WO2013026742A1

WO2013026742A1 - Ceramic composition

Info

Publication number: WO2013026742A1
Application number: PCT/EP2012/065879
Authority: WO
Inventors: Martin Schubert
Original assignee: Robert Bosch Gmbh
Priority date: 2011-08-25
Filing date: 2012-08-14
Publication date: 2013-02-28
Also published as: DE102011081536A1; JP6238896B2; EP2748120A1; KR20140068890A; KR101945691B1; JP2014529567A

Abstract

The present invention relates to a ceramic composition for a plastic shaping process, which comprises at least one ceramic component, at least one binder component, at least one pore former component and in particular at least one dispersant component, where the composition comprises at least one organic compound as pore former component. The use of such a ceramic composition makes it possible to produce mechanically very stable ceramic components which additionally have good gas permeability. The present invention further relates to the use of a ceramic composition according to the invention for producing a ceramic component (1), in particular a gas-permeable electrode, using a plastic shaping process, where the plastic shaping process is, in particular, selected from the group consisting of extrusion processes, injection moulding processes, roller shaping processes and plate pressing processes.

Description

Description title

Ceramic composition

The present invention relates to a ceramic composition and to the use of a ceramic composition. In particular, the present invention relates to a ceramic composition for producing a ceramic component, such as an electrode, by a plastic

Molding process.

State of the art

For the production of electrodes, such as gas-active

High temperature electrodes, a carrier material is advantageous, which gives the electrodes the necessary mechanical stability. In particular, the highest possible strength of the carrier material is advantageous in order to be able to absorb operational mechanical stresses, otherwise a

Component damage may occur. In this case, a required Mindestdurchlässigkett for gases is useful for the carrier material used, in particular when used for gas-active electrodes, so that the gas can be implemented on the reactive electrode side.

Usually ceramic materials are used for such support materials, which in principle do not sinter dense and therefore are gas permeable. However, these non-densely sinterable materials often have low strengths, which can then lead to rapid loss of function of the component with the carrier substrate, ie in particular the electrode.

From the document DE 100 31 123 A1 a method for producing continuous porous substrates is known in which the substrates Film casting ceramic slip systems are produced. The

The slurry system may further include a burn-out placeholder, namely graphite or carbon fibers, to adjust the porosity. A slip system used herein further comprises zirconia powder and

Nickel oxide powder, said stabilized zirconia powder being a wide

having a discrete bimodal distribution in the form of a mixture of a coarse grain and Feinkomanteil. This is intended to change the sintering process in such a way that a high proportion of open porosity is obtained.

Disclosure of the invention

The present invention is a ceramic composition for a plastic molding process, comprising

at least one ceramic component,

at least one binder component,

at least one pore-forming component, and

in particular at least one dispersant component, wherein the composition comprises at least one organic compound as

Pore-forming component comprises.

For the purposes of the present invention, a ceramic composition may, in particular, be a composition that can be further processed to form a ceramic body or component. In particular, the ceramic composition may be formed by a molding process and sintered in a firing process at elevated temperature to the ceramic body. Consequently, the ceramic composition

for example, serve as a ceramic raw material. In the context of the present invention, a ceramic body may in particular be a body which is essentially of an inorganic and non-metallic nature.

The ceramic composition may in particular comprise at least one ceramic component. The ceramic component can therefore serve in particular as the actual ceramic raw material. The

Ceramic component can in the sense of the present invention

in particular comprising a material which consists of an inorganic, non-metallic material is formed or includes this.

Ceramic materials may include, for example, silicate-based materials, oxides, such as metal oxides, nitrides or carbides. Examples of ceramic components which can be used in the context of the invention include, for example, forsterite, a magnesium silicate, or zirconium dioxide. In this case, the ceramic composition may comprise one or a suitable plurality of ceramic components.

