DE102007023897A1 - Production of a ceramic functional element, useful for the pollutant reduction of exhaust gases, comprises coating the ceramic carrier with an organic material, applying a particle coating on the carrier and calcining the coated carrier - Google Patents

Abstract

Production of a ceramic functional element (114) for the pollutant reduction of exhaust gases, comprising a ceramic carrier (130) and a ceramic functional coating (110), comprises wet-chemically coating the ceramic carrier with an organic material, preferably a polymer (140); applying a ceramic functional particle coating on the organically coated carrier in a wet-chemical step; and thermally calcining the coated carrier, where the organic material is at least partly removed and a solution, a dispersion and/or an emulsion of the organic material are used during the organic coating. Production of a ceramic functional element (114) for the pollutant reduction of exhaust gases, comprising a ceramic carrier (130) and a ceramic functional coating (110), comprises wet-chemically coating the ceramic carrier with an organic material, preferably a polymer (140); applying a ceramic functional particle coating on the organically coated carrier in a wet-chemical step; and thermally calcining the coated carrier, where the organic material is at least partly removed and a solution, a dispersion and/or an emulsion of the organic material are used during the organic coating, which exhibits an additive for improving the wetting of the ceramic carrier.

Description

State of the art

The Invention is based on known ceramic functional elements, as in particular in the field of pollutant reduction of exhaust gases be used. Such ceramic functional elements come for example in the field of catalyst and / or particle filter technology used, for example in the context of diesel particulate filters (DPF). Such filters generally have a ceramic carrier material usually made of ceramic materials, such as silicon carbide, cordierite or aluminum titanate composed. Filters made of sintered metal are also used.

The Functional elements can be in different structures are used, which depend on the type of exhaust gas purification. Especially with ceramic filters, the functional elements be used in the context of a honeycomb structure. For the Use in filters, especially in diesel particulate filters, can the functional element, for example, mutually closed channels whose walls have a certain porosity exhibit. The gas stream entering through inlet channels is then forced to pass through the pores of the channel walls.

Out said ceramic materials of the ceramic carrier cordierite and / or aluminum titanate are the cheapest Materials proved. The disadvantage of these materials, in particular of cordierite, lies in the comparatively low thermal Resilience. However, this is in the field of filter technology Of considerable importance, since these filters partially thermal loads of 1000 ° C and more are exposed.

Especially the carrier cordierite and other ceramic Carrier materials exhibit due to their manufacturing process a series of microcracks in the structure. These microcracks are partially desired, and make a significant contribution for example, the filter effect or catalyst effect of the functional elements.

The Although microcracks lead to lower strength of the ceramic Carrier material, but also lead at the same time to a lower elastic modulus and to a lower one Coefficients of thermal expansion and contribute to that thermal stresses in the ceramic are degraded and the thermal Resilience is increased. A low thermal expansion coefficient and ensure a low modulus of elasticity low induced stresses under thermal stress of the substrate. This is due in particular to the fact that the micro-cracks in the ceramic carrier material are after and after close at temperature increase and form such a buffer for thermal expansion.

On the ceramic support, a catalytic coating is usually applied in the prior art. This coating is often referred to as a "washcoat." For this coating, ceramic materials, such as, for example, porous aluminum oxide (Al ₂ O ₃ ) are often ground to a desired particle size, and then a suspension with a certain particle size distribution is produced, and this suspension (also known as slurry) called) then applied to the ceramic carrier.

The Problem of this known method, however, is that the Suspensions contain even the smallest particles, which in the microcracks of can penetrate ceramic support. This causes, that these microcracks in a heating of the ceramic Do not close the carrier to the extent described above can. This in turn increases the thermal expansion coefficient of the ceramic carrier, and there are unwanted, increased thermal stresses.

One Another problem of the known methods is that in In many cases, catalytically active substances are deposited in places become, at which these show no effect. In particular, divorce catalytically active particles in many cases in places in the Substrate from where only a small gas exchange takes place. This means that at these points the catalytic conversion of Harmful gases is extremely low. Thus, become catalytic active substances without benefit for the functional element wasted. As these catalytically active substances in many cases expensive precious metals, this makes the process considerably more expensive.

to Avoiding the problems mentioned are so-called pre-coating procedures in which the surface of the substrate to be coated is known is coated with organic polymers. This will cause the microcracks at least partially closed, where by an entry of harmful Components during the subsequent coating process is reduced with washcoat particles.

