DE102009026104A1 - Process for the production of a ceramic body, catalytic converter and support body for such - Google Patents

Abstract

The invention relates to a method for producing a ceramic body of an exhaust gas catalytic converter with ducts carrying exhaust gas, characterized by the process steps: - producing a preform from paper containing cellulose fibers, - loading the paper before or after producing the preform with at least one filler with a weight fraction x and pyrolyzing the paper preform, the weight fraction x of the filler being selected such that a volume shrinkage of the preform does not occur or substantially does not occur during pyrolysis.

Description

The The invention relates to a method for producing a ceramic body of a Catalytic converter with the exhaust gas leading channels.

at The combustion of fuels arise in addition to harmless Gases in the form of carbon dioxide and water vapor harmful to health and polluting substances. These include carbon monoxide, hydrocarbons and nitrogen.

Around the gaseous To reduce pollutants, catalysts are used, the make it possible to carry out a chemical reaction at relatively low temperatures, wherein by adding oxygen carbon monoxide to carbon dioxide, hydrocarbon to carbon dioxide and water vapor, nitrogen oxides by reaction with carbon monoxide is converted to carbon dioxide and elemental nitrogen.

Such used in motor vehicles for catalytic converters and diesel engines have catalysts with large contact areas, the by the use of ceramic and metallic honeycomb bodies as support material be achieved. On the carriers Then an intermediate layer, the so-called washcoat is applied, causing the surface of the catalyst carrier increased many times over becomes. The actual noble metal catalyst is then vapor-deposited.

at the use of ceramic bodies as a carrier they are wrapped with a wire mesh in a stainless steel case, whereas metallic honeycomb bodies directly into a housing shrink wrapped become.

adversely The known catalysts is that the preparation consuming and is costly and that the lightning behavior is not mandatory so is that, even at low temperatures to a sufficient extent the required chemical conversion of pollutants into environmentally friendly substances he follows.

Of the The present invention is based on the object, a method for producing a ceramic body for one Catalytic converter, in such a way that a cost-effective production possible is, with a high strength are achieved with low weight should. Also is a high dimensional accuracy be given.

• – Herstellen einer Preform aus Cellulosefasern enthaltendem Papier,
• – Beladen des Papiers vor oder nach Herstellen der Preform mit zumindest einem Füllstoff mit einem Gewichtsanteil x und
• – Pyrolisieren der Papierpreform,
• – wobei der Gewichtsanteil x des Füllstoffs derart gewählt wird, dass bei der Pyrolyse eine Volumenschrumpfung der Preform unterbleibt oder im Wesentlichen unterbleibt.

In terms of procedure, the task is solved by the steps

• Preparing a preform of cellulose fiber-containing paper,
• - Loading the paper before or after making the preform with at least one filler with a weight fraction x and
• - pyrolyzing the paper preform,
• - Wherein the weight fraction x of the filler is chosen such that during the pyrolysis, a volume shrinkage of the preform is omitted or substantially omitted.

there is the preform before pyrolization or carbonation to a Cylindrical shape wound. However, there is also the possibility that the preform consists of layered layers.

Of course it will Do not leave the invention, when the ceramic body of sections of a Cylinder exists, d. h., That the preforms corresponding partial geometries demonstrate.

Also can Preforms to a cylinder geometry having a preform composed be, with the connection of the individual sections by means of carbonizable Glue done.

Suitable fillers are those which are carbonizable. But ceramic fillers such as Al ₂ O ₃ or ZiO ₂ can be used to load the paper of the preform accordingly. Another preferred filler is carbon black. Inert fillers such as SiC are also to be preferred, which may be used alone or in conjunction with at least one other filler.

Of Further can the paper to be pyrolyzed additives in the form of binders such as phenolic resin and / or cellulose are added.

preferably, is the weight fraction x of the filler 5 wt .-% to 85 wt .-% based on the cellulose fibers of the paper and filler existing dry matter of the paper, with additives included are. The proportion of filler is adjusted so that a shrinkage of the preform during the heat treatment is omitted or substantially omitted.

