Graphene super-hydrophobic anticorrosion composite coating, and preparation method and application thereof

Abstract

The application discloses a graphene super-hydrophobic corrosion-resistant composite coating and a preparation method and application thereof, and comprises the following steps: S1, graphene material and hydrochloric acid dopamine are dissolved in water, and ultrasonic treatment is carried out in a weak alkali environment; S2, fluorosilane is dissolved in ethanol and then added to the solution after ultrasonic treatment in S1, continuous stirring is carried out at a first temperature, then the temperature is increased to a second temperature, continuous stirring is carried out, then cooling, filtering and drying are carried out to obtain a composite filler; S3, the composite filler obtained in S2 is ultrasonically dispersed in a solvent, PDMS and a curing agent are added and stirred, and a coating is obtained after ultrasonic treatment; and S4, the coating prepared in S3 is coated on the surface of a metal substrate, curing is carried out, and a graphene super-hydrophobic corrosion-resistant composite coating is obtained. The composite coating prepared by the application can inhibit the "corrosion promotion activity" of graphene, has excellent corrosion inhibition performance, and can achieve super-hydrophobicity by cross-linking with PDMS having low surface energy, and simultaneously has excellent self-cleaning performance.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion protection, and particularly relates to a graphene superhydrophobic anti-corrosion composite coating, its preparation method and application. Background Technology

[0002] Metal corrosion is an extremely common electrochemical phenomenon. Because it impairs the durability and longevity of products, leading to premature failure of metal components and resulting in economic losses, improving the corrosion resistance of metals is particularly important for metal infrastructure such as bridges and ships. Currently, how to enhance the corrosion resistance of metals remains a pressing problem to be solved.

[0003] Common methods for protecting metals include cathodic protection, electrodeposition, and coating protection. Among these, coating protection is one of the most effective methods due to its strong corrosion resistance, low cost, and simple preparation process. Coatings are generally classified into inorganic, organic, and organic-inorganic hybrid coatings. Inorganic coatings can be prepared by methods such as electrodeposition and exhibit good properties such as high-temperature resistance, but their poor mechanical properties often limit their practical applications. Organic coatings have good wear resistance, but solvent evaporation during preparation can lead to shrinkage, cracking, and defects within the coating, making it impossible to maintain long-term protection for the metal substrate. To improve overall performance, micro / nano-structured inorganic particles are often mixed with an organic polymer matrix as fillers to prepare organic-inorganic hybrid composite coatings, which can simultaneously combine the advantages of both inorganic and organic coatings.

[0004] In recent years, two-dimensional inorganic fillers such as graphene, boron nitride (BN), zirconium phosphate (ZrP), and molybdenum disulfide (MoS2) have attracted widespread attention due to their excellent barrier properties. When incorporated into organic coatings, they can extend the penetration path of corrosive media, creating a "maze" effect. Among these, graphene stands out due to its high specific surface area, good chemical stability, and excellent barrier properties. However, graphene has a more positive electrode potential than metals such as copper. Once the coating is damaged, galvanic corrosion can occur between the graphene at the cathode and the metal at the anode. The high conductivity of graphene further accelerates the corrosion activity of the metal. Therefore, the "corrosion-promoting activity" problem of graphene coatings reduces the effectiveness of long-term metal protection.

[0005] Most existing anti-corrosion composite coatings neglect the "corrosion-promoting activity" problem inherent in graphene coatings, and their preparation processes are complex. Chinese invention patent CN 113789109 A suppresses this "corrosion-promoting activity" by doping with boron and fluorine atoms, resulting in a coating with antibacterial and anti-corrosion properties. However, the heteroatom doping process may introduce corrosive substances that cause lattice defects and may also increase the conductivity of graphene, thus exacerbating corrosion. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a graphene superhydrophobic anticorrosion composite coating that can inhibit the "corrosion-promoting activity" of graphene, its preparation method and application.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A method for preparing a graphene superhydrophobic anti-corrosion composite coating includes the following steps:

[0009] S1. Dissolve graphene material and dopamine hydrochloride in water and perform ultrasonic treatment in a weakly alkaline environment;

[0010] S2. Dissolve fluorosilane in ethanol and add it to the ultrasonic solution of S1. Stir continuously at the first temperature, then raise the temperature to the second temperature and continue stirring. Then cool, filter and dry to obtain the composite filler.

