WO2006134086A1 - Conductive paste for producing an electric strip conductor and method for producing the electric strip conductor while using the conductive paste - Google Patents

Abstract

The invention relates to a conductive paste for producing an electric strip conductor (11), comprising a solid matter dispersion with powder particles of at least one electrically conductive solid substance. The conductive paste is characterized in that the solid matter dispersion has at least one cross-linkable siloxane. The invention also relates to a method for producing a strip conductor on a supporting body (10) while using the conductive paste, comprising the following method steps: a) applying the conductive paste to a surface (101) of the supporting body, and; b) creating the strip conductor during which the siloxane is cross-linked. The cross-linkable siloxane is, in particular, methylpolysiloxane. The electrically conductive solid substance is preferably aluminum. The strip conductor is obtained by pyrolyzing the conductive paste. From the conductive paste, a conductive material with a ceramic skeletal structure comprised of silicon dioxide is formed into which aluminum particles are embedded. The conductive paste is preferably used in order to produce a strip conductor of a checking device for detecting a degradation of a ceramic component and, in particular, of a ceramic heat shield of a combustor of a gas turbine. The brittle strip conductor and the heat shield are placed next to another so that a degradation (102) of the heat shield leads to a degradation (112) of the strip conductor. The degradation of the strip conductor leads to a change in the electrical property of the strip conductor that is detected via the checking device.

Description

description

Conductor paste for producing an electrical conductor and manufacturing method of the electrical conductor using the conductor paste

The invention relates to a conductor paste for producing an electrical conductor track, comprising a solid-state dispersion with powder particles of at least one electrically conductive solid. In addition, a method for producing the electrical conductor using the conductor paste is specified.

A paste is a dispersion of liquid to doughy consistency. The dispersion consists of at least two phases (components). In a continuous phase (dispersing agent) at least one further phase (dispersed phase, dispersant) is finely divided. In the present case, the dispersion is a solid state dispersion with a more or less liquid dispersant and a dispersant with powder particles of a solid. In order to achieve a fine distribution of the dispersant in the dispersant, a so-called dispersant (dispersant) is used. The dispersant facilitates the dispersion of the

Powder particles in the dispersant, for example, by lowering the interfacial tension between the two components of the solid state dispersion. This increases the wettability of the powder particles with the dispersing agent. The dispersant acts as a physical binder between the two phases of the solid state dispersion. The dispersant can also function as a chemical binder. In this case, the dispersion is achieved by forming chemical bonds between constituents of the two phases. It is also possible that the

Dispersion has multiple dispersants or binders. The dispersion has a dispersant and / or binder system. From DE 102 23 985 Al an arrangement of a component and at least one control device for detecting a degradation of the component is known. The component is, for example, a heat shield of a combustion chamber of a gas turbine. In the combustion chamber of the gas turbine, a fossil fuel is burned. During combustion, a temperature of up to 1500 ° C is reached. This gives rise to corrosive gases that can attack the combustion chamber. To protect against the high temperatures and against attack of corrosive gases, the combustion chamber is lined with a variety of so-called ceramic heat shields.

A heat shield is a component made of a component material which has a very good temperature and corrosion resistance. The component material is, for example, a ceramic material in the form of mullite. Due to a porous structure with a large number of microcracks, the ceramic material shows a very good thermal shock behavior. A very large temperature variation, which occurs for example when interrupting the combustion process in the combustion chamber of the gas turbine, is compensated, without the heat shield is destroyed. However, a mechanical overload of the heat shield can lead to a degradation of the heat shield. It can be a crack

