MODIFIED GRAPHENE AND GRAPHENE NANOPLATELET FOR ANTI-CORROSION COATINGS

Abstract

A graphene-based zinc containing coating is provided to prevent or slow down the corrosion of steel. The graphene-based materials are selected from a group of modified single-layer graphene, double-layer graphene, few layer graphene, graphene nanoplatelet, doped graphene, and a combination thereof. The modified graphene-based materials in zinc-containing paints or coatings act as a barrier to prevent or slow down the diffusion of corrosive species to the steel surface to be protected. For such a purpose, the graphene has a high aspect ratio and good structural integrity, especially a lack of defects on the basal plane of the graphene.

Claims

1. A graphene-based and zinc containing anti-corrosion paint or coating comprising: a graphene-based material; a sacrificial zinc metal or compound; and a resin where the resin contains the graphene-based material and the sacrificial zinc metal or compound.

2. The paint or coating of claim 1 wherein the graphene-based material is made from mechanically or chemically exfoliated from graphite and functionalized with oxygen or other functionalities so that the paint or coating does not electrochemically corrode steel.

3. The paint or coating of claim 1 wherein the graphene-based material is one or more of graphene, bi-layer graphene, few layer graphene, graphene nanoplatelet, functionalized graphene, doped graphene, and a combination thereof.

4. The paint or coating of claim 1 wherein the resin comprises one or more of epoxy, polyurethane, acrylic, alkyd, and other polymeric compounds.

5. The paint or coating of claim 1 wherein the graphene-based material is functionalized by one or more of functional groups selected from epoxide, carbonyl, carboxyl, hydroxyl, and amine.

6. The paint or coating of claim 1 wherein the graphene-based material is modified by grafting a polymer to an edge or a surface of the graphene-based material.

7. The paint or coating of claim 1 wherein zinc is present as zinc metal, zinc compound, or a combination thereof.

8. The paint or coating of claim 1 wherein the graphene-based material is present with an oxygen content of 2-20 atomic percent.

9. The paint or coating of claim 1 wherein the graphene-based material is present with an oxygen content of 4-15 atomic percent.

10. The paint or coating of claim 1 wherein the graphene-based material is present with an oxygen content of 5-10 atomic percent.

11. The paint or coating of claim 1 wherein the graphene content in a formulation of the paint is in the range of 0.1-10 weight percent.

12. The paint or coating of claim 1 wherein the graphene content in a formulation of the paint is in the range of 0.5-5 weight percent.

13. The paint or coating of claim 1 wherein the graphene content in a formulation of the paint is in the range of 0.5-1 weight percent.

14. The paint or coating of claim 1 wherein the zinc content in a formulation of the paint is in the range of 20-90 weight percent.

15. The paint or coating of claim 1 wherein the zinc content in a formulation of the paint is in the range of 30-60 weight percent.

16. The paint or coating of claim 1 wherein the zinc content in a formulation of the paint is in the range of 30-50 weight percent.

17. The paint or coating of claim 1 wherein the zinc content in a formulation of the paint is in the range of 20-90 weight percent.

18. A method of forming the paint or coating of claim 1, the method comprising: mixing the graphene-based material, the sacrificial zinc metal or compound, and the resin to form the paint or coating; and wherein the graphene-based material is first dispersed in a solvent to form a dispersion or a wet cake.

19. A method of forming the paint or coating of claim 1, the method comprising: mixing the graphene-based material, the sacrificial zinc metal or compound, and the resin to form the paint or coating; and wherein the graphene-based material is a dry powder.

20. The method of claim 18 further comprising applying the paint or coating to a steel structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further detailed with respect to the following drawing that is intended to show certain aspects of the present of invention, but should not be construed as limit on the practice of the invention, wherein:

[0031] FIG. 1 is a flowchart of a method for preparing and applying a graphene-based zinc-containing anti-corrosion paint when graphene is applied as a dry powder in accordance with embodiments of the invention; and

[0032] FIG. 2 is a flowchart of a method for preparing and applying a graphene-based zinc-containing anti-corrosion paint when graphene is applied as a pre-dispersion or wet cake in accordance with embodiments of the invention.

DETAILED DESCRIPTION

[0033] The present invention has utility as a graphene-based zinc containing coating to prevent or slow down the corrosion of steel. The graphene-based materials are selected from a group of modified single-layer graphene, double-layer graphene, few layer graphene, graphene nanoplatelet, doped graphene, and a combination thereof.