In particular, according to the invention provided that the pyrolyzed, d. H. the carbonized paper is silicified. This can be done with pure silicon, with excess or deficit is worked. The silicating is with usual Perform procedure. In particular, however, the pyrolyzed paper becomes to be silicided contacted with a silicon melt, for example by Wicks, transfer plates or similar Techniques.

The pyrolyzed paper is preferably silicated in a reaction space at reduced pressure, which should be in a range from 50 mbar to 0.05 mbar, in particular in the range of 0.1 mbar. After the reaction of the C with the Si to SiC is then the Vented reaction space with inert gas atmosphere in order to provide the possibility that excess silicon can form on the siliconized ceramic substrate as an Si layer.

Becomes a corresponding Si layer desired, the process should be such that the Si layer has a thickness D of 0.5 μm ≦ D ≦ 50 μm, in particular 10 μm ≤ D ≤ 20 μm.

The Silicate itself takes place in a temperature range of 1350 ° C ≤ T ≤ 2000 ° C, especially in Range of 1650 ° C ≤ T ≤ 1700 ° C instead.

When Preform is in particular used in corrugated cardboard geometry. additional or alternatively also layers of embossed Paper used for making the preform or sections of these become.

Especially However, it is envisaged that such a preform will be used, the three layers with an inner first layer, one connected with this as glued a shaft geometry having intermediate layer and one associated with this as glued covering the liner level third layer includes. The first and second position are about the Spacer spaced.

Mentioned exists but also the possibility shaped as a preform Choose paper layers which are arranged and supported on one another in such a way that that the desired channel training given for that the flow through of the gas through the ceramic body is required.

Especially can the layers form a honeycomb structure, wherein z. B. zigzag or wavy Layers z. B. are connected together in their tips.

The pyrolyzed and optionally silylated interlayer should a Have thickness Dz with 50 microns ≤ Dz ≤ 1000 microns. Same dimensions come for the first and second layer in question.

Further Details, advantages and features of the invention do not arise only from the claims, the characteristics to be taken from these - alone and / or in combination - but also to be taken from the following description of the drawing preferred embodiment.

It demonstrate:

1 a schematic diagram of a catalyst,

2 a portion of a carrier body of ceramic material and

3a ) - 3g ) Examples of carrier bodies in detail.

In 1 is basically a three-way catalyst 10 shown, the essential components of a particular existing stainless steel housing 12 and in this arranged coated ceramic body 14 comprising, with a knitted wire in the housing 12 can be taken. The housing 12 has funnel-shaped inlet and outlet channels 16 . 18 on, wherein in the inlet channel 16 a lambda probe 22 is arranged. This is the oxygen content of the catalyst through the 10 flowing exhaust gas measured in order to regulate the fuel-air mixture before combustion can.

The ceramic body 14 points in the longitudinal direction of the catalyst 10 or ceramic body 14 running channels 20 on. Furthermore, the ceramic body 14 coated in the usual way for surface enlargement with a washcoat on which in turn the actual catalyst is deposited from noble metal. In that regard, however, reference is made to well-known techniques and constructions.

According to the invention, the ceramic body 14 from a ceramized Papierpreform, which in principle the 2 can be seen. So is in the 2 a paper preform having a cylindrical shape 24 shown. The paper reform 24 consists in the embodiment of a wound into a cylindrical shape forming a corrugated board layers of at least one cellulose fibers and at least one filler containing paper. The filler may be carbon black, a carbonizable filler, a reactive filler such as B or Si, or a ceramic filler.

Preferred fillers are carbon black or Al ₂ O ₃ or ZiO ₂ as ceramic fillers.

The However, paper can also be loaded or impregnated with SiC or Si + SiC. Combinations with one or more fillers are also possible.

Independent of this should be the weight fraction of the filler 5 wt .-% to 80 wt .-% based on the cellulose fibers of the paper and filler existing dry substance of the paper. Also can more Additives such as binders such as phenolic resin or cellulose be added.

Like the enlarged section of the 2 clarifies, that is made up of a first and a two flat paper layer 26 . 28 and this spaced apart liner 30 formed paper web - more precisely corrugated cardboard sheet - wound into a cylinder, with the spaces between the liner 30 and the flat layers 26 . 28 the channels 20 limit.