One Another advantage of pre-coating is that small micropores with low gas sales and tight microchannels where due the high flow rate of the gases a low Interaction with the catalyst particles, specifically with a reduced washcoat coating can be provided.

After coating with washcoat particles, which are also referred to below as functional particles, the polymer is burned out in a calcining step. This process of pre-coating is for example off US 4,483,940 . US 2005/0191480 A1 and US 2005/0037147 A1 known.

especially the US 2005/0037147 A1 and US 2005/0191480 A1 disclose that polyacrylic acid, polyvinyl alcohol, polyacrylamine, amine-functionalized ionic polymers, acid-activated amino acrylates, ionene polymers or aliphatic acrylic acid-wax polymers can be used as polymer coatings. The polymers are used inter alia in conjunction with a cross-linker. The Crosslinker are used to improve the degree of separation. In this case, a cross-link promoter is added to the polymer solution, which crosslinks the existing polymer supports.

adversely to the use of the described polymers and to the use of the However, Crosslinker it is that an additional chemical Substance is incorporated. This causes an extra Process control (and therefore costs). In particular, such Crosslinking reactions often very much from the pH dependent. The pH, in turn, must be frequent special bases are set. As examples of cross-linking promoters Epichlorohydrin and hexamethylenediamine are mentioned.

One Another disadvantage of this prior art is that the range of usable polymers is limited, since not all Polymers can be used for cross-linking reactions. The advantage of improved deposition are therefore numerous Disadvantages.

Disclosure of the invention

It Accordingly, starting from the prior art, a method for producing a ceramic functional element for pollutant reduction proposed by exhaust gases, which has the disadvantages described above avoids known method. In particular, by the inventive Method the thermomechanical strength of microcracked increased ceramic surfaces, while at the same time the catalytic function is maintained.

One The main advantage of the proposed method is the Compared to the prior art more homogeneous deposition of organic Substances on the substrate surface. In particular, let thereby exhaust gas components, such as in particular diesel particulate filter (DPF) with increased durability and improved generate catalytic activity. The invention relates in particular to exhaust gas components based on Cordierite and / or aluminum titanate constructed as a ceramic material are.

As in the prior art, so are also according to the proposed method Washcoat particles with the aid of a polymer at least largely prevented from entering the microcracks of the ceramic carrier penetrate. Other than one polymer may be others organic materials are used, including non-polymeric, higher molecular weight water-soluble organic compounds, such as As starch and / or cellulose. Without restriction In the scope of protection, these organic materials will be described below however, referred to as polymers.

at The ceramic supports may be, in particular, cordierite honeycomb bodies act. Accordingly, the thermomechanical strength increases the ceramic produced by the proposed method Functional elements.

in the Difference to the prior art uses the proposed method but not simple polymer solutions or polymer dispersions, but based on the knowledge that a uniform Distribution of the polymer is of essential importance. Will that be Polymer evenly on the carrier material deposited, so may in the subsequent coating process also the washcoat be distributed more homogeneously.

in the Unlike the prior art, the invention shows a possibility on, with the deposition of the polymers can be improved, without to penetrate into the structure of the polymer. It will be accordingly the use of polymer solutions, polymer dispersions or polymer emulsions, which as auxiliaries a water-soluble An additive for improving the wetting of the ceramic carrier exhibit.

Under an additive is here as well as below a wetting agent and / or to understand a dispersant which the deposits of Polymers on different surfaces improved. When In particular, additives are one or more of the following substances in question: polysiloxanes; with epoxy, vinyl, ether, acrylic, amino, Diamines or styreneamines functional silylated polysiloxanes; polyacrylates; Polyester; sulfosuccinates; silicone polyether; non-ionic silicone emulsions. These are comparatively simple chemical compounds, which do not interact with the substrate which does not enter the Structure of the polymer penetrate and which no consuming Require process control.

The proposed method thus leads to the considerable Advantage that by using the additive, a variety of polymers is available, even if these polymers, for taken, only over comparatively poor wetting properties feature. Thus, a variety of polymers can be used become unavailable without additive.