[0011] S3. The composite filler obtained in S2 is ultrasonically dispersed in a solvent, PDMS and curing agent are added and stirred, and the coating is obtained after ultrasonication.

[0012] S4. Apply the coating prepared in S3 to the surface of the metal substrate and cure it to obtain a graphene superhydrophobic anti-corrosion composite coating.

[0013] As a further improvement, the graphene-based material described in S1 is one of graphene, graphene oxide, or reduced graphene oxide.

[0014] As a further improvement, the mass ratio of graphene material to dopamine hydrochloride in S1 is 0.5 to 12.5:1.

[0015] As a further improvement, the pH of the weakly alkaline environment described in S1 is 8.0 to 8.8; and the ultrasonic treatment time is 0.5 h to 2.0 h.

[0016] As a further improvement, the fluorosilane mentioned in S2 is one or any combination of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltrimethoxysilane, or tridecafluorooctyltriethoxysilane.

[0017] As a further improvement, the mass ratio of the fluorosilane to dopamine hydrochloride is 1.25 to 5:1.

[0018] As a further improvement, in S2, the first temperature is 25-40°C, the second temperature is 60-90°C, and the stirring time at the first temperature and the second temperature are both 11-14 hours.

[0019] As a further improvement, the mass ratio of PDMS to composite filler in S3 is 5 to 10:1.

[0020] The present invention also provides a graphene superhydrophobic anticorrosive composite coating, which is prepared by the preparation method described above, wherein fluorosilane nanoparticles are loaded on the graphene material by using polydopamine as a binder.

[0021] The present invention also provides an application of the graphene superhydrophobic anti-corrosion composite coating in metal corrosion protection.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] To suppress the "corrosion-promoting activity" of graphene coatings, this invention utilizes polydopamine as a binder and loads fluorosilanes to insulate and passivate graphene, thereby blocking electron transport between graphene and the metal substrate and alleviating the "corrosion-promoting activity" problem. Simultaneously, a superhydrophobic composite coating is prepared using fluorosilane modification. The non-stickiness and non-wetting properties of the superhydrophobic surface reduce the contact between corrosive media and the coating, further improving corrosion resistance.

[0024] This invention utilizes the self-oxidative polymerization of dopamine under alkaline conditions to form polydopamine, which is then grafted onto graphene. The abundant functional groups of polydopamine not only covalently modify the graphene, reducing the aggregation tendency of graphene-based fillers in the organic polymer matrix, but also improve the compatibility of the filler with PDMS, facilitating better dispersion of the filler in PDMS and preparing a uniform coating, thereby further improving corrosion resistance. Furthermore, polydopamine can act as a binder, providing numerous "anchoring sites" for the loading of fluorosilanes, promoting fluorosilane loading, and thus achieving insulating passivation of the graphene.

[0025] Therefore, this invention utilizes fluorosilane for superhydrophobic modification and graphene oxide for insulating passivation, working synergistically with polydopamine to improve corrosion resistance.

[0026] This invention utilizes a simple one-pot method to prepare the composite filler GDF by mixing graphene oxide (GO) dispersion, dopamine hydrochloride (DA), and fluorosilane, thus completing the modification. The prepared composite filler is then mixed with polydimethylsiloxane (PDMS), a curing agent is added, and the mixture is cured at high temperature to crosslink the silicone resin with the filler, resulting in a GDF / PDMS composite coating. This invention utilizes an organic-inorganic hybrid to prepare the composite coating, and the composite filler can be obtained through a single mixing step, resulting in a simple preparation process and low cost.