[0034] In some inventive embodiments, the graphene-based material is oxygen-functionalized graphene nanoplatelet. The graphene nanoplatelet is produced by mechanical exfoliation with a surface area of ≥150 m.sup.2/g. Preferably, the surface area of the graphene nanoplatelet is ≥300 m.sup.2/g, more preferably ≥500 m.sup.2/g. The particle size of the graphene nanoplatelet on average is ≤5 microns, and preferably ≤2 microns, and yet more preferably ≤1 micron. The thickness of the graphene nanoplatelet on average is ≤20 layers, preferably ≤15 layers, and yet more preferably between 2-10 layers. The graphene nanoplatelet described above gives good particle count, aspect ratio, and coating quality in anti-corrosion coatings, especially for relatively thin coatings.

[0035] In another inventive embodiment, the graphene-based material is oxygen-functionalized graphene nanoplatelet. The graphene nanoplatelet is produced by wet chemical exfoliation of graphite. The surface area of the material is ≥40 m.sup.2/g, preferably ≥100 m.sup.2/g, and yet more preferably ≥150 m.sup.2/g. The particle size of the graphene nanoplatelet on average is ≤25 microns, and preferably ≤10 microns, and yet more preferably ≤5 micron. The thickness of the graphene nanoplatelet on average is ≤60 layers, preferably ≤20 layers, and yet more preferably between 5-15 layers. The graphene nanoplatelet described above gives good aspect ratio, good electrical conductivity, and decent coating quality in anti-corrosion coatings, especially for relatively thick coatings.

[0036] In some inventive embodiments, a combination of both mechanically exfoliated graphene nanoplatelet and chemically exfoliated graphene nanoplatelet are used.

[0037] In some inventive embodiments, the graphene nanoplatelet is functionalized with oxygen. The functionalization can be done by plasma, wet chemistry, or other methods. The oxygen content in the modified graphene nanoplatelet is between 2-20 atmospheric percent (at. %), preferably between 4-15 at. %, and more preferably between 5-10 at. %.

[0038] In some inventive embodiment, the graphene nanoplatelet may be functioned with other chemical groups including, but are not limited to, epoxide, carbonyl, carboxyl, hydroxyl, and amine, etc. Yet in another embodiment, the graphene-based material is modified by grafting one or more of polymer molecules to the surface of graphene to obtain proper electrochemical, electric, and barrier properties.

[0039] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

[0040] One aspect of the instant invention is to use modified graphene-based materials in zinc-containing paints or coatings as a barrier to prevent or slow down the diffusion of corrosive species to the steel surface to be protected. For such a purpose, it is desirable to have a graphene with high aspect ratio and good structural integrity, especially a lack of defects on the basal plane of the graphene. Graphene oxide (GO) may not be desirable due to such defects as a result of its manufacturing process. Reduced graphene oxide (rGO) will not solve this problem.

[0041] Another aspect of the instant invention is to use the graphene-based materials to provide enough conductivity to help form a conductive network that connects zinc particles for better utilization and protection, especially when zinc content is reduced to below 30-50 wt % in the coatings. For this purpose, graphene oxide and heavily functionalized graphene might not be good candidates since they usually do not have good electric conductivity. Graphene, graphene nanoplatelet, or reduced graphene oxide could provide such conductivity.

[0042] Yet another aspect of the instant invention is to use a modified graphene whose electrochemical potential has been significantly shifted to a level that it will not electrochemically corrode steel. Pure graphene, like graphite, has a very positive reduction potential and in theory can corrode all metals with the presence of an electrolyte by forming an electrochemical cell between the metal and graphene. Therefore, graphene needs to be modified to an extent that its reduction potential is more negative than the metal to be protected.

[0043] Graphene oxide contains many oxygen functionalities such as carboxyl, carbonyl, hydroxyl, epoxy, and peroxy moieties with a carbon:oxygen ratio of approximately 2:1. Most of these oxygen-containing groups are electroactive, resulting in an electrochemical activity or potential of graphene oxide different from pure graphene. It was reported that graphite oxide and chemically reduced graphene oxide (CRGO) exhibit large reduction currents starting at −0.75 V and increasing to −1.4 V versus an Ag/AgCl reference electrode.sup.1. Given that most types of steel have a reduction potential in the range of −0.07 to −0.53V (Ag/AgCl reference electrode), graphene oxide is not likely to corrode steel, much different from graphite or graphene. Therefore, it is desirable to modify graphene-based materials with oxygen or other functional groups so that their reduction potential is shifted away from directly corroding steel, yet the material is still electrically conductive enough to connect sacrificing zinc particles for more effective steel protection.

