DE102009039702A1 - Method for coating a substrate with a ceramic layer, comprises applying initial stage of ceramics to be produced with a solvent or dispersion agent on the substrate and evaporating the solvent or dispersion agent - Google Patents

Abstract

The method for coating a substrate (11) with a ceramic layer (15), comprises applying initial stage of ceramics to be produced with a solvent or dispersion agent on the substrate, evaporating the solvent or dispersion agent under remaining the initial stage of the ceramics to be produced on the substrate and cross-linking the initial stage of the ceramics to be produced to ceramic layer in which the ceramic is heated up to a cross-linking temperature. An energy supply in the layer present in the construction is carried out simultaneously during coating the substrate. The method for coating a substrate (11) with a ceramic layer (15), comprises applying initial stage of ceramics to be produced with a solvent or dispersion agent on the substrate, evaporating the solvent or dispersion agent under remaining the initial stage of the ceramics to be produced on the substrate and cross-linking the initial stage of the ceramics to be produced to ceramic layer in which the ceramic is heated up to a cross-linking temperature. An energy supply in the layer present in the construction is carried out simultaneously during coating the substrate that suffices so that a temperature corresponding or above the cross-linking temperature reaches during the coating. The energy supply is carried out in the layer present in the construction through heat energy stored in the substrate or through UV-radiation, infrared radiation or microwave radiation. The initial stage of the ceramics to be produced is mixed to absorber particles for the related radiation energy. The substrate is heated during the coating. The ceramic layer is produced in several layers, where the respective near layer is already applied if the previously applied layer is not yet completely cross-linked. The respective near layer is first applied, if the solvent or dispersion agent is completely evaporated from the previously applied layer.

Description

The invention relates to a method for coating a substrate with a ceramic layer, in which precursors of the ceramic to be produced are applied to the substrate with a solvent or dispersion medium, the solvent or dispersant is evaporated on the substrate leaving the precursors of the ceramic to be produced, and the precursors the ceramic to be produced are cross-linked to the ceramic layer by being heated at least up to a cross-linking temperature for the ceramic precursors.

A method of the type specified, for example, from WO 2004/104261 A1 known. Thereafter, ceramic precursors are applied to a substrate, these precursors containing the chemical elements which is to contain the ceramic to be formed. By a subsequent heat treatment, a solvent and / or dispersing agent is first removed from the layer, which should only allow the application of the ceramic precursors to the substrate. The order of the ceramic precursors can be done in a conventional manner by spraying, rolling, dipping or other conventional methods.

Furthermore, the said heat treatment (pyrolysis) serves to crosslink the precursors of the ceramic to be formed (in the following also referred to as ceramic precursors for short) to the desired ceramic. For this purpose, it is necessary that the required for the resulting ceramic curing temperature is at least reached or exceeded.

The temperature control during the heat treatment must be such that evaporation of the solvent or dispersant can take place before the ceramics are crosslinked. The evaporation of the solvent or dispersing agent must not be abrupt, because this may result in unwanted pores in the forming layer. The temperature control in the heat treatment is therefore usually two-stage, wherein the first heat treatment step is carried out at lower temperatures, which allow a slow evaporation of the solvent or dispersant taking into account the layer thickness. Only then is a further heating to the crosslinking temperature made.

Furthermore, it is from the abstract to JP 05138044 A It is known that precursors of a ceramic to be produced can also be applied to a preheated substrate. This should serve to evaporate the solvent applied with the precursors of the ceramic as early as possible during application, in which case crosslinking of the layer by heating above the crosslinking temperature for the ceramic (pyrolysis) is then carried out in the manner already described.

Also according to the WO 00/00660 A1 For example, it is known that precursors of a ceramic can be applied as small droplets to a preheated surface to be coated so that the droplets are solidified immediately upon evaporation of the solvent. The layer formed in this way must then be heated above the crosslinking temperature to crosslink the ceramic in order to achieve crosslinking with the ceramic.