(Macro crack) in the heat shield. Such a crack forms in particular at the edge of the heat shield. During operation, the crack may spread in the direction of the center of the heat shield. The crack does not adversely affect the functionality of the heat shield up to a certain length and can therefore be tolerated. But if the crack exceeds a certain length, the functionality of the heat shield is no longer guaranteed. Replacement of the heat shield is required to avoid breakage of the heat shield caused by the crack during operation of the gas turbine. This is where DE 102 23 985 A1 begins. It is shown how the formation of a crack can be detected and a length of an existing crack can be determined by means of a suitable control device. An essential part of the control device is an electrical conductor track. The trace is applied to the back of the heat shield, which faces away from an interior of the combustion chamber. A crack occurring on the back of the heat shield leads to a crack of the conductor track. The track is severed. As a result, an electrical property of the conductor track changes. For example, the DC resistance and the impedance of the conductor increases. The control device is designed so that the electrical property of the conductor can be queried. Will a change in the electrical

Property of the conductor track is closed on the formation of a crack or on the growth of an existing crack of the heat shield. The heat shield must be replaced.

Based on the described scenario, the conductor material (interconnect material) used for the conductor track of the control device must have certain properties. The conductor material must be electrically conductive. At the same time, the conductor material must be brittle, so that a degradation of the heat shield also leads to a degradation of the conductor path. In addition, these properties may change only insignificantly under thermal stress.

The object of the present invention is therefore to specify a conductor paste which is suitable for producing an electrical conductor track. The electrical and mechanical properties of the resulting conductor track should be adjustable within wide ranges. In particular, it should be possible with the help of the conductor paste an electrical conductor can be produced, which is used in the described control device. To achieve the object, a conductor paste for producing an electrical conductor track is specified, comprising a solid-state dispersion with powder particles of at least one electrically conductive solid. The conductor paste is characterized in that the solid-state dispersion has at least one crosslinkable siloxane.

To achieve the object, a method for producing a conductor track on a carrier body using the conductor paste is also specified with the following method steps: a) applying the conductor paste to a surface of the carrier body and b) generating the conductor track, with crosslinking of the siloxane being carried out.

The powder particles of the electrically conductive solid form the dispersant of the solid state suspension. The siloxane acts as a dispersant and / or as a dispersant. In particular, the siloxane acts as a chemical binder for the powder particles of the electrically conductive solid. In addition to the siloxane and the powder particles of the electrically conductive solid, the solid dispersion may contain further constituents, for example further dispersants, further dispersants or further (chemical or physical) binders. These further constituents are, for example, terpinol or ethyl cellulose.

The siloxane is an organosilicon compound. The siloxane may be present as a monomer and / or as an oligomer. In particular, the siloxane is a polysiloxane

(Polyorganosiloxane, silicone). The siloxane is present as a polymer. It is also conceivable that the siloxane is monomeric, oligomeric and polymeric.

The siloxane has organic side chains, for example ethyl or phenyl groups. It has been found that a siloxane with methyl groups and in particular a polysiloxane with methyl groups as side chains are particularly good suitable is. In a particular embodiment, therefore, the polysiloxane is methylpolysiloxane. The side chains of this polysiloxane are formed by methyl groups.

The silicone is crosslinkable. This means that the siloxane is a (poly) condensation reaction and / or

Polymerization reaction can go. For this purpose, the siloxane has one or more reactive functional groups which are available for a condensation reaction and / or polymerization reaction. A reactive functional group is, for example, an OH group. With or without a crosslinking agent, for example methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES) or tetraethoxysilane (TEOS), the condensation reaction occurs. There is a crosslinking of the siloxane instead. It forms a polymeric network of siloxane.

The crosslinking of the siloxane is initiated in a known manner. For example, a crosslinking agent is added. Also conceivable is a temperature increase. It is carried out during the crosslinking, a temperature treatment. For example, the conductor paste is dried after application to the carrier body at 200 ° C. By drying at this temperature, curing or crosslinking of the siloxane takes place. In the crosslinked state, inorganic constituents consisting of silicon-oxygen-silicon chains (Si-O-Si) and organic side chains (for example methyl, ethyl or phenyl groups) are present.