[0027] The composite coating prepared by this invention can inhibit the "corrosion-promoting activity" of graphene, exhibits excellent corrosion inhibition performance, and achieves superhydrophobicity through crosslinking with PDMS, which has low surface energy. It also possesses excellent self-cleaning properties. It has significant application value in the field of metal corrosion protection. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is the FT-IR plot of the composite packing GDF;

[0030] Figure 2 This is a SEM image of the composite packing material GDF;

[0031] Figure 3 These are optical photographs of the GDF / PDMS coating during the process of (a) immersion in cola, (b) immersion in coffee, and (c) self-cleaning performance. The numbers 1, 2, and 3 represent the time points in chronological order.

[0032] Figure 4 It is a modulus diagram of the composite coating and the bare copper sheet;

[0033] Figure 5 These are the potentiodynamic polarization curves of the composite coating and the bare copper sheet;

[0034] Figure 6 It shows the modulus values ​​of the composite coating after scratch treatment and the bare copper sheet. Detailed Implementation

[0035] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0038] In some specific embodiments, the preparation method of the graphene superhydrophobic anticorrosion composite coating of the present invention includes the following steps:

[0039] S1. Graphene material and dopamine hydrochloride (DA) are mixed and dissolved in water, and then subjected to ultrasonic treatment in a weakly alkaline environment.

[0040] Preferably, the graphene-based material can be one of graphene, graphene oxide, or reduced graphene oxide.

[0041] Preferably, the mass ratio of graphene oxide to dopamine hydrochloride is 0.5 to 12.5:1, more preferably 0.5 to 2.5:1, even more preferably 0.5 to 1:1, and most preferably 0.5:1.

[0042] Preferably, the weakly alkaline environment can be achieved by adding ammonia, with the pH controlled at 8.0-8.8, preferably 8.5, and the dosage can be 0.05-0.15g / 200mL (mass of ammonia / volume of water).

[0043] Preferably, the ultrasound duration can be 0.5h to 2.0h.

[0044] S2. Dissolve fluorosilane in ethanol and add it to the ultrasonically treated solution from S1. Stir the system continuously at a first temperature, then raise the temperature to a second temperature and continue stirring. Cool, filter, and dry to obtain the composite filler GDF.

[0045] Preferably, the fluorosilane can be one of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltrimethoxysilane, and tridecafluorooctyltriethoxysilane. The amount used (the mass ratio of fluorosilane to dopamine hydrochloride) can be 1.25 to 5:1.

[0046] Preferably, the amount of ethanol used can be 30-50 mL / 1.5 g fluorosilane.

[0047] Preferably, the first temperature can be 25-40℃, and the second temperature can be 60-90℃. Stirring at low temperature causes dopamine to self-polymerize into polydopamine, which is then loaded onto graphene. Increasing the temperature accelerates the reaction rate.

[0048] Preferably, the stirring times for both stirring (stirring at the first temperature and stirring at the second temperature) can be 11-14 hours.

[0049] Preferably, after cooling and filtration, the product is washed with ethanol and dried. The drying temperature can be 80-100℃ and the drying time can be 12-24h.

[0050] S3. The composite filler obtained in S2 is ultrasonically dispersed in a solvent (e.g., methanol), then polymer PDMS (polydimethylsiloxane) is added and stirred. Then, a curing agent is added and stirred again. After ultrasonication, a coating is obtained.

[0051] Preferably, the mass ratio of PDMS to composite filler can be 5 to 10:1. The preferred mass ratio of PDMS to curing agent is 10:1. In the following examples, Dow Corning 184PDMS (Sylgard 184A) is used as the PDMS. In the following examples, the curing agent used is component B, Sylgard 184B, which is compatible with Dow Corning 184PDMS.

[0052] Preferably, the ultrasonic dispersion in methanol is performed for 0.5-2.0 h. The stirring time after adding PDMS is 1-3 h. The stirring time after adding the curing agent is 5-30 min.

[0053] S4. Apply the coating prepared in S3 to the surface of the metal substrate and cure it to obtain a composite coating.