While in earlier writings mainly of polyacrylic acids, Polyvinyl alcohols and polyacrylamines is mentioned with the aid of additives also other polymers advantageous be used, such as copolymers based on acrylate, Polyvinyl pyrrolidones, celluloses, polyethylene glycols, polymaleates and maleate-based copolymers, polyvinyl acetates, polyvinyl butyrals, Polyoxazolines, polyacrylamides and amide-based copolymers, polystyrenes, Polyvinyl derivatives, polyvinyl styrenesulfonates or epoxy-based polymers or mixtures of said polymers with each other or with others Polymer types are used. The polymers can in the polymer solutions and / or polymer dispersions in addition the polymer or polymers and the auxiliary solvent or contain additional agents, such as dispersants or similar.

The Additive is advantageously chosen such and in such Concentrations used that the slurry, thus the watery Washcoat particle dispersion optimally on the polymer surface distributed. Typical values of aqueous solutions on polymer surfaces (measured on coated Glass substrates) at above 70 °, so at comparatively high values. Accordingly, the wetting is bad. With additives are advantageously the contact angle below 70 °, for example at 50-70 °, more preferably still below of 50 °.

When In particular, additives have the following commercially available Products proved to be suitable: Worlée Add 345 (Worlée Chemie GmbH), Dow Corning 67 (Dow Corning GmbH), BYK 380 N and BYK 381 (BYK-Chemie GmbH). Usually you can the additives in a concentration of about 0.1 to 5 weight percent (based on the total mass) use.

The proposed method thus comprises a polymer coating step, in which the ceramic support wet-chemically with a Polymer is coated. Furthermore, the method comprises a Step in which the polymer-coated carrier in a further wet-chemical step, a ceramic functional particle coating is applied. Subsequently, the thus coated Carrier thermally calcined, wherein the polymer at least partially removed.

The proposed method is thus characterized in comparison to known Process by a significant reduction of the process costs out, as well as a reduction in the process control to be operated. The means of the invention Process produced ceramic functional elements are more homogeneous coated than in conventional methods and still have a high temperature stability and a low thermal expansion on which only a little of the uncoated ceramic carriers different.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description explained in more detail.

It demonstrate:

1A and 1B : SEM images of washcoat-coated cordierite surfaces without pre-coating;

2A and 2 B : SEM image of washcoat-coated cordierite surfaces without ( 2A ) and with ( 2 B ) Pre-coating;

3A and 3B : SEM images of conventionally polymer-coated cordierite surfaces with inhomogeneous polymer deposition;

4A and 4B : SEM images of homogeneous coated polymer coated cordierite surfaces according to the invention;

5A and 5B Photos: SEM recordings washcoat-coated ( 5A ) as well as polymer and washcoat-coated ( 5B ) Cordierite surfaces;

6 a honeycomb body of a diesel particulate filter in a sectional view;

7A a schematic representation of a section through a channel wall of a diesel particulate filter;

7B the duct wall according to 7A after coating with a polymer;

7C the duct wall according to 7B after washcoat coating; and

7D the duct wall according to 7C after burnout of the polymer.

In the 1A and 1B are Rasterelekt SEM micrographs (SEM images) of cordierite surfaces at different magnifications are shown. The cordierite surfaces in this case were coated with washcoat coatings without the aid of a polymer pre-coating.

These images show that the washcoat particles 110 Cover the surface of the cordierite support homogeneously and cover this substrate with a thin veil. Thus, the washcoat particles penetrate 110 also in microcracks on the surface of the cordierite substrate and deteriorate the thermomechanical properties of cordierite.

In the 2A and 2 B Washcoat coatings are juxtaposed, in which a conventional washcoat process without polymer pre-coating and a "conventional" washcoat process with previous polymer pre-coating (but without additive) are compared with each other 2A worked with a process without previous polymer coating, the product in 2 B however, with a polymer coating prior to application of the washcoat particles. The inclusion in 2A corresponds to the 1B ,

It can be clearly seen that by the previous polymer coating according to 2 B the deposition of washcoat particles 110 becomes inhomogeneous. So there are areas that are sufficient with washcoat particles 110 are wetted, and places where there are no such particles 110 are located. It continues with the product in 2 B numerous cracks 112 to observe in the coating, which suggests that the polymer film with the washcoat particles 110 has lifted off the substrate. The adhesion is therefore not sufficient in this case of a conventional pre-coating.