The solid state dispersion can have only one type of siloxane. This forms a condensation and / or polymerization, which is composed only of this one type of siloxane. In particular, it is also possible that various types of monomeric, oligomeric and / or polymeric siloxanes are present. Also, other organometallic or non-organometallic, condensable and / or polymerizable constituents may be present. By Crosslinking produces co-condensation and / or copolymerization products.

By crosslinking the siloxane, the electrical conductor can be produced directly. It forms an electrical conductor with a composite material of crosslinked siloxane and the powder particles of the electrically conductive solid. For this purpose, a solids content of the electrically conductive solid is selected according to the solid state dispersion.

Preferably, a temperature treatment is carried out during and / or after the crosslinking of the siloxane. By the temperature treatment, as described above, the crosslinking of the siloxane can be influenced. This concerns, for example, a crosslinking rate and a degree of crosslinking. The temperature treatment can also lead to a chemical reaction of the siloxane and / or the crosslinked siloxane. In a particular embodiment, a ceramizing or sintering of the crosslinked or crosslinking siloxane takes place during the temperature treatment. For example, in a first

Temperature treatment step at a lower temperature (for example, up to 200 ° C) carried out the crosslinking of the siloxane. The result is a solid precursor (precursor) of the conductor. In a second temperature treatment step (above 500 ° C) it comes to ceramization. The crosslinked siloxane is converted into a ceramic material. There is a kind of sintering. From the conductor paste with the solid-state dispersion, a composite material with a ceramic material with silicon dioxide and the powder particles of the electrically conductive solid forms indirectly via the precursor. It is particularly advantageous to ensure that when transferring the siloxane in the ceramic material to almost no chemical

Reaction comes, in which the powder particles of the electrically conductive solid are involved. Such a chemical reaction is, for example, a reaction of Solid of the powder particle with components of the crosslinked siloxane, an intermediate of the ceramic material, the resulting ceramic material or an atmosphere in the presence of which the reaction is carried out. The electrically conductive solid in the form of the powder particles is essentially chemically inert. The electrical conductivity of the solid is maintained during the conversion of the siloxane into the ceramic material.

The conversion into the ceramic material can be carried out at a temperature above 600 ° C, for example at a temperature in the range of 600 ° C to 1500 ° C. In a preferred embodiment, the temperature treatment is carried out at a temperature of less than 600 ° C and in particular at a temperature in the range of 500 ° C - 600 ° C. During the temperature treatment, the polymeric network of the siloxane is decomposed and restructured via thermal intermediates from amorphous to crystalline phases. Depending on the pyrolysis atmosphere different

Go through intermediate stages. For example, the pyrolysis is carried out in the presence of argon (argon atmosphere). In this process, silicon-oxygen-silicon chains are formed, which are connected to one another via carbon atoms (Si-O-Si-C-Si-O-Si chains). In the presence of atmospheric oxygen, however, only silicon-oxygen-silicon (Si-O-Si) chains form. The organic components are expelled in the presence of oxygen.

Pyrolysis or ceramization produces a conductor material in the form of a ceramic composite material. The composite material has the ceramic material obtained by the pyrolysis of the siloxane and the powder particles of the electrically conductive solid. The choice of siloxane, the conditions under which the crosslinking and the ceramization are carried out, the nature of the electrically conductive solid and the proportions of the substances involved in the conductor paste, can be used Properties of the conductor material of the resulting connection line can be adjusted in a wide range.

For example, the electrically conductive solid is a ceramic material. As a result, a brittle conductor material is obtained. In a preferred embodiment, the solid has at least one metal. During pyrolysis, a so-called cermet (metal ceramics) is created. The resulting particle composite consists of at least two phases. One of the phases is metallic, the other one is ceramic.