The ceramic composition of the invention further comprises at least one binder component. A binder component may serve in the ceramic composition in particular to those in the

Composition components to bind together. In this case, only a single binder component, ie a single substance serving as a binder, may be provided in the ceramic composition. Furthermore, a suitable mixture of two or more than two different substances serving as binders may be provided. For example, the ceramic composition may comprise one or more water-insoluble and, additionally or alternatively, one or more water-soluble binders. When

water-soluble binder component, for example, polyethylene glycols or polyvinylpyrrolidone are suitable, whereas as water-insoluble

Binder component, for example polyvinyl butyral, polyamide or polyethylene are suitable.

The ceramic composition further comprises at least one

Porenbildnerkomponente. In this case, a pore-forming component may be a material which is intended in particular to form a suitable and desired, in particular, defined porosity in the ceramic component or body to be produced from the ceramic composition. In this way, a desired gas permeability of the produced ceramic body can be achieved, which is suitable, for example, for use as a gas-active electrode or for its carrier substrate. It is thus obvious to the person skilled in the art that the term porosity can be understood in particular to mean open porosity. As a result, in an advantageous embodiment, the pore-forming component is not present exclusively in the interior of the material, but likewise at the outer region or at the interface to the outer side. Furthermore, the contacting individual structures of the pore-forming component in the interior of the structure. As a result, preferably a continuous channel

Pore forming components may be provided so that can set in a later burnout continuous gas channels. In order to achieve this, a pore-forming component is an organic compound which is thermally decomposable or becomes gas in particular during a burning process or sintering process of the ceramic compound for producing the ceramic body. It can be in the ceramic

Composition be provided only a Porenbildnerkomponente or a suitable plurality of Porenbildnerkomponenten.

In the context of the present invention, an organic pore-forming component or an organic component as such can be understood in particular to mean a component which, or whose molecular structure, comprises or can consist of carbon, hydrogen and oxygen. In this case, a component which or whose molecular structure consists of carbon, hydrogen and oxygen may also comprise a component which consists of> 90%, in particular> 95%, for example> 99%, of these materials. In this case, for example, <10%, in particular <5%,

For example, <1% of other substances, for example, at the molecular level or as an impurity, such as nitrogen or sulfur, are present in the organic pore-forming component. In this way, on the one hand, the pore-forming component component can preferably be removed from the microstructure in a sintering process in a secure and substantially residue-free manner so as to set the desired porosity. In addition, at the

Provision of such an organic pore-forming component, especially in the conditions prevailing in a sintering conditions, the formation of interfering or even toxic compounds or pollutants, such as harmful sulfur or nitrogen compounds, significantly reduced or even prevented.

The person skilled in the art will thus understand that a pore-forming component based on an organic material is in particular not

Pore-forming component which is purely based on a carbon material, such as graphite or carbon fibers. Such compounds are Not according to the invention comprises an organic material or an organic pore-forming component.

Furthermore, the inventive ceramic composition

especially a dispersant component. A

Dispergatorkomponente can serve in the context of the present invention, in particular to homogenize the ceramic composition according to the invention or to produce a sufficient miscibility, in particular for a plastic molding process. By adding a dispersant component, a particularly homogeneous process of the corresponding shaping method can thus be achieved, which can produce particularly qualitatively homogeneous and therefore particularly advantageous ceramic components. This may be particularly suitable in particular for use in plastic molding processes. For the purposes of the present invention, none, one or a suitable plurality of dispersant components can be present. Suitable substances which as

Dispergatorkomponente for the purposes of the present invention can be used particularly advantageously comprise, for example, oleic acid or under the trade name EFKA 5207 from BASF, Ludwigshafen, available hydroxyl-functionalized, unsaturated, modified carboxylic acids. Also suitable are polyalkylene glycol ethers, such as those available under the trade name Brij, such as Brij72 (polyoxyethylene (2) stearyl ether), from Uniqema Americas LLC, Wilmington Del., US.