This inhomogeneous distribution of the pre-coating and the partial separation, which in 2 B can be seen, has negative effects on the deposition of the catalytically active components.

The cause of this inhomogeneous deposition of the washcoat particles lies in the inhomogeneous deposition of the polymer. So show the 3A and 3B polymer-coated ceramic carriers (without washcoat) at different magnifications. It will be appreciated that the polymer preferentially deposits in wells and depressions, whereas elevations are insufficiently wetted.

In the case of polymer coating, the substrates to be coated are usually immersed in the polymer solutions. These polymer solutions (which may also be polymer dispersions or polymer emulsions) usually have solvents in addition to the polymers. If the surface tensions of substrate and polymer solution or polymer dispersion are significantly different, then the polymer can not adequately wet the substrate. This leads to the in the 3A and 3B discernible preferential deposition in depressions, depressions and depressions, as well as islanding.

In the 4A and 4B On the other hand, according to the invention, ceramic substrates coated with additive are shown at different magnifications. Again, no washcoat coating is applied here. A cordierite substrate was used, which was wetted by immersion in a polymer emulsion of acrylic acid esters (Alberdingk-Boley GmbH, type AC-2597) in a concentration of 4 percent by weight in water. The polymer solution contained an additive (DC 67, Dow Corning GmbH) in a concentration of 0.5 percent by weight. After wetting, the polymer was thermally cured at elevated temperatures between 60 ° C and 150 ° C, preferably 110 ° C.

In comparison between the surfaces according to the 4A and 4B , which were prepared by the method according to the invention, with the surfaces in the 3A and 3B It can be seen that the inventive method leads to a much more uniform and homogeneous deposition of the polymer on the ceramic substrate. By using the additives, a variety of polymers can be used, which would not be available without additive.

Subsequently at the thermal curing of the polymer at elevated Temperatures, the polymer-coated substrate with washcoat be coated. For this purpose, the polymer-coated Substrate in particular in an aqueous washcoat slurry be immersed. The catalytically coated washcoat particles deposit on the polymer surface. Leave as slurry For example, aqueous dispersions noblemetallgeträgerter Use alumina particles. The polymer-coated carrier is usually immersed in the slurry, so that the precious metal-borne particles on the surface can separate the carrier.

Subsequently, the polymer- and washcoat-coated carrier or the functional element (for example a DPF and / or a catalyst) can be calcined at high temperatures, for example at temperatures between 300 ° C. and 800 ° C. Preferably, the polymer burns completely, and the washcoat particles 110 stay on the Surface of the substrate.

In the 5A and 5B such washcoat-coated surfaces are shown. It shows the 5A a surface prepared according to a conventional process without prior polymer coating, which conforms to the photographs according to the 1B and 2A equivalent. 5B on the other hand shows a surface prepared by the process according to the invention with previous polymer coating, also, such as 5A , after the process of calcination.

The homogeneous distribution of the washcoat particles is clear in comparison 110 to recognize. There are no accumulations and island formations as in the case without the addition of additives to recognize (see 2 B ). Furthermore, in both figures, a continuous veil is visible, covering the entire surface. In contrast to 2 B shows 5B no tearing and peeling of the washcoat layer. The few cracks in the 5A and 5B are typical unavoidable drying cracks that occur independently of the addition of a polymer. The difference in distribution between surfaces with and without polymer, so in the 5A and 5B , therefore, is not significant.

However, this was according to the previously polymer-coated substrates 5B in contrast to the substrates without polymer coating according to 5A , the coefficient of thermal expansion of coated specimens at a similar level to that of wholly uncoated specimens. The coefficient of thermal expansion of polymer-free and washcoat-coated specimens, however, was significantly higher, which is due to the fact that in the case of the polymer-coated specimens, the polymer at least partially adds the microcracks and thus a deposition of washcoat particles 110 prevented in these cracks.

The results clearly show that with the help of polymers washcoat particles 110 be prevented from penetrating into the microcracks of cordierite honeycomb bodies. This increases the thermomechanical strength. For the same or similar surface tension of cured polymer and washcoat particles, the distribution of the washcoat particles on the surface is approximately homogeneous. Equal surface tensions can be achieved, for example, by the use of additives. The catalytic function of the washcoat particles is unaffected by the deposition of the polymer.