[0044] It is the combination of all the three aspects that makes the instant invention unique. In one exemplary inventive embodiment, oxygen functionalized graphene nanoplatelets are used in zinc-containing anti-corrosion primer coating. Preferably, the graphene nanoplatelets are manufactured by mechanical or thermal exfoliation of graphite instead of by a graphene oxide route. The materials are further functionalized with oxygen or other functional groups in a controlled manner so that the overall oxygen content is between 5-20 wt %. More preferably, the oxygen content is between 5-15 wt %, and yet more preferably, the oxygen content is between 5-10 wt %.

[0045] As used herein, graphene-based material is defined as a two dimensional material constructed by close-packed carbon atoms including a single-layer graphene, double-layer graphene, few layer graphene, graphene nanoplatelets, functionalized graphene, doped graphene, graphene oxide, reduced graphene, and a combination thereof.

[0046] As used herein, single-layer graphene is defined as a single layer of close-packed carbon atoms.

[0047] As used herein, double-layer graphene is defined as a stack graphene of two layers.

[0048] As used herein, few layer graphene, is defined as a stack graphene of 3-10 layers.

[0049] As used herein, graphene nanoplatelet is defined as a stack of graphene of more than 10 layers.

[0050] As used herein, graphene oxide is defined as one or more graphene layers with various oxygen-containing functionalities such as epoxide, carbonyl, carboxyl, and hydroxyl groups and a typical C:O ratio around 2.

[0051] As used herein, reduced graphene oxide is defined as graphene oxide that has been chemically or thermally reduced with a total oxygen content of typically in the range of 10%-30 atmospheric percent (at. %) depending on the extent of reduction.

[0052] As used herein, functionalized graphene is defined as graphene, few layer graphene, graphene nanoplatelets, graphene oxide, and reduced graphene oxide that are attached certain functional groups at their surfaces or edges. The functional groups include, but are not limited to, epoxide, carbonyl, carboxyl, hydroxyl, and amine, etc.

[0053] As used herein doped graphene is defined as graphene and graphene oxide that are doped in their crystal structures of certain metallic or non-metallic elements such as nitrogen, fluorine, oxygen, etc. The graphene materials can be made by chemical or mechanical exfoliation of graphite. The graphene materials can also be made by oxidizing graphite with or without a reduction step.

[0054] Among them, graphene nanoplatelet is a preferred reinforcement filler wherein the graphene nanoplatelet is a new type of nanoparticles made from graphite. These nanoparticles consist of small stacks of graphene that are 1 to 15 nanometers thick, with diameters ranging from sub-micrometer to 100 micrometers. U.S. Patent Publication 2010/0092809 describes an exemplary process for forming exfoliated graphite nanoparticles.

[0055] In some inventive embodiments, additional additives can be used in combination with the aforementioned graphene-based materials. Such additives include carbon, carbon black, graphite, carbon nanotube, metals, ceramics, and polymeric materials. Additional additives common to the industry are readily accommodated by an inventive formulation with these additives typically including but not limited to, metallic zinc particles or zinc-based compounds, dispersants, talc, barium sulfate, coupling agent, wetting agent, and curing agent.

[0056] Embodiments of the invention provide a method to prepare a graphene-based zinc-containing anti-corrosion paint or coating. The graphene-based materials are dispersed in a resin, together with other components to form a paint formulation with a graphene content of <10 wt %, preferably <5 wt %, more preferably <1 wt %, and yet more preferably <0.5 wt %. The resin includes, but is not limited to epoxy, polyurethane, acryic, alkyd, and other polymeric materials. The other components include, but not limited to, solvents, metallic zinc particles or zinc-based compounds, dispersants, talc, barium sulfate, coupling agent, wetting agent, and curing agent. It is appreciated that the resin is curable by a variety of mechanisms including free radical, light, oxygen exclusion, acid, heat, or combinations thereof. Curing agents and stabilizers consistent with a given resin are conventional available and operative herein as additives.