In the context of the present invention, a plastic shaping method may in particular be a method in which the organic ceramic compound undergoes a primary molding process via the molten phase. Suitable plastic molding methods for which the ceramic composition of the present invention is particularly suitable may include, for example, extrusion methods, injection molding methods, roller molding methods, or plate press techniques.

The ceramic composition of the invention is in a particularly advantageous manner, especially in combination with a plastic

Shaping process suitable, high strength ceramic materials

or to produce high-strength ceramic components. They can do this have a gas permeability suitable for a variety of applications. In detail, by providing organic additives or the organic pore-forming component in the ceramic composition, a ceramic member having a suitable porosity for generating the gas permeability can be produced. The organic pore-forming component leaves behind after their burn-out, in particular during a sintering process, cavities which are not closed again during or after the burn-out or sintering process. If the individual structures of the pore-forming agent component and thus also the individual cavities produced during the further course of the production of a ceramic component touch, an open porosity can be generated by which a permeability for gas can be generated.

In addition, can be made from a ceramic according to the invention

Composition in particular using plastic

Shaping process particularly simple and inexpensive to produce the desired ceramic components.

In one embodiment, the composition may comprise at least one polymer as an organic compound. In particular organic

Polymers can provide structures of the pore-forming component which, in the further course of the production of a ceramic component, create cavities and thus porosity which are particularly suitable for gas permeability. In this case, polymers are in their structure usually well adapted to the respective field of application or the polymers to be used well selectable. As a result, particularly reproducible gas permeability results can be achieved in this embodiment.

In a further embodiment, the composition may comprise an organic compound as pore-forming component, which consists of

Carbon and oxygen, carbon and hydrogen or off

Carbon, oxygen and hydrogen is formed or exists. In particular, with such pore-forming components, it has surprisingly been found that these are particularly preferred pores when used in a plastic molding process

or cavities can form to high gas permeability, for example, when using the molded ceramic component as a gas-active electrode. These can be removed from the ceramic structure in a further manufacturing process of a ceramic component, in particular in a sintering process or burnout, without damaging or even toxic compounds, such as sulfur or nitrogen compounds, in particular oxides to form. In this case, the presence of the corresponding substances may in particular mean presence on the molecular level, that is to say in the molecular structure of the organic compound.

In a further embodiment, the Porenbildnerkomponente at a temperature of <450X, in particular <300 ° C, for example, decompose <200 ° C or go into the gas phase. In this embodiment, therefore, a removal of the pore-forming component already in a

conventional sintering process prevailing temperatures from the

ceramic structure can be realized. In this case, the temperatures may be so low that removal of the pore-forming component begins already at a temperature which is far below the maximum to be reached

Temperature is. In this way, it can be made particularly certain that the pore-forming component is completely removed from the ceramic structure, as a result of which the desired gas permeability is reliably established.

Within the scope of a further embodiment, the pore-forming component may be selected from the group consisting of resins, in particular

Phenolic resins, carbohydrates, especially cellulose and starch, and / or

Coconut shell, or any mixture of the aforementioned substances. When using such materials as

Pore-forming component particularly advantageous gas permeabilities can be achieved, which are suitable for a large number of applications. In addition, such materials are particularly advantageous processable. in the

Detail can be a very homogeneous mixture of ceramic

Even without adding a dispersant component, which can lead to a homogeneous ceramic component. In addition, such materials are also in a conventional

Sintering process prevailing temperatures easily and completely removed from the ceramic structure bar what the desired gas permeability ensures. Furthermore, the aforementioned materials can be shaped or provided in suitable structures.

In another embodiment, the composition may comprise:

- 17% by volume to 48% by volume of ceramic component; and or

-> 28 vol .-% to <58 vol .-% of binder component; and or

from 6% by volume to .5% by volume of pore-forming component; and or

In particular> 1% by volume to <7% by volume of dispersant component, it being possible for the aforementioned constituents in particular to add up to 100% by volume in particular.