In 6 is a honeycomb body 114 shown, which can be used in an exhaust aftertreatment device. In particular, this exhaust aftertreatment device may be a filter in which soot particles are removed from an exhaust gas stream of an internal combustion engine (diesel particle filter, DPF). The filter is arranged in an exhaust line of the internal combustion engine. The honeycomb body 114 is cylindrical in this embodiment, with an axis of symmetry 116 , The honeycomb body 114 can then be used for example in a rotationally symmetrical filter housing in the exhaust system.

The honeycomb body 114 is designed as a monolithic ceramic functional element, which can be prepared for example by means of an extrusion process. For example, the ceramic materials described above can be used for this purpose, for example magnesium aluminum silicate, preferably cordierite.

The honeycomb body 114 is being used in a diesel particulate filter in the direction of the arrows 118 flows through the exhaust gas. The exhaust gas passes over an entrance surface 120 in the honeycomb body 114 and leaves it via an exit surface 122 ,

Parallel to the symmetry axis 116 of the honeycomb body 114 run several entry channels 124 , in alternation with outlet channels 126 , The entrance channels 124 are on the Austrittsflä surface 122 locked. In the embodiment shown here are sealing plugs for this purpose 128 intended. Accordingly, the outlet channels 126 at the entrance area 120 locked.

Instead of the sealing plugs 128 However, it is also possible that the entrance channels 124 to the exit surface 122 Rejuvenate until they are the walls of an entrance channel 124 touch and the entrance channel 124 closed in this way. In this case, the inlet channel 124 in the direction parallel to the axis of symmetry 116 a triangular cross section.

Accordingly, the outlet channels 126 at the exit surface 122 open and in the area of the entrance area 120 locked. The flow path of the unpurified exhaust gas thus leads into one of the inlet channels 124 and from there through a filter wall 130 in one of the exit channels 126 , This is exemplified by the arrows 132 in 6 shown.

In the 7A to 7D is the ceramic substrate of the filter wall 130 at various stages of the above-described manufacturing or coating process in a schematic, not to scale representation (eg, the polymer layer is shown exaggerated thickness) shown. It can be seen that the filter substrate in addition to a variety of microcracks or cracks 112 a lot number of microchannels 134 , Micropores 136 and pores 138 having. Named "microchannels" 134 thereby transitions between large pores 138 designated. 7A shows a representation of the flow path 132 through the filter wall 130 , which is not to scale and which illustrates that the flow path 132 essentially through the pores 138 runs. Under "micropores" 136 Below are bulges of larger pores 138 to understand.

These cracks 112 , Microchannels 134 , Micropores 136 and pores 138 contribute differently to the flow and the filter effect or catalyst effect of the honeycomb body 114 or the filter wall 130 at. So is in the microchannels 134 the gas velocity is very high due to the smaller diameter. In the micropores 136 however, it is very low. There is a very small exchange with the rest of the gas instead.

This means that in the described areas, ie in the micropores 136 and in the microchannels 134 , the catalytic conversion of noxious gases in the exhaust stream 118 itself will be extremely low. Either the gas velocity is too high, so that the noxious gases can not come into contact with the catalyst particles for a sufficiently long time, or the gas exchange is so small that too few noxious gas molecules can react with the catalyst.

This clarifies the problem of conventional coating methods described above, namely that catalyst particles which are in the micropores 136 and in the microchannels 134 are deposited, show substantially no effect and thus represent a procedural and economic waste of costly materials.

By means of the pre-coating process described above, it is possible to prevent washcoat particles in the areas described which scarcely contribute to the catalytic conversion 110 deposit. This is in the 7B to 7D clarified.

In 7B is the filter wall 130 after coating with one of the described organic materials using a solution or dispersion with an additive. As described above, this organic material may be, in particular, a polymer. The polymer layer is in 7B with the reference number 140 designated.

It is in 7B to recognize that the polymer layer 140 due to the capillary forces acting on the polymer solution, polymer dispersion or polymer emulsions in the coating, amplified in the microcracks 112 , the microchannels 134 and in the micropores 136 deposits.