[0054] Preferably, the metal substrate is pretreated by sanding with sandpaper and then ultrasonically cleaned with deionized water and anhydrous ethanol in sequence.

[0055] Preferably, the coating method can be spraying or dripping.

[0056] Preferably, the curing temperature can be 120-170℃, and the curing time can be 15-60min.

[0057] Example 1

[0058] Superhydrophobic composite coating G 0.2 Preparation method of DF / PDMS:

[0059] 1.1 Dissolve 0.2 g graphene oxide, 0.4 g dopamine hydrochloride, and 0.1 g ammonia in 200 mL deionized water (pH = 8.5) and sonicate for 1 h. Then, dissolve 1.5 g fluorosilane (1H,1H,2H,2H-heptadecyltrimethoxysilane) in 40 mL ethanol and add it to the sonicated solution. The system is then continuously magnetically stirred in an oil bath at 40 °C for 12 h. The temperature is then increased to 70 °C, and magnetic stirring continues for another 12 h. After cooling to room temperature, the system is vacuum filtered, and the filter cake is washed with ethanol and dried to obtain the composite packing material GDF.

[0060] 1.2 Polish the copper sheet sequentially with 400 grit, 800 grit, 1000 grit, 1500 grit and 2000 grit metallographic sandpaper. Clean the copper sheet with deionized water and anhydrous ethanol for 10 minutes each time, and then blow it dry for later use.

[0061] 1.3 Weigh 0.05 g of the composite filler prepared in 1.1 and disperse it in 15 mL of methanol. Disperse the mixture evenly by ultrasonication for 1 h. Then add 0.50 g of PDMS, stir at room temperature for 1 h, and then add 0.05 g of curing agent and stir for 5 min. Finally, ultrasonicate for 30 min to obtain the coating.

[0062] 1.4 Apply the coating obtained in 1.3 to the copper sheet surface treated in 1.2. Adjust the spray gun to a smaller spray volume and keep it about 5 cm away from the copper sheet. Cur at high temperature (160℃) for 15 minutes.

[0063] Figure 1 This is the FT-IR plot of the composite packing GDF at 3423 cm⁻¹. -1 There is a broad absorption peak at 1145 cm⁻¹, which is a typical hydroxyl absorption peak (including the stretching vibration of hydroxyl groups in water); -1 The absorption peak at 1614 cm⁻¹ is caused by the C-C stretching vibration. -1 A strong absorption peak appears at 1513 cm⁻¹, which can be attributed to the stretching vibrations of C=C and CN, as well as the bending vibrations of CH; -1 The absorption peak at 459 cm⁻¹ should be attributed to the NH bending vibration, fully verifying the successful loading of polydopamine onto graphene oxide. Furthermore, at 459 cm⁻¹... -1 809cm -1 There is an absorption peak at each of the following locations, which are caused by the bending vibration and the symmetric stretching vibration of Si-O-Si, respectively. And at 1205 cm⁻¹... -1 A strong absorption peak appears at the point, which can be attributed to the CF stretching vibration, indicating that fluorosilane has been successfully loaded onto the graphene oxide surface.

[0064] Figure 2 The image shows a SEM image of the composite filler GDF, indicating that multiple fluorosilane (FS) nanoparticles with low surface energy are loaded on the graphene oxide (GO) sheet due to the effect of the polydopamine binder, making the smooth graphene oxide sheet rougher.

[0065] Example 2

[0066] Same as Example 1, except that 0.2g of graphene oxide was replaced with 1.0g, and the prepared coating was G. 1.0 DF / PDMS.

[0067] Example 3

[0068] Same as Example 1, except that 0.2g of graphene oxide was replaced with 5.0g, and the prepared coating was G. 5.0 DF / PDMS.

[0069] Example 4

[0070] Similar to Example 1, except that the prepared composite coating is scratched, i.e., a 2mm long scratch is artificially created.

[0071] Example 5

[0072] Similar to Example 2, except that the prepared composite coating is scratched, i.e., a 2mm long scratch is artificially created.