This is a particularly advantageous ceramic composition that can be processed in particular in connection with a plastic shaping process. With such a composition, homogeneous ceramic components can be produced particularly advantageously in the production, which have the desired gas permeabilities with a simultaneously high mechanical stability.

In the context of a further embodiment, the composition may be solvent-free. This allows the ceramic composition to be processed as desired without the insertion and removal of another component. In this embodiment, therefore, materials and work steps can be saved, which is particularly the use of the ceramic composition for producing a ceramic component

inexpensive and simply designed. In addition, the environment is relieved by the absence of solvents. In this case, a solvent-free

For the purposes of the present invention, composition means, in particular, that there is no component which is used conventionally, for example in film casting processes, as a solvent. In detail, in this embodiment, it may be meant that there is no component in the composition, in particular, no step of processing the ceramic composition which is liquid at temperatures below 40 ° C.

In the context of a further embodiment, the pore-forming component can be designed like a fiber. By a fibrous configuration of Pore forming component or the individual structures of

Pore-forming component can be improved in comparison to, for example, spherical Porenbildnem at comparable volume fractions of the pore-forming component used, ie, higher gas permeabilities can be achieved. Although in principle spherical pore-forming components are also in the

Scope of the present invention possible and will not be here

excluded, however, are fibrous pore-forming due to

improved gas permeability to be achieved is preferred. Irrespective of whether spherical or fibrous pore-forming components are present, the individual structures of the pore-forming components can still be very different

Have shape. For example, they may have a smooth, ragged or irregular surface. In the context of the present invention, a fibrous structure may in particular be a structure which may have a greater length compared to the diameter, that is to say has a particularly elongate extent as maximum dimension. In this case, the fibrous Porenbildnerkomponenten may have approximately a rice-shaped or tubular structure, which of course deviations from this form are within the meaning of the invention mitumfasst. It may be advantageous in one embodiment, when the fiber

Ratio of diameter to length of <1: 30, in particular of <1: 15, for example, of <1: 10, and / or if the fiber has a length of <40Όμιη, in particular <30Όμηι having. In particular, in such fibers compositions can be produced easily, in which the

Contact pore-forming structures, whereby a porosity can be achieved, in which a

Gas can flow through the pores largely unhindered. Consequently, a particularly advantageous gas permeability can be achieved.

The present invention further relates to the use of a

ceramic composition according to the invention for the production of a ceramic component, in particular a gas-permeable electrode, using a plastic molding method, wherein the plastic molding method can be selected in particular from the group consisting of extrusion process, injection molding,

Roller forming method or plate press method. In particular, by such shaping methods, the inventive ceramic composition in a particularly advantageous manner simple and inexpensive shapes. In detail, for example, inert-supported fuel cells or the inert carrier substrate for electrodes of

Produce fuel cells.

Drawings and examples

Further advantages and advantageous embodiments of the subject invention are illustrated by the drawings and explained in the following description. It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. Show it

Fig. 1 is a schematic sectional view through a ceramic component made of an embodiment of a ceramic composition according to the invention;

2 is a schematic sectional view through a ceramic component produced from an embodiment of a ceramic composition according to the invention showing pores of a spherical pore-forming component; and

3 shows a schematic sectional view through a ceramic component produced from an embodiment of a ceramic composition according to the invention showing pores of a fibrous pore-forming component.

FIG. 1 shows a schematic sectional illustration through a ceramic component 1, produced from an embodiment of a ceramic composition according to the invention. The ceramic component 1 comprises a ceramic matrix or basic structure 2, in which a plurality of cavities

or pores 3 are arranged. The pores 3 according to FIG. 1 have a tubular structure.

The ceramic component 1 can be produced from a ceramic composition according to the invention using a plastic

Shaping process, wherein the plastic forming process in particular may be selected from the group consisting of

Extrusion process, injection molding, roller molding or Plattenpresstechnikverfahren. In this case, the ceramic component 1

For example, a gas-permeable electrode or their

Be carrier substrate.