The corresponding cylinder 24 is then pyrolyzed in a temperature range between 800 ° C and 1400 ° C, ie carbonized. Subsequently, a siliconizing of the carbonized paper in a temperature range between 1650 ° C and 1700 ° C take place. In particular, a siliconizing by means of a wick with a silicon melt is preferred. When silicating, the carbonized preform can be arranged in a reaction space in which a negative pressure in the range of 0.1 mbar prevails.

It is not mandatory that the ceramic body 14 forming preform 24 is a unitary entity. Rather, the preform 24 also be composed of several sections.

Instead of A corrugated board geometry of the layers can also be embossed paper are wound into a cylinder, the embossing is to be chosen such that the desired Channel formation is ensured.

To the individual layers 26 . 28 . 30 It should be noted that these should have a thickness between 50 microns and 1000 microns after carbonization and optionally silicidation. In this case, the proportion of the filler and of the additive (s) should be determined so that shrinkage of the preform during pyrolysis or carbonization is omitted or substantially eliminated.

The 3a ) to 3g ) extracts of preforms are shown, from which a ceramic body of a catalytic converter can be made. So after the 3a ) a honeycomb body produced by zigzag-shaped layers 30 . 32 . 34 are supported on each other in their tips.

In 3d ) channeling is provided by that between inner layers 36 . 38 a location 40 is arranged in wave geometry.

As the 3c ), it is not necessary that the position forming a wave geometry 40 is arranged between two flat layers. Rather, a single level location is enough 38 out.

After 3b ) is a channel formation by a U-shaped extending intermediate layer 42 and these limiting flat layers 44 . 46 educated. As shown in FIG 3e ) can - as in the embodiment according to the 3c ) - the U-shaped position 42 only from a level position, namely the location 44 out.

The embodiment of 3f ) and 3g ) illustrates that a zigzag-shaped, ie from roof-shaped sections existing intermediate layer 46 either between two flat liners 48 . 50 is arranged or from a flat liner 48 emanates.

Appropriate Preforms can wrapped into a cylindrical shape or even layered, to achieve a geometry that corresponds to the desired ceramic body.

Further Details and features of the invention will become apparent from the Examples described below.

Example 1:

It is a paper web with a basis weight of 200 g / m ² used, which is loaded with a carbon black filler. The proportion by weight of the filler is about 75%, based on the existing of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is silicated by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The silicating is done with excess of silicon. After the reaction of the silicon with carbon to SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For the siliciding itself, high purity silicon is used.

It resulted in a thin-walled highly stable structure. Micrographs show that the substrate is essentially consists of free silicon surrounding SiC. Unreacted C im vanishing scope may be included.

The ceramic can be used as a catalyst support of a catalytic converter for gasoline and diesel engines be used.

Example 2:

It is a paper web with a basis weight of 200 g / m ^{2 is} used, which is loaded with an existing SiC powder filler. The proportion by weight of the filler is about 75%, based on the existing of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is silicated by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The silicating is done with excess of silicon. After the reaction of the silicon with carbon to SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, Poly-Silizum is used in solar quality.

It resulted in a thin-walled highly stable structure. Micrographs show that the substrate is essentially consisting of free silicon surrounding SiC. Unreacted C im vanishing scope may be included.

The Ceramics can act as catalyst supports an exhaust gas catalyst for Petrol and diesel engines are used.

Example 3:

It is used a paper web with a basis weight of 100 g / m ² , which is loaded with a filler consisting of carbon black. The proportion by weight of the filler is about 50% based on the consisting of cellulose fibers and filler dry matter of the paper. The thus loaded paper is then further processed into a paper semi-finished product, which has a corrugated cardboard geometry and wound into a preform and glued. The resulting preform is pyrolyzed in an inert atmosphere at a temperature between 800 ° C and 1400 ° C. Then, the carbonized paper is silicated by means of a wick with a silicon melt at a temperature in the range between 1650 ° C and 1700 ° C. In the reaction space itself, there is a negative pressure in the range of 0.1 mbar. The silicating is done with excess of silicon. After reaction of the silicon with carbon to SiC, the reaction space is vented to avoid that the excess silicon is discharged. As a result, an Si layer is formed on the ceramic substrate, the process being controlled such that the thickness is in the range between 10 .mu.m and 20 .mu.m. The solidified layer is then remelted at a temperature just above the melting point of silicon and recrystallized. For siliconizing itself, solar grade poly-silicon is used.