The heat input during the heat treatment of the coated substrate is usually carried out in an oven by heating the substrate with the applied layer to the desired temperature. According to the DE 10 2007 026 626 B3 However, it is described that a heat input can also be made more targeted by, for example, particles of a UV light absorber, such as titanium oxide or tin oxide, are incorporated into the layer. The heat treatment can then take place by means of UV light irradiation or at least be supported. As a result, a much more direct introduction of the heat energy is possible, whereby a thermal load of the substrate can be reduced. In addition, certain layer areas can be more strongly heated by introducing the particles than others, thereby providing additional degrees of freedom for the layer design. Furthermore, microwave energy can be used to heat the layer under construction, the selected excitation frequencies of the microwaves are tuned to components of the layer or specially introduced for this purpose particles in the layer. This allows absorption of the microwave energy and consequent heating. A method of this kind is in the DE 10 2007 030 585 A1 described.

The object of the invention is to improve a method of the type mentioned in that the desired ceramic layers can be produced in a relatively short time.

The object is achieved with the method mentioned in the present invention, that during the coating of the substrate with the precursors of the ceramic to be produced simultaneously an energy input is made in the layer under construction, which is sufficient so that the precursors of the ceramic to be produced during the coating a Reach temperature corresponding to or above the crosslinking temperature. As a result, it is advantageously achieved that not only the solvent evaporated immediately upon application of the precursors of the ceramic and thereby pore formation can be largely avoided, but at the same time a subsequent heat treatment step is saved, which advantageously a more efficient coating process is possible. In addition, layers can be produced in this way, which have a greater thickness without the formation of too high clamping. For this purpose, the layer is preferably applied in several layers, these layers being crosslinked by the energy input in each case immediately. The layers themselves are so thin that the dissolving or dispersing agent which evaporates immediately upon application forms no pores, or the pores can be closed again when the next layer is applied.

According to an advantageous embodiment of the method it is provided that an energy input into the layer under construction takes place by stored in the substrate heat energy. This advantageously allows a very simple entry method for energy to be realized. The substrate only needs to be preheated in an oven, for example. When subsequently the precursors of the ceramic are applied, the energy stored in the substrate is transferred to the layer being built up and, with a suitable choice of the temperature of the substrate, immediately effects a crosslinking of the applied precursors of the ceramic.

According to another embodiment of the invention, it is provided that an energy input into the layer under construction by irradiation with a radiation energy, in particular UV radiation, IR radiation or microwave radiation takes place. In this way, an energy source can advantageously be made available, which makes it possible to transfer the energy directly into the layer under construction. A thermal load of the substrate can be avoided thereby. In addition, the energy input is independent of the heat capacity of the substrate even when building thicker layers. Of course, even with an energy input into the layer under construction by energy radiation, an additional preheating of the substrate can take place.

The radiation energy must be suitably selected to allow heating by absorption of the energy by the substances present in the layer being built up. For example, microwave energy of a wavelength that is directly absorbed by the solvent and / or dispersant can be used. Other radiant energies may be absorbed by particles which are introduced into the layer under construction for this purpose. However, this requires that these particles do not endanger the intended use of the layer to be used. Examples of usable particles can be mentioned at the outset DE 10 2007 030 585 A1 and DE 10 2007 026 626 B3 remove.

According to yet another embodiment of the invention, it is provided that the ceramic layer is produced in several layers, wherein the respective next layer is always applied only when the previously applied layer is completely crosslinked. Thus, for example, a multilayer layer can advantageously be produced, wherein the individual layers (that is to say layers) can have different layer compositions. In this way, a specific requirement profile of the layer can be satisfied, which is why, in addition to the already mentioned advantage of efficient production, it is also possible to produce layers for different requirement profiles in a simple manner.