The ceramic composition according to the invention, in particular as starting material for the ceramic component 1, comprises at least one ceramic component, at least one binder component, at least one organic compound as pore-forming component, and in particular at least one dispersant component.

In this case, the pore-forming component may comprise or be at least one polymer as organic compound. In one embodiment, the

Composition comprising an organic compound as a pore-forming agent, which is formed from carbon and oxygen, from carbon and hydrogen or from carbon, oxygen and hydrogen. By way of example only, the pore-forming component may be selected from the group consisting of resins, especially phenolic resins, carbohydrates, especially cellulose and starch, and / or coconut husk, or any

Mixture of the aforementioned substances.

In order to improve the removal of the pore-forming component as described later, the pore-forming component may further decompose at a temperature of <450 ° C, especially <300 ° C, for example <200 ° C, or pass into the gas phase.

The ceramic composition may include in detail:

-> 17% by volume to <48% by volume of ceramic component; and or

-> 28 vol .-% to <58 vol .-% of binder component; and or

-> 6 vol .-% to <37 vol .-% of pore-forming component; and or

In particular> 1% by volume to <7% by volume of dispersant component, it being possible for the proportions to add up to 100% by weight.

Here, a typical recipe for a ceramic composition may include ceramic powder as a ceramic component (32.4% by volume); Pore forming agent component (21, 6 vol.%); Binder (43 vol .-%, wherein, for example, a mixture of two different water-insoluble binders (each 9.5 vol .-%) and a water-soluble binder (24 vol .-%) may be provided) and a Dispergatorkomponente (3 vol. %). In this case, forsterite (magnesium silicate) or alumina (Al ₂ 0 ₃₎ may be about as a ceramic component of zirconia (Zr0 _2), are used. As binder polyvinyl butyral (PVB), polyethylene glycol (PEG) or polacrylates can be used. Suitable pore formers are, for example, phenolic resin fibers and oleic acid dispersants or, under the trade name EFKA 5207, BASF, Ludwigshafen, available hydroxyl-functionalized, unsaturated, modified carboxylic acids. Also suitable are polyalkylene glycol ethers, such as, for example, those sold under the trade name Brij, for example Brij72

(Polyoxyethylene (2) stearyl ether), from Uniqema Americas LLC,

Wilmington Del., US.

From the foregoing it will be seen that the ceramic

Composition can completely dispense with solvents, so

can be solvent-free. For example, the ceramic composition of the present invention may be first formed by a suitable plastic molding method such as an injection molding method or an extrusion method. Following this, the resulting blank can be debinded by removing the binder, for example, by exposure to heat or by a solvent. Subsequently, the debindered blank can be sintered, the

Pore-forming component is removed by burning out of the ceramic structure. In this way, the basic structure 2 shown in FIG. 1 can be formed comprising the pores 3 or cavities.

A typical composition may include: Ceramic: Zr0 ₂ 32.4 Vol%

Binder: PVB (water insoluble) 8,7 Vol%

Polyacrylates (water-insoluble) 9.0% by volume

PEG (water soluble) 24.0% by volume

Pore Former: Phenolic Resin Fibers 21, 6 Voi%

Dispersants: oleic acid 2.2% by volume

EFKA5207 2.1% by volume

Gas permeabilities achieved using the above composition using different pore-forming components are shown in Table 1.

According to Table 1, the numbers 1 to 3 are fibrous

Pore former components, whereas Nos. 4 and 5 show spherical pore-forming components. Particularly good values with smooth, geometrically uniform, artificially produced

Phenolharzfasem be achieved. It can be seen that the fibrous pore-forming components, especially phenolic resins, can produce very high gas permeabilities of up to 8.0E-10 cm ² using a plastic molding process, extrusion or injection molding. But even with spherical pore-forming components, such as starch or coconut shell, good gas permeabilities of 1, 1-10 cm ² or 6.0E-11 cm ² can be achieved.