[0073] Example 6

[0074] Similar to Example 3, except that the prepared composite coating is scratched, i.e., a 2mm long scratch is artificially created.

[0075] Comparative Example 1

[0076] Composite coatings without fluorosilane superhydrophobic modification:

[0077] The only difference from Example 1 is that fluorosilane and ethanol are not added in 1.1, and the prepared coating is G. 0.2 D / PDMS.

[0078] Comparative Example 2

[0079] Bare copper sheet:

[0080] The same as step 1.2 in Example 1.

[0081] Comparative Example 3

[0082] The only difference from Example 1 is that dopamine hydrochloride and ammonia are not added in step 1.1. Fluorosilane is difficult to load in step 1.1.

[0083] Results Test Analysis

[0084] 1. Contact Angle Test

[0085] Equipment: Contact angle measuring instrument

[0086] Conditions: Use a syringe or pipette to control the volume of the wetting liquid to 10 μL.

[0087] In Example 1, the contact angle of the GDF / PDMS coating is 151.5° ± 0.5°.

[0088] 2. Sliding angle test

[0089] Equipment: Set up a simple inclined platform to allow water droplets to slide off the coating surface. Use a protractor to measure the angle of inclination of the coating when the water droplets can slide, which is the sliding angle of the coating.

[0090] Conditions: Use a syringe or pipette to control the volume of the wetting liquid to 10 μL.

[0091] In Example 1, the sliding angle of the GDF / PDMS coating was 7.9° ± 0.1°.

[0092] The coating has a water contact angle of 151.5°±0.5° and a sliding angle of 7.9°±0.1°, indicating that the coating is superhydrophobic.

[0093] 3. Self-cleaning performance test

[0094] like Figure 3 When the superhydrophobic coating GDF / PDMS of Example 1 was immersed in cola and coffee respectively, and then lifted out, no substance remained on the coating surface, indicating that the coating has excellent anti-fouling properties. When the surface of the GDF / PDMS coating was rinsed with water to remove mud and sand, the mud and sand were quickly washed away by the water, and no water droplets were left along the path of the mud and sand, indicating that the coating has excellent self-cleaning properties.

[0095] 4. Electrochemical testing

[0096] Equipment: Shanghai Chenhua CHI760E

[0097] Conditions: The test was conducted using a conventional three-electrode system: a saturated calomel electrode as the reference electrode, a platinum electrode as the counter electrode, and the coatings from the above examples and comparative examples as the working electrodes with a working area of ​​1 cm × 1 cm. 3.5 wt% sodium chloride was used as the corrosive medium to test the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (EMP) curves of the coatings. The EIS parameters were set as follows: initial frequency 100,000 Hz, termination frequency 0.01 Hz, and sinusoidal AC signal amplitude 20 mV. Before testing, each coating was immersed in 3.5 wt% sodium chloride for 15 min, and testing began after the open-circuit voltage stabilized. The EMP curves were scanned within the range of -350 mV to -180 mV at a scan rate of 0.5 mV·s. -1 The EIS test data were fitted using ZSimpWin software by establishing an equivalent circuit.

[0098] The prepared GDF / PDMS coating exhibited a corrosion inhibition efficiency of 96.07% (see...). Figure 5 The low-frequency impedance is improved by an order of magnitude compared to bare copper (see...). Figure 4 And the scratch-treated coating exhibited an inhibitory effect on "corrosion-promoting activity" (see...). Figure 6 ).

[0099] Figure 4 This is a modulus diagram of the composite coating and the bare copper sheet. Low-frequency impedance modulus (|Z|) 0.01 The higher the |Z|, the better the anti-corrosion performance of the coating. In Example 1, |Z|... 0.01 The highest. From the modulus graph, it is clear that |Z| of Comparative Example 2 (bare copper sheet) is the highest. 0.01 The corrosion inhibition performance of the copper substrate is lower than that of each coating. It is evident that GDF / PDMS can improve the corrosion inhibition performance of the copper substrate. Furthermore, the |Z| of Comparative Example 1 (GD / PDMS) is... 0.01 The lower values ​​compared to the previous example indicate that the modification with fluorosilanes is beneficial for improving the corrosion resistance of the coating.