On the other hand, it is also advantageous if the ceramic layer is produced in several layers, the next layer in each case always being applied even if the previously applied layer has not yet been completely crosslinked. This method has the advantage that homogeneous layers can be produced with a large thickness, wherein the individual layers adhere well to one another, since the crosslinking process is always completed when the next layer has already been applied. It is also possible, with incomplete crosslinking, to apply a plurality of layers of different composition in order to produce so-called gradient layers. With gradient layers, it is possible to continuously change the layer composition over the layer thickness, whereby, as already mentioned, layers with different requirement profiles can be produced. However, it is particularly advantageous for an application of the next respective layer in the case of an incompletely crosslinked previous layer if the respective next layer is always applied only when the solvent or dispersion medium has completely evaporated from the previously applied layer. This makes it possible to produce very dense, largely pore-free layers, since a sudden evaporation of individual solvent droplets can be avoided. On the other hand, however, it is also possible to use a solvent or dispersion medium which evaporates at comparatively high temperatures so that it is not completely vaporized when the next layer is applied. Since the crosslinking at least already begins (although not completely finished) due to the heating of the layer being built up, the evaporation of the solvents can be used specifically for the pore formation of a porous layer if this requires the requirement profile of the layer to be produced.

By way of example, the following layers and their production processes are described without restricting the generality of the invention.

According to a first example, a layer consisting of a single layer is produced. For this purpose, first the precursors of the ceramic to be produced (hereinafter also referred to as precursor) from 15 to 60 wt .-% zirconium 2-ethylhexanoate, 0.5 to 0.7 wt .-% yttrium 2-ethylhexanoate and propionic acid as dispersion or solvent produced. In a second step, a workpiece is heated so far that the crosslinking temperature of the coating material is achieved. In this case, these are temperatures higher than 400 ° C. In a third step, the precursor produced in the first step is sprayed onto the heated workpiece. Here, the thickness of the prepared layer is selected so that on the one hand crosslinking of the precursor can be done undisturbed, on the other hand, evaporation of the solvent or dispersant without pore formation is possible. To avoid explosive evaporation of the solvent or dispersant, its concentration must not be too high. The third step can be repeated until the desired layer thickness is reached from the individual layers.

Precursor with dispersed solids in the form of oxides, such as. As aluminum, titanium or silicon oxide, nitrides, such as. As hexagonal or cubic Bohrnitrid, or carbides, such as. As boron or silicon carbide, as well as pure metals, for. As Al, Cu, Cr, Fe, Co, Ni, Pt, Pd or Ag, can also be applied to the substrate and crosslinked in the manner described. The solids can be dispersed in the precursor solutions both as microparticles and as nanoparticles. The particles used also have a multi-layered structure (core-shell structure) exhibit.

As a second example, the production of a multilayer composite layer (multilayer layer) is described. In a first step, a precursor is prepared which contains 15 to 60% by weight of zirconium 2-ethylhexanoate, 0.5 to 7.5% by weight of yttrium 2-ethylhexanoate and propionic acid as a dispersing or reading agent. In a second step, the precursor for producing the multilayer layer is modified. The layer should consist of four layers a, b, c, d and a cover layer e. For the layers a to c, pure iron in the concentrations of 5% by weight (layer a), 3% by weight (layer b) and 1% by weight is used for the physical adaptation to the substrate consisting of iron. (Layer c) added. To improve the corrosion protection, the layer c contains pure zinc in addition to the pure iron with a proportion of 1 wt .-% and the layer d only pure zinc in a proportion of 5 wt .-%. The cover layer is added only nanoparticles of silicon oxide, so that the violation of the composite layer by the negatively charged nanoparticles of silicon oxide in conjunction with the cathodic acting zinc-containing layer a self-healing effect. In a third step, the workpiece is brought back to the temperatures mentioned in the first example. In a fourth step, the precursors produced in the second step are applied successively (sequence a to e) on the preheated surface. In this case, the surface is additionally heated with an infrared lamp in order to maintain the crosslinking temperature during the coating. In each case a few minutes is waited between the application of the different layers a to e, so that the solvent of the preceding layer is at least largely evaporated.

As heat sources and UV lamps or a hot air blower can be used, the energy input takes place in the latter case by brushing the surface with the hot air.

In a third example, a layer is produced in which steps 1 and 2 are carried out according to the first example. In a third step, the precursor applied to the preheated substrate is additionally irradiated with a UV or IR lamp or a hot-air blower until the dispersion or solvent has completely evaporated. The next layer is applied to the hot workpiece, if the crosslinking of the precursor has at least already started on the previous layer. The described steps 3 and 4 are repeated until the layer has reached the desired thickness.

