METHOD FOR COATING A COMPONENT

Abstract

A method for coating a component including the following steps: providing a gas phase containing at least one tetra-alkoxy silane as first silicon-containing precursor, at least one functionalised silicic acid ester with a phenyl, vinyl, allyl, thiol, amino, acryloxy, epoxy, nitrile, isocyanate, isothiocyanate or methacrylate group as second silicon-containing precursor, at least one catalyst, water and inert gas, the silicon-containing precursors being added in metered fashion to the gas phase separately from one another and separately from the water and the catalyst, chemically reacting the first silicon-containing precursor with water in the gas phase so ss to form first reaction products, chemically reacting the second silicon-containing precursor with water in the gas phase so as to form second reaction products, depositing the reaction products on the component. The reaction products of all precursors together form a coating on the component based on amorphous silicon dioxide.

Claims

1. A method for coating a component, wherein the method comprises the following steps: providing a gas phase containing at least one tetraalkoxysilane as first silicon-containing precursor, at least one functionalized silicic ester having a phenyl, vinyl, allyl, thiol, amino, acryloxy, epoxide, nitrile, isocyanate, isothiocyanate or methacrylate group as second silicon-containing precursor, at least one catalyst, water and inert gas, optionally hydrogen, or consisting of these substances, wherein the silicon-containing precursors are metered into the gas phase separately from one another and separately from the water and the catalyst, chemically reacting the first silicon-containing precursor with water in the gas phase to form first reaction products, chemically reacting the second silicon-containing precursor with water in the gas phase to form second reaction products, depositing the reaction products onto the component, wherein the reaction products of all precursors together form a coating based on amorphous silicon dioxide on the component.

2. The method as claimed in claim 1, wherein the volume fraction of all functionalized silicic esters as a whole in the gas phase is at least 0.05% by volume and at most 0.62% by volume.

3. The method as claimed in claim 1, wherein, in the gas phase, the volume ratio of all functionalized silicic esters as a whole to the catalyst is at least 0.08 and at most 0.12.

4. The method as claimed in claim 1, wherein, the amount of substance of all functionalized silicic esters is 20 to 40% of the amount of substance of all silicon-containing precursors.

5. The method as claimed in claim 1, wherein the gas phase contains a further functionalized silicic ester having a phenyl, vinyl, allyl, thiol, amino, acryloxy, epoxide, nitrile, isocyanate, isothiocyanate or methacrylate group as third silicon-containing precursor, and in that the third silicon-containing precursor chemically reacts in the gas phase with water to form third reaction products.

6. The method as claimed in claim 5, wherein the gas phase contains a silicic ester having a methacrylate group as second silicon-containing precursor and a silicic ester having an amino group and/or isocyanate group as third silicon-containing precursor.

Description

[0046] The invention will be explained in more detail on the basis of the following exemplary embodiment.

[0047] In the production of plate heat exchangers, metal solder foils, for example of copper or nickel, are placed between stamped stainless steel plates that are stacked on top of one another. The stainless steel plates are then soldered to one another, by heating the stack up to the melting point of the solder foils. The task was to reduce the release of copper and nickel ions into drinking water in the case of such a plate heat exchanger. For test purposes, the surfaces coming into contact with water in the case of such plate heat exchangers were coated by means of a process based on the CVD process described in document WO 2011/026565 A1. The process gas used during the coating of the plate heat exchangers contained approximately 93% by volume of forming gas, consisting of 95% by volume of nitrogen and 5% by volume of hydrogen, as well as acetic acid, water and, as silicon-containing precursors, tetramethyl orthosilicate and 3-isocyanatopropyltrimethoxysilane. The overall proportion of all silicon-containing precursors in the gas phase was between 1.0% and 1.5% by volume. In the gas phase, the volume ratio of the 3-isocyanatopropyltrimethoxysilane to the acetic acid was approximately 1:10. Furthermore, the amount of substance of the 3-isocyanatopropyltrimethoxysilane based on the entire amount of substance of the silicon-containing precursors, i.e. the sum of tetramethyl orthosilicate and 3-isocyanatopropyltrimethoxysilane, was approximately 30%. Acetic acid was added in excess based on the volume fraction of water, but not more than in the ratio of 2:1.

[0048] During the coating process, the temperature in the reactor was 300° C., the pressure was 1013 hPa and the carrier gas flow was 0.4 m.sup.3/h. The coating time was 3 hours.

[0049] As a reference, heat exchangers of the same type were coated with a reference coating by means of a CVD process. In this case, only tetramethyl orthosilicate was used as precursor, without any functionalized silicic ester. The rest of the test conditions were identical.

[0050] The effectiveness of the coating was tested by subjecting sections of the coated heat exchanger plates and sections of uncoated heat exchanger plates to an accelerated corrosion test. For this purpose, the sections were dipped into sulfuric acid (25% by weight concentration) at 65° C. After a test duration of 3 hours, the concentration of the copper and nickel ions in the acid was determined. In the case of the samples coated using the method according to the invention, the concentration of the metal ions was only 0.2% of the value that was determined for the uncoated samples. In the case of the coated reference samples, the concentration of the metal ions was approximately 11% of the value that was determined for the uncoated samples. The coating according to the invention thus reduced the release of metal ions to 1/500 of the ion release of the uncoated samples and to 1/55 of the ion release of the coated reference samples. Furthermore, cracks appeared in the coatings of the reference samples, which can be attributed to the low level of elasticity of the reference coating.

[0051] In the case of the samples coated using the method according to the invention, the amino group formed from the reaction of the cyanate group with water is detectable in the infrared spectrum of the coating by means of its characteristic signal at wavenumbers of 3100 cm.sup.−1, 1651 cm.sup.−1 and 1556 cm.sup.−1. The methylene group originating from the CH.sub.2 chain that connects the nitrogen to the silicon in the 3-isocyanatopropyltrimethoxysilane is identifiable on the basis of characteristic signals at 2937 cm.sup.−1 and 600 cm.sup.−1.