A conductor paste with a metal as an electrically conductive solid is the preferred starting point for adapting the properties of the conductor material to corresponding requirements for the electrical conductor. For example, by increasing a proportion of siloxane and the resulting higher proportion of silica brittleness of the conductor material can be increased. By increasing the proportion of the metal powder, however, the electrical conductivity of the conductor material can be increased. At the same time, the brittleness of the conductor material is lowered with the increased proportion of metal powder.

As an electrically conductive solid any metal is conceivable, for example, chromium, iron, copper, nickel or silver. Alloys are just as possible as mixtures of powder particles of different metals. The choice of metal depends on different points of view. In addition to the electrical conductivity, the chemical reactivity of the metal plays a role. For example, copper is used when pyrolyzed under an argon atmosphere, that is, in the absence of oxygen. In the presence of oxygen, oxidation of the copper would occur. Likewise attention is paid to the melting point of the metal. A metal is chosen whose melting point is above the pyrolysis temperature of the conductor paste. The metal remains in the ceramizing Mass distributed homogeneously. It flows during the

Pyrolysis process not from the ceramizing mass. Likewise, inhomogeneities (locally different proportions of metal and ceramic material) do not occur in the resulting printed circuit due to the flow.

In a particular embodiment, silver is used as the metal. It is characterized by a relatively high oxidation resistance. According to a particular embodiment, the metal is aluminum. The powder particles are made of pure aluminum or an aluminum alloy. Pure aluminum is characterized by a relatively high electrical conductivity. By forming a passivation layer, pure aluminum is relatively inert even in the presence of oxygen. In particular, the combination of powder particles of aluminum and of crosslinkable methylpolysiloxane has proved to be advantageous. Methyl polysiloxane acts as an efficient binder for aluminum powder particles. In addition, the pyrolysis of the methylpolysiloxane can be carried out below 600 ° C. in the

In comparison, the melting point of aluminum is about 660 ° C.

According to a particular embodiment, the powder particles of the conductor paste have a mean particle diameter dso selected from the range from 1.0 μm to 50.0 μm inclusive and in particular from the range from 10.0 μm to 30 μm inclusive. Such particle diameter lead to a homogeneous and easy to process conductor paste. At the same time, the electrical conductivity of the resulting conductor material is very easily adjustable with these particle diameters. Larger or smaller particle diameters are also conceivable.

The conductor paste can be used to produce any desired electrical conductor on any carrier body (component). In particular, with the help of Conductor prepared a conductor track of a control device for detecting a degradation of the carrier body. In a particular embodiment, the heat shield of a combustion chamber of a gas turbine is used as the carrier body or component. By varying the constituents of the paste and the reaction or pyrolysis conditions, the properties of the conductor material can be adapted to the properties of the component material. These properties are, for example, a coefficient of thermal expansion or brittleness or fracture toughness. At the same time with the

Powder particles from the electrically conductive solid achieves the necessary electrical conductivity of the conductor material.

In summary, the invention provides the following essential advantages:

- With the conductor paste, an electrical conductor can be made of a conductor material with a variety of properties.

The composition of the conductor paste can be matched to the carrier body. In addition to physical properties, this also concerns a chemical compatibility (non-reactivity) between the

Conductor paste and the carrier material of the carrier body.

In particular, at a temperature treatment (sintering temperature) of less than 600 ° C undergoes the carrier body on which the conductor paste is applied, a relatively low thermal stress during the transfer of the conductor paste in the conductor track.

In addition, a viscosity of the paste can be adjusted for the desired processing.

Reference to an embodiment and the accompanying figure, the invention will be described in more detail below. The figure is schematic and does not represent a true to scale illustration.

According to the exemplary embodiment, a conductor paste for producing an electrical conductor 11 made of a brittle conductor material is provided. The conductor paste has a solid state dispersion. The solid-state dispersion contains as essential components a crosslinkable methylpolysiloxane and powder particles of aluminum. The average particle diameter dso of the aluminum powder particles is about 30 μm. In addition to these two components, further constituents are present which act as dispersants and / or binders. These ingredients are terpinol and ethyl cellulose.