If UV or IR lamps are additionally used for crosslinking the precursor, the precursor may also contain suitable absorber particles which bring about absorption of the radiation energy. These must be selected so that the wavelength of the UV or IR radiation excites the particles and leads to their heating. When selecting the absorber particles, attention must still be paid to the necessary cross-linking temperature of the precursor. It is possible to use absorbers of inorganic as well as absorbers of organic nature, these preferably still being chemically stable at the crosslinking temperature. Examples of inorganic absorbers are metal oxides such as zinc oxide, silicon oxide, tin dioxide or synthetic iron oxides. As organic IR absorbers phthalo-, naphthalo- and carbocyanines, polymethines and methylene chloride can be used.

An embodiment of the method according to the invention with two variants will be described below with reference to the drawing. The 1 to 4 represent typical stages of the process. The same or corresponding drawing elements are each provided with the same reference numerals in the individual figures and will only be explained several times as far as there are differences between the individual figures.

1 shows a substrate 11 , which by means of an induction coil 12 should be brought to a crosslinking temperature of a layer to be produced. Once the substrate 11 , which is metallic, has reached the crosslinking temperature is according to 2 by means of a spray nozzle 13 a first location 14 a layer to be produced 15 (see. 3 ) applied. By the temperature of the substrate 11 immediately rise steams 16 of the evaporating solvent. This process is characterized by an additional warming of the situation 14 by means of UV radiation 17 supported. At the same time and after the evaporation of the solvent, a crosslinking of the in position 14 located precursor.

In 3 is shown as another location 18 on the location 14 is applied, wherein the layer 15 thereby forming. Otherwise, the method corresponds to that 2 explained. The heating of the substrate 11 by means of the induction coil 12 can be continued throughout the entire procedure.

In 4 an alternative process guide is shown as the layer 15 can be generated. In the method according to 4 are the process steps according to 2 and 3 summarized. Next to the spray nozzle 13 will be another spray nozzle 19 used, which in the direction of movement 20 seen the spray nozzles behind the first spray nozzle. These are guided one behind the other, with the layers of the layer 15 be made shortly after each other, so that the individual layers then merge into a single layer without recognizable layers.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2004/104261 A1 [0002]
• JP 05138044 A [0005]
• WO 00/00660 A1 [0006]
• DE 102007026626 B3 [0007, 0012]
• DE 102007030585 A1 [0007, 0012]

Claims (8)

Process for coating a substrate ( 11 ) with a ceramic layer ( 15 ), in which precursors of the ceramic to be produced with a solvent or dispersant on the substrate ( 11 ), the solvent or dispersing agent remaining on the substrate with the precursors of the ceramic to be produced ( 11 ) and the precursors of the ceramic to be produced to the ceramic layer ( 15 ) are heated by heating them at least up to a crosslinking temperature, characterized in that during the coating of the substrate ( 11 ) with the precursors of the ceramic to be produced simultaneously an energy input into the layer under construction ( 15 ) is carried out, which is sufficient so that the precursors of the ceramic to be produced during the coating reach a temperature corresponding to or above the crosslinking temperature. A method according to claim 1, characterized in that an energy input into the layer under construction ( 15 ) is effected by stored in the substrate heat energy. Method according to one of claims 1 or 2, characterized in that an energy input into the layer under construction ( 15 ) by irradiation with a radiation energy, in particular UV radiation ( 17 ), IR radiation or microwave radiation occurs. A method according to claim 3, characterized in that the precursors of the ceramic to be produced absorber particles are blended for the radiation energy used. Method according to one of the preceding claims, characterized in that the substrate ( 15 ) is heated during coating. Method according to one of the preceding claims, characterized in that the ceramic layer ( 15 ) in several layers ( 14 . 18 ), the next layer ( 18 ) is always applied when the previously applied layer ( 14 ) is fully networked. Method according to one of claims 1 to 5, characterized in that the ceramic layer ( 15 ) in several layers ( 14 . 18 ), the next layer ( 18 ) is always applied when the previously applied layer ( 14 ) is not fully networked. Method according to claim 7, characterized in that the respective next layer ( 18 ) is applied only when the solvent or dispersant from the previously applied layer ( 14 ) is completely evaporated.

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