The present invention relates to corrosion-resistant coatings, and, more particularly, relates to a method of providing a hydrophobic coating using non-functionalized nanoparticles.
The diffusion of water through polymer coatings on infrastructure assets has been identified as the major contributor to asset corrosion damage. This damage leads to frequent coating replacement, which is associated with significant maintenance costs. Corrosion resistance can be increased, and related maintenance costs decreased, by the application of organic coatings to metal structures. Superhydrophobic coatings, having low surface energy and roughness, have been developed on which water forms nearly spherical droplets and can be easily shaken away. To date, hydrophobic coatings have been developed using several approaches including plasma deposition, sol-gel method, layer-by-layer assembly, chemical etching, chemical vapor deposition, and casting. Unfortunately, these methods have proven costly and time-consuming to produce and not practicable for large-scale structures.
Efforts have also been made to produce low cost superhydrophobic coatings based on cheaper materials such as zinc oxide (ZnO), titanium dioxide (TiO2), cupric oxide (CuO) and silica (SiO2). These efforts have focused on “functionalizing” the surface of pure particles with long carbon chains to increase their hydrophobicity. Functionalization is also time consuming and costly.
What is therefore needed is a cost-effective and efficient technique for providing anti-corrosive coatings, particularly for large structures.
Embodiments of the present invention provide an anti-corrosive coating for a substrate surface. The coating comprises an insulation layer positioned over the substrate and a cured epoxy layer positioned on the insulation layer. The cured epoxy layer includes a plurality of nanoparticles having diameters within a range of about 200 nm to about 350 nm. Water droplets positioned on an external surface of the cured epoxy layer form a contact angle of at least 130 degrees.
In some embodiments, the plurality of nanoparticles is composed of silica. In other embodiments, the plurality of nanoparticles is composed of other materials or combinations thereof or with silica. The substrate on which the coating is used can be any structure subject to corrosion, such as the metallic surface of a pipe. The disclosed coating is highly hydrophobic; in some embodiments, water droplets positioned on an external surface of the cured epoxy layer form a contact angle of at least 134 degrees.
Embodiments of the present invention also provide a method of increasing the resistance of a structure covered with insulation to corrosion under insulation (CUI). The method comprises preparing a powder composed of nanoparticles having diameters in a range of about 200 nm to 350 nm, depositing a layer of epoxy material over the insulation on the structure, and embedding the powder of nanoparticles within the deposited epoxy material. Upon curing of the epoxy material, the nanoparticles become set in position within the layer of epoxy.
In some implementations, the powder of nanoparticles is prepared using the Stöber process. In certain embodiments, the plurality of nanoparticles is composed of silica. The disclosed method produces a highly hydrophobic coating; water droplets positioned on an external surface of the cured epoxy layer including the embedded nanoparticles form a contact angle of at least 130 degrees. In some embodiments, water droplets positioned on an external surface of the cured epoxy layer form a contact angle of at least 134 degrees.
These and other aspects, features, and advantages can be appreciated from the following description of certain embodiments of the invention and the accompanying drawing figures and claims.
A method of producing hydrophobic, anti-corrosive coatings is disclosed herein. Hydrophobicity is increased by adding non-functionalized silica nanoparticles having diameters in a range of about 200 nm to about 350 nm to the coating surface. The method is highly applicable to installed infrastructure, as it does not require the modifications of the already existing coatings.
Silica nanoparticles of various sizes were tested for hydrophobicity. During testing, silica nanoparticles were prepared using the Stöber synthesis method. The Stöber synthesis method is a chemical process used to prepare silica (SiO2) particles of controllable and uniform size. The process is initialized by reacting a molecular precursor with water in an alcoholic solution. The products of the process aggregate and grow in size depending on the duration of the process. The Stöber process can produce silica particles with relatively uniform diameters within in a range of 50 to 2000 nm, depending on pH, timing and other conditions.
In some embodiments of the present invention, the Stöber process reaction is initiated by stirring tetraethyl ortho-silicate (Si(OC2H5)4) with ethanol, deionized water and ammonium hydroxide for a specified duration. Silica nanoparticles of different (uniform) sizes were generated using this process. In particular, generally spherical particles of 140 nm, 200 nm, 350 nm and 430 nm diameter were generated for testing. In addition, 25 nm particles, produced by a different process, were procured. The silica nanoparticles were then heated in air (calcined) at 550° C. for 4 hours to remove all organic residue or functional groups on the surfaces of the nanoparticles.
After calcining the silica nanoparticles, tests, including Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FT-IR), were performed to determine the purity of the nanoparticle surfaces.
To produce the anti-corrosive corrosive coating on an asset, such as a steel pipe, an epoxy-based pre-coating is first applied on the outer surface of the asset. The epoxy pre-coating can be applied to the asset surface by hand brushing, for example. The synthesized silicon nanoparticles are then gathered to form a powder which is then dispersed onto the epoxy pre-coating using a sieve to set a maximum aggregated particle size. In some implementations a 450 μm sieve can be used. For the purpose of testing, powders containing specific particle sizes of 140 nm, 200 nm, 350 nm and 430 nm were produced. The coating, comprised of the epoxy and dispersed silica nanoparticles is then cured to harden. While different temperatures and durations can be used for curing, in some implementations, coatings can be cured at room temperature over a period of days (e.g., 2 days).
The prepared nanoparticle samples of various size bins were used to create anti-corrosive coatings.
Exemplary coatings made according to this method were then tested for water contact angle (CA). The contact angle is that angle that water droplets form on the coating surface. The higher the contact angle, the greater the hydrophobicity of the surface, and the more resistant it will tend to be to water-based corrosion. Images of contact angle measurements on coatings using 25 nm, 140 nm, 200 nm, 350 nm, and 430 nm are shown in
While non-functionalized silica nanoparticles powders having particles with the 200 nm to 350 nm size range have been used to improve the hydrophobicity of epoxy coatings, non-functionalized, generally spherical nanoparticles of other materials can also be used, for example, metal oxides and other inorganic particles.
It is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the systems and methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the methods.
It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Terms of orientation are used herein merely for purposes of convention and referencing, and are not to be construed as limiting. However, it is recognized these terms could be used with reference to a viewer. Accordingly, no limitations are implied or to be inferred.
Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Number | Date | Country | |
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Parent | 16117627 | Aug 2018 | US |
Child | 17809748 | US |