It resulted in a thin-walled highly stable structure. Micrographs show that the substrate is essentially consists of free silicon surrounding SiC. Unreacted C im vanishing scope may be included.

The Ceramics can act as catalyst supports an exhaust gas catalyst for Petrol and diesel engines are used.

Claims (21)

Process for producing a ceramic body of a Catalytic converter with exhaust gas leading channels, characterized through the process steps: - Making a preform cellulose-containing paper, - Loading the paper before or after producing the preform with at least one filler with a weight fraction x and - pyrolyzing the paper preform, - in which the weight fraction x of the filler chosen like that is that in the pyrolysis volume shrinkage of the preform is omitted or substantially omitted. Method according to claim 1, characterized in that that the carbonized Papierpreform is siliconized. Method according to at least one of the preceding Claims, characterized in that as a filler carbonisierbarer filler is used. Method according to at least one of the preceding Claims, characterized in that carbon black is used as filler. Method according to at least one of the preceding Claims, characterized in that the filler is a reactive filler how Si or B is used. Method according to at least one of the preceding Claims, characterized in that as filler an inert filler how SiC is used. Method according to at least one of the preceding claims, characterized in that a ceramic filler such as Al ₂ O ₃ or ZiO _{2 is} used as the filler. Method according to at least one of the preceding Claims, characterized in that the paper to be carbonized as Additive, a binder such as phenolic resin and / or cellulose added or the paper is impregnated with this. Method according to at least one of the preceding Claims, characterized in that the paper or the preform produced therefrom with a mixture of the filler and the additive impregnated becomes. Method according to at least one of the preceding Claims, characterized in that the filler with a weight fraction x with 5% by weight ≦ x ≦ 85% by weight, in particular 60% by weight ≦ x ≦ 80% by weight, based on the consisting of cellulose fibers and the filler dry substance of the Including paper any additive is introduced into the paper. Method according to at least one of the preceding Claims, characterized in that the carbonized Papierpreform with Reinstsilizium is siliconized. Method according to at least one of the preceding Claims, characterized in that the pyrolyzed Papierpreform with Pure silicon in excess or deficiency is siliconized. Method according to at least one of the preceding Claims, characterized in that the carbonized Papierpreform means is siliconized a silicon melt. Method according to at least one of the preceding Claims, characterized in that the pyrolyzed Papierpreform in one Reaction space at a pressure p with 0.50 mbar ≤ p ≤ 0.05 mbar, preferably p in is siliconized about 0.1 mbar. Method according to at least one of the preceding Claims, characterized in that the reaction of the carbonized Papierpreform with Si to SiC at a temperature T of 1350 ° C ≤ T ≤ 2000 ° C, preferably 1650 ° ≤ T ≤ 1700 ° C is performed. Method according to at least one of the preceding Claims, characterized in that as Papierpreform a corrugated cardboard geometry comprising paper wound into a cylinder or a corrugated cardboard geometry forming and wound into a cylinder paper layers are used. Method according to at least one of the preceding Claims, characterized in that as Papierpreform an embossed paper is used. Method according to at least one of the preceding Claims, characterized in that used as Papierpreform such will, the three layers with a flat first layer, one with this connected a shaft geometry having intermediate layer and a associated with this and that covering level third position includes. Method according to at least one of the preceding Claims, characterized in that as such a preform is used, the three layers with a flat first layer, one connected with this a wave geometry or a U-geometry or a V-geometry having intermediate and one associated with this and these covering third layer covers. Method according to at least one of the preceding Claims, characterized in that as such a preform is used, which includes two layers, one of which is a wavy, U-shaped or V-shaped Geometry, which assumes a flat position. Method according to at least one of the preceding Claims, characterized in that as a preform one with a honeycomb structure is used.

Images