After curing of the polymer or the polymer layer 140 can the honeycomb body 114 , as described above, are immersed in the aqueous washcoat dispersion (slurry). The result of this washcoat coating is in 7C shown.

The polymer layer 140 is characterized by a neutral to hydrophilic surface. The polymer is preferably chosen such that it does not dissolve in the cured state in water or only slightly dissolves. The catalytically coated washcoat particles 110 therefore divide on the surface of the polymer layer 140 from.

In the micropores 136 and the microchannels 134 in which the organic material, in particular the polymer, is located, however, no or only a few washcoat particles 110 deposited. As a result, these areas, which, as described above, contribute substantially nothing to the catalytic effect are specifically excluded from the washcoat coating or coated to a lesser extent. This can be saved by avoiding these ineffective coatings, significant amounts of catalytically active materials.

The one with the polymer layer 140 and the washcoat particles 110 coated honeycomb body 114 can then be calcined at high temperatures (for example, temperatures between 300 ° C and 800 ° C). The result of this calcination is in 7D shown, which, as already stated above, is not to scale. Such is in particular the polymer layer 140 in the preceding figures for reasons of clarity exaggerated shown thick. During calcination, the polymer layer burns 140 completely, and the washcoat particles 110 stay on the surface of the filter wall 130 , as in 7D is shown. Due to the small thickness of the polymer layer 140 change the washcoat particles 110 their position at this calcination not or only insignificantly. The micropores 136 that cracks 112 and the microchannels 134 remain essentially free of the catalytically coated washcoat particles 110 , The result of this method thus consists in a substrate, which on the one hand has the above-described, advantageous thermal properties and in which also a process-saving material can be made.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 4483940 [0011]
• US 2005/0191480 A1 [0011, 0012]
• US 2005/0037147 A1 [0011, 0012]

Claims (9)

Method for producing a ceramic functional element ( 114 ) for pollutant reduction of exhaust gases, comprising a ceramic carrier ( 130 ) and a ceramic functional coating ( 110 ), the method comprising the following steps: 130 ) is wet-chemically mixed with an organic material, in particular a polymer ( 140 ), coated; - on the organically coated carrier ( 130 ) is a ceramic functional particle coating in a wet chemical step ( 110 ) applied; and - the coated carrier ( 130 ) is thermally calcined, wherein the organic material is at least partially removed, characterized in that the organic coating is a solution and / or dispersion and / or an emulsion of the organic material is used, which is an additive for improving the wetting of the ceramic support ( 130 ) having. A method according to the preceding claim, wherein the additive comprises at least one of the following substances: a polysiloxane; one with epoxy, vinyl, ether, acrylic, amino, diamino or styreneamino groups, functionalized polysiloxane; a polyacrylate; a polyester; a sulfosuccinate; a siloxane polyether; a non-ionic silicone emulsion. Method according to one of the preceding claims, wherein the additive in the solution and / or dispersion and / or Emulsion of the organic material in a concentration of approx. 0.1 to 5 weight percent is present. Method according to one of the preceding claims, wherein the additive is selected and used in such an amount in the solution and / or dispersion and / or emulsion of the organic material that an aqueous dispersion of the functional particles ( 110 ) has a contact angle of less than 70 ° and preferably less than 50 ° on a glass surface. Method according to one of the preceding claims, wherein the additive is selected such that this with the organic material does not react. Method according to one of the preceding claims, wherein the organic material before application of the ceramic functional particle coating ( 110 ) is at least partially cured. A method according to the preceding claim, wherein the curing at a thermal curing at 60 ° C to 150 ° C includes. Method according to one of the preceding claims, wherein the organic material is at least one of the following polymers comprising: a polyvinyl alcohol; a polyacrylamine; a polyvinylpyrrolidone; a cellulose; a polyethylene glycol; a polymaleat; a copolymer on maleate basis; a polyvinyl acetate; a polyvinyl butyral; one polyoxazoline; an acrylic ester; a copolymer Acrylic acid and styrene; a polyacrylate; an acrylate-based copolymer; a polyacrylamide; an amide-based copolymer; a polystyrene; a polyvinyl derivative; a polystyrenesulfonate; an epoxy-based polymer. Method according to one of the preceding claims, wherein the calcination after application of the ceramic functional particle coating ( 110 ) is carried out at a temperature between 300 ° C and 800 ° C.