10 g of the conductor paste are prepared as follows: In a (dry) beaker, 6.77 g of aluminum powder, 3.33 g of methylpolysiloxane (solid silicone resin) are mixed. To the resulting mixture terpinol is added dropwise with stirring. Terpinol acts as a dispersant. It is obtained a homogeneous mixture. Thereafter, a mixture of terpinol and ethylcellulose is added. With the help of this mixture, a desired for the subsequent processing of the conductor paste viscosity is set.

The conductor paste is used to produce an electrical conductor 11 on a carrier body 10. The carrier body 10 is a component in the form of a ceramic heat shield of a combustion chamber of a gas turbine.

To produce the conductor track 11, the conductor paste is applied in a structured manner in the form of the conductor track 11 to be produced on a surface 111 of the rear side of the heat shield. The structured application takes place in an injection molding process. Alternatively, the structured application is carried out with the aid of a mask. After application becomes a first

Temperature treatment step performed at about 200 ° C. This leads to crosslinking or condensation of the methylpolysiloxane. The first temperature treatment step takes about 90 minutes.

After crosslinking the methylpolysiloxane, a second temperature treatment step is carried out at 600 ° C. The second temperature treatment step is carried out in the presence of oxygen and takes about 30 minutes. This leads to the pyrolysis of the conductor paste. There is a kind of sintering. This forms the trace with the brittle conductor material. The conductor material is a particle composite in which powdered aluminum is embedded in a ceramic network of silicon dioxide. In this second

Temperature treatment step creates a solid and intimate contact between the conductor 11 and the heat shield 10 by sintering.

The brittle trace 11 made on the backside of the heat shield 10 is used as part of a control device for detecting a crack 102 of the heat shield 10. Due to the brittleness of the conductor track 11 and due to the firm contact between the component 10 and the conductor track 11, a crack 102 propagating in the heat shield 10 leads to a crack 112 in the conductor track 11. Due to the crack 112 in the conductor track 11, an electrical property changes the trace 11. The change in the electrical property of the trace is detected by means of the control device.

In variants of the embodiment, silver and a silver-palladium alloy is used instead of the aluminum.

Claims

claims 1. Conductor paste for producing an electrical conductor (11), comprising a solid-state dispersion with powder particles of at least one electrically conductive solid, characterized in that the solid-state dispersion comprises at least one crosslinkable siloxane. 2. Conductor paste according to claim 1, wherein the crosslinkable siloxane is a polysiloxane. The conductor paste of claim 2, wherein the polysiloxane is methylpolysiloxane. 4. Conductor paste according to one of claims 1 to 3, wherein the electrically conductive solid comprises at least one metal. 5. Conductor paste according to claim 4, wherein the metal is aluminum or silver. The conductor paste according to any one of claims 1 to 5, wherein the powder particles have a mean particle diameter d 50 selected from the range of 1.0 μm to 50.0 μm inclusive. 7. The conductive paste according to claim 6, wherein the average particle diameter is selected from the range of 10 μm to 30 μm inclusive. 8. A method for producing a conductor track on a carrier body using the conductor paste according to one of claims 1 to 7 with the following method steps: a) applying the conductor paste on a surface (101) of the Carrier body (10) and b) generating the conductor track (11), wherein a crosslinking of the siloxane is performed. 9. The method of claim 8, wherein during and / or after crosslinking, a temperature treatment is carried out. 10. The method of claim 9, wherein a ceramizing of the crosslinked siloxane takes place during the temperature treatment. 11. The method according to claim 9 or 10, wherein the Temperature treatment is carried out at a temperature of less than 600 'C. 12. The method according to any one of claims 8 to 11, wherein a conductor track (11) of a control device for detecting a degradation (102) of the carrier body (10) is produced. 13. The method according to any one of claims 8 to 12, wherein the carrier body is a heat shield of a combustion chamber of a Gas turbine is used.