[0057] The formulation may be divided into two parts wherein Part A contains the resin and most of the formulation components and Part B contains mainly the curing agent. The two parts are mixed prior to the application for anti-corrosion coating. It is appreciated that the volume ratio between the Parts A and B routinely vary between 0.05-20:1. The two parts are routinely storage stable separately for time periods from weeks to several years with exclusion of light and maintenance of temperature at 20 degrees Celsius. Typically, part A includes resins optionally with fillers, thixotropes, solvent, and colorant, and a second component part (component B) that includes a curing agent and optionally a blend of fillers, solvent, and colorant.

[0058] An inventive formulation in certain embodiments includes a diluent that is otherwise unreactive and serves to modify the volume of the formulation. A diluent is defined herein as a miscible and non-reactive compound relative to the components of the part in which the diluent resides.

[0059] A cure inhibitor is optionally present in an inventive formulation. A cure inhibitor operative herein illustratively includes benzoquinone, naphthoquinone, hydroquinone, 4-hydroxy 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL) or TEMPO, halogenated tallow alkyl amines, aziridine, polyaziridines, dihydrocarbyl hydroxyl amine, 2,2,6,6-tetra-methyl-piperidimyloxyl (TEMPO); 2,2,5,5-tetra-methyl-pyrolyloxy (PROXYL) or a combination thereof that operate synergistically to provide storage stability to an inventive formulation. Typically, a cure inhibitor is present from 0 to 0.2 total weight percent of Part A.

[0060] A cure accelerator is also present in an inventive formulation to kinetically speed curing of the formulation monomer compared to inventive formulations devoid of a cure accelerator. Cure of the monomers in contact with at least one substrate allows the formulation to function as an adhesive. Accelerators operative herein illustratively include a pyridine derivative, a butaraldehyde aniline condensate, N,N-dimethylaniline, N,N-dimethyltoludiene, N,N-diethyltoludiene, metal acetyl acetonate, and combinations thereof. Typically, cure accelerators are present from 0 to 2.5 total weight percent of Part A. In certain inventive embodiments, the cure accelerator is present in both Parts A and B; however, storage stability is generally enhanced by segregation of the cure accelerator in Part B and separate from any cure initiators in the inventive formulation, that are commonly in Part A.

[0061] Additives operative herein illustratively include a thixotrope, a silane coupling agent, a pigment, a plasticizer, an inert filler, a chain terminating agent, a fire retardant, and combinations thereof. Such additives are limited only by the requirement of compatibility with the other components of an inventive formulation.

[0062] In some inventive embodiments, the graphene-based materials can be added to the resin mix as a dry powder as shown in method 10 of FIG. 1. Graphene-based materials are used as a dry powder (Block 12). The graphene based dry powders are mixed (Block 20) with resin and solvent (Block 14) and other components illustratively including zinc and other additives (Block 16) in the paint formulation to obtain an anti-corrosion paint (Block 22). The mixing can be done by any of the conventional mixing equipment including high shear mixer, three-roll mill, attritor mill, high energy mill, double planetary mixer, nozzle mixer, cavity mixer, and other mixers. The paint can be applied (Block 24) to the surface of the articles to be protected by forming a coating. The coating can be done by brush coating, spray coating, roller coating, electro static spray coating, and any other conventional or unconventional coating methods.

[0063] In some inventive embodiments, and more preferably, the graphene-based materials can be added to the resin mix as a pre-dispersion or a wet cake as shown in method 30 of FIG. 2. Graphene-based materials are first dispersed in a solvent to form a dispersion or a wet cake (Block 32). The dispersion or cake is then mixed (Block 40) with resin and solvent (Block 34) and other components illustratively including zinc and other additives (Block 36) in the paint formulation to obtain an anti-corrosion paint (Block 42). The mixing can be done by any of the conventional mixing equipment including high shear mixer, three-roll mill, attritor mill, high energy mill, double planetary mixer, nozzle mixer, cavity mixer, and other mixers. The paint can be applied (Block 44) to the surface of the articles to be protected by forming a coating. The coating can be done by brush coating, spray coating, roller coating, electro static spray coating, and any other conventional or unconventional coating methods.

[0064] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the described embodiments in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes may be made in the function and arrangement of elements without departing from the scope as set forth in the appended claims and the legal equivalents thereof.

REFERENCES

[0065] 1. Her Shuang Toh, Adriano Ambrosi, Chun Kiang Chua, and Martin Pumera, J. Phys. Chem. C 2011, 115, 17647-17650.