The generated gas permeability is shown in FIGS. 2 and 3. In particular, the pores 3 in a ceramic component 1, which are arranged in the ceramic basic structure 2, are shown in FIGS. 2 and 3. figure 2 shows the pores 3 or cavities produced by a spherical pore-forming component, whereas in FIG. 3 the pores 3 or cavities produced by a fibrous pore-forming component are shown.

It could be shown that in addition to the total porosity for the

Gas permeability can rather be decisive, whether the gas must flow through many small bottlenecks to flow through the ceramic component 1. Such bottlenecks may be, in particular, former contact points of the pore-forming component or of its individual structures. Such contact points are therefore especially in spherical

Pore formers present, whereas fibrous

Pore forming components resulting tubular cavities already constructively have wide areas without bottlenecks that affect a gas flow significantly less.

Accordingly, Figure 2 shows the path of a gas molecule, represented by the arrow 4, through a ceramic component 1 with pores 3, which were produced by a spherical pore-forming component. In Figure 2, the gas molecules flow through many small ports formed by the former points of contact of the spherical pore-forming component.

Accordingly, Figure 3 shows the path of a gas molecule, represented by the arrow 5, through a ceramic component 1 with pores 3, which were produced by a fibrous pore-forming component. In Figure 3, the gas molecules can also flow long distances without much resistance through the tubular pores 3 formed by the fibrous pore-forming component.

In addition, it was found that for a given

Gas flow path tends to require a larger proportion of spherical Porenbildnem, as in the use of fibrous

Entraining agents. This may result in the use of fibrous

Pore formers further material can be saved, which offers a further advantage of fibrous pore formers.

Claims

claims

A ceramic composition for a plastic molding process, comprising

at least one ceramic component,

at least one binder component,

at least one pore-forming component, and

in particular at least one dispersant component, wherein the composition comprises at least one organic compound as pore-forming component.

2. A ceramic composition according to claim 1, wherein the

Composition comprises at least one polymer as an organic compound.

3. A ceramic composition according to claim 1 or 2, wherein the

Composition an organic compound as

Pore forming component comprises, which is formed of carbon and oxygen, of carbon and hydrogen or of carbon, oxygen and hydrogen.

4. The ceramic composition according to any one of claims 1 to 3, wherein the Porenbildnerkomponente decomposes at a temperature of <450 ° C, in particular <300 ° C, for example <200 ° C or passes into the gas phase.

5. A ceramic composition according to any one of claims 1 to 4, wherein the Porenbildnerkomponente is selected from the group consisting of resins, in particular phenolic resins, carbohydrates, in particular cellulose and starch, and / or coconut shell, or any mixture of the aforementioned substances. A ceramic composition according to any one of claims 1 to 5, wherein the composition comprises:

-> 17% by volume to <48% by volume of ceramic component; and or

-> 28 vol .-% to <58 vol .-% of binder component; and or

from 6% by volume to <37% by volume of pore-forming component; and or

In particular> 1% by volume to <7% by volume of dispersant component.

A ceramic composition according to any one of claims 1 to 6, wherein the composition is solvent-free.

A ceramic composition according to any one of claims 1 to 7, wherein the pore-forming component is fibrous.

Ceramic composition according to claim 8, wherein the fiber has a diameter to length ratio of <1: 30, in particular of <1: 15, for example of <1: 10, and / or wherein the fiber has a length of <400 m, in particular <300pm.

Use of a ceramic composition according to any one of claims 1 to 9 for the manufacture of a ceramic component (1), in particular a gas-permeable electrode, using a plastic molding process, wherein the plastic

Shaping process is in particular selected from the group consisting of extrusion processes, injection molding,

Roller forming method or plate press method.