[0100] Figure 5 These are the potentiodynamic polarization curves of the composite coating and the bare copper sheet. The more positive the corrosion potential, the less likely the coating is to corrode; the lower the corrosion current density, the slower the corrosion rate of the coating. Compared to Comparative Example 2 (bare copper sheet), the corrosion potential of the examples (GDF / PDMS coating) shifts sequentially in the positive direction (Example 1 is better than Example 2, and Example 2 is better than Example 3). Furthermore, the corrosion current density shifts sequentially in the more negative direction. The tendency to corrode gradually decreases. The GDF / PDMS coating exhibits a lower corrosion rate and better corrosion resistance.

[0101] Table 1 lists the corrosion potential and corrosion current density of each coating. It can be seen that Comparative Example 1 has a more positive corrosion potential and a lower corrosion current density compared to Comparative Example 2, indicating that dopamine is beneficial for improving corrosion resistance. Furthermore, the examples show better performance than the comparative examples, demonstrating that the loading of fluorosilane improves the corrosion resistance of the coating.

[0102] Table 1

[0103]

[0104] EIS and potentiodynamic polarization curve tests were performed on coatings with different filler contents and bare copper sheets. The composite coatings in the examples all exhibited good corrosion resistance. Among them, coating G in Example 1... 0.2 DF / PDMS has the highest low-frequency impedance modulus, which is an order of magnitude higher than that of bare copper sheets, and it also has a lower corrosion current density and a more positive corrosion potential, exhibiting the best corrosion protection performance.

[0105] Figure 6 The images show the modulus values ​​of the scratch-treated composite coating and the bare copper sheet. The scratch-treated GDF / PDMS coating (Examples 4-6) still exhibits a higher low-frequency impedance modulus (|Z|) compared to Comparative Example 2 (bare copper sheet). 0.01 The coating still provides protection for the bare copper sheet, indicating that it can suppress the "corrosion-promoting activity" of graphene.

[0106] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a graphene superhydrophobic anticorrosion composite coating, characterized in that, Includes the following steps: S1. Graphene material and dopamine hydrochloride are dissolved in water and subjected to ultrasonic treatment in a weakly alkaline environment; the graphene-based material is graphene oxide; the mass ratio of graphene material to dopamine hydrochloride is 0.5~12.5:1; the pH of the weakly alkaline environment is 8.0~8.8; S2. Dissolve fluorosilane in ethanol and add it to the ultrasonically treated solution from S1. Stir continuously at a first temperature, then raise the temperature to a second temperature and continue stirring. Then cool, filter, and dry to obtain the composite filler. The fluorosilane is one or any combination of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltrimethoxysilane, or tridecafluorooctyltriethoxysilane. The mass ratio of fluorosilane to dopamine hydrochloride is 1.25~5:

1. The first temperature is 25~40 ℃, and the second temperature is 60~90 ℃. S3. The composite filler obtained in S2 is ultrasonically dispersed in a solvent, PDMS and curing agent are added and stirred, and the coating is obtained after ultrasonication. S4. Apply the coating prepared in S3 to the surface of the metal substrate and cure it to obtain a graphene superhydrophobic anti-corrosion composite coating.

2. The preparation method according to claim 1, characterized in that, In S2, the stirring time at the first temperature and the stirring time at the second temperature are both 11~14 h.

3. The preparation method according to claim 1, characterized in that, The mass ratio of PDMS to composite filler in S3 is 5~10:

1.

4. A graphene superhydrophobic anti-corrosion composite coating, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3, wherein fluorosilane nanoparticles are loaded onto the graphene material using polydopamine as a binder.

5. The application of the graphene superhydrophobic anti-corrosion composite coating of claim 4 in metal corrosion protection.

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