JP2013544956A - Method for in-situ placement of coating and product manufactured using the method - Google Patents

Abstract

Methods for placing a coating on a metal surface include heating the metal surface to a temperature below its melting point, applying a vacuum thereto while heating the metal surface, and heating the metal surface. , Releasing the vacuum and backfilling with a first purge gas, the first purge gas reacts with the metal surface to place at least one layer of coating on the metal surface. The disclosed method can place an in-situ coating during the manufacture of a solar receiver, in which case the solar receiver includes an annulus defined by a metal tube as the inner surface, and an outer surface. And materials that are at least partially transparent to solar radiation.
[Selection] Figure 1

Description

  The present invention relates generally to coatings, and more particularly to a method of producing a coating.

(Description of related applications)
This application claims the priority of US Provisional Patent Application No. 61 / 385,899, filed on September 23, 2010, based on the provisions of US Patent Act 119 (e). It is incorporated into this application by reference.

(Federal support research or development statement)
Not applicable.

  Coatings are frequently used in a variety of applications to protect the material under the coating from environmental exposure or to improve other physical properties of the material under the coating. Physical properties that can be altered by coating include, but are not limited to, optical properties, thermal properties, and mechanical properties. More specifically, the thermal and electromagnetic absorption and emission properties of a product can be greatly affected by its presence, even if the coating placed thereon is a thin layer that is not visible.

  Many different techniques have been developed to place thin film coatings. These techniques include, for example, sputtering, vapor deposition, pulsed laser desorption, electroplating, chemical plating, chemical vapor deposition and the like. In product manufacture, many of these coating techniques must be performed separately from the other manufacturing steps used to manufacture the product. In addition, many of these deposition techniques require specialized equipment that increases the time and cost required to produce a product that includes the coating.

  In view of the foregoing, a simple and inexpensive technique for producing a coating, especially during manufacture of a product, would be a substantial advantage in the art. The present disclosure fulfills this need and provides related advantages as well.

  In certain embodiments, a method for placing a coating on a metal surface is described herein. The method includes heating the metal surface to a temperature below its melting point, applying a vacuum thereto while heating the metal surface, and releasing the vacuum while heating the metal surface, Backfilling with one purge gas. The first purge gas reacts with the heated metal surface to place at least one layer of coating on the metal surface.

  In certain embodiments, a method for placing a coating on a solar receiver is disclosed herein. The method includes applying a vacuum to an annulus having an outer surface defined by a material that is at least partially transparent to solar radiation and an inner surface defined by a metal tube, to which the vacuum is applied. Heating the metal tube to a temperature below its melting point while heating and releasing the vacuum and backfilling with the first purge gas while heating the metal tube, in which case the first purge gas Reacts with the heated metal tube to place at least one layer of coating on the metal surface.

  In certain embodiments, a solar receiver applies a vacuum to an annulus having an outer surface defined by a material that is at least partially transparent to solar radiation and an inner surface defined by a metal tube, wherein Created by a process that includes heating a metal tube to a temperature below its melting point while applying a vacuum to the metal, and releasing the vacuum and backfilling with a first purge gas while heating the metal tube In this case, the first purge gas reacts with the heated metal tube to place at least one layer of coating on the metal tube.

  The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims.

  For a more complete understanding of the present disclosure and its advantages, the following detailed description is set forth in conjunction with the accompanying drawings, which set forth specific embodiments of the disclosure.

1 shows a schematic diagram of an exemplary solar heat receiver.

  The present disclosure is directed, in part, to a method of placing a coating on a metal surface. The present disclosure is also directed, in part, to a metal surface having a coating disposed specifically on a solar heat receiver.

  Although coatings are very useful and frequently used in a wide variety of applications, the technique of placing the coating significantly increases the time and cost required to produce a product that includes the coating. . The methods described herein can advantageously address these shortcomings in the art by providing a simple technique for creating a coating on a metal surface. More particularly, in some cases, the coating methods described herein are used for in-situ placement of a coating on a metal surface. That is, during the manufacture of the product, the coating can be advantageously applied to the product with a simple improvement of at least some of the steps already used in the manufacture of the product. For example, if vacuum bakeout (eg, hydrogen bakeout) is used during the manufacture of the product, the coating can be applied to the product according to the disclosed method.

  An example of a product that includes a metal surface with a coating placed in situ during the manufacture of the product is a solar heat receiver. FIG. 1 shows a schematic diagram of an exemplary solar heat receiver 100. The solar heat receiver 100 can be used as a thermal energy collector that is aligned in a radial plane and absorbs thermal energy from focused solar radiation without releasing most of the heat into the original ambient environment. The exemplary solar receiver 100 includes an inner metal tube 110 and a heat transfer fluid (eg, oil or high boiling fluid) that flows through its interior space to carry away heat collected from the solar receiver 100. Etc.). In order to maximize the amount of heat collection and reduce thermal radiation, the inner metal tube 110 is typically surrounded by a vacuum. To achieve this goal, the solar receiver 100 includes an outer surface 120 (e.g., glass or the like) that is at least partially transparent to solar radiation, which defines an annulus 115 with an inner metal tube 110; Contains a vacuum. A vacuum can be applied to the annulus through port 130. In most cases, the inner metal tube 110 is modified with a coating that increases its heat absorption.

  During the manufacture of a conventional solar receiver, the annulus 115 is used to achieve a type of outgassing and desorption that would otherwise reduce the quality of the applied vacuum and potentially alter heat absorption. While applying the vacuum, a heater (not shown) is used to heat the inner metal tube 110. However, instead of sealing the annulus 115 and maintaining the vacuum while the inner metal tube 110 is heated, if the vacuum is broken and the annulus 115 is embedded with a purge gas, the in-situ coating will be Has been found to be advantageous by the embodiments described herein. After that, by reapplying the vacuum to the annulus 115 and subsequently sealing with the vacuum maintained, the manufacture of the solar heat receiver 100 can be completed easily. Thus, the method of the present disclosure provides an opportunity to easily improve the surface of the inner metal tube 110 with a coating using only a simple improvement of the already established process during the manufacture of a solar heat receiver.

As used herein, the term “vacuum” refers to all pressures below atmospheric pressure. Unless otherwise specified, the term vacuum should not be construed as constituting a specific vacuum scale. In certain embodiments, a suitable vacuum is about 1 × 10 ⁻⁵ Torr or lower. In some embodiments, a suitable vacuum is about 1 × 10 ⁻⁶ Torr or lower.

  As used herein, the term “coating” refers to a material on a metal surface that is at least as thick as a monolayer. Exemplary coatings that can be applied to metal surfaces by the methods described herein include, but are not limited to, metal oxide coatings, metal nitride coatings, metal carbonized coatings, and metal fluoride coatings. It is not a thing. Unless otherwise specified, the term coating should not be construed as constituting a specific type of coating or a specific number of coating layers.

  In certain embodiments described herein, methods for placing a coating on a metal surface include heating the metal to a temperature below its melting point, and applying a vacuum to the metal surface while it is being heated. And releasing the vacuum while heating the metal surface and backfilling with a first purge gas that reacts with the heated metal surface to place at least one layer of coating on the metal surface. In certain embodiments, the method further includes disposing at least one layer of the coating.

  In general, all types of metal surfaces can be improved by coating according to the embodiments described herein. At that time, both pure metals and metal alloys can be used. In various embodiments, suitable metals include, without limitation, titanium, copper, iron, aluminum, tungsten, and any combination thereof. Other suitable metals are possible for those skilled in the art. In certain embodiments, the metal surface is polished to remove native oxide to facilitate placement of the coating. In some embodiments, the metal surface is a metal tube, such as, for example, in a solar heat receiver. In particular, in the case of a metal tube used for a solar heat receiver, for example, steel such as stainless steel, carbon steel, or a combination thereof can be used.

  Although certain embodiments of the present disclosure have been described in the context of solar heat receivers, it should be appreciated that any type of product having a metal surface can be improved by coating in accordance with the embodiments described herein. . That is, the description of the present specification regarding the solar heat receiver should be considered as illustrative in nature and not limiting. More specifically, it should be understood that any type of product having a metal surface can be obtained by heating the metal surface and directly on the metal surface (eg, via annulus, product cavities or holes, etc.) Or by applying a vacuum indirectly (eg by placing the product or part thereof in a heating device such as a vacuum furnace that can be placed under vacuum and then backfilled with purge gas). Can be improved by a coating according to the embodiments described in.

  In various embodiments, a method of placing a coating on a metal surface of a solar receiver includes an outer surface defined by a material that is at least partially transparent to solar radiation, and an inner surface defined by a metal tube. Applying a vacuum to an annulus having, heating a metal tube to a temperature below its melting point while applying the vacuum, and releasing the vacuum while heating the metal tube to heat the metal Refilling with a first purge gas that reacts with the tube and places at least one layer of coating on the metal tube is included.

  In the case of solar receivers, various materials are used to form the outer surface of the annulus. In general, the material forming the outer surface of the annulus needs to be at least partially transparent to solar radiation so that solar radiation can act on the inner surface defined by the metal tube. Furthermore, since considerable heat is generated when solar energy is focused on a solar heat receiver, the material forming the outer surface of the annulus usually needs to have at least some deformation resistance under heating. In certain embodiments, a suitable material that is at least partially transparent to solar radiation is glass. In certain embodiments, the glass further includes an anti-reflective coating suitable for minimizing reflections to maximize the amount of solar radiation transmitted through the metal tube.

  After placing the coating on the solar receiver metal tube according to the method described herein, the manufacturing of the solar receiver can be easily completed by continuing the standard manufacturing process. To achieve this goal, the method further includes repositioning the vacuum on the annulus after heating the metal tube after placing the coating. In certain embodiments, the method further includes sealing the annulus to maintain a vacuum and complete the manufacture of the solar heat receiver. In an alternative embodiment, at least one layer of coating added to the metal tube can be placed by repeating the methods described herein.

  In certain embodiments, at least one additional layer of the coating can be placed by repeating the methods described herein. In an embodiment of the disclosed method, a vacuum can be reapplied to the metal surface while it is being heated after the coating is placed. In an embodiment of the method of the present disclosure, while heating the metal surface, at least one additional layer of the coating can be placed by releasing the vacuum and backfilling with a second purge gas.

  In some embodiments, the first and second purge gases can be the same. That is, in some embodiments, the coating includes multiple layers where all layers are the same. In other embodiments, the first and second purge gases can be different. That is, in certain embodiments, the coating includes multiple layers in which at least some of the layers are different. By repeating the steps of the method of the present disclosure, for example, 1 to about 100 layers, or 1 to about 20 layers, or 1 to about 10 layers, or 1 to about 5 layers, or 1 layer, or 2 layers, or 3 A coating having any number of layers can be placed, such as a layer, or 4 layers, or 5 layers, or 6 layers, or 7 layers, or 8 layers, or 9 layers, or 10 layers. In embodiments where there are multiple layers, the various layers of the coating impart different properties to the metal surface. For example, the first layer can improve the electromagnetic absorption characteristics of the metal surface, and the second layer of a different substrate can reduce its heat release characteristics.

  Various types of coatings can be formed on a metal surface according to the embodiments described herein. In certain embodiments, the coating includes, for example, at least one of an oxide coating, a nitride coating, a carbonized coating, or a fluorinated coating. The type of coating formed on the metal surface can be selected according to its intended use and will be apparent to those having ordinary skill in the art. For example, an oxide coating can be formed by reacting a metal surface with an oxygen-containing purge gas under heating conditions. Nitrided coatings can be formed by reacting a metal surface with a nitrogen-containing purge gas, particularly nitrogen molecules, under heating conditions. Carbonized coatings can be formed by reacting a metal surface with a carbon-containing purge gas, including but not limited to organic compounds, under heating conditions. The fluoride coating can be formed by reacting the metal surface with a fluorine-containing purge gas, particularly hydrogen fluoride, under heating conditions. Other types of coatings are readily conceivable to those skilled in the art.

  In the embodiments described herein, various purge gases and combinations thereof are used. A purge gas suitable for use in this embodiment is either a substance that is a gas at room temperature and room pressure, or a liquid or solid that has a high vapor pressure and easily volatilizes to form a gas phase. It is recognized. Exemplary purge gases suitable for use in this embodiment include, for example, air, water vapor, oxygen, carbon dioxide, carbon monoxide, nitrogen, fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, bromide. Hydrogen, hydrogen iodide, boron trifluoride, boron trichloride, boron tribromide, silicon tetrafluoride, sulfur hexafluoride, sulfur tetrafluoride, phosphorus trifluoride, phosphorus pentafluoride, nitrogen trifluoride, Nitrous oxide, nitrogen oxides, nitrogen dioxide, dinitrogen tetroxide, diimide, hydrogen, gaseous organics, and any combination thereof are included.

  In certain embodiments, the purge gas further includes a diluent gas that does not react with the metal surface. In certain embodiments, the diluent gas is a noble gas such as, for example, helium, argon, neon, krypton, or xenon. When present, the diluent gas includes amounts ranging from about 0.1% to about 99.9% of the gas mixture, including all of their partial ranges. In certain embodiments, the diluent gas is present in an amount ranging from about 1% to about 90% of the gas mixture, or from about 5% to about 50% of the gas mixture, or from about 10% to about 70% of the gas mixture. Without being bound by theory or mechanism, it is believed that the thickness of the coating on the metal surface can be controlled by adjusting the amount of purge gas present to react with the metal surface, and increasing or decreasing the amount of dilution gas. ing.

  The thickness of the coating can vary over a considerable range. In certain embodiments, each layer of coating on the metal surface ranges from about 1 nm to about 1 μm thick, including all partial ranges therebetween. In certain embodiments, the thickness of each layer of the coating ranges from about 1 nm to about 250 nm, or from about 1 nm to about 100 nm, or from about 5 nm to about 50 nm, or from about 5 nm to about 100 nm, or from about 10 nm to about 50 nm. Is done. That is, in at least some embodiments, the coating is nanostructured.

  Suitable temperatures for carrying out this embodiment can be varied over a wide range as well. As will be appreciated by those skilled in the art, the maximum temperature over which this embodiment can be implemented depends primarily on the melting point of the selected metal surface. Except for low melting point metals (eg, metals having a melting point of less than about 800 degrees, such as aluminum), suitable temperatures for implementing this embodiment vary over temperatures ranging from about 200 degrees to about 1000 degrees. All partial ranges in between are included. In certain embodiments, suitable temperatures range from about 400 degrees to about 800 degrees. In other embodiments, suitable temperatures range from about 300 degrees to about 600 degrees. In still other embodiments, suitable temperatures range from about 400 degrees to about 600 degrees. In certain embodiments, the suitable temperature is at least about 400 degrees. In other embodiments, a suitable temperature is at least about 500 degrees, or at least about 600 degrees, or at least about 700 degrees, or at least about 800 degrees, or at least about 900 degrees, or at least about 1000 degrees. It will further be appreciated that factors other than the melting point of the metal surface can determine the selected temperature at which this embodiment is implemented. For example, if the temperature is very high, some purge gases may be flammable, explosive, or otherwise unstable. Thus, the temperature at which a particular coating is made in accordance with this embodiment will be a problem for a series of experimental designs that are within the tolerance of those having ordinary knowledge in the art.

  In some embodiments, the purge gas undergoes a preheating step before being backfilled into a vacuum around the metal surface. One reason that it may be desirable to preheat the purge gas includes, but is not limited to, purging the purge gas due to adiabatic expansion resulting from backfilling the vacuum space. The cooling of the purge gas can potentially affect the reaction with the metal surface.

  Although the present invention has been described with respect to the disclosed embodiments, those of ordinary skill in the art will readily appreciate that these embodiments are illustrative of the present invention. Of course, it should be understood that various modifications can be made without departing from the spirit of the invention. The specific embodiments described above are exemplary only, and the present invention may be modified and implemented in different but equivalent forms, which will be apparent to those skilled in the art having the benefit of the teachings herein. Further, the details of construction or design described herein are not limited except as described in the appended claims. It is therefore evident that the particular exemplary embodiments described above may be modified, combined, and modified and all such variations are within the scope and spirit of the present invention. Although configurations and methods are described as “comprising”, “including”, or “including” various components or steps, the configurations and methods may also be described as various components and steps. It can be “consisting essentially of” or “consisting of”. All the above numbers and ranges can be varied by a certain amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, all numbers within the wide range and all partial ranges are also disclosed in detail. Also, unless otherwise explicitly and clearly defined by the patentee, the terms in the claims have their plain and ordinary meanings. Where there is a conflict in the usage of a word or term in this specification and in one or more patents or other documents that may be incorporated herein by reference, a definition consistent with this specification should be taken. It is.

Claims (25)

Heating the metal surface to a temperature below its melting point,
Applying a vacuum thereto while heating the metal surface, and releasing the vacuum and backfilling with a first purge gas while heating the metal surface;
A method for disposing a coating on a metal surface comprising:
The method of disposing a coating on a metal surface, wherein the first purge gas reacts with the heated metal surface to dispose at least one layer of coating on the metal surface.   The method of claim 1, further comprising re-applying a vacuum thereto after placing the coating and while heating the metal surface.   The method of claim 2, comprising disposing at least one additional layer of the coating by releasing the vacuum and backfilling with a second purge gas while heating the metal surface. Method.   4. The method of claim 3, wherein the first and second purge gases are the same.   4. The method of claim 3, wherein the first and second purge gases are different.   The method of claim 1, wherein the temperature is at least about 400 degrees.   The first purge gas is air, water vapor, oxygen, carbon dioxide, carbon monoxide, nitrogen, fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, boron trifluoride, Boron trichloride, boron tribromide, silicon tetrafluoride, sulfur hexafluoride, sulfur tetrafluoride, phosphorus trifluoride, phosphorus pentafluoride, nitrogen trifluoride, nitrous oxide, nitrogen oxides, nitrogen dioxide, 2. The method of claim 1 selected from the group consisting of dinitrogen tetroxide, diimide, hydrogen, gaseous organics, and any combination thereof.   The method of claim 1, wherein the coating comprises at least one of an oxide coating, a nitride coating, a carbonized coating, or a fluoride coating.   The method of claim 1, wherein the first purge gas further comprises a diluent gas that does not react with the metal surface. Applying a vacuum to an annulus having an outer surface defined by a material that is at least partially transparent to solar radiation and an inner surface defined by a metal tube;
Heating the metal tube to a temperature below its melting point while applying the vacuum there, and releasing the vacuum and refilling with the first purge gas while heating the metal tube. ,
A method of disposing a coating on a solar heat receiver comprising:
The method of disposing a coating on a solar heat receiver, wherein the first purge gas reacts with the heated metal surface to dispose at least one layer of coating on the metal surface.   The method of claim 10, further comprising re-applying a vacuum to the annulus after placing the coating and while heating the metal tube.   The method of claim 11, further comprising maintaining the vacuum to seal the annulus.   12. The method of claim 11, further comprising disposing at least one additional layer of the coating by releasing the vacuum and backfilling with a second purge gas while heating the metal tube. the method of.   The method of claim 13, wherein the first and second purge gases are the same.   The method of claim 13, wherein the first and second purge gases are different.   The method of claim 10, wherein the material that is at least partially transparent to solar radiation comprises glass.   The method of claim 10, wherein the temperature is at least about 400 degrees.   The first purge gas is air, water vapor, oxygen, carbon dioxide, carbon monoxide, nitrogen, fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, boron trifluoride, Boron trichloride, boron tribromide, silicon tetrafluoride, sulfur hexafluoride, sulfur tetrafluoride, phosphorus trifluoride, phosphorus pentafluoride, nitrogen trifluoride, nitrous oxide, nitrogen oxides, nitrogen dioxide, The method of claim 10 selected from the group consisting of dinitrogen tetroxide, diimide, hydrogen, gaseous organics, and any combination thereof.   The method of claim 10, wherein the coating comprises an oxide coating, a nitride coating, a carbonized coating, or a fluoride coating.   The method of claim 10, wherein the first purge gas further comprises a diluent gas that does not react with the metal tube.   The method of claim 10, wherein the metal tube comprises a metal selected from carbon steel, stainless steel, and any combination thereof.   A solar heat receiver produced by the process of claim 10.   The solar heat receiver according to claim 22, comprising a heat transfer fluid disposed in an internal space of the metal tube.   The solar heat receiver according to claim 22, wherein the coating includes at least one of an oxide coating, a nitride coating, a carbonized coating, or a fluoride coating.   The solar heat receiver of claim 22, wherein the coating comprises a nanostructured coating.