyl-vinyl hydrogen polysiloxane, and Si3N4 or CrSi2 are used as the organosilicon polymer to explain the invention.
  • the invention is not restricted to the use of these materials. Rather, the effect sought with the method according to the invention can also be achieved when using the other materials claimed in the claims.
  • the polysiloxane is dissolved in a solvent such as acetone, hexane, alicyclic or aromatic hydrocarbons.
  • a solvent such as acetone, hexane, alicyclic or aromatic hydrocarbons.
  • the filler is dispersed in this solution, for example using a conventional stirrer.
  • the solvent is expelled from the suspension obtained, for example in a forced-air drying cabinet.
  • a kneadable mass is obtained which compresses in a press mold and under pressure
  • the molded body obtained is pyrolyzed under a flowing gas which does not react with the polymer and the filler, for example argon, the temperature being the same a speed in the range between about 0.1 and about 5 ° C per minute first to a temperature of about 450 ° C, at which it is stopped for about two hours, and then to the final pyrolysis temperature, which is in the range between about 780 and about 1200 ° C and which is held for about four hours, heated. The mixture is then cooled again to room temperature at a speed which is within the specified range.
  • a flowing gas which does not react with the polymer and the filler
  • the temperature being the same a speed in the range between about 0.1 and about 5 ° C per minute first to a temperature of about 450 ° C, at which it is stopped for about two hours, and then to the final pyrolysis temperature, which is in the range between about 780 and about 1200 ° C and which is held for about four hours, heated.
  • the mixture is then cooled again
  • a matrix of SiOC glass is obtained, in which the filler is installed.
  • the filler particles for example made of CrSi2, can react externally with the polymer during pyrolysis to form carbide.
  • the porosity In order to control the porosity, more precisely the open or apparent porosity, one or more of the parameters from the group, type and grain size of the filler, filler content and final pyrolysis temperature are changed according to the invention. These parameters also influence other properties of the pyrolysis product. It is therefore very favorable that according to the invention the porosity can be controlled by means of various parameters, because one can thereby set a desired porosity by appropriate selection of the parameter (s) without having to accept the fact that a other product property significantly deteriorated, which is important for the intended application.
  • organosilicon polymers in addition to polysiloxane, in particular polysilane, polycarbosilane or polysilazane, and as a filler, in addition to Si3N4 and CrSi2, in particular MoSi2, Si, SiC, graphite, Al2O3, Fe, Pt, Zr ⁇ 2, A1N, BN and combinations of two or more of these substances can be used.
  • the applicable range of the end pyrolysis temperature is limited on the one hand - insofar as the mechanical strength of the pyrolysis product is important - in that a continuous ceramization only takes place from temperatures of approximately 800 ° C and on the other hand in that the end pyrolysis temperature is at least as high as the temperature at which the pyrolysis product is used.
  • the upper limit sets the economy: you will not set the final pyrolysis temperature higher than necessary.
  • the pyrolysis product is to be electrically conductive or electrically insulating and whether the filler is available at low cost.
  • the filler content is the most important parameter for controlling the porosity.
  • Another parameter that is preferably used is the final pyrolysis temperature, which is particularly useful when there is nothing else to prevent a low (approx. ⁇ 800 ° C.) final pyrolysis temperature.
  • the apparent porosity is measured using the immersion method (see DIN EN 623, part 2), which in principle proceeds in such a way that the mass of the dried sample is first determined, then on the sample penetrated under vacuum with immersion liquid by immersion in the same Liquid and weighing, the apparent mass of which is determined and the sample which is still penetrated but freed from adhering surface liquid is measured in air. From the so obtained The apparent porosity is calculated from measured values.
  • a kneadable mass was obtained which was compressed in a mold and cured at a pressure of 10 MPa and a temperature of 200 ° C. for 30 minutes.
  • the shaped body thus obtained was heated under flowing argon (about 5 l / h) at a heating rate of 5 ° C / min. first heated to 450 ° C, kept at this temperature for two hours, then heated to 1200 ° C at the same heating rate and left at this temperature for four hours before cooling down to 2.5 ° C / min. was cooled back to room temperature.
  • the measured apparent porosity was 5.5% (see the table).
  • the porosities obtained in Examples 1 to 5 are plotted against the corresponding filler contents in the diagram shown in FIG. As can be seen in the diagram, the porosity surprisingly has a minimum at a CrSi2 content of about 40% by volume.
  • Example 7 Except that a CrSi2 powder with an average grain size of 1.1 ⁇ m was used, the same procedure as in Example 1 was followed. A comparison of the porosity achieved in Example 6 with that achieved in Example 4 shows that by reducing the average grain size from 3.7 to 1.1 ⁇ m, the porosity decreased by more than a factor of 5. Examples 7 to 9
  • the porosities achieved in Examples 3 and 7 to 9 are plotted against the corresponding pyrolysis end temperatures.
  • the diagram surprisingly has a maximum at an end pyrolysis temperature in the range of approximately 800 ° C.
  • Examples 10 to 12 were the same as in Examples 1, 3 and 4.
  • Si3N4 can be used at higher heights their contents reach a much higher porosity than with CrSi2.
  • the porosities measured in Examples 10 to 12 are plotted against the associated Si3N4 contents in the diagram in FIG.
  • the diagram shows that the porosity increases almost linearly with increasing filler content, so that it can be extrapolated that porosities of well over 40% can be obtained at even higher Si 3 4 contents.
  • the other results allow the conclusion that, if at the same time the grain size of the filler is increased and / or the pyrolysis temperature is brought close to 800 ° C., the porosity can be increased to values of over 50% .

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Dispersion Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Ceramic Products (AREA)

Abstract

Pour ajuster la porosité de matériaux composites céramiques obtenus par pyrolyse de polymères organosilicés et de mélanges contenant au moins une charge inorganique non fusible et réagissant avec le polymère au plus superficiellement, il est prévu d'ajuster la porosité par détermination coordonnée du type et de(s) la grosseur(s) moyenne(s) de grain de la charge, de la teneur en charge et de la température finale de la pyrolyse.
PCT/DE1997/000276 1996-05-15 1997-02-13 Procede permettant d'ajuster la porosite de materiaux composites ceramiques en polymeres organosilices WO1997043229A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19619616.7 1996-05-15
DE1996119616 DE19619616A1 (de) 1996-05-15 1996-05-15 Verfahren zum Einstellen der Porosität von keramischen Verbundwerkstoffen aus siliciumorganischen Polymeren

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Publication Number Publication Date
WO1997043229A1 true WO1997043229A1 (fr) 1997-11-20

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WO (1) WO1997043229A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19910447A1 (de) * 1999-03-10 2000-09-14 Bosch Gmbh Robert Keramischer elektrischer Widerstand
DE10201516A1 (de) * 2002-01-17 2003-08-07 Fraunhofer Ges Forschung Leitfähiges Formteil und Verfahren zu seiner Herstellung

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0684217A1 (fr) * 1994-05-24 1995-11-29 Exxon Research And Engineering Company Céramiques microporeux et leur synthèse
EP0684218A1 (fr) * 1994-05-24 1995-11-29 Exxon Research And Engineering Company Céramiques microporeux et leur synthèse
WO1996013044A1 (fr) * 1994-10-19 1996-05-02 Robert Bosch Gmbh Resistance electrique en ceramique et son utilisation

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3926077A1 (de) * 1989-08-07 1991-02-14 Peter Prof Dr Greil Keramische verbundkoerper und verfahren zu ihrer herstellung
DE19538695C2 (de) * 1994-10-19 2003-05-28 Bosch Gmbh Robert Keramischer elektrischer Widerstand und dessen Verwendung

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0684217A1 (fr) * 1994-05-24 1995-11-29 Exxon Research And Engineering Company Céramiques microporeux et leur synthèse
EP0684218A1 (fr) * 1994-05-24 1995-11-29 Exxon Research And Engineering Company Céramiques microporeux et leur synthèse
WO1996013044A1 (fr) * 1994-10-19 1996-05-02 Robert Bosch Gmbh Resistance electrique en ceramique et son utilisation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
GREIL P ET AL: "Modelling of dimensional changes during polymer-ceramic conversion for bulk component fabrication", JOURNAL OF MATERIALS SCIENCE, vol. 27, 1992, LONDON,GB, pages 1053 - 1060, XP